Abstract
The crystal and molecular structures of one of the substances reported by Rouschias and Wilkinson to have the general formula RegClsCOiCRFIPCCelDsh, namely, the one with R = C2HS, have been determined in an X-ray crystallographic
study; It was found that the formula as previously given is incorrect, lacking one oxygen atom. The Re20C]s(02CC2H3)2- [P(C6H5)3]2 molecule consists of two structurally equivalent Re atoms each surrounded by six ligand atoms at the vertices of a slightly distorted octahedron. The octahedra are joined on a common edge formed by bridging O and Cl atoms. The other two Cl atoms occupy positions trans to the bridging 0 atom, and the P atoms occupy positions irons to the bridging Cl atom. The pairs of vertices above and below the plane defined by these six ligand atoms and the two Re atoms are occupied by bridging bidentate C2HsCOO groups. The symmetry of the two Re atoms and the ten atoms coordinated to them is C2v neglecting small packing distortions. The Re-Re distance is 2.514 (1) A. The entire structure is nearly identical with that of Re20Cl5(02CC2Hs)[P(C6H6)3]2 except for the replacement of two Cl atoms by a propionato group. The crystals studied belong to space group P2i/c with dimensions a = 14.059 ± 0.003 A, 6 = 17.477 ± 0.003 A, c = 17.556 + 0.003 A, and ß = 97.80 ± 0.01°. The observed and calculated densities were 1.81 + 0.01 and 1.82 g cm"3 (for Z = 4), respectively. The structure was solved and refined using 2125 statistically significant independent reflections. Refinement was by a full-matrix, least-squares program in which the phenyl groups were treated as rigid bodies with separate isotropic temperature parameters for each carbon atom; anisotropic temperature parameters were used for Re, Cl, and P atoms. Final weighted and unweighted discrepancy indexes were 0.034 and 0.031, respectively. Mean values of bond lengths to rhenium atoms are (A): Re-Cl (terminal), 2.360 (3); Re-Cl (bridge), 2.403 (3); Re-P, 2.455 (3); Re-0 (carboxyl), 2.108 (5);Re-0 (bridge), 1.916 (6).