Inorganic anion induced supramolecular architectures and luminescent properties of flexible bis(pyridyl) based ionic salts

Self-assembly of four bis(pyridyl) organic molecules with long flexible spacer, 1,4-bis(2-pyridylaminomethyl) benzene (M1), 1,4-bis(3-pyridylaminomethyl) benzene (M2), 1,3-bis(2-pyridylaminomethyl) benzene (M3) and 1,3-bis(3-pyridylaminomethyl) benzene (M4), and different inorganic acids (HNO3 and HClO4) leads to the formation of eight salts, H(2)M1(2+)center dot 2NO(3)(-) (1), H2M22+center dot 2NO(3)(-) (2), H(2)M3(2+)center dot 2NO(3)(-) (3), H(2)M4(2+)center dot 2NO(3)(-) (4), H(2)M1(2+)center dot 2ClO(4)(-) (5), H(2)M2(2+center dot)2ClO(4-) (6), H(2)M3(2+)center dot 2ClO(4)(-) (7), and H(2)M4(2+)center dot 2ClO(4)(-) (8), which have been characterized by elemental analysis, IR, TG, PL and single-crystal X-ray diffraction. Salts 1, 3 and 7 exhibit 2-D supramolecular structures extended by hydrogen bonds, C-H center dot center dot center dot pi and anion center dot center dot center dot pi, while salts 2, 4, 5, 6 and 8 exhibit 3-D supramolecular networks extended by hydrogen bonds, pi center dot center dot center dot pi stacking, C-H center dot center dot center dot pi and anion center dot center dot center dot pi. The diverse supramolecular networks depend on the various conformation modes (trans-trans-trans, trans-trans-cis and cis-trans-trans) of the four flexible bis(pyridyl) cations, various weak non-covalent interactions as well as the configuration of anions. These supramolecular aggregations 1-8 exhibit intense emissions in the solid-state at room temperature, and the emission intensities of the perchlorates are far stronger than those of nitrates.