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Tellurides have attracted an enormous interest in the quest for materials addressing future challenges, because many of them are at the cutting edge of basic research and technologies due to their remarkable chemical and physical properties. The key to the tailored design of tellurides and their properties is a thorough understanding of their electronic structures including the bonding nature. While a unique type of bonding has been recently identified for post-transition-metal tellurides, the electronic structures of tellurides containing early and late-transition-metals have been typically understood by applying the Zintl−Klemm concept; yet, does the aforementioned formalism actually help us in understanding the electronic structures and bonding nature in such tellurides? To answer this question, we prototypically examined the electronic structure for an alkaline metal lanthanide zinc telluride, i.e., RbDyZnTe3, by means of first-principles-based techniques. In this context, the crystal structures of RbLnZnTe3 (Ln = Gd, Tb, Dy), which were obtained from high-temperature solid-state syntheses, were also determined for the first time by employing X-ray diffraction techniques.

Understanding the bonding nature of solids is decisive, as knowledge of the bonding situation for any given material provides valuable information about its structural preferences and physical properties. Although solid-state tellurides are at the forefront of several fields of research, the electronic structures, particularly their nature of bonding, are typically understood by applying the Zintl‒Klemm concept. However, certain tellurides comprise ionic as well as strong (polar) mixed-metal bonds, in obvious contrast to the full valence-electron transfers expected by Zintl‒Klemm’s reasoning. How are the valence-electrons really distributed in tellurides containing ionic as well as mixed-metal bonds? To answer this question, we carried out bonding and Mulliken as well as Löwdin population analyses for the series of ALn2Ag3Te5-type tellurides (A = alkaline-metal; Ln = lanthanide). In addition to the bonding analyses, we provide a brief description of the crystal structure of this particular type of telluride, using the examples of RbLn2Ag3Te5 (Ln = Ho, Er) and CsLn2Ag3Te5 (Ln = La, Ce), which have been determined for the first time.

The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by Zintl and Hume–Rothery help to understand and forecast the bonding motifs in several intermetallic compounds, there is an emerging group of compounds dubbed as polar intermetallic phases whose electronic structures cannot be categorized by the aforementioned conceptions. These polar intermetallic compounds can be divided into two categories based on the building units in their crystal structures and the expected charge distributions between their components. On the one hand, there are polar intermetallic compounds composed of polycationic clusters surrounded by anionic ligands, while, on the other hand, the crystal structures of other polar intermetallic compounds comprise polyanionic units combined with monoatomic cations. In this review, we present the quantum chemical techniques to gain access to the electronic structures of polar intermetallic compounds, evaluate certain trends from a survey of the electronic structures of diverse polar intermetallic compounds, and show options based on quantum chemical approaches to predict the properties of such materials.