TDDFT studies on the electronic structures and chiroptical properties of mono-tin-substituted Wells-Dawson polyoxotungstates.

The UV/CD spectra of tin-bearing acetonyl-substituted Wells-Dawson polyoxotungstates α(1)- and α(2)-P(2)W(17)O(61){SnCH(2)CH(2)C(═O)} were systematically investigated using the time-dependent density functional theory (TDDFT) method. The electronic circular dichroism (ECD) spectra were produced over the range of 3.3-5.8 eV. The calculated ECD spectra of the α(1)-R isomer were generally in agreement with the experimental spectra. The CAM-B3LYP hybrid functional was found to predict the excitation energies of tin-containing polyoxotungstates well. The fact that the UV/ECD spectra of α(1)-isomers are different from those of α(2)-isomers demonstrates the effect of the tin substitution site on the chiroptical properties of the studied isomers. The origins of the ECD bands are mainly ascribed to charge-transfer (CT) transitions from oxygen atoms to W atoms, from organic fragments to W atoms, or from the combination of two CT transitions. The results suggest that the organic fragment and polyoxometalate (POM) cage are chiroptical chromophores.