The photoelectron spectra of cyclooctatetraene and its hydrogenated derivatives

The photoelectron spectrum of cyclooctatetraene (COT; 1) has been re-examined. Correlation with the spectra of the dihydro- (2, 3), tetrahydro- (4, 5, 6), hexahydro- (7) and octahydro- (8) derivatives confirms the orbital sequence originally proposed by Eland, namely 5a₁ (π), 7e (π), 4b₂ (π), σ. It is shown that the positions and the relative spacing of the π-orbitals are the result of a competition between through-space and through-bond interactions.The photoelectron spectroscopic results for the hydrogenated derivatives of COT yield information about their conformation; in particular about the twist angles between consecutive π-bonds. The spectrum of 1,5-cyclooctadiene (6) confirms that this molecule preferentially adopts the boat conformation.An empirical rule is proposed which yields estimates for the orbital energies of basis π-orbitals in monocyclic hydrocarbons.     

Photoelectron (He(I), He(II) and X-ray) spectroscopy of γ-pyrone and its related sulphur derivatives: valence and core ionization energies and shake-up satellites

The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one (1), 4H-thiopyran-4-one (2), 4H-pyran-4-thione (3) and 4H-thiopyran-4-thione (4) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are n_X (σ), 3b₁ (π), 1a₂(π) for 1, 2 and 4; and 3b₁(π), n_X(σ) and 1a₂(π) for 3. The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3b₁ (π) → 4b₁(π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom.     

Effect of the group IV elements on the Π anion and cation states of thiophene and furan determined by means of ETS and UPS

The electron-transmission and He(I) photoelectron spectra of Si(CH₃)₃, Sn(CH₃)₃ and CH₂Si(CH₃)₃ derivatives of thiophene and furan have been recorded. The first two substituents perturb the energies of the outer filled π orbitals and of the empty π* orbitals in opposite directions, causing a reduction of the HOMO/LUMO energy separation. The stabilization experienced by the π* MO's depends on their wavefunction coefficients at the site of substitution, and is attributed to interaction with low-lying empty orbitals of the substituent groups. The relatively small size (～ 0.4 eV) of this effect on the unoccupied ring MO's suggests that it should not appreciably affect the energy of the filled MO's.The strong conjugation between the π* unoccupied orbital of the nitro group and those of thiophene has also been investigated.     

The photoelectron spectra of tricyclo[3.3.0.02,6]Octene and tricyclo[3.3.0.02,6]Octane

The photoelectron spectra of tricyclo[3.3.0.0^2,6]octene (1) and tricyclo[3.3.0.0^2,6]octane (2) have been recorded. The first bands in these spectra are correlated with orbitals which are linear combinations of the Walsh orbitals and of the olefinic π-orbital. This assignment is based on a zero differential overlap molecular orbital model as well as on the results of extended Hückel calculations. The resonance integral <π|H|W > for 1 is found to be ?1.34 eV.     

H3PAuPh与(H3PAu)2(1,4-C6H4)2光谱性质的密度泛函研究

用密度泛函(DFT)方法优化了配合物H₃PAuPh(a),(H₃PAu)₂(1,4-C₆H₄)₂(b)的基态的几何结构,并用含时密度泛函方法计算了它们的吸收光谱.结果表明配合物a与 b的最低能量吸收谱线的波长分别为257.5 nm和307.6 nm,皆具有C(2p)→Au(6p)电荷转移参与下的p_π 关键词： 激发态 光谱 密度泛函 3')" href="#">AuPH₃     

Two potassium rare-earth polyphosphates KLn(PO3)4 (Ln=Ce, Eu): Structural, optical, and electronic properties

Two potassium rare-earth polyphosphate single-crystals KLn(PO₃)₄ (Ln=Ce (1), Eu (2)) have been synthesized by the high-temperature solution reaction and characterized by single-crystal X-ray diffraction. The two isostructural compounds crystallize in the monoclinic system with space group P2₁, and all cell parameters shrink with the decrease of Ln³⁺ ion radius. The main structural feature is (PO₃)₄⁴⁻ wavy chains and infinite tunnels delimited by LnO₈ and KO₈ polyhedra. The energy band structures, density of states (DOS), and optical response functions for 1 have been calculated with the density functional theory (DFT) method, and the dielectric functions and refractive indices have been discussed. The measurements of the absorption and emission spectra show that 1 exhibits the ultraviolet emissions, and 2 displays the characteristic yellow-red emissions of Eu³⁺.     

