Two new Keggin-type polyoxometalate-based organic-inorganic hybrid compounds with metal ions and chelate ligands

Two new hybrid compounds with chemical formulas [Co(L₁)₂(H₂O)₂]₂[SiW₁₂O₄₀]·6H₂O (1) and [Cu₂(C₉H₂₂ N)₂(L₂)₂][SiW₁₂O₄₀]·2H₂O (2) (L₁ = 3,3′-diamino-5,5′-bis(1H-1,2,4-triazole), L₂ = 1,2-bis(3-(2-pyridyl)pyrazole-1-ylmethyl)benzene, C₉H₂₂ N = tripropylamine) were prepared in a hydrothermal reaction system containing Keggin-type polyoxometalates (POMs), transition metal (TM) salts (cobalt salts and copper salts), and chelate L₁/L₂ ligands. X-ray structural analysis reveals that 1 and 2 possess 3-D supramolecular host frameworks with large cavities and the polyoxoanions SiW₁₂ reside in these cavities as the guest templates. The photocatalytic activities of 1 and 2 were investigated. Both compounds show efficient catalytic activity for degradation of RhB with 1 > 2. The loading amount of the POM units and the structural features of these POM-based organic-inorganic hybrid compounds may be necessary factors that affect the activity of catalysts in the photocatalytic degradation.     

Two New 2D and 1D Ni(II) Coordination Polymers Bridged by Vanadium-Substituted Keggin Polyoxotungstophosphates: Hydrothermal Synthesis and Crystal Structure

Two coordination polymers based on vanadium-substituted Keggin polyoxotungstophosphates as bridging ligands, {[Ni(4,4′-bipy)_1.5(OH)(H₂O)]₂[H₃PW₁₀V₂O₄₀]}·4H₂O (4,4′-bpy = 4,4′-bipyridine) 1 and {[Ni(dpa)₂][Ni(dpa)(H₂O)₃]₂[PW₉V₃O₄₀]}·4H₂O (dpa = 2,2′-dipyridylamine) 2, have been obtained by hydrothermal reactions and characterized by elemental analysis, IR, XRD, TGA and single-crystal X-ray Diffraction analysis. Compound 1 is a 2D layered structure built from 1D infinite zigzag {Ni₂(4,4′-bipy)₃(OH)₂(H₂O)₂}_n²⁺ chains bridged via [H₃PW₁₀V₂O₄₀]²⁻ anions. Compound 2 exhibits a one-dimensional chain-like structure constructed from [Ni(dpa)₂]²⁺ fragments bridged via bis-supported Keggin polyoxoanions [Ni(dpa)(H₂O)₃]₂[PW₉V₃O₄₀]²⁻. The two examples demonstrate that vanadium-substituted Keggin polyoxometalates have greater coordination capability.     

Hydrothermal Synthesis, Crystal Structures and Electrochemical Properties of Two Phosphatotungstates Containing Keggin Clusters, [Cu(2,2′-bipy)2]5[PW12O40] · 2H2O and (Hpip)3[PW12O40]

