Thermochromisms of Some β-Diketone Chelate Copmlexes of Copper(II) in Pure Pyridine

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Two types of thermochromisms have been found for several β-diketone chelate complexes of copper(II) in pure pyridine or γ-picoline. One is observed for such complexes as bis(acetylacetonato)copper(II). In this case, the visible absorption spectra at various temperatures have well-defined isosbestic points; there are two different complex species, L and H, at equilibrium in the solvent, where L and H represent the low-temperature and high-temperature species respectively; they are different in the interaction between the complex and pyridine or γ-picoline molecules. The other is observed for such complexes as bis(salicylaldehydato)copper(II), where the spectral intensity increases remarkably with a rise in the temperature. The equilibrium for bis(acetylacetonato)copper(II) was studied over the temperature range of 0–60°C, and the results were used to derive the approximate thermodynamic parameters, <I>ΔH</I>=4.0±1.0 kcal/mol and <I>ΔS</I>=13±4 e.u., for the L→H change. The most probable structures for L and H were suggested from a spectrophotometrical point of view.
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