Reactivity of hexafluoride complexes of group IV-a elements

By means of the SCF MO LCAO method in the MNDO approximation, electronic and spatial structures have been calculated for complexes EF ₆ ^2– (E = Si, Ge, Sn) and also certain aqua derivatives of these complexes. It has been shown that an associative substitution mechanism may be realized for SnF ₆ ^2– , a conclusion that is supported by data on the kinetics of hydrolysis.Dnepropetrovsk Institute of Rail Transport Engineers. Translated from Teoreticheskaya i Éksperimental'naya khimiya, Vol. 27, No. 4, pp. 491–493, July–August, 1991. Original article submitted October 12, 1990.     

Tetragonal distortions of some tetragonal Cr3+ centers in fluoroperovskite ABF3 crystals

The tetragonal distortions [characterized by the displacement DeltaR of the F(-) ion intervening in Cr(3+) and V(B) (B(2+) vacancy) or M(+) ion in B(2+) site] for Cr(3+)-V(B) and Cr(3+)-Li(+) centers in Cr(3+)-doped fluoroperovskites KBF(3) (B=Mg, Zn) and ACdF(3) (A=K, Rb, Cs) and also for Cr(3+)-Na(+) center in KZnF(3) have been studied by calculating the EPR parameters D, g(parallel) and g(perpendicular) from the crystal-field theory. From the studies, an interesting trend is suggested, i.e., when the size of the co-doped monovalent impurity M(+) in the nearest neighbor B(2+) site is comparable to that of the replaced B(2+) ion, the displacement DeltaR of the intervening F(-) ion in Cr(3+)-M(+) center is smaller than that in Cr(3+)-V(B) center and if the M(+) iron is much smaller or much larger than that of the replaced B(2+) ion, the displacement DeltaR in Cr(3+)-M(+) center is greater than that in Cr(3+)-V(B) center. The causes of the trend are discussed.     

Spin-mixed states of ferric ion in complexes of tetragonal symmetry

Using a strong crystal field model for ferric ion complexes with tetragonal symmetry and allowing spin-orbit coupling between sextet, quartet, and doublet states, a mechanism is obtained whereby ferric ion can exist in four qualitatively different ground states: a sextet, a quartet, a doublet or a substantially spin-mixed state. We have delineated the regions in crystal field parameter space in which these various possible ground states prevail. Also, we have calculated the eigenfunctions and eigenvalues typical of each region. We discuss in detail the nature of the 5 lowest ferric ion functions in these different regions, particularly in the regions of spin-mixed states. With this model we obtain a picture of these various ferric ion states consistent with the behavior of known complexes of ferric ion, particularly of the ferric heme compounds. The results presented here will be used in a subsequent calculation of some of the observed properties of these compounds.

---

Zusammenfassung Das Fe(III)-Ion wird in einem starken tetragonalen Ligandenfeld unter Berücksichtigung der Spin-Bahn-Kopplung behandelt. Je nach Größe des kubischen Ligandenfeldes, der beiden Parameter der tetragonalen Verzerrung und des Spin-Bahn-Kopplungsparameters ist der Grundzustand ein Sextett, ein Dublett, ein Quartett oder ein spin-gemischter Zustand. Eigenwerte und Eigenfunktionen der fünf untersten Zustände in Abhängigkeit von den Parameterwerten werden eingehend diskutiert. Die Parameter werden physikalisch interpretiert. Die hier gewonnenen Resultate werden in den folgenden Arbeiten zur Berechnung der Eigenschaften von Eisen-Hämin-Komplexen herangezogen.

---

Résumé En utilisant un modèle de champ cristallin fort pour les complexes de l'ion ferrique á symétrie tétragonale et en tenant compte du couplage spin-orbite entre les états sextet, quartet et doublet, on obtient un mécanisme pour l'existence de l'ion ferrique dans quatre états fondamentaux qualitativement différents: un sextet, un quartet, un doublet et un état mixte. Nous avons délimité les zones de paramètre du champ cristallin où dominent ces différents états fondamentaux. Nous avons aussi calculé les fonctions et les valeurs propres typiques dans chaque zone. Nous discutons en détail la nature des cinq plus basses fonctions de l'ion ferrique dans ces différentes zones, en particulier dans les zones á états de spin mixtes. A l'aide de ce modèle nous obtenons une image de ces différents états de l'ion ferrique en accord avec le comportement des complexes ferriques connus, en particulier du type hémique. Les résultats présentés ici seront utilisés dans un calcul de propriétés observées de ces composés.

