Nature of the LnIII–CoII magnetic interactions in compounds [Ln2Co3(C5H4NPO3)6] · 4H2O with open-framework structures

The reactions of Ln(NO3)3 · xH2O, CoSO4 · 7H2O or ZnSO4 · 6H2O and 2-pyridylphosphonic acid under hydrothermal conditions result in heterometallic phosphonate compounds with formula [Ln2M3(C5H4NPO3)6] · 4H2O (Ln2M3; M = CoII or ZnII; Ln = LaIII, CeIII, PrIII, NdIII, SmIII, EuIII, GdIII, TbIII, DyIII). These compounds are isostructural and crystallize in a chiral cubic space group I213. Each structure contains the {LnO9} polyhedra and {MN2O4} octahedra which are connected by edge-sharing to form an inorganic open-framework structure with a 3-connected 10-gon (10, 3) topology. The nature of LnIII–CoII magnetic interactions in Ln2Co3 is investigated by a comparison with their LnIII–ZnII analogues. It is found that the LnIII–CoII interaction is weak antiferromagnetic for Ln = Ce and ferromagnetic for Ln = Sm, Gd, Tb and Dy. In the cases of Ln = Pr, Nd and Eu, no significant magnetic interaction is observed.