Abstract
The first synthetic pathway using a series of four nonlacunary 4f-heterometal-substituted polyoxotungstate clusters Na21[(Ln(H2O)(OH)2(CH3COO))3(WO4)(SbW9O33)3]·nH2O (NaLnSbW9; Ln = TbIII, DyIII, HoIII, ErIII, YIII) as precursors for the directed preparation of nine new 3d–4f heterometallic tungstoantimonates K5Na12H3[TM(H2O)Ln3(H2O)5(W3O11)(SbW9O33)3]·nH2O (KTMLnSbW9; TM = CoII, NiII; Ln = TbIII, DyIII, HoIII, ErIII, YIII) 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 KCoLnSbW9 (Ln = TbIII, DyIII, HoIII, ErIII, YIII) heterometallic tungstoantimonates exhibiting the SbW9 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 SbW9 units encapsulating a planar triangle of LnIII ions in the case of NaLnSbW9 and a heterometallic core of one TMII and three LnIII for KTMLnSbW9 (TM = CoII, NiII; Ln = TbIII, DyIII, HoIII, ErIII, YIII). 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 KTMDySbW9 (TM = CoII, NiII) and KCoYSbW9 of the series revealed field-induced slow magnetic relaxation.
Highlights
Polyoxometalates (POMs)[1] are polyanions constructed of early-transition-state metals mostly in their highest oxidation states (V and VI), which are bridged by O atoms
Lacunary POMs have attracted significant attention in the past decades because they can be regarded as inorganic multidentate ligands toward electrophiles like transition metals (TMs) or lanthanides (Ln) to form more stable metal−oxo cluster structures.[7]
In order to prevent the formation of insoluble lanthanide hydroxides, a low pH value in the range of 5.5 was combined with high acetate concentrations considering the templating effect of organic ligands, which temporarily coordinate to the LnIII metal ions to decrease their overreactivity.[16]
Summary
Polyoxometalates (POMs)[1] are polyanions constructed of early-transition-state metals mostly in their highest oxidation states (V and VI), which are bridged by O atoms. Can be associated with the depopulation of MJ (Stark) sublevels of the DyIII centers.[28] In the case of KCoDySbW9, an additional contribution to decreasing the temperature dependence of magnetic susceptibility can be associated with the strong spin orbital component characteristic of octahedral CoII ions.[27,29,30] This contribution is present in the heterometallic compound KCoYSbW9, in which the strong paramagnetic ions are replaced by the diamagnetic yttrium(III) analogue. The dynamic properties of compounds KCoDySbW9 (Figure S24), KNiDySbW9 (Figure S26), and KCoYSbW9 (Figure S25) were studied by measuring the temperature- and field-dependent ac magnetic susceptibility (Figures 3 and 4). Second mechanism may be Raman or Orbach with a satisfactory agreement factor (R; Table S29 and Figures S27 and S28)
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