Penta- and tetracarbonyls of Ru, Os, and Hs: Electronic structure, bonding, and volatility

Application of a novel gas phase synthesis approach to carbonyl complexes of accelerator-produced 5d transition metals

In 2014 the first synthesis of a transactinide carbonyl complex – seaborgium hexacarbonyl – was reported. This was achieved in gas-phase chemical experiments in a beam-free environment behind the recoil separator GARIS. Extending this work to heavier elements requires more efficient techniques to synthesize carbonyl complexes as production rates of transactinide elements drop with increasing atomic number. A novel approach was thus conceived, which retains the benefit of a beam-free environment but avoids the physical preseparation step. The latter reduces the yields for products of asymmetric reactions such as those used for the synthesis of suitable isotopes of Sg, Bh, Hs and Mt. For this a series of experiments with accelerator-produced radioisotopes of the lighter homologues W, Re and Os was carried out at the tandem accelerator of JAEA Tokai, Japan. A newly developed double-chamber system, which allows for a decoupled recoil ion thermalization and chemical complex formation, was used, which avoids the low-efficiency physical preseparation step. Here, we demonstrate the feasibility of this newly developed method using accelerator-produced short-lived radioisotopes of the 5d homologues of the early transactinides.

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

First bond dissociation energies and other properties have been predicted for carbonyl compounds of group-9 elements including those of element 109, Mt, from relativistic DFT and CC calculations. A remarkable Λ-shape of the trends is observed, caused by strong relativistic effects on the valence AOs of Mt.

Relativity in the electronic structure of the heaviest elements and its influence on periodicities in properties

Theoretical chemical studies demonstrated crucial importance of relativistic effects in the physics and chemistry of superheavy elements (SHEs). Performed, with many of them, in a close link to the experimental research, those investigations have shown that relativistic effects determine periodicities in physical and chemical properties of the elements in the chemical groups and rows of the Periodic Table beyond the 6th one. They could, however, also lead to some deviations from the established trends, so that the predictive power of the Periodic Table in this area may be lost. Results of those studies are overviewed here, with comparison to the recent experimental investigations.

Production and study of chemical properties of superheavy elements

Some highlight examples on the study of production and chemical properties of heaviest elements carried out mostly at GSI Darmstadt are presented. They focus on the production of some of the heaviest known elements (114Fl, 115Mc, and 117Mc), studies of non-fusion reactions, and on chemical studies of 114Fl. This is the heaviest element, for which chemical studies have been performed to date.

Carbonyl compounds of Tc, Re, and Bh: Electronic structure, bonding, and volatility

Calculations of molecular properties of M(CO)₅ and MH(CO)₅, where M = Tc, Re, and Bh, and of the products of their decomposition, M(CO)₄ and MH(CO)₄, were performed using density functional theory and coupled-cluster methods implemented in the relativistic program suits such as ADF, DIRAC, and ReSpect. The calculated first M-CO bond dissociation energies (FBDEs) of Bh(CO)₅ and BhH(CO)₅ turned out to be significantly weaker than those of the corresponding Re homologs. The reason for that is the relativistic destabilization and expansion of the 6d AOs, responsible for weaker σ-forth and π-back donations in the Bh compounds. The relativistic FBDEs of M(CO)₅ have, therefore, a Λ-shape behavior in the row Tc-Re-Bh, while the non-relativistic values increase toward Bh. Using the results of the molecular calculations and a molecule-slab interaction model, adsorption enthalpies, ΔH _ads, of group-7 carbonyl hydrides on quartz and Teflon were estimated for future gas-phase chromatography experiments. It was found that BhH(CO)₅ should be almost as volatile as the homologs, although its interaction with the surfaces should be somewhat stronger than that of MH(CO)₅ (M = Tc and Re), while the M(CO)₄ (M = Tc, Re, and Bh) molecules should be non-volatile. It will, therefore, be difficult to distinguish between the group-7 MH(CO)₅ species by measuring their ΔH _ads on surfaces of Teflon and quartz with an error bar of ±4 kJ/mol. The trends in properties and ΔH _ads of group-7 carbonyl hydrides are similar to those of group-8 carbonyls of Ru, Os, and Hs.