Quantum-Chemical Calculations of Ruthenium Nitrosyl Complexes with Tetradentate Macrocyclic Ligands

The geometric structure of the ground state and of metastable isomers of nitrosyl complexes trans-[Ru(P)(NO)(Cl)] (P = porphinate dianion) and trans-[Ru(NO)(salen)(X)]^q [salen = N,N'-ethylenebis(salicylideniminate) dianion; X = Cl^- (q = 0), H₂O (q = +1)] was optimized within the framework of the density functional method (SVWN/LanL2DZ+6-31G). The local minima corresponding to metastable isomers with a linear NO coordination through the oxygen atom and with a side ² NO coordination were found on the potential energy surfaces of these compounds. The second metastable states of all the three complexes have a lower energy. The difference in energies between the stable and metastable isomers is the least in the case of the complex trans-[Ru(NO)(salen)(Cl)].     

Synthesis,Characterization, Electrochemical and Spectroscopic Properties of [Ru(dppt)(bpy)Cl]+ and [Ru(pta)(bpy)Cl]+

Two novel Ru^II complexes [Ru(dppt)(bpy)Cl]ClO₄ (1) and [Ru(pta)(bpy)Cl]ClO₄ (2)[dppt, pta and bpy = 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine, 3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]acenaphthylene and 2,2-bipyridine, respectively] were synthesized and characterized by elemental analysis and electrospray mass spectrometry, ¹H-n.m.r., and u.v.–vis spectroscopy. The redox properties of the complexes were examined using cyclic voltammetry. Due to the strong -accepting character of asymmetric ligands, the MLCT bands of (1) and (2) are shifted significantly to lower energies by comparison with [Ru(tpy)(bpy)Cl]⁺.     

Mixed-Ligand Ruthenium(II) Complexes as Structural Units of Polynuclear Systems

Spectral and kinetic parameters were studied for phosphine-bipyridyl ruthenium(II) complexes, namely, cis-[Ru(Bipy)₂(PPh₃)X](BF₄), cis-[Ru(Bipy)(Dppe)X₂], and cis-[Ru(Bipy)(Dppene)X₂] (where Bipy is 2,2"-bipyridyl, PPh₃is triphenylphosphine, Dppe is 1,2-bis(diphenylphosphino)ethane, and Dppene iscis-1,2-bis(diphenylphosphino)ethylene; X = CN^–, NO₂ ^–), in the frozen (77 K) alcohol glasses (EtOH–MeOH, 4 : 1). The energies of the singlet and triplet metal-to-ligand charge transfer states d(Ru) *(Bipy) were found to increase in the order [Ru(Bipy)₂X₂] < [Ru(Bipy)₂(PPh₃)X]⁺< [Ru(Bipy)(Dppe)X₂] < [Ru(Bipy)(Dppene)X₂]. The luminescence quantum yields and the rate constants of the nonradiative deactivation of the lowest excited state ³MLCT increase in the same order.     

Metastable States of Ruthenium Nitrosyl Complexes. Density Functional Quantum-Chemical Calculations

Geometry optimization for the ground state and metastable isomers of the nitrosyl complexes trans-[Ru(NO)(NH₃)₄(L)]^{3 +} (L = imidazole, pyridine, pyrazine, nicotinamide), [Ru(NO)(CN)₅]^{2 -}, and [Ru(NO)Cl₅]^{2 -} was performed in terms of the density functional theory (SVWN/LanL2DZ + 6-31G). The energy gap between the stable structure and the isomer with linear coordination of NO via the oxygen atom is practically independent of the nature of ligand L in the series of ammonia complexes with the same charge, and the energy gap between the stable structure and the isomer with side ² coordination of NO gets slightly smaller if ligand L possesses -acceptor properties.     

