A new redox-based approach for synthesizing a mixed-valence hybrid polymolybdate uncommonly bicapped by Cr(III) coordination complexes

摘要

The grafting of Cr(III) coordination complexes as capping units onto polyoxometalates (POMs), still remains a considerable synthetic challenge due to the difficulty in replacement of aqua-ligands in [Cr(H2O)(6)](3+) complexes. A new synthetic method was developed, from in situ reduced dichromate ions, to generate Cr(III) ions, which were designed to coordinate to organic ligands simultaneously, while they were linking to nucleophilic oxygen atoms of the POM. Using two-step redox reactions, we successfully synthesized a new mixed-valence hybrid polymolybdate, [H3O][Hdmab[H(2)phen]{[Cr(phen)](2) [(Mo9Mo3O36)-Mo-V-O-VI(PO4)])}center dot nH(2)O (n approximate to 1) (1) (where dma = dimethylamine (C2H7N); phen = 1,1 0-phenanthroline (C12H8N2)) under hydrothermal conditions. The single-crystal X-ray diffraction analysis indicated that compound 1 contains the first reported example of {[Cr(phen)](2) [(Mo9Mo3O36)-Mo-V-O-VI(PO4)])}(6-) polyanion, a type of Keggin-structural heteropoly blue building block, uncommonly bicapped by Cr(III) coordination complexes. The structure was further characterized by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, elemental analysis, cerate oxidimetry, and thermal analysis measurements. This study provides a new method for the syntheses of other novel capped structural POMs using rate-controlling redox steps. (C) 2014 Published by Elsevier Ltd.