Synthesis and X-ray powder diffraction characterization of (OC)2RhCl2Rh(cod) (cod = cycloocta-1,4-diene)

In order to elucidate the nature and the structure of the elusive (OC)(2)Rh(Ph3SiO)(2)Rh(cod) (cod)=cycloocta-1,5-diene) complex, an important model compound for surface catalysis, (OC)(2)RhCl2Rh(cod) has been synthesized, and structurally characterized by ab initio X-ray powder diffraction. Crystals of (OC)(2)RhCl2Rh(cod) are monoclinic, space group P2(1)/c, a = 6.659(1), b = 12.274(1) and c = 16.096(1) Angstrom, beta = 92.176(5)degrees, Z = 4, rho(calc),,,, = 2.209 g cm(-3). The structure has been solved, from powder diffraction data only, by Patterson and Fourier-difference methods and has been ultimately refined, by the Rietveld method, down to R-p, = 0.116 and R-wp, = 0.154 for 4050 data points collected in the 12-93 degrees (2 theta) range. The molecule contains two square-planar rhodium atoms, one bearing two terminal carbonyls and the other bound to the chelating cod fragment, and two chlorine atoms bridging the Rh ... Rh vector. The Rh2Cl2, core is markedly non-planar, the dihedral angle about the Cl ... Cl hinge being 135.4(6)degrees.