First Organic–Inorganic Hybrid Compounds Formed by Ge-V-O Clusters and Transition Metal Complexes of Aromatic Organic Ligands

Three compounds based on Ge-V-O clusters were hydrothermally synthesized and characterized by IR, UV-Vis, XRD, ESR, elemental analysis and X-ray crystal structural analysis. Both [Cd(phen)(en)]2[Cd2(phen)2V12O40Ge8(OH)8(H2O)]∙12.5H2O (1) and [Cd(DETA)]2[Cd(DETA)2]0.5[Cd2(phen)2V12O41Ge8(OH)7(0.5H2O)]∙7.5H2O (2) (1,10-phen = 1,10-phenanthroline, en = ethylenediamine, DETA = diethylenetriamine) are the first Ge-V-O cluster compounds containing aromatic organic ligands. Compound 1 is the first dimer of Ge-V-O clusters, which is linked by a double bridge of two [Cd(phen)(en)]2+. Compound 2 exhibits an unprecedented 1-D chain structure formed by Ge-V-O clusters and [Cd2(DETA)2]4+ transition metal complexes (TMCs). [Cd(en)3]{[Cd(η2-en)2]3[Cd(η2-en)(η2-μ2-en)(η2-en)Cd][Ge6V15O48(H2O)]}∙5.5H2O (3) is a novel 3-D structure which is constructed from [Ge6V15O48(H2O)]12− and four different types of TMCs. We also synthesized [Zn2(enMe)3][Zn(enMe)]2[Zn(enMe)2(H2O)]2[Ge6V15O48(H2O)]∙3H2O (4) and [Cd(en)2]2{H8[Cd(en)]2Ge8V12O48(H2O)}∙6H2O (5) (enMe = 1,2-propanediamine), which have been reported previously. In addition, the catalytic properties of these five compounds for styrene epoxidation have been assessed.

Three Si-substituted polyoxovanadates as efficient catalysts for Knoevenagel condensation and selective oxidation of styrene to benzaldehyde

Three new Si-substituted polyoxovanadates (POVs), [Cd₂(dien)₂][Cd(dien)][Cd(Hdien)₂][V₁₅Si₆O₄₆(OH)₂(H₂O)]·7H₂O (1), [Co(enMe)₂]₃[Co₂(enMe)₂(H₂O)₂][V₁₆Si₄O₄₄(OH)₂(H₂O)]·6H₂O (2), and [Co(teta)]₄[V₁₆Si₄O₄₂(OH)₄(H₂O)]·10H₂O (3) (dien = diethylenetriamine; enMe = 1,2-diaminopropane; teta = triethylenetetramine) were synthesized by the hydrothermal method and characterized. Structural analysis sheds light on the fact that the {V₁₅Si₆O₄₈}/{V₁₆Si₄O₄₆} clusters of compounds 1-3 were formed by replacing {VO₅} square pyramids in the classical {V₁₈O₄₂} cluster with {Si₂O₇} units. Compound 1 is a 2D bilayer structure formed by the [V₁₅Si₆O₄₆(OH)₂(H₂O)]^10- cluster and two types of bridging Cd complexes containing binuclear groups [Cd₂(dien)₂]⁴⁺. Compound 2 is a 3D framework constructed from the [V₁₆Si₄O₄₄(OH)₂(H₂O)]^10- cluster and two types of Co complex fragments including binuclear [Co₂(enMe)₂(H₂O)₂]⁴⁺. In compound 3, the [V₁₆Si₄O₄₂(OH)₄(H₂O)]^8- cluster is connected with bridging [Co(teta)]²⁺ to expand into a 2D network. Compounds 1 and 3 represent the first 2D assemblies based on a vanadosilicate cluster. 1-3 served as heterogeneous catalysts and exhibited highly efficient catalytic activities for the Knoevenagel condensation under mild ambient conditions with low catalyst loading, featuring the open Lewis base {V₁₅Si₆O₄₈}/{V₁₆Si₄O₄₆} sites and Lewis acid Cd²⁺/Co²⁺ sites. The conversion of benzaldehyde was up to 99.3% in 80 min at room temperature using 1 as a heterogeneous catalyst with only 0.37% catalyst loading. Moreover, compounds 1-3 as catalysts for selective oxidation of styrene to benzaldehyde exhibited excellent catalytic performance, high selectivity and could be readily recycled. Most strikingly, compound 1 showed excellent catalytic performance with 97.6% conversion of styrene and 100% selectivity of benzaldehyde in 15 min. In addition, the catalytic activity of catalyst 1 was well maintained after five cycling reactions.

