3Pb₈O₇I₂·2CsI: the salt-inclusion strategy enriches the structural chemistry in lead oxyhalides

The design and synthesis of new mid-infrared functional crystals with novel structures and excellent properties is a hot topic in the materials science research field. Different from the traditional mid-far infrared crystal systems, such as chalcogenides and phosphides, a recently developed heavy metal oxyhalide, with a wide bandgap and transmittance range, is a very promising mid-infrared crystal material research system. Herein, the first case of a salt-inclusion compound in lead oxyhalides, Cs₂Pb₂₄O₂₁I₈ (3Pb₈O₇I₂·2CsI), has been synthesized by a high-temperature solution method. Cs₂Pb₂₄O₂₁I₈ features a "rod-like chain" structure constructed from [Pb₈O₇]²⁺composed of [OPb₄] tetrahedra, [OPb₃] pyramids, and 1∞[CsI₄] chains inserted in the tunnel. The results show that the salt-inclusion strategy significantly enriches the structural diversity of lead oxyhalides and provides a new research idea for exploring new infrared functional materials.