Solvothermal synthesis and characterization of polyselenidoarsenate salts of transition metal complex cations.

The polyselenidoarsenates [Fe(phen)(3)][As(2)Se(6)] (1), [Zn(phen)(dien)][As(2)Se(6)]·2phen (2), {Mn(phen)(2)}(2)(μ-η(2),η(2)-AsSe(4))[As(2)Se(6)]·H(2)O (3), and [Ni(phen)(3)][As(2)Se(2)(μ-Se(3))(μ-Se(5))] (4) (dien = diethylenetriamine and phen = 1,10-phenanthroline) were prepared by the reaction of As(2)O(3), Se, dien, and phen in the presence of transition metals in a methanol solvent under solvothermal conditions. Compounds 1-3 consist of As(2)Se(6) anions with Fe(phen)(3), Zn(phen)(dien), and {Mn(phen)(2)}(2)(μ-η(2),η(2)-AsSe(4)) complex counter cations, respectively. The As(2)Se(6) anion is formed from two As(III)Se(3) trigonal pyramids linked through two Se-Se bonds. Compound 3 is the first example of a mixed-valent selenidoarsenate(III,V) and exhibits the coexistence of As(III)Se(3) trigonal pyramidal and As(V)Se(4) tetrahedral units. Compound 4 is composed of a helical chain of As(2)Se(2)(μ-Se(3))(μ-Se(5))(2-) and octahedral Ni(phen)(3) cations. The As(2)Se(2)(μ-Se(3))(μ-Se(5))(2-) chain is constructed from AsSe(+) units alternatively linked by μ-Se(3)(2-) and μ-Se(5)(2-) bridging ligands. When the structures of compounds 1-4 are compared, the transition metal ions show different structural directing effects during the synthesis of arsenic polyselenides in methanol. Compounds 1, 2, 3, and 4 exhibit semiconducting properties with band gaps of 1.88, 2.29, 1.82, and 2.01 eV, respectively.