Directed evolution of the periodic table: probing the electronic structure of late actinides

Creation of an unexpected plane of enhanced covalency in cerium(III) and berkelium(III) terpyridyl complexes

Controlling the properties of heavy element complexes, such as those containing berkelium, is challenging because relativistic effects, spin-orbit and ligand-field splitting, and complex metal-ligand bonding, all dictate the final electronic states of the molecules. While the first two of these are currently beyond experimental control, covalent M‒L interactions could theoretically be boosted through the employment of chelators with large polarizabilities that substantially shift the electron density in the molecules. This theory is tested by ligating BkIII with 4'-(4-nitrophenyl)-2,2':6',2"-terpyridine (terpy*), a ligand with a large dipole. The resultant complex, Bk(terpy*)(NO3)3(H2O)·THF, is benchmarked with its closest electrochemical analog, Ce(terpy*)(NO3)3(H2O)·THF. Here, we show that enhanced Bk‒N interactions with terpy* are observed as predicted. Unexpectedly, induced polarization by terpy* also creates a plane in the molecules wherein the M‒L bonds trans to terpy* are shorter than anticipated. Moreover, these molecules are highly anisotropic and rhombic EPR spectra for the CeIII complex are reported.

Covalency of Trivalent Actinide Ions with Different Donor Ligands: Do Density Functional and Multiconfigurational Wavefunction Calculations Corroborate the Observed "Breaks"?

A comprehensive ab initio study of periodic actinide-ligand bonding trends for trivalent actinides is performed. Relativistic density functional theory (DFT) and complete active-space (CAS) self-consistent field wavefunction calculations are used to dissect the chemical bonding in the [AnCl₆]^3-, [An(CN)₆]^3-, [An(NCS)₆]^3-, [An(S₂PMe₂)₃], [An(DPA)₃]^3-, and [An(HOPO)]^- series of actinide (An = U-Es) complexes. Except for some differences for the early actinide complexes with DPA, bond orders and excess 5f-shell populations from donation bonding show qualitatively similar trends in 5f ⁿ active-space CAS vs DFT calculations. The influence of spin-orbit coupling on donation bonding is small for the tested systems. Along the actinide series, chemically soft vs chemically harder ligands exhibit clear differences in bonding trends. There are pronounced changes in the 5f populations when moving from Pu to Am or Cm, which correlate with previously noted "breaks" in chemical trends. Bonding involving 5f becomes very weak beyond Cm/Bk. We propose that Cm(III) is a borderline case among the trivalent actinides that can be meaningfully considered to be involved in ground-state 5f covalent bonding.

Systematic investigation of the magneto-electronic structure and optical properties of new halide double perovskites Cs2NaMCl6 (M = Mn, Co and Ni) by spin polarized calculations

A cohesive study using density functional theory simulations is performed to reveal and understand the structural stability, optoelectronic and magnetic properties of Cs₂NaMCl₆ (M = Mn, Co and Ni) halide double perovskites. The exchange-correlation potential, which is the only unknown parameter in the state-of-the-art formulism is determined through the well-known generalized gradient approximation and integration of the mBJ potential to it. The structural optimization, mechanical stability criteria and tolerance factor confirmed the stability of the double perovskites in a cubic structure with Fm3̄m symmetry. The elastic constants endorsed the mechanical stability and justify the brittle character of these double perovskites. The spin polarized electronic band profile and behaviour of the dielectric constant and absorption coefficient in the spin up and down channels revealed the presence of half-metallic nature in these materials. Moreover, herein, we have discussed the origin of the half-metallic gap and magnetism. The unpaired electrons in the crystal field splitted d-orbitals of the M-sited constituents are responsible for the half-metallic and magnetic character. The total magnetic moment was determined to be 4μ_B, 4μ_B and 1μ_B for the Mn-, Co- and Ni-based double perovskites, respectively, with main contributions solely coming from the transition metal atoms. The perfect spin polarization at the Fermi level suggests the application of double perovskites in spintronic technology.

The unpaired electrons in the crystal field splitted d-orbitals of the M-site constituents are responsible for the half metallicity and magnetic character of the halide double perovskites.

Evolution of the periodic table through the synthesis of new elements

This brief introduction to the synthesis and chemistry of elements discovered since 1940 is focused primarily on Z=93–118. The goal of this work is not to simply catalogue the nuclear fusion reactions needed to prepare new elements, but rather to focus on the chemical and physical properties that these elements possess. These elements share a single common feature in that they all have large Z values, and thus have electronic structures that are significantly altered by both scalar relativistic effects and spin-orbit coupling. These effects scale nonlinearly with increasing Z and create unexpected deviations both across series and down groups of elements. The magnitude of these effects is large enough that orbital energies rearrange and mix in ways that complicate incomplete depictions of electronic structure that are based solely on electron repulsion. Thus, the primary aim of this review is to document the impact of relativistic effects on electronic structure and how this has altered not just our understanding of the chemistry of heavy elements, but has even created in the need to rearrange the Periodic Table itself.

Structural Characteristics, Population Analysis, and Binding Energies of [An(NO3)]2+ (with An = Ac to Lr)

Efficient predictive capabilities are essential for the actinide series since regulatory constraints for radioactive work, associated costs needed for specialized facilities, and the short half-lives of many actinides present great challenges in laboratory settings. Improved predictive accuracy is advantageous for numerous applications including the optimization and design of separation agents for nuclear fuel and waste. One limitation of calculations in support of these applications is that the large variations observed from predictions obtained with currently available methods can make comparisons across studies uncertain. Benchmarking currently available computational methodologies is essential to establish reliable practices across the community to guarantee an accurate physical description of the systems studied. To understand the performance of a variety of common theoretical methods, a systematic analysis of differences observed in the prediction of structural characteristics, electron withdrawing effects, and binding energies of [An(NO3)]2+ (with An = Ac to Lr) in gas and aqueous phases is reported. Population analysis obtained with Mulliken and Löwdin reflect a large dependence on the level of theory of choice, whereas those obtained with natural bond orbital show larger consistency across methodologies. Predicted stability across the actinide series calculated with coupled cluster with perturbative doubles and triples at the triple ζ level is equivalent to the one obtained when extrapolated to the complete basis set limit. The ground state of [Fm(NO3)]2+ and [Md(NO3)]2+ is predicted to have an electronic structure corresponding to An III state in gas and An IV in aqueous phase, whereas the ground state of [An(NO3)]2+ (with An = Ac to Es, Lr) presents an electronic structure corresponding to An IV in the gas and aqueous phase. The compounds studied with No in gas and aqueous phase present a preferred No III state, and the Lr compounds did not follow trends predicted for the rest of the actinide series, as previously observed in studies regarding its unusual electronic structure relative to its position in the periodic table.