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The cage-like cyclobutyltellurium(IV)-containing tungstoarsenate(III) dimers [(C4H8Te-OH)2(C4H8Te)6{As2W17O61(H2O)}2]14− (1) and [{(C4H8Te)2W2O5(H2O)2As2W19O67(H2O)}2]16− (2) were synthesized in moderately acidic aqueous medium by reaction of C4H8TeI2 with the lacunary tungstoarsenates(III) [B-α-AsW9O33]9− and [As2W19O67(H2O)]14−, respectively. Polyanion 1 was isolated as a mixed cesium-guanidinium salt Cs8.5(C(NH2)3)5.5[(C4H8TeOH)2(C4H8Te)6{As2W17O61(H2O)}2]·60H2O (1a), whereas 2 crystallized as a mixed cesium-potassium salt Cs9K7[{(C4H8Te)2W2O5(H2O)2As2W19O67(H2O)}2]·90H2O (2a). Single crystal X-ray analysis demonstrated that 1a and 2a crystallized in the triclinic space group $$ P \bar{1} $$ , with a = 12.7738(8) A, b = 18.7490(14) A, c = 21.9831(14) A, α = 111.155(4)o, β = 93.312(3)o, γ = 99.530(4) and Z = 1 for 1a and a = 19.309(6) A, b = 24.674(8) A, c = 26.071(8) A, α = 63.218(17)°, β = 89.26(16)°, γ = 79.948(17)° and Z = 2 for 2a. The polyanion salts 1a and 2a were characterized by solid state NMR (1H, 13C, 125Te), FT-IR, TGA-DSC, and elemental analysis.

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The oxalato-titanium(IV)-containing, dimeric 18-tungsto-2-phosphate [Ti8(C2O4)8P2W18O76(H2O)4]18− (1) and the 32-tungsto-4-phosphate [Ti6(C2O4)4P4W32O124]20− (2) are formed upon reaction of the oxalato-titanium complex [TiO(C2O4)2]2− with the trilacunary Keggin precursor [A-α-PW9O34]9− and the hexalacunary Wells–Dawson precursor [H2P2W12O48]12−, respectively. Polyanion 1 consists of two {PW9} units encapsulating eight titanium centers and connected to each other via two Ti–O–Ti bridges, and crystallizes as a mixed potassium-sodium-lithium salt in the triclinic space group $$P{\bar{1}}$$ . Polyanion 2 comprises two {P2W16} units containing each two titanium atoms, and the two half-units are connected via two titanium atoms decorated by two oxalate groups each, and crystallizes as a mixed potassium-lithium salt in the rhombohedral space group $$R{\bar{3}}c$$ . Polyanions 1 and 2 were characterized in the solid state by single-crystal XRD, FT-IR, and TGA, whereas polyanion 2 was also investigated by 31P and 183W NMR.

We report on an improved synthesis and structural characterization of the cyclic 48-tungsto–8-arsenate(V) [H4As8W48O184]36− (1). The mixed lithium–potassium salt of this polyanion, K26.5Li9.5[H4As8W48O184]·90H2O (KLi-1), has been studied in the solid state by IR, single-crystal X-ray diffraction, and elemental analysis, and in solution by 183W NMR spectroscopy.

Polyoxometalates (POMs) are inorganic metal oxoanions with a negative charge, stabilized in the solid state by the corresponding number of countercations and possibly protons. In aqueous solution, the dissociation of all ion pairs is not necessarily quantitative because this would result in strong electrostatic repulsion among the polyanions. In the present communication, we show that the effective charge of the donut-shaped 30-tungsto-5-phosphate [NaP5W30O110]14− (P5W30) is close to its “structural charge” of 14 elementary negative charges in the presence of linear polyamines, namely, poly(allylamine hydrobromide) and poly(l-lysine hydrobromide) in a 10-mM NaBr electrolyte. When phase separation occurs, leading to a precipitate (rich in polyanion) and an almost clear supernatant, the charge ratio of the number of moles of cationic groups to polyanion is close to 14, showing that the effective charge in a solution of P5W30 is indeed equal to −14e in the presence of polycations.

