Cation-Directed Synthetic Strategy Using 4f Tungstoantimonates as Nonlacunary Precursors for the Generation of 3d-4f Clusters.

The first synthetic pathway using a series of four nonlacunary 4f-heterometal-substituted polyoxotungstate clusters Na[(Ln(HO)(OH)(CHCOO))(WO)(SbWO)]·HO (; Ln = Tb, Dy, Ho, Er, Y) as precursors for the directed preparation of nine new 3d-4f heterometallic tungstoantimonates KNaH[TM(HO)Ln(HO)(WO)(SbWO)]·HO (; TM = Co, Ni; Ln = Tb, Dy, Ho, Er, Y) has been developed. Systematic studies revealed an increased K content in the aqueous acidic reaction mixture to be the key step in the cation-directed preparation of 3d-4f compounds; among those, the Co-containing members represent the first examples of (Ln = Tb, Dy, Ho, Er, Y) heterometallic tungstoantimonates exhibiting the building block. All 13 compounds have been characterized thoroughly in the solid state by powder and single-crystal X-ray diffraction (XRD), revealing a cyclic trimeric polyoxometalate architecture with three units encapsulating a planar triangle of Ln ions in the case of and a heterometallic core of one TM and three Ln for (TM = Co, Ni; Ln = Tb, Dy, Ho, Er, Y). The results obtained by XRD are supplemented by complementary characterization methods in the solid state such as IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by UV-vis spectroscopy. Detailed magnetic studies on the representative compounds (TM = Co, Ni) and of the series revealed field-induced slow magnetic relaxation.