Arsenic-containing chalcophosphate molecular anions.

We report five new discrete molecular arsenic-based chalcophosphates, K(7)As(3)(P(2)Se(6))(4) (1), K(6)As(2)(P(2)Se(6))(3) (2), Cs(6)As(2)(P(2)Se(6))(3) (3), and Cs(5)As(P(2)Q(6))(2) [Q = Se (4a) and S (4b)]. Each of the compounds contains unique complex anions comprised of common building blocks that have condensed to produce these anions. Phosphorus forms well-known [P(2)Q(6)](4-) moieties in all of the compounds that are bridged by arsenic trigonal pyramids in 1 and 2 and distorted octahedra in 3, 4a, and 4b. Although 2 and 3 have the same molecular formula, the structural difference between the two salts is attributed to the size of the alkali metal. The influence of flux basicity also seems to play a role in the formation of the molecular anion in 4a and 4b, which has been observed with other trivalent main-group elements at the octahedral position but only with the highly basic cesium alkali metal as the counterion. All structures were determined by single-crystal X-ray diffraction and are discussed along with phase-purity powder X-ray diffraction, thermal analyses, electronic absorption, and Raman spectroscopy.