ON THE SYNTHESIS OF ALKALINE-EARTH DIHALI DES AND THE STRUCTURES OF CA3BR2CBN AND SR3CL2CBN

The reaction of alkaline-earth carbonates with ammonium chloride or br omide yields alkaline-earth dihalides at relatively low temperatures ( 300-degrees-C). Ca3Br2CBN and Sr3Cl2CBN were synthesized in sealed nio bium containers at 950-degrees-C from the metal, its dihalide, boron n itride and graphite. The crystal structure of Sr3Cl2CBN was refined fr om single crystal data. Sr3Cl2CBN crystallizes isotypic with Ca3Cl2CBN in the orthorhombic space group Pnma (No. 62) with a = 1448.4(2) pm b = 405.46(5) pm, c = 1170.0(1) pm. The lattice constants of Ca3Br2CBN and Sr3C12CBN were determined by orthorhombic indexing of the powder p atterns (Ca3Br2CBN: a = 1444.3(2) pm, b = 390.64(6) pm, c = 1139.2(2) pm; Sr3Cl2CBN: a = 1444.0(4) pm, b = 405.27(8) pm, c = 1167.8(2) pm). There was no success in preparing homologues with Barium.