Spectroscopic investigation and thermal behavior of new carbonyl complexes [M(CO)4(N—N)(CuX)], (M = W,Mo; N—N = 2,2′-bipyridine, 1,10-phenanthroline; X = Cl,SCN)

[M(CO)₄(N—N)] reacts with CuCl to give new heterobimetallic metal carbonyls of the type [M(CO)₄(N—N)(CuCl)], M = W, Mo; N—N = 2,2-bipyridine (bipy), 1,10-phenanthroline (phen). Reactions of [M(CO)₄(N—N)(CuCl)] with NaSCN produced the series of complexes of general formula [M(CO)₄(N—N)(CuSCN)]. The i.r. spectral of all the bimetallic carbonyls exhibited the general four (CO) band patterns of the precursors. The u.v.–vis. spectral data for precursors and products showed bands associated with * (nitrogen ligands), dd (intrametal), as well as MLCT d* (nitrogen ligands) and MLCT d *(CO) transitions. The [M(CO)₄(N—N)(CuX)] (X = Cl, SCN) emission spectra showed only one band associated with the MLCT transition. The t.g. curves revealed a stepwise loss of CO groups. The initial decomposition temperatures of the [M(CO)₄(N—N)(CuX)] series suggest that the bimetallic compounds are indeed thermally less stable than their precursors, and the X-ray data showed the formation of MO₃, CuMO₄, Cu₂O and CuO as final decomposition products, M = W, Mo. The spectroscopic data suggests that the heterobimetallic compounds are polymeric.     

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solution. XII. Angular Overlap Studies of Salicylideneethylenediamine Cu(II) Complex in Various Solvents

As a part of our general interest in the UV-Vis spectroscopy of multidentate mixed-donor ligands, the (salicylideneethylenediamine)Cu(II) complex has been prepared and characterized by elemental analyses, solubility in common solvents, molar conductivities, and ultraviolet (UV), and visible (Vis) spectroscopy. The combined results of spectrophotometric measurements and EPR spectra, as well as known the X-ray structure for solids, were used to determine the structure of the investigated complex in solutions. The spectra of [Cu(salen)] (H₂salen = salicylideneethylenediamine), were measured in various solvents at room temperature, resolved by Gaussian analysis, and angular overlap model (AOM) treated in C _2v symmetry. Because of overparametrization problems, the bis(salicylaldehyde)Cu(II) complex has been characterized and AOM treated. The results of this have been used for AOM studies of [Cu(salen)]. The effect of the solvents upon the - and -bonding ligand abilities is discussed.     

Ab initio SCF and CI study of the electronic spectrum of pyridine N-oxide

Configuration interaction (CI) studies of ground, n *, * * electronically excited states are reported for pyridine N-oxide. The transition energy to the lowest * excited ¹ B ₂ state is calculated at 4.35 eV, compared to the experimental spectrum range of 3.67–4.0 eV. This state lies below the lowest n * excited ¹ A ₂ state calculated at 4.81 eV above the ground state. The only experimentally reported triplet state at 2.92 eV above the ground state is predicted to be the ³ A ₁ (*) state. The calculated energy lies at 3.27 eV. Numerous other high-lying singlet states as well as the triplet states have also been calculated. The intramolecular charge transfer character of the ground and the excited states have been studied in terms of the calculated dipole moment and other physical properties.     

Electronic structure of the Fe3S4 cluster and its quasi-aromaticity

The localized molecular orbitals and their energy levels for the clusters [Fe₃S₄(SH)₃]^2–, [(HS)₃Fe₃S₄·Ni(PH₃)]^2–, [Mo₃S₄(OH₂)₉]⁴⁺, and [Mo₃S₄·Ni]⁴⁺ have been calculated by mean of the Edmiston-Ruedenberg energy localization technique under the CNDO/2 approximation in order to reveal the resemblance between [Fe₃S₄]⁺ and [Mo₃S₄]⁴⁺ in the geometrical configurations and the addition reactivities with heterometal atoms. It is shown that in these two cluster species with core {M ₃(₃-S)(-S)₃} of similar structure (M = Mo, Fe) there exist three synergically connected three-centered two-electron (M-S-M) -bonds around the puckered six-membered {M₃S₃} rings on account of delocalization of a lone electron pair on each bridging S atom; these (M-S-M) -bonds are thus capable of forming cubane-like heterometal clusters with intruder metal atoms through the ( M) bonding. It is therefore seen that unlike the [Mo₃S₄]⁴⁺ with appreciable bonding between the Mo atoms, the extra d-electrons on the metal atoms in the [Fe₃S₄]⁺ cluster are localized on the Fe atoms, exhibiting an electronic structure significantly different from that of the [Mo₃S₄]⁴⁺ cluster.     

