UV Raman spectroscopic study on the crystallization of microporous boron-aluminum crystalline BAC(10)

Boron aluminum oxo chloride [BAC(10)], a microporous material, and its crys tallization were investigated by X-ray diffraction (XRD), adsorption isothe rms of probing molecules, infrared (IR), magic-angle spinning nuclear magne tic resonance (MAS NMR), visible Raman and ultraviolet (UV) Raman spectrosc opy. XRD and adsorption isotherms indicate that BAC(10) consists of novel m icroporous crystals, and IR and NMR results confirmed that the primary buil ding units are triangular BO3, tetrahedral BO4 and octahedral AlO6. No Rama n signal in the visible Raman spectrum of BAC(10) was detected owing to the weakness of Raman scattering and strong fluorescence interference. However , strong Raman bands of this material were observed in the UV Raman spectra owing to the avoidance of fluorescence. The UV Raman spectra show that, du ring the crystallization process, the number of BO3 groups (bands at 300-70 0 cm(-1)) decrease with increasing number of BO4 groups (bands at 900-1000 cm(-1)) in the solid phase. These results suggest that in the crystallizati on of BAC(10), the polyborate anions are quickly depolymerized to monoborat e species including BO3 and BO4 groups, which are then gradually crystalliz ed to the framework of microporous BAC(10).