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Application of chemical bonding analysis in position-space techniques based on combined topological analysis of the electron density and electron-localizability indicator distributions has recently led to the formulation of a polarity-extended 8 − Neff rule for consistent inclusion of quantum chemically obtained polar-covalent bonding data into the classical 8 − N scheme for main-group compounds. Previous application of this scheme to semiconducting main-group compounds of the cubic MgAgAs type of structure with 8 valence electrons per formula unit (8 ve per f.u.) has shown a covalent bonding tendency preferring one zinc blende type partial structure over the other one, which seems to corroborate the classical Lewis picture of maximally four covalent bonds per main-group element. In contrast to the MgAgAs type, the orthorhombic TiNiSi type of structure displays a much higher geometrical flexibility to incorporate different kinds of metal atoms. The analysis of polar-covalent bonding in semiconducting 8 ve per f.u. containing main-group compounds AA′E of this structure type reveals a transition to non-Lewis type bonding scenarios of species E with up to ten polar-covalently bonded metal atoms. This kind of situation is consistently included into the extended 8 − Neff type bonding scheme. A systematic increase of partially covalent bonding from chalcogenides E16 to the tetrelides E14 is found, summing up to as much as 2 covalent bonds E14–A and E14–A′, and correspondingly remaining 4 lone pair type electrons on species E14. The familiar notion of this structure type consisting of a '[NiSi]'-type framework with 'Ti'-type atoms filling the voids cannot be supported for the compounds investigated. [ABSTRACT FROM AUTHOR]

Several alkaline earth or rare earth binary monosilicides and -germanides possess complex bonding properties, such as polycation formation exceeding the scope of classical electron counting rules. In this study, we present characterization by powder and single-crystal diffraction and thermal analysis of CeGe, one of the few monogermanides crystallizing in the FeB-type structure. Comparative computational investigations for structure types experimentally observed for monogermanides and alternative structures with different structural motifs were performed to gain energetical insights into this family of compounds, underlining the preference for infinite germanium chains over other structural motifs. Formation enthalpy calculations and structural chemical analysis highlight the special position of FeB-type compounds among the monogermanides. [ABSTRACT FROM AUTHOR]

The La 2 Pd 3 Si 5 intermetallic and the La 2 Pd 3 (Si x Ge 1- x) 5 solid solution were targeted for structural and computational investigations. The ternary compound and quaternary alloys with varying silicon contents (x = 0.25, 0.50, 0.70, 0.75) were prepared by arc melting and turned out to crystalize with the oI 40–U 2 Co 3 Si 5 (Ibam , N. 72) type structure based on powder X-ray diffraction data. The crystal structure of La 2 Pd 3 Si 5 was additionally solved through X-ray diffraction on single crystal grown by recrystallization in Sn flux. Chemical bonding investigations based on QTAIM effective charges and DOS/(I)COHP analysis indicate the formation of heteropolar interactions between Si and the surrounding La/Pd metals, and between La and Pd. Covalently bonded zigzag chains of Si are also formed and considered to be the main responsible for the higher melting point of La 2 Pd 3 Si 5 , measured by DSC, with respect to that of La 2 Pd 3 Ge 5. The formation of a complete solid solution between La 2 Pd 3 Si 5 and La 2 Pd 3 Ge 5 was confirmed and refined unit cell parameters and volumes change linearly with composition, displaying a Vegard trend. The calculation of atomic volumes on a quantum chemical basis (QTAIM) provides detailed insights into the volume chemistry of La 2 Pd 3 (Si x Ge 1- x) 5. Through this analysis La is found to be responsible, together with the gradual substitution of Ge with Si, for the volume contraction. [Display omitted] • The complete solid solution La 2 Pd 3 (Si,Ge) 5 forms between La 2 Pd 3 Ge 5 and La 2 Pd 3 Si 5. • Cell volume linearly changes with composition according to Vegard's rule. • Lanthanum plays a role in volume contraction as revealed by QTAIM analysis. • La 2 Pd 3 Si 5 shows polar Si−Pd/La and La–Pd interactions and covalent Si−Si bonds. [ABSTRACT FROM AUTHOR]

Ni-based intermetallics and commercial CO 2 hydrogenation catalysts have been compared in Sabatier's reaction. For RENi 5 intermetallics (RE = La, Ce), the analysis of the chemical bonding shows a charge transfer from the RE to the Ni species and the formation of polar two- and four-atomic RE-Ni and four-atomic Ni bonds. Surface simulations and chemical understanding based on the ELI-D mapping approach indicate that dangling bonds originate from the multi-atomic ones and they are the preferred adsorption sites for H 2 molecules. This leads to H 2 dissociation, its reduction to hydrides, Ni QTAIM-anion oxidation to the metallic state, and diffusion toward the surface. LaNi 5 is active toward rWGS while the best catalytic activity is obtained over CeNi 5 (49% methane yield) at 723 K; the exhaust catalyst is composed of Ni particles supported over CeO 2 with a mean size of 10 nm and thus, promising material could be developed on intermetallic based compounds. [Display omitted] • Intermetallics are suitable catalytic precursors for highly loaded Ni-based catalysts. • Catalytic performances of RE Ni 5 are a function of chosen pretreatment. • CeNi 5 reaches 49% yield CH 4 at 723 K after reduction at 873 K for 4 h. • Chemical bonding analysis and surface simulation successful for RENi 5 • Dangling bonds are suitable attack sites for H 2 molecules. [ABSTRACT FROM AUTHOR]

