Discrete Platinum(II/IV)-Arsenito Clusters with Pt-As and Pt-O Bonding: [PtIV(As3O6)2]2-, [Pt4II(H2AsO3)6(HAsO3)2]2-, and [Pt2IIAs6W4O28]10

The first two discrete, fully inorganic platinum(II/IV)-arsenito clusters, [fac-PtIV(As3O6)2]2- (PtAs6) and [Pt4II(H2AsO3)6(HAsO3)2]2- (Pt4As8), as well as the platinum(II)-arsenito heteropolytungstate [Pt2IIAs6W4O28]10- (Pt2As6W4), have been synthesized in aqueous media using simple one-pot reaction conditions. In PtAs6, a PtIV ion is coordinated to two cyclic, tridentate As3O6 units via oxo-donation (PtIV-O ∼ 2.02 Å). In Pt4As8, each PtII ion is coordinated to four AsO3 ligands via two oxygens and two AsIII atoms in a square-planar fashion (PtII-AsIII 2.31 Å, PtII-O 2.07 Å), resulting in an open cage-like structure, which forms a strong tetrameric assembly in the solid state mediated by two K+ counterions. In Pt2As6W4, each PtII ion is coordinated by the As atoms of three AsO3 ligands (PtII-AsIII 2.38 Å) and an oxo group (PtII-O 2.07 Å) in addition to bridging two tungsten ions, and this polyanion was characterized in solution by 195Pt NMR.

Gallium(III)- and Thallium(III)-Encapsulated Polyoxopalladates: Synthesis, Structure, Multinuclear NMR, and Biological Activity Studies

Three gallium(III)- and thallium(III)-containing polyoxopalladates (POPs) have been synthesized and structurally characterized in the solid state and in solution, namely, the phosphate-capped 12-palladate nanocubes [XPd12O8(PO4)8]13- (X = GaIII, GaPd12P8; X = TlIII, TlPd12P8) and the 23-palladate double-cube [Tl2IIIPd23P14O70(OH)2]20- (Tl2Pd23P14). The cuboid POPs, GaPd12P8 and TlPd12P8, are solution stable as verified by the respective 31P, 71Ga, and 205Tl nuclear magnetic resonance (NMR) spectra. Of prime interest, the spin-spin coupling schemes allowed for an intimate study of the solution behavior of the TlIII-containing POPs via a combination of 31P and 205Tl NMR, including the stoichiometry of the major fragments of Tl2Pd23P14. Moreover, biological studies demonstrated the antitumor and antiviral activity of GaPd12P8 and TlPd12P8, which were validated to be as efficient as cis-platinum against human melanoma and acute promyelocytic leukemia cells. Furthermore, GaPd12P8 and TlPd12P8 exerted inhibitory activity against two herpetic viruses, HSV-2 and HCMV, in a dose-response manner.

PtIV-Containing Hexaplatinate(II) [PtIVPtII6O6(AsO2(CH3)2)6]2- and Hexapalladate(II) [PtIVPdII6O6(AsO2(CH3)2)6]2

The first PtIV-containing discrete polyoxoplatinate(II) [PtIVPtII6O6(AsO2(CH3)2)6]2- (Pt7) and polyoxopalladate(II) [PtIVPdII6O6(AsO2(CH3)2)6]2- (PtPd6) have been prepared and characterized in the solid state, in solution, and in the gas phase. The molecular structures of the noble metal-oxo clusters Pt7 and PtPd6 comprise a central, octahedral PtIVO6 hetero group surrounded by six square-planar MO4 (M = PtII, PdII) units, which are capped by six dimethylarsinate ligands. The polyanions were prepared under simple one-pot aqueous solution conditions by reacting H2Pt(OH)6 with either K2PtCl4 or Pd(NO3)2 in sodium dimethylarsinate buffer (pH 7) at 80 °C. Catalytic studies were performed on Pt7 supported on SBA15-apts for o-xylene hydrogenation at 300 °C and 90 bar H2 pressure and indicated excellent activity and recyclability with low activation temperature.

Mixed noble metal-oxo clusters: platinum(IV)-gold(III) oxoanion [PtIV2AuIII3O6((CH3)2AsO2)6]. Chem Commun (Camb) 2023;59:5918-5921. [PMID: 37171021 DOI: 10.1039/d3cc00243h]

The first discrete mixed platinum(IV)-gold(III) oxoanion [Pt^IV₂Au^III₃O₆((CH₃)₂AsO₂)₆]^- (1) was synthesized by reaction of H₂Pt(OH)₆ with H[AuCl₄] in a simple one-pot procedure in aqueous solution at pH 7 and comprises two equivalent Pt^IVO₆(As(CH₃)₂)₃ units which are linked by three square-planar Au^IIIO₄ units. Polyanion 1 could be isolated as a potassium or sodium salt in good yield, which were structurally characterized in the solid state by single-crystal XRD and TGA, and in solution by multinuclear (¹H, ¹³C, ¹⁹⁵Pt) NMR, indicating that polyanion 1 is stable in solution, which was confirmed by ESI-MS studies. The sodium salt of 1 undergoes a clean single-crystal-to-single-crystal (SCSC) structural transformation upon rehydration and dehydration.

