New binuclear copper(II) coordination polymer based on mixed pyrazolic and oxalate ligands: structural characterization and mechanical properties

A new inorganic-organic coordination polymer based on a copper(II) binuclear complex coordinated with pyrazole (L1), 1-(hydroxymethyl) pyrazole) (L2) and oxalate (Ox) ligands has been unexpectedly obtained. The crystal structure of this coordination polymer has been unequivocally determined from single crystal X-ray diffraction. One copper(II) center (Cu1) is four-coordinated with two nitrogens (N2, L1 and N3, L2), one oxygen (O1, L1) and one chlorine atom, while the other copper(II) nucleus (Cu2) is five-coordinated with one nitrogen (N1, L1), three oxygens (O1, L2; O2 and O3, Ox) and one chlorine atom, giving slightly distorted square-planar and square-pyramidal geometries, respectively. To the best of our knowledge, such coordination environments have never been previously observed to coexist in the same structure. The terminal chlorine (Cl1) forms the connecting bridge between the planar binuclear [Cu2Cl(Ox)(0.5)-(L1)(L2)](n) units ending in an attractive structural framework. An extended layered structure staggered along the b-axis is observed in the supramolecular view. Nanoindentation experiments were carried out and relevant mechanical parameters such as hardness, Young's modulus, indentation energies and elastic recovery were determined. Additionally, a comparative analysis between the supramolecular structure and the mechanical properties is reported.