Carbonyl compounds of Rh, Ir, and Mt: electronic structure, bonding and volatility

Abstract

With the aim to render assistance to future experiments on the production and investigation of chemical properties of carbonyl compounds of element 109, Mt, calculations of the molecular properties of M(CO)₄ and MH(CO)₄, where M = Rh, Ir, and Mt, and of the products of their decomposition, M(CO)₃ and MH(CO)₃, were performed using relativistic Density Functional Theory and Coupled-Cluster methods implemented in the ADF, ReSpect and DIRAC software suites. According to the results, MH(CO)₄ should be formed at experimental conditions from the M atom with a mixture of CO and He gases. The calculated first M–CO bond dissociation energies (FBDE) of Mt(CO)₄ and MtH(CO)₄ turned out to be significantly weaker than those of the corresponding Ir homologs. The reason for that is the relativistic destabilization and expansion of the 6d AOs, responsible for both the weaker σ(CO) → d(M) forth and d(M) → π(CO) back electron density donation in the Mt compounds. The relativistic FBDEs of MH(CO)₄ have, therefore, a Λ-shape behavior in the row Rh–Ir–Mt, while the non-relativistic values increase towards Mt. Using the results of the calculations and a molecule–slab interaction model, the adsorption enthalpies, ΔH_ads, serving as a measure of volatilty, of the group-9 carbonyl hydrides on surfaces of quartz and Teflon were estimated. Accordingly, MtH(CO)₄ should be almost as volatile as RhH(CO)₄ and IrH(CO)₄; however, its interaction with the surfaces should be somewhat weaker than that of IrH(CO)₄. It will, therefore, be difficult to distinguish between group-9 MH(CO)₄ species by measuring their ΔH_ads on surfaces of Teflon and quartz with an experimental uncetainty of ±3 kJ mol⁻¹. The trends in the properties of group-9 carbonyl hydrides should be similar to those of group-6, 7 and 8 carbonyl compounds including those of Sg, Bh and Hs, respectively.