Double-helical dinuclear copper(I) and mononuclear copper(II) complexes of a compartmental tetradentate bridging ligand: crystal structures and spectroscopic properties

Abstract

Reaction of 3-(2-pyridyl)pyrazole with α,α′-dibromoxylene affords a new tetradentate ligand L having two bidentate pyridyl-pyrazole compartments linked by an o-CH₂C₆H₄CH₂ spacer. With Cu^I, L forms a dinuclear double helicate [Cu₂L₂][PF₆]₂ in which both ligands are bridging both pseudo-tetrahedral metal ions, which are 5.05 Å apart. However L does not support a double helical architecture with Cu^II. Reaction of L with CuCl₂ affords [CuLCl][BF₄] which is trigonal bipyramidal both in the solid state (by X-ray crystallography) and in solution (by EPR spectroscopy). Reaction of L with Cu(MeCO₂)₂·H₂O affords [Cu₂L₃][BF₄]₄ which was characterised by mass spectroscopy and elemental analysis. By analogy with the (known) nickel(II) analogue, this complex has one ligand acting as a bis-bidentate bridge between two {CuL}²⁺ fragments in which L acts as a terminal tetradentate chelating ligand. Recrystallisation of this afforded a few crystals of the decomposition product [CuL(MeOH)][CuL(SiF₆)][BF₄]₂, which contains trigonal-bipyramidal [CuL(MeOH)]²⁺ and six-co-ordinate [CuL(SiF₆)] fragments, the latter displaying the first known example of the hexafluorosilicate anion acting as a bidentate chelating F,F-donor.