Argentophilic interaction and anionic control of supramolecular structures in simple silver pyridine complexes

The synthesis and characterization of three simple 1:2 silver(l) pyridine adducts of different counter-anions, [Ag(PY)(2)](+). X- (X = ClO4 BF4, 2; PF6, 3), are reported. The structural studies for 1-3 reveal the presence of strong ligand-unsupported argentophilic interactions between [Ag(py)(2)](+) ions, forming pairs of [Ag(py)(2)](2)(2+). The Ag... Ag contact distances are 2.96-3.00 angstrom. In 1 and 2, pairs of [Ag(PY)(2)](2)(2+) are further linked into 1-D infinite chains by a combined set of multiple Ag... Ag close contacts (3.34-3.37 angstrom), offset 'head to head' pi-pi stacking, and anion bridging interactions. Such combined set of interactions is anion-dependant with 1 and 2 containing anions of tetrahedral geometry ClO4- and BF4- affording essentially the same supramolecular architecture. Metal-anion interactions are crucial in organizing the 1-D chains into 3-D networks. The ES-MS studies of 1 and 2 provide positive evidence for the aggregation of silver(I) ions in solution. In contrast, for 3 with the counter-anion of octahedral PF6-, pairs of [Ag(py)(2)](2)(2+) are organized into a 3-D network via a combined set of (AgF)-F-... contacts, C(H)F-... hydrogen bonds, and 'head to tail' pi-pi stacking interactions. No extended 1-D polymeric chains of silver ions are present in 3. (c) 2006 Elsevier B.V. All rights reserved.