Migrating hydrogen in 2,4,6‐triaminopyrimidinium(1+)x hydrogen trioxofluorophosphate(−)x monohydrate/2,4,6‐triaminopyrimidinium(2+)1–x trioxofluorophosphate(2–)1–x monohydrate (0.0 < x < 0.73) with changing temperature

Abstract

The data of the title structure of 2,4,6-tri­amino­pyrimidinium(1+)x hydrogen trioxo­fluoro­phosphate(1−)x monohydrate/2,4,6-tri­amino­pyrimidinium(2+)1−x tri­oxo­fluoro­phosphate(2−)1−x monohydrate (0.0 < x < 0.73), with the sum formula C4H11FN5O4P, were collected in 10 K inter­vals between 290 and 150 K, as well as at 100 K. The most inter­esting feature is the presence of a moderate though still strong O—H⋯N/O⋯H—N hydrogen bond. Its bridging H atom was found to be disordered over two positions in the temperature inter­val 290–220 K, with the larger occupation towards the O atom. The occupation in the latter position decreased with decreasing temperature, though not monotonously. At 210 K and below, the difference electron-density maps showed just one maximum which was closer to the N atom. Though difference scanning calorimetry (DSC) revealed no anomaly in the inter­val 303–93 K, the dependence of the length of the unit-cell axes b and c on temperature showed a kink in the slope at about 190 K. The N⋯O distance of the mentioned hydrogen bond or the occupational parameter of the electron density of the disordered H atom indicate less pronounced anomalies for the temperatures 270 and 230 K. The cation and the anion, as well as the water mol­ecules, form layers which are parallel to (10\overline{1}) and which are inter­connected by O—H⋯N (in the inter­val 290–220 K), N—H⋯O and O—H⋯O hydrogen bonds of moderate strength. The layers are arranged into centrosymmetric double layers in which the F atoms are directed outwards. The layers are inter­connected by water–acid O—H⋯O hydrogen bonds, weak N—H⋯F inter­actions and π-electron ring⋯π-electron ring inter­actions. The dependence of P—F bond lengths on bonding properties of the trioxo­fluoro­phosphate or hydrogen trioxo­fluoro­phosphate anions is discussed. It has been recognized that a carbon-bonded F atom avoids participation in a hydrogen-bond pattern; however, this property seems to be also common to fluorine bonded to P, As and S, especially if an oxygen ligand is also present in a mol­ecule. The deposited material contains an overview of the determined structures with trioxo­fluoro­phosphate or hydrogen trioxo­fluoro­phosphate anions.