Molecular and electronic structure of Tc_2(O_2CCH_3)_2Cl_4 studied by multiconfigurational quantum chemical methods

摘要

The molecular and electronic structure, as well as the electronic absorption spectrum of Tc_2(O_2CCH_3)_2Cl_4 were studied by multiconfigurational quantum chemical methods. The computed ground state geometry is in excellent agreement with the experimental structure determined by single crystal X-ray diffraction (SCXRD). The total bond order (i.e., 3.20) is consistent with the presence of a moderately strong quadruple Tc-Tc bond and is the largest bond order reported so far for a multiple Tc-Tc bonded complex. Effective bond order analysis indicates stronger p and d bonds for Tc_2(O_2CCH_3)_2Cl_4 (i.e., 1.71 for π and 0.59 for δ) than for Tc_2Cl_8~(2-) (i.e., 1.68 for π and 0.47 for δ). The electronic absorption spectrum was recorded in dichloromethane and shows three distinct bands in the range 10000-35000 cm~(-1). Assignment of the bands, as well as their excitation energies and intensities were performed at the CASSCF/CASPT2 level of theory. The lowest energy band corresponds to the δ→δ~* transition; the next higher energy bands are attributed to δ→π~* and π→δ~* transitions, respectively.