     

Sulfur hexafluoride as a mobile phase for supercritical fluid chromatography

Summary The capabilities of sulfur hexafluoride as a mobile phase for supercritical-fluid chromatography are investigated. An evaluation of its overall utility on the basis of separations of standard aromatic hydrocarbon odel mixtures performed on a variety of bonded-phase, packed columns with UV detection is presented. The dependence of separation performance upon operational parameters is also examined. A comparative evaluation of the chroamtographic properties of supercitrical sulfur hexafluoride and those of supercritical carbon dioxide is developed from these separations under corresponding supercritical state conditions.     

Application of the ΔΛ isomerism of octahedral metal complexes as a chiral source in photochemistry

Photochemical studies on the use of chiral metal complexes in homogenous and heterogeneous systems are surveyed and commented on their significance. A main focus is laid on the utility of the ΔΛ isomerism of octahedral metal complexes as a chiral source. The reported works demonstrate that chiral metal complexes are effective as a molecular element in achieving varieties of functions such as chiral discrimination, chiral transfer, sensing and photoresponsive guests for biomolecules or liquid crystals.     

Electronic structures of tetragonal nitrido and nitrosyl metal complexes

The standard oxidation states of central metal atoms in C _4v nitrido ([M(N)(L)₅] ^z ) complexes are four units higher than those in corresponding nitrosyls ([M(NO)(L)₅] ^z ) (L=CN: z = 3−, M = Mn, Tc, Re; z = 2−, M = Fe, Ru, Os; L = NH₃: z = 2+, M = Mn, Tc, Re; z = 3+, M = Fe, Ru, Os). Recent work has suggested that [Mn(NO)(CN)₅]³⁻ behaves electronically much closer to Mn(V)[b ₂(xy)]², the ground state of [Mn(N)(CN)₅]³⁻, than to Mn(I)[b ₂(xy)]²[e(xz,yz)]⁴. We have employed density functional theory and time-dependent density functional theory to calculate the properties of the ground states and lowest-lying excitations of [M(N)(L)₅] ^z and [M(NO)(L)₅] ^z . Our results show that [M(N)(L)₅] ^z and [M(NO)(L)₅] ^z complexes with the same z value have strikingly similar electronic structures.     

Jahn—teller distortions in copper(II) complexes as determined from ESR powder spectra

Cations Cu(ligand)²⁺₆ doped in lattices of non-cubic Zn(ligand)₆(anion)₂ are shown to have ESR powder spectra, corresponding with two types of cations, distorted octahedral and regular octahedral. Upon lowering of the temperature the number of distorted molecules increases. Despite of the non-cubic symmetry the results are essentially similar to single crystal observations and investigations on cubic lattices.     

Blue copper model complexes with distorted tetragonal geometry acting as effective electron-transfer mediators in dye-sensitized solar cells

The electron self-exchange rate constants of blue copper model complexes, [(-)-sparteine-N,N'](maleonitriledithiolato-S,S')copper ([Cu(SP)(mmt)])(0/)(-), bis(2,9-dimethy-1,10-phenanthroline)copper ([Cu(dmp)(2)](2+/+)), and bis(1,10-phenanthroline)copper ([Cu(phen)(2)](2+/+)) have been determined from the rate constants of electron transfer from a homologous series of ferrocene derivatives to the copper(II) complexes in light of the Marcus theory of electron transfer. The resulting electron self-exchange rate constant increases in the order: [Cu(phen)(2)](2+/+) < [Cu(SP)(mmt)](0/)(-) < [Cu(dmp)(2)](2+/+), in agreement with the order of the smaller structural change between the copper(II) and copper(I) complexes due to the distorted tetragonal geometry. The dye-sensitized solar cells (DSSC) were constructed using the copper complexes as redox couples to compare the photoelectrochemical responses with those using the conventional I(3)(-)/I(-) couple. The light energy conversion efficiency (eta) values under illumination of simulated solar light irradiation (100 mW/cm(2)) of DSSCs using [Cu(phen)(2)](2+/+), [Cu(dmp)(2)](2+/+), and [Cu(SP)(mmt)](0/)(-) were recorded as 0.1%, 1.4%, and 1.3%, respectively. The maximum eta value (2.2%) was obtained for a DSSC using the [Cu(dmp)(2)](2+/+) redox couple under the light irradiation of 20 mW/cm(2) intensity, where a higher open-circuit voltage of the cell was attained as compared to that of the conventional I(3)(-)/I(-) couple.     

