Crystal structure of di-µ-[1,2-bis(dimethylarsino)tetrafluorocyclobutene]-octacarbonyl-tetrahedro-tetracobalt

Abstract

The X-ray crystal structure of the title compound C₂₄H₂₄As₄Co₄F₈O₈, has been determined from counter data. The crystals are monoclinic, space group C2/c, with Z= 4 in a unit cell of dimensions: a= 23·623(4), b= 9·326(2), c= 16·674(4)Å, and β= 90·70(2)°. The structure was solved by direct phasing methods and refined by full-matrix least-squares method to R 0·034 for 1057 observed reflections. The cobalt atoms form a tetrahedral cluster and each arsine ligand forms a bridge between two cobalt atoms. Each cobalt atom is bonded to three other cobalt atoms [Co(3)–Co(4) 2·446, Co(3)–Co(3′) 2·510(4), and Co(4)–Co(4′) 2·343 Å] and co-ordinated to three other atoms, these six atoms forming a very distorted octahedron. The two halves of the molecules are related by a crystallographic two-fold axis passing through the midpoints of Co(3)–Co(3′) and Co(4)–Co(4′). Co(3)–As(1) and Co(4)–As(2) are 2·307(2) and 2·242 Å and the two arsenic atoms and the cyclobutene ring are co-planar. The carbon atoms of some carbonyl groups have weak interactions with an adjacent cobalt atom.