Triazolyl, Imidazolyl, and Carboxylic Acid Moieties in the Design of Molybdenum Trioxide Hybrids: Photophysical and Catalytic Behavior


Three organic ligands bearing 1,2,4-triazolyl donor moieties, (S)-4-(1-phenylpropy1)-1,2,4-triazole (trethbz), 4-(1,2,4-triazol-4-yl)benzoic acid (trPhCO(2)H), and 3-(1H-imidazol-4-y1)-2-(1,2,4-triazol-4-yl)propionic acid (trhis), were prepared to evaluate their coordination behavior in the development of molybdenum(VI) oxide organic hybrids. Four compounds, [Mo2O6(trethbz)(2)]-H2O (1), [Mo4O12(trPhCO(2)H) center dot 0.5 H2O (2a), [Mo4O12(trPhCO(2)H)(2)]center dot H2O (2b), and [Mo8O25(trhisH)(2)(trhisH)(2)]center dot 2H(2)O (3), were synthesized and characterized. The monofunctional tr-ligand resulted in the formation of a zigzag chain [Mo2O6(trethbz)(2)] built up from cis-{MoO4N2} octahedra united through common mu(2)-O vertices. Employing the heterodonor ligand with tr/-CO2H functions afforded either layer or ribbon structures of corner- or edge-sharing {MoO5N} polyhedra (2a or 2b) stapled by tr-links in axial positions, whereas -CO2H groups remained uncoordinated. The presence of the im-heterocycle as an extra function in trhis facilitated formation of zwitterionic molecules with a protonated imidazolium group (imH(+)) and a negatively charged -CO2- group, whereas the tr-fragment was left neutral. Under the acidic hydrothermal conditions used, the organic ligand binds to molybdenum atoms either through [N-N]-tr or through both [N-N]-tr and mu(2)-CO2- units, which occur in protonated bidentate or zwitterionic tetradentate forms (trhisH' and trhis, respectively). This leads to a new zigzag subtopological motif (3) of negatively charged polyoxomolybdate {Mo8O25}(n)(2n-) consisting of corner- and edge -sharing cis-{MoO4N2} and {MoO6} octahedra, while the tetradentate zwitterrionic trhis species connect these chains into a 2D net. Electronic spectra of the compounds showed optical gaps consistent with semiconducting behavior. The compounds were investigated as epoxidation catalysts via the model reactions of achiral and prochiral olefins (cis-cyclooctene and trans-beta-methylstyrene) with tert-butylhydroperoxide. The best -performing catalyst (1) was explored for the epoxidation of other olefins, including biomass -derived methyl oleate, methyl linoleate, and prochiral DL-limonene.



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Lysenko, AB; Senchyk, GA; Domasevitch, KV; Kobalz, M; Krautscheid, H; Cichos, J; Karbowiak, M; Neves, P; Valente, AA; Goncalves, IS

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Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged. The Portuguese (PT) group acknowledge the FCT and the European Union for a postdoctoral grant to P.N. (SFRH/BPD/110530/2015) cofunded by MCTES and the European Social Fund through the program POPH of QREN. This work was developed in the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 [FCT (Fundacao para a Ciencia e a Tecnologia) ref UID/CTM/50011/2013], financed by national funds through the FCT/MEC and when applicable cofinanced by FEDER (Fundo Europeu de Desenvolvimento Regional) under the PT2020 Partnership Agreement. DFT calculations have been carried out using resources provided by the Wroclaw Centre for Networking and Supercomputing (, grant no. 415, using Materials Studio 8.0 software provided by PLATON U3, Service Platform for e-Science. J.C. acknowledges financial support from the Foundation for Polish Science.

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