STRUCTURAL SYSTEMATICS OF TRANSITION METAL TRIPHOSPHORUS MACROCYCLES. Simon J. Coles and Michael B. Hursthouse Department Of Chemistry University of Wales, Cardiff.P.O. Box 912, Cardiff. Cf1 3Tb. U.K.

A number of transition metal triphosphacyclododecane complexes have been structurally characterised by X-ray crystallography, enabling a systematic structural study, the results of which have been incorporated into the development of extended force field parameter sets for transition metal complexes.

Data for the air-sensitive crystals of these complexes were collected on the FAST TV Area detector, equipped with an Oxford Cryosystems low temperature device, using the oil drop mounting method. Structures were solved using the SHELX suite of programs to give experimental parameters.

A force field parameter set for the complex [Cr(CO)₃{cyclo-(HPC₃H₆)₃} ] was derived, using the classical approach, giving force constants for stretch and bend parameters and energy barriers for torsional and nonbonded interaction parameters. This extended force field parameter set is applied to the molecular modelling of structures determined by X-ray diffraction, in order to determine the accuracy of the derived parameters, and then used to model uncharacterised structures. Molecular mechanics calculations were performed using the software packages HyperChem and Cerius², which have also been used to perform semi-empirical calculations upon these systems.