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

Abstract

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-dicarboxylate (HPIDC(2-)) has been proven to be an excellent multidentate ligand due to its multiple deprotonation and coordination modes. Crystals of poly[aquabis[μ3-5-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(II)Cu(I)2(C10H5N3O4)2(H2O)]n, (I), were obtained from 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid (H3PIDC) 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 (CuN2O3), 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 [CuN2O] unit, deprotonated HPIDC(2-) 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(2-) ligands in the polymer serve as T-shaped 3-connectors and adopt a μ3-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 crosslinking of these chains by HPIDC(2-) ligands along the b axis in a -Cu2-HPIDC(2-)-Cu3-HPIDC(2-)-Cu1- 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 thermogravimetric analysis shows the loss of the apical aqua ligand before decomposition of the title compound.

Toward a Rational Design of 3d-4f Heterometallic Coordination Polymers based on Mixed Valence Copper Centers

“…Another interesting feature in the compound reported by Luo et al is the presence of Cu I centers in the linear CuO 2 and CuN 2 environment, similar to that of 1 and 2 . Linear conformations are common in other d 10 coordination polymers such as Au I , and Ag I ; , however, Cu I is usually reported presenting trigonal , and tetrahedral , geometries, while Cu I /Cu II and Cu I CPs containing linear Cu I are more scarce . On the other hand, according to the Robin and Day classification, 1 and 2 can be described as Class I mixed valence compounds, since in both structures the Cu I and Cu II cations can be identified by the difference in their coordination geometries. , …”

“…48 Another interesting feature in the compound reported by Luo et al is the presence of Cu I centers in the linear CuO 2 and CuN 2 environment, similar to that of 1 and 2. Linear conformations are common in other d 10 coordination polymers such as Au I49,50 and Ag I ; 51,52 however, Cu I is usually reported presenting trigonal 53,54 and tetrahedral 55,56 geometries, while Cu I /Cu II and Cu I CPs containing linear Cu I are more scarce. 57 On the other hand, according to the Robin and Day classification, 1 and 2 can be described as Class I mixed valence compounds, since in both structures the Cu I and Cu II cations can be identified by the difference in their coordination geometries.…”