On the hyperfine coupling in tetragonal copper(II) complexes

The vibronic effect on the hyperfine coupling (HFC) parameters in tetragonal copper(II) complexes was studied. The parameters of the vibronic contributions from the - and 4s-AOs of the Cu²⁺ ion to the ground-state function were estimated. The anomalous behavior of the isotropic HFC was analyzed in terms of the static model with consideration of the vibronic coupling. The static and vibronic contributions to the anisotropic portions of the components of the HFC tensor were estimated.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 204–206.Original Russian Text Copyright © 2005 by Muravev.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Strong distortions in hexacarbonyldicobalt complexes by push-pull effects

Push-pull substituted alkynes with a thioether moiety in the α position and a sulfoxide or a sulfone moiety in the α′ position are reacted with octacarbonyldicobalt to create highly distorted hexacarbonyldicobalt complexes.     

Theoretical analysis of the Jahn-Teller distortions in tetrathiolato iron(II) complexes

Crystallographic studies of [Fe(SR)(4)](2-) (R is an alkyl or aryl residue) have shown that the Fe(II)S(4) cores of these complexes have (pseudo) D2d symmetry. Here we analyze the possibility that these structures result from a Jahn-Teller (JT) distortion that arises from the e(3z(2) - r(2), x(2) - y(2)) orbital ground state of Fe(II) in T(d)symmetry. Special attention is paid to the influence of the second-nearest neighbors of Fe, which lowers the symmetry and reduces the full JT effect to a smaller, pseudo JT effect (PJT). To estimate the size of the PJT distortion, we have determined the vibronic parameters and orbital state energies for a number of [Fe(SR)(4)](2-) models using density functional theory (DFT). Subsequently, this information is used for evaluating the adiabatic potential surfaces in the space of the JT-active coordinates of the FeS(4) moiety. The surfaces reveal that the JT effect of Fe(II) is completely quenched by the tetrathiolate coordination.     

EPR Parameters of quantum mixed-spin ferric complexes with rhombic and tetragonal symmetry

Calculations are presented for the EPR g values of ferric iron in a crystal field with axial and rhombic symmetry components for a spin state which is a quantum mechanical mixture of intermediate-spin (S = 3/2) and high-spin (S = 5/2) components. The crystal field parameter μ/δ₁ is discussed as a more fundamental measure of rhombic distortion than the spin Hamiltonian ratio E/D.     

Excited-state distortions determined from structured luminescence of nitridorhenium(V) complexes

The nitridorhenium(V) complexes ReNCl(2)(PCy3)(2) (1), ReNBr(2)(PCy3)(2) (2), ReNCl(2)(PPh3)(2) (3), and ReNBr(2)(PPh3)(2) (4) produce structured emission spectra upon excitation at low temperature. The origin, E(00), occurs at 15 775, 16 375, 15 875, and 16 300 cm(-1), respectively. The vibronic peaks are regularly spaced with an average energy separation corresponding to the Re triple bond N stretching frequency. The nitridorhenium stretching frequency ranges from 1095 to 1101 cm(-1), as determined by Raman and IR spectroscopy. The excited-state distortions are calculated by fitting the emission spectra. The excited state arises primarily from a d(xy) (ReN nonbonding) to d(yz) (ReN pi antibonding) transition. The rhenium-nitrogen bond length in the excited state is 0.08 A longer than in the ground electronic state, which is consistent with the difference in bond lengths of ReN bonds of bond order 3 and bond order 2.5 as determined from molecular structures.     

