Synthesis and Crystal Structure of K3AsSe4 and K4As2Se5 Containing [AsSe4]3- Anions and a Novel [As2Se5]4- Isomer Featuring an As-As Bond

Two novel selenoarsenates, K3AsSe4 and K4As2Se5, were synthesized by the mild solvothermal reaction of potassium carbonate and arsenic and selenium powder in the presence of super-heated ethylenediamine and structurally characterized by single-crystal X-ray diffraction. K3AsSe4 crystallizes in the orthorhombic space group Pnma (no. 62) with a = 9.4169(4), b = 10.9695(5), c = 9.7568(8) angstrom, Z = 4 and V = 1007.86(10) angstrom(3) and contains [AsSe4](3-) anions with pentavalent arsenic. K4As2Se5 crystallizes in the monoclinic space group P2(1)/n (no. 14) with a = 7.6167(2), b = 22.8733(4), c = 8.4687(2) angstrom, beta = 107.241(2)degrees, Z = 4 and V = 1409.14(5) angstrom(3), and shows isolated [As(2)Sed](4-) anions. The most prominent feature of the latter anions is the presence of arsenic in two different formal oxidation states (+4/+ 2) due to the presence of an As-As bond.