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 K(3)AgAs(2)Se5 . 0.25MeOH (I) are formed after reaction in MeOH at 130 degrees C for similar to 2 h. Its structure is built up of psi-bitetrahedral [As2Se5](4-) units, which are connected by Ag+ ions to form anionic one-dimensional chains. These chains are separated from each ether 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 UI possess Ag2Se2 four-membered rings, which lead to Ag ... Ag distances between 3 and 3.3 Angstrom. The thermal, optical, and spectroscopic properties of the compounds an reported. They melt incongruently between 259 and 284 degrees 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: K3AgAs2Se5. 0.25MeOH (I), monoclinic, P2(1)/c, a = 9.229(1) Angstrom, b = 11.508(2) Angstrom, c = 12.905(2) Angstrom, beta = 104.272(2)degrees Z = 4; K2AgAs3Se6 (II), monoclinic, P2(1)/n, a = 12.5994(6) Angstrom, b = 7.4980(4) Angstrom, c = 14.2648(7) Angstrom, beta = 96.625(2)degrees, Z = 4; Rb2AgAs3Se6 (III), monoclinic, P2(1)/n, a 12.717(2) Angstrom, b = 7.7329(8) Angstrom, c 14.368(2) Angstrom, beta = 95.745(2)4 Z = 4.