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).

Mixed-valent palladium(IV/II)-oxoanion, [PdIVO6PdII6((CH3)2AsO2)6]2

We report on the first example of a Pd^IV-containing polyoxopalladate(II). The discrete mixed-valent polyoxopalladate(IV/II), [Pd^IVPdII6O₆((CH₃)₂AsO₂)₆]^2-, comprising a central Pd^IV ion that is surrounded by a six-membered Pd^II-oxo ring capped by six dimethylarsinate groups, was synthesized and structurally characterized in the solid state, in solution and in the gas phase by multiple analytical techniques.

Organically Functionalized Mixed-Valent Polyoxo-30-molybdate Wheel and Neutral Tetramolybdenum(V) Oxo Cluster

The first organofunctionalized mixed-valent polyoxo-30-molybdate wheel, [Mo^VI₁₈Mo^V₁₂O₈₄{AsO₂(CH₃)₂}₁₈]^18- (Mo₃₀), was synthesized in aqueous, mildly acidic conditions, and upon further acidification, the neutral tetramolybdenum(V) oxo cluster [Mo^V₄O₈{AsO₂(CH₃)₂}₄] (Mo₄) was obtained. Single-crystal X-ray diffraction (XRD) revealed that Mo₃₀ comprises 18 Mo^VI and 12 Mo^V ions arranged in a cyclic fashion with alternating {Mo^V₂} and {Mo^VI₃} groups, which are capped by 18 dimethylarsinate ligands, resulting in a novel polyoxo-30-molybdate wheel with a central cavity of ∼1.5 nm. On the other hand, Mo₄ has a distorted-cubic structure, with the corners of the cube being occupied by alternating Mo^V ions and oxo ligands. The compounds were characterized in solution by ¹H and ¹³C NMR and UV-vis spectroscopy and in the solid state by X-ray photoelectron spectroscopy and powder XRD. Mo₃₀ represents a novel type of polyanionic cycle with manyfold possibilities regarding host-guest chemistry.

Discovery of Polythioplatinate(II) [Pt3S2(SO3)6]10- and Study of Its Solution and Catalytic Properties

We have discovered the first polythioplatinate(II), [Pt^II₃S₂(SO₃)₆]^10- (1), which was synthesized in aqueous basic medium (pH 11) by hydrothermal heating at 150 °C. Polyanion 1 comprises a discrete, triangular assembly of three Pt²⁺ ions linked by two μ₃-sulfido ligands, and their square-planar coordination geometry is completed by two terminal S-bound sulfito ligands. Polyanion 1 was isolated as a hydrated sodium salt, Na₁₀[Pt^II₃(μ₃-S)₂(SO₃)₆]·22H₂O (Na-1), which was characterized in the solid state by single-crystal X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectra, and elemental analysis, in solution by ¹⁹⁵Pt NMR and atomic absorption spectroscopy, and in the gas phase by electrospray ionization mass spectrometry. Density functional theory calculations were performed, and the ¹⁹⁵Pt NMR chemical shifts of 1 were computed theoretically and shown to match well with the experimental data. Furthermore, the discrete title polyanion 1 was immobilized on mesoporous SBA-15 support and used as a precatalyst for the hydrogenation of o-xylene.

Discrete, Cationic Palladium(II)-Oxo Clusters via f-Metal Ion Incorporation and their Macrocyclic Host-Guest Interactions with Sulfonatocalixarenes

We report on the discovery of the first two examples of cationic palladium(II)‐oxo clusters (POCs) containing f‐metal ions, [Pd^II₆O₁₂M₈{(CH₃)₂AsO₂}₁₆(H₂O)₈]⁴⁺ (M=Ce^IV, Th^IV), and their physicochemical characterization in the solid state, in solution and in the gas phase. The molecular structure of the two novel POCs comprises an octahedral {Pd₆O₁₂}¹²⁻ core that is capped by eight M^IV ions, resulting in a cationic, cubic assembly {Pd₆O₁₂M^IV₈}²⁰⁺, which is coordinated by a total of 16 terminal dimethylarsinate and eight water ligands, resulting in the mixed Pd^II‐Ce^IV/Th^IV oxo‐clusters [Pd^II₆O₁₂M₈{(CH₃)₂AsO₂}₁₆(H₂O)₈]⁴⁺ (M=Ce, Pd₆Ce₈; Th, Pd₆Th₈). We have also studied the formation of host‐guest inclusion complexes of Pd₆Ce₈ and Pd₆Th₈ with anionic 4‐sulfocalix[n]arenes (n=4, 6, 8), resulting in the first examples of discrete, enthalpically‐driven supramolecular assemblies between large metal‐oxo clusters and calixarene‐based macrocycles. The POCs were also found to be useful as pre‐catalysts for electrocatalytic CO₂‐reduction and HCOOH‐oxidation.

