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Trinuclear Cu II Structural Isomers: Coordination, Magnetism, Electrochemistry and Catalytic Activity towards the Oxidation of Alkanes
Author(s) -
Sutradhar Manas,
Martins Luísa M. D. R. S.,
Guedes da Silva M. Fátima C.,
Mahmudov Kamran T.,
Liu CaiMing,
Pombeiro Armando J. L.
Publication year - 2015
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.201500440
Subject(s) - chemistry , cyclohexanol , catalysis , cyclohexane , electrochemistry , cyclohexanone , inorganic chemistry , copper , ligand (biochemistry) , crystallography , redox , polyoxometalate , medicinal chemistry , organic chemistry , biochemistry , receptor , electrode
The reaction of the Schiff base (3,5‐di‐ tert ‐butyl‐2‐hydroxybenzylidene)‐2‐hydroxybenzohydrazide (H 3 L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu 3 (L) 2 (MeOH) 4 ] ( 1 ), [Cu 3 (L) 2 (MeOH) 2 ] · 2MeOH ( 2 ) and [Cu 3 (L) 2 (MeOH) 4 ] ( 3 ), respectively, in which the ligand L exhibits dianionic (HL 2– , in 1 ) or trianionic (L 3– , in 2 and 3 ) pentadentate 1κ O , O′ , N :2κ N′ , O″ chelation modes. Complexes 1 – 3 were characterized by elemental analysis, IR spectroscopy, single‐crystal X‐ray crystallography, electrochemical methods and variable‐temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3 . Electrochemical experiments showed that in complexes 1 – 3 the Cu II ions can be reduced, in distinct steps, to Cu I and Cu 0 . All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31 % (TON = 1.55 × 10 3 ) after 6 h in the presence of pyrazinecarboxylic acid.