Clusters [Co(As3S3)2]2–, [Ni(As3S3)2]2–, and [{Co(en)}6(μ3‑S)4(AsS3)4]2– with Co–As or Ni–As Bonds: Solvothermal Syntheses and Characterizations of Thioarsenates Containing Transition-Metal Complexes

Solvothermal reactions of As2O3 and S with CoCl2·6H2O or NiCl2·6H2O in an aqueous solution of dien produced novel thioarsenates [Co­(dien)2]­[Co­(As3S3)2] (1) and [Ni­(dien)2]­[Ni­(As3S3)2] (2) (dien = diethylenetriamine), and the reaction with CoCl2·6H2O in an aqueous solution of en afforded complex [Hen]2[{Co­(en)}6(μ3-S)4(AsS3)4] (3) (en = ethylenediamine). In 1 and 2, one transition-metal ion is coordinated by two dien ligands to form [TM­(dien)2]2+ (TM = Co, Ni) complex cations. The As3S3 unit coordinates to the other TM­(II) ion with both As- and S-donor atoms to form the [TM­(As3S3)2]2– anionic cluster, in which TMAs2, TMAs2S2, and TMAs3S2 rings are formed. In 3, each Co3+ ion is coordinated by an en ligand. Six Co­(en) units are interlinked by four μ3-S and four AsS3 ligands to form a [{Co­(en)}6(μ3-S)4(AsS3)4]2– cluster containing an adamantane-like Co6S4 core. The AsS3 unit coordinates to Co atom in the η1-As1,η2-S coordination mode with As binding Co(1) and S(1) binding Co(1) and Co(2). The As3S3 and AsS3 ligands with both As- and S-donor atoms in 1–3 have never been obtained in amine solution before. The same reactions in pure dien and en solvents afforded compounds [Co­(dien)2]3[As3S6]2 (4) and [Co­(en)3]2As2S5 (5) containing discrete anions [As3S6]3– and [As2S5]4–, respectively. The band gaps of 1–3 are in the range of 1.37–1.55 eV, and the band gaps of 4 and 5 are 2.24 and 2.26 eV, which show the influence of the coordination mode of thioarsenate ligands on the electronic transitions in the TM-thioarsenates.