NICKEL(II) COMPLEXES BONDED TO 12-MEMBERED MACROCYCLIC LIGANDS

Information has been obtained on how ring size, steric factors and the mode of coordination of tetraaza macrocycles will affect the field st rength of the macrocycle and how these parameters affect the equilibri um 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 CH3 and CH2C6H5, and the planar [Ni(R(4)[12]aneN(4))](2+) specie s. On the basis of spectral data it is concluded that steric factors i nfluence the ligand field strength more than the size of the macrocycl e for macrocycles that do not bond in a planar manner to the nickel(II ), However, for square planar complexes both the size of the macrocycl ic 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))H2O](2+) complexes and the planar or nearly plan ar [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 t he K, Delta S and Delta H values for the above equilibrium. In the pre sence of excess chloride ions, [Ni(Me(4)[R(4)[12]aneN(4))H2O](2+) is c onverted 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, t he equilibrium shifts to produce more [Ni(Me(4)[12]aneN(4))Cl](+) and less [Ni(Me(4)[12]aneN(4))H2O](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 complexe s are easier to oxidize than the nitrate complexes in CH,CN. In water and in ethanol-water mixtures the 4)[12]aneN(4))H2O](2+)[Ni(Me(4)[12]a neN(4))H2O](+) couple is quasireversible but in CH,CN only the cathodi c reaction is observed.