Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M-2((AsW6O25)-W-III)(2)((AsOH)-O-III)(x)](n-) (M = Cr-III, Fe-III, Sc-III, In-III, Ti-IV, Mn-II) and Their Magnetic Properties

摘要

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M-2((AsW6O25)-W-III)(2)((AsOH)-O-III)(x)](n-) (M = Cr-III, 1; Fe-III, 2; Sc-III, 3; In-III, 4; Ti-IV, 5; Mn-II, 6) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions 1-6 are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW6} units, resulting in a structure with C-2h point-group symmetry. Polyanions 1-5 contain tri- and tetravalent metal ion guests M (M = Cr-III Fe-III, Sc-III, In-III, and Ti-IV, respectively), and they have one {As-III OH} group grafted on each {AsW6} unit, whereas the divalent Mn-II-containing derivative 6 has two such {(AsOH)-O-III} groups grafted on each {AsW6} unit. Magnetic studies on polyanions 3-5 over the temperature range 1.8-295 K and magnetic fields of 0-7 T confirmed that they are diamagnetic. On the other hand, polyanions 1, 2, and 6 are strongly magnetic and follow the Curie-Weiss law above 30 K. The susceptibility plots of 1 and 6 exhibit broad peaks suggesting short-range antiferromagnetic ordering, while the very weak antiferromagnetic ordering of 2 is overshadowed by traces of a paramagnetic impurity. The magnetization data of 1, 2, and 6 at 1.8 K over 0-7 T were analyzed by using the Heisenberg exchange procedure. Small (negative) values of the obtained J values help in understanding the absence of long-range antiferromagnetic ordering.