The Zintl‐Klemm Concept – A Historical Survey

Abstract

The Zintl‐Klemm concept (ZKC) is a combination of a valence electron counting rule and a set of structure‐chemical considerations which works well for a continuously growing class of compounds between classical salts and classical covalent compounds on the on hand, and intermetallic phases on the other. In this historical article the lines of development of the ZKC are reviewed. They originate from Eduard Zintl in Darmstadt and were carried on and extended by Wilhelm Klemm in Münster, early on. After World War II different schools developed their own points of view on the ZKC which converged in the 1990s, backed by blossoming quantum mechanical schemes of treating complex solids. The limits of applicability of the ZKC are subject of ongoing investigations, still, and it seems that the concept has reached a state of quite general acceptance in solid state sciences.

The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds

“…For instance, Wade´s rules [77,78] or the Zintl concept [5][6][7][8][9][10] are prominent electron-counting schemes being typically applied to recognize the valence bonds in solid-state materials with polyanionic clusters and monoatomic counterions. More recent research on the components of the active-metal (main-groups I, II, and the scandium-group elements)−gold−post-transition-metal systems identified several materials composed of polyanionic clusters possessing fewer valence electrons relative to those in Zintl phases [15].…”

“…For the case of solid-state materials, in particular ionic salts, first explorations to establish relationships between the structural arrangements and the electron counts of such solids employed empirical data and resulted in various solid-state rules which, for instance, were based on the ratios of ionic radii, the "strengths" of the electrostatic bonds, and the connectivities between diverse coordination polyhedra [4]. Further research on the distributions of the valence electrons in intermetallic compounds revealed additional notions, e.g., those first proposed by Zintl [5][6][7][8][9][10] and Hume-Rothery [11][12][13], respectively, to somehow correlate structural arrangements and the atoms' electronic nature. Even today, however, the existence of intermetallic compounds for which the electronic structures and, furthermore, the nature of bonding cannot be trivially categorized by applying one of the aforementioned concepts [14,15] underlines the need for different means in order to reveal the bonding nature in such materials.…”

Revealing Tendencies in the Electronic Structures of Polar Intermetallic Compounds

“…(a) The Fermi levels in these materials are often located in pseudogaps or gaps of the band structures to accomplish electronically favorable situations-features that are also expected for Hume-Rothery [24] and Zintl [23] phases, respectively. (b) The largest proportions to the net bonding capabilities are frequently achieved for the interactions providing large bond energies such that the overall bonding is optimized for a given material.…”

“…The electronic structures of the tellurium-rich (≥50 at.-% Te) tellurides are frequently illustrated by applying the Zintl-Klemm concept assuming that the valence electrons are formally transferred from the more electropositive to the more electronegative elements, which assemble fragments (Zintl anions) being isostructural to the modifications of isoelectronic elements [23,113,114]. For instance, in the crystal structure of Rb 2 Te 2 , the tellurium atoms assemble dumbbells, [Te 2 ] 2− (Figure 3a), which are isoelectronic to halide dumbbells based on a formal electron transfer from rubidium to tellurium after applying the Zintl-Klemm concept [80,114].…”

Crystal growth and electrical transport properties of niobium and tantalum monopnictide and dipnictide semimetals

“…Niobium and tantalum dipnictides are semimetallic as well. The Pn-Pn dimer has an electron number of 4 − and the valences of the niobium and tantalum dipnictides can be written as (Nb/Ta) 5+ 2 (Pn-Pn) 4− Pn 6− 2 [13,14], which leads to an electron-number balanced Zintl phase. Previous band-structure calculations [14] have confirmed their semimetal electronic states.…”