Reaction of Re-2{mu-O2CC(CH3)(3)}(4)Cl-2 with [(CO)(5)M-CN]Na (M = Cr, Mo, W) leads to tetranuclear complexes of formula Re-2{mu-O2CC(CH3)(3)}(4)[-NC-M(CO)(5)](2) (M = Cr, Mo, W). These complexes were characterized by H-1-, C-13-, and Mo-95-NMR, IR and Raman spectroscopy, elemental analysis and examined by cyclic voltammetry. The applied methods show the donor capabilities of the [(CO)(5)M-CN](-) ligands which shift electron density towards the Re centers weakening the Re-Re quadruple bond. The Re-Re bond lengths and the v(Re-Re) force constants are estimated based on the FT-IR and Raman examinations. Photochemical examinations and TG/MS experiments have also been conducted. The latter methods shows that the product complexes decompose around 100 degrees C, by first loosing their carbonyl substituents; as do the Cr, Mo, W precursor compounds. The dirhenium tetrapivalate unit decomposes only at higher temperatures in a distinct second step.

The multistate/multifunctional properties of 4'-hydroxyflavylium in a water/ I -n-butyl-3 -methyl-imidazolium hexalluorophosphate (fbmim][PF6]) biphasic system are described. The kinetics and thermodynamics of this flavylium salt have been fully characterised in aqueous solutions and compared to those obtained in [bmim][PF6]. The trans-chalcone is thermally more stable in the ionic liquid but shows efficient photoisomerisation to the cis-chalcone, allowing to define write-read-erase cycles in this biphasic system. (C) 2004 Elsevier B.V. All rights reserved.