Molecular mechanics studies of a series of dicopper complexes of a 20-membered macrocycle containing differing types of bridges between the metal centres

Abstract

The molecular mechanics method has been used to investigate a series of metal complexes of the macrocycle L¹{23,24-dioxa-3,7,14,18-tetra-azatricyclo[18.2.1.1^9,12]tetracosa-1(22),2,7,9,11,1,18,20-octaene}, which are model compounds for Type 3 dicopper proteins. The macrocycle hole-size profile has been calculated for L¹ and shows that with one metal atom in a central position, the minimum-energy conformation of the macrocycle has metal–donor atom distances of 2.75 Å. Force-field calculations have also been carried out on several dicopper complexes of the 20-membered macrocycle L¹ in which the metal co-ordination spheres show a variety of co-ordination numbers and geometries and the metal atoms are bridged by zero, one, two, or three atoms. These calculations indicate that many of the properties of these complexes of L¹ can be explained by the steric effect of imposing a particular metal co-ordination geometry within the macrocycle.