Coordination capacity of Keggin anions as polytopic ligands: case study of [VNb12O40]15

An Organodiphosphate-Containing Polyoxoniobate Ring and Its Assembly into a Three-Dimensional Framework through Hydrogen Bonding

In this work, a novel organodiphosphate-containing inorganic-organic hybrid polyoxoniobate (PONb) ring {(PO3CH2CH2PO3H)4Nb8O16}4- (Nb8P8) has been achieved by a one-pot hydrothermal method. The ring is constructed from a tetragonal {Nb8O36} motif and four {PO3CH2CH2PO3H} ligands. Interestingly, Nb8P8 can be joined together via K-H2O clusters {K2(H2O)4(OH)2} to form one-dimensional chains {[K2(H2O)4(OH)2]Nb8P8}n and further linked by {Cu(en)2}2+ (en = ethylenediamine) complexes, resulting in a three-dimensional supramolecular framework {[Cu(en)2]2[K2(H2O)4(OH)2]Nb8P8}·3en·H2O (1). 1 exhibits good chemical and thermal stability and has a high water vapor adsorption capacity of ≤224 cm3 g-1 (22.71 mol·mol-1) at 298 K, outperforming most of the known polyoxometalate-based materials. Impedance measurements prove that 1 can transfer protons with moderate conductivity. This study not only contributes to the structural diversity of organodiphosphate-containing PONbs and PONb rings but also provides a reference for the development of PONb-based materials with unique performance.

Reactivity of Organoiridium Tungsten Oxide Clusters with Transition Metal Aquo Cations

Organometallic-polyoxometalate (POM) complexes form a unique class of molecular organometallic oxides characterized by the dynamic behavior of the organometallic cations. Herein, we investigated the reactivity of Cp*Ir-octatungstate clusters (where Cp* represents pentamethylcyclopentadienyl, C5Me5-) with Werner-type transition-metal aquo cations. The addition of Ag+, Co2+, Ni2+, and M3+ (M = Cr, Fe, or In) cations to the aqueous solution of Cp*Ir-octatungstate clusters resulted in the formation of [{Ag(OH2)2}2{Cp*Ir(OH2)}2{Cp*IrW3O12(OH)}2(WO2)2] (1), Co1.5K0.8Na0.2[{trans-Co(OH2)2}{Cp*IrW3O12(OH)}2(WO2)1.3{cis-Co(OH2)2}0.7] (2-Co), Ni0.2K1.4Na0.2[{Ni(OH2)4}2{Cp*IrW3O12(OH)}2(WO2)1.1{cis-Ni(OH2)2}0.9] (2-Ni), and [{M(OH2)4}2{Cp*IrW3O12(OH)}2{cis-M(OH2)2}2](NO3)2 (M = Cr, 3-Cr; Fe, 3-Fe; or In, 3-In), respectively. All clusters share the same cubane-type {Cp*IrW3O12(OH)}5- building block, representing the first examples of organoiridium-POMs functionalized by transition-metal aquo cations. These compounds are insoluble in water, facilitating the evaluation of their heterogeneous water-oxidation properties. Notably, 2-Co generates the highest catalytic water oxidation current. This work provides a new synthetic method to introduce metal-aquo complexes on an organometallic oxide cluster, producing multimetallic molecules that model the catalytic sites of complex oxides.

Molar-Ratio-Dependent Coordination Assembly of Organoiridium(III)-Octatungstate Complexes in Aqueous Solution

