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.