Ligand oxidation as a method for intramolecular activation of metal complexes

The results of investigations of organometallic and coordination compounds whose ligands contain redox fragments based on 2,6-di-tert-butylphenol and linked to the metal by various coordinating groups are summarized. The redox properties of -aryl, - and -allyl complexes, -diketonates, hydrazides, hydroxamates, glyoximates, and metalloporphyrins and metallophthalocyanines are considered. The possibility of changing the reactivity of organometallic and coordination compounds by changing the magnetic state due to oxidation of the redox-active phenolic group in the ligand is demonstrated. It is proposed to use ligand oxidation as a method for intramolecular activation of metal complexes.     

Spin exchange between transition metal complexes and nitroxyl radicals in nonaqueous media

New complexes of diaza- and tetraaza-containing crown ethers, viz., 1,10-diaza-18-crown-6 (1), 1,4,8,12-tetraazacyclopentadecane (2), 1,4,8,11-tetraazacyclotetradecane (3), and 1,4,8,11-tetraazacyclotetradecane 1,4,8,11-tetrachloride tetraacetic acid tetrahydrate (4), with the divalent copper and nickel ions and the Cl^–, Br^–, ClO₄ ^–, NO₃ ^–, and AcO^– counterions were synthesized. The exchange interactions of these compounds and paramagnetic copper and nickel salts with the TEMPO radical in MeOH—CHCl₃ binary mixtures of different compositions were studied. The plots of the linewidths of the hyperfine coupling components of TEMPO vs. concentration of the ions and temperature show that the frequency of diffusion collisions is the rate-limiting step for spin exchange (strong exchange regime). A strong dependence of the exchange rate constant (k _ex) on the crown ether and counterion structure was found. The isotropic hyperfine coupling constants (a _Cu) and g factors (g _i ) were measured for the Cu^II complexes with the crown ethers. In the case of the crown ether complexes 1—3 with CuCl₂, the a _Cu constant decreases linearly with an increase in g _i = g _i – 2.0023 in the series 3 < 2 < 1, whereas k _ex increases linearly in the same series with a decrease in the contact HFC on the Cu^II nucleus (K) and a decrease in covalence of bonding. For the complexes of 2 with Cu^II and different axial ligands (counterions), k _ex increases in the series Cl^– < ClO₄ ^– AcO^– Br^–; < NO₃ ^–. In the case of the complexes of 2 with NiCl₂, k _ex increases in the series 1 < 4 < 3 2. For the Cu^II and Ni^II salts with the Cl^–, ClO₄ ^–, and NO₃ ^– anions, the k _ex values are almost independent of the anion nature. The correlation of the k _ex values with the electron-spin parameters of the complexes is discussed.     

Electron spin exchange in isoviscous solvent mixtures

Electron spin exchange rate constants and hyperfine coupling constants have been measured for two nitroxide spin probes in a number of isoviscous mixed solvents. Collision rate constants, normalized to 1 cP, are lower for solvents in which the major component is water. Further anomalies in the coupling constant for the systemtert-butanol-water are explained in terms of the marked concentration fluctuations known to occur in this solvent mixture. Substitution of a hydrophobic spin probe by one containing an –OH group leads to lowering of the spin exchange rate, possibly due to solvation of the probe.     

Solid-phase mechanochemical incorporation of a spin label into cellulose

Samples of cellulose labeled with stable nitroxyl radicals were prepared by mechanochemical synthesis. The samples were studied by IR and EPR spectroscopies, X-ray phase analysis, and electron microscopy. The EPR spectral patterns indicate a uniform distribution of “grafted” paramagnetic centers over the cellulose macromolecular chains. X-Ray diffraction patterns obtained and the results of crystallinity index calculations for the samples showed that strong bonding of spin labels causes changes in the cellulose structure up to nearly complete amorphization of the material. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1127–1130, May, 2005.     

