Journal of Molecular Structure

Published by Elsevier BV

Online ISSN: 0022-2860

Articles


A 2D Metal-Organic Framework with a Flexible Cyclohexane-1,2,5,6-tetracarboxylic Acid Ligand: Synthesis, Characterization and Photoluminescent Property
  • Article

April 2010

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244 Reads

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Jian Zhang

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A novel metal-organic framework, [Zn(2)(OH)(Hcht)(4,4'-bpy)](n).4nH(2)O (1) (H(4)cht = cyclohexane-1,2,4,5-tetracarboxylic acid and 4,4'-bpy = 4,4'-bipyridine), was synthesized by the hydrothermal reaction of Zn(NO(3))(2).6H(2)O, 4,4'-bipyridine, and cyclohexane-1,2,4,5-tetracarboxylic acid in the presence of sodium carbonate. The complex was obtained by controlling the ratio of the starting materials and a reaction temperature at 120 degrees C and was characterized by IR, X-ray powder diffraction, thermogravimetric analysis, fluorescent spectrum, and single crystal X-ray diffraction. Single-crystal X-ray investigation reveals that the structure features a two-dimensional framework with novel coordination mode of Hcht ligand and all Hcht ligands exclusively convert to a sole conformation in the complex. IR spectrum reveals the characteristic absorption peaks of asymmetric stretching vibrations that result from the protonated and deprotonated carboxyl groups,. Thermogravimetric analysis shows four clear courses of weight loss, which corresponds to the decomposition of different ligands. Fluorescent spectrum displays that complex 1 is a potential blue-luminescent material.
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Synthesis and characterization of mixed-ligand diimine-piperonal thiosemicarbazone complexes of ruthenium(II): Biophysical investigations and biological evaluation as anticancer and antibacterial agents

April 2011

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139 Reads

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Jeffrey Thessing

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Michael Shaloski

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[...]

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We have used a novel microwave-assisted method developed in our laboratories to synthesize a series of ruthenium-thiosemicarbazone complexes. The new thiosemicarbazone ligands are derived from benzo[d][1,3]dioxole-5-carbaldehyde (piperonal) and the complexes are formulated as [(diimine)(2)Ru(TSC)](PF(6))(2) (where the TSC is the bidentate thiosemicarbazone ligand). The diimine in the complexes is either 2,2'-bipyridine or 1,10-phenanthroline. The complexes have been characterized by spectroscopic means (NMR, IR and UV-Vis) as well as by elemental analysis. We have studied the biophysical characteristics of the complexes by investigating their anti-oxidant ability as well as their ability to disrupt the function of the human topoisomerase II enzyme. The complexes are moderately strong binders of DNA with binding constants of 10(4) M(-1). They are also strong binders of human serum albumin having binding constants on the order of 10(4) M(-1). The complexes show good in vitro anticancer activity against human colon cancer cells, Caco-2 and HCT-116 and indeed show some cytotoxic selectivity for cancer cells. The IC(50) values range from 7 - 159 μM (after 72 h drug incubation). They also have antibacterial activity against Gram-positive strains of pathogenic bacteria with IC(50) values as low as 10 μM; little activity was seen against Gram-negative strains. It has been established that all the compounds are catalytic inhibitors of human topoisomerase II.

Infrared spectrum of the complex of formaldehyde with carbon dioxide in argon and nitrogen matrices

February 1989

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47 Reads

The complex of formaldehyde with carbon dioxide has been studied by infrared spectroscopy in argon and nitrogen matrices. The shifts relative to the free species show that the complex is weak and similar in argon and nitrogen. The results give evidence for T-shaped complexes, which are isolated in several configurations. Some evidence is also presented which indicates that, in addition to the two well-known sites in argon, carbon dioxide can be trapped in a third site.

