Syntheses, structures and properties of 3D inorganic-organic hybrid frameworks constructed from lanthanide polymer and Keggin-type tungstosilicate

Inorganic-organic hybrid frameworks, namely [Ce(H₂O)₃(pdc)]₄[SiW₁₂O₄₀]·6H₂O 1, [M(H₂O)₄(pdc)]₄[SiW₁₂O₄₀]·2H₂O (M=Ce for 2a, La for 2b, Nd for 2c; H₂pdc=pyridine-2,6-dicarboxylic acid) were assembled through incorporation of Keggin-type heteropolyanion [SiW₁₂O₄₀]⁴⁻ within the voids of lanthanides-pdc network as pillars or guests under hydrothermal condition. Single-crystal X-ray analyses of these crystals reveal that compound 1 presents 3D pillar-layered framework with the [SiW₁₂O₄₀]⁴⁻ anions located on the square voids of the two-dimensional Ce-pdc bilayer. Compounds 2a-c are isostructural and constructed from 3D Ln-pdc-based metal-organic framework (MOF) incorporating noncoordinating guests Keggin structure [SiW₁₂O₄₀]⁴⁻. Solid-state properties of compounds 1 and 2a-c such as thermal stability and photoluminescence have been further investigated.     

Polyoxometalate immobilization in Cu/Ag-pz porous coordination polymers: The influences of them on the structural properties of frameworks

Three new high dimensional Cu^I/Ag-pz porous coordination polymers (PCPs) with different Keggin polyoxometalate templates have been hydrothermally synthesized: [Cu^I₅(pz)₆Cl][HPMo^VI₁₀Mo^V₂O₄₀] (1) [Ag₅(pz)₇(BW₁₂O₄₀)] (2) and [Cu^I₅(pz)₆H(H₂W₁₂O₄₀)]·4H₂O (3) (pz=pyrazine). The choice of the particular Keggin POM templates is shown to influence the structural properties of the Cu/Ag PCPs. Compound 1 shows a Cl-bridged Cu-pz-Cl double layer, between which two kinds of [HPMo^VI₁₀Mo^V₂O₄₀]⁴⁻(PMo₁₂) polyanions are located. Compound 2 presents a 3D Ag-pz framework with parallelogram-like voids, into which BW₁₂O₄₀⁵⁻ (BW₁₂) Keggin ions are incorporated. Compound 3 contains a Cu-pz cationic layer framework, between which are located [H(H₂W₁₂O₄₀)]⁵⁻ (W₁₂) Keggin ions. Primary photocatalytic experiment indicates that compound 1 presents excellent photocatalytic activity. The photoluminescence properties and electrochemistry properties of the compounds are also discussed.     

Facile preparation of an α-Keggin-type [H3W12O40] complex: Does it exist in aqueous solution?

The formation processes of α-Keggin-type [H₂W₁₂O₄₀]⁶⁻ and [H₃W₁₂O₄₀]⁵⁻ complexes were investigated in aqueous W^VI (0.05–0.50 M) solutions. The formation of [H₂W₁₂O₄₀]⁶⁻ was ascertained by the appearance of a ¹⁸³W NMR line at −117 ppm, but no evidence was found for the existence of [H₃W₁₂O₄₀]⁵⁻ in the solution at the accessible pH range. The addition of (CH₃)₄N⁺ (Me₄N⁺) to the W^VI solution directly precipitated the (Me₄N)₆[H₂W₁₂O₄₀] salt. On the other hand, the addition of the larger Bu₄N⁺ cation precipitates the (Bu₄N)_4.5H_0.5[H₃W₁₂O₄₀] salt, because a naked proton formed during the crystallization process or in the solid state may enter into the Keggin shell to produce [H₃W₁₂O₄₀]⁵⁻. This explanation is based on the fact that [H₂W₁₂O₄₀]⁶⁻ is not spontaneously converted into [H₃W₁₂O₄₀]⁵⁻ in acidified aqueous solution. On the basis of their voltammetric properties, a simple diagnostic criterion was developed to distinguish between [H₂W₁₂O₄₀]⁶⁻ and [H₃W₁₂O₄₀]⁵⁻.     

