Ligand substitution dynamicsA thesis presented for the degree of
Doctor of Philosophy in Chemistry
in the University of Canterbury,
Christchurch, New Zealand.
I am grateful to Dr D.A. House hi.s advice and
encouragement throughout work, to Dr H.K.lJ. Powell
his valuable sti.ons, particularly in regard to the acid
dissociation constant work, during Dr House's absence in
Denmark, and to Pro sor B.R, Penfold and Dr J. Browning
their assistance during course of the crystallographic
work.
I acknm.vledge the mvard of a University Gran·ts Committee
Post-Graduate Scholarship, and thank British Petroleum (N.Z.)
Ltd for the provision of a scholarship during the course of
· this study.
M.C. Couldwell
August, 1973.
some linear polyamine ligands have been studied, primarily
from a reaction rate point of view.
rrhe complexeE t:.r_9n~·,[C:rc1 2 (tmd) 2 ]Br, ~~:-[CrBr2 (trod) 2 ]X
(X== Br, Cl04), ~:C'.12?-E..~[crcl 2 (en) (trnd)]Clo4 , :tra!?;.~.--
[Cocl2 (en) (tmd) ]X (X = Cl.H2o, Clo4;) and :!:rans-
[Cocl2(NH3) (dien) ]Clo4 have been prepared to investigate their
kinetics of acid hydrolysis in aqueous HN0 3 • . +
From these, the cations !:!~-crx2 (tmd) 2 , (X = Cl,Br),
:tr~-MC1 2 (en) (tmd) + (M = Cr., C~), tr~,!l~·-CoC1 2 (NH 3) (dien) +,
!=-..rall~_-crx (t.rnd) 2 (OH 2) 2+ (X = Cl, Br), :t:r~!!:.~~CrCl (en) (trod) (OH 2) 2 ~-
2+ 3+ cis-CoCl (en) (tmd) (oH2 ) ~ , :t~n~~cr (AA) (t.md) (on2) 2 (AA = en P
tmd), ~:Ps-Co (NH 3) (dien) (OH 2 ) 2 J+, ~~~"Cr (AA) (trod) (OH 2) 2 3+
?..1
(AA == en, tmd), 9i~~co (en) (trnd) (oH2) 2 J ', ~~-Co (NH 3) (dien)-
3+ 3+ + (OH2) 2 r Cr (tmd) (OH 2) 4 , :~Eans·~Co (OII) 2 (en) (trnd) and !:,:r~a"~~-
Co(OH~2(NH3) (dien)+ have been isolated and characterised in
solution.
+ The complexes tr~-crx2 (tmd) 2 (X = Cl, Br) and tr_~~-
+ CrC1 2 (en) (tmd) aquate with complete retention of configuration
t.o their corresponding tr:aps~-·aquachloro isomer. At 298.2 K
5 -1 the first-order rate constants are 10 k (sec ) = 2.08±0.06
( 0 • 1 F HN 0 3 ) , 3 6 • 2 ± 1. 3 ( 0 • 3 !'.:_ HN 0 3
) , 1 • 9 3 ± 0 • 0 9 ( 0 • 4 !:::, HN 0 3 ) ,
respectively. The secondary hydrolysis of these cations is
complicated by isomerisation and concurrent Cr-N bond rupture.
The first-order halide release rate constants for trans-
2+ 2+ CrX (tmd) 2 (OH 2) · (X = Cl, Br) and !:_ra~-~-~CrCl (en) (tmd) (OH 2 )
5 -1 in 1.0 F HNO~ at 318.2 K are 10 k(sec ) = 2.88±0,06, - J
13.6±0.8, 3.15±0.18, respectively.
In the primary hydrolysis step the cation
CoC1 2 (en) (trod)+, 66±5% ~Js .. ·CoCl (en) (trod) (OH2) 2+ produced,
and the first:.-order rate constant for this in 0. 3 F HNCL, at - J
The fir hal
se rate constant for cis~:Cf.>Cl (en) (tlnd) (oH 2
) 2+ in 1.0 F 5 ~1
HN0 3
The rate of acid hydrolysis of
has been measured both rophotometrically and by chloride
' release. In 0.3 F HN03 at 298.2 K, the f st-order rate 5 -1
constants for the primary hydrolysis are 10 kspectro(sec ·) 5 -1 = 39.8±0,3 and 10 kc1 (sec ) = 52.1±0.8. These data have been
interpreted in terms of a mechanism whereby the tran:~-d ichloro
cation hydrolyses in acid solution to produce three aquachloro
species. The major component has assigned fac- . ' 2
a,b, ,c-CoCl(NH3) (dien) (OH 2) + configuration, and the rate
of hydrolysis of this isomei has been measured by chlor
5 -1 ease, and in 1.0 F HN0 3 at ~98.2 K, 10 kc1 (sec ) -
7.89±0.28.
meters have been calculated and are discussed.
The acid d sociation constants for the equilibria
3·'-trans-Cr (AA) (BB) (OH 2
) 2
3 0 (aq) pi<
2
where AA = BB c-:: en; AA = en, BB tmd; AA :::.:: BB = trod have been
determined. Similar ts were obtained each complex:
pK1 ca. 4.2, pK2 ~· 7.6; 1 !::. Na~o 3 , 298.2 K. The results are
compared with pK data for related complexes of chromium and
cobalt. The complex Cr(OH) (en) 2 (oH 2 ) 2+ undergoes extensive
Cr-N bond rupture to yield deaminated products.
The crystal structure of one isomc~r of [Co (ox) (NH 3
) (cHen) ] ··
N0 3 has been determined. The three nitrogen atoms of the
diethylenetriamine ligand are in a plane with one oxygen atom
of the oxalate ligand, while the second oxalate oxygen atom is
~~~ ·to Jche ammonia group. The orientation about the
secondary nitrogen group of the diethylenetriamine ligand is
such that the NH proton is adjacent ·to the coordinated ammonia
ligand.
CONTENrrs
2.3 Kinetic Measurements
2.5 Chemical Analyses
2.6 Spectral Measurements
3~1 Introduction
+ ~-~-MX2 (AA) (tmd) Systems
+ ~-MX2 (AA) (tmd) Systems
4.1 Introduction
4.2 Results
4.3 Discussion
5.1 Introduction
5.2 Results
5.3 Discussion
(Ammine) (diethy lenetr:Lamine) oxalatocobalt (III)
Nitrat.e 129
6.4 Chemical Implications 143
CHAPTER 7: Conclusion 146
2.2 Analytical Data for Cation Complexes in Solution 19
2.3 Visible Absorption Maxima and Minima (320-650 nm) of
some Aqua-, Aquahalo- and Dihalo(diamine)chromium(III)
and Cobalt(III) Complexes in Aqueous Acidic Solution
at 285-·296 K.
some Diaqua·-, Aquachlo~o- and Dichloro(tetraamine)-
cobalt(III) Complexes in Aqueous Acidic Solution at
285-296 K.
Hydrolysis of tra_r;.§.~Crx 2 (AA) (tmcl) + --~--)' 2+
tJ~~~crx (AA) (tmd) (oH 2 )
3.2 Percentage ~-Diaqua in the cis~~~!:E~~~­
Co(en) (tmd) (OH 2
Hydrolysis of ~-~-crc1 2 (tlud) 2+
3.4 Spectrophotometric Kinetic Data for
Hydrolysis of ~-CrBr2 (t:.md) 2 +
3.5 Spectrophotometric Kinetic Data for
+ Hydrolysis of tr~~-crc1 2 (en) (trod)
3.6 Spectrophotometric Kinetic Data for
Hydrolysis of ~~-coc1 2 (en) (t.:md) +
3.7 Halide Release Kinetic Data for the
+ Hydrolysis of tr~}1S_-crcl 2 (tmd) 2
3.8 Halide Release Kinetic Data for the
Hydrolysis of t~~-CrBr 2 (tmd) 2+
the Primary
the Primary
the Primary
Hydrolysis of ~':2:.~!:E_~Cocl 2 (en) (tmd) +
3.11 Chromatographic Kinetic Data for the Primary
Hydrolysis of trans-CrCl (tmd) + ·---~--~-·-- 2 2
3.12 First-Order Rate Constants for the Primary
Hydrolysis of ~ns-MX2 (AA) (tmd)+ (l\1 = Co,Cr; .. X = Cl,Br; AA = en,tmd) in Acidic Solution
3.13 Kinetic Parameters for the Primary and Secondary
Hydrolysis of some MX2 (AA) (BB)+ Cations (M == Co,Cr;
X= Cl,Br;M,BB =en,pn,.t.md) in Acidic Solution at
2 9 8 I<.
3.14 Halide Release Kinetic D~ta for the Hydrolysis of
2+ ~-CrCl (tmd)
2 (OH 2 )
2+ !:yan~-CrBr (tmd) 2 (OH 2 )
3.16 Halide Release Kinetic Data for the Hydrolysis of
2+ t::~.r:.~·~CrCl (en) (tmd) (OH2 )
3.17 Halide Release Kinetic Data fo~ the Hydrolysis of
~is-CoCl (en) (tmd) (OH 2 ) 2+
3.18 First-Order Rate Constants for the Formation of X
in the Hydrolysis of HX(AA) (tmd) (OH 2
) 2+ (M = Co,Cr;
4.1 Titration Data for the Addition of Alkali to
. 3+ Solutions of trans-Cr(A) 2 (oH 2 )
2
Tetraaminediaqua Complexes of Cobalt(III) and
Chromium (I I I)
Hyc':l.rolysis of ~·~CoC12 (NH3) (ellen)+ 102
5.2 Halide Release Kinetic Data for the Primary
. . + Hydroly::ns of !:E.::~~~cocl 2 (NH 3
) (dJ.en) 104
Hydrolysis of _!:}'arw-coc1 2
106
~~~:-CoCl (NH 3 ) (dien) (OH 2
) 2+
) 2+ in 1. 0 F
108
HN0 3 110
5. 6 Percentage of ~rans-Co~l (NH 3 ) (dien) (OH 2 ) 2+ in the
Aquachloro Product Mixture
5. 7 Percentage 9~-co (NH 3) (dien) (OH2 ) 2 3+ in the
cis trans Equilibrium Mixture
5.8 Rate Constants Estimated for the Primary Hydrolysis
of trans-coc1 2 (NH 3) (cHen)+ in 0. 3 F HN0 3
5.9 Kinetic Parameters for the Primary Hydrolysis of
+ _!:ra~::?..~Cocl 2 (NH 3 ) (dien) at 298 K
5.10 Kinetic Parameters and Steric Course for the Acid
112
117
120
124
5.11 Kinetic Parameters for the Acid Hydrolysis of some
~}_s,-Tetraamineaquachl.orocobal t (I I I) Corn.plexes at.
