Argentophilic Interactions in Two AgI Complexes of 3-(2-(Pyridin-4-yl)ethyl)pentane-2,4-dione, a Promising Ditopic Ligand

Reactions of 3-(2-(pyridin-4-yl)ethyl)pentane-2,4-dione (HacacPyen) with AgPF6 and AgBF4 afforded cationic silver complexes [Ag(HacacPyen)2]+ with essentially linear coordination of the AgI cation by two pyridine N atoms. Rather unexpectedly, the HacacPyen ligands in the PF6− salt 1 adopt the diketo form, in contrast to the uncoordinated HacacPyen molecule, whereas the corresponding BF4− salt 2 and the majority of 3-substituted acetylacetones crystallizes as the enol tautomer. In both compounds 1 and 2, complex cations aggregate via short Ag···Ag interactions to pairs. These contacts amount to 3.21 Å in 1 and 3.26 Å or 3.31 Å in 2. As they are unsupported by any additional bridging ligands and correspond to the closest interionic interactions between neighbouring complex cations, they may be addressed as argentophilic interactions. The PF6− anions in 1 and the BF4− counter ions in 2 are involved in long and presumably electrostatic Ag···F contacts of ca. 2.9 Å. Additional coordination between AgI and keto O atoms of symmetry-equivalent ligands occurs in 1 and leads to an extended two-periodic supramolecular structure.