Influence of metal ions on the structures of Keggin polyoxometalate-based solids: Hydrothermal syntheses, crystal structures and magnetic properties |
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| Authors: | Zhenyu Shi Carlos J Gómez-García Xiaojun Gu |
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| Institution: | a Institute of Polyoxometalate Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China
b Instituto de Ciencia Molecular, Universidad de Valencia. Pol. La Coma s/n 46980 Paterna, Valencia, Spain |
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| Abstract: | Three new Keggin polyoxometalate (POM)-based compounds linked to 3d metal complexes have been synthesized under hydrothermal conditions: Cu(phen)2]2{Cu(phen)]2 SiMo12O40(VO)2]} (1), {Zn(phen)2]2GeMo12O40(VO)2]}{Zn(phen)2(H2O)]2 GeMo12O40(VO)2]}·3H2O (2) and {Co(phen)2]2PMo12O40(VO)2]}{Co(phen)2(OH)]2 PMo12O40(VO)2]}·2.5H2O (3) (phen=1,10-phenanthroline). These three compounds present, as building blocks, the bicapped Keggin anions XMo12O40(VO)2] (X=Si, Ge and P). Compound 1 consists of a bicapped Keggin anion SiMo12O40(VO)2]2− linked to two Cu(phen)]+ complexes with two Cu(phen)2]+ countercations. Compound 2 contains two bicapped Keggin anions GeMo12O40(VO)2]4−, one linked to two Zn(phen)2(H2O)]2+ cations and the other one linked to two Zn(phen)2]2+ cations. Compound 3 is a two-dimensional POM-based square network formed by bicapped Keggin anions PMo12O40(VO)2]4− connected by Co(phen)2]2+ cations. Discrete bicapped Keggin anions PMo12O40(VO)2] linked to two Co(phen)2(OH)]+ cations are located between the layers. The magnetic properties show the presence of antiferromagnetic interactions among the reduced Mo(V) atoms (in the three compounds) plus a paramagnetic contribution from the V(IV) atoms (in 1 and 2). Compound 3 shows, in addition, an antiferromagnetic interaction between the Co(II) and the V(IV) ions directly linked through an oxygen bridge. The low-temperature ESR spectra of compound 3 confirm the presence of the reduced Mo(V) ions and the antiferromagnetic coupling between the Co(II) and the V(IV) ions. |
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| Keywords: | Hydrothermal synthesis Bicapped Keggin Magnetic polyoxometalates |
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