Simon Steinberg

To understand the nature of multicenter interactions in periodic solids and their associated materials (transport) properties, we investigate and quantify multicenter bonding on the basis of the underlying wave function, namely by a combination of quantum-chemical tools for a diverse series of functional materials. First, we probe all compounds by projected force constants based on plane-wave phonon calculations, followed by a projection from plane waves onto a local-orbital framework and its thorough quantum-chemical analysis. While the three-center crystal orbital bond index is used to quantify multicenter bonding between atomic orbitals, the linear combination of fragment orbitals provides a molecular-orbital lens. Eventually, both approaches are fused into the molecular orbital contribution index that directly attributes the contributions of a single molecular orbital to a multicenter bond.

Nitridometallates with extended anionic frameworks exhibit a variety of intriguing electronic properties, including band magnetism, metal‐metal bonding, and superconductivity. Such extended framework materials are scarce with late transition metals due to the requirement of high metal oxidation states and nitrogen content. This study presents a family of nitridocobaltates Ln Co ₂ N ₂ ( Ln = La, Pr, Nd) with an extended layered cobalt‐nitrogen network related to the Kagome lattice that was synthesized at 8 GPa in a large volume press. The compounds crystallize in the trigonal space group R with alternating layers of unusual trigonal planar CoN ₃ and octahedral Ln N ₆ polyhedra. Magnetization and powder neutron diffraction studies indicate a metallic ground state and the suppression of magnetic ordering of the rare earth moments due to their arrangement on a trigonal lattice. The compounds have a surprising mixed‐valent Co ^+I/+II state, which is high for nitridocobaltates. This study demonstrates the structural diversity available in late nitridometallates via high‐pressure synthesis, which can now be explored systematically.

Tellurides are of increasing interest owing to their emerging applications in energy and electronics, as well as their diverse structural chemistry. We introduce Cu ₅ Ge ₂ Te ₇ , a novel ternary telluride, synthesized using traditional high-temperature synthesis and non-equilibrium methods. This is the first report on the Ge-based phase of the Cu ₅ Sn ₂ Ch ₇ ( Ch : S, Se, Te) family, which has been extensively studied. The phase-pure Cu ₅ Ge ₂ Te ₇ was synthesized by heating for 30-120 seconds using Direct Joule heating Synthesis (DJS), followed by quenching. DJS was used to develop an ex - situ “panoramic” reaction map that provides insight into phase formation at different DJS temperatures. The structure of Cu ₅ Ge ₂ Te _{7 was characterized by X-ray diffraction techniques on the crystals grown by traditional high-temperature synthesis. The structure consists of corner-sharing distorted Te 4 -tetrahedral units surrounding copper and germanium atoms. The germanium atoms reside in tellurium tetrahedra, which condense into [Ge 2 Te 7 ]-dimers, and such a Ge–Te interaction has been rarely reported in inorganic systems so far. Electronic structure calculation shows that Cu 5 Ge 2 Te 7 is a poor metal, as a finite density of states is present at the Fermi level. Bonding analysis displays that the [Ge 2 Te 7 ]-unit in the structure exhibits Zintl-phase-like electronic features, though the overall electronic structure indicates that this Cu 5 Ge 2 Te 7 is not a true Zintl phase. Transport measurements reveal an ultralow lattice thermal conductivity of 0.4 W·m ^-1 ·K ^-1 at 683 K, making it a suitable candidate for thermal insulation applications.}

Tellurides attract enormous attention among the scientific community due to their emerging energy, electronic applications, and diverse crystal chemistry. We report a new ternary telluride, Cu5Ge2Te7, synthesized via both traditional high-temperature synthesis and direct Joule heating synthesis (DJS). The phase was discovered within the product mixture formed by the traditional high-temperature method. An ongoing challenge lies in synthesizing high-quality bulk tellurides, as traditional synthesis requires prolonged annealing at elevated temperatures, offers limited control over reactions, and frequently yields impurity phases. Herein, a phase-pure product was obtained in two minutes using DJS method. Moreover, DJS was used for the first time to develop an ex-situ “panoramic” reaction map that provides insight into the phase evaluation across different temperatures during the heating process. The structure of the new phase was characterized using X-ray diffraction techniques on the crystals grown by traditional high-temperature synthesis. The structure adopts the Cu5Sn2Se7-type and consists of corner-sharing distorted Te4-tetrahedral units surrounding copper and germanium atoms. Moreover, it is quite striking that the germanium atoms reside in tellurium tetrahedra, which are condensed into [Ge2Te7] dimers. Electronic structure calculation shows that the compound is a poor metal, as a finite density of states is present at the Fermi level. Bonding analysis displays that the [Ge2Te7]-unit in the structure exhibits Zintl-phase-like electronic features, though the overall electronic structure indicates that this Cu5Ge2Te7 is not a true Zintl phase. The transport measurements reveal that the compound exhibits a metal-like behaviour and has an ultralow lattice thermal conductivity of 0.4 W·m-1·K-1 at 683 K.

