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

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&rsquo
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 L&ouml
wdin 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.