Utility of Bis-4-pyridines as Supramolecular Linkers for 5-Sulfosalicylic Acid Centers: Structural and Optical Investigations

Abstract

Supramolecular aggregation through a less explored {Ar-SO3···H-py} synthon, formed by 5-sulfosalicylic acid (5-SSA-3H) and bis-4-pyridines viz. 1,2-di(4-pyridylethylene) (4,4′-BPE) and 4,4′-trimethylenedipyridine (4,4′-BPP), has been reported. Four molecular salts [(5-SSA-2H)−(4,4′-BPE-H)+·MeOH·2H2O] (1), [(5-SSA-3H)(5-SSA-2H)−(4,4′-BPE-H)+·2H2O] (2), [(5-SSA-H)2–(4,4′-BPP-2H)2+] (3), and [(5-SSA-2H)2–(4,4′-BPP-2H)+·2H2O] (4) have been obtained by varying the flexibility and stoichiometry of the bis-4-pyridine linker. Two types of steplike chains formed by formers in 1 are associated by rare {(H2O)4(MeOH)2} clusters into a three-dimensional (3-D) network. The lattice water molecule in 2 associates 5-SSA units into double layer chains that are further associated by a bis-4-pyridine linker into a 3-D supramolecular network. Four crystallographically different, one-dimensional chains in nonsolvated 3 are interwoven and held together by weak van der Waals forces. 4 forms a layered structure, and the layers are further aggregated through weak C–H···O interactions into a 3-D assembly. The UV–visible absorption and photoluminescence properties of these compounds have been examined in their solid state. Due to hydrogen and π–π bonding between the ligands and protonation of bis-4-pyridines, a remarkable red-shift of the absorption spectra has been observed. The photoluminescence properties examined for compound 4 show intense blue photoluminescence.