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

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)]·xH2O}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)]·2H2O}n (8), and [Ni2(bcpb)2(4,4′-bimbp)2]n (9), were synthesized under hydrothermal
conditions in the presence of N-donor ancillary ligands [H2bcpb = 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 H2bcpb ligand is partially
deprotonated to give the Hbcpb– form in 1 and 3, and completely deprotonated to afford the bcpb2– form in 2 and 4–9. Complex 1 exhibits a two-dimensional (2D)
(3,6)-connected kgd topology with the Schläfli symbol of (43)2(46·66·83). The three-dimensional (3D) framework of 2 is
defined as a (4,4)-connected pts topology with the Schläfli
symbol of (42·84). Complex 3 displays a (4,6)-connected pcu topology with the Schläfli
symbol of (412·63) built from 44 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 (4·62)­(4·66·83). The supramolecular isomers of 7 and 8, resulted from the different pH in the
reaction, exhibit (3,5)-connected (42·67·8)­(42·6) 3,5-L2 and (4,6)-connected (44·610·8)­(44·62) 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 (42·65·83)­(42·6). The results revealed that the crystal
architectures and the coordination modes of H2bcpb are
attributed to the factors, including metal cations, pH, and the N-donor
ancillary ligands.