Electronic states of pyrene single crystal and of its single molecule inserted in a molecular vessel of cyclodextrin

Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The absorption spectra of the single crystal have been transformed from the reflection spectra between 2.5 and at 2, and room temperature. The dry powder of β-cyclodextrin including pyrene single molecule were prepared in vacuum to investigate the electronic states of the isolated molecule. The absorption spectra of the single molecule show similar spectra to those of the single crystal. The pyrene molecule keeps its electronic character even in the single crystal.     

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solutions. VIII. Angular Overlap Treatment of a Schiff Base Copper(II) Complex in Various Solvents

The electronic absorption spectra of trans-[Cu(Brsap)₂], where [HBrsap = 5-bromosalicylidine-o-aminopyridine (Schiff base)], were measured in various solvents at room temperature. The d-d transition energies were used to derive the angular overlap model (AOM) parameters in the C _2h symmetry. The experimental curves were resolved by Gaussian analysis. A comparison of the spectra and ligand field parameters in various solutions was made. The effect of the solvents upon the -, -bonding, and bite angle of the bidentate asymmetric ligand is discussed.     

A comparative study of mid-infrared diffuse reflection (DR) and attenuated total reflection (ATR) spectroscopy for the detection of fungal infection on RWA2-corn

An investigation into the rapid detection of mycotoxin-producing fungi on corn by two mid-infrared spectroscopic techniques was undertaken. Corn samples from a single genotype (RWA2, blanks, and contaminated with Fusarium graminearum) were ground, sieved and, after appropriate sample preparation, subjected to mid-infrared spectroscopy using two different accessories (diffuse reflection and attenuated total reflection). The measured spectra were evaluated with principal component analysis (PCA) and the blank and contaminated samples were classified by cluster analysis. Reference data for fungal metabolites were obtained with conventional methods. After extraction and clean-up, each sample was analyzed for the toxin deoxynivalenol (DON) by gas chromatography with electron capture detection (GC-ECD) and ergosterol (a parameter for the total fungal biomass) by high-performance liquid chromatography with diode array detection (HPLC-DAD). The concentration ranges for contaminated samples were 880–3600 g/kg for ergosterol and 300–2600 g/kg for DON. Classification efficiency was 100% for ATR spectra. DR spectra did not show as obvious a clustering of contaminated and blank samples. Results and trends were also observed in single spectra plots. Quantification using a PLS1 regression algorithm showed good correlation with DON reference data, but a rather high standard error of prediction (SEP) with 600 g/kg (DR) and 490 g/kg (ATR), respectively, for ergosterol. Comparing measurement procedures and results showed advantages for the ATR technique, mainly owing to its ease of use and the easier interpretation of results that were better with respect to classification and quantification.     

Solid state Mössbauer,e.p.r., magnetic properties and thermally induced stereochemical studies on double complex salts of cyclic diamine containing cationic copper(II) complexes and a hexacyanoferrate(III) anion

Summary Double complex salts containing cationic Cu^II having cyclic ligand piperazine (pipz), N-methylpiperazine (mpipz) and N,N-dimethylpiperazine (dmpipz) and hexacyanoferrate(III) ion have been synthesized and characterized by elemental analyses, i.r. and electronic spectra, and magnetic moment measurements. Mössbauer spectra at room temperature and at 80 K, were recorded in order to evaluate the metal-metal charge transfer and the impact of the cyclic ligand present in cationic moiety of the double complex salt upon the Mössbauer spectra of the hexacyanoferrate(III) ion. Evidence for metal-metal charge transfer is supported by electronic spectra and magnetic susceptibilities. Variable temperature e.p.r. spectra were recorded in order to determine the distortion of crystal system. Thermally induced stereochemical studies have been carried out with the help of i.r. spectral data. Kinetics of thermochemical reactions have also been studied. Activation energies (E _infa ^sup* ) and inception temperatures for the thermochemical reactions show the order of stability of the double complex salts follows the trend: dmpipz > mpipz > pipz, which indicates that the + I effect is more pronounced than steric effect.     

Angular Overlap Studies of Mono-(Aminodiphosphonato)Copper(II) Complexes in Aqueous Solutions

Electronic absorption spectra of copper(II) complexes with iminodimethylenephosphonates R-N(CH₂PO₃H₂)₂ type (L, R-dmp), in aqueous solution have been characterized and quantitatively interpreted. The geometry of species in aqueous solution at pH 7–8 has been assumed on the basis of our previous combination of UV spectrophotometric measurements and ESR spectra, as well as data obtained from potentiometric titration. The ligand-field spectra (d–d transitions) of the [CuL(H₂O)_x]^2– chromophores (where x = 2, 3) have been treated by the angular overlap model (AOM) and C _2v symmetry. Low-symmetry splittings of the broad asymmetric bands in the spectra of solutions at room temperature were resolved by Gaussian analysis. The effect of the and bonding of the tridentate (and tetradentate) ligands (with oxygen-donor and nitrogen-donor ligators) on the central metal ion has been described in the ligand-field framework.     