Reaction of (C2H5)2SnCl2 with the trilacunary 9-tungstoarsenate(V) [A–α–AsW9O34]9− in aqueous pH 5 medium resulted in the diethyltin-containing polyanion [{Sn(C2H5)2}3(H2O)6(A–α–AsVW9O34)]3− (1), which crystallized as a hydrated guanidinium salt, [C(NH2)3]3[{Sn(C2H5)2}3(H2O)4(A–α–AsVW9O34)]·9H2O (1a). Polyanion 1 represents the first example of a diethyltin-containing polyanion. The diethyltin groups are bound to the trilacunary Keggin units via two Sn–O(W) bonds involving edge-shared WO6 octahedra. Each Sn atom also has two terminal, cis-related water ligands, and two terminal, trans-related ethyl groups. Multinuclear (1H, 13C, 119Sn, 183W) NMR spectrometry indicated that polyanion 1 is stable in solution. Compound 1a was structurally characterized in the solid state by single-crystal XRD, FT-IR, as well as thermogravimetric and elemental analyses. Single-crystal X-ray analysis showed that 1a crystallizes in the orthorhombic system, space group P nma , with a = 23.5280(10) A, b = 15.5435(6) A, c = 18.6191(9) A, V = 6809.1(5) A3 and Z = 4. The structure of 1a is an extended 2D assembly of individual polyanion units 1 linked via Sn–O(W) bridges.

Polyoxometalates (POMs) show significant importance in medicine due to their enzyme inhibition, antiviral and anticancer properties. In this study, some polyoxotungstates were identified as potent inhibitors of acetyl and butyrylcholinesterases. Compounds [H2W12O42]10− and [TeW6O24]6− have the most potent acetylcholinesterase activity, exhibiting IC50 values of 0.29 ± 0.01 and 0.31 ± 0.01 μM, respectively. Whereas, compound [(O3PCH2PO3)4W12O36]16− was a potent and selective inhibitor of butyrylcholinesterase with IC50 value of 0.18 ± 0.05 μM. In general, POMs were found to be effective cholinesterase inhibitors in terms of efficiency as well as selectivity and represent non-classical cholinesterase inhibitors.

The 20-tungsto-4-tellurate(IV) polyanion [H2Te4W20O80]22− (1) has been synthesized and isolated in the form of its hydrated sodium salt Na22[H2Te4W20O80]·64H2O (Na-1). Na-1 has been characterized in the solid state by FTIR and TGA. Single-crystal X-ray diffraction analysis revealed that Na-1 crystallizes in the triclinic space group P $${\bar 1}$$ , with a = 12.741(2) A, b = 16.842(3) A, c = 17.197(4) A, α = 93.961(10)°, β = 107.466(8)°, γ = 108.548(8)°, V = 3281.5(11) A3 and Z = 1. The polyanion 1 comprises two [HTe2W10O40]11− fragments, connected through Te−O–W μ2-oxo bridges, and each containing a pair of face-shared WO6 octahedra. Furthermore, the 15-tungstotellurate(IV) polyanion [NaTeW15O54]13− (2) was synthesized and crystallized as a sodium salt in the orthorhombic space group Pccn, with a = 11.8841(5) A, b = 20.8934(11) A, c = 31.801(2) A, V = 7896.3(7) A3 and Z = 4.

The mixed-valence 24-vanadophosphate \( {\left[ {{\left\{ {{\text{Ru}}^{{{\text{II}}}}_{3} (dmso)_{9} {\text{PV}}^{{\text{V}}}_{{11}} {\text{V}}^{{{\text{IV}}}} {\text{Ru}}^{{{\text{III}}}} {\text{O}}_{{37}} {\text{(OH)}}_{3} } \right\}}_{2} } \right]}^{{8 - }} \) (1) has been synthesized and characterized in the solid state by IR, magnetism, EPR, XPS, and elemental analysis. Single-crystal X-ray analysis was carried out on \( {\text{Na}}_{8} {\left[ {{\left\{ {{\text{Ru}}^{{{\text{II}}}}_{3} (dmso)_{9} {\text{PV}}^{{\text{V}}}_{{11}} {\text{V}}^{{{\text{IV}}}} {\text{Ru}}^{{{\text{III}}}} {\text{O}}_{{37}} {\text{(OH)}}_{3} } \right\}}_{2} } \right]} \cdot 46{\text{H}}_{2} {\text{O}} \) (Na-1), which crystallizes in the triclinic system, space group \( \hbox{P}\overline{1} \), with a = 17.168(3) A, b = 18.1971(14) A, c = 20.1422(13) A, α = 114.753(3)°, β = 99.390(4)°, γ = 95.124(4)°, and Z = 2. Polyanion 1 has an unusual, open structure composed of 2 RuIIIO6 octahedra, 2 VIVO6 octahedra, 14 VVO5 square-pyramids, 8 VVO4 tetrahedra, and 2 PO4 tetrahedra which are all directly linked via edges and corners. The outer surface of 1 is decorated with six RuII(dmso)3 groups. XPS studies on Na-1 confirm the presence of 2 RuIII and 6 RuII as well as 22 VV and 2 VIV centers. Magnetic susceptibility data on Na-1 show that the VIV–RuIII pairs are coupled antiferromagnetically, with J1 = −13 K and J2 ∼ −3 K. We did not detect any peak in our EPR measurements on Na-1, thus supporting the conclusion that Na-1 is diamagnetic in its ground state.

