Quantum Chemical Characterization of Single Molecule Magnets Based on Uranium

Abstract

Multiconfigurational electronic structure theory calculations including spin-orbit coupling effects were performed on four uranium-based single-molecule-magnets. Several quartet and doublet states were computed and the energy gaps between spin-orbit states were then used to determine magnetic susceptibility curves. Trends in experimental magnetic susceptibility curves were well reproduced by the calculations, and key factors affecting performance were identified.

DFT Investigations of the Magnetic Properties of Actinide Complexes

“…Moreover, the discovery in 2009 of the slow magnetic relaxation for the mononuclear complex U(Ph 2 BPz 2 ) 3 [53], which is a signature of a single-molecule magnet (SMM) behavior, has motivated more research, even though lanthanide SMMs have been described in the literature for a longer time [54,55]. A growing number of uranium-containing systems [56][57][58][59][60][61][62][63][64][65][66][67][68][69]-mononuclear as well as binuclear species-have been synthesized to develop SMMs; the results have been the subject of recent reviews [70][71][72][73][74][75]. Such systems are of great interest, owing to the well-known larger spin-orbit coupling for actinide than for lanthanide ions [72], and the more diffuse 5f orbitals (5f covalency) [63,[76][77][78] than the lanthanide 4f ones, which could lead to strong magnetic super-exchange [53].…”

“…Therefore, these unique features of actinides relatively to transition metals and lanthanides open the way to the design of new actinide-based SMMs with high blocking temperatures [71,72,75]. Moreover, over the last twenty years, much effort has been devoted to investigating the magnetic properties of actinide complexes by quantum chemical methods [62][63][64][65]67,[70][71][72][73][74][75][76][79][80][81]. Indeed, investigating the electronic structure of actinide complexes is essential to understanding their magnetic behavior [1,2,[71][72][73].…”

“…Indeed, investigating the electronic structure of actinide complexes is essential to understanding their magnetic behavior [1,2,[71][72][73]. However, for such a purpose, the use of a multiconfigurational post-Hartree-Fock approach is required, as stated by several authors [63,64,82,83], but such an approach is computationally demanding (vide infra) for polymetallic systems, notably for actinide ones, and usually simplified models are computed instead of the actual systems [63,64]. Thus, Density Functional Theory (DFT) appears as an alternative tool to compute magnetic exchange coupling and to explore the electronic structure and magnetic properties of actinide-containing molecules, especially when the considered systems are very large [6,8,21,37,60,79,80,84,85].…”

“…This is true not only in the case of d-transition metal systems [82,83,[90][91][92][93][94][95][96][97][98][99][100][101][102][103][104], but also for actinide-containing molecules [105][106][107]. It is worth noting that actinide-based SMMs are multiconfigurational systems, and the use of the monodeterminantal approach with DFT is a subject of debate [63,[108][109][110].…”

Future Directions for Transuranic Single Molecule Magnets

“…Interesting developments are promised by multiconfigurational electronic structure theory calculations including spin-orbit coupling. Such first principles techniques have recently been applied to study trends in magnetic properties of uranium-based SMMs with encouraging results [46]. Although the treatment of heavier atoms increases the computational cost, this approach can easily be extended to transuranics and can provide valuable indications about the most favourable coordination topologies.…”