Na₂B₂S₅ and Li₂B₂S₅: Two Novel Perthioborates with Planar 1,2,4‐Trithia‐3,5‐Diborolane Rings

Abstract

Abstract For the first time perthioborates with trigonal planar coordination of boron were prepared. Na 2 B 2 S 5 (Pnma, a = 12.545(2) Å, b = 7.441(1) Å, c = 8.271(1) Å, Z = 4) and Li 2 B 2 S 5 (Cmcm, a = 15.864(1) Å, b = 6.433(1) Å, c = 6.862(1) Å, Z = 4) were obtained by reaction of the metal sulfides with stoichiometric amounts of boron and an excess of sulfur (effective molar ratio M:B:S = 1:1:4) at 600°C (650°C) and subsequent annealing. The non‐isotypic structures contain exactly planar [B 2 S 5 ] 2− groups consisting of five‐membered B 2 S 3 rings with one additional exocyclic sulfur on each of the boron atoms. The alkaline metal cations are four‐coordinate (lithium) and (four + four)‐coordinate (sodium) respectively.