The2 E↔4 A 2 transition in tetragonal Cr3+ complexes

The² E⁴ A ₂ absorption and emission spectra of [Cr(NH₃)₅(NO₃)](NO₃)₂, [Cr(NH₃)₅(NO₂)] ·(NO₃)₂, and [Cr(NH₃)₅(H₂O)](NO₃)₃ microcrystals have been recorded at 77°K. Tetragonal²E splittings are 209, 188 and 87 cm^–1, respectively. An analysis of the limited vibronic structure has been made and compared to the results for the parent octahedral complex, [Cr(NH₃)₆](NO₃)₃. Vibrations of approximately 270 and 700 cm^–1 are prominent.

---

Zusammenfassung Die² E⁴ A ₂ Absorptions- und Emissionsspektren von [Cr(NH₃)₅(NO₃)](NO₃)₂-, [Cr(NH₃)₅ (NO₂)](NO₃)₂- und [Cr(NH₃)₅(H₂O)](NO₃)₃-Mikrokristallen werden für 77° angegeben. Die tetragonalen² E Aufspaltungen sind209, 188 bzw. 87 cm^–1. Eine Analyse der begrenzten vibronischen Struktur wurde vorgenommen und mit den Resultaten für den oktaedrischen Stammkomplex, [Cr(NH₃)₆](NO₃)₃ verglichen. Schwingungen von etwa 270 und 700 cm^–1 treten besonders hervor.

---

Résumé Les spectres d'émission et d'absorption² E⁴ A ₂ de microcristaux de [Cr(NH₃)₅(NO₃)](NO₃)₂, [Cr(NH₃)₅(NO₂)](NO₃)₂ et [Cr(NH₃)₅(H₂O)](NO₃)₃ ont été enregistrés à 77° K. Les écartements tétragonaux² E sont respectivement 209, 188 et 87 cm^–1. Une analyse de la structure vibronique limitée a été effectuée et comparée aux résultats pour le complexe octaédral parent [Cr(NH₃)₆](NO₃)₃. Les vibrations au voisinage de 270 et 700 cm^–1 émergent.

---

---

This contribution is dedicated to the memory of Prof. Hans-Ludwig Schläfer, a stimulating colleague and valued friend.     

Synthesis of chromium N-heterocyclic carbene complexes using chromium Fischer carbenes as a source of chromium carbonyls

Chromium Fischer carbene complexes, [Cr{OMe(R)}(CO)₅] have been utilized as a source of chromium carbonyls in the synthesis of chromium NHC complexes. Using the synthetic method, chromium complexes of various NHC ligands were isolated in reasonable yields. Moreover, the method can be employed for the synthesis of molybdenum and tungsten NHC compounds.     

An investigation of the adiabatic potential energy surface of a Pseudo-Jahn-Teller complex using X-ray diffraction

X-ray diffraction combined with theoretical results obtained for isolated molecules can reveal many topologic features of the adiabatic potential energy surface (APS) of pseudo-Jahn-Teller Cu(II) complexes. Single-crystal x-ray results of acetatobis (1,10-phenanthroline)copper(II) perchlorate from 10 to 351 K are presented. The observed Cu-O bond length changes of 0.26 and 0.38 Å are rationalized in terms of a one-dimensional APS with two nonequivalent minima. The Silver and Getz model of vibronic coupling applied to the temperature variation of the Cu-O bond lengths is not obeyed. The actual structures of the conformers associated with the energy minima were determined from the x-ray data. A means of estimating the pseudo-Jahn-Teller radius using mean-square vibrational amplitudes along the Cu-O bonds is also discussed.     

Phenylhydrosilocane as a source of silatranylium cations

Quantum chemical calculations were used for comparative analysis of the cations of the atrane structure [M(OCH₂CH₂)₃N]⁺ (M = Si or Ge) with classic three-coordinate cations R₃M⁺ of Group 14 elements. The possibility of nuclear chemical generation of atranylium cations in the condensed phase was experimentally demonstrated with silatranylium ions as examples.

     

Plant callus as a source of biochemicals

This article presents a review of the recent literature describing the use of plant callus for the production of biochemicals, as well as specific examples of work done in our laboratory to analyze the production of ribosome inactivating proteins fromTrichosanthes kirilowii callus. The article discusses research advances in the development, characterization, and improvement of plant callus cell lines, including new cell lines and potentially useful products, influence of media composition, and environmental conditions on growth and product distribution, cell line selection strategies, and long-term stability.