- Temperature Dependence of the Ion Association between Hexaamminecobalt(III) Ion and Monovalent Anions
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Conductivity measurements at temperatures between 0 and 50 deg C were made for aqueous solutions of the chloride, bromide, iodide, nitrate, and perchlorate of hexaamminecobalt(III) complex.The ion association constants (KA) obtained had minimum values at temperatures (tmin) characteristic of the anions.The tmin increased in the order Cl----- and correlated with standard entropy and enthalpy of ion association.The order in the magnitude of KA among the salts was variously dependent on temperature, e.g., I--=Br-=Cl-- at 0 deg C and I-=ClO4---=Cl- at 25 deg C, but, with increasing temperature, it seemed to approach the electrostatic prediction: ClO4-----.The presence of tmin for the halides was explained to be due to the weak hydrations of the anions related to their structure-breaking properties.The remarkable increases of the KA values with decreasing temperatures for the nitrate and the perchlorate and the relatively small entropy changes compared with those for the halides were ascribed to specific short-range interactions between ammine ligands of the complex and oxygen atoms of the anions in the contact ion pairs.
- Yokoyama, Haruhiko,Kon, Hiroyuki
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p. 8956 - 8963
(2007/10/02)
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