Anion-controlled conformational variation: Structural modulation and anion exchange of Ag(I) coordination networks

From our recently reported [Ag2L2](2+) metallacyclic species (L = 2,5-bis(4-pyridinylmethylthio)-1,3,4-thiadiazole), four coordination networks [Ag2L2](n)center dot 2n(ClO4)center dot 7nH(2)O (1), [Ag2L2](n)center dot 2n(BF4)center dot 5nH(2)O (1a), [Ag2L2](n)center dot n[Ag2L2]center dot 4n(NO3) (2) and [AgL(NO2)](n) (3) were synthesized under the different anion conditions, which can be classified into three distinct supramolecular structures. Complexes 1/1a are constructed by disilver(I) macrocyclic motifs with the chair conformation, whereas 2 consists of two types of boat-form metallacycles. In 3, the bridging L adopts an extended conformation in sharp contrast to that in 1/1a/2. In this system, conformations of the metallacyclic subunit and flexible ligand L are modulated by various counter anions. For weakly coordinating anions, anion-exchange results indicate that complexes 1/1a maintain the primary structures and have an affinity order in agreement with the Hofmeister series. It is noteworthy that when complexes 1/1a/2 are treated with an aqueous solution containing NO2-, they all undergo a fast and quantitative anion-exchange process to afford complex 3. This process accompanies remarkable conformational conversion of L from cis, cis, syn to trans, trans, syn form. Atomic force microscopy studies indicate a solvent-mediated rather than a solid-state mechanism for the anion exchange.