Determination Of Bond Lengths Research Articles

Direct determination of Fe-C bond lengths in iron(II) and iron(III) cyanide solutions using EXAFS spectroelectrochemistry

Direct determination of Fe-C bond lengths in iron(II) and iron(III) cyanide solutions using EXAFS spectroelectrochemistry

Model calculations of the effective phase factors for extended absorption fine-structure measurements on oxidized aluminum and silicon

Model calculations are made of the effective phase factors for surface extended x-ray-absorption fine-structure (SEXAFS) and extended appearance-potential fine-structure (EAPFS) measurements on oxidized aluminum and silicon surfaces. The potentials used in this work have a muffin-tin form and were constructed from overlapping atomic and/or ionic charge densities. Plots are made of these effective phase factors as a function of the momentum, $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ of the extended x-ray absorption fine structure (EXAFS)-like electron. These plots exhibit a "breakover" between a high- and low-momentum region at $k\ensuremath{\simeq}3\ensuremath{-}4$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$. For these oxide systems the analyzed SEXAFS data extend into this breakover region while the analyzed EAPFS data lie entirely in the well-behaved, high-momentum region. Extrapolating from the high-momentum region into the low-momentum region could lead to underestimating the O---Al and O---Si bond lengths. This is consistent with the differences noted in analyzing the SEXAFS data using extrapolated theoretical phase shifts and experimental phase shifts determined from bulk standards. The model calculations do not agree well with the experimental results over the fairly low-momentum range of the SEXAFS data but do seem to give reasonable bond-length determinations using the higher-momentum range of the EAPFS data.

Simple method of bond-length determinations and test of phase transferability with the use of extended x-ray-absorption fine-structure linear phase functions

Simple method of bond-length determinations and test of phase transferability with the use of extended x-ray-absorption fine-structure linear phase functions

Comment on EXAFS and EXELFS above MII,III- edges in Cu and Ni

Quite recently, the analysis of electron energy loss spectra above the M II,III-edges of Cu and Ni has revealed oscillations in strict analogy to the well known EXAFS and EXELFS structures above the K- and L II,III- edges . We comment here on the central atom phase shift to be used in the interpretation of the M II,III- spectra . The main result is that the use of the L II,III- phase shift is fully justified in the case of Cu and that the error in the bond length determination introduced by the use of the L II,III- phase shift instead of the M II,III- one is at most 0.05 Å in the case of Ni.

Pseudopotential SCF and Cl investigation of the electronic structure of PdH, PdC and PdCO

The electronic structure of PdH, PdC and PdCO molecules has been investigated by means of pseudopotential multireference double-excitations configuration interaction method (PP MRD Cl). Three different optimized AO basis sets have been adopted for determination of bond lengths, dissociation energies, dipole moments and population analysis. The basis set optimized for the Pd 3D)rd 95s 1) excited state is more suitable for describing the electronic redistribution occurring on Pd during formation of the band than that derived from the 1S(4d 10) ground state. Differences in the bonds of PdH, PdC and PdCO can be explained with these calculations. Correlation effects are crucial for understanding the chemical bonding.

Determination of bond lengths from extended x-ray absorption fine structure using the linear phase functions

The extended x-ray absorption fine-structure (EXAFS) spectra of many elements and compounds have been analyzed to determine their phase functions as a function of the zero of kinetic energy, ${E}_{0}$, of the excited electron and the weighting power of the wave vector used in the Fourier transforms. It is found that a linear phase function exists for any material at some particular value of ${E}_{0}={E}_{c}$. The procedure for determining this ${E}_{c}$ value is described. A linear-phase-function method of determining bond lengths is proposed and compared to other existing methods of EXAFS bond-length determinations. The many advantages of using these linear phase functions in EXAFS analysis are discussed. With the use of the linear phase functions with a linear extrapolation of their parameters, it is demonstrated that it is possible to verify the existence of a more general form of phase transferability which relates the phase functions of different atom pairs. Such relations allow the number of phase functions needed to characterize a system of $N$ atoms to be reduced from ${N}^{2}$ to $2N\ensuremath{-}1$. This type of comparison is not feasible with the usual nonlinear phase functions.

