Crystal and Molecular Structures of Some Alkynyl–Group 9/Group 11 Complexes [M2m4(C2R)8(PPh3)2] (M = Rh, Ir; m = Cu, Ag; R = Ph, Fc (Ir/Cu only))

Abstract

The crystal and molecular structures of five complexes [M₂m₄(C≡ CR)₈(PPh₃)₂] (M = Rh, Ir; m = Cu, Ag; R = Ph, Fc (Ir/Cu only)) are described. Each consists of an approximately octahedral arrangement of the six metal atoms, with atoms M occupying opposite apical positions and atoms m forming an approximate plane. Four alkynyl groups are σ-bonded to each M. Two of these, one from each M, also interact by an asymmetric π-bonding mode with each atom m. Each M is also coordinated to one PPh₃ ligand. The M–m distances range between 2.7698(9) and 3.2050(9) Å, although average values fall within the tight ranges 2.86(8) and 2.90(5) (m = Cu) or 3.06(5), 3.09(9) Å (m = Ag). Formally non-bonding M ··· M distances range between 4.1511(8) and 4.654(1) Å, while the shorter m ··· m separations range between 2.659(1) and 2.918(2) Å, which suggests that only weak intermetallic bonding exists. Both the geometries of these complexes and their intense colours suggest that the M₂m₄ cluster formulation is a major contributor to the structure, rather than a more simplistic, formally zwitterionic assemblage of two [M(C≡ CR)₄(PPh₃)]²⁻ centres held together by the four m⁺ cations.