On the Phase Width of MgZn ₂ /KHg ₂ ‐Type Intermetallics <i>A</i> ^II Mg _{2− <i>x</i>} Zn _<i>x</i> ( <i>A</i>  = Ca, Sr, Ba) and the New Compounds (Sr/Ba) ₁₁ Mg ₁₆ Zn <sub>

In the course of an investigation on the role of Mg in ternary alkaline‐earth ( A = Ca, Sr, Ba) zincides, formation and structure of intermetallics along the sections A Mg 2 – A Zn 2 are investigated experimentally, crystallographically, and bond theoretically. Along these pseudo‐binary sections, the structure of the AM 2 compounds changes from the Laves /MgZn 2 ‐type [magnesides] to the KHg 2 ‐type structure [zincides]. Whereas the KHg 2 ‐type zincides do not take up significant amounts of Mg, the MgZn 2 ‐type phase CaMg 2 remains stable up to a Zn‐content of 60 %. Instead of extended phase widths, the heavier alkaline‐earth elements Sr and Ba form the Mg‐rich stoichiometric compounds (Sr/Ba) 11 Mg 16 Zn 6 crystallizing in the rare Ca 11 Cd 18 Au 4 ‐type structure. Barium in addition yields the new Zn‐rich phase Ba 6 Mg 2.8 Zn 8.2 . In the latter two rare/new structure types, an “optimized” bonding situation according to different sizes of Mg and Zn, Mg–Zn heteropolar bonding (“coloring”) and adapted coordinations number of the larger A counter cations is achieved.