Synthesis, characterization and X-ray crystal structures of cyclam derivatives. Part IV. 1,4,8,11-Tetraazacyclotetradecane-5,12-dione and its diprotonated forms

Abstract

The synthesis, spectroscopic characterization (NMR, IR, MS) and protonation constants of a dioxocyclam derivative, 1,4,8,11-tetraazacyclotetradecane-5,12-dione (1), are described. The crystal structures of the free-base macrocycle and two diprotonated forms, with bromide and perchlorate as counter ions, have been determined by X-ray diffraction studies in order to evaluate the influence of both the secondary amine's protonation state and of the intermolecular hydrogen-bonding interactions on the macrocycle conformation. The spectroscopic, potentiometric and structural data indicate that both secondary amines behave independently from each other, their protonation inducing only limited conformational changes of the macrocyclic framework. In the crystal, the diprotonated species adopt two different [3,4,3,4] diamond-lattice-type conformations as a consequence of intermolecular hydrogen bonds involving the oxo groups and the surrounding anions.