Synthesis,structures and electrochemical properties of four organic–inorganic hybrid polyoxometalates constructed from polyoxotungstate clusters and transition metal complexes

Four novel organic–inorganic hybrid compounds [Cu₅ ^I(4,4′-bpy)₃(2,2′-bpy)₄][BW₁₂O₄₀] · H₂O (1), [Ni_0.5(2,2′-bpy)_1.25][Ni(2,2′-bpy)₃][Ni(2,2′-bpy)₂(H₂O)(SiW₁₁^VIW^VO₄₀)] · 0.5H₂O (2), [H₂bpy]₂[Zn(2,2′-bpy)₃]₂[Si₂W₁₈O₆₂] · 1.5H₂O (3) and [Cu^II(2,2′-bpy)₂]₂[SiW₁₂O₄₀] · 2H₂O (4) (2,2′-bpy = 2,2′-bipyridine, 4,4′-bpy = 4,4′-bipyridine) have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal gravimetric analysis, electrochemical measurements and single-crystal X-ray diffraction. Compound (1) is a novel [BW₁₂O₄₀]⁵⁻ polyoxoanion bisupported by copper(I) coordination cations with mixed 2,2′-bpy and 4,4′-bpy ligands. Compound (2) is constructed from the [SiW₁₁^VIW^VO₄₀]⁵⁻ polyoxoanions supported by [Ni(2,2′–bpy)₂]²⁺. Compound (3) is composed of a novel [Si₂W₁₈O₆₂]⁸⁻ cluster and [Zn(2,2′–bpy)₃]²⁺ complexes, which held together into a three-dimensional (3D) supramolecular network through hydrogen-bonding interactions. Compound (4) shows a 2D layer framework constructed from a bisupporting Keggin polyoxoanion cluster and [Cu(2,2′–bpy)₂]²⁺ coordination polymer fragments, resulting in 3D networks via supramolecular interactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of Coordination Geometry on the Ring Opening of Benzoxazine: Oxidovanadium(V), Dioxidomolybdenum(VI) and Dioxidotungsten(VI) Complexes of Benzoxazine Based Ligands and their Bio Inspired Catalytic Applications

Mono benzoxazine appended N-capped amino bis(disubstitutedphenol) ligands [ II ( a–c )] upon reaction with V^VO(OEt)₃ in a 1 : 1 molar ratio in EtOH/MeOH give [{V^VO}en(3,5-dtbb)₃] ( 1 ), [{V^VO}en(3-tb,5-mb)₃] ( 2 ) and [{V^VO}en(3,5-dmb)₃] ( 3 ). During the reaction, the benzoxazine ring opens with the loss of methylene group and the newly formed ligands, N,N-bis(2-hydroxy-3,5-disubstitutedbenzyl)-N’-2-hydroxy-3,5-disubstituted benzyledene-1,2-diaminoethane [ III ( a–c )], behave as tribasic pentadentate in these complexes. Under similar conditions, when [M^VIO₂(acac)₂] (M=Mo or W; Hacac=acetylacetone) reacts with II ( a–c ), these ligands retain their identity and form cis-[M^VIO₂] complexes, [{Mo^VIO₂}{en(3,5-dtbb)₂(6,8-dtbbenzox)}] ( 4 ), [{Mo^VIO₂}{en(3-tb,5-mb)₂(6-tb,8-mbbenzox)}] ( 5 ) and [{Mo^VIO₂}{en(3,5-dmb)₂(6,8-dmbenzox)}] ( 6 ), [{W^VIO₂}{en(3,5-dtbb)₂(6,8-dtbbenzox)}] ( 7 ), and [{W^VIO₂}{en(3-tb,5-mb)₂(6-tb,8-mbbenzox)}] ( 8 ). However, the benzoxazine ring ruptures in case of ligand IIc under these conditions and form [{W^VIO₂}{en(3,5-dmb)₃}] ( 10 ), similar to complexes 1–3 . Complex [{W^VIO₂}{en(3,5-dmb)₂(6,8-dmbenzox)}] ( 9 ), having structure similar to 4–8 , could only be obtained when the reaction was carried out in toluene. Not only 9 , even complexes 4–8 can be isolated in toluene. Rupturing of both benzoxazine rings has also been experienced when ligands 1,2-bis(6,8-disubstitutedbenzo[e][1,3]oxazin-3(4H)-yl)ethane [ I ( a–c )] react with [M^VIO₂(acac)₂] (M=Mo or W) in MeOH and give salan type complexes [(M^VIO₂)en(3,5-dtbb)₂] [M=Mo ( 11 ), M=W ( 14 )], [(M^VIO₂)en(3-tb,5-mb)₄] [M=Mo ( 12 ), M=W ( 15 )] and [(M^VIO₂)en(3,5-dmb)₄] [M=Mo ( 13 ), M=W ( 16 )]. Complexes 1–9 have been used as catalyst for the multicomponent Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) and oxidative bromination of phenol derivatives.     