Influence of Benzannulation on Metal Coordination Geometries: Synthesis and Structural Characterization of Tris(2-mercapto-1-methylbenzimidazolyl)hydroborato Cadmium Bromide, {[Tm(MeBenz)]Cd(μ-Br)}2

February 2015

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69 Reads

The tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complex, {[Tm(MeBenz)]Cd(μ-Br)}2, may be synthesized via the reaction of [Tm(MeBenz)]K with CdBr2. X-ray diffraction demonstrates that {[Tm(MeBenz)]Cd(μ-Br)}2 exists as a dimer, which is in marked contrast to the monomeric structure of the non-benzannulated counterpart, [Tm(Me)]CdBr, and thereby demonstrates that benzannulation of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato ligands can have a distinct impact on the molecular structure of their metal complexes. In accord with this observation, density functional theory calculations indicate that the benzannulated dimers, {[Tm(MeBenz)]Cd(μ-X)}2 (X = Cl, Br, I), are more stable with respect to dissociation than are their non-benzannulated counterparts, {[Tm(Me)]Cd(μ-X)}2. Furthermore, the calculations also indicate that the stability of the dimer depends on the nature of X, such that the dimer becomes more stable in the sequence I < Br < Cl.

Synthesis, characterization and crystal structure of a dinuclear iron nitrosyl complex with 2-mercapto-1-[2-(4-pyridyl)-ethyl]-benzimidazolyl

April 2009

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96 Reads

A new dinuclear iron nitrosyl complex [Fe(2)(C(14)H(12)N(3)S)(2)(NO)(4)] (1) (C(14)H(12)N(3)S = 2-mercapto-1-[2-(4-pyridyl)-ethyl]-benzimidazolyl) has been obtained by the reaction of Fe(NO)(2)(CO)(2) with 2-mercapto-1-[2-(4-pyridyl)-ethyl]-benzimidazole in CH(3)OH under moderate condition. Complex 1 was characterized by IR, UV-vis, electrochemistry and single crystal X-ray diffraction. IR spectrum displays two strong characteristic NO stretching frequencies (nu(NO)) in solution and in solid state. Cyclic voltammetry shows one irreversible, two quasi-reversible and two reversible one-electron reductions and irreversible oxidizations. This result is consistent with the fact that complex 1 is very unstable and ready to lose NO in the air. As showing in the single crystal X-ray diffraction, complex 1 forms a "chair-shape" structure by the connections of two iron centers and S-C-N frames of benzimidazole. The dihedral angle of benzimidazole ring and 2Fe-2S plane is 73.6 degrees . The crystal data are the following: 1, monoclinic, space group P2(1)/c, a = 10.43940(10) A, b = 16.0900(2) A, c = 10.13240(10) A, alpha = 90 degrees , beta = 111.0940(10) degrees , gamma = 90 degrees , V = 1587.89(3) A(3), Z = 4.

X-ray, kinetics and DFT studies of photochromic substituted benzothiazolinic spiropyrans

April 2010

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48 Reads

Photochromic molecules have the potential to find utility in a wide variety of applications including photoswitchable binding and optical memory. This work explores the relationship between photochromism and structural parameters such as particular bond lengths for this class of compounds for which very few crystal structures have been published. Photochemical kinetics, Density Functional Theory (DFT) and X-ray crystallography were used to study the benzothiazolinic spiropyran 3-methyl-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline]. A second benzothiazolinic spiropyran 3-methyl-8-methoxy-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline] was synthesized and subjected to photochemical and computational studies. Selected structural and photochemical data for these, related benzothiazolinic spirooxazines and spiropyrans, and related thiazolidinic spiropyrans are compared. Both benzothiazolinic spiropyrans exhibit photochromic properties that are influenced by substituents, solvent, and temperature. The crystallographic C(spiro)-O bond distance of 3-methyl-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline] that has been shown to correlate with photochromic properties is 1.458 A. The crystallographic C(spiro)-O bond distance matches that of the structure generated by DFT calculations exactly. The effect of substituents on calculated bond lengths and photochemical parameters was determined. For this class of compounds, both X-ray geometry and DFT optimized geometry may be used to predict photochromism, but not degree of photocolorability.

