Organic–inorganic hybrid [NH3(CH2)6NH3]ZnBr4 crystal: structural characterization, phase transitions, thermal properties, and structural dynamics

Abstract

Organic–inorganic hybrid [NH₃(CH₂)₆NH₃]ZnBr₄ crystals were prepared by slow evaporation; the crystals had a monoclinic structure with space group P2₁/c and lattice constants a = 7.7833 Å, b = 14.5312 Å, c = 13.2396 Å, β = 90.8650°, and Z = 4. They underwent two phase transitions, at 370 K (T_C1) and 430 K (T_C2), as confirmed by powder X-ray diffraction patterns at various temperatures; the crystals were stable up to 600 K. The nuclear magnetic resonance spectra, obtained using the magic-angle spinning method, demonstrated changes in the ¹H and ¹³C chemical shifts were observed near T_C1, indicating changing structural environments around ¹H and ¹³C. The spin–lattice relaxation time, T_1ρ, increased rapidly near T_C1 suggesting very large energy transfer, as indicated by a large thermal displacement around the ¹³C atoms of the cation. However, the environments of ¹H, ¹⁴N, and C1 located close to NH₃ in the [NH₃(CH₂)₆NH₃] cation did not influence it significantly, indicating a minor change in the N–H⋯Br hydrogen bond with the coordination geometry of the ZnBr₄ anion. We believe that the information on the physiochemical properties and thermal stability of [NH₃(CH₂)₆NH₃]ZnBr₄, as discussed in this study, would be key to exploring its application in stable, environment friendly solar cells.