Tetrapalladium-Containing Polyoxotungstate [PdII4(α-P2W15O56)2]16–: A Comparative Study

A Palladium-Containing Polyoxotungstate with Anisotropic Proton Conductivity

Here, a case of bilayer heterojunction Pd-containing polyoxotungstate (POW), connecting a Te3Pd3 ring and an Anderson-like TeW6 cluster, has been synthesized. The Anderson-like cluster is the first example in POW. The coordination of Pd in the ring with the S atom on the sulfo group breaks the traditional coordination configuration of Pd and O in polyoxometalates (POMs), enriching the structural types of Pd-containing POMs. In addition, the hybrid bilayer heterojunction structure at the molecular level not only provides high thermal stability but also results in spatial arrangement anisotropy, leading to up to five times the anisotropic proton conductivity.

Coordination of Palladium(II) and Platinum(II) Complexes to One Vacant Site in an α-Keggin-Type Polyoxotungstate

A palladium-platinum bimetal complex containing a mono-lacunary α-Keggin-type polyoxotungstate is demonstrated. The bimetallic complex Cs_2.5{Pd^II(bpy)}_0.25[α-PW₁₁O₃₉{Pd^II(bpy)}{cis-Pt^II(NH₃)₂}]·12H₂O·2CH₃CN (bpy = 2,2'-bipyridine) (PdPt) was synthesized by the reaction of Cs_4.9K_0.1[α-PW₁₁O₃₉{cis-Pt^II(NH₃)₂}]·10H₂O (Pt1) with Pd^II(bpy)Cl₂ in aqueous solution. The compound PdPt was characterized via elemental analysis, thermogravimetric/differential thermal analysis, and Fourier transform infrared, ultraviolet-visible, cold-spray ionization mass, and solution (¹H, ¹³C, and ³¹P) nuclear magnetic resonance spectroscopies. The coordination of {cis-Pt^II(NH₃)₂} and {Pd^II(bpy)} moieties to the mono-vacant site of [PW₁₁O₃₉]^7- resulted in an asymmetric, monomeric compound. A unique exchange reaction between the counter cation [Pd^II(bpy)]²⁺ and {cis-Pt^II(NH₃)₂} moiety in [α-PW₁₁O₃₉{Pd^II(bpy)}{cis-Pt^II(NH₃)₂}]^3- in a dimethylsulfoxide solution was also observed.

Synthesis and high proton conductivity of an indium-substituted Keggin-type quaternary heteropoly acid

The synthesis and characterization of an indium-substituted quaternary heteropoly acid with a Keggin structure, H4[In(H2O)PW9Mo2O39]·11H2O (PMo9W2In), is reported. At 18 °C under 80% relative humidity, PMo9W2In displays protonic conductivity of 2.32 × 10-4 S cm-1 with an activation energy of 35.52 kJ mol-1, indicating that it is a potential solid protonic conductor following the vehicle mechanism. Its conductivity increases with temperature in the measured temperature range.

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.

Classical/Non-classical Polyoxometalate Hybrids

Two polyanions [Se^I V₂ Pd^II₄ W^VI₁₄ O₅₆ H]^11- and [Se^I V₄ Pd^II₄ W^VI₂₈ O₁₀₈ H₁₂ ]^12- are the first hybrid polyoxometalates in which classical (Group 5/6 metal based) and non-classical (late transition-metal based) polyoxometalate units are joined. Requiring no supporting groups, this co-condensation of polyoxotungstate and isopolyoxopalladate constituents also provides a logical link between POM-Pd^II coordination complexes and the young subclass of polyoxopalladates. Solid-state, solution, and gas-phase studies suggest interesting specific reactivities for these hybrids and point to several potential derivatives and functionalization strategies.