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.