Equatorially connected diruthenium(II,III) units toward paramagnetic supramolecular structures with singular magnetic properties

The reaction of Ru2Cl(O2CMe)(DPhF)3 (DPhF = N,N'-diphenylformamidinate) with mono- and polycarboxylic acids gives a clean substitution of the acetate ligand, leading to the formation of complexes Ru2Cl(O2CC6H5)(DPhF)3 (1), Ru2Cl(O2CC6H4-p-CN)(DPhF)3 (2), [Ru2Cl(DPhF)3(H2O)]2(O2C)2 (3), [Ru2Cl(DPhF)3]2[C6H4-p-(CO2)2] (4), and [Ru2Cl(DPhF)3]3[C6H3-1,3,5-(CO2)3] (5). The preparation of [Ru2(NCS)(DPhF)3]3[C6H3-1,3,5-(CO2)3] (6) and {[Ru2(DPhF)3(H2O)]3[C6H3-1,3,5-(CO2)3]}(SO3CF3)3 (7) from 5 is also described. All complexes are characterized by elemental analysis, IR and electronic spectroscopy, mass spectrometry, cyclic voltammetry, and variable-temperature magnetic measurements. The crystal structure determinations of complexes 2.0.5THF and 3.THF.4H2O (THF = tetrahydrofuran) are reported. The reactions carried out demonstrate the high chemical stability of the fragment [Ru2(DPhF)3]2+, which is preserved in all tested experimental conditions. The stability of this fragment is also corroborated by the mass spectra. Electrochemical measurements reveal in all complexes one redox process due to the equilibrium Ru2(5+) <--> Ru2(6+). In the polynuclear complex 7, some additional oxidation processes are also observed that have been ascribed to the presence of two types of dimetallic units rather than two consecutive reversible oxidations. The magnetic behavior toward temperature for complexes 1-7 from 300 to 2 K is analyzed. Complexes 1-7 show low values of antiferromagnetic coupling in accordance with the molecular nature in 1 and 2 and the absence of important antiferromagnetic interaction through the carboxylate bridging ligands in 3-7, respectively. In addition, the magnetic properties of complex 7 do not correspond to any magnetic behavior described for diruthenium(II,III) complexes. The experimental data of compound 7 are simulated considering a physical mixture of S = 1/2 and 3/2 spin states. This magnetic study demonstrates the high sensitivity of the electronic configuration of the unit [Ru2(DPhF)3]2+ to small changes in the nature of the axial ligands. Finally, the energy gap between the pi and delta orbitals in these types of compounds allows the tentative assignment of the transition pi --> delta.     

Spectral and photophysical studies of substituted indigo derivatives in their keto forms.

The spectral and photophysical properties of indigo derivatives with di-, tetra-, and hexa-substitution in their neutral (keto) form are investigated in solution. The study comprises absorption and emission spectra, together with quantitative measurements of quantum yields of fluorescence (phi(F)) and singlet oxygen formation (phi(Delta)) and fluorescence lifetimes. The energy difference between the HOMO and LUMO orbitals is dependent on the degree (number of groups) and relative position of substitution. The phi(F) and phi(Delta) values were found to be very low S(0) internal conversion yields and thus, with the other data, to determine the rate constants for all decay processes. From these, several conclusions are drawn. Firstly, the radiationless rate constants, k(NR) , clearly dominate over the radiative rate constants, k(F) , (and processes). Secondly, the main deactivation channel for the compounds in their keto form is the radiationless S(1) approximately approximately -->S(0) internal conversion process. Finally, although the changes are relatively small, internal conversion yield seems to be independent of the overall pattern of substitution. A more detailed investigation of the decay profiles with collection at the blue and red emission of the fluorescence band of indigo and one di-substituted indigo reveals the decays to be bi-exponential and that at longer emission wavelengths these appear to be associated with both rise and decay times indicating that two excited species exist, which is consistent with a keto-excited form giving rise (by fast proton transfer) to the enol-form of indigo. Evidence is presented which supports the idea that intramolecular (and possibly some intermolecular) proton transfer can explain the high efficiency of internal conversion in indigo.     

