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

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 NMR linewidths 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: (τm)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 (T1e)183°C=4.6×10−13 sec, assuming T1e=T2e. Earlier observations relevant to those reported here are discussed and, in some cases, reinterpreted.