Organorhodium(III)- and Iridium(III)-Substituted 20-Tungstobismuthates(III) and -Antimonates(III), [(MCp*)2X2W20O70]10- (M = RhIII and IrIII; X = BiIII and SbIII)

The synthesis of four organometallic RhCp*- and IrCp*-containing heteropoly-20-tungstates, [{RhCp*}₂Bi₂W₂₀O₇₀]^10- (1), [{IrCp*}₂Bi₂W₂₀O₇₀]^10- (2), [{RhCp*}₂Sb₂W₂₀O₇₀]^10- (3), and [{IrCp*}₂Sb₂W₂₀O₇₀]^10- (4) has been accomplished by reaction of (MCp*Cl₂)₂ with [X₂W₂₂O₇₄(OH)₂]^12- in aqueous solution at pH 6 and 70 °C. The four polyanions 1-4 were structurally characterized in the solid state by single-crystal XRD, FTIR, and TGA and in solution by ¹⁸³W and ¹³C NMR. For the Rh derivatives 1 and 3 the ¹⁸³W-¹⁰³Rh coupling (² J _W-Rh 3.0 Hz) could be identified by ¹⁸³W NMR.

Metallodrug Profiling against SARS-CoV-2 Target Proteins Identifies Highly Potent Inhibitors of the S/ACE2 interaction and the Papain-like Protease PLpro

The global spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has called for an urgent need for dedicated antiviral therapeutics. Metal complexes are commonly underrepresented in compound libraries that are used for screening in drug discovery campaigns, however, there is growing evidence for their role in medicinal chemistry. Based on previous results, we have selected more than 100 structurally diverse metal complexes for profiling as inhibitors of two relevant SARS-CoV-2 replication mechanisms, namely the interaction of the spike (S) protein with the ACE2 receptor and the papain-like protease PLpro . In addition to many well-established types of mononuclear experimental metallodrugs, the pool of compounds tested was extended to approved metal-based therapeutics such as silver sulfadiazine and thiomersal, as well as polyoxometalates (POMs). Among the mononuclear metal complexes, only a small number of active inhibitors of the S/ACE2 interaction was identified, with titanocene dichloride as the only strong inhibitor. However, among the gold and silver containing complexes many turned out to be very potent inhibitors of PLpro activity. Highly promising activity against both targets was noted for many POMs. Selected complexes were evaluated in antiviral SARS-CoV-2 assays confirming activity for gold complexes with N-heterocyclic carbene (NHC) or dithiocarbamato ligands, a silver NHC complex, titanocene dichloride as well as a POM compound. These studies might provide starting points for the design of metal-based SARS-CoV-2 antiviral agents.

Discovery of a Neutral 40-PdII-Oxo Molecular Disk, [Pd40O24(OH)16{(CH3)2AsO2}16]: Synthesis, Structural Characterization, and Catalytic Studies

We report on the synthesis and structural characterization of a giant, discrete, and neutral molecular disk, [Pd₄₀O₂₄(OH)₁₆{(CH₃)₂AsO₂}₁₆] (Pd₄₀), comprising a 40-palladium-oxo core that is capped by 16 dimethylarsinate moieties, resulting in a palladium-oxo cluster (POC) with a diameter of ∼2 nm. Pd₄₀, which is the largest known neutral Pd-based oxo cluster, can be isolated either as a discrete species or constituting a 3D H-bonded organic-inorganic framework (HOIF) with a 12-tungstate Keggin ion, [SiW₁₂O₄₀]^4- or [GeW₁₂O₄₀]^4-. ¹H and ¹³C NMR as well as ¹H-DOSY NMR studies indicate that Pd₄₀ is stable in aqueous solution, which is also confirmed by ESI-MS studies. Pd₄₀ was also immobilized on a mesoporous support (SBA15) followed by the generation of size-controlled Pd nanoparticles (diameter ∼2-6 nm, as based on HR-TEM), leading to an effective heterogeneous hydrogenation catalyst for the transformation of various arenes to saturated carbocycles.

NiII 36 -Containing 54-Tungsto-6-Silicate: Synthesis, Structure, Magnetic and Electrochemical Studies

The 36-NiII -containing 54-tungsto-6-silicate, [Ni36 (OH)18 (H2 O)36 (SiW9 O34 )6 ]6- (Ni36 ) was synthesized by a simple one-pot reaction of the Ni2 -pivalate complex [Ni2 (μ-OH2 )(O2 CCMe3 )4 (HO2 CCMe3 )4 ] with the trilacunary [SiW9 O34 ]10- polyanion precursor in water and structurally characterized by a multitude of physicochemical techniques including single-crystal XRD, FTIR, TGA, elemental analysis, magnetic and electrochemical studies. Polyanion Ni36 comprises six equivalent {NiII 6 SiW9 } units which are linked by Ni-O-W bridges forming a macrocyclic assembly. Magnetic studies demonstrate that the {Ni6 } building blocks in Ni36 remain magnetically intact while forming a hexagonal ring with antiferromagnetic exchange interactions between adjacent {Ni6 } units. Electrochemical studies indicate that the first reduction is reversible and associated with the WVI/V couple, whereas the second reduction is irreversible attributed to the NiII/0 couple.

Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, FeIII, ScIII, InIII, TiIV, MnII) and Their Magnetic Properties

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M₂(As^IIIW₆O₂₅)₂(As^IIIOH)_x]^n- (M = Cr^III, 1; Fe^III, 2; Sc^III, 3; In^III, 4; Ti^IV, 5; Mn^II, 6) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions 1-6 are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW₆} units, resulting in a structure with C_2h point-group symmetry. Polyanions 1-5 contain tri- and tetravalent metal ion guests M (M = Cr^III, Fe^III, Sc^III, In^III, and Ti^IV, respectively), and they have one {As^IIIOH} group grafted on each {AsW₆} unit, whereas the divalent Mn^II-containing derivative 6 has two such {As^IIIOH} groups grafted on each {AsW₆} unit. Magnetic studies on polyanions 3-5 over the temperature range 1.8-295 K and magnetic fields of 0-7 T confirmed that they are diamagnetic. On the other hand, polyanions 1, 2, and 6 are strongly magnetic and follow the Curie-Weiss law above 30 K. The susceptibility plots of 1 and 6 exhibit broad peaks suggesting short-range antiferromagnetic ordering, while the very weak antiferromagnetic ordering of 2 is overshadowed by traces of a paramagnetic impurity. The magnetization data of 1, 2, and 6 at 1.8 K over 0-7 T were analyzed by using the Heisenberg exchange procedure. Small (negative) values of the obtained J values help in understanding the absence of long-range antiferromagnetic ordering.

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.

Synthesis, structure, electrochemistry and magnetism of cobalt-, nickel- and zinc-containing [M4(OH)3(H2O)2(α-SiW10O36.5)2]13- (M = Co2+, Ni2+, and Zn2+)

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW₉O₃₄]^10- with cobalt(ii), nickel(ii) and zinc(ii) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M₄-containing heteropolytungstates [M₄(OH)₃(H₂O)₂(α-SiW₁₀O_36.5)₂]^13- (M = Co²⁺ (1), Ni²⁺ (2), and Zn²⁺ (3)). Polyanions 1-3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co²⁺ ions in 1 can be oxidized to Co³⁺ and the CVs of the W^VI centers of the polyanions feature well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic and antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction.

Discovery and Supramolecular Interactions of Neutral Palladium-Oxo Clusters Pd16 and Pd24

We report on the synthesis, structure, and physicochemical characterization of the first three examples of neutral palladium-oxo clusters (POCs). The 16-palladium(II)-oxo cluster [Pd16 O24 (OH)8 ((CH3 )2 As)8 ] (Pd16 ) comprises a cyclic palladium-oxo unit capped by eight dimethylarsinate groups. The chloro-derivative [Pd16 Na2 O26 (OH)3  Cl3  ((CH3 )2  As)8 ] (Pd16 Cl) was also prepared, which forms a highly stable 3D supramolecular lattice via strong intermolecular interactions. The 24-palladium(II)-oxo cluster [Pd24 O44 (OH)8 ((CH3 )2 As)16 ] (Pd24 ) can be considered as a bicapped derivative of Pd16 with a tetra-palladium-oxo unit grafted on either side. The three compounds were fully characterized 1) in the solid state by single-crystal and powder XRD, IR, TGA, and solid-state 1 H and 13 C NMR spectroscopy, 2) in solution by 1 H, 13 C NMR and 1 H DOSY spectroscopic methods, and 3) in the gas phase by electrospray ionization mass spectrometry (ESI-MS).

Growth of ultra-thin large sized 2D flakes at air–liquid interface to obtain 2D-WS2 monolayers

Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for future electronics. Currently, the growth of TMD large area thin films/flakes is one of the biggest challenges. A novel method for the growth of ultra-thin and large area WS2 monolayer flakes has been developed by introducing a solution-based temperature-dependent process. This two-dimensional WS2 growth process is low cost and environmentally friendly. WO3 flakes are grown at the air–liquid interface using ammonium tetrathiotungstate ((NH4)2WS4, ATTW) as WS2 precursor. The process requires a moderate activation temperature as no flakes are formed at room temperature. Successful growth of flakes was observed in an aqueous solution of the precursor at a temperature between 70 °C and 90 °C. These flakes could be transferred to any substrate by a controlled dip-coating process. Large 2D WS2 flakes with a lateral size of up to 100 μm were obtained after sulfurization. The thickness ranged from a WS2 monolayer to five monolayers, as verified by atomic force microscope. The chemical reaction mechanism behind the formation of the flakes was investigated by FTIR, Raman, UV–Vis and x-ray photoelectron spectroscopy. The initial flakes were found to be made of WO3, which were successfully converted to WS2 by a post annealing step at 500 °C–900 °C. This simple and environmentally friendly growth technique can be used to produce large WS2 flakes for next generation electronics.

