Abstract

Information has been obtained on how ring size, steric factors and the mode of coordination of tetraaza macrocycles will affect the field strength of the macrocycle and how these parameters affect the equilibrium in water or in a water-ethanol mixture between the five-coordinate nickel(II) complexes containing the macrocycle, R 4[12]aneN 4, where R is CH 3 and CH 2C 6H 5, and the planar [Ni(R 4[12]aneN 4)] 2+ species. On the basis of spectral data it is concluded that steric factors influence the ligand field strength more than the size of the macrocycle for macrocycles that do not bond in a planar manner to the nickel(II). However, for square planar complexes both the size of the macrocyclic ligand and the steric factors play significant roles in the ligand field strength. The equilibrium between the high spin, five-coordinate, [Ni(R 4[12]aneN 4)H 2O] 2+ complexes and the planar or nearly planar [Ni(R 4[12]aneN 4)] 2+ is dominated by the solvation properties of these complexes. The more carbon atoms on the R group, the larger the K, ΔS and ΔH values for the above equilibrium. In the presence of excess chloride ions, [Ni(Me 4[12]aneN 4)H 2O] 2+ is converted to [Ni(Me 4[12]aneN 4)Cl] +. By increasing the percentage of ethanol in an ethanol-water mixture of [Ni(Me 4[12]aneN 4)Cl 2, the equilibrium shifts to produce more [Ni(Me 4[12]aneN 4)Cl] + and less [Ni(Me 4[12]aneN 4)H 2O] 2+. The tetrabenzyl[12]aneN 4 nickel(II) complex is more difficult to oxidize and easier to reduce than the tetramethyl[12]aneN 4 nickel(II) complexes and the chloride complexes are easier to oxidize than the nitrate complexes in CH 3CN. In water and in ethanol-water mixtures the [Ni(Me 4[12]aneN 4)H 2O] 2+/[Ni(Me 4[12]aneN 4)H 2O] + couple is quasi-reversible but in CH 3CN only the cathodic reaction is observed.

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