Solid-state Raman Spectra Research Articles

Comparative study of the carbonization process and structural evolution during needle coke preparation from petroleum and coal feedstock

To explore the carbonization behavior and structural evolution of needle coke prepared from different types of rich-aromatic materials, petroleum feedstock hydrocracking tail oil (HCTO) and coal feedstock low-temperature coal tar (LCT) were selected to prepare needle coke. The detailed comparative investigation focused on the properties of feedstocks and the structure of the derived needle cokes by using gas chromatography-mass spectrometry (GC–MS), 1H nuclear magnetic resonance (1H-NMR), 13C nuclear magnetic resonance (13C-NMR), polarizing microscope, thermogravimetric analysis (TGA), 13C solid-state nuclear magnetic resonance (13C-ssNMR) and Raman spectra. It was found that the colloids in LCT3 accelerated the growth and evolution of carbonaceous structure and were not conducive to the preparation of needle coke. In addition, phenols in LCT3 led to oxygen-containing crosslinking during the secondary pyrolysis, which resulted in the spatial configuration of poor planarity and wider fringe spacing in optical texture. The calcination process further enlarged the structural defects of pyrolysis products, the steric hindrance and structural strains were aggravated as well.

Oxabicyclic Guest Compounds as sII Promoters: Spectroscopic Investigation and Equilibrium Measurements.

In this study, we investigate three oxabicyclic compounds, 3,6-dioxabicyclo[3. 1.0]hexane (C4H6O2, ETHF), 7-oxabicyclo[2.2.1]heptane (C6H10O, 14ECH), and 7-oxabicyclo[4.1.0]heptane (C6H10O, 12ECH) as novel promoters for gas hydrates. According to the outcomes of powder X-ray diffraction (PXRD) and synchrotron high-resolution powder diffraction (HRPD), all CH4 hydrates formed with ETHF, 14ECH, and 12ECH were identified to be sII (Fd-3m) hydrates with corresponding lattice parameters of 17.195, 17.330, and 17.382 Å, respectively. It was also clearly demonstrated that CH4 molecules are accommodated in the sII-S cages through solid-state 13C NMR and Raman spectra. Consequently, we clarified that the three compounds observed are large guest molecules (LGMs) that occupy the sII-L cages. Moreover, the thermodynamic stability of each LGM + CH4 (and N2) hydrate system was remarkably improved compared to that of the simple CH4 (and N2) hydrate. In particular, 14ECH manifested several unique features compared to the other two promoters. First, the 14ECH + CH4 hydrate did not dissociate up to room temperature (298 K), even at a moderate pressure of approximately 60 bar. At a given pressure, 14ECH increased the dissociation temperature of the CH4 hydrate by ~18 K, indicating that its promotion capability is as strong as that of tetrahydrofuran (THF), currently considered to be the most powerful promoter. Second, more interestingly, it was revealed by further PXRD, NMR, and Raman analyses that 14ECH forms a simple sII hydrate in the absence of help gases. According to differential scanning calorimetry (DSC) outcomes, we revealed that the simple 14ECH hydrate dissociates at 270~278 K under ambient pressure. In addition to the thermodynamic stability, we also note that the 14ECH + CH4 hydrate presented a sufficiently high temperature of formation, requiring little additional cooling. Given these promising features, we expect that the 14ECH hydrate system can be adopted to realize hydrate-based technologies. We also believe that the LGMs introduced here have considerable potential to serve as alternates to conventional promoters and that they can be widely utilized in both engineering and scientific research fields.

Modeling the Solvent Extraction of Cadmium(II) from Aqueous Chloride Solutions by 2-pyridyl Ketoximes: A Coordination Chemistry Approach.

