Diverse structures and multi-step dielectric relaxation of three lead bromide hybrid crystals based on 1-aminopyridinium and its cyano-substituted Schiff bases

Oriented design of crystal structures to obtain specific properties is one of the hot topics in the field of chemistry and materials. In this paper, three organic–inorganic hybrid crystals were synthesized by the reaction of 1-aminopyridinium salts with o-, m-, and p-cyanobenzaldehyde and PbBr2. The asymmetric unit of 1 ([1- aminopyridinium][Pb2Br5], P21/m) contains half of the 1-aminopyridinium cation and the anion forms a zig-zag shaped puckered sheet of [Pb2Br5]∞; while 2 ([m-cyanobenzaldehyde-1-aminopyridinium][PbBr3], Pna21) includes a m-cyanobenzaldehyde-1-aminopyridinium Schiff base cation, and the anion forms a [PbBr3]∞ single chain. On the other hand, 3 ([p-cyanobenzaldehyde-1- aminopyridinium][PbBr3], P21/c) consists of a p-cyanobenzaldehyde-1- aminopyridinium Schiff base cation, with the anion forming a [Pb2Br6]∞ double chain. Structural analysis and energy framework calculations show that 2 possesses stronger π-π stacking and hydrogen bonding interactions, and its lattice energy and thermal stability are higher than those of 1 and 3. The combined use of CE and dielectric modulus analysis reveals a good correlation between multi-step dielectric relaxation and intermolecular forces. This strategy of modulating the crystal structure and dielectric properties by altering the position of the substituents provides useful assistance in the design of new relaxation dielectric materials.