Two new phosphatotungstates containing Keggin clusters, [Cu(2,2′-bipy)₂]₅[PW₁₂O₄₀] · 2H₂O (1) (2,2′-bipy = 2,2′-bipyridine) and (Hpip)₃[PW₁₂O₄₀] (2) (pip = piperazine) have been hydrothermally synthesized and characterized by IR, element analysis and cyclic voltammogram. Compound 1 consists of one discrete Keggin polyanion [PW₁₂O₄₀]^5?, five isolated complex cations [Cu(2,2′-bipy)₂]⁺ and two water molecules. The organic moieties exhibit regular packing with offset aromatic–aromatic interactions between the bipys, leading to a compact supramolecular framework structure. Compound 2 is made up of one discrete Keggin polyanion [PW₁₂O₄₀]^3? and three pip cations. Compounds 1 and 2 were employed to fabricate bulk-modified carbon paste electrode to research on their electrochemistry properties. Their electrochemical behaviors and electrocatalysis that 1- and 2-CPEs have electrocatalytic activities toward the oxidation of nitrite. Compound 1 is in the orthorhombic system, space group Pna2₁, with a = 28.1928(9), b = 21.5479(6), c = 19.9088(6) Å, V = 12,094.5(6) Å³ and Z = 4. Compound 2 is in the rhombohedral system, space group R $ \overline{3} Two new phosphatotungstates containing Keggin clusters, [Cu(2,2′-bipy)₂]₅[PW₁₂O₄₀] · 2H₂O (1) (2,2′-bipy = 2,2′-bipyridine) and (Hpip)₃[PW₁₂O₄₀] (2) (pip = piperazine) have been hydrothermally synthesized and characterized by IR, element analysis and cyclic voltammogram. Compound 1 consists of one discrete Keggin polyanion [PW₁₂O₄₀]⁵⁻, five isolated complex cations [Cu(2,2′-bipy)₂]⁺ and two water molecules. The organic moieties exhibit regular packing with offset aromatic–aromatic interactions between the bipys, leading to a compact supramolecular framework structure. Compound 2 is made up of one discrete Keggin polyanion [PW₁₂O₄₀]³⁻ and three pip cations. Compounds 1 and 2 were employed to fabricate bulk-modified carbon paste electrode to research on their electrochemistry properties. Their electrochemical behaviors and electrocatalysis that 1- and 2-CPEs have electrocatalytic activities toward the oxidation of nitrite. Compound 1 is in the orthorhombic system, space group Pna2₁, with a = 28.1928(9), b = 21.5479(6), c = 19.9088(6) ?, V = 12,094.5(6) ?³ and Z = 4. Compound 2 is in the rhombohedral system, space group Rc, with a = 17.9191(5), c = 23.7439(9) ?, V = 6,602.6(4) ?³ and Z = 6. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Subtle difference of [SiMo12O40]4− and [PMo12O40]3− inducing two new distinct Keggin-Ag-(1H-Pyrazole) compounds

Two new inorganic-organic hybrid compounds based on α-Keggin clusters and Ag-(1H-Pyrazole) subunits, [AgL₂]₄[SiMo₁₂O₄₀] (1) and [AgL₂]₃[PMo₁₂O₄₀] (2) (L = pyrazole), have been synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction. In 1, there are two kinds of chains, the chains linked by two [AgL₂]⁺ clusters and the other linked only by one [AgL₂]⁺, which further connect by sharing [SiMo₁₂O₄₀]^4? anions to construct a 2-D layer. In 2, four-supporting [PMo₁₂O₄₀]^3? anions are fused by [Ag(1)L₂]⁺ subunits to form a 1-D chain. Through weak interactions of Ag?O (3.091 Å) a 2-D supramolecular layer is constructed. Additionally, the electrochemical properties of title compounds and the photocatalytic properties of 2 have been studied.     

Three 2-(4-thiazolyl)benzimidazole-based supramolecular assemblies oriented by Keggin and Wells–Dawson anions

Three polyoxometalate supramolecular assemblies based on rigid 2-(4-thiazolyl)benzimidazole (L) and two types of polytungstate anions, [Cu^II₂Cl(L)₄(PW₁₂O₄₀)]·3H₂O (1), [Cu^II(L)₂(H₂O)]₂[P₂W₁₈O₆₂]·(HL)₂·6H₂O (2), and [Zn^II(L)₃]₄[H(KPW₁₂O₄₀)₃] (3), have been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, and IR spectra. Compound 1 contains binuclear copper clusters {Cu₂L₄Cl}³⁺ with Cl^– as bridges. These binuclear clusters and [PW₁₂O₄₀]^3– anions construct a supramolecular 2-D layer through hydrogen-bonding interactions. In 2, the [CuL₂(H₂O)]²⁺ subunits and Wells–Dawson anions build a 1-D supramolecular chain. In 3, the [PW₁₂O₄₀]^3– anions are covalently linked by K⁺ to form an inorganic chain. These chains and discrete [Zn^II(L)₃]²⁺ subunits construct a 3-D supramolecular structure. The electrochemical and photocatalytic properties of 1–3 have been studied.     

