Determination of Bond Energies by Mass Spectrometry. Some Transition Metal Carbonyls

摘要

Two groups of transition metal carbonyls have been studied, M(CO) sub 6 and M(CO) sub 5 CS complexes of the Group VIB metals and M sub 2 (CO) sub 10 complexes of the Group VIIB metals. Results for the hexacarbonyl complexes indicate that the measured fragmentation energies are in error by 0.25 +- 0.02 eV per CO produced. This is attributed to excitation of CO to the first vibrational state. Least-squares dissociation energies calculated from corrected data for M(CO) sub 5 CS complexes indicate that the M--CS bond is 3 to 4 times stronger than the M--CO bonds. Substitution of CS for CO in going from M(CO) sub 6 to M(CO) sub 5 CS weakens the remaining M--CO bonds by an average of 0.2 eV. Previously unreported MnTc(CO) sub 10 and TcRe(CO) sub 10 are prepared by halide substitution of Tc(CO) sub 5 Br and Re(CO) sub 5 Br with Mn(CO) sub 5- and Tc(CO) sub 5- , respectively. In the positive ion, metal and mixed-metal decacarbonyls are considered as (CO) sub 5 M exp + --M(CO) sub 5 complexes possessing five strong and five weak M--CO bonds. For Mn sub 2 (CO) sub 10 and Re sub 2 (CO) sub 10 , M exp + --M dissociation energies are 3.0 +- 0.1 and 4.0 +- 0.3 eV, respectively. These energies are 2.5 times greater than those reported for homolytic cleavage to M(CO) sub 5+ and M(CO) sub 5 . (ERA citation 04:030986)