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⁺, Ru^I(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.