SYNTHESES AND STRUCTURES OF A SERIES OF VERY LOW COORDINATE BARIUM COMPOUNDS - BA[N(SIME3)2]2(THF)2, (BA[N(SIME3)2]2(THF))2, AND (BA[N(SIME3)2]2)2

Barium hexamethyldisilazide tetrahydrofuranate, Ba[N(SiMe3)2]2(THF)2 (1), is synthesized from barium granules and 1,1,1,3,3,3-hexamethyldisilazane at 25-degrees-C in THF. Gaseous ammonia is a necessary catalyst. In the solid state, the compound is a monomer containing a tetrahedral four-coordinate barium center. Crystal data (-157-degrees-C): a = 17.952 (3) angstrom, b = 20.740 (3) angstrom, c = 17.652 (3) angstrom with Z = 8 in the space group Pbca. One of the coordinated THF molecules is removed from 1 by stripping a toluene solution of 1 to dryness in vacuo, yielding {Ba[N(SiMe3)2]2(THF)}2 (2). In the solid state, 2 is a dimer containing two bridging and two terminal hexamethyldisilamido groups. The four-coordinate, tetrahedral geometry at each barium is completed by terminal THF molecules. Crystal data (-155-degrees-C): a = 20.356 (3) angstrom, b = 15.632 (3) angstrom with Z = 4 in space group Pnab. The solvent-free compound {Ba[N(SiMe3)2]2}2 (3) is obtained by sublimation of 1. This compound is a dimer in the solid state, with three-coordinate barium centers. Crystal data (-172-degrees-C): a = 11.154 (6) angstrom, b = 12.262 (6) angstrom, c = 9.834 (4) angstrom, alpha = 95.87 (2)-degrees, beta = 106.74 (2)-degrees, gamma = 115.13 (2)-degrees with Z = 1 in the space group P-1BAR.