Spectroscopic Characteristics of Differently Produced Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X‐ray absorption near edge structure, along with X‐ray photoemission by following the total valence bands and C 1s core‐level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp² hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence‐band X‐ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition.     

Dissolution and Doping of Polyaniline Emeraldine Base in Imidazolium Ionic Liquids Investigated by Spectroscopic Techniques

Polyaniline is a model molecular system in the study of conductive polymers. Ionic liquids, on the other hand, are becoming more and more a very convenient alternative for conventional organic solvents. The dissolution of polyaniline‐emeraldine base (PANI‐EB) in imidazolium ILs leads to its doping, as indicated by optical and resonance Raman spectroscopies. In this study, it is proposed that the interaction of PANI‐EB and imidazolium ILs involves the specific interaction of the quinoid moiety of the former with the imidazolium ring of the latter, an interpretation that is also based on N K‐edge XANES measurements of neat PANI‐EB, neat ILs, and of their solutions.

     

Compressibility of Gas Hydrates

Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0–2 GPa), xenon (cubic structure I, pressure range 0–1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0–3 GPa) are presented. Approximation of the data using the cubic Birch–Murnaghan equation, P=1.5B₀[(V₀/V)^7/3?(V₀/V)^5/3], gave the following results: for ethane hydrate V₀=1781 ų, B₀=11.2 GPa; for xenon hydrate V₀=1726 ų, B₀=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V₀=5323 ų, B₀=8.8 GPa. In the last case, the approximation was performed within the pressure range 0–1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch–Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86 % of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen‐bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones.     

Hydration of lanthanoid(III) ions in aqueous solution and crystalline hydrates studied by EXAFS spectroscopy and crystallography: the myth of the "gadolinium break"

The structures of the hydrated lanthanoid(III) ions including lanthanum(III) have been characterized in aqueous solution and in the solid trifluoromethanesulfonate salts by extended X-ray absorption fine structure (EXAFS) spectroscopy. At ambient temperature the water oxygen atoms appear as a tricapped trigonal prism around the lanthanoid(III) ions in the solid nonaaqualanthanoid(III) trifluoromethanesulfonates. Water deficiency in the capping positions for the smallest ions starts at Ho and increases with increasing atomic number in the [Ln(H(2)O)(9-x)](CF(3)SO(3))(3) compounds with x=0.8 at Lu. The crystal structures of [Ho(H(2)O)(8.91)](CF(3)SO(3))(3) and [Lu(H(2)O)(8.2)](CF(3)SO(3))(3) were re-determined by X-ray crystallography at room temperature, and the latter also at 100 K after a phase-transition at about 190 K. The very similar Ln K- and L(3)-edge EXAFS spectra of each solid compound and its aqueous solution indicate indistinguishable structures of the hydrated lanthanoid(III) ions in aqueous solution and in the hydrated trifluoromethanesulfonate salt. The mean Ln--O bond lengths obtained from the EXAFS spectra for the largest ions, La-Nd, agree with estimates from the tabulated ionic radii for ninefold coordination but become shorter than expected starting at samarium. The deviation increases gradually with increasing atomic number, reaches the mean Ln-O bond length expected for eightfold coordination at Ho, and increases further for the smallest lanthanoid(III) ions, Er-Lu, which have an increasing water deficit. The low-temperature crystal structure of [Lu(H(2)O)(8.2)](CF(3)SO(3))(3) shows one strongly bound capping water molecule (Lu-O 2.395(4) A) and two more distant capping sites corresponding to Lu-O at 2.56(1) A, with occupancy factors of 0.58(1) and 0.59(1). There is no indication of a sudden change in hydration number, as proposed in the "gadolinium break" hypothesis.     

Distribution of Butane in the Host Water Cage of Structure II Clathrate Hydrates

To understand host–guest interactions of hydrocarbon clathrate hydrates, we investigated the crystal structure of simple and binary clathrate hydrates including butane (n‐C₄H₁₀ or iso‐C₄H₁₀) as the guest. Powder X‐ray diffraction (PXRD) analysis using the information on the conformation of C₄H₁₀ molecules obtained by molecular dynamics (MD) simulations was performed. It was shown that the guest n‐C₄H₁₀ molecule tends to change to the gauche conformation within host water cages. Any distortion of the large 5¹²6⁴ cage and empty 5¹² cage for the simple iso‐C₄H₁₀ hydrate was not detected, and it was revealed that dynamic disorder of iso‐C₄H₁₀ and gauche‐nC₄H₁₀ were spherically extended within the large 5¹²6⁴ cages. It was indicated that structural isomers of hydrocarbon molecules with different van der Waals diameters are enclathrated within water cages in the same way owing to conformational change and dynamic disorder of the molecules. Furthermore, these results show that the method reported herein is applicable to structure analysis of other host–guest materials including guest molecules that could change molecular conformations.     

