Determination of bond energies by mass spectrometry. Some transition metal carbonyls

Two groups of transition metal carbonyls have been studied, M(CO)6 and M(CO)5CS complexes of the Group VIB metals and M2(CO)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)5CS 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)6 to M(CO)5CS weakens the remaining M--CO bonds by an average of 0.2 eV. Previously unreported MnTc(CO)10 and TcRe(CO)10 are prepared by halide substitution of Tc(CO)5Br and Re(CO)5Br with Mn(CO)5- and Tc(CO)5-, respectively. In the positive ion, metal and mixed-metal decacarbonyls are considered as (CO)5M+--M(CO)5 complexes possessing five strong and five weak M--CO bonds. For Mn2(CO)10 and Re2(CO)10, M+--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)5+ and M(CO)5