Thermal cis-to-trans isomerization of (CoX2en2)X (X=Cl,Br).
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概要
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By measuring calorimetrically the heats of reaction of solid <I>cis</I>- and <I>trans</I>-[CoX<SUB>2</SUB>en<SUB>2</SUB>]X (X=Cl, Br) with alkaline sodium sulfide solution, the heats of isomerization were obtained as −11.4 kJ mol<SUP>−1</SUP> for <I>cis</I>-[CoCl<SUB>2</SUB>en<SUB>2</SUB>]Cl(s)=<I>trans</I>-[CoCl<SUB>2</SUB>en<SUB>2</SUB>]Cl(s) and −6.4 kJ mol<SUP>−1</SUP> for <I>cis</I>-[CoBr<SUB>2</SUB>en<SUB>2</SUB>]Br(s)=<I>trans</I>-[CoBr<SUB>2</SUB>en<SUB>2</SUB>]Br(s). Assuming the entropy changes from cis- to trans-form, Δ<I>S</I>, to be −0.0116 kJ mol<SUP>−1</SUP> K<SUP>−1</SUP> at 25 °C statistically, the free energy changes were calculated as Δ<I>G</I><SUP>°</SUP>=8.0 kj mol<SUP>−1</SUP> and −3.0 kJ mol<SUP>−1</SUP> for the isomerization of <I>cis</I>-[CoCl<SUB>2</SUB>en<SUB>2</SUB>]Cl and <I>cis</I>-[CoBr<SUB>2</SUB>en<SUB>2</SUB>]Br respectively. From these thermodynamic data, cis-to-trans isomerization was expected to occur in [CoX<SUB>2</SUB>en<SUB>2</SUB>]X (X=Cl or Br), which was verified experimentally by thin-layer chromatography and the spectral measurement.
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