Effect of peripheral modification of manganese(III) porphyrazine on its reactivity in the coordination of imidazole

Coordination of imidazole to manganese(III) porphyrazine and phthalocyanine modified by multiple peripheral substitution by trifluoromethylphenyl, trifluoromethylphenoxy, tert-butylphenyl, and 3,5-ditert-butylphenoxy groups was studied by spectrophotometric titration, and UV, visible, and IR spectroscopy. Manganese(III) complexes were found to react with imidazole with formation of 1: 1 complexes in one-step reversible process. Specificity of the effect of multiple substitution of the macroring on quantitative parameters of reactions with the organic base is related to structural features of the organic complexes.     

The influence of interatomic distances on magnetic ordering in RMnSi compounds (R=La, Y, Sm, and Gd)

Magnetic ordering in the RMnSi (R=La, Y, Sm, and Gd) compounds is investigated. It is found that the type of magnetic ordering depends on the d _Mn-Mn distance between manganese atoms inside the magnetic layers located in the planes perpendicular to the c axis. This inference is based on the results of studies performed with SmMnSi and GdMnSi compounds in which the distances between manganese atoms are close to the critical value d _Mn-Mn that corresponds to the crossover between ferromagnetic and antiferromagnetic ordering in RMnSi compounds. The introduction of lanthanum and yttrium atoms into the rare-earth sublattice leads to an increase and a decrease in the unit cell size, respectively, and brings about magnetic phase transitions in the compounds under investigation.     

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 ΔS _m(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.     

Magnetic properties and structure of the nanocrystalline Gd-Ti-Ge intermetallic compound

This paper reports an experimental study of the magnetization processes and structure of the Gd-Ti-Ge compound in the initial coarse-grained state and a nanostructured state obtained under torsion at a high quasihydrostatic pressure. It is established that in a nanocrystalline sample, the magnetic ordering temperature is 30 K lower, the coercive force is eight times higher, and the magnetization is 3.7 times lower than their respective values in a coarse-grained sample. The observed changes in the magnetic properties are shown to be related primarily with the conversion of a part of the initial phase with the CeScSi-type lattice to a CeFeSi-type weakly magnetic phase. The effect of structural defects and of partial disorder on the magnetic characteristics of the compound are also discussed.     

Porphyrin–Fullerene Dyad Based on Indium(III) Complex. Donor–Acceptor Complex Formation Equilibrium

Formation kinetics and spectral properties of the donor–acceptor complexes of (5,10,15,20- tetra(2-methoxyphenyl)porphinato)chloroindium(III) with 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin- 2-yl)methylpyrrolidinyl[3′,4′:1,2][60]fullerene were studied. The formation of the donor–acceptor dyad [(Py₃F)InTPP(2-OCH₃)₄]⁺Cl^– occurs as a two-step reaction, including fast reversible coordination of the fullerene base molecule and slow irreversible displacement of the axial chloride ion to the second coordination sphere. Quantitative characteristics for the reaction rate and equilibrium were obtained. The reaction products were identified by IR and ¹H NMR spectroscopy. The most important electron optical and stability parameters of the porphyrin–fullerene dyads with inner- and outer-sphere chloride ions were determined. These results are important for studies of the photophysics of porphyrin–fullerene dyads and development of photoconverters based on them.     

Synthesis and properties of a new (octaethylporphyrinato)-manganese(III)–pyridinyl-substituted pyrrolidinofullerene dyad

The formation of a porphyrin–fullerene dyad from 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-3-ylmethyl)-2′,5′-dihydro-1′H-pyrrolo[3′,4′: 1,9](C₆₀-I_h)[5,6]fullerene and (2,3,7,8,12,13,17,18-octaethylporphyrinato) manganese(III) with axial chloride ligand has been studied on a quantitative level with the goal of obtaining supramolecules possessing biological activity. Preliminarily, the reaction of manganese(III) porphyrin with pyridine has been studied. The donor–acceptor dyads are formed either instantaneously and reversibly (pyridine) or slowly and irreversibly (substituted fullerene). In both cases, the reaction is a one-step process for which thermodynamic and kinetic parameters have been determined. The results can be used to optimize conditions for the synthesis of porphyrin–fullerene dyads. The obtained dyads have been characterized by spectral data and stability constants.     

