Cyclische Polyselenidoarsenate(III) und -antimonate(III): PPh4[Se5AsSe], PPh4[AsSe6–xSx], (PPh4)2[As2Se6] · 2 CH3CN und (PPh4)2[Se6SbSe]2

Cyclic Polyselenidoarsenates(III) and Polyselenidoantimonates(III): PPh₄[Se₅AsSe], PPh₄[AsSe_6–xS _x ], (PPh₄)₂[As₂Se₆] · 2 CH₃CN, and (PPh₄)₂[Se₆SbSe]₂ In acetonitrile, AsCl₃ and sodiumphenolate formed Cl₂AsOPh which then was reacted with PPh₄Se₅ and finally with Na₂Se to yield PPh₄[Se₅AsSe]. With Na₂S instead of Na₂Se, PPh₄[AsSe_6–xS_x] was obtained; the sulfur contents increased with increasing reaction temperature and time (x = 0.21 to 1.09). With PPh₄Se₂ instead of PPh₄Se₅, (PPh₄)₂[1,4-As₂Se₆] · 2 CH₃CN and PPh₄[Se₅AsSe] were the products. With SbCl₃ instead of AsCl₃, (PPh₄)₂[Se₆SbSe]₂ formed. PPh₄[Se₅AsSe] can also be produced from As₂Se₃, PPh₄Br, Na₂Se and selenium in acetonitrile. The crystal structure of PPh₄[SeAsSe₅] is isotypic with PPh₄[S₅AsS] (X-ray structure analysis with 2414 observed reflexions, R = 0.038). The Se₅AsSe^– ion consists of a six-membered AsSe₅ ring in chair conformation, and the As atom has an additional terminal Se atom. The compounds PPh₄[AsSe_6–xS_x] have the same crystal structures, with sulfur atoms taking all selenium positions at random, but with a preference for the terminal position. The anion in (PPh₄)₂[As₂Se₆] · 2 CH₃CN also has a six-membered ring structure in chair conformation, with two arsenic atoms in positions 1 and 4. The centrosymmetric anion in (PPh₄)₂[Se₆SbSe]₂ consists of a central Sb₂Se₂ ring, and a Se₆ ligand is bonded in a chelating manner to each Sb atom (X-ray structure analysis with 2669 observed reflexions, R = 0.099). ⁷⁷Se-NMR spectra are reported.