Synthesis, spectroscopic properties, and tautomerism of mono-meso-substituted octamethylporphyrins

The synthesis spectroscopic properties and tautomerism of four novel mono-meso substituted(R)-octamethylporphyrins (R=o-hydroxybenzyl, p-aminobenzyl, 4-pyridinyl, and ferro-cenyl) were investigated. It was found that the porphyrins 2, 3 could be directly prepared in good yields via the coupling reaction of salicylaldehyde and p-aminobenzyl aldehyde with octamethyl-l',8'-dideoxy-ac-biladiene dihydrobromide, respectively. The free energy of activation (G) of the tautomerism of the porphyrins was calculated and interpreted in terms of electronic and steric nature. In contrast with 2-substituted-5,10,15,20-tetraphenylporphyrins, the substituents in meso position do not change the relative amount of two tautomers a and 6.     

Electrodeposition,properties, and composition of rhenium–nickel alloys

The process of deposition of the Re–Ni alloy, its current efficiency, and the alloy composition are studied as a function of the current density and the solution temperature. The hydrogen content in the deposits, their surface morphology, internal structure, and properties as the cathodic material for HER are examined. It is assumed that besides the high rhenium content, the high catalytic activity of nickel–rhenium alloys is associated with the high degree of their structural disordering.     

Dicyano and pyridine derivatives of β-carotene: synthesis and vibronic, electronic, and photophysical properties

Density functional theory and time-dependent density functional theory calculations provide pictures of the molecular orbitals involved in the ground and excited states of two cyano derivatives of 8'-apo-β-caroten-8'-al synthesized via an acid-base-catalyzed Knoevenagel condensation reaction. Population analysis shows that the symmetry-allowed transition, S(0) ((1)A(g)) → S(2) ((1)B(u)) based on the C(2h) symmetry is a HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) π → π* transition with electron densities located mostly on the polyene chain. Calculated and actual steady-state absorption spectra show similar features with low-energy peak maxima between 550 and 600 nm.     

Möbius and twisted graphene nanoribbons: stability, geometry, and electronic properties

Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists N(t) varying from 0 to 7 (the case N(t)=1 corresponds to a half-twist M?bius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO-->LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.     

Phenazineoxonium chloranilatomanganate and chloranilatoferrate: synthesis,structure, magnetic properties,and Mössbauer spectra

Russian Chemical Bulletin - Crystalline compounds (H3O)2(phz)3M2(C6O4Cl2)3·(CH3COCH3) n ·(H2O) n (n = 0?2, M = Mn (1), Fe (3)) were obtained in an acetone-water-tetrahydrofuran...     

Quinoxaline-walled π-stacking molecules: synthesis,conformation, and luminescence properties

A series of semi-rigid N-phenylsuccinimides I (11Xy), N-arylmethylsuccinimides II (18Xy), and N,N′-(1,4-arylenebis(methylene))disuccinimides III (19XyX) walled by quinoxaline (QX), dimethylquinoxaline (diMQX), or benzoquinoxaline (BQX) ring were synthesized. Intramolecular π–π interactions in solution were detected by NMR and fluorescence spectroscopy, in terms of reciprocal anisotropic shielding and exciplex formation, respectively. The X-ray crystallographic analysis revealed the preferential conformations in solid state, which were compatible with the results of conformational studies by NMR and fluorescence spectroscopy. The results collectively indicated that 18Xy and 19XyX are driven by intramolecular π–π interactions in the mode of π-stacking (face-to-face) or T-shaped (edge-to-face) configuration to preferentially adopt the folded- and the double folded-conformation, respectively, where the spaced aromatic rings are oriented syn to each other in close proximity.     

Preparation and spectroscopic properties of 2'''',5''''-dideoxynucleosidylcobalamins

Two new coenzyme B12 analogues, 2',5'-dideoxycytidylcobalamin (2a) and 2',5'-dide-oxyuridinylcobalamin (2b), and two others, 2',5'-dideoxyadenosylcobalamin (2c), and 5'-deoxy-thymidylcobalamin (2d) were prepared by an improved method. All the four analogues were investigated by UV-vis and 2D 1H NMR spectroscopy. The comparisons and discussion about their spectroscopic properties were done.     

Preparation and properties of diuridine 3'''',5''''-boranophosphate

Diuridine 3', 5'-boianophosphate has been synthesized. Its diastereomers were separated and their configurations were tentatively assigned based on the selective snake venom phosphodiesterase (SVPDE) hydrolysis. It is found that, compared to the unmodified parent compound diuridine phosphate, the nucleophilicity and the stability of the modified compounds to SVPDE are significantly enhanced.     

