Zhangang Han

Highly reduced molybdophosphate as a noble-metal-free catalyst for the reduction of chromium using formic acid as a reducing agent

Highly reduced molybdophosphates with the formula (H2bpp)6{Co[Mo6O12(OH)3(HPO4)3-(H2PO4)]2}2·13H2O (1), (H2bpp)6[Co(H2O)2]4{Co[Mo6O12(OH)3(HPO4)2(H2PO4)(PO4)]2}2·2(HPO4)·12H2O (2), [Na(H2O)]2[Co(mbpy)(H2O)3]2[Co(mbpy)(H2O)]2{Co[Mo6O12(OH)3(HPO4)3(PO4)]2}·8H2O (3), and Na2[Co(mbpy)(H2O)3]4{Co[Mo6O12(OH)3(HPO4)3(PO4)]2}·13H2O (4) (bpp = 1,3-bi(4-pyridyl)propane, mbpy = 5,5′-dimethyl-2,2′-dipyridyl) have been synthesized and characterized. The primary structure of an anionic moiety in 1–4 consists of a Co(II) ion bridging two highly reduced [P4Mo6VO28(OH)3]9− ({P4Mo6}) units into an hourglass-shape {Co(P4Mo6)2} cluster. Four supramolecular assemblies have isomers and polymorphs with the difference in organic moieties: flexible bpp for 1 and 2 and chelated mbpy for 3 and 4, revealing that pH values play important roles in the assembling process of hybrids. Electrochemical and catalytic properties of these hybrids are investigated. The preliminary experiments show that this type of hybrid system is active for the electron transfer reaction of chromium(VI) reduction using formic acid at ambient temperature. Experimental results indicate that the reduction reaction can be carried out in a heterogeneous system with a lower reaction temperature and shorter reaction time. This kind of hybrid material is easy to prepare and structurally design, and has the potential to replace precious metals such as Pt/Pd nanoparticles used in this field.

Polyanionic clusters embedded in lattice-type hydrogen bonding networks involving in situ bond activation and coupling of organic cations

Two inorganic–organic supramolecular polyoxometalates, (H2chtpy)2[SiW12O40] (1) (chtpy = 1,3,4,6-tetra(4-pyridyl)cyclohexane-1,3-diol) and [Co(Hbztpy)2]H[AlW12O40]·3H2O (2) (bztpy = 1,2,4,5-tetra(4-pyridyl)benzene), have been hydrothermally synthesized and characterized. Both of them consist of complex supramolecular interactions between inorganic polyanions and organic cations. During the formation process of 1 and 2, in situ organic reactions involving C–C coupling through dehydrogenative cyclodimerization of two flexible 1,3-bis(4-pyridyl)propane (bpp) molecules were observed. The tetradentate pyridyl chtpy and bztpy molecules serve as 4-connected nodes to enrich the structural topologies of 1 and 2. The typical centered N–H⋯N (N⋯N = 2.6–2.7 A) hydrogen bonding interactions link the organic cations to form grid-type networks for capturing the pseudo-spherical Keggin-type anions. The pH values of the reaction solutions are important for the intermolecular C–C coupling of the organic molecules, and their transformation mechanisms are discussed.

Manganese-phosphomolybdate molecular catalysts for the electron transfer reaction of ferricyanide to ferrocyanide

Three manganese-containing phosphomolybdate hybrids (H2bpp)5[Na(Hbpp)]6H10{Mn[Mo6O12(OH)3(HPO4)4]2}4·14H2O (1), [Na4(H2bpp)2Mn(H2O)7]{Mn[Mo6O12(OH)3(HPO4)3(PO4)]2}·2H2O (2), and Na(H2O)2(Hbpp)3[Na2(bpp)(H2O)][Mn2(H2O)5]{Mn[Mo12O24(OH)6(HPO4)6(H2PO4)(PO4)]}·(HPO4)·H2O (3) (bpp = 1,3-bi(4-pyridyl)-propane) have been constructed and characterized. The inorganic moieties of the three hybrids consist of ‘hourglass-shaped’ anionic clusters, composed of two reduced polymolybdenum phosphate units [P4VMo6VO28(OH)3]9 {P4Mo6} bridged by one manganese ion. Preliminary experiments show that these hybrids, as a unique class of molecular catalyst, are highly active for promoting the inorganic electron transfer (redox) reaction of ferricyanide to ferrocyanide by thiosulphate with high rate constants under mild conditions. These catalysts maintain their structural identity both in solution and solid state and can be easily separated from the reaction solution for the next catalytic cycle.