Structural Characterization of [HxRe3(CO)12]x-3 (x = 2,3) by Extended X-ray Absorption Fine Structure Spectroscopy

Extended x-ray absorption fine structure (EXAFS) measurements on the ReL{sub III} edge have been used to elucidate the structures of H{sub 3}ReP{sub 3}(CO){sub 12} and (H{sub 2}Re{sub 3}(CO){sub 12}){sup {minus}}. The data analysis is based on empirically determined EXAFS functions, including that of Os{sub 3}(CO){sub 12}, to account for the multiple scattering effects characteristic of metal carbonyls. The results confirm the presence of a triangular Re{sub 3} skeleton in each cluster, with the Re-Re bonds in the neutral cluster being of equal length (3.285 {angstrom}). The disorder in the Re-Re shell characterizing the anionic cluster indicates that not all the Re-Re bonds are of equal length, which implies the presence of bridging hydride ligands associated with the longer Re-Re bonds. Comparison of the EXAFS data with published x-ray diffraction data characterizing (HRe{sub 3}(CO){sub 12}){sup 2{minus}} shows a trend of decreasing Re-C distances and increasing C-O distances with increasing negative charge on the cluster, which is explained by {pi}-back-bonding.