Silver(i) coordination polymers based on halogenated cyanoformamidine: roles of oxyanions and halogen atoms in the structural diversity

Abstract

The reactions of asymmetrical N-(4-halophenyl)-N′-cyanoformamidine (L–X, X = F, Cl, Br or I) with AgClO₄ and AgNO₃ afforded six coordination polymers, including {[Ag(L–Cl)](ClO₄)}_n [(L–Cl = N-(4-chlorophenyl)-N′-cyanoformamidine)], 1; {[Ag(L–Br)](ClO₄)}_n [(L–Br = N-(4-bromophenyl)-N′-cyanoformamidine)], 2; {[Ag(L–I)₂](ClO₄)}_n [(L–I = N-(4-iodophenyl)-N′-cyanoformamidine)], 3; {[Ag(L–F)](NO₃)}_n [(L–F = N-(4-fluorophenyl)-N′-cyanoformamidine)], 4; {[Ag(L–Cl)](NO₃)}_n, 5 and {[Ag(L–Br)](NO₃)}_n, 6. Complexes 1 and 2 are 1D helical chains, and 3 features a 2D layer with the (6³)-hcb topology. Complexes 4–6 are 1D linear chains supported by Ag---O interactions, which are further linked through Ag---Ag interactions and N–H---O hydrogen bonds to form 3D supramolecular structures. Halogen substituents on ligands and oxyanions in complexes affect the structures of complexes due to differences in the electronegativity, volume and Ag---O strengths. Although fluorine, chlorine and bromine atoms exhibit a similar structural effect and the iodine atom has the opposite effect, the larger ClO₄⁻ anion hinders the formation of the argentophilic interaction and the smaller NO₃⁻ anion is involved in this interaction.