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.     

Synthesis and characterization of two novel organic–inorganic hybrid solids from Keggin ions and metal coordination complexes

Two new hybrid compounds, [Co(4,4′-bpy)₂(H₂O)₄][(4,4′-bpyH₂]₂[CoW₁₂O₄₀]·8H₂O (1) and [Fe(2,2′-bpy)₃]₃[H₂W₁₂O₄₀]·6H₂O (2), (4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine) have been hydrothermally synthesized. These solids were characterized by elemental analysis, thermogravimetric analysis, UV–Vis spectroscopy and X-ray diffraction. The hydrogen-bonding interactions in 1 lead to the formation of a three dimensional network consisting of [CoW₁₂O₄₀]⁶⁻ anionic clusters, [Co(4,4′-bpy)₂(H₂O)₄]²⁺ cations and lattice water molecules, while the discrete Keggin ion [H₂W₁₂O₄₀]⁶⁻ in compound 2 is surrounded by 14 [Fe(2,2′-bpy)₃]²⁺ complexes through CH?O interactions (2.24–2.56 Å).     

Influence of metal ions on the structures of Keggin polyoxometalate-based solids: Hydrothermal syntheses, crystal structures and magnetic properties

Three new Keggin polyoxometalate (POM)-based compounds linked to 3d metal complexes have been synthesized under hydrothermal conditions: [Cu(phen)₂]₂{[Cu(phen)]₂ [SiMo₁₂O₄₀(VO)₂]} (1), {[Zn(phen)₂]₂[GeMo₁₂O₄₀(VO)₂]}{[Zn(phen)₂(H₂O)]₂ [GeMo₁₂O₄₀(VO)₂]}·3H₂O (2) and {[Co(phen)₂]₂[PMo₁₂O₄₀(VO)₂]}{[Co(phen)₂(OH)]₂ [PMo₁₂O₄₀(VO)₂]}·2.5H₂O (3) (phen=1,10-phenanthroline). These three compounds present, as building blocks, the bicapped Keggin anions [XMo₁₂O₄₀(VO)₂] (X=Si, Ge and P). Compound 1 consists of a bicapped Keggin anion [SiMo₁₂O₄₀(VO)₂]²⁻ linked to two [Cu(phen)]⁺ complexes with two [Cu(phen)₂]⁺ countercations. Compound 2 contains two bicapped Keggin anions [GeMo₁₂O₄₀(VO)₂]⁴⁻, one linked to two [Zn(phen)₂(H₂O)]²⁺ cations and the other one linked to two [Zn(phen)₂]²⁺ cations. Compound 3 is a two-dimensional POM-based square network formed by bicapped Keggin anions [PMo₁₂O₄₀(VO)₂]⁴⁻ connected by [Co(phen)₂]²⁺ cations. Discrete bicapped Keggin anions [PMo₁₂O₄₀(VO)₂] linked to two [Co(phen)₂(OH)]⁺ cations are located between the layers. The magnetic properties show the presence of antiferromagnetic interactions among the reduced Mo(V) atoms (in the three compounds) plus a paramagnetic contribution from the V(IV) atoms (in 1 and 2). Compound 3 shows, in addition, an antiferromagnetic interaction between the Co(II) and the V(IV) ions directly linked through an oxygen bridge. The low-temperature ESR spectra of compound 3 confirm the presence of the reduced Mo(V) ions and the antiferromagnetic coupling between the Co(II) and the V(IV) ions.     

Two one-dimensional mono-substituted heteropolytungstates based on Keggin anion units

