Polar‐Covalent Bonding Beyond the Zintl Picture in Intermetallic Rare‐Earth Germanides

Abstract

A comparative chemical bonding analysis for the germanides La2MGe6 (M=Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2PdGe6 is presented, together with the crystal structure determination for M=Li, Mg, Cu, Ag. The studied compounds adopt the two closely related structure types oS72‐Ce2(Ga0.1Ge0.9)7 and mS36‐La2AlGe6, containing zigzag chains and corrugated layers of Ge atoms bridged by M species, with La/Y atoms located in the biggest cavities. Chemical bonding was studied by means of the quantum chemical position‐space techniques QTAIM (quantum theory of atoms in molecules), ELI‐D (electron localizability indicator), and their basin intersections. The new penultimate shell correction (PSC0) method was introduced to adapt the ELI‐D valence electron count to that expected from the periodic table of the elements. It plays a decisive role to balance the Ge−La polar‐covalent interactions against the Ge−M ones. In spite of covalently bonded Ge partial structures formally obeying the Zintl electron count for M=Mg2+, Zn2+, all the compounds reveal noticeable deviations from the conceptual 8−N picture due to significant polar‐covalent interactions of Ge with La and M ≠ Li, Mg atoms. For M=Li, Mg a formulation as a germanolanthanate M[La2Ge6] is appropriate. Moreover, the relative Laplacian of ELI‐D was discovered to reveal a chemically useful fine structure of the ELI‐D distribution being related to polyatomic bonding features. With the aid of this new tool, a consistent picture of La/Y−M interactions for the title compounds was extracted.

In‐Cage Interactions in the Clathrate Superconductor Sr8Si46

“…[73] Integration of the electron density in the basins bounded by zero-flux surfaces of the electron density or ELI-D gradient fields yield the atomic charges or bond populations, respectively.T his procedure follows the quantum theory of atoms in molecules (QTAIM) [44] .C ombined analysis of electron density and ELI-D yields basis information for the bonding situation in solids, [41,74,75] in particular for the intermetallic compounds. [76][77][78]…”

“…This procedure follows the quantum theory of atoms in molecules (QTAIM). Combined analysis of electron density and ELI‐D yields basis information for the bonding situation in solids, in particular for the intermetallic compounds …”

Unkonventionelle Metall‐Netzwerk‐Wechselwirkungen in MgSi5

“…[18] Die Verfeinerung der Rçntgendiffraktionsdaten erfolgte mit dem kristallographischen Programmpaket WinCSD. [16,[23][24][25][26] Danksagung Wir danken Susann Leipe für die Unterstützung bei den Hochdrucksynthesen. Die Analyse der chemischen Bindung von MgSi 5 im Realraum wurde im Rahmen des Elektronen-Lokalisierungs-Ansatzes vorgenommen (Hintergrundinformationen).…”

“…Die Analyse der chemischen Bindung von MgSi 5 im Realraum wurde im Rahmen des Elektronen-Lokalisierungs-Ansatzes vorgenommen (Hintergrundinformationen). [16,[23][24][25][26]…”

Uncovering new transition metal Zintl phases by cation substitution: the crystal chemistry of Ca3CuGe3 and Ca2+nMnxAg2−x+zGe2+n−z (n = 3, 4)

“…[2][3][4][5] In fact, they represent intermediates between semiconductors and typical metallic systems. [5][6] Hence, their bonding pictures are often very complex and, it is virtually impossible to apply simple heuristic concepts to reliably deduce their compositions, structural features or the nature of the bonding. This is, because unlike molecular systems, PICs show a much higher degree of electronic flexibility, allowing them to violate the electronic stability factors (valence rules), despite their dominant effects on the structure stability.…”