The assembly of POM-induced inorganic–organic hybrids based on copper ions and mixed ligands

Three inorganic–organic hybrid materials based on Keggin-type polyoxometalates (POMs), [Cu^II₂(phen)₂(4,4′-bipy)(H4,4′-bipy)₂(H₂O)₂][PMo₁₂O₄₀]₂·2H₂O (1), [Cu^II(phen)₂(H4,4′bipy)][PW₁₂O₄₀]·H₂O (2), and [Cu^II₂(phen)₂(4,4′-bipy)(BW₁₂O₄₀)(H₂O)₂](H₂4,4′-bipy)_0.5·3H₂O (3) (phen = 1,10-phenanthroline, 4,4′-bipy = 4,4′-bipyridine), were synthesized using different POMs in the hydrothermal conditions. Compounds 1–3 were characterized by single-crystal X-ray diffraction, IR spectra, elemental analyses, powder X-ray diffraction analyses, and thermogravimetric analyses. Compound 1 presents a two-dimensional (2-D) network containing the Keggin-type [PMo₁₂O₄₀]^3? anion and dinuclear metal–organic units [Cu^II₂(phen)₂(4,4′-bipy)(H4,4′-bipy)₂(H₂O)₂]³⁺. Compound 2 is a 2-D architecture constructed from a [PW₁₂O₄₀]^3? and mononuclear metal–organic units [Cu^II(phen)₂(H4,4′-bipy)]³⁺. In 3, the [BW₁₂O₄₀]^5? anions link [Cu^II₂(phen)₂(4,4′-bipy)] units to form a one-dimensional (1-D) chain [Cu^II₂(phen)₂(4,4′-bipy)(BW₁₂O₄₀)(H₂O)₂]; the 1-D chain connects with protonated 4,4′-bipy ligands and lattice waters, yielding a 2-D layer. Fluorescence spectra, UV–vis spectra, and electrochemical properties of 1–3 have been investigated.     

Hydrothermal synthesis and characterization of two novel tungstovanadophosphate derivatives

Two novel tungstovanadophosphate derivatives, namely [Fe(phen)₃]₂[PW₈^VIV^VV₅^IVO₄₂] · H₂O (1) and [Fe(phen)₃]₂[PW₉V₃O₄₀] (2), were synthesized under hydrothermal conditions, and characterized by elemental analysis, IR, ESR, XPS, TGA, and single-crystal X-ray diffraction analysis. The crystal structure analyses reveal that the ‘mixed-addenda’ Keggin polyoxoanion in 1 is decorated with VO²⁺ units, such that four V atoms are disordered over eight metal sites; the anion in compound 2 has a typical Keggin structure with three V atoms disordered over 12 metal sites. The two compounds are ionic crystals with slightly different packing modes for the polyoxoanions and [Fe(phen)₃]³⁺ cations. π–π stacking interactions between phen molecules, weak hydrogen bonding interactions between phen ligands and polyoxoanions, and electrostatic forces lead to an extended 3D supramolecular framework. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A sandwich-type POM containing mixed cations: synthesis,thermal performance and proton-conducting properties

A new sandwich-type polyoxometalate, Na₅H[N(CH₃)₄]₂[Co(C₃N₂H₄)₂(H₂O)₄][Co₄(H₂O)₂(PW₉O₃₄)₂]·21H₂O (1), has been synthesized. 1 is composed of a Weakley-type polyanion, [Co₄₍H₂O)₂(PW₉O₃₄)₂]^10?, four kinds of cations (five Na⁺, two [N(CH₃)₄]⁺, one [Co(C₃N₂H₄)₂(H₂O)₄]²⁺, and one H⁺), and 21 crystalline H₂O molecules. The surface oxygen of the polyanion in 1, the crystalline water, and coordinated water molecules make an extended 3-D hydrogen-bonding network. Alternating current (AC) impedance experiments of 1 reveal good proton conductivity for 1 of 5.03 × 10^??4 S cm^?1 at 25 °C under 98% relative humidity (RH). Activation energy of 1 calculated from Arrhenius plots is 0.358 eV, indicating Grotthuss mechanism is dominant in the proton transfer. Thermal decomposition behavior of 1 was examined by thermogravimetry/mass spectrometry (TG/MS) measurements.     