Molecular geometries - Accuracy test of the PCILO method

Applicability of the PCILO method for investigation of stationary points of the energy hypersurface has been tested with a set of 11 small organic molecules. From comparison of the molecular geometries, completely optimized with the use of the Payne algorithm, with experimental data and with the results obtained by the MINDO/3 and MNDO methods it follows that the PCILO method is suitable for semiquantitative estimate of molecular geometry (mean error in the bond length determination 5 . 10-3 nm, valence angles 3.4°). The Payne algorithm is little efficient, if the starting geometry is far from the stationary point and if the assumption of quadratic form of the hypersurface is not fulfilled.

14N NMR determination of NH bond lengths in solids

14N NMR determination of NH bond lengths in solids

Determination of Bond Lengths from EXAFS with High Resolution

The investigation of EXAFS has grown to an important tool for the analysis of the local geometrical structure in complex systems. The development of the method has been stimulated by the availability of high intensity X-ray sources. Improved techniques of data evaluation are reviewed which permit accuracies for bond lengths better than 0.001 nm.

Determination of Bond Lengths from LIII-Edge EXAFS of Heavy Elements

An analysis of EXAFS above the L-edges of Au shows the preference of transitions to d-symmetric compared to s-symmetric final states. A splitting of peaks in the magnitude of the Fourier transform of the LIII,-spectum is attributed to the oscillating form of the amplitude function of the fine structure.

Tentative De Corrélation Entre Les Fréquences De Vibration Des Modes ν(So) et ν(SS) et Les Distances Interatomiques d(SO) et d(SS) Des Groupements S2O3 Coordonnés Dans Quelques Thio‐Sulfates Inorganiques

AbstractThe empirical relationship between sulfur‐oxygen stretching frequency and the corresponding bond length proposed by Gillepsie and Robinson(1) has been tested in the case of S2O3 ions coordinated in various inorganic thiosulfates. It is inadvisible to use the ν(SO)‐d(SO) plot for predicting d(SO) values for different thiosulfate‐to‐metal associations as the bond length change upon coordination does not lead to a sufficiently accurate deviation from the experimental error in many of the bond length determinations. Only the precise values of the symmetric and asymmetric S‐O stretching frequencies can be fairly correlated to a given thiosulfate‐to‐metal coordination. Similar conclusions have been obtained from a tentative correlation between thiosulfate sulfur‐sulfur bond lengths and stretching frequencies.

X-ray spectroscopic study of cobalt-zinc ferrites

Abstract K-absorption edges and the associated fine structures of cobalt and iron in cobalt-zinc ferrites of composition, ZnxCo1-xFe2O4 (x = 0, 0.25, 0.50 and 0.75) have been recorded employing a 40cm curved crystal spectrograph of transmission type. It is found that the cobalt and iron ions in these samples exist in valence states two and three respectively. Bond lengths have been determined using the X-ray fine structure methods. It is noted that estimated bond lengths are close to those obtained from crystallographic data. It is pointed out that the X-ray fine structure methods can be used to complement diffraction methods for the determination of bond lengths in samples containing atoms of nearly equal scattering power.

Metallchelate mit Acetophenon-Benzoylhydrazon und Acetophenon-Salicoylhydrazon

The stoichiometry and structure of acetophenone benzoylhydrazone and acetophenone salicoylhydrazone chelates with some divalent metal ions are studied by conductometric titration and visible and infra-red absorption spectrophotometry. The results are supported by analysis of the solid complexes. The infra-red study revealed that coordination occurs through C=O and C=N groups. The shift in the C=O and C=N bands is utilised for the determination of bond lengths.

