G. R. Nasybullina

Methyl viologen and tetraviologen calix[4]resorcinol as mediators of the electrochemical reduction of [PdCl4]2− with formation of finely dispersed Pd0

Methyl viologen and tetraviologen calix[4]resorcinol with decyl substituents in the resorcinol cycles (MVCA-C108+) are mediators of the electrochemical reduction of complex dianion [PdCl4]2− facilitating its reduction on the glassy carbon electrode at 0.5–0.6 V. The reduction product of Pd2+ salt is finely dispersed metallic palladium, and its structure and some properties are determined by the mediator nature. When using methyl viologen, palladium is deposited on the electrode and dispersed as flakes in a solution, whereas in the case of MVCA-C108+ palladium is completely deposited on the electrode as nanoparticles together with calixresorcinol.

Electrochemical control of association and deposition of tetraviologen calix[4]resorcin

The association and deposition of tetraviologen calix[4]resorcin MVCA-C58+ can be controlled using the electrochemical reduction-reoxidation cycle of viologen units. The monomeric MVCA-C58+was converted into the highly molecular (MVCA-C54+·)n associate (π-polymer) by reducing it to the MVCA-C54+· tetra(radical cation) and completely returns to the starting monomeric state by reverse oxidation. The reduction to the neutral state MVCA-C50 allowed calixresorcin to pass from solution to precipitate and the reverse oxidation led to its returning in solution.

Binding of 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane with tetra(methyl viologen) calix[4]resorcinol

Binding of an amphiphilic dianion 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane (APCO2−) with an amphiphilic octacation tetra(methyl viologen) calix[4]resorcinol (MVCA8+) in media containing different amounts of water and DMSO using NaClO4 or NaCl as supporting electrolytes was shown for the first time by cyclic voltammetry and spectrophotometry. The stoichiometry of the complex depends on the MVCA8+: APCO2− ratio, medium, and supporting electrolyte. A 1: 1 charge-transfer complex is mainly formed (λmax = 480 nm) in 30% DMSO at a ratio of the compounds of 1: 1. A similar 1: 1 complex of APCO2− with a model compound methyl viologen MV2+ (λmax = 482 nm) is formed under these conditions. A donor-acceptor interaction occurs between the acceptor viologen units and nitrogen-centered electron-donating fragments of the APCO2− dianion. An increase in the content of APCO2− in the solution leads to an additional binding of one (30 vol.% DMSO, water, NaClO4) or two (30 vol.% DMSO, water, NaCl) particles of APCO2− with the hydrophobic fragments of MVCA8+. The complexes aggregate to form insoluble precipitates in aqueous and water-DMSO media. A selective reversible electroswitching from the bound to free state of one of the three bound APCO2− particles was performed when reducing MVCA8+ to MVCA4·+ in a 30 vol.% DMSO/NaCl medium.

Binding of 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane with tetramethylviologen calix[4]resorcin with a methyl radical in the resorcinol ring

The binding of the amphiphilic 1,5-bis(para-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane dianion (APCO2−) with the octacation of the amphiphilic tetramethylviologen calix[4]resorcin having a methyl radical in the resorcinol ring (MVCA-C18+) in 30% aqueous DMSO in a 0.1M NaCl supporting solution was studied by various methods. The dianion was bound at the upper rim of calixresorcin due to the donor-acceptor interactions between the viologen acceptor units and the nitrogen- and phosphorus-centered electron-donor fragments of APCO2− and at the lower rim due to hydrophobic interactions. The composition of the complex depended on the MVCA-C18+: APCO2− ratio. The complexes aggregated, forming insoluble precipitates. MVCA-C18+-APCO2− is a system with reversibly electro-switchable aggregation. The starting MVCA-18+ octacation partially bound APCO2−, a certain quantity of both substrates remaining in a free state in solution. The MVCA-C14+· tetraradical tetracation formed as a result of the reduction of MVCA-C18+ completely bound APCO2− due to hydrophobic interactions when the MVCA-C18+: APCO2− ratio was 1: 3. The reversible oxidation of MVCA-C14+· to the starting MVCA-C18+ octacation brought the system back to its starting state

Electricoswitchable bonding of metal ions and complexes by calixarenes

The results of authors on designing electroswitchable supramolecular systems based on calix[4]arenes, calix[4]resorcinols, and transition metal ions and complexes are summarized. We consider systems in which the switching is performed owing to electrochemical reactions both of groups grafted to the macrocycle and bound substrates. Examples of electrochemically switchable luminescence are given.

Electrochemical switching of monomer—associate in the system tetraviologen calix[4]resorcinol—3,7-di(l-menthyl)-1,5-di(p-sulfonatophenyl)-1,5-diaza-3,7-diphosphacyclooctane

The possibility of controlling the association of tetraviologen calix[4]resorcinol (MVCA-C58+) with 3,7-di(l-menthyl)-1,5-di(p-sulfonatophenyl)-1,5-diaza-3,7-diphosphacyclooctane (APCO-22−) in the electrochemical cycle of reduction-reoxidation of viologen units was shown. Reduction to tetra(radical cation) MVCA-C54+· transforms monomeric MVCA-C58+ and APCO-22- into the associate (π-polymer) (xAPCO-22−·yMVCA-C54+·)n, which is completely returned by reoxidation to the initial state.

Electrochemically controlled binding of bis-P,P-chelate platinum(II) dication to 3,7-di(2-pyridyl)-1,5-diphenyl-1,5-diaza-3,7-diphosphacyclooctane complex and ferrocyanide ion with tetraviologen calix[4]resorcinol

Two new types of systems with an electrochemically controlled binding of electron-accepting particles with tetra(methyl viologen) calix[4]resorcinol MVCA-C58+ were developed. Control is carried out by the reversible reduction of viologen units. In one of the systems, an equimolar amount of the dication of bis-P,P-chelate platinum(II)—3,7-di(2-pyridyl)-1,5diphenyl-1,5-diaza-3,7-diphosphacyclooctane complex ([PtL12]2+) is bound by the reduced form MVCA-C50 and is not bound to the octacation MVCA-C58+ and tetra(radical cation) MVCA-C54+•. In another ternary system MVCA-C58+—[PtL12]2+—[Fe(CN)6]3–, the reversible switching occurs from the original unbound state to the state with selective binding of equimolar amounts of [Fe(CN)6]4– or [PtL12]2+ by calixresorcinol. Supramolecular complexes form insoluble associates in both systems.