DFT predictions of vibrational spectra of titanium tetramethoxide oligomers and the structure of titanium tetraalkoxides in liquid and solid phases

Plausible structures of the titanium tetramethoxide trimer were optimized at the B3LYP/6-31+G^* level. From the four types of structures of the Ti₃O₁₂ cage found earlier for the Ti(OH)₄ trimer only two isomers were found as energy minima on the Ti₃(OMe)₁₂ potential energy surface. One isomer (I), belonging to the C_i point group, is built from three interconnected titanium oxide tetrahedra with a linear arrangement of titanium atoms. This structure have a titanium oxide skeleton similar to that of Ti₃(OH)₁₂. The other isomer (II), of C₂ symmetry, is built by edge sharing TiO₆ groups. Theoretical IR spectra of these isomers are compared with reported experimental IR spectra of solid titanium tetramethoxide and newly obtained Raman spectra of commercial powders. It was shown that the number and position of observed bands in the CO stretching region of the IR spectra of the so-called modification A of solid titanium tetramethoxide are in a good agreement with the predicted vibrational spectrum of trimer I. The equilibrium structure and IR and Raman spectra were also obtained for the Ti₄(OMe)₁₆ tetramer. The comparison of the predicted vibrational spectrum with the experimental IR spectra of modification B as well as of the Raman spectrum of solid titanium tetramethoxide allows us to confirm the tetrameric structure of this modification and to propose the similar structure for commercial samples.