The goal of this work is to model the nature of the chemical species [CdCl2(extractant)2] that are formed during the solvent (or liquid-liquid) extraction of the toxic cadmium(II) from chloride-containing aqueous media using hydrophobic 2-pyridyl ketoximes as extractants. Our coordination chemistry approach involves the study of the reactions between cadmium(II) chloride dihydrate and phenyl 2-pyridyl ketoxime (phpaoH) in water-containing acetone. The reactions have provided access to complexes [CdCl2(phpaoH)2]∙H2O (1∙H2O) and {[CdCl2(phpaoH)]}n (2); the solid-state structures of which have been determined by single-crystal X-ray crystallography. In both complexes, phpaoH behaves as an N,N’-bidentate chelating ligand. The complexes have been characterized by solid-state IR and Raman spectra, and by solution 1H NMR spectra. The preparation and characterization of 1∙H2O provide strong evidence for the existence of the species [CdCl2(extractant)2] that have been proposed to be formed during the liquid-liquid extraction process of Cd(II), allowing the efficient transfer of the toxic metal ion from the aqueous phase into the organic phase.

Highly Conducting Polythiophene Thin Films with Less Ordered Microstructure Displaying Excellent Thermoelectric Performance.

Polythiophene (PTh) with highly regular molecular structure is synthesized as nearly amorphous thin films by electrochemical methods in a BFEE/DTBP mixed medium (BFEE = boron fluoride ethyl ether; DTBP = 2,6-di-tert-butypyridine). The doping level and film morphology of PTh are modulated through adjusting the current density applied during the polymerization process. A combined analysis with solid-state NMR, FT-IR, and Raman spectra reveals the molecular structural regularity of the resulted PTh films, which leads to the highest electrical conductivity up to 700 S cm-1 for films obtained under an optimized current density of 1 mA cm-2 . By applying the self-heating 3ω-method, thermal conductivities are measured along the in-plane direction. A highly reduced Lorenz number of 6.49 × 10-9 W Ω K-2 and low lattice thermal conductivity of 0.21 W m-1 K-1 were extracted based on the analyses of the electrical and thermal conductivities according to the Wiedemann-Franz Law; the former is about one-third of the Sommerfeld value. Finally, the maximized ZT value can reach up to 0.10 under room temperature, which shows that the highly conducting polymers with less ordered structure is the practical direction for developing organic thermoelectric materials.

Structure of arsenic selenide glasses by Raman and 77Se NMR with a multivariate curve resolution approach

Solid-state Nuclear Magnetic Resonance and Raman data are usually reconstructed using devoted software. Most of the time, the experimental results must be compared to structural models obtained, for example, by Molecular Dynamics or Reverse Monte Carlo. This procedure is sophisticated, time consuming and requires specialized skills. In this paper, it is shown that chemometric unsupervised methods provide quickly interesting information from poorly resolved experimental data. In particular, it is shown that correlation maps and multivariate curve resolution enable to distinguish structural contributions and provide spectral reconstructions when applied to sets of 77Se solid-state NMR and Raman spectra of glasses with varying compositions in the AsxSe1−x glassy system, corroborating previous works. Interestingly, such an approach may provide a new way to assign unknown Raman vibration modes.

Oxidative Coupling or Reductive Coupling? Effect of Surroundings on the Reaction Route of the Plasmonic Photocatalysis of Nitroaniline

Recent studies demonstrated that aromatic amines and aromatic nitro compounds could be converted to the corresponding azo species during surface-enhanced Raman experiments. It is very interesting to study the reaction mechanism for molecules that contain both an amino group and a nitro group, nitroaniline isomers. DFT calculations are applied to study the surface-enhanced Raman scattering and plasmonic photocatalysis of nitroaniline isomers on silver surfaces. The normal Raman and surface Raman spectra of nitroaniline isomers are first simulated and compared with experimental results. The calculated Raman spectra of o-nitroaniline (ONA), m-nitroaniline (MNA), and p-nitroaniline (PNA) correspond to their solid-state Raman spectra. However, the simulated surface Raman spectra of nitroaniline–silver complexes are significantly different from the experimental SERS spectra. According to the theoretical simulation, the appearance of new peaks in the SERS experiments of nitroaniline is attributed to the formatio...

Structural Ordering and Charge Variation Induced by Cation Substitution in (Sr,Ca)AlSiN3:Eu Phosphor.

