Synthesis of a new μ-chlorido-bridged tetra-nuclear copper(II) complex containing 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz), chlorido and perchlorato ligands: non-planar central pyrazine rings

Abstract

A μ-chlorido-bridged tetra-nuclear copper(II) complex containing 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz), chlorido, and perchlorato ligands, starting from 2-aminomethyl pyridine (AMP) and Cu(OAc)2·H2O, was synthesized. The structure of the complex was determined by single-crystal X-ray diffraction (SCXRD), Fourier transform infrared spectroscopy (FT-IR), and electronic absorption spectroscopy (UV–Vis). The redox behavior of the complex was explored by cyclic voltammetry. The tetra-nuclear structure is formed by combining the di-nuclear copper complex of the two tppz ligands with a chloride bridge. The Cu(1) center adopts a distorted octahedral geometry, whereas the other three Cu centers adopt square pyramid geometries. Crystal data of the complex are monoclinic, P21/c, a = 13.602(4) Å, b = 13.438(4) Å, c = 29.412(8) Å, α = 90°, β = 95.258(8)°, γ = 90°, V = 5353(3) Å3, Z = 4. When the SCXRD structure was examined, it was determined that the two central pyrazine rings deviated from planarity, which is one of the four criteria for aromaticity. The aromaticity of the central pyrazine rings, whose planarity is disturbed, is decreased. Based on these bond lengths, the harmonic oscillator aromaticity model (HOMA) values of the non-planar central pyrazine rings were calculated as 0.964926 and 0.942886, respectively.