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pH‐Dependent Imidazolato Bridge Formation in Dicopper Complexes: Magnetic, Electrochemical, and Catalytic Repercussions
Author(s) -
MontePérez Inés,
Sosa Ana M.,
Bernès Sylvain,
AliagaAlcalde Núria,
UgaldeSaldívar Víctor M.,
Gasque Laura
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201200167
Subject(s) - chemistry , potentiometric titration , protonation , electron paramagnetic resonance , electrochemistry , ligand (biochemistry) , crystallography , catalysis , inductive coupling , inorganic chemistry , stereochemistry , nuclear magnetic resonance , electrode , ion , organic chemistry , biochemistry , physics , receptor , engineering , electrical engineering
Abstract The dicopper complexes of two dinucleating ligands derived from 2‐methylimidazole and 2 equiv. of an L ‐amino acid are presented (H 3 bphenim derived from L ‐phenylalanine and H 3 bleuim derived from L ‐leucine). For each ligand L, three different protonation states for the complex, Cu 2 HL 2+ , Cu 2 L + , and Cu 2 LOH, have been characterized in solution by potentiometric, spectrophotometric, and electrochemical techniques. X‐ray diffraction studies enabled the characterization, in the solid state, of the [Cu 2 (bphenim)] + and [Cu 2 Hbleuim] 2+ cations. Magnetic measurements showed that while only a very slight coupling could be detected in [Cu 2 Hbleuim] 2+ , [Cu 2 (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 [Cu 2 L] + is low, however, an important increase in activity is observed above pH = 8.5 where the concentration of the species [Cu 2 LOH] starts to become significant.