An improved approach to the analysis of drug—protein binding by distance geometry

February 1986

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28 Reads

The calculation of side chain centers of coordinates and the subsequent generation of side chain-side chain and side chain-backbone distance matrices is suggested as an improved method for viewing interactions inside proteins and for the comparison of protein structures. The use of side chain distance matrices is demonstrated with free PTI, and the use of difference distance matrices for side chains is shown for free and trypsin-bound PTI as well as for the X-ray structures of trypsin complexes with PTI and with benzamidine. It is found that conformational variations are reflected in the side chain distance matrices much more than in the standard C-C distance representations.

A molecular dynamics study of chloride binding by the cryptand SC24

February 1988

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25 Reads

The capture of chloride from water by the tetraprotonated form of the spherical macrotricyclic molecule SC24 was studied using molecular dynamics simulation methods. This model ionophore represents a broad class of molecules which remove ions from water. Two binding sites for the chloride were found, one inside and one outside the ligand. These sites are separated by a potential energy barrier of approximately 20 kcal mol-1. The major contribution to this barrier comes from dehydration of the chloride. The large, unfavorable dehydration effect is compensated for by an increase in electrostatic attraction between the oppositely charged chloride and cryptand, and by energetically favorable rearrangements of water structure. Additional assistance in crossing the barrier and completing the dehydration of the ion is provided by the shift of three positively charged hydrogen atoms of the cryptand towards the chloride. This structural rigidity is partially responsible for its selectivity.

Comments on the nature of the bonding in oxygenated dinuclear copper enzyme models

June 2006

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38 Reads

The nature of the bonding in model complexes of di-copper metalloenzymes has been analyzed by means of the electronic localization function (ELF) and by the quantum theory of atoms in molecules (QTAIM). The constrained space orbital variations (CSOV) approach has also been used. Density functional theory (DFT) and CASSCF calculations have been carried out on several models of tyrosinase such as the sole Cu2O22+ central core, the Cu2O2(NH3)62+ complex and the Cu2O2(Imidazol)62+ complex. The influence on the central Cu(2)O(2) moiety of both levels of calculation and ligand environment have been discussed. The distinct bonding modes have been characterized for the two major known structures: [Cu(2)(mu-eta(2): eta(2)-O(2))](2+) and [Cu(2)(mu-O(2))](2+). Particular attention has been given to the analysis of the O-O and Cu-O bonds and the nature of the bonding modes has also been analyzed in terms of mesomeric structures. The ELF topological approach shows a significant conservation of the topology between the DFT and CASSCF approaches. Particularly, three-center Cu-O-Cu bonds are observed when the ligands are attached to the central core. At the DFT level, the importance of self interaction effects are emphasized. Although, the DFT approach does not appear to be suitable for the computation of the electronic structure of the isolated Cu(2)O(2) central core, competitive self interaction mechanisms lead to an imperfect but acceptable model when using imidazol ligands. Our results confirm to a certain extent the observations of [M.F. Rode, H.J. Werner, Theoretical Chemistry Accounts 4-5 (2005) 247.] who found a qualitative agreement between B3LYP and localized MRCI calculations when dealing with the Cu(2)O(2) central core with six ammonia ligands.

9-Triptycenecarboxylate-Bridged Diiron(II) Complexes: Capture of the Paddlewheel Geometric Isomer

November 2008

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65 Reads

The synthesis and characterization of diiron(II) complexes supported by 9-triptycenecarboxylate ligands ((-)O(2)CTrp) is described. The interlocking nature of the triptycenecarboxylates facilitates formation of quadruply bridged diiron(II) complexes of the type [Fe(2)(μ-O(2)CTrp)(4)(L)(2)] (L = THF, pyridine or imidazole derivative) with a paddlewheel geometry. A systematic lengthening of the Fe-Fe distance occurs with the increase in steric bulk of the neutral donor L, resulting in values of up to 3 Å without disassembly of the paddlewheel structure. Reactions with an excess of water do not lead to decomposition of the diiron(II) core, indicating that these quadruply bridged complexes are of exceptional stability. The red-colored complexes [Fe(2)(μ-O(2)CTrp)(4)(4-AcPy)(2)] (10) and [Fe(2)(μ-O(2)CTrp)(4)(4-CNPy)(2)] (11) exhibit solvent-dependent thermochromism in coordinating solvents that was studied by variable temperature UV-vis spectroscopy. Reaction of [Fe(2)(μ-O(2)CTrp)(4)(THF)(2)] with N,N,N',N'-tetramethylethylenediamine (TMEDA), tetra-n-butyl ammonium thiocyanate, or excess 2-methylimidazole resulted in the formation of mononuclear complexes [Fe(O(2)CTrp)(2)(TMEDA)] (13), (n-Bu(4)N)(2)[Fe(O(2)CTrp)(2)(SCN)(2)] (14), and [Fe(O(2)CTrp)(2)(2-MeIm)(2)] (15) having an O(4)/N(2) coordination sphere composition.