Reflexionsspektroskopische Untersuchung des Oxidschichtwachstums auf Metalloherfl?chen

Summary Polycrystalline iron, low carbon steel, and copper were oxidized thermally at T = 800–870 K in air, and electrochemically in alkaline electrolytes. The growth of the oxide layer and the nature of the oxidation products were analyzed in situ by reflection spectroscopy using a combined setup of a diode array spectrometer for fast recording of the whole spectra and several reflectometers for continuous registration at selected wavelengths and angles of observation. The data were subdivided into specular, off-specular, and diffuse reflectance. On iron and steel, the thermally formed layers grow perfectly linearly with time up to d 300 nm, and the electrochemically formed layers grow with t ^1/2. The latter ones could be separated into a topochemically grown passive film and into a strongly light scattering corrosion layer with bad contact to the substrate.     

Fourier transform spectroscopy of surface polariton bragg reflection in gratings

Periodic gratings on metal surface have been used for surface polariton decay length measurements for 5–15m wavelength by means of a commercial Fourier-transform spectrometer. The effect of different grating parameters as well as that of the spectrometer light beam configuration on transmission spectra has been investigated. Gaps in the transmission spectrum due to Bragg reflection have been studied in details.     

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solutions. IX. The Mixed Tetragonal Distorted Bis(Salicylato)Cobalt(II) Complex in Various Solvents

Mixed cobalt(II) complexes with the monodentate ligands: 2-hydroxybenzoic acid deprotonated (sal^–, the salicylate ion) and water, have been investigated. The combined results of the spectrophotometric and conductance measurements, as well as known the X-ray structure for solids, were used to determine the structure of the studied complexes in solution. The electronic absorption spectra in aqueous acid (0.01M HClO₄), ethylene glycol (glycol), formamide (FM), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) solutions have been recorded. The d-d electronic spectra have been treated by the crystal-field model (CFM) and angular overlap model (AOM). Low-symmetry splittings of the broad asymmetric bands in the experimental spectra (solutions at room temperature) were found by Gaussian analysis. The effect of the and bonding of the monodentate ligands (with oxygen-donor ligators) on the central metal ion was described in the ligand–field framework. A comparison of the stereochemistry of the complex species in various solutions was made.     

Complex formation of hexakis(2,6-di-O-methyl)-α-cyclodextrin with substituted benzenes in aqueous solution

The host-guest interaction of hexakis(2,6-di-O-methyl)--cyclodextrin (DM--CDx) with substituted benzenes in aqueous solution has been investigated by circular dichroism spectra. From the resemblance of the spectra, it is concluded that the guest molecules are included in the DM--CDx ring in a manner similar to that of corresponding -cyclodextrin complexes. Thermodynamic parameters of the complex formation were determined on the basis of the temperature dependent intensity change of the spectra. In spite of the considerable variation in H and AS values, the free energy does not change much among complexes because of the strong compensation effect. The compensation temperature was 309 ± 11K. Negative values of H and S, suggesting that the complex formation is not governed by the hydrophobic interaction, can be interpreted in terms of the tight binding of the guest molecule within the host cavity.     

Theory of Low-Frequency Scattering of Light by Superionic Glasses with Nanosize Structure

In the Raman spectra of glasses of (AgI) _x (Ag₂O · nB₂O₃)_{1 – x} type, along with so-called boson peak (at frequencies of about 10 cm^–1), a wide central component is pronounced even at room temperature. The component is similar to that in the spectra of crystalline superionic -AgI. The emergence of such a central component in the spectra for glasses containing AgI indicates that size effects, which are associated with the glass structure, can significantly modify the relaxation modes associated with ionic conduction. For the first time, low-frequency spectra of superionic glasses are theoretically analyzed taking into account that, in nanocrystalline AgI, the mobile ion concentration is increased. A theoretical treatment of experimental spectra can provide information on important physicochemical characteristics of such glasses.     

Bis-(tetraethylammonium)[tetraazidocuprate(II)] and catena-di-μ-1,1-azido-[di-μ-1,1-azido-bis-(2,4-dimethylpyridine)dicopper(II)]

Two new copper(II) azido complexes, namely bis-(tetraethylammonium)[tetraazidocuprate(II)] (1) and catena-di--1,1-azido-[di--1,1-azido-bis-(2,4-dimethylpyridine)dicopper(II)] (2), have been prepared and characterized by spectroscopic and crystallographic methods. Complex (1) consists of isolated NEt⁺ ₄ cations and [Cu(N₃)₄]^2– anions. The site symmetry around the copper atom in the anion is 4/m. Complex (2) features a 1 D chain structure, five coordinated square pyramidal copper(II) atoms with both azides functioning as -1,1-bridges. The i.r. spectra reveal that both complexes contain asymmetric azido ligands. The solid and solution electronic spectra of (1) and (2) show very strong absorption bands in the visible region associated with N^– ₃ Cu^II charge-transfer transitions. The e.p.r. spectra of powder samples and solutions at room temperature were recorded and discussed.     

