Kinetics and mechanism of hydrogen peroxide decomposition in the presence of the tetraaquapalladium(<Emphasis Type="SmallCaps">II</Emphasis>) complex

Kinetics of hydrogen peroxide decomposition in the presence of the tetraaquapalladium(II) complex in an aqueous solution at 40–70 °C was studied. The reaction rate is the first order with respect to the concentration of both Pd^II and H₂O₂ and the negative first order with respect to perchloric acid. Using free radicals traps, the reaction mechanism was found to differ from the traditional free-radical mechanism known for d-metal aqua ions and proceeds without generation of hydroxyl radicals. The kinetic data obtained suggest a mechanism involving the formation of an intermediate palladium complex with oxygen. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1077–1082, May, 2005.     

Synthesis and studies of spectroscopic and electrochemical properties of dinuclear ruthenium(<Emphasis Type="SmallCaps">II</Emphasis>) and manganese(<Emphasis Type="SmallCaps">II</Emphasis>) complexes

New dinuclear ruthenium manganese complexes of general composition (bpy)₂Ru(L)MnCl_x(H₂O)₂ (L is 1,10-phenanthroline-5,6-dione, 3,3′-dicarboxy-2,2′-bipyridyl, or bis(pyrazolyl); x = 2 or 4) were synthesized by the reaction of (bpy)₂Ru(L) with MnCl₂ · 4H₂O. These compounds and the starting mononuclear ruthenium complexes were studied by spectrophotometric and electrochemical methods in MeCN. The position of the charge-transfer band Ru^II → L in the spectra depends on the donor-acceptor characteristics of the ligand L. For the dinuclear complex under study, the formal potentials of reversible one-electron oxidation of Ru^II are in the range of 0.9–1.2 V (vs. the standard hydrogen electrode), whereas oxidation of Mn^II occurs at more positive (by 0.1–0.2 V) potentials. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2281–2285, October, 2005.     

Formation of palladium nanoparticles in olefin oxidation with iron(III) aqua ions in the presence of the Pd/ZrO2/SO4 metallic catalyst

The reactions of the Pd/ZrO₂/SO₄-catalyzed oxidation of ethylene, propene, and but-1-ene in a 0.1–1.5 M solution of perchloric acid with iron(III) aqua ions to carbonyl compounds, viz., acetaldehyde, acetone, and methyl ethyl ketone, respectively, were studied. The formation of palladium nanoparticles (5 nm) in solution on contact of the initial heterogeneous Pd/ZrO₂/SO₄ catalyst with perchloric acid was proved by transmission electron microscopy. The palladium nanoparticles are assumed to play the key role in olefin oxidation with the iron(III) aqua ions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 627–632, April, 2006.     

Heterospin mixed-ligand heterotrinuclear Co<Superscript>II</Superscript>, Gd<Superscript>III</Superscript>, Co<Superscript>II</Superscript> complex with nitronyl nitroxide

A method was developed for the synthesis of mixed-metal heterospin compounds with the direct coordination of the nitroxide fragment based on the replacement of acetonitrile molecules in the heterotrinuclear complex [Co₂Gd(NO₃)Piv₆(CH₃CN)₂] with nitroxide molecules. The molecular and crystal structure of the heterospin mixed-ligand heterotrinuclear Co^II, Gd^III, Co^II complex [Co₂Gd(NO₃)Piv₆(NIT-Me)₂], where NIT-Me is stable nitronyl nitroxide, was established. The magnetic properties of this complex were investigated in the temperature range of 2–300 K. The coordination of nitroxide groups to Co^II ions is responsible for strong exchange interactions between the unpaired electrons in the exchange clusters {>-·O-Co^II}, resulting in the virtually complete spin coupling between each coordinated >N-·O group and one of the unpaired electrons of each Co^II ion at temperatures below 200 K. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1742–1745, September, 2007.     

