Syntheses, Crystal Structures, and Properties of the Novel Thioborates KBa4(BS3)3 and K4Ba11(BS3)8S

Our systematic studies on quaternary thioborates containing both a comparably small alkali metal ion and a large alkaline earth cation lead to the two new crystalline phases KBa4(BS3)3 and K4Ba11(BS3)8S. The former consists of isolated BS3 units and the corresponding counter-ions while in the latter BS33– and S2– anions coexist. In both compounds boron is found in a trigonal-planar coordination, in the case of K4Ba11(BS3)8S the additional sulfide anions are located inside an octahedron built of six barium cations. The two compounds were prepared in solid state reactions from the metal sulfides, amorphous boron and sulfur. Evacuated carbon coated silica tubes were used as reaction vessels since temperatures up to 870 K were applied. KBa4(BS3)3 crystallizes in the monoclinic space group C 2/c (no. 15) with a = 14.299(6) Å, b = 8.808(3) Å, c = 13.656(5) Å, β = 98.72(4)°, and Z = 4, while for K4Ba11(BS3)8S the trigonal space group R 3 c (no. 167) was found with a = 18.146(3) Å, c = 25.980(7) Å, and Z = 6. X-ray powder patterns are compared to calculated diffraction data obtained from single crystal X-ray structure determination, in the case of K4Ba11(BS3)8S vibrational spectra were recorded.