The structure elucidation of isomalyngamide K from the marine cyanobacterium Lyngbya majuscula by experimental and DFT computational methods

March 2011

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38 Reads

The 2Z-isomer of malyngamide K has been isolated along with the known compounds malyngamide C, deoxy-C and K, and characterized from a Papua New Guinea field collection of the cyanobacterium Lyngbya majuscula. The planar structure was deduced by 1D and 2D NMR spectroscopic and mass spectral data interpretation. The absolute configurations were determined on the basis of spectroscopic techniques, chemical degradation and DFT theoretical calculations.

A molecular orbital study of a model of the Mg2+ coordination complex of the self splicing reaction of ribosomal RNA

February 1988

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13 Reads

Recent discoveries have established the fact that RNA is capable of acting as an enzyme. In this study two different types of molecular orbital calculations, INDO and ab initio, were used in an attempt to assess the structural/functional role of the Mg2+ hydrated complex in ribozyme reactions. Preliminary studies indicate that the reaction is multistep and that the Mg2+ complex exerts a stabilizing effect on the intermediate or midpoint of the reaction.

The linkage between ribosomal crystallography, metal ions, heteropolytungstates and functional flexibility

November 2008

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48 Reads

Crystallography of ribosomes, the universal cell nucleoprotein assemblies facilitating the translation of the genetic-code into proteins, met with severe problems owing to their large size, complex structure, inherent flexibility and high conformational variability. For the case of the small ribosomal subunit, which caused extreme difficulties, post crystallization treatment by minute amounts of a heteropolytungstate cluster allowed structure determination at atomic resolution. This cluster played a dual role in ribosomal crystallography: providing anomalous phasing power and dramatically increased the resolution, by stabilization of a selected functional conformation. Thus, four out of the fourteen clusters that bind to each of the crystallized small subunits are attached to a specific ribosomal protein in a fashion that may control a significant component of the subunit internal flexibility, by "gluing" symmetrical related subunits. Here we highlight basic issues in the relationship between metal ions and macromolecules and present common traits controlling in the interactions between polymetalates and various macromolecules, which may be extended towards the exploitation of polymetalates for therapeutical treatment.

Shape-Dependent Global Deformation Modes of Large Protein Structures

May 2010

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27 Reads

Conformational changes are central to the functioning of pore-forming proteins that open and close their molecular gates in response to external stimuli such as pH, ionic strength, membrane voltage or ligand binding. Normal mode analysis (NMA) is used to identify and characterize the slowest motions in the gA, KcsA, ClC-ec1, LacY and LeuT(Aa) proteins at the onset of gating. Global deformation modes of the essentially cylindrical gA, KcsA, LacY and LeuT(Aa) biomolecules are reminiscent of global twisting, transverse and longitudinal motions in a homogeneous elastic rod. The ClC-ec1 protein executes a splaying motion in the plane perpendicular to the lipid bilayer. These global collective deformations are determined by protein shape. New methods, all-atom Monte Carlo Normal Mode Following and its simplification using a rotation-translation of protein blocks (RTB), are described and applied to gain insight into the nature of gating transitions in gA and KcsA. These studies demonstrate the severe limitations of standard NMA in characterizing the structural rearrangements associated with gating transitions. Comparison of all-atom and RTB transition pathways in gA clearly illustrates the impact of the rigid protein block approximation and the need to include all degrees of freedom and their relaxation in computational studies of protein gating. The effects of atomic level structure, pH, hydrogen bonding and charged residues on the large scale conformational changes associated with gating transitions are discussed.