Syntheses,structures, and luminescent properties of zinc(II) complexes based on imidazole derivative

Two new Zn(II) coordination complexes [ZnL₂(SCN)₂] (I) and [ZnL₂Cl₂] (II) have been pre-pared by self-assembly of corresponding metal salts with (E)-2-(3-(4-(1H-imidazole-1-yl)styryl)-5,5-dimethylcyclohexo-2-enylidene) malononitrile (L) and characterized by IR spectrum, elemental analysis and single-crystal X-ray diffraction. Complexes I and II are two-dimensional (2D) networks with different topology structures. The luminescence properties were investigated.     

Synthesis,crystal structures,and biological activities of silver(I) and cobalt(II) complexes with an azole derivative ligand

Abstract  Two new complexes, [Ag(L)₂](NO₃) · (H₂O) (1) and [Co(L)₂Cl₂] (2) [L = 1-(imidazol-1-yl-methyl)-benzotriazole], have been synthesized and structurally characterized by X-ray diffraction techniques. In complex (1), the Ag(I) atom adopts a linear coordination geometry involving the imidazole nitrogens of two ligands. The [Ag(L)₂] units are developed into a three-dimensional structure by intermolecular hydrogen bonds, π–π interactions, and Ag···O interactions. In complex (2), the Co(II) atom is in a distorted tetrahedral environment with two imidazole nitrogens and two chloride ligands. The [Co(L)₂Cl₂] units are assembled into a three-dimensional structure by intermolecular hydrogen bonds and π–π interactions. The bioactivities of both complexes have been studied, and the results indicate that complex (1) exhibits excellent radical-scavenging (RS) and fungicidal (FG) activities while complex (2) only has weak fungicidal activity. Graphical abstracts   Synthesis, crystal structures and biological activities of silver(I) and cobalt(II) complexes with an azole derivative ligand. Chang-Xue An, Xin-Li Han, Peng-Bang Wang, Zhi-Hui Zhang*, Hai-Ke Zhang and Zhi-Jin Fan Two novel complexes, [Ag(L)₂](NO₃) · (H₂O) (1) and [Co(L)₂Cl₂] (2) [L = 1-(imidazol-1-yl-methyl)-benzotriazole] have been synthesized and structurally characterized. The molecules of complexes (1) and (2) are extended to 2-D and 3-D structures by the non-coordinated bonds. The ligand and complex (1) exhibit excellent radical-scavenging and fungicidal activities. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Oxidimetric determination of indigo with iron(III) and hexacyanoferrate(III)

The use of iron(III) in sulphuric acid medium and of potassium hexacyanoferrate(III) in hydrochloric acid medium has been investigated for the oxidimetric determination of indigo and indigo sulphonic acid. Conditions have been established for the assay of the dye with iron(III) sulphate at 100 degrees and with potassium hexacyanoferrate(III) at room temperature.     

Photophysics of the interaction between a fluorescein derivative and Ficoll

Ficoll has been widely used as a crowding agent to mimic intracellular media because it is believed to be noninteracting and is composed of mixed sizes such that smaller and larger diffusing solutes can be studied. Due to the interest that the fluorescent dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II) as a fluorometric probe of phosphate ions in intracellular media could generate, we describe the spectral characteristics of the system TG-II-Ficoll in aqueous solution by means of absorption spectroscopy, steady-state fluorescence, time-resolved fluorescence, time-resolved emission spectroscopy, and fluorescence lifetime correlation spectroscopy. The spectral characteristics found are consistent with the formation of an adsorption complex on the surface of Ficoll, probably due to hydrogen bonding between TG-II and Ficoll. In addition, the diffusion coefficient calculated for the association was similar to the diffusion coefficient previously recovered for Ficoll in the same experimental conditions. Therefore, our overall data clearly demonstrate that Ficoll is not an inert crowding agent when in the presence of fluorescein derivative dyes.     

Thermal and colour properties of leuco dye-based thermochromic composite with dodecanol solvent

Leuco dye–developer–solvent composites with thermochromic properties were studied. The applied 1-dodecanol solvent shows β crystalline, α solid (rotator) and liquid phases. The inclusion of the crystal violet lactone dye increases transition temperatures of all phases and strengthens the α phase. The benzyl 4-hydroxybenzoate developer causes opposite effects and prevents the appearance of the α phase. These consequences combine in ternary composites, where lower transition temperatures were obtained as in the solvent, but the α phase is formed more likely as expected due to the presence of the developer. The hydration of the composite strengthens its crystalline network, but makes α phase more unstable. The thermal properties were related to the temperature-dependent colour. Composites with well-resolved α and β phases at cooling show a typical colour hysteresis. If only weak α phase or none at all was found in DSC curves, the colour hysteresis has an unusual shape with heating and cooling curves crossing each other. The hydration of the composite changes the colorimetric properties in accordance with the relation found for anhydrous composite. More conclusions and interrelations between the two properties require application of other analytical methods.     

