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

Abstract

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((Cu_1/2)₄I₄)_1/4]}_n (iPC⁺ = N-isopropyl-4-cyanopyridium) (3), {[EV]_1/4[((Cu_1/2)₄I₄)_1/4]}_n (EV²⁺ = N,N′-diethyl-4,4′-bipyridinium) (4) and {[PV]_1/2[(Cu₂I₄)_1/4((Cu_1/2)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.