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

Abstract

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, H₂M1²2⁺+·2NO₃⁻ (1), H₂M2²2⁺+·2NO₃⁻ (2), H₂M3²2⁺+·2NO₃⁻ (3), H₂M4²2⁺+·2NO₃⁻ (4), H₂M1²2⁺+·2ClO₄⁻ (5), H₂M2²2⁺+·2ClO₄⁻ (6), H₂M3²2⁺+·2ClO₄⁻ (7), and H₂M4²2⁺+·2ClO₄⁻ (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⋯π and anion⋯π, while salts 2, 4, 5, 6 and 8 exhibit 3-D supramolecular networks extended by hydrogen bonds, π⋯π stacking, C–H⋯π and anion⋯π. 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.