Effect of coordinated and lattice neutral co-ligands on the dielectric properties of cadmium and magnesium based coordination polymers†

Abstract

Two new coordination polymers, CPs [Cd₂(FBA)₂(DMA)₂]·THF (1) and [Mg₃(SBA)₂(EtOH)₂(H₂O)₂(μ₃-OH)₂]·DMA (2) {where, FBA = 4,4′ (hexafluoroisopropylidene)bisbenzoate, SBA = 4,4′-sulfonyldibenzoate, THF = tetrahydrofuran and DMA = N,N-dimethylacetamide}, were synthesized from cadmium and magnesium salts, 1,10-phenanthroline and two different V-shaped flexible ligands by solvothermal methods. The structures were determined by using single crystal X-ray diffraction analysis which revealed that solid 1 crystallizes in the monoclinic space group (P2/n) and adopts a 2D square channel structure with a unique dimeric {Cd₂O₁₂}_n secondary building unit (SBU). Solid 2 also showed a 2D square channel structure and crystallizes in the monoclinic space group C2/c with an extended trimeric SBU of {Mg₃(μ₃-OH)O₂₂}_n. The dielectric measurement study showed dielectric constants (κ) of ∼10.5 for 1 and ∼12.6 for 2 at room temperature. The values of the dielectric constants (κ) of solids 1 and 2 decreased significantly to values of ∼4.6 (solid 1′) and ∼5.6 (solid 2′) after removing the polar solvents, indicating that neutral co-ligand molecules present in the framework significantly affect the material dielectric behaviour. Furthermore, the investigation of impedance spectroscopy (Z′ and Z′′) revealed that the low and high dielectric constant values in the reported solids are attributed to the inherent properties of the bulk material. The reported work offers a suitable example for the construction of high and low-κ coordination polymers (CPs) as gate and interlayer dielectrics for electronic devices by altering the polar solvents present in the framework.