RAMAN FREQUENCIES AND METAL-METAL FORCE CONSTANTS FOR M2(CO)1O SPECIES

Raman spectra are reported for Mn2(CO)10, Re2(CO)10, and MnRe(CO)10. A simple normal-coordinate analysis was applied to the low-frequency vibrations of the transition metal decacarbonyls in order to estimate metal-metal stretching force constants. The following values (in mdyn/Å) were obtained: fMn-Mn = 0.59, fTc-Tc = 0.72, fRe-Re = 0.82, fMn-Re = 0.81. The force Constances correlate satisfactorily with bond dissociation energies obtained from electron impact measurements. The present results are discussed together with previous analyses of Ru3(CO)12, Os3(CO)12, and Ir4(CO)12. For the polynuclear carbonyls, metal-metal force constants increase with increasing atomic number within a given row or period, in accord with the expectation based on chemical stabilities, mass spectral fragmentation patterns, and internuclear distances. Metal-metal force constants calculated with neglect of the carbonyl ligands are not seriously in error and are quite satisfactory for the third transition row. © 1969, American Chemical Society. All rights reserved.