Investigation of the structure and multi-stimuli-responsive behavior of ion-associated salt solvates of binary crystals

Abstract

Investigation of the intermolecular interactions and crystal packing to understand crystal growth is a prime objective of crystal engineering. Solvent molecules within crystal assist the supramolecular aggregation, however, control over their lattice incorporation remains uncertain. In this work, we report three solvates of an ionic organic salt of a diazo-naphthol sulfonate (1) and 1,10-phenanthroline with one (2), three (3) and four (4) lattice water molecules. Attempts to isolate the dihydrate form were unsuccessful, while the monohydrate of 1 has been crystallised for comparative structural investigations. Structural studies reveal the existence of intriguing sulfonate-diazo intermolecular interactions responsible for centrosymmetric dimerization of the organosulfonate 1, which also persist in 2–4, validating higher preference and robustness of the synthon. Repetitive aggregation of the sulfonate-diazo interaction in 1 leads to the formation of linear π-stacked aggregate, which further aggregates through the lattice water molecules. The structural comparison indicates the preferential formation of the organo-sulfonate dimers in hydrated salts 2–4. Further, sandwich tetramers in 2 and 4 are formed by charge transfer interaction of the organo-sulfonate dimers with pyridinium coformer on either side, which are further associated by the lattice water molecules into disparately packed 3-dimensional supramolecules. The organo-sulfonates in 3 form a similar type of extended π-stacked chains as in 1, which are flanked by pyridinium ions to form hydrogen-bonded tapes, which are helped by the lattice water molecules to grow as segregated stacked layer solid. The characteristic absorption frequency of the diazo functionality is blue-shifted in infrared spectra of the cocrystal forms, indicating the presence of charge transfer interactions. The presence of dynamic solvent and protons in the lattice makes the solid forms multi-stimuli-responsive to exhibit mechano and vapochromic response. These phenomena have been studied in detail with the help of thermal, spectroscopic, and powder-diffraction studies.