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

Abstract

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 Co(3+) 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 η(1)-As1,η(2)-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.