An “S”-shaped pentanuclear CuII cluster derived from the metal-assisted hydrolysis of pyCOpyCOpy: structural, magnetic and spectroscopic studies

Abstract

Reaction of [Cu₂(O₂CMe)₄(H₂O)₂] with 2,6-di-(2-pyridylcarbonyl)-pyridine (pyCOpyCOpy or dpcp) in MeCN–H₂O 10 : 1, led to the pentanuclear copper(II) complex [Cu₅(O₂CMe)₆{pyC(O)(OH)pyC(O)(OH)py}₂] (1) which crystallizes in the triclinic P space group. The copper(II) atoms are arranged in an “S”-shaped configuration, and are bridged by the doubly deprotonated bis(gem-diol) form of the ligand, pyC(O)(OH)pyC(O)(OH)py²⁻. Magnetic susceptibility data indicate the interplay of both ferro- and antiferromagnetic intramolecular interactions stabilizing an S = 3/2 ground state. Fitting of the data according to a next-nearest-neighbour model {Ĥ = −[J₁(Ŝ₁Ŝ₂ + Ŝ_1′Ŝ_2′) + J₂(Ŝ₂Ŝ₃ + Ŝ_3′Ŝ_2′) + J₃(Ŝ₁Ŝ₃ + Ŝ_3′Ŝ_1′) + J₄(Ŝ₂Ŝ_2′)]} yields exchange coupling constants J₁ = +39.7 cm⁻¹, J₂ = −15.9 cm⁻¹, J₃ = −8.3 cm⁻¹ and J₄ = +4.3 cm⁻¹, leading to an S = 3/2 ground state. X-Band EPR spectroscopy indicates a zero-field splitting of the ground state with |D_3/2| = 0.38 cm⁻¹.