Acquiring a record barrier height for magnetization reversal in lanthanide encapsulated fullerene molecules using DFT and ab initio calculations

Abstract

Ab initio calculations performed on a series of lanthanide encapsulated fullerenes reveal {DyOSc}@C to be one of the best host-guest pairs to offer a barrier height exceeding 1400 cm. The high-symmetry environment preserved inside the cage quenches the QTM effects up to third-excited states leading to very larger barrier heights and this opens up a new possibility of obtaining attractive SMMs based on lanthanide based endohedral metallo-fullerenes (EMFs).

Single‐Molecule Magnets DyM2N@C80 and Dy2MN@C80 (M=Sc, Lu): The Impact of Diamagnetic Metals on Dy3+ Magnetic Anisotropy, Dy⋅⋅⋅Dy Coupling, and Mixing of Molecular and Lattice Vibrations

“…The reason for the low‐temperature U eff barriers of 24 K in both DyM 2 N@C 80 molecules is not clear. Due to the very strong LF splitting of dysprosium in the NCFs, the energies of the lowest‐energy excited states exceed hundreds of K (see the discussion of the ab initio calculations below) –. In addition, the τ 0 values are many orders of magnitude longer than are usually found for the Orbach mechanism.…”

A Design Criteria to Achieve Giant Ising‐Type Anisotropy in CoII‐Encapsulated Metallofullerenes

“…Molecular dynamics studies on Co@C 28/38/48 cages suggests that as we move to larger fullerene, this yield fewer isomers which are low‐lying in energy and the D values are more robust. Besides, our previous studies also suggest that enhancing the axial ligand field strength by introducing one extra bridging atom inside fullerene−Co−X, here X denotes oxygen or nitrogen atom (for example, CoNScZn@C 76/82 and CoOZn@C 70/80 , see Figure ), is expected to enhance the magnitude of axial anisotropy . This incorporation of additional co‐ligand inside the cage is also likely to arrest the movement of the Co II ion inside the cage leading to less number of isomers and hence a robust SMMs.…”

“…Moreover, these methods are robust towards prediction, and several such predictions made on lanthanide‐encapsulated fullerene cages with varying size and shape has been duly verified by experimental groups . These lanthanide endohedral metallofullerenes (EMFs) are fullerenes that have metal ions, dinuclear fragments, trinuclear or mixed systems encapsulated in various C n cages exhibiting fascinating magnetic properties . If doped fullerene cages such as C 79 N are utilised, this leads to extremely strong magnetic coupling between the Ln III and the radical centres, again predicted by theory and verified lately by experiments .…”

Role of Ab Initio Calculations in the Design and Development of Organometallic Lanthanide‐Based Single‐Molecule Magnets

“…Before we begin, we would like to put fortht he nature of Ln-C interaction and how they could potentially yield very large blocking barriers. To assesst his we have constructed the mechanism of magnetic relaxation for two toy models [Dy(CH 2 ) 2 ] 3 + (model a)a nd [Dy(CH 3 ) 2 ] + (model b)u sing the established methodology [29] andt hese are shown in Figure 3( see ref. note).…”

“…In the next phase of the fullerene type SMMs, other models focusing on the Dy III ion within C 72 ( 9 c ), C 76 ( 9 d ) and C 82 ( 9 e ) cages where the Dy‐C distance estimated in the range of 2.4 to 2.6 A o and the Dy III ion is bridged to the Sc III ion via an oxo bridge inside the fullerene cages have been explored . The knowledge behind such an approach is that the metal atom Sc III being a diamagnetic element helps to avoid weak exchange coupling between the lanthanide centres, which generally leads to close‐lying excited states and faster relaxation.…”