TABLE 1 - EQUILIBRIUM CoNSTANTS OF UO.I+-dcacCoMPLEXES

ffemp. 25·C. ; IL = O.IOM)

Equilibrium Values of log K* under situationconstant

(iii)(i) (ii)

log KI 8.43t 8.45t 8.22log KIP 15.78 15.78 15.48log K.p 7.35 7.35 7.26log Ksp 22.17 22.16 21.78log K.p 6.39 6.38 6.30log K6P 23.75 23.74 23.30log K. 24.68t 24.67t 24.19log K.p -8.86 -8.86 -8.92log K,p -10.25 -10.25 -10.29

*Error of log K is given by standard deviation which liesbetween ± 0.01 and ±0.04 (number of determinations 8 forK2; 5 for K3P and K.p; and 6 for others). Values obtained :(i) considering metal hydroxo species; (ii) ignoring metalhydroxo species; and (Hi) assuming 100 %metaI-ligand asso-ciation.

tValues from ref. 3.

this range, thereby confirming the existence o~ . ro.ute(iii). Thus, the previously described eqUlhbnl;\~,between a = 4 and 8, will be replaced by the equili-bria (1-7) :

M+H2A+OH-.,. MH2A(OH) ;[MH2A(OH)]

KlP = [M][H2A][OH-]

MHaA + OH- ••• MH2A (OH) ;K _ [MH2A(OH)1

2P - [MHJAJ[OH-]

M + H2A + 20H- ¢ MHaA(OH)2 ;K - [MH2A(OH '2]

aP - [M][HaA][OH-j"2

MH2A(OH) + OH- •• MH2A(OH)2 ;_ [MH21\(OH)2]

K,p - [MH2A(OH)][OH-]

M + HA + 20H- •• MHA(OH)2;[MHA(OH)J

Kr,P = [MllHA1[OH-]2

MH2A(OH)2'" MHA(OH)a + H+;K _ [MHA(OHMH+]

aP - --[MH2A(OH)J

MHA(OH)a ¢ MA(OH)2 + H+;K. _ [MA(OH)d[H+]. 7

P- [MHA(OH)2J

... (1)

... (2)

... (3)

'" (4)

... (5)

... (6)

... (7)

Equilibrium constants KIP, K~p, ... K7P have beenevaluated using the relations, KIP = K3.Kr. IOU;K. - KH' 1014.· K. - K KH KH 1028• K - KH'~P - 2' ,3P - "S' 6' ,(p - J

NOTES

1014; Kr,P = K". Kl!- IOU; KeP = K.p'. 10-14; andK7P = kH'.IO-u respectively as has been done inother sy~temsl'2". The values of equilibrium cons-tants (Table I) for the situations (Q and ~!!)are al~ostidentical while those of situation (1Il), obtainedassuming 100% metal-ligand association beyonda = 3, show considerable deviations and are low. .

The author is thankful to the UGC, New Deihlfor financial assistance.

References1. NAYAN, R., Indian J. Chem .• 20A (1981), 382.2. NAYAN, R., J. inorg. nucl. Chem .• 42 (1980), 1743.3. NAYAN, R. & DEY, A. K., Transition met. Chem .• 1 (1976),

61.4. NAYAN, R. & DEY, A. K., Transition met. Chem .• 2 (1977),

110.

Substituted Alkanolamine Complexes of Nickel(II)

G. N. RAo·, C. S. R. MURTHY & A. PRAKASHDepartment of Chemistry, Indian Institute of Technology

New Delhi 110016

Received 3 November 1980; revised 19 JUlIe 1981; accepted3 July 1981

pH-titration method is employed in studying the nickeJ(II)-(substituted alkanolamlne) systems. The alkanolamines used areisopropanolamine (IPA), diisopropanolamine (DIPA), trlisopro-panolamine (TIPA), l-dimethylaminopropan-2-ol (DMAP), 2-amino-2-methylpropan-I-ol (AMP), 2-amino-2-methyl-I, 3-pro-panedlol (AMPD) and 2-amino-2-(hydroxymethY)-1,3-propanediol(AHMPD). Mononuclear complex species of 1 :1, 1:2 and 1:3ratios in all the cases bave been identified except in the case ofAHMPD where only 1:1 and 1:2 species are formed due to steriehindrance. Stability constants of these complexes have beenevaluated and discussed in terms of basicity and sterle hindrance.

MOST of the work in the case of nickel(II) isrestricted to mono-, di- and triethanolaminesv-',

The present study reports the results of potentiometricstudies on Ni(II) complexes with isopropanolamine(IPA), diisopropanolamine (DIP A), triisopropanola-mine (TIPA), L-dimethylaminopropan-z-oj (DMAP),2-amino-2-methylpropan- I -01 (AMP), 2-amino-2-methyl- I, 3-propanediol (AMPD), and 2-amino-2-(hydroxymethyl)- I ,3-propanediol (AHMPD).

