The Coordination Chemistry of Benzimidazole-5,6-dicarboxylic Acid with Mn(II), Ni(II), and Ln(III) Complexes (Ln = Tb, Ho, Er, Lu)

The first coordination chemistry of a multidentate ligand benzimidazole-5,6-dicarboxylic acid (H2L) was investigated, and six novel two-dimensional (2D) coordination polymers based on this ligand, namely, [MnL]n (1), {[Ni2L2(H2O)4]·3H2O}n (2), {[Tb(L)(HL)(H2O)]·H2O}n (3) and {[Ln2L2(HL)2(H2O)2]}n (Ln = Ho (4), Er (5), Lu (6)), were synthesized under hydrothermal conditions. Compund 1 shows a novel coordination network with 4462 topology and contains unusual five-coordinated one-dimensional {Mn−O}n chains along the b-axis. Compound 2 is a 2D layer structure of 4.82 topology in the ab plane and displays a three-dimensional (3D) supramolecular network via multiple intermolecular hydrogen bonds. Compound 3 also shows a 4462 topology, but its coordination network is completely different from compound 1. Compounds 4−6 were isostructural, and each Ln (Ln = Ho (4), Er (5), Lu (6)) center in the framework acts as a five-connected node to give rise to a unique network with a (3.4.6)(32.4.5.62.74) topology in the ab plane. Six complexes exhibit six types of bridging modes of the ligand. The numbers of L ligands around the metal centers increase from 3 (Ni) to 4 (Mn) and finally to 5 (Ln) as a result of an increase in metal ionic radii. The temperature-dependent magnetic susceptibility data have been explained with the Fisher model, with parameters g = 2.05, J = −3.06 cm−1 for 1, and g = 2.09, J = −0.35 cm−1 for 2, indicating antiferromagnetic coupling. The luminescent properties of 3 were studied.