Solvation Effects on the Stability of Silver(I) Complexes with Pyridine-Containing Ligands Studied by Thermodynamic and DFT Methods

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.