An infrared and raman spectroscopic investigation of copper(II) tetracyanonickelate complexes ofα-,β- andγ-picoline

Copper(II) dipicoline tetracyanonickelate complexes, CuL₂Ni(CN)₄ (L=,- or-picoline), have been prepared for the first time and their infrared and Raman spectra are reported. Their structure consists of polymeric layers of {Cu-Ni(CN)₄} with picoline molecules bound directly to the copper. It is proposed that the Cu-NC bonds are in two nonequivalent pairs in trans positions. Low temperature (83K) IR spectra have also been recorded and it is noted that the Ni(CN)₄ group frequencies increase with decreasing temperature while the picoline frequencies are insensitive to temperature.     

Mössbauer spectroscopic studies of thermal decomposition of substituted pentacyanoferrate(II) complexes

The thermal behaviour of substituted pentacyanoferrates(II) of the type Na₃[Fe(CN₅)L]·xH₂O, whereL=n-, sec-, tert- oriso-butylamine,di-iso-butylamine ortri-n-butylamine, was investigated with the aid of Mössbauer spectroscopy, XRD and TG-DTG-DTA. The Mössbauer spectra of these complexes exhibit a quadrupole doublet with E _Q=0.70–0.83 mm s^–1 at room temperature. The isomer shift, =0.00±0.03 mm s^–1 suggests that the iron atom is in the +2 low-spin state. The complexes start to decompose at 50°C, yielding a residual mass of 5.8 –21.3% in the temperature range 900–950°C. The Mössbauer spectra recorded after heating at 150 and 300°C exhibit an asymmetric doublet, suggesting partial decomposition. The Mössbauer spectra at higher temperature are complex. At different stages of the thermal process, the presence of -Fe₂O₃, -Fe₂O₃, -Fe, Fe₃C and Fe₃O₄ was demonstrated.On leave from A. N. College, Anandwan-442 914, IndiaWe are grateful to the Monbusho (Ministry of Education, Science, Sports and Culture) for the award of a fellowship to RBL and for financial assistance for the research work. Thanks are also due to Dr. T. Nakamoto for valuable cooperation.     

Complexes of N-nicotinoyl-N′-2-furanthiocarbohydrazide with oxovanadium(IV), manganese(II), iron(II & III), cobalt(II), nickel(II), copper(II) and zinc(II)

A new potential tetradentate ligand, N-nicotinoyl-N-2-furanthiocarbohydrazide (H₂Nfth), and its complexes with VO^IV, Mn^II, Fe^II,III, Co^II, Ni^II, Cu^II and Zn^II have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis, i.r., n.m.r., ES⁺ and FAB mass spectral data. The room temperature e.s.r spectra of the VO^IV and Fe^III complexes yield g values, characteristic of octahedral complexes. The Mössbauer spectra of [Fe(HNfth)₂] and [Fe₂(Nfth)₃] at room temperature and at 78 K suggest the presence of high-spin iron(II) and iron(III), respectively. The complexes are electrically insulating at room temperature, however, their conductivities increase as the temperature increases from 333–383 K, with a band gap of 0.46–0.77 eV, indicating their semiconducting behaviour. H₂Nfth and its soluble complexes have been screened against several bacteria and fungi.     

In-situ FTIR spectroscopy of iron electrodes

The reactions of an iron electrode in alkaline electrolytes of different concentrations are studiedin-situ using internal reflection and external reflection FTIR spectroscopy. Fe(OH)₂ is formed during the reaction Fe(O) Fe(II) at all investigated concentrations. The product of the reaction Fe(II) Fe(III) is-FeOOH in concentrated and-FeOOH in diluted alkaline solutions.     

Stereochemie und1H-NMR-Spektren einiger vom Pentaerythrit abgeleiteten Spiro-1,3-dioxane

Summary Mono- and trispiro-1,3-dioxanes with mobile, fixed and semimobile structures were obtained by the condensation reaction of pentaerythritol with aldehydes and symmetrical or unsymmetrical ketones. The conformational analysis of the obtained compounds was undertaken by means of¹H-NMR spectroscopy. The spiro-1,3-dioxanes obtained with aldehydes or nonsymmetrical ketones represent fixed (anancomeric) structures. Ketalisation with 4-t-butyl-cyclohexanone leads to a semimobile structure of a trispiro-1,3-dioxane in which the two marginal cyclohexanic rings are fixed, while the two middle ones are mobile, continuously flipping at room temperature. The solvent effect on the NMR spectra is also discussed. Utilisation of benzene-d ₆ makes it possible to interpret some of the complex spectra with superposed signals on the basis of the aromatic solvent induced shift (ASIS).

