Diverse Cd^II coordination complexes derived from bromide isophthalic acid binding with auxiliary N-donor ligands

The coordination characteristics of 4-bromoisophthalic acid (4-Br-H₂ip) have been investigated in a series of Cd^II-based frameworks. Hydrothermal reactions of Cd^II salts and 4-Br-H₂ip together with flexible or semiflexible N-donor auxiliary ligands resulted in the formation of four three-dimensional coordination complexes with diverse structures: (Cd(bix)_0.5(bix)_0.5(4-Br-ip)]·H₂O)_n (1), [Cd(bbi)_0.5(bbi)_0.5(4-Br-ip)]_n (2), ([Cd(btx)_0.5(4-Br-ip)(H₂O)]·0.5CH₃OH·H₂O)_n (3) and ([Cd(bbt)_0.5(4-Br-ip)(H₂O)]·3·5H₂O)_n (4). These compounds were characterized by elemental analyses, IR spectra, single-crystal and powder X-ray diffraction. They displayed diverse structures depending on the configuration of the 4-connected metal node, the coordination mode of the 4-Br-H₂ip, the coordination ability and conformationally flexibility of the N-donor auxiliary. Compound 1 exhibits 3-fold interpenetrated 6⁶ topology and compound 2 has a 4¹² topology. Compounds 3–4 have similar 3D pillar-layered structures based on 3,4-connected binodal net with the Schläfli symbol of (4·3⁸). The thermal stabilities and photoluminescence properties of them were discussed in detail. - Graphical abstract: Four 3D Cd^II coordination complexes on the basis of 4-bromoisophthalic acid (4-Br-H₂ip) and two types of flexible (bbi, bbt) and semiflexible (bix, btx) N-donor ligands are prepared. They displayed diverse topology structures of 6⁶ (1), 4¹² (2) and 4·3⁸ (3−4), depending on the configuration of the 4-connected metal node, the coordination mode of the 4-Br-H₂ip, the coordination ability and conformationally flexibility of the N-donor auxiliary ligand. - Highlights: • Four 3D Cd^II coordination complexes based on 4-Br-H₂ip and flexible/semiflexible N-donor ligands have been synthesized. • They displayed diverse topology structures of 6⁶ for 1, 4¹² for 2 and 4·3⁸ for 3–4. • The structural diversity depends on the configuration of 4-Br-H₂ip and the coordination behaviors of the auxiliary ligand.