Preparation and crystal structures of an ionic triple-hydrogen-bridged derivative of 9-BBN hydroborate zirconium(IV)

An ionic dinuclear triple-hydrogen-bridged 9-BBN hydroborate zirconium complex, [K(Et₂O)₄][{(μ-H)₂BC₈H₁₄}₃Zr(μ-H)₃Zr{(μ-H)₂BC₈H₁₄}₃] (1) was formed from the reaction of Zr{(μ-H)₂BC₈H₁₄}₄ with KH and aniline in diethyl ether. The molecular structure of compound 1 was determined by single-crystal X-ray diffraction analysis. Six 9-BBN hydroborate ligands are coordinated to two Zr atoms via two bridging H atoms, and two Zr atoms are connected by three bridging hydrogens in the anion part of this molecule. The distance of Zr?Zr is 3.1025(5) Å. The crystal structure of 1 suggests that agostic interactions between the zirconium metal center and α-C-H of the 9-BBN hydroborate ligand exist in the solid state. The Zr?H distances corresponding to the α-C-H?Zr agostic interactions are 2.579(4) Å and 2.743(4) Å.     

Photophysics of an electrophosphorescent platinum (II) porphyrin in solid films

We examine electronic processes in platinum (II) octaethyl porphyrin (PtOEP) embedded in an organic solid state matrix and in the form of vacuum-evaporated neat films in conjunction with potential applications of this compound to organic photovoltaic and electrophosphorescent devices. Absorption, photoexcitation, and luminescence spectra indicate the excitonic dimers to be dominant excited states, and their dissociation underlies the charge photogeneration process. Different charge separation distance (1.5 nm and 2.6 nm) in opposite charge carrier pairs preceding dissociation can be distinguished based on the fit of the three-dimensional Onsager theory of geminate recombination to electromodulated luminescence and photoconduction measurements. The near-positive electrode concentrated triplet dimer excitons, produced by strongly 370 nm absorbed light in neat PtOEP films, are efficiently quenched by electron transfer to the metal (Al), generating the positive charge with an efficiency eta+ exceeding 0.15 at high electric fields and dominating the measured photocurrent. Their dissociation efficiency in the bulk, eta- (negatively biased illuminated electrode), is more than one order of magnitude lower than eta+. The dissociation of singlet dimer states dominates the bulk photogeneration process induced by the weakly-absorbed light at 450 nm, with comparable eta+ and eta-. The "hot excited state" underlying the temperature-increasing emission at 540 nm has been attributed to the upper excitonic component Q+ of the first absorption band Q consistent with the exciton concept applied successfully to the interpretation of all dimer-underlain spectroscopic features of PtOEP samples studied.     

Synthesis and properties of triphenylantimony(V) dithiolate derivative

Interaction of substituted benzene-1,2-dithiols I–III with triphenylantimony(V) dichloride was studied. As a result of the exchange reaction of 3,6-dichlorobenzene-1,2-dithiol with Ph₃SbCl₂ in the presence of triethylamine triphenylantimony(V) 3,6-dichlorobenzene-1,2-dithiolate IV was obtained. Electrochemical properties of the free dithiols and the complex were explored. According to the cyclic voltammetry, the oxidation of the complex is irreversible and corresponds to one electron transfer with follow-up chemical stage. The antioxidant activity of compounds I–IV was examined in the process of oleic acid autoxidation. A more effective inhibition of the oleic acid oxidation was found at adding dithiol and better protective effect was observed in the presence of Ph₃SbCl₂ compared with the complex IV.     

