Future Directions for Transuranic Single Molecule Magnets

Abstract

Single Molecule Magnets (SMMs) based on transition metals and rare earths have been the object of considerable attention for the past 25 years. These systems exhibit slow relaxation of the magnetization, arising from a sizeable anisotropy barrier, and magnetic hysteresis of purely molecular origin below a given blocking temperature. Despite initial predictions that SMMs based on 5f-block elements could outperform most others, the results obtained so far have not met expectations. Exploiting the versatile chemistry of actinides and their favorable intrinsic magnetic properties proved, indeed, to be more difficult than assumed. However, the large majority of studies reported so far have been dedicated to uranium molecules, thus leaving the largest part of the 5f-block practically unexplored. Here, we present a short review of the progress achieved up to now and discuss some options for a possible way forward.

DFT Investigations of the Magnetic Properties of Actinide Complexes

“…This linkage forms an oxo-bridge between metal centers affording a great number of oxo-bridged systems exhibiting significant coupling between U V centers [27,49], mixed U V /transition metal [28][29][30][31][32]111] or lanthanide centers [47,112,123], with the largest actinide-based multinuclear complex affording the unique structure of a wheel-shaped cluster {[UO2(salen)]2Mn(Py)3}6 (Py = pyridine) which is assembled through UO2 + and Mn II interactions [29]. Additionally, CCIs were observed between Np IV /Np V ions in neptunyl complexes [75]. Beside the great number of synthesized CCI systems, few theoretical studies of their magnetic properties have been carried out [ Plots of the magnetic susceptibility vs. temperature of these linkages present shoulders that could be interpreted as evidence of uranium-uranium magnetic exchange.…”

“…Additionally, CCIs were observed between Np IV /Np V ions in neptunyl complexes [75]. Beside the great number of synthesized CCI systems, few theoretical studies of their magnetic properties have been carried out [1][2][3][4]7,8,37,60,63,64,71,72,80,81].…”

“…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].…”

“…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].…”

“…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].…”