Chemical bonding in RFe6Ge4 (R = Li, Sc, Zr) and LuTi6Sn4 with rhombohedral LiFe6Ge4 type structure.

The germanide ScFe 6 Ge 4 was synthesized from the elements by arc-melting. Its crystal structure was refined from single crystal X-ray diffractometer data: LiFe 6 Ge 4 type, R 3 ¯ m , a = 507.9(3), c = 2000.9(1) pm, wR 2 = 0.0737, 242 F 2 values, 16 variables. The structure has two main building units. The iron atoms form double-layers of Kagomé networks (248–297 pm Fe–Fe) which are separated by layers of edge-sharing Sc@Ge 8 hexagonal bipyramids (265–293 pm Sc–Ge). Chemical bonding has been studied based on DFT calculations for the A Fe 6 Ge 4 ( A = Li, Sc, Zr) series and isotypic LuTi 6 Sn 4 . Existence of MgFe 6 Ge 4 is proposed on the basis of full geometry optimization. Major differences are observed between the electronic structures and the magnetic properties and bonding of LuTi 6 Sn 4 on the one hand and the A Fe 6 Ge 4 family on the other hand whereby the iron Kagomé substructure develops magnetization in all A Fe 6 Ge 4 compounds, in contrast to LuTi 6 Sn 4 . The Ti–Ti Kagomé substructure is found with bonding character throughout the valence band whereas Fe–Fe interactions are both bonding and antibonding with characteristic spin-dependent bonding. Spin-polarized calculations hint for magnetic ordering in the iron containing representatives. This was proven experimentally for ScFe 6 Ge 4 . Temperature-dependent susceptibility measurements show a Curie temperature of T C = 491(3) K. 57 Fe Mössbauer spectroscopic measurements at ambient temperature show a single resonance at an isomer shift of 0.22(1) mm s −1 with a magnetic hyperfine field of 19.1(1) T . [ABSTRACT FROM AUTHOR]