A novel carbonyl bridging mode: the structure of the metal carbonyl complex [Mn₂(CO)₅(Ph₂PCH₂PPh₂)₂]

Abstract

The crystal structure of the solvated complex Mn₂(CO)₅(dpm)₂,CH₂Cl₃,C₆H₁₄ (where dpm = Ph₂PCH₂PPh₂) has been determined by three-dimensional X-ray diffraction methods. The crystals are monoclinic, of space group Cc, with a 19.650(3), b 16.908(2), c 22.253(4) Ǻ and β 130.89(1)°, containing four molecules per unit cell. The structure, solved by conventional Patterson and Fourier methods, was refined by a least- squares method, using individual isotropic temperature factors, to R and R_w of 0.105 and 0.125 respectively, for 1893 independent statistically significant reflections collected by counter methods. The crystals are molecular, being composed of discrete molecules of complex and solvent. The principal feature of interest in the binuclear manganese complex is the presence of a carbonyl ligand simultaneously bonded to both manganese atoms in a manner quite different from the normal symmetrical bridging mode. This novel arrangement, which seems to involve a metal-carbonyl bond analogous to that found for many metal-olefin complexes, accounts for the anomalously low carbonyl stretching frequency observed at 1645 cm^-1. The Mn-Mn distance is 2.934(6) Ǻ.