Photophysics of a xanthenic derivative dye useful as an "on/off" fluorescence probe

The photophysical behavior of a new fluorescein derivative has been explored by using absorption and steady-state and time-resolved fluorescence measurements. The influence of ionic strength, as well as total buffer concentration, on both the absorbance and fluorescence has been investigated. The apparent acidity constant of the dye determined by absorbance is almost independent of the added buffer and salt concentrations. A semiempirical model is proposed to rationalize the variations in the apparent pKa values. The excited-state proton-exchange reaction around the physiological pH becomes reversible upon addition of phosphate buffer, inducing a pH-dependent change of the steady-state fluorescence and decay times. Fluorescence decay traces, collected as a function of total buffer concentration and pH, were analyzed by global compartmental analysis, yielding the following values of the rate constants describing excited-state dynamics: k01 = 1.29 x 10(10) s(-1), k02 = 4.21 x 10(8) s(-1), k21 approximately 3 x 10(6) M(-1) s(-1), k12B= 6.40 x 10(8) M(-1) s(-1), and k21B = 2.61 x 10(7) M(-1) s(-1). The decay rate constant values of k01, k21, k21B, along with the low molar absorption coefficient of the neutral form, mean that coupled decays are practically monoexponential at buffer concentrations higher than 0.02 M and any pH. Thus, the pH and buffer concentration can modulate the main lifetime of the dye.     

A new imidazophenanthroline derivative and its Hg(II) complex: structures,photophysical properties,and DFT calculations

A new ligand (L) and its mercury(II) complex have been synthesized under mild conditions. X-ray single-crystal structural analyses reveal 1-D, 2-D, and 3-D supermolecular structure of L and HgLI₂. Solvent molecules and various weak interactions, including hydrogen bonds (N–H···N, O–H···O, and O–H···N) and π–π interactions play signi?cant roles in the ?nal supermolecular structures. Detailed investigation on ¹H NMR spectra of L and HgLI₂ are presented. Their photophysical properties were investigated both experimentally and theoretically.     

Spectrophotometric determination of H(2)O(2) in marine waters with leuco crystal violet

H₂O₂ in marine waters may be determined by measuring the absorbance of crystal violet (CV⁺), formed by the oxidation of leuco crystal violet (LCV) by H₂O₂ in the presence of the enzyme horseradish peroxidase, at 592 nm at pH 4. The detection limit and the precision of the method are about 0.02 μM and ± 1% (at a concentration of 0.03 μM), respectively. The results obtained by this method and by a widely used fluorimetric method agreed with each other well. After color development, samples together with the sub-samples for constructing the calibration curve may be stored for up to 5 days before their absorbances are measured without significantly changing the estimated concentration of H₂O₂.     

A chromium(III) bis-acetylide complex containing a trans-diethyl-ethylenedithio-substituted tetrathiafulvalene (TTF) derivative: synthesis,crystal structures,and magnetic properties

A new Cr(III) bis-acetylide complex containing redox-active ethynyl-substituted 4-methyl-4′,5′-trans-diethyl-ethylenedithio-tetrathiafulvalene, [Cr(III)cyclam(C≡C-MeEt₂EDT-TTF)₂]ⁿ⁺ ([1]ⁿ⁺) was synthesized. The crystal structures of two salts, [1][Ni(dmit)₂] (dmit?=?2-thioxo-1,3-dithiole-4,5-dithiolate) and [1][Ni(mnt)₂]₃ (mnt?=?maleonitriledithiolate), were determined by single-crystal X-ray diffraction. In the crystal of [1][Ni(dmit)₂], the trans-diethyl group of [1]⁺ is in the axial position and prevents π-stacking of the TTF units, resulting in a negligibly weak spin–spin interaction between Cr³⁺ and [Ni(dmit)₂]^?. In contrast, in [1][Ni(mnt)₂]_3, the trans-diethyl group is in the equatorial position in [1][Ni(mnt)₂]₃ owing to the strong attractive force between the π-stacked TTF⁺ units and the [Ni(mnt)₂]^? anions. This π-stacking has a significant effect on the magnetic property of [1] [Ni(mnt)₂]₃. The π-stacked TTF⁺ units and [Ni(mnt)₂]^? anions behave approximately as a one-dimensional S?=?1/2 antiferromagnetic chain connecting the spins of Cr³⁺ antiferromagnetically.

     

Photophysics properties of 4-formacyl-triphenylamine and 4,4''''-bisformacyl-triphenylamine

The photophysical processes of 4-formacyl-triphenylamine (FTA) and 4,4'-bisformacyl-triphenyl-amine (BTA) have been studied. The fluorescences of FTA and BTA with donor (triamine) and acceptor (formacyl) moieties show the twisted intramolecular charge transfer (TICT) emission in polar solvents and photoinduced charge transfer (ICT) emission in nonpolar solvents. These could be supported by the solvent effect, temperature effect and the quenching process by strong electron-deficient compounds.     

