Double exchange in polynuclear mixed-valence clusters. 2. Iron-sulfur proteins [Fe4S4]+ and [Fe4S4]3+

The energy states of tetrameric iron clusters with d⁶-d⁶-d⁶-d⁵ and d⁵-d⁵-d⁵-d⁶ electronic configurations, which form the metal frameworks of the [Fe₄S₄]⁺ and [Fe₄S₄]³⁺ iron-sulfur proteins, are calculated using a general approach. It is revealed that the structural distortions of these systems significantly affect the composition of the magnetic states. The effect of the isotropic Heisenberg exchange is considered. Valencia University, Spain. Bordeaux University, France. Moldova State University. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 816–825, September–October, 1996. Translated by I. Izvekova     

Magnetic properties of Mn(III)−Mn(IV) mixed-valence dimers in a dynamic vibronic model

For Mn(III)−Mn(IV) mixed-valence dimers, a dynamic pseudo-Jahn-Teller vibronic problem is solved. Temperature dependences of the magnetic moment of the clusters are calculated with inclusion of Heisenberg and double exchange as well as vibronic coupling. Conditions for antiferromagnetic, intermediate, and ferromagnetic ground spin-vibronic states and the accompanying low-temperature limits of magnetic moments are determined. State University, Moldova Republic. Valencia University, Spain. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4, pp. 28–34, July–August, 1994. Translated by L. Smolina     

Double exchange in polynuclear mixed-valence clusters. 1. General solution of the electronic problem

The problem of calculating the electronic energy spectra of mixed-valence clusters with one “extra” electron (dⁿ-dⁿ...dⁿ⁺¹) or hole (dⁿ⁺¹-dⁿ⁺¹...dⁿ) delocalized in the paramagnetic cores of transition metals is solved. Unlike the available particular solutions, which are restricted to small numbers of ions and electrons, the solution proposed in this work is general and is suitable for many-electron systems of arbitrary numbers of nuclei and arbitrary symmetries. The new microscopic approach to the double exchange problem is based on the combination of the sequential (“chain”) scheme of spin coupling and angular momentum method. In terms of this approach, an analytical dependence of the matrix elements of the double exchange, Heisenberg exchange, and vibronic interaction on all spin quantum numbers is obtained. The final equations contain only the 6j symbols and are free of the higher-order nj symbols, which obstructed the solution of the double exchange problem in previous works. Valencia University, Spain. Bordeaux University, France. Moldova State University. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 805–815, September–October, 1996. Translated by I. Izvekova     

Tunnel-exchange states of square-planar bielectron transfer clusters

The tunnel states of square-planar bielectron transfer dⁿ-dⁿ-dⁿ⁺¹-dⁿ⁺¹ (n=0–4) clusters are considered. The nature of the ground spin state is revealed in the limiting case of a strong double exchange. It is shown that the magnetic properties of these systems radically differ from those of clusters with one migrating electron (hole) and tetrameric tetrahedral bielectron transfer clusters. Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 826–833, September–October, 1996. Translated by I. Izvekova     

Magnetic properties of tetrameric tetrahedral clusters with two-electron transfer

Tunnel-exchange states of tetrahedral tetrameric clusters dⁿ-dⁿ-dⁿ⁺¹-dⁿ⁺¹ with double transfer are considered to calculate the energy levels and wave functions. A method based on the second quantization technique and group-theoretical approach is developed. The nature of the ground spin state of the above systems is determined. It is shown that the structures have magnetic properties that radically differ from the properties of clusters with one migrating electron (hole). Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 3, pp. 458–470, May–June, 1996.     

Hole-type mixed-valence tetrahedral cluster: Exchange-tunnel states and magnetic properties

The paper deals with the exchange-tunnel states of a tetrahedral tetrameric hole-type cluster d¹-d²-d²-d² used as a model of metal core of vrious protiens. A new method for group-theoretic classification ofthe quantum states of mixed-valence clusters is suggested. The nature ofthe ground spin state of the above systems has been investigated. The effect of partial spin alignment depending on the double exchange parameter value is discussed.Moldova State University. Translated fromZhumal Strukturnoi Khimii, Vol. 34, No. 3, pp. 14–25, May–June 1993.Translated by L. Smolina     

