Mixed-valent ternary sulfide Eu5In5S13

Europium indium sulfide, Eu 5 In 5 S 13 , was prepared at 1000 °C. Single-crystal X-ray diffraction reveals that it adopts the Pb 4 In 2 Bi 4 S 13 -type structure (orthorhombic, space group Pbam , a = 20.722(2) Å, b = 25.911(3) Å, c = 3.9883(4) Å, Z = 4), built up from Eu-centred bicapped trigonal prisms and In-centred tetrahedra and octahedra; two metal sites are disordered with Eu and In atoms in octahedral coordination. Magnetic susceptibility measurements, electron paramagnetic resonance spectroscopy, and 151 Eu Mössbauer spectroscopy indicate the coexistence of magnetic Eu 2+ and non-magnetic Eu 3+ . The optical diffuse reflectance spectrum shows a 1.5 eV band gap, which is a direct one as indicated by electronic structure calculations. In atoms occupy tetrahedral and then disorder in octahedral sites on progressing from La 4 Cd 4 In 2 S 13 to Eu 5 In 5 S 13 . • Eu 5 In 5 S 13 was prepared at 1000 °C. • In atoms occupy tetrahedral sites and disorder with Eu atoms in octahedral sites. • Eu 2+ and Eu 3+ are supported by bond valence sums, magnetism, and Mössbauer spectra. • The optical band gap is 1.5 eV.