Raman spectroscopic study of the multi‐anion uranyl mineral schroeckingerite

Raman spectroscopy complemented with infrared (IR) spectroscopy has been used to study the mineral schroeckingerite. The mineral is a multi‐anion mineral and has (UO₂)²⁺, (SO₄)²⁻ and (CO₃)²⁻ units in its structure, and bands attributed to these vibrating units are readily identified in the Raman spectra. Symmetric stretching modes at 815, 983 and 1092 cm⁻¹ are assigned to (UO₂)²⁺, (SO₄)²⁻ and (CO₃)²⁻ units, respectively. The antisymmetric stretching modes of (UO₂)²⁺, (SO₄)²⁻ are not observed in the Raman spectra but may be readily observed in the IR spectrum at 898 and 1180 cm⁻¹. The antisymmetric stretching mode of (CO₃)²⁻ is observed in the Raman spectrum at 1374 cm⁻¹, as is also the ν₄ (CO₃)²⁻ bending modes at 742 and 707 cm⁻¹. No ν₂ (CO₃)²⁻ bending modes are observed in the Raman spectrum of schroeckingerite. All the spectroscopic evidence points to a highly ordered structure of this mineral. Copyright © 2007 John Wiley & Sons, Ltd.     

A new quasi-one-dimensional molecular solid based on Ni(mnt)2 anion: Crystal structure and spin-gap transition

A new molecular solid, [1-(4′-bromo-2′-fluorobenzyl)-4-dimetylaminopyridinium]-bis(maleonitriledithiolato)nickel(III), (BrFBzPyN(CH₃)₂(Ni(mnt)₂)(1), has been prepared and characterized by elemental analyses, IR, ESI-MS spectra, single crystal X-ray diffraction and magnetic measurements. Compound 1 crystallizes in the orthorhombic space group Pnma, a=20.579(4) Å, b=7.078(1) Å, c=17.942(4) Å, α=β=γ=90°, V=2613.3(9) Å³, Z=4. The Ni(III) ions of 1 form a quasi-one-dimensional Zigzag magnetic chain within a Ni(mnt)₂⁻ column through Ni?S, S?S, Ni?Ni, or π?π interactions with an Ni?Ni distance of 4.227 Å. Magnetic susceptibility measurements in the temperature range 2-300 K show that 1 exhibits a spin-gap transition around 200 K, and antiferromagnetic interaction in the high-temperature phase (HT) and spin gap in the low-temperature phase (LT). The transition for 1 is second-order phase transition as determined by DSC analyses.     

Variable Activity of Reagents with C=C and N=N Bonds in Cycloaddition Reactions

Data on rates and enthalpies of the reactions of quadricyclane (4) and diadamantylidene (5) with N-phenylmaleimide (1), 4-phenyl-1,2,4-triazoline-3,5-dione (2), and tetracyanoethylene (3) are obtained for the first time. Reagent 2 with the N=N reaction center is found to be six orders of magnitude more active than its structural analog 1. A strong π-acceptor 3 is 370 times more active than reagent 2 in the reaction with a strong π-donor substrate 4 but is less active than reagent 2 in many [4π + 2π], [2π + 2π + 2π], and [2π + 2π] cycloaddition reactions, and, especially, in ene reactions. The possible causes of the strong difference and variable activity of compounds 1–3 with C=C and N=N bonds are discussed.     

Surface-modification of TiO2 with new metalloporphyrins and their photocatalytic activity in the degradation of 4-notrophenol

A new mono-functionalized porphyrin derivative, 5-mono-[4-(2-(4-hydroxy)-phenoxy)ethoxy]-10,15,20-triphenylporphyrin (3) and its Cu(II) (3a), Zn(II) (3b) and Ni(II) (3c) metalloporphyrins were synthesized and characterized by using various spectroscopic techniques. The corresponding 3a, 3b, 3c-TiO₂ photocatalysts were then prepared and characterized by means of FT-IR and diffused reflectance spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activities of 3a, 3b, 3c-TiO₂ were investigated by testing the photodegradation of 4-nitrophenol (4-NP) in aqueous solution under the halogen lamp irradiation. The results indicated that all the 3a, 3b, 3c enhanced the photocatalytic efficiency of bare TiO₂ in photodegrading the 4-NP, and 3a-TiO₂ exhibited the highest photocatalytic activity. The result is considered a combined action of potential match of 3a with TiO₂ CB and effective impregnated of 3a onto the surface of TiO₂.     

