A comparative study of the topology of the experimental electron density within 2 and 4e− donor alkyne complexes

Abstract

A comparison of the topology of the experimental electron density, as revealed by high resolution X-ray diffraction, is provided for two prototypal transition metal alkyne complexes where the alkyne formally behaves as a 2 or 4e⁻ donor. A higher value of the electron density ρ(r)_bcp at the M_T⋯C bond critical point (bcp), a lower value of ρ(r)_bcp at the coordinated CC bcp, outwardly bent M⋯C bond paths and a close to zero ellipticity for the CC bond constitute the topological signature of a 4e⁻ donor alkyne ligand.