Synthesis, crystal structure, and magnetic properties of a ferromagnetically coupled angular trinuclear copper(II) complex [Cu₃(O₂CMe)₄(bpy)₃(H₂O)](PF₆)₂

Abstract

The synthesis, X-ray crystal structure, and magnetic properties of an angular trinuclear copper(II) complex [Cu₃(O₂-CMe)₄(bpy)₃(H₂O)](PF₆)₂ (1), obtained from a reaction of Cu₂(O₂CMe)₄(H₂O)₂ with 2,2'-bipyridine (bpy) and NH₄PF₆ in ethanol, are reported. Complex 1 crystallizes in triclinic space group P1̅ with a=11.529(1) Å, b=12.121(2) Å, c=17.153(2) Å, α=82.01(1)°, β=79.42(1)°, γ=89.62(1)°, and Z=2. A total of 6928 data with I>2.5σ(I) were refined to R=0.0441 and R_w=0.0557. The structure consists of a trinuclear core bridged by four acetate ligands showing different bonding modes. The coordination geometry at each copper is distorted square-pyramidal with a CuN₂O₂···O chromophore. The Cu···Cu distances are 3.198(1) Å, 4.568(1) Å, and 6.277(1) Å. There are two monoatomic acetate bridges showing Cu-O-Cu angles of 93.1(1) and 97.5(1)°. Magnetic studies in the temperature range 39-297 K show the presence of a strong ferromagnetically coupled dicopper(II) unit (2J = +158 cm^-1) and an essentially isolated copper(II) center (2J' = -0.4 cm^-1) in 1. The EPR spectra display an axial spectrum giving g_||=2.28 (A_||=160×10^-4 cm^-1) and g_⊥ = 2.06 (A_⊥= 12×10^-4 cm^-1) for the normal copper and two intense isotropic signals with g values 2.70 and 1.74 for the strongly coupled copper pair. The structural features of 1 compare well with the first generation models for ascorbate oxidase.