Radical pairs generated by electron phototransfer in peroxide complexes of titanium(IV)

During irradiation of frozen alcohol solutions of the peroxide complexes of titanium(VI) in the near UV region corresponding to the peroxide ligand-central ion charge-transfer band a series of paramagnetic products, identified by the ESR spectra as radical pairs (RP), are formed. They represent associated or dimeric complexes of titanium(IV), containing not less than two radical particles (HO ₂ ^. or O ₂ ^. ) at strictly specified distances from each other, as ligands. The spectroscopic parameters D, D and E characterizing each of the radical pairs in a zero field were determined, and the distances between the paramagnetic centers in the pairs were calculated. Geometric models of the possible initial dimeric peroxide complexes of titanium(IV), the photolysis of which leads to the formation of the radical pairs, were analyzed. It was shown that all the discovered radical pairs can be obtained from one type of structure, i.e., dimeric peroxide complexes of titanium(IV) containing double bridges from the peroxide ligand and also O^2– or OH^–.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 568–576, September–October, 1988.     

Photochemical properties of peroxo complexes of titanium,intermediate products in the photocatalytic liquid-phase oxidation of alcohols

A study has been made of the photochemical reactions of titanium(IV) peroxo complexes formed in the reaction of titanium tetrachloride with hydrogen peroxide in alcoholic solutions and which are characterized by intense charge transfer bands at 360–425 nm. Irradiation of the solutions with light of = 254 nm leads to the decomposition of the titanium(IV) peroxo complexes, the formation of titanium(III) compounds, as well as the oxidation of the alcohol to aldehyde. In the irradiated frozen solutions associated complexes of titanium(III), organic free radicals formed from the alcohol molecule, as well as peroxy radicals have been identified by EPR. Irradiation with light corresponding to the longwave band of the peroxo complexes leads to their decomposition but titanium(III) compounds and alcohol oxidation products are not formed in this case. In irradiated frozen solutions the formation of paramagnetic titanium(IV) complexes containing the fragment Ti...O ₂ has been established, as well as other paramagnetic particles identified tentatively as coordinated Ti...O ₂ ^· radicals or radical pairs. It is shown that the decomposition of hydrogen peroxide in the presence of titanium(IV) compounds is photocatalytic.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 67–74, January–February, 1988.     

Photolysis of titanium (III) complexes in alcoholic matrices at 77‡k

Using the electron spectroscopy and EPR methods, it was found that during UV irradiation of frozen alcoholic solutions of distorted octahedral complexes [Ti(ROH)₄Cl₂]⁺ and [Ti(ROH)₆]³⁺, distorted tetrahedral hydroxide complexes of titanium (III) are obtained. The mechanism of the process, including successive redox reactions of the titanium compounds has been discussed. As the result of a phototransfer of an electron from the central atom orbitals to the vacant orbitals of the ligands (alcohol molecules) a titanium (IV) compound is obtained containing an anion radical of the alcohol as the ligand. The compound is unstable and undergoes ultraspheric transformations. Rupture of the C-O bond occurs in the anionradical of the alcohol; ethyl radicals and hydroxide complexes of titanium (IV) are thus formed, which by the action of light quanta transform into hydroxide complexes of titanium (III).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 480–484, July–August, 1985.     

Mass-spectrometric investigation of coordination compounds of nickel(II) with radical anions of S-alkyl-1-phenylisothiosemicarbazides

The electron-impact mass spectra of coordination compounds of nickel(II) with the general formula NiL₂, in which the radical anions [C₆H₅N -N-C(SR)=NR¹]^–, where R=CH₃ and R=H(I), R=CD₃ and R=H(II), R=C₂H₅ and R=H(III), and R=CH₃ and R=C₆H₅(IV), serve as the ligands, have been studied. In the mass spectra of compounds I–IV the peaks of the molecular ions have the highest intensity among the organometallic fragments. The initial stage of the fragmentation of [M]^+. is associated with the formation of the rearrangement ions [NiL + H]⁺, [NiL + C₆H₅]⁺, and [NiL + SR]⁺, ions, whose appearance becomes understood, if it is taken into account that the removal of one ligand is accompanied by the impairing of spins and the mass spectra of compounds I–IV is the presence of lines for the [NiL]⁺ ion in them. The dissociative ionization of compounds I–IV is strongly reminiscent of the behavior of ordinary complexes of metals with ligands of the nonradical type. The fragmentation scheme of the molecular ions under the effects of electron impact has been presented and discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 368–371, May–June, 1990.     