Synthesis and electrochemical study of 2-(2-pyridyl)benzothiazole complexes with transition metals (CoII, NiII, and CuII). Molecular structure of aquabis[2-(2-pyridyl)benzothiazole]copper(II) diperchlorate

The reactions of 2-(2-pyridyl)benzothiazole (1) with MX₂·nH₂O salts (M = Ni^II, Co^II, or Cu^II; X = Cl or ClO₄; n = 0–2) in EtOH afforded the corresponding complexes. Depending on the nature of the counterion in the starting metal salt, the reactions give compounds of composition M(1)Cl₂·nH₂O or Cu(1)₂(ClO₄)₂·H₂O. The molecular and crystal structure of the Cu^II(1)₂(ClO₄)₂·H₂O complex was established by X-ray diffraction. The copper atom in this complex has a distorted tetragonal-pyramidal ligand environment and is coordinated by four nitrogen atoms of two ligand molecules and one water molecule. Electrochemical study of the ligand and the resulting complexes by cyclic voltammetry and at a rotating disk electrode demonstrated that ligand 1 stabilizes reduced forms of complexes containing Ni, Co, or Cu atoms in the oxidation state +1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1738–1744, October, 2006.     

Synthesis and electrochemical characterization of CoII, NiII, and CuII complexes with organic N2S2-type ligands derived from 2-thio-substituted benzaldehydes and aromatic amines

Transition metal complexes (Ni^II, Co^II, and Cu^II) with tetradentate N₂S₂-type ligands (L), which are reaction products of 2-thio-substituted benzaldehydes with aromatic amines (3-aminopyridine or 2-aminothiophenol), were synthesized for the first time. The complexes have the composition L·MX₂ or L·2MX₂ (X = Cl or ClO₄). The electrochemical behavior of the ligands and complexes was studied by cyclic voltammetry and rotating disk electrode voltammetry. Depending on the structure of the complexes, the metal atom in the latter is initially reduced in a one-or two-electron process. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2115–2124, November, 2007.     

Change in regioselectivity in the monoreduction of 2,4,6-trinitrotoluene with titanium(III) and vanadium(II) ions in the presence of iron(II) and copper(II) salts

Small additives of iron(II) or copper(II) salts change the regioselectivity of 2,4,6-trinitrotoluene monoreduction with titanium(III) chloride affording predominantly less accessible 2-amino-4,6-dinitrotoluene over 4-amino-2,6-dinitrotoluene (from 25% when the reduction occurs in the absence of the iron and copper salts to 70% in the presence of these salts). A possible mechanism of the process is discussed. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1172–1176, May, 2005.     

5-[2-(Methylthio)ethyl]-3-phenyl-2-thioxoimidazolidin-4-one and its complexes with transition metals (Co<Superscript>II</Superscript>, Ni<Superscript>II</Superscript>, and Cu<Superscript>II</Superscript>). Synthesis and electrochemical investigation

The reaction of 5-[2-(methylthio)ethyl]-3-phenyl-2-thioxoimidazolidin-4-one (LH) with salts MCl₂· xH₂O (M = Co, Ni, Cu; x = 2, 6) afforded the [M(L)Cl]_n complexes of Ni^II, Co^II, and Cu^II. The electrochemical behavior of the LH ligand and its complexes was studied using the cyclic voltammetry and rotating disk electrode techniques. The structures of the synthesized compounds were determined by the data of UV—Vis and IR spectroscopy, mass spectrometry, and electrochemical characteristics. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339–343, February, 2007.     