Two kinds of complexes [Ni(DETA)₂]₃[SiNiW₁₁O₃₉]·2.5H₂O (DETA=diethylenetriamine) (1) and [H₂en]₂[Ba_0.15(H₂O)₂(Hen₂)]H_1.7[SiNaW₁₁O₃₉]·2H₂O (2) were obtained from the hydrothermal reaction and characterized by single crystal X-ray diffraction analysis and IR spectra. Crystal data: C₂₄H₈₃N₁₈Ni₄O_41.5SiW₁₁ (1), monoclinic, Pn, a=10.926(2) Å, b=23.022(5) Å, c=13.221(3) Å, β=94.27(3)°, V=3316.4(11) Å³, Z=2; C₈H_46.7N₈Ba_0.15NaO₄₃SiW₁₁ (2), monoclinic, P2₁, a=12.840(3) Å, b=11.174(2) Å, c=16.693(3) Å, β=91.14(3)°, V=2394.4(8) Å³, Z=2. Both of them consists of one mono-substituted Keggin unit [SiMW₁₁O₃₉]⁽⁸⁻ⁿ⁾⁻ (MNi, Na, n=2, 1) obtained by metal atom substituting for a W atom from the plenary anion [SiW₁₂O₄₀]⁴⁻. This unit then connects with other adjacent units via M-O-W bridges constructing an infinitely one-dimensional chain-like structure in which the metal cation and polyanion alternate. Moreover, both of Ni or Na atoms are in a distorted octahedral environment with six oxygen atoms and occupy one position in the oxometalate shell of the Keggin structure.     

Peroxide derivatives of heteropoly compounds with Keggin anions [PW<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>3−</Superscript> and [SiW<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>4−</Superscript>: Synthesis and structure

Peroxide derivatives of heteropoly compounds with Keggin anions [PW₁₂O₄₀]^3? and [SiW₁₂O₄₀]^4? are isolated in an individual state from concentrated hydrogen peroxide solutions and characterized by physicochemical methods. The structure of Ba₂[SiW₁₂O₄₀] · 4H₂O₂ · 11H₂O (I) is solved by X-ray crystallography. Crystals of compound I (H₃₀Ba₂O₅₉Si₁W₁₂, FW = 3483.21) are monoclinic, space group C2/c, a = 24.981(2) Å, b = 12.2103(11) Å, c = 18.7142(17) Å, β = 122.620(2)^o, V = 4808.0(8) ų, Z = 4. The structure contains Keggin anions [SiW₁₂O₄₀]^4?; all hydrogen peroxide molecules are coordinated to Ba²⁺ cations.     

Assembly of a Supramolecular Architecture Based on Keggin POMs and Lanthanide Coordination Cations

Two new compounds based on Keggin polyoxometalates (POMs) [SiW₁₂O₄₀]⁴⁻ (SiW₁₂), [Na(H₂O)₃(H₂L)SiW₁₂O₄₀](H₂L)₂   6H₂O (1), and [Ce(H₂O)₃(HL)₂(H₂L)]₂[SiW₁₂O₄₀]₂ 10H₂O (2) (HL = C₆H₅NO₂ = isonicotinic acid), have been conventionally synthesized and characterized by routine methods. Compound 1 possesses a 1D right-handed helical structure constructed by SiW₁₂O₄₀ ⁴⁻ {SiW₁₂} and [Na(H₂O)₃(HL)] complexes. Interestingly, these right-handed helical chains are linked together via H-bonds forming a novel chiral layer. By using the similar synthesis method to that for compound 1, except for employing Ce³⁺ cations in instead of La³⁺ cations, a 3D supramolecular compound 2 based on SiW₁₂ and Ce³⁺ coordination cations has been obtained, which contains 1D channels along a axis. Additionally, the luminescence properties of 2 were studied. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Two new organic-inorganic hybrid compounds based on metal-pyrazine coordination polymers and Keggin polyoxometalates: effect of metal ions on thestructure