Flash photolysis of chloride complexes of Cu(II) in organic solvents

By means of flash photolysis and low-temperature spectrophotometry, the formation of a complex between a Cu(I) ion and a peroxy radical of the solvent has been detected in ethanol, isopropanol, and dimethylformamide. The peroxy radical is generated in a reaction of a solvent radical with a molecule of dissolved oxygen. The solvent radical appears as a result of photoreduction of chloride complexes of Cu(II). The radical complex has a band in the optical absorption spectrum with a maximum at 415–420 nm in ethanol and isopropanol. The rate of formation of this complex is determined mainly by the reaction of the radical of the matrix (R^.) with complexes of bivalent copper. The rate constant of this process in isopropanol at room temperature is (2–3)·10⁸ liters/ mole·sec. Disappearance of the radical complex Cu(I)...RO₂ ^. takes place in a reaction with complexes Cu²⁺ _solv and CuCl⁺ with a rate constant of 2.3·10⁷ liters/mole·sec at room temperature.Translated from Teoreticheskaya in iÉksperimental'naya Khimiya, Vol. 22, No. 1, pp. 39–44, January–February, 1986.     

Synthesis,spectral and electrochemical studies of alkoxo-bonded mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor azophenolalcoholate/aldiminealcoholates

Mixed-ligand vanadyl(IV) and vanadyl(V) complexes with tridentate ONO donor azophenolalcoholate/aldiminealcoholates [viz., 2-hydroxy-2-hydroxymethyl-5-methylazobenzene (H₂L¹), N-(2-hydroxymethylphenyl)-salicylaldimine (H₂L²) and N-(2-hydroxymethylphenyl)1-hydroxy-2-naphthaldimine (H₂L³)] and bidentate NN [viz., 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen)] or NO [viz., 8-hydroxyquinoline (Hhq)] donor ligands have been prepared and characterized by elemental analyses and by i.r., e.p.r. and u.v.–vis. spectroscopies. The data show that the vanadyl(IV) complexes exist in two isomeric solid forms viz., monomers and polymers, whereas vanadyl(V) complexes exist only in the monomeric form. The polymeric structure results from intermolecular V=OV=O interactions. The complexes with NN donor ligands are one electron paramagnetic and display two ligand-field transitions in the visible region, whereas the complexes with ON donor ligands are diamagnetic and exhibit only LMCT bands. The vanadyl(IV) complexes display an irreversible oxidation peak near +0.30 V for complexes with (L¹)^2– and near +0.55 V for complexes with (L²)^2– and (L³)^2– ligands, while the vanadyl(V) complexes display a quasi-reversible one electron reduction couple near –0.23 V versus s.c.e. The trends in the (V=O), values for the visible region transitions and the redox potential values for the vanadyl(IV) complexes have been scrutinized.     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.     

Electronic and ESR spectroscopic study of thiocyanate-containing coordination compounds of titanium(III) in alcohol solutions

In an investigation of electronic and ESR spectra, it has been established that titanium(III) with the thiocyanate ion (in ethanol) forms distorted tetrahedral and octahedral complexes. The tetrahedral compounds, which are hydroxo complexes of titanium(III) that contain one hydroxyl group and three thiocyanate ions in the coordination sphere, give signals in the ESR spectra with g_o=1.960, A_o=15.0·10^–4 cm^–1 g=1.958, A ^Ti =26.4·10^–4cm^–1, g= 1.691, A^Ti=9.0·10^–4 cm^–1. In the ESR spectra of liquid solutions, additional splitting on the nitrogen atoms is manifested(A _o ^N =2.2·10^–4 cm^–1), which indicates bonding of thiocyanate ions through the nitrogen atom. The pseudo-octahedral complexes of titanium(III), containing from two to six thiocyanate ions in the coordination sphere, are characterized by d-d absorption bands in the 520–590 nm region; and at 77°K, they give anisotropic ESR signals. On the basis of the temperature dependences of the equilibrium constants for the reaction of conversion of the tetrahedral complexes to the octahedral complexes, and also the lifetimes of the tetrahedral complexes, values have been estimated for the heat of reaction (H=26.8 kJ/mole) and the entropy change (S=–1.66 kJ/mole·°K) of the equilibrium process, and also the activation energy for the reaction of titanium(III) thiocyanate formation (E=37 kJ/mole).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 560–567, September–October, 1985.     