Gamma resonance spectroscopic study of compounds containing the π-allylirontricarbonyl group

The gamma resonance (GR) spectra of a series of -allylirontricarbonyl compounds and -cyclopentadienyldicarbonyl complexes of iron have been recorded. The relationship between the GR spectra of these compounds and the electronic structure of the iron atom in the complexes has been examined. It has been shown that tetrahydrofuran, benzene, and acetonitrile do not react with -allylirontricarbonyl chloride, whereas dimethylformamide decomposes it with the formation of high-spin complexes of iron. The formation of the [-C₃H₅Fe(CO₃)]^– anion in the reduction of [C₃H₅Fe(CO₃)]I by naphthalene-sodium in benzene has been confirmed.     

Chemistry of Electronically Excited Ruthenium Polypyridine Complexes: III.1 Electronic Structure of Complexes cis-[Ru(2,2'-bpy)2(4,4'-bipy)(X)]q

The results of ab initio quantum-chemical calculations of isolated ruthenium(II) complexes cis- [Ru(bpy)₂(bipy)(X)]⁴4q (bpy is 2,2'-bipyridyl, bipy is 4,4'-bipyridyl; X = NH₃, Cl^-, Br^-, CN^-, NO^- ₂, ONO^-, MeCN, and NO⁺) are presented. Analysis of the charge distributions and the orbital structures of the complex ions points to absence of strong -acceptor bonds Ru-bpy, Ru-bipy, and Ru-X (X = NO⁺), to delocalization of -electron density under the action of strong donors X, to localized nature of lowest unoccupied molecular orbitals, and to special position of the nitrosyl complexes in this series.     

A 2pπ, 3dπ valence bond wave function for the 1B1u state of ethylene

A 2p, 3d valence bond wave function for the lowest ¹ B _1u state of the -system of ethylene is variationally optimized with respect to the atomic orbital exponents using a non-empirical -approximation. The resulting energy compares favourably with previous calculations and leads to a satisfactory value for the lowest ¹ A _1g-¹ B _1u transition energy. The optimized exponent for the 2p orbital is close to the Slater value whereas the exponent for the 3d orbital is found to be nearly hydrogenic. The implications of this result are discussed in some detail.

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Zusammenfassung Für den tiefsten ¹ B _1u -Zustand des -Elektronensystems des Äthylens wird nach der Variations-methode eine 2p, 3d-Valenzbindungs-Wellenfunktion bezüglich der Orbitalkoeffizienten optimiert, wobei eine nicht-empirische -Approximation zugrunde gelegt wird. Die berechnete Energie stimmt gut mit den Ergebnissen vorausgegangener Rechnungen überein. Für den tiefsten ¹ A _1g ¹ B _1u -Übergang ergibt sich ein befriedigender Energiewert. Der optimierte Orbitalkoeffizient für das 2p-Orbital stimmt gut mit dem nach der Slaterschen Regel bestimmten Koeffizient überein, während man für den 3d-Orbitalkoeffizienten einen Wert findet, der dem des Wasserstoffs ähnlich ist.

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Résumé Une founction d'onde V.B.(2p , 3d ) est optimée pour l'état ¹ B _1u d'aethylen. L'energie calculé aussi que l'energie de transition la plus basse ¹ A _1g -¹ B _1u est en bon accord avec des valeurs connues.

