1 CH7. Intro to Coordination Compounds

2 Inner-sphere vs outer-sphere

3 Nomenclature 1. Learn common ligand names (Table 7.1) Ex::OH 2 aqua :O 2  oxo (oxido) :CN  cyano (cyanido) :Br  bromo (bromido) :NH 3 ammine Note that anionic ligands end in “o” 2. List ligands in alphabetical order 3. Metal name at end, add “ate” if it’s an anionic complex some common names – ferrate, stannate, plumbate, cuprate 4. Add (and metal oxidation number in Roman numerals) or add metal (and total complex charge in Arabic numerals)

4 Nomenclature ex: [Cu(OH 2 ) 6 ] 2+ is hexaaquacopper(II) or hexaaquacopper(2+) [CuCl 4 ]  is tetrachlorocuprate(III) or tetrachloridocuprate(III) 5. Add prefixes to indicate number of each ligand type mono, di, tri, tetra, penta, hexa or use bis, tris, tetrakis if less confusing due to ligand name ex: [PtBr 2 {P(CH 3 ) 3 } 2 ] is dibromobis(trimethylphosphine)platinum(II) Stereoisomers cis- and trans- platin. The cis isomer is an anti- cancer drug. ~ C 2v ~D 2h

5 Cis-platin binding to DNA

6 Nomenclature 6. To write the formula: [metal, then anionic ligands, then neutral ligands] net charge superscript 7.Special ligands: a. ambidentate -SCN (thicyanato) vs  NCS (isothiocyanato)  NO 2 (nitrito) vs  ONO (isonitrito) [Pt(SCN) 4 ] 2  D 4h tetrathiocyanatoplatinate(II) [Cr(NCS)(NH 3 ) 5 ] 2+ pentaammineisothiocyanatochromium(III)

7 Nomenclature b. bidentate – ligands bind to M at two sites ex: H 2 NCH 2 CH 2 NH 2 ethylenediamine (en) [Cr(en) 3 ] 3+ tris(ethylenediamine)chromium(III) View looking down C 3 axis D 3 (-> no , no S axes, chiral) enantiomers

8 Nomenclature Another bidentate example is acetato c. polydentate ligands – bind at multiple sites ex: tetraazamacrocycles porphine (a simple porphyrin) the 4 N atoms are approximately square planar

9 Geometric Isomers There have distinct physical and chemical properties Oh coordinationMX 5 Y1 isomer MX 4 Y 2 2 isomers (cis or trans) MX 3 Y 3 2 isomers (fac = C 3V or mer = C 2V ) ex: [CoCl 2 (NH 3 ) 4 ] + tetraamminedichlorocobalt(III) cis – purple trans – green

10 Optical Isomers Enantiomers = non-superimposable mirror images of a chiral molecule enantiomers have identical physical properties (except in a chiral environment, for example retention times on a chiral column are not the same) enantiomers rotate the plane of polarized light in opposite directions (optical isomers)

11 Polymetallic complexes (also called cage compounds) no direct M-M bonding ex: S 8 + NaSR + FeCl 3  [Fe 4 S 4 (SR) 4 ] n  model for ferrodoxins MeOH (dry) / N 2

12 Cluster compounds direct M-M bonding ex: [Re 2 Cl 8 ] 2  octachlorodirhenate(III) D 4h (eclipsed)

13 Crystal Field Theory Oh complexes – put 6 e  pairs around central metal in Oh geometry this splits the 4 d-orbitals into 2 symmetry sets t 2g (xz, yz, xy) and e g (x 2 – y 2, z 2 )  0 can be determined from spectroscopic data (see Table 8.3)

14 UV/Vis spectrum for Ti(OH 2 ) ,300 cm -1 (wavenumber units) = 493 nm (wavelength units) = 243 kJ/mol (energy units) violet solution

15 Crystal Field Theory  0 depends on: 1. ligand (spectrochemical series)  0 I  < Br  < Cl  < F  < OH  < NH 3 < CN  < CO weak field strong field more complete list in text 2.metal ion  0 greater for higher oxidation number – stronger, shorter M-L interaction  0 greater going down a group – more diffuse d-orbitals interact more strongly with ligands  0 Mn 2+ < Fe 2+ < Fe 3+ < Ru 3+ < Pd 4+ < Pt 4+ small  large 

16 Ligand Field Stabilization Energy for electronic config t 2g x e g y the LFSE = (0.4x  0.6y)  0 high spin case # d electrons e  config-t 2g 1 t 2g 2 t 2g 3 t 2g 3 e g 1 t 2g 3 e g 2 t 4 e g 2 t 5 e g 2 t 2g 6 e g 2 t 2g 6 e g 3 t 2g 6 e g 4 LFSE (  0 ) # unpaired e  depends of relative values of  0 and pairing energy.

17 High spin vs low spin d 4 t 2g 3 e g 1 t 2g 4 LSFE = 0.6  0 LFSE = 1.6  0  PE high spinlow spin (weak field)(strong field) [Cr(OH 2 ) 6 ] 2+ [Cr(CN) 6 ] 4 

18  hyd for first-row TM 2+ ions All are high spin complexes M 2+ (g)  [M(OH 2 ) 6 ] 2+ (aq)  H calc from Born Haber analyses H2OH2O

19 Magnetic Measurements Magnetic moment (  ) is the attractive force towards a magnetic field (H)  ≈ [N(N + 2)] 1/2  B  where N = number of unpaired electrons N  /  B this is the paramagnetic contribution from unpaired e  spin only, it ignores both spin- orbit coupling and diamagnetic contributions ex: [Mn(NCS) 6 ] 4  experimental  /  B = 6.06, Mn(II) is d 5 it must be a high spin complex

20 CN = 5

21 d-orbital splitting in a T d field

22 CFT for CN 4 For Td complexes  T <<  0 due to fewer ligands and the geometry of field vs ligands ex: Δ [CoCl 4 ] 2  3300 cm  1 [Co(OH 2 ) 6 ] 3+ 20,700 cm  1 therefore Td complexes are nearly always high spin (pairing E more important than LFSE) Co(II) d 7 LSFE = 1.2  T ex: Fe 3 O 4 magnetite Fe(II)Fe(III) 2 O 4 oxide is a weak field ligand, so high spin case Fe(II) is d 6 (only in Oh sites); Fe(III) is d 5 (1/2 in Oh sites, ½ in Td sites)

23 Tetragonal distortion of Oh

24 Square planar complexes D 4h is a common structure for d 8 complexes (full z 2, empty x 2 – y 2 orbitals) Group 9: Rh(I), Ir(I) Group 10: Pt(II), Pd(II) Group 11: Au(III), for example AuCl 4  Note: [Ni(CN) 4 ] 2  is D 4h but [NiCl 4 ] 2  is T d Ni(II) has a smaller  than Pd, PT so Td is common but we see D 4h with strong field ligands

25 Jahn-Teller effect Jahn-Teller effect: degenerate electronic ground states generate structural disorder to decrease E Ex: [Cu(OH 2 ) 6 ] 2+ Cu(II) d 9 We see a tetragonal distortion But fluxional above 20K, so appears Oh by NMR in aqueous solution

26 Jahn-Teller effect CuF 2

27 Ligand Field Theory CFT does not explain ligand field strengths; MO theory can Start with SALCs that are ligand combinations shown to the right

28 MO for O h TM complexes SF 6 - no metal d valence orbitals considered

29  -bonding in O h complexes  -acceptor ligands Increase  O Example: CO  -donor ligands Decrease  O Example: Cl -

30 O h character table