Two organic–inorganic hybrid compounds constructed from [PMoV1MoVI7VIV2VV4O42]4− and different transition metal fragments

Two new organic–inorganic hybrid compounds, [Cu(phen)(prz)]₂[PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂]·4H₂O (1) and [Ag₂(phen)₄]₂[PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂] (2) (phen = 1,10-phenanthroline, prz = pyrazine), have been synthesized and characterized by IR, XPS, XRD, UV–vis, fluorescent spectra analyses, elemental analyses, X-ray diffraction analyses, TG analyses, and cyclic voltammetric measurements. Both compounds are formed by Keggin POM cores and transition metal fragments. Compound 1 exhibits an unprecedented 1-D chain structure constructed from [PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂]^4? and [Cu(phen)(prz)]²⁺ in the –A–B↑–C–B↓– linking mode. Compound 2 shows a supramolecular structure formed by [PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂]^4? and [Ag₂(phen)₄]²⁺.     

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

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

两个新颖的铜-二氮杂菲和钼(磷,硒)杂多酸组成的有机-无机杂合化合物:合成和晶体结构

水热法合成了两个新颖的有机-无机杂合化合物{[Cu(o-phen)(H₂O)]₃[Mo₅P₂O₂₃]}•4.5H₂O (1) 和{[Cu(o-phen)- (H₂O)]₂[Mo₅Se₂O₂₁]} (2) (o-phen＝1,10-phenanthroline). 通过红外光谱和单晶X射线衍射分析确定了它们的结构. 结构分析表明两个分子结构中的相邻[Mo₅P₂O₂₃]^6－或[Mo₅Se₂O₂₁]^4－阴离子均由两个桥式的[Cu(o-phen)(H₂O)]单元连接成分别为风车状和双侧桥联状一维聚合链, 化合物1的双金属链又通过若干链间氢键形成层状堆积结构. 讨论了钼杂多酸阴离子和第二种金属-配体亚单元阳离子之间的相互匹配关系.     

Syntheses,crystal structures,and magnetic properties of the banana-shaped tungstophosphates: [M6(H2O)2(PW9O34)2(PW6O26)]17− (MII=NiII,CoII)

Two new banana-shaped tungstophosphates [M₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]^{17 ?} (M^II?=?Ni^II, Co^II) incorporating two types of lacunary polyoxometalate units have been synthesized in aqueous solution and characterized by elemental analyses, IR, and UV spectra, and single-crystal X-ray diffraction. Structural analyses show that Na₆H₁₁[Ni₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]?·?32H₂O (1) and Na₇H₁₀[Co₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]?· 31H₂O (2) are generated from two tri-M^II substituted B-α-[(MOH₂)M₂PW₉O₃₄] Keggin units connected by a hexavacant [PW₆O₂₆]^11? Keggin fragment, leading to the M^II-containing banana-shaped tungstophosphates. Magnetic properties of 2 show decrease of the molar magnetic susceptibility at higher temperatures results from spin-orbit coupling of Co^II and antiferromagnetic interactions whereas the maximum at the lower temperatures is indicative of the ferromagnetic interactions within the trinuclear Co^II spin cluster in the sandwich belt.     

Synthesis,structural characterization,and properties of two new polyoxovanadates based on decavanadate [V10O28]6−

Two new decavanadate metal compounds, [Co(pyim)₃]₂[V₁₀O₂₈]·7H₂O (1) and [Ni(pyim)₃]₂[H₂V₁₀O₂₈]·4H₂O (2) (pyim?=?2-(2-pyridyl)-imidazole), have been synthesized under hydrothermal conditions and characterized by elemental analysis, single-crystal X-ray diffraction analysis, infrared spectra, powder X-ray diffraction analysis, and thermogravimetric analysis. Crystallographic analysis reveals that 1 is constructed from [V₁₀O₂₈]^6?, metal cation [Co(pyim)₃]³⁺, and water. [V₁₀O₂₈]^6? clusters are connected by waters through O–H?O hydrogen bonds to form a sheet structure which is further connected by N–H?O hydrogen bonds to form a 3-D supermolecular framework. In 2, although [Ni(pyim)₃]²⁺ is similar to [Co(pyim)₃]³⁺ in 1, the M?O cluster anion is protonated [H₂V₁₀O₂₈]^4?.     

