Synthesis, structure and dielectric behavior study of Mn (II)-4,4′-sulfonyldibenzoate-auxiliary ligand system based coordination polymers (CPs)

Abstract

Based on MnCl2.4H2O, V-shaped ligand 4,4′-sulfonyldibenzoic acid (H2SBA), and two N-containing auxiliary ligands three new coordination polymers (CPs), namely: [Mn3(SBA)2(pyzc)2(DMA)2].DMA.H2O 1, [Mn3(SBA)2(phen)2(OAc)2].2DMA 2, and [Mn3(SBA)2(phen)2(OAc)2].2EtOH 3 [where, SBA = 4,4′-sulfonyldibenzoate, pyzc = 2-pyrazinecarboxylate, phen = 1,10-phenanthroline, OAc = acetate, DMF = N, N'-dimethylformamide, DMA = N, N'-dimethylacetamide] were synthesized using mixture of polar protic/aprotic solvents under solvothermal conditions. Single crystal X-ray study revealed that solid 1 is composed of tetrameric {Mn4O20N2} and dimeric units {Mn2O8N2}, whereas solids 2 and 3 are built of trimeric cluster {Mn3N2O14}. The structurally similar 2D coordination solids 2 and 3 showed comparable dielectric constant (ɛ'∼15.0) at room temperature. Solid 1 exhibited a higher value of dielectric constant (ɛ'∼30.5) probably due to the contribution from disordered polar guest solvent molecules, and 1D manganese carboxylate chains interaction. The crystal engineering of soluble 1:1 manganese carboxylate complex species, with or without coordination with an auxiliary ligand, is also explained mechanistically in this study. The approach not only provides a rationale for the composition and variation in the coordination linkage but also describes the crystal packing in terms of the dominant directional coordination and H-bonding forces.