PtIV- or MoVI-substituted decavanadates inhibit the growth of Mycobacterium smegmatis

Inhibitory effects of two monosubstituted decavanadates by Pt^IV in monoplatino(IV)nonavanadate(V) ([H₂Pt^IVV₉O₂₈]^5-, V₉Pt), and by Mo^IV in monomolybdo(VI)nonavanadate(V) ([Mo^VIV₉O₂₈]^5-,V₉Mo) were investigated against the growth of Mycobacterium smegmatis with the EC₅₀ values of 0.0048 mM and 0.015 mM, respectively. These compare to the reported inhibitory value for decavanadate ([V₁₀O₂₈]^6-/[HV₁₀O₂₈]^5-, V₁₀) on Mycobacterium smegmatis (EC₅₀ = 0.0037 mM). Time-dependent ⁵¹V NMR spectroscopic studies were carried out for all three polyanions in aqueous solution, biological medium (7H9), heated and non-heated supernatant to evaluate their stability in their respective media, monitor their hydrolysis to form various oxovanadates over time and calculate the EC₅₀ values. These studies allow us to calculate adjusted and maximum EC₅₀ for the polyoxovanadate (POV) present in solution at the beginning of the study when there is most intact anion in the media and thus the EC₅₀ values represent the initial effects of the POVs. The results have shown that V₁₀ is 1.3 times more potent than V₉Pt and 4 times more potent than V₉Mo, indicating that the inhibitory effects of monosubstituted polyanions are related to the V₁₀ structure. We attributed the minor differences in the growth inhibitory effects to the differences in charges (5- vs 6-) of V₉Pt and V₉Mo compared to V₁₀ and/or the differences in the chemical composition. We concluded that the potency of the growth inhibition by V₁₀ is mainly due to the chemical properties of the vanadium and the decametalate's unique structure even though the presence of the Mycobacterium smegmatis facilitate hydrolysis of the anions. SYNOPSIS: Two decavanadate derivatives, monoplatino(IV)nonavanadate(V) ([H₂Pt^IVV₉O₂₈]^5-), monomolybdo(VI)nonavanadate(V) ([Mo^VIV₉O₂₈]^5-) and decavanadate are more potent growth inhibitors of Mycobacterium smegmatis than monomeric vanadate. The spectroscopic characterization carried out in the growth medium led to the conclusion that both the decavanadate structure and its properties are important for its growth effects.

Peroxouranyl-Containing W48 Wheel: Synthesis, Structure, and Detailed Infrared and Raman Spectroscopy Study

We report on the first example of a peroxouranium-containing {P₈W₄₈} wheel, [{(UO₂)₄(O₂)₄}₂(P₈W₄₈O₁₈₄)]^40- (1), which was synthesized by a one-pot reaction of UO₂(NO₃)₂·6H₂O with the 48-tungsto-8-phosphate wheel [H₇P₈W₄₈O₁₈₄]^33- and aqueous hydrogen peroxide in a pH 6 lithium acetate solution at 50 °C. Polyanion 1 comprises two tetrauranyl squares with side-on peroxo bridging ligands in the cavity of the {P₈W₄₈} wheel, and was isolated as the hydrated potassium-lithium salt K₁₈Li₂₂[{(UO₂)₄(O₂)₄}₂(P₈W₄₈O₁₈₄)]·133H₂O (KLi-1), which was characterized in the solid state by single-crystal X-ray diffraction, as well as thermogravimetric and elemental analyses. A detailed Fourier transform infrared and Raman spectroscopy study was also performed.

Shape and Size Tuning of BiIII-Centered Polyoxopalladates: High Resolution 209Bi NMR and 205/206Bi Radiolabeling for Potential Pharmaceutical Applications

We have discovered five bismuth(III)-containing polyoxopalladates (POPs) which were fully characterized by solution and solid-state physicochemical techniques: the cube-shaped [BiPd₁₂O₃₂(AsPh)₈]^5- (BiPd₁₂AsL), [BiPd₁₂O₃₂(AsC₆H₄N₃)₈]^5- (BiPd₁₂AsL_N), and [BiPd₁₂O₃₂(AsC₆H₄COO)₈]^13- (BiPd₁₂AsL_C) as well as the star-shaped [BiPd₁₅O₄₀(PO)₁₀H₆]^11- (BiPd₁₅P) and [BiPd₁₅O₄₀(PPh)₁₀]^7- (BiPd₁₅PL), respectively. The organically modified capping groups phenylarsonate, p-azidophenylarsonate, and p-carboxyphenylarsonate were chosen as the azido (-N₃) and carboxyl (-COOH) groups open up opportunities to covalently conjugate (via click reaction, amide coupling, etc.) with targeting vectors. The synthesis of p-azidophenylarsonate is reported here for the first time. The effects of the Bi^III template and the organoarsonate vs -posphonate capping groups on the resulting POP shape (cube vs star) are discussed. The ²⁰⁹Bi NMR (I = 9/2) spectra of BiPd₁₂AsL, BiPd₁₂AsL_N, and BiPd₁₂AsL_C revealed narrow peaks (ν_1/2 ∼ 200 Hz) at 5470 ppm with a longitudinal relaxation time in the millisecond range (at 8.46 T). The absence of a quadrupolar relaxation contribution could be attributed to the allocation of Bi^III in the highly symmetrical cuboid POP host cage. Similar peaks were absent in the ²⁰⁹Bi-NMR spectra of the star-shaped POPs BiPd₁₅P and BiPd₁₅PL due to the less symmetric coordination environment around the central Bi^III ion. Further, ^205/206Bi-radiolabeled POPs have been synthesized by incorporating a ^205/206Bi^III ion in the center of the POP structures. Carrier-free ^205/206Bi radioisotopes (as surrogates of α-emitting ²¹³Bi) were incorporated into the POP host-cage for the preparation of ^205/206BiPd₁₂AsL, ^205/206BiPd₁₂AsL_N, ^205/206BiPd₁₂AsL_C, and ^205/206BiPd₁₅PL, respectively. The radiometal incorporation was complete (>99% radiochemical yield) in 10 min according to radio-thin-layer chromatography. The ^205/206BiPd₁₂AsL polyanion was purified by solid-phase extraction. The incubation in rat serum showed the formation of a ^205/206BiPd₁₂AsL-protein aggregate.

