Crystal structure of nonacarbonyl-µ-dimethylarsino-µ-[2-(diphenylphosphino)tetrafluorocyclobut-1-enyl]-tri-iron

Abstract

The crystal structure of the title compound has been solved using X-ray counter data. Crystals are orthorhombic, space group P2₁2₁2l, with Z= 8 in a cell of dimensions: a= 12·172(3), b= 48·935(8), and c= 10·233(2)Å; there are two molecules in the asymmetric unit which have been shown to be chemically equivalent. The structure was solved by tangent refinement procedures and refined by full-matrix least-squares methods to R 0·052 for 2175 observed reflections. The molecule is based on three Fe(CO)₃ groups and an Me₂As group which are linked to form a four-membered ring. The mean Fe–As is 2·387 Å. The ligand, (Ph₂P)·[graphic omitted]F₂, forms a bond with each iron atom through the phosphorus atom, Fe–P 2·48 Å, the cyclobutenyl double bond, Fe–(midpoint)CC 1·96 Å, and a carbon atom of the cyclobutene ring, Fe–C 1·94 Å, and thus bridges the two iron–iron bonds. Every iron atom has approximate octahedral co-ordination. The two iron–iron distances in each molecule are inequivalent, 2·676 and 2·866 Å, and this appears to be a result of constraints caused by the ligand bridges. One of the methyl groups bonded to arsenic has close non-bonded intramolecular contacts with a phenyl ring.