Crystal structure, Hirshfeld surface analysis and physicochemical characterization of bis-[4-(di-methyl-amino)-pyridinium] di-µ-chlorido-bis[di-chlorido-mercurate(II)].

The title mol-ecular salt, (C7H11N2)2[Hg2Cl6], crystallizes with two 4-(di-methyl-amino)-pyridinium cations (A and B) and two half hexa-chlorido-dimercurate(II) anions in the asymmetric unit. The organic cations exhibit essentially the same features with an almost planar pyridyl ring (r.m.s. deviations of 0.0028 and 0.0109 Å), which forms an inclined dihedral angle with the dimethyamino group [3.06 (1) and 1.61 (1)°, respectively]. The di-methyl-amino groups in the two cations are planar, and the C-N bond lengths are shorter than that in 4-(di-methyl-amino)-pyridine. In the crystal, mixed cation-anion layers lying parallel to the (010) plane are formed through N-H⋯Cl hydrogen bonds and adjacent layers are linked by C-H⋯Cl hydrogen bonds, forming a three-dimensional network. The analyses of the calculated Hirshfeld surfaces confirm the relevance of the above inter-molecular inter-actions, but also serve to further differentiate the weaker inter-molecular inter-actions formed by the organic cations and inorganic anions, such as π-π and Cl⋯Cl inter-actions. The powder XRD data confirms the phase purity of the crystalline sample. Furthermore, the vibrational absorption bands were identified by IR spectroscopy and the optical properties were studied by using optical UV-visible absorption spectroscopy.