Crystal Structure and Spectroscopic Investigations of POF3

Phosphoryl fluoride was characterized by Raman spectroscopy and X‐ray diffraction analysis. The X‐ray structure was obtained by in‐situ crystallization. Phosphoryl fluoride crystallizes in the trigonal space group P$\bar{3}$ m1 with two formula units in the unit cell. In the crystal structure zigzag chains are observed which are formed by intermolecular P–O contacts. The Raman spectra of neat and matrix isolated POF₃ display an extra line, which indicates intermolecular interaction in the solid state. Therefore quantum chemically calculation of a POF₃ oligomer was performed. The theoretical calculation indicates that the extra Raman line is caused by side splitting of the P–O valence vibration.     

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

Novel cis‐1,2‐bis(di‐tert‐butyl‐phosphinomethyl) carbocyclic ligands 6 – 9 have been prepared and the corresponding palladium complexes [Pd(O₃SCH₃)(L‐L)][O₃SCH₃] (L‐ L=diphosphine) 32 – 35 synthesised and characterised by NMR spectroscopy and X‐ray diffraction. These diphosphine ligands give very active catalysts for the palladium‐catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9 , containing four‐ and six‐membered ring backbones giving more active systems. The acid used as co‐catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O₃SCH₃)(L‐ L)][O₃SCH₃], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism.     

Catching an Entatic State—A Pair of Copper Complexes

The structures of two types of guanidine–quinoline copper complexes have been investigated by single‐crystal X‐ray crystallography, K‐edge X‐ray absorption spectroscopy (XAS), resonance Raman and UV/Vis spectroscopy, cyclic voltammetry, and density functional theory (DFT). Independent of the oxidation state, the two structures, which are virtually identical for solids and complexes in solution, resemble each other strongly and are connected by a reversible electron transfer at 0.33 V. By resonant excitation of the two entatic copper complexes, the transition state of the electron transfer is accessible through vibrational modes, which are coupled to metal–ligand charge transfer (MLCT) and ligand–metal charge transfer (LMCT) states.     

Development of a simultaneous measurement system of x‐ray diffraction and raman spectra: Application to structural study of crystalline‐phase transitions of chain molecules

The development of a bench‐top‐type system for simultaneous measurement of X‐ray diffraction and Raman spectra has been made to investigate structural changes in the phase transitions of chain molecules such as polyethylene, n‐alkane, and so forth from various viewpoints. For the X‐ray diffraction measurement an imaging plate or a charge‐coupled device camera was used as a two‐dimensional detector. For the Raman spectral measurement a miniature Raman spectrometer was used with optical fibers for the irradiation of incident laser beams and collection of scattered signals. For example, in the heating process of the n‐C₃₀H₆₂ sample, the phase transition from orthorhombic‐to‐hexagonal lattices could be detected clearly by the X‐ray and Raman measurements. By comparing these two different types of data in detail, an intimate relationship between conformational disordering and rotational motion of molecular chains is detected more clearly than before. Also, similar discussion can be made for the orthorhombic‐to‐hexagonal phase transition of the geometrically constrained polyethylene sample occurring immediately below the melting point. Another example concerns the structural change in the photoinduced solid‐state polymerization of cis,cis‐diethylmuconate single crystal. From the shifts in the X‐ray reflection position and Raman frequency characteristic of the produced polymer, it was found that the molecular deformation of the polymer chains and lattice strain was induced in the early stage of the polymerization reaction. For the ferroelectric‐phase transition of vinylidene fluoride copolymer, the simultaneous measurement was made for collecting triple information of small‐angle and wide‐angle X‐ray scatterings and Raman spectra to know the relationship between the structural change in the crystal lattice and the morphological change in the lamellar stacking mode. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 495–506, 2002; DOI 10.1002/polb.10112     

Structural investigation of water‐induced phase transitions of poly(ethylene imine). III. The thermal behavior of hydrates and the construction of a phase diagram

