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The stability constants of the Cu II chelates with the tripodal heptadentate ligand tris{2-[(2-pyridylmethyl)amino]ethyl}amine ( N'-(pyridin-2-ylmethyl)-N,N-bis{2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine; tpaa), determined by potentiometry and UV spectrometry, show the formation of [Cu(tpaaH)] 3 and [Cu(tpaa)] 2 species. In the solid state, two mononuclear Cu II compounds, [Cu(tpaa)](PF 6 ) 2 (1) and [Cu(tpaaH)](ClO 4 ) 3 ¥ H 2 O (2), and one trinuclear [Cu 3 (tpaa) 2 (ClO 4 ) 2 ](ClO 4 ) 4 ¥ 2 H 2 O (3) complex were isolated and characterized by IR, UV/VIS, and EPR spectroscopy. An X-ray structure of the mononuclear protonated complex 2 shows that the Cu 2 ion has a distorted square-pyramidal geometry (t 0.21). and the proton is bound to the secondary-amine function of one uncoordinated arm of the tripod ligand (Fig. 4). The crystal lattice for 2 is stabilized by the H-bonds between the N-atom of the free pyridinyl group with the proton of the free secondary-amine function of the neighboring molecule. The linear trinuclear complex 3 consists of two entities of the pyramidal mononuclear complex 1 bound to the third central Cu 2 ion by the free unprotonated arms of the ligands in equatorial position (Fig. 5). The octahedral geometry of the third Cu II atom is achieved by two perchlorate anions in the axial positions. The redox properties of 1 ± 3 compounds was examined by cyclic voltammetry.

Stoichiometry, equilibrium constants and spectra of iron(III) complexes with noradrenaline have been determined from spectrophotometric measurements; in addition equilibrium constants of complexes with Mg II , Cd II and Pb II have been determined from potentiometric measurements.

Potentiometric studies in aqueous medium and spectrophotometric study in non-aqueous medium were used to understand the behavior of hexamethylenetetramine (HMTA) complexes. The protometric studies of HMTA enabled us to confirm that only one basic site of this ligand is protonated in acidic medium and this ligand is decomposed in acidic medium. In aqueous medium, only hexa-aqua complexes in which HMTA is present in the second coordination sphere forming H-bonds with hydrogen atoms of coordinated and uncoordinated water molecules are obtained. In non-aqueous solvents, HMTA coordinates to metal ions displaying diversity in the structures of the resulting complexes in which HMTA can either be monodentate, bridged bidentate, tridentate, or tetradentate.

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