Coordination polymers of alkali metal trithiocyanurates: structure determinations and ionic conductivity measurements using single crystals

Abstract

Six novel crystalline coordination polymers composed of alkali metal ions and trithiocyanurate anions (C₃N₃S₃H₂⁻ = ttcH₂⁻) were synthesized. Single crystals were used both for structure determinations by X-ray diffraction and ionic conductivity measurements by AC impedance methods. The structures are: (i) sodium trithiocyanurate trihydrate, Na(ttcH₂)(H₂O)₃ in space group P2₁; (ii) potassium trithiocyanurate hydrate, K(ttcH₂)(H₂O) in P; (iii) rubidium trithiocyanurate hydrate, Rb(ttcH₂)(H₂O) in P; (iv) rubidium trithiocyanurate hydrate, Rb₃(ttcH₂)₂(ttcH₃)₂(H₂O)₅(OH) in P; and (v, vi) two anhydrous polymorphs of caesium trithiocyanurates, Cs(ttcH₂) in P and Cc. With the exception of the sodium phase, which is layered, all of these compounds consist of three dimensional coordination networks. In all systems, the inorganic regions are interleaved by arrays of ttcH₂⁻ anions. The most interesting feature of this system is the thiol-rich environment formed between the trithiocyanurate layers, where alkali metal ions are located. Water molecules, where present, are always coordinated to a cation. Among these crystals, K(ttcH₂)(H₂O) exhibited proton conductivity under atmospheric conditions (25 ± 0.2 °C): 1.1 × 10⁻⁵ S cm⁻¹ in the direction perpendicular to the bc plane and 3.1 × 10⁻⁶ S cm⁻¹ along the c axis.