Synthesis and characterization of 2D and 3D structures from organic derivatives of polyoxometalate clusters: role of organic moiety, counterion, and solvent

Fluorinated Arylarsonate-Containing Polyoxomolybdates: pH-Dependent Formation of Mo6 vs Mo12 Species and Their Solution Properties

We report on the synthesis and structural characterization of six novel arylarsonate-containing polyoxomolybdates with fluorinated-functionalities in the para position of the phenyl ring. The reaction of the various arylarsonic acids, RAsO3H2 [R = 4-F-C6H4 (H2LF), 4-F3C-C6H4 (H2LCF3), 4-F3CO-C6H4 (H2LOCF3)] with Na2MoO4·2H2O in aqueous pH 3 solution resulted in the heteropoly-6-molybdates [{(4-F-C6H4)As}2Mo6O24(H2O)]4- (1), [{(4-F3C-C6H4)As}2Mo6O24]4- (2) and [{(4-F3CO-C6H4)As}2Mo6O24(H2O)]4- (3), which were isolated as guanidinium salts. When the reaction was performed in aqueous pH 1 solution the inverted-Keggin type heteropoly-12-molydates [{(4-F-C6H4)As}4Mo12O46]4- (4), [{(4-F3C-C6H4)As}4Mo12O46]4- (5) and [{(4-F3CO-C6H4)As}4Mo12O46]4- (6), were obtained and isolated as sodium salts. The 6-molybdates 1-3 and the 12-molybdates 4-6 can be easily interconverted reversibly in solution as a function of pH (3 vs 1). Polyanions 1 and 3 are isostructural and they exhibit a bent hexamolybdate ring, whereas the ring is flat for 2. The inverted-Keggin polyanions 4-6 are isostructural and the metal-oxo core is capped by four arylarsonate groups. All six polyanions have been characterized in the solid state by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, and hermogravimetric analysis as well as in solution by multinuclear NMR (1H, 19F). The synthetic procedures for the arsonic acids (4-F3C-C6H4)AsO3H2 (H2LCF3) and (4-F3CO-C6H4)AsO3H2 (H2LOCF3) are reported for the first time.

Discrete Arsonate-Grafted Inverted-Keggin 12-Molybdate Ion [Mo12O32(OH)2(4-N3C2H2-C6H4AsO3)4]2- and Formation of a Copper(II)-Mediated Metal-Organic Framework

The discrete inverted-Keggin ion [Mo₁₂O₃₂(OH)₂(4-N₃C₂H₂-C₆H₄AsO₃)₄]^2- (1) has been prepared in an aqueous acidic (pH 0.8) medium by the reaction of MoO₃ with the (4-triazolylphenyl)arsonic acid 4-N₃C₂H₂-C₆H₄AsO₃H₂ under hydrothermal conditions and was isolated as a sodium salt in 21% yield. The exact same reaction in the presence of Cu²⁺ ions resulted in the neutral metal-organic framework (MOF) Cu₂[Mo₁₂O₃₄(4-N₃C₂H₂-C₆H₄AsO₃)₄] (Cu-1) in 68% yield. The inverted-Keggin ion 1 comprises a metal-oxo core, which is capped by four organoarsonate groups, and in Cu-1, individual polyanions are linked in the solid state by coordination of the Cu²⁺ ions with the triazolyl groups. The discrete ion 1 was characterized by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic absorption (AA) spectroscopy, as well as thermogravimetric analysis (TGA), and the POM-MOF Cu-1 was characterized by single-crystal and powder XRD, FT-IR, TGA, and gas sorption. Cu-1 has channels with a diameter of around ∼0.9 nm and exhibits a water-vapor adsorption capacity of 89.7 cm³ g^-1 (p/p₀ = 0.95).

