An EXAFS study of methyl-substituted benzene chromium tricarbonyl complexes

An extended X-ray absorption fine structure (EXAFS) study is presented of the complexes (eta(6)-C6H6-nMen)Cr(CO)(3), where n = 0-6, to determine the molecular structures and explore the variation in electron charge density on chromium with sequential arene methylation. Structural parameters for the complexes, determined by EXAFS analysis, are found to agree closely with literature data from X-ray crystal structures. The structure of (eta(6)-p-xylene)Cr(CO)(3) is described, for which no previous determination has been reported. From analysis of the K-edge absorptions, chromium Is electron threshold energies were obtained; a small increase in these energies is observed with each methyl insertion on the benzene ring. This trend is interpreted to indicate a progressive accumulation of electron density on the chromium atom. The results agree with a bonding model previously constructed from vibrational spectral and XPS studies. (C) 1997 Elsevier Science B.V.