فهرست نشریات علمی دسترسی آزاد ایران

The decomposition pathway of the mixed-chelate copper(II) complex [Cu(L)(acac)(ClO4)]ClO4 (where L = 2-[(2-diisopropylamino-ethylamino)-methyl]-pyridine, acac = acetylacetonate) in neat pyridine was investigated using time-resolved UV-vis spectroscopy. While similar mixed-chelate copper complexes are known to exhibit solvatochromism through reversible solvent interactions, this study aims to quantitatively characterize an unexpected multi-step decomposition process observed specifically in pyridine. Upon dissolution in pyridine, the complex exhibited a slow, time-dependent color change from green to yellow (~12 h), then to brown, with eventual precipitation of blue crystals after 26 h. The visible absorption spectra recorded at 30-min intervals revealed two well-separated isosbestic points at 591 nm (first 12 h) and 562 nm (12-26 h) a diagnostic feature characteristic of a consecutive two-step reaction mechanism (A → B → C). The data are fitted to a pseudo-first-order consecutive model, yielding approximate rate constants of k1 = 6.9 × 10-5 s-1 for the first step and k2 = 5.9 × 10-5 s-1 for the second step. Ligand addition experiments confirmed that the first step involves dissociation of the diamine ligand (common-ion effect), while the second step corresponds to full substitution by pyridine. The final blue crystals were identified as [Cu(Py)6](ClO4)2 by microanalysis and IR spectroscopy. This study provides the first quantitative kinetic description of the decomposition of a solvatochromic copper(II) complex in a strongly coordinating solvent, offering insights for evaluating the long-term stability of such chromotropic materials in practical sensing applications.