SYNTHESIS AND STRUCTURE OF THE SUBNITRIDES BA2GEGAN AND (BAXSR1-X)(3)GE2N2, X-APPROXIMATE-TO-0.7

We report the structure of the new subnitride Ba2GeGaN synthesized as crystals from the elements in a sealed Nb tube at 760 degrees C usi a Na/Ba melt as the growth medium. Shiny black prisms of Ba2GeGaN crysta llize in P2(1)/m (No.11) with a = 7.249(1) Angstrom, b = 4.210(1) Angs trom, c = 9.314(1) Angstrom, beta = 108.87(1)degrees and Z = 2. It con tains infinite zigzag chains, (1)(infinity)[GeCaN4-], composed of alte rnating Ge2- and GaN2- units joined by Ge-Ga bonds. The structure is r elated to that of BaGe with alternate Ge atoms replaced by the isoelec tronic GaN fragment. Such GaN2- fragments occur in CaGaN. We also repo rt the occurrence of a solid solution between the previously reported subnitrides Ba3Ge2N2 and Sr3Ge2N2 which contain infinite chains, (1)(i nfinity)[Ge2-], and GeN24- units. We have characterized one member of this solid solution with composition (Ba-0.79(1)Sr-0.21(1))(3)Ge2N2 an d crystallizing in P2(1)/m (No. 11) with a = 9.5109(9) Angstrom, b = 4 .0201(3) Angstrom, c = 10.0412(9) Angstrom, beta = 113.06(1)degrees an d Z = 2. (C) 1997 Elsevier Science S.A.