The thermochemistry of carbonyl complexes of Cr,Mo and W with pyridine and acetonitrile |
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Authors: | Festus A. Adedeji Joseph A. Connor Christopher P. Demain Jose A. Martinho-Simoes Henry A. Skinner Mohamed T. Zafarani Moattar |
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Affiliation: | Department of Chemistry, University of Manchester, Manchester, M13 9PL Great Britain |
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Abstract: | Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and of iodination of a number of [M(CO)nL6-n] complexes (M = Cr, Mo, W; n = 3, 4; L = py, MeCN) have led to values for the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol?) at 25°C: fac-[Mo(CO)3py3](275 ± 12), fac-[Mo(CO)3(NCCH3)3] (410 ± 12), fac-[W(CO)3py3](250 ± 12), fac-[W(CO)3(NCCH3)3](405 ± 12) and cis-[Cr(CO)4py2](505 ± 20). From these and other data, including estimated heats of sublimation, the bond enthalpy contributions of the various metalligand bonds in the gaseous metal complexes were evaluated as follows (values in kJ mol?): D(Crpy) 102, D(Mopy) 146, DWPy) 173, D(Mo7z.sbnd;NCMe) 135 and D(WNCMe) 169. For a given metal the bond enthalpy contribution decreased in the order D(MCO) > D(Mpy) > D(Mz.sbnd;NCMe). This order is related to the σ- and π-bonding character of the ligand. |
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