High-accuracy X-ray absorption spectra from mMsolutions of nickel (II) complexes with multiple solutions using transmission XAS

Abstract

A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X-ray absorption fine structure (XAFS) along the lines of the high-accuracy X-ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N-n-propyl-salicylaldiminato) nickel(II) and bis(N-i-propyl-salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mM and 1.5 mM dilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X-ray absorption near-edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordination geometries. For the first time, (transmission) XAS of the isomers have been determined from low-concentration solutions on an absolute scale with a 1-5% accuracy, and with relative precision of 0.1% to 0.2% in the active XANES and XAFS regions after inclusion of systematic corrections.

Solving self-absorption in fluorescence

“…The complexes considered in this work have local metal environments with approximate tetrahedral and square-planar coordination geometries (Fox et al, 1964;Britton & Pignolet, 1989). A previous publication has confirmed these structures using transmission-mode XAFS (Chantler et al, 2015). This system therefore provides an excellent test of fluorescent multi-pixel data and processing (Best et al, 2016;Islam et al, 2017).…”

“…This is well known and common in XAS fluorescence-mode data collection. Published transmission spectra for the active Ni in the Ni i-pr complex, on an absolute scale, displaying the expected XAS spectral trend for absorption coefficients (Chantler et al, 2015). These measurements were taken simultaneously on the same samples as Fig.…”

“…The beam was incident upon the sample at 45 . Sample (cell) thicknesses were 1.9577 (17) mm (i-pr) and 1.981 (2) mm (n-pr) [ Table 3, column 4 in the report by Chantler et al (2015)]. The frozen solutions were contained in cells fashioned from a 25 Â 2 mm Teflon pellet, designed to allow a 1.5 Â 2 mm X-ray beam to pass through.…”

High accuracy determination of photoelectric cross sections, X-ray absorption fine structure and nanostructure analysis of zinc selenide using the X-ray extended range technique

“…In situations where attenuation coefficients are available and accurate, the absorption and scattering interactions of X-rays with matter can be used to create a more precise probe. X-ray absorption fine structure (XAFS) can measure dilute or disordered systems (Chantler et al, 2015) which cannot be probed by other methods such as X-ray diffraction (XRD) or electron microscopy. This has led to new and important discoveries in a variety of disciplines from chemistry to biomedicine to agriculture (Waychunas et al, 1993;Neidig et al, 2011;Chevallier et al, 2014).…”

Rotation of X-ray polarization in the glitches of a silicon crystal monochromator

“…The special design of I20-scanning has allowed the performance of EXAFS measurements on samples as dilute as 10 micromolal (Bowron & Diaz-Moreno, 2014). Dilute samples cannot easily be examined by measuring their X-ray absorp-tion as a function of incident photon energy in transmission because the absorption of the matrix dominates the EXAFS near the absorption edge of the absorber, although such studies have been successful for millimolar samples when great care was taken to remove systematic errors from the data collection (Chantler et al, 2015;Islam et al, 2015). Instead, the fluorescence yield of the absorber in the sample is measured using a large-area fluorescence detector.…”