Comprehensive structural and spectroscopic study of intrazeolite anchoring of ruthenium carbonyl clusters

Abstract

[Ru3(CO)12] guests in Na56Y were thermally activated from 298 to 363 K, in a hydrogen atmosphere, generating intrazeolitic [H4Ru4(CO)12]. Hexaammineruthenium(III) complexes in Na56X have been thermally activated progressively from 298 to 393 K, in CO and H2 atmospheres. The generation process is via conversion of the intermediate [Ru(NH3)5(CO)]2+, RuI(CO)3 to [Ru6(CO)18]2−. The characterization of the structure and properties of these samples used a multi-analytical approach based on FTIR, UV-VIS, EXAFS spectroscopies and CO and H2 gas chemisorption. The research encompassed several key points as follows: (i) kinetics of the intrazeolitic diffusion of [Ru3(CO)12] clusters; (ii) oxidation fragmentation under O2 atmosphere and reductive regeneration under CO and H2 chemisorption with temperature-programmed heating for the intrazeolite anchoring of [Ru6(CO)18]2−; (iii) internal vs. external confinement of ruthenium carbonyl clusters; (iv) intrazeolite anchoring of ruthenium carbonyl clusters shows a strong reaction with the extraframework Na+ α-cage cations, through involvement of the oxygen end of the bridging or equatorial terminal carbonyl ligands; (v) comparison of orbitally degenerate ground-state for free Ru carbonyl clusters vs. the intrazeolitic anchoring site provides a theoretical indication of the symmetry distortion.These multi-analytical spectroscopic methods should motivate both new and established scientists to study further the anchoring of metal carbonyl clusters with other types of zeolite (such as ZSM-5 or MCM-41). Faujasite mediated synthesis of metal carbonyl clusters can provide routes to compounds which are not accessible by conventional solution techniques. Further, higher yield clusters, as well as a better understanding of the nucleation process of cluster formation and of the resulting chemical properties can be expected.