Nitride phosphors are suitable for white light-emitting diode applications. In this study, the structure of phosphor has been modified through cation substitution to induce charge variation and a rearrangement of neighboring nitride clusters, and consequently enhance its luminescent behavior. Substitution of Ca(2+) by Sr(2+) cations expanded the lattice volume and the bc plane, but shortened the distance between the layers along the a axis. Lattice distortion of the framework introduced high-coordination sites in the Sr/Eu centers and adequate space, thereby facilitating charge variation of activators under reduced atmosphere, as detected through X-ray absorption near-edge structure spectroscopy. As such, the photoluminescent intensity of the phosphors increased by more than 10% and a blue shift occurred. The microstructures of the samples were also analyzed using high-resolution transmission electron microscopy. Cation substitution induced a special change in the anion environment, as indicated in the solid-state Raman spectra. Moreover, typical ordering variations in the SiN4 and AlN4 clusters are generated in the lattice. Meanwhile, neighbor sequence of (Si/Al)N4 around the divalent centers were observed through solid-state nuclear magnetic resonance spectroscopy. The modified ordering distribution resulted in a rigid structure and improved the thermal quenching behavior. Thermal stability has been enhanced by 10% at 473 K when x = 0.9 in SrxCa0.993-xAlSiN3:Eu(2+)0.007 compared with that at x = 0. This study promotes the research of neighbor sequence for selective tetrahedral sites such as Li, Mg, Al, and Si coordinated by N atoms in contact with cation sites.

Synthesis, crystal structure, spectral characterization, and theoretical study of glycolato peroxido complexes of vanadium(V)

We present the crystal structures and spectral characterization of two glycolato peroxido complexes of vanadium(V) with divalent cations. Assignment of their experimental infrared and Raman solid-state spectra was corroborated by gas-phase and periodic density functional calculations. First, the conventional BP86, PBE, and B3LYP exchange–correlation functionals were applied; their long-range-corrected variants LC-BP86 and CAM-B3LYP were subsequently utilized to evaluate their applicability in reproducing the solid-state structures and spectroscopic properties of the [V2O2(O2)2(C2H2O3)2]2− anion. Band assignments are presented in terms of potential energy distribution contributions. The structure of [Zn(H2O)6][V2O2(O2)2(C2H2O3)2]·2H2O obtained in solid state using the PBE functional is in very good agreement with the X-ray single-crystal structure. Computed vibrational frequencies and infrared intensities provided a satisfactory fit for the observed spectrum. 51V NMR chemical shifts were calculated using optimized gas-phase geometries with the GIAO approach employing the B3PW91 functional, and they were correlated with experimentally observed shift measured for the aqueous solutions.

Xenon(IV)-carbon bond of [C6F5XeF2]+; structural characterization and bonding of [C6F5XeF2][BF4], [C6F5XeF2][BF4]·2HF, and [C6F5XeF2][BF4]·nNCCH3 (n = 1, 2); and the fluorinating properties of [C6F5XeF2][BF4

The [C6F5XeF2](+) cation is the only example of a Xe(IV)-C bond, which had only been previously characterized as its [BF4](-) salt in solution by multi-NMR spectroscopy. The [BF4](-) salt and its new CH3CN and HF solvates, [C6F5XeF2][BF4]·1.5CH3CN and [C6F5XeF2][BF4]·2HF, have now been synthesized and fully characterized in the solid state by low-temperature, single-crystal X-ray diffraction and Raman spectroscopy. Crystalline [C6F5XeF2][BF4] and [C6F5XeF2][BF4]·1.5CH3CN were obtained from CH3CN/CH2Cl2 solvent mixtures, and [C6F5XeF2][BF4]·2HF was obtained from anhydrous HF (aHF), where [C6F5XeF2][BF4]·1.5CH3CN is comprised of an equimolar mixture of [C6F5XeF2][BF4]·CH3CN and [C6F5XeF2][BF4]·2CH3CN. The crystal structures show that the [C6F5XeF2](+) cation has two short contacts with the F atoms of [BF4](-) or with the F or N atoms of the solvent molecules, HF and CH3CN. The low-temperature solid-state Raman spectra of [C6F5XeF2][BF4] and C6F5IF2 were assigned with the aid of quantum-chemical calculations. The bonding in [C6F5XeF2](+), C6F5IF2, [C6F5XeF2][BF4], [C6F5XeF2][BF4]·CH3CN, [C6F5XeF2][BF4]·2CH3CN, and [C6F5XeF2][BF4]·2HF was assessed with the aid of natural bond orbital analyses and molecular orbital calculations. The (129)Xe, (19)F, and (11)B NMR spectra of [C6F5XeF2][BF4] in aHF are reported and compared with the (19)F NMR spectrum of C6F5IF2, and all previously unreported J((129)Xe-(19)F) and J((19)F-(19)F) couplings were determined. The long-term solution stabilities of [C6F5XeF2][BF4] were investigated by (19)F NMR spectroscopy and the oxidative fluorinating properties of [C6F5XeF2][BF4] were demonstrated by studies of its reactivity with K[C6F5BF3], Pn(C6F5)3 (Pn = P, As, or Bi), and C6F5X (X = Br or I).

