Ancillary Ligands Dependent Structural Diversity of A Series of Metal–Organic Frameworks Based on 3,5-Bis(3-carboxyphenyl)pyridine

Abstract

A series of novel multidimensional transition metal–organic frameworks (MOFs), [Cu(Hbcpb) 2 ] n ( 1 ), [Co(bcpb)] n ( 2 ), [Co(Hbcpb) 2 (1,4-bib)] n ( 3 ), {[M(bcpb)(1,4-bimb)]·xH 2 O} n ( M = Co ( 4 ), Cu ( 5 ), Ni ( 6 ), x = 1 for 5, 2 for 4 and 6 ), [Co(bcpb)(4,4′-bibp)] n (7), {[Co(bcpb)(4,4′-bibp)]·2H 2 O} n ( 8 ), and [Ni 2 (bcpb) 2 (4,4′-bimbp) 2 ] n ( 9 ), were synthesized under hydrothermal conditions in the presence of N-donor ancillary ligands [H 2 bcpb = 3,5-bis(3-carboxyphenyl)pyridine, 1,4-bib = 1,4-bis(1H-imidazol-4-yl)benzene, 1,4-bimb = 1,4-bis(imidazol-1-ylmethyl)benzene, 4,4′-bibp = 4,4′-bis(imidazol-1-yl)biphenyl, 4,4′-bimbp = 4,4′-bis(imidazol-1-ylmethyl)biphenyl]. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. By adjusting the reaction pH, the H 2 bcpb ligand is partially deprotonated to give the Hbcpb – form in 1 and 3, and completely deprotonated to afford the bcpb 2– form in 2 and 4 – 9 . Complex 1 exhibits a two-dimensional (2D) (3,6)-connected kgd topology with the Schläfli symbol of (4 3 ) 2 (4 6 ·6 6 ·8 3 ). The three-dimensional (3D) framework of 2 is defined as a (4,4)-connected pts topology with the Schläfli symbol of (4 2 ·8 4 ). Complex 3 displays a (4,6)-connected pcu topology with the Schläfli symbol of (4 12 ·6 3 ) built from 4 4 2D nets with the help of 1,4-bib. Complexes 4 – 6 are isomorphism and show a 3D (3,5)-connected mbm framework with the Point Schläfli symbol of (4·6 2 )(4·6 6 ·8 3 ). The supramolecular isomers of 7 and 8, resulted from the different pH in the reaction, exhibit (3,5)-connected (4 2 ·6 7 ·8)(4 2 ·6) 3,5-L2 and (4,6)-connected (4 4 ·6 10 ·8)(4 4 ·6 2 ) fsc topology, respectively. Complex 9 can be regard as an unprecedented (3,5)-connected 3D 3,5-T1 frameworks with the point Schläfli symbol of (4 2 ·6 5 ·8 3 )(4 2 ·6). The results revealed that the crystal architectures and the coordination modes of H 2 bcpb are attributed to the factors, including metal cations, pH, and the N-donor ancillary ligands.