Effect of the hydration shell on the red shift of the optical absorption bands of diketonate complexes†

This article considers the problem of the influence of the solvation shell on the ultraviolet-visible absorption spectra of π-conjugated complexes of different metal ions with dicarbonyl ligands. Based on a wide spectral dataset that has been previously collected, we report the direct correlation between the wavelength of maximum absorbance of the complexes and the coordination properties of the metal ions. Chalcogen-bearing diketones (2-furoyl-trifluoroacetone, 2-thenoyl-trifluoroacetone, 2-selenophen-trifluoroacetone, and 2-tellurophen-trifluoroacetone) demonstrate a significant redshift (17–29 nm) of the absorption bands for complexes of metal ions with various solvation shells. The spectral shift increases with an increasing number of water molecules in the hydration sphere. Detailed measurements show the red shift even for different lanthanide complexes. The discovered relationships allow us to compare at a qualitative level the structure of the solvation shell of π-conjugated dicarbonyl complexes.