1:14 Heteropolyvanadate of phosphorus: preparation and structure

Crystal-to-crystal polymerisation of monosubstituted [PW11O39Cu(H2O)]5- Keggin-type anions

The reaction between neutral bis(picolinate)copper(II) complexes and copper(II)-monosubstituted Keggin-type phosphotungstate anions formed in situ leads to the formation of the hybrid [C(NH2)3]10[{PW11O39Cu(H2O)}2{Cu(pic)2}]·10H2O compound (1, pic = picolinate) in the presence of structure-directing guanidinium cations. Single-crystal X-ray diffraction studies demonstrate that 1 contains dimeric {PW11O39Cu(H2O)}2{Cu(pic)2} molecular species constituted by two Keggin-type anions linked by one {Cu(pic)2} octahedral complex through axial coordination to their terminal oxygen atoms. The extensive hydrogen-bonding network established by guanidium cations and Keggin clusters plays a key role in retaining the crystallinity of the system throughout dehydration to allow a single-crystal-to-single-crystal (SCSC) transformation into the anhydrous [C(NH2)3]10[{PW11O39Cu}2{Cu(pic)2}] (2a) at 170 °C. Structural modifications involve the re-orientation, shifting in ca. 1.5 Å and condensation of all the {PW11O39Cu} units to result in {PW11O39Cu}n chains in an unprecedented solid-state polymerisation. This phase transition also implies the cleavage of Cu-O bonds induced by the rotation and translation of Keggin-type anions, in such a way that hybrid dimeric units in 1 are dismantled and {Cu(pic)2} complexes become square planar. The irreversibility of the phase transition has been confirmed by combined thermal and diffractometric analyses, which evidence that the anhydrous phase adsorbs only one water molecule per cluster to become the [C(NH2)3]10[{PW11O39Cu}2{Cu(pic)2}]·2H2O (2h) hydrated derivative without any significant alteration in its cell parameters, nor in its crystalline structure. Phase transformations have been monitored by electron paramagnetic resonance spectroscopy.

Organo-functionalized polyoxovanadates: crystal architecture and property aspects

Polyoxovanadates (POVs), as one of the most prominent members of polyoxometalates (POMs), have been subject to extensive studies by virtue of their aesthetically intriguing structures and potential applications in catalysis, magnetism, and optics, among others. In recent years, organo-functionalized POVs have received considerable attention due to the combination of the advantages of POVs with the importance of organic species. In this review, the key developments of polyoxovanadates and, particularly, the achievements that are related to polyoxovanadates modified with organic ligands and transition metal-organic ligand are summarized. Herein, we systematically introduce the structural features of organo-functionalized POVs and their main applications involved in the magnetism and catalysis aspects. Finally, the current challenges and future prospects in the design, synthesis, and property investigation of polyoxovanadates are also discussed.

Synthesis, structures and stability of three V-substituted polyoxoniobate clusters based on [TeNb9O33]17- units

Three structurally intriguing polyoxoniobates (PONbs) based on the trivacant B-type α-Keggin ion {TeNb9O33}, H4K(CN3H6)2{[Cu4(2,2'-bipy)4(H2O)2][TeNb9V2O37]}·29H2O (1, 2,2'-bipy = 2,2'-bipyridine), H0.5K5Na2.5{[Cu(en)H2O]3[TeNb9V3O39]}·10H2O (2, en = ethylenediamine), and K3Na5{[Cu(1,3-dap)H2O]3[TeNb9V3O39]}·11H2O (3, 1,3-dap = 1,3-diaminopropane), are assembled by the conventional aqueous solution methods using a series of N-containing organic ligands. In 1, each of the two {VO4} units is attached to two coplanar NbO6 octahedra on the {Nb3O13} cluster of the {TeNb9O33} unit. Differently, three {VO4} units in 2 and 3 are linked to two edge-sharing NbO6 octahedra, respectively. Compounds 1-3 represent the first oxo NbTeV clusters and also the first vanadoniobates based on the trivacant Keggin PONb units. All three compounds were characterised by single-crystal X-ray structural analysis, TGA and IR, ESI-MS and 51V NMR spectroscopy. Furthermore, the magnetic properties of compounds 1 and 2 were also studied.

Self-Assembly of a Phosphate-Centered Polyoxo-Titanium Cluster: Discovery of the Heteroatom Keggin Family

Over the past 200 years, the most famous and important heteroatom Keggin architecture in polyoxometalates has only been synthesized with Mo, W, V, or Nb. Now, the self-assembly of two phosphate (PO₄ ^3- )-centered polyoxo-titanium clusters (PTCs) is presented, PTi₁₆ and PTi₁₂ , which display classic heteroatom Keggin and its trivacant structures, respectively. Because Ti^IV has lower oxidate state and larger ionic radius than Mo^VI , W^VI , V^V , and Nb^V , additional Ti^IV centres in these PTCs are used to stabilize the resultant heteroatom Keggin structures, as demonstrated by the cooresponding theoretical calculation results. These photoactive PTCs can be utilized as efficient photocatalysts for highly selective CO₂ -to-HCOOH conversion. This new discovery indicates that the classic heteroatom Keggin family can be assembled with Ti, thus opening a research avenue for the development of PTC chemistry.