298 K. 128
[Co (ox) (NH 3) (cHen) ]No3 136
6.2 Observed and Calculated Structure Amplitudes for
[Co (ox) (NII3 ) (dien) ]No3 138
6.3
6.4
Co(ox) (NH 3
141
142
Cr(tmd)2(oH2)23+ in 0.6-L~) ~~ IIN0 3
a·t 293-296 K. 41
3.2 Visible Absorption Spectra of 9i~- and ~ns~
Cr(en) (-tmd) (OH 2
at 293~296 K 42
3.3 Spectral Changes in the Primary Hydrolysis of trans-
crcl 2
(tmd) 2 + 45
3.3(a) Visible Absorption ·Lr~-crcl 2 (trnd) 2 + in 0.6 F HN03 and tri!E~-CrCl(tmd) 2 (oH 2 )cl 2+ in 1.0
~ HN0 3
3.5
tr~-CrBr2 (tmd) 2+ Spectral Changes in the Primary Hydrolysis of
+ trans-crcl 2 (en) (tmd)
3. 6 Visible Absorption Spectra of t:ra;.~~-CoC1 2 (en) (-trod)+,
cj::~-CoCl (en) (tmd) (OH 2
) 2+, cis~·Co (en) (tmd) (OH2 ) 2 3 +,
and F Formed Product ( s) of Hydrolysing !=-rans~~
47
48
3.7 Spectrophotometric Kinetic Data for the Primary
3.8
Hydrolysis of ~~-CrC1 2 (en) (trod)+
3.9 Halide Release Kinetic Data for the Primary
Hydrolys
Hydrolysis of ~!!~-cocl 2 (en) (±:md)+
3.11 Concentration-Time Curves for the Hydrolysis of
+ ~--:CrC1 2 (tmd) 2 in 0.1 ~ HN0 3 at 300.7 K
59
62
66
69
71
2+ tr~--CrCl (en) (trod) (OH
2 ) 84
2+ ~i~.--cocl (en) ('crnd) (oH 2 ) 86
3.14 A Possible Reaction Scheme for the Loss of trans-
2+ CrX(AA) (tmd) (OH
2 ) in 1.0 ~ HN0
"t11td; X ""' Cl,Br) 90
CoC1 2
gydrolysis of trans-cocl 2 (NH 3) (~ien)+ 103
5.3 Halide Release Kinetic Data for the Primary
Hydrolysis of ~~.-coc1 2 . (NH 3
) (di~n) + 10 5
ci~-CoCl (NH 3
Co (NH 3) (dien) (OH 2 ) 2
3+ and the cis ~~~2..~
Equilibrium Mixture in 1.0-1.5 ~ HN03 at 293-296 K 116
5.6
5.7
6.1
Cocl2(NH3) (dien)+
:t:_r?-.~-coc12 (NH 3 ) (dien) +
Cation
119
122
139
ABBREVIATIONS
dpt == dipropylenetriamine = H2N(CH 2
NH 2
3,3,3-tet = H2N(C~2 ) 3NH(CH2 ) 3NH(CH 2 ) 3NH 2 eye lam = 2,3,2,3-tet = 1,4,8,11-tetraazacyclotetra-
decane
azacyc1otetradecane
methy1-1,4,8,11-tetraaza-
cyc1otetradecane
!=-r~[ 14 ]diene = 5 r 7, 7' 12,14 '14-hexamethyl-1, 4, 8, 11-te·traaza­
cyclotetradeca-4,11-diene
1
GENERAL IN'I'RODUCTION
octahedral transi metals have been the subject of intensive
investigations. By far the greatest amount of da·ta has been
obtained for substituted cobalt.: (III) -amine complexe$,
presumabl.y because of their ease of formaJc:Lon and their
relatively inert behaviour, so that conventional techniques
can be used to follow the reactions. ~any of these studies
are investigated by kinetic methods in aqueous acidic solution,
where the reaction is generally referred to as solvolytic
aquation. Here the aniono ligand is being replaced by a water
molecule and the stoichiometric equation can be written as
k MA BXn+ + H 2 o ~~--) · NA BOH (n+l) + +
4 slow 4 2
reactions of this type usually follow first-order kinetics.
Since the concentration of water remains unchanged during
aquation, the kinetic form alone cannot be used to deduce the
teaction mechanism. However, the way in which the rate
constant is affected by various changes in the nature of the
complex ion is expected to give us some information about
mechanism of octahedral substitution.
principal mechanisms by which ligand sub tution reactions
can be expected to occur. They are the SN1 (substitution,
nucleophilic, unimo ular) and the SN 2
( substi ·t:ution, nuc
rate law is compatible with the above t:wo mechanisms and
can be illustrated as lows:
k SN ( MA BX]n+ ---~-> [MA Bj(n+l)+ +X
4 1 . 4 {dissociative) slow
[MA B] (n+l)+ + H 0 4 2
fast· [MA BH O] (n+l)+ 4 2
SN2 (associative)
It difficult to classify substitution reactions between
these two extreme stic possibil as the problem of
the mechanism of the actual replacement remains. Between
se two extremes are all degrees of "concerted 11 mechanisms,
in which the loss of the aniono ligand X does not become
2
2 kinetic studies toge·ther with theoretical arguments can be
employed to discuss differing requirements of the
unimolecular (SN1 ) and the bimolecular (SN 2 ) ·transition s-L~ate
and hence to elucidate the mechanism of aquation. Approaches
3
such as the correlation of reaction rates with steric effects,
charge effect, nature of the leaving groups, natUre of the
entering groups, electronic effects df ligands, solvent effect,
and steric courses of the reaction are used in order to under-
stand the mechanism for a particular reaction. In a recent
. 3 h t f h . . . d' . revlew on t e na-ure o· t e reactlve lnterme lates ln octa-
hedral substitution mechanisms, Sargeson seems to favour the
existence of species of reduced coordination number.
The major part of this thesis is a study of the aquation
reaction rates of some cobalt(III) and chromiurn(III) tetra··
~mines in order to highlight the similarities and differences
in reactivity between c6mplexes of the two central metal ions
and, if possible, to provide further insight aB to the nature
of the aquation mechanism.
EXPEIUl\tENTAL
2 .1 PREPARATION OF' SOI,ID COMPLEXES
4 5 !.ran?_- [ CrC1 2 ( tmd) 2 ]ClO 4 , !:E~l?_~ [ CrP 2 (py) 4 ]N0 3 :t:r:,~~l!:?:-
[CrF2(en)2)Cl04 5 , t:t;:,a~·-·[CrBr 2 (en) 2 ]Br.n2o 6 , Co(N0 2) 3 (dien) ·;
Co(Cl) (N0 2) 2 (dien) 7 and Na 3[co(co3) 3 ].3H2o 8 were all
prepared by the literature methods using the commercial am:i.nes.
Crystals for the crysial structure analysis of [Co(ox) (NH 3) (d~n)]­
N03 were supplied by Dr D.A. House. 1,2-Diaminoethane was
obtained from Fluka AG Laboratories, 1,3-diaminopropane from
Aldrich Chemical Co., and diethylenetriamine from Koch-Light
Laboratories; all were used without further purification. All
other chemicals were of Reagent grade quality. Analytical
data for the previously described compounds were in satisfactory
agreement with the formula, and data for the previously
unreported complexes are presented in Table 2.1.
tra.n_s_~Bis ( 1, 3-diaminopropane) dichlorochr.omium (III) Bromide:
A modification of the preparation 4 of the perchlorate salt
was used. CrC1 3 .6H2o (16.2 g) in DMSO (75 ml) was boiled for
10 min. A mixture of tmd (10.2 ml) and DMSO (45 ml) was added
and the solution was boiled for a further 2 min. After cooling
to 333 K, the dull-green coloured solution was poured into 900
ml of well-stirred acetone. The purple precipitate that
deposited was filtered off, washed with acetone (3 x 50 ml),
and the still damp solid was suspended in HBr (60 ml, 48%).
This suspension was heated on a steam bath for 10-15 min.,
during which·time green crystals deposited~ These were
collected from the ice-cooled solution and washed with ethanol
(3 x 25 ml), ether (2 x 25 ml) and air-dried. The yield was
5 g (24%).
The mother liquors from the previous preparation were returned
to the steambath for 15 min. HClo 4 (15 ml, 60%) was added and
the solution allowed to cool slowly. The green crystals (1 g)
that deposited overnight were collected, washed with 2-
propanol and ether and air-dried.
This complex was prepared by heating ~~ns-[Cr(OH) (tmd) 2 (oH 2)]­
(Cl04) 2 (2 g) in HBr (20 ml, 48%) on a steambat:h for 10 min.
to form an orange-brown solution containing bright green
crystals. After cooling to room temperature, the crystals
were collected, washed with 2-propanol and ether and ~ir-dried.
The yield was 1.7 g (80%).
Perchlorate: This salt was obtained using a modification of the
4 preparation used for !~·-[Crc1 2 (trod) 2 Jc1o 4
A solution of
green crcl 3
.GH 2o (16.2 g) in DMSO (75 ml) was boiled for 10
min. An equimolar mixture of the diamines (9.3 ml) in DMSO
(45 ml) was added to the hot solution and boiling was continued
for a further 2 min. After cooling to 333 K, the dull green
solution was poured into 900 ml of well-stirred acetone. The
purple precipitate that deposited was filtered, washed with
acetone (3 x 50 ml portions) and the still damp solid was
suspended in HCl (60 ml, 12 F). This suspension was heated on
a steambath for 10 min., when HCl0 4 (30 ml, 60%) was added.
The solution was cooled slowly and the green crystals that
deposited ov~rnight were collected, washed with 2-propanol and
then ether, and air-dried. The mother liquors were returned
6
to the s·tearnbath for 15 min. HCl ( 15 ml, 12 ~) was <:1dded
the solution cooled slowly. This procedure was repeated
several times to give either or purple crystals. The
total yield was 6.5 g or 29%. Microscopic examination of all
the crystal c showed them to be mixtures. Those contain-
ing the bulk of the green product were recrystallised from hot
0 .1 !:_ HCl by the addil:.i.on of equal volumes of 12 ~ HCl and
60% HClo4 • Green crystals
obtained was £i~- [Crcl2 (en}) Cl. H2o.
trans-Bis(l,3-diaminopropane)aquahydroxochromium(III) ~~~------.-·-~---·-,~=,.,~--~-
Perchlorate: A suspension of 3 g of !,~ns·m[CrC1 2 (tmd} 2 ]ClO 4
in 30 ml of water containing 10 ml of pyridine was heated on a .
steambath for 10 min. to form a red~brovm solution.
NaClo4 .H2o (5 g) was added and the orange crystals
deposited from the ice-cooled solution were collected, washed
with 2-propanol and ether and air-dried. The yield was 1.4 g
(41%).
trans-(1,2-Diaminoethane) (1,
[crc12 (en) (tmd) ]clo4 usincg a method analogous to that above.
trans-Bis(1,2-diaminoethane)aquahydroxochromium(III) Perchlorate: ~~~~ _, ___ ,.. ____ • ._.__~~-""'-"' n: - ""~"""""--"' =- ~--=-~~~··
tr~§:-(Cr (OH) (en) 2 (OH2)] (Clo4) 2 was prepared from ~ra~­
{CrBr2 (en) 2 ]Br.H2o 6 via tran_::J_-[CrF 2.(py) 4.]N~ 3 ~ and~­
[CrF2(en)2]clo4 5 • The preparation followed the method r
trans- [ Cr (OH) (tlud) 2 (OH 2) ] (ClO 4) 2 •
7
~E~;t~~::.~~~~i~~~ti_r:o:thane~-~l,~~-·dial~P!:'OJ2~~~~~2:~~:::::~.::o~.~~t (I2.Il_
~hlo2:Lcl~Mo2:w~l]Y~E~t~.: A modification of ·the method of
Schlessinger9 for tr~·-[CoC1 2 (en) 2 ]Cl was used. A solution
of cocl 2 .6n2o (30 g) in water (90 ml) was added to an equi­
molar mixture of the diamines (19.1 ~1) in 100 ml of water and
a vigorous stream of air was drawn through the liquid for six
hr. The dark red oxidised solution was placed in an evaporat-
ing dish and HCl (66 ml, 12 ~) was added. The volume was
reduced to 100 ml on a steambath and the green crystals that
were obtained on cooling overnight were washed with 2-propanol,
ether and air-dried. 'I'he mother liquors with added HCl (20
ml, 12 F) were returned to the steambath for 20 min. to obtain
a second crop. The total yield was 11.6 g (31%).
!:J~2-Diaminoethan:) ( 1, 3~dia.:nir:ogr::.,p~~2.~~~!-J!2:.2_
Perchlorate: The mother liquors from the previous preparation
were returned to the steambath for 30 min. with 20 ml of 60%
HClo 4 added. An additional 10 ml of HC1o 4
(60%) was added and
the solution allowed to cool slowly. The green crystals
obtained (12 g) were washed and dried as above.
