Influence of metal ions on the structures of Keggin polyoxometalate-based solids: Hydrothermal syntheses, crystal structures and magnetic properties

摘要

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)](2)[GeMo12O40(VO)(2)]}{[Zn(phen)(2)(H2O)](2) [GeMo12O40(VO)(2)]}center dot 3H(2)O (2) and [Co(phen)(2)](2)[PMo12O40(VO)(2)]}{[Co(phen)(2)(OH)](2) [PMo12O40(VO)(2)]}center dot 2.5H(2)O (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 anti ferromagnetic interactions among the reduced Mo(V) atoms (in the three Compounds) plus a paramagnetic contribution from the V(IV) atoms (in I 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. (c) 2005 Elsevier Inc. All rights reserved.