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 21 [(Ln(H 2 O)(OH) 2 (CH 3 COO)) 3 (WO 4 )(SbW 9 O 33 ) 3 ]· n H 2 O ( NaLnSbW 9 ; Ln = Tb III , Dy III , Ho III , Er III , Y III ) as precursors for the directed preparation of nine new 3d-4f heterometallic tungstoantimonates K 5 Na 12 H 3 [TM(H 2 O)Ln 3 (H 2 O) 5 (W 3 O 11 )(SbW 9 O 33 ) 3 ]· n H 2 O ( KTMLnSbW 9 ; TM = Co II , Ni II ; Ln = Tb III , Dy III , Ho III , Er III , Y III ) 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 KCoLnSbW 9 (Ln = Tb III , Dy III , Ho III , Er III , Y III ) heterometallic tungstoantimonates exhibiting the SbW 9 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 SbW 9 units encapsulating a planar triangle of Ln III ions in the case of NaLnSbW 9 and a heterometallic core of one TM II and three Ln III for KTMLnSbW 9 (TM = Co II , Ni II ; Ln = Tb III , Dy III , Ho III , Er III , Y III ). 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 KTMDySbW 9 (TM = Co II , Ni II ) and KCoYSbW 9 of the series revealed field-induced slow magnetic relaxation.