Fullerene-Based Switching Molecular Diodes Controlled by Oriented External Electric Fields

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.

Fullerene-Based Switching Molecular Diodes Controlled by Oriented External Electric Fields.pdf

Complexes of phosphonate and phosphinate derivatives of dipicolylamine

Four dipicolylamine (DPA) derivatives bearing methylphosphonic or methylphosphinic acid (P–R; R = H, Me, CH2PO2H2) groups were synthesized. Their acid–base and coordination properties were studied by potentiometry, UV-Vis and NMR measurements. The phosphonate derivative shows increased basicity (log K1 = 8.39), whereas the phosphinate derivatives show decreased basicity (log K1 = 6–7) compared to the parent dipicolylamine. Consequently, the stability constants of the phosphonate complexes are 3 to 4 orders of magnitude higher than those of the phosphinate complexes. All ligands show excellent selectivity for Zn(II) over Ca(II) and Mg(II) ions. The structures of several Cu(II) and Ni(II) complexes in the solid state were determined by X-ray diffraction analysis. The complexes mostly show dimeric or polymeric structures and the two metal ions induce a different coordination geometry of the DPA group. The coordination geometry is always (pseudo)octahedral. The DPA fragment is bound in mer geometry in the Cu(II) complexes, whereas the Ni(II) complexes have fac geometry. In conclusion, the phosphonate and phosphinate derivatives of DPA are efficient complexing agents for divalent transition metal ions and the DPA-phosphinate grouping is a suitable fragment for sensing Zn(II) ions.

Complexes of phosphonate and phosphinate derivatives of dipicolylamine.pdf

How Does a Container Affect Acidity of its Content: Charge‐Depletion Bonding Inside Fullerenes

A recent study (Sci. Adv. 2017, 3, e1602833) has shown that FH⋅⋅⋅OH2 hydrogen bond in a HF⋅H2O pair substantially shortens, and the H−F bond elongates upon encapsulation of the cluster in C70 fullerene. This has been attributed to compression of the HF⋅H2O pair inside the cavity of C70. Herein, we present theoretical evidence that the effect is not caused by a mere compression of the H2O⋅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, H2O, and NH3) and their pairs enclosed in fullerene cages (C60, C70, and C90) has been performed. Bonding analysis revealed unique LP–πcage interactions with a charge-depletion character in the bonding region, unlike usual LP–π bonds. The LP–πcage 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⋅⋅⋅OH2 contact in (HF⋅H2O)@C70 originates from an increased acidity of the HF inside the fullerenes. Such trends were also observed in other studied systems.

How does a Container Affect Acidity of its Content: Charge-Depletion Bonding Inside Fullerenes.pdf