Syntheses, structures and luminescent properties of lithium(i)-sulfonate complexes constructed from ortho-hydroxyl arenedisulfonic acids: structural evolution tuned by the pH, coordination geometry and modes

Abstract

Six novel lithium(I) complexes constructed from ortho-hydroxyl arenedisulfonic acids, [Li(H2L1)0.5(H2O)2]n (1), [Li(H2L1)0.5(H2O)]n (2), [Li12(L1')3(H2O)19]n (3), {(NH4)·[Li(H2L2)]}n (4), [Li2(H2L2)(H2O)]n·nH2O (5) and [Li2(L2)0.5(H2O)2]n·nH2O (6) (H4L1 = 2,5-dihydroxyl-1,4-benzenedisulfonic acid; H4L1' = 2,3,5,6-tetraoxocyclohexane-1,4-disulfonic acid; H4L2 = 2,4-dihydroxyl-1,5-benzenedisulfonic acid), have been synthesized and characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. Complex 1 has a 1-D chain motif, while complex 2 exhibits a 2-D hybrid grid formed by phenyl rings bridged by infinite 1-D Li–O–S chains, in which the H2L12- dianions act in different μ3:η4 coordination modes (sulfonate: μ2:η2, hydroxyl: μ2:η2 in 1; sulfonate: μ3:η3, hydroxyl: monodentate in 2). Complex 3 exhibits a 2-D wave-like layer incorporating scarce alternate helical chains, in which the H4L1' ligand is generated in situ from H4L1 under alkaline conditions. Complex 4 presents a 2-D layer structure, which is extended into 3-D hydrogen bonding host networks encapsulating the NH4+ cations as guests. Both complexes 5 and 6 show 3-D pillared layered frameworks with the free water molecules occupying the channels. The H2L22- dianions in complexes 4 and 5 act in different μ2:η2 and μ4:η5 coordination modes. By contrast, the ligand in complex 6 is fully deprotonated and exhibits a μ5:η7 coordination mode. The structural diversities and evolution of these complexes can be attributed to the coordination modes of the sulfonate groups and the hydroxyl groups induced by the pH, as well as the diverse polyhedra of Li(I) cations. The solid-state luminescent properties demonstrate that some of the complexes exhibit violet emission at room temperature.