Authors:Andrea Melchior, Marilena Tolazzi, and Silvia Del Piero
The complex formation of Cd(II) with N-donor ligands in dimethylsulfoxide (DMSO) is investigated by means of potentiometry and titration calorimetry. The ligands considered in this work are tripodal polyamines and polypyridines: 2,2′,2″-triaminotriethylamine (TREN), tris(2-(methylamino)ethyl)amine (Me3TREN), tris(2-(dimethylamino)ethyl)amine (Me6TREN), tris[(2-pyridyl)methyl]amine (TPA) and 6,6′-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine (BTPA). These ligands are characterized by a systematic modification of the donor groups to relate their structure to the thermodynamics of the complexes formed. The TREN and Me3TREN ligands form highly stable species. The stability of the complex formed with the fully methylated Me6TREN is much lower than with other polyamines and the enthalpic and entropic terms suggest an incomplete coordination to the metal ion. In general, the TPA ligand forms complexes less stable than TREN and Me3TREN as a result of the combination of higher structural rigidity of TPA and lower basicity of pyridine moiety with respect to primary and secondary amines. Pyridine-containing ligands display, in general, a less unfavorable formation entropy than tripodal polyamines here considered. In particular, TPA forms a more stable 1:1 species with respect to Me6TREN due to the entropic term, being the enthalpy less negative. The ligand BTPA is able to form only a monometallic complex, where the metal ion is likely to be encapsulated as indicated by the obtained thermodynamic parameters.
Authors:Silvia Piero, Andrea Melchior, Davide Menotti, Marilena Tolazzi, and Anders Døssing
An investigation on the thermodynamics of complex formation between Ag(I) ion and two tripodal ligands tris[(2-pyridyl)methyl]amine
(TPA) and 6,6′-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine (BTPA) has been carried out in the aprotic solvents
dimethylsulfoxide (DMSO) and dimethylformamide (DMF) by means of potentiometry and titration calorimetry. The results for
TPA are compared with those already obtained for other aliphatic tripodal polyamines. In general, the TPA ligand forms complexes
less stable than 2,2′,2″-triaminotriethylamine (TREN) and tris(2-(methylamino)ethyl)amine (Me3TREN) as a result of the combination of higher structural rigidity of TPA and lower σ-donor ability of pyridinic moieties
with respect to primary and secondary amines. The same trend is found if the stability of Ag(I) complex with TPA is compared
with that of tris(2-(dimethylamino)ethyl)amine (ME6TREN), despite the pyridinic nitrogen is formally a tertiary one. Theoretical calculations run to explain the reasons of this
weaker interaction indicate that this difference is due to solvation, rather than to steric or σ-donor effects. The ligand
BTPA is able to form bimetallic species whose relative stability is largely influenced by the different solvation of Ag(I)
ion in DMSO and DMF rather than by the difference in the dielectric constants of these two media.
Authors:L. Cavallo, J. Ducéré, Rosalisa Fedele, A. Melchior, Maria Mimmi, G. Morini, F. Piemontesi, and Marilena Tolazzi
A calorimetric investigation on the reactions of TiCl4 with phthalates in 1,1,2,2-tetrachloroethane (TCE) is presented in order to better understand the complex interactions present
in Ziegler-Natta catalytic systems. The Lewis bases diethyl isophthalate (L1), diethyl terephthalate (L2) and the ortho-isomer diethylphthalate (L3), have been chosen to study how the substituent positions could influence the energy and the stoichiometry of the complexation
FTIR spectroscopy was used to obtain information on the coordination mode of the ligands and diffusion measurements by NMR
was carried out to verify the presence of oligo-or polymeric species. Experimental results were compared with theoretical
calculations based on Density Functional Theory (DFT).
Authors:Daniele Bergamasco, Franco Bulian, Andrea Melchior, Davide Menotti, Paolo Tirelli, and Marilena Tolazzi
In previous studies some waterborne coatings, specifically formulated for the scope of the research, were studied during an artificial weathering process by means of dynamic mechanical analysis (DMA) technique. In those studies the chemical and physical parameters which mainly affect the performance of coatings and their evolution during weathering were measured. The aim was to predict the performance of coatings for exterior wood during their service life by means of accelerated artificial tests and instrumental measures. In this study four commercial products were artificially weathered following the European standard EN 927-6. The changes in the mechanical properties were measured by means of the DMA as reported in the previous studies. With this research the authors have verified the capability of this method to predict the performance in use of coatings.