Semiempirical local spin: Theory and implementation of the ZILSH method for predicting Heisenberg exchange constants of polynuclear transition metal complexes

The local spin formalism ( 3 ) for computing expectation values 〈S_A · S_B〉 that appear in the Heisenberg spin model has been extended to semiempirical single determinant wave functions. An alternative derivation of expectation values in restricted and unrestricted cases is given that takes advantage of the zero differential overlap (ZDO) approximation. A formal connection between single determinant wave functions (which are not in general spin eigenfunctions) and the Heisenberg spin model was established by demonstrating that energies of single determinants that are eigenfunctions of the local spin operators with eigenvalues corresponding to high‐spin radical centers are given by the same Heisenberg coupling constants {J_AB} that describe the true spin states of the system. Unrestricted single determinant wave functions for transition metal complexes are good approximations of local spin eigenfunctions when the metal d orbitals are local in character and all unpaired electrons on each metal have the same spin (although spins on different metals might be reversed). Good approximations of the coupling constants can then be extracted from local spin expectation values 〈S_A · S_B〉 energies of the single determinant wave functions. Once the coupling constants are obtained, diagonalization of the Heisenberg spin Hamiltonian provides predictions of the energies and compositions of the spin states. A computational method is presented for obtaining coupling constants and spin‐state energies in this way for polynuclear transition metal complexes using the intermediate neglect of differential overlap Hamiltonian parameterized for optical spectroscopy (INDO/S) in the ZINDO program. This method is referred to as ZILSH, derived from ZINDO, Davidson's local spin formalism, and the Heisenberg spin model. Coupling constants and spin ground states obtained for 10 iron complexes containing from 2 to 6 metals are found to agree well with experimental results in most cases. In the case of the complex [Fe₆O₃(OAc)₉(OEt)₂(bpy)₂]⁺, a priori predictions of the coupling constants yield a ground‐state spin of zero, in agreement with variable‐temperature magnetization data, and corroborate spin alignments proposed earlier on the basis of structural considerations. This demonstrates the potential of the ZILSH method to aid in understanding magnetic interactions in polynuclear transition metal complexes. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

A new series of lipophilic pH-sensitive spin probes

A series of new lipophilic spin probes with pH-dependent ESR spectra was synthesized: cyano-substituted enamino ketones, viz., derivatives of imidazolidine nitroxyl radicals. The use of these compounds makes it possible to measure the acidity of the medium in the pH 6—12 range.     

配合物在单晶状态下二价中心金属离子交换研究进展

配合物中心金属离子交换是合成异质同构配合物的重要方法,在调节配合物的药物活性、气体吸附、催化等性质以及重金属解毒方面具有潜在的应用价值．本文介绍了配合物在单晶状态下二价中心金属离子交换的研究现状、中心金属离子交换机理、交换后配合物性能改变以及配合物中心金属离子交换存在的问题,并对未来研究方向进行了展望．     

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.     

Unusual exchange of functional groups at the silicon and metal atoms

Reactions of α,ω-dichlorooligosilanes with metal hydroxides in the presence of pyridine results in the exchange of halogen and oxygen atoms and the formation of cyclic siloxyoligosilanes and pyridine complexes of metal halides. The metallosiloxane groups are not formed. A scheme for the transformations observed is proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1658–1659, August, 1998.     

Electron Spin Resonance(ESR)Spectroscopy of the Transition-metal Complexes and Clusters I.Systematic Investigations of Real-and Complex-Orbital Methods for Calculating the d-Orbital Energies of a Low-spin(S=1/2)nd~5(t_2~5,~2T_2)(n=3

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Electron spin resonance studies on deuterated nitroxyl spin probes used in Overhauser‐enhanced magnetic resonance imaging

The electron spin resonance studies were carried out for 2 mm concentration of ¹⁴N‐labeled and ¹⁵N‐labeled 3‐carbamoyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl, 3‐carboxy‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl, 3‐methoxycarbonyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl and their deuterated nitroxyl radicals using X‐band electron spin resonance spectrometer. The electron spin resonance line shape analysis was carried out. The electron spin resonance parameters such as linewidth, Lorentzian component, signal intensity ratio, rotational correlation time, hyperfine coupling constant and g‐factor were estimated. The deuterated nitroxyl radicals have narrow linewidth and an increase in Lorentzian component, compared with undeuterated nitroxyl radicals. The dynamic nuclear polarization factor was observed for all nitroxyl radicals. Upon ²H labeling, about 70% and 40% increase in dynamic nuclear polarization factor were observed for ¹⁴N‐labeled and ¹⁵N‐labeled nitroxyl radicals, respectively. The signal intensity ratio and g‐value indicate the isotropic nature of the nitroxyl radicals in pure water. Therefore, the deuterated nitroxyl radicals are suitable spin probes for in vivo/in vitro electron spin resonance and Overhauser‐enhanced magnetic resonance imaging modalities. Copyright © 2017 John Wiley & Sons, Ltd.     

Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes

The application of broken symmetry density functional calculations to homobinuclear and heterobinuclear transition metal complexes produces good estimates of the exchange coupling constants as compared to experimental data. The accuracy of different hybrid density functional theory methods was tested. A discussion is presented of the different methodological approaches that apply when a broken symmetry wave function is used with either Hartree–Fock or density functional calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1391–1400, 1999     

Ternary inclusion complexes of cyclodextrins with spin-labeled indoles and hydrocarbons. The formation of 2: 1: 2 complexes and partial dissociation of spin-labeled guests in the presence of a hydrocarbon liquid phase

The interaction of ternary complexes γ-or β-cyclodextrin (CD)-spin-labeled indole (pyrrolidine (1) or piperidine (2) derivative)-hydrocarbon (benzene or cyclohexane) with the liquid phase of these hydrocarbons gives rise to a new type of complexes (s) the ESR spectra of which are indicative of a much lower rotational mobility and its weaker temperature dependence for the spin-labeled guests compared with the initial ternary complexes (w). The formation of s-complexes is accompanied by a decrease in the proportion of the initial w-complexes. This gives rise to several isosbestic points in the ESR spectra, which indicates the formation of s-complexes from w-complexes. The rotational diffusion coefficient of 2 in s-complexes decreases 6–10-fold with respect to its value for w-complexes and the libration amplitude of 1 in the s-complexes decreases to 5–6° at 295 K. Transition between the two types of complexes occurs with characteristic times of 10³–10⁵ s and is reversible: upon the removal of the hydrocarbon, the proportion of the strongly immobilized s-signal decreases, while upon its addition, it increases again. These results indicate that the strongly immobilized ESR signals belong to 2: 1: 2 complexes, which are formed upon the insertion of the second hydrocarbon molecule into the initial ternary 2: 1: 1 w-complexes. According to PM3 quantum-chemical calculations, 2: 1: 2 complexes are stable in energy and the geometry of hydrocarbon arrangement depends on the structure of the spin-labeled guest. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2094–2100, December, 2006.     

Guest—host complexes of spin-labeled indoles with cyclodextrins in the solid phase: an esr study

Inclusion complexes of spin-labeled pyrrolidine-(1) and piperidine-containing (2) indole derivatives with β-cyclodextrin and γ-cyclodextrin (CD) were prepared in the solid phase and studied by ESR in a wide temperature interval. For all complexes and free spin probes in solvents of different polarity, local environment polarities of the NO group of the guest molecules were determined from the outer extrema separations in the ESR spectra measured at 77 K. From analysis of the Saturation Transfer (ST) ESR spectra and temperature dependences of linear ESR spectra of the complexes it follows that both guest molecules in γ-CD undergo rapid librations. The libration amplitude of the p-orbit axis of the NO group in molecule 2 increases with temperature and reaches about 16° at 333 K. The ESR lineshape of the β-CD complexes depends on the spin probe/β-CD molar ratio (ρ) even at ρ < 0.01. Lineshape analysis of the spectra recorded at different ρ showed that they consist of two components, one of them corresponding to strong spin-spin interaction between guest molecules and the other corresponding to almost absence of this interaction. The spectral components can be attributed to microphases of the complexes and to isolated complexes in the β-CD matrix, respectively. Simulation of the ST ESR and linear ESR spectra of the magnetically diluted complexes showed that the guest motion inside the CD cavity is better described by rotational jumps rather than Brownian diffusion in an orientation potential. In the temperature range 238—333 K, the rotational frequencies of 1 and 2 are in intervals 1.8·10⁷−6·10⁷ s⁻¹ and 4·10⁷⁻¹.3·10⁸ s⁻¹, respectively. The rotation occurs over the whole solid angle. Significant differences in the character of molecular dynamics in the γ-CD and β-CD complexes can be explained by different stoichiometry, namely, 1: 1 for the former and 2: 1 for the latter and by different orientation of guest molecules in the complexes. In both cyclodextrins the rotational mobility of molecules 2 is higher than that of 1 owing to intramolecular conformational transitions in the piperidine ring of 2 and steric hindrances produced by the methyl group in 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 233—241, February, 2006.     

