Abstract
The oxidation of [Co
II
(nta)(ox)(H
2
O)
2
]
3−
and [Co
II
(nta)(ph)(H
2
O)
2
]
3−
(nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [Co
II
(nta)(ox)(H
2
O)
2
]
3−
by periodate, obeys the following equation: d[Co
III
]/dt = [Co
II
(nta)(ox)(H
2
O)
2
3−
][H
5
IO
6
] {
k
4
K
5
+ (
k
5
K
6
K
2
/[H
+
]} while the reaction of [Co
II
(nta)(ph)(H
2
O)
2
]
3−
with periodate in aqueous acidic medium obeys the following rate law: d[Co
III
]/dt =
k
6
K
8
[Co
II
]
T
[I
VII
]
T
/{1 + [H
+
]/
K
7
+
K
8
[I
VII
]
T
}. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes by periodate is proposed and supported by an excellent isokinetic relationship between Δ
H
* and Δ
S
* values for these reactions.