TiNiSi-Type ALiAu (A = Ca, Sr, Ba, Eu, Yb) Compounds: Alternative Use of "Excess" Electrons.

New TiNiSi-type compounds ALiAu (A = Ca, Sr, Ba, Eu, Yb) were obtained in the form of mm-sized single crystals by high-temperature centrifugation-aided filtration from lithium melt. They are the first examples of TiNiSi-type representatives containing Li and a transition metal. The metallic phases show paramagnetic (Ca) or diamagnetic (Sr, Ba, Yb) behavior or antiferromagnetic ordering below 19 K (Eu). A new structural description is based on a hexagonal close packing with A occupying all octahedral and Li occupying half of the tetrahedral voids in an ordered fashion. Chemical bonding analysis supports the structural description and reveals the formation of eight-atomic stella-quadrangula bonds pinned on the empty tetrahedral holes, a bonding picture known from elemental metals.