Li₃₅Ln₉Si₃₀N₅₉O₂F with Ln = Ce, Pr - highly condensed nitridosilicates

The isotypic nitridosilicates Li₃₅Ln₉Si₃₀N₅₉O₂F (Ln = Ce, Pr) were synthesized by reaction of LnF₃ and LiN₃ with Si(NH)₂ in liquid lithium flux in weld shut tantalum ampoules. The crystal structures of the isotypic compounds were solved and refined on the basis of single-crystal X-ray diffraction (P anti 3c1 (no. 165), Z = 2; Li₃₅Ce₉Si₃₀N₅₉O₂F:, a = 1479.9(2), c = 1538.3(3) pm, R₁ = 0.0526, 1671 data, 175 parameters; Li₃₅Pr₉Si₃₀N₅₉O₂F: a = 1477.3(2), c = 1533.9(3) pm, R₁ = 0.0441, 1331 data, 175 parameters). The silicate substructure represents a 3D network of all side corner sharing SiN₄ tetrahedra. At one discrete and not condensed mixed anion position an atomic ratio O:F = 2:1 is assumed in order to achieve charge neutrality. With an atomic ratio Si:N = 30:59, the degree of condensation of the silicate substructure is slightly above κ = 1/2. Accordingly, there are triply crosslinking N^[3] atoms in the silicate substructure. The obtained structures prove that by employing the lithium flux technique not only nitridosilicates with a low degree of condensation can be obtained by using rather mild reaction conditions at low temperatures. Lattice energy calculations (MAPLE) and EDX measurements confirmed the electrostatic bonding interactions and the chemical composition. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)