Molecular sieves are of increasing importance in catalysis, the oil industry, and biomedicine. Traditional molecular sieves are generally oxides that inevitably show some absorption in the mid- and far-IR range due to the vibrations of metal-oxygen bonds, which are unfavorable for the in situ observation of the reactions in molecular sieves through IR techniques. In this study, a new metal halide In[Ba3Cl3F6] has been synthesized. It exhibits a quite transparent window from 0.366 to 22 μm and good adsorption and desorption processes.