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

Two
atomic arrangements were found near the equiatomic composition in
the strontium–lithium–arsenic system. Orthorhombic o-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 h-SrLi1–xAs was obtained from annealing of o-SrLiAs at 550 °C in dynamic vacuum. The structures
of both phases were determined by single-crystal X-ray diffraction: o-SrLiAs, structure type TiNiSi, space group Pnma, Pearson symbol oP12, a = 7.6458(2)
Å, b = 4.5158(1) Å, c =
8.0403(3) Å, V = 277.61(2) Å3, RF = 0.028 for 558 reflections; h-SrLi1–xAs, structure
type ZrBeSi, space group P63/mmc, Pearson symbol hP6, a = 4.49277(9)
Å, c = 8.0970(3) Å, V =
141.54(1) Å3, RF = 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 Sr1.3+Li0.8+As2.1–, in agreement with the electronegativities of the
individual elements. The electron localizability indicator distribution
indicated the formation of a 3D anionic framework [LiAs] in o-SrLiAs and a rather 2D anionic framework [LiAs] in h-SrLi1–xAs. Magnetic
susceptibility measurements point to a diamagnetic character of both
phases, which verifies the calculated electronic density of states.