Polynuclear Glycinehydroximate Cu(II)–Gd(III) Metallamacrocyclic Complexes: Halochromic Properties

It was shown by electronic spectroscopy that the visible absorption spectrum of the polynuclear Cu(II)–Gd(III) metallamacrocyclic complex is pH-sensitive. The intensity of the absorption peak at 577 nm decreases 5-fold as the pH decreases from 6.8 to 3.3 and restores the initial level as the pH increases up to 12.4. On the basis of DFT calculations and analysis of topological electron density characteristics, the spectral changes were attributed to protonation of the glycinehydroximate ligand.