X-r characterisation. In view of the possibility that the
mixed amine compounds could contain the [CrC1 2 (AA) 2 ]clo4 or
[ Cr (OH) (AA) 2
) ·] (ClO 4 ) 2 . (AA = en, ·trod) products, two sets of
X-ray powder photographs were obtained. Photographs were taken
for all three dichloro and all three aquahydroxo perchlorate
salts. In both cases the series of lines in each three
photographs were different and non-superimposable. This
provides additional evidence for the formation of the mixed
diamine complex.
~~~-~~~:::l:~~!:J~l-~~.hy~~!:E~~~~ne·} ~~-:3~~~-
Pe:t.::?_~~d::::,: Co (N0 2) 3 (dien) was converted to Co (Cl) (N0 2) 2 (dien)
by the literature rnethod7 • !;r~~ ... [Co (N0 2 ) 2 (NH 3
) (dien)] Cl was
prepared using a modification of the method of Crayton and
7 Mattern . Co (Cl) (No 2
) 2 (dien) ( 79 g·) in 4 00 ml of water contain-
ing 100 ml of concentrated NH 3 was evaporated to ca. 200 ml on
a stearnbath. Trw solution was allowed to cool overnight ·when ,
the product was filtered, washed with ethanol and ether and
air-dried. The mother liquors were evaporated to half-volume
to obtain a second crop. The total yield was 33.7 g (41%).
10 A modified version of the preparation of .Ablov and Papa
was used to obtain tr~- [ coc1 2 <.NH 3
) (dien)] ClO 4 • A
) 2
) (dien) ]Cl ( 13.2 g) in HCl
(200 ml, 12 ~) was boiled for 15 min, when it was transferred
to a steambath and HClo 4
(40 rnl, 60%) was added. The green
crystals that deposited were digested at 353 K for 15 min.,
the solution cooled to room temperature, and finally cooled
for one hr in an ice-bath. The product (10 g, 67%) was
collected, washed with 2-propanol and ether and air-dried.
PREPARATIONS AND ATTEMPTED PREPARATIONS OF' COIVi.PI.EXES NOT USED
IN KINETIC STUDIES
trans~(l,2-Diaminopropane) (1,3-diaminopropane)dichlorochromiumQII)
Perchlorate: A preparation following the same lines as that used
for trans-[Crcl 2
(en) (tmd) ]Clo 4
was obtained.
trans-(1,2-Diaminopropane) (1,3-diarninopropane)dichlorocobalt(III) ·-.,.~~ . ~'""""""~~-~~ ......... =----~-,.,._,_. --~------~~,_,.__---=,..,..~~...,.,.~-"""·-""~~-·-'=·~~-·-·~"-"-·<>"'-''"....-=~··- Perchlorate: A solution of cocl 2 .GH2o (10 g) in water (30 ml)
was added to an equirnolar solution of the diamines (7.1 ml) in
34 rnl of water, and a vigorous stream of air was drawn through
9
the liquid for 6 hr. The dark red oxidised solution was
placed in an evaporating dish and HCl (22 ml, 12 ~) was added.
The volume was reduced to 34 ml on a steambath and HClo 4 (20 rnl,
60%) was added. The green crystals (8 g, 50%) that were
obtained on cooling the solution slowly were washed with 2-
propanol, ether and air-dried.
trans-Bis(2,2-dimethyl-1,3-diaminopropane)dichlorochromium(III) ~~~~~._.-__,.,_~"'---~=·-"'=~"""'-0 -="""""'~~="""~~~~-"'-'-~=~-~~~-=-~~"'"'"""'=~-~--
Pe~·a te.: The diamine, dan, was prepared as the dihydro- . . 11 12
chloride salt, dan2HC1, by the l1terature methods ' . Using
this salt, the preparation of :cra._~-[CrC1 2 (dan) ]Cl04 was
at·t:empted using methods similar to that for tr~'_-[Crcl 2 (trod) 2 ]-
4 5 Clo4 and tra~-[CrF 2 (en) 2 ]~lo 4 , but no product was
obtained.
[co(co 3
o 8 (8.3g) was added
dan.2HC1 (8 g) in water (46 ml). The solution was heated on a
steambath for 10 min., when HCl (14 ml, 12 F) and HClo 4 (12 rnl,
60%) were added. The solution was cooled slowly and the green
product was filtered, washed with 2-propanol and ethe~ and
air-dried. The yield was 1.2 g (12%).
trans-(1,2-Diaminoethane) (1,3-diaminopropane)dibromochromium(III) ·-~- ,'
---·-~----·----,~-----~-~~-~--
~amide _!1o~<;>h~~: A method similar to that used for the
preparation of t~-[CrBr2 (en) 2 ]Br.n2o S,G was used, bu·t only
the analogous bis (1, 2-diaminoethane) complex was ob·tained as
product.
:t;:~~-Bis ( 1, 3-diaminopropane) d.iaquachre>rnium (III) 'J~ribromide -----=---~==~--'"""'==~ .... """"-~~"'-~=~----=~""""""·'"""'"'"""~-·--~-,~--~~· ~ . ~o~ohydra"l:~: ~!~::.- [ Cr (OH) ( tmd) 2 (OH 2 ) ] (ClO 4 ) 2 was converted
into ~~-[Cr(trnd) 2 (oH 2 ) 2 ]Br 3 .n2o using· a modification of
Woldbye's preparation of tr~~~.-[cr(en) 2 (oH 2 ) 2 ]Br 3 .H2o 13
~ran~-[Cr (OH) (trod) 2
(oH2 )] (Cl0 4
minimum quantity of HBr (63%) on a steambath. After cooling
the solution in ice the orange crystals were filtered, and
10
washed with 2-propanol and ether. The yield was 1.4 g (62%).
This salt was cJ.lso prepared direr..:tly from _!.}?an~- [crcl 2 ~
(tmd) 2 ]clo4 by c1 solving 1 g 30 ml of 0.5 F NaOH at 313 K.
HBr (40 ml, 63%) was added and the orange solution cooled in
ice. The product (0.2 g, 18%) was filtered and washed and
dried as above.
:;rribromi:§e ~llonoh~drat!l: A method analogous to the prepara:td.on
of trc;m~-[Cr(tmd) 2 (oH 2 ) 2 ]Br 3 .H 2o from ~.£§..-[Cr(OH) (tmd) 2- . .
(OH 2)] (Cl04 ) 2 was used. A 44% yield was obtained.
cis-(Ammine)aquachloro(diethylenetriamine)cobalt(III Sulphate:
A 30 x 3 em anion~exchange column of Anlberl IRA-400 resin
in the Cl- form was washed with 1200 ml of 0.3 !:'..H2so 4 to
convert it to the so; form. When it had been left standing
over 0.3 F H2so4 for one hour, the coluw1 was washed with 40
trans-
[Cocl2 (NH 3) (dien) ]Clo4 (1 g) was dissolved in 200 ml of 0.01 F
H2so4 and left at 298 K for 2 hr. The red solution was
adsorbed onto the· prepared column. 'AJhen red. effluent began to
appear it was collected in a 600 ml beaker. The column was
washed with 0.01 ~H2so4 (40 ml) until all the :ced colour had
been removed from the column. The solution "ms then set as
to evaporate slowly, but no crystall product was obtained.
TABLE 2.1
Analytical Data
*!n the case of c1o 4
salts, only ligand halide was determined.
FowJ.d C% H£,
42.4
35.6
53.9
19.99
34.90
The ionrexchange material used was Zeo-Karb 225, SRC-6
cation-exchonge resin in the Na+ form (52-100 mesh) for all
preparations except !:r~-crcl 2 (tmd) 2 + where Zeo-Karb 225,
SRC-13 cat:Lon-,exchange resin (14-·52 mesh) was used. The
dichloro and dibromo cations were isolated ush1.g 6 x 1 em
columns cooled by a jacket of circulating ice-water, and all
12
others using a 10 x 1 em column; ic~~water cooled in the case
of the complexes der.ived from !~-cocl2 (NH 3 ) (dien)+ and tap­
.water cooled for the remainder. The preparation and analyses
of the cationic complexes were repeated at least three times
to check the reproducibility of the ion-exchange separations
and the visible absorption spectral parameters. Data for the
analyses of the effluent solutions are presented in Table 2,2 •.
The !:£~-Bis ( 1, 3-diaminopropane) dichlorochromi urn (III). Cation:
The green tra~-crc1 2 (tmd) 2 + cation was isolated by suspending
- ca. 150 mg of trans-[crcl
2 (tmd)
dripped directly onto the top of an ion-exchange column, pre-
washed with 1.0 F and then 0.025 ~ HN0 3 . The green band that
formed at the top of the resin column was washed with 30 ml of
0.025 F HN0 3 and the green dichloro cation was then eluted
with 50 ml of 0.6 F HN0 3 into an ice-cooled flask. The
absorption spectrum was recorded in@ediately.
The trans-Bis(l,3-diaminopropane)dibromochromium(III) Cation: -~~~~-·-·-- :0 ==-'""""..,'''''"''-~-~-~~"""~~=-~--~--""----·~-,-.,.,...,.....,~
The green trans-CrBr 2
(tmd) 2+ cation was isolated in solution
+ by a method similar to that used for t~~crc12 (tmd) 2 ,
except that 0.3! HN0 3 was the eluting agent.
13
The trans-(1,2-Diaminoethane) (1,3-diaminopropane)dich1oro­
--------:=·-·~·.L·~C-·"-a~t __ i.~o __ n~: The green trans -"ere 12 (en) ( trnd) + cat ion
was genera"l:ecl solution by methods analogous to those
+ ~2~.-·CrC1 2 (tmd) 2 except that 0.4 F HN0 3 was the eluting
agent.
'rhe trcms- (1, 2 arninoethane) ( l, 3-diaminopropcme) dichloro~
-~~"--~-_;.__c_a __ "~t~-i~o~n: 'I'he gre(-:Jn _!:r.l!:.!ls-CoC1 2 (en) (tmd) + cation was
isolated in solut:ion by me·t:.hods similar to those for tr;:t~-
+ CrBr 2 (tmd) 2
) {dien) cation was generated
in solution by analogous methods to those used for ~r:~­
Crcl2(tmd}2+, except that the green band was washed with 30
ml 0.1 ~ HN0 3 , and the dichloro cation was eluted with 0.3 ~
HN0 3 •
The orange _!:ra~~~-CrCl (tmd) 2
(oH 2
) 2+ cation was generated. in
solution by allowing !;r;'l~-[CrC1 2 (tmd) 2 ]clo4 (~. 150 mg 50
ml of 0.1 F HN03) to hydrolyse for 1.5 hr at 318 I<. The cooled
reaction solution was adsorbed on an ion-exchange column
which had been pre-washed with 2 F and then 0.1 F HN0 3 •
Elution with 30 ml of 0.6 ~' followed by 20 ml of 0.8 HN0 3
removed the unreacted t~~~~-crcl 2 (tmd) 2+ cation and the orange
2+ ~~s-CrCl (tmd) (OH2) cation \.Yas eluted with 50 ml of 1.0 F
HN0 3
The trans (1,3-diaminopropane} (III) Cation:
The green-brown ~:2.·-CrBr (tmd) 2 (OH 2) 2+ cation was prepared by
a similar method to that used for the aquachloro analogue,
except that the heating time v;ras reduced to 20 min. before
adsorption on an ion-exchange column.
