Hydrogen and Copper Ion-Induced Molecular Reorganizations in Scorpionand-like Ligands. A Potentiometric, Mechanistic, and Solid-State Study

Two aza scorpionand-like macrocycles (L2 and L3) have been prepared. L2 consists of a tren amine with two of
its arms cyclizized with a 2,6-bis(bromomethyl)pyridine. In L3, the remaining pendant arm has been further
functionalized with a fluorophoric naphthalene group. X-ray data on the compounds [H(L3)]ClO4·H2O (1) and
[H3(L3)](H2PO4)3·H2O (2) as well as solution studies (pH-metry, UV−vis, and fluorescence data) show the movement
of the pendant arm as a result of the protonation degree of the macrocycles and of the formation of intramolecular
hydrogen bonds. X-ray data on the complexes [Cu(L2)](ClO4)2]2·H2O (3) and [Cu(L3)](ClO4)2 (4) and solution studies
on Cu2+ coordination show the implication of the nitrogen of the arm in the binding to the metal ion. Kinetic studies
on the decomposition and formation of the Cu2+ complexes provide additional information about the pH-dependent
molecular reorganizations. Moreover, the obtained information suggests that the kinetics of the tail on/off process
is essentially independent of the lability of the metal center.