The demand for a highly efficient and clean energy supply makes it necessary to develop new technologies whose components meet all materials’ properties that are requested to realize a specific task. As the transport properties of materials are related to the electronic and vibrational characteristics, it is quite beneficial to be fully aware of the exchange between electrons as well as phonons. In order to project the electronic peculiarities, the well-established Zintl−Klemm−Busmann formalism has been applied to many solids including certain silicides as well as tellurides, but is it actually helpful to make use of that approach in the case of tellurides? In the framework of this progress review, it is the overall objective to answer that question. In doing so, the electronic structures will be reviewed for the examples of several tellurides hence serving as prototypes.

Unraveling the relationship between thermodynamic factors, interatomic interactions, and electronic structure remains a crucial yet elusive challenge in the discovery of novel materials in solid‐state (SS) chemistry. In the quest for new thermoelectric (TE) materials, we overcame that fundamental problem for the case of CuGe ₂ Se ₃ , whose synthesis, unique crystal structure, and transport properties are reported herein. The giant two‐dimensional (2D) structure of CuGe ₂ Se ₃ , consisting of Se/(Cu─Ge)/Se and Se/(Ge─Ge)/Se slabs stacked along the c ‐axis, exhibits short Cu─Ge and Ge─Ge interactions, as evidenced by single‐crystal X‐ray diffraction (SCXRD) and SS NMR spectroscopic studies. These homopolar bonds might be surprising, as such interactions are rarely observed in group IV‐chalcogenides. The compound is thermally stable up to ∼823 K. Transport properties measurements revealed a high Seebeck coefficient (∼373.6 µV·K ⁻¹ ) and ultralow thermal conductivity (∼0.35 W·m ⁻¹ K ⁻¹ ) at 755 K, ascribed to its weak bonding interactions. We followed up with a theoretical analysis to gain insight into its structural peculiarities, focusing on vibrational properties and the nature of chemical bonding. The formation of Ge─Ge bonds is favored in light of the presence of multicenter bonds, which receive contributions from stereochemically non‐active Ge lone pairs.

Unraveling the relationship between thermodynamic factors, interatomic interactions, and electronic structure remains a crucial yet elusive challenge in the discovery of novel materials in solid‐state (SS) chemistry. In the quest for new thermoelectric (TE) materials, we overcame that fundamental problem for the case of CuGe ₂ Se ₃ , whose synthesis, unique crystal structure, and transport properties are reported herein. The giant two‐dimensional (2D) structure of CuGe ₂ Se ₃ , consisting of Se/(Cu─Ge)/Se and Se/(Ge─Ge)/Se slabs stacked along the c ‐axis, exhibits short Cu─Ge and Ge─Ge interactions, as evidenced by single‐crystal X‐ray diffraction (SCXRD) and SS NMR spectroscopic studies. These homopolar bonds might be surprising, as such interactions are rarely observed in group IV‐chalcogenides. The compound is thermally stable up to ∼823 K. Transport properties measurements revealed a high Seebeck coefficient (∼373.6 µV·K ⁻¹ ) and ultralow thermal conductivity (∼0.35 W·m ⁻¹ K ⁻¹ ) at 755 K, ascribed to its weak bonding interactions. We followed up with a theoretical analysis to gain insight into its structural peculiarities, focusing on vibrational properties and the nature of chemical bonding. The formation of Ge─Ge bonds is favored in light of the presence of multicenter bonds, which receive contributions from stereochemically non‐active Ge lone pairs.

An unbridged Mn–Mn dimer was stabilized in calcium nitridomanganate( iv ) oxide, Ca ₆ [Mn ₂ N ₆ ]O, via hot isostatic pressing.

Future problems request the development of materials, which serve as components in technologies addressing these challenges. In this context, tellurides are of great interest since many members of that remarkable family of solids are at the frontline of fundamental research and technological applications. The tailored design of novel tellurides showing task-specific features also demands a proper understanding of their electronic structures, as the knowledge of them provides invaluable insights into the materials characteristics. Therefore, it will be quite helpful if there is a fundamental design principle that allows us to plan electronic peculiarities in tellurides in a straightforward manner. Eventually, the Zintl−Klemm−Busmann idea is a recipe that can guide us through electronic structures based on the corresponding crystal structures and it has been applied to several tellurides to date; yet, how helpful is that approach with regard to the prediction of electronic peculiarities for tellurides in general? In the framework of this review, it will be the overall goal to answer that question.

The design of solid-state materials requests a thorough understanding of the structural preferences among plausible structure models. Since the bond energy contributes to the formation energy of a given structure model, it also is decisive to determine the nature of chemical bonding for a given material. In this context, we were motivated to explore the correlation between chemical bonding and structural distortions within the low-dimensional tellurium fragments in TbCu_0.33Te₂. The ternary telluride was obtained from high-temperature solid-state reactions, while structure determinations based on x-ray diffraction experiments did not point to the presence of any structural distortion above 100 K. However, the results of first-principles-based computations indicate that a potential structural distortion within the low-dimensional tellurium fragments also correlates to an optimization of overall bonding.