Employing multiscale in silico modeling, we propose switching
molecular
diodes on the basis of endohedral fullerenes (fullerene switching
diode, FSD), encapsulated with polar molecules of general type MX
(M: metal, X: nonmetal) to be used for data storage and processing.
Here, we demonstrate for MX@C70 systems that the relative
orientation of enclosed MX with respect to a set of electrodes connected
to the system can be controlled by application of oriented external
electric field(s). We suggest systems with two- and four-terminal
electrodes, in which the source and drain electrodes help the current
to pass through the device and help the switching between the conductive
states of FSD via applied voltage. The gate electrodes then assist
the switching by effectively lowering the energy barrier between local
minima via stabilizing the transition state of switching process if
the applied voltage between the source and drain is insufficient to
switch the MX inside the fullerene. Using nonequilibrium Green’s
function combined with density functional theory (DFT-NEGF) computations,
we further show that conductivity of the studied MX@C70 systems depends on the relative orientation of MX inside the cage
with respect to the electrodes. Therefore, the orientation of the
MX inside C70 can be both enforced (“written”)
and retrieved (“read”) by applied voltage. The studied
systems thus behave like voltage-sensitive switching molecular diodes,
which is reminiscent of a molecular memristor.
A recent study (Sci. Adv. 2017, 3, e1602833) has shown that FH⋅⋅⋅OH hydrogen bond in a HF⋅H O pair substantially shortens, and the H-F bond elongates upon encapsulation of the cluster in C fullerene. This has been attributed to compression of the HF⋅H O pair inside the cavity of C . Herein, we present theoretical evidence that the effect is not caused by a mere compression of the H O⋅HF pair, but it is related to a strong lone-pair-π (LP-π) bonding with the fullerene cage. To support this argument, a systematic electronic structure study of selected small molecules (HF, H O, and NH ) and their pairs enclosed in fullerene cages (C , C , and C ) has been performed. Bonding analysis revealed unique LP-π interactions with a charge-depletion character in the bonding region, unlike usual LP-π bonds. The LP-π interactions were found to be responsible for elongation of the H-F bond. Thus, the HF appears to be more acidic inside the cage. The shortening of the FH⋅⋅⋅OH contact in (HF⋅H O)@C originates from an increased acidity of the HF inside the fullerenes. Such trends were also observed in other studied systems.
Actinide–actinide
bonds are rare. Only a few experimental
systems with An–An bonds have been described so far. Recent
experimental characterization of the U2@I
h
(7)-C80 (J. Am. Chem.
Soc.
2018, 140, 3907) system
with one-electron two-center (OETC) U–U bonds as was predicted
by some of us (Phys. Chem. Chem. Phys.
2015, 17, 24182) encourages the search for more examples
of actinide–actinide bonding in fullerene cages. Here, we investigate
actinide–actinide bonding in An2@D
5h
(1)-C70, An2@I
h
(7)-C80, and An2@D
5h
(1)-C90 (An = Ac–Cm) endohedral metallofullerenes (EMFs).
Using different methods of the chemical bonding analysis, we show
that most of the studied An2@C70 and An2@C80 systems feature one or more one-electron two-center
actinide–actinide bonds. Unique bonding patterns are revealed
in plutonium EMFs. The Pu2@I
h
(7)-C80 features two OETC Pu–Pu
π bonds without any evidence of a corresponding σ bond.
In the Pu2@D
5h
(1)-C90 with r
Pu–Pu = 5.9 Å, theory predicts the longest metal–metal bond
ever described. Predicted systems are thermodynamically stable and
should be, in principle, experimentally accessible, though radioactivity
of studied metals may be a serious obstacle.
Endohedral fullerenes with a dipolar molecule enclosed in the fullerene cage have great poten-tial in molecular electronics, such as diodes, switches, or molecular memristors. Here, we study a series of...
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