Extensive calorimetric investigations on the interaction of TiCl 4 with some Lewis bases are presented. Some of the bases were chosen for their industrial relevance in heterogeneous Ziegler-Natta polymerization of propene (ethyl benzoate, L2, diisobutyl phthalate, L3, (2R,3S)-diethyl 2,3-diisopropylsuccinate, L6, (2S,3S)diethyl 2,3-diisopropylsuccinate, L7, and 9,9-bis(methoxymethyl)-9H-fluorene, L13) while other bases were chosen as probe molecules to explore the electronic and steric effects on the complexation energy (ethyl acetate, L1, diethyl phthalate, L4, diethyl succinate, L5, tetrahydrofuran, L8, dimethoxyethane, L9, dimethoxypropane, L10, dimethoxybutane, L11, and 3,3-bis(methoxymethyl)-2,6-dimethylheptane, L12). 1,1,2,2,-Tetrachloroethane was selected as the solvent for its low donating properties, which allows the focus to be on the metal-donor interaction. The calorimetric data are discussed and compared with the efficiency of the derived catalysts. Further understanding is obtained by comparison of the experimental results with theoretical calculations based on density functional theory (DFT). The performance of different computational approaches was validated by comparison of the calculated and experimental complexation energies.

The formation of Ag(I) complexes with 2,2'-bipyridine (bipy), 2,2'6',2' '-terpyridine (terpy), 2-(aminomethyl)pyridine (amp), and bis((2-pyridyl)methyl)amine (dpa) is studied in dimethyl sulfoxide (dmso) by means of potentiometric and calorimetric measurements. Enthalpy-stabilized mononuclear MLj complexes are formed, whereas entropy changes counteract complex formation. Additionally, a comparison with analog Ag-polyamine species is made to evidence the significant different coordination behavior of these classes of ligands. The results are discussed in terms of different basicity and steric requirements of the ligands and solvation effects. The dpa ligand, with an unprecedented coordination pattern, forms also a bimetallic complex [Ag2(dpa)2]2+ that has been structurally characterized in the solid state by X-ray diffraction. The influence of solvent, water and dmso, on the binding energy of the monodentate pyridine to Ag(I) has also been assessed by means of density functional theory (DFT) calculations. This study has been extended also in vacuum to the reaction of Ag(I) with the simple monoamine methylamine (mea). These results are correlated with the experimental evidence and used to interpret the different affinities of pyridine for the Ag(I) ion in the two media.

CdII and CoII complex formation with pyridine (py), 2,2′‐bipyridine (bipy), 2,2′6′,2″‐terpyridine (terpy), 2‐(aminomethyl)pyridine (amp), and bis[(2‐pyridyl)methyl]amine (dpma) was studied at 298 K in the aprotic solvent dimethyl sulfoxide (DMSO) and in an ionic medium set to 0.1 mol dm–3 with Et4NClO4 in anaerobic conditions. Potentiometric, UV/Vis spectrophotometric, and calorimetric measurements were carried out to obtain the thermodynamic parameters of the systems investigated. Enthalpy‐stabilized mononuclear MLj complexes are formed, whereas entropy changes counteract complex formation. These results are discussed in terms of different basicities, steric requirements, and solvation, of both the ligands and the resulting complexes. Density functional theory (DFT) calculations were carried out in order to obtain structural information and binding energies in vacuo. The DFT results are correlated with the solution studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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