Solvothermal Synthesis and Characterization of Polyselenidoarsenate Salts of Transition Metal Complex Cations

The polyselenidoarsenates [Fe(phen)3][As2Se6] (1), [Zn(phen)(dien)][As2Se6]·2phen (2), [{Mn(phen)2}2(μ–η2,η2-AsSe4)]2[As2Se6]·H2O (3), and [Ni(phen)3][As2Se2(μ-Se3)(μ-Se5)] (4) (dien = diethylenetriamine and phen = 1,10-phenanthroline) were prepared by the reaction of As2O3, Se, dien, and phen in the presence of transition metals in a methanol solvent under solvothermal conditions. Compounds 1–3 consist of [As2Se6]2– anions with [Fe(phen)3]2+, [Zn(phen)(dien)]2+, and [{Mn(phen)2}2(μ-η2,η2-AsSe4)]+ complex counter cations, respectively. The [As2Se6]2– anion is formed from two AsIIISe3 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 AsIIISe3 trigonal pyramidal and AsVSe4 tetrahedral units. Compound 4 is composed of a helical chain of [As2Se2(μ-Se3)(μ-Se5)2–]∞ and octahedral [Ni(phen)3]2+ cations. The [As2Se2(μ-Se3)(μ-Se5)2–]∞ chain is constructed from AsSe+ units alternatively linked by μ-Se32– and μ-Se52– 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.