Ca3[BN2]I3: the first halide-rich alkaline earth nitridoborate with isolated [BN2]3 - units

Abstract

The title compound Ca-3[BN2]I-3 was obtained from reactions of mixtures of the starting materials Ca-3[BN2](2) and CaI2 in a 1:4 ratio in sealed Nb tubes at 1223 K. The crystal structure was solved from powder synchrotron diffraction data. Ca-3[BN2]I-3 is the first example of a halide-rich nitridoborate crystallizing in the rhombohedral space group R32 [no. 155, Pearson code: hR96; Z = 12; a = 16.70491(2) angstrom, c = 12.41024(2) angstrom]. The crystal structure is built up by two interpenetrating networks of condensed edge-sharing [BN2]@Ca-6 and [square]@I-6 trigonal antiprisms (square = void). In Ca-3[BN2]I-3 two crystallograhically distinct [BN2](3-) anions are present with d(B1-N) = 1.393(2) angstrom and d(B2-N) = 1.369(9) angstrom. Their bond angles are practically linear, varying only slightly: N-B1-N = 179(1)degrees and N-B2-N = 180 degrees. Vibrational spectra were interpreted based on the D-infinity h symmetry of the discrete linear [N-B-N](3-) moieties, considering the site symmetry reduction and the presence of two distinct [BN2](3-) groups.