'rhe trans-· (1,2~·Diaminoethane) (1, 3~diaminopropane) aquachloro~ --~~~~~==,....""""-""""""""-...-.. --""""'-__ ~ ... ...-"'"_.~·-=-"""_"",_~~·~'~=~~..._.=--... ~--· ~-"""~--.-~~._,.,~=o,._~""=•'=·~
Cat.ion:
cation was isolated in solu·tion by a method similar to t.hat
2+ used for ~~~-CrCl(tmd) 2 (oH 2 )- •
The cis-(1,2-Diaminoethane) (1,3-diaminopropane)aquachloro- --=~~-,"'--~-~··~· ~~----~~.~--~"--" -~-~~~---~-. -~~-·--· -· -·~·~
14
---~=~~"~~C~~~a.~t_i_o_n.: The purple cis-CoCl (en) (tmd) (OH 2) 2+ cation
was generated in solution by allowing !:£<::-~- [cocl2 (en) (tmd)] ClO 4
(~. 200 mg in 30 ml of 0.1 £:. HN0 3) to hydrolyse for 5 min. at
. 313 K. The cooled solution was treated as outlined for trans-
2+ erCl(tmd) 2 (oH2) •
The cis*:;>: trans- (Ammine) aquachloro (die·thy lenetriamine) cobalt (III) ---=~-..-:.z,;:==--·~- . ~ - ---~"·-~------· Cation Equ~~ibrium Solution: 'rhe pink cis*~tran~-CoCl (NH 3)-
(dien) (OH2 ) 2+ equilibrium solution was isolated by allowing
~· 120 rng of trans- [ CoC12 (NH 3) (dien) ]ClO 4 to hydroly.se in 50
ml of 0.1 ~ HN0 3 for 6 hr at 286.5 K. The solution was then
treated by a method analogous to that used for trans-
2+ CrCl(tmd) 2 (oH2) • When 'chis a.quachloro product(s) mixture
was left at room temperature until no further change in the
visible absorption spectrum was observed (~ •. 24 hours), an
equilibrium cis-diaqua-cis-aquachloro mixture was obtained.
Analysing the equilibrium solution for total cobalt and free
chloride ions showed that it contained about 90% diaqua with
about 10% of the chloride still coordinated.
The trans-Bis(l,3-diaminopropane)diaquachromium(III) Cation: -~=~~;;.~------..- --·~. ='"-'"'"-"""-~-==~=,-~----~~--
The orange ~-Cr(tmd) 2 (oH2 ) 2 3 + cation was synthesised by
allowing£.~· 150 mg of ~s-[crcl 2 (tmd) 2 ]clo 4 to hydrolyse
* See Section 5.2.1 for nomenclature.
15
in 50 ml of distilled water for 6 hr at 308 K before cooling.
HN0 3 (6 ml, 1.0 F) was then added and the resulting orange
s~lution was adsorbed on an ion-exchange column which had been
pre-washed with 2 F and 0.1 ~ HN0 3 . The orange band was
washed with 2 x 50 ml of 1.0 F, follciwed by 30 ml of 1.25 F
HN0 3 and the desired cation was eluted with 1.5 F HN0 3 into an
ice-cooled 50 ml flask, discarding the first 10 ml. The
absorption spectrum was measured immediately. This cation \·,·as
also obtained by using the same procedure with trax~-
[CrBr 2 (tmd) 2 ]Br.
The same complex was also prepared from trans-
[ Cr (OH) (trod) 2 (OH 2) ] (ClO 4) 2 , ~i ther by dissolving an accurately
weighed amount in 0.6 F HN0 3 and measuring the absorption
spectrum, or by taking ~· 120 mg in 30 ml of 0.6 ~ HN0 3 and
adsorbing this solution on a cation-exchange resin (pre-washed
with 2F and then 0.6 ~ HN0 3). The orange band was washed with
30 ml of 1.25 ~ HN0 3 and the cation was eluted with 1.5 ~ HN0 3
into a 50 ml ice-cooled flask, the first 15 ml being discarded.
All four methods gave absorption spectra which were identical
in the position of the maxima and minima and in molar
absorbancy indices.
The trans-(1,2-Diaminoethane) (1,3-diaminopropane)diaqua- n·.,· ~~-~===--=-
ct!£omium(III) Cation: The orange trans-Cr(en) (trod) (OH 2) 2 3+
was generated from trans-[crcl2 (en) (tmd) ]Clo4 by allowing ca.
150 mg to hydr6lyse in 50 ml of distilled water for 3~5 hr at
313 K. The cooled solution was treated as outlined for trans- --"~"'"""'
3+ Cr(tmd) 2 (oH2 ) 2 • The same complex was formed from trans-
[Cr(OH) (en) (tmd) (oH2)] (Clo4 ) 2 by the two methods used for
3+ ~s-Cr (tmd·) 2 (oH2) 2 • All three methods gave absorption
spectra which were identical in the position of the maxima and
minima and in molar absorbancy indices.
16
The trans-· (Ammine) diaqua (diethylenetr.iamine) cobalt: (III) Cation: --;~~~~~""""' .... =---=--=m=-.>=-~~---~~~-~-~""~""-""~·"$'-"'--"""-'=~-~~·.:.o-""'""'"-'=.,..-__..,-=>~~..-_,._-c~· ~-~
The yellow-orange t:rans_-·Co (NH 3) (cHen) (OH 2) 2 3+ cation was
generated by dissolving an accurately weighed amount of ,!-,.rans~
[cocl2 (NH 3)(dien) ]Clo4 in s::a. 25 ml of 0.5 F NaOH and after
3-4 min. making up to 50 ml with 1 ~ HN0 3 • The absorption
spectrum was measured immediately.
'I'he same complex was formed by taking ~~· 100 mg ~.-
[Cocl2 (NH 3) (dien) ]Clo4 in 30 ml .of 0.025 ~ HN0 3 and filtering '
the unreacted solid from the solution which dripped directly
onto the top of an ion-exchange column (pre-washed with 2 ~,
and 0,025 ~ HN0 3). The green band was washed with 30 ml of
distilled water, 30 ml of 0.1·~ NaOH, and eluted with 40 ml of
0.1 F NaOH into an ice-cooled 50 ml flask. 10 ml of l ~ HN0 3
was added to make the solution ~p to_the mark. Both methods
gave absorption spectra which were identical in the position
of maxima and minima and molar absorbancy indices.
The cis-Bis(l,3-diaminopropane)diaquachromium(III) Cation: ~':;,c·~~=·"--·----~""""'=~·-~--=~-.... ~~.~..._..,~.~-... ~-=-
3+ The orange ~-Cr(tmd) 2 (oH2 ) 2 cation was prepared by dissol-
ving ~· 150 mg of tra~- [crcl 2 (tmd) 2J ClO 4 (or ~~­
[CrBt2(tmd)2]Br) and 500 mg mercuric acetate in 50 ml of 0.6 F
HN0 3 and leaving the solution at room temperature in the dark
for three days. The solution was then adsorbed on an ion-
exchange column which· had been pre--washed with 2 ~ and then
0.6 ! HN0 3 • The orange band that formed was washed with 40 ml
of 1. 0 ~' followed by 20 ml of 1. 25 F HN0 3 and tb.e desired
c6mplex was eluted with 50 ml of 1.5 ! HN0 3 •
The cis-(1,2-Diaminoethane) (1,3-diaminopropane)diaquachromium(III) ---='"-~- " -----~~-----~---"~--~-~~-----~-------~~~"- Cation: The orange cj;~-Cr (en) (tmd) (OH 2) 2
3+ was isolated in
solution by ~ethods analogous to those used for cis-Cr(tmd) - -- 2
17
The cis-(1,2-Diaminoethane) (1,3-diaminopropane)diaquacobalt(III) -~~~-"""'~~=-----"'----·-· ••«<l--""""'-""-''14-~·-~,.,..,~~~-~-~-=-.. .,.....,""""'~-=~-~=,==-~·'"''_,~
Cat.ion: The orange-pink c~E.:;.~Co (en) (tmd) (OH 2) 2 3+ cation was
generated by a method similar to that used for the Cr(III)
analogue.
The ~~~~- (~~~=L~-ia~'I:~~n~die~~)'~~net.~m1th~::) cc:~a~II_I) _ca~~:
The orange·-pink S:i.~·~Co (NH 3) (dien) (OH 2) 2 3+ cation was isolated
in solution by a similar method to that used for cis-
3+ Cr(tmd) 2 (oH 2) 2 , except that the solution was left for one .. day before adsorbing on an ion-e~change column, and the orange
band was washed wii:h 80 ml of 0. 6 ~~ 100 ml of 0. 8 F and 50 ml
of 1.0 ~ HN0 3 before elution with 1.0 F HN0 3 .
An identical absorption spectrum was obtained by dissolving
ca. 150 mg of !~-[coc12 (NH 3) (dien) ]Clo4 in 50 ml of 0.3 F
HN0 3 and leaving the solution at room temperature for two
days. The solution was adsorbed on an ion-exchange column
that had been prewashed with 2 F and then 0.3 ~ HN0 3 • The
resulting orange band was washed with 30 ml of 0.6 F, 50 ml of
0.8 ~' 30 ml of 1.0 F HN0 3 , and then eluted with 1.5 ~ HN0 3 ,
the first 20. ml being discarded. The absorption spectral
parameters were measured immediately and until no further
change was observed.
The cis,=: ~r~m~s- ( 1, 2-Diaminoethane) ( 1, 3-diaminopropane) diaqua-
cobalt (III) Equilibrium So}.uti_£.!!..!. An accurately weighed amount
of trans-[Cocl 2 (en) (tmd) ]Clo4 was dissolved in 0.5 F NaOH (25
ml) and left for 3 min. before making up to 50 ml with 1.0 F
HN0 3 • The absorption spectral parameters remained constant
after 3 day~ at room temperature.
18
( An identical spectrum was obtained by leaving a solution
of trans [Coc1 2 (en) (tmd) ]Clo4 and excess mercuric acetate in
50 ml of 1.0 F HN0 3 for three days at room temperature.
The cis<:~ t:rans- (Anuni.ne) (die1:hy1 amine} cobalt (III)
librium Solution:
constant.
IJ.'he Cation: The
pink Cr(tmd) (oH2) 4J+ was isolated in solution by dissolving ca.
150 mg of tr~- [ Cr (OH) (tmd) 2 (on2) ] (ClO 4) 2 in 50 ml of 0. 6 F
HN0 3 and leaving solution five days at 308 K (or by
dissolving ~· 150 mg of tra~-[Cr (OH) (en) (tmd) (OH 2)} (Clo 4 ) 2
in 50 ml of 0.6 ~ HN03 and leaving solution for three days
at 308 K.) The cooled solution was adsorbed on an ion-exchange
column which had been pre-v.mshed with 2 F and then 0. 6 £:. HN0 3•
The resulting pink band was washed with 40 ml of 0.8 F HN0 3
and then eluted with 50.ml of 1.0 ~ HN0 3 , the absorption
spectrum being recorded immediately.
cobalt Cation: IJ.'he magenta tr~-Co (OH) 2 (en) (trod) +
cation was prepared from ~~-[cocl2 (en) (tmd) ]clo4 , either by
dissolving an accurately weighed amount in 0.5 ~ NaOH and
measuring the absorption spectrum, or by taking ~· 200 mg in
30 ml 0.025 F HN0 3 and adsorbing this solution on a cation­
exchange resin (pre-washed with 2 ~and then 0.025 ! HN0 3).
The green band was washed with di lled water until the
effluent was neutral. The magenta coloured cation was then
eluted with 0.1 F NaOH into a 50 ml -co6led flask, the
first 20 ml being discarded. Both meth6ds gave identical
absorption spectral parameters.
Complex
trans-CoC1 2
(en) (tmd)+
trans-CrBr(tmd) 2 (oH 2
cis~trans-CoCl(dien) (NH 3) (OH2 ) 2+
trans-Co(NH3) (dien) (OH2 )~ 3+ cis-Co(NH3 ) (dien) (OH2 ) 2
3+
Cr (tmd) (OH2 ) 4
1: : 2. o s ± o .14 I 1: :2.03±0.041
1: :1.94±0.05 I :l
1: :2.03±0.031
1:0.99±0.04:2.07±0.071
1: :1.00±0.071
1: :1.04±0.03
1:1.01±0.03:1.03±0.03
1:1.00±0.01 I 1:1.02±0.03 I 1:1.02±0.03 I 1:2.08* I
Number of determinations
5
7
11
19
10
9
9
6
6
8
6
12
6
2
*For Cr(tmd) (OH2 ) 4 3+, analysis of the amine nitrogens was determined.
