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The thermodynamic dissociation constants of [Co(en)3]Cl3 and [Co(NH3)6]Cl3 in aqueous solutions at 25℃ and at the pressure from 1 bar to 2000 bars were measured by conductometric method. The dissociation constants were increased with pressure elevation because of volume decreasing by the formation of charged ions during dissociation reaction. That is, the pKT values of [Co(en)3]Cl3 were 2.16 for I bar, 2.08 for 500 bars, 2,08 for 1000 bars, 2.05 for 1500 bars and 2.03 for 2000 bars, respectively and those of [Co(NH3)6]Cl3 were 2.02 for 1 bar 1.96 for 500 bars, 1.90 for 1000 bars, 1. 88 for 1500 bars and 1. 87 for 2000 bars, respectively. Comparing and analyzing the values of Stokes' radii and KT, the formation of ion pair compound was affected by not only the electrostatic interaction, but also the Interal Conjugate Base(ICB), which was increased by the elevation of the pressure.
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