Explorations of new phases in the Ga(III)/In(III)-Cu(II)-Se(IV)-O system.

Four new gallium(III)/indium(III), copper(II), selenium(IV) oxides, namely, Ga(2)Cu(SeO(3))(4) (1), Ga(2)CuO(SeO(3))(3) (2), and M(2)Cu(3)(SeO(3))(6) (M = Ga 3, In 4), have been synthesized by hydrothermal or high-temperature solid-state reactions. The structure of Ga(2)Cu(SeO(3))(4) (1) features a 2D layer of corner-sharing GaO(6) and CuO(6) octahedra with the SeO(3) groups hanging on both sides of the 2D layer. Ga(2)CuO(SeO(3))(3) (2) features a pillared layered structure in which the 1D Cu(SeO(3))(3)(4-) chains act as the pillars between 2D layers formed by corner- and edge-sharing GaO(n) (n = 4, 5) polyhedra. Although the chemical compositions of M(2)Cu(3)(SeO(3))(6) (M = Ga 3, In 4) are comparable, they belong to two different structural types. Ga(2)Cu(3)(SeO(3))(6) (3) exhibits a pillared layered structure built by Ga(2)Cu(3)(SeO(3))(4) thick layers with Se(3)O(3)(2-) groups as pillars. The structure of In(2)Cu(3)(SeO(3))(6) (4) features a 3D network composed of In(2)(SeO(3))(2) layers and Cu(3)(SeO(3))(4) layers interconnected through Se-O-Cu and In-O-Cu bridges, exhibiting 8-MR helical tunnels along the a-axis. Results of magnetic property measurements indicate that there are considerable antiferromagnetic interactions between copper(II) centers in Ga(2)CuO(SeO(3))(3) (2) and M(2)Cu(3)(SeO(3))(6) (M = Ga 3, In 4). Interestingly, Ga(2)Cu(3)(SeO(3))(6) (3) behaves as a weak ferromagnet below the critical temperature of T(c) = 15 K. Further magnetic studies indicate that the compound is a canted antiferromagnet with a large canting angle of about 7.1 degrees.