Two-dimensional layer polyoxometalate-based inorganic metal–organic hybrid supramolecular networks woven by Cu ··· Opolyoxoanion short contact weak interactions

Two polyoxometalate-based inorganic metal-organic hybrid supramolecular complexes [Cu(2,2′-bpy)₂]₂[V^IV ₂Mo^V ₅Mo^VI ₇O₃₈(PO₄)] (1) (2,2′-bpy?=?2,2′-bipyridine) and [Cu(2,2′-bpy)₂]₂[Mo^VMo^VI ₁₁O₃₆(PO₄)]?·?3H₂O (2), have been hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. Both complexes are constructed from polyoxoanions (the bivanadyl capped α-Keggin polymolybdate anion [V^IV ₂Mo^V ₅Mo^VI ₇O₃₈(PO₄)]^4? for 1 and the reduced 12-molybdophosphate anion [Mo^VMo^VI ₁₁O₃₆(PO₄)]^4? for 2) and copper(II) complex cations [Cu(2,2′-bpy)₂]²⁺, forming two-dimensional (2D) layer network structures, in which the polyoxoanion and the complex fragment cation connect with each other through Cu?···?O_polyoxoanion short contact weak interactions, which mediate ferromagnetic interaction.     

Hydrothermal Synthesis and Crystal Structure of Two New α-Keggin Derivatives Decorated by Transition Metal Complexes

Two new neutral Keggin-polyoxometalate derivatives: [{Co(2,2′-bipy)₂(H₂O)}₂]–[PMo^VI₇Mo^V₅O₄₀(V^IVO)₂] (1) and [{Ni(phen)₂(H₂O)}₂](H₃O) [PMo^VI₁₀Mo^V₂O₄₀] · 4H₂O (2) have been synthesized under hydrothermal conditions and characterized by i.r., t.g. analysis, x.p.s. spectra and single-crystal X-ray diffraction. In the case of (1), the polyoxoanion cluster [PMo₁₂O₄₀]⁸⁻ is capped by two vanadium atoms via four bridging oxo groups on two opposite {Mo₄O₄} pits of the Keggin polyoxoanion. Two {Co (2,2′-bipy)₂(H₂O)} fragments are supported on the two vanadium atoms through two terminal oxygen atoms from two vanadium atoms. In (2), two {Ni(phen)₂(H₂O)}²⁺ moieties are linked to the molybdophosphate cluster [PMo₁₂O₄₀] core to form a neutral bimetallic cluster. Furthermore, through the linkages of π – π stacking interactions and hydrogen bond contacts, extended three-dimensional supramolecular networks in the solid of (1) and (2) were formed.     

Syntheses and characterization of three hybrid materials based on polymeric copper complexes and saturated Keggin polyoxoanions

Three novel heteropolytungstates, [Cu(phen)₂]₄[α-SiW₁₂O₄₀] (1), [Cu₄(4,4′-bpy)₃(2,2′-bpy)₄][α-SiW₁₂O₄₀] · H₂O (2) and [Cu(4,4′-bpy)(4,4′-Hbpy)_0.5]₂[PW₁₂O₄₀] (3) (phen = 1,10-phenanthroline, 4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine), have been synthesized and characterized by elemental analyses, IR, TG analyses and single-crystal X-ray diffraction. Compound (1) exhibits interesting chiral layer constructed from interperpendicular helical chains running along a crystallographic 2₁ axis in the c and a directions. Furthermore, the chiral layers are connected by the [α-SiW₁₂O₄₀]⁴⁻ anions via hydrogen bonding interactions to form a 3D superamolecular structure. The [Cu₄(4,4′-bpy)₃(2,2′-bpy)₄]⁴⁺ coordinated complexes in compound (2) are packed together via the aromatic π–π stacking interactions and exhibit an interesting 3D sandglasslike “host” network with 1D channels, in which [α-SiW₁₂O₄₀]⁴⁻ anions “guests” reside. Compound (3) has a unique 2D superamolecular network, which is composed of cationic Cu^I coordination polymer chains and discrete [PW₁₂O₄₀]³⁻ polyoxoanions as linkers. It is noteworthy that the monprotonated 4,4′-bpy ligands of (3) act as arms and connect the adjacent 2D network, generating a 3D interpenetrating superamolecular structure.     