We present the first examples of materials based on the Strandberg type polyanion [(O2CCH2PO3)2Mo5O15]6−, linked by Cu2+ centers via coordination to the carboxylate functions of the polyanion. Simple one-pot reaction of Rb4KNa[(O2CCH2PO3)2Mo5O15]·H2O with CuCl2·2H2O in aqueous acidic media followed by crystallization resulted in the three hybrid organic–inorganic materials {K2.6Rb1.4[(PO3CH2CO2)2Mo5O15Cu(H2O)3]·7H2O} n (KRb-1), {Na2Cs3[(PO3CH2CO2)2Mo5O15(Cu(H2O)2Cl)]·6H2O} n (NaCs-2) and {Na2.75Rb1.25[(PO3CH2CO2)2Mo5O15Cu(H2O)3]·9H2O} n (NaRb-3), which were characterized by single-crystal X-ray diffraction, IR, TGA and elemental analysis. All three compounds are 1:1 polymers of the polyanion and the Cu2+ centers are all five-coordinate with two carboxylate oxygens in a trans fashion. However, the chains in KRb-1, NaCs-2 and NaRb-3 are packed differently along b leading to different solid state structures, indicating an important role of the alkali counter cations.

The trimeric, cyclic dimethyltin-containing tungstophophate [{(Sn(CH3)2)(Sn(CH3)2O)(A-PW9O34)}3]21− (1) has been synthesized in aqueous acidic medium and characterized by IR, elemental analysis, electrochemistry, and FT-ICR MS. Single-crystal X-ray analysis was carried out on Cs12Na9[{(Sn(CH3)2)(Sn(CH3)2O)(A-PW9O34)}3]·20H2O (1a), which crystallizes in the trigonal system, space group R3, with a = b = 29.7445(7) A, c = 15.5915(7) A and Z = 3. Polyanion 1 is composed of three trilacunary (A-PW9O34) Keggin fragments that are linked on one side via three isolated dimethyltin groups and on the other side by a (Sn3(CH3)6O3) unit and three cesium ions, resulting in a cyclic assembly with C 3v symmetry. The discrete molecular, hybrid organic–inorganic 1 was synthesized by reaction of (CH3)2SnCl2 with Na9[A-PW9O34] in 0.5 M sodium acetate buffer (pH 4.8). Comparison of several characteristics of the cyclic voltammograms of 1 and (A-PW9O34)9−, including the potential location of their reduction peaks, the difference in their current intensities and their qualitative relative electron transfer speeds, supports the conclusion that the solid-state structure of 1 is retained in solution. The presence of (PW9O34)-based species in solutions of 1 was also confirmed by FT-ICR mass spectrometry.

The lanthanum-substituted polyoxometalate [{La(CH3COO)(H2O)2(α2-P2W17O61)}2]16− (1) and the neodymium-substituted species [{Nd(H2O)3(α 2 -P2W17O61)}2]14− (2) have been synthesized and characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray analysis was carried out on K16[{La(CH3COO)(H2O)2(α 2 -P2W17O61)}2]⋅36H2O, which crystallizes in the triclinic system, space group P¯1, with a=12.3863(6) A, b=12.8934(6) A, c=31.7285(14) A, α=84.2000(10)°, β=81.2300(10)°, γ=61.6500(10)°, and Z=1; K6.5Nd2.5[{Nd(H2O)3(α2-P2W17O61)}2]⋅55H2O, which crystallizes in the monoclinic system, space group P21/n, with a=17.5030(9) A, b=23.7842(12) A, c=19.1869(10) A, β=100.6610(10)°, and Z=1. The head-on, trans-oid dimer 1 consists of two (α 2 -P2W17O61)10− fragments connected by a lanthanum-acetate dimer, (La2(CH3COO)2(H2O)4)4+. Each La3+ ion is nine-coordinated in a monocapped, square-antiprismatic fashion. The neodymium-derivative 2 is also a trans-oid dimer, but the mode of binding is different from 1 and is best described as side-on. Each Nd3+ ion is eight-coordinated in a square-antiprismatic fashion with three terminal water molecules.