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.

本研究首次对多齿配体苯并咪唑-5,6-二羧酸（benzimidazole-5,6-dicarboxylic acid，H₂L）开展配位化学研究，并通过水热条件合成得到6种基于该配体的新型二维（2D）配位聚合物，分别为[MnL]ₙ（1）、{[Ni₂L₂(H₂O)₄]·3H₂O}ₙ（2）、{[Tb(L)(HL)(H₂O)]·H₂O}ₙ（3）以及{[Ln₂L₂(HL)₂(H₂O)₂]}ₙ（Ln = Ho（4）、Er（5）、Lu（6））。配合物1呈现出具有4⁴6²拓扑结构的新型配位网络，沿b轴方向存在罕见的一维{Mn−O}ₙ五配位链。配合物2为ab平面内具有4.8²拓扑结构的二维层状结构，并通过多重分子间氢键构筑出三维（3D）超分子网络。配合物3同样具有4⁴6²拓扑结构，但其配位网络与配合物1完全不同。配合物4~6为同构体，骨架中的每个Ln（Ln = Ho（4）、Er（5）、Lu（6））中心均作为五连接节点，在ab平面内形成具有(3.4.6)(3².4.5.6².7⁴)拓扑结构的独特配位网络。6种配合物展现出6种配体桥联模式。随着金属离子半径增大，金属中心周围的配体L数目从3（Ni）依次增至4（Mn），最终达到5（Ln）。配合物1的变温磁化率数据可通过费舍尔模型（Fisher model）拟合，得到参数g=2.05、J=−3.06 cm⁻¹；配合物2的拟合参数为g=2.09、J=−0.35 cm⁻¹，二者均表明存在反铁磁耦合作用。对配合物3的发光性能进行了研究。