Adsorption mechanism of physiologically active l-phenylalanine phosphonodipeptide analogues: Comparison of colloidal silver and macroscopic silver substrates

Here we present SERS spectra of several l-phenylalanine (Phe) phosphonodipeptides, i.e., l-Phe-l-Ala-PO₃H₂ (MD1), l-Phe-l-Val-PO₃H₂ (MD2), l-Phe-β-Ala-CH(OH)-PO₃H₂ (MD3), l-Phe-l-Ala-CH(OH)-PO₃H₂ (MD4), l-Ala-(3,4-dimethoxy)-l-Phe-PO₃H₂ (MD5), and l-Ala-(3,4-dimethoxy)-(des-CH₂)-l-Phe-PO₃H₂ (MD6), immobilized on electrochemically roughened silver electrodes. These spectra are analyzed by theoretical calculations using density functional theory (DFT) at the B3LYP level with 6-31++G∗∗ basis set. In addition, these spectra are compared with SERS spectra of these species adsorbed on a colloidal silver surface. We showed that on the macroscopic silver substrate, the Phe aromatic ring of MD3 and MD4 is oriented vertically, while for MD1 it almost “stands up” on this surface. In the other three cases, the Phe ring adopts a tilted orientation in regard to the substrate. We also find that the phosphonate , methyl/methane, or dimethoxy groups of MD1, MD2, MD3, MD5, and MD6 are involved in the interaction of these phosphonodipeptides with the electrochemically roughened surface. This phenomenon is clearly seen for -CH₂-/-CH₃/-OCH₃ moieties as well as for the group that adsorbs on the macroscopic silver substrates mainly via the PO fragment. We also showed that MD4 binds to the macroscopic silver substrate through the hydroxyl, amine, and phosphonate groups, while the methylene/methane moieties are remote from this surface. We found that studied phosphonodipeptides often adsorb differently on the macroscopic silver substrate and on the colloidal silver nanoparticles. For example, MD1 adopts an almost vertical orientation on the electrochemically roughened silver substrate and is tilted or close to flat on the silver nanoparticles.     

Photoelectron spectroscopy of some thiocyanates,isocyanates and isothiocyanates

Photoelectron spectra of some thiocyanates (RSCN, R = CH₃, C₂H₅, n-C₄H₉), isocyanates (RNCO, R = C₂H₅, n-C₄H₉) and isothiocyanates (RNCS, R = C₂H₅, n-C₄H₉) have been measured, to study interactions between nonbonding and π orbitals, mainly localized on the SCN, NCO or NCS fragments. The spectral interpretation of CH₃SCN is based on semiempirical CNDO/S calculations, sum-rule considerations, and intensity differences between He(I) and HE(II) spectra. For the larger molecules, comparison of the spectra is used as an aid in the interpretation. In a number of aromatic isocyanates (o?, m?, p-tolylisocyanate and m?, p-chlorophenylisocyanate), interactions between the isocyanate group and the highest occupied π and σ orbitals of the phenyl ring are studied. Spectra are assigned on the basis of semiempirical INDO/S calculations.     

Sonochemical synthesis and characterization of new nanostructures cobalt(II) metal-organic complexes derived from the azo-coupling reaction of 4-amino benzoic acid with anthranilic acid,salicylaldehyde and 2-naphtol

Nanostructures of three new cobalt(II) complexes, (CoL₁)·0.5DMF·1.5MeOH (1), [H₂L₁ = 5-(4-Carboxy phenyl azo) anthranilic acid], (Co(L₂)₂)·1.5MeOH (2), [HL₂ = 5-(4-Carboxy phenyl azo) salicylaldehyde] and (Co(L₃)₂)·0.5 DMF·0.5MeOH (3), [HL₃ = 1-(4-Carboxy phenyl azo) 2-naphtol], have been synthesized by the reaction of H₂L₁, HL₂ and HL₃ with Co(OAc)₂·4H₂O through sonochemical process. Calcination of the nano-sized compounds 1–3 yield Co₃O₄ nanoparticles at 450 °C under air atmosphere. These nanostructures were characterized by X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM). Thermal stability of compounds 1–3 was studied by thermogravimetric (TG) and differential thermal analyses (DTA).     

