Zusammenfassung
New germanides ScAuGe, TmAuGe, and LuAuGe were prepared by melting
mixtures of the elements in an are furnace and subsequent annealing at
1070 K. The structures of ScAuGe and LuAuGe were refined from X-ray
single-crystal diffractometer data: P6(3)mc (No. 186), Z=2, a=430.82(5)
pm, c=684.58(10) pm, V=0.1100(1) nm(3), wR2=0.0688, 275 F-o(2) values,
ten variables for ScAuGe; P6(3)me (No. 186), Z=2, a=437.75(4) pm,
c=711.38(6) pm, V=0.1181(1) nm(3), wR2=0.0340, 355 F-o(2) values, 11
variables, and a batch scale factor of 0.47(3) for LuAuGe. The lattice
constants for TmAuGe are a=439.08(4) pm, c=716.59(7) pm, and V=0.1196(1)
nm(3). The crystal structures of these germanides are derived from the
CaIn2-type structure by an ordered arrangement of Au and Ge atoms at the
indium position. The crystal chemistry of ScAuGe and LuAuGe is compared
with that of the recently reported cerium compound. Although the Au-Ge
intralayer distances at 259.6 pm in CeAuGe, 260.5 pm in LuAuGe, and
257.6 pm in ScAuGe are similar, the Au-Ge interlayer distances at 364.2
pm in CeAuGe, 292.7 pm in LuAuGe, and 275.2 pm in ScAuGe differ
significantly. Thus, the [AuGe] polyanions are changed from
two-dimensional layers in CeAuGe to a three-dimensional network of
distorted tetrahedra in ScAuGe. Chemical bonding within the structures
was investigated by TB-LMTO-ASA band structure calculations. The energy
bands, the densities of states and the valence charge densities are
discussed. Bonding is characterized by intralayer bonds between Au and
Ge within the puckered AuGe hexagons. In addition, in the case of ScAuGe
strong bonds are directed from the Au atoms of one layer to the Ge atoms
of the neighbouring layer. Weaker interlayer bonding is observed in
LuAuGe and no interlayer interaction in CeAuGe, as already indicated by
the pronounced increase of the interlayer distances.
