Isolation and Structural Characterization of Di- and Tetra-protonated Forms of the Macrocyclic Hexaamine trans-6,13-Dimethyl-1,4,8-11-tetraazacyclodecane-6,13-diamine

Cations derived by protonation of the ligand title compound (L-1) have been structurally characterized in their di- and tetra- protonated forms in the salts [H2L1][ClO4]2 center dot 2H(2)O and [H4L1][ZnCl4](2)center dot 4H(2)O. In both structures, one half of the formula unit comprises the asymmetric unit of the structure, the macrocycle being centrosymmetric, with the two macrocycles adopting similar conformations. In both salts, a pair of diagonally opposed macrocyclic secondary amine groups are protonated; in the [H4L1](4+) salt, the additional pair of protons are accommodated on the exocyclic pendant amine groups. The dispositions of the pendent amines differ between the two structures, being 'equatorial' with respect to the macrocyclic ring in the [H2L1](2+) salt, and 'axial' in the [H4L1](4+) salt. In other structurally characterized compounds containing [H4L1](4+) the equatorial disposition was found in the ferricyanide adduct, while in the tetraperchlorate salt the axial disposition was identified. The differences in disposition of the exocyclic groups are ascribed to the extensive H-bonding in the lattices.