Electronic Structure and Bonding in Molecular f Element Chemistry

Lead Research Organisation: University of Manchester
Department Name: Chemistry

Abstract

For calculations on molecules containing f-elements, relativistic effects must be explicitly included in calculations and the near-degeneracy of many valence atomic orbitals results in many closely-spaced electronic states. These complications necessitate the use of ab initio wave functional theory (WFT) to obtain a detailed understanding of the electronic structure of f-element containing molecules.

The first focus of the project is on molecules of the general formula EAnF3, where E = N, P, As, Sb and Bi; and An = U, Np, and Pu. Previous calculations suggest that NUF3, NNpF3 and NPuF3 have triple An-N bonds; however other electronic states (corresponding to the unpairing of electrons in the triple bond) are computed to be very close in energy. These excited states may match better with the experimental vibrational spectroscopy of these molecules [Inorg. Chem. 48 (2009) 6594], and so the true electronic structure is not clear.
Initial DFT calculations present a seemingly clear picture for EUF3; increasing multiplicity down group 15 (N: singlet; P, As: triplet; Sb, Bi: quintet), with a bond order of ~1 for all but NUF3 (with a bond order of 3). This does not reflect existing literature which predicts singlet, triple-bonded structures for PUF3 and AsUF3 [Inorg. Chem. 48 (2009) 6594]. Ab initio calculations will be employed to explore this discrepancy.

The initial DFT calculations present a considerably less clear picture for ENpF3 and EPuF3, where spin contamination is very large for low multiplicities. Open-shell electronic ground states are challenging to calculate with DFT, so WFT techniques will be employed to be able to describe their structures.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
1931609 Studentship EP/N509565/1 03/09/2017 31/03/2021 Benjamin Edward Atkinson
 
Description We have performed computational studies on several inorganic molecules containing uranium, most of which feature uranium-nitrogen bonds.

In the first part of the project, we performed calculations on the molecules NUF3, PUF3 and AsUF3 using CASSCF and CASPT2. With these multiconfigurational techniques, certain orbitals must be selected (the 'active space') and all configurations of those orbitals are included in the wavefunction. We identified a triple N-U bond, consistent with previous work, however for PUF3 and AsUF3 we identified a ~single-double bond due the larger active space used in our study,

In the second part, in collaboration with Steve Liddle, University of Manchester, we performed calculations on a novel U(V) - N2 complex; end on pi coordination is typically only observed for low/negative oxidation states. Standard density functional theory (DFT) calculations predict a significantly shorter U-N bond length than observed in the crystal structure. We performed calculations at several levels of theory to explore this, including CASSCF calculations which give a U-N bond distance closer to experiment. This highlights the importance of using appropriate techniques in studying complexes containing uranium.
Exploitation Route The first part highlights the importance of using an appropriate active space in studies on such molecules.

The second highlights the importance of using appropriate techniques in studying complexes containing uranium.
Sectors Chemicals

URL https://pubs.rsc.org/en/content/articlelanding/2018/cc/c8cc05581e#!divAbstract,https://www.nature.com/articles/s41557-019-0306-x