Catalytic conversions of chloroolefines over iron oxide nanoparticles 3. Electronic and magnetic properties of γ-Fe2O3 nanoparticles immobilized on different silicas

Catalytic properties of superparamagnetic γ-ferric oxide nanoclusters, which are uniform in terms of size and magnetic properties were studied. The catalysts were supported on the activated silica gel matrix (AGM) prepared from the KSK-2 silica gel of globular structure and on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher that of usual supported catalysts based on α-ferric oxide. Analysis of the Mössbauer spectra of the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at T = 3–300 K shows that during the reaction some Fe^III ions arranged in ～2–3-nm γ-Fe₂O₃ nanoclusters magnetically ordered at 6 K are reduced to form a high-spin Fe^II complex in the paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at T = 2 K demonstrates a linear field dependence of the magnetization passing through the coordinate origin. Analysis of the Mössbauer spectra and magnetic properties suggests that during the catalytic reaction the Fe^III ions in the γ-Fe₂O₃ nanoclusters interact with chloroolefin with the allylic structure to be partially reduced to the Fe^II ions that are bound in a complex containing chloride ions and O^II ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic activity of γ-Fe₂O₃ nanoparticles.     

Synthesis and electrochemical characterization of complexes of 1,2-bis[2-(pyridylmethylideneamino)phenylthio]ethanes with transition metals (CoII, NiII, CuII)

Transition metal (Ni^II, Co^II, and Cu^II) complexes with 1,2-bis[2-(3-pyridylmethylideneamino)phenylthio]ethane (1) and 1,2-bis[2-(4-pyridylmethylideneamino)phenylthio]ethane (2) were synthesized for the first time by slow diffusion of solutions of compounds 1 or 2 in CH₂Cl₂ into solutions of MX₂ · nH₂O (M = Ni, Co, or Cu; X = Cl or NO₃; n = 2 or 6) in ethanol. The reactions with Co^II and Cu^II chlorides afford complexes of composition M(L)Cl₂ (L = 1 or 2). The reactions of compound 1 with Ni^II salts produce complexes with 1,2-bis(2-aminophenylthio)ethane. The molecular structure of dinitrato[1,2-bis(2-aminophenylthio)ethane]nickel(ii) was confirmed by X-ray diffraction. The ligands and the complexes were investigated by cyclic voltammetry and rotating disk electrode voltammetry. The initial reduction of the complexes proceeds at the metal atom. The oxidation of the chlorine-containing complexes proceeds at the coordinated chloride anion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 350–355, February, 2008.     

Palladium(<Emphasis Type="SmallCaps">I</Emphasis>) and palladium(0) carbonyl bromide complexes

New Pd^I and Pd⁰ carbonyl bromide complexes co-existing in the same crystal were synthesized and studied by X-ray diffraction analysis. The crystals consist of dimeric complex anions composed of the central Pd(μ-CO)₂Pd fragment and four partially disordered terminal ligands (CO and Br⁻). The complexes were characterized by IR, ESR, and X-ray photoelectron spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1349–1355, June, 2005.     

ESR spectra of γ-irradiated samples of iron(iii) binuclear complexes

-Irradiation of -oxo-bridged binuclear iron complexes Fe^III ₂OL _n in a glycerol or dimethylformamide matrix at 77 K affords unstable mixed-valence Fe^IIF^III forms resulting from the transfer of a mobile electron generated by the ionizing radiation. These nonequilibrium forms retain the ligand environment of the original complexes, and their ESR spectra at 77–200 K are characterized by an asymmetric signal with an axially anisotropicg-factor, which is in agreement with the spectra of the Fe^IIFe syu forms obtained by chemical reduction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 869–871, April, 1996.     

New cobalt and iron pivalate complexes with 2,2′:6′,2″-terpyridine: synthesis, structure, and magnetic properties

The mononuclear complexes (η³-terpy)M(Piv)²·MeCN (M = Fe ⁱⁱ (3) and Co ⁱⁱ (4), and Piv is the pivalate anion) were synthesized by the reactions of polymeric iron(ii) and cobalt(ii) pivalates with 2,2′:6′,2″-terpyridine (terpy). The oxidation of compound 3 affords the pentanuclear heterospin iron(ii,iii) complex (η³-terpy)Fe₅(μ₄-O)(μ₃-OH)(μ-OH)₂(μ-Piv)₇(η¹-Piv)₂ (5). All compounds were characterized by X-ray diffraction. Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1186–1190, June, 2008.     

