Guest dependent dielectric properties of nickel(ii)-based supramolecular networks

Abstract

Two nickel(II)-based low dielectric supramolecular compounds {[Ni₂(bbim)(H₂bbim)₄]·2CH₃COO·CH₃CN}₂ (1, H₂bbim = bisbenzimidazole) and (±)-[Ni(H₂bbim)₃]·2Cl·2H₂O (2) were synthesized and characterized by single-crystal X-ray crystallography. Compound 1 was found to have a dimeric structure with guest molecules such as acetate ions and acetonitrile in its environment, while compound 2 had a monomeric structure with chloride ions and water molecules associated with it. Both compounds were highly thermally stable, especially compound 1, which was stable at temperatures of up to 500 °C. More importantly, compound 1 adopted a sharp different frequency dependent dielectric behaviour when compared with 2. Compound 2 with highly polarizable guest molecules showed a significant higher value of dielectric constant (ε_r′(ω) = 12.6 at 40 Hz) than that of 1 (ε_r′(ω) = 4.76 at 40 Hz), indicating that solvent molecules and counterions play a crucial role in regulating the value of the dielectric constant. This study serves as a good example of the design of both high and low-κ materials with a judicious selection of guest molecules in the supramolecular networks.