Novel Hybrids Constructed from Keggin-Polyoxometalate and Mixed Copper Complex

Abstract  Two new Keggin-polyoxometalate hybrids, {[Cu₂(4,4′-bpy)₂][PW₁₀^VIW₂^VO₄₀]}[Cu₂(obpy)₂]₄ · 2 H₂O (1) and {[Cu₄(2,2′-bpy)₄(4,4′-bpy)₃][SiW₁₂O₄₀]} · 2H₂O (2) (4,4′-/2,2′-bpy = 4,4′-/2,2′-bipyridyl, Hobpy = 6-hydroxy-2,2′-bipyridyl), were hydrothermally synthesized and structurally characterized. Gillard type hydration of 2,2′-bipy is observed during the synthesis of 1, resulting in a new obpy ligand in situ. X-ray structural analyses show that 1 consists of 1D hybrid chain {[Cu₂(4,4′-bpy)₂][PW₁₀^VIW₂^VO₄₀]}_∞ and [Cu₂(obpy)₂] dimer, whereas 2 possesses 1D hybrid structure based on Keggin-type [SiW₁₂O₄₀]⁴⁻ anions and tetra-nuclear copper complexes [Cu₄(2,2′-bpy)₄(4,4′-bpy)₃]⁴⁺. Both compounds present interesting supramolecular architectures based on π–π stacking and hydrogen bonds. Graphical Abstract  Compounds {[Cu₂(4,4′-bpy)₂][PW₁₂O₄₀]}[Cu₂(obpy)₂]₄ · 2H₂O (1) and [Cu₄(2,2′-bpy)₄(4,4′-bpy)₃][SiW₁₂O₄₀] · 2H₂O (2) were hydrothermally synthesized. 1 features that the [Cu₂(obpy)₂] dimers based on in situ generated obpy ligands are stumped between the layers where 1D hybrid chain {[Cu₂(4,4′-bpy)₂][PW₁₂O₄₀]}_∞ locates, while 2 exhibits 1D chain-like structure based on anions [SiW₁₂O₄₀]⁴⁻ and tetra-copper complexes [Cu₄(2,2′-bpy)₄(4,4′-bpy)₃]⁴⁺.      

Synthesis,structural and catalytic activity of binaphthyl macrocyclic complexes

The binaphthyl macrocyclic ligand, N,N′-diethyl-[3,3′-(2,2′-dihydroxy-1,1′-binaphthyl)carboxamide]-2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic acid (DDCDB), has been synthesized and investigated. The ligand (DDCDB) and its metal complexes involving Cu^II, Zn^II, UO ₂ ^II , Th^IV, Ce^III, Mo^VI and W^VI ions have been prepared and characterized by spectral (i.r., u.v.–vis.), elemental analyses, magnetic moments and thermal analyses measurements. DDCDB behaves as a tridentate ligand towards Cu^II, Zn^II and UO ₂ ^II ions coordinating via CO, NH and the deprotonated naphthyl OH groups in a ratio of 2:1 (M:L). On the other hand, DDCDB behaves in a bidentate manner coordinatingvia the NH and the deprotonated naphthyl OH groups only in case of the Th^IV, Ce^III, Mo^VI, and W^IV ions and in ratio 1:1 (M:L). Results of thermal measurements confirm the existence of solvent molecules inside and outside the coordination sphere. Th^VI complex has been applied for the hydrolysis of phosphodiester and the results show a significant rate enhancement of ~5.8 million fold with respect to the auto-hydrolysis of bis-(p-nitrophenyl) phosphate (BNPP) under the same conditions Also, Cu^II complex accelerates the photodegradation of the hazardous pollutant (acid green dye) in the presence of hydrogen peroxide by degrading 90% of the dye within 23 min.     