A Simple Coulombic Model for 31P NMR Spectra of Cluster-Encapsulated Phosphorus Atoms

While sophisticated computational methods can predict ³¹P NMR spectra of phosphorus atoms encapsulated within Keggin-derived heteropoly tungstate and molybdate cluster anions, calculated and experimental chemical shift values typically deviate considerably from one another. Motivated by the observation that experimentally determined ³¹P chemical shift values within a series of water-soluble plenary and metal-cation substituted lacunary Keggin anions, [PM ⁿW₁₁O₃₉]^{(7- n)-} (M ⁿ = Ag⁺, Zn²⁺, Nb⁵⁺, W⁶⁺) and [(PW₁₁O₃₉)₂M ⁿ]^{(14- n)-} (M ⁿ = Y³⁺, Zr⁴⁺), varied as a linear function of the oxidation states, n, of the complexed M ⁿ cations, a linear correlation was sought between observed chemical shift values and the net Coulombic forces experienced by the encapsulated phosphorus atoms. The Coulombic model based on Shannon radii, published electronegativity values, and bond angles from X-ray crystallographic data remarkably accounted for the relative ³¹P chemical shift values of phosphorus atoms in over 50 metal-oxide cluster anions, including large structures comprised of up to four Keggin-derived fragments with an overall R² value of 0.974. With the model being applied here to three cluster anions whose ³¹P chemical shift values are reported here for the first time, predicted and experimental values differed by only ±0.4 ppm.

Bis(alkylidynyl)tellurides and ditellurides

The tellurocarbonylates [M(CTe)(CO)₂(Tp*)]⁻ (M = Mo, W; obtained from [M(CBr)(CO)₂(Tp*)] and Li₂Te or [M(CLi)(CO)₂(Tp*)] and Te) react with an additional equivalent of [M(CBr)(CO)₂(Tp*)] to give bis(alkylidynyl)tellurides, [M₂(μ-CTeC)(CO)₄(Tp*)₂], whilst oxidation with [Fe(η-C₅H₅)₂]PF₆ affords the corresponding ditellurides [M₂(μ-CTe₂C)(CO)₄(Tp*)₂].

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.

Lanthanide complexes of macrocyclic polyoxovanadates by VO4 units: synthesis, characterization, and structure elucidation by X-ray crystallography and EXAFS spectroscopy

Reactions of a tetravanadate anion, [V(4)O(12)](4-), with a series of lanthanide(III) salts yield three types of lanthanide complexes of macrocyclic polyoxovanadates: (Et(4)N)(6)[Ln(III)V(9)O(27)] [Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6)], (Et(4)N)(5)[(H(2)O)Ho(III)(V(4)O(12))(2)] (7), and (Et(4)N)(7)[Ln(III)V(10)O(30)] [Ln = Er (8), Tm (9), Yb (10), Lu (11)]. Lanthanide complexes 1-11 are isolated and characterized by IR, elemental analysis, single-crystal X-ray diffraction, and extended X-ray absorption fine structure spectroscopy (EXAFS). Lanthanide complexes 1-6 are composed of a square-antiprism eight-coordinated Ln(III) center with a macrocyclic polyoxovanadate that is constructed from nine VO(4) tetrahedra through vertex sharing. The structure of 7 is composed of a seven-coordinated Ho(III) center, which exhibits a capped trigonal-prism coordination environment by the sandwiching of two cyclic tetravanadates with a capping H(2)O ligand. Lanthanide complexes 8-11 have a six-coordinated Ln(III) center with a 10-membered vanadate ligand. The structural trend to adopt a larger coordination number for a larger lanthanide ion among the three types of structures is accompanied by a change in the vanadate ring sizes. These lanthanide complexes are examined by EXAFS spectroscopies on lanthanide L(III) absorption edges, and the EXAFS oscillations of each of the samples in the solid state and in acetonitrile are identical. The Ln-O and Ln···V bond lengths obtained from fits of the EXAFS data are consistent with the data from the single-crystal X-ray studies, reflecting retention of the structures in acetonitrile.