[-' \.0
The trans- (Ammine) (diethylenet.riamine) dihydroxocobal t (III) ~~;:_~~-=~__,,_~_ -~-'"'-"'=--· --~--===~~""'-"'"'"""'='-"'""'""""""'""~·='"~-"'--~~·~--~--~~- Cation: The two methods used to isola·te the magenta tran~·-
Co(OH) 2 (NH 3
used for !£_~-Co (OH) 2 (en) (tmd) +.
2.3 KINETIC MEASUREMENTS
20
+ For the primary hydrolysis studies of !:!_~~-·CrC1 2 (tmd) 2 1
weighed samples of the perchlorate salt were dissolved in the
appropriate HN0 3-NaN0 3 solutions in glass ~oppered volumetric
flasks which were V.frapped in Al foil to exclude light14 115 ,
and immersed in a ternperature controlled water bath. For all
other primary hydrolysis studies, and all the secondary
hydrolysis runs, the cations ~-CrBr2 (tmd) 2 +, trans­
crcl2(en) (tmd)+ 1 ~-CoC12 (en) (tmd)+ 1 trans-CoC1 2 (NH 3) (dien)+,
2+ 2+ ~-CrCl(tmd) 2 (oH 2 ) , ~-CrBr(tmd) 2 (oH2 ) , trans-CrCl-
(en) (tmd) (OH 2) 2+, ci!'_-CoCl (en) (tmd) (oH2) 2+ and 9is-CoCl (NH3)­
(dien) (OH 2) 2+ were chromatographically isolated with 0.3, 0.4,
0.3, 0.3, 1.0, 1.0, 1.0~ 1.0 and 1.0 F HN0 3 respectively. The
cations were allowed to react at the appropriate temperature
in glass stoppered flasks which were wrapped in Al foil. Zero
reaction time was taken 5-15 min. after the reaction flasks
were immersed in the temperature controlled baths.
In the titrimetric method, 5 ml aliquots of reaction
solution, removed at known time intervals, were quenched by
delivery into 20 ml of ice-cold water containing 2 ml of
concentrated HN0 3 • The free halide was determined by
potentiometric titration with standard AgN0 31 using a silver­
silver halide electrode with a saturated calomel reference
electrode and a Radiometer pH meter. All titrations were
21
performed in an :Lee-bath. To test the reliability of the
chloride release data in the ~-CoC12 (NI-! 3 ) (dien) + system,
titrations were carried out where the free chloride ions were
chromatographically separated from the reaction mixture. Each
5 ml aliquot from a kinetic run at 286.8 K was chromatographed
on a 3 x 1 em ice~·cooled column which had been· pre-·washed with
2 ~and then 0.3 ~ HN0 3 • The band was washed with distilled
water to elute the free chloride :Loris and the reacting species
were retained on the column. The halide titration was then
performed as above.
followed by leaving the cells containing the reaction solution
in the temperature controlled cell compartment of the spectra-
photometer. The visible absorption spectra were scanned at
known time intervals, or a constant wavelength scan was t~ken
over a known time interval.
The cation exchange chromatographic procedure used was
essentially the same as that of MacDonald and Garner15 with
slight modifications. Aliquots (5 ml) were adsorbed (2.8 ml/
min.) on a 3 x 1 em cation exchange resin column cooled by
circulating ice-water. The complex cations were selectively
displaced from the resin by stepwise elution with increasing
acid concentrations using the following scheme. Fif·ty ml of
0.3 ~ HN0 3 , and then 50 ml of 0.6 F HN0 3 removed the :!;ran~­
CrC12 (tmd) 2 + cation and the trans-CrCl (trod) 2 (OH2 ) 2+ cation vms
then removed with 50 ml of 1.0 ~followed by 50 ml of 1.5 F
HN0 3 • Each 50 ml fraction was analysed for Cr content.
22
All pH measurements were recorded using a Beckman 101901
Research pH meter with a Beckman E2 glass electrode type 39004
and Beckman frit junction calomel reference electrode of type
39071 (saturated KCl). B.D.H. AnalaR chemicals were used in
the preparation of the standard buffers. The methods are
t] ' d ' B t 16 ou _lne 1n a.es • Before any set of pH measurements the
assembly was standardised using .t:he 1: i phosphate buffer (pHs
6.865 at 298 K). Agreement with the linearity and slope of
th S t . 1 t. . t 1 16 h J d l . -.e NB conven 1ona. ac lVl y sea e was c ecte JY measur1ng
the response to borax and potassium hydrogen phthalate buffers
with respect to the 1:1 phosphate buffer. The borax solution
gave a pH' value in agreement with the pH s value (9.180) ob-
tained by Bates 16
(phthalate; pH' 4.026; pHs 4~008).
+ The electrode system was calibrated as a [H ] probe
17 against standard acid solutions, as described by McBryde o
Stock acid solutions, Ool to 0.001 !::_containing NaNo 3 (1 ~)
were titrated over a small pH range with standard NaOH using
an "Agla" micrometer glass syringe. From 33 data points the
derived relationship between measured pH (pH ) and p[H+] was . m + pHm = 1.006 p[H ] - 0.065; apH ( the standard deviation of
pH from the computed curve) = 0.015. It is valid to extra­ m
. 17 18 palate the calibration curve into the alkaline reg1on '
The pH titration cell was similar to Perrin's 19
•
standardised against potassium hydrogen phthalate by pH
titrations.
chromium solutions were kept in the dark and the titration
cell was wrapped wit.h metal foil. The ~~-aquahydroxo
complexes were dissolved in 1 ~ NaN0 3 solution containing a
small excess of acid and the resultant solutions were back
23
titrated to pH 10.3 with standard NaOH. During the titrations
each aquahydroxo and each dihydroxo complex underwent measur-
able isomerisation to the c~~ isomer (confirmed by spectro·­
photometric measurement) • This reaction caused a steady up-
ward drift in pH readings; the drift was most marked in the
first buffer region. 'l'he diaqua complexes· ~-Cr (en) (tmd)­
(OH 2 ) 2
3+ and ~-Cr(tmd) 2 (oH 2 ) 2 3 + did not isomerise (or
undergo Cr-N bond rupture) measurably at 298 K. For these
complexes, titrations were performed on samples from a stock
solution of the trm;.s-aquahydroxo complex dissolved in excess
acid, pH 2.95. From each titration, 6 data points were
quickly recorded for a small segment of the titration curve.
Data for subsequent tit~ations were overlapped with those for
the previous titrations.
In contrast, acid solutions (pH 2.96) of the complex
3+ !-.£..~_-cr (en) 2 (OH 2 ) 2 showed an increase of pH with time (ca.
0.096 pH in 60 min.) and it was inferred that as well as iso-
mer ising, the complex was undergoing Cr - N bond rupture to
yield products which were reacting with the excess acid. To
minimise errors, weighed samples of tr~..E_- [ Cr (OH) (en) 2 (OH2 ) ] -
(Cl04 ) 2 (~. 20 mg) ~.vere transferred directly into the titration
vessel which contained the acid- NaNo 3 solution. Titration
data were collected in 5 to 6 minutes and the total titration
curve was covered in four t.i t.rations. pH drift was noticeable
24
in the first buffer region (but not in the second, because the
t d ' h d 1 h ' '1 1 13 ) ~ns- an ~~~::~-aqua y roxo comp exes ave s1.m1. ar pi< va ues ;
measurements indicated that the possible error in the pH data
was $ +0.03 pH.
2.5 CHEMICAL ANALYSES
ammonium peroxodisulphate and estimating the Co (II) spectra·- ,
photometrically at 620 nm as the tetrathiocyanate complex in
aqueous acetone. The standard s6lution used in this analysis
was prepared by dis~olving an accurately weighed amount of
pure IT--[CoCl(en) (dien) ]Zn01.1 20
(supplied by Dr A.R. Gainsford) . .
in distilled water, decomposing with hot ammonium peroxodi-
·sulphate, and then making up to 500 ml in a standard flask.
Standards were always measured in duplicate when unknown
solutions were being analysed.
2-Cr was analysed as Cro 4 by measuring the absorption
spectrophotometrically at 372 nm after decomposition of the
complex with hot alkaline ammonium peroxodisulphate. A
standard chromate solution was prepared by dissolving an
accurately weighed amount of AR potassium dichromate (K 2cr2o 7 )
in 500 ml of 0.1 F NaOH to give a 0.004 F Cr solution (as
Cro 4-) . Dilution of this solution by taking 25 ml and making
-4 up to one litre gave a 1.0 x 10 F standard chromate solution.
Whenever analyses were carried out, a standard was also
measured to compensate for day-to-day base line fluctuations
in the spectrophotometer.
complex was decompo with hot NaOH solution, and the re
ammonia was steam dis lled into 2% boric acid and titrated
3+ with standard HCl. The Cr (tmd) (OH2 ) 4 complexes were
chromatographically isolated with H2so4
Cl and Br were determined by potentiometric titration
with standard AgN0 3
complexes were decomposed with hot NaOH and the solutions
acidified with HN0 3
Professor A.D. Campbell's laboratory at. the University of
Otago, New Zealand, performed the c, H and N analyses of the
solid complexes.
The visible absorption spectra and spectrophotometric
' kinetic data were obtained with a Beckman DBG recording
spectrophotometer using·matched 4 em quartz cells. Spectra-
photometric analyses Co and Cr were formed on the same
instrument using matched 1 em cells.
The absorption maxima and minima of each complex were
measured by scanning spectra of at least three solution
concentrations over range 320-700 nm 285-296 K. The
molar absorption coeff -1 -1
ients (~r"i in ~ em ) of the maxima
and minima of each spectrum were calculated using the Beer­
A Lambert law ~-1 = CXf where A = absorbancy, C = concentration of
the solution and ! = the path length of the cell. The data
are presented in Tables 2.3 and 2.4 along with values for
rela·ted complexes.
TABLE 2.3
Visible absorption maxima and minima (320-650 nm) of some aqua-, aquahalo- and dihalo(diamine)chromium(III) and
cobalt(III) complexes in aqueous acidic solution at 285-296 K.
Cation I Acid, F . a
I a
trans- HN0 3
CrC1 2
(en) 2
HCl0 4
' + c (38.4) (26. 5) I (27.3) (10.8) I (27.9) Crcl
2 (pn)
2 - 0.1
3 I 450sh-
+ d I I CrCl 2
Cen) (tmd) - 0.4(16) ~ (41. 3±1. 2) (29.6±1.0) (10. 3±1. 6)
I (24.8±0. 7)
trans- HN0 3
398 457sh 525 596 I ·;~~1 =-c trod)+ ~' ~ e (38.8±1. 3) (24. 9±1.1) I (8.9±1.8) I (25.5±0.8) 0.1-0.6(9)- I I --2 2-
' . 'I I trans- HC1o
+ h
!
trans- I HN0 3
I I + d CrBr
2 ( tmd)_r- ! 0.3(7):: I (3{j.9±0.6) (26.7±0.8) (5.8±0.8) (35.5±0.6) ' I I I i I
trans- MeOH-H 2
cocl 2
[\.)
-·--····-··-···-··-·-
Cation Acid, F . a . a a I a m~n- ~n- max- max-
trans- HN0 3
394 422 450sh I 536 625 + d
0.3{10) ~ I (43.9±0.9) (46.8±0.8) I l Cocl 2
(en) (tmd) - ! (43.1±0. 7) (7.7±0.6) (38.2±0.6)
i traps- MeOH-H
2 0 398
2 ) - 0.2 (45.5) (23. 7) (24.4) I (15 .4) (20.
I I
CrCl(pn) 2
(oH 2
trans- HN0 3 l
387 I 434 456
I 509 545
!
I 456 I 506 556
. 2+ d 1.0(9) ~ .5±1.0) (23.3±0. 7) (24.9±0.7) I (15.7±1.1) (20.6±0.8) CrCl (-cmd) 2
(OH 2
L:",.. - ! I
I trans-
2+ h I CrBr(en) 2 (oH
2 ) - 1.4 I (44. 8) (24. 7) {24.9) (14. 2) ! (23.2)
I I
I 384 432 ! '445 l 502 I 560 !