Sodium ion intercalation and multi redox behavior of a Keggin type polyoxometalate during [PMo10V2O40]5- to [PMo10V2O40]27- as a cathode material for Na-ion rechargeable batteries

Recently, the development of cathode materials for Na-ion batteries has gained much attention due to the abundance, low cost, and easy availability of resources. Apart from the usual metal oxides, multi-electron redox materials grabbed attention due to their high energy density and practical capacity with long cycle life. Polyoxometalates (POMs) are inorganic clusters of higher valent metals, and act as electron sponges with multi-electron redox properties. Herein we report a Keggin-type polyoxometalate [PMo₁₀V₂O₄₀]⁵⁻ with Na⁺ and H⁺ counter cations as a cathode material for Na-ion batteries. Further the formation of POM is evidenced by PXRD, FT-IR, flame photometry and XPS studies. In Na-POM, Na⁺ ions in the intercluster cavities provide a better pathway and easy diffusion during the charge/discharge process, and contribute to better electrochemical properties than H-POM. The DFT studies further explore the detailed mechanistic pathway of Na⁺ ions around the clusters in the normal and super-reduced states. Na-POM enables better cycling stability and capacity retention with a specific discharge capacity of 123 mA h g⁻¹ at 0.1C rate at room temperature.

The versatile property of the Keggin type POM is the multi-electron transfer that happens during the switching between [PMo₁₀V₂O₄₀]⁵⁻ to [PMo₁₀V₂O₄₀]²⁷⁻. This tunable behavior makes it unique, efficient material as a cathode for Na-ion batteries.

Arylarsonate- and Phosphonate-Capped Polyoxomolybdates, [(RC6H4As)2Mo6O24]n- and [(R'C6H4P)2Mo5O21]n

We report on the synthesis and structural characterization of four arylarsonate- and phosphonate-capped polyoxomolybdates that exhibit different organic substituents in the para position of the phenyl group. The reaction of arylarsonates (RAsO₃, wherein R = 4-BrC₆H₄ or 4-N₃C₆H₄) with molybdate in aqueous pH 3.5 media resulted in the cyclic hexamolybdates [(BrC₆H₄As)₂Mo₆O₂₄]^4- (Mo₆As₂L_a) and [(N₃C₆H₄As)₂Mo₆O₂₄]^4- (Mo₆As₂L_b), whereas the reaction of arylphosphonates (R'PO₃, wherein R' = 4-O₂CC₆H₄ or 4-O₂CC₆H₄CH₂) with molybdate in aqueous pH 3 media resulted in the cyclic pentamolybdates [(O₂CC₆H₄P)₂Mo₅O₂₁]^6- (Mo₅P₂L_c) and [(HO₂CC₆H₄CH₂P)₂Mo₅O₂₁]^4- (Mo₅P₂L_d), respectively. Polyanions Mo₆As₂L_a and Mo₆As₂L_b comprise a ring of six MoO₆ octahedra that is capped on either side by an organoarsonate group, whereas Mo₅P₂L_c and Mo₅P₂L_d consist of a ring of five MoO₆ octahedra that is capped on either side by an organophosphonate group, with the organic arms protruding away from the metal-oxo core of the polyanions. All four polyanions Mo₆As₂L_a, Mo₆As₂L_b, Mo₅P₂L_c, and Mo₅P₂L_d have been characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analysis and in solution by multinuclear NMR (³¹P, ¹³C, and ¹H). The synthetic procedure of (4-bromophenyl)arsonic acid, BrC₆H₄AsO₃H₂, is reported here for the first time.

Organoarsonate Functionalization of Heteropolyoxotungstates

Functionalization of the {P₈W₄₈} polyoxotungstate (POT) archetype with aromatic organoarsonates results in the first homometallic {P₈W₄₈} derivatives, with the general formula [(RAs^VO)₄P^V₈W^VI₄₈O₁₈₄]³²⁻ [R = C₆H₅ (1) or p-(H₂N)C₆H₄ (2)]. Short As−O bonds here induce unusual bending of the otherwise rigid {P₈W₄₈} macrocycle, breaking its D_4h symmetry. The obtained species also represent the first lacunary POTs functionalized with organoarsonates and can potentially act as polyoxometalate precursors themselves. We elaborate solution stability in different aqueous media using ¹H and ³¹P NMR spectroscopy and possible pathways for subsequent transformations in aqueous solutions of the functionalized polyanions. Recrystallization of the K⁺/Li⁺/dimethylammonium salt of 2 from 4 M LiCl solution yielded a further functionalized POT, [(H₃NC₆H₄AsO)₃P₈W₄₈O₁₈₄H_x{WO₂(H₂O)₂}_0.4]^{(30.2−x)−} (3), revealing dissociation of the organoarsonate fragments in slightly acidic aqueous solutions followed by their rearrangement within the inner POT cavity.

