Equilibria of 3-pyridylmethanol with copper(II). A comparative electron spin resonance study by the decomposition of spectra in liquid and frozen solutions.
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+), [CuL 2] (2+), [CuL 3] (2+), and [CuL 4] (2+) are formed up to pH approximately 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 ([CuL 3] (2+) and in particular [CuL 4] (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.
Sípos
Rastislav
R
Department of Inorganic Chemistry, Slovak Technical University, Bratislava, Slovakia.
Szabó-Plánka
Terézia
T
Rockenbauer
Antal
A
Nagy
Nóra Veronika
NV
Sima
Jozef
J
Melník
Milan
M
Nagypál
István
I
D003198:Computer Simulation; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005615:Freezing; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008956:Models, Chemical; D015394:Molecular Structure; D009540:Nicotinyl Alcohol / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism
D008024:Ligands; D009942:Organometallic Compounds; D012996:Solutions; D012997:Solvents; D003300:Copper; D009540:Nicotinyl Alcohol