Intermetallic compounds with near Zintl phase behavior: RE ₂Zn₃Ge₆ (RE = La, Ce, Pr, Nd) grown from liquid indium

A series of compounds has been discovered while investigating reactions of rare earth, transition metals, and Ge in excess indium. These compounds, RE ₂Zn₃Ge₆ (RE = La, Ce, Pr, Nd), are isostructural, crystallizing in the orthorhombic space group Cmcm with lattice parameters a = 5.9691(9) Å, b = 24.987(4) Å, and c = 5.9575(9) Å for La₂Zn₃Ge₆, a = 5.9503(5) Å, b = 24.761(2) Å, and c = 5.9477(5) Å for the Ce analogue, a =5.938(2) Å, b = 24.708(8) Å, and c = 5.936(2) Å for Pr ₂Zn₃Ge₆, and a = 5.9094(7) Å, b = 24.619(3) Å, and c = 5.9063(5) Å for the Nd analogue. The structure is composed of PbO-like ZnGe layers and ZnGe₄ cage layers and is related to the Ce₄Zn₈Ge_11-x structure type. The bonding in the system can be rationalized using the Zintl concept resulting in a material that is expected to be a valence precise semiconductor, although its behavior is more consistent with it being a semimetal, making it an intermediate case. The results of band structure calculations and magnetic measurements of these compounds are discussed.