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

Supramolecular aggregation through a less explored {Ar-SO3 center dot center dot center dot 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)(+)center dot MeOH center dot 2H(2)O] (1), [(5-SSA-3H)(5-SSA-2H)(-)(4,4'-BPE-H)(+)center dot 2H(2)O] (2), [(5-SSA-H)(2-)(4,4'-BPP-2H)(2+)] (3), and [(5-SSA-2H)(2)(-)(4,4'-BPP-2H)(+)center dot 2H(2)O] (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 center dot center dot center dot 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 pi-pi 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.