User:Benjah-bmm27/degree/2/CAR

Transition metals 1, CAR

"Coordination Chemistry of the Transition Metals, Part 1"

• Review of d-block chemistry

Structure and bonding in transition metal complexes

• Revision of crystal field theory, which does not explain the spectrochemical series
• Ligand field theory (application of molecular orbital theory to bonding in complexes)
  • e_g* orbitals are antibonding, so when occupied, metal-ligand bonds weaken and lengthen (and substitution rxns happen faster)
  • Stronger metal-ligand interaction raises e_g* (and lowers e_g), while t_2g is unaffected → greater Δ_o
  • Pi bonding: by symmetry, t_2g can and e_g and e_g* cannot do π bonding, π backbonding
    • π donor ligands – Δ_o ↓ (weak field ligands)
    • π acceptor ligands – Δ_o ↑ (strong field ligands)
    • good σ donors – Δ_o ↑
    • poor σ donors – Δ_o ↓
• Metal ligand multiple bonds, such as imido ligands
• Structural consequences of particular d electron counts
  • Jahn-Teller effect: J-T theorem
    • "any non-linear molecule in a degenerate electronic ground state will undergo a geometrical distortion that removes that degeneracy"
    • for symmetry reasons, tend to get elongation of bonds along z-axis and shortening of bonds in xy plane, so in Cu²⁺, d⁹, get (d_z²)²(d_x²−y²)¹
  • Planar-octahedral and planar-tetrahedral equilibria in d⁸ complexes
    • Lifschitz salts: [Ni(L-L)₂]X₂ vs. [Ni(L-L)₂X₂]
    • [NiBr₂PEtPh₂] brown, square planar, diamagnetic vs. green, tetrahedral, paramagnetic: Acta Cryst. (1992). C48, 406-408
• Stability constants of complexes

Thermodynamic stability in transition metal complexes

• Chelate effect
  • Chelation
  • Chelation therapy
• Macrocyclic effect
• Template reaction
• HSAB theory
• Effects of CFSE
• Irving-Williams series
• Redox in transition metal complexes: Co(II)-Co(III) and Cu(I)-Cu(II)
  • Frost diagrams

Application to group 6 chemistry

• Group 6 elements: Cr, Mo, W
• Polyoxometallate