Hydrogen-bonding in mono-, di- and tetramethylammonium dihydrogenphosphites

Abstract

Abstract The crystal structures of methylammonium and dimethylammonium dihydrogenphosphite (MA⋅H2PO3, I2/a and DMA⋅H2PO3, P 2 1 / c $P{2}_{1}/c$ ) are built of infinite chains of hydrogen bonded H 2 P O 3 − ${\mathrm{H}}_{\mathrm{2}}\mathrm{P}{\mathrm{O}}_{\mathrm{3}}^{-}$ anions. The chains are connected by the ammonium cations via hydrogen bonding to di- (DMA⋅H2PO3) and triperiodic (MA⋅H2PO3) networks. Tetramethylammonium dihydrogenphosphite monohydrate (TMA⋅H2PO3⋅H2O) features temperature dependent dimorphism. The crystal structure of the high-temperature (HT, cubic P213) and low-temperature (LT, orthorhombic P212121) phases were determined at 150 and 100 K, respectively. The hydrogen bonding network in the HT phase is disordered, with H 2 P O 3 − ${\mathrm{H}}_{\mathrm{2}}\mathrm{P}{\mathrm{O}}_{\mathrm{3}}^{-}$ and H2O being located on a threefold axis and is ordered in the LT phase. On cooling, the point symmetry is reduced by an index of 3. The lost symmetry is retained as twin operations, leading to threefold twinning by pseudo-merohedry. The hydrogen-bonding networks of the HT and LT phases can be represented by undirected and directed quotient graphs, respectively.