Evans-Showell-type polyoxometalate constructing novel 3D inorganic architectures with alkaline earth metal linkers: syntheses, structures and catalytic properties.

Abstract

Four new architectures containing [Co2Mo10H4O38]6- polyoxoanions, (C2N2H10)2[Sr(H2O)5][Co2Mo10H4O38]·2H2O 1, (C2N2H10)2[Ba(H2O)3][Co2Mo10H4O38]·3H2O 2, (C3N2H12)2[Sr(H2O)5][Co2Mo10H4O38]·3H2O 3 and (C3N2H12)[Ba(H2O)4][Ba(H2O)4][Co2Mo10H4O38]·2H2O 4 (C2N2H10 = ethylenediamine; C3N2H12 = 1,3-propanediamine) have been synthesized and characterized by elemental analysis, IR spectroscopy, solid diffuse reflective spectroscopy, TG analysis, powder X-ray diffraction and single crystal X-ray diffraction. Compounds 1 and 2 obtained in the presence of ethylenediamine, are made of Evans-Showell-type anions [Co2Mo10H4O38]6-, linked by Sr2+ or Ba2+ cations to form 3D frameworks. To our knowledge, compound 1(2) represents the first example of 3D architecture in which the Evans-Showell anions [Co2Mo10H4O38]6- were linked by pure alkaline earth cations. When propanediamine was used instead of ethylenediamine, compounds 3 and 4 with 2D networks were obtained. This phenomenon indicates that the organic cations, which adjust the reaction pH values, can induce different dimensional inorganic frameworks. As heterogeneous catalysts, compounds 1-4 show excellent catalytic performance in the cyanosilylation of carbonyl compounds. Furthermore, these catalytic reactions were performed under solvent-free conditions using only a low amount of the catalysts, and these catalysts can be recovered and reused without displaying any significant loss of activity. As far as we know, compounds 1-4 represent the first examples of cyanosilylation catalyzed by POM-based species containing alkaline earth metal cations.