Coordination Polymers of Flexible Bis(benzimidazole) Ligand: Halogen Bridging and Metal···Arene Interactions

A new organic ligand, namely 1,4-bis[2-(1-methylbenzimidazol-2-ylmethyl)]benzene (L), was synthesized, and its crystal structure has been determined. The ability of L to form coordination polymers was explored with various metal salts under different conditions. Six complexes of L[Cu2(L)I2], 1; [Cu2(L)I2], 2; [Cd3(L)Cl6·2DMF], 3; [Cu(L)Cl2], 4; [Zn(L)I2·MeOH], 5; and [Cd(L)(NO3)2·H2O]·2THF, 6have been synthesized by the reaction of L with the corresponding metal salts at room temperature, either by direct mixing or by a layering technique. Single crystal X-ray analyses revealed that complexes 1 and 2 are isomers of each other and that both contain Cu2I2 building units. The crystal structure of 1 contains a discrete unit that contains a strong Cu(I)···arene interaction, whereas, in 2, the Cu2I2 units act as a linear linker and form a one-dimensional zigzag chain. Complex 3 exhibits a two-dimensional layer in which the 1D polymeric chains of halide bridged Cd(II) ions are linked by the organic ligand L. The crystal structures of 4 and 5 contain a 1D zigzag chain and a discrete hydrogen bonded dimer, respectively. The crystal structure of complex 6 contains nitrate as a counterion and forms an interesting one-dimensional helical chain containing cavities that are occupied by THF molecules. In these crystal structures, the ligand L is found to exhibit four different conformations. The Cambridge Structural Database was used to rationalize the results obtained here and to provide some insight into the metal coordination geometries, the halide bridging of metal centers, as well as metal···arene interactions.本研究合成了一种新型有机配体1,4-双[2-(1-甲基苯并咪唑-2-基甲基)]苯（L），并确定了其晶体结构。探索了配体L在不同条件下与多种金属盐形成配位聚合物的能力。通过室温下直接混合或分层扩散法，将配体L与相应金属盐反应，成功合成了6种配合物：1. [Cu₂(L)I₂]；2. [Cu₂(L)I₂]；3. [Cd₃(L)Cl₆·2DMF（N,N-二甲基甲酰胺）]；4. [Cu(L)Cl₂]；5. [Zn(L)I₂·MeOH（甲醇）]；6. [Cd(L)(NO₃)₂·H₂O]·2THF（四氢呋喃）。单晶X射线衍射分析结果表明，配合物1与2互为同分异构体，二者均含有Cu₂I₂结构基元。配合物1的晶体结构中存在一个离散单元，其中包含强Cu(I)···芳环相互作用；而配合物2中，Cu₂I₂结构基元作为线性连接体，构筑出一维锯齿形链状结构。配合物3呈现二维层状结构，其中卤桥联Cd(II)离子构成的一维聚合物链通过有机配体L相互连接。配合物4和5的晶体结构分别为一维锯齿链和离散氢键合二聚体。配合物6的晶体结构以硝酸根作为抗衡离子，构筑出一种有趣的一维螺旋链结构，链内存在可供THF分子占据的空腔。在上述所有晶体结构中，配体L共呈现四种不同的构象。本研究借助剑桥结构数据库（Cambridge Structural Database, CSD）对实验结果进行了合理化分析，并为金属配位几何构型、金属中心的卤桥联作用以及金属···芳环相互作用的研究提供了新的见解。