Keggin-based Compounds Research Articles

Three anderson-, mo-capped weakley- and keggin-based compounds modified by viologens acting as photochromic and thermochromic materials

Three viologen compounds were synthesized under hydrothermal conditions based on three kinds of POM anions, namely, [Co2(Cbybpy)2(H2O)6(TeMo6O24)]·5H2O (1), {[Ni(Cbybpy)2(H2O)3]·[Ni4(H2O)2Ge2Mo18O68(MoO2)2]0.5}·7H2O (2), (HCbybpy)2·(SiW12O40) (3), (Cbybpy·Br = 1-(2′-cyano-biphenyl-4-ylmethyl)-[4,4′]bipyridinyl-1-ium bromide). These three viologen compounds are based on Anderson, two {MoO2}-capped Weakley and Keggin anions. When the temperature increased, 1–2 showed excellent reversible thermochromic abilities, and 1–2 showed good fluorescence quenching effect, too. In addition, 2–3 showed photochromic properties when exposed to irradiation of a Xe lamp with filter (300–400 nm), both of which displayed rapid light response and differences in color-changing.

Four octamolybdate- and Keggin-based compounds constructed by flexible bis(triazole) ligands with different spacers

By using two kinds of flexible bis(triazole) ligands 1,3-bis(1,2,4-triazol-1-y1)propane (btp) and 1,6-bis(1,2,4-triazol-1-y1)hexane (btx), four compounds based on octamolybdate and Keggin anions were obtained, respectively, under hydrothermal conditions, namely [Cu(btp)2(H2O)(α-Mo8O26)1/2]·H2O (1), [Cu2(btx)4(β-Mo8O26)] (2), [Ag3(btp)2(PW12O40)] (3) and [Cd(btx)3(SiW12O40)]·H2btx (4). These compounds were structurally characterized by physico-chemical and spectroscopic methods. In compound 1, there is a metal–organic layer containing square tetra-nuclear cycles. Two layers cover [Mo8O26]4− anions to form a new layer. Adjacent new layers penetrate to build a three-dimensional (3D) framework. Compound 2 contains a rhomboid tetra-nuclear cycle to surround a Mo1-containing anion. These cycles are connected by btx ligands to form a two-dimensional (2D) layer. Adjacent layers are connected by Mo5-containing anions, and a 3D structure is constructed. Compound 3 contains bi-nuclear cycles which are further linked by anions and Ag2 atoms to form a 2D layer. The metal–organic chains in compound 4 are linked by Keggin anions to form a 2D structure. We also studied the photocatalytic and electrochemical behavior of compounds 1–4.

Five Keggin-based compounds modified by bis- and mono-[1,3,4]triazole ligands: characterization, and selective photocatalytic and electrochemical properties

By using three kinds of triazole-containing ligands under hydrothermal conditions, five kinds of 0D to 3D POM-based compounds were successfully synthesized. These compounds have good photocatalytic selectivity and electrocatalytic activity.

Four Keggin-based compounds constructed by a series of pyridine derivatives: synthesis, and electrochemical, photocatalytic and fluorescence sensing properties

Four compounds based on Keggin anions and AgI ions were obtained, the photocatalytic and electrochemical properties were studied. Compound 4 can act as a Hg2+ fluorescence sensor.

A series of Wells-Dawson and Keggin-based compounds with uncoordinated S donors as fluorescence sensors to Hg2+

Through using a S-containing ligand 2,2’-dimethyl-4,4’-bithiazole (dbt), a series of Wells-Dawson and Keggin-based compounds, {Zn(dbt)3}{Zn(dbt)2(H2O)}2{HP2WVWVI17O62}·4H2O (1), {Cd(dbt)2(H2O) (HP2WVWVI17O62)}{Cd(dbt)3}{Cd(dbt)2(H2O)}·13H2O (2), {Cd2(dbt)4Cl} {PW12O40} (3) and {Cd2(dbt)4}{SiW12O40} (4), were synthesized under hydrothermal conditions and structurally characterized. In 1, there are three dissociated subunits: Wells-Dawson anion, {Zn(dbt)3}2+ and {Zn(dbt)2(H2O)}2+. In 2, the mono-supporting Wells-Dawson anions exhibit abundant hydrogen bonding interactions with discrete {Cd(dbt)3}2+ and {Cd(dbt)2(H2O)}2+ mononuclear coordination complexes, constructing a supramolecular layer. Compound 3 has a binuclear Cd cluster {Cd2(dbt)4Cl}4+ with a Cl as a bridging atom. The Keggin anions link these binuclear Cd clusters alternately to build a 1D chain. In 4, a pair of {Cd(dbt)2}2+ subunits connect adjacent Keggin anions and a 1D chain is formed. In these four compounds, only the N donors coordinate with Zn or Cd and the S atoms are uncoordinated. These compounds show good fluorescence sensing performance to Hg2+. We also studied the electrochemical and photocatalytic properties of 1–4. These compounds also can act as electrochemical sensors for the detection of nitrite.