The monogermanide LuGe is obtained via high‐pressure high‐temperature synthesis (5–15 GPa, 1023–1423 K). The crystal structure is solved from single‐crystal X‐ray diffraction data (structure type FeB, space group Pnma, a=7.660(2) Å, b=3.875(1) Å, and c=5.715(2) Å, RF=0.036 for 206 symmetry independent reflections). The analysis of chemical bonding applying quantum‐chemical techniques in position space was performed. It revealed—beside the expected 2c‐Ge‐Ge bonds in the germanium polyanion—rather unexpected four‐atomic bonds between lutetium atoms indicating the formation of a polycation by the excess electrons in the system Lu3+(2b)Ge2−×1 e−. Despite the reduced VEC of 3.5, lutetium monogermanide is following the extended 8‐N rule with the trend to form lutetium‐lutetium bonds utilizing the electrons left after satisfying the bonding needs in the anionic Ge‐Ge zigzag chain. [ABSTRACT FROM AUTHOR]

Das Monogermanid LuGe wurde durch Hochdruck‐Hochtemperatursynthese (5–15 GPa, 1023–1423 K) erhalten. Die Kristallstruktur wurde aus Einkristall‐Röntgenbeugungsdaten gelöst und verfeinert (Strukturtyp FeB, Raumgruppe Pnma, a=7.660 (2) Å, b=3.875 (1) Å und c=5.715 (2) Å, RF=0.036 für 206 symmetrie‐unabhängige Reflexe). Die Analyse der chemischen Bindung wurde mit Hilfe quantenchemischer Techniken im Ortsraum durchgeführt. Neben den erwarteten 2c‐Ge‐Ge‐Bindungen im Germaniumpolyanion wurde eine eher unerwartete vieratomige Wechselwirkung zwischen Lutetium‐Atomen gefunden, was auf die Bildung eines Polykations durch die überschüssigen Elektronen im System Lu3+(2b)Ge2−×1 e− hinweist. Trotz der reduzierten Valenzelektronen‐Konzentration von 3.5 folgt Lutetium‐Monogermanid der erweiterten 8‐N‐Regel durch die Bildung von Lutetium‐Lutetium‐Bindungen unter Verwendung der Elektronen, die nach der Bindungssättigung in der anionischen Ge‐Ge‐Zickzackkette übrigbleiben. [ABSTRACT FROM AUTHOR]

The R2PdGe6 series (R = rare earth metal) was structurally characterized, and the results achieved were extended for a comprehensive study on R2MGe6 (M = another metal) compounds, employing symmetry-based structural rationalization and energy calculations. Directly synthesized R2PdGe6 exists for almost all R-components (R = Y, La–Nd, Sm and Gd–Lu) and even if with La is probably metastable. Several single crystal X-ray analyses (R = Y, Ce, Pr, Nd, Er and Lu) indicated oS72-Ce2(Ga0.1Ge0.9)7 as the correct structure. The alternative In-flux method, once optimized, produced three good quality R2PdGe6 single crystals: La2PdGe6 and Pr2PdGe6 turned out to be mS36-La2AlGe6-type non-merohedrally twinned crystals and Yb2PdGe6 is of oS72-Ce2(Ga0.1Ge0.9)7-type. The vacancy ordering phenomenon was considered as a possible cause of the symmetry reduction relations connecting the most frequently reported 2 : 1 : 6 structural models (oS18, oS72 and mS36) with the oS20-SmNiGe3 aristotype. The detected twin formation is consistent with the symmetry relations, which are discussed even considering the validity of the different structural models. DFT total energy calculations were performed for R2PdGe6 (R = Y and La) in the three abovementioned structural models, and for La2MGe6 (M = Pt, Cu, Ag and Au) in the oS18 and oS72 modifications. The results indicate that the oS18-Ce2CuGe6 structure, prevalently proposed in the literature, is associated with the highest energy and thus it is not likely to be realized in these series. The oS72 and mS36 polytypes are energetically equivalent, and small changes in the synthetic conditions could easily stabilize any of them, in agreement with experimental results obtained by direct and flux syntheses. [ABSTRACT FROM AUTHOR]

Direct synthesis and structural characterization of a series of polar rare earth palladium germanides of RPdGe composition (R = La-Nd, Sm) is reported. The crystal structure of the Nd representative was determined by single-crystal X-ray diffraction analysis (UCoSi-type, SG: Ibam, oI40, Z = 4, a = 10.1410(6), b = 12.0542(8), c = 6.1318(4) Å, wR = 0.0306, 669 F values, 31 variables). The crystal structures of the other homologues were ensured by powder X-ray diffraction pattern analysis. A smooth variation of the cell dimensions is observed through the rare earth series. The structure of the studied compounds can be interpreted as consisting of a complex three-dimensional [PdGe] network spaced by the rare earth cations. Within the concept of symmetry reduction, a Bärnighausen tree is used to rationalize the related crystal structures of the RPdGe, RPdGe and RPdGe ternary compounds, enriching the large family of the BaAl derivatives. Moreover, syntheses with metal fluxes were performed, some of which were successful to obtain large crystals of LaPdGe (using Bi as solvent) and NdPdGe (using Pb as solvent) stoichiometry. [ABSTRACT FROM AUTHOR]