FeIII 48 -Containing 96-Tungsto-16-Phosphate: Synthesis, Structure, Magnetism and Electrochemistry

The 48‐Fe^III‐containing 96‐tungsto‐16‐phosphate, [Fe^III₄₈(OH)₇₆(H₂O)₁₆(HP₂W₁₂O₄₈)₈]³⁶⁻ (Fe₄₈), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {Fe^III₆P₂W₁₂} units that are linked in an end‐on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe₄₈ was synthesized by a simple one‐pot reaction of an {Fe₂₂} coordination complex with the hexalacunary {P₂W₁₂} POM precursor in water. The title polyanion was characterized by single‐crystal XRD, FTIR, TGA, magnetic and electrochemical studies.

Palladium(II)-Containing Tungstoarsenate(V), [PdII4(As2W15O56)2]16-, and Its Catalytic Properties

We have synthesized and structurally characterized the 4-palladium(II)-containing 30-tungsto-4-arsenate(V), [Pd₄(As₂W₁₅O₅₆)₂]^16- (1), which represents the first palladium(II)-containing tungstoarsenate(V). The title polyanion 1 was prepared by a simple one-pot procedure in aqueous medium and characterized by single-crystal X-ray diffraction (XRD), thermogravimetric analysis (TGA), cyclic voltammetry, elemental analysis, and ¹⁸³W nuclear magnetic resonance (NMR), infrared (IR), and ultraviolet-visible (UV-vis) spectroscopies. Polyanion 1 consists of four Pd²⁺ ions that are coordinated in a square-planar geometry to two trilacunary [As₂W₁₅O₅₆]^12- Wells-Dawson fragments resulting in a sandwich-type assembly. Catalytic studies on 1 revealed that it is an efficient catalyst precursor for the Suzuki-Miyaura cross-coupling reactions of various aryl halides in aqueous and nonaqueous media.

In Operando X-ray Studies of High-Performance Lithium-Ion Storage in Keplerate-Type Polyoxometalate Anodes

Polyoxometalates (POMs) have emerged as potential anode materials for lithium-ion batteries (LIBs) owing to their ability to transfer multiple electrons. Although POM anode materials exhibit notable results in LIBs, their energy-storage mechanisms have not been well-investigated. Here, we utilize various in operando and ex situ techniques to verify the charge-storage mechanisms of a Keplerate-type POM Na₂K₂₃{[(Mo^VI)Mo^VI₅O₂₁(H₂O)₃(KSO₄)]₁₂ [(V^IVO)₃₀(H₂O)₂₀(SO₄)_0.5]}·ca200H₂O ({Mo₇₂V₃₀}) anode in LIBs. The {Mo₇₂V₃₀} anode provides a high reversible capacity of up to ∼1300 mA h g^-1 without capacity fading for up to 100 cycles. The lithium-ion storage mechanism was studied systematically through in operando synchrotron X-ray absorption near-edge structure, ex situ X-ray diffraction, ex situ extended X-ray absorption fine structure, ex situ transmission electron microscopy, in operando synchrotron transmission X-ray microscopy, and in operando Raman spectroscopy. Based on the abovementioned results, we propose that the open hollow-ball structure of the {Mo₇₂V₃₀} molecular cluster serves as an electron/ion sponge that can store a large number of lithium ions and electrons reversibly via multiple and reversible redox reactions (Mo⁶⁺ ↔ Mo¹⁺ and V⁵⁺/V⁴⁺↔ V¹⁺) with fast lithium diffusion kinetics (D_Li⁺: 10^-9-10^-10 cm² s^-1). No obvious volumetric expansion of the microsized {Mo₇₂V₃₀} particle is observed during the lithiation/delithiation process, which leads to high cycling stability. This study provides comprehensive analytical methods for understanding the lithium-ion storage mechanism of such complicated POMs, which is important for further studies of POM electrodes in energy-storage applications.