Using a flexible bis(pyrazol) ligand to construct four new Keggin-based compounds: syntheses, structures and properties

Four new Keggin-based compounds were constructed. A discrete mono-supporting structure and a supramolecular chain were obtained. Compounds 3 and 4 were formed in one pot containing either bi-nuclear cycles and nested cycle subunits.

A series of Keggin-based AgI-belt/cycle structures constructed from 5-phenyl-1H-tetrazole and its derivative through Ag–N and Ag–C bonds

Three Keggin-based compounds containing AgI belts and cycles constructed from 5-phenyl-1H-tetrazole (L1) and its derivative 5-m-tolyl-1H-tetrazole (L2), [Ag9L15(PWVWVI11O40)]·H2O (1), [Ag11L16(H2O)2(SiMoVMoVI11O40)] (2) and [Ag10L28(HPMo12O40)]·H2O (3), have been synthesized under hydrothermal conditions and characterized by IR spectra and single crystal X-ray diffraction. Compound 1 shows a channel-like 3-D metal-organic framework with Keggin anions in channels. Adjacent layers of 2 share the same anions to construct a 3-D framework. Compound 3 has a 2-D metal-organic layer containing AgI cycles. Adjacent layers link through sharing Ag–N bonds and a channel-like 3-D framework is formed. Electrochemical and photocatalytic properties of 1–3 have been studied. The experimental results show that 1–3 have excellent catalytic performance for reduction of nitrite and bromate and also have photocatalytic properties for degradation of MB and RhB.

Tuning N donor sites of pendent ligands to induce mono- and multi-nuclear Keggin-based compounds

Tuning N donor sites of pendent ligands to induce mono- and multi-nuclear Keggin-based compounds

A series of Keggin-based compounds constructed by conjugate ring-rich pyrazine and quinoxaline derivatives.

Through the use of conjugate ring-rich pyrazine and quinoxaline derivatives, five new Keggin polymolybdate based compounds, [Ag(I)3L(1)2(H2O)2(PMo12O40)] (1), [Ag(I)4L(1)5(SiMo12O40)] (2), [Ag(I)6L(2)6(PMo12O40)2] (3), [Ag(I)2L(2)2(C16H36N)2](SiMo12O40)] (4), [Cu(I)3L(2)3(PMo12O40)] (5) (L(1) = 2,3-diphenylpyrazine, L(2) = 2,3-diphenylquinoxaline, C16H36N = tetrabutylammonium), were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. In compound 1, three Ag(I) ions are fused by two L(1) molecules to form a [Ag3L(1)2](3+) subunit, and these subunits link the PMo12 anions to construct two kinds of 1D chains (I and II). Chains I and II connect to each other by sharing the same PMo12 anions and a 2D grid-like layer is built. The asymmetric unit of compound 2 is linked to form a dimer by sharing Ag ions, and a 1D double strand is formed. The SiMo12 anions connect adjacent 1D double strands through Ag3-O23 bonds and a 2D network is built. In compound 3, there exists a 1D ladder-like double chain with PMo12 anions as linking bars. A 2D layer is formed by linkage Ag2-O24 between adjacent chains. In compound 4, the PMo12 anions act as inorganic linkages to connect adjacent zigzag chains through Ag1-O3 bonds to construct a 2D grid-like layer. In compound 5 two Cu(I)-L(2) lines are fused by PMo12 anions to build a 1D ladder-like chain. Additionally, the electrochemical and photocatalytic properties of the title compounds have been studied.

Highly efficient usage of the hydrothermal technique through the one-pot method to construct four Keggin-based compounds containing pendent ligands.

By utilizing two kinds of pendent organic ligands, four new Keggin-based compounds, [Ag(bpz)2(pz)(H2O)(H3PMo12O40)2] (), [Ag(bpz)2(H3PMo12O40)]·2H2O (), [Ag(btz)4(PMo12O40)] () and [Ag(btz)3(PMo12O40)]·H2O () (bpz = 4-butyl-1H-pyrazole, pz = pyrazole, btz = 1-benzyl-1H-(1,2,4)triazole), were synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction. Compounds and were obtained in one-pot reaction, as well as compounds and . In compound , six Ag(I) ions are fused by four bpz and two pz molecules to form a hexa-nuclear cycle, with two coordinated water embedding through Ag-O bonds. The three-connected Mo13-containing PMo12 anions connect these cycles alternately to construct 1D chains, which are further linked by four-connected Mo1-containing PMo12 anions to build a 3D framework of . Compound contains 1D Ag(I) chains, linked by four-connected Mo1-containing PMo12 and two-connected Mo7-containing PMo12 respectively to construct a 3D structure. The pz ligand was not observed in . In compound , there exist [Ag(btz)4](3+) subunits, which are alternately connected by PMo12 anions to form a 1D chain. In compound , there exists a zigzag Ag-btz chain. The adjacent chains are further linked by Ag-C bonds and a 2D metal-organic layer is constructed. The PMo12 anions link adjacent layers to build a 3D framework of . The syntheses of compounds and , and prove that the one-pot method under hydrothermal conditions is efficient for pursuing even two more kinds of crystals.

