ON THE STRUCTURE OF SR3(BN2)2

The structure of Sr3(BN2)2 was determined on single-crystal X-ray data collected with a four-circle diffractometer. Sr3(BN2)2 crystallizes i n the cubic space group Im3mBAR (no. 229) with a = 764.56(3) pm and Z - 3. The structure contains linear BN23- ions with a B-N bond length o f 135.8(6) pm. The straight forward synthesis employing metal nitrides plus boron nitride yielded crystalline powders Of M3(BN2)2 (M Ca, Sr) at 1100-degrees-C (5 days). Cubic indexing of guinier patterns gave a = 765.8(1) pm for M = Sr and a = 734.7(2) pm for M = Ca. The structur e refinement on a single crystal of Sr3(BN2)2 revealed that one stront ium site (2a; 0,0,0) is occupied by only about 50%. It has been tried to fully occupy this site with an alkali metal (A) to obtain ASr4(BN2) 3 (Z = 2). Reactions with A = Na yielded crystalline powders. Cubic in dexing of the guinier pattern analogous to that of Sr3(BN2)2 gave a = 754.2(1) pm.