Ca₃[BN₂]I₃: The First Halide-Rich Alkaline Earth Nitrido­borate with Isolated [BN₂]³⁻ Units

The title compound Ca_3[BN_2]I_3 was obtained from reactions of mixtures of the starting materials Ca_3[BN_2]_2 and CaI_2 in a 1:4 ratio in sealed Nb tubes at 1223 K. The crystal structure was solved from powder synchrotron diffraction data. Ca_3[BN_2]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) Å, c = 12.41024(2) Å]. The crystal structure is built up by two interpenetrating networks of condensed edge-sharing [BN_2]@Ca_6 and [□]@I_6 trigonal antiprisms (□ = void). In Ca_3[BN_2]I_3 two crystallograhically distinct [BN_2]^(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 [BN_2]^(3–) groups.