Synthesis,characterization and electrochemical investigation of a new inorganic–organic hybrid compound constructed by Keggin-type polyoxometalate and cyanoguanidine

An inorganic–organic hybrid complex [HDCD]₃[PW₁₂O₄₀]·3H₂O (1) (DCD = 2-cyanoguanidine) has been synthesized from the reaction of Keggin polyanion and cyanoguanidine (C₂N₄H₄) under mild condition, and characterized by using elemental analysis, infrared spectrum, thermogravimatric analysis and single crystal X-ray diffraction. X-ray crystallography reveals that 1 displays an inorganic–organic hybrid frameworks constructed by [PW₁₂O₄₀]³⁻ Keggin-type polyoxoanion and three {(HDCD)}⁺ monocationic hydrogen-bonded units. The electrochemical behavior and electrocatalysis of 1 have been studied in detail.     

Polyoxometalates decorated with metal-organic moieties as new molecular photo- and electro-catalysts

Abstract

Three new polyoxometalate-based organic-inorganic hybrid compounds (POIHCs), [Cu(PBI)₂(H₂O)][{Cu(PBI)(OH)(H₂O)}{PW₁₂O₄₀}]·5H₂O (1), [Cu(PBI)₂(H₂O)][{Cu(PBI)₂(H₂O)}{SiW₁₂O₄₀}]·4H₂O (2) and [Cu₄(HPO₄)(PO₄)(H₂O)₂(PBI)₄][PMo₁₂O₄₀]·H₂O (3) (PBI =2-(pyridin-2-yl)-1H-benzo[d]imidazole), have been synthesized under hydrothermal conditions. All three compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. In 1 and 2, the Keggin-type polyoxometalate (POM) units are decorated by the {Cu/PBI} metal-organic fragments, together with additional {Cu/PBI} isolated cations, which further stack into 3-D supramolecular frameworks with porous structural features. Compound 3 consists of a rare cationic cluster [Cu₄(HPO₄)(PO₄)(H₂O)₂(PBI)₄]³⁺ and the Keggin-type POM anion, forming a 3-D supramolecular framework with limited interspaces for the entry of guest molecules. Comparable photocatalytic properties of 1–3 were investigated by the use of methylene blue (MB) and Rhodamine B (RhB) degradation under UV light. All compounds showed good catalytic activity for the degradation of MB in contrast to RhB. The possible catalytic mechanism was discussed based on the size of dye molecules, the low adsorption ability and crystal packing mode of the as-synthesized compounds. Additionally, the electrochemical properties of 1–3 have also been investigated, exhibiting good electrocatalytic performance for nitrite reduction.     

Green and efficient oxidation of benzylic alcohols with hydrogen peroxide catalyzed by an inorganic–organic hybrid catalyst

Inorganic–organic hybrid catalysts 1-POM(M) were prepared by electrostatic interaction between transition metal-substituted polyoxometalates, {[PW₁₁MO₃₉]^4? [M?=?Cr(III), Fe(III)], [PW₁₁MO₃₉]^5?, [M?=?Mn(II), Co(II), Ni(II), Cu(II), Zn(II)], [PW₁₁VO₄₀]^4?}, and branched organic polyammonium, (tris[2-(dimethylammonium)ethyl]-1,3,5-benzenetricarboxylate), and characterized by elemental analyses, UV–vis and FT IR spectroscopic techniques, XRD, SEM, and Thermogravimetric-Differential thermogravimetric analyses. The hybrid material 1-POM(Zn) was an efficient and selective heterogeneous catalyst in the oxidation of benzylic alcohols to their corresponding carbonyl compounds with hydrogen peroxide. The catalyst was reused several times without significant loss of catalytic activity.     

Synthesis, structure, and characterization of a silicotungstate anion-supported organic-inorganic hybrid complex [Zn(2,2′-Bipy)3]1.5[SiW12O40Zn(2,2′-Bipy)2(OH)] · 0.25H2O

A new Keggin-type silicotungstate anion-supported organic-inorganic hybrid transition metal complex, [Zn(Bipy)₃]_1.5[SiW₁₂O₄₀Zn(Bipy)₂(OH)] · 0.25H₂O (I) (Bipy = 2,2′-bipyridine), has been synthesized by the hydrothermal method and characterized by elemental analysis, IR, UV, and EPR spectra, TG-DTA analysis, and single crystal X-ray diffraction. The structural analysis indicates that each structural unit of I consists of one [SiW₁₂O₄₀Zn(Bipy)₂(OH)]³⁻ heteropolyanion, one and a half isolated [Zn(Bipy)₃]²⁺ cations, and a quarter of crystal water molecule. The [Zn(Bipy)₂(OH)]⁺ unit is covalently bonded to one Keggin polyoxoanion [SiW₁₂O₄₀]⁴⁻ in the [SiW₁₂O₄₀Zn(Bipy)₂(OH)]³⁻ cluster. The EPR spectrum indicates the existence of Zn²⁺ with the high-spin state, and TG-DTA analysis exhibits that I has two steps of weight loss and the polyoxoanion framework is collapsed at 618°C.     

