Outline of Topics on Coordination Chemistry

You must be familiar with common ligands, their charge, and dn for each T-metal

Ti V Cr Mn Fe Co Ni Cu Zn

+2 ion 2 3 4 5 6 7 8 9 10

1. Structures of the basic Coordination Geometries 2 thru 8

2. Stereoisomers in Octahedral and Square Planar Complexes

3. VBT, CFT, and MO Theory in brief /applications

4. Applications of LFSE , magnetism, and spectra

5. Mechanisms of Octahedral Substitution in Co(III) and Cr(III)

6. Mechanism of Square Planar Substitution in Pt(II)

the trans effect

7. Electron Transfer Reactions - Marcus theory.

Nobel Prizes related to Inorganic Chemistry1901 van’t Hoff LeBel Tetrahedral carbon/ stereochemistry (1867)1913 Alfred Werner Coordination chemistry (1893)1912 Victor Grignard RMgX reagent1954 L. Pauling nature of chemical bond 1962 Max Perutz Hemoglobin structures1963 Ziegler & Natta Titanium catalysts for stereoreg polymerization1964 Dorothy Crowfoot Hodgkin Vitamin B12 structure (Co)1973 G. Wilkinson and E. O. Fischer ferrocene and sandwiches1979 H. C. Brown, G. Wittig hydroboration, P ylids1983 Henry Taube electron transfer reactions of metal complexes1985 H. Hauptman and J. Karle Direct methods to solve phase problem1987 Lehn, Pedersen, Cram supramolecular chem/crown ether/host guest1992 Rudy Marcus adiabatic theory of electron transfer1996 Kroto, Curl, Smalley C60 2001 Nyori, Knowles, Sharpless chiral metal catalysts Rh, Ti2005 Grubbs, Chauvin, Schrock metathesis / carbenes Ru, Mo 2010 Heck, Suzuki, Negishi organometallic catalysis PdP4

Kolbe on van’t Hoff http://ursula.chem.yale.edu/~chem125/125/history/Kolbe.html

I have recently published an article in Journal für praktische Chemie (14, 288 ff.) giving as one of the reasons for the contemporary decline of chemical research in Germany the lack of well-rounded as well as thorough chemical education. Many of our chemistry professors labor with this problem to the great disadvantage of our science. As a consequence of this, there is an overgrowth of the weed of the seemingly learned and ingenious but in reality trivial and stupefying natural philosophy. This natural philosophy, which had been put aside by exact science, is at present being dragged out by pseudoscientists from the junk-room which harbors such failings of the human mind, and is dressed up in modern fashion and rouged freshly like a whore whom one tries to smuggle into good society where she does not belong.

A J. H. van't Hoff who is employed at the Veterinary School in Utrecht appears to find exact chemical research not to his taste. He deems it more convenient to mount Pegasus (evidently loaned from the Veterinary School) and to proclaim in his "La chimie dans l'espace" how, to him on the chemical Parnassus which he ascended in his daring flight, the atoms appeared to be arranged in the Universe.

Werner Theory of Coord. Complexes 1893 at age 26

# AgCl ppt # ions from Conductivity Werner CoCl3 - 6 NH3 3 4 luteo [Co(NH3)6]Cl3

- 5 NH3 2 3 purpeo [Co(NH3)5 Cl]Cl2- 4 NH3 1 2 violo/praeseo [Co(NH3)4Cl2]Cl *1

IrCl3 - 3 NH3 0 0 Ir(NH3)3Cl3

PtCl4 -6 NH3 4 5 [Pt(NH3)6]Cl4- 5 NH3 3 4 [Pt(NH3)5Cl]Cl3- 4 NH3 2 3 [Pt(NH3)4Cl2]Cl2 *-3 NH3 1 2 [Pt(NH3)3Cl3]Cl *-2 NH3 0 0 Pt(NH3)2Cl4 *

-KCl - NH3 0 2 K[Pt(NH3)Cl5]- 2 KCl 0 3 K2[PtCl6] 2

1 cis or trans-dichlorotetraamminecobalt (III) chloride2. potassium hexachloroplatinate(IV)

