Bonding situation in "early-late" transition metal complexes Cl₃M-M′(PCl₃)₄ (M = Ti, Zr, Hf; M′ = Co, Rh, Ir) - Theoretical study for a ligand fine tuning of M-M′ bonds

Density functional theory calculations using the BP86 functional in combination with triple-ζ quality basis sets have been carried out for the "early-late" transition metal complexes Cl₃M- M′(PCl₃)₄ (M = Ti, Zr, Hf; M′ = Co, Rh, Ir) and the derivatives R₃M-M′L₄ (R = Cl, NH ₂; L = PCl₃, PH₃, CO). The calculations demonstrate that the metal-metal bond strength in R₃M-M′L ₄ can be strongly influenced by the nature of the ligands R and L. The intrinsic interaction energy ΔE_int and the bond dissociation energy of the M-M′ bonds in Cl₃M-M′(PCl ₃)₄ are much smaller than in the previously investigated species (H₂N)₃M-M′(CO)₄. The M-M′ bonds become stronger in both sets of compounds when the metal atoms become heavier. The equilibrium geometries of Cl₃M-M′(PCl ₃)₄ which have bipyramidal structures have C₃ symmetry. The M-Co bonds in Cl₃Zr-Co(PCl₃)₄ and Cl₃Hf-Co(PCl₃)₄ and to a lesser degree in Cl₃Ti-Co(PCl₃)₄ are unusually long because of direct interactions between the equatorial PCl₃ groups and the group 4 atoms Zr, Hf. The analysis of the metal-metal interactions suggests that Cl₃M-M′(PCl₃)₄ has M-M′ single bonds.