AB-INITIO XRPD STRUCTURE DETERMINATION OF METAL-CARBONYL CLUSTERS - THE CASE OF [HGRU(CO)4]4

The crystal and molecular structure of the new [HgRu(CO)4]4 cluster ha s been determined exclusively from X-ray powder diffraction data from standard laboratory equipment and refined with a (modified) Rietveld p rocedure. The title compound crystallizes in the monoclinic space grou p P2(1)/n, with a = 13.032(1) angstrom, b = 18.293(2) angstrom, c = 6. 501 (1) angstrom, beta = 111.81(2)-degrees, V = 1438.9(4) angstrom3, a nd Z = 2; the final refinement converged to R(p) and R(wp) values of 0 .097 and 0. 126, respectively, for 3351 data collected (Cu Kalpha) at room temperature in the 18-85-degrees (20) range. [HgRu(CO)4]4 consist s of a planar, centrosymmetric, eight-membered ring of alternating Hg and cis-Ru(CO)4 units of idealized D4h symmetry. XRPD is shown to be a powerful tool to obtain useful structural information on moderately c omplex organometallic systems, when single crystals cannot be grown, i f all the available chemical knowledge is included in the refinement t hrough constraints.