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Evaluation of Hydration Enthalpies of Monatomic Cations by Considering Both Long-Range and Short-Range Interactions
journal contribution
posted on 2003-08-29, 00:00 authored by Nobuyuki Ichieda, Megumi Kasuno, Khaleda Banu, Sorin Kihara, Hirohide NakamatsuThe standard hydration enthalpy, ΔH°hyd, of a monatomic cation was calculated as the sum of (1) the enthalpy
due to the long-range interaction between a hydrated ion and bulk water, ΔH°LR, (2) the enthalpy due to the
short-range interaction between the ion and water molecules in the first hydration shell, ΔH°SR, and (3) the
enthalpy due to the ligand field stabilization of an ion, ΔH°LF, which arises for a transition-metal ion. ΔH°LR
was estimated on the basis of the Born theory assuming the radius of the hydrated ion as the interatomic
distance between the ion and the oxygen atom of a water molecule in the first hydration shell, rM-O, determined
experimentally. ΔH°SR was evaluated on the basis of the donor−acceptor interaction between an ion and a
water molecule coordinating to the ion, which was evaluated by the molecular orbital calculation of a
monohydrated cluster of an ion combined with the Mulliken population analysis. ΔH°LF was calculated on
the basis of the crystal field theory. Hydration enthalpies of 48 monatomic cations thus calculated agreed
well with those observed experimentally.