Catalytic hydroallylation of norbornadiene with allyl formate

Norbornadiene (NBD) reacts with allyl esters All—OC(O)R (R = Me, Bu^t, Ph, CCl₃, CF₃) in acetonitrile solutions of palladium(0) complexes to give a mixture of four isomeric nontraditional allylation products and the corresponding carboxylic acids. Under similar conditions, the reaction of NBD with allyl formate in solutions of Pd⁰ and Pd^II complexes occurs selectively, resulting in the product of addition of the allyl fragment and the H atom to an NBD double bond, 5-allylbicyclo[2.2.1]hept-2-ene, and CO₂. The hydroallylation of NBD is accompanied by catalytic addition of formic and acetic acids to one double bond of the diene to give bicyclo[2.2.1]hept-2-en-5-ol and nortricyclan-3-ol acetates and formates. Unlike most known palladium-based catalyst systems, these complexes exhibit catalytic activity also in the absence of phosphines. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 309–313, February, 2007.     

Critical phenomena in ethylbenzene oxidation in acetic acid solution at high cobalt(<Emphasis Type="SmallCaps">II</Emphasis>) concentrations

Critical phenomena in ethylbenzene oxidation in an acetic acid solution at high cobalt(III) concentrations (from 0.01 to 0.2 mol L⁻¹) were studied at 60–90 °C by the gasometric (O₂ absorption), spectrophotometric (Co^III accumulation), and chemiluminescence (relative concentration of radical RO₂ ^·) methods. These phenomena are as follows: (1) increase in the oxidation rate above the theoretical limiting rate of radical autooxidation (k ₃ ²[RH]²/2k ₆); (2) achievement of a maximum and a sharp decrease in the oxidation rate and concentration of radical RO₂ ^· with the further increase in the Co^II concentration (existence of critical concentrations). The oxidation rate increases due to the reaction RO₂ ^· + Co^II + H⁺ → → ROOH + Co^III, while the inhibition effect is caused by the decay of RO₂ ^· radical involving two cobalt(II) atoms: RO₂ ^· + 2 Co^II → R′CO + Co^III + Co^II (k(70 °C) ≈ 300 L² mol⁻² s⁻¹). The detailed scheme (through the formation of the complex RO₂ ^·Co^II) describing the conjugation of these reactions was proposed. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1823–1827, August, 2005.     

N,S,O-Containing organic ligands based on salicylaldehyde and 2-thiosubstituted ethylamines and their complexes with CoII, NiII, and CuII

The reaction of 2,2′-di(2-hydroxybenzaliminoethyl) disulfide (H₂L¹) and 2-[(2-thioethyl)iminomethyl]phenol (H₂L²) with MCl₂·xH₂O (M = Co, Ni, Cu) afforded the [M₂(L¹)Cl₂] and [M(L²)]₂ complexes, respectively. Their structures were determined by the data of electronic and IR spectroscopy and PM3 quantum chemical calculations. The H₂L¹ ligand and the complexes were studied by electrochemistry (CV and using a rotating disk electrode). The primary electronic changes are localized on the ligand fragment upon the electrochemical oxidation and reduction of the complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1325–1330, July, 2007.     

Structure of polynuclear palladium(ii) hydroxocomplexes formed upon alkaline hydrolysis of palladium(ii) chloride complexes

The structure of polynuclear Pd^II hydroxocomplexes (PHC) formed as a result of alkaline hydrolysis of Pd^II chloride complexes was studied by EXAFS, SAXS, and TEM methods. It is established that in aqueous solutions a hydroxocomplex particle is a filament curled into a ball containing about 100 Pd atoms. The filament consists of planar coordination squares of PdO₄ units linkedvia one or two oxygen bridges of different geometry. Aging of samples results in an increase in the number of single bridging ligands and a decrease in the diameter of particles. Interatomic distances around palladium atoms were determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimlcheskaya, No. 10, pp. 1901–1905, October, 1995.     

