Quadrupole resonance studies of hydrogen bonding in alkylammonium halides under high pressure

Abstract

The temperature and pressure dependence of the ⁷⁹Br and ¹²⁷I quadrupole resonance frequencies have been studied in the salts [MeNH₃]⁺Br^–, [MeNH₃]⁺I^–, [EtNH₃]⁺Br^–, and [EtNH₃]⁺I^–, and their N-deuterated derivatives. The observed pressure coefficients of the quadrupole coupling constant can be large, as much as 11 kHz (MPa)^–1 for ¹²⁷I resonance in [MeNH₃]⁺I^–. The effects of rise in temperature and deuteration are explained mainly in terms of an anisotropic expansion of the hydrogen bonds between the cation and the bromide or iodide ions; pressure appears both to compress the hydrogen bonds and to change their angular configuration at the halide ion.