M. E. Klyueva

Magnetocaloric effect and heat capacity of high-spin manganese complexes in a disperse state

Magnetothermal properties of high-spin chloro(2,3,7,8,12,13,17,18-octaethylporphyrinato)manganese(III), chloro(5,10,15,20-tetraphenylporphyrinato) manganese(III), bromo(5,10,15,20-tetraphenylporphyrinato)manganese(III), and (acetato)(5,10,15,20-tetraphenylporphyrinato)manganese(III) complexes as 6% water suspensions were determined by the microcalorimetric method at 298 K in a magnetic field of 0–1.0 T. It was established that when the magnetic field was applied, the temperature of the systems increases, leading to positive values of the magnetocaloric effect: the higher the magnetic field induction, the higher the values. It is shown that the dependences of the heat capacity of the complexes’ solid particles on the magnetic field induction are of an extreme nature with a heat capacity in the area above 0.6 T less than that in the zero field. The regularities of the dynamics of the numerical values of the change in enthalpy and magnetic entropy of the manganese complexes when a growing magnetic field was applied and the regularities of the influence of the acidoligand in pentacoordinated complexes on their magnetothermal properties were considered.

The kinetics of disproportionation of hydrogen peroxide in the presence of palladium(II)porphyrins with regularly changing macroring structures

The kinetics and spectral manifestations of alkaline decomposition of H2O2 in a water-dimethylformamide medium catalyzed by PdIIP (P is the dianion of octaethylporphyrin and its monophenyl, 5,15-diphenyl,5,10-diphenyl, triphenyl, and tetraphenyl derivatives substituted at meso positions) was studied over a wide range of reagent concentrations under polythermal conditions. A complete kinetic description of the reacting systems was given, and the rates and set of elementary reactions, intermediate compounds, and kinetically significant equilibria were determined. The ion-molecular mechanism of hydrogen peroxide decomposition was substantiated. According to this mechanism, the only stable radicals involved in the reaction are the π radical cation forms of palladium(II)porphyhrin catalysts.

The magnetothermal properties of substituted (tetraazoporphynato)manganese(III) in aqueous suspension

The magnetocaloric effect (MCE), heat capacity, and enthalpy and entropy of magnetization of the high-spin (acetato)(2,3,7,8,12,13,17,18-octa-para-tert-butylphenyltetraazaporphynato)manganese(III) complex in a 6% aqueous suspension were determined microcalorimetrically at 298 K in magnetic fields of 0.1–1.0 T, that is, under the conditions comparable with those used with (2,3,7,8,12,13,17,18-octaethylporphynato)chloromagnanese(III) studied earlier. High-dispersity complex particles were found to have paramagnetic properties. Positive MCE values were obtained. These values grew as magnetic field induction increased. MCE sensitivity to the nature and electronic structure of the aromatic macroring was studied. The presence of aza groups in the structure of the complex decreases the MCE value compared with the porphyrin complex. The specific heat capacity of the complex strongly depended on the magnetic field value; field dependences had a maximum close to 0.3 T. Changes in the ΔSm(H, T) molar entropy part were also extremal and had maxima at 0.3–0.4 T. Prospects for the use of magnetothermal properties in the quantitative determination of thermodynamic characteristics and for revealing trends of changes in the magnetic activity of porphyrin complexes are discussed.

Reactivity of mixed manganese complexes with porphyrins and anionic ligands. effect of modification of the organic part of the molecule

Manganese(III) complexes with octaethyl-, 5-phenyloctaethyl-, 5,10-and 5,15-diphenyloctaethyl-, 5,10,15-triphenyloctaethyl-, and 5,10,15,20-tetraphenyloctaethylporphyrins were synthesized, and the kinetics and mechanism of their dissociation in mixed AcOH-H2SO4 system were studied. The complete stability series of octaethylporphyrin manganese(III) complexes with increasing number of phenyl substituents at the meso positions of the porphyrin ligand was obtained.

Pyridine coordination to manganese(III) porphyrins: The effect of multiple functional substitution in porphyrin

To synthesize donor–acceptor complexes exhibiting biological activity, the reaction of (2,3,7,8,12,13,17,18-octaalkylporphinato)manganese(III) containing axial acetate and chloride ions with pyridine has been quantitatively studied. In all cases, equilibrium is established instantaneously to give 1 : 1 donor–acceptor complexes. The key spectral characteristics and stability parameters have been obtained for donor–acceptor dyads. Multiple functional substitution of the porphyrin macroheterocycle can be used to control the properties of porphyrins and dyads based on them.

Synthesis and investigation of 2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5,15-bis(2-thienyl)-21H,23H-porphin and its complexes with manganese (III) acetate and chloride

Abstract2,8,12,18-Tetrabutyl-3,7,13,17-tetramethyl-5,15-bis(2-thienyl)-21H,23H-porphin and its complexes with manganese(III) with additional acetate and chloride acido ligands were synthesized. Basing on the UV, IR, and NMR spectra and the kinetic properties of the proton transfer and the dissociation of free and coordinated porphyrin respectively it was established that in the change of porphyrin basicity at thienyl substitution the effect of the sulfur atom vacant d-orbitals involved in the conjugation was predominant. The stability of thienyl-substitued complexes of manganese(III) rises when the axial Cl− is replaced by acetate ion.

Synthesis and chemical stability of (5,15-bis(2-thienyl)- and 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-butyl-21H,23H-porphinato)copper(II)

Abstract(5,15-Bis(2-thienyl)-and 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-butyl-21H,23H-porphinato)copper(II) complexes were synthesized and the basicity, absorption spectra (UV-Vis, IR, 1H NMR) of the macrocyclic ligands and the stability of the complexes in AcOH-H2SO4 mixed solvents were studied with the aim to reveal the effect of 2-thienyl substituent on the properties of substituted porphyrins. Data on kinetics were obtained, reaction mechanism of complex dissociation was reasoned, and the effect of functional substitution on the properties of macrocyclic bases and their complexes with copper(II) were determined.

Disproportionation of Hydrogen Peroxide in the Presence of Mn(III) Complexes with Various Porphyrins and Acid Anions

The kinetics of homogeneous decomposition of H2O2 in the presence of Mn(III) complexes with octaethylporphine or meso-phenyloctaethylporphines and acid anions Cl−, AcO−, and SCN− was studied by volumetry. The ionic-molecular mechanism of the transformation, involving reversible coordination of the H2O2 molecule, its irreversible decomposition with the release of H2O and removal of two electrons from the metal porphyrin, reversible coordination of the second peroxide molecule in the form of HO2−, and slow irreversible reduction of the catalyst with the release of O2 and H2O was substantiated by electronic absorption spectra. The catalytic activity of Mn(III) porphyrin complexes is independent of the acid anion present as extra ligand, but depends on the structure of the porphyrin ligand, which can be used for controlling the catalytic activity. Unsymmetrical (chloro)(monophenyloctaethylporphinato)managanese(III) is the most active; it increases the rate of O2 evolution by a factor of 2 at the peroxide: catalyst molar ratio of (3 × 105): 1.