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

Abstract

The title compound Ca3[BN2]I3 was obtained from reactions of mixtures of the starting materials Ca3[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. Ca3[BN2]I3 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) Å, c = 12.41024(2) Å]. The crystal structure is built up by two interpenetrating networks of condensed edge-sharing [BN2]@Ca6 and [□]@I6 trigonal antiprisms (□ = void). In Ca3[BN2]I3 two crystallograhically distinct [BN2]3– anions are present with d(B1–N) = 1.393(2) Å and d(B2–N) = 1.369(9) Å. Their bond angles are practically linear, varying only slightly: N–B1–N = 179(1)° and N–B2–N = 180°. Vibrational spectra were interpreted based on the D∞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.