Influence of Aromatic Cations on the Structural Arrangement of Hg(II) Halides

Understanding the structure and arrangement of hybrid metal halides and their contribution to the optoelectronic properties is, thus far, a challenging topic. In particular, new materials composed of d¹⁰ metal halides and pyridinium cations are still largely unexplored. Therefore, we report the synthesis and characterization of six Hg(II) salts built up from (Hg₂Cl₆)^2- or (HgX₄)^2- anions (X = Cl, Br, I) and 2,2'-bipyridium (2,2'-Hbipy)⁺, 2,2'-bipyridine-1,1'-diium (2,2'-H₂bipy)²⁺, or 1,10-phenantrolinium (1,10-Hphen)⁺ cations, using the same experimental conditions. All of them have been characterized by PXRD, EA, FTIR-ATR, and ¹H NMR spectroscopies; single-crystal X-ray diffraction; and TG/DTA determinations. The study of their packing via Hirshfeld surface analysis and 3D deformation density mapping revealed the contributions of the intermolecular interactions to the structural arrangement, notably, the effect of the cation planarity on them. Successively, periodic DFT calculations showed that (i) the valence and conducting bands are mainly composed of the p orbitals of the halide and the organic cation, respectively, and (ii) the corresponding band gap depends mainly on the halide.