Investigations of organic–inorganic hybrids based on homopiperidinium cation with haloantimonates(iii) and halobismuthates(iii). Crystal structures, reversible phase transitions, semiconducting and molecular dynamic properties

Abstract

A description of the thermal, structural, ¹H NMR, electric and optical properties of four organic–inorganic hybrids, haloantimonates(III) and halobismuthates(III), based on homopiperidinium cation: (C₆H₁₄N)₂SbCl₅ (abbrev. HSC), (C₆H₁₄N)₂SbBr₅ (HSB), (C₆H₁₄N)₂BiCl₆[H₃O] (HBC), (C₆H₁₄N)₂BiBr₅ (HBB), is presented. The common feature of the crystal structures of the studied compounds is the 1D (one-dimensional) chain for the anionic network in HSC, HSB and HBB, 1D hydrogen bond chain between 0D (zero-dimensional, isolated) BiCl₆ octahedrons and hydronium moieties in HBC as well as a rich polymorphism in the solid state for all title compounds. The structures of the Sb(III) and Bi(III) derivatives are not isomorphous and they crystallize in the following space groups: HSC in P2₁2₁2₁ both at 280 and 150 K, HSB in Pmna and P2₁2₁2₁ at 310 and 150 K, respectively, HBC in C2/m, C2/m and C2/c at 300, 260 and 200 K, respectively, and HBB in P2₁/n both at 280 and 200 K. The anionic networks are in the forms of either pseudo- and zig-zag chains or a chain of a hydrogen bond. The band gap values, using the Tauc plot as well as the ac and dc conductivity parameters, were estimated. On the basis of the ¹H NMR spin–lattice relaxation times, T₁, and second-moment, M₂, measurements and the dielectric responses, the molecular mechanisms of the phase transitions (PTs) have been postulated. The structural PTs are discussed in terms of the changes in cationic dynamics and distortions of the anionic sublattice. The powder technique of SHG (Kurtz and Perry method) has been used to analyze the second-order nonlinear optical properties of HSC.