Structure of Hydrogen Bonds and 1H NMR Spectra of Water at the Interface of Oxides

Abstract

Chemical shifts (δ) in the 1H NMR spectra of free water and water adsorbed onto fumed silica, silicalite, and fumed silica/alumina were analyzed using ab initio calculations and experimental data. Nearly linear relationships between isotropic δH,iso values and the atomic charge of H (qH), the valence (rOH) and hydrogen (rO···H) bond lengths, and the angle ∠O−H···O were found from the theoretical calculations of the NMR spectra of free and adsorbed water. An estimation of δH,iso for large water clusters involving several tens of molecules or relatively large oxide fragments was performed using the calibrated function δH(qH) obtained on the basis of the ab initio quantum chemical studies of small clusters and the PM3 calculations of both small and large ones.