The thermal behavior of poly(ethylene imine) (PEI) hydrates in a water vapor atmosphere was investigated through temperature‐dependent measurements of infrared spectra and X‐ray diffraction. Almost perfectly dried anhydrate melted at about 60 °C during the heating process. Anhydrate containing a small amount of water showed a phase transition to a mixture of hemihydrate and sesquihydrate around 40 °C, at which point the ethylene imine (EI)/water ratio was 1/0.5 in the hemihydrate and 1/1.5 in the sesquihydrate. The hemihydrate transferred to the sesquihydrate around 60 °C, and the latter melted above 80 °C. When the starting PEI sample contained a greater amount of water and consisted of hemihydrate and sesquihydrate, the hemihydrate transferred to the sesquihydrate via heating, and the latter melted around 75 °C. For a sample of dihydrate (EI/water ratio = 1/2) containing an appreciably large amount of water, it transferred to the sesquihydrate around 65 °C, and the latter melted above 90 °C. A sample of dihydrate with a much higher water content existed up to 110 °C and then melted; during this period, no transition to the sesquihydrate was observed. In this way, the starting crystalline phases were found to change for anhydrate and various types of hydrates. Their transition behaviors varied according to the water content. From these data, a phase diagram was successfully derived as a function of the temperature and water content. This phase diagram allowed us to predict the transition behavior during the hydration process at various constant temperatures. For example, at 60 °C, a molten sample should crystallize into a mixture of hemihydrate and sesquihydrate at first, and the hemihydrate should transfer to the sesquihydrate with increasing water content. The latter should change to the dihydrate in the final stage. This prediction was checked with time‐resolved measurements of X‐ray diffraction and infrared spectra during the hydration process at the corresponding temperature; this led to the establishment of the phase diagram. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2937–2948, 2003     

Structural and Vibrational Studies of Sr2[W(CN)8]·10H2O

The crystal structure of distrontium octacyanotungstate decahydrate, Sr₂[W(CN)₈] · 10H₂O, was solved using X‐ray single crystal diffraction. The tungsten atom lies on a two fold axis. Eight cyanide anions create tetragonal antiprismatic coordination sphere of tungsten atom. The two edge‐sharing tetragonal antiprisms of [Sr(NC)₃(OH₂)₅], create a dimer, [Sr₂(CN)₆(H₂O)₆(μ‐H₂O)₂], which lies on the inversion center. One symmetry independent water molecule is located in a void of 40 Å³. Vibrational (FT‐IR and FT‐Raman spectroscopic) behavior of main structural units is discussed. It was spectroscopically confirmed that the geometry of [W(CN)₈]^4– anion is slightly distorted from that corresponding to “free” anion. The number of observed bands is significantly lower than that expected for C₂ point group.     

Temperature- and Pressure-induced Structural Transition of Binary Clathrate Hydrates

We discover new structure II (sII) hydrate forming agents of two C₄H₈O molecules (2-methyl-2-propen-1-ol and 2-butanone) and report the abnormal structural transition of binary C₄H₈O+CH₄ hydrates between structure I (sI) and sII with varying temperature and pressure conditions. In both (2-methyl-2-propen-1-ol+CH₄) and (2-butanone+CH₄) systems, the phase boundary of the two different hydrate phases (sI and sII) exists at the slope change of the phase-equilibrium curve in the semi-logarithmic plots. We confirm the crystal structures of two hydrates synthesized at low (278 K and 6 MPa) and high (286 K and 15 MPa) temperature and pressure conditions by using high-resolution powder diffraction and Raman spectroscopy. 2-Methyl-2-propen-1-ol and 2-butanone can occupy the large cages of sII hydrate at low temperature and pressure conditions; however, they are excluded from the hydrate phase at high temperature and pressure conditions, resulting in the formation of pure sI CH₄ hydrate.     

Effect of PIP2 on Bilayer Structure and Phase Behavior of DOPC: An X‐ray Scattering Study

Phosphatidylinositol 4,5‐bis‐phosphate (PIP₂) is an important lipid in regulation of several cellular processes, particularly membrane fusion. We use X‐ray diffraction from solid‐supported multilamellar 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC)/PIP₂ samples to study changes in bilayer structure and the lyotropic phase behavior induced by physiologically relevant concentrations of PIP₂. Electron‐density profiles reconstructed from X‐ray reflectivity measurements indicate that PIP₂ strongly affects structural parameters such as lipid head‐group width, bilayer thickness, and lamellar repeat spacing of DOPC bilayer stacks. In addition, at lower degrees of hydration, a few molar per cent of PIP₂ facilitates stalk‐phase formation and also leads to formation of a hexagonal phase, which is not observed in pure DOPC. These results indicate that the role of PIP₂ in membrane fusion could be, in part, due to its effect on the properties of the lipid bilayer matrix. Furthermore, coexistence of two lamellar phases with different lattice constants is observed in single‐component PIP₂ samples.     

