Ternary amalgams: expanding the structural variety of the Gd14Ag51 family

Abstract In intermetallic chemistry, the Gd14Ag51 structure type is rather common and has many amalgam representatives. Up to today, binary amalgams of this type have been described for M = Na, Ca, Sr, Eu, Yb, and the structure family still is growing. Yb11Hg54 is the only representative with a fully ordered crystal structure, and all other representatives exhibit individual disorder phenomena or patterns. The diversity of disorder phenomena in this structural family is unique. In order to shed a light on the underlying reasons for this unexpected structural complexity, we compare the available literature structure models with three new ternary variants, Yb10.7Sr0.3Hg54, Ca4.5Eu6.5Hg54 and Ca6.9Na4.1Hg54 (all in space group type P 6 ‾ $P\overline{6}$ , a = 13.5379(12), 13.5406(8) and 13.564(5) Å, c = 9.7488(14), 9.7149 and 9.810(7) Å for Yb10.7Sr0.3Hg54, Ca4.5Eu6.5Hg54 and Ca6.9Na4.1Hg54, respectively). Their crystal structures have been examined in detail on the basis of both single crystal and powder X-ray diffraction data. Each of the three new amalgams exhibits its own set of disorder phenomena that is again different from those of the respective binary variants. The synopsis of the crystal structures and their individual disorder phenomena indicates that the reason for the disorder phenomena cannot be found only by analyzing geometric details such as atomic radii quotients or coordination polyhedral volumina, and additional electronic reasons must be assumed.