Martin Nastran, B. Stöger
Jun 1, 2021
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Journal
Zeitschrift für Kristallographie - Crystalline Materials
Abstract
Abstract Hypophosphorous acid, H3PO2 is dimorphic with a phase transition in the 200–225 K range. The H3PO2 molecules are connected by hydrogen bonding to infinite chains extending in the [100] direction. In the high-temperature phase (P21212, Z′=12${Z}^{\prime }=\frac{1}{2}$), the hydrogen bonds are disordered about a two-fold rotation axis. On cooling below the phase transition temperature, the hydrogen bonds become ordered, resulting in a symmetry reduction of the klassengleiche type of index 2. In the low-temperature phase (P212121, Z′=1${Z}^{\prime }=1$), the c parameter is doubled with respect to the high-temperature phase. The hydrogen-bonding topology of the high- and low-temperature phases are double-infinite directed and undirected linear graphs, respectively.