Calorimetric and spectrophotometric studies of chloro complexes of nickel(II) and zinc(II) ions in N,N-dimethylformamide.
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概要
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Complexation of Ni(II) and Zn(II) with Cl<SUP>−</SUP> ions has been studied by calorimetry and spectrophotometry in <I>N</I>,<I>N</I>-dimethylformamide (DMF) containing 0.4 mol dm<SUP>−3</SUP> (C<SUB>2</SUB>H<SUB>5</SUB>)<SUB>4</SUB>NClO<SUB>4</SUB> as a constant ionic medium at 25 °C. Calorimetric titration curves obtained in each system were well-explained in terms of formation of [MCl<I><SUB>n</SUB></I>]<SUP>(2−<I>n</I>)+</SUP> (<I>n</I>=1–4 and M<SUP>2+</SUP>=Ni<SUP>2+</SUP> or Zn<SUP>2+</SUP>), and their formation constants, enthalpies and entropies were determined. Formation of the nickel(II) chloro complexes in DMF was also supported by spectrophotometry. In the nickel(II) chloride system, the stepwise enthalpy Δ<I>H</I><SUB>3</SUB>° and entropy Δ<I>S</I><SUB>3</SUB>° values are remarkably large and positive as compared with the Δ<I>H<SUB>n</SUB></I>° and Δ<I>S<SUB>n</SUB></I>° (<I>n</I>=1, 2, and 4) values. Individual electronic spectra of nickel(II) ion, [NiCl]<SUP>+</SUP> and [NiCl<SUB>2</SUB>] are significantly different in both intensities and peak positions from those of [NiCl<SUB>3</SUB>]<SUP>−</SUP> and [NiCl<SUB>4</SUB>]<SUP>2−</SUP> over the range 300–850 nm. These thermodynamic and spectrophotometric results were explained in terms of formation of the octahedral [NiCl]<SUP>+</SUP> complex as well as [Ni(dmf)<SUB>6</SUB>]<SUP>2+</SUP> and of formation of the tetrahedral [NiCl<SUB>3</SUB>]<SUP>−</SUP> and [NiCl<SUB>4</SUB>]<SUP>2−</SUP> complexes in DMF. On the other hand, in the zinc(II) chloride system, the Δ<I>S<SUB>n</SUB></I>° (<I>n</I>=1 and 2) values are large and positive, but the Δ<I>S<SUB>n</SUB></I>° (<I>n</I>=3 and 4) values are significantly small. The corresponding Δ<I>H<SUB>n</SUB></I>° (<I>n</I>=1 and 2) values are positive but the Δ<I>H<SUB>n</SUB></I>° (<I>n</I>=3 and 4) values are significantly negative. It is thus postulated that the [ZnCl<I><SUB>n</SUB></I>]<SUP>(2−<I>n</I>)+</SUP> (<I>n</I>=2 and 3) complexes have the tetrahedral coordination structure as well as the [ZnCl<SUB>4</SUB>]<SUP>2−</SUP> complex in DMF.
著者
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Ohtaki Hitoshi
Department Of Chemistry Faculty Of Science And Engineering Ritsumeikan University
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Ishiguro Shin-ichi
Coordination Chemistry Laboratories, Institute for Molecular Science
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Ozutsumi Kazuhiko
Coordination Chemistry Laboratories, Institute for Molecular Science
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