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The equilibria of chemical reaction between α-Ni(rac-[14]-decane)2+ and polar solvents(L; ANT, MFA, DMSO, DMF, and DMA) have been investigated by the spectrophotometric method at 25℃. (The equilibrium constants(K1) of) the first step in ANT, MFA, DMSO, DMF, and DMA were 31.0, 27.5, 21.3 15.9, and 6.4, respectively. The smallness of equilibrium constants (K2) of the second step compared with K1, was observed. α-Ni(rac-[14]-dacane)2+ + L ↔ [α-Ni(rac-[14]-decane)·L]2+ : K1[α-Ni(rac-[14]-decane)·L)2+ + L ↔ [α-Ni(rac-[14]-decane)·L2)2+ : K2. The relationship between d-d absorption energy and half-wave potential of complex ions at ACT was considered. Macrocyclic ligands increasing d-d transition energy caused half-wave potentials of Ni(Ⅱ)-macrocycle to be shifted more positively. The half-wave potentials for Ni(rac-1[14]7-diene)2+, Ni(meso-1[14]7-diene)2+, Ni(1[14]4-diene)2+, α-Ni(rac-[14]-decane)2+, β-Ni(rac-[14]-decane)2+, and Ni(meso-[14]-decane)2+ reductions were -1.419, -1.431, -1.450, -1.473, and -1.480 (V vs. SCE), respectively. The d-d transition energies (νmax, cm-1) of the Ni(meso-[14]-decane)2+ isomer were discussed with the dielectric constant (ε/εo) of the various solvents, νmax(cm-1) increased with increasing ε/εo.
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