Cluster synthesis—XXIII. The synthesis, structure and bonding of Fe4(CO)10(μ-CO)(μ4-S)2

Abstract The compound Fe 4 (CO) 10 (μ-CO)(μ 4 -S) 2 ( 1 ) was synthesized in 38% yield by the UV induced decarbonylation of Fe(CO) 5 in the presence of Fe 3 (CO) 9 (μ 3 -S) 2 . Compound 1 was characterized by a single-crystal X-ray diffraction analysis. Space group: Pccn , a = 6.603(1), b = 15.429(3), c = 17.292(4) A, Z = 4. The structure was solved by direct methods and was refined (807 reflections) to the final values of the residuals R = 0.043 and R w = 0.054. The molecule consists of a planar array of four iron atoms with a quadruply bridging sulphido ligand on each side of the plane. The shortest metal-metal bond, 2.489(3) A, contains a bridging carbonyl ligand. Semi-bridging carbonyl ligands bridge the two adjacent metal-metal bonds, 2.532(2) A. The longest metal-metal bond, 2.605(2) A, has no carbonyl bridge. Compound 1 is unsaturated (by EAN rule) by the amount of two electrons. The two semi-bridged carbonyl-metal bonds in 1 are significantly shorter than those in the saturated cluster Fe 2 CO 2 (CO) 11 (μ 4 -S) 2 . A molecular orbital description which explains the differences in bonding between the two compounds is proposed.