Co-ion Effects in the Self-Assembly of Macroions: From Co-ions to Co-macroions and to the Unique Feature of Self-Recognition

Macroions, as soluble ions with a size on the nanometer scale, show unique solution behavior different from those of simple ions and large colloidal suspensions. In macroionic solutions, the counterions are known to be important and well-explored. However, the role of co-ions (ions carrying the same type of charge as the macroions) is often ignored. Here, through experimental and simulation studies, we demonstrate the role of co-ions as a function of co-ion size on their interaction with the macroions (using {Mo₇₂Fe₃₀} and {SrPd₁₂} as models) and the related self-assembly into blackberry-type structures in dilute solutions. Several regimes of unique co-ion effects are clearly identified: small ions (halides, oxoacid ions), subnanometer-scaled bulky ions (lacunary Keggin and dodecaborate ions), and those with sizes comparable to the macroions. Small co-ions have no observable effect on the self-assembly of fully hydrophilic {Mo₇₂Fe₃₀}, while due to hydrophobic interaction and intermolecular hydrogen bonds, the small co-ions show influences on the self-assembly of hydrophobic {SrPd₁₂}. Subnanometer ions, a.k.a. "superchaotropic ions", are still too small to assemble into a blackberry by themselves, but they can coassemble with the macroions, showing a strong interaction with the macroionic system. When the co-ion size is comparable to that of the macroions, they assemble independently instead of assembling with the macroions, leading to the previously reported unique self-recognition phenomenon for macroions.

Lanthanide-Containing 22-Tungsto-2-germanates [Ln(GeW11O39)2]13-: Synthesis, Structure, and Magnetic Properties

We report on the synthesis and structural characterization of two series of lanthanide-containing 22-tungsto-2-germanates. The first series corresponds to a family of polyanions with the formula [Ln(β₂-GeW₁₁O₃₉)₂]^13- (Ln^III = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Gd (6), Dy (7)), and the second series corresponds to a family with the formula [Ln(β₂-GeW₁₁O₃₉)(α-GeW₁₁O₃₉)]^13- (Ln^III = Ho (8), Er (9), Tm (10)). All compounds were characterized in the solid state by single-crystal and powder XRD, IR, TGA, and SQUID magnetometry. The polyanions were synthesized in aqueous medium by direct reaction of the monolacunary [β₂-GeW₁₁O₃₉]^8- POM precursor with the corresponding lanthanide salts. The structure of the polyanions consists of an 8-coordinated lanthanide ion in a square-antiprismatic geometry, which is sandwiched either between two [β₂-GeW₁₁O₃₉]^8- units for 1-7 or between a [β₂-GeW₁₁O₃₉]^8- and a [α-GeW₁₁O₃₉]^8- unit for 8-10. Furthermore, the effect of the central paramagnetic lanthanide ion on the magnetic behavior of the polyanions was investigated, with the erbium-derivative [Er(β₂-GeW₁₁O₃₉)(α-GeW₁₁O₃₉)]^13- (9) showing single-molecule magnet (SMM) behavior.

Polyoxometalates in Biomedicine: Update and Overview

BACKGROUND

Polyoxometalates (POMs) are negatively charged metal-oxo clusters of early transition metal ions in high oxidation states (e.g., WVI, MoVI, VV). POMs are of interest in the fields of catalysis, electronics, magnetic materials and nanotechnology. Moreover, POMs were shown to exhibit biological activities in vitro and in vivo, such as antitumor, antimicrobial, and antidiabetic.

METHODS

The literature search for this peer-reviewed article was performed using PubMed and Scopus databases with the help of appropriate keywords.

RESULTS

This review gives a comprehensive overview of recent studies regarding biological activities of polyoxometalates, and their biomedical applications as promising anti-viral, anti-bacterial, anti-tumor, and anti-diabetic agents. Additionally, their putative mechanisms of action and molecular targets are particularly considered.

CONCLUSION

Although a wide range of biological activities of Polyoxometalates (POMs) has been reported, they are to the best of our knowledge not close to a clinical trial or a final application in the treatment of diabetes or infectious and malignant diseases. Accordingly, further studies should be directed towards determining the mechanism of POM biological actions, which would enable fine-tuning at the molecular level, and consequently efficient action towards biological targets and as low toxicity as possible. Furthermore, biomedical studies should be performed on solutionstable POMs employing physiological conditions and concentrations.

In vivo toxicity evaluation of two polyoxotungstates with potential antidiabetic activity using Wistar rats as a model system

Study of the in vivo hypoglycemic effect, hepatotoxicity and nephrotoxicity of a donut-shaped polyanion salt (NH₄)₁₄[Na@P₅W₃₀O₁₁₀]·31H₂O {NaP5W30} and its Ag-containing derivative K₁₄[Ag@P₅W₃₀O₁₁₀]·22H₂O·6KCl {AgP5W30}.