Hydrothermal syntheses, crystal structures, and properties of two polyoxometalates [Cd(2,2′-bpy)3]2[PMoVMoVI 11O40] and [H3PMo12O40]·3(4,4′-bpy)·4H2O

Two Keggin-type phosphododecamolybdate compounds [Cd(2,2′-bpy)₃]₂[PMo^VMo^VI ₁₁O₄₀] (1) and [H₃PMo₁₂O₄₀]·3(4,4′-bpy)·4H₂O (2) (bpy=bipyridine) were prepared by the hydrothermal method for the first time and characterized by elemental analyses, X-ray single-crystal diffraction, ESR spectra, and IR spectra, showing that compound 1 consists of a mixed valence Keggin polyanion [PMo^VMo^VI ₁₁O₄₀]⁴⁻ and two isolated coordinated cations [Cd(2,2′-bpy)₃]²⁺, while compound 2 is an intermolecular compound based on organic substrate 4,4′-bpy and heteropoly acid unit H₃PMo₁₂O₄₀. Furthermore, both the compounds show strong photoluminescence properties in the solid state at room temperature. The catalytic activities of the two compounds were also determined by the oxidation of benzaldehyde to benzoic acid using H₂O₂ as oxidant in a liquid–solid triphase system.     

Hydrothermal Synthesis and Structural Characterization of a Tubular Arsenic-Vanadate: [CoII(2,2′-bpy)2]2[AsIII8VIV14O42(H2O)]·H2O

The hydrothermal reaction of VOSO₄, As₂O₃, CoC₂O₄·2H₂O and 2,2-bipy yields a novel arsenic-vanadate [Co^II(2,2-bpy)₂]₂[As^III₈V^IV ₁₄O₄₂(H₂O)]·H₂O (1), which is characterized by IR, elemental analysis, TGA, magnetic susceptibility and single crystal X-ray diffraction analysis. X-ray diffraction shows that compound 1 is the first example of tubular arsenic–vanadium cluster containing infinite {[Co(2,2-bpy)₂]₂[As₈V₁₄O₄₂(H₂O)]} chain constructed from [As₈V₁₄O₄₂(H₂O)] clusters interconnected through [Co(2,2-bpy)]²⁺ units. Crystal data: 1, orthorhombic, P 2₁2₁2₁, a=12.1401(2) Å, b=15.8722(1) Å, c=39.9533(5) Å, Z=4.Graphical Abstract: A novel polyoxoarsenicvanadate, [Co^II(2,2-bipy)₂]₂ [As^III₈V^IV ₁₄O₄₂(H₂O)]·H₂O, is depicted along with a tubular hybrid solid with a rhombic tube formed within the chain.     

Synthesis and Electrochemical Properties of a New 1D Organic–Inorganic Hybrid Compound Based on Keggin-Type Heteropolyanions and Isopolyanions Decorated by Transition Metal Fragments

A new chain-like organic–inorganic hybrid compound composed of the heteropolyanions and isopolyanions, [{Cu^II(2,2′-bpy)}₆(Mo^VMo^VI ₅O₂₂)] [PMo^VI ₁₂O₄₀] · H₂O 1 (bpy = 2,2′-bipyridine) has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, TG analysis, XPS spectrum and single-crystal X-ray diffraction. Crystal data for compound 1: monoclinic, space group P _2(1)/c, a = 13.9382(14) Å, b = 20.0300(19) Å, c = 17.1757(17) Å, β = 94.054(2)°, V = 4783.2(8) ų, Z = 2. The Keggin-heteropolyanion [PMo₁₂O₄₀]^3? and the Cu-supporting isopolyanion [{Cu(2,2′-bpy)}₆(Mo₆O₂₂)]³⁺ building units are bridged through the O–Cu–O bridges into 1D infinite chain. Note that, the [{Cu(2,2′-bpy)}₆(Mo₆O₂₂)]³⁺ unit, which contains a rarely reported isopolyanion [Mo₆O₂₂]^9? decorated by six [Cu(2,2′-bpy)] fragments. Furthermore, the electrochemical behavior of a 1-modified carbon paste electrode (1-CPE) and its electrocatalytic reduction of nitrite were investigated.     

Synthesis and characterization of a novel Anderson-type tungstotellurate decorated by transition metal complexes: [Na(H2O)3]2[{Cu(2,2′-bipy)2}2(TeW6O24)]?·?4H2O

A novel organic–inorganic hybrid tungstotellurate [Na(H₂O)₃]₂[{Cu(2,2′-bipy)₂}₂(TeW₆O₂₄)] · 4H₂O, has been synthesized and characterized by elemental analyses, IR spectra, TG analyses, and single-crystal X-ray diffraction. The saturated Anderson-type polyoxoanions are covalently bonded with two [Cu(2,2′-bipy)₂]²⁺, and linked by Na⁺ into an infinite one-dimensional chain. Furthermore, the three-dimensional supramolecular architectures are formed by π–π stacking interactions of the 2,2′-bipyridine groups between adjacent layers and the hydrogen-bonding interactions respectively.     