Through changing the metal ions, two Keggin polyoxometalates-based hybrid compounds, [Cu₅(pz)₆(Cl)(SiW₁₂O₄₀)] (1) and [Ag₄(pz)₃(H₂O)₂(SiW₁₂O₄₀)] (2) (pz=pyrazine), were hydrothermally synthesized and characterized by an elemental analysis, IR spectroscopy, thermogravimetric analyses, and single X-ray diffraction. In compound 1, the metal-organic motif exhibits a 6³ topological 2-D sheet, which is further fused by the [SiW₁₂O₄₀]⁴⁻ anions to construct a (6·7·8)(6³·7·8²)(6³)(6⁵·7)(6⁵·8) topological 3D structure. In compound 2, the bridging groups Ag₂(pz) connect the [SiW₁₂O₄₀]⁴⁻ anions to form a (5³)₂(5⁴·8²) topological 2-D layer, which is further linked by an [Ag(pz)]_nⁿ⁺ chains to construct a 3D structure with the (3⁴·4¹⁶·5²⁴·6¹²·7⁸·8²)(3⁴·4⁶·5⁴·6)₂(4·5²)₂ topology. It represents the highest connected network topology presently known for the polyoxometalates system. The structure differences of compounds 1 and 2 reveal that the coordination numbers and geometries of the metal ions have a great influence on the final structure and topology of the Keggin POMs-based hybrid compounds. In addition, the electrochemistry properties of the two compounds have been studied.     

Synthesis,properties and photochromism of novel charge transfer compounds with Keggin anions and protonated 2,2′-biquinoline

Several novel compounds with protonated 2,2′-biquinoline (biqui) and Keggin polyoxoanions (α-isomers), having the general formula (Hbiqui)_m[XM₁₂O₄₀]·nsolv, X=P (m=3), Si (m=4); M=Mo, W; n=0, 3; solv=H₂O, N,N-dimethylformamide (dmf), were synthesized and characterized by analytical, spectroscopic and X-ray diffraction techniques. Electronic spectroscopy (visible/UV) indicated the presence of intermolecular charge transfer between the organic and inorganic moieties in the solid state. Evidence for the existence of intermolecular electronic interaction in solution was found for compounds with the [SiW₁₂O₄₀]⁴⁻ anion, a fact quite uncommon for charge transfer compounds based on Keggin anions. A single crystal X-ray diffraction study could be performed on (Hbiqui)₄[SiW₁₂O₄₀]·3dmf crystals, but the refinements revealed the presence of highly disordered 2,2′-biquinoline molecules and α-[SiW₁₂O₄₀]⁴⁻ anions. Photosensitivity to sunlight and to W-lamp visible light was assessed for all compounds. Photochromic properties were found for solids with [XMo₁₂O₄₀]^m− Keggin anions. Reduction of these anions upon irradiation was observed by diffuse reflectance and EPR spectroscopy. After a minimum of 5 h under sunlight, the extent of anion reduction followed the order (Hbiqui)₃[PMo₁₂O₄₀]·3dmf>(Hbiqui)₄[SiMo₁₂O₄₀]·3dmf>(Hbiqui)₃[PMo₁₂O₄₀]>(Hbiqui)₄[SiMo₁₂O₄₀]·4H₂O. The Kurtz powder test was used to evaluate the second-order non-linear optical properties of the prepared compounds. (Hbiqui)₄[SiW₁₂O₄₀]·3H₂O originated a second harmonic generation signal with intensity about 15% that of urea for 1064 nm radiation.     

pH-controlled assembly of two new supramolecular hybrid compounds based on Keggin polyoxotungstates

Two supramolecular compounds based on Keggin polyoxotungstates, (4,4′-H₂bpy){[Cu(4,4′-bpy)]₂[SiW₁₂O₄₀]} (1) and (4,4′-H₂bpy)₂[SiW₁₂O₄₀]·2H₂O (2) have been synthesized and characterized by elemental analyses, IR, UV, XPS spectra, TG analyses, and single crystal X-ray diffraction analyses. Compound 1 exhibits an infinite 1-D ladder like structure, which is further interconnected into a 3-D supramolecular framework via hydrogen bonding interactions. Compound 2 contains 4,4′-bipyridine (4,4′-bpy), pseudo-Keggin polyoxoanions [SiW₁₂O₄₀]^4?, and water molecules. Polyoxoanions together with water molecules in 2 construct a 3-D inorganic supramolecular network through O···O and O···Ow(1) interactions. The electrochemical behaviors and photocatalytic properties of 1 and 2 have been investigated.     

