Subtle role of polyatomic anions in molecular construction:: Structures and properties of AgX bearing 2,4′-thiobis(pyridine) (X- = NO3-, BF4-, ClO4-, PF6-, CF3CO2-, and CF3SO3-)

Studies on the subtle effects and roles of polyatomic anions in the self-assembly of a series of AgX complexes with 2,4'-Py2S (X- = NO3-, BF4-, ClO4-, PF6-, CF3CO2-, and CF3SO3-; 2,4'-Py2S = 2,4'-thiobis(pyridine)) have been carried out. The formation of products appears to be primarily associated with a suitable combination of the skewed conformers of 2,4'-Py2S and a variety of coordination geometries of Ag(I) ions. The molecular construction via self-assembly is delicately dependent upon the nature of the anions. Coordinating anions afford the 1:1 adducts [Ag(2,4'-Py2S)X] (X- = NO3- and CF3CO2-), whereas noncoordinating anions form the 3:4 adducts [Ag-3(2,4'-Py2S)(4)]X-3 (X- = ClO4- and PF6-). Each structure seems to be constructed by competition between pi-pi interactions of 2,4'-Py2S spacers vs (AgX)-X-... interactions. For ClO4- and PF6-, an anion-free network consisting of linear Ag(I) and trigonal Ag(I) in a 1:2 ratio has been obtained whereas, for the coordinating anions NO3- and CF3CO2-, an anion-bridged helix sheet and an anion-bridged cyclic dimer chain, respectively, have been assembled. For a moderately coordinating anion, CF3SO3-, the 3:4 adduct [Ag-3(2,4'-Py2S)(4)](CF3SO3)(3) has been obtained similarly to the noncoordinating anions, but its structure is a double strand via both face-to-face (pi-pi) stackings and (AgAg)-Ag-... interactions, in contrast to the noncoordinating anions. The anion exchanges of [Ag-3(2,4'-Py2S)(4)]X-3 (X- = BF4-, ClO4-, and PF6-) with BF4-, ClO4-, and PF6- in aqueous media indicate that a [BF4-] analogue is isostructural with [Ag-3(2,4'-Py2S)(4)]X-3 (X- = ClO4- and PF6-). Furthermore, the anion exchangeability for the noncoordinating anion compounds and the X-ray data for the coordinating anion compounds establish the coordinating order to be NO3- > CF3CO2- > CF3SO3- > PF6- > ClO4- > BF4-.