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

Reaction of 3-(2-pyridyl)pyrazole with alpha,alpha'-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 Angstrom 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 CuO(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-coordinate [CuL(SiF6)] fragments, the latter displaying the first known example of the hexafluorosilicate anion acting as a bidentate chelating F,F-donor.