Synthesis, properties and crystal structures of α-Ca 3(BN 2) 2 and Ca 9+x(BN 2, CBN) 6—two compounds with BN 23− and CBN 4− anions

Abstract

The isotypic compounds Ca 3(BN 2) 2 and Ca 9+0.5 x (BN 2) 6− x (CBN) x contain linear anions BN 2 3 − and BN 2 3 − together with isoelectronic linear CBN 4 − anions, respectively. Ca 3(BN 2) 2 is obtained in sealed niobium ampoules between 1480–1970 K from a stoichiometric mixture of Ca 3N 2 and BN and Ca 9+0.5 x (BN 2) 6− x (CBN) x from Ca 3N 2, BN, graphite and calcium. α-Ca 3(BN 2) 2 and Ca 9+0.5 x (BN 2) 6− x (CBN) x crystallize in the space group Im3̄ m with a x=0 =732.24(3) pm and a x = 2=739.82(8) pm. Compounds with a composition of Ca 3(BN 2) 2 and Ca 1 0(Bn 2) 4(CBN) 2 as well as solid solutions Ca 9+0.5 x (BN 2) 6− x (CBN) x with x=0.36, 1.43 were investigated. The compounds were characterized by X-ray structure analysis, DTA, IR-, Raman- and solid state NMR spectroscopic methods. A phase transition of α-Ca 3(BN 2) 2 to a low-temperature polymorph β-Ca 3(BN 2) 2 at 538 K was found.