Molecular and electronic structure of Tc2(O2CCH3)2Cl4 studied by multiconfigurational quantum chemical methods

Abstract

The molecular and electronic structure, as well as the electronic absorption spectrum of Tc2(O2CCH3)2Cl4 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 π and δ bonds for Tc2(O2CCH3)2Cl4 (i.e., 1.71 for π and 0.59 for δ) than for Tc2Cl82− (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 10000–35000cm−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.