Zintl phase

In chemistry, a Zintl phase is a product of a reaction between a group 1 (alkali metal) or group 2 (alkaline earth metal) and main group metal or metalloid (from groups 13, 14, 15, or 16). It is characterized by intermediate metallic/ionic bonding. Zintl phases are a subgroup of brittle, high-melting intermetallic compounds that are diamagnetic or exhibit temperature-independent paramagnetism and are poor conductors or semiconductors. This type of solid is named after German chemist Eduard Zintl who investigated them in the 1930s. The term "Zintl Phases" was first used by Laves in 1941. In his early studies, Zintl noted that there was an atomic volume contraction upon the formation of these products and realized that this could indicate cation formation. He suggested that the structures of these phases were ionic, with complete electron transfer from the more electropositive metal to the more electronegative main group element. The structure of the anion within the phase is then considered on the basis of the resulting electronic state. These ideas are further developed in the Zintl-Klemm-Busmann concept, where the polyanion structure should be similar to that of the isovalent element. Further, the anionic sublattice can be isolated as polyanions (Zintl ions) in solution and are the basis of a rich subfield of main group inorganic chemistry. A "Zintl Phase" was first observed in 1891 by M. Joannis, who noted an unexpected green colored solution after dissolving lead and sodium in liquid ammonia, indicating the formation of a new product. It was not until many years later, in 1930, that the stoichiometry of the new product was identified as Na4Pb94- by titrations performed by Zintl et al.; and it was not until 1970 that the structure was confirmed by crystallization with ethylenediamine (en) by Kummer. In the intervening years and in the years since, many other reaction mixtures of metals were explored to provide a great number of examples of this type of system.