CRYSTAL-STRUCTURES OF [W(CO)5(PPH3)], [M(CO)5(ASPH3)] AND [M(CO)5(SBPH3)] (M=MO OR W) - A COMPARATIVE-STUDY OF STRUCTURE AND BONDING IN [M(CO)5(EPH3)] COMPLEXES (E=P, AS OR SB M=CR, MO OR W)

Crystal structures have been determined for [W(CO)5(PPh3)], [M(CO)5(AsPh3)] and [M(CO)5-(SbPh3)](M = Mo or W) as part of a systematic study of a series of nine [M(CO)5(EPh3)] complexes (M = Cr, Mo or W; E = P, As or Sb). Trends in bond lengths and angles are rationalised in terms of steric and electronic interactions between the bonded M(CO)5 and EPh3 fragments. Comparison is made between the solid-state geometry of the free and co-ordinated EPh3. Torsion angles defining the disposition of the EPh3 groups in relation to M(CO)5 show little variation within the [M(CO)5(EPh3)] series. For all nine complexes the EPh3 groups have propeller geometry with small deviations from symmetric C3 structures. The studies were extended to include other related [M(CO)5L] complexes. Trends in the structural parameters of 29 such compounds are related to the steric behaviour and pi-acceptor capacity of the ligands L. It is shown that M-P bond dimensions are not adequately explained by hybridisation changes of the phosphorus atom in the ligand L.