pH-Dependent Imidazolato Bridge Formation in Dicopper Complexes: Magnetic, Electrochemical, and Catalytic Repercussions

• Published in: European journal of inorganic chemistry Vol. 2012; no. 29; pp. 4739 - 4749
• Main Authors: Monte-Pérez, Inés, Sosa, Ana M., Bernès, Sylvain, Aliaga-Alcalde, Núria, Ugalde-Saldívar, Víctor M., Gasque, Laura
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.10.2012; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Amino acids; Antiferromagnetism; Bridges (structures); Cations; Chemistry; Chemistry, Inorganic & Nuclear; Copper; Cyclic voltammetry; Enzymes; Formations; Joining; Ligands; N ligands; Physical Sciences; Science & Technology; Spectroscopy; Antiferromagnetism; CATECHOL OXIDASE ACTIVITY; Enzymes; ELECTRON-SPIN-RESONANCE; MOLECULAR-STRUCTURE; ACTIVE-SITE; CRYSTAL-STRUCTURE; MACROCYCLIC LIGAND; Amino acids; Cyclic voltammetry; COPPER(II) COMPLEXES; N ligands; PYRAZOLE-IMIDAZOLE; Copper; SUPEROXIDE-DISMUTASE; BINUCLEAR
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201200167

The dicopper complexes of two dinucleating ligands derived from 2‐methylimidazole and 2 equiv. of an L‐amino acid are presented (H3bphenim derived from L‐phenylalanine and H3bleuim derived from L‐leucine). For each ligand L, three different protonation states for the complex, Cu2HL2+, Cu2L+, and Cu2LOH, have been characterized in solution by potentiometric, spectrophotometric, and electrochemical techniques. X‐ray diffraction studies enabled the characterization, in the solid state, of the [Cu2(bphenim)]+ and [Cu2Hbleuim]2+ cations. Magnetic measurements showed that while only a very slight coupling could be detected in [Cu2Hbleuim]2+, [Cu2(bphenim)]+ is strongly antiferromagnetically coupled. The extent of this coupling can also be appreciated from room temperature, pH‐dependent EPR spectroscopic studies, where the signal is quenched at pH values where the imidazolato‐bridged species is predominant. These observations are consistent with the cyclic voltammetric studies. The catecholase activity of the complexes in the form [Cu2L]+ is low, however, an important increase in activity is observed above pH = 8.5 where the concentration of the species [Cu2LOH] starts to become significant. The dicopper complexes of two dinucleating ligands undergo a strong antiferromagnetic coupling upon formation of an imidazolato bridge. UV/Vis and EPR spectroscopy as well as electrochemical studies confirmed the potentiometric solution speciation.