A series of Cd(II) supramolecular architectures based on polycarboxylate and 2-amino-benzimidazole mixed-ligands

By reaction of Cd(II) salts, different aromatic/aliphatic carboxylic acid and 2-amino-benzimidazole (Abm), four crystalline supramolecular coordination polymers, {[Cd2(tma)2(Abm)4]·2(HAbm)·5.5(H2O)}n (1), {[Cd(tp)(Abm)2]·(DMF)}n (2), {[Cd(ip)2]·2(HAbm)}n (3), and {[Cd(ga)2]·2(HAbm)}n (4) (H3tma = trimesic acid; H2tp = terephalatic acid; H2ip = isophthalic acid; H2ga = glutaric acid), have been successfully synthesized. In 1 pairs of 1D right- and left-hand helical structure and in 2 1D zigzag chains can be found, which are further extended into 3D hydrogen bonded frameworks via strong intra- and inter-chain N–H···O interactions. In contrast, 3 and 4 with 2D layer structure are stacked together in the ABAB way, where protonated HAbm cations are located between 2D layers and further stabilized by cooperative N–H···O, π···π and C–H···π interactions. Interestingly, single crystal 3 can reversibly transform into single crystal of its hydrated compound 3a, indicating small guest water molecules can be effectively absorbed in the host framework of 3. The FT-IR spectra of 1–4 have also been discussed briefly.