Structure and characterization of zero- to two-dimensional compounds built up of the sandwich-type clusters and transition-metal linkers

Five new heteropolyoxotungstates K₂Na₂Mn₂(H₂O)₁₂[Mn₂(H₂O)₁₀Mn₄(H₂O)₂(XW₉O₃₄)₂]·18H₂O (X=Ge, 1; X=Si, 2), Na₄[Mn₄(H₂O)₁₈Mn₄(H₂O)₂(XW₉O₃₄)₂]·22H₂O (X=Ge, 3; X=Si, 4) and K₃Na₅[Mn₂(H₂O)₆Mn₄(H₂O)₂(SiW₉O₃₄)₂]·23.5H₂O (5) have been obtained by the routine synthetic reactions in aqueous solution. In 1 and 2, two isolated Mn²⁺ ions are covalently linked to the sandwich-type polyoxoanions [Mn₄(H₂O)₂(B-α-XW₉O₃₄)₂]¹²⁻ (X=Ge or Si) by two μ₂-oxygen atoms resulting in the disupporting sandwich-type polyoxometalates (POMs). Compounds 3 and 4 are built from the disupporting sandwich-type polyoxoanions 1 and 2, linked by additional four Mn²⁺ ions to construct a 1D ladder-like chain-like structure, which is rarely observed in the POM chemistry. Compound 5 represents the first example of the 2D structure consisting of the sandwich-type polyoxoanion [Mn₄(H₂O)₂(SiW₉O₃₄)₂]¹²⁻ and the binuclear {Mn₂(H₂O)₆}⁴⁺ group. The magnetic studies of compounds 1, 4 and 5 indicate that the antiferromagnetic interactions are predominant in the three compounds between Mn(II) metal ions.     

Ligation of the quinolone antibacterial agent pipemidic acid to Keggin polyoxotungstates

Three new drug molecules modifying Keggin polyoxometallate compounds have been synthesized under hydrothermal conditions and structurally characterized by routine techniques. Single-crystal X-ray diffraction analysis shows that compound 1 is constructed by a Keggin cluster and two [Cu(PPA)₂] drug complexes, formulated as [Cu(PPA)₂]₂·[PW₁₂O₄₀]·6H₂O. Compound 2 consists of a Cd substituted Keggin cluster [PW₁₁CdO₃₉] and five isolated HPPA drug molecules, formulated as [HPPA]₅·[PW₁₁CdO₃₉]·2H₂O. Compound 3 consists of a full oxidised Keggin [PW₁₂O₄₀] cluster and three isolated HPPA drug molecules, formulated as [HPPA]₃·[PW₁₂O₄₀]·2H₂O. Additionally, the antitumor activity of the three new compounds and their parent components in vitro were studied by a MTT experiment. The results show that introduction of TM-PPA/PPA into the polyoxoanion surface could increase their antitumor activity and make the compounds penetrate into the cells easily. Furthermore, the antitumor activity of the compounds can be modulated by their different structures.     

One-dimensional polyoxometalate polymer constructed from V–W cluster by using asymmetrical bipyridine ligand

The asymmetrical organic molecule 2,4′-bipyridine (bpy) is explored to assemble polyoxometalate into a one-dimensional hybrid and compound [Cu^I(bpy)₂]₃[Cu^I₃(bpy)₄][V^VW^VI₉W^V₃O₄₀] (1) is achieved. Compound 1 represents a V-centered Keggin [V^VW^VI₉W^V₃O₄₀]⁶⁻ cluster bonded together by incorporating secondary metal coordination group of Cu–bpy. The thermogravimetric analysis of 1 has also been researched.     

Synthesis and characterization of one- to three-dimensional compounds composed of paradodecatungstate-B cluster and transition metals as linkers

