Crystal structure of bis(tetraphenylphosphonium) hexathiotetraarsenate, [Ph4P]2[As4S6

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Source of material: Arsenic oxide, sulfur, manganese and tetraphenylphosphoniumbromide (molar ratio: 1:5:1:1 ) in 5 ml of 2m ammonia solution were reacted in teflon coated steal autoclaves at 398 К for 6 days. The product was filtered off and washed with deionized water. The structure of the title compound is built up of well-separated Ph4P' -cations and [As4S6]^~-anions. The tetraphenylphosphonium cations form pairs with sixtuple embracements of the phenyl rings with the midpoint located on a centre of inversion and relatively short Ρ···Ρ distances of 6.331(3) Â and 6.351(3) Â. These pairs are arranged in corrugated sheets parallel to ((Ю1) with a honey-comb like arrangement of the Ρ atoms, a pattern which is found in many compounds containing tetraphenylphosphonium cations. The [As4S6]^~-anion forming a bicyclic ring system of alternating As and S atoms consists of two five-membered rings with the two common arsenium centers As3 and As4. The structure of the [As4S6]^-anion is related to that of AS4S4 (see ref. 1 ) by replacement of an As-As bond by two As-S~ units. The As3-As4 bond length of 2.621(2) Â is significantly longer than that in elemental As by about 0.12 Â. The other two arsenium atoms Asl and As2 are each bound to an additional exocyclic sulfur atom. All arsenium atoms have trigonal pyramidal coordination with sums of angles around Asl and As2 of 3(Ю.7(9)° and 298.4(9)° and around As3 and As4 of 308.1(8)° and 307.2(8)°. The As-S bond lengths to As3 and As4 are shorter than those to Asl and As2 by about 0.1 Â. The longer As-S distances as well as the stronger pyramidalization of Asl and As2 suggest that the negative charge is predominantely located on these centers. It is noted that the geometrical parameters of the [As4S6]^~-anion are comparable to those in piperidinium hexathiotetraarsenate (see ref. 2). C48H40AS4P2S6, orthorhombic, Pbca (No. 61), α =11.1998(6) Â, b =19.657(1) Â, с =44.177(5) Â, V=9725.5 Â^Z=8,R{F) =0.050, A w f f ^ ) = 0 . 1 1 6 .