Metal-ion complexation of imidazo[1,2-a]pyrazin-3(7H)-ones: continuous changes in absorption spectra of complexes depending on the Lewis acidity of the metal ion

The spectroscopic properties of metal-ion complexes of several imidazopyrazinone derivatives with Li+, Mg2+, Ca2+, Ba2+, Sc3+, and La3+ ions were studied. The spectral characteristics and the formation constants of the complexes changed continuously depending on the Lewis acidity of the metal ion, suggesting that the imidazopyrazinones can find application as indicators of Lewis acidity. In the case of bis-imidazopyrazinone derivatives, the complexation abilities were enhanced by chelate effects.