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

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]}·3H2O (2) and {[Co(phen)2]2[PMo12O40(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.

Three new Keggin polyoxometalate-based compounds have been synthesized under hydrothermal condition. These three compounds present the bicapped Keggin anions [XMo12O40(VO)2] (X=Si, Ge and P) as building blocks. Among the three compounds, compound 3 is a two-dimensional polyoxometalate-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.Figure optionsDownload as PowerPoint slide