Ternary nitridoborates. 2. Synthesis, crystal structure, and vibrational spectra of new ternary compounds with the [N-B-N](3-) anion

The isotypic compounds LiM4[BN2](3) (M = Ca, Sr, Ba, Eu) and NaM4[BN2](3) ( M = Sr, Ba) are formed as colorless to pale yellow prismatic crystals (blac k with Eu) by reaction of the binary components Li3N, M3N2, EuN and Na, NaN 3, Ba3N2 and BN in sealed niobium ampoules at 1375 and 1275 K, respectively . The linear anions [N-B-N](3-) have bond lengths d(B-N) between 132.6 and 136.6 pm. Vibrational frequencies and force constants f(B-N) = 7.25-7.89 Nc m(-1) reveal significant drifts related to bond length and effective anioni c charge. The cubic crystal structures (Im (3) over bar m (No.229), Z = 2; LiM4[BN2](3): a(Ca) = 711.5 pm; a(Sr) = 745.6 pm; a(Eu) = 742.5 pm, a(Ba) = 788.0 pm and NaM4[BN2](3): a(Sr) = 756.8 pm; a(Ba) = 791.7 pm)) are stuffe d derivatives of the beta-PtHg4 structure type, and the range of existence of this cubic structure is derived from the molar volume and the ionic radi i. The cations form a partial structure of centered cubes E1(E2)(8) which a re condensed to a (3)(infinity)[E1(E2)(8/2)] network (E1 = Li, Na; E2 = Ca, Sr, Ba, Eu). The remaining open cubes are filled by the [BN2](3-) anions y ielding two interpenetrating (3)(infinity)[E1(BN2)(6/2)] networks. Periodic Nodal Surfaces (PNS) of Im (3) over bar m symmetry show the regions of dif ferent interactions.