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2001
Journal Article
Title
The effect of alkylation of N- and O-donor atoms on their strength of coordination to silver(I)
Abstract
The observation that alkylation of amine ligands can lead to enhanced coordination to silver(I) is investigated through the determination of structures and incremental binding enthalpies for Ag+(L), ionic clusters (with L = NH3, NH2Me, NHMe2, NMe3, H2O, MeOH, and Me2O for n = 1-2), using density-functional and CCSD(T) electronic structure methods. For the nonalkylated complexes Ag+(H2O), Ag+(NH3), Ag+(H2O)(2), and Ag+(NH3)(2), the calculated binding enthalpies agreed well with experimental values for all but Ag+(NH3)(2), while good agreement between the binding entropies was achieved for all but Ag+(H2O). As a function of the degree of alkylation, the calculated binding enthalpies initially increase but then decrease. The results are interpreted in terms of the bonding models of Meyerstein and of Deng et al. as arising from increased ligand sigma -donating ability and reduced ion-ligand electrostatic interactions. It is clear that gas-phase effects are insufficient to explain the sometimes observed increased binding energies of tertiary macrocyclic amines compared to secondary ones.