Cs3CuAs4Q8 (Q = S, Se): unique two-dimensional layered inorganic thioarsenates with the lowest Cu-to-As ratio and remarkable photocurrent responses

A novel bifunctional thioarsenate based on unprecedented molecular [Cd4As8Se16(Se2)2]8- cluster anions

Exploring and developing new functional inorganic chalcogenides with unique structures is always one of the most important missions in solid-state chemistry, especially those with molecular structures. Herein, a novel quaternary thioarsenate, Cs2CdAsSe5, is found to be based on an unprecedented molecular (poly)chalcogenide cluster architecture, which has never been discovered in inorganic chalcogenide systems. This rare windmill-like [Cd4As8Se16(Se2)2]8- cluster is made of four [CdSe4] and [As(V)Se4] tetrahedra via corner-sharing Se atoms and Se-Se bonds. Specifically, Cs2CdAsSe5 exhibits a remarkable photocurrent response and a large computationally predicted birefringence, and the origin of the optoelectronic performance and optical anisotropy is confirmed by detailed theoretical investigation.

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.

Ba3HgGa2S7: A Zero-Dimensional Quaternary Sulfide Featuring a Unique [Hg2Ga4S14]12- String and Exhibiting a High Photocurrent Response

The discovery of new types of metal sulfides is attractive because of their rich structures and diverse physical properties. Here, a novel quaternary sulfide, Ba₃HgGa₂S₇ (BHGS), is obtained by a solid-state reaction at 1123 K. It crystallizes in the monoclinic space group P2₁/c, and its zero-dimensional structure features two seesaw-like HgS₂ units and four GaS₄ tetrahedra, constructing a unique [Hg₂Ga₄S₁₄]^12- string. BHGS has a wide band gap of 3.64 eV and a large birefringence of 0.09 at 2100 nm. Specifically, BHGS exhibits a remarkable photocurrent response. This work may be extended to a new family of AE₃M^IIM^III₂Q₇ (AE = Mg, Ca, Sr, Ba; M^II = Zn, Cd, Hg; M^III = Al, Ga, In; Q = S, Se) chalcogenides.