Coordination Chemistry of Silver Cations

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Abstract
While in pure solvents Ag+ is known to be tetrahedrally coordinated, in the presence of ligands such as ammonia it forms linear complexes, usually explained by the ion's tendency toward sd-hybridization. To explore this disparity, we have investigated the reaction of ammoniated silver cations Ag+(NH3)n, n = 11−23, with H2O as well as the complementary process, the reaction of Ag+(H2O)n, n = 25−45, with NH3 by means of FT-ICR mass spectrometry. In both cases, ligand exchange reactions take place, leading to clusters with a limited number of NH3 ligands. The former reaction proceeds very rapidly until only three NH3 ligands are left, followed by a much slower loss of an additional ligand to form Ag+(NH3)2(H2O)m clusters. In the complementary process, the reaction of Ag+(H2O)n with NH3 five ammonia ligands are very rapidly taken up by the clusters, with a much less efficient uptake of a sixth one. The accompanying DFT calculations reveal a delicate balance between competing effects where not only the preference of Ag+ for sd-hybridization, but also its ability to polarize the ligands and thus affect the strength of their hydrogen bonding, as well as the ability of the solvent to form extended hydrogen-bonded networks are important.