Macrocyclic Ligand Design. Structure—Function Relationships Underlying the Interaction of Substituted Derivatives of Oxygen-Nitrogen Macrocycles with Selected Transition and Post Transition Metal Ions

Abstract

The effect of methyl substitution on 15- and 17-membered macrocycles (incorporating N₂O₂- and N₃O₂-donors, respectively) on their interaction with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II) has been investigated. The results are compared with those obtained for the corresponding complexes of the unsubstituted (parent) rings. Binding constants for the formation of the metal complexes have been determined potentiometrically in 95% methanol (I = 0·1; Et₄NClO₄). An X-ray crystallographic study of [NiL(H₂O)] (ClO₄)₂ (where L is the dimethyl derivative of a 17-membered, N₃O₂-donor macrocycle) confirms that the nickel ion is six-coordinate, with the complex cation exhibiting a distorted octahedral geometry defined by all five donor atoms of the O₂N₃-macrocycle (in its meso form) and the oxygen of the water molecule. In this structure the macrocyclic backbone incorporating the N₃-donor fragment is arranged facially. Molecular mechanics modelling of this complex predicts that the observed facial configuration will be favoured over an alternative facial arrangement or a meridional one.