New copper (II) complexes of tridentate dibasic ONO donor ligands derived from salicylaldehyde or substituted salicylaldehydes ando-hydroxybenzylamine

Summary Copper(II) complexes with the Schiff bases derived from Salicylaldehyde and its 5-chloro-, 5-bromo-, 5-nitro-, 3-ethoxy- and 3,5-dichloro derivatives, or from 2-hydroxy-1-naphthaldehyde ando-hydroxybenzylamine, have been synthesized and characterized on the basis of elemental analysis, i.r. and electronic spectra and magnetic susceptibility measurements. The Schiff bases behave as tridentate dibasic O, N and O donor ligands and form complexes with 11 metal: ligand stoichiometry which exhibit subnormal magnetic moments ( _eff=0.88–0.98 B.M.) and are involved in strong antifer-romagnetic exchange (–J=482–525 cm^–1). The complexes exhibit a d-d band atca. 1600 cm^–1. A dimeric structure with aminophenolic oxygen atoms as the bridging atoms is proposed on the basis of i.r. and magnetic data.     

Electrochemical reduction of cobalt and nickel complexes with ligands stabilizing metal in low oxidation state

Electrochemical reduction of cobalt(ii) complexes containing -acceptor ligands (L = bpy, Ph₂Ppy) proceeds through three consecutive reversible steps: one-electron transfer to form a more stable Co^IL complex, transfer of two electrons at more negative potentials to form an anionic [NiL]^– complex, and reduction of the ligand to the radical anion. The stability of the cobalt complexes with different ligands decreases in the series Ph₂Ppy > Ph₃P > bpy.     

Dimeric Complexes of Manganese(II) and Nickel(II) Hexafluoroacetylacetonates with Pyrazole-Containing Nitronylnitroxyl Radicals

Reactions of Ni(II) and Mn(II) hexafluoroacetylacetonates with pyrazole-containing nitronylnitroxyl radicals (L) result in dimeric heterospin complexes [M(hfac)₂L]₂or [M(hfac)₂L]₂· C₆H₆. The paramagnetic ligands in the centrosymmetric binuclear molecules function as a bridge, with the nitroxyl O atom being bound to one metal and the imine N atom of the pyrazole ring to the other metal atom. The metal environment is a cis-octahedron with short M–O_NOdistances, which specifies a strong antiferromagnetic interaction between the lone electrons of paramagnetic centers in M–O–N< exchange clusters.     

Solvent extraction and spectrophotometric determination of titanium (IV) with 3-phenyl-3-methyl-2-mercaptopropenoic acid by use of the synergistic effect of pyridine

Summary The distribution equilibria of 3-phenyl-3-methyl-2-mercaptopropenoic acid (PhMMP), pyridine and the titanium (IV)-PhMMP complex in the presence of pyridine have been studied in the chloroform-water system. An extraction-photometric method for the determination of micro amounts of titanium has been developed. The synergistic effect of pyridine, and the influence of pH, the reagent concentration and the presence of electrolytes and masking agents on the equilibrium have been determined. From slope analysis of the distribution curves, the composition of the extracted species has been found to be Ti(OH)₂(HR)₂·py. The complex is extracted quantitatively. Beer's law is obeyed over the range 0.09–4.30g/ml titanium (IV) and the molar absorptivity is 1.30×10⁴1·mole^–1·cm^–1 at 447 nm. The method has been applied to the determination of titanium in ceramics.

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Über die Extraktion und spektrophotometrische Bestimmung von Titan(IV) mit 3-Phenyl-3-methyl-2-mercaptopropensäure mit Hilfe der synergistischen Wirkung des Pyridins

