Structural characterization and properties of bis (1,4-H2-1,2,4-triazolium) pentachlorobismuthate (III) and cocrystal of ammonium chloride with tris (1,4-H2-1,2,4-triazolium) hexachlorobismuthate (III)

• New hybrid, organic–inorganic 1,2,4-triazolium compounds.
• Unique, mixed cationic sublattice built up of triazolium and ammonium ions.
• The relationship between the type of the anionic chains and acentric symmetry.

The crystal structure of two novel 1,2,4  -triazolium analogues: [C2N3H4]2[BiCl5][C2N3H4]2[BiCl5] (TBC) and [NH4][C2N3H4]3[BiCl6][Cl][NH4][C2N3H4]3[BiCl6][Cl] (TCBA), isolated from one system, has been determined. The structure of TCBA is built up from cationic substructures consisting of 1,2,4  -triazolium and ammonium cations, [Cl]-[Cl]-, and discrete [BiCl6]3-[BiCl6]3- octahedral anions. The two-component cationic sublayer of TCBA is unique in the case of halobismuthates(III). TCBA adopts the triclinic space group (P1¯) at 100 K. Differential scanning calorimetry (DSC) and dilatometric measurements showed that it undergoes reversible first-order phase transition (PT) at 420/405 K (heating/cooling) governed by an ’order–disorder’ mechanism. The crystal structure of TBC (Cmca at 100 K) contains the [BiCl5]∞2- chains of cis-connected octahedra and a hydrogen-bonded array of 1,2,4-triazolium cations. The statistical disorder of the 1,2,4-triazolium cations is found at low temperatures. No PT is detected between 100 and 400 K in TBC.

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