Synthesis, crystal structure, and electrochemical properties of µ-{2,5-bis[N,N-bis(2′-pyridylmethyl)aminomethyl]pyrazine}-bis[chlorocopper(II)] perchlorate

Abstract

Reaction of the octadentate ligand 2,5-bis[N,N-bis(2′-pyridylmethyl)aminomethyl]pyrazine (L¹) and copper(II) chloride produces a binuclear complex, which crystallized in green (1) and blue (2) forms, [Cu₂L¹Cl₂][ClO₄]₂·nCH₃OH [n= 2 for (1) and 0 for (2)]. The structures of the two complexes have been determined by X-ray analysis. Complex (1) crystallizes in the orthorhombic space group Pcab with a= 14.895(2), b= 19.559(3), c= 13.263(2)Å, and Z= 4, and complex (2) crystallizes in the triclinic space group P with a= 10.004(1), b= 12.212(2), c= 7.791(1)Å, α= 100.99(1), β= 86.26(1), γ= 111.76(1)°, and Z= 1. The complex cations in (1) and (2) have centrosymmetric binuclear structures with copper atoms in distorted trigonal-bipyramidal and square-pyramidal geometries, respectively. The electronic spectrum in acetonitrile solution revealed that the structure in solution is the same as in complex (1). E.s.r. and magnetic susceptibility data for (1) and (2) show the absence of a strong magnetic interaction between the copper atoms. The compound in acetonitrile shows a quasi-reversible cyclic voltammogram which has E_pc and E_pa at –0.29 and –0.13 V vs. Ag–AgCl with shoulders observable. Controlled-potential electrolysis demonstrates that the process involves the transfer of two electrons. The two-step reduction potentials leading to Cu^II–Cu^I and Cu^I–Cu^I from Cu^II–Cu^II were estimated to be –0.14 and –0.26 V, respectively, by using the width method for the ΔE_p and E_p–E_p^½ values.