Coordination arrays: Synthesis and characterisation of rack-type dinuclear complexes

A series of mono- and dimetallic complexes of rack type containing a dinucleating bis-tridentate ligand and Ru-II-2,2':6',2 ''-terpyridyl (tpy) sites were synthesised and characterised. The H-1 NMR spectra of the dimetallic complexes were correlated to structural features, and the crystal structures of the dimetallic complexes were determined, They provide information about the way in which the central substituent affects the overall shape of the racks and the relative disposition of the metal centres, measured by the pinching angle of the bis-tridentate ligand and the convergence angle of the ancillary tpy units. The latter demonstrates that a CH3 group yields the least bent complex and indicates how parallel the tpy units are. The dimetallic racks exhibit metal-metal interactions mediated by the bis-tridentate ligands as indicated by electrochemical and spectroscopic methods. The bridging-ligand pi(*) orbital and the d(pi) metal orbital are stabilised by complexation of a second metal. The results obtained provide guidelines for the design of extended racks bearing several metal centres in a linear arrangement, which also represent potential components of molecular electronic devices.