To what extent does the Zintl-Klemm formalism work? The Eu(Zn(1-x)Ge(x))2 series

The series of ternary polar intermetallics Eu(Zn(1-x)Ge(x))(2) (0 < or = x < or = 1) has been investigated and characterized by powder and single-crystal X-ray diffraction as well as physical property measurements. For 0.50(2) < or = x < 0.75(2), this series shows a homogeneity width of hexagonal AlB(2)-type phases (space group P6/mmm, Pearson symbol hP3) with Zn and Ge atoms statistically distributed in the planar polyanionic 6(3) nets. As the Ge content increases in this range, a decreases from 4.3631(6) A to 4.2358(6) A, while c increases from 4.3014(9) A to 4.5759(9) A, resulting in an increasing c/a ratio. Furthermore, the Zn-Ge bond distance in the hexagonal net drops from 2.5190(3) A to 2.4455(3) A, 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 AlB(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 P3m1(00gamma)00s reveals puckered 6(3) nets. Temperature-dependent magnetic susceptibility measurements for two AlB(2)-type compounds show Curie-Weiss behavior above 40.0(2) K and 45.5(2) K with magnetic moments of 7.98(1) mu(B) for Eu(Zn(0.48)Ge(0.52(2)))(2) and 7.96(1) mu(B) for Eu(Zn(0.30)Ge(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 AlB(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.