Sodium Transition Metal Vanadates from Hydrothermal Brines: Synthesis and Characterization of NaMn4(VO4)3, Na2Mn3(VO4)3, and Na2Co3(VO4)2(OH)2

Three new examples of transition metal vanadates have all been synthesized by a related hydrothermal synthetic route using variations of sodium hydroxide/sodium chloride brines as mineralizers. Compound1, NaMn4(VO4)(3), is built from equivalent interlocking chains of Mn(2+)edge shared octahedra, further coordinated to one another by (VO4)(3-)vanadate groups to form a three-dimensional structure. Compound2, Na2Mn3(VO4)(3), forms a complex three-dimensional structure of mixed-valence 2+/3+ manganese edge-sharing octahedra forming chains, with (VO4)(3-)tetrahedra acting as space-fillers in the structure. Structure3, Na2Co3(VO4)(2)(OH)(2), is built of a two-dimensional distorted honeycomb of edge shared Co(2+)layers decorated by, but not connected by, vanadate groups. The layers bear a relationship to Kagome nets but the structure contains no ideal trigonal symmetry. All compounds were characterized by single-crystal X-ray diffraction. Compounds1and3were characterized by magnetic susceptibility. The magnetic susceptibility of1displays the moment characteristic of Mn(2+)and a transition at 46 K to a spin canted antiferromagnet. Compound3shows evidence of spin-orbit coupling in the Co(2+)ions with antiferromagnetic ordering at 4.4.K and highly anisotropic field-dependent behavior with multiple metamagnetic transitions.