Indium in Polyoxopalladate(II) Chemistry: Synthesis of All-Acetate-Capped [InPd12O8(OAc)16]5- and Controlled Transformation to Phosphate-Capped Double-Cube and Monocube

We have prepared the indium(III)-centered, all-acetate-capped polyoxopalladate(II) nanocube [InPd₁₂O₈(OAc)₁₆]^5- (InPd₁₂Ac₁₆), which can be further used as precursor to form the phosphate-capped (i) double-cube [In₂Pd₂₃O₁₇(OH)(PO₄)₁₂(PO₃OH)]^21- (In₂Pd₂₃P₁₃) and (ii) monocube [InPd₁₂O₈(PO₄)₈]^13- (InPd₁₂P₈). All three novel polyoxopalladates (POPs) were synthesized using conventional one-pot techniques in aqueous solution and characterized in the solid state (single-crystal XRD, IR, elemental analysis), in solution (¹¹⁵In, ³¹P, and ¹³C NMR), and in the gas phase (ESI-MS).

9-Cobalt(II)-Containing 27-Tungsto-3-germanate(IV): Synthesis, Structure, Computational Modeling, and Heterogeneous Water Oxidation Catalysis

The 9-cobalt(II)-containing trimeric, cyclic polyanion [Co₉(OH)₃(H₂O)₆(PO₄)₂(B-α-GeW₉O₃₄)₃]^21- (1) was synthesized in an aqueous phosphate solution at pH 8 and isolated as a hydrated mixed sodium-cesium salt. Polyanion 1 was structurally and compositionally characterized in the solid state by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, as well as thermogravimetric and elemental analyses. The magnetic and electrochemical properties of 1 were also studied and compared with those of its phosphorus analogue, [Co₉(OH)₃(H₂O)₆(HPO₄)₂(B-α-PW₉O₃₄)₃]^16- (Co₉-P). The electrochemical water oxidation activity of the cesium salt of 1 under heterogeneous conditions was also studied and shown to be superior to that of Co₉-P. The experimental results were supported by computational studies.

Tetravalent Metal Ion Guests in Polyoxopalladate Chemistry: Synthesis and Anticancer Activity of [MO8Pd12(PO4)8]12- (M = SnIV, PbIV)

The first two examples of polyoxopalladates(II) (POPs) containing tetravalent metal ion guests, [MO₈Pd₁₂(PO₄)₈]^12- (M = Sn^IV, Pb^IV), have been prepared and structurally characterized in the solid state, solution, and gas phase. The interactions of the metal ion guests and the palladium-oxo shell were studied by theoretical calculations. The POPs were shown to possess anticancer activity by causing oxidative stress inducing caspase activation and consecutive apoptosis of leukemic cells.

A 224Ra-labeled polyoxopalladate as a putative radiopharmaceutical

Despite their attractive properties, internal targeted alpha therapies using 223/224Ra are limited to bone-seeking applications. As there is no suitable chelator available, the search for new carriers to stably bind Ra2+ and to connect it to biological target molecules is necessary. Polyoxopalladates represent a class of compounds where Ra2+ can be easily introduced into the Pd-POM core during a facile one-pot preparation. Due to the formation of a protein corona, the connection to other targeting (bio)macromolecules is possible.

Discrete Polyoxopalladates as Molecular Precursors for Supported Palladium Metal Nanoparticles as Hydrogenation Catalysts

We have used discrete polyoxopalladates(II) (POPs) of the MPd₁₂X₈ nanocube- and Pd₁₅X₁₀ nanostar-types (M = central metal ion, X = capping group) as molecular precursors (diameter ca. 1 nm) for the formation of supported (SBA-15) metallic nanoparticles. These materials proved to be highly active in the hydrogenation of o-xylene. The characterization of such hydrogenation catalysts revealed that the average size of the resulting alloy particles is quite uniform with diameters ranging from 1 to 3 nm (indicating little to no agglomeration). The central transition-metal ion M ⁿ⁺ (Mn^II, Fe^III, Co^II, Ni^II, Cu^II, Zn^II, Pd^II) in the POP structure and also the nature of the capping group (AsO₄^3-, SeO₃^2-, PO₄^3-, phenyl-AsO₃^2-) influence the resulting catalytic performance.

Anti-zika virus activity of polyoxometalates

Zika virus (ZIKV) is an emerging infectious viral pathogen associated with severe fetal cerebral anomalies and the paralytic Guillain-Barrè syndrome in adults. It was the cause of a recent global health crisis following its entrance into a naïve population in the Americas. Nowadays, no vaccine or specific antiviral against ZIKV is available. In this study, we identified three polyoxometalates (POMs), the Anderson-Evans type [TeW₆O₂₄]^6- (TeW₆), and the Keggin-type [TiW₁₁CoO₄₀]^8-_ (TiW₁₁Co), and [Ti₂PW₁₀O₄₀]^7- (Ti₂PW₁₀), that inhibit ZIKV infection with EC₅₀s in the low micromolar range. Ti₂PW₁₀, the POM with the greatest selectivity index (SI), was selected and the step of ZIKV replicative cycle putatively inhibited was investigated by specific antiviral assays. We demonstrated that Ti₂PW₁₀ targets the entry process of ZIKV infection and it is able to significantly reduce ZIKV progeny production. These results suggest that the polyanion Ti₂PW₁₀ could be a good starting point to develop an effective therapeutic to treat ZIKV infection.