Vibrational Spectra and Molecular Association of Titanium Tetraisopropoxide

The Fourier transform-infrared (FT-IR) and polarized FT-Raman spectra of titanium tetraisopropoxide (tetraisopropoxytitanium, TPT), in pure and diluted forms, and of 2-propanol have been investigated in conjunction with previous assignments for related compounds to obtain a comprehensive assignment of the vibrational spectra. Evidence was obtained for the presence of both monomeric and associated species of TPT. The latter are formed by coordination expansion through bridging isopropoxy ligands. For both monomeric and associated TPT species, vibrational modes of isopropoxy ligands with nu(C-O) mode character were coupled to nu(s)(Ti-O) and nu(as)(Ti-O) modes (interligand coupling). The symmetrically coupled ligand modes gave rise to intense, strongly polarized bands in the Raman spectrum. The antisymmetrically coupled ligand modes gave rise to strong bands in the IR spectrum at lower wavenumbers than the corresponding Raman bands. Molecular association of TPT produced negligible shifts in the ligand modes coupled to the nu(s)(Ti-O) mode in the Raman spectrum. In contrast, the degeneracy of the strong ligand modes coupled to the nu(as)(Ti-O) mode was lifted upon molecular association, yielding band shifts and splittings in the IR spectrum of neat TPT.