Hydrated phosphorus oxyacids alone and adsorbed on nanosilica.

Abstract Low-temperature 1 Н NMR spectroscopy was used to study states of water bound to phosphoric and phosphonic acids (phosporus oxyacids, POA) alone or adsorbed onto nanosilica OX-50 (specific surface area S BET  = 52 m 2 /g) or A-300 ( S BET  = 297 m 2 /g). Concentrated solutions or weakly hydrated solid POA or dried silica/POA powders placed in CCl 4 medium are characterized by different temperature dependences of the chemical shift of the proton resonance ( δ H ) because of partial dissociation of PO–H bonds strongly affected by water amounts and temperature. NMR cryoporometry results show that both small water clusters and nanodomains are present at the interfaces of hydrated solid POA and silica/POA powders. Quantum chemical calculations of the 1 H NMR spectra demonstrate the influence of POA/water cluster structure and dissociation of the PO–H bonds on the δ H values.