Crystal structure of octacarbonylbis-µ-[bis(dimethylarsino)tetrafluorocyclobutene-AsAs]-triangulo-triruthenium

Abstract

Crystals of octacarbonylbis-µ-[bis(dimethylarsino)tetrafluorocyclobutene-AsAs]-triangulo-triruthenium, [graphic omitted] (CO)₈, are orthorhombic, space group Pbcn, a= 9·07, b= 18·53, c= 21·81 Å, Z= 4 (one-half molecule per asymmetric unit). The structure was determined with Mo-K_α diffractometer data by direct and Fourier methods, and was refined by least-squares procedures to a final R of 0·078 for 1507 observed (of a total of 1712) reflexions. The molecule lies on a crystallographic two-fold rotation axis, and is best described as a derivative of Ru₃(CO)₁₂ in which two carbonyls on one ruthenium atom and one carbonyl on each of the other ruthenium atoms are replaced by the arsenic atoms of the bidentate diarsine ligands, in such a way that each ligand bridges two ruthenium atoms, and one Ru–Ru bond remains unbridged. This unbridged Ru–Ru bond (2·785 Å) is significantly shorter than the bridged bonds (2·853 Å) and than those of the parent Ru₃(CO)₁₂(average 2·848 Å). The skeletons of the diarsine ligands do not deviate significantly from planarity, the plane of each ligand being twisted 18° with respect to the plane of the ruthenium triangle. The mean Ru–As bond length is 2·407 Å.