NA2B2SE7, K2B2S7, AND K2B2SE7 - 3 PERCHAL COGENOBORATES WITH A NOVEL POLYMERIC ANION NETWORK

Na2B2Se7 (I2/a; a = 11.863(4) Angstrom, b = 6.703(2)Angstrom, c = 13.8 11(6) Angstrom, beta = 109.41(2)degrees; Z = 4), K2B2S7 (I2/a; a = 11. 660(2)Angstrom,beta = 6.827(1)Angstrom, c = 12.992(3)Angstrom,beta = 1 06.78(3)degrees; Z = 4), and K2B2Se7 I2/a; a = 12.092(4) Angstrom, b = 7.054(2)Angstrom, c = 13.991(5) Angstrom, beta = 107.79(3)degrees; Z = 4) were prepared by reaction of stoichiometric amounts of sodium sel enide (potassium sulfide) with boron and sulfur or of potassium seleni de and boron diselenide, respectively, at 600 degrees C with subsequen t annealing. The crystal structures consist of polymeric anion chains of composition ([B2S7](2-))(n) or ([B2Se7](2-))(n) formed by spirocycl ically connected five-membered B2S3 (B2Se3) rings and six-membered B2S 4 (B2Se4) rings. The nine-coordinate alkaline metal cations are situat ed in between.