ChemInform Abstract: Modulated Lanthanum Chains in the Crystal Structure of La3.65[Ru(C2)3]

Lanthanum ruthenium carbide La3.65[Ru(C2)3] crystallizes hexagonal (P63/m) with a = 887.9(2) pm and c = 1606.8(6) pm, V = 1096.8(4)·106 nm3, and Z = 6. The crystal structure contains trigonal-planar Ru(C2)3 groups and lanthanum atoms, which form a partial structure of the chemical composition La3Ru(C2)3. Additional lanthanum atoms occupy hexagonal channels built by those carbon atoms of the C2 ligands, which are non-bonded to the central ruthenium atoms. The distribution of these lanthanum atoms along the c axis results in a threefold superstructure, which was refined as a commensurate modulated structure (P63/m (00g)s0, q = (0, 0, {}^1/{}_3)). Harmonic occupational and displacive modulation functions were used for the structure refinement. The structure converged to R1 = 4.9 % for all data (R1 = 2.6 % for the main reflections, R1 = 11.1 % for the 1st order satellite reflections). A small homogeneity range for this phase is predicted by total energy calculations using the PAW-GGA method (VASP). Chemical bonding analysis reveals that the C2 pairs are best described as acetylide C22– units.