New Light on an Old Story: The Crystal Structure of Boron Tetrathiophosphate Revisited

The crystal structure of boron tetrathiophosphate BPS₄ was reinvestigated using single‐crystal X‐ray diffraction. The structure shows unidimensional chains similar to SiS₂ as structural motifs. BPS₄ crystallizes in the orthorhombic space group Ibam (no. 72), with a = 5.6173(3), b = 8.9929(4), c = 5.2433(3) Å and V = 264.87(2) ų and is closely related to the orthorhombic high‐temperature modification of AlPS₄ (ht‐AlPS₄). The SiS₂‐like chains are all oriented parallel to the c axis, which explains the needle‐like morphology and that the crystals easily cleave to thinner needles under mechanical stress. While ht‐AlPS₄ shows an ordered Al‐P sublattice, the B‐P sublattice in BPS₄ is substantially disordered. The thermal properties of BPS₄ were investigated by DTA measurements and a detailed analysis of the Raman spectrum assisted by quantum mechanical calculations is presented. The crystallographic disorder in BPS₄ is the result of inter‐chain disorder, whereas local intra‐chain ordering of B and P can be concluded from Raman spectroscopy.     

1H,89Y HMQC and Further NMR Spectroscopic and X‐ray Diffraction Investigations on Yttrium‐Containing Complexes Exhibiting Various Nuclearities

2D ¹H,⁸⁹Y heteronuclear shift correlation through scalar coupling has been applied to the chemical‐shift determination of a set of yttrium complexes with various nuclearities. This method allowed the determination of ⁸⁹Y NMR data in a short period of time. Multinuclear NMR spectroscopy as function of temperature, PGSE NMR‐diffusion experiments, heteronuclear NOE measurements, and X‐ray crystallography were applied to determine the structures of [Y₅(OH)₅(L ‐Val)₄(Ph₂acac)₆] ( 1 ) (Ph₂acac=dibenzoylmethanide, L ‐Val=L ‐valine), [Y( 2 )(OTf)₃] ( 3 ), and [Y₂( 4 )(OTf)₅] ( 5 ) ( 2 : [(S)P{N(Me)N?C(H)Py}₃], 4 : [B{N(Me)N?C(H)Py}₄]^?) in solution and in the solid state. The structures found in the solid state are retained in solution, where averaged structures were observed. NMR diffusion measurements helped us to understand the nuclearity of compounds 3 and 5 in solution. ¹H,¹⁹F HOESY and ¹⁹F,¹⁹F EXSY data revealed that the anions are specifically located in particular regions of space, which nicely correlated with the geometries found in the X‐ray structures.     

Superoxide Compounds of the Large Pseudo‐Alkali‐Metal Ions Tetramethylammonium, ‐Phosphonium,and ‐Arsonium

Compounds of the three large cations tetramethylammonium, tetramethylphosphonium, and tetramethylarsonium with the superoxide radical anion were synthesized by either metathesis or ion exchange in liquid ammonia. They were obtained from concentrated solutions as ammoniates in the form of long needle‐shaped single crystals. [N(CH₃)₄]‐(O₂)?3NH₃ crystallizes in the monoclinic crystal system, whereas the two compounds [E(CH₃)₄](O₂)?2NH₃ (E=P, As) are isostructural and belong to the orthorhombic crystal system. The cation–anion packing in all three crystal structures is related to the sodium chloride structure. All structures contain hydrogen bonds between the ammonia molecules and between ammonia and the superoxide. The solvent of crystallization was easily released from the crystals upon complete removal of the solvent from the reaction vessel, leading to polycrystalline samples. The Raman spectra of all three solvent‐free compounds show the symmetric stretching mode of the superoxide ion at about 1123 cm^?1. The desolvated [N(CH₃)₄](O₂) was investigated by powder X‐ray diffraction, and the crystal structure was solved by ab initio simulated annealing methods by using rigid‐body models of the constituent molecular ions. The superoxide ion shows rotational disorder. The magnetic susceptibility of tetramethylammonium superoxide follows the Curie–Weiss law with a high‐temperature effective magnetic moment of 1.66(3) μ_B and a paramagnetic Curie temperature of Θ=?13(6) K. Complementary electron paramagnetic resonance spectroscopy revealed that the average g factor is temperature‐dependent. It decreased from 2.15 at 10 K to 1.66 at 100 K, possibly due to the onset of rotational motion of the superoxide ion and in accordance with the lower‐than‐expected effective magnetic moment.