Energetics of copper diphosphates – Cu 2P 2O 7 and Cu 3(P 2O 6OH) 2

Abstract

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu 2P 2O 7 and Cu 3(P 2O 6OH) 2. α-Cu 2P 2O 7 is reversibly transformed to β-Cu 2P 2O 7 at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol −1. Enthalpies of formation from oxides of α-Cu 2P 2O 7 and Cu 3(P 2O 6OH) 2 are −279.0 ± 1.4 kJ mol −1 and −538.8 ± 2.7 kJ mol −1, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol −1 and −4302.7 ± 6.7 kJ mol −1, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu 3(P 2O 6OH) 2, thus decreasing its thermodynamic stability.