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 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.     

Controlling the Self‐Assembly of a Mixed‐Metal Mo/V–Selenite Family of Polyoxometalates

Five mixed‐metal mixed‐valence Mo/V polyoxoanions, templated by the pyramidal SeO₃^2? heteroanion have been isolated: K₁₀[Mo^VI₁₂V^V₁₀O₅₈(SeO₃)₈]?18 H₂O ( 1 ), K₇[Mo^VI₁₁V^V₅V^IV₂O₅₂(SeO₃)]?31 H₂O ( 2 ), (NH₄)₇K₃[Mo^VI₁₁V^V₅V^IV₂O₅₂(SeO₃)(Mo^V₆V^V‐ O₂₂)]?40 H₂O ( 3 ), (NH₄)₁₉K₃[Mo^VI₂₀V^V₁₂V^IV₄O₉₉(SeO₃)₁₀]?36 H₂O ( 4 ) and [Na₃(H₂O)₅{Mo_18?xV_xO₅₂(SeO₃)} {Mo_9?yV_yO₂₄(SeO₃)₄}] ( 5 ). All five compounds were characterised by single‐crystal X‐ray structure analysis, TGA, UV/Vis and FT‐IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X‐ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing η,μ and μ,μ coordination motifs. Compounds 1 and 2 were characterised in solution by using high‐resolution ESI‐MS. The ESI‐MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2? and 3? anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self‐assembly process of the mixed‐metal systems by controlling the interplay between the cation “shrink‐wrapping” effect, the non‐conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM‐based architectures.     

Arsenic-Centered Molybdenum–Vanadium Polyoxometalate Supporting Three Copper Complexes

A novel compound [HMo ₈ ^VI V ₆ ^V As^VO₄₂][Cu(2,2′-bpy)₂]₂[Cu(2,2′-bpy)]·2H₂O (2,2′-bpy = 2,2′-bipyridine) 1 has been hydrothermally synthesized and structurally characterized by elemental analyses, infrared spectroscopy, ultraviolet spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and single crystal X-ray diffraction. Crystal structure analysis reveals that compound 1 is a bi-capped As/Mo/V Keggin polyoxometalate tri-supported copper complexes, and exhibits an extended three-dimensional supramolecular network via hydrogen-bonding and π–π stacking interactions. The electrochemical and magnetic properties of compound 1 have been studied.     

Temperature-dependent synthesis, crystal structures, characterizations, and DFT calculations of two new copper(II) complexes with p-fluorobenzoic acid and 2,2′-bipyridine ligands

Two new copper(II) complexes, [Cu(p-FBA)₂(2,2′-bpy)]·(H₂O) (1) and [Cu(p-FBA)(2,2′-bpy)₂]·(p-FBA)₂ (2) {p-FBA = p-fluorobenzoic acid, 2,2′-bpy = 2,2′-bipyridine} have been obtained from an identical starting mixture using temperature as the only independent variable and characterized by X-ray single crystal diffraction as well as with infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The results reveal that 1 has 1D infinite chain structure formed by O–H···O hydrogen bonds, while 2 features a 0D structure. Additionally, there exist C–H···O hydrogen bonds and π–π stacking interactions in 1, forming 2D supramolecular structure. Furthermore, density functional theory (DFT) calculations of the structures, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the [Cu(p-FBA)₂(2,2′-bpy)] of 1 and [Cu(p-FBA)(2,2′-bpy)₂]⁺ cation of 2 were performed by means of Gaussian 03W package and taking B3LYP/lanl2dz basis set.     

Sandwich-type polyoxotungstate hybrids decorated by nickel-aromatic amine complexes

Three new sandwich-type polyoxotungstates (POTs) decorated by nickel-2,2′-bpy complexes [{Ni(2,2′-bpy)₂(H₂O)}₂{Ni(2,2′-bpy)}₂ {Ni₄(H₂O)₂(B-α-XW₉O₃₄)₂}]ⁿ⁻ (X=P^V, n=4 for 1; X=As^V, n=4 for 2; X=Ge^IV, n=4 for 3) (2,2′-bpy=2,2′-bipyridine) were successfully synthesized under hydrothermal conditions and structurally characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction, and magnetic properties. Single-crystal structural analyses indicate that 1 and 2 are isostructural and both crystallize in the monoclinic space group C2/c, whereas 3 belongs to the triclinic space group . To our knowledge, 1, 2 and 3 represent rare examples of the organic-inorganic hybrid sandwich-type polyoxometalates functionalized by multiple nickel-aromatic amine complexes. Magnetic measurements of 1 exhibit the presence of ferromagnetic interactions within the rhombic tetranuclear-Ni^II cluster.     

