Crystal and molecular structure of H2FeRu3(CO)13; a tetrahedral hydridocarbonyl of iron and ruthenium containing asymmetric carbon bridges

Abstract

The iron–ruthenium hydridocarbonyl H₂FeRu₃(CO)₁₃ forms red, monoclinic crystals of unit cell dimensions a= 47·00(6), b= 8·75(1), c= 9·56(1)Å, β= 90° 57′(10′), space group P2₁/a. The structure was refined to R 0·95 for 1934 unique reflections. The asymmetric unit of the structure comprises two molecules of the same gross geometry, though with significant detailed differences. The two molecules occur in different orientations in the unit cell with their molecular centres ¼a apart; an arrangement which gives rise to problems of pseudosymmetry in the structure analysis. Each molecule comprises a tetrahedron of three Ru atoms and one Fe atom, with three terminal carbonyl groups on each Ru atom and two terminal carbonyl groups on each Fe atom. In addition, there are two asymmetric carbonyl bridges between Fe and Ru, for which the Fe–C distances range from 1·68 to 1·86(7)Å, and the Ru–C distances from 2·18 to 2·45(6)Å. In the metal cluster the Ru–Ru distances range from 2·78 to 2·92 (σ 0·008)Å and the Fe–Ru distances from 2·63 to 2·70(1)Å. For the terminal carbonyl groups the mean Ru–C distance is 1·82(8)Å, the mean Fe–C distance is 1·72(5)Å, and the mean C–O distance 1·18(8)Å. Evidence is presented that the two hydrogen atoms bridge Ru–Ru bonds so as to retain approximate mirror symmetry for the molecule as a whole.