Tuning the oxidation states of copper ions (+I/+II) to construct different Keggin-based topology structures

Through tuning the oxidation states of CuI/II, two Keggin-based compounds with different topologies, [(btx)4(PO40)] (1) and [(btx)4(SiW12O40)] (2) (btx = 1,6-bis(1,2,4-triazol-1-y1)hexane), were synthesized and structurally characterized. In 1, there exist decanuclear CuI circuits, which are linked through N1-containing btx ligands to construct a grid-like 2-D layer. Three sets of these layers interpenetrate to build a three-fold interpenetrating framework. The Keggin polyanions connect the adjacent three-fold interpenetrating frameworks to construct a 3-D structure. In 2, the CuII-btx moiety shows a (66) 3-D hexagonal channel-style framework. The Keggin polyanion offering four terminal oxygen atoms incorporates with this metal–organic framework imbedding the channels. The different oxidation states of copper ions (+I/+II) induces distinct coordination modes of btx and Keggin polyanions and affects the whole structural topologies. Tuning the oxidation states of copper ions is an effective strategy for obtaining POM-based topologies. In addition, the electrochemical properties of 1 and 2 bulk-modified carbon-paste electrodes are reported.

Assembly of a series of Keggin-based multi- and mono-nuclear structures by tuning the bis(tetrazole)-functionalized thioether ligands

Four Keggin-based compounds, [CuI2(bmtm)3]2·[CuI2(bmtm)4]·(PW12O40)2 (1), (bmtm=1,1′-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)methane), [CuI3(bmte)3(PW12O40)] (2) (bmte=1,2-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)ethane), [CuII(bmtb)3(HPW12O40)] (3) and [CuII(bmtb)3(HPMo12O40)] (4) (bmtb=1,4-bis(1-methyl-5-mercapto-1,2,3,4-tetrazole)butane), have been designed and synthesized under hydrothermal conditions. By tuning the bis(tetrazole)-functionalized thioether ligands, compounds 1–4 exhibit Keggin-based bi-, tri- and mono-nuclear structures respectively, in which copper ion is +I oxidation state in compounds 1–2, and +II oxidation state in compounds 3–4. Compound 1 is composed of three moieties, [PW12O40]3− anion and two kinds of bi-nuclear subunits [CuI2(bmtm)3]2+ and [CuI2(bmtm)4]2+. There exist abundant hydrogen-bonding and aryl stacking interactions inducing a two-dimensional (2D) supramolecular network of compound 1. Compound 2 exhibits a tri-nuclear cluster [CuI3(bmte)3]3+, which is connected by [PW12O40]3− anions to construct a 1D chain. Compounds 3 and 4 are isostructural, and show 2D layer structures, which are constructed from Keggin anions and mono-nuclear [CuII(bmtb)3]2+. In this 2D layer, the Keggin anions act as bidentate linkages to connect the CuII-btmb chains. The oxidation states of copper ions show great influence on the mono- and multi-nuclear structures of this series. In addition, the electrochemical properties of the title compounds have been investigated.

Novel Doped Tungstovanadate and Molybdovanadate with Bi-antimony-Capped Keggin Structure

Three novel V-centred Keggin-based compounds containing cap-shaped Sb atoms: (HDMF)2[(VO4)W5.65V7.74Sb2.61O36.77]·6H2O (1), [Co(phen)3]2[(VO4)Mo9.58V2.42Sb2O36]·6H2O (2) and [Ni(phen)2(H2O)]2[(VO4)Mo8V4Sb2O36]·2H2O (3) (DMF = dimethylformamide; phen = 1,10-phenanthroline) have been synthesized and characterized. X-ray diffraction analysis revealed that compound 1 consists of an unusually one-dimensional 12-tungstovanadate Keggin-based polymer, in which the reduced tungstovanadate Keggin species are stabilized by introducing capping {VO} and {Sb} groups and then linked into chains via V(Sb)–O–V(Sb) interactions. Both 2 and 3 are built from secondary metal–ligand groups (Co-phen for 2, Ni-phen for 3) and 12-molybdovanadate doped Keggin-type cores with two antimony atoms capping two opposite sites. The anion in 3 represents a bi-capped and bi-supported Keggin-type structure. The electrochemical properties of 2- and 3-modified carbon paste electrodes (2-CPE and 3-CPE) are also studied.