Infrared and Raman spectra of [Re(CN)5NO]3- complex isolated in KCl matrix

We report here the infrared and Raman spectra of [Re(CN)5NO]3- complex as guest diluted in the KCl crystal lattice. According to the chemical analysis, the anion concentration in the KCl host matrix is in excess of 2% (in mole). The solid state Raman spectrum of this complex is reported for the first time. The information obtained from the relative intensities of infrared and Raman bands affords a reexamination of vibration mode assignments. The observed bands splitting may be explained by the interactions of the guest complex with the host lattice, including the ways in which the K+ vacancies are distributed around [Re(CN)5NO]3- to achieve lattice charge neutrality.

Identification of mixed bromidochloridotellurate anions in disordered crystal structures of (bdmim)2[TeX2Y4] (X, Y = Br, Cl; bdmim = 1-butyl-2,3-dimethylimidazolium) by combined application of Raman spectroscopy and solid-state DFT calculations

The discrete mixed [TeBrxCl6−x]2− anions in their disordered crystal structures have been identified by using the phases prepared by the reaction of 1-butyl-2,3-dimethylimidazolium halogenides (bdmim)X with tellurium tetrahalogenides TeX4 (X=Cl, Br) as examples. Homoleptic (bdmim)2[TeX6] [X=Cl (1), Br (2)] and mixed (bdmim)2[TeBr2Cl4] (3), and (bdmim)2[TeBr4Cl2] (4) are formed depending on the choice of the reagents, and their crystal structures have been determined by single-crystal X-ray diffraction. The coordination environments of tellurium in all hexahalogenidotellurates are almost octahedral. Because of the crystallographic disorder, the mixed [TeBr2Cl4]2− and [TeBr4Cl2]2− anions in 3 and 4 cannot be identified in their crystal structures. Pawley refinement of the X-ray powder diffraction patterns of 1–4 indicates the presence of single phases in all four products. The solid state Raman spectra of 1–4 were assigned with help of DFT calculations that were performed both for the discrete anions in vacuum and for the complete crystal structures employing periodic boundary conditions. The fundamental vibrations of the homoleptic [TeX6]2− (X=Cl, Br) anions could be well reproduced by the solid-state DFT computations and enabled a complete assignment of the Raman spectra. While the presence of cis-isomers in both [TeBr2Cl4]2− and [TeBr4Cl2]2− could be inferred by the computed fundamental vibrations, that of trans-isomers among the reaction products is, however, also possible. The pathway of the formation of [TeX4Y2]2− isomers from TeX4 and Y− (X, Y=Cl, Br) was also explored by DFT calculations both in vacuum and in solution and indicated that both reactions afforded 80mol% of cis-isomers and 20mol% of trans-isomers.

Effect of Immobilization on Gold on the Temperature Dependence of Photochromic Switching of Dithienylethenes

We report the properties and switching characteristics of a series of dithienylethene photochromic switches immobilized on gold. Self-assembled monolayers (SAMs) of three structurally related dithienylethenes were formed on roughened gold bead substrates and studied by surface-enhanced Raman spectroscopy (SERS). These data were compared to SERS spectra obtained by aggregation of colloidal gold, solid state Raman spectra, and Raman spectra calculated using density functional theory (DFT). Two of the dithienylethenes studied have an “asymmetric” design, which was demonstrated earlier to lower the thermal barrier for photochemical ring opening in solution. Herein, we show that, when immobilized on a gold surface, the asymmetric dithienylethenes in fact display a higher thermal barrier than that of their symmetric counterparts. In addition, we show that photochemical ring closing of asymmetric dithienylethenes is inhibited when immobilized on gold.

