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

摘要

Four new architectures containing [Co2Mo10H4O38](6-) polyoxoanions, (C2N2H10)(2)[Sr(H2O)(5)] [Co2Mo10H4O38]center dot 2H(2)O 1, (C2N2H10)(2)[Ba(H2O)(3)][Co2Mo10H4O38]center dot 3H(2)O 2, (C3N2H12)(2)[Sr(H2O)(5)] [Co2Mo10H4O38]center dot 3H(2)O 3 and (C3N2H12)[Ba(H2O)(4)][Ba(H2O)(4)][Co2Mo10H4O38]center dot 2H(2)O(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.