     

Kinetics and mechanism of the homogeneous reaction between some manganese(III)-Schiff base complexes and hydrogen peroxide in aqueous and sodium dodecyl sulphate solutions

Summary The kinetics of the reaction between H₂O₂ and some Schiff base complexes of Mn^III have been investigated in both aqueous and micellar sodium dodecyl sulphate (SDS) solution. The reaction rate is first order in both H₂O₂ and [complex], and inversely proportional to [H⁺]. The second-order rate constant increases in the sequence [Mn(salophen)(OAc)] > [Mn(salen)(OH₂)]-ClO₄ > [Mn(salen)(OAc)]H₂O, where salen = N,N-bis-(salicylidene)ethylenediamine and salophen = N,N-bis-(salicylidene)-o-phenylenediamine. At SDS concentrations below the critical micellar concentration, there is almost no effect on the rate of reaction whereas at higher concentrations the reaction rate increases slightly. A mechanism involving Mn^II and a peroxo intermediate is proposed.     

The electronic structures of some tetrazaborolines and dimethyltetrazadieneirontricarbonyl

Self-consistent field calculations have been performed on some ² tetrazaborolines using both an ab initio and a semi-empirical (CNDO) approach. The first method was employed in order to examine completely the ground-state and the properties of the -electrons in the parent molecule. The excited states of several boron-substituted derivatives of tetrazaboroline have also been calculated semi-empirically, including configuration interaction, and good agreement with the observed electronic absorption spectra was obtained. The results of the calculations were also invoked to distinguish between isomeric boron-substituted derivatives of tetrazaborolines. The electronic structures of two of the possible geometries of dimethyltetrazadieneirontricarbonyl, in which the N₄ moiety is attached in a or a fashion were examined by CNDO calculations and it was found that the more stable form involves bonding between the nitrogens and the iron atom.

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Zusammenfassung Für einige ²-tetrazaborwasserstoff-Derivate wurden SCF-Rechnungen nach einem ab initio- und nach einem semiempirischen (CNDO)-Verfahren durchgeführt. Die erste Methode wurde angewandt, um den Grundzustand und die Eigenschaften der -Elektronen im Ausgangsmolekül zu untersuchen. Die angeregten Zustände einiger am Boratom substituierter Derivate wurden semiempirisch unter Einschluß von Konfigurationenwechselwirkung berechnet, wobei gute Übereinstimmung mit den experimentellen Elektronenspektren erzielt wurde. Die Resultate wurden ebenfalls zur Unterscheidung verschiedener isomerer Derivate benutzt. Die Elektronenstruktur von zwei möglichen Geometrien des Dimethyltetrazadieneisentricarbonyl, in denen der N₄-Rest mit einer -oder -Bindung gebunden ist, wurde mit CNDO-Rechnungen untersucht. Es wurde gefunden, daß die stabilere Form -Bindungen zwischen den Stickstoffatomen und dem Eisenatom enthält.

     

Organometallic complexes containing thiosemicarbazone and related ligands. Part II(1). η3-allyl dicarbonyl complexes of molybdenum(II) with attached thiosemicarbazone ligands

Summary The -allylmolybdenum(II) complexes [MoX(CO)₂-(NCMe)₂(³-C₃H₄R)] (X=Cl, Br and I; R=H and 2-Me) react either in dichloromethane or acetonitrile with thiosemicarbazones to give the new complexes [MoX-(CO)₂(RRCNNHCSNH₂)(³-C₃H₄R)] (R=H or Me; R'=Me, Et, Pr or Ph)via displacement of acetonitrile ligands.     

Electronic Structure, Aromaticity, and Physicochemical Characteristics of Carbene, Radical, and Ionic Forms of Compounds of the Imidazole Series, and their Oxo and Thio Analogs

The effects of benzannellation, phenyl substitution at the nitrogen atom, protonation at the carbene carbon, ionization, and the state of the carbene center (² or ²) on the electronic structure, diamagnetic susceptibility, induced -electron ring currents, the ¹H, ¹³C, and ¹⁴N chemical shifts, and the energies of the lowest electronic transitions of imidazol-2-ylidenes and their oxo and thio analogs were examined in the bound version of -electron perturbation theory. The calculated and experimental data are compared.     