Conformational and spectroscopic properties of π-extended, bipyrrole-fused rubyrin and sapphyrin derivatives

Two new expanded porphyrins, naphthorubyrin and naphthosapphyrin, were synthesized. The π-extended rubyrin was isolated and structurally characterized in its monoprotonated form. The sapphyrin congener undergoes pyrrole inversion as a function of the protonation state. These conformational effects are reflected in the spectroscopic features, including the excited singlet state lifetimes.     

Synthesis and spectral properties of 1,2,5-thiadiazolo-, 1,2,5-selenadiazolo-, and benzo-fused β-phenyl-substituted porphyrazines

Cross cyclotetramerization of trans-2,3-diphenylbutanedinitrile with 1,2,5-thia(selena)diazole-3,4-dicarbonitriles or phthalodinitrile in the presence of magnesium butoxide gave mixtures of Mg(II) porphyrazine complexes which were treated with trifluoroacetic acid to isolate unsymmetrical hexaphenyl-substituted 1,2,5-thia(selena)diazolo-and benzo-fused porphyrazines together with diphenyltribenzoporphyrazine. Their ¹H NMR and electronic absorption spectra (in the UV and visible regions) were recorded. The effect of benzene and heteroring fusion on the electronic and steric structure and spectral properties of porphyrazine derivatives was studied in terms of the molecular orbital perturbation theory and semiempirical quantum-chemical calculations (AM1, PM3, ZINDO/S, CNDO/S).     

Optical,electrical, and thermochromic properties of polyazothiophene Langmuir–Blodgett films

The conductivity and luminescence of conjugated polymers may be combined with the photoisomerization capability of azobenzene materials to achieve unique properties for a variety of applications, particularly if conjugated polymers with azobenzene side chains are processed as nanostructured films. In this study, we report on Langmuir–Blodgett (LB) films of a polythiophene-bearing azobenzene moieties, which displayed photoluminescence, thermochromism, electroactivity, and photoinduced birefringence. The latter three properties were enhanced in the LB films, as compared to spin-coated films of the polyazothiophene, and this has been attributed to differences in film morphology that could be probed with atomic force microscopy.     

The pyridazine–tetrathiafulvalene conjugates: synthesis,photophysical, and electrochemical properties

To study the electronic interactions in donor–acceptor (D–A) conjugates as a precursor of optoelectronic materials, a series monopyridazine-annulated tetrathiafulvalenes and a bispyridazine-annulated tetrathiafluvalene were synthesized by a condensation reaction of 2,3-dimethoxycarbonyl-6,7-dibutylthiotetrathiafulvalene or/and 2,3,6,7-tetramethoxycarbonyltetrathiafulvalene with hydrazine hydrate and structurally characterized by conventional chemical and physical methods. Their electronic properties have been studied experimentally by the combination of electrochemistry and UV–vis spectroscopy. All of monopyridazine-tetrathiafulvalene conjugates 7–13 show intramolecular charge transfer interaction in ground states, which is rationalized on the basis of density functional theory. Their HOMO energy levels and E_g^opt values were estimated to be ?4.88 to ?5.07 eV from cyclic voltammetry and 2.43–2.79 eV from the absorption spectra, respectively. The X-ray crystallographic analyses of the pyridazine–tetrathiafulvalene conjugates 7, 11–13 are also reported.     

Synthesis,characterization and redox properties of mono- and bis-β-diketonate ruthenium complexes

Complexes of the type [RuIII(L)Cl2(PPh3)2] and [RuII(L)2(PPh3)2] (HL=benzoylacetone or acetylacetone) have been synthesized by the reaction of [RuCl2(PPh3)3] with HL under various experimental conditions. The [RuIII(L)Cl2(PPh3)2] complexes are one-electron paramagnetic species and, in solution, they show intense LMCT transitions in the visible region together with weak ligand-field transitions at lower energies. The [RuII(L)2(PPh3)2] complexes are diamagnetic and their solutions show sharp 1H n.m.r. signals and also show intense MLCT transitions in the visible region. In MeCN solution, the [RuIII(L)Cl2(PPh3)2] complexes show a reversible RuIII-RuII reduction near –0.3V and an irreversible RuIII- RuIV oxidation near 1.2 V versus s.c.e. A reversible RuII-RuIII oxidation is displayed by the [RuII(L)2(PPh3)2] complexes in MeCN solution near 0.3 V versus s.c.e. followed by another reversible RuIII-RuIV oxidation near 1.1 V versus s.c.e. The [RuII(L)2(PPh3)2] complexes have been oxidized to the corresponding [RuIII(L)2(PPh3)2]+ analogues and isolated as ClO4– salts in the solid state. The oxidized complexes are one-electron paramagnetic. They are 1:1 electrolytes in solution and show intense LMCT transitions in the visible region along with weak ligand-field transitions at lower energies.     

