Equilibria of 3-pyridylmethanol with copper(II). A comparative electron Spin resonance study by the decomposition of spectra in liquid and frozen solutions

Rastislav Šípoš, Terézia Szabó-Plánka, Antal Rockenbauer, Nóra Veronika Nagy, Jozef Šima, Milan Melník, István Nagypál

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Abstract

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 ≈ 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.

Original languageEnglish
Pages (from-to)10280-10286
Number of pages7
JournalJournal of Physical Chemistry A
Volume112
Issue number41
DOIs
Publication statusPublished - Oct 16 2008

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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