Synthesis, structure, and properties of rare-earth germanium sulfide iodides RE3Ge2S8I (RE = La, Ce, Pr)

Abstract The rare-earth germanium sulfide iodides RE 3 Ge 2 S 8 I ( RE  = La, Ce, Pr) have been prepared by reaction of the elements at 900 °C. They adopt the monoclinic La 3 (SiO 4 ) 2 Cl-type structure (space group C 2/ c , Z  = 4; a  = 16.156(4)–15.9760(9) A, b  = 7.9776(18)–7.8786(5) A, c  = 11.081(3)–10.9281(6) A, β  = 98.192(5)–98.4525(10)° on progressing from La to Pr for the RE component) consisting of isolated thiogermanate tetrahedral groups [GeS 4 ] 4– separated by RE 3+ and I − ions. The optical band gaps fall in the range of 2.7–3.1 eV. Magnetic measurements indicated simple paramagnetic behaviour for Ce 3 Ge 2 S 8 I and Pr 3 Ge 2 S 8 I.