Molecular structures of Fe<SUB>4</SUB>(CO)<SUB>10</SUB>(&#956;-CO)(&#956;<SUB>4</SUB>-Se)<SUB>2</SUB> and Fe<SUB>3</SUB>Ru(CO)<SUB>10</SUB>(&#956;-CO)(&#956;<SUB>4</SUB>-Se)<SUB>2</SUB>

The results of the X-ray analyses of Fe4(CO)10(&#956;-CO)(&#956;4-Se)2 and Fe3Ru(CO)10(&#956;-CO)(&#956;4-Se)2 are reported. The two compounds are isomorphous and belong to the orthorhombic space group Pccn with a = 6.655(1), b = 15.587(2), c = 17.387(2) &#197; for Fe4(CO)10(&#956;-CO)(&#956;4-Se)2 and a = 6.630(1), b = 15.785(2), c = 17.629(3) &#197; for Fe3Ru(CO)10(&#956;-CO)(&#956;4-Se)2. The structures were solved by direct methods and refined, correcting for extinction, to R = 0.0306 and 0.0312 for 1171 and 1277 observed reflections for Fe4(CO)10(&#956;-CO)(&#956;4-Se)2 and Fe3Ru(CO)10(&#956;-CO)(&#956;4-Se)2 respectively. They belong to the [M4(CO)11XY] clusters which are formally unsaturated according to the 18-electron rules but conform to the Wade's rules of electron counting. Both complexes contain terminal, bridging and semibridging carbonyl groups