Add time:08/17/2019         Source:sciencedirect.com

Complexes of type A4[VO(tart)]2·nH2O, where A = Rb or Cs and tart =d,l-tartrate(4−) (n = 2) or d,d-tartrate(4−) (n = 2 for Rb and n = 3 for Cs), were prepared from an aqueous mixture of V2O5, AOH and H4tart. These complexes were studied by single-crystal X-ray diffraction methods: Rb4[VO(d,l-tart)]2·2H2O, space group P1 with a = 8.156(1),b = 8.246(1),c = 8.719(1)Å, α = 66.09(1)°, β = 65.07(1)°, γ = 82.40(1)°,Z = 2, 1917 observed reflections, and final Rw = 0.035; Cs4[VO(d,l-tart)]2·2H2O, space group P21/c with a = 9.350(1),b = 13.728(2),c = 8.479(1)Å, β = 106.77(1)°,Z = 4, 2235 observed reflections, and final Rw = 0.054; Rb4[VO(d,d-tart)]2·2H2O, space group P4122 with a = 8.072(1),c = 32.006(3)Å,Z = 8, 1014 observed reflections and final Rw = 0.038; Cs4[VO(d,d-tart)]2·3H2O, space group P122 with a = 8.184(1),c = 33.680(5)Å,Z = 8, 1310 observed reflections, and final Rw = 0.063. Bulk magnetic susceptibility data (1.5–300 K) for these compounds and A4[VOl,l-tart)]2·nH2O (A = Rb, Cs) were obtained on polycrystalline samples. These data were analyzed in terms of a Van Vleck exchange coupled S = 1/2 model which was modified to include an interdimer exchange parameters Θ. Analysis of the low-temperature (1.5–20 K) susceptibility data gave 2J = +1.30 cm−1 and Θ = −1.86 K for Rb4[VO(d,l-tart)]2·2H2O, 2J = +1.16 cm−1 and Θ = −1.69 K for Cs4[VO(d,l-tart)]2·2H2O, 2J = +1.90 cm−1 and Θ = −0.82 K for Rb4[VO(d,d-tart)]2·2H2O, 2J = +2.04 cm−1 and Θ = −0.80 K for Rb4[VO(l,l-tart)]2·2H2O, 2J = +1.52 cm−1 and Θ = −0.25 K for Cs4[VO(d,d-tart)]2·3H2O, and 2J = +1.64 cm−1 and Θ = −0.31 K for Cs4[VO(l,l-tart)]2·3H2O. These results suggest the magnitudes of intradimer (ferromagnetic and interdimer (antiferromagnetic) exchange interactions are similar in these complexes, as observed for the analogous Na salts.

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