Polar‐Covalent Bonding Beyond the Zintl Picture in Intermetallic Rare‐Earth Germanides. Issue 26 (17th April 2019)

• Record Type: Journal Article
• Authors: Freccero, Riccardo; Solokha, Pavlo; De Negri, Serena; Saccone, Adriana; Grin, Yuri; Wagner, Frank R.
• Is Part Of: Chemistry. Volume 25:Issue 26(2019)
• Page Start: 6600
• Page End: 6612
• Publication Date: 2019-04-17
• Subjects: chemical bonding -- ELI-D -- intermetallic phases -- QTAIM -- quantum chemistry; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201900510
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: A comparative chemical bonding analysis for the germanides La2 M Ge6 ( M =Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2 PdGe6 is presented, together with the crystal structure determination for M =Li, Mg, Cu, Ag. The studied compounds adopt the two closely related structure types oS 72‐Ce2 (Ga0.1 Ge0.9 )7 and mS 36‐La2 AlGe6, 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 =Mg 2+, Zn 2+, 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 [La2 Ge6 ] 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. Abstract : Bond issue : Extension of recently introduced techniques for bonding analysis in position space permits characterization of the external polar‐covalent bonding of the Zintl‐type polyanion with respect to the (8− N )‐rule implemented in the Lewis model. This is exemplarily demonstrated for a series of intermetallic rare‐earth germanides with variable electron count around the ideal Zintl value using CaGe for comparison.