La2Pd3Ge5 and Nd2Pd3Ge5 Compounds: Chemical Bonding and Physical Properties.

Herwig Michor,Gerda Rogl,Serena De Negri,Georg Binder,Pavlo Solokha,Adriana Saccone,Riccardo Freccero,Peter F Rogl

doi:10.1021/acs.inorgchem.0c03744

Herwig Michor, Gerda Rogl + Show 6 more

Open Access

https://doi.org/10.1021/acs.inorgchem.0c03744

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Abstract

The two La2Pd3Ge5 and Nd2Pd3Ge5 compounds, crystallizing in the oI40-U2Co3Ge5 crystal structure, were targeted for analysis of their chemical bonding and physical properties. The compounds of interest were obtained by arc melting and characterized by differential thermal analysis, scanning electron microscopy, and X-ray diffraction both on powder and on a single crystal (for the La analogue), to ensure the high quality of the samples and accurate crystallographic data. Chemical bonding was studied by analyzing the electronic structure and effective QTAIM charges of La2Pd3Ge5. A significant charge transfer mainly occurs from La to Pd so that Ge species assume tiny negative charges. This result, together with the -(I)COHP analysis, suggests that, in addition to the expected homopolar Ge bonds within zigzag chains, heteropolar interactions between Ge and the surrounding La and Pd occur with multicenter character. Covalent La–Pd interactions increase the complexity of chemical bonding, which could not be adequately described by the simplified, formally obeyed, Zintl–Klemm scheme. Electric resistivity, specific heat, magnetization, and magnetic susceptibility as a function of temperature indicate for both compounds a metallic-like behavior. For Nd2Pd3Ge5, two low-temperature phase transitions are detected, leading to an antiferromagnetic ground state.

Highlights

Combination of Ge with more electropositive metals leads to a great variety of compounds, containing different Ge-based fragments, the extension and shape of which depend both on the composition and on the nature of the other constituent(s)
With a decrease in germanium content, discrete and stable anionic Ge clusters form, which can even be extracted from the solid and functionalized with various molecular ligands, as, for example, in K4Ge9.2,3 Chemical bonding in these compounds is frequently approached by applying the Zintl−Klemm concept
Chemical bonding in La2Pd3Ge5 was studied, and the results are reported in this work together with some measurements of physical properties

Summary

INTRODUCTION

Combination of Ge with more electropositive metals leads to a great variety of compounds, containing different Ge-based fragments, the extension and shape of which depend both on the composition and on the nature of the other constituent(s). When the electronegativity difference is decreased by substituting an alkali with an alkaline-earth metal, the reduced charge transfer leads to covalent interactions among cations and the anionic partial structures In these cases, the Zintl−Klemm rules are frequently fulfilled, they are, not sufficient to account for all of the different kinds of interactions taking place.[4] Modern quantum chemical approaches based on QTAIM5 and electron localizability. The increased complexity of the bonding situation when moving from the main group to the transition metal analogues was revealed by the presence of La−M heteropolar interactions, traceable when deeply analyzed by means of the ELI-D fine structure based on its relative Laplacian Another large family of ternary germanides with a lower Ge content is that with a general formula of R2M3Ge5. Chemical bonding in La2Pd3Ge5 was studied, and the results are reported in this work together with some measurements of physical properties

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

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