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

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 [SiMo 12O 40(VO) 2]} ( 1), {[Zn(phen) 2] 2[GeMo 12O 40(VO) 2]}{[Zn(phen) 2(H 2O)] 2 [GeMo 12O 40(VO) 2]}·3H 2O ( 2) and {[Co(phen) 2] 2[PMo 12O 40(VO) 2]}{[Co(phen) 2(OH)] 2 [PMo 12O 40(VO) 2]}·2.5H 2O ( 3) (phen=1,10-phenanthroline). These three compounds present, as building blocks, the bicapped Keggin anions [ XMo 12O 40(VO) 2] ( X=Si, Ge and P). Compound 1 consists of a bicapped Keggin anion [SiMo 12O 40(VO) 2] 2− linked to two [Cu(phen)] + complexes with two [Cu(phen) 2] + countercations. Compound 2 contains two bicapped Keggin anions [GeMo 12O 40(VO) 2] 4−, one linked to two [Zn(phen) 2(H 2O)] 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 [PMo 12O 40(VO) 2] 4− connected by [Co(phen) 2] 2+ cations. Discrete bicapped Keggin anions [PMo 12O 40(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.