Ca-2[BN2]H: The first nitridoborate hydride - synthesis, crystal structure, and vibrational spectra

Abstract

Ca-2[BN2]H was synthesized from a mixture of the binary components Ca3N2, CaH2 and BN (molar ratio 1 : 1 : 2) in a sealed steel ampoule encapsulated in an evacuated silica tube at 1273 K. Ca-2[BN2]H crystallizes in the orthorhombic space group Pnma (no. 62) with a = 9.2015(8) Angstrom, b = 3.6676(2) Angstrom and c = 9.9874(12) Angstrom (Z = 4; Pearson symbol oP24). The crystal structure is a filled variant of the Co2P type and can be formulated as Co2P(square(t))(3)(square(py))(3) drop Ca-2[N-B-N]H(square(t))(2)(square(py))(3) (square(t) and square(py) = tetrahedral and square-pyramidal hole, respectively). The d(B-N) bond lengths and bond angle for the linear [N-B-N](3-) anion are: d(B-N1) = 1.324(3) Angstrom, d(B-N2) = 1.350(2) Angstrom and angleN-B-N = 177.2(2)degrees. The vibrational spectra of Ca-2[BN2]H confirm the presence of [N-B-N](3-) groups deviating only slightly from the ideal D-infinityh symmetry. The vibrational frequencies and the f(B-N) force constants are discussed and compared with those of the isotypic compound Ca-2[BN2]F.