Determination of bond lengths in some compounds of rhenium from the x-ray LIII absorption discontinuity

The shapes and the fine structure of the x-ray LIII absorption discontinuity of rhenium have been studied in seven octahedral (K2ReCl6, K2ReBr6, (pyH)2ReCl6, (dipyH)2ReCl6, Re(dipy)Cl4, K3ReO2(CN)4 and ReO3) and three tetrahedral (KReO4, NH4ReO4 and NaReO4) compounds. The bond lengths in these compounds have been determined by applying Levy’s theory to the data on the fine structure associated with the edge beyond the molecular orbital region.

Cathodoluminescence of carbonates, 2. Geological applications

Cathodoluminescence may be used for determination of bond length and composition, if distortion is not an important factor. Spectral emission of Mn 2+ in two different sites in a structure can be used to describe population density of manganese for those sites. The dependence of luminescence on Fe/Mn concentration and in heating of the host mineral was instrumental in allowing the use of emission intensity for the detection, in a general manner, of the location of a hydrothermal ore body in a limestone sequence. A variety of applications employing wavelength and intensity response to crystallographic phase differences and changing Mn/Fe concentrations were utilized to delineate changes in the composition of biogenic carbonate material. Minor regenerative phases such as calcite and vaterite can be detected easily in an aragonitic shell. In a similar manner, minor original aragonite can be found in a sample altered to calcite. Cathodoluminescence arising out of the excitation of Mn 2+ in carbonate structures was found to be useful in distinguishing changes in coordination, symmetry, bond length, composition and in a variety of geological applications.

π-Bindungsordnung-bindungslängenbeziehung für ungesättigte kohlenwasserstoffe

Bond lengths of unsaturated hydrocarbons, determined experimentally with an accuracy of at least 0·015 Å, in combination with π-bond orders, calculated by simple HMO-methods, form a linear relation. The equation, determined by linear least squares methods, is: R rs HMO = 1·585 – 0·295 p rs for 132 points with a standard deviation of 0·017 Å. Application of the ω-technique for non-alternant hydrocarbons results in the same equation with a reduced standard deviation of 0·016 Å. The use of Pariser, Parr and Pople —SCF-π-bond orders leads to the linear least squares equation: R rs PPP = 1·531 – 0·205 p rs with a standard deviation of 0·014 Å for 85 values. Bond orders determined by HMO calculations with variation of β according to Coulson give the equation: R rs β = 1·548 – 0·233 p rs with a standard deviation of 0·016 Å. Each of these relations allows the determination of bond lengths from the corresponding calculated π-bond orders with an accuracy which is comparable with the experimental values.

Raman and infrared spectroscopic studies of the uranyl ion: the symmetric stretching frequency, force constants, and bond lengths

The symmetric stretching frequency of the uranyl ion has been measured for some uranyl compounds with the use of Raman excitation. The symmetric and asymmetric stretching frequencies have been used in the calculation of stretching and interaction force constants from which have been derived an estimate of the uranium–oxygen bond lengths by use of Badger's rule. These bond lengths are in good agreement with the few crystallographic data available. Previous calculations of force constants have ignored interaction constants, and bond-length determinations have relied upon an estimate of the bending frequency of the uranyl ion or upon force constants derived from the asymmetric stretching frequency only. The present measurements confirm that the uranyl ion is linear or very nearly so. The overtone and combination bands of some uranyl nitrate complexes have been re-investigated.

The electronic structure of AlH4-

The electronic structure of AlH4 - has been studied by using a determinantal wave function constructed from a minimal basis set of one-centre atomic orbitals of analytical form. Besides the determination of the molecular energy and bond length, values were also found for the ‘breathing’ force constant, the coherent x-ray scattering factor and the purely diamagnetic contribution to the molar magnetic susceptibility. The results of the present treatment for AlH4 - were compared with the recent calculations of Albasiny and Cooper who used a one-centre Hartree-Fock approach within a spherical and a non-spherical approximation. In the light of the relative labour involved in each treatment, the comparison of physical properties proved to be quite favourable.