Stabilization of Ni-containing Keggin-type polyoxometalates with variable oxidation states as novel catalysts for electrochemical water oxidation.

The development of new recyclable and inexpensive electrochemically active species for water oxidation catalysis is the most crucial step for future utilization of renewables. Particularly, transition metal complexes containing internal multiple, cooperative metal centers to couple with redox catalysts in the inorganic Keggin-type polyoxometalate (POM) framework at high potential or under extreme pH conditions would be promising candidates. However, most reported Ni-containing POMs have been highly unstable towards hydrolytic decomposition, which precludes them from application as water oxidation catalysts (WOCs). Here, we have prepared new tri-Ni-containing POMs with variable oxidation states by charge tailored synthetic strategies for the first time and developed them as recyclable POMs for water oxidation catalysts. In addition, by implanting corresponding POM anions into the positively charged MIL-101(Cr) metal-organic framework (MOF), the entrapped Ni2+/Ni3+ species can show complete recyclability for water oxidation catalysis without encountering uncontrolled hydrolysis of the POM framework. As a result, a low onset potential of approximately 1.46 V vs. NHE for water oxidation with stable WOC performance is recorded. Based on this study, rational design and stabilization of other POM-electrocatalysts containing different multiple transition metal centres could be made possible.

A one-dimensional chain of manganese(II) bridged peroxomolybdate isolated from an aqueous Mn-polymolybdate-H2O2 system.

A new manganese(II)-peroxomolybdate complex, Cs4[Mn(OH2)2(Mo7O22(O2)2)]·4.25H2O (Cs-1), was isolated from an aqueous solution containing manganese(II) sulfate, sodium heptamolybdate and hydrogen peroxide by the addition of Cs+ salt. Cs-1 was characterized by single crystal X-ray diffraction, thermogravimetry (TG), IR spectroscopy, powder X-ray diffraction (PXRD), cyclic voltammetry (CV) and ultraviolet-visible spectroscopy (UV-vis). The diperoxoheptamolybdate [Mo7O22(O2)2]6- units were linked by Mn(II) ions to form a one-dimensional infinite chain of [Mn(OH2)2(Mo7O22(O2)2)]n4n-, which represents a unique structure with the coexistence of the oxidant-reductant pair O22-/Mn2+. The interconversion between [MnII(OH2)2(Mo7O22(O2)2)]4- and [MnMo9O32]6- in the aqueous solution was monitored by UV-vis spectrophotometry. It indicates that 1 is a key intermediate during the redox cycle of Mn(II) and Mn(IV) in the Mn-polyoxometalate-H2O2 system. In the oxidation process of 3,3',5,5'-tetramethylbenzidine and ortho-phenylenediamine by H2O2, Cs-1 shows notable activity as an enzyme mimetic catalyst.

H3PMo12O40 Immobilized on Amine Functionalized SBA-15 as a Catalyst for Aldose Epimerization.

In this work various amount of phosphomolybdic acid (PMo) were immobilized on amine functionalized SBA-15 and used as heterogeneous catalysts in the epimerization of glucose in aqueous solution. 13.3PMo/NH2-SBA-15 exhibited the best catalytic performance with a glucose conversion of 34.8% and mannose selectivity of 85.6% within two hours at 120 °C. The activation energy of 80.1 ± 0.1 kJ·mol-1 was lower than that of 96 kJ·mol-1 over the homogeneous H3PMo12O40 catalyst. The catalytic activities of 13.3PMo/NH2-SBA-15 for the transformation of some other aldoses including mannose, arabinose and xylose were also investigated.

Eremophilane-type sesquiterpene lactones from Ligularia hodgsonii Hook.

A dimeric eremophilane sesquiterpene lactone with a cyclobutane ring, biliguhodgsonolide (1) and an uncommon seco-sesquiterpene derivative, (4S,5S,6R,10R)-8,9-seco-12-hydroxyeremophil-7(11)-en-14,6;12,8-diolid-9-al (2), were isolated from the roots and rhizomes of Ligularia hodgsonii Hook. Their structures, including the absolute stereochemistry, were elucidated by spectroscopic data and CD analysis. The cyclobutane ring was confirmed by single-crystal X-ray diffraction.

Chemical constituents of Gentiana macrophylla Pall.

A novel dimeric secoiridoid glucoside, gentimacroside (1), and six known compounds (2-7) were isolated from the roots of Gentiana macrophylla Pall. Their structures were established on the basis of spectroscopic analysis, especially by means of 1D-, 2D-NMR and HRESIMS analyses.