Thermodynamic parameters of complex formation between d10 metal ions, such as Zn2+, Cd2+, Hg2+ and
Ag+, and the macrocyclic thioether 1,4,7-trithiacyclononane ([9]AneS3) or the monodentate diethylsulfide
(Et2S), in acetonitrile (AN) at 298.15 K, were studied by a systematic methodology including
potentiometry, calorimetry and polarography. [9]AneS3 is able to form complexes with all the target
cations, Et2S only reacts with Hg2+ and Ag+. Mononuclear MLj ( j = 1, 2) complexes are formed with all
the metal ions investigated, where the affinity order is Hg2+ > Ag+ > Cd2+ ≈ Zn2+ when L = [9]AneS3 and
Hg2+ > Ag+ when L = Et2S. Enthalpy and entropy values are generally negative, as a consequence of both
metal ion interactions with neutral ligands, the reagents’ loss of degrees of freedom and the release of
solvating molecules. DFT calculations on the complexes formed with [9]AneS3 in vacuum and in AN are
also carried out, to correlate experimental and theoretical thermodynamic values and to highlight the
interplay between the direct metal–thioether interaction and the solvation effects. Trends obtained for
the stability constants and enthalpies of the 1 : 1 and 1 : 2 complexes in solvent well reproduce the experimental
ones for all the divalent metal ion complexes with [9]AneS3 and indicate the release of 3 AN
molecules in the formation of each consecutive octahedral complex. In addition, calculated and experimental
values for Ag+ complex formation in solution suggest that in AgL2 species [9]AneS3 ligands are
not both tridentate.
