Cations derived by protonation of the ligand title compound (L¹) have been structurally characterized in their di- and tetra- protonated forms in the salts [H₂L¹][ClO₄]₂·4H₂O and [H₄L¹][ZnCl₄]₂·4H₂O. 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.
Zeitschrift fur Anorganische und Allgemeine Chemie Vol. 633, Issue 7, p. 1036-1039