Soliton model of electron transfer in mixed-valence dimers and trimers

The soliton approximation is examined for mixed-valence dimers and trimers with one migrating electron. The calculations use Hamilton's canonical equations and a time-dependent wave function of the soliton type. In the two limiting cases (strong and weak vibronic coupling), the soliton approximation correlates well with the exact analytical solution. As in the adiabatic approximation at g²/v=1, the delocalized limit (quasifree electron) is transformed to the localized one (electron locked on the center). For molecular trimers, the soliton approximation allows us to reveal the cases where the transfer of an electron from the first to the third center is accompanied by electron density concentration on the intermediate center. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 46–53, November–December, 1994. Translated by L. Smolina     

Electron delocalization in asymmetric trimeric mixed-valence clusters

The statistical distribution of electron density in a C_2v one-electron trimeric mixed-valence cluster is considered in terms of the Piepho-Krausz-Schatz vibronic model using the adiabatic approximation. Conditions are revealed under which the lower branch of the adiabatic potential shows three minima, each corresponding to predominant localization of the electron on one of the three ionic centers. It is shown that when the symmetry of the system is disturbed, the potential has two minima, with the system localized on one of two equivalent centers at either minimum. Conditions are considered under which these minima merge into one minimum, which corresponds to delocalization of the electron over a pair of ions, i.e., partial delocalization. For a D_3h symmetric trimer, it is demonstrated that in the region of transfer parameters and vibronic couplings, where the localized and completely delocalized states coexist, even with insignificant distortions there are only three localization minima, and the central minimum, which corresponds to a completely delocalized state, vanishes. Valencia University, Spain. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 4, pp. 654–666, July–August, 1995 Translated by I. Izvekova     

Magnetic properties and tunnel exchange states of dimeric mixed-valence clusters with two-electron transfer

Tunnel states of dimeric mixed-valence clusters with dⁿ-dⁿ⁺² type two-electron transfer are considered. General expressions for the matrix elements of the double exchange operator are obtained taking into account the contributions of the excited states. The energy spectrum of the clusters is calculated and the magnetic properties are studied. Allowance for the dⁿ⁺¹-dⁿ⁺¹ excited states considerably affects the energy spectrum and the magnetic properties of the systems. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1038–1045, November–December, 1997.     

Refinement of the crystal and molecular structure of 4-phenylthiosemicarbazide diacetic acid monohydrate

Institute of Applied Physics, Academy of Sciences, Moldova Republic. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 154–158, May–June, 1994.     

Double exchange in polynuclear mixed-valence clusters

A method for calculating the energies of the tunnel states of mixed-valence, clusters is proposed. It is based on the secondary quantization technique and allows one to obtain analytical expressions for all matrix elements that appear in double exchange theory as well as to determine the microstructures of the parameters of this theory. The energy spectra of trimeric systems are calculated with allowance made for the three-center transfer integrals, and the magnetic properties of these systems are investigated. Moldova State University. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 4, pp. 644–653, July–August, 1995. Translated by I. Izvekova     

Synthesis and structure of the product of bis-condensation of 4-methyl-2,6-diformylphenol with dimethyl N′,N′-hydrazine diacetate

Bis-condensation of 4-methyl-2,6-diformylphenol with dimethyl N′,N′-hydrazine diacetate gave product I. The structure of I was determined by X-ray analysis. The conformations of the two side chains of dimethyl N′,N′-hydrazine diacetate are significantly different. The position of one chain is fixed by the intramolecular H-bond of O−H.…N type. Due to its conformation, compound I is partly ready for complex formation with d-metals. Institute of Applied Physics, Academy of Sciences, Moldova Republic. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 3, pp. 91–98, May–June, 1994. Translated by L. Smolina     

To the theory of electron scattering by polyatomic molecules

Within the Born-Oppenheimer adiabatic perturbation theory, an equation was obtained for the intensity of fast electron scattering by polyatomic molecules. All of its parameters are explicitly defined by vibronic interaction in a molecule; due to this, quantum chemical calculations are fully applicable to electron diffraction studies of molecular geometries. Engels Anti-Aircraft Missile Higher Military School. Translated fromZhurmal Strukturnoi Khimii, Vol. 35, No. 2, pp. 40–45, March–April, 1994. Translated by L. Smolina     

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     

S 1←S 0 vibronic spectra and inversion potentials in theS 1 states of acetyl and formyl halides

