Not Too Big and Not Too Small: “Goldilocks” Anion Size for Three-Dimensional Metal–Organic Frameworks Containing Oligothiophene Dinitrile Ligands (C4H2S)n(CN)2 (n = 1, 2, 3) Bridging Silver(I) Cations

A series of oligothiophene dinitriles, containing one, two, or three oligothiophene rings between nitrile donors NC-(C4H2S)n-CN are reacted with silver­(I) salts to form coordination compounds. In most cases, the resulting metal–organic frameworks are one-dimensional coordination polymers containing roughly linear divalent Ag­(I) centers. However, in the case of bithiophene (n = 2) and terthiophene (n = 3) bridges, a three-dimensional structure is also possible if the silver­(I) counterion is just the right size to fit into the diamondoid pores that form with four-coordinate tetrahedrally oriented Ag­(I) centers. Thus, only ClO4– and BF4– form three-dimensional structures with the bithiophene-bridged ligands, while the larger CF3SO3– and SbF6– anions will support a three-dimensional structure for the terthiophene-bridged ligand. Any counterion larger or smaller than the “just right” size will result in the one-dimensional structure instead.