Syntheses, crystal structures and luminescent properties of Zn(ii)/Cd(ii) supramolecular complexes incorporating 4-sulfinobenzoate and its in situ oxidized ligand

Abstract

Four new complexes containing d¹⁰ metal ions, 4-sulfinobenzoic acid (H₂222L) and two types of N-heterocyclic ligands, namely, {[Zn(HL)₂(H₂O)₂]_n·2nH₂O} (1), {[Cd(HL)₂(H₂O)₂]_n·2nH₂O} (2), [CdL(2,2′-bipy)(H₂O)₂]₂ (3) and [ZnL(4,4′-bipy)(H₂O)₃]_n (4), have been prepared and characterized by element analysis, IR, TG, PL, and powder and single crystal X-ray diffraction. The adjacent Zn(II)/Cd(II) octahedra in complexes 1 and 2 are bridged by the sulfinate group of the HL⁻−− monoanion in bis-monodentate mode to form 1-D covalent chains. Two Cd(II) pentagonal bipyramids in complex 3 are bridged by a pair of L²⁻2− dianions in μ₂-η²(carboxyl):η¹(sulfinate) mode to generate a dinuclear motif. The Zn(II) octahedra in complex 4 are bridged by the 4,4′-bipy into a 1-D chain, whereas the sulfinate groups of L²⁻2− dianions act as terminal coordinate groups and arrange along the same side of the chain. The aforementioned four complexes are all extended into 3-D supramolecular networks through extensive hydrogen bonds together with π–π stacking interactions. When the Zn(II)/Cd(II) salts, 4,4′-bipy and H₂222L are introduced to hydrothermal reactions, two new complexes of {[Zn(4,4′-bipy)₂(H₂O)₄]_n·n(SB)·4nH₂O} (5) and {[Cd₂(SB)₂(4,4′-bipy)₄(H₂O)₃]_n·3nH₂O} (6) are obtained (H₂2SB = 4-sulfobenzoic acid), in which the SB²⁻2− dianion is in situ oxidized from H₂222L. Complex 5 is a 3-D host–guest supramolecular network by regarding the SB²⁻2− dianions as guest counteranions. In contrast, the adjacent Cd(II) cations in complex 6 are bridged by the 4,4′-bipy to generate a 1-D zig-zag chain, in which the SB²⁻2− dianion acts in chelating mode of carboxylate. The structure analyses of these complexes indicate that the coordination ability obeys the following sequence: sulfinate group > carboxyl group > sulfonate group. Moreover, the solid-state luminescent properties of these complexes are also investigated at room temperature.