A unique borotungstate containing a discrete Keggin-type anion and a trimeric saturated Keggin-type anion

A unique hybrid borotungstate, [Cu(En)(Phen)(H₂O)]₄[α-BW₁₂O₄₀]{[Cu(En)(Phen)]₂[Cu(En)₂ · (H₂O)]₂[Cu(En)(Phen)(H₂O)]₂[α-BW₁₂O₄₀]₃]} sd 10H₂O (I) (Phen = 1,10-phenanthroline, En = ethylenediamine), has been hydrothermally synthesized and characterized by elemental analyses, IR, and UV spectra, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and singlecrystal X-ray diffraction analysis. X-ray crystallography shows that I contains a discrete saturated Keggin-type [BW₁₂O₄₀]⁵⁻ polyoxoanion and a rare trimeric saturated Keggin-type polyoxoanion {[Cu(En)(Phen)]₂[Cu(En)₂(H₂O)]₂[Cu(En)(Phen)(H₂O)]₂[α-BW₁₂O₄₀]₃]}³⁻. It is noteworthy that I represents the first example of borotungstate containing four saturated Keggin-type units in one molecule.     

Dimerization of cobalt-substituted Keggin phosphotungstate, [PW11O39Co(X)]5−, in nonpolar solvents

The tetraheptylammonium (THA) salt of cobalt-substituted polyoxotungstate with Keggin-like structure, (THA)₅[PW₁₁O₃₉Co^II(X)], was investigated by ³¹P NMR and UV/VIS spectroscopies in toluene. A solution obtained after transferring PW₁₁Co from aqueous solution into toluene, using THABr as a transfer agent, and rigorous drying, gives multiple peaks in the ³¹P NMR spectrum. The spectrum in dry toluene significantly simplifies, after extracting a hexane solution several times with water, which removes simple inorganic ions. However, even the dry toluene solution after purification has ³¹P NMR and UV/VIS spectra which cannot be explained using the known equilibrium between (THA)₅[PW₁₁O₃₉Co(H₂O)] and (THA)₅[PW₁₁O₃₉Co(__)]. Both ³¹P NMR and UV/VIS spectroscopies indicate the existence of dimers in dry toluene solutions, (THA)₁₀[(PW₁₁O₃₉Co)₂]. Pure (THA)₅[PW₁₁O₃₉Co(_)] with five-coordinate cobalt can, however, be obtained in dry toluene in the presence of excess inert salt (high ionic strength conditions). Quantum mechanical/molecular mechanical calculations also support dimer formation in toluene.     

Synthesis and characterization of hybrid materials based on 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and Dawson-type tungstophosphate K7[H4PW18O62]·18H2O and K6[P2W18O62]·13H2O

In this study, we synthesized hybrid materials using well-Dawson polyoxometalates (POMs), K₇[H₄PW₁₈O₆₂]·18H₂O or K₆[P₂W₁₈O₆₂]·13H₂O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). K, W, P and CHN elemental analysis showed that one mole of [H₄PW₁₈O₆₂]⁷⁻ reacts with 6 moles of BMIM⁺ and one mole of [P₂W₁₈O₆₂]⁶⁻ reacts with 4 moles of BMIM⁺ to form, respectively, K[BMIM]₆H₄PW₁₈O₆₂ and K₂[BMIM]₄P₂W₁₈O₆₂. X-ray diffraction illustrated amorphous structure of the hybrid materials. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid materials compared to the parents Dawson POMs. Cyclic voltammetry showed that the reduction peak potentials of the Dawson anion in the hybrid materials shift towards negative values and the shift is more pronounced for K[BMIM]₆H₄PW₁₈O₆₂ compared to K₂[BMIM]₄P₂W₁₈O₆₂. This was attributed to a decrease in the acidity of the Dawson POM anion in the hybrid material.