(trans-1,4-bis[(4-pyridyl)ethenyl]benzene)(2,2'-bipyridine)ruthenium(II) complexes and their supramolecular assemblies with beta-cyclodextrin

Two novel ruthenium polypyridine complexes, Ru(bpy)(2)Cl(BPEB)](PF(6)) and (Ru(bpy)(2)Cl](2)(BPEB))(PF(6))(2) (BPEB = trans-1,4-bis2-(4-pyridyl)ethenyl]benzene), were synthesized and their characterization carried out by means of elemental analysis, UV-visible spectroscopy, positive ion electrospray (ESI-MS), and tandem mass (ESI-MS/MS) spectrometry, as well as by NMR spectroscopy and cyclic voltammetry. Cyclic and differential pulse voltammetry for the mononuclear complex showed three set of waves around 1.2 V (Ru(2+/3+)), -1.0 V (BPEB(0/)(-)), and -1.15 (BPEB(-/2-)). This complex exhibited aggregation phenomena in aqueous solution, involving pi-pi stacking of the planar, hydrophobic BPEB ligands. According to NMR measurements and variable-temperature experiments, the addition of beta-cyclodextrin (betaCD) to Ru(bpy)(2)Cl(BPEB)](+) leads to an inclusion complex, breaking down the aggregated array.