Structural investigation of protein kinase C inhibitors

February 1991

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15 Reads

The phospholipid and Ca2+ dependent protein kinase (PKC) plays an essential role in a variety of cellular events. Inhibition of PKC was shown to arrest growth in tumor cell cultures making it a target for possible antitumor therapy. Calphostins are potent inhibitors of PKC with high affinity for the enzyme regulatory site. Structural characteristics of calphostins, which confer the inhibitory activity, are investigated by comparing their optimized structures with the existing models for PKC activation. The resulting model of inhibitory activity assumes interaction with two out of the three electrostatic interaction sites postulated for activators. The model shows two sites of hydrophobic interaction and enables the inhibitory activity of gossypol to be accounted for.

Interstellar problems and matrix solutions

April 1987

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15 Reads

The application of the matrix isolation technique, which is but one of the experimental techniques pioneered in George Pimentel's laboratories, to interstellar problems is described. Following a brief discussion of the interstellar medium (ISM) three areas are reviewed in which matrix experiments are particularly well-suited to contribute the information which is sorely needed to further our understanding of the ISM. The first involves the measurement of the spectroscopic properties of reactive species. The second is the determination of reaction rates and the elucidation of reaction pathways involving atoms, radicals and ions which are likely to interact on grain surfaces and in grain mantles. The third entails the determination of the spectroscopic, photochemical and photophysical properties of interstellar and cometary ice analogs. Significant, but limited, progress has been made in these three areas and a tremendous amount of work is required to fully address the variety of unique chemical and spectroscopic questions posed by the astronomical observations.

From non-random molecular structure to life and mind

September 1989

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15 Reads

The evolutionary hierarchy molecular structure-->macromolecular structure-->protobiological structure-->biological structure-->biological functions has been traced by experiments. The sequence always moves through protein. Extension of the experiments traces the formation of nucleic acids instructed by proteins. The proteins themselves were, in this picture, instructed by the self-sequencing of precursor amino acids. While the sequence indicated explains the thread of the emergence of life, protein in cellular membrane also provides the only known material basis for the emergence of mind in the context of emergence of life.

Frequency measurement of pure rotational transitions of H2O from 0.5 to 5 THz

January 1994

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22 Reads

Frequencies of H<sub>2</sub>O pure rotational transitions from 0.5 to 5 THz have been measured with an accuracy of one part in 10<sup>9 </sup> using a tunable far-infrared spectrometer. Measured frequencies of more than a hundred spectral lines provide an excellent wavelength and frequency calibration standard for the far infrared

Hydrothermal synthesis and characterization of an asymmetric binuclear molybdenum complex with oxalate ligand, NH4(enH2)0.5[Co(en)3][Mo2O7(C2O4)]·H2O

June 2003

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37 Reads

A new binuclear complex NH4(enH2)0.5[Co(en)3][Mo2O7(C2O4)]·H2O was obtained from the hydrothermal reaction of (NH4)6Mo7O24·4H2O, CoC2O4·2H2O, ethylenediamine and H2O at 120 °C, and characterized by single crystal X-ray diffraction and spectroscopic methods. The crystal structure is composed of dimeric [Mo2O7(C2O4)]4− anions, complex [Co(en)3]2+ cations, ethylenediamine cations, ammonium cations and crystallization water molecules, which are held together to an extensive three-dimensional network via hydrogen-bonding interactions. The dimeric structure of [Mo2O7(C2O4)]4− is formed by one MoO4 tetrahedron and one MoO6 octahedron through sharing a bridging oxygen atom, where oxalate acts as a bidentate ligand coordinating to the octahedral molybdenum atom though two deprotonated corboxylate groups. It is shown that the title compound possesses well-separated paramagnetic Co2+ centers.

