Solvothermal syntheses and characterization of three quaternary selenidoarsenates containing mercury [TM(en)3][HgAs2Se4](TM Mn, Ni, Zn)

AgMAsS3 (M = Cd, Hg): Double d10 Cation-Containing Thioarsenites(III) Exhibiting High Photocurrent Response and Moderate Second Harmonic Generation

Thioarsenites(III) are an advanced functional material platform owing to the stereochemically active lone pair cations. In this paper, two novel quaternary thioarsenites(III), AgMAsS3 (M = Cd, Hg), are successfully obtained by introducing double d10 cations. In the compounds, d10 cations show a variety of different coordination modes ([AgS4] and [HgS4] in AgHgAsS3 vs [AgS5] and [CdS6] in AgCdAsS3). As a result, AgHgAsS3 and AgCdAsS3 crystallize in the noncentrosymmetric Cc space group and centrosymmetric C2/c space group, respectively. The band gaps of AgHgAsS3 and AgCdAsS3 are determined experimentally as 1.90 and 2.20 eV, respectively. Meanwhile, title compounds exhibit strong photocurrent responses. Specifically, AgHgAsS3 has a large birefringence of 0.18 at 2100 nm and a moderate second harmonic generation of (0.5 × AgGaS2). Moreover, the origin of linear and nonlinear optical responses is investigated based on first-principles calculations. This study enriches the family of MI-MII-As-Q (M = Ag, Cu; MII = Zn, Cd, Hg; Q = chalcogen) chalcogenides and helps to understand and design other multifunctional optical materials.

Strong Photocurrent Response of Selenoarsenates With Different Transition Metal Complexes as Structure-Directing Agents

Four selenoarsenates with different transition-metal complexes [Co(tren)₂H]AsSe₄ [tren = tris(2-aminoethyl)amine] (1); [Ni₂(dien)₄](As₂Se₅) (dien = diethylenetriamine) (2); [Zn(tren)]₂(As₂Se₅) (3) and [Mn(tren)]₂(As₂Se₅) (4) were solvothermally synthesized in a mixed solvent of organic amine and alcohol solution. The compounds 1-4 have pyramidal/tetrahedral structures (AsSe₃/AsSe₄), and contain transition metal (Co²⁺, Ni²⁺, Zn²⁺ and Mn²⁺) complex that form distinct zero-dimensional (0-D) clusters. Arsenic atoms form a tetrahedron in compounds 1 and 2; 1 consists of discrete tetrahedral (AsSe₄) and transition metal complex [Co(tren)₂]²⁺; 2 is composed of an anion [As₂Se₅]^4- cluster and transition metal complex [Ni(dien)₂]²⁺. In compounds 3 and 4, arsenic atom forms a pyramidal AsSe₃ and the two pyramidal AsSe₃ share a corner connection to form a dimer [As₂Se₅]^4-; 3 is characterized as a cluster consisting of two unsaturated [Zn(tren)]²⁺ caiton linked by a dimer (As₂Se₅)^4- linkage; in 4, unsaturated [Mn(tren)]²⁺ caiton is linked to two trigonal-bipyramidal [Mn(tren)]Se via dimer (As₂Se₅)^4- to form [Mn(tren)]₄[As₄Se₁₀] cluster. To our knowledge, [Zn(tren)]₂(As₂Se₅) (3) is the first zinc selenoarsenate containing the (As₂Se₅)^4- anion type. Furthermore, the Mn²⁺ ions adopt a trigonal-biyramidal (five-coordinate) and octahedral (six-coordinate) environment. Adding K₂CO₃/Cs₂CO₃ to the synthesis system is necessary and may act as a mineralizer. Several properties of compounds 1-4 have been characterized in our studies, in particular their strong photocurrent response characteristics under visible light irradiation.