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 crystallize in P2(1)/m (No.11) with a = 7.249(1) Angstrom, b = 4.210(1) Angstrom, c = 9.314(1) Angstrom, beta = 108.87(1)degrees and Z = 2. It contains infinite zigzag chains, (1)(infinity)[GeCaN4-], composed of alternating Ge2- and GaN2- units joined by Ge-Ga bonds. The structure is related to that of BaGe with alternate Ge atoms replaced by the isoelectronic GaN fragment. Such GaN2- fragments occur in CaGaN. We also report the occurrence of a solid solution between the previously reported subnitrides Ba3Ge2N2 and Sr3Ge2N2 which contain infinite chains, (1)(infinity)[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 and 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 and Z = 2. (C) 1997 Elsevier Science S.A.