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CH7. Intro to Coordination Compounds

CH7. Intro to Coordination Compounds. Inner-sphere vs outer-sphere. Nomenclature. . 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”

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CH7. Intro to Coordination Compounds

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  1. CH7. Intro to Coordination Compounds

  2. Inner-sphere vs outer-sphere

  3. Nomenclature • . Learn common ligand names (Table 7.1) • Ex: :OH2 aqua • :O2 oxo (oxido) • :CN cyano (cyanido) • :Br bromo (bromido) • :NH3 ammine • Note that anionic ligands end in “o” • . List ligands in alphabetical order • . Metal name at end, add “ate” if it’s an anionic complex • some common names – ferrate, stannate, plumbate, cuprate • . Add (and metal oxidation number in Roman numerals) • or add metal (and total complex charge in Arabic numerals)

  4. ~ C2v ~D2h Nomenclature • ex: [Cu(OH2)6]2+ is hexaaquacopper(II) or hexaaquacopper(2+) • [CuCl4] is tetrachlorocuprate(III) or tetrachloridocuprate(III) • . 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: [PtBr2{P(CH3)3}2 ] is dibromobis(trimethylphosphine)platinum(II) Stereoisomers cis- and trans-platin. The cis isomer is an anti-cancer drug.

  5. Cis-platin binding to DNA

  6. - [Pt(SCN) ] D tetrathiocyanatoplatinate(II ) 2 4 4h [Cr(NCS)(NH3)5] pentaammineisothiocyanatochromium(III ) 2+ Nomenclature • 6. To write the formula: • [metal, then anionic ligands, then neutral ligands] net charge superscript • Special ligands: • a. ambidentate • -SCN (thicyanato) vs NCS (isothiocyanato) •  NO2 (nitrito) vs ONO (isonitrito)

  7. Nomenclature b. bidentate – ligands bind to M at two sites ex: H2NCH2CH2NH2 ethylenediamine (en) [Cr(en)3]3+ tris(ethylenediamine)chromium(III) View looking down C3 axis D3 (-> 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 coordination MX5Y 1 isomer MX4Y2 2 isomers (cis or trans) MX3Y3 2 isomers (fac = C3V ormer = C2V ) ex: [CoCl2(NH3)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: S8 + NaSR + FeCl3 [Fe4S4(SR)4]n model for ferrodoxins MeOH (dry) / N2

  12. Cluster compounds direct M-M bonding ex: [Re2Cl8]2 octachlorodirhenate(III) D4h (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 t2g (xz, yz, xy) and eg (x2 – y2, z2) 0 can be determined from spectroscopic data (see Table 8.3)

  14. UV/Vis spectrum for Ti(OH2)63+ 20,300 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 < NH3 < CN < CO • weak field strong field • more complete list in text • 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 Mn2+ < Fe2+ < Fe3+ < Ru3+ < Pd4+ < Pt4+ small  large 

  16. Ligand Field Stabilization Energy for electronic config t2gx egy the LFSE = (0.4x  0.6y) 0 high spin case # d electrons 0 1 2 3 4 5 6 7 8 9 10 e config - t2g1 t2g2 t2g3 t2g3eg1 t2g3eg2 t4eg2 t5eg2 t2g6eg2 t2g6eg3 t2g6eg4 LFSE (0) 0 0.4 0.8 1.2 0.6 0 0.4 0.8 1.2 0.6 0 # unpaired e 0 1 2 3 4 5 4 3 2 1 0 depends of relative values of 0 and pairing energy.

  17. High spin vs low spin d4 t2g3eg1 t2g4 LSFE = 0.6 0 LFSE = 1.6 0 PE high spin low spin (weak field) (strong field) [Cr(OH2)6]2+ [Cr(CN)6]4

  18. DHhyd for first-row TM2+ ions All are high spin complexes H2O M2+(g)  [M(OH2)6]2+ (aq) H calc from Born Haber analyses

  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 1 1.73 2 2.83 3 3.87 4 4.90 5 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 d5 it must be a high spin complex

  20. CN = 5

  21. d-orbital splitting in a Td field

  22. CFT for CN 4 For Td complexes T << 0 due to fewer ligands and the geometry of field vs ligands ex: Δ [CoCl4] 2 3300 cm 1 [Co(OH2)6]3+ 20,700 cm 1 therefore Td complexes are nearly always high spin (pairing E more important than LFSE) Co(II) d7 LSFE = 1.2T ex: Fe3O4 magnetite Fe(II)Fe(III)2O4 oxide is a weak field ligand, so high spin case Fe(II) is d6 (only in Oh sites); Fe(III) is d5 (1/2 in Oh sites, ½ in Td sites)

  23. Tetragonal distortion of Oh

  24. Square planar complexes D4h is a common structure for d8 complexes (full z2, empty x2 – y2 orbitals) Group 9: Rh(I), Ir(I) Group 10: Pt(II), Pd(II) Group 11: Au(III), for example AuCl4 Note: [Ni(CN)4]2 is D4h but [NiCl4]2 is Td Ni(II) has a smaller  than Pd, PT so Td is common but we see D4h with strong field ligands

  25. Jahn-Teller effect Jahn-Teller effect: degenerate electronic ground states generate structural disorder to decrease E Ex: [Cu(OH2)6]2+ Cu(II) d9 We see a tetragonal distortion But fluxional above 20K, so appears Oh by NMR in aqueous solution

  26. Jahn-Teller effect CuF2

  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 Oh TM complexes SF6 - no metal d valence orbitals considered

  29. p-bonding in Oh complexes p-donor ligands Decrease DO Example: Cl- p-acceptor ligands Increase DO Example: CO

  30. Oh character table

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