Structure evolution and luminescence properties of lithium(i)–sulfonate complexes constructed from multifunctional arenedisulfonic acids

Abstract

Self-assembly of three multifunctional arenedisulfonic acids and different lithium(I) salts leads to the formation of eight lithium(I)–sulfonate complexes, namely, [Li(H₃L1)(H₂O)₂]₂ (1), [Li₂(H₂L1)(H₂O)_3.5]_n·1.5nH₂O (2), [Li₂(H₂L2)(H₂O)₃]_n·nH₂O (3), [Li₃(H₃L2)(H₂L2)(H₂O)₂]_n·nH₂O (4), [Li(H₃L3)(H₂O)]_n·nH₂O (5), [Li₂(H₂L3)(H₂O)₄]_n·3nH₂O (6), [Li₂(H₂L3)(H₂O)_2.5]_n·3nH₂O (7), and [Li₃(HL3)(H₂O)₅]_n·0.5nH₂O (8) (H₄L1 = 2,3-dihydroxyl-5-carboxylbenzenesulfonic acid; H₄L2 = 2,5-dihydroxyl-3-carboxylbenzenesulfonic acid; H₄L3 = 2,4-dihydroxyl-5-carboxylbenzenesulfonic acid), which have been synthesized and characterized by elemental analysis, IR, TG, PL, and powder and single-crystal X-ray diffraction. The H₃L1⁻ monoanion in complex 1 acts in μ₂ (κ¹O1:κ¹O6) mode and bridges two adjacent Li(I) cations to generate a dinuclear motif. By contrast, the H₂L1²⁻ dianion in complex 2, exhibiting an intricate μ₅ (κ¹O3:κ¹O4:κ¹O5:κ²O6:κ¹O7) coordination mode, connects adjacent Li(I) cations to form a layer structure, in which a strong Li⋯Li interaction (2.574(8) Å) is firstly observed among Li(I)–sulfonates. Complex 3 exhibits a ladder chain formed by the H₂L2²⁻ dianion bridging Li(I) cations in simple μ₃ (κ¹O1:κ¹O3:κ¹O4:κ²O6) coordination mode. Complex 4 shows a 3-D host–guest framework with free water molecules occupying the channels, in which the H₃L2⁻ monoanion and the H₂L2²⁻ dianion act in μ₄ (κ¹O9:κ²O10:κ¹O11:κ¹O13) and μ₅ (κ¹O1:κ²O3:κ¹O4:κ¹O6:κ¹O7) coordination modes, respectively. Complex 5 exhibits a linear chain motif with the H₃L3⁻ monoanion acting in simple μ₂ (κ¹O1:κ¹O2:κ¹O4) coordination mode. The H₂L3²⁻ dianions in complexes 6 and 7 present different μ₃ (κ¹O2:κ¹O3:κ¹O4:κ¹O5) and μ₅ (κ¹O1:κ²O2:κ¹O3:κ¹O4:κ¹O6) coordination modes, which then result in the formation of linear chains and layer structures. Complex 8 also shows a 3-D host–guest framework with free water molecules occupying the channels, in which the HL3³⁻ trianion acts in μ₄ (κ¹O2:κ¹O3:κ¹O4:κ¹O5:κ¹O7) mode. The structural diversities and evolution of these complexes can be attributed to the diverse polyhedra of Li(I) cations and the coordination modes of the different functional groups induced by the pH value. The solid-state luminescence properties demonstrate that all of these complexes exhibit strong emission in the range of 374–537 nm at room temperature.