CHEM 3030 LAB EXPTS

1. Synthesis of [Co(NH3)4(CO3)]NO3 , [Co(NH3)5Cl]Cl2 IR, Conductivity

2. [Cr(NH3)6](NO3)3 liq NH3, UV-Vis

3. Magnetic Susceptibility Gouy and Evans Methods

4. Linkage Isomers of Co(NH3)5(NO2)2+ UV-Vis, IR

5. X-ray Structure of an Iron Macrocyle in P212121 SHELX software

6. Coordination Chemistry of Nickel UV-Vis , IR, or magnetism

Common Ligands HS 184 , 204 3rd

monodentates: aqua, halides, NH3, CN-, PR3, thf, py, dmso, NCS-

bidentates: en, acac-, oxalate2-, bipy, phen, diphos, glycinate-

, dmgh- mono or bi : RCOO- CO32-

polydentates : dien, trien, porphyrin2-, Pc2-, edta4-, 18crown, cyclam

Paramagnetism HS 579 673 3rd

µ in Bohr magnetons = sqr(n(n+2) where n = # unpaired e’s

1. 1.73 2. 2.84 3. 3.87 4. 4.89 5. 5.9 BM spin only values

Bonding Approaches to Coordination Complexes

1. Lewis. Electron pair bond concept. Ligands are e-pair donors, metals e-pair acceptors. dative bond -both electrons in bond come from ligand.

2. VBT (Pauling) Vacant hybrid orbitals on metal are generated from LCAO suited to each geometry ( tetrahedral sp3 etc)

Bonds are formed by e-pair donation from ligand orbital into vacant hybrid orbitals on metal.

3. CFT. Bethe 1930. The degeneracy of d orbitals is lifted by the electrostatic field of ligands (taken as point charges) in various symmetries. In octahedral symmetry t2g (-4Dq) and eg (+6Dq) separated by ∆o = 10 Dq. Bonding is presumed to be purely ionic.

4. MOT LCAO-MO’s are generated by combining symmetry adapted LGO’swith metal orbitals. Bonding and antibonding combos. Electrons then fill levels from bottom up according to Hund’s rules.

Valence Bond Theory Pauling 1930’s hs-555/ 639

AO’s lack the directional character necessary for bond formation in many geometries. Hybrid orbitals are linear combinations of AO’s with suitable directionality .

linear sp Ag(CN)2- d10 (sp)4 0 BM

trigonal sp2 Fe(N(SiMe3)2)3 d5 (sp2)6 5.9 BMtetrahedral sp3 NiCl42- d8 (sp3)8 2.8 BMsquare planar dsp2 PtCl42- d8 (dsp2)8 0 BM5 coordinate dsp3 PF5 d0 (dsp3)10 0 BMoctahedral d2sp3 (inner) Co(NH3)6

3+ d6 (hyb)12 0 BMsp3d2 (outer) Ni(NH3)6

2+ d8 (hyb)12 2.84 BM 7 coordinate d3sp3 V(CN)7

4- d2 (hyb)14 2.84 BM8 coordinate d4sp3 W(CN)8

4- d2 (hyb)16 0 BM 9 coordinate d5sp3 ReH9

2- d0 (hyb)18 0 BM

In CFT the energies of the d orbitals are obtained from perturbation theory using the electrostatic potential V and the d orbital wavefunctions.

Edz2 = ∫ ψdz2 Voctψdz2 = +6Dq and Exy = -4Dq etc. Dq = 1/6 ze2 r4/a5 where r4 is the mean radius4 of the electron and a is

the metal ligand bond length.

