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 H₂L1^2- 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 H₂L2^2- 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.