Chain-Type Lithium Rare-Earth Nitridosilicates - Li5Ln5Si4N12 with Ln = La, Ce

The quaternary lithium rare-earth nitridosilicates Li(5)Ln(5)Si(4)N(12) with Ln = La, Ce were synthesized at moderate temperatures below 900 degrees C in closed tantalum ampoules employing liquid lithium as a flux. Thereby, nitridosilicate substructures with a low degree of condensation were obtained. The air and moisture sensitive title compounds are the first representatives of quaternary lithium rare-earth nitridosilicates and crystallize in space group P (4) over bar b2 [Li5La5Si4N12: a = 1104.28(16), c = 557.30(11) pm, Z = 2, R-1 = 0.0498, 873 data, 56 parameters; Li5Ce5Si4N12: a = 1097.78(16), c = 551.43(11) pm, Z = 2, R-1 = 0.0334, 748 data, 56 parameters]. The nitridosilicate substructure consists of infinite non-branched zweier single-chains of vertex sharing SiN4 tetrahedra running parallel to [001]. The chains exhibit a stretching factor f(s) = 0.981 for La and 0.977 for Ce, respectively. The two crystallographically independent Li+ sites are each coordinated by four nitrogen atoms. Lattice energy calculations (MAPLE) and EDX measurements confirmed the electrostatic bonding interactions and the chemical compositions. For the La containing compound Li-7 solid-state MAS NMR investigations are reported.