A novel dinuclear double-stranded helical complexes of bis(terdentate) N4O2 donor ligand with silver(I) and zinc(II) d10 metal ions

Reaction of the hexadentate N4O2-donor ligand 6,6'-bis(3-hydrazonobutan-2-one)-2,2'-bipyridine (L) with Ag-(I) and Zn-(II) affords a dinuclear double stranded helicate species [Ag2L2](2+) (1a) and [Zn2L2](2+) (1b), in which partitioning of the ligand into two bis-tridentate pyridyl-ketoimine chelating units allow each ligand to bridge both metal centres. X-ray crystallography, ESI-MS and UV-Vis spectrophotometric titration experiments reveal that the complex (1a) retains its solid-state structure in solution. The crystal structure of(1a) provides the first example of dinuclear silver(I) complex in which both of the metal centres can be approximated as a seven coordinate distorted mono-capped trigonal prism in which the Ag center dot center dot center dot Ag close contact of 3.034(4) angstrom is taken into account and forms the cap. The counter-ions do not interact with metal centres but hydrogen bond to N-H protons of the hydrazonic arms from the separate strands. The adjacent helical units are cross-linked together via NH center dot center dot center dot O-keto hydrogen bonding to maintain the supramolecular structure. (C) 2008 Elsevier Ltd. All rights reserved