Synthesis\nand Characterization of Low-Dimensional\nQuaternary Sulfides of Thallium, Tl₂Cu₂GeS₄, Tl₂Ag₂GeS₄, and Tl₂Ag₂SnS₄

Abstract

Three new low-dimensional quaternary\nsulfides, namely, Tl₂Cu₂GeS₄(<b>1</b>), Tl₂Ag₂GeS₄(<b>2</b>), and Tl₂Ag₂SnS₄(<b>3</b>) were synthesized by solid-state\nreactions and characterized by single-crystal X-ray diffraction, spectroscopic,\nthermal, and photocatalytic studies. The compounds <b>1</b>, <b>2</b>, and <b>3</b>, respectively, have centrosymmetric\nlayered, noncentrosymmetric layered, and noncentrosymmetric one-dimensional\nstructures, in which Cu⁺, Ge⁴⁺, and Sn⁴⁺ ions have tetrahedral coordination and Ag⁺ ion has linear,\ntrigonal planar and tetrahedral coordinations. The monovalent thallium\ncations have TlS₈ dodecahedral coordination and TlS₇ and TlS₆ coordination polyhedra of irregular shape.\nThe compounds <b>1</b>, <b>2</b>, and <b>3</b> are\nsemiconductors with the respective energy band gap values of 1.68,\n2.02, and 1.90 eV. Compared to compounds <b>1</b> and <b>2</b>, compound <b>3</b> has a higher efficiency value of\n22.9% for the photodegradation of aqueous solution of methylene blue.\nBand structures and projected density of states of all three compounds\nwere computed using density functional theory, and these results are\nin good agreement with experiments.