Structural, optical, and magnetic properties of Na8Eu2(Si2S6)2 and Na8Eu2(Ge2S6)2: Europium(II) quaternary chalcogenides that contain an ethane-like (Si2S6)6− or (Ge2S6)6− moiety

Abstract

Two isostructural europium(II) quaternary chalcogenides, Na8Eu2(Si2S6)2, 1, and Na8Eu2(Ge2S6)2, 2, containing an ethane-like (Si2S6)6− or (Ge2S6)6− moiety have been synthesized by employing the polychalcogenide molten flux method. Single-crystal X-ray diffraction reveals that both compounds crystallize in the C2/m space group, and their structures contain layers of {[Na2Eu2(Si2S6)2]6−}∞ or {[Na2Eu2(Ge2S6)2]6−}∞ anions held together by six interlayer sodium cations to yield {Na6[Na2Eu2(Si2S6)2]}∞ and {Na6[Na2Eu2(Ge2S6)2]}∞. Compound 2 is a semiconductor with an optical band gap of 2.15(2)eV. The temperature dependence of the magnetic susceptibility indicates that compounds 1 and 2 are paramagnetic with μeff=7.794(1)μB per Eu and g=1.964(1) for 1 and μeff=8.016(1)μB per Eu and g=2.020(1) for 2, moments that are in good agreement with the europium(II) spin-only moment of 7.94μB. The europium-151 Mössbauer isomer shift of 2 confirms the presence of europium(II) cations with an electronic configuration between [Xe]4f6.81 and 4f76s0.32.