Mg 2 [BN 2 ]Cl and Mg 8 [BN 2 ] 5 I: Novel Magnesium Nitridoborate Halides — Syntheses, Crystal Structures, and Vibrational Spectra

The title compounds have been synthesized at 1473 K from stoichiometric mixtures of the binary components Mg 3 N 2 , MgX 2 (X = Cl, I) and BN in arc‐welded steel ampoules encapsulated in evacuated silica tubes. Mg 2 [BN 2 ]Cl ( 1 ) and Mg 8 [BN 2 ] 5 I ( 2 ) crystallize in the orthorhombic space groups Pbca (no. 61) and Imma (no. 74), respectively, with a = 6.6139(8)Å, b = 9.766(1)Å, c = 10.600(1)Å, Z = 8 for 1 and a = 13.535(3)Å, b = 9.350(2)Å, c = 11.194(2)Å, Z = 4 for 2 . The crystal structures are characterized mainly by Mg 6 trigonal prisms which are condensed to 3D frameworks in different ways. Part of the trigonal prisms are centered by the [N—B—N] 3— anions and other voids in the framework by the X — anions. The magnesium environment around Cl — is a very distorted monocapped trigonal prism (CN = 6+1) and that of I — is a bicapped heptagonal prism (CN = 14+2). The bond lengths and bond angles for the relevant [BN 2 ] 3— anions are d (B—N) = 1.330 — 1.338Å, ∠N—B—N = 175.8° in 1 and d (B—N) = 1.330 — 1.339Å, ∠N—B—N = 176.8° — 178.0° in 2 . The vibrational spectra of the title compounds have been recorded and interpreted based on the D ∞ h symmetry of the relevant [N—B—N] 3— groups considering the site symmetry splitting.