Structure and Characterization of a Zero-Dimensional Alkali Tin Dihalides Compound Cs₃Sn₃F₂Cl₇ with the [Sn₂F₂Cl₄]^2– Clusters

A new perovskite stoichiometric alkali tin dihalides compound, Cs3Sn3­F2Cl7, is synthesized by a hydrothermal method. This compound belongs to the monoclinic space group of P21/c with cell parameters of a = 9.5645(4) Å, b = 14.2057(7) Å, c = 13.5828(6) Å, and β = 93.2450(10)°. Unlike the common perovskites in which octahedra are interconnected to be a three-dimensional network, Cs3Sn3­F2Cl7 possesses a zero-dimensional structure consisting of Cs+ cations, isolated [SnCl3]− trigonal pyramids, and dimer structural units [Sn2F2­Cl4]2–; the latter microscopic unit is found for the first time. The thermal stability and UV–vis–NIR diffuse reflectance spectroscopy in Cs3Sn3­F2Cl7 are measured, and the electronic structure is calculated. Interestingly, the 5s2 lone-pair electrons on Sn2+ cations are stereochemically active, which results in a pretty good photocatalytic activity of the title compound.