Two-Dimensional Lanthanide Heteropolyvanadates of Manganese(IV) and Nickel(IV) Containing Two Types of Heteropoly Anions with 1:13 and 1:12 Stoichiometry

Reactions of 1:13 heteropoly anions [MV13O38](7-) (M = Mn, Ni) and lanthanide cations Ln3+ (Ln = La, Ce, or Pr) produce five isomorphic compounds, which are crystallized in the triclinic crystal system, space group P1, and formulated as [Ln6(H2O)25(MV12O38)(HMV13O38)].nH2O ((1) Ln = La, M = Mn, and n approximately 31; (2) Ln = Ce, M = Mn, and n approximately 29; (3) Ln = Pr, M = Mn, and n approximately 31; (4) Ln = La, M = Ni, and n approximately 28; (5) Ln = Pr, M = Ni, and n approximately 33). These compounds are two-dimensional polymeric structures constructed by hydrated lanthanide cations and two types of heteropoly anions, [MV13O38](7-) and [MV12O38](12-). In contrast to the previous reported 1:13 heteropoly anions, all with disordered structures, [MV13O38](7-) clusters in 1-5 are non-disordered with a distinct mode. The second kind of anionic cluster [MV12O38](12-) with O(h) symmetry, which consists of 13 entire edge-sharing MO(6) (M = V, Mn or Ni) octahedra, has not been reported hitherto. The emergence of the new cluster may be correlated to the six capping lanthanide cations surrounding it with a stabilization effect. In this paper, the syntheses and structures of the five polymeric lanthanide heteropolyvanadates of manganese(IV) and nickel(IV) have been presented.

Vanadium-Based, Extended Catalytic Lifetime Catechol Dioxygenases: Evidence for a Common Catalyst

In 1999, a catechol dioxygenase derived from a V-polyoxometalate was reported which was able to perform a record >100 000 total turnovers of 3,5-di-tert-butylcatechol oxygenation using O2 as the oxidant (Weiner, H.; Finke, R. G. J. Am. Chem. Soc. 1999, 121, 9831). An important goal is to better understand this and other vanadium-based catechol dioxygenases. Scrutiny of 11 literature reports of vanadium-based catechol dioxygenases yielded the insight that they all proceed with closely similar selectivities. This, in turn, led to a "common catalyst hypothesis" for the broad range of vanadium based catechol dioxygenase precatalysts presently known. The following three classes of V-based compounds, 10 complexes total, have been explored to test the common catalyst hypothesis: (i) six vanadium-based polyoxometalate precatalysts, (n-Bu4N)4H5PV14O42, (n-Bu4N)7SiW9V3O40, (n-Bu4N)5[(CH3CN)(x)Fe(II).SiW9V3O40], (n-Bu4N)9P2W15V3O62, (n-Bu4N)5Na2[(CH3CN)(x)Fe(II).P2W15V3O62], and (n-Bu4N)4H2-gamma-SiW10V2O40; (ii) three vanadium catecholate complexes, [V(V)O(DBSQ)(DTBC)]2, [Et3NH]2[V(IV)O(DBTC)2].2CH3OH, and [Na(CH3OH)2]2[V(V)(DTBC)3]2.4CH3OH (where DBSQ = 3,5-di-tert-butylsemiquinone anion and DTBC = 3,5-di-tert-butylcatecholate dianion), and (iii) simple VO(acac)2. Product selectivity studies, catalytic lifetime tests, electron paramagnetic resonance spectroscopy (EPR), negative ion mode electrospray ionization-mass spectrometry (negative ion ESI-MS), and kinetic studies provided compelling evidence for a common catalyst or catalyst resting state, namely, Pierpont's structurally characterized vanadyl semiquinone catecholate dimer complex, [VO(DBSQ)(DTBC)]2, formed from V-leaching from the precatalysts. The results provide a considerable simplification and unification of a previously disparate literature of V-based catechol dioxygenases.

Hydrothermal synthesis of the first vanadomolybdenum polyoxocation with a "metal-bonded" spherical framework

The heteropoly compound [(V(V)O(4))Mo(VI)(12)O(36)(V(IV)O)(6)][(OH)(9)].11H(2)O (1), synthesized by hydrothermal method under weak basic conditions, represents the first mixed Mo/V six-capped Keggin structural derivative with a spherical skeleton, and the first transition metal polyoxocation. The successful synthesis of 1 demonstrates that basic hydrothermal synthesis might be a power synthetic route to the isolation of more new polycationic metal-oxo clusters.

Synthesis and structural characterization of a new series of vanadoselenites, [Se(x)V(4-x)O(12-x)](4-x)- (x=1,2)

Two new vanadoselenites, [SeV(3)O(11)](3)(-) and [Se(2)V(2)O(10)](2)(-), were synthesized by reacting SeO(2) with VO(3)(-). Single-crystal X-ray structural analyses of [(n-C(4)H(9))(4)N](3)[SeV(3)O(11)].0.5H(2)O [orthorhombic, space group P2(1)2(1)2, a = 22.328(5) A, b = 44.099(9) A, c = 12.287(3) A, Z = 8] and [[(C(6)H(5))(3)P](2)N](2)[Se(2)V(2)O(10)] [monoclinic, space group P2(1)/n, a = 12.2931(3) A, b = 13.5101(3) A, c = 20.9793(5) A, beta = 106.307(1) degrees, Z = 2] revealed that both anions are composed of Se(x)()V(4)(-)(x)()O(4) rings. The (51)V, (77)Se, and (17)O NMR spectra established that both [SeV(3)O(11)](3)(-) and [Se(2)V(2)O(10)](2)(-) anions maintain this ring structure in solution.