Study of new polar intermetallic compounds: synthesis, structural relations and real space chemical bonding analysis

The syntheses, structural characterizations and theoretical DFT-based investigations for different R\u2013M\u2013Ge (R = rare earth metal; M = another metal) germanides are reported. The R2PdGe6 and R2LiGe6 series, together with La2CuGe6 and La2AgGe6 compounds, were structurally characterized by single crystal X-ray diffraction, indicating the oS72-Ce2(Ga0.1Ge0.9)7 modification as the correct one. The alternative In-flux method, once optimized, produced three good quality R2PdGe6 single crystals: Pr2PdGe6 and the metastable La2PdGe6, which turned out to be mS36-La2AlGe6-type non-merohedrally twinned crystals, and the Yb2PdGe6 of oS72-Ce2(Ga0.1Ge0.9)7-type. These results were extended for a comprehensive study on the R2MGe6 (M = Li, Mg, Al, Cu, Zn, Pd, Ag, Pt, Au) family of compounds, employing symmetry-based structural rationalization and total energy calculations, revealing that the highest energy is always associated to the more reported oS18-Ce2CuGe6 structure. The knowledge of the correct structural models allowed a comparative chemical bonding analysis for La2MGe6 (M = Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2PdGe6 germanides. State of the art position-space techniques (QTAIM, ELI-D and their basin intersection) were employed together with the proposal of new approaches developed during this work; i.e. the penultimate shell correction (PSC0) method and the ELI-D fine structure based on its relative Laplacian. The former was crucial to balance Ge\u2013La polar-covalent interactions against the Ge\u2013M ones, whereas the latter allows to reveal polyatomic bonding features. With these new tools at hand, it was possible to go beyond the Zintl picture (formally fulfilled only with M = Mg2+ and Zn2+) revealing Ge\u2013La and Ge\u2013M (M 60 Li, Mg) polar-covalent interactions. For M = Li, Mg a formulation as germanolanthanate M[La2Ge6] is appropriate. In addition, a consistent picture of La/Y\u2013M polar interactions was also described. A systematic study on the existence of R2Pd3Ge5 (R = La-Nd, Sm, Gd-Lu) was conducted and the desired phase was revealed to exist with R = La-Nd, Sm, Yb crystallizing with the oI40-U2Co3Si5 structure. A B\ue4rnighausen tree was constructed in order to rationalize the related crystal structures of the RPd2Ge2, RPdGe3 and R2Pd3Ge5 ternary compounds, enriching the large family of the BaAl4 derivatives. After magnetization and susceptibility measurements Yb2Pd3Ge5 was described as a paramagnet with \u3bceff close to 0.8 \u3bcB/Yb-atom, suggesting a nearly divalent Yb state. The new Lu5Pd4Ge8 and Lu3Pd4Ge4 intermetallics were synthesized. The former crystallizes with non-merohedral monoclinic twinned crystals (P21/m, mP34) and the latter is orthorhombic (Immm, oI22). COHP- and preliminary ELI-D-based chemical bonding analysis revealed the expected Ge-covalent fragments and in addition Ge\u2013Lu, Ge\u2013Pd and Pd-Lu polar-covalent interactions. These findings, together with the aforementioned results for La2MGe6 compounds, indicate the importance of these interactions within ternary rare-earth germanides. Finally, the existence of R4MgGe10-x and R4LiGe10-x phases along the R series was investigated. X-ray single crystal diffraction experiments show that all the phases, obtained with R = La-Nd, Sm, Gd-Dy, are non-merohedrally twinned with mS60-La4MgGe10-x structure. The presented results constitute a step forward in the comprehension of composition-structure-properties relationships and a good playground for further studies on analogous systems

Lu5Pd4Ge8 and Lu3Pd4Ge4: Two more germanides among polar intermetallics

In this study, two novel Lu5Pd4Ge8and Lu3Pd4Ge4polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4Ge8is monoclinic, P21/m, mP34, a = 5.7406(3), b = 13.7087(7), c = 8.3423(4) \uc5, \u3b2 = 107.8(1), Z = 2; Lu3Pd4Ge4is orthorhombic, Immm, oI22, a = 4.1368(3), b = 6.9192(5), c = 13.8229(9) \uc5, Z = 2. The Lu5Pd4Ge8analysed crystal is one more example of non-merohedral twinning among the rare earth containing germanides. Chemical bonding DFT studies were conducted for these polar intermetallics and showing a metallic-like behavior. Gathered results for Lu5Pd4Ge8and Lu3Pd4Ge4permit to described both of them as composed by [Pd\u2013Ge]\u3b4\u2013three dimensional networks bonded to positively charged lutetium species. From the structural chemical point of view, the studied compounds manifest some similarities to the Zintl phases, containing well-known covalent fragment i.e., Ge dumbbells as well as unique cis-Ge4units. A comparative analysis of molecular orbital diagrams for Ge26\u2013and cis-Ge10\u2013anions with COHP results supports the idea of the existence of complex Pd\u2013Ge polyanions hosting covalently bonded partially polarised Ge units. The palladium atoms have an anion like behaviour and being the most electronegative cause the noticeable variation of Ge species charges from site to site. Lutetium charges oscillate around +1.5 for all crystallographic positions. Obtained results explained why the classical Zintl-Klemm concept can\u2019t be applied for the studied polar intermetallics

Unpredicted but It Exists: Trigonal Sc2Ru with a Significant Metal-Metal Charge Transfer

The Sc2Ru compound, obtained by high-temperature synthesis, was found to crystallize in a new trigonal hP45 structure type [space group P3\u305m1; a = 9.3583(9) \uc5 and c = 11.285(1) \uc5]: Ru@Sc8 cubes, Ru@Sc12 icosahedra, and uncommon Ru@Sc10 sphenocoronae are the building blocks of a unique motif tiling the whole crystal space. According to density functional theory studies, Sc2Ru is a metallic compound characterized by multicenter interactions: a significant charge transfer occurs from Sc to Ru, indicating an unexpectedly strong ionic character of the interactions between the two transition metals. Energy calculations support our experimental results in terms of stability of this compound, contributing to the recurrent discussion on the limits of the high-throughput first-principles calculations for metallic materials design

New Insights into the Crystal Chemistry of FeB-Type Compounds : The Case of CeGe

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

Conjugation, Substituent, and Solvent Effects on the Photogeneration of Quinone Methides

4- and 5-arylethynyl water-soluble Mannich bases and related quaternary ammonium salts were synthesized and investigated as a model of conjugated quinone methide precursors (QMPs) by UV–vis light activation. Preparative photohydration and trapping reactions by thiols were studied, together with the detection of both transient QMs and competing QMP lowest triplet excited states (T₁), by laser flash photolysis. The efficiency of the arylethynyl derivatives as QMPs was remarkably affected by structural features (i.e., conjugating arylethynyl moieties, substituents, and leaving groups) and protic vs aprotic solvation. Our collective data clarify the dichotomy in the photoreactivity of conjugated Mannich bases and related quaternary ammonium salts as alkylating agents and singlet oxygen sensitizers

The R2Pd3Ge5 (R\ua0=\ua0La\u2013Nd, Sm) germanides: synthesis, crystal structure and symmetry reduction

Direct synthesis and structural characterization of a series of polar rare earth palladium germanides of R2Pd3Ge5 composition (R = La\u2013Nd, 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) \uc5, 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]\u3b4 12 network spaced by the rare earth cations. Within the concept of symmetry reduction, a B\ue4rnighausen 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