RESUMEN
Reaction of the mixed-valent Mn12-acetato complex [MnIII8MnIV4O12(CH3COO)16(H2O)4] with the trilacunary Wells-Dawson-type heteropolytungstate [P2W15O56]12- in acidic acetate solution (pH 1.1) resulted in the tetra-MnIII-containing polyanion [MnIII4(H2O)2(P2W15O56)2]12- (1). Single-crystal XRD on Na12[MnIII4(H2O)2(P2W15O56)2]·84H2O (1a) revealed that four MnIII ions form a rhombic Mn4O16 core encapsulated by two [P2W15O56]12- units. X-ray photoelectron spectroscopy (XPS) data confirm the +3 oxidation state of the four manganese ions in 1. Magnetic measurements from 1.8-300 K in a 100 Oe magnetic field allowed for the extraction of full fitting parameters from the susceptibility data for 1. The negative Ja value (Ja = -2.16 ± 0.08 K, Jb = 3.24 ± 1.73 K, g = 2.35 ± 0.040, and ρ = 0.34 ± 0.03) suggests a dominant antiferromagnetic spin exchange interaction between the four MnIII ions, with the positive Jb being an accompanying result of Ja. Electrochemical studies revealed a reversible MnIV/MnIII redox couple in 1 at the +0.80 to +1.1 V potential region with E1/2 = +0.907 V.
RESUMEN
We report on the synthesis and characterization of the first polyoxo-noble-metalate-containing metal-organic framework (MOF) material, wherein the preformed MIL-101 has been impregnated with the discrete, cuboid-shaped polyoxopalladate [Pd13Se8O32]6- (Pd13Se8), leading to the composite Pd13Se8@MIL-101. This material was characterized by FTIR, TGA, elemental analysis, powder-XRD, N2 sorption (BET), SEM-EDX, and XPS. Furthermore, the Pd13Se8@MIL-101 composite was shown to be an effective, stable, and recyclable heterogeneous precatalyst for the Suzuki-Miyaura cross-coupling reaction at room temperature utilizing environmentally benign solvents, such as water and methanol.
RESUMEN
The class of peroxo-cerium-containing polyoxometalates has been discovered via the synthesis of the 9-peroxo-6-cerium(IV)-containing 30-tungsto-3-germanate, [CeIV6(O2)9(GeW10O37)3]24- (1). Polyanion 1 consists of a cyclic [Ce6(O2)9]6+ assembly that is stabilized by three dilacunary [GeW10O37]10- Keggin fragments. The title polyanion 1 is solution-stable, on the basis of 183W nuclear magnetic resonance, and was shown to act as a recyclable homogeneous catalyst for the selective, microwave-activated sulfoxidation of the model substrate methionine to the sulfoxide in the absence and to the sulfone in the presence of hydrogen peroxide. Solution and solid-state Raman as well as solid-state infrared studies of 1 demonstrated the complete loss (and regain) of the nine peroxo groups in situ during the catalytic cycle, suggesting that the peroxo-free {Ce6(GeW10)3} skeleton remains most likely intact during the catalytic cycle. Solid-state X-ray photoelectron spectroscopy measurements showed that peroxo loss is accompanied by reduction of the cerium ions from +4 to +3, which is fully reversible. Density functional theory calculations are in complete agreement with all of these observations and furthermore suggest that the reduction of the six cerium(IV) ions is accompanied by the formation of molecular dioxygen.
RESUMEN
Here we report on the synthesis, structure, and characterization of the first example of a polyoxopalladate (POP)-based metal-organic framework (MOF). This novel class of materials comprises discrete polyoxo-13-palladate(II) nanocubes [Pd13O8(AsO4)8H6]8- decorated by four Ba2+ ions on each of two opposite faces. These secondary building units (SBUs) are linked to each other via rigid linear organic groups, resulting in a stable 3D POP-MOF framework, which exhibits interesting sorption as well as catalytic properties.