Vanadoborates: cluster-based architectures, preparation and properties

The different connections of [VO_x] (x = 4, 5, 6) and [AO_x] (A = B, x = 3, 4; A = P, x = 4) polyhedral units ultimately result in a fascinating variety of vanadoborate anionic clusters.

A Bicadmium-Substituted Polyoxometalate Network Based on a Vanadosilicate Cluster for the Selective Oxidation of Styrene to Benzaldehyde

A new bicadmium-substituted vanadosilicate, [Cd(en)₂]₂[(en)₂Cd₂Si₈V₁₂O₄₀(OH)₈(H₂O)_0.5]·5H₂O (1; en = ethylenediamine), had been hydrothermally synthesized and characterized. Structural analysis revealed that the kind of new [(en)₂Cd₂Si₈V₁₂O₄₀(OH)₈(H₂O)_0.5]^4- polyoxoanionic cluster was derived from the classical {V₁₈O₄₂} cluster by replacing six {VO₅} square pyramids with four {Si₂O₇} and two [Cd(en)]²⁺ groups. Notably, such mixed substitution of both main-group and transition metals in polyoxovanadates is much less developed. Furthermore, compound 1 displays efficient catalytic activity toward the selective oxidation of styrene to benzaldehyde with a conversion of 97% and a selectivity of 87% in 8 h.

Ordnung muss sein: heteroelement order and disorder in polyoxovanadates

Three new mixed antimonato–germanato polyoxovanadates exhibit different degrees of order of their unique crystallographic heterometal atom positions.

An unprecedented antimonato-polyoxovanadate (SbPOV) based on both α-[V14Sb8O42]4− and β-[V14Sb8O42]4− isomers

An unprecedented antimonato-polyoxovanadate (SbPOV) based on both α-[V₁₄Sb₈O₄₂]⁴⁻ and β-[V₁₄Sb₈O₄₂]⁴⁻ isomers has been synthesized.

Catalysis of "outer-phase" oxygen atom exchange reactions by encapsulated "inner-phase" water in {V15Sb6}-type polyoxovanadates

Antimonato polyoxovanadate (POV) cluster compounds {M(en)3}3[V15Sb6O42(H2O) x ]·nH2O (M = FeII, CoII, NiII and x = 0 or 1) obtained under solvothermal conditions exhibit unusual high water solubility making these compounds promising synthons for generation of new POV structure types. Electrospray ionization mass spectrometry provides evidence (i) for a water molecule encapsulated inside the cavity of a fraction of the spherical cluster shells, (ii) for a post-functionalization in water, namely a slow exchange of VO against Sb2O, (iii) for the inner-phase reactivity of the encapsulated water that is capable of opening an oxo-bridge, and (iv) for a significant acceleration of the 16O/18O exchange reactions of oxygen atoms in the cluster periphery with surrounding H218O, when encapsulated water is present. To the best of our knowledge, this is the first example in polyoxovanadate chemistry for the transduction of inner-phase reactivity of an encapsulated guest molecule into changes in the outer-phase reactivity of the cluster. Magnetic susceptibility measurements reflect the individual contributions of the frustrated {V15} spin polytope and the {M(en)3}2+ complexes, with very weak coupling between these groups.

Coordination and supramolecular assembly of {Cd2Ge8V12O48} building block and cucurbit[6] to form rotaxane-shaped hybrids

Assembly of cucurbit[6] and a {Cd2Ge8V12O48} cluster produced two rotaxane-shaped and polyrotaxane-shaped solids by changing the ratio of starting precursors in the system. The high oxygen density of the polyoxoanion surface provides active sites to extend a single rotaxane-shaped hybrid 1 to a 1D polyrotaxane-shaped hybrid 2. This construction strategy may afford an entirely new methodology for polyoxometalate-based hybrid chemistry.

Supramolecular hexagonal nano tubes assembled by vanadium diamine complexes with thiogermanates

A supramolecular hexagonal nano tube is characterized, which is assembled by oxo-vanadium thiogermanate in a sulfur–diamine reduction system.

A rare polyniobotungstate-based framework and its structural transformation in a single-crystal-to-single-crystal process induced by iodide ions

A rare polyniobotungstate-based framework constructed from Lindqvist [Nb₃W₃O₁₉]⁵⁻ polyanions and mixed-valent copper ions has been made, which can undergo a solid–liquid reaction with KI solution to form a copper halide via a single-crystal-to-single-crystal process.

