Zur Strukturchemie der Alkyl- und Arylhalogenoarsenate(III), [Me2As2Cl5]–, [RAsCl3]–, [R2As2Br6]2– (R = Me,Et, Ph) und [Ph2AsX2]– (X = Cl,Br)

Structural Chemistry of the Alkyl- and Arylhaloarsenates(III) Me₂As₂Cl₅]^–, RAsCl₃]^–, R₂As₂Br₆]^2– (R = Me, Et, Ph) and Ph₂AsX₂]^– (X = Cl, Br) The alkyl- and arylhaloarsenates(III) Ph₄P]Me₂As₂Cl₅] ( 1 ), Ph₄P]RAsCl₃] (R = Me, Et, Ph, 2 – 4 ), Me₃PhN]PhAsCl₃] ( 5 ), Ph₄P]₂R₂As₂Br₆] (R = Me, Et, Ph, 6 – 8 ), n-Pr₄N]Ph₂AsCl₂] ( 9 ) and n-Bu₄N]Ph₂AsBr₂] ( 10 ) have been prepared and their structures established by X-ray diffraction. In contrast to the chloroarsenates(III) 2 – 5 , which all contain isolated ψ-trigonal bipyramidal anions RAsCl₃]^–, the analogous bromoarsenates(III) 6 – 8 exhibit dimeric structures. Whereas the trans sited As–Cl distances in 2 and 3 are very similar a pronounced degree of asymmetry is apparent for the Cl–As–Cl three-centre bonds in 4 and 5 2.396(1) and 2.602(1) Å in 5]. In 6 and 7 C_i symmetry related RAsBr₂ units are connected through long As…Br bonds 2.926(1) and 3.116(2) Å in 6 ]. The bromophenylarsenate(III) anion of 8 which contains two effectively undistorted ψ-trigonal bipyramids PhAsBr₃]^– associated by weak As…Br interactions 3.117(2) Å]. In view of its very long bridging As…Cl distances the Me₂As₂Cl₅]^– anion in 1 can, as 6 an 7 , be regarded as two MeAsCl₂ molecules weakly linked through a chloride ion.