Through strong As−O−W bonds, integration of organoarsonates into heteropolyoxometalates can result in structural distortion, as demonstrated for the seminal wheel-shaped {P₈W₄₈} polyoxotungstate archetype, which binds to up to four phenyl or aminophenyl arsonate groups.

Photoluminescent lead(II) coordination polymers stabilised by bifunctional organoarsonate ligands

Four lead(II) coordination polymers were isolated under hydro(solvo)thermal conditions. The applied synthetic methodology takes advantage of the coordination behaviour of a new bifunctional organoarsonate ligand, 4-(1, 2, 4-triazol-4-yl)phenylarsonic acid (H2TPAA) and involves the variation of lead(II) reactants, metal/ligand mole ratios, and solvents. The constitutional composition of the four lead(II) coordination polymers can be formulated as [Pb2(TPAA)(HTPAA)(NO3)]·6H2O (1), [Pb2(TPAA)(HTPAA)2]·DMF·0.5H2O (DMF = N, N-Dimethylformamide) (2), [Pb2Cl2(TPAA)H2O] (3), and [Pb3Cl(TPAA)(HTPAA)2H2O]Cl (4). The compounds were characterized by single-crystal and powder x-ray diffraction techniques, thermogravimetric analyses, infra-red spectroscopy, and elemental analyses. Single-crystal x-ray diffraction reveals that 1 and 2 represent two-dimensional (2D) layered structures whilst 3 and 4 form three-dimensional (3D) frameworks. The structures of 1, 2, and 4 contain one-dimensional (1D) {PbII/AsO3} substructures, while 3 is composed of 2D {PbII/AsO3} arrays. Besides their interesting topologies, 1-4 all exhibit photoluminescence properties in the solid state at room temperature.

Controlled assembly of hybrid architectures based on carboxylic acid ligands and [(O3PCH2PO3)Mo6O22]12−

Polyanion 2a with a reverse symmetrical “crown-type” structure is composed of two {(HO₃PCH₂PO₃)Mo₆O₁₈(CH₃CO₂)₂} subunits and a linking bridge.

Exploring the coordination chemistry of bifunctional organoarsonate ligands: syntheses and characterisation of coordination polymers that contain 4-(1,2,4-triazol-4-yl)phenylarsonic acid

The syntheses, crystal structures, luminescent and magnetic properties of five triazol-phenylarsonic acid-based M(ii) coordination polymers are reported (M = Co, Cu, Mn, Cd).

Bottom-up construction of POM-based macrostructures: coordination assembled paddle-wheel macroclusters and their vesicle-like supramolecular aggregation in solution

A bottom-up approach to obtain nanoclusters and large, uniform vesicle-like structures containing organic functionalized hexamolybdates in solution state were developed. Hexamolybdate functionalized carboxylic acid coordinated with two copper ions to form paddle-wheel tetrapolyoxometalate clusters with the features of macro-ions, which can spontaneously assemble into large, stable blackberry-type structures in suitable solvents, completing a hierarchical organization from small POM molecules to nanoscale complexes and then to supramolecular structures.

Silver pyroarsonates obtained from Ag(I)-mediated in situ condensation of aryl arsonate ligands under solvothermal conditions

Four new layered silver(I) organoarsonates, namely, [Ag(3)(L(3))(CN)] (1) (H(2)L(3) = (PhAsO(2)H)(2)O), [Ag(3)(L(4))(CN)] (2) (H(2)L(4) = (2-NO(2)-C(6)H(4)-AsO(2)H)(2)O), [Ag(3)(HL(5))(H(2)L(5))] (3) (H(3)L(5) = 3-NO(2)-4-OH-C(6)H(3)-AsO(3)H(2)) and [Ag(2)(HL(5))] (4), were synthesized under solvothermal conditions. During the preparations of 1 and 2, condensation of organoarsonate ligands (H(2)L(1) = Ph-AsO(3)H(2); H(2)L(2) = 2-NO(2)-C(6)H(4)-AsO(3)H(2)) and the decomposition of acetonitrile molecules to cyanide anions occurred. Single crystals of H(2)L(4) ligand and compounds 1-4 were isolated, and their crystal structures have been determined by single crystal X-ray diffraction studies. In 1, the one-dimensional (1D) chains based on Ag(I) ions and {L(3)}(2-) anions are further interconnected by CN(-) into two-dimensional (2D) layers. In 2, adjacent Ag(I) ions within the silver(I) organoarsonate layer are further bridged by μ(4)-CN(-) anions with very short Ag···Ag contacts. In 3, the hexanuclear {Ag(6)O(12)} clusters are interconnected by bridging organoarsonate ligands into a silver(I) arsonate hybrid layer. In 4, the right-handed {Ag(4)O(4)} chains are further interconnected by organoarsonate ligands as well as additional Ag-O-Ag bridges into a novel silver(I) arsonate layer. Compounds 1 and 2 display red and orange-red emissions, respectively, which may be assigned to be an admixture of ligand-to-metal charge transfer (LMCT) and metal-centered (4d-5s/5p) transitions perturbed by Ag(I)···Ag(I) interactions. Upon cooling from room temperature to 10 K, compound 1 exhibits interesting temperature-dependent emissions.

