SYNTHESIS AND STRUCTURE OF BA[ZRN2] AND BA-2[NBN3]

Ba3N2 reacts at 950 degrees C under pure N-2 with Zr to yield dark red, air-sensitive Ba[ZrN2]. This new compound crystallizes in the tetragonal space group P4/nmm with a = 416.10(2), c = 839.2(1) pm and Z = 2. The crystal structure was solved and refined using X-ray and neutron powder diffraction data. In the nitrido zirconate [ZrN2](2-) the Zr atoms exhibit a square-pyramidal coordination by five N atoms at distances of 201(3) and 220.2(2) pm. The pyramids share all the edges in the basal plane to form layers parallel to (001) with their apices alternately pointing up and down. The Ba2+ cations are integrated into these layers at the levels of the pyramidal apices. The structure can be interpreted as a stuffed PbFCl type. Ba-2[NbN3] is formed by the reaction of Ba3N2 and NbN or of Ba and Nb at 1000 degrees C under N-2. Isostructural to Ba-2[TaN3] it crystallizes in the monoclinic space group C2/c with a = 613.2(3), b = 1176.8(3), c = 1322.9(4) pm, beta = 91.65(2)degrees, Z = 8. The nitrido niobate anions form chains of corner sharing NbN4 tetrahedra with distances Nb-N between 188(1) and 199.9(9) pm.