Three cobalt(ii) coordination polymers based on V-shaped aromatic polycarboxylates and rigid bis(imidazole) ligand: syntheses, crystal structures, physical properties and theoretical studies

Abstract

To investigate the effect of organic anions on the coordination frameworks, we synthesized three new complexes, namely, Co(SDBA)(BIMB) (1), Co2(SA)(BIMB)1.5(H2O) (2) and Co(FBA)(BIMB)0.5·H2O (3) (H2SDBA = 4,4′-dicarboxybiphenylsulfone, H4SA = 3,3′,4,4′-diphenylsulfonetetracarboxylate acid and H2FBA = 4,4′-(hexafluoroisopropylidene)bis(benzoic acid)), which were obtained by the reactions of 4,4′-bis(1-imidazolyl)biphenyl (BIMB), and three V-shaped aromatic polycarboxylates as organic anions with Co(NO3)2·6H2O. Single crystal structure analysis shows that complex 1 features a 3-fold interpenetrating three-dimensional (3D) framework with CdSO4-type topology. Complex 2 has a previously unknown 3D trinodal (4,4,6)-connected framework with a Schläfli symbol of (4·64·8)2(43·63)2(44·610·8). Complex 3 exhibits a three-dimensional 2-fold interpenetrating pillared helical-layer open framework of α-Po topology based upon binuclear paddlewheel units. The results reveal that the carboxylic building blocks with different conformations play a significant role in promoting the diversity of the observed structural motifs. The magnetic properties of the three complexes as well as the SHG and ferroelectric properties for 1 have also been investigated. Finally, theoretical calculations were carried out on the conformation of the BIMB ligand in the three complexes.