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.

The new intermetallic compound Eu 2 Pd 2 Sn has been investigated. A single crystal was selected from the alloy and was analyzed by single-crystal X-ray diffraction, revealing that this compound possesses the noncentrosymmetric Ca 2 Pd 2 Ge structure type being, so far, the only rare-earth-based representative. Bonding analysis, performed on the basis of DOS and (I)COHP, reveals the presence of strong covalent Sn–Pd bonds in addition to linear and equidistant Pd–Pd chains. The incomplete ionization of Eu leads to its participation in weaker covalent interactions. The magnetic effective moment, extracted from the magnetic susceptibility χ(T) is μ eff = 7.87 μ B , close to the free ion Eu 2+ value ( μ eff = 7.94 μ B ). The maximum of χ(T) at T N ∼ 13 K indicates an antiferromagnetic behavior below this temperature. A coincident sharp anomaly in the specific heat C P ( T ) emerges from a broad anomaly centered at around 10 K. From the reduced jump in the heat capacity at T N a scenario of a transition to an incommensurate antiferromagnetic phase below T N followed by a commensurate configuration below 10 K is suggested.

Direct synthesis and structural characterization of a series of polar rare earth palladium germanides of R2Pd3Ge5 composition (R = La–Nd, Sm) is reported. The crystal structure of the Nd representative was determined by single-crystal X-ray diffraction analysis (U2Co3Si5-type, SG: Ibam, oI40, Z = 4, a = 10.1410(6), b = 12.0542(8), c = 6.1318(4) Å, wR2 = 0.0306, 669 F2 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 [Pd3Ge5]δ− 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 RPd2Ge2, RPdGe3 and R2Pd3Ge5 ternary compounds, enriching the large family of the BaAl4 derivatives. Moreover, syntheses with metal fluxes were performed, some of which were successful to obtain large crystals of La2Pd3Ge5 (using Bi as solvent) and Nd2Pd3Ge5 (using Pb as solvent) stoichiometry

The RPdGe series (R = rare earth metal) was structurally characterized, and the results achieved were extended for a comprehensive study on RMGe (M = another metal) compounds, employing symmetry-based structural rationalization and energy calculations. Directly synthesized RPdGe 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-Ce(GaGe) as the correct structure. The alternative In-flux method, once optimized, produced three good quality RPdGe single crystals: LaPdGe and PrPdGe turned out to be mS36-LaAlGe-type non-merohedrally twinned crystals and YbPdGe is of oS72-Ce(GaGe)-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-SmNiGe 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 RPdGe (R = Y and La) in the three abovementioned structural models, and for LaMGe (M = Pt, Cu, Ag and Au) in the oS18 and oS72 modifications. The results indicate that the oS18-CeCuGe 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.