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Abstract:
The crystal structures of the trigermanides AEGe(3) (tI32) (AE = Ca, Sr,
Ba; space group I4/mmm, for SrGe3 : a = 7.7873(1), c =
12.0622(3)angstrom) comprise Ge-2 dumbbells forming layered Ge
substructures which enclose embedded AE atoms. The chemical bonding
analysis by application of the electron localizability approach reveals
a substantial charge transfer from the AE atoms to the germanium
substructure. The bonding within the dumbbells is of the covalent
two-center type. A detailed analysis of SrGe3 reveals that the
interaction on the bond-opposite side of the Ge-2 groups is not lone
pair-like-as it would be expected from the Zintl-like interpretation of
the crystal structure with anionic Ge layers separated by alkaline-earth
cations-but multi-center strongly polar between the Ge-2 dumbbells and
the adjacent metal atoms. Similar atomic interactions are present in
CaGe3 and BaGe3. The variation of the alkaline-earth metal has a merely
insignificant influence on the superconducting transition temperatures
in the s,p-electron compounds AEGe(3).