CFSE ( in units of Dq) see p-563 of HS

z2 x2-y2 xy xz yzOne on z 5.14 -3.14 -3.14 0.57 0.57Linear 10.28 -6.28 -6.28 1.14 1.14trigonal -3.21 5.46 5.46 -3.85 -3.85trigonal bipy 7.07 -0.82 -0.82 -2.71 -2.71square -4.28 12.28 2.28 -5.14 -5.14tetrahedral -2.67 -2.67 1.78 1.78 1.78square pyram 0.86 9.14 -0.86 -4.57 -4.57

octahedral +6.00 +6.00 -4.00 -4.00 -4.00

Spectrochemical series - orders ligand in terms of increasing Dq

I- < F- < OH- < ox2- ~ H2O < NH3 < en < bipy < phen < CN- < R- < CO

Dq values in cm-1 and pairing energies (avg PE/electron) hs 559/642

+2 ions Ti V Cr Mn Fe Co Ni6F- 730 6 H2O 1240 1400 780 940 930 850 6 NH3 1020 1080 3 en 910 1100 1150 PE 23,500 25,500 17,600 22,500

+3 ions Ti V Cr Mn Fe Co Rh6F- 1700 1500 1400 1310 2264 6 H2O 2030 1785 1740 2100 1370 1820 27203 ox2- 1800 1700 1400 1800 26006 NH3 2160 2290 34103 en 2190 2400 34606 CN- 2660 3500 3220 4490 PE 28000 30,000 21,000

Predicting Hi or Low spin from PE and ∆0.Pairing energy for Co+3 PE = 21,000 cm-1 per electron

CoF63- ∆0 = 10Dq = 13,000

∆ cfse for low spin = 24Dq - 4 Dq = 20 Dq =26,000 cm-1

cost of pairing 2 electrons = 42,000 cm-1 cost exceeds benefit.

Co(NH3)63+ ∆0 = 10Dq = 23,000 cm-1

∆cfse = 20Dq = 46,000 cm-1 benefit exceeds cost

*This calculation assumes that PE is independent of ligand. A better criterion is to

compare ∆/B for the complex with the crossover point in the Tanabe Sugano

diagram at ∆/B = 20

CoF63- ∆0/B = 13,000/763 = 17 high spin 5T2g

Co(NH3)63+ ∆0/B = 23,000/530 = 43 low spin 1A1g

Examples of CFSE effects. 1. Stability constants, lattice energies, ∆Hhyd, etc (Fig 20.26-28 of HS) show a

big M or W pattern across the transition series. (V for strong field)

weak field cfse = 4,8,12,6,0,4,8,12,6,0 Dq for d1 thru d10 max at d3 and d8

strong field cfse = 4,8,12,16,20,24,18,12,6,0 Dq for d1 thru d10 max at d6

2. Structural preferences (using cfse’s in units of Dq)

cfse d3 hs d6 ls d6 hs d7 ls d8 d9

OCT 12 4 24 8 12 6

TET 3.56 2.67 8.90 5.34 3.56 1.78

SQUARE 15.56 5.14 21.56 10.28 24.56 12.28

low spin d6 and d3 are always octahedral and the most inert of the first t-series

Co3+ and Cr3+ . Pt2+ d8 square Pt+4 d6 and oct.

Dq is large for CN- but small for halides, oxygen donors.

∆tet = 4/9 ∆oct and 3rd series> 2nd > 1st All 3rd and 2nd are low spin

All amine or O-donor complexes of 1st t-series are hi-spin except Co(III)

CFT Energetics 1000 cm-1 = 1 kK = 11.96 kJ/mol

Ti(H2O)63+ absorbs at 500 nm or 20,000 cm-1

or 240 kJ/mol

10 Dq = 20,000 cm-1 or Dq = 2000 cm-1

cfse = 4 Dq = 8000 cm-1 or 96 kJ/mol

Ti3+(gas) → Ti(H2O)6

3+(aq)

∆Hhyd = -5400 kJ/mol

∆Hhyd includes the 6 Ti -water bonds plus the solvation.

cfse thus makes up only a small fraction of the total energy

Jahn-Teller Theorem - A non-linear molecule in an orbitally degenerate ground state (T or E) will distort to remove the degeneracy.

Significant distortion in metal complexes are observed for E states.