Synthesis,structure, and magnetic properties of lanthanide ferrocenoylacetonates with nitrate and 2,2′-bipyridine ligands

Ferrocenoylacetonate complexes of several lanthanides, [Ln(fca)₂(NO₃)(bpy)]·nMeC₆H₅ (Ln = Sm (1), Dy (3), Er (4), Yb (5), n = 1; Eu (2), n = 0.5; fca = FcC(O)CHC(O)Me; bpy = 2,2′-bipyridine), were synthesized and characterized by X-ray single-crystal analysis. Complexes 1, 4, and 5 are isostructural; 2 has a similar molecular structure with cis-disposition of fca ligands. The molecular structure of 3 is different, with trans-disposition of the fca ligands. Crystal lattices of the complexes are stabilized by π-stacking interactions. The Ln³⁺ ions in the complexes are eight-coordinate. According to mass spectroscopic data, the complexes are unstable in the gas phase. Magnetic properties of 2 and 4 were studied in a DC field; for 4, AC studies were also carried out. The values of spin-orbital parameters obtained using two estimation methods for 2 are in satisfactory agreement. Slow relaxation of the magnetization was found for the Er complex.     

New 1,2,4‐ and 1,3,4‐oxadiazole materials: synthesis,and mesomorphic and luminescence properties

The synthesis and liquid crystalline properties of new series of 1,2,4‐ and 1,3,4‐oxadiazole derivatives (2a–f and 5a–f respectively) are reported. These compounds contain only one terminal flexible alkoxy chain, the other terminal substituent is a protecting benzyl group. All compounds of series 2 exhibit an enantiotropic nematic phase. The homologue with the longest chain (2f) displays an enantiotropic dimorphism smectic A– nematic. None of the compounds of series 5 shows mesomorphism and only crystal–isotropic transitions were observed. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X‐ray measurements. Luminescence properties, in chloroform solution, of 2f and the series 5 compounds were evaluated. Good photoluminescence quantum yields for compounds of series 5 were observed. Compound 2f, incorporating the 1,2,4‐oxadiazole ring shows a very strong reduction in emissive properties.     

β-Protic pyrazole and N-heterocyclic carbene complexes: synthesis, properties, and metal-ligand cooperative bifunctional catalysis

This Minireview provides an overview of the chemistry of pyrazole and N‐heterocyclic carbene (NHC) complexes bearing an NH group at the β‐position to the metal. The synthesis and structures as well as the Brønsted acidic nature of the β‐NH group are described in detail. These complexes are attractive candidates for novel metal–ligand cooperative bifunctional catalysts, which would benefit highly effective molecular and energy transformations.     

Synthesis, electrochemical and photophysical properties of β-carboxy triaryl corroles

An unswerving one-pot conversion of 3-formyl-5,10,15-triaryl substituted corroles and their copper(III) derivatives to the corresponding 3-carboxy-5,10,15-triaryl substituted corroles was achieved by adopting mild reaction conditions by using hydroxylamine hydrochloride and phthalic anhydride. All these substituted carboxy corroles were completely characterized by using Mass, CHN analysis, IR, ¹H NMR, UV-vis., Fluorescence spectroscopies, and cyclic voltammetry. Both the absorption maxima and emission maxima of carboxy corroles were red shifted by 5-13 nm. The LUMO level of these corroles is above the TiO₂ conduction band and HOMO level was below the redox electrolytes. These β-carboxy corroles confined with may find applications as sensitizers in dye-sensitized solar cells.     

Synthesis and some properties of diethoxyaluminum α,α-dimethylbenzyl peroxide

Summary The previously undescribedorganoaluminum peroxide of composition (C₂H₅O)₂AlOOC₉H₁₁ was synthesized, and some of its properties were studied.     

Synthesis,structure and properties of an imidazolate bridged copper,zinc binuclear complex

A new imidazolate bridged Cu~(2+),Zn~(2+)binuclear complex[(dtma) CulmZn (dtma)]ClO_4·2.5H_2O taken as active site model for Cu,Zn-SOD has been synthesized and its crystal structuredetermined.All the bond lengths, bond angles and the distance between Cu and Zn atoms in Cu-Im-Zn core of the model complex are close to those in Cu,Zn-SOD.ESR parameters of the modelcomplex as a function of pH show that the imidazolate bridge is stable in pH range 10—12,and isbroken on Zn side at pH～9.With decreasing pH,the imidazole is released at pH～4 and the dtmaligand dissociates from the Cu containing fragment at pH～2.4.