Département de chimie moléculaire

The metal bonded ruthenium polymer [Ru0(bpy)(CO)2]n (bpy = 2,2'-bipyridine) is known to be a very promising and efficient solid material for catalysis applications, such as carbon dioxide electroredn. in pure aq. media and the water-gas shift reaction. It also exhibits potential application for mol. electronics as a conductive mol. wire. The insoly. and relative air-sensitivity of [Ru0(bpy)(CO)2]n as well as the lack of monocrystals make its structural characterization very challenging. A first approach to det. the structure of this polymer has been obtained by ab initio x-ray powder diffraction, based on the known X-ray structure of [Ru(CO)4]n. In order to refine this structure, a non-conventional solid-state NMR study was performed. The results of this study are presented here. The comparison of high-resoln. solid-state 13C NMR spectra of the polymer with those of the corresponding monomeric [Ru(bpy)(CO)2Cl2] or dimeric [Ru(bpy)(CO)2Cl]2 precursor complexes showed a clear shift and splitting of carbonyl ligand resonances, which turns out to be linearly correlated with the redox state of the Ru(II, I or 0, resp.). Bipyridine resonances are also affected but in a non-trivial way. Finally, in the case of the dimer, the CO peak splitting (2.7 ppm) contains structural information, e.g. the ligand staggering angle. Based on DFT chem. shift calcns. on corresponding model mols. (n = 1-2), all the described exptl. observations could be reproduced. Moreover, upon extending these calcns. to models of increasing length (n = 3-5), information about the staggering angle between successive ligands is actually retained in the CO NMR computed peak splitting. Turning back to expts., the CO broad signal measured for the wire could be decompd. into a major component (at 214.9 ppm) assigned to the internal CO ligands, and a minor doublet component (216.9 and 218.1 ppm) whose splitting (2.8 ppm) contains the staggering angle information. Finally, from the relative integrals of these three components, expected to be in the ratio 1:1 : n-2, it was possible to tentatively est. the length n of the polymetallic wire (n = 7). [on SciFinder(R)]