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.