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]_<i>n</i> (<b>1</b>), [Co­(bcpb)]_<i>n</i> (<b>2</b>), [Co­(Hbcpb)₂(1,4-bib)]<i>n</i> (<b>3</b>), {[M­(bcpb)­(1,4-bimb)]·xH₂O}<i>n</i> (<i>M</i> = Co (<b>4</b>), Cu (<b>5</b>), Ni (<b>6</b>), <i>x</i> = 1 for <b>5</b>, 2 for <b>4</b> and <b>6</b>), [Co­(bcpb)­(4,4′-bibp)]_<i>n</i> (7), {[Co­(bcpb)­(4,4′-bibp)]·2H₂O}_<i>n</i> (<b>8</b>), and [Ni₂(bcpb)₂(4,4′-bimbp)₂]_<i>n</i> (<b>9</b>), 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 <b>1</b> and <b>3</b>, and completely deprotonated to afford the bcpb^2– form in <b>2</b> and <b>4</b>–<b>9</b>. Complex <b>1</b> 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 <b>2</b> is defined as a (4,4)-connected pts topology with the Schläfli symbol of (4²·8⁴). Complex <b>3</b> 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 <b>4</b>–<b>6</b> 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 <b>7</b> and <b>8</b>, 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 <b>9</b> 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