Crystal structures, phase transitions, thermodynamics, and molecular dynamics of organic-inorganic hybrid crystal...

Understanding the physical properties of organic-inorganic hybrid [NH(CH₃)₃]₂ZnCl₄ is necessary for its potential application in batteries and fuel cells due to its environmentally-friendly, and highly stable character. Here, we determine its overall properties in detail, such as its orthorhombic crystal structure, and phase transition temperatures associated with five different phases. Structural geometry was studied by the chemical shifts caused by the local field around ¹H. No changes were observed for the environment around ¹H for CH₃, whereas the ¹H chemical shifts around NH in the cation were shown due to the change in the hydrogen bond N‒H···Cl. This is related to the change in Cl around Zn in the anion. In addition, the coordination geometry of ¹⁴N and ¹H around ¹³C exhibited increased symmetry at high temperatures. Finally, we were able to understand its molecular dynamics by the significant change with temperature observed from the spin-lattice relaxation time T_1ρ values, which represent the energy transfer for the ¹H and ¹³C atoms of the cation. The activation energies obtained from the T_1ρ results were 3-4 times large at phase I (> 348 K) than at phase V and IV (< 286 K). The relaxations show that the energy barriers in phases IV and V are related to the reorientation of methyl groups around the triple symmetry axis, while the reorientation of methyl groups of the cation in phase I is related to as a whole.