Pb₆Ba₃Si₂S₈I₁₀: a new thiohalide with a quasi-two-dimensional structure and wide band gap

Pb-based chalcogenides display abundant structural diversity and distinguished properties. Based on a mixed anion and dimensional reduction combined strategy, a wide band gap Pb-based thiohalide, Pb₆Ba₃Si₂S₈I₁₀, has been rationally designed and synthesized experimentally by the flux method. The compound crystallizes in the R3̄c space group with cell parameters a = 9.7925(2) Å, b = 9.7925(2) Å, and c = 70.628(3) Å and is composed of [SiS₄] tetrahedra and unprecedented [PbI₅S₂] polyhedral units, resulting in a unique quasi-two-dimensional structure, which enriches the chemical and structural diversity of Pb-based thiohalides. The experimental band gap of Pb₆Ba₃Si₂S₈I₁₀ was determined to be 2.80 eV. Based on statistical analyses and to the best of our knowledge, it is the largest experimental optical band gap among the known Pb-based thiohalides. The results demonstrate the feasibility of using highly electropositive Ba atoms to regulate the dimensions of the structural framework of thiohalides and give new insights into the structure and property modifications of thiohalides by the mixed anion and dimensional reduction combined strategy.