Lando P. Wolters and F. Matthias Bickelhaupt, VU University, The Netherlands, show that not all d¹⁰-ML₂ complexes are linear. They investigated the molecular geometries and electronic structure of a series of d¹⁰-ML₂ complexes (M = Co⁻, Rh⁻, Ir⁻, Ni, Pd, Pt, Cu⁺, Ag⁺, Au⁺; L = NH₃, PH₃, CO) by using relativistic density functional theory (DFT).

By analyzing the bonding mechanism in ML₂ as a function of the ligand-metal-ligand (L-M-L) angle with quantitative Kohn–Sham molecular orbital (MO) theory in combination with an energy decomposition analysis (EDA) scheme, they show that the L-M-L angle can vary. Necessary for the occurrence of bent d^₁₀-ML₂ complexes is sufficiently strong π backdonation. Smaller angles increase the overlap of the ligand’s acceptor orbital with a higher-energy donor orbital on the metal–ligand fragment and, therefore, favor π backdonation, resulting in additional stabilization. The balance between the additional stabilization and the increased steric repulsion, occurring as the complexes are bent, determines the resulting angle of the complex.

The analyses explain the phenomenon and provide a tool for rationally tuning the bite angle.

• Nonlinear d¹⁰-ML₂ Transition-Metal Complexes
  Lando P. Wolters, Prof. Dr. F. Matthias Bickelhaupt
  ChemistryOpen 2013, 3, 106–114,
  DOI: 10.1002/open.201300009