Zusammmenfassung Das Verteilungsgleichgewicht von 3-Phenyl-3-methyl-2-mercaptopropensäure (PhMMP), Pyridin und Titan-PhMMP-Komplex in Gegenwart von Pyridin wurde in einem Wasser-Chloroform-System untersucht. Eine extraktionsphotometrische Methode für die Bestimmung von Mikromengen Titan(IV) wurde ausgearbeitet. Die synergistische Wirkung des Pyridins sowie der Einfluß des pH, des Reagens und der Gegenwart von Elektrolyten und maskierenden Reagenzien in der wäßrigen Phase auf das Gleichgewicht wurden bestimmt. Aus der Richtung der Verteilungskurven wurde für den extrahierten Komplex die Zusammensetzung Ti(OH)₂(HR)₂·py ermittelt. Der Komplex wird quantitativ extrahiert. Das Beersche Gesetz ist von 0,09–4,30g·ml^–1 Ti(IV) erfüllt, der molare Absorptionskoeffizient ist 1,13·10⁴1·mol^–1·cm^–1; die Sandell-Empfindlichkeit beträgt 3,7ng·cm^–2 bei 447 nm. Diese Methode wurde für die Bestimmung von Titan in keramischem Material verwendet.

     

Synthesis,spectral, electrochemical and magnetic properties of new asymmetric dicopper(II) complexes bearing chemically distinct coordination sites

Two new unsymmetrical binucleating ligands, 2-[bis(3-N, N-dimethylaminopropyl)-aminomethyl]-6-[prolin-1-yl)methyl]-4-bromophenol [H ₂L¹] and 2-[bis(3-N, N -dimethylaminopropyl)aminomethyl]-6-[prolin-1-yl)methyl]-4-methylphenol [H₂L²], and their dicopper(II) complexes with different exogenous bridging motifs (OAc, Br and Cl) have been prepared and characterized by spectral, electrochemical, magnetic and e.p.r. studies. Electrochemical studies indicate the presence of two irreversible reduction peaks in the cathodic region. Variable temperature magnetic susceptibility studies of the complexes show that the extent of antiferromagnetic coupling increases in the order: OAc^–< Cl^–< Br^–. Broad isotropic or axial symmetric spectral features are observed in powder e.p.r. spectra of the complexes at 77K. A comparison of the electrochemical and magnetic behaviour of the complexes derived from the ligands is discussed on the basis of an exogenous bridge as well as the substituent at the para position of the phenolic ring.     

Electrochemical Behavior of Novel Bis(β-diketonate)phthalocyanine Complexes of Zr(IV) and Hf(IV)

We have used cyclic voltammetry to study the electrochemical properties of novel bis(-diketonate)phthalocyanine complexes of Zr(IV) and Hf(IV) in dichloromethane. We found three waves for the studied complexes that can be attributed to one-electron processes MPc(L)^0/1– ₂, MPc(L)^1+/0 ₂ and MPc(L)^2+/1+ ₂. We have shown that the electrochemical behavior of the complexes depends on the nature of the substituents in axial ligands and does not depend on the nature of the metals. We have analyzed the stability of the one-electron oxidation products of the complexes relative to disproportionation.     

The structure of binuclear molybdenum(VI) oxocomplexes with dianionic tridentate Schiff bases

Summary The new Mo^VI complex [Mo(O) (-O) (SAE)]₂ was prepared and characterized by means of spectroscopic (i.r.,¹Hn.m.r.) and crystallographic measurements. Crystals of the [Mo(C₉H₈NO₂)(H₂O)]₂, M=582.3, orthorhombic, space group Pbca,a=13.108(4),b=8.982(2),c=16.842(4) Å, v=1982.9 ų, z=4, D_m=1.93(2), D_c=1.95 g cm^–3, MoK =0.71069 Å, =1.3 mm^–1, F(000)=1152, T=295K, R=0.035 for 2413 reflections.The crystal structure consists of [Mo(O)(-O)(L)]₂, in dimeric units. The coordination geometry around each molybdenum atom is distorted octahedral with Mo–O (terminal) and Mo–O (bridge) distances of 1.694(3) and 1.760(3) Å, respectively, and with the angle O(1)–Mo–O(2) of 105.6(1)^o, typical for manycis-dioxocomplexes of Mo^VI. The asymmetric bridge is characterized by the following parameters: Mo–O(2)ⁱ and Mo–Moⁱ distances equal 2.408(3) and 3.319(3) Å, respectively, and the Mo–O(2)–Moⁱ and O(2)–Mo–O(2)ⁱ angles equal 104.5(1)^o and 75.5(1)^o, respectively.The i. r. and Raman spectra of molybdenum complexes with an asymmetric double oxygen bridge display a strong absorption the 800–850 cm^–1 range.     

