CR3-5 - SINGLE-CRYSTAL UV-VIS SPECTROSCOPY OF AS-SYNTHESIZED AND MODIFIED CRYSTALS( IN ALPO4)

Large Cr:AlPO4-5 single crystals have been characterized by microcryst al absorption spectroscopy using a CCD array spectrometer and a fiber optics technique. For Cr3+ in AlPO4-5 crystals a polarization-dependen t absorption is observed. This indicates an anisotropic coordination o f Cr3+ distorted by the molecular sieve structure. Polarized absorptio n measurements on Cr: AlPO4-5 crystals loaded with p-nitrodimethyl ani line (pNDMA) and with p-nitroaniline (pNA) show a strong alignment of the guest molecules in the pore system parallel to the straight channe ls. The reduced ability to adsorb large molecules into the channels of the Cr:AlPO4-5 crystals supports the hypothesis of the nonframework i ncorporation of Cr3+. (C) Elsevier Science Inc. 1997.