The effects of various salts and HClO
4 on the configuration change of cobalt(II)-halide complexes in CHCl
3/CTAC or CTAB/H
2O reverse micelle systems were examined at 25°C by means of spectrophotometry, where CTAC and CTAB represent cetyltrimethylammonium chloride and bromide, respectively. The formation of the [CoCl
4]
2- or [CoBr
4]
2- species of the tetrahedral configuration from [Co(H
2O)
6]
2+ of the octahedral configuration in the reverse micelles was greatly promoted not only by a decrease in the
W value (
W = [H
2O]/[surfactant]), but also, at a constant
W value (
e.g.,
W = 2.0), by the addition of relatively low concentrations of salts or the acid (
e.g., 4.0 mol dm
-3 in the aqueous phase or 4.0 × 10
-2 mol dm
-3 in the whole reverse micelle system). The effects of perchlorate salts increased as Na
+ ≤ Li
+ ∼ H
+ < Sr
2+ < Ca
2+ < Mg
2+. Non-metallic salts, various tetraalkylammonium (R
4N
+) salts at lower concentrations, gave minor effects. The enhanced effects of metal salts on the configuration change of the cobalt(II)-halide complexes were interpreted by a further distortion of the hydrogen-bonded structure of the water in a “water pool” in the presence of salts of even relatively low concentrations. A conformation change with increasing temperature was also attributed to a further distortion of the water structure. An almost completed formation of [CoBr
4]
2- as well as [CoCl
4]
2- was attained in the reverse micelles at a low W value of 0.69 containing LiClO
4 or HClO
4. A partial transfer of the [CoX
4]
2- species from a “water pool” into the CHCl
3 phase by the addition of the metal salts may be suspected. An examination of cobalt(II)-bromide complexes in dichloromethane/CTAB/H
2O at
W = 1.3 - 5.55 justified all the arguments concerning the chloroform systems. The Raman spectra of D
2O containing concentrated LiBr and LiClO
4 have supplied conclusive evidence that the hydrogen-bonded structure of the bulk water is completely distorted by extremely concentrated salts.
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