Water-chloride and water-bromide hydrogen-bonded networks: Influence of the nature of the halide ions on the stability of the supramolecular assemblies

Two compounds, namely, [TTPH₂](C1)₂·4H ₂O (1) and [TTPH₂](Br)₂·4H₂O (2), (TTP = 4′-p-tolyl-2,2′:6′,2"-terpyridine) were synthesized from purely aqueous media and characterized by physical techniques. In the solid-state structures of these compounds, interesting supramolecular assemblies are observed. In 1, an unusual staircase-like architecture of the tape of edge-shared planar water hexamer is of importance, where the chloride ions are at the two edges of the tape. In 2, the polymeric nature of the water-bromide assembly is of interest, where discrete open-cube water octamers are doubly bridged by bromide ions. Semiempirical and DFT calculations confirm that the nature of the anion indeed affects the topology of the water-halide assemblies. We conclude that the protonated [TTPH₂]²⁺ species can act as appropriate receptors for halide ions, which in turn act as a matrix for the formation of polymeric 1D water-halide assemblies.