Endodentate conformation

Interestingly, for these compounds simple halide ions constitute the counter anion in salt formation. The compactness of the ring, especially in the case of L3, does impose a severe steric constriction at the metal centre. In the case of uncomplexed L2 the preferred endodentate conformation identifies it as an (almost) ideal ligand for occupation of three metal coordination sites (fac-octahedral)16-20. For free L3 there are four chair conformers... 

The tetraprotonated form of (7), as the CuCl salt, shows the typical quadrangular conformation [3434] with a methylene group in each corner <89HCA1253). This conformation belongs to the diamond lattice type and is the most stable conformation of cyclotetradecane itself <76ACS(A)I55). Whereas in its metal complexes and as a diprotonated cation (7) is endodentate, in its tetraprotonated form it is exodentate, so that the charges are as far apart as possible. 

---