Photophysics and Inverted Solvatochromism of 7,7,8,8-Tetracyanoquinodimethane (TCNQ)

We report absorption, fluorescence, and Raman spectroscopy of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a variety of solvents. The fluorescence quantum yields (QYs) of linear alkane solutions are similar to one another, but QY is shown to acutely decrease in other solvents with increasing polarities. The slope of the solvatochromic plot of absorption maxima is inverted from negative to positive with an increase in solvent polarity. A significant change in the frequency of carbon-carbon double bond stretching modes is not observed in Raman spectra of TCNQ in different solvents. The molar absorption coefficient is determined to calculate the oscillator strength of the absorption band. The radiative decay rate constant calculated from the oscillator strength is approximately ten times larger than that elucidated from the fluorescence lifetime and QY. These spectroscopic parameters reveal that the relaxation occurs from a Franck-Condon excited state to a distinct fluorescence emissive state with a smaller transition dipole moment.     

Photophysics, photoelectrical properties and photoconductivity relaxation dynamics of quantum-sized bismuth(III) sulfide thin films

Electrical and photoelectrical properties (including both the stationary photoresponse and the photocarriers' relaxation dynamics) of nanocrystalline semiconducting bismuth(III) sulfide thin films were investigated. The experimental design of photoelectrical properties was achieved by controlling the chemistry of the deposition process (varying the reagent concentration in the reaction system) and also by physical means (controlling the crystal dimensions by post-deposition annealing). The band gap energy of thin films characterized by most pronounced photoelectrical properties was calculated, on the basis of measured photoconductivity spectral response curves, by several approaches. All of the obtained values are in very good agreement with the corresponding ones obtained from optical spectroscopy data within the framework of parabolic approximation for dispersion relation. On the basis of measured temperature dependence of dark electrical resistivity of nanocrystalline bismuth(III) sulfide films, the thermal band gap energy and the ionization energy of the impurity level (of donor type) were calculated. The corresponding values are 1.50 and 0.42 eV. Dynamics of non-equilibrium charge carriers' relaxation processes was studied with the oscilloscopic method. By analysis of the photoconductivity decay kinetics data it is found that recombination of non-equilibrium charge carriers is carried out according to the linear mechanism. The calculated relaxation time of photoexcited charge carriers is 1.58 ms, the relaxation processes occurring via local trapping centers. Recombination processes occurring via a single-type trapping center can be described within the framework of the Schockley-Read model. The practically linear regime detected in the measured lux-ampere characteristics of the studied films (Δσ∼Φ^0.98) indicate as well a linear recombination mechanism of the photoexcited charge carriers.     

Kinetics of the (photo)oxidation of the thionine leuco base with uranyl nitrate

Spectrophotometry and lamp and laser flash photolysis have been used to investigate the kinetics of the formation and decay of thionine and semithionine, obtained in the photooxidation of the thionine leuco base with uranyl nitrate. It has been shown that after the light flash a certain amount of thionine is formed in the cage oxidation of semithionine with uranoyl UO₂ ⁺ (concentration ratio of thionine and semithionine leaving the cage 595). A kinetic scheme of the reaction has been proposed, which describes satisfactorily the experimental data. The equilibrium constant K=1.2±0.3)·10^–4 has been obtained for the dark oxidation of the thionine leuco base with uranyl nitrate in aqueous sulfuric acid (pH 1.0) which is close to the calculated value.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 13–18, January, 1990.     

Syntheses,structures, and properties of seven-coordinate calcium(II) and five-coordinate lead(II) complexes with 1-D structures

Two new 1-D heterometallic coordination polymers (CPs), {[Ca(NiL)(H₂O)₄]?·?3H₂O} _n (1) and {[Pb(NiL)(H₂O)₂]?·?3H₂O)} _n (2), have been prepared by reactions of CaCl₂ and NiL and Pb(NO₃)₂ and NiL in CH₂Cl₂–H₂O. H₂L denotes dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo-9,10-benzo-[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate. Single-crystal X-ray diffraction studies show that the coordination geometries around Ni(II) in both 1 and 2 are similar distorted N₄ square planar. All Ni–N bonds are short. Complex 1 has 1-D zigzag chain, while 2 shows 1-D “head-to-tail” structure. In crystals 1 and 2, 1-D CP chains were parallel-packed and 3-D supramolecular networks were formed via weak hydrogen bond interactions between aqua ligands and lattice water. The effects of water on the assemblies of the two CPs are discussed. Coordinated water plays an important role on the assembly procedure.