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

Abstract

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 Ag I 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 Ag I and keto O atoms of symmetry-equivalent ligands occurs in 1 and leads to an extended two-periodic supramolecular structure.

Molecular Motion and Ligand Stacking Influence Thermal Expansion Behavior and Argentophilic Forces in Silver Coordination Complexes

“…These ligands differ in their abilities to undergo molecular pedal motion in the solid state; Azo and SB are motion-capable, while PAB is not. The silver atoms are expected to interact through argentophilic (Ag···Ag) interactions − to direct assembly into discrete dimers, which does occur in solids containing SB or PAB (Scheme b). Unexpectedly, we obtained a second polymorph with the SB ligand that lacks argentophilic forces entirely.…”

Coordination of a Potentially Tritopic Ligand via Phosphorus, Nitrogen and Oxygen: From Ligand Design to Heterobimetallic Metal–Organic Frameworks and Supramolecules

“…Among the examples for the second strategy the β-diketone moiety is a frequent choice for a Pearson hard functionality because of its reliable and predictable coordination behavior. − Nearly all of these examples use N donor functionalities as the Pearson soft function. − Only a few examples are known for other donor atoms such as carbon and sulfur, , with one of the latter being from our group. The thioether function we used proved successful for the formation of semiporous networks, but its low donor strength made the emerging networks predominantly labile and heavily dependent on the solvent mixtures during the crystallization process.…”