Revisiting the Zintl‒Klemm Concept for ALn2Ag3Te5-Type Alkaline-Metal (A) Lanthanide (Ln) Silver Tellurides

Abstract

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 ALn 2 Ag 3 Te 5 -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 RbLn 2 Ag 3 Te 5 (Ln = Ho, Er) and CsLn 2 Ag 3 Te 5 (Ln = La, Ce), which have been determined for the first time.

Bonding diversity in rock salt-type tellurides: examining the interdependence between chemical bonding and materials properties

“…The corresponding Mulliken and Löwdin charges of YTe, on the other side, clearly point to a small valence-electron transfer unlike that observed for the ionic SrTe, so the Y-Te contacts cannot be depicted as ionic. This outcome is in stark contrast to literature data [59][60][61][62] suggesting ionic rareearth-tellurium interactions, but agrees well with more recent research 23,25,26,28 revealing polar-covalent bonding nature and suggesting the Zintl-Klemm formalism as potentially misleading. Examining the projected COHP of YTe brings to light that the largest bonding contribution originates from Y-4d-Te-5p which changes from bonding to antibonding below the Fermi level.…”

“…In the cases of the tellurides containing transition-metals, the bonding nature is better described as polar-covalent such that applying the Zintl-Klemm idea to such tellurides could be misleading. [23][24][25][26][27][28] Within the most recent efforts on tellurides comprising posttransition-metals, a new bonding type dubbed 'metavalent' 21,29 or 'hyperbonding' 30 has been proposed. This type of bonding is expected to be at the frontier between entire valence-electron localization as well as delocalization and was introduced based on a portfolio of various quantities, seen both in experiment and calculation.…”

Revealing the Bonding Nature in an ALnZnTe3-Type Alkaline-Metal (A) Lanthanide (Ln) Zinc Telluride by Means of Experimental and Quantum-Chemical Techniques

“…A comparison of the volumes of the unit cells of RbLnZnTe 3 (Ln = Gd, Tb, Dy; Table 1) to those of the isostructural cesium-containing [59] tellurides (V CsGdZnTe 3 = 863.55 Å 3 ; V CsTbZnTe 3 = 857.10 Å 3 ; V CsDyZnTe 3 = 851.11 Å 3 ) shows that the unit cell volumes of the latter are larger than those of the former. This is because of the decreased covalent radius [60] from cesium (2.44 Å) to rubidium (2.20 Å); yet, the unit cell volumes within the series RbLnZnTe 3 (Ln = Gd, Tb, Dy) solely exhibit a very small variation-a circumstance that has also been encountered for different polar intermetallics containing heavier lanthanides [24,[61][62][63]. In the following, the crystal structure of this type of quaternary telluride will be prototypically depicted for RbDyZnTe 3 .…”

Probing the Validity of the Zintl−Klemm Concept for Alkaline-Metal Copper Tellurides by Means of Quantum-Chemical Techniques

“…In the spirit of this formalism, the interactions between tellurium atoms and early as well as late TM atoms are frequently described [23][24][25][26] as ionic and covalent, respectively. Yet, more recent research [27][28][29][30] on the electronic structures of certain tellurides, particularly, their nature of bonding, showed that such pictures of the bonding nature should be regarded with concern. Hence, do such Zintl−Klemm treatments help us understanding the nature of bonding in these particular cases, and how else should the bonding nature in such tellurides be described?…”

“…The aforementioned quantum-chemical examinations [27][28][29][30] of the electronic structures of these tellurides containing (early and) late transition-metals revealed that the TM−tellurium states are well populated such that the majorities of the bonding interactions reside between these states. Since this outcome is indicative of an absence of full valence-electron transfers (like in ionic bonds) from the TM to the tellurium atoms, it was concluded that the TM−tellurium interactions should be depicted as strong (polar) mixed-metal-like bonds rather than ionic bonds.…”