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

摘要

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-)}(infinity) or {[Na2Eu2(Ge2S6)(2)](6-)}(infinity) anions held together by six interlayer sodium cations to yield (Na-6[Na2Eu2(Si2S6)(2)]}(infinity) and {Na-6[Na2Eu2(Ge2S6)(2)]}(infinity). 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 mu(eff)=7.794(1) mu(B) per Eu and g=1.964(1) for 1 and mu(eff)=8.016(1) mu(B) per Eu and g=2.020(1) for 2, moments that are in good agreement with the europium(II) spin-only moment of 7.94 mu(B). The europium-151 Mossbauer isomer shift of 2 confirms the presence of europium(II) cations with an electronic configuration between [Xe]4f(6.81) and 4f(7)6s(0.32). Published by Elsevier Inc.