Axial elongation or compression is observed for octahedral cases.

d4 Cr2+ CrBr2 (s) Cr-Br bond 4 at 2.54 2 at 3.00 Å

d9 Cu2+ CuCl2 4 at 2.3 , 2 at 2.95 Å ( x2-y2 hole)

CuF2 4 at 2.08 , 2 at 1.95 (z2 hole)

While T states are predicted to distort, the effect seems to be too small to detect.

What MO Theory tells us about T-metal chemistry in Oh

1. Bonding is delocalized over metal and all ligands. A1g bonding MO is a 7 centre 2-electron bondφbonding = c1 φ4s + c2{φa + φb + φc + φd + φe + φf }where φ4s is the metal 4s orbital and φa-f are the ligand donor orbitals. for pure covalent bond c1 = c2 = √2)/2 for more ionic bond c1 << c2

2. 10Dq depends on sigma and pi bonding 3. The 6 sigma bonds are A1g, T1u, and Eg

4. The eg metal d orbitals in Oh are antibonding eg*

5. Pi bonding LGO’s are T1g, T1u, T2g, T2u

for pi acceptor ligands the metal t2g from CFT is πfor pi donor ligands the metal t2g from CFT is π*

Note spectrochemcial series I- < F- < OH- < ox2- ~ H2O < NH3 < en < bipy < phen < CN- < R- < COπ-donors weak σ strong σ / π-acceptors

MO for Octahedral Complex Sigma only

Pi Bonding a) pi donor I- b) pi acceptor CO

Diagram shows interaction along one axis, T2g in Oh

Bonding and Symmetry Basics

Geometry VB hybrids pt grp LGO’s sigma pi

Linear spz D∞h σg σu πu πg

Tetrahedral sp3 Td a1 t2 t1 t2 e

Square Planar dx2-y2spxy2 D4h a1g b1g eu in eu b2g a2g

out eg b2u a2u

Octahedral d2sp3 Oh a1g t1u eg t1u t2g t2u t1g

AO symmetry : Oh s (a1g) p (t1u) d (t2g eg) D4h s (a1g) pxy (eu) pz (a2u) dz2 (a1g) dxz,yx (eg) dxy (b2g) dx2-y2 (b1g) Td s (a1) p (t2) d (e, t2)

Note that the symmetry adapted sigma LGO’s belong to the same irred. reps as the AO’s used to form the hybrid orbital sets in VBT

Examples of things that ain’t .

1. Co(NH3)6Cl3 is 6-coordinate not 9

2. BeCl2 is tetrahedral in the solid state

3. NaCl is 6-coordinate in the solid state.

4. Ca2+(aq) is 6 coordinate in water

5. Mn(CO)5 is a dimer octahedral Mn2(CO)10

6. P2O5 is actually P4O10

7. PCl5 (s) is actually [PCl4]+ [PCl6]-

8. N2O5 (s) is [NO2]+[NO3]- nitronium nitrate

9. “BiCl” contains 2 Bi95+ 4 BiCl52- and 1 Bi2Cl82-

more precisely Bi24Cl28 with a tricapped trigonal prism and sq pyramids

“You can’t readily assume the coordination number from the formula”

Factors influencing Coordination and Geometry

1.Maximize number of bonds and Bond energy

2. Minimize L-L repulsion

3. LFSE if not d0 or d10

4. chelate ring strain, conditions, other factors

Example: 6 vs. 4 coordinate 1 vs. 2 & 3

Tetrahedral vs. Square 2 vs. 3

Do not delude yourself into thinking there are simple principleswhich allow you to decide matters where 1 kcal/mol can tip the balance either way.

Pentacoordination Four Coordinate

1. VSEPR or ligand repulsion dominant

Trigonal Bipyramid D3h Tetrahedral

PF5 Ni(CN)53- , Fe(CO)5 CH4 Ni(CO)4 Pt(PPh3)4

2. LFSE dominant

Square Pyramid C4v Square Planar

d8 Ni(CN)53- d8, d9 Cu2+ Pt2+ Au3+

pentacoordination was once thought rare but is now rather common.

It is not usually possible to predict which 5 or 7 coordinate geometry might be preferred. Neither is stereochemically rigid enough to study isomers.

