Synthesis, structure and properties of a monomeric copper(II) complex with a multidentate pyridylpyrazole ligand

Abstract

Using a potentially multidentate ligand, L⁶ (2,6-bis[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine), having five N donor sites, a new mononuclear copper(II) compound, [Cu(L⁶)][ClO₄]₂, has been synthesized. X-ray crystallographic analysis reveals that it is in the monoclinic space group C2/c with all five donor sites coordinating with copper(II) to provide a distorted trigonal bipyramidal coordination environment around copper. Closer inspection of crystal packing diagram reveals the formation of 2D network structure, assembled via two types of noncovalent interactions. Notably, π … π interactions between π electron cloud of pyridine rings of pyridylpyrazole unit lead to the formation of a linear chain, which is then connected to another chain via C–H … π interactions involving pyridyl C–H (4-position) of central pyridine ring of L⁶ and π electron cloud of pyridine ring of pyridylpyrazole unit in a bifurcated fashion. Coordination geometry in solution (MeCN) state has been assessed by absorption and EPR spectroscopy. Cyclic voltammetry reveals inherent flexibility of the ligand system to allow stabilization of copper(I) oxidation state.