A two-dimensional mixed-valence Cu~II/Cu~I coordination polymer constructed from 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate

摘要

Coordination polymers are a thriving class of functional solid-state materials and there have been noticeable efforts and progress toward designing periodic functional structures with desired geometrical attributes and chemical properties for targeted applications. Self-assembly of metal ions and organic ligands is one of the most efficient and widely utilized methods for the construction of CPs under hydro(solvo)thermal conditions. 2-(Pyridin-3-yl)-1H-imidazole-4,5-di-carboxylate (HPIDC~2- ) has been proven to be an excellent multidentate ligand due to its multiple deprotonation and coordination modes. Crystals of poly-[aquabis[μ_3-5-carboxy-2-(pyridin-3-yl)-1H-imidazole-4-carboxylato-κ~5: N~1 ,O~5 :-N~3,O~4:N~2]copper(II)dicopper(I)], [Cu~IICu~I_2(C_10H_5N_3O_4)_2(H_2O)]_n, (I), were obtained from 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid (H_3PIDC) and copper(II) chloride under hydrothermal conditions. The asymmetric unit consists of one independent Cu~II ion, two Cu~I ions, two HPIDC~2- ligands and one coordinated water molecule. The Cu~II centre displays a square-pyramidal geometry (CuN_2O_3), with two N,O-chelating HPIDC~2- ligands occupying the basal plane in a trans geometry and one O atom from a coordinated water molecule in the axial position. The Cu~I atoms adopt three-coordinated Y-shaped coordinations. In each [CuN_2O] unit, deprotonated HPIDC acts as an N,O-chelating ligand, and a symmetry-equivalent HPIDC~2- ligand acts as an N-atom donor via the pyridine group. The HPIDC ligands in the polymer serve as T-shaped 3-connectors and adopt a μ_3-κ~2 N,O:κ~2 N' ,O':κN''-coordination mode, linking one Cu~II and two Cu~I cations. The Cu cations are arranged in one-dimensional -Cu1-Cu2-Cu3- chains along the [001] direction. Further cross-linking of these chains by HPIDC~2- ligands along the b axis in a -Cu2-HPIDC~2-Cu3-HPIDC~2-Cul- sequence results in a two-dimensional polymer in the (100) plane. The resulting (2,3)-connected net has a (12~3)_2(12)_3 topology. Powder X-ray diffraction confirmed the phase purity for (I), and susceptibilty measurements indicated a very weak ferromagnetic behaviour. A thermogravi-metric analysis shows the loss of the apical aqua ligand before decomposition of the title compound.