The potential functions of inversion in the S₁ states are determined from the inversion transitions (out-of-plane C=O vibrations) found in the S₁←S₀ vibronic spectra of acetyl halide molecules. The high intensities of the hot inversion transitions are explained by the high probabilities of these transitions. The literature values of the inversion potentials (equilibrium values of angles formed by the C=O bonds deviating from the planes) of formyl halide molecules in the S₁ states are refined. The inversion potentials of formyl and acetyl halides are similar. M. V. Lomonosov Moscow State University, Chemical Faculty. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 316–321, March–April, 1995. Translated by L. Smolina     

Group-theoretical classification of the resonance states of mixed-valence clusters

Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 4, pp. 743–747, July–August, 1995.     

S 1 ←S 0 vibronic spectrum and the structure of the chloral molecule in theS 1 stateS 0 vibronic spectrum and the structure of the chloral molecule in theS 1 state

The vibronic absorption spectrum of chloral (CCl₃COH) vapors is studied in the region of S₁ ← S₀ electron transition (32,000–28,700 cm⁻¹). The 29,070 cm⁻¹ vibronic transition (not observed because of low intensity) is believed to be the ‘start’ of the electron transition. Several fundamentals are found in the S₀ and S₁ states. Inversion splitting of the zero vibrational level in the S₁ state of chloral, indicating a nonplanar structure of the carbonyl fragment, is found. The intensity ratio of the torsional transition bands indicates that the S₁ ← S₀ electronic excitation of the chloral molecule causes significant changes in the orientation of the −CCl₃ group relative to the molecular framework. The potential functions of internal rotation (S₀ and S₁ states) and inversion (S₁ state) of the chloral molecule are determined from experimental data. The potential barriers of internal rotation (S₀ and S₁ states) and inversion (S₁ state) are 380, 780, and 760 cm⁻¹ (4.5, 9.3, and 9.1 kJ/mole), respectively. M. V. Lomonosov Moscow State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 507–513, May–June, 1998.     

Selectivity of vibronic coupling in complex molecules with benzene fragments

This paper deals with the mechanisms of localization of Franck-Condon vibronic coupling of πσ^*- or πlπ^*-orbital type in a few vibrational modes, (LVM) in excited electronic states of polyatomic molecules. The analysis of vibronic coupling uses highly symmetric basis sets (for representing MO structures and normal coordinates ξ_R) as well as simplified models that relate the shift Δ_R of the electron potential minima along the normal coordinates to the MO structure and to ξ_R in the form of analytical expressions. The modes that are active in LVM are determined from the experimental luminescence spectra. These ideas about approximately high local symmetry of vibronic coupling in benzene fragments as well as the estimates of Δ_R depending on variations in the MO structure explain the experimental results. L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 286–291, March–April, 1995. Translated by L. Smolina     

Electronic absorption spectrum of pyridine N-oxide in the gas phase. General characterization

The full electronic absorption spectrum of pyridine N-oxide vapor in the near ultraviolet region has been obtained. The vibronic structure has been analyzed in detail. The four absorption bands, which are observed at 341, 290, 228, and 217 nm, correspond to four 0–0 vibronic transitions. The spectrum is interpreted in terms of the CNDO/S method. The symmetry of the vibrations that exhibit activity due to the Herzberg-Teller effect in different electronic states has been studied. N. G. Chernyshevskii Saratov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 345–349, March–April, 1995. Translated by I. Izvekova     

Vibronic spectra of the allyl radical at 6–8 eV with resonance-enhanced multiphoton ionization technique

The allyl radical was produced in molecular beam by pyrolysis of allyl iodide. The vibronic spectra from ground state to six new electronic states of the allyl radical at 6–8 eV, π →3d^xz, π →3d^xy and π →ns (n=4, 6, 7, 8) were observed firstly with the aid of time-of-flight mass spectros copy and resonance-enhanced multiphoton ionization technique. Vibrational progression ofv ₇(C₃ bend) with gross spacing of about 430 cm⁻¹ was observed inns Rydberg states. The adiabatic ionization potential of the allyl radical was obtained to be (65641 ± 20) cm⁻¹ ((8.138 ± 0.002) eV) by fitting the term values ofns (n=4,6,7,8) Rydberg states with Rydberg formula.