Standard Redox Potentials of Fe(III) Aqua Complexes Included into the Cavities of Cucurbit[n]urils (n = 6–8): A DFT Forecast

Abstract

An approach for estimating at the DFT level of the standard redox potentials of the inclusion compounds based on Fe­(III) and Fe­(II) aqua complexes inside the cavities of cucurbit­[n]­urils (n = 6–8) has been proposed. These inclusion compounds were established to have compositions which can be described by the formulas [Fe­(H2O)6]3+/2+@CB­[6] and [Fe­(H2O)6·4H2O]3+/2+@CB­[7,8]. Redox potentials E 0 relative to the standard hydrogen electrode for the half-reaction Fe­(III)/Fe­(II) in the CB­[n] cavities calculated at the PBE/TZVP level within the molecular-continuum solvation model are 1.607, 0.949, and 0.847 V for n = 6, 7, and 8, respectively. The obtained values indicate a relative increase of the oxidative ability of Fe­(III) aqua-ions in the cavities of the examined CB­[n], especially in CB[6], compared to the calculated value (E 0 = 0.786 V) for the same half-reaction in the bulk of aqueous solution. Possible causes of the detected trend are discussed. The calculations also showed that the Fe­(III) aqua complex inside the CB[6] changes its magnetic properties, transforming into a low-spin state with a total spin S = 1/2, whereas for all other systems high-spin states in accord with the classical ligand field theory are realized.

A computational protocol for the calculation of the standard reduction potential of iron complexes: application to Fe2+/3+-Aβ model systems relevant to Alzheimer's disease

“…It is worth mentioning that the calculated SRP may improve with the inclusion of explicit solvent molecules, as have been reported for the aquo–iron complexes. 36 Nevertheless, this approach requires an exhaustive conformational search for the position of water molecules in the second coordination shell and therefore it increases significantly the computational cost of such calculations, which is beyond the scope of this work. In our case, using SMD as implicit solvent model reproduces quite well the reported SRP at the M06L/cc-pVDZ (Fe)-6-31+G(d,p) (O, H) level of theory.…”

Structure and thermodynamic properties of adducts based on cucurbit[6]uril and Fe(III)/Fe(II) aqua complexes: A DFT examination

“…In the present work, we studied the structures and thermodynamic properties of adducts formed via interactions of CB[6] with Fe(III) and Fe(II) aqua complexes. These studies are preceded by our prior study [40], where we have proposed an approach for estimating at the DFT level the standard redox potentials of the inclusion compounds based on Fe(III) and Fe(II) aqua complexes inside the cavities of cucurbit[ n ]urils ( n = 6–8). These inclusion compounds were established to have compositions which can be described by the formulas [Fe(H 2 O) 6 ] 3+/2+ @CB[6] and [Fe(H 2 O) 6 ·4H 2 O] 3+/2+ @CB[7,8].…”

“…In [40], the structure and thermodynamics of only the final products of the formation of inclusion compounds of Fe(III)/Fe(II) aqua complexes with CB[ n ] were reported, while the detailed mechanism of this process was not considered. However, detailed examinations of this process seem to be very relevant, since the inclusion of any particle into the cavitand is necessarily carried out through successive stages that involve the formation of a number of intermediate adducts.…”

Controllable synthesis of Co nanoparticles with the assistance of cucurbit[6]uril and its efficient photoelectrochemical catalysis in water splitting on a g-C3N4 photoanode

“…18 Cucurbit [6]uril (Q [6]) includes six carbonyl groups on two portals, [19][20][21][22] exhibiting the ability of selective supramolecular interactions with organic molecules and coordination to metal cations. [23][24][25][26] In addition, Q [6] can be regarded as an outstanding stabilizer and carrier for nanoparticles due to its unique rigid structure and stable chemical properties. [27][28][29] Herein, an innovative photoanode with good catalytic performance was developed for photocatalytic water oxidation by depositing Co nanocatalysts on the surface of the g-C 3 N 4 film.…”

“…18 Cucurbit[6]uril (Q[6]) includes six carbonyl groups on two portals, 19–22 exhibiting the ability of selective supramolecular interactions with organic molecules and coordination to metal cations. 23–26 In addition, Q[6] can be regarded as an outstanding stabilizer and carrier for nanoparticles due to its unique rigid structure and stable chemical properties. 27–29…”