A Novel Organic−Inorganic Hybrid Based on an 8-Electron-Reduced Keggin Polymolybdate Capped by Tetrahedral, Trigonal Bipyramidal, and Octahedral Zinc: Synthesis and Crystal Structure of (CH3NH3)(H2bipy)[Zn4(bipy)3(H2O)2MoV8MoVI4O36(PO4)]·4H2O

Hydrothermal reaction of H(3)PO(3), CH(3)NH(2), zinc(II) acetate, 4,4'-bipyridine (bipy), and (NH(4))(6)Mo(7)O(24).4H(2)O at 180 degrees C led to a novel organic-inorganic layered hybrid, [CH(3)NH(3)][H(2)bipy][Zn(4)(bipy)(3)(H(2)O)(2)Mo(V)(8)Mo(VI)O(36)(PO(4))].4H(2)O (1). Its structure was established by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P2(1)/c with cell parameters of a = 17.3032(2), b = 17.8113(3), and c = 23.4597 (4) A, beta = 106.410(1) degrees, V = 6935.6(2) A(3), and Z = 4. The structure of compound 1 features a novel 2D layer built from the 8e-reduced tetracapped Keggin [Zn(4)Mo(12)O(36)(PO(4))](3)(-) anions, which are further interconnected by bridging bipy ligands. The four zinc(II) ions are in tetrahedral, trigonal bipyramidal, and octahedral coordination geometries, respectively.

Anion dependent structures of luminescent silver(i) complexes

The reaction of AgX, where X = trifluoroacetate (CF(3)CO(2)(-), tfa), nitrate (NO(3)(-)), trifluoromethanesulfonate (triflate, CF(3)SO(3)(-), OTf), hexafluorophosphate (PF(6)(-)), or perchlorate (ClO(4)(-)), with 2,2',3' '-tripyridylamine (tpa) yields five novel silver(I) complexes, which have been structurally characterized. The five complexes have the same 1:1 stoichiometry of Ag/tpa but exhibit different modes of coordination, depending upon the counterion present in the compound. Compound 1, [Ag(tpa)(tfa)](n)(), forms a 1D coordination polymer of [Ag(tpa)(tfa)](2) dimer units linked through bridging tfa counterions. Compound 2, [Ag(tpa)(CH(3)CN)(NO(3))](n), forms a zigzag chain 1D coordination polymer exclusively through Ag-N bonds. In compounds 1 and 2, each tpa ligand is bound to two Ag(I) ions via a 2-py and a 3-py group. Compound 3, [Ag(tpa)(OTf)](n), forms a ribbonlike 1D coordination polymer, in which each tpa ligand binds to three different silver centers via all three pyridyl groups, and the counterion remains coordinated to the Ag(I) center. Compounds 4, [Ag(tpa)(CH(3)CN)](n)(PF(6))(n), and 5, [Ag(tpa)(CH(3)CN)](n)() (ClO(4))(n), display ribbonlike structures resembling that of 3, except that the counterions are not coordinated. All complexes are luminescent in acetonitrile solution, with emission maxima in the near-UV region (lambda(max) = 366, 368, 367, 367, and 368 nm for 1-5, respectively). At 77 K, the emission maxima are red-shifted to lambda(max) = 452, 453, 450, 450, and 454 nm for 1-5, respectively.