Interplay between structure, phase transition, and molecular dynamics in the organic–inorganic hybrid [N(C2H5)4]2ZnCl4

The crystal structure, thermal behavior, and molecular dynamics of [N(C 2 H 5 ) 4 ] 2 ZnCl 4 were systematically examined by means of X-ray diffraction (XRD), thermal analysis, and multinuclear NMR spectroscopy. XRD analysis confirmed that the compound crystallizes in a tetragonal phase with good crystallinity. Differential scanning calorimetry measurements revealed the presence of a first-order transition at 231 K with a thermal hysteresis between the heating and cooling processes. Thermogravimetric analysis indicated that the material remains thermally stable up to approximately 580 K. The 1 H, 13 C, and 14 N NMR spectra showed progressive narrowing of the resonance linewidths as the temperature increased, suggesting activation of molecular motions. Near the phase transition temperature (T C ), the 1 H and 14 N NMR spectra exhibited almost no noticeable variation in either chemical shift or line splitting. In contrast, at temperatures below T C , the lower symmetry of the 13 C environments gave rise to nonequivalent 13 C sites, resulting in split resonance lines. Above T C , the local symmetry became higher, leading to equivalent 13 C environments and consequently the disappearance of the line splitting. The phase transition mechanism is considered to originate primarily from changes in the local symmetry around the 13 C sites rather than from variations in the environments surrounding the 1 H and 14 N sites.