Dielectric relaxation and C-F…π (benzene ring) halo-bond interactions in a lead halide hybrid crystal with bromine/iodine heterogeneous double-chain layer

Abstract

Hybrid materials of lead halide have numerous structural variations and superior optoelectronic capabilities. The hybrid crystal 1 prepared by the hybrid halogen method has the chemical formula [p-F-Bz-1-APy][Pb2Br3.2I2.8] (C24H20F2N4Br3.2I2.8Pb2) (p-F-Bz-1-APy = p-fluoro-phenyl-1-aminopyridinium) with a space group of P21/c, two unequal [F1/F2-Bz-1-APy]+ cations, and a heterogeneous double-chain inorganic layer made of edge-sharing Pb2Br3.2I2.8 octahedron. The two cations adopt a lower-energy and more stable structural configuration, according to potential energy scans of the dihedral angles of the benzene and pyridine rings. The stacked structures are held together by a variety of intermolecular interactions, including hydrogen bonds (anion-cation, cation-cation), stacking (cation-cation), and the rare C-F2…π halo-bond. Hirshfeld surface analysis quantifies intermolecular interactions, revealing that interactions involving Br atoms and [F2-Bz-1-APy]+ cations contribute more to the formation of stacking structures than interactions involving I atoms and [F1-Bz-1-APy]+ cations. The logarithmic derivative method clearly reveals two dielectric relaxation processes, one in the low frequency region (<102 Hz) masked by the DC conductance and one in the high frequency region (102-107 Hz), which were then fitted by the Arrhenius formula to obtain their corresponding activation energies of 77.75 KJ/mol and 144.14 KJ/mol, respectively. Our research offers inspiration and a framework for the development of novel lead halide-based optoelectronic materials and dielectric analyses.