We scrutinized the speciation of Cp*Ir-containing tungsten oxide clusters (Cp* is pentamethylcyclopentadienyl anion) in aqueous mixtures of [(Cp*IrCl)₂(μ-Cl)₂] and Na₂WO₄ in varying molar ratios. ¹H nuclear magnetic resonance (NMR) spectroscopy revealed the formation of three distinct Cp*Ir-polyoxotungstate species in the reaction solution, and they were isolated as Na₄[(Cp*Ir)₂(μ-OH)₃]₂[(Cp*Ir)₂H₂W₈O₃₀] (1), [(Cp*Ir)₂(μ-OH)₃]₂[(Cp*Ir)₂{Cp*Ir(OH₂)}₂H₂W₈O₃₀] (2), and [(Cp*Ir)₂{Cp*Ir(OH₂)}₂{Cp*Ir(OH₂)₂}₂H₂W₈O₃₀](NO₃)₂ (3) from the mixtures in which iridium concentration is less than, equal to, and more than the tungsten concentration, respectively. These results show the octatungstate [H₂W₈O₃₀]^10- anion is the major polyoxotungstate species in the presence of {Cp*Ir}²⁺ cations, and it has high nucleophilicity enough to bind up to six {Cp*Ir}²⁺ cations on its surfaces producing a cationic Cp*Ir-octatungstate complex. The octatungstate anion was also generated from the reaction of [(Cp*IrCl)₂(μ-Cl)₂] and methylammonium paratungstate-B, (CH₃NH₃)₁₀[H₂W₁₂O₄₂], and was isolated as a methylamine-coordinated complex (CH₃NH₃)₂[(Cp*Ir)₂{Cp*Ir(NH₂CH₃)}₂H₂W₈O₃₀] (4), indicating {Cp*Ir}²⁺ cations function as a structure-directing agent that converts tungsten species into octatungstate anions in aqueous solution. In addition, the coordination environment of {Cp*Ir}²⁺ can be further modified by coordination with pyridine forming [{Cp*Ir(NC₅H₅)}₂(μ-OH)₂][(Cp*Ir)₂{Cp*Ir(NC₅H₅)}₂H₂W₈O₃₀] (5).

NMR-Relaxometric Investigation of Mn(II)-Doped Polyoxometalates in Aqueous Solutions

Solution behavior of K;₅[(Mn(H₂O))PW₁₁O₃₉]·7H₂O (1), Na_3.66(NH₄)_4.74H_3.1[(Mn^II(H₂O))_2.75(WO(H₂O))_0.25(α-B-SbW₉O₃₃)₂]·27H₂O (2), and Na_4.6H_3.4[(Mn^II(H₂O)₃)₂(WO₂)₂(β-B-TeW₉O₃₃)₂]·19H₂O (3) was studied with NMR-relaxometry and HPLC-ICP-AES (High Performance Liquid Chromatography coupled with Inductively Coupled Plasma Atomic Emission Spectroscopy). According to the data, the [(Mn(H₂O))PW₁₁O₃₉]^5- Keggin-type anion is the most stable in water among the tested complexes, even in the presence of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA). Aqueous solutions of 2 and 3 anions are less stable and contain other species resulting from dissociation of Mn²⁺. Quantum chemical calculations show the change in Mn²⁺ electronic state between [Mn(H₂O)₆]²⁺ and [(Mn(H₂O))PW₁₁O₃₉]^5-.

Proton Affinity in the Chemistry of Beta-Octamolybdate: HPLC-ICP-AES, NMR and Structural Studies

The affinity of [β-Mo₈O₂₆]^4- toward different proton sources has been studied in various conditions. The proposed sites for proton coordination were highlighted with single crystal X-ray diffraction (SCXRD) analysis of (Bu₄N)₃[β-{Ag(py-NH₂)Mo₈O₂₆]}] (1) and from analysis of reported structures. Structural rearrangement of [β-Mo₈O₂₆]^4- as a direct response to protonation was studied in solution with ⁹⁵Mo NMR and HPLC-ICP-AES techniques. A new type of proton transfer reaction between (Bu₄N)₄[β-Mo₈O₂₆] and (Bu₄N)₄H₂[V₁₀O₂₈] in DMSO results in both polyoxometalates transformation into [V₂Mo₄O₁₉]^4-, which was confirmed by the ⁹⁵Mo, ⁵¹V NMR and HPLC-ICP-AES techniques. The same type of reaction with [H₄SiW₁₂O₄₀] in DMSO leads to metal redistribution with formation of [W₂Mo₄O₁₉]^2-.

Interactions of aromatic rings in the crystal structures of hybrid polyoxometalates and Ru clusters

Computational analysis for π–π interaction energies of {(arene)Ru}2+ containing complexes and relative group 5 hybrid polyoxometalates reveals different frameworks. Some perspectives on πOF materials processing and crystal engineering were discussed.