Synthesis and characterization of two new photochromic inorganic-organic hybrid materials based on Keggin-type polyoxometalates

Two new photochromic inorganic-organic hybrid materials formed from Keggin-type polyoxometalates (POMs) and metronidazole (C6H9N3O3, MNZ), formulated as H3PMo12O40·3MNZ·3H2O (1) and H3PW12O40·3MNZ·3H2O (2), were synthesized and characterized by elemental analysis, IR spectra, electronic spectra, electron spin resonance (ESR) spectra and thermogravi-metry-differential thermal analysis (TG-DTA). Reflectance spectra show the presence of weak intermolecular charge transfer between the organic and inorganic moieties in the solid state. The photochromic properties were studied by solid diffuse reflectance spectra and ESR spectra, and the photochromic reactions were found to exhibit first-order kinetics. TG-DTA showed that two hybrid materials have similar thermal behavior.