Theoretical predictions of properties and gas-phase chromatography behaviour of carbonyl complexes of group-6 elements Cr, Mo, W, and element 106, Sg

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

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, ΔHads, 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 ΔHads 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.

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.

The periodic table – an experimenter’s guide to transactinide chemistry

The fundamental principles of the periodic table guide the research and development of the challenging experiments with transactinide elements. This guidance is elucidated together with experimental results from gas phase chemical studies of the transactinide elements with the atomic numbers 104–108 and 112–114. Some deduced chemical properties of these superheavy elements are presented here in conjunction with trends established by the periodic table. Finally, prospects are presented for further chemical investigations of transactinides based on trends in the periodic table.

Reactions of fission products from a 252Cf source with NO and mixtures of NO and CO in an inert gas

Fission products recoiling from a 252Cf spontaneous fission source were stopped in various mixtures of inert gases containing CO and NO. For the elements of the transisition metal series Mo, Tc, Ru, and Rh previous observations of pure carbonyl complexes were reproduced. However, no formation of volatile mixed nitrosyl-carbonyl complexes or pure nitrosyl complexes for these elements have been observed. Instead, efficient production of volatile nitrosyl compounds for single iodine atoms, presumably nitrosyl iodide, NOI, was detected. This observation is of interest as potential transport path for iodine in nuclear accident scenarios and as a model for radiochemistry with the recently discovered heaviest halogen tennessine (Z=117).

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.

Encoding of coordination complexes with XML

An in-silico system to encode structure, bonding and properties of coordination complexes is developed. The encoding is achieved through a semantic XML markup frame. Composition of the coordination complexes is captured in terms of central atom and ligands. Structural information of central atom is detailed in terms of electron status of valence electron orbitals. The ligands are encoded with specific reference to the electron environment of ligand centre atoms. Behaviour of ligands to form low or high spin complexes is accomplished by assigning a Ligand Centre Value to every ligand based on the electronic environment of ligand centre atom. Chemical ontologies are used for categorization purpose and to control different hybridization schemes. Complexes formed by the central atoms of transition metal, non-transition elements belonging to s-block, p-block and f-block are encoded with a generic encoding platform. Complexes of homoleptic, heteroleptic and bridged types are also covered by this encoding system. Utility of the encoded system to predict redox electron transfer reaction in the coordination complexes is demonstrated with a simple application.

Decomposition studies of group 6 hexacarbonyl complexes. Part 2: Modelling of the decomposition process

The decomposition behavior of group 6 metal hexacarbonyl complexes (M(CO)6) in a tubular flow reactor is simulated. A microscopic Monte-Carlo based model is presented for assessing the first bond dissociation enthalpy of M(CO)6 complexes. The suggested approach superimposes a microscopic model of gas adsorption chromatography with a first-order heterogeneous decomposition model. The experimental data on the decomposition of Mo(CO)6 and W(CO)6 are successfully simulated by introducing available thermodynamic data. Thermodynamic data predicted by relativistic density functional theory is used in our model to deduce the most probable experimental behavior of the corresponding Sg carbonyl complex. Thus, the design of a chemical experiment with Sg(CO)6 is suggested, which is sensitive to benchmark our theoretical understanding of the bond stability in carbonyl compounds of the heaviest elements.

Chemistry. Superheavy carbonyls

The radioactive superheavy element seaborgium can form a carbonyl compound during its short lifetime [Also see Report by Even et al. ]

Nuclear chemistry. Synthesis and detection of a seaborgium carbonyl complex

Experimental investigations of transactinoide elements provide benchmark results for chemical theory and probe the predictive power of trends in the periodic table. So far, in gas-phase chemical reactions, simple inorganic compounds with the transactinoide in its highest oxidation state have been synthesized. Single-atom production rates, short half-lives, and harsh experimental conditions limited the number of experimentally accessible compounds. We applied a gas-phase carbonylation technique previously tested on short-lived molybdenum (Mo) and tungsten (W) isotopes to the preparation of a carbonyl complex of seaborgium, the 106th element. The volatile seaborgium complex showed the same volatility and reactivity with a silicon dioxide surface as those of the hexacarbonyl complexes of the lighter homologs Mo and W. Comparison of the product's adsorption enthalpy with theoretical predictions and data for the lighter congeners supported a Sg(CO)6 formulation.

Theoretical predictions of properties and volatility of chlorides and oxychlorides of group-4 elements. II. Adsorption of tetrachlorides and oxydichlorides of Zr, Hf, and Rf on neutral and modified surfaces

With the aim to interpret results of gas-phase chromatography experiments on volatility of group-4 tetrachlorides and oxychlorides including those of Rf, adsorption enthalpies of these species on neutral, and modified quartz surfaces were estimated on the basis of relativistic, two-component Density Functional Theory calculations of MCl4, MOCl2, MCl6(-), and MOCl4(2) with the use of adsorption models. Several mechanisms of adsorption were considered. In the case of physisorption of MCl4, the trend in the adsorption energy in the group should be Zr > Hf > Rf, so that the volatility should change in the opposite direction. The latter trend complies with the one in the sublimation enthalpies, ΔH(sub), of the Zr and Hf tetrachlorides, i.e., Zr < Hf. On the basis of a correlation between these quantities, ΔH(sub)(RfCl4) was predicted as 104.2 kJ/mol. The energy of physisorption of MOCl2 on quartz should increase in the group, Zr < Hf < Rf, as defined by increasing dipole moments of these molecules along the series. In the case of adsorption of MCl4 on quartz by chemical forces, formation of the MOCl2 or MOCl4(2-) complexes on the surface can take place, so that the sequence in the adsorption energy should be Zr > Hf > Rf, as defined by the complex formation energies. In the case of adsorption of MCl4 on a chlorinated quartz surface, formation of the MCl6(2-) surface complexes can occur, so that the trend in the adsorption strength should be Zr ≤ Hf < Rf. All the predicted sequences, showing a smooth change of the adsorption energy in the group, are in disagreement with the reversed trend Zr ≈ Rf < Hf, observed in the "one-atom-at-a-time" gas-phase chromatography experiments. Thus, currently no theoretical explanation can be found for the experimental observations.