To check the purity of alkanolamines (BDH orEastman) the pKa values were determined by pH-titration with standard acid and compared with re-ported values. Alkanolamines were standardised by(i) visual titration using mixed indicators of bromo-cresol green and methyl red and (ii) pH-titration withstandard nitric acid. The solution of nickel nitrate(AR, BDH) was standardised by complexometrictitration with EDT A.

An expanded scale EC-pH-823 pH-meter with ex-ternal glass electrode and saturated calomel electrode,reading pH accurately upto 0.02 unit was used tomeasure pH.

203

INDIAN J. CHEM., VOL 2IA, FEBRUARY 1982

In this method 50 ml of nickel(lI) nitrate (0.01 M)solution containing 0.2 M alkanolamine nitrate wastitrated against alkanolamine solution. at 30±0.I°Cand ,.,.= 1.0 M (KN03). The formation curves(ii versus pA) for Ni-AMP, Ni-AMPD and Ni-AHMPDare shown in Fig. 1. The values of free ligand con-centration [A] at different values of ii were used in thefollowing equations for getting linear plots (Fig. 1) :

-n (2 - Ii) [A](1-n)

(Ii - 1)~11(3-n)[A]2 =

(2 - ii) ~n(3-,,) [A] +~13

~12 + ~ll(I-Ii) [A]n +

(3-n) [A]I

The values of ~11' ~12 and ~13 were obtained fromthe slopes and intercepts of the linear plots and aregiven in Table 1.

Except in the case of nickel(II)-isopropano-lamine system, the highest n value obtained in allthe systems is not more than two. This indicatedthat only 1 : I, 1 : 2 and I : 3 species are formed insolution. The region where n < 2 represents theregion of mononuclear complex and has been analysedby the method of Irving and Rossetti", as applied bySubrahmanya and Mahapatras to the copper(ll)-monoethanolamine system. The stability constantvalues are listed in Table 1.

From the observed values of stability constantsit is concluded that DMAP, AMP, AMPD andAHMPD, though potential bi-and tridentates, actas monodentate ligands, coordinating through theamino nitrogen. This is supported by the fact thatthe stability constants of nickel-ammine complexes(given in Table 1) are comparable to the stabilityconstants of the nickel (In complexes of these ligands.

The stabilities of complexes of IPA, DIPA andTIP A are relatively higher than those of the complexesof other alkanolamines. This may be due to sterichindrance caused by the substituted groups in alka-nolamines other than IPA, DIPA and TIPA. Theeffect of steric hindrance can also be seen in 1: 3

2.S

Fig 1 _ Plot of n versus pA [(A). AMP; (B), AMPD; and• (C). AHMPD]

204

TABL!! 1 - STABDlTY CoNSTANTS· FOR THE SUIISTITUTI!D AtKA-NOLAMINI!CoMPLRXFSOP Ni(ll)

Ligand log ~ll log ~11 log Ih.Isopropanolamine 3.46 6.48 8.56Diisopropanolamine 3.50 5.61 6.60Triisopropanolamine 3.89 5.16 6.55I-Dimethylaminopropan-2-o1 2.33 3.58 5.02-Amino-2-methylpropan-l-01 2.305 4.18 4.722-Amino-2-methyI-l,3-propa-

nedioI 2.70 4.70 5.972-Amino(2-hydroxymethyI)-I,

3-propanedioI 2.54 4.74Ammonia 2.80 5.04 6.77

·Average deviation in log ~ is ± 0.10

complexes of TIPA, DIPA and IPA. The log ~13values of TIPA and DIPA are two units less thanthe log ~13 value of IPA. The stability constants ofthe 1 : 2 and 1: 3 complexes with these threeligands follow the order: Ni (IPAH+ > Ni (DIPA):+> Ni (TIPA)~+ (l :2); and Ni (IPA);+ > Ni (DIPA):+> Ni (TIPAH+ (1 : 3).

The decreasing order of the stability constantsin the 1 : 2 and 1 : 3 complexes may be attributed tothe decrease in the basic character of the ligandsfrom IPA to TIPA, as reflected from their pKa valueswhich are 9.8, 9.0 and 8.27 respectively. Since thestability constants of the nickel (II) complexes ofIPA, DIPA and TIPA are greater than the corres-ponding values for ammonia complexes, (taking pKavalue of ammonia also into account) it may be con-cluded that these ligands are coordinated to nickel(II) through the amino nitrogen and one alcoholicgroup thus acting as bidentate ligands. This issupported by the studies on solid complexes=".

