Disilver(I) Macrocycles: Variation of Cavity Size with Anion Binding

Reaction of the N-methylated bis(amidopyridine) ligand, LL = C6H4(1,3-CONMe-4-C5H4N)2, with the silver salts
AgNO3, AgO2CCF3, AgO3SCF3, AgBF4, and AgPF6 gave the corresponding cationic disilver(I) macrocycles [Ag2(μ-LL)2]X2, 2a−e. The transannular silver···silver distance in the macrocycles varies greatly from 2.99 to 7.03 Å,
and these differences arise through a combination of different modes of anion binding and from the presence or
absence of silver···silver secondary bonding. In all complexes, the ligand adopts a conformation in which the
methyl group and oxygen atom of the MeNCO units are mutually cis, but the overall macrocycle can exist in either
boat (X = PF6 only) or chair conformation. Short transannular silver···silver distances are found in complexes
2b,c, in which the anions CF3CO2- and CF3SO3- bind above and below the macrocycle, but longer silver···silver
distances are found for 2a,d,e, in which the anions are present, at least in part, inside the disilver macrocycle.
Easy anion exchange occurs in solution, and studies using ESI-MS indicate that the anion binding to form [Ag2X(μ-LL)2]+ follows the sequence X = CF3CO2- > NO3- > CF3SO3-.