Full spectroscopic characterization of an hydrolytically stable and colored Ti(IV)-precursor in solution

The orange-colored and hydrolytically stable compound {[Ti2O(bhmpc)(Hbhmpc)(H2bhmpc)].C4H8O2.HX}2 (with H3bhmpc = 2,6-bis(hydroxymethyl)-p-cresol and X = OEt or CCl3) has been studied by a combination of single crystal X-ray diffraction data, U.V.-vis. spectroscopy, IR and Raman spectroscopies, 1H, 13C and 17O solution NMR spectroscopies, electron density and statistical thermodynamics modeling. We observed that the molecular structure found in the solid state is conserved in solution. Based on X-ray diffraction data, we also propose a complete and non-ambiguous assignment for the fully resolved 1H and 13C solution NMR spectra through the use of 2D-techniques (COSY, ROESY, HSQC, HMBC) and 1H relaxation time measurements. The ability of the partial charge model introduced more than 20 years ago by J. Livage's group to reproduce observed 13C NMR chemical shifts in solution is demonstrated. Statistical thermodynamic modeling between Ti(OR)4 (monomers, trimers or tetramers) has shown that complexation was in all cases under entropy control. Possible applications of this soluble and stable precursor to the sol-gel processing of hybrid organic-inorganic are addressed.