Coordination Behaviour of Bis-Terdentate N-Donor Ligands: Double- and single-stranded helicates, mesocates, and cyclic oligomers

Three new ligands have been prepared in which two terdentate chelating pyrazolyl-bipyridine units are connected by a central aromatic spacer via methylene hinges: the spacers are o-phenylene (LPh), 2,6-pyridine-diyl (LPy) and 2,3-naphthalenediyl (Lnaph). The ligands act as potentially hexadentate bridging ligands, with the central pyridyl N atom of LPy not involved in coordination. The following complexes were prepared and structurally characterised: [M2(LPh)2][ClO4]4 (M = Ni, Cu), which are dinuclear double helicates; [Ag2(LPh)(MeCN)2][BF4]2, a dinuclear complex with an Ag···Ag bond in which the ligand adopts a helical twist around the pair of metal ions; [Ni2(LPy)2][BF4]4, an achiral mesocate with a box-like structure and a face-to-face arrangement of ligands; [Ag3(Lnaph)2](BF4)3, which contains a linear trinuclear array of AgI ions with the two ligands arranged in a shallow helical twist, each ligand spanning one terminal and the central metal ion; and [Cd6(Lnaph)6](ClO4)12, a cyclic hexanuclear helicate with a perchlorate anion in the central cavity. Both [Cu2(LPh)2][ClO4]4 and [Cd6(Lnaph)6](ClO4)12, which have architecturally similar bridging ligands, show evidence by electrospray mass spectrometry for formation of a range of cyclic oligomers in solution up to 11-mers for the CdII/Lnaph system.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)