     

Dynamics of probe in network of polymeric cation exchanger studied by Fourier transform analysis of Mössbauer spectra

Limited diffusion of the ferric hydroxide (ferrihydrite) nanoparticles in the polymeric network of the AG 50W-X2 sulfonated cation exchanger solvated with aqueous solutions of glycerol (70 and 90 wt.%) was studied in the temperature interval from 90 to 293 K. The Mössbauer spectra were obtained in three windows (250, 25, and 5 mm/s) because of large line broadenings observed in the experiment. The procedure of seaming of the time-dependent correlation functions <[x(t)]²> obtained by the Fourier transform analysis of the initial Mössbauer spectra made it possible to observe the behavior of the function in the extremely wide time range from 0.4 to 360 ns. The observed plateau of the function at long times is a direct proof of the limited nature of the motion. The experimental data were interpreted in the framework of physical models of limited diffusion.     

Microspectroscopic infrared specular reflection chemical imaging of multi-component urinary stones: MIR <Emphasis Type="Italic">vs.</Emphasis> FIR

Specular reflection infrared microspectroscopy was used for chemical imaging of cross-sectioned urinary stones to determine their chemical composition and morphology simultaneously. Absorption spectral bands were recovered from reflection spectra by Kramers-Kronig transform. FUse of far-infrared radiation provides high-contrast images and allows more precise constituent distribution determinations than mid-infrared because band asymmetry after the transform caused by diffuse reflection is less in the far-infrared.

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Tautomerism and Atropisomerism in Free‐Base (meso)‐Strapped Porphyrins: Static and Dynamic Aspects

We report herein some outstanding examples of atropisomerism and tautomerism in five (meso‐)strapped porphyrins. Porphyrins S0 – S4 have been synthesised, characterised and studied in detail by spectroscopic and spectrometric techniques, and their isomeric purity verified by HPLC analysis. In particular, they exhibit perfectly well‐defined NMR spectra that display distinct patterns depending on their average symmetry at room temperature: C_2v, D_2d, C_2h, C_2v, and D_2h for S0 – S4 , respectively. NH tautomerism was evidenced by variable‐low‐temperature ¹H NMR experiments in [D₂]dichloromethane performed on S0 (Δ${G{{{\ne}\hfill \atop {\rm 298K}\hfill}}}$ =48±1 kJ mol^?1) and S1 (Δ${G{{{\ne}\hfill \atop {\rm 298K}\hfill}}}$ =55±3 kJ mol^?1), which has led to an understanding of the average spectra observed for the five porphyrins at room temperature. On the other hand, S2 and S3 are stable atropisomers at room temperature, easily separated and characterised, as a result of restricted rotation of their strapped bridges due to their high rotational barrier energies. Upon heating to 82 °C, they slowly equilibrate to a thermodynamic ratio of 64:36 in favour of the more stable S2 isomer. This atropisomerisation process was evidenced by ¹H NMR spectroscopy and monitored by HPLC, from which high rotational energy barriers of 115.2 (Δ${G{{{\ne}\hfill \atop {\rm S2}\rightarrow {\rm S3}\hfill}}}$ ) and 116.9 kJ mol^?1 (Δ${G{{{\ne}\hfill \atop {\rm S2}\rightarrow {\rm S3}\hfill}}}$ ) were deduced.     

Vibrational spectra of 2-biphenylmethanol. Spectrum simulation and molecular structure

The vibrational spectra of a solid crystalline sample of 2-biphenylmethanol have been measured at room temperature. The IR absorption spectra were recorded in the range 400 cm^–1–3600 cm^–1; Raman spectra were measured in the range 10 cm^–1–1640 cm^–1. The direct mechanical and optoelectronic problems were solved using the fragment method realized as Lev-100 software; the intensity distribution in the IR spectrum of 2-biphenylmethanol was obtained by the same method. The experimental Raman and IR absorption spectra were interpreted by analyzing the calculated data on the frequencies and forms of normal vibrations and their intensities in the IR spectra. IR absorption spectra were simulated for several models of 2-biphenylmethanol conformers that differ in the mutual orientation of fragments. Based on the results of simulation and comparison of the calculated and experimental spectra of conformers we suggested a model for the conformer realized in the solid phase under normal conditions.Original Russian Text Copyright © 2004 by L. M. Babkov, J. Baran, N. A. Davydova, J. I. Kukielskii, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 624–631, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.