A pes study on 1,3-thiazole and its monosubstituted halogen derivatives

The photoelectron (HeI) spectra of 1,3-thiazole and its 2F, 2Cl, 2Br, 4Br and 5Br-derivatives are reported. The assignment of the first few bands of the various spectra to the corresponding molecular orbital is based, for thiazole, on the results of an ab initio SCF—MO calculation, while for the various halogen derivatives, on reasonings based on perturbation theory.In particular, the first five outermost molecular orbitals of thiazole probably correspond to π₃ (9.50 eV), π₂ (10.24), σ_N (10.48; orbital mainly localized on the nitrogen atom), σ_S (12.78; orbital mainly localized on the sulphur atom) and π₁ (13.5).     

Complexing equilibria of Ag(I) ion in the presence of heterocyclic amines in DMSO. Comparison with other solvents

The stability constants of Ag(I) complexes with aromatic heterocyclic amines: pyridine (py), 2,2′-bipyridine (bipy), 1,10-phenantroline (phen), 2,2′-bipyridil-6′-phenyl (bpp) and 2,2′:6′,2″-terpyridine (tp) as well as with saturated cyclic amines: piperidine (ppd), piperazine (ppz), 1,4-diazacycloheptane (dach), 1,4,7-triazacyclononane (tacn) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmtact) have been determined in DMSO using potentiometry. The polarizability and dipole moments of the investigated amines have been calculated by means of AM1 and PM3 methods (from the MOPAC 6 packet). The role of the Ag(I) ion and ligand solvation in thermodynamics of the complex formation process in four solvents (H₂O, AN, PC, DMSO) has been discussed.     

Photoelectron spectroscopic assignment of symmetry to the ground state and first excited state of the 1,4-cyclohexadiene radical cation

The empirical correlation of the photoelectron spectra of 1,4-cyclohexadiene (molecule 4), 1, 4, 5, 8-tetrahydronaphthalene (molecule 5), 1, 4, 5, 6, 9, 1 0-hexahydroanthracene (molecule 6), and 1, 4, 5, 6, 7, 10, 11, 12-octahydronaphthacene (molecules 6) proves that the electronic ground state of these molecules is ²B_1u, assuming that they have D_2h symmetry. In particular this confirms previous predictions for 1,4-cyclohexadiene (molecule 4), for which the “inverted” orbital sequence 2b_1u(π) above lb_3g(π) had been proposed under the assumption that hyperconjugative “through-bond” interaction dominates the “through-space” interaction of the two semi-localized π-orbitals.     

The ionization energies of bent and twisted double bonds. Part II. Tricyclo[4.2.2.22,5] Dodecadiene-1 (2),5 (6)

The electronic structure of the title compound (1) has been investigated using He(Iα) PE spectroscopy and assuming the validity of Koopmans' theorem. It is found that: (a) in analogy to the situation prevailing in the cyclophanes, hyperconjugation of the out-of-phase linear combination of the π-orbitals with the ethano-bridge σ orbitals is symmetry-forbidden; (b) in agreement with the ideas developed in Part I of this series [1], the strong local B_1u-type bending of the ethylene moieties does not affect their basis energy significantly; and (c) the “through-space” coupling of the two double-bond π orbitals is of the same order as the benzene π-orbital coupling in [2ⁿ] cyclophanes, even if the net contribution to the repulsion of the two double bonds is probably small. Because of the near degeneracy of the HOMO and HOMO — 1 of 1, the ground state of the radical cation 1⁺ cannot be determined uniquely: it is either²A_g or²B_1u.     

Theory and experiment: Anion binding property of novel phenanthroline or aromatic bridged compounds

