Synthesis, Structure, and Properties of Two Zintl Phases around the Composition SrLiAs

Abstract

Two atomic arrangements were found near the equiatomic composition in the strontium–lithium–arsenic system. Orthorhombic <i>o</i>-SrLiAs was synthesized by reaction of elemental components at 950 °C, followed by annealing at 800 °C and subsequent quenching in water. The hexagonal modification <i>h</i>-SrLi_1–<i>x</i>As was obtained from annealing of <i>o</i>-SrLiAs at 550 °C in dynamic vacuum. The structures of both phases were determined by single-crystal X-ray diffraction: <i>o</i>-SrLiAs, structure type TiNiSi, space group <i>Pnma</i>, Pearson symbol <i>oP</i>12, <i>a</i> = 7.6458(2) Å, <i>b</i> = 4.5158(1) Å, <i>c</i> = 8.0403(3) Å, <i>V</i> = 277.61(2) ų, <i>R</i>_F = 0.028 for 558 reflections; <i>h</i>-SrLi_1–<i>x</i>As, structure type ZrBeSi, space group <i>P</i>6₃/<i>mmc</i>, Pearson symbol <i>hP</i>6, <i>a</i> = 4.49277(9) Å, <i>c</i> = 8.0970(3) Å, <i>V</i> = 141.54(1) ų, <i>R</i>_F = 0.026 for 113 reflections. The analysis of the electron density within the framework of the quantum theory of atoms in molecules revealed a charge transfer according to the Sr^1.3+Li^0.8+As^2.1–, in agreement with the electronegativities of the individual elements. The electron localizability indicator distribution indicated the formation of a 3D anionic framework [LiAs] in <i>o</i>-SrLiAs and a rather 2D anionic framework [LiAs] in <i>h</i>-SrLi_1–<i>x</i>As. Magnetic susceptibility measurements point to a diamagnetic character of both phases, which verifies the calculated electronic density of states