Thus isomer studies are limited mostly to sq Pt(II) and Oct d3 and d6

[Cr(en)3][Ni(CN)5] Raymond, Inorg Chem 7, 1362 (1968)

Ax 2.17 Å Eq 1.87 Å Ax 1.83 Å Eq 1.91 Å

cfse= 2(9.04 Dq) cfse = 2(7.07 Dq)

19F NMR of PF3Cl2 Holmes, Inorg Chem 3, 1748 (1964)

JPF =1051 Hz

JFF = 124 Hz

Some Novel Nickel (II) ComplexesEx 1 Lifschitz Salts [Ni(stien)2]2+ square � Ni(stien)2X2 oct

Ni(stien)2X2 is sometimes yellow and diamagnetic and sometimes blue and paramagnetic.

blue : X = Cl- or CH3COO- or in humid air or in dmso soln.

yellow X = CF3COO- or ClO4- or dry or in CCl4 soln

stien = meso stilbenediamine NH2CH(Ph)CH(Ph)NH2

Nyburg and Wood, Inorg Chem 3, 468 (1964)

Ni(stien)2(CH3COO)2 µ = 3.13 blue pwd

Ni(stien)2(CCl3COO)2 diamagnetic yellow pwdNi(stien)2(ClCH2COO)2 - 2/3 EtOH 4/3 H2O µ = 1.76 yellow-grn xtal

triclinic P-1 Z=3 [Ni(stien)2(X)2] at (0,0,0)* (1/2,0,1/2)* and [Ni(stien)2]2+

at (0,0,1/2) Ni(stien)2(ClCH2COO)2 -4H2O blue xtal

P21/c Z =2 [Ni(stien)2(H2O)2]2+ at ( 0,0,0) and (0,1/2,1/2)

Ex 2 Kilborne and Powell, J. Chem Soc A 1168 (1970)Ni(PPh3)2Br2 tetrahedral µ = 3.2 BM Ph = phenyl

Ni(PR3)2Br2 square µ = 0 BM R = alkyl

Xtals of Ni(PPh2(CH2Ph))2Br2 have 3 Ni per unit cell P-1. Which Ni complex lies on a special position in P-1?

2 are tetrahedral and 1 square (trans) µ = 2.7 BM.

Tet Ni-P 2.31Å Square Ni-P 2.26Å

Ni-Br 2.35Å Ni-Br 2.30Å

In tet form the antibonding t2* is occupied. In square b1g* (x2-y2) vacant. Thus

the bonds are stronger in the d8 square form as long as steric repulsion is not a factor. By changes in the nature of the phosphine and halide ligandsit is possible to tip the balance either way.

Ex 3 Holm, JACS 92, 1855 (1970)Ni2+ complexes of mixed arylalkylphosphines show an

equilibrium between square and tetrahedral forms. Holm has studied some 30 of the general form NiP2X2

where P = P(CH2Ph)(Ph-Z)2 (Z para substituent) X = halide

NiP2X2 (SQUARE) � NiP2X2 (TET)

µ = 0 BM 1B1g µ = 3.2 BM 3T1

Z= CF3, X = Cl 11% tet µ = 1.1 BM Z= NMe2, X = I 92% tet µ = 3.02Vis (xy� x2-y2) 20kK vis 3 d-d (5.5, 11.8, 20 kK) ∆Go = +1.1 kcal/mol ∆Go = -1.3 kcal/mol

for various subst. ∆Ho = 1 to 2 kcal/mol ∆So = 2 to 4 eu

cfse, bonds favor square entropy favors tet {S = Rln(9) }

Z= CF3 favors π-acceptor higher cfse Z= NMe2 π-donor, lower cfse

X = Cl small steric effect X = I large steric effect favors tet

Ex 4 Byrne, JACS 109 1282 (1987) Co(NOR)4+,o,-

Chem Comm 1491 (1986)

Alkyl cobalt complexes of the norbornyl ligand(C7H11) provide a rare example of a low spintetrahedral complex of Co (III)

+ cation Co(V) µ = 0o neutral Co(IV) µ = 1.73 BM

- anion Co(III) µ = 3.18 BM

alkyl ligands lie high in the spectrochemical series ( strong σ-donors)Norbornyl is a bulky ligand thus favoring tetrahedral structure.

