Synthesis\nand Characterization of Low-Dimensional\nQuaternary Sulfides of Thallium, Tl<sub>2</sub>Cu<sub>2</sub>GeS<sub>4</sub>, Tl<sub>2</sub>Ag<sub>2</sub>GeS<sub>4</sub>, and

Three new low-dimensional quaternary\nsulfides, namely, Tl<sub>2</sub>Cu<sub>2</sub>GeS<sub>4</sub>(<b>1</b>), Tl<sub>2</sub>Ag<sub>2</sub>GeS<sub>4</sub>(<b>2</b>), and Tl<sub>2</sub>Ag<sub>2</sub>SnS<sub>4</sub>(<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<sup>+</sup>, Ge<sup>4+</sup>, and Sn<sup>4+</sup> ions have tetrahedral coordination and Ag<sup>+</sup> ion has linear,\ntrigonal planar and tetrahedral coordinations. The monovalent thallium\ncations have TlS<sub>8</sub> dodecahedral coordination and TlS<sub>7</sub> and TlS<sub>6</sub> 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.