Inclusion of nickel(<Emphasis Type="SmallCaps">II</Emphasis>) and copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with aliphatic polyamines in cucurbit[8]uril

The inclusion compound of macrocyclic cavitand cucurbit[8]uril (CB[8]) with the nickel(II) complex containing the tetraazamacrocyclic ligand cyclam, {[Ni(cyclam)]@CB[8]}Cl₂··16H₂O (1), and the inclusion compounds of CB[8] with the copper(II) bis-ethylene-diamine complex, {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·{CB[8]}·42H₂O (2a) and {trans-[Cu(en)₂(H₂O)₂]@CB[8]}Cl₂·17H₂O (2b), were synthesized and characterized by X-ray diffraction analysis, IR and ESR spectroscopy, and electrospray mass spectrometry. Guest—host inclusion compounds can be directly synthesized starting from a metal complex and cucurbit[8]uril, as was exemplified by the preparation of compounds 2a and 2b.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2414–2419, November, 2004.     

Estimation of the specific content and nature of sorption sites of iron(<Emphasis Type="SmallCaps">III</Emphasis>) and zirconium(<Emphasis Type="SmallCaps">IV</Emphasis>) oxyhydroxides

The sorption of anions H₂PO₄ ⁻, HPO₄ ²⁻, PO₄ ³⁻, [Fe(CN)₆]³⁻, and [Fe(CN)₆]⁴⁻ from aqueous solutions on the surface of Fe^III and Zr^IV oxyhydroxide hydrogels freshly precipitated at pH 4–13 was studied. The region of sorbate concentrations was from 0.00025 to 0.06 mol L⁻¹. The plots of the anion uptakes vs. their equilibrium concentrations are represented by isotherms of the first type, which are well described by the Langmuir equation if the quantity of the amount adsorbed is expressed as mol-site g⁻¹. The maximum uptakes and constants of the Langmuir equation were calculated. The phosphate anions occupy the same number of sorption sites on the sorbents precipitated at different pH. The average specific content of sorption sites for the ferro- and zirconogels in the metastability period is independent of the pH of their precipitation, being 3.1·10⁻³ and 3.2·10⁻³ mol-site g⁻¹, respectively. The [Fe(CN)₆]³⁻ and [Fe(CN)₆]⁴⁻ anions are sorbed only on the positively charged sites of the hydrogels and occupy not more than 2·10 mol-site g⁻¹ in the studied interval of pH of precipitation. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1736—1741, August, 2005.     

Spacered dinuclear copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with acyldihydrazones of aliphatic dicarboxylic acids and 2-hydroxy-5-nitroacetophenone

Dinuclear copper(II) complexes with acyldihydrazones of 2-hydroxy-5-nitroacetophenone (H₄L) of the composition Cu₂(Py)_xL·mEtOH were synthesized and characterized. In these complexes, the coordination polyhedra of the copper atoms are linked to each other by a polymethylene chain of different lengths, from one to five monomer units. The structure of the [Cu₂L·4Mrf] complex (Mrf is morpholine) based on acyldihydrazone of malonic acid was established by X-ray diffraction. The copper(II) atoms in this complex are [4+1]-coordinated and are spaced by 6.94 Å. At room temperature, the signal in the ESR spectra of solutions of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids has a seven-line hyperfine structure with the constant of (35.3–38.8)·10⁻⁴ cm⁻¹ (g = 2.109–2.112) due to exchange interactions between unpaired electrons and two equivalent copper nuclei. An increase in the length of the polymethylene chain to five monomer units hinders exchange interactions, and the ESR signal of the complex based on acyldihydrazone of pimelic acid has a four-line hyperfine structure with a _Cu = 72.7·10⁻⁴ cm⁻¹ typical of mononuclear copper(II) complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 229–234, February, 2007.