2+ i ' I CrBr(pn)~OH2 ) - 2.0 {47.7) (26.0) (26. 6) (12.8) l (23.1) I ' I trans- HN03
386 ' 443 456 I 512 573 2+ d e
' .....)
2 L -
I Acid, ~ I HC1o
I HN0 3
' HNO I 0.6-l.~ (6) ~
442
(35)
373
(67)
I ! I
I ! l ' ' ,
cis- HN0 3
trans- ,0.05 -340
- 1 F NaN0 3
2 CoH
1.5(5)~ Co(en) (tmd) (oH 2 l
2 _-
2 (70.2±0.9)
2 (en) (trod) - (24.0±1.0)
i (87. 9±1. 3)
· 3+ m ' Cr(en)(OH
I 383
L-·~- I e 1.0(4)- (26. 4±1. 0)
I
I
I I 410 444
410
I ~ l ~
TABLE 2.3 (contd)
a In nanometers (±2 niT, for this work). -1 -1
A = log (I /I) = a c d, in M em 0 -+i--
b Data from reference 15.
c Data from reference 14.
d This work.
Values in parenthesis are the molar absorption coefficients, a , defined by . - ---t'\1
The data in this work are the mean ± the standard deviation (see footnote e).
e The nUJ.-uber of individual determinations used to obtain ·the mean.
f sh = shoulder.
g Data from references 4 and 35. J.W. Vaughn, G.J. Seiler, M.W. Johnson and G.L. Traister, Inorg. Chern. ~~ 2786 (1970).
h Data from reference 29.
~ N.A. Maes, M.S. Nozari and J.A. McLean, Inorg. Chern. 12, 750 (1973).
i J. Bjerrw~, A.W. Adamson and 0. Bostrup, Acta Chern. Scand. 10, 329 (1956);
H. Kawaguchi, N. Yano and S. Kawaguchi, Bull. Chern. Soc. Japan 42; 136 (1969).
k Data from reference 13.
£ C.K. Poon and M.L. Tobe, j, Chern. Soc., 1549 (1968); data from reference 45.
m Data from reference 70.
n D.A. House, R.G. Hughes and C.S. Garner, Inorg. Chern. ~' 1077 (1967).
f.A)
0
TABLE 2.4
Visible absorption maxima and minima (320-650 of some diaqua-, aquachloro- and dichloro(tetraamine)coba1t(III)
Cation
e.stimate of cis­
product mixture
CoCl(NH 3
trans- 3+ d Co(NH3) (dien) (OH
2 l 2_
Acid, F
(33.5±1.2) w 1-'
Cation I Acid, !_ . a a . a a I . a a m~n- max- m1.n- max- m1.n- max-
cis- HN0 3
Co(en) 2 (oH2 )~+ ~ I
1 F NaN0 3
I cis- HN0
(79. 2±1.2) (19.1±0.5) (101. 7±1.6) 1.0-1.5 (7)-
cis =F trans- HN0 3
357 418 496
) (dien) (OH2~~~ ~ 1.0(4)·:: (71. 6±1.6) .1±0.8) (92.1±0.8)
trans- NaOH !
317 364 428 506 I Co(NH
3 ) (dien) (OH);_~ 0.1(4):: (26.6±1.1) (72.3±0. {31.8±1.1) {81.2±0. 9)
cis-diaqua-cis- HN0 3 _l 356sh 415 498
aquachloro equilibrium~ 1.0(3):: (68.8±1.2) (18.3±1.0) I (91. 3±1. 3) ---· . ··----- ~----------1 -·--
a In nanometers ( ±2 nm for this -1 = a c d, in M
work). -1
Values in parenthesis are the molar absorption coefficients, defined by
b
A= log(I /I) 0
H. Kawaguchi, ~-- - The data in this work are the mean± the standard deviation (see footnote e).
N. Yano and s. Kawaguchi, Bull. Chern. Soc. Jap~~ 42, 136 (1969).
c Data estimated from spectral curve in reference 75.
d This work.
e The number of individual determinations used to obtain the mean.
f br = broad.
i sh = shoulder.
'I'HE trans
3.1 INTRODUCTION
In the past several years, much effort has been focused
on the kinetic and mechanistic behaviour of octahedral
transition metal complexes 21 , and in particular the
33
dianionobis ( 1, 2-·diaminoethane) Co (III) complexes have received
considerable a·ttention. It is of interest to see if complexes
of other transition metals, for example, Cr(III) behave
similarly. This object is often frustrated by the lack of
suitable Cr(III) analogues as Cr(III)~amine complexes are
considerably more difficult to synthesise than the coirespon-
ding Co(III) systems.
One aim of this thesis has been to investigate the
kinetics of some recently prepared Cr(III)-amine systems and
in particular, to
the reactivity of
+ trans-CrC1 2 (AA) 2 complexes.
ring size on
For ~s.-CoC1 2 (AA) 2 + cations (rrable 3 .13) Basolo and
Pearson 21
hydrolysis in a progressive manner.
Except for single methyl substitution on N, every
increase in the number or size of the alkyl. groups in place of
hydrogen atoms on 1,2-diaminoethane leads to an increase in the
rate of acid hydrolysis.· This is strongly suggestive of a
dissociative mec;hanism because a sterically crowded complex is
unstable due to repulsion and distortion of ligands.
34
complexes (Table 3.13) react about 100 times slower than uni-
valent dichloro complexes. Separa'l:ion of the negative charge
in the form of chloride is more difficult the greater the
remaining char9e on the complex. This suggests that bond
breaking is important and tha·t the mechanism is not bimolecular
in any event.
On expanding the size of the chelate ring from five to
six members using 1,3-diaminopropane instead of 1,2-diamino-
ethane the rate is increased 1500 times. This increase in
rate is possibly connected to the observation that complexes
with six-membered chelate rings are much less stable than
·those with five-membered rings because of increased Co-N- C
bond angles, Release of one group from the octahedrdn and
reduction of this bond angle will release the strain in the
complex with the six-membered ring. A peculiar result is that
methyl substitution in the six-membered ring (dan, NH 2CH 2C(CH 3 ) 2-
CH2NH2) leads to a decrease in the rate rather than an in-
crease. 1 22 . b h t . f 1 2 Jonassen eta • ascr1 e t e ra-e 1ncrease rom . , -
diaminoethane to 1,3-diaminopropane as due to "release of
steric strain in forming a dissociated transition state", but
this does not explain why·the related ~~-cocl2 (dan) 2+ cation, also having six-membered chelate ring systems, and
presumably similar Co-N- C angle strain, aquat.es at only 86
times greater than the 1,2-diaminoethane analogue. An
alternative explanation for these results will be presented in
the subsequent discussion.
Alexander 23 has pointed out an interesting steric
correlation .beh·;reen the number of axial methyl groups on the
+ diamine ligands in a series of ,!:~~-coc1 2 (AA) 2 complexes and
35
their aquation rates at 298 I< (rate increases with the number
of axial methyls). This finding further favours a dissociat-
ive mechanism because lengthening of the Cl-Co(III) bond in
the activated complex could relieve. some of the steric inter-
action between axial methyls and chloro ligands, and hence
increase the reactivity toward aquation in a dissociative
process.
of Co(III) aquation reactions. For ~-Co(III) substrates,
as much as 7 5% ster ic change is noted; for ~..::~s substrates
there is usually retention of configuration within experimental
error. This behaviour has been rationalised by Tobe 24 in
terms of an essentially dissociative mechanism in which the
duality of response to the elec.tron displacement properties . n+ of A for CoACl(en) 2 in rates and steric course arises from
the two possible shapes of the five coordinate intermediate.
n+ For CoACl(en) 2 and similar Co(III) complexes with four amine
Co - N bonds 11 steric change is as soc ted with a higher (and
positive) entropy of activation than is retention of
configuration 11 • Tobe has postulated that high activation
entropies are diagnostic of a trigonal bipyramidal intermediate
(which predicts steric change) and low activation entropies
indicate a tetragonal pyramid (which predicts retention of con-
figuration by virtue of attack of the entering groups on the
open face). . +
The only exceptions to Tobe 1 s concept are tra~~-CoX2A4 (A4 = tet~, tetb, trans 14]diene25 , ·RR,SS,-3,2,3-tet26 , X= Cl,
Br) all of which seem to aquate with no stereochemical change
but have posi~ive entropies of activation. These observations
+ can be explained in terms of solva-tion of the !:,E,~-cox2A4
36
complexes. As chelation tends to break up the solvation shell
of the complex, these complexes will have l<:>.ss efficient
solvation than others in which the chelation is not as great.
Thus the entropies of activation will be positive as the
complex makes greater demands on solvation in going to the
transition state. The effect of less efficient solvation, and
h th b t · f · t · As* 1 · ~ · f ence -eo serva·1on o pos1· 1ve u~ va ues, lS aom1nant -or
these complexes and obscures the expected low entropies of ..
activation associated with retention of configuration.
For the amine complexes of Cr(III), ayuation tends to be
complicated by side reac·tions in which partial or complete
substitution of a multidentat·e amine ligand by one or more
water molecules competes with the aquation of unidentate
an ~o·l'lO l1' gands 27 A tl tl · f E t · 1 l ..._ pparen y - 11s e :-ec 1.s on y rare y . 28
observed with Co(III)-amine complexes , perhaps because of
the seemingly greater tendency fo:r: Cr (III) to form M- 0 bonds
in place of Jvl ·- N bonds. The factors contributing to Cr - N
bond rupture are not yet understood.
In acid hydrolysis reactions, provided the M- N bond
remains intact, there is some similarity between the rates of
reactions of analogous Co(III) and Cr(III) complexes. The
following comparisons ca:n be made.
Aquation of cis isomers of Cr(III) complexes give cis
product only, as has been found for related Co(III) complexes.
The trans isomers of these Cr(III) complexes, which aquate
roughly one order of magnitude more slowly than Jche cis
analogues, give predominantly, and possibly wholly, ~rans_
29 product in contrast to the Co(III) analogues.
Tobe's.comparisons, when extended to include those Cr(III)
* complexes for which 68 values have been determined, seem ·to
37
be valid here also. However, the application of this concept
for the aqua tion of Cr (III) ·-amine complexes must await the
experimental evaluation of entropies of activation of many
27 more such complexes •
3.2 SYNTHESES
3.2.1 Results
The complexes .!;!_~ns-[Crcl 2 (tmd). 2 ]Br, ~ns-[CrBr2 (tmd) 2 ]x
·(X = c1o4 and Br), trans-[crcl 2 (en) (tmc1) ]clo4 , ~ra~-
(Cr(OH) (AA) (BB) (OH 2 )] (Cl04 ) 2 (AA = BB .=en; AA == en,BB -- tmd;
AA = BB = tmd), and trans-[Cr(AA) (tmd) (OH 2 ) 2 ]Br 3 .n2o (AA =en
and trod) have been prepared as crystalline solids. A one-step
synthesis of :trm~-[cocl 2 (en) (tmd)]X (X= Cl.H2o and Clo 4 ) is
described and tra~-[coc1 2 (pn) (tmd)]Clo 4 has also been
prepared by this method.
3.2.2 Discussion
House 4 has observed that the reaction between crc1 3 .6n2o,
dehydrated in DMSO, and 1,3-diarninopropane forms~­
crcl2(tmd)2+ and it was found in this investigation, that
trans-[CrC1 2 (en) (tmd) ]clo4 could be obtained using the mixed
amines but with the more soluble cis--[CrC1 2 (en) 2 ]cl.H2o as a
major impurity. The yields of the ~~--dichloro are low, but
sufficient material was isolated for kinetic study. The
conversion of the trans-dichloro to the ~ran~-aquahyc1roxo v.'a.s
•
been prepared
(NH 3
material from this source was used in a previous kinetic
38
31 study In this work the direct air oxidation of an aqueous
solution of a Co(II) salt, together with an equimolar mixture
of the diamines, followed by subsequent reaction with HCl/
HClo 4 was successful in producing !:E~~s-[cocl 2 (en) (tmd)]Cl.H 2o
and the perchlorate salt. The good agreement between the
kinetic data found here and that reported earlier 31 (Tables
3.12 and 3.13) suggests that the two different routes give the
same material.
