Multi-dimensional iodocuprates of 4-cyanopyridinium and N,N′-dialkyl-4,4′-bipyridinium: syntheses, structures and dielectric properties

Solvothermal reactions of CuI with 4-cyanopyridine (4-cypy) or 4,4′-bipyridine (4,4′-bipy) and alcohols (methanol, ethanol, propanol, isopropanol) in the presence of I2 and a trace amount of water in acetonitrile gave rise to a family of multi-dimensional iodocuprate complexes of 4-cyanopyridinium and N,N′-dialkyl-4,4′-bipyridinium including {[MC]2[Cu4(μ3-I)4(μ-I)2]}n (MC+ = N-methyl-4-cyanopyridium) (1), {[PC][(Cu2I4)1/4(Cu2I4)1/4]}n (PC+ = N-propyl-4-cyanopyridinium) (2), {[iPC][(Cu2I4)1/4((Cu1/2)4I4)1/4]}n (iPC+ = N-isopropyl-4-cyanopyridium) (3), {[EV]1/4[((Cu1/2)4I4)1/4]}n (EV2+ = N,N′-diethyl-4,4′-bipyridinium) (4) and {[PV]1/2[(Cu2I4)1/4((Cu1/2)4I4)1/4]}n (PV2+ = N,N′-dipropyl-4,4′-bipyridinium) (5). The resulting 4-cyanopyridinium and viologen cations were generated in situ via the cleavage of the C–O bond of alcohols followed by alkylation of 4-cypy or 4,4′-bipy. X-ray analysis revealed that compound 1 consists of a unique three-dimensional anionic [Cu4I6]n2n− framework while compounds 2–5 contain one-dimensional anionic [Cu2I4]n2n− chains that are enclosed into different cationic channels formed by either 4-cyanopyridinium or N,N′-dialkyl-4,4′-bipyridinium. The dielectric properties of 1–5 were investigated.