Iodobismuthates with N-alkyl- or N,N′-dialkyl-4,4′-bipyridinium: syntheses, structures and dielectric properties

Abstract

The solvothermal reactions of BiI₃, KI, I₂, 4,4′-bipyridine (4,4′-bipy), and a small amount of water in alcohol and acetonitrile produced four bipyridinium iodobismuthates {[MQ]₃[Bi₂I₆(μ-I)₃][Bi₂I₆(μ-I)₂(MQ)₂]₃} (1, MQ⁺ = N-methyl-4,4′-bipyridinium), {[EQ]₃[Bi₂I₆(μ-I)₃][Bi₂I₆(μ-I)₂(EQ)₂]₃} (2, EQ⁺ = N-ethyl-4,4′-bipyridinium), [MV][BiI₅] (Eur. J. Inorg. Chem., 2010, 5326) (3, MV²⁺ = N,N′-dimethyl-4,4′-bipyridinium), and [EV]₂[Bi₄I₁₀(μ-I)₄(μ₃-I)₂] (4, EV²⁺ = N,N′-diethyl-4,4′-bipyridinium). In these reactions, 4,4′-bipy was partly or completely alkylated by alkyl groups generated from the cleavage of C–O bond of alcohols, forming the N-alkyl-4,4′-bipyridinium cation (Q⁺) and the N,N′-dialkyl-4,4′-bipyridinium dication (V²⁺), respectively. Compounds 1–4 were characterized by elemental analysis, IR, ¹H NMR and single-crystal X-ray diffraction analysis. The optical, electrical conductive and dielectric properties of these compounds were investigated. The dielectric constants of the Q⁺-based compounds were larger than the values of the V²⁺-based ones, which showed that the weak electrostatic interactions in the structures may benefit the polarizability of molecules, thereby resulting in a larger dielectric response of the structures under an external electric field, while the strong electrostatic interactions between the positive and negative charge units would lead to a low dielectric constant (low-k) behavior of these compounds.