The poor yields, or no product at all, obtained in the
at·tempted prepara·t.ions of !£c;tn;.~~[crcl 2 (AA) (BB) ]Clo4 (AA = en,
BB = tmd; AA = pn, BB = tmd; AA = BB = dan) compared with the
yields obtained for the analogous Co(III) complexes illustrates
the restrictive nature of Cr(III)-amine chemistry.
3.3 CATIONS
Absorption spectral parameters for the isolated cations
are presented in Table 2.3 along with similar data for related
species.
From aged solutions of the dihalo complexes, the cations
tr~ns-CrX (trod) 2 (OH 2 ) 2+, cis- and tr~~-Cr (tmd) 2 (OH 2 ) 2 3 ~ and
3+ Cr(tmd) (OH 2 ) 4
have been isolated by ion-exchange methods and
characterised in solution by their visible absorption spectra
and Cr:ligand atom ratios.
From acid solutions of ~~-[CrC1 2 (en) (tmd) ]Clo4 , the
+ 2+ tra~-crc1 2 (en) (tmd) and trans-CrCl (en) (tmd) (OII 2 ) cations
have been isolated by ion-exchange techniques and characterised
39
in solution by their visible absorption spectra and Cr:Cl atom
ratios. The c~s-Cr(en) (tmd) (OH 2
) 2
and characterised in a similar manner from acidic solutions of
!::EEps·~Crcl 2 (en) (tmd) + containing Hg 2+ and the tr~s~~diaqua
from solut.ions of t.~~-[Cr (OH) (en) (-tmd) (OH 2 )] (Clo
4 )
The ~~-CrCl (en) (tmd) (on 2
) 2·1- cation hydrblyses both via
3+ chloride release and Cr - N bond rupture and the Cr (tmd~· (OH 2
) 4
(en) (tmcl) ]ClO 4 , the
~~-dichloro and cis-CoCl (en) (·tmd) (OH 2 ) 2+ cations have been
isolated. Although evidence·was obtained for the formation of
2+ ~-CoCl (en) (tmd) (OH 2 ) , this cation is sufficiently
unstable as to preclude its isolation and characterisation.
Similarly, the trans~Co(en) (tmd) (OH 2 ) 2
3+ cation could not be
isolated although the £i-~-Co (en) (tmd) (OH 2
) 2 J+ and !:,~~2?:.:_~- + Co(OH) 2 (en) (tmd) cations have been characterised.
3.3.4 Discussion of cations
The three green trans-[CrX2 (AA) (tmd)]clo4 salts (AA =
tmd, X = Cl and Br; AA = en, X = Cl) are soluble in dilute
HN0 3 at room temperature .to give green solutions which change
to orange-pink. The absorption spectral parameters and ion-
exchange properties of these green cations are typical of
~-dihalo complexes of this type (Table 2.3).
The daughter products, ~-crx (AA) (trod) (OI-1 2 ) 2+, have
been characterised in solution by satisfactory Cr:X atom
ratios, ion-exchange behaviour characteristic of a +2 charged
ion and constant visible absorption spectral parameters. The
pos:L tions of the maxima and minirna, the values of the mola.r
40
absorption coefficients and the shapes of the spectral curves
2+ are very similar to the trans-CrX(CC) 2 (oH2) (CC = en,pn)
analogues and a !:!_~ configuration is confidently assigned to
the isolated CrX(AA) (bud) (OH2) 2+ ions.
· The secondary hydrolysis step appears to be complicated
by concurrent ·cr - N bond rupture and/or isomerisation as isos-
bestic points were not observed for hydrolysing solutions
~-CrX (AA) (tmd) (OH2) 2+ ·in 1. 0 ~ HN03 • Due to the icul . ..
of working with low concentratio'ns of the trans-aquahalo
cation, the characterisation of the products of this reaction
was not attempted. Rather, the~- and trans-Cr(AA) (tmd) (oH2) 2 . 3+
and Cr (trod) (OH2 ) 4 cations \vere generated directly from the
trans-dihalo or trans-aquahydroxo salts.
acidification and ion-exchange separation, produced the :tr~-
Cr(AA) {tmd) (OH2 ) 2 3+ cation, sumably via the labile !2:2n~-
CrCl {OH) (AA} (tmd) + intermediate. 'l'he use of neutral solutions
apparently avoids the competing Cr - N bond rupture paths
observed in the secondary hydrolysis. An identical species
(Figures 3.1 and 3.2) was produced by pre~aring solutions of
trans.-[cr(OH) (AA) (tmd) (OH2)] (Clo4) 2 in acid, and the spectral
3+ parameters are similar to those of related ~~-Cr(CC) 2 (oH 2 ) 2 cations (Table 2.3).
Treatment of acid solutions of the trans-dihalo with
2+ excess Hg produces a Cr(III) cation with ion-exchange
properties compatible with a +3 charge but with an absorption
spectrum different from that of the !raE2?_-diaqua. The
positions of the absorption maxima and minima are similar to
those of ~_is.-Cr (en) 2 (OH 2) 2 3+ (Table 2. 3} and the -diaqua
configuration is tentatively assigned to the isolated ies
I
..--u 40--- \, l. · · I .. ~ 2 ' I
X w 0 z ~
0 .... ~ L
' ! .......... I .... .... .............. :.._., -, ...
... , l ............ -,l .... .. , .... ~-----------.r-,c.d~
0 400 500 600 . 700 \J\fi\VCL"NG-i 'H' ~, r, , L t: I ~ i nm.
Figure 3.2 ""'.J..
,-::,.
(Figures 3.1 and 3.2).
+ 15 32 33 The cations t~-Mcl2 (en) 2 ' v and tr~~~-~
MC1 2 (pn) 2
+ 14 , 31 (M =Co, Cr) hydrolyse slowly (half-lives of
3-8 hr at 298 K) in aqueous acidic solution. In the Cr(III)
systems, halide release accounts for abou·t 9 0% of the reaction
and Cr - N bond rupture for the remainder. Some isornerisa tion
+ also occurs in the tran~·-·Crcl 2 (pn) 2
systern. In tho Co (III)
systems, considerable isomerisation occurs ( 35% £2.:.~-
1 ( ) ( ) 2 + . . 3 4 ) .,.
CoC. en 2 OH2 1.s observed , but no Co - N bond rupture has
been detected, (See, however, reference 28).
Thus the primary step in the hydrolysis of ~Ea!2-.::?:-
Crx2 (AA) (tmd) + could conceivably involve three reaction path·­
ways - Cr -X bond rupture, Cr- N bond rupture, or isornerisation
to the cis form, followed by either of the two postulated bond
rupture processes. The characterisation of trans-
CrX (AA) (tmd) (OH 2 ) 2+ as the Only (>98%) * reaction product, is
convincing evidence that the latter two pathways have a
negligible contribution in the loss of the parent. Neverthe-
less, a slow preisomerisation of the resulting aquahalo would
also account for the observed product. Such a reaction scheme
would be highly fortuitous and the observation 35
that cis-
to this proposed pathway.
All the available evidence points to a single pathway for
the primary hydrolysis of the dihalo ions in acidic solution
according to the equation
* The experimental uncertainty could allow up to 2% of other
plausible'cr(III) species to be present.
44
Thus, the spectrophotometric scans hold sharp isosbestic
points (Figures 3.3 to 3.5) for 2-3 half-lives and the observed
positions and intensities are in good agreement with those
predicted fromfue spectra of the two pure components (Table
3.1) •
Isosbestic points observed and predicted in the acid hydrQlysis
~=....-=~ .....
X AA t..2 c /..·- t..2 t..S: t..2 ~..s:
Cl tmd 571 445 407 570 445 407
( 19 • 0) (24.3) ( 3 7'. 4) ( 19. 8) (25.0) (37. 5)
Cl en 560 454 405 562 454 406
(19.1) (29.2) (40.7) (19.4) (29.4) (40. 5)
Br tmd 590 498 479 588 498 479
(21.1) (13.8) (22.9) (20.7) (13.4) (22.7)
453 423 456 423
(27.0) (29.8) (26.4) (29.9)
reaction.
+ b Predicted from the superposition of the ~~crx2 (AA) (tmd)
and tran~.-CrX(AA) (tmd) (OH 2 ) 2+ spectra.
c Wavelengths in nm (±2 nm) • Values in parenthesis are the
-1 -1 M-1 -1 molar absorption coefficien·ts ~M, M ·- em ( ±2 em ) •
"-0
~ ' . 30 ~
j 0 ~ 10
DIT'-
Figure 3.3 Spectral changes in the primary hydr~lysis of trans-Crcl2 {tmd) 2+ in 0.1 ~ 3?8 K.
t~mes are , , 40, 80, 120, 160, 200 m~n.
600 650
~ (Jl
I /
I
_J L{)
l ( j )
I I
I 0
...... . . :E
X U..J 0 z :>­ u z <: m 0:: 0 (j) co <1:.
5 0 ~
(tmd) 2
+ (----) in 0.3 ~ HN0 3
at 28& K. the reactions ·times are 0, , 70, 130, 190 and 250 min. ~~e final curve
CrBr(tmd) 2
(0H 2 )- •
,:::,. --.1
: ' ~~ ' ' , . , •, I t
J
>- ,,, ~~/~' . l u '\\ . . ~' ~ ~ ~ I \, ----------,,~~\ _I ~ 20~ . ~/, ----,,\\ ~~~\ J OJ I ~. \ ~- I <f. I \ '~, i
L , ' I a:: . I ----- ::s.' -1 <t --- ~~- I _j L ',,, ~~
<I 0 ',, ~-----~-'~ 0 I ·
1 · _ - nm. 0
·-- "\JCI ;-NG I H Vv f...,\ , '- "-
Figure 3.5 Spectral changes in the primary hydrolysis of trans-CrCl (en) (trod)+ (---) in 0.4 F HNO
- 2 - 3 (or upwards at 390 nm) the reaction times are 0, 20, 40, 80, 120 and 160 m~~- The final
_ CrCl (en) (trod) (OH 2
) •
""" at 308 K. Reading downwards at 585 nm co curve (----) is that of trans-
49
These data suggest that the reactions proceed as in (1)
as sharp isosbestic points are usually indicative of a reaction
giving a single product or two products in a constant ratio
(see, however, reference 36). 'This latter alternative is un-
likely, as only one daughter product., trans·-CrX (AA) (trnd) ---·-- '
2+ (OH2 ) w , was detected by ion-exchange chromatography from
parent solutions aged for 3-5 half-lives. The good agreement
between tl1e chr:onl.c.l.tographically detennined rate constant and that
calculated from the spectral and halide release data also
indicates only one daughter.
Despite a careful search for Cr - N bond ruptured products
+ in the primary hydrolyses of trans~-·Crx 2 (AA) (tmd) , none were
detected. This contrasts with the ~~-crx2 (cc) 2+ cations
(CC = en, pn), where about 10% of Cr- N bond rupture occurs in
't' 'th h l'd 1 lS,l4 t t cornpet:L :ton w1· a. 1 ere ease An even grea~er amoun
of bond rupture occurs in the acid hydrolysis of Cr(III)
complexes with more chelated ring systems 37 v 38 •
Of considerable interest is the nature of the Cr·-N bond
ruptured intermediate in the reaction
---1 Cr (OH 2) 6 3+ + enH2
2+ + tmdH 2
as this may provide some information as to the kinetic
stability of five- or six-membered rings attached to Cr(III).
