Transcript cis
CH7. Intro to Coordination Compounds
1
Inner-sphere vs outer-sphere
2
Nomenclature 1. Learn common ligand names (Table 7.1) Ex: :OH :O 2 :CN :Br :NH 3 2 aqua oxo (oxido) cyano (cyanido) bromo (bromido) 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) 3
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) ~ C 2v ~D 2h Stereoisomers
cis-
and
trans-
platin. The
cis
isomer is an anti cancer drug.
4
Cis-platin binding to DNA
5
6. To write the formula: Nomenclature 7.
[metal, then anionic ligands, then neutral ligands] net charge superscript Special ligands: a. ambidentate -SCN (thicyanato) vs NCS (isothiocyanato) [Pt(SCN) 4 ] 2 D 4h tetrathiocyanatoplatinate(II) [Cr(NCS)(NH 3 ) 5 ] 2+ pentaammineisothiocyanatochromium(III) NO 2 (nitrito) vs ONO (isonitrito) 6
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 7
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 8
Geometric Isomers There have distinct physical and chemical properties Oh coordination MX 5 Y 1 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 9
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) 10
Polymetallic complexes (also called cage compounds) no direct M-M bonding ex: S 8 + NaSR + FeCl 3 MeOH (dry) / N 2 [Fe 4 S 4 (SR) 4 ] n model for ferrodoxins 11
Cluster compounds
direct M-M bonding ex: [Re 2 Cl 8 ] 2 octachlorodirhenate(III) D 4h (eclipsed) 12
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) 13
UV/Vis spectrum for Ti(OH 2 ) 6 3+ 20,300 cm -1 (wavenumber units) = 493 nm (wavelength units) = 243 kJ/mol (energy units) violet solution 14
0 depends on: Crystal Field Theory 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 strongly with ligands – more diffuse d-orbitals interact more 0 Mn 2+ < Fe small 2+ < Fe 3+ < Ru 3+ < Pd 4+ < Pt 4+ large 15
Ligand Field Stabilization Energy for electronic config t 2g x e g y the LFSE = (0.4x 0.6y) 0 # d electrons e config LFSE ( 0 ) # unpaired e 0 0 0 1 t 2g 1 0.4
1 2 t 2g 2 0.8
2 3 t 2g 3 1.2
3 high spin case 4 5 6 7 8 9 10 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 0.6
0 0.4
0.8
1.2
0.6
0 4 5 4 3 2 1 0 depends of relative values of 0 and pairing energy.
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High spin vs low spin d 4 t 2g 3 e g 1 LSFE = 0.6 0 high spin (weak field) [Cr(OH 2 ) 6 ] 2+ t 2g 4 LFSE = 1.6 0 PE low spin (strong field) [Cr(CN) 6 ] 4 17
H hyd for first-row TM 2+ ions All are high spin complexes M 2+ (g) H 2 O [M(OH 2 ) 6 ] 2+ (aq) H calc from Born Haber analyses 18
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
1 2 3 4 5 1.73
2.83
3.87
4.90
5.92
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 19
CN = 5
20
d-orbital splitting in a T d field 21
CFT for CN 4 For Td complexes T << 0 due to fewer ligands and the geometry of field vs ligands ex: [CoCl 4 ] 2 [Co(OH 2 ) 6 ] 3+ Δ 3300 cm 1 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) 22
Tetragonal distortion of Oh
23
Square planar complexes
D 4h is a common structure for d orbitals) 8 complexes (full z 2 , empty x 2 – y 2 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 24
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 25
CuF 2 Jahn-Teller effect 26
Ligand Field Theory CFT does not explain ligand field strengths; MO theory can Start with SALCs that are ligand combinations shown to the right 27
MO for O h TM complexes SF 6 - no metal d valence orbitals considered 28
p -bonding in O h complexes p -donor ligands Decrease O Example: Cl p -acceptor ligands Increase O Example: CO 29
O
h
character table
30