Magnetic Resonance Studies of Ion Solvation. The Hydration of the Cobaltous Ion

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Abstract
Evidence is presented that cobaltous ion in aqueous solution retains a coordination number of 6 in a temperature range of −10° to +183°C. The temperature dependence of the oxygen‐17 NMRlinewidths and chemical shifts of the noncoordinated water were measured. The parameters of water exchange between the first hydration sphere and the bulk were determined and found to be: (τ m )27°C=4.2×10−7 sec, ΔH ‡=10.4 kcal/mole, ΔS ‡=5.3 e.u. The oxygen‐17 hyperfine coupling constant with the unpaired electrons of the cobaltous ion was found to be A/h=—(1.70±0.02)×107 Hz. The relaxation time of the unpaired electrons of the cobaltous ion was calculated and found to be (T 1e )183°C=4.6×10−13 sec, assuming T 1e =T 2e . Earlier observations relevant to those reported here are discussed and, in some cases, reinterpreted.