X-Ray structure determination of a new metal cluster complex: di-µ3-arsino-tris(tricarbonyliron)(3Fe–Fe)

Abstract

Arsenic trifluoride and iron pentacarbonyl react at 120 °C to give dark violet crystals of As₂[Fe(CO)₃]₃ with orthorhombic symmetry, space group Bmmb, cell dimensions a₀= 10·82(2), b₀= 10·96(2), and c₀= 13·29(2)Å, and Z= 4.

The structure was solved from photographic data by three-dimensional Patterson and Fourier methods and refined by least squares methods to R 0·107 for 630 independent reflections. The structure is disordered with one molecule randomly distributed in two orientations which are related by a crystallographic two-fold rotation axis. The idealized molecular symmetry is 3/m(C_3h). The molecule is characterized by an equilateral triangle of iron atoms, mean Fe–Fe 2·62(1)Å. The two arsenic atoms lie above and below the iron triangle, and are related by a mirror plane containing the iron atoms. Both arsenic atoms are bonded equally to the iron triangle, mean As–Fe 2·35 Å. Other mean bond lengths: Fe–C 1·80, C–O 1·12 Å.