+ Solutions of ~-crcl2 (en) (tmd) in 0.4 ~ HN0 3 were allowed
to hydrolyse at 308 K for 3 days (approximately 4 half-lives
for the reaction corresponding to chloride release from :tra~:;;-­
CrCl(en) (tmd) (OH2 ) 2+) and the colour changed from green,
through orange, to pink. The major component isolated by
Sf
corresponding to Cr(tmd) (OH 2
) 4
2 with s sfact.ory Cr:N atom ratios) and
considerably fferent from Cr(en) ( 3+ ) 4 (Tab 2. 3) • Thus, . . 3+ ~n trans(?) -·Cr (en) (tmd) (OH
2 )
diaminoethane ring is the k.ine-r.ically less stable with respect:
to Cr ~ N bond rup)cure, despite the much cited information 39 ' 4 0
that complexes with six-membered rings are normally 'less
stable' than those with five--membered rings*. Additional
support for the hypothesis that for Cr(III) at least, the trod
complexes are more robust than the en complexes, with respect:
to Cr - N rupture, spite an increase in ring size, comes from
. . ( d) 3+ . 1 1 l the observat~on that Cr tm 3
hydrolyses more s ow y t 12.n
C ( ) 3+ . . d 1 t . 41 r en 3 1n ac~ so u ~on •
3.3.5 Discussion cat.ions
+ green ~"-coc12 (en) {trod) were found to quite rapidly· (t!:z
ca. 30 min. at 298 K) t~rn purple. The spectral parameters of
the chromatographically isolated aquachloro product did not
* It is well known that complexes with six-membered rings are
thermodynamically less stable than those with five-membered
rings, for example, for the formation of Cu(AA) 2 2+ and
Ni {AA) 3 , where AA = en, tmd; the following da·ta has been
obtained42
___:_ -1 . ~·1
2 ,kJ .mol
53.6 51.5 58.2
31.4 36.4 34.3
a Data obtained at 283-313 K, and with the ionic strength extrapolated to zero.
However, little mention has been made of the kinetic stability
which is ieferred to here.
51
d t th ' a31 f J ' d ~h correspon .o .. ose expec-ce _ ..:or a y:r~~l:~~ J.somer, an c e
formation of an early and later set of isosbestic points in
the spectrophotometric scans, suggests that the reaction is
proceeding according to equation (3).
+ Cl ( 3)
+ Cl
At 298 K, the first set of isosbestic points at 407
(45.6), 481 (32.9) and 602 nm (30.8 ~2.-l cm- 1 ) was maintained
from 0-24 min, (almost one chloride release half-life) and a
-] -1 second set at .380 (59.5), 453 (29.0) and 580 nm (31.2 M ·em ')
was stable from 60-360 min.
Attempts to isolate tr~~CoCl(en) (tmd) (OH 2
) 2+ by ion­
exchange chromatography were unsuccessful and only the cis
isomer was obtained. Also unsuccessful were attempts to
+ isolate sal·ts of ~-CoCl (OH) (en) (1:md) using the liJcerature
methods 43 r 44 •
+ hydrolysing ~-cocl2·(en) (tmd) were estimated at 12, 20, 28
and 36 min. at 298 K by subtracting out from the observed
spectrum, the contribution· from the ~~-dichloro remaining
(80, 65, 50 and 38% respectively). The mean spectrum is shown
in Figure 3.6 and the product~s) - trans-dichloro isosbestic
points so obtained [405(45), 481(33) and 602 nm (31 M~ 1cm- 1 )]
are in satisfactory agreement with the first formed set. The
product(s) spectrum is similar in shape to that of cis-
CoCl (en) (tmd) (OH 2 ) 2+ which suggests that, like the t~~DE'.­
cocl2(en)2+ system34 , the parent hydrolyses directly to form a
mixture of the cis and ·tr~n~--aquachloro products.
5?.
As there is general similarity between the spectral
+ + parameters of ~tr:an.:.;!~-cocl 2 (en) 2 and tragE~cocl 2 (en) (tmd)
(Table 2.3), a parallel behaviour would be expected for the
related !:£ans-aquachloro ions. 7\.ssuming ·that t:r:i:l:.E:~~-
2+ CoCl (en) (bnd} (OH 2 ) has a minimum near 510 nm wi·th a molar
absorption coefficient of 14 ± 5 t~~l cm-l F it can be calculated
from molar absorp·tion coefficients of cis-·CoCl (en) (tmd) (OH 2) 2+ -1 -1
and the product(s) spectrum (52.0 arid 39.5 ~ em , respec--
tively, at 510 nm) that about 66 ± 5% ~--aquachloro is produced
in the primary hydrolysis step.
£ = % cis (scis) + % trans (£trans) c+t ~,.......,....,..,.,. ___ _ .,..,.,.,.,""""""_
39.5 X (52.0) + (100-x) (£trans) == roo T~ -
£ trans x=% cis E:trans x=% cis --- ·-~~
9 70.8 15 66.2
10 70.2 16 65.3
11 69.5 17 64.3
12 68.8 18 63.2
13 68.0 19 62.1
The second set of isosbestic points are probably
composite and could be due to a combination of reactions (4)
as these are maintained for approximately three half-lives for
the ch.loride release path from 9J.s-CoCl (en) (tmd) (OH2 ) 2+,
( 4)
and do not correspond to intersections of any of the spectral
1QQI\ I I I . 1 1
' ·, . , \
\ \
0
2 (-·-·-·) , and first formed product(!i;) ····) (0.3!_HN0
3 ) of~hydrolysing ...;..;:;...;:.;......:....
298 K. Observed isosbestic hydrolysis are marked (first and · (o) (second set) . at
U1 w
curves shown in Fi~ure 3.6. Nevertheless the rate constants
+ for hydrolysing !~~-coc1 2 (en) (-tmd) obtained spectrophoto-
metrically at the wavelengths defined by this second set are
in good agreement with those obtained from chloride release
ti tra'L:ions.
54
'l'reatrnent of !~r<~l~u~cocl 2 (en) (t.md) + with excess Hg 2+ in
acidic solution, and subsequent ion-exchange separation of the
products, produced a +3 charged cation with spectral parameters
compatible with those expected for
(Figure 3.6). Attempts to prepare
~~-Co (en) (trod) (OH 2 ) 2 3+
3+ ~--Co (en) (trod) (OH 2 )
2
.· + Co(OH) 2
spectral parameters differing from those of the ci_:::-diaqua and
3+ probably correspond to near ~-·Co (en) (tmd) (OH 2 )
2 . These
changed (within 15 min. at 308 K) to those corresponding to
the c~s ~ tra~~diaqua equilibrium mixture obtained from the
!-r~ns .. ·dichloro and excess Hg 2+, prior to ion~exchange
separation. From the abs9rption spectral parameters of near
~-diaqua and those of cis-diaqua and the cis ~ ·~
equilibrium mixture, using the expression*
::::
it was calculated that there is 5 ± 3% (mean of seven wave-
( 5)
This is comparable to the <2% :t:.Eans-diaqua observed in the
* A (c+t) is the absorbance of a ci_~ ~ tr~ps equilibrium mix·t:ure
with-a total Co(III) concentrat.ion of [C ] in a cell of d ern 0 -
path-length, ~c and ct are the molar absorption coefficients
of the ci..:::_ and-near trar~-diaqua ions and [ t] is the unknown
~~-diaqua ion concentration.
~is~ !::_":,"~12~-bis ( 1, 2-diaminoethane) diaquacobal t (III) equilibri. urn
. t 45 mlx .ure •
'I'ABLE 3.
Percentage !,r~:::~~-d:i.aqua in 'che cis-> !:,~~!?:~~··Co (eri.) (tmd) (OH 2) 2 3+
equilibrium mixture
M~--::'1 -I---1 A c+t ~/tr~ % trans ...,......, .. ,.""""'-
nm em M em ...._.,,., - mF - - ---·-· ____ ., ... ~----r----~~-~-~ r---~-- 600 23.0 10.1 0.140 0.215 13.8 7
550 31.3 38.5 0.483 0.287 10.1 10
512~ 38.0 70.0 0.877 0.126 24.3 4
500 40.5 73.5 0.922 0.120 25.6 4
487~ 42.5 69.5 '0.870 0.156 19.5 5
450 40.6 31.5 0.398 ·o.1o9 28.2 4
400 41.7 27.0 0 ·• 345 0.090 34.4 3
---------~~-·-· ~--="'"""""~---· -~=~-~----·-· -~,.---~~~~~-
The relative stability of the ~raE~·-dihydroxo and the
rapid isomerisation of the tr:_~n~-diaqua are in agreement with
the observations that the :t:t.:~ ~-->~-Co (trod) (OH2) 2 3+
isomerisation has a half-life of ca. one min. at 298 K (i.e.
1450 times faster than the corresponding bis(l,2~diamino­
ethane) sys·tem) , whereas the related t:c_~·-> ~-·Co (OH) 2 (tmd) 2 +
isomerisation is only 13 times faster than the bis(l,2-
diaminoethane) system22 •
SYSTEMS
56
+ + + Crcl 2 (en) (tlnd) , !:}:_ans~·-CrBr 2 (tmd) 2 and tran~~~cocl 2 (en) (tmd)
was followed by halide release titration and spectrophoto-
metrically. + The hydrolysis of ~-crcl2 (tmd) 2 was also
followed chromatographically.
analysed from the relationship
kt == log [.(A -A ) I (A-A ) ] e o oo oo
where A is the zero time absorbance and A the absorbance 0 00
assuming 100% aquation to MX (AA) (tmd) (OII 2 ) 2 + For the
chromium complexes the wavelengths· used correspond to the
maximum absorbance difference between parent and daughter,
2+ ~~-CrX (AA) (bud) (OH 2) • Good agreement was observed bet'lveen
the ra·te constants obtained at the two wavelengths.
Wavelength and molar absorption coefficient data used for
the kinetic analysis:
+ ~-crc12 (en) (tmd)
390 nm (38. 2~-1_ ·em )
390 (50.4)
Repetitive spectrophotometric scans for t~~- . +
Cocl 2 (en) (t.md) showed the production of two sets of isosbestic
points and the second set (at 380 and 580 nm) were used for
57
analysis of the kine)cic data. The ~:-CoCl (en) ( t:md) (oH2 ) 2+
cation was not isolated in solution, but at these wavelengths
the ~ values are known if the isosbestic points correspond to
a combination of reactions (see equa.tion (4)) involving cis-
2+ CoCl (en) (bod) (oH 2 ) . At 380 and 580 nm, the ~~ values for ~]_ ~1 ~'~ .
~!l:~-CoC12(en) (tmd) + are 45.3 and 19.2 H em , respec·t1vely,
2+ and those for ci~-CoCl(en) (tmd) (OH2 ) are 62.5 and 34.2
-1 -1 M ern respectively.
ReprPsentative experimental data collected by this method
are shown in Tables 3.3 to 3.6, and Figures 3.7 and 3.8.
Halide Release Titrations: For the halide release titrations,
the data were analysed using the equation
kt = log [C /(C -Ct)] e oo oo
where C is-the halide ion concentration assuming complete 00
release of one halid~ ion (equals the initial M(III)
concentration, C 0
) and Ct is the halide ion concentration at
time, t. Specimen data obtained by this method are given in
Tables 3.7 to 3.10, and Figures 3,9 and 3.10.
Log plots and point-by-point calculations were used for
both the spectrophotometric and halide release methods. The
first-order kinetic plots for the Cr(III) complexes were linear
over 2-3 half-lives and the point-by-point calculations shm.,red
only random fluctuations over the same period. For the Co(III)
complex, negative deviation from linearity was observed after
2 half-lives. Point-by-point calculations showed only random
fluctuations over the period where linearity was observed.
There was good agreement between the rate constants obtained
from both techniques.
rate constant for aquation reaction
trans-crc1 2 ( k
Initial t!;'E]~~~crcl 2 ( tmd) 2 + concentration = 4. 78 x 10- 3
F
... -....,. .... """"'&