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We have systematically studied the catalytic activity of a series of substituted bisphenanthroline Cu complexes adsorbed on glassy carbon electrodes for the oxygen reduction reaction (ORR) in aqueous media. The aim of this work is to test reactivity descriptors for ORR previously proposed for MN4 complexes. As the active site is the Cu(I) center, the foot of the wave for O 2 reduction on electrodes modified with Cu bisphenanthrolines appears at potentials very close to the [Cu(II)phen 2 ] ad ++ + e − ⇆ [Cu(I)phen 2 ] ad + redox process. Generally, the catalytic activity as (log i)E versus the E Cu(II)/(I) °redox potentials follows a linear correlation with a slope close to +0.120 V/decade, where the activity increases as the E Cu(II)/(I) °becomes more positive. This indicates that electron-withdrawing substituents on the ligand favor the reaction by shifting the E Cu(II)/(I) °to more positive values, making the Cu center more noble. This shift in the E Cu(II)/(I) °is essentially an electronic effect. However, another way to stabilize the Cu(I) state is by placing groups on the ligand that hinder the [Cu(II) square-planar ] ad ++ /[Cu(I) tetrahedral ] ad+ change. We have found that this steric effect seems to be more prominent than the electronic effects caused by electron-withdrawing groups and the increase in the catalytic activity for ORR is more pronounced.

Artículo de publicación ISIThe first borate-vacant deca-vanadoborate of formula (NH3CH2CH2CH2NH3)(5) [ (NH3CH2CH2CH2NH3)V10B24O66H8]center dot 13.23H(2)O with an occluded 1;3-propanediammonium cation; using molten methylboronic acid flux reaction is reported. This cluster lacks four borate units with respect to all known deca-vanadoborates. It crystallizes in the orthorhombic P2(1)2(1)2 space group which is non-centrosymmetric, leading to the first non-centrosymmetric deca-vanadoborate reported In the literature. Even though the decavanadoborates formed by 28 borate units have an inner space large enough to host a molecule, no examples have been reported before. The electronic properties were studied using electronic spectroscopy, corroborating a fully reduced species, due to the lack Of intervalence charge transfer transitions in the 1000 to 1500 nm region. The magnetic behavior provided evidence that the studied cluster presents strong antiferromagnetism among the ten V-IV spin-carriers, with an S = 0 ground state. tiring a model considering three different exchange pathways, three different J values were obtained, all of them antiferromagnetic in nature.FONDECYT Project 112000