Tuning affinity and reversibility for O2binding in dinuclear Co(ii) complexes

The O2 binding affinity of a series of dicobalt(II) complexes can be tuned between p(O2)50% = 2.3 × 10(-3) and 700 × 10(-3) atm at 40 °C by varying the number of H and Cl atoms in the bridging acetato ligands of [Co2(bpbp)(CH(3-n)ClnCO2)(CH3CN)2](2+), where bpbp(-) = 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolate and n = {0, 1, 2, 3}. O2 binds most strongly to the deoxy complex containing the acetato bridge and the O2 affinity decreases linearly as the number of Cl atoms is increased from 0 to 3 in [Co2(bpbp)(O2)(CH3CO2)](2+), [Co2(bpbp)(O2)(CH2ClCO2)](2+), [Co2(bpbp)(O2)(CHCl2CO2)](2+) and [Co2(bpbp)(O2)(CCl3CO2)](2+). The O2 affinities can be qualitatively correlated with both the pKa value of the parent acetic or chloroacetic acid and the redox potential of the O2(2-)/O2˙(-) couple measured for the peroxide-bridged complexes. The redox potential varies between 510 mV (vs. Fc(0/+)) for the acetato-bridged complex to 696 mV for the trichloroacetato-bridged system. Despite the clear difference in reactivity in solution, there are no clear trends which can be correlated to O2 affinity in the O-O bond lengths in the X-ray crystal structures at 180 K (1.415(4)-1.424(2) Å) or in the frequencies of the peroxido O-O stretch in the solid-state resonance Raman spectra at 298 K (830-836 cm(-1)). Using density functional theory calculations, we conclude that the Co(II) atoms of the deoxy complexes coordinate solvent molecules as auxiliary ligands and that a conformation change of the ligand is involved in the reversible O2 binding process. The alternative of five coordination in the deoxy Co(II) complexes is therefore seen as less likely. The crystal structure and p(O2)50% are also reported for the 1-naphthoato-bridged oxy complex [Co2(bpbp)(O2)(C10H7O2)](2+), and the O2 binding affinity in that case is also qualitatively consistent with the expectation from the pKa of the parent 1-naphthoic acid.

The electronic structure of pyracene: a spectroscopic and computational study

We report a synthetic, spectroscopic and computational study of the polycyclic aromatic molecule pyracene, which contains aliphatic five-membered rings annealed to a naphthalene chromophore. An improved route to synthesize the compound is described. Gas-phase IR and solid-state Raman spectra agree with a ground-state D2h structure. The electronically excited S1 A(1)B3u state has been studied by resonance-enhanced multiphoton ionisation. An adiabatic excitation energy T0 = 30,798 cm(-1) (3.818 eV) was determined. SCS-ADC(2) calculations found a D2h minimum energy structure of the S1 state and yielded an excitation energy of +3.98 eV, including correction for zero point vibrational energy. The spectrum shows a rich low-frequency vibrational structure that can be assigned to the overtones of out-of-plane deformation modes of the five-membered rings by comparison with computations. The appearance of these modes as well as the frequency reduction in the excited state indicate that the potential in the S1 state is very flat. At higher excess energies most bands can be assigned to fundamentals, overtones and combination bands of either totally symmetric ag modes or of b2g modes that appear due to vibronic coupling. Lifetimes between 43 ns and 76 ns were measured for a number of vibronic bands. For the S2 state an equilibrium geometry with a non-planar carbon framework was computed. In addition a signal from the pyracene dimer was present. The spectrum shows several broad and structureless transitions. The origin band has a maximum at around 329 nm (30,400 cm(-1)). Again lifetimes between 60 ns and 70 ns were found. The dimer ion signal rises within less than 10 ps. Computations show that a crossed geometry with the long axis of one unit aligned with the short axis of the second constitutes the most stable structure. The broadening of the bands is most likely caused by excimer formation.

The ionic nature of methylsulfur trichloride species

Abstract The Raman spectrum of the methyldichloro-sulfonium(IV) chloride, CH 3 SCl 2 + Cl − , is reported. The unambiguous vibrational assignment for the CH 3 SCl 2 + cation is made on the basis of the solid state Raman spectra aided by high-level quantum chemical calculations and a normal mode analysis. Actually, the former reported methylsulfur trichloride, CH 3 SCl 3 , can be now described as CH 3 SCl 2 + Cl − .

