Structural changes, thermodynamic properties, 1H magic angle spinning NMR, and 14N NMR of (NH4)2CuCl4·2H2O

Abstract

The structural changes and thermodynamic properties of (NH₄)₂CuCl₄·2H₂O were studied by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. In addition, the chemical shift, line width, and spin-lattice relaxation time of the crystals were also investigated by ¹H magic angle spinning nuclear magnetic resonance (MAS NMR), focusing on the role of NH₄ and H₂O near the phase transition temperature. The change at T_C2 (=406 K) and T_C3 (=437 K) seems to be a chemical change caused by thermal decomposition rather than a physical change such as a structural phase transition. The changes in the temperature dependence of these data near T_C2 are related to variations in the environments surrounding NH₄ and H₂O. The ¹⁴N NMR spectrum is also measured in order to investigate local phenomena related to the phase transition.