Co(IV) structure is Pmn21 (#31) z =4 with Co on a mirror.

EX 5. Tetrahedral Pd(II) HS 671 Yeo Chem Comm 1477 (1999)

µ = 2.5 BM paramagnetic

bite angle O-Pd-O = 1050 -how does this change d orb energies? chelate is diphenylphospinoxido ferrocene

Lower coordination numbers 2 , 3Ag(NH3)2

+ , HgI3- , Cu(tu)2Cl , MnL*2 , AuL3+ FeL*3

• bulky ligands L= PPh3 , L* = N(Si(Me)3)2-

• filled d shells Ag+ Cu+ Au+

Higher coordination numbers7 pentagonal bipy ZrF7

3- Zr(acac)3Cl V(CN)74-

capped trig prism TaF72- Mo(CNR)6I+ Mn(EDTA)(H2O)2-

capped oct NbOF63-

8 sq anti prism Ti(NO3)4 , TaF8-3 dodecahedron Mo(CN)8

4-

cube CsCl9 tricapped trig prism ReH9

2-,• vacant d shells • small ligands• chelates with tight bites NO3

- , acac-1 , ox-2 , trop-1

T-shaped 3 Coordinate [RhP3]ClO4Reed, JACS 99, 7076 (1977)RhP3Cl + TlClO4 → [RhP3]ClO4 + TlCl in dry CH2Cl2in even weakly coordinating solvents one obtains square [RhP3S]+

triclinic spacegroup P -1 ; a = 11.925 , b = 14.466 c = 15.553 8;

α = 92.637 , β = 88.931 , γ = 112.744 (15)';

diamagnetic d8 cannot be trigonal planar D3h(why).

Angles 98, 103, 160o

Rh-P 2.21, 2.24 Å

Linear bis- (trimethylsilylamido)iron and Trigonal trisLappert, Inorg Chem. 27, 1782 (1988),

Bis Fe(II) in gas phase by electron diffraction Fe-N 1.84 Å

N-Bridged Fe(II) Dimer in solid state µ = 3.52 BM. Tris Fe(III) as solid by X-ray Fe-N 1.91Å (high spin)

Data input as CIF or SHELX RES fileunit cell dimensions, space group SYMM codes, and atom locations in

fractional coordinates.view asymmetric unit in variety of modes, stick, ball, spacefill etc.computes and displays X-ray powder patternpacking display hkl planesmeasure distances, angles, mean planes identify H-bond and close contacts

SOFTWARE FOR STRUCTURE VIEWING Free Mercury graphic package from Cambridge

http://www.ccdc.cam.ac.uk/products/mercury/

WINGX free software for solving structures http://crick.chem.gla.ac.uk/~louis/wingx/download.html

requires X-ray diffraction data in an HKL file - see Expt 5.

Some recent structures viewed via the MERCURY software.

[Et4N]2 [Fe(CN)2(CO)3 P21/n z=4 IC 42,5046 (2003)

[Cu(CH3CN)2 ] [BPh4] C2/c Z = 4 Cu on -1 site

[YbIII(PY)5I2] I (0.5 PY) Z =8 in P21/c 7 coord Yb

2 independent Yb’s per unit cell

Au2(dpim)]2+[ClO4]2 in P21/n Z =4 IC 42, 8430 (2003)

Au(dpim)Cl

in P212121

Z=4

chiral C1

TbIII (W)4(µ-SQ)2] [NO3] W P21/c Z =4 square antiprismSQ is the enolate anion of 3-methyl-4-hydroxycyclobut-3-ene-1,2-dione , W= H2O

SQ

sq

LaIII(SQ)3W6 -W in P21/c Z =4 9 coordinate La

B. Alleyne et al, Inorg Chem., 40, 1045 (2001)