The solvothermal reaction of 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium chloride (H2L+Cl–) with different anionic Zn(II) salts leads to three diverse metal–viologen complexes, formulated as {[Zn(HL)Cl2]2·2H2O} (1), {[Zn3(L)2(H2O)8]·2(SO4)·2(H2O)}n (2), and {[Zn(L)H2O]·NO3·H2O}n (3). Single-crystal X-ray analyses revealed that complex 1 displays dinuclear structure. Complex 2 features a 2D layered structure, which consists of four-fold interpenetrating stacked layers with sulfate ions locating between the sheets. Complex 3 shows a 3D two-fold interpenetrating framework with nitrate anions interspersing the void space of the framework, and it features an uninodal three-connected ThSi2 (ths) topology. The structural disparities reveal that the different geometries of counterions, coordination modes, and conformations of ligand L–, together with the deprotonation degree of aromatic carboxylate, have great influence on the formation of various structures. Interestingly, complexes 1–3 are all photoactive to UV–visible light and undergo obvious and reversible color transformations from light yellow to blue/green. Structural analyses indicated that not only the carboxylate-O donor and N acceptor of the bipyridinium moiety can provide an effective electron transfer pathway for photochromic behavior, but the Cl → L electron transfer in complex 1 also has a crucial effect on the photochromic behavior of it.

A rhodamine B derivative bearing a NS2-containing receptor (L) is developed as a dual chemosensor for detection of Cu2+ and Hg2+ in aqueous media. L shows highly sensitive colorimetric response to Cu2+ and selectively turn-on fluorescent response to Hg2+ with very low detection limits of 1.63 and 2.36 μM, respectively. The significant absorption enhancement (251-fold) accompanied with a visual color change from colorless to purple upon interaction with Cu2+, making L a suitable “bare-eye” indicator for Cu2+. By means of Job's plot, 1H NMR titration and ESI-MS studies, both 1:1 binding modes (L/Cu2+ and L/Hg2+) are confirmed and a possible sensing mechanism is further proposed. The response behaviours of L toward Cu2+ and Hg2+ are pH independent in a wide range (pH 4.0–9.0). Proof-of-concept experiment demonstrates the potential application of L for trace Cu2+ and Hg2+ detection in complicated environmental water samples. More importantly, the turn-on fluorescent chemosensor L with good membrane-permeable property is successfully applied to microscopic imaging for the detection of Hg2+ in PC3 cells.

•The self-assembly of PbAc2 with H2btapca affords different crystal structures.•Varying the ratio of mixed reaction solvents•Novel discrete cage structure•Enhanced fluorescence compared free ligandBy varying the ratio of mixed reaction solvent, the reactions of PbAc2 with N,N′-bis(1,3,4-thiobiazolyl)-2,6-pyridyldicarboxamide (H2btapca) afford two different crystal structures: a novel discrete hexanuclear cage of formula [Pb6(btapca)6]·(H2O)2 (1) and a 1-D double-chain polymer [Pb2(btapca)2(H2O)2]n (2). Fluorescence investigations reveal that both complexes display enhanced emissions in contrast to the free ligand H2btapca.A discrete hexanuclear cage of [Pb6(btapca)6]·(H2O)2 and a 1-D double-chain polymer [Pb2(btapca)2(H2O)2]n have been assembled by the reactions of PbAc2 with N,N′-bis(1,3,4-thiobiazolyl)-2,6-pyridyldicarboxamide (H2btapca) under different mixed reaction solvents. Both complexes have enhanced fluorescence in contrast to the free ligand.

The reactions of semi-rigid bidentate ligand 4,4′-bis(benzimidazol-1-ylmethyl)biphenyl (bbmb) with NiCl2 and CuCl2 and Cd(OAc)2 afford novel complexes {[M(bbmb)2(Cl)(OH)](H2O)2}n (M = Ni(1), Cu(2)) and [Cd2(OAc)4(bbmb)3]2(CH3OH)3(H2O)2 (3). Both complexes 1 and 2 feature parallel 2-fold interpenetrating (4,4)-windmill-like layer morphology. Complex 3 presents unique discrete quad-nuclear motif comprised by two couples of alternating single and double twisting chains. The three complexes exhibit active second-order NLO effects.The reactions of rigid 4,4′-bis(benzimidazol-1-ylmethyl)biphenyl (bbmb) with NiCl2 and CuCl2 and Cd(OAc)2 afford novel complexes {[M(bbmb)2(Cl)(OH)](H2O)2}n (M = Ni(1), Cu(2)) and [Cd2(OAc)4(bbmb)3]2(CH3OH)3(H2O)2 (3). Both complexes 1 and 2 feature parallel 2-fold interpenetrating (4,4)-windmill-like layer morphology. Complex 3 presents unique discrete quad-nuclear motif comprised by two couples of alternating single and double twisting chains. The three complexes exhibit active second-order NLO effects.