Design and synthesis of purely inorganic 3D frameworks composed of reduced vanadium clusters and manganese linkers

Two purely inorganic three-dimensional (3D) frameworks [Mn4(H2O)11V(IV)(18)O42(PO4)](7-) (1) and [Mn2(H2O)7V(IV)(18)O42(PO4)](11-) (2) were synthesized under hydrothermal conditions and fully characterized by single-crystal X-ray structural analysis, IR spectroscopy, thermogravimetric analysis and PXRD. Structural analysis revealed that these two compounds contained a similar all reduced polyoxoanion [V(IV)(18)O42(PO4)](15-) linked by different amounts of manganese centers to form 3D framework materials. The V centers in these two compounds were all reduced to the +IV oxidation state, resulting in an all reduced polyoxoanion, which was firstly used as the building block for constructing 3D framework materials. The all reduced typical polyoxoanion [V(IV)(18)O42(PO4)](15-) with 15 negative charges supplied enough charge amount to accept TM cations. In these two structures, the anions were surrounded by 12 and 5 Mn(2+) ions, respectively, adjusted by varying the feeding amount of MnCl2·4H2O. An electrocatalytic study revealed that compound 1 exhibits electrocatalytic activity for reduction of H2O2.

Semimetal-functionalised polyoxovanadates

Polyoxovanadates (POVs), known for their wide applicability and relevance in chemical, physical and biological sciences, are a subclass of polyoxometalates and usually self-assemble in aqueous-phase, pH-controlled condensation reactions. Archetypical POVs such as the robust [VO42](12-) polyoxoanion can be structurally, electronically and magnetically altered by heavier group 14 and 15 elements to afford Si-, Ge-, As- or Sb-decorated POV structures (heteroPOVs). These main-group semimetals introduce specific chemically engineered functionalities which cause the generally hydrophilic heteroPOV compounds to exhibit interesting reactivity towards organic molecules, late transition metal and lanthanoid ions. The fully-oxidised (V(V)), mixed-valent (V(V)/V(IV) and V(IV)/V(III)), "fully-reduced" (V(IV)) and "highly-reduced" (V(III)) heteroPOVs possess a number of intriguing properties, ranging from catalytic to molecular magnet characteristics. Herein, we review key developments in the synthetic and structural chemistry as well as the reactivity of POVs functionalised with Si-, Ge-, As- or Sb-based heterogroups.

Two tetra-Cd(II)-substituted vanadogermanate frameworks

Two new tetra-Cd(II)-substituted vanadogermanate frameworks {(CdX)4Ge8V(IV)10O46(H2O)[V(III)(H2O)2]4(GeO2)4}·8H2O (X = ethylenediamine (en, 1) and 1,2-diaminopropane (dap, 2)) were hydrothermally prepared and characterized by IR spectra, elemental analysis, powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. Both are isomorphic, and their 3-D frameworks are made up of tetra-Cd(II)-substituted {(CdX)4Ge8V(IV)10O46(H2O)}(12-) fundamental building units interconnected through planar tetra-V(III) [V(III)4O2(H2O)8](8-) clusters and tetrahedral GeO4 bridges. In the unique {(CdX)4Ge8V(IV)10O46(H2O)}(12-) cage, four [Ge2O7] dimers and four CdO4N2 trigonal prisms are alternately concatenated by μ3-O bridges to create a round {Ge8Cd4O28(X)4}(16-) fragment, five VO5 groups are linked by sharing edges to generate a pentanuclear [V5O17] subunit, and then the {Ge8Cd4O28(X)4}(16-) fragment is sandwiched by two V5O17 subunits via sharing O-atoms producing a D4h-symmetric {(CdX)4Ge8V(IV)10O46(H2O)}(12-) cage with a free water molecule located at the center. As we know, both display unprecedented 3-D organic-inorganic hybrid frameworks built up from the largest number of transition-metal-substituted vanadogermanate {(CdX)4Ge8V(IV)10O46}(12-) cluster shells linked by both GeO4 tetrahedra and rare [V(III)4O2(H2O)8](8-) clusters. Magnetic measurements reveal the antiferromagnetic couplings within the magnetic vanadium centers.

From 1D to 3D single-crystal-to-single-crystal structural transformations based on linear polyanion [Mn4(H2O)18WZnMn2(H2O)2(ZnW9O34)2]4-

A 1D anionic polyoxometalate, [Mn(4)(H(2)O)(18)WZnMn(2)(H(2)O)(2)(ZnW(9)O(34))(2)](4-), undergoes 1D to 3D single-crystal-to-single-crystal structural transformations that are induced by transition-metal cations (Co(2+) and Cu(2+)) and solvent molecules. These solid materials present interesting catalytic activity for the oxidative aromatization of Hantzsch 1,4-dihydropyridines that is dependent on the inserted heterogeneous metal cations.