Electronic g Tensors in U^V Complexes–A Computational Study

Abstract

Abstract:The theory and computation of EPR parameters from first principles has seen a great deal of development over the past two decades. In particular, various techniques for the computation of the electronic g tensor have been implemented in many quantum chemistry packages. These methods have been successfully applied to paramagnetic organic species and transition metal systems. The situation is less well-understood and established in the case of actinide containing molecules and there is a dearth of experimental data available for validation of computations. In this study we have used quantum chemical techniques to evaluate the g tensor for U(V) complexes, for which experimental data are available for comparison. The g tensors were calculated using, relatively simple, state averaged CASSCF calculations. We show that this approach is capable of providing useful accuracy. We discuss aspects of the computations that should be refined to provide a more quantitative approach. The key features of the underlying electronic structure that influence the computed g values are delineated, providing a simple physical picture of these subtle molecular properties.

Redox Properties of Monocyclooctatetraenyl Uranium(IV) and (V) Complexes: Experimental and Relativistic DFT Studies

“…The U–O distance and the Ct–U–O and O–U–O angles of [(Cot)­U­(O i Pr) 3 ] ( 2 ), of 2.06, 123.2, and 92.9°, respectively, are consistent with those found recently by Moylan (2.03 Å, 124.3 and 91.4°) in a DFT study at the ZORA/PBE0 level on similar compounds. In the same way, the computed U–N and U–C­(Cot) distances of the oxidized form of [(Cot)­(Cp)­U­(NEt 2 ) 2 ] ( 1 ), of 2.18 and 2.79 Å, respectively, can be compared with those of 2.19 and 2.78 Å of [(Cot)­(Cp)­U­(NEt 2 ) 2 ] + .…”

“…The U–O distance and the Ct–U–O and O–U–O angles of [(Cot)­U­(O i Pr) 3 ] ( 2 ), of 2.06, 123.2, and 92.9°, respectively, are consistent with those found recently by Moylan (2.03 Å, 124.3 and 91.4°) in a DFT study at the ZORA/PBE0 level on similar compounds. In the same way, the computed U–N and U–C­(Cot) distances of the oxidized form of [(Cot)­(Cp)­U­(NEt 2 ) 2 ] ( 1 ), of 2.18 and 2.79 Å, respectively, can be compared with those of 2.19 and 2.78 Å of [(Cot)­(Cp)­U­(NEt 2 ) 2 ] + . In addition, the same U–N and U–C­(Cot) bonds of the oxidized form of [(Cp)*U­(NEt 2 ) 3 ] ( 6 ) compound presenting calculated distances of 2.18 and 2.78 Å, respectively, similar to those of Moylan (2.14 and 2.74 Å), accurately reproduce the experimental data (2.16 and 2.77 Å) of the analogue cationic amide complex (Cp*) 2 U­(NEt 2 ) 2 + .…”

“…The authors are grateful to GENCI-IDRIS and GENCI-CINES for an allocation of computing time (Grant No. 2016-2017. ME and DH thank Dr C. Clappe…”

Modelling the Effect of Zero-Field Splitting on the 1H, 13C and 29Si Chemical Shifts of Lanthanide and Actinide Compounds

“…Due to the presence of uranium, relativistic effects are important, but it is sufficient to only consider scalar relativistic effects. We prefer an all-electron approach and previously created a program in which implements the ZORA [27,60], and applies the correction to the one-electron Hamiltonian in atomic blocks, removing the gauge dependence issue. This program was interfaced to the GAUSSIAN programs and used in all geometry optimisations.…”

“…The g tensor was evaluated within the effective Hamiltonian approach. The number of states included in the SA-CASSCF calculations were explored empirically, by increasing the number of states, until some convergence in the principal values of the g tensor was achieved [17,60].…”