A series of artificial compounds, phenanthroline or aromatic bridged indoline derivatives, have been designed and synthesized. The interaction of these compounds with biologically important anions fluoride (F^?), acetate (AcO^?), dihydrogen phosphate (H₂PO₄^?), chloride (Cl^?), bromide (Br^?) and iodide (I^?) was determined by UV–vis, fluorescene titration and theoretical experiments. Results indicate that compound 1 (Di((1″,2″-dihydro-indol-3″-one-2″-hydrazone-1′-hydrazyl)-2′-methylene)-1,3-did-ehydebenzo) and 2 (Di((1″,2″-dihydro-indol-3″-one-2″-hydrazone-1′-hydrazyl)-2′-methylene)-1,3-didehyde-5-nitrobenzo) containing aromatic bridge do not show binding ability for various anions, and that compound 3 (Di((1″,2″-dihydro-indol-3″-one-2″-hydrazone-1′-hydrazyl)-2′-methylene)-2,9-dial-dehyde-1,10-phenanthroline) containing phenanthroline bridge shows the strongest binding ability for F^? among various anions, the moderate binding ability for AcO^? and H₂PO₄^?, and almost no binding ability for Cl^?, Br^?, I^?. The different binding ability of aromatic and phenanthroline bridged compounds may be related to the conjugative effect. What's more, the binding ability of compound 3 with F^? is not interfered by the existence of other anions. Hence, theoretical investigations explore the reasons of different binding ability between compound 3 and anions.     

Copper(I) Complexes of N-(2-{[(2E)-2-(4-Nitrobenzylidenyl)Hydrazinyl]Carbonyl}Phenyl)Benzamide and Triphenylphosphine: Synthesis,Characterization and Luminescence Properties

Copper(I) complexes of the formula [Cu(L)(PPh₃)₂]X (1–4) (X = Cl(1), ClO₄(2), BF₄(3) and PF₆(4)) [where L = N-(2-{[(2E)-2-(4-nitrobenzylidenyl)hydrazinyl]carbonyl}phenyl)benzamide; PPh₃ = triphenylphosphine] have been prepared by the condensation of N-[2-(hydrazinocarbonyl)phenyl]benzamide with 4-nitrobenzaldehyde followed by the reaction with CuCl, [Cu(MeCN)₄]ClO₄, [Cu(MeCN)₄]BF₄ and [Cu(MeCN)₄]PF₆ in presence of triphenylphosphine as a coligand. Complexes 1–4 were then characterized by elemental analyses, FTIR, UV-visible and ¹H NMR spectroscopy. Mononuclear copper(I) complexes 1–4 were formed with L in its keto form by involvement of azomethine nitrogen and the carbonyl oxygen along with two PPh₃ groups. A single crystal X-ray diffraction study of the representative complex [(Cu(L)(PPh₃)₂]CIO₄ (2) reveals a distorted tetrahedral geometry around Cu(I). Crystal data of (2): space group = C2/c, a = 42.8596 (9) Å, b = 14.6207 (3) Å, c = 36.4643 (7) Å, V = 20,653.7 (7) ų, Z = 16. Complexes 1–4 exhibit quasireversible redox behaviour corresponding to a Cu(I)/Cu(II) couple. All complexes show blue-green emission as a result of fluorescence from an intra-ligand charge transition (ILCT), ligand to ligand charge transfer transition (LLCT) or mixture of both. Significant increase in size of the counter anion shows marked effect on quantum efficiency and lifetime of the complexes in solution.     

Synthesis and luminescent study of diphosphine-Pt-disulfide complexes for OLED

Three novel diphosphine-Pt-disulfide complexes were synthesized and characterized by ¹H NMR, mass spectrometry and elemental analysis. As a diphosphine, 1,8-bis(diphenylphosphino)naphthalene (dppn), rac-2,2^′-bis(diphenylphosphino)-1,1^′-binaphthyl (dppbn), or 1,1^′-bis(diphenylphosphino)ferrocene (dppf) was employed and chelated to the Pt(II) center. As an anion, p-tolylsulfide (4-SC₆H₄CH₃) was incorporated to Pt(II) center subsequently, yielding (dppn)Pt(4-SC₆H₄CH₃)₂ (1), (dppbn)Pt(4-SC₆H₄CH₃)₂ (2), or (dppf)Pt(4-SC₆H₄CH₃)₂ (3). The photophysical properties of the resulting Pt complexes were investigated with UV–VIS spectroscopy, photoluminescence (PL) spectroscopy and transient PL. Charge Transfer absorptions between the metal and the ligand of 2 and 3 were observed at 320–350 nm in the UV–VIS spectra whereas such noticeable absorption was not observed in 1. The solid films of 1 and 3 showed luminescence at 600 and 580 nm, respectively, while that of 2 did not show emission at the room temperature. The complex 3 exhibited two excited state lifetimes, 23 and 125 ns, at room temperature, and the weighting factor for 125 ns state is only 10% of that for 23 ns one. It means that the prominent luminescence was fluorescence and the intersystem crossing through LS coupling is relatively weak.