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

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: [Mg-3(FBA)(2)(DMF)(2)(HCOO)(2)(H2O)(2)]center dot 2DMF (1), [Ca(EBA)(DMF)] (2) [Ca-4(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 (similar to 18.0 and similar to 13.4 respectively) in comparison to 2 and 4 (similar to 7.8 and similar to 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.