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

With the aim to render assistance to future experiments on production and investigations of chemical properties of carbonyl compounds of element 109, Mt, calculations of 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 the mixture of the 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 weaker both the σ(CO) → d(M) forth and d(M) → π(CO) back electron density donations in the Mt compounds. The relativistic FBDEs of MH(CO)4 have, therefore, Λ-shape behavior in the row Rh-Ir-Mt, while the non-relativistic values increase towards Mt. Using results of the molecular calculations and a molecule-slab interaction model, adsorption enthalpies, ΔHads, serving as a measure of volatility, of the group-9 carbonyl hydrides on surfaces of quartz and Teflon were estimated. Accordingly, MtH(CO)4 should be also 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 ΔHads on surfaces of Teflon and quartz with an experimental uncertainty of ± 3 kJ/mol. 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.