Titanium butoxide sol-gel structures are stabilized through water and alcohol via weak interactions: a DFT-QTAIM...

A thermo-reversible sol-gel transition of titanium butoxide-based materials was recently reported. Experimentally, the gel formation was attributed to the direct interaction between the nitrate ions and titanium atoms forming bridging and chelates nitrates. The exposed oxygen atoms of the nitrate groups, bonded to titanium, form hydrogen bonds with water and alcohol molecules of the circulant medium to build up the gel molecular structure. In this work, DFT-QTAIM computer calculations confirm the experimentally predicted oligomer formation mechanism. According to our DFT-QTAIM calculations, water and/or alcohol molecules link, upon weak bond formation, two titanium butoxide-based neighboring monomers stabilizing the oligomer structure. The QTAIM hydrogen-bonding topology shows an elaborate network of relatively short and long "weak bonds" including interactions not only with nitrates but with other functional groups.

We have performed DFT computer simulations on a series of monomers and dimers of titanium butoxide-based thermoreversible sol-gel systems. Stable structures were obtained through a geometry optimization procedure using the PBE exchange-correlation functional along with a Slater DZP basis set, considering a convergence criterion of 1 × 10^-6 hartree/Å. QTAIM properties and IR spectra were obtained as a single-point calculation at the stable structure of the corresponding system.