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), is related to the {V18O42}-archetype cluster by replacing three VO5 square pyramids with three O2Sb-O-SbO2 moieties. Every V15Sb6O42(H2O) 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) 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), 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.