Copper(ii) complexes of 2,6-bis(3-tert-butylpyrazol-1-yl)pyridine

Abstract

The stereochemical preferences of copper complexes of 2,6-bis(3-tert-butylpyrazolyl)pyridine (L¹Bu^t) have been investigated. The single crystal X-ray structures of [{Cu(μ-Cl)(L¹Bu^t)}₂][BF₄]₂ (3a), [{Cu(μ-Cl)(OH₂)(L¹Bu^t)}₂][BF₄]₂ (3b) and [Cu(NCMe)₂(L¹Bu^t)][BF₄]₂ (4) show distorted tetragonal geometries at Cu, with one or two axial solvent and/or BF₄⁻ ligands. The Cu centres in 3a and 3b are weakly associated into dimers, through axial Cu–Cl⋯Cu bridging. Single crystals of 4 undergo an unusual substitution of their MeCN ligands upon exposure to air, yielding [Cu(OH₂)₂(L¹Bu^t)][BF₄]₂ (1). A combination of UV/vis, EPR and conductivity studies has shown that Cu(II)-bound L¹Bu^t is labile in solution. Susceptibility data show that the Cu ions in 3a are weakly antiferromagnetically coupled through the Cl⁻ bridges, although this compound exhibits a spin-triplet EPR spectrum in the solid. Cyclic voltammograms of 3a and 4 in MeCN–0.1 M NBuⁿ₄BF₄ confirm the lability of Cu-bound L¹Bu^t.