Synthesis, spectroscopic and structural characterization of [Cu(phen)(C5O5)(H2O)]center dot H2O, [Ni(terpy)(C5O5)(H2O)]center dot H2O and [Ni(terpy)(2)](NO3)(2)center dot 0.5H(2)O

May 2005

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106 Reads

The new mononuclear complexes [Cu(phen)(C5O5)(H2O)]·H2O (1), [Ni(terpy)(C5O5)(H2O)]·H2O (2) and [Ni(terpy)2](NO3)2·0.5H2O (3) [phen=1,10-phenanthroline, =dianion of the 4,5-dihydroxycyclopent-4-ene-1,2,3-trione and terpy=2,2′:6′,2″-terpyridine] have been synthesized and characterized by single-crystal X-ray diffraction. The copper atom of 1 has a distorted square pyramidal environment with two phen-nitrogen and two croconate-oxygen atoms building the equatorial plane and a water molecule in the apical position. The nickel atom of 2 exhibits a distorted NiN3O3 octahedral coordination, which may be described either as tetragonally compressed or as skewed trapezoidal bipyramidal. The nickel atom of 3 is situated on a twofold axis and it has a distorted NiN6 octahedral coordination, with an appreciable tetragonal compression along the N(2)–Ni–N(4) axis [N(2) and N(4) being the central terpy-nitrogens]. The structures of 1 and 2 are compared with related ones from the literature and their potential use as ligands is analyzed.

Local phenomena in relaxor-ferroelectric PbSc0.5B″0.5O3 (B″=Nb, Ta) studied by Raman spectroscopy

December 2003

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34 Reads

Raman spectroscopy was applied to study nano-scale structure and related phonon anomalies in relaxor-ferroelectric materials of type PbB′0.5B″0.5O3. By comparing the polarized spectra of single crystals, measured at temperature higher than the maximum of the dielectric permittivity, Tm, and by performing normal mode calculations the observed Raman peaks were assigned to definite atomic vibrations. Further, the temperature evolution of the phonon anomalies was investigated on the basis of calculated modes of representative structural units at various atomic positions. It is shown that within a few nm doubling of the unit cell should exist, independently of the degree of B-site ordering. The Raman activity of the silent F2u mode reveals the existence of dynamical off-centred structural fluctuations. The structural perturbation consists of a non-coplanarity of the Pb and O atoms in the planes perpendicular to the cubic body diagonal and non-centre-symmetrical deformations of the BO6 octahedra. On cooling, different structural changes are preferential: for B″=Nb the temperature decrease amplifies the deformation of the individual BO3–Pb species; for B″=Ta the temperature decrease favours the non-coplanarity of Pb and O atoms and enhances the correlation between the stereoactive electron lone pairs of Pb atoms. Besides, within nano-scale spatial regions, PbSc0.5Ta0.5O3 undergoes an additional phase transition near 180 K that involves a reduction of the rotational symmetry. The comparison between the temperature dependence of the inelastic light scattering in stoichiometric and Nb-doped PbSc0.5Ta0.5O3 shows that the presence of Nb even in small concentrations affects the Pb–O sublattice and changes the direction of the local structural transformations.

Doppler-limited dye laser excitation spectroscopy of the PH2 radical: the Ã2A1(000)X̃2B1(000) band

June 1995

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4 Reads

The cw dye laser excitation spectrum of the vibronic transition of the PH2 radical was observed between 18 158 and 18 443 cm−1 at Doppler-limited resolution. The PH2 radical was produced by the reaction of discharged hydrogen with powdered red phosphorus. About 1000 lines were observed for Ka up to 7 and N up to 9. Using the ground-state parameters reported by Endo et al. [Y. Endo, S. Saito and E. Hirota, J. Mol. Spectrosc., 97 (1983) 204–212], upper-state term values were calculated from the observed transition frequencies and were subjected to a least-squares analysis to derive rotational constants, centrifugal distortion constants, and spin-rotation interaction constants in the state. The perturbations observed for the upper state are briefly discussed.