Crystal structure of the La3+ sandwich complex based on 8-membered macrocyclic siloxanolate ligands

The product of the reaction between anhydrous lanthanum trichloride and potassium vinylsiloxanolate, K₅[VinSiO₂]₈La₄(₄-OH)[O₂SiVin]₈ · 5n-BuOH·2H₂O has been studied by X-ray diffraction. The compound is a «sandwich»-type complex where macrocyclic vinyloctasiloxanolate ligands with regularcis-configuration have co-axial and antiparallel orientation. These ligands coordinate a planar «cationic layer» formed by four La³⁺ ions and stabilized by an additional ₄-OH^– bridge ligand. A three-dimensional cage structure of complex lanthansiloxanolate pentaanions linked through the coordinated K⁺ counter-ions is formed in the crystal studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 184–189, January, 1993.     

Thermochemical investigation

The stoichiometry of the thermal decomposition and the stereochemistry of the following compounds was studied: NiR₄Cl₂ (I), NiR₄Br₂ (II), NiR₄I₂·2H₂O (III) and NiR₄(NCS)₂ (IV) (R=3-pyridylcarbinol, ronicol). In complexes I and II the loss of the volatile ligands (on the TG curves) occurs in three steps (–2R, –R, –R), in complex III in four steps (–2H₂O, –2R, –R, –R) and in complex (IV) in one step (–4R). According to the quasi-equilibrium decomposition temperatures, the thermodynamic stability of NiR₄X₄ complexes can be ordered in the sequence (according to X):Cl相似文献   

Synthesis,Spectral and Electrochemical Studies of Mixed-Ligand Oxovanadium(IV) and Oxovanadium(V) Complexes Incorporating the Tridentate ONO Donor Schiff Base Derived from Acetylacetone and Benzoylhydrazine

Mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes with a tridentate dinegative ONO donor Schiff base ligand [viz., 4-(1-hydroxybenzylidenehydrazono)-2-penten-2-ol (H₂L)] and bidentate NN [viz., 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen): complexes (1) and (2), respectively] or OO^–[viz., ethylene glycol (H₂gol), salicylaldehyde (Hsal) and vanillin (Hvan): complexes (3)–(5), respectively] donor ligands have been prepared and characterized by elemental analyses and by i.r., e.p.r., n.m.r., and u.v.–vis. spectroscopies. The complexes with NN donor ligands are one electron paramagnetic, displaying axial e.p.r. spectra and exhibiting two ligand-field transitions in the visible region, whereas the complexes with OO^– donor ligands are diamagnetic and display only LMCT bands. ¹H n.m.r. spectral data indicate that the pentavalent complexes (4) and (5) exist in two isomeric forms [(4A), (4B) and (5A), (5B) in 1:1 and 4:1 ratios, respectively]. The vanadyl(IV) complexes display an irreversible oxidation peak near +0.67 V while among the vanadyl(V) complexes, (3), displays an irreversible reduction peak near –0.20 V and (4) and (5) display a quasi-reversible one electron reduction peak near +0.25 V versus s.c.e. The trend in redox potential values and the selective stabilization of VO²⁺ and VO³⁺ motifs have been explained on the basis of the basicity of the bidentate auxiliary ligands.     

Crystal structure of the Nd,Gd, and Dy sandwich complexes involving 8-membered macrocyclic phenylsiloxanolate ligands

An X-ray structural investigation of the interaction products of anhydrous trivalent neodymium, gadolynium, and dysprosium chlorides with sodium phenylsiloxanolate was carried out. The synthesized compounds with the general formula Na₆[PhSiO₂]₈M₄(₄-O)[O₂SiPh]₈ · 10EtOH · 8H₂O (M = Nd, Gd, Dy) were found to be isomorphous isostructural sandwich complexes. The macrocyclic octaphenyloctasiloxanolate ligands in the complexes have anall-cis-configuration and are arranged in co-axial antiparallel pairs and coordinate the square planar groups of the four Nd³⁺, Gd³⁺, or Dy³⁺ ions stabilized by an additional central ₄-bridging O^2– ligand. Six Na⁺ counterions form the outer coordination sphere of the complexes such that four of them coordinate the siloxane macrocycle O atoms in pairs in analogy with crown-ether complexes.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 193–198, January, 1993.