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 affo rds a new tetradentate ligand L having two bidentate pyridyl-pyrazole compartments linked by an o-CH2C6H4CH2 spacer. With Cu-I, L forms a di nuclear double helicate [Cu2L2][PF6](2) in which both ligands are brid ging 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 bipy ramidal both in the solid state (by X-ray crystallography) and in solu tion (by EPR spectroscopy). Reaction of L with CuO(MeCO2)(2).H2O affor ds [Cu2L3][BF4](4) which was characterised by mass spectroscopy and el emental analysis. By analogy with the (known) nickel(II) analogue, thi s complex has one ligand acting as a bis-bidentate bridge between two {CuL}(2+) fragments in which L acts as a terminal tetradentate chelati ng ligand. Recrystallisation of this afforded a few crystals of the de composition product [CuL(MeOH)][CuL(SiF6)][BF4](2), which contains tri gonal-bipyramidal [CuL(MeOH)](2+) and six-coordinate [CuL(SiF6)] fragm ents, the latter displaying the first known example of the hexafluoros ilicate anion acting as a bidentate chelating F,F-donor.