title: Crystal structures of two polymorphs of Ca3[Al2N4].
abstract: Green transparent single crystals of alpha-Ca3[Al2N4] (monoclinic, P2(1)/c, No. 14, a = 957.2(3) pm, b = 580.2(3) pm, c = 956.3(5) pm, beta = 111.62(3) degrees; Z = 4) were obtained from reactions of mixtures of the representative metals with nitrogen above temperatures of 1000 degrees C. beta-Ca3[Al2N4] (monoclinic, C2/c, No. 15, a = 1060.6(2) pm, b = 826.0(2) pm, c = 551.7(1) pm, beta = 92.1(1) degrees; Z = 4) was formed as a byproduct of a reaction of calcium with alumina under nitrogen at T = 930 degrees C in form of colorless crystals. The crystal structures of the two polymorphs contain edge- and corner-sharing AlN4 tetrahedra, leading to different layered anionic partial structures: infinity 2[AlN2/2N2/3)2(AlNN2/2N1/3)6/3(12-)] in the alpha-phase and infinity 2[Al2N2N4/2(6-)] in the beta-polymorph.
authors.affiliation: Eduard-Zintl-Institut der Technischen Universität, Hochschulstrasse 10, D-64289 Darmstadt, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Ludwig
authors.forename: J
authors.initials: J
authors.lastname: Jäger
authors.forename: R
authors.initials: R
authors.lastname: Niewa
authors.forename: R
authors.initials: R
authors.lastname: Kniep