In the case of DMAP, the formation of 1 : 1, 1 : 2and 1 : 3 complex species has been observed andat pH - 8.9 the solution becomes slightly turbidindicating the formation of mixed hydroxy complexes.The stability constant values of DMAP complexes areless than those of IPA complexes despite the compar-able pKa values of these two amines. This may bedue to the presence of methyl groups on nitrogen inDMAP, hindering the coordination. Thus undersame conditions pure complexes are not formedshowing that this sterically hindered amiD:e is a w~akligand compared to the other alkanolamines studiedpresently.

The stability constants of the 1 : 1, 1 : 2 and 1 : 3complexes of AMP, AMPD and AHMPD are in thefollowing order : Ni(AMP)2+ < Ni(AMPDY~+ >Ni(AHMPD)2+ (1 : 1); Ni(AMPH+ < Ni(AMPDH+~ Ni(AHMPDH+ (1 : 2) ; and Ni(AMPH+ < Ni(AMPD)~+ (1: 3) .

References1. CocKEREL,L. & WALTON,H. F., J. phys, Chem .• 66 (1962),

75.2. SYCHEV, A. YA. & GORBEKu. A. N., Russ. J. inorg.

Chem •• 7 (1962), 138.3. BHAT. G. A. & SUBRAHMANYA.R. S., J. inorg, nucl,

Chem., 33 (1971), 3487.

4. BHAT,G. A. & SUBRAHMANYA,R. S., Indian J. Chem.,11 (1973), 584.

5. IRVING, H. & ROSSOTI1,H., J. chem. Soc., (1953), 3397.6. MAHAPATRA, S. & SUBRAHMANYA,R. S., Proc. Indian

Acad. s«, 59A (1964), 299.7. RUSTAGI, S. C. & RAo, G. N., J. inorg . nucl. Chem., 36

(1974), 1161.8. RUSTAGI,S. C. & RAo, G. N., J. inorg. nucl. Chem., 36

(1974), 1889.9. RUSTAGI,S. C., Ph.D. Thesis, Indian Institute ofTechnoiogy,

New Delhi, 1974.

Mixed Complexes of Neodymium(lll), Samarium(III),Gadolinium(lll) & Holmium(lII) in Aqueous Medium

D. G. MARATHE& K. N. MUNSHI*Department of Chemistry, Nagpur University, Nagpur 440 010

Received 28 March 1981; revised and accepted 27 May 1981

The 1:1 trivalent rare earth-c)'c1ohexanediaminetetraaceticacid (CyDTA) complexes form 1:1:1 mixed chelates in aqueousmedium with Ali%arin Red-S (ARS), 8-hydroxyquinoline-5-sulphonic acid (OSA), 8-hydroxy-7 -iodoquinoline-S-sulphonicadd (lOSA), and iminodiacetic acid (lMDA) at 25°C and IA =0.1 M (NaOO.). The stability constants have been detenninedemploying modified Irvlng-Rossotti pH-metric method.

THE tendency of lanthanides to expand theircoordination number greater than six has beenreported by different workers in the study of themixed ligand complexes':", This prompted us tostudy some mixed ligand complexes of Nd(III),Sm(III), Gd(lII) and Ho(III) with cyclohexanediami-netetraacetic acid (CyDT A) as a primary ligandand 2,4-dihydroxyanthraquinone-2-sulphonic acid(Alizarin Red-S, ARS), 8-hydroxyquinoline-5-sulpho-nic acid (OSA), 8-hydroxy-7-iodoquinoline-5-sulphonicacid (IOSA) or iminodiacetic acid (IMDA) as asecondary ligand in aqueous medium employingmodified Irving-Rossotti pH-metric method. Thestability constants for ternary system of Nd(III)and OSA is reported in literature but the conditionsof study are different", The secondary ligands arechosen in such a manner that exchange does notoccur between primary and secondary ligands, i.e.the primary complexes are more stable as comparedto those of the secondary ligands.

All the chemicals employed were of reagent gradepurity (BDH or E. Merck). The ligand solutions

NOTES

were prepared in doubly distilled water. A s.tocksolution of disodium salt of CyDTA (Koch-Light)was prepared by dissolving a weig~cd amount ofthe corresponding acid in the reqUJ~ed volum~ ofstandardized NaOH solution. All ligand solutionswere standardised potentiometrically. Metal solu-tions were prepared from their chlorides (IndianRare Earths Ltd) in perchloric acid, to prevent t~ehydrolysis and were estimated by complexornetrictitrations. All the experiments were carried outunder nitrogen atmosphere at the desired temperaturemaintained with an accuracy of ±0.02o•

The experimental procedure involved potentio-metric titration against carbonate-free sodium hy-droxide of the following four mixtures (total volume100 ml): (A) 2.0x1O-2M HCl04; (B) 2.0xIo-2MHCIO. + 1.0 X 10-3 M secondary ligand; (C)2.0xl0-2 M HCI04 + 1.0 X l()-3M CyOTA +1.0 X lo-3M metal solution; and (D) 2.0