Layered Quaternary Germanides-Synthesis and Crystal and Electronic Structures of AELi2In2Ge2 ( AE = Sr, Ba, Eu).

Three new quaternary germanides with the composition AELi2In2Ge2 ( AE = Sr, Ba, Eu) have been synthesized and structurally characterized. The layered crystal structure of these phases features homoatomic In-In bonding, but there are no direct Ge-Ge bonds. Such a crystallographic arrangement can be regarded as an ordered quaternary derivative of the CaCu4P2 structure (trigonal syngony, Pearson code hR7). Comprehensive analysis of the structural genealogy suggests relationships with the structures of other layered pnictides and chalcogenides, which are discussed. Partitioning of the available valence electrons and the assignment of the formal charges indicate that the composition of the new germanides is charge-balanced. First-principles calculations and electrical transport measurements indicate poor metallic behavior, resulting from significant hybridization of the electronic states.