Novel Alkaline Earth Metal Chalcogenoborates: Syntheses and Crystal Structures of Sr4.2Ba2.8(BS3)4S and Ba7(BSe3)4Se

Systematic studies on quaternary thio‐ and selenoborates containing heavier alkaline earth metal cations led to the two new isotypic crystalline phases Sr_4.2Ba_2.8(BS₃)₄S and Ba₇(BSe₃)₄Se. Both compounds consist of trigonal‐planar BQ₃ (Q = S, Se) units, isolated Q^2– anions and the corresponding counter‐ions. The two new chalcogenoborates were prepared in solid state reactions from the metal sulfides (selenides), amorphous boron and sulfur (selenium). Evacuated carbon coated silica tubes were used as reaction vessels since temperatures up to 870 K were applied. Sr_4.2Ba_2.8(BS₃)₄S and Ba₇(BSe₃)₄Se crystallize in the monoclinic space group C2/c (no. 15) with a = 9.902(3) Å, b = 23.504(9) Å, c = 9.884(3) Å, β = 90.01(3)° and Z = 4 in the case of the thioborate, while for the selenoborate the lattice parameters a = 10.513(2) Å, b = 25.021(5) Å, c = 10.513(2) Å, β = 90.10(3)° were determined. X‐ray powder patterns are compared to calculated diffraction data obtained from single crystal X‐ray structure determination.