Three Viologen Compounds Containing Keggin and Mo-Capped Weakley Polyoxometalates: Photo-/Thermo-/Electro-Chromic Studies

Multiresponsive color-changing materials have important applications in daily life. In this work, three photochromic, thermochromic, and electrochromic compounds were synthesized by introducing two kinds of polyoxometalates into the viologen system, namely, {[Ni(dibipy)(4,4′-bipyH)(H2O)3]·[Ni4(H2O)2Ge2Mo18O68(MoO2)2]0.5}·10H2O (1), {[NiII(nibipy)2(4,4′-bipy)(H2O)2]·(SiMo12O40)}·2H2O (2), and [(Hnibipy)2·(SiMo12O40)]·2.5H2O (3) (dibipy·Cl = 1-(3,5-dimethyl-isoxazol-4-ylmethyl)-[4,4’]bipyridinyl-1-ium chloride, nibipy·Cl = 1-(4-Nitro-benzyl)-[4,4’]bipyridinyl-1-ium chloride and 4,4′-bipy = 4,4′-bipyridine). Compound 1 contains the Mo-capped weakley anion [Ni4(H2O)2(Ge2Mo18O68(MoO2)2]8–, which is very rare in polyoxometalates. Both 1 and 2 own mixed organic ligands to modify anions, such as viologen and 4,4′-bipy. Compounds 1 and 3 exhibit fast responsive photochromic effects, while compound 2 has rapid recovery of thermochromic properties. Sandwich-type rigid devices based on compounds 1–3 also exhibit electrochromic properties. In addition, hydrogels and poly(methyl methacrylate)-based mixed matrix membrane systems were introduced to achieve portable visual UV detectors. The applications of these compounds in metal ion detection and anticounterfeiting were also studied

A Series of POM–Viologen Photo-/Electrochromic Hybrids and Hydrogels Acting as Multifunctional Sensors for Detecting UV, Hg²⁺, and Organic Amines

In this work, POM anions were introduced into the viologen system in order to synthesize POM–viologen hybrid compounds with excellent properties. Three new POM–viologen compounds, {CdII(tybipy)(DMF)2[β-Mo8O26]0.5Cl} (1), {CoII(tybipy)2(DMF)2[H2(β-Mo8O26)]2}·4C2H7N (2), and (tybipy)4·(β-Mo8O26) (3) (tybipy·Br = 1-thiophen-3-ylmethyl-[4,4′]bipyridinyl-1-ium bromide), have been prepared by a solvothermal method, and their structures were characterized. POM anions are modified by mixing organic ligands with transition metals in compounds 1 and 2. However, compound 3 is a supramolecular structure constructed by hydrogen bonding interactions between the dissociative viologen and POM anions. These three compounds have rapid photoresponse and photochromic ability, which can be made into mixed matrix membranes and hydrogels for UV detection. The rigid sandwich devices prepared by compounds 1–3 have achieved ultrafast electrochromism and recovery. In addition, photochromic hydrogels based on compounds 1–3 can achieve ultrafast photochromic recovery. Compounds 1–3 can be used in ink-free printing and Hg2+ fluorescence detecting. Compounds 1 and 2 can also be used as organic amine detectors. Combined with photochromism and fluorescence detection of Hg2+, visual test papers for Hg2+, Cu2+, and Co2+ were successfully realized, which can improve the portability and detection speed of heavy metal ions in the actual environment

Introduction of secondary pyridyl-1H-tetrazole derivatives into Keggin–Ag–(1,10-phenanthroline) system for tuning dimensionalities and architectures: assembly and properties

