The reactivity of europium with As species in Lewis basic alkali-metal polysulfide fluxes was investigated along with compound formation and the As 3+/As 5+ interplay vis-à-vis changes in the flux basicity. The compound Na 2EuAs 2S 5 containing trivalent As 3+ is stabilized from an arsenic-rich polysulfide flux. It crystallizes in the monoclinic centrosymmetric space group P2 1/c. Na 2EuAs 2S 5 has [As 2S 5] 4- units, built of corner sharing AsS 3 pyramids, which are coordinated to Eu 2+ ions to give a two-dimensional (2D) layered structure. A sodium polysulfide flux with comparatively less arsenic led to the As 5+ containing compounds NaEuAsS 4 (orthorhombic, Ama2) and Na 4Eu(AsS 4) 2 (triclinic, P1) depending on Na 2S/S ratio. The NaEuAsS 4 and Na 4Eu(AsS 4) 2 have a three-dimensional (3D) structure built of [AsS 4] 3- tetrahedra coordinated to Eu 2+ ions. All compounds are semiconductors with optical energy gaps of ∼2 eV.
ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry