EFFECT OF UNCOORDINATED TERTIARY NITROGEN-ATOMS IN HEXAAZA MACROCYCLIC NICKEL(II) COMPLEXES ON AXIAL BINDING OF ANIONS AND WATER IN ACIDIC SOLUTIONS

Axial coordination of anions or water to the square-planar nickel(II) complexes of the hexaaza macrocyclic ligands 1, 2, and 3, which contai n two extra uncoordinated tertiary nitrogens, have been investigated i n aqueous solutions containing HX (X=Cl-, Br-, NO3-, or CLO(4)(-)) and /or NaX. The nickel(II) complexes exist in the acidic solutions as equ ilibrium mixtures of the square-planar [Ni(L)](2+) (L=1, 2, and 3) and octahedral species [Ni(H(2)L)X(2)](2+) (H(2)L= diprotonated form of L ). Some octahedral complexes have been isolated and characterized. The solution behaviors of the complexes indicate that the formation of th e octahedral complexes are significantly promoted by the protonation o f the uncoordinated tertiary amines. The proportion of the octahedral complexes depends on the type of acid, and increases in the order of H Br<HNO3<HCl.