pH Dependent Formation of Unprecedented Water–Bromide Cluster in the Bromide Salts of PTP Assisted by Anion−π Interactions: Synthesis, Structure, and DFT Study

Two new terpyridine derivatives [PTPH₃]­(Br)₃·3H₂O (1) and [PTPH₃]­(Br₃)­(Br)₂·H₂O (2), (PTP = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) were synthesized and characterized by single crystal X-ray diffraction analyses. In 1, intricate combination of anion···π/π–π/π···anion interactions generates the supramolecular network while 2 exhibits a combination of two different anion···π/π–π/π···anion and anion···π···anion assemblies. As anticipated, both of them are interlinked through hydrogen bonds affording molecular networks, but surprisingly, 1 shows hydrate aggregation and interactions with anions to generate water–bromide cluster blends in the solid lattices. A search of the crystal structure database (CSD) yielded only eight hits presenting an infinite tape in the solid state structure formed by bromide anions and water molecules, none of which had similar distribution of bromide and water as observed in 1. Interestingly, in compound 1, the bromide anion is involved in the formation of anion–water cluster and also engaged in anion···π interactions, thus generating a unique cluster of water–anion/anion···π/π–π/π···anion/anion–water cluster network. The different networks have been investigated by means of DFT calculations and the interactions characterized using the Bader’s theory of “atoms-in-molecules”.