Kinetics and mechanism of decomposition of hydrogen peroxide in the presence of manganese(III) porphyrins

The kinetics of homogeneous decomposition of hydrogen peroxide in the presence of manganese complexes with anionic ligands and various aromatic macrocycles were studied by the volumetric method. Ionmolecular mechanism was proposed on the basis of spectrophotometric data for catalytic decomposition of hydrogen peroxide with participation of manganese(III) porphyrins. The catalytic activity of the porphyrin complexes was higher by a factor of 1.5–3 than the activity of the corresponding solvate complexes with anionic ligands. The catalytic activity of porphyrin manganese complexes can be controlled by variation of the electronic structure of the macroring and the nature of anionic ligand coordinated at the apical position.     

Synthesis and Antimicrobial Activity of a Pyridine Complex of (Acetato)[5,10,15,20-tetrakis(<Emphasis Type="Italic">N</Emphasis>-methylpyridin- 4-yl)porphinato]manganese(III) Tetratosylate

Aiming at preparation of new biologically active donor?acceptor complexes, a water-soluble manganese(III) complex with 5,10,15,20-tetrakis(N-methylpyridin-4-yl)porphine tetratosylate was synthesized and its reaction with pyridine was studied by spectrophotometry using the molar ratio method. In water a 1: 1 donor?acceptor complex with pyridine is formed. The chemical structure of the compounds was established by spectral methods. (Acetato)[5,10,15,20-tetrakis(N-methylpyridin-4-yl)porphinato]manganese(III) tetratosylate and especially its donor?acceptor complex with pyridine showed an antifungal activity against Candida albicans.     

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.     

Donor–Acceptor Complexes of (5,10,15,20-Tetra(4-methylphenyl)porphyrinato)cobalt(II) with Fullerenes C60: Self-Assembly,Spectral, Electrochemical and Photophysical Properties

The noncovalent interactions of (5,10,15,20-tetra(4-methylphenyl)porphinato)cobalt(II) (CoTTP) with C₆₀ and 1-N-methyl-2-(pyridin-4-yl)-3,4-fullero[60]pyrrolidine (PyC₆₀) were studied in toluene using absorption and fluorescence titration methods. The self-assembly in the 2:1 complexes (the triads) (C₆₀)₂CoTTP and (PyC₆₀)₂CoTTP was established. The bonding constants for (C₆₀)₂CoTTP and (PyC₆₀)₂CoTTP are defined to be (3.47 ± 0.69) × 10⁹ and (1.47 ± 0.28) × 10¹⁰ M⁻², respectively. ¹H NMR, IR spectroscopy, thermogravimetric analysis and cyclic voltammetry data have provided very good support in favor of efficient complex formation in the ground state between fullerenes and CoTTP. PyC₆₀/C₆₀ fluorescence quenching in the PyC₆₀/C₆₀–CoTTP systems was studied and the fluorescence lifetime with various CoTTP additions was determined. The singlet oxygen quantum yield was determined for PyC₆₀ and the intensity decrease in the ¹O₂ phosphorescence for C₆₀ and PyC₆₀ with the CoTTP addition leading to the low efficiency of intercombination conversion for the formation of the ³C₆₀* triplet excited state was found. Using femtosecond transient absorption measurements in toluene, the photoinduced electron transfer from the CoTTP in the excited singlet state to fullerene moiety was established. Quantum chemical calculations were used for the determination of molecular structure, stability and the HOMO/LUMO energy levels of the triads as well as to predict the localization of frontier orbitals in the triads.