Raman and IR spectroscopic studies of fenamates – Conformational differences in polymorphs of flufenamic acid, mefenamic acid and tolfenamic acid

Solid-state Raman and IR spectra of two polymorphic forms of each of three fenamates (flufenamic acid, mefenamic acid and tolfenamic acid) display subtle but highly reproducible differences. Many of these spectral differences can be ascribed to different conformations of these molecules, involving two of four possible orientations of one substituted benzene ring with respect to the other. Interpretation of the vibrational spectra in terms of conformational differences has been facilitated by DFT calculations at the B3LYP/cc-pVDZ level for each conformer. The calculated spectra are compared with the experimental spectra in order to identify the conformers present in two polymorphic forms in each case, and detailed band assignments are obtained from the DFT calculations.

Solid-state Raman spectra of non-centrosymmetric crystals – Theoretical vs. experimental study towards an application in THz-regime

Abstract Experimental and theoretical solid-state Raman spectroscopic study of five model derivatives of amino acids ( AAs ), crystallizing in the non-centrosymmetric space groups, with the number molecules per unit cell Z = 1–8 were studied. The self-assembly association effects within the frame of crystals with P 2 1 , Pca 2 1 , and P 2 1 2 1 2 1 , space groups and their effect on the Raman frequencies, within 10–0.3 THz were discussed. The assignment of the spectroscopic properties and the hydrogen bond interactions, depending of the crystal packing of the model tyramine hemihydrate was performed. The paper aims to make a bridge between the methods for analysis of the optical phenomena within the THz-region, such as far -IR, Raman and THz-spectroscopy. The observed individual characteristic excitations of materials within THz-region, provided unique opportunity for chemical identification in solid-state. The specific advantages of each of the methods provided unique combination allowing both qualitative and quantitative analysis, especially of macro-components, and achievement of the analytical information at an extremely high degree of certainty towards the individual characteristics of each of the studied chemicals as properties of evidence, and would contributed in varying degrees to the evidence in the field of forensic chemical analysis.

Photocrystallographic identification of metastable nitrito linkage isomers in a series of nickel(ii) complexes

Single crystal photocrystallographic experiments and solid state Raman spectroscopy have been used to determine the low temperature, metastable structures of the nickel(ii) nitrito complexes [Ni(aep)(2)(η(1)-ONO)(2)] 1#O (aep = 1-(2-aminoethyl)piperidine), [Ni(aem)(2)(η(1)-ONO)(2)] 2#O (aem = 1-(2-aminoethyl)morpholine), and [Ni(aepy)(2)(η(1)-ONO)(2)] 3#O (aepy = 1-(2-aminoethyl)pyrrolidine and where the #O denotes the oxygen-bound nitrito metastable molecule). These linkage isomers of the equivalent nitro complexes [Ni(aep)(2)(η(1)-NO(2))(2)] 1, [Ni(aem)(2)(η(1)-NO(2))(2)] 2 and [Ni(aepy)(2)(η(1)-NO(2))(2)] 3 are formed by LED irradiation at temperatures below 120 K. The behavior of the three complexes upon irradiation is generally similar, but some subtle differences have been observed. From the crystallographic studies all three complexes 1-3 exhibit the endo-nitrito linkage isomer upon irradiation, however, for 3# (a crystal structure that contains components of both 3 and 3#O) an exo-nitrito isomer is also observed. Under conditions of 90-100 K, with blue light, the conversion percentages to the nitrito isomers, 1#O, 2#O and 3#O were 16%, 22% and 30%, respectively. At temperatures below 110 K all three nitrito isomers were stable for over four hours but while 2#O and 3#O could be detected at temperatures down to 30 K, at temperatures below 60 K the metastable structure 1#O appeared to be quenched and only the nitro isomer 1 was identified in the crystal. The solid state Raman spectra for 1#, 2# and 3# confirmed the photocrystallographic results with the nitrito isomers being identified from the O-N-O deformation vibrations.

