The Zintl‐Klemm Concept – A Historical Survey

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.