Exploring the Borders of the Zintl‐Klemm Concept: On the Isopunctual Phases Eu_5+<i>x</i>Mg_{18–<i>x</i>}Ge₁₃(<i>x</i> = 0.1) and Eu₈Mg₁₆Ge₁₂

Abstract

Abstract Two new ternary compounds Eu 5+ x Mg 18– x Ge 13 ( x = 0.1) and Eu 8 Mg 16 Ge 12 were obtained by solid state synthesis and their crystal structures determined by single crystal X‐ray diffraction. The two compounds crystallize in the hexagonal crystal system (space group P $\bar{6}$ 2 m ). Eu 5+ x Mg 18– x Ge 13 ( x = 0.1) is a Zintl phase with nine isolated Ge 4– ions and a [Ge 4 ] 10– star, which is isoelectronic with PF 3 but surprisingly almost planar. Eu 8 Mg 16 Ge 12 contains a [ M Ge 3 ] ( M = Eu, Mg) unit, instead of the [Ge 4 ] 10– , and can be described as a salt‐like compound, containing 12 “isolated” Ge 4– anions. The structural similarity of these two compounds allows to analyze the chemical bonding of different Zintl anions, which belong to a structural greater isosteric unit. The metallic conductivity of Eu 8 Mg 16 Ge 12 originates from the ecliptic stacking of the “so‐called isolated” anions along the c direction. In Eu 5+ x Mg 18– x Ge 13 the deviation of the Zintl anion from the planarity causes a semi‐metallic behavior. In both cases, the magnetic response is dominated by the local moments of the europium atoms, which are all found in a 2+ oxidation state. Deviations from the Curie–Weiss law are observed for T &lt; 20 K in the cation‐richer compound and at lower temperatures in the other. The behavior in the low‐temperature range changes with the replacement of the [Ge 4 ] 10– star by the M Ge 3 unit. These studies show that metallic behavior through ecliptic stacking of planar anions can be achieved even with monatomic anions, up to 4.4 Å with germanium at least, and can be destroyed by small deviations from planarity in an extended anion.