X-ray Crystal Structures of [XeF][MF6] (M = As, Sb, Bi), [XeF][M2F11] (M = Sb, Bi) and Estimated Thermochemical Data and Predicted Stabilities for Noble-Gas Fluorocation Salts using Volume-Based Thermodynamics

The crystal structures of the xenon(II) salts, [XeF][SbF(6)], [XeF][BiF(6)], and [XeF][Bi(2)F(11)], have been determined for the first time, and those of XeF(2), [XeF][AsF(6)], [XeF][Sb(2)F(11)], and [XeF(3)][Sb(2)F(11)] have been redetermined with greater precision at -173 °C. The Bi(2)F(11)(-) anion, which has a structure analogous to those of the As(2)F(11)(-) and Sb(2)F(11)(-) anions, has been structurally characterized by single crystal X-ray diffraction for the first time as its XeF(+) salt. The fluorine bridge between the bismuth atoms is asymmetric with Bi---F(b) bond lengths of 2.092(6) and 2.195(6) A and a Bi---F(b)'---Bi bridge bond angle of 145.3(3)°. The XeF(+) cations interact with their anions by means of Xe---F(b)---M bridges. Consequently, the solid-state Raman spectra of [XeF][MF(6)] (M = As, Sb, Bi) were modeled as the gas-phase ion pairs and assigned with the aid of quantum-chemical calculations. Relationships among the terminal Xe-F(t) and bridge Xe---F(b) bond lengths and stretching frequencies and the gas-phase fluoride ion affinities of the parent Lewis acid that the anion is derived from are considered. The analogous krypton ion pairs, [KrF][MF(6)] (M = As, Sb, Bi) were also calculated and compared with their previously published X-ray crystal structures. The calculated cation-anion charge separations indicate that the [XeF][MF(6)] salts are more ionic than their krypton analogues and that XeF(2) is a stronger fluoride ion donor than KrF(2). The lattice energies, standard enthalpies, and free energies of formation for salts containing the NgF(+), Ng(2)F(3)(+), XeF(3)(+), XeF(5)(+), Xe(2)F(11)(+), and XeOF(3)(+) (Ng = Ar, Kr, Xe) cations were estimated using volume-based thermodynamics (VBT) based on crystallographic and estimated ion volumes. These estimated parameters were then used to predict the stabilities of noble-gas salts. VBT is used to examine and predict the stabilities of, inter alia, the salts [XeF(m)][Sb(n)F(5n+1)] and [XeF(m)][As(n)F(5n+1)] (m = 1, 3; n = 1, 2). VBT also confirms that XeF(+) salts are stable toward redox decomposition to Ng, F(2), and MF(5) (M = As, Sb), whereas the isolable krypton compounds and the unknown ArF(+) salts are predicted to be unstable by VBT with the ArF(+) salts being the least stable.

A Rare Example of a Krypton Difluoride Coordination Compound: [BrOF2][AsF6]·2KrF2

The synthesis of [BrOF(2)][AsF(6)] x 2 KrF(2), its structural characterization, and bonding are described in this study. Although several KrF(2) adducts with transition metal centers have been previously reported, none have been crystallographically characterized. The solid-state Raman spectrum of [BrOF(2)][AsF(6)] x 2 KrF(2) has been assigned with the aid of quantum-chemical calculations. The low-temperature (-173 degrees C) X-ray crystal structure of [BrOF(2)][AsF(6)] x 2 KrF(2) consists of isolated molecular units and represents an example of KrF(2) coordinated to a main-group atom. The coordination geometry around the BrOF(2)(+) cation renders the free valence electron lone pair more compact than in free BrOF(2)(+). The KrF(2) ligands are coordinated trans to the fluorine atoms of BrOF(2)(+) with the AsF(6)(-) anion coordinated trans to oxygen. The quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF) analyses have been carried out in order to define the nature of the bonding in the complex. A significant amount of charge (0.25 e) is transferred to BrOF(2)(+) from the two KrF(2) ligands (0.10 e each) and from the AsF(6)(-) anion (0.05 e). Significant polarization also occurs within the KrF(2) ligands, which enhances the anionic characters of the fluorine bridges. The interaction energy is mostly governed by the electrostatic interaction of the positively charged bromine atom with the surrounding fluorine atoms.