To what extent does the zintl-klemm formalism work? The Eu(Zn ₁- _XGe _X) ₂ series

The series of ternary polar intermetalllcs Eu(Zn _1-x Ge _x) ₂0≤x≤ 1) has been investigated and characterized by powder and single-crystal X-ray diffraction as well as physical property measurements. For 0.50(2) <x< 0.75(2), this series shows a homogeneity width of hexagonal AIB ₂-type phases (space group P6/mmm, Pearson symbol hP3) with Zn and Ge atoms statistically distributed In the planar polyanionlc 6 ³ nets. As the Ge content increases In this range, a decreases from 4.3631(6) Å to 4.2358(6) Å, while c Increases from 4.3014(9) Å to 4.5759(9) Å, resulting In an increasing da ratio. Furthermore, the Zn-Ge bond distance in the hexagonal net drops from 2.5190(3) Å to 2.4455(3) Å, while the anisotropy of the displacement ellipsoids significantly increases along the c direction. For x < 0.50 and x > 0.75, respectively, orthorhombic KHg ₂-type and trigonal EuGe ₂-type phases occur as a second phase in mixtures with an AIB ₂-type phase. Diffraction of the x= 0.75(2) sample shows Incommensurate modulation along the c direction; a structural model In super space group P31 (00y)00s reveals puckered 6 ³ nets. Temperature-dependent magnetic susceptibility measurements for two AIB ₂-type compounds show Curie-Weiss behavior above 40.0(2) K and 45.5(2) K with magnetic moments of 7.98(1 ) μB for Eu(Zn _0.48Ge _0.52(2)) ₂ and 7.96(1 ) μB for Eu(Zn _0.30Ge _0.70(2)) ₂, respectively, Indicating a (4f) ⁷ electronic configuration for Eu atoms (Eu ²⁺). The Zintl- Klemm formalism accounts for the lower limit of Ge content in the AIB ₂-type phases but does not identify the observed upper limit. In a companion paper, the intrinsic relationships among chemical structures, compositions, and electronic structures are analyzed by electronic structure calculations.