Antimonato polyoxovanadate based three-dimensional framework exhibiting ferromagnetic exchange interactions: synthesis, structural characterization, and magnetic investigation of {[Fe(C6H14N2)2]3[V15Sb6O42(H2O)]}·8H2O.

The new polyoxovanadate {[Fe(C6H14N2)2]3[V15Sb6O42(H2O)]}·8H2O (1) was obtained under solvothermal conditions using the amine that acts at the same time as the ligand, solvent, and reducing agent. The central structural motif of 1, [V15Sb6O42(H2O)](6-), is related to the {V18O42}-archetype cluster by replacing three VO5 square pyramids with three O2Sb-O-SbO2 moieties. Every [V15Sb6O42(H2O)](6-) cluster anion is expanded by six FeN4O2 octahedra, thus generating a rare three-dimensional network with differently sized pores hosting the crystal water molecules. In 1, two [V15Sb6O42(H2O)](6-) cluster anions with different orientations coexist. According to bond-valence-sum calculations, the anionic cluster can be formulated as [V(IV)15Sb(III)6O42(H2O)](6-), i.e., in line with the valence states of all other known {V15Sb6} clusters. The optical band gap of 1 was determined as 2.47 eV. Investigation of the magnetic behavior indicates dominating ferromagnetic exchange interactions between the V(4+) centers of the cluster and the Fe(2+) d(6) cations.