Three new extended frameworks built from paratungstate and transition metals have been synthesized and characterized. In the compound Na₈[{Cd (H₂O)₂}(H₂W₁₂O₄₂)]·32H₂O (1), two neighboring paratungstate-B ions [H₂W₁₂O₄₂]¹⁰⁻ are linked by [Cd(H₂O)₂]²⁺ units, leading to the formation of infinite one-dimensional (1D) anion chain [{Cd(H₂O)₂}(H₂W₁₂O₄₂)]_n⁸ⁿ⁻. The anion [{Co(H₂O)₃}{Co(H₂O)₄}(H₂W₁₂O₄₂)]_n⁶ⁿ⁻ of the compound Na₆[{Co(H₂O)₃}{Co(H₂O)₄}(H₂W₁₂O₄₂)]·29H₂O (2) shows a layer-like (2D) structure in which paratungstate-B units are linked by CoO₆ octahedra, while the anion [{Co(H₂O)₃}₃(H₂W₁₂O₄₂)]_n⁴ⁿ⁻ of the compound (H₃O⁺)₃[{Na(H₂O)₄}{Co(H₂O)₄}₃(H₂W₁₂O₄₂)]·24.5H₂O (3) is a three-dimensional (3D) anionic polymer that consists of paratungstate-B units linked by CoO₆ octahedra. Compound 3 can reversibly adsorb and desorb water molecules leading to the color reversibly change from pink to violet. The preliminary magnetic measurement and electrochemical properties of compounds are performed. The crystal structure of unexpected product Na₄[NiW₆O₂₄H₆]·13H₂O (4) is described here for the rare report of crystal structure information on the Anderson-type polyoxotungstate which has nickel as a heteroatom.     

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.     

New 3D two-fold interpenetrating polyoxometallate compounds built up of dititanium-substituted Keggin polyoxotungstates and transition metals

The unprecedented transition metals (TMs) bridged 1,4-dititanium(IV)-substituted Keggin-type polyoxotungstates K₃{M(H₂O)₄}₂PTi₂W₁₀O₄₀ · 8H₂O (M = Co^II (1), Ni^II (2), Mn^II (3)) have been synthesized and characterized by FT-IR, UV, element analyses, X-ray powder diffraction analyses,¹⁸³W NMR spectroscopy, cyclic voltammetry, TG and X-ray single-crystal analyses. It is the first time that Ti-containing polyoxotungstate [α-PTi₂W₁₀O₄₀]⁷⁻ fragments are linked by TMs based on novel Ti–O–M bonds, and it is the first example of a three-dimensional (3D) two-fold interpenetrating pure inorganic framework structure based on Keggin polyoxometallates and TMs.     

Structural stability index of heteropoly- and isopolyanions—IV. Application to site-vacant Keggin polyanions,mixed-type Keggin polyanions,some molybdo- and tungsto-vanadates and Jeannin-type polyanion

The theory of structural stability, being based on the number of closed loops per MO₆ octahedral unit in the polyanion-cage, has been applied to a variety of heteropoly- and isopoly-compounds with previously unreported structures. The discussion includes the prediction of the structure of lacunary Keggin heteropoly-compound, Cs₇Na₂[PW₁₀O₃₇]·8H₂O, recently obtained by Knoth and Harlow, the reinvestigation of mixed-type Keggin polyanions, [SiW₉Co₃(H₂O)₃O₃₇]^10? and [SiW₁₁CoO₃₉]^6?, recently prepared by Pope's group, the interpretation of chemical behaviours of some molybdo- and tungsto-vanadates, the structural stabilities of Jeannin-type [As₂W₂₁O₆₉(H₂O)]^6? polyanion and its related compounds, and some remarks on Weakley-type [X(W₅O₁₈)₂]^n? polyanions and Flynn-Stucky-type [X(Nb₆O₁₉)₂]^n? complexes belonging to the hybrid-complex of polyanion.     

Two new hybrid compounds assembled from Keggin-type polyoxometalates and transition metal coordination complexes

Two new hybrid compounds based on Keggin-type polyoxometalates: {[PMo₁₂O₄₀][Ni(Phen)₂(H₂O)]₂}·K·2OH⁻ (1) and [Cd₂(Phen)₄Cl₂][HPW₁₂O₄₀]·H₂O (2) (Phen=1,10-phenanthroline), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Compound 1 exhibits a 1-D chain structure constructed from Pseudo-Keggin polyoxometalate bi-supported transition metal coordination complexes linked by K⁺ ions. Compound 2 contains Pseudo-Keggin polyoxoanions [HPW₁₂O₄₀]²⁻ and novel metal-chloride-ligand coordination complexes [Cd₂(Phen)₄Cl₂]²⁺.