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

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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[18.2.1.19,12]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.