A Five-Coordinated d6 Complex: Structure of Dichlorotris(triphenylphosphine)ruthenium(II)

A complete X-ray structure determination of dichlorotris(triphenylphosphine)ruthenium(II), RuCl₂[P(C₆H₅)₃]₃, has been carried out in order to ascertain if in this compound the Ru(II) (d⁶) is five-coordinated. The compound crystallizes in space group C_2h ⁵-P₂1/c of the monoclinic system in a cell of dimensions a = 18.01, b = 20.22, c = 12.36 A., /3 = 90.5°. The observed density is 1.43 g./cm.³, and the density calculated for four molecules in the cell is 1.415 g./cm.³. There are no crystallographic symmetry conditions imposed on the molecule. The structure consists of the packing of individual monomeric molecules. In these molecules the Ru lies toward the center of a distorted square pyramid which consists of trans CI atoms and trans P atoms in the base and an apical P atom. The apical Ru-P distance of 2.23 A. is about 0.16 A. shorter than the basal Ru-P distances. This is the only known example from X-ray structural studies of a five-coordinated d⁶ complex, and it probably occurs not because of an inherent tendency toward five-coordination, but rather because the unused octahedral site about the square-pyramidal configuration is effectively blocked by a phenyl ring.