Synthesis, crystal structure and properties of a new organic-inorganic hybrid Dawson-like polyoxotungstate [Co(2,2''''-bpy)3]2[Co(2,2''''-bpy)2Cl][Co(2,2''''-bpy)2]H2-[SbW18O60]·4H2O

A new organic-inorganic hybrid polyoxometalate based on Dawson-like polyoxotungstate anion [SbW18O60]9-, formulated [Co(2,2'-bpy)3]2[Co(2,2'-bpy)2Cl][Co(2,2'-bpy)2]H2[SbW18O60]·4H2O (2,2'-bpy= 2,2(-bipyridine) has been synthesized from Sb2O3, Na2WO4, CoCl2, and 2,2'-bipyridine materials by hydrothermal method, and which was characterized by elemental analyses, IR, XPS, EPR, TG, and X-ray single crystal diffraction. Structure analysis shows that the polyoxoanion self-assembled under hydrothermal conditions consists of a Dawson-like polyoxotungstate cluster anion [SbW18O60]9- encapsulating a pyramidal {SbO3} group within the {W18} cluster cage. EPR spectra show that the high-spin octahedral CoⅡ and low-spin CoⅡ ions coexist in the title compound. Magnetic properties indicate that the compound is antiferromagnetic.     

Bridging function mediated intermetallic coupling in diruthenium- bis (bipyridine) complexes

The interactions of potentially dinucleating bridging functionalities (I–VI) with the ruthenium-bis(bypyridine) precursor [Ru^II(bpy)₂(EtOH)₂]²⁺have been explored. The bridging functionsI,II andVI directly result in the expected dinuclear complexes of the type [(bpy)₂Ru^IILⁿRu^II(bpy)₂]^z+ (1,2,7 and 8) (n = 0,z =4 andn = -2,z = 2). The bridging ligandIII undergoes N-N or N-C bond cleavage reaction on coordination to the Ru^II(bpy)₂ core which eventually yields a mononuclear complex of the type [(bpy)₂Ru^II(L)]⁺,3, where L =^-OC₆H₃(R)C(R′)=N-H. However, the electrogenerated mononuclear ruthenium(III) congener, 3⁺in acetonitrile dimerises to [(bpy)₂Ru^III {^-OC₆H₃(R)C(R′)=N-N=(R′)C(R)C₆H₃O^-}Ru^III(bpy)₂]⁴⁺ (4). In the presence of a slight amount of water content in the acetonitrile solvent the dimeric species (4) reduces back to the starting ruthenium(II) monomer (3). The preformed bridging ligandIV undergoes multiple transformations on coordination to the Ru(bpy)₂ core, such as hydrolysis of the imine groups ofIV followed by intermolecular head-to-tail oxidative coupling of the resultant amino phenol moieties, which in turn results in a new class of dimeric complex of the type [(bpy)₂Ru^{II -}OC₆H₄-N=C₆H₃(=NH)O^-Ru^II(bpy)₂]²⁺ (5). In5, the bridging ligand comprises of twoN,O chelating binding sites each formally in the semiquinone level and there is ap-benzoquinonediimine bridge between the metal centres. In complex6, the preformed bridging ligand, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine, H₂L (V) undergoes oxidative dehydrogenation to aromatic tetrazine based bridging unit, 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine, L. The detailed spectroelectrochemical aspects of the complexes have been studied in order to understand the role of the bridging units towards the intermetallic electronic coupling in the dinuclear complexes.     

Synthesis and characterization of a reduced heteropoly-tungstovanadate: (NH4)7[VvO4W 10IV V 2IV O36].ca. 22H2O

The compound (NH₄)₇[ V^vO₄W ₁₀ ^VI V ₂ ^VI O₃₆]·ca.22H₂O (1) has been synthesized from an aqueous ammonium acetate buffer (pH 4) containing sodium vanadate, sodium rungstate_and sodium dithionite. Compound (1) crystallizes in a cubic space groupFm — 3, witha = 22.2001(6) ? and Z = 8. The anion [V^vO₄W ₁₀ ^VI V ₂ ^IV O₃₆]^7- is a typical Keggin type structure with V^VO₄ as the central tetrahedron. (1) has further been characterized by elemental analyses, redox titration, IR, EPR, and electronic spectroscopy and room temperature magnetic moment measurement.