Alkaline-earth metal based coordination polymers assembled from two different V-shaped ligands: Synthesis, structure, and dielectric properties

Abstract

Four new coordination polymers built of Group(II) metals (Mg, Ca and Ba) and two V-shaped ligands viz. FBA 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) and SBA (4,4′-sulfonyldibenzoic acid) have been crystallized via solvothermal reaction: [Mg3(FBA)2(DMF)2(HCOO)2(H2O)2].2DMF (1), [Ca(FBA)(DMF)] (2) [Ca4(SBA)4(DMF)2].2DMF (3) and [Ba(FBA)(DMA)(H2O)2] (4). Single crystal X-ray analysis established that all the four solids are built of extended metal carboxylate interaction. 1 is a 2D CP with square-shaped channels while 2, 3 and 4 are 3D CPs with rhombic channels. Frequency and temperature dependent dielectric behavior of solids 1–4 showed dielectric constants in the range 8–18 at room temperature. The solids 1 and 3 containing highly polarizable guest molecules (DMF, DMA and H2O) showed relatively higher value of dielectric constants (∼18.0 and ∼13.4 respectively) in comparison to 2 and 4 (∼7.8 and ∼8.0 respectively). Impedance spectroscopy studies (Z′ and Z″) showed that significantly higher dielectric constants in 1–4 arise from intrinsic behavior of the solids. The present work also highlights the influence of polar guest molecules in the structure in altering the dielectric constant.