<p>By introducing three pyridyl-1H-tetrazole derivatives to Keggin–Ag-(1,10-phenanthroline) system, five new polyoxometalate-based inorganic–organic hybrid compounds with different dimensionalities and structures, [Ag₃(4-ptz)₂Na(phen)(HPMo₁₂O₄₀)]·2H₂O (<b>1</b>), [Ag₄(3-ptz)₂(phen)₂(HPMo₁₂O₄₀)] (<b>2</b>), [Ag₄(3-ptz)₂(phen)₂(HVW₁₂O₄₀)] (<b>3</b>), [Ag₃(3-bptzb)(phen)₂(PMo₁₂O₄₀)] (<b>4</b>) and [Ag₃(3-bptzb)(phen)₂(VW₁₂O₄₀)] (<b>5</b>) (phen = 1,10-phenanthroline, x-ptzH = 5-(x-pyridyl)-1H-tetrazole (x = 3, 4), 3-bptzb = 1,4-bis(5-(3-pyridyl)-tetrazolyl)butane), have been synthesized under hydrothermal conditions. Compound <b>1</b> is a 1-D belt architecture constructed from an Ag-4-ptz metal–organic chain and two Ag–PMo₁₂O₄₀–Na–phen inorganic–organic chains. When 3-ptzH was introduced as secondary ligand in <b>2</b> and <b>3</b> instead of 4-ptzH, two isostructural architectures were obtained, which contain a 1-D zigzag Ag-3-ptz chain with phen ligands hanging on both sides of the chain. The Keggin anions connect adjacent Ag-3-ptz chains to construct 2-D networks. When the flexible 3-bptzb was selected, isostructural <b>4</b> and <b>5</b> with 2-D networks were obtained, which were constructed from binuclear subunits and Keggin–Ag inorganic chains. The influence of three pyridyl-1H-tetrazole derivatives as secondary ligands on the dimensionalities and architectures of <b>1</b>–<b>5</b> was discussed. The electrochemical and photocatalytic properties of the compounds were investigated.</p

Photo-, Thermo-, Electrochromic, Erasable Inkless Printing, Ions Detection, and UV Detector Properties of Viologen Compounds Based on Homomolybdate/Keggin POMs

Three POMs-based viologen compounds with different structures were successfully constructed under solvothermal and hydrothermal conditions, [Cu(1,4-cby)2(H2O)0.5(β-Mo8O26)0.5]·C3H7NO·3H2O (1), [H2(1,4-cby)2]·(β-Mo8O26) (2) (1,4-cby·Cl = 1-(4-carboxybenzyl)-4,4′-bipyridine chloride), [H2(1,4-cbyy)2]·(SiMo12O40) (3) (1,4-cbyy·Cl = 1-(4-cyanobenzyl)-4,4′-bipyridine chloride). Compound 1 is a structure with the number “eight-like” metal–organic chain with Cu as the nodes, and compounds 2 and 3 are fascinating structures connected by hydrogen bonding interactions. More importantly, compounds 1–3 exhibit a good response to both light and electricity and the thermal response of compound 1 was also studied. The reasons for the response of compounds 1–3 to external stimuli were analyzed through methods such as UV–Vis, EPR, and XPS. In addition, the transient photocurrent response results of compounds 1–3 are the same as those obtained from kinetic calculations. Meanwhile, the coated filter paper based on compound 3 has been successfully applied in erasable inkless printing and anti-counterfeiting, the test paper of 3 can also detect metal ions, and the films based on compounds 1–3 are a flexible and portable ultraviolet (UV) detector

The rigid isomeric 5-(x-pyridyl)-1H-tetrazole ligands-directed various isopolymolybdate-based compounds: Assembly, structures and properties

<div><p></p><p>Two new isopolymolybdate-based metal-organic complexes, [Cu₂(2-ptz)₂(Mo₄O₁₄)_0.5] (<b>1</b>) and [Cu₃(OH)₂(3-ptz)₄(γ-H₄Mo₈O₂₆)(H₂O)₄]·10H₂O (<b>2</b>) (2-ptzH = 5-(2-pyridyl)-1H-tetrazole, 3-ptzH = 5-(3-pyridyl)-1H-tetrazole), constructed from isomeric ligands with different N-donor sites were synthesized under hydrothermal conditions. In <b>1</b>, each [Mo₄O₁₄]^4- cluster connected with six neighboring [Mo₄O₁₄]^4- clusters through six binuclear [Cu₂(2-ptz)₂]²⁺ subunits to yield a two-dimensional (2D) layer. In <b>2</b>, bidentate inorganic [Mo₈O₂₆]^4- anions link the trinuclear [Cu₃(OH)₂(3-ptz)₄] clusters to construct a 1D chain. Adjacent chains connect through Mo-N bonds between the [Mo₈O₂₆]^4- anions and pyridyl groups from the trinuclear clusters to form a 2D layer. The effect of the N-donor sites of the rigid isomeric ligands on the structures of <b>1</b> and <b>2</b> was discussed. The electrochemical properties and photocatalytic activities of <b>1</b> and <b>2</b> have also been studied.</p></div