Three novel quaternary selenoarsenates could be synthesized by the solventothermal reaction of [AsSe3]3- anions with AgBF4 in the presence of the respective alkali metal cation. Orange crystals of K3AgAs2Se50.25MeOH (I) are formed after reaction in MeOH at 130 °C for ∼2 h. Its structure is built up of ψ-bitetrahedral [As2Se5]4- units, which are connected by Ag+ ions to form anionic one-dimensional chains. These chains are separated from each other by the K+ cations. Longer reaction time, i.e., 3 days, at the same temperature provides red crystals of K2AgAs3Se6 (II) and, correspondingly, the isostructural Rb2AgAs3Se6 (III), which possess two-dimensional (2D) polyanions [AgAs3Se6]2-. They consist of double layers of strongly waved, infinite [AsSe2]- chains, which are interconnected by tetrahedral Ag+ ions. The structure can also be described as [Ag2As6Se14]8- cores, which are connected by bridging Se atoms to build the sheet anion. Both II and III possess Ag2Se2 four-membered rings, which lead to AgAg distances between 3 and 3.3 Å. The thermal, optical, and spectroscopic properties of the compounds are reported. They melt incongruently between 259 and 284 ̊C and are wide band gap semiconductors with values between 1.9 and 2.1 eV. Raman spectroscopic data show typical patterns for the respective selenoarsenate anionic building units in the range 100-300 cm-1. Crystal data: K3AgAs2Se50.25MeOH (I), monoclinic, P21/c, a = 9.229(1) Å, b = 11.508(2) Å, c = 12.905(2) Å, β= 104.272(2)°, Z = 4; K2AgAs3Se6 (II), monoclinic, P21/n, a = 12.5994(6) Å, b = 7.4980(4) Å, c = 14.2648(7) Å, β= 96.625(2)°, Z = 4; Rb2-AgAs3Se6 (III), monoclinic, P21/n, a = 12.717(2) Å, b = 7.7329(8) Å, c = 14.368(2) Å, β= 95.745(2)°, Z = 4.
|Number of pages||8|
|Publication status||Published - Dec 1 1999|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry