Magnetic moments of multielectron mixed-valency dimer clusters in a dynamic intermediate vibronic coupling approach

The vibronic aspect of the Jahn-Teller effect is considered for multielectron mixed-valency dimer clusters. A basic intermediate-coupling set is used in the numerical diagonalization of the vibronic Hamiltonian. The temperature dependence of the vibronic magnetic moment is derived for symmetrical and distorted mixed-valency dimer clusters. Strong vibronic interaction can suppress double exchange and lead to an antiferromagnetic ground state for the cluster. Distortions that eliminate the inversion center localize the surplus electron and suppress the ferromagnetic effect caused by double exchange.Chemical Institute, Moldovian Academy of Sciences. Moldovian State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 11–19, March–April, 1993.     

Vibronic reduction of Heisenberg and double exchange in multielectron mixed-valency clusters

Vibronic reduction is considered for Coulomb interaction between centers for Heisenberg and double exchange in multielectron mixed-valency d²-d³ clusters. A simplified multimode vibration model indicates how effects arise via vibrations from the correlation interaction between electron shells. Vibronic reduction in double exchange can alter the magnetic parameters for the cluster's ground state.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 114–121, March–April, 1992.     

Spectral-band multiplet structures in intervalency electron transfer in exchange-coupled mixed-valency dimers

A study is made on the effects of exchange interaction on the shapes of intervalency-transfer electron spectra in binuclear mixed-valency complexes. The spectrum is determined by means of calculated spin-vibronic cluster states. It is shown that it is a superposition of components from the different spin states. The temperature dependence of the maximal intensity is not uniquely determined by the sign of the exchange interaction and is dependent on the order of the spin-vibronic states.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 2, pp. 211–215, March–April, 1987.We are indebted to I. B. Bersuker and J. J. Girerd for their useful advice and discussions.     

Vibronic coupling effects in trimeric mixed-valence clusters

The spectrum of a trimeric mired-valence cluster d₁–d₁–d₂ is calculated in the Piepha-Krausz-Schatz vibronic model. Based on the vibronic spectra obtained magnetic properties of the d₁–d₁–d₂ cluster are investigated It is shown that spin of the system's ground state may change not only as a result of double exchange reduction by vibronic coupling, but also due to a diflerence in the eneqy dependence of the lowest vibronic states on the vibronic coupling constant for diflerent total spin values. Unlike previous studies of vibronic interactions in the d₁–d₁–d₂ cluster, in this study the diagonalizations of the vibronic-coupling and double-exchange matrices are fuljilled simultaneously, using Lanczos' method. Due to this, all types 4 vibronic state mixing by double exchange could be taken into account properly.Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 20–32, September–October, 1993.Translated by L. Smolina     

The possibility of separate determination of the conformational characteristics of azoxide biradicals according to rapid-exchange ESR spectra of solutions

Conclusions Exact measurement of mean values of the exchange integral for various azoxide biradicals with rapid exchange has shown the possibility of utilizing these as sensitive spin probes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1776–1779, August, 1976.The authors wish to thank V. P. Ivanov for having kindly furnished the biradical (I) used in this work.     

Sorption of cesium on montmorillonite and effects of salt concentration

The sorption behavior of cesium on montmorillonite type clay was studied by using radioactivity measurements. Concentrations of Cs⁺ ions ranged from 10^–6 to 10^–2M. Cesium retention reduced with increasing salt concentration which was varied between 10^–4 and 10^–1M. Selectivity coefficients K_Cs–Na for the exchange between Cs and Na were calculated for different equivalent fractions of Cs on the solid phase. Using theK _Cs–Na values, free energy change was found to be 7.8 kJ/mol. The data could be fitted to a Freundlich isotherm, and empirical Freundlich parameters enabled the generation of a site distribution function. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm, a mean energy of sorption of 8.6 kJ/mole was calculated which corresponds to the energy of ion exchange reactions. The values of energy changes calculated by using two different methods were in good agreement.     

The first oxalato-bridged dinuclear CoII–VIVO complexes: synthesis and magnetism

Two novel CoII–VIVO oxalato complexes have been synthesized and characterized, namely [CoL2VO(OX)2·3H2O [L = 1,10-phenanthroline (phen) or 2,2-bipyridyl (bipy), OX = oxalate dianion]. Based on i.r. and electronic spectra and elemental analyses, extended oxalato-bridged structures consisting of VO2+ and CoII species, in which each VIV has a distorted square pyramidal environment and each CoII has a distorted octahedral environment are proposed for the two complexes. The temperature dependence of the magnetic susceptibility for [CoL2VO(OX)2]·3H2O (L = phen, bipy) was measured over the 77–300 K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator H^=–2JS^1S^2 giving the exchange integral J=–62.5 cm–1 and J=–40.3 cm–1 for the phen and bipy complexes, respectively. These indicate antiferromagnetic spin exchange interaction between the CoII and VO2+ centres.     

Magnetic Properties and Structure of Polynuclear Compounds Based on Macrocyclic Azacyclam Complexes of Nickel(II) and Bridging Oxalate Ions

By X-ray diffraction analysis, we have established the structure of a binuclear complex of nickel(II) with an azacyclam ligand and a bridging oxalate ion. Study of the magnetic properties of a series of complexes of this type with related macrocyclic ligands has allowed us to observe antiferromagnetic coupling between the metal ions and a magnitude of the exchange integral J that varies in the range from –11.8 cm^–1 to –25.6 cm^–1. We have shown that, despite the close structural parameters of the macrocyclic ligands, the complexes are characterized by different magnetochemical behavior.     

Synthesis and magnetism of tetrachlorophthalato-bridged cobalt(II) binuclear complexes

Three new cobalt(II) binuclear complexes have been prepared and characterized, namely [Co2(TCPHTA)(L)4](ClO4)2 [L=1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline(NO2-phen) and 2, 2-bipyridyl (bipy), respectively], where TCPHTA is the tetrachlorophthalate dianion. Based on i.r. spectra, elemental analyses and conductivity measurements, tetrachlorophthalato-bridged structures consisting of two cobalt(II) ions in which each cobalt(II) ion has a distorted octahedral environment are proposed for these complexes. The temperature dependence of the magnetic susceptibility for [Co2(TCPHTA)(L)4](ClO4)2·nH2O (L=phen, NO2-phen and bipy) has been measured over the 77–300 K range and the observed data successfully simulated by an equation based on the spin Hamiltonian operator (H=–2JS1S2), giving the exchange integral J=–2.92, –3.45, –4.03 cm–1, respectively. This result indicates the presence of a weak antiferromagnetic spin exchange interaction between the metal ions.     

Synthesis and magnetic properties of dithiooxamide-bridged nickel(II) complexes

Two novel nickel(II) dinuclear complexes [Ni2(cyclam)2- (DTA)](ClO4)2 (1) and [Ni2(TAA)2(DTA)] (ClO4)2 (2) (TAA=N(CH2CH2NH2)3 , cyclam = 1,4,8,11-tetraazacyclotetradecane, DTA=dithiooxamide) have been prepared and studied by elemental analyses, i.r. and electronic spectra and magnetic measurements. The magnetic susceptibility temperature dependence was measured over the 77–300K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator (H=–2JS1S2) giving the exchange integral J=–23.09cm–1 for (1) and J= –26.0cm–1 for (2).     

Aqueous partial molar heat capacities and volumes for NaTcO4 and NaReO4

A flow microcalorimeter/densimeter system has been commissioned to measure heat capacities and densities of solutions containing radioactive species as a function of temperature. Measurements were made for NaTcO₄(aq) at six temperatures (189.15 K to 373.15 K for the heat capacities, 287.43 K to 396.67 K for the densities) over the molality range 0.01 to 0.29 mol-kg^–1. Measurements for NaReO₄(aq) (NaReO₄ is a common nonradioactive analogue for NaTcO₄) were made under similar conditions, but for eight temperatures and a more extensive range of molalities, 0.05 to 0.65 mol-kg^–1. Heat capacities of NaCl(aq) reference solutions were also measured from 293.15 K to 398.15 K.The heat capacity and density data are analysed using Pitzer's ioninteraction model. Equations for the apparent molar heat capacities and volumes are reported. Values of the NaReO₄(aq) partial molar heat capacities are compared to literature values based on integral heats of solution. The agreement between the two sets of NaReO₄ results is good below 330 K, but only fair at the higher temperatures. Values of the partial molar volumes have also been derived. Using literature values and the results of our experiments, it is calculated that the disproportionation of hydrated TcO₂(s) to form TcO ₄ ^– (aq) and Tc(cr) occurs more readily at high temperatures. The uncertainties introduced by using thermodynamic values for ReO ₄ ^– (aq), in the absence of values for TcO ₄ ^– (aq), are discussed.     

Kinetics of Gold Electrodeposition from Alkali–Cyanide Solutions: The Effect of Infinitesimal Quantities of Thallium(I) Nitrate

The effect of infinitesimal quantities of thallium ions on the gold electrodeposition from alkali–cyanide solutions is studied in conditions of a controlled time of the electrode contact with solution using the technique of renewal of the electrode surface by cutting off a thin slice of the metal. As opposed to the behavior of pure alkali–cyanide solutions, where a polarization dependence represented in the Tafel coordinates experiences an inflection, in the presence of infinitesimal quantities of thallium nitrate, no inflection is present in the curves recorded on a freshly-renewed electrode and a considerable depolarization of the process is observed. Effective values of the exchange current and the transfer coefficient increase, respectively, from values of 3 × 10^–5 A cm^–2 and 0.23 in pure alkali–cyanide solutions to 10^–4 A cm^–2 and 0.5 in the presence of thallium nitrate. It is shown that, if the potential scan is preceded by an exposure of the electrode in solution, with an increase in its duration, the depolarization effect passes through a maximum. A probable explanation for the regularities observed is suggested.     

Equilibrium of Br− and Cl− exchange on strong-basic anion-exchanger

The equilibrium of Br^– and Cl^– exchange is studied on the strong-basic anionexchangers. Quantitative characteristics which can be used for elaboration of dual-temperature separation processes have been obtained. An empirical equation for the dehydration extent of an anion in a phase of a sorbent has been suggested, allowing one to calculate the Br^– and Cl^– exchange equilibrium constants on the anion-exchanger in a wide temperature range.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2083–2089, December, 1994.     

Synthesis and magnetism of a binuclear copper(II)–manganese(II) complex with N,N-bis(N-hydroxyethylaminoethyl)oxamido as a bridging ligand

The heterobinuclear complex, [CuMn(L)(phen)2](ClO4)2· H2O, [L = N,N-bis(N-hydroxyethyleneamine)oxamido, phen=1,10-phenanthroline], has been synthesized with N,N-bis(N-hydroxyethylaminoethyl)oxamido as the bridging ligand. The electronic reflectance spectrum indicates the presence of exchange-coupling interaction between bridging MnII and CuII ions. The variable-temperature magnetic susceptibility of the complex was measured over the 4–300K range. The magnetic coupling parameter is consistent with an antiferromagnetic exchange between the MnII ion and CuII ion and fits the data for a heterobinuclear CuII–MnII magnetic exchange model based on the Hamiltonian operator (H= –2JS1S2, S1=1/2, S2=5/2), giving the antiferromagnetic coupling parameter of 2J=–74.0cm–1.     

Investigation of the kinetics and equilibrium of the transfer of protons from dithiophosphoric acids to amines

The transfer of protons from dithiophosphoric acids R₂PSSH to substituted pyridines and proton exchange between the SH groups of the same acids and NH of protonated pyridines in chloroform solution were studied. The results obtained are compared with the analogous data for monothiocarboxylic acids RCOSH. The mechanism of SH-NH exchange was established; its slow step, just as for RCOSH, is transfer of a proton in the ion pairs. In the transition from RCOSH to R₂PSSH, an increase in the thermal effect of the deprotonation of the acids by amines and the activation energy E of SH-NH proton exchange is observed, which is due to the greater stability of the R₂PSS^– anions in comparison with RCOS^– on account of the greater delocalization of charge on the two sulfur atoms. With increasing excess of acid (above two-fold), the values of E are increased, since the excess acid molecules more effectively solvate the ion pairs than the original molecular complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 6, pp. 676–681, November–December, 1985.     

An NMR study of hydrogen exchange in p-hydroxybenzoic acid

The compound has been used over a temperature range in dimethylsulfoxide, with trichloroacetic acid and triethylamine as catalysts. The rate constant for uncatalyzed bimolecular exchange at 25 C is k_N=131 M^–1 sec^–1; the constant for acid-catalyzed exchange is k_A=0.9 · 10⁴ M^–1 sec^–1; and that for base-catalyzed exchange is k_B=0.5 · 10⁴ M^–1 sec^–1. The activation energy for uncatalyzed exchange is 5.75 kcal/mole. The exchange rates in dimethylformamide and acetone are higher, on account of differences in the hydrogen bond. The exchange rates of the isomers fall in the sequence ortho > para > meta, which is due to conjugation and intramolecular hydrogen bonding. The exchange mechanism is discussed. Simple relationships in dimensionless parameters are given for calculating the exchange rate from the shape of the NMR signal.     

Synthesis and magnetic properties of nickel(II) complexes with the nitronyl nitroxides

Four novel complexes of nickel(II), Ni(tfac)2(NITPa)2 (1), Ni(tfac)2(NITPhNO2)2 (2), Ni(pfpr)2(NITPa)2 (3) and Ni(pfpr)2(NITPhNO2)2 (4), [tfac=trifluoro- acetato, NITPa=2-(3,4-methylenedioxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxy-3-oxid, NITPhNO2= 2-(3-nitrophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxid, pfpr=pentafluoropropionato], have been prepared and characterized by elemental analysis, i.r., and electronic spectra, and molar conductances. The temperature dependence of the magnetic susceptibility for complexes (1) and (3) was measured (4–300K). The observed data were successfully simulated giving the exchange integral J=–1.48cm–1 for (1) and J=–1.25cm–1 for (3). These results indicate a weak antiferromagnetic spin exchange interaction between nickel(II) ion and the radicals.     

Studying the O2, Metal/O2– (Solid Electrolyte) Electrode System with Use of Model Electrodes: The Exchange Current Density Determination

Cells with model gold and platinum electrodes are studied by an impedance spectroscopy method. Distinguishing features of these electrodes are a large characteristic size of the metal/electrolyte contact (up to 100 m) and such well definable geometrical parameters as the length of triple-phase boundary (TPB) and the contact area. E. Shouler discovered that the electrolyte resistance, measured in an electrochemical cell, varies with the oxygen activity. Modern view is that this is connected with the TPB expansion. The expansion parameters determined here depend on the electrolyte prehistory and reach a few tens of micrometers. Specific (referred to a unit TPB length) values of polarization conductivities of both electrodes are obtained. Depending on the electrode prehistory, they amount to (2–6.5) × 10^–4 and (3–22)× 10^–4 S cm^–1 for Pt and Au, respectively, at 977°C in an oxygen atmosphere. The polarization conductivity, calculated per unit active area of electrolyte, is independent of the Pt electrode prehistory. Calculated exchange current densities are compared with radioisotope assay results.     

UV radiation and skin cancer in Norway

A distinct increase in skin cancer incidences is observed since the registration started in Norway in the 1950s. As UV radiation is assumed to be the main risk factor for skin cancer, hourly values of the UV irradiance were reconstructed for the period 1957–2005 for 17 of the Norwegian counties (58–70°N). For reconstruction, a radiation transfer model is run with total ozone amount and cloud information as meteorological input. Reconstructed hourly erythemally weighted UV irradiances for about 5 years are compared to measurements at four stations, two stations representing the north–south extension of Norway, and two stations at about 60°N representing the eastern inland – Western coastal contrasts. The agreement between reconstructed and measured UV varies between 0% for the northernmost site to 10–15% overestimation for the other locations. For clear sky, a reasonable agreement between reconstructed and measured data was found for all stations, while for overcast, an overestimation of 10–20% was found for all but the northernmost station. Both the cancer incidences and the reconstructed UV values have a distinct north–south increase. The UV increase towards south is mostly due to increasing solar elevation. The west to east increase is much smaller, and differences in UV are due to differences in both cloud optical thickness and total cloud amount. One additional outcome from this work is that long-term UV-data are reconstructed for Norway, data that can be used in further biological and medical studies related to UV effects.     

Certain aspects of heterophase ion exchange

Ion exchange between an aqueous solution of KCl and a solution of tetraoctylammonium bromide in toluene has been studied at 20–70°C. Equilibrium exchange constants were measured. The free energy of the ion exchange is determined to a large extent by Coulombic interaction, which increases with decrease in the radius of the ion. The strength of the Q⁺X^– bond is weakened on passing from the normal onium salt to the hydrate and the rate of ion exchange increases. The position of equilibrium during approach to it from different sides may be affected by different formation processes of complexes with low activity in respect to exchange.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1773–1776, August, 1991.