Titanosilicates as Supports for an Enzymatic Alcoholysis Reaction

Novel [Cr^III(amp)(bipy)(Cl)] (1) (H₂amp = N-(hydroxyphenyl)salicyldimine; bipy = 2,2-bipyridyl) and [Cr^III(app)(bipy)(Cl)]⁺ (2) (H₂app = N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy = 2,2-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). The significance of the results with respect to oxo-functionalization of C-H bonds both in unsaturated and saturated hydrocarbons is noted.     

Chemistry of Ruthenium Polypyridine Complexes: V. Electronic Structure of Ruthenium(II) Bipyridine-Diphosphine Mixed-Ligand Complexes

Comparative analysis of the donor-acceptor capacities of diphosphine ligands in two series of complexes: cis-[Ru(bpy)2(LL)]^{q +} [LL = 2,2'-bipyridine (bpy), o-benzoquinonediimine (bqdi), cis-1,2-bis(diphenylphosphino)ethane, cis-1,2-bis(diphenylphosphino)ethylene (dppen), (NH3)2, and (CO)2] and [Ru(NH₃)₄. (LL)]^{2 +} (LL = bpy, dppen, and bqdi), was performed. Diphosphines are the strongest donors; they compare in -acceptor capacity which is associated with phosphorus d orbitals with 2,2'-bipyridine and fall far short of o-benzoquinonediimine and carbonyl.     

Ru(II) Chloro-Bis(bipyridyl) Complexes with Substituted Pyridine Ligands: Interpretation of Their Electronic Absorption Spectra

A number of complexes were synthesized with the general formula cis-[Ru(Bipy)₂(L)(Cl)](BF₄), where Bipy is 2,2"-bipyridine, L is pyridyne (Py), 4-aminopyridine (4-NH₂py), 4-picoline (4-Mepy), nicotin-amide (3-CONH₂py), isonicotinamide (4-CONH₂py), 3- and 4-cyanopyridine (3-CNpy, 4-CNpy), 4,4"-bipyridine (4,4"-Bipy), trans-1,2-bis(4-pyridyl)ethylene (Bpe), 4,4"-azopyridine (Azpy), pyrazine (Pyz), imidazole (Imid), and NH₃. The semiempirical CINDO-CI method was used to calculate the energies and intensities of transitions in the electronic absorption spectra. The differences observed in the spectra of these compounds are mainly due to the positions of the charge-transfer transitions d (Ru) *(L). Depending on the positions of these transitions, ligands L can be divided into three groups: 1) transitions Ru L lie in the region of the first long-wavelength band d (Ru) *(Bipy) (L = Azpy, Pyz); 2) transitions Ru L lie between the first and second bands due to the charge transfer to Bipy (L = 3-CONH₂py, 4-CONH₂py, 4,4"-Bipy, Bpe, 4-CNpy), and 3) transitions Ru L lie in the region of the second band d (Ru) *(Bipy) (L = Py, 4-Mepy, 3-CNPy, 4-NH₂py, Imid).     

Complexation of three uranium(IV) ions at two α-B-[SbW9O33]9- trilacunary Keggin units: A spectroscopic investigation

The sandwich-type uranium(IV)-polyoxometalate Na₆ [U₃ (SbW₉ O₃₃ )₂ ]·22H₂ O was prepared and investigated by FT-IR and UV-VIS methods. The uranium(IV) coordination at the trilacunary Keggin units shifts the _as (W-O_b,c -W), _as (W=O_d ), _as (W-O_a ) antisymmetric stretching vibration bands in the 700 ÷ 950 cm^-1 region of the FT-IR spectrum of U(IV)-complex. The visible electronic absorption spectrum of the complex indicates a ³ H₄ electronic ground state of uranium ions and a quasicubic local symmetry around them. The UV electronic spectra of the U(IV)-POM complex and of the ligand present the broad bands assigned to p -d electronic transitions in the W=O bonds (at 46640 cm^-1 for the ligand and 47280 cm^-1 for the complex) and d -p -d transitions in tricentric W-O-W bonds (at 40880 cm^-1 for the ligand and 39920 cm^-1 for the complex).