Analysis of torsional spectra of molecules with two internal C3v rotors: Part XXII11For Part XXI, see J. Chem. Phys., 75 (1981) 000.. Barrier to internal rotation of dimethylselenide and dimethylselenide-d3 and vibrational assignment for dimethylselenide-d3

5 Reads

The low frequency vibrational spectra of gaseous dimethylselenide and dimethylselenide-d3 have been investigated from 50 to 500 cm−1. A number of torsional transitions have been resolved in the far infrared spectra for both molecules and their analyses have given a torsional potential function based on a semirigid model. For the light molecule the effective barrier to internal rotation was found to be 507 ± 17 cm−1 (1450 cal mol−1) and the cosine-cosine coupling term, V33 was found to be 54 ± 12 cm−1 (154 cal mol−1), whereas the sine-sine coupling term, V33, has a value of 10 10 ± 4 cm−1 (29 cal mol−1). An interaction between the low frequency CSeC bending mode and the (2,0) - (1,0) torsional transition is proposed as a possible explanation for the assignment of the torsional transitions for dimethylselenide-d3. The effective barrier for the -d3 molecule was found to have a value of 520 ± 6 cm−1 (1487 cal mol−1) with a sine-sine coupling term value of −35 ± 7 cm−1 (−100 cal mol−1). A complete vibrational assignment is given for the dimethylselenide-d3 molecule and a normal coordinate calculation has been carried out using a modified valence force field. These results are compared to the similar quantities in some corresponding molecules.

Luminescence and electroluminescence of bis (2-(benzimidazol-2-yl) quinolinato) zinc. Exciplex formation and energy transfer in mixed film of bis (2-(benzimidazol-2-yl) quinolinato) zinc and N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine

February 2005

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63 Reads

The absorption and emission properties of benzimidazol-2-yl-quinoline (BIQ) and bis (2-(benzimidazol-2-yl) quinolinato) zinc (ZnBIQ) a new emitter used for organic light emitting device (OLED) were reported. Exciplexes are observed for ZnBIQ with N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) system, in both electro- and photoluminescent processes. The identification of exciplex emission in co-evaporated and multi-layer ZnBIQ thin film was reported for the first time. The optical formation of the exciplex involves the excitation of a single molecule, followed by the relaxation of that exciton into a lower energy exciplex state. Both BIQ and ZnBIQ possess very high thermal stabilities and can be purified by subliming under the high vacuum condition. Devices consisting of ZnBIQ as the emitting layer have been fabricated, and the emission spectra of ZnBIQ-base devices gave a voltage-dependent spectrum, with the red emission observed (3–7 V), switching over to strong white emission as the bias was raised.

Fluorescence spectra and decay kinetics of 1,1'-binaphthyl and related compounds at high pressures

December 1978

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7 Reads

Relative to the sterically hindered model compounds (I) 2,2'-dimethoxy-1,1'-binaphthyl and (II) 3,3'-dimethyl-1,1'-binaphthyl-20-crown-6, the pressure dependence of the fluorescence of racemic crystals of 1,1'-binaphthyl (III) is complex. Compression to 40 kbar at room temperature shifts the 1La fluorescence spectra of all three compounds to longer wavelengths but, for I and II does not change the Intensity profile, except for some 0-0 reabsorption. For III, this red shift characteristic of 1La fluorescence spectra is dominated by growth of new bands about 3.5 to 5.0 × 10 cm−1 to lower energy. Similar new bands are observed when racemic 1,1'-binaphthyl crystals are compressed at 77 K or resolved crystals are compressed at room temperature, but are not found to 50 kbar for dilute solutions of 1,1'-binaphthyl in polyacrylonitrile. Time-resolved fluorescence spectra, excited at 285nm by doubling the 570nm cavity-dumped output of a mode-locked Spectra-Physics 375-01 rhodamin 6G dye laser synchronously pumped by a mode-locked Spectra-Physics 171-05 argon laser, show that the new bands originate from a state with a longer lifetime (τ = 2.0 nsec at 20 kbar) than the 1La state (τ = 1.1 nsec). The planes of adjacent naphthyl residues along →b in the racemic crystal are parallel but offset, the normal distance between planes being 355pm; Raman spectra provide no evidence for a structural phase transformation upon compression. These new bands are assigned as the binaphthyl excimer.

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