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)]}.8H(2)O (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 VOs 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 bondvalence-sum calculations, the anionic cluster can be formulated as [V(15)(IV)Sb(III)6O(42)(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 V4+ centers of the cluster and the Fe2+ d(6) cations.