Crystal and molecular structure of nonacarbonyl-µ-(1,2,3,4-tetraphenylbutadiene-1,4-diyl)-triangulo-triosmium, (Ph4C4)Os3(CO)9

Abstract

Crystals of the title compound occur in two forms: (i) M-form, monoclinic, space group P2₁/c, Z= 4, a= 12·148(5), b= 9·796(4), c= 29·565(16)Å, β= 91·79(5)°; and (ii) O-form, orthorhombic, space group Iba2, Z= 8, a= 38·45(8), b= 18·59(4), c= 9·80(2)Å. The structures of both modifications were solved by Patterson and Fourier syntheses, and refined by least-squares methods to R 0·095 (4807 reflexions, M-form) and 0·080 (1916 reflexions, O-form); they have the same molecular structure. The molecule is built up of the organic ligand Ph₄C₄, with a cluster of three osmium atoms at the corners of an isosceles triangle, bonded to two, three, or four carbonyl groups. Co-ordination between Ph₄C₄ and the cluster is attained viaσ-bonds and the donation of four π-electrons of the osmacyclopentadiene ring. The cluster and the ligand configurations are discussed in relation to those of similar compounds.