Molecular mechanics studies of the conformation of the macrocycle β-2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) in the free state and in a series of nickel complexes. Crystal and molecular structure of L1

Abstract

The crystal structure of the free macrocycle β-2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1 (17),13,15-triene (L¹) is reported. Crystals are monoclinic, space group P2₁/a, with a= 8.433(9), b= 23.697(12), c= 8.653(10)Å, β= 113.9(1)°, and Z= 4. A total of 810 independent reflections above background have been refined to R 0.077. The free macrocycle has a folded shape very different from the conformation that is found in metal complexes. Empirical force-field methods have been used to calculate the steric energies of the various conformations of this ligand in the free state and in a series of nickel complexes, viz. [NiL¹]²⁺, [NiL¹(NO₂)(ONO)], and [NiL¹(en)]²⁺(en = ethylenediamine), and also to provide a hole-size profile for the macrocycle.