Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters

In this report we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M−M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from highly symmetric to fully asymmetric by 57Fe Mössbauer and X-ray diffraction to explore the relationship between MAD-derived data and the data available from these widely used characterization techniques. The compounds examined include the all-ferrous clusters [nBu4N][(tbsL)Fe3(μ3–Cl)] (1) ([tbsL]6– = [1,3,5-C6H9(NC6H4-o-NSitBuMe2)3]6–]), (tbsL)Fe3(py) (2), [K(C222)]2[(tbsL)Fe3(μ3–NPh)] (4) (C222 = 2,2,2-cryptand), and the mixed-valent (tbsL)Fe3(μ3–NPh) (3). Redox delocalization in mixed-valent 3 was explored with cyclic voltammetry (CV), zero-field 57Fe Mössbauer, near-infrared (NIR) spectroscopy, and X-ray crystallography techniques. We find that the MAD results show an excellent correspondence to 57Fe Mössbauer data; yet also can distinguish between subtle changes in local coordination geometries where Mössbauer cannot. Differences within aggregate oxidation levels are evident by systematic shifts of scattering factor envelopes to increasingly higher energies. However, distinguishing local oxidation levels in iso- or mixed-valent materials can be dramatically obscured by the degree of covalent intracore bonding. MAD-derived atomic scattering factor data emphasize in-edge features that are often difficult to analyze by X-ray absorption near edge spectroscopy (XANES). Thus, relative oxidation levels within the cluster were most reliably ascertained from comparing the entire envelope of the atomic scattering factor data.

Calculation of The Imaginary Part of Atomic Form Factor For X-ray In Nickel

In the present study, we calculated the imaginary part of the x-ray scattering factor of nickel based on the principles of quantum mechanics to find a wave function that describes the electronic state of atoms by approximate methods, observed the study suggested that in both low energy values , and at high energy values , the imaginary part is approximately zero, this means that the electrons are intensely connected to the atom, where in the spectrum the photon energies are approximately equal to the electron bonding energy we note the study pointed out that the imaginary part of the atomic scattering factor become prominent and the electron becomes highly absorbent, the relative accuracy varies within range (0.03-0.22)%, and there was also a good agreement between the behavior we obtained for the imaginary part of the atomic scattering factor and the behavior that was calculated using other models. http://dx.doi.org/10.25130/tjps.23.2018.171

Modelling of cation displacements in SrTiO3by means of multi-energy anomalous X-ray diffuse scattering

X-ray diffuse scattering of SrTiO3has been measured at two photon energies, the first just below the absorption edge and the second far from theKabsorption edge of strontium, in order to vary the atomic scattering factor of the strontium cations. It is shown that two different models of cation displacement comply with the single-energy diffuse scattering patterns, because single-energy diffuse scattering provides only ambiguous information on the directions of displacement of the Sr2+and Ti4+cations. However, the application of multi-energy anomalous diffuse scattering determines unambiguously that the Sr2+cations are moved from their ideal positions in the [100] direction and the Ti4+cations are shifted in {111} directions.

X-ray standing wave as a result of only the imaginary part of the atomic scattering factor

The X-ray standing wave has been studied when the real part of the scattering factor is zero. In the symmetric Laue case, the phase of the standing wave advances by π when the deviation parameter W changes from −1 to 1, which is the same variation as in the usual symmetric Bragg case when only the real part of the scattering factor exists. However, the phase in the former case is different from that in the latter by \pi/2. By using the standing waves, the origins of the anomalous transmission and anomalous absorption effects reported by Fukamachi & Kawamura [Acta Cryst. (1993), A49, 384–388] have been analysed. The standing wave in the Laue case can give rise to a more accurate method of site determination of a specified impurity atom as well as a wider range of applications than a conventional standing-wave approach.