Systematic Study of the Interaction Between V~(IV) Centres and Ln~(III) Ions in Well Defined {V_2~(IV)Ln~(III)}{As~(III)W_9O_(33)}_2 Sandwich-Type Clusters: Part 2

摘要

The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK_6Gd_(0.33) [((VO)_2Gd(H_2O)_4K_2(H_2O)_2(Na)(H_2O)_2)(α-BAsW_9O_(33))_2]?24H_2O (1) was prepared from acidified aqueous solutions of Na_2WO_4?2H_2O, As_2O_3 and VOSO_4?5H_2O to which Gd~(3+) ions were added. The single crystal X-ray structure analysis (monoclinic, space group P2_1/m) shows that the anion consists of two [α-B-AsIIIW_9O_(33)]~(9-) trilacunary Keggin-type units linked by two VO~(2+), one Gd~(3+) as well as weakly by two K~+ and one Na~+ ions, resulting in a sandwich-type structure with idealized C_(2v) symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J_(VV) = -2.55 cm~(-1) (anti-ferromagnetic) between the vanadium ions and J_(GdV) = 0.6 cm~(-1) (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na~+ sites in the counter-cation-water system by Gd~(3+) ions (0.33 Gd~(3+) ions in total).