M?ssbauer and other spectral studies of Fe(III) complexes of benzothiazolines

Different molar reactions of Fe(OPr¹)₃, and FeCl₃ with benzothiazolines having an NSH donor system. derived by the condensation ofo-aminothiophenol with heterocyclic aldehydes. viz. pyridine-2-aldehyde. furfuraldehyde and thiophene-2-aldehyde. lead to the formation of [Fe.Pr¹(NS)₂]₂, [Fc(NS)₃] and [Fe(NS)₂Cl| type of complexes. The resulting derivatives have been characterized by elemental analysis, conductivity measurements, molecular weight determinations and magnetic studies. IR, electronic, M?ssbauer and ESR spectral data have been used to deduce the structures of the resulting derivatives.     

Synthesis,structure, and antitumor properties of platinum(iv) complexes with aminonitroxyl radicals

The platinum(iv) complexes cis,trans,cis-Pt^IV(RNH₂)(NH₃)(OH)₂Cl₂, where R is 2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl (1) or 2,2,5,5-tetramethyl-1-oxyl-3-pyrrolidinyl (2), were prepared by oxidation of the corresponding cis-Pt^II(RNH₂)(NH₃)Cl₂ complexes with hydrogen peroxide. The reactions are catalyzed by tungstate salts, which makes it possible to carry out oxidation under mild conditions. The resulting complexes were characterized by elemental analysis, HPLC, and IR, UV, and ESR spectroscopy. The structure of complex 1 was established by X-ray diffraction analysis. Complex 1 exhibits the highest antitumor activity in an experimental tumor, viz., in P388 leukemia. The resistance of the tumor to this complex developed much slower than that to Cisplatin.     

Effect of the complex forming ion on the physicochemical characteristics of solvation of tetraphenylporphine complexes

The enthalpies of dissolution, transfer, and axial coordination for the Cd(II), Co(II), Mn(III), Fe(III), and Cr(III) complexes of tetraphenylporphine, H₂(TPP), in nonpolar (C₆H₆, CCl₄) and electron-donating solvents (DMF, DMSO, Py,c-C₅H₁₀NH) have been determined calorimetrically at 298.15 K. On the basis of thermogravimetrical data for the corresponding crystallosolvates the composition, thermal stability, and energy of intermolecular interaction of the metal-porphine complexes with pyridine have been calculated. Complexing in noncoordinating solvents brings about no radical change in the physicochemical characteristics of axial coordination which depend critically on the electron structure of the complex-forming metal.Translated fromfzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–850, May, 1993.     

Divalent transition metal complexes of 3,5-pyrazoledicarboxylate

New divalent transition metal 3,5-pyrazoledicarboxylate hydrates of empirical formula Mpz(COO)₂(H₂O)₂, where M=Mn, Co, Ni, Cu, Zn and Cd (pz(COO)₂=3,5-pyrazoledicarboxylate), metal hydrazine complexes of the type Mpz(COO)₂N₂H₄ where M=Co, Zn or Cd and Mpz(COO)₂nN₂H₄·H₂O, where n=1 for M=Ni and n=0.5 for M=Cu have been prepared and characterized by physico-chemical methods. Electronic spectroscopic data suggest that Co and Ni complexes adopt an octahedral geometry. The IR spectra confirm the presence of unidentate carboxylate anion (Δν=ν_asy(COO^–)–ν_sym(COO^–)>215 cm^–1) in all the complexes and bidentate bridging hydrazine (ν_N–N=985–950 cm^–1) in the metal hydrazine complexes. Both metal carboxylate and metal hydrazine carboxylate complexes undergo endothermic dehydration and/or dehydrazination followed by exothermic decomposition of organic moiety to give the respective metal oxides as the end products except manganese pyrazoledicarboxylate hydrate, which leaves manganese carbonate. X-ray powder diffraction patterns reveal that the metal carboxylate hydrates are isomorphous as are those of metal hydrazine complexes of cobalt, zinc and cadmium.     

Spectroscopic study of hydrogen exchange processes and structure of intermediate complexes with intermolecular hydrogen bonds

The kinetics of hydrogen exchange in molecular systems with H-bonds has been studied by means of kinetic IR spectroscopy and low-temperature NMR spectroscopy. The experimental values of the rate constants and activation energies for molecules capable of forming H-bonds as both proton donors and proton acceptor are collected and analyzed from the point of view of the influence of H-bond formation ability of the molecules-partners. The evidence available testifies to a molecular mechanism of the H-exchange reactions in inert solvents and in the gas phase via the formation of cyclic bimolecular intermediates. The different mechanisms and the structure of intermediate complex of molecular H-exchange process in inert media are discussed and the possible paths of experimental elucidation of reaction mechanism are offered.