Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 112, Issue 41, Pages 10280-10286Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp805210v
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Funding
- Hungarian Scientific Research Fund OTKA [K-72781]
- Slovak Fund VEGA [1/0353/08]
- Hungarian-Slovak Intergovernmental ST Cooperation [TeT SK-25/2006]
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The copper(II)-3-pyridylmethanol (L) system was investigated in aqueous solution by two-dimensional ESR evaluation at 298 K, and computer simulation of the individual anisotropic spectra at 77 K. The data revealed that the paramagnetic copper(II) complexes [CuL](2+), [CuL2](2+), [CuL3](2+), and [CuL4](2+) are formed up to pH approximate to 7 at a moderate or high excess of ligand. As compared with chelating ligands, two differences were observed for the complexation of 3-pyridylmethanol with copper(II): (1) In contrast with the well-resolved spectra in frozen solution, considerable line-broadening and distortion of the spectral shapes were seen at 298 K, which was interpreted in terms of isomeric equilibria and the medium-rate interconversion of various complexes on the ESR time-scale. (2) At low temperature, there were dramatic changes in the concentration distribution, the minor complexes with higher numbers of coordinating ligands ([CuL3](2+) and in particular [CuL4](2+)) becoming strongly favored. This phenomenon is explained by the significant differences in the formation enthalpy values of various species, shifting the equilibria according to the van't Hoff equation, and a significant undercooling in the course of fast freezing of the solution, which enhances the changes of the concentration distribution.
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