Towards Heteroleptic Dicoordinate Cu(II) Complexes

In this work we detail our efforts to systematically generate stable dicoordinate CuII complexes. Initial experiments via metathesis reactions of a bulky potassium carbazolide (RK) with copper(II) salts indeed yielded a stable product, RCuOTf (1). However, subsequent attempts to grasp systematic synthetic access to complexes of the type RCuX (X=monoanionic ligand) proved difficult as many of the complexes rapidly decomposed in solution. By using triflate-related ligands such as ethyl sulfate and bistriflimide, the additional dicoordinate copper complexes RCuOSO3Et (2), [RCu(THF)][Cu(NTf2)2] (3) and RCuNTf2 (4) could be isolated. Spectroscopic indications corroborate more CuI than CuII character in all RCuX derivatives

Chemical environment of unusually Ge- and Pb-rich willemite, Tres Marias mine, Mexico

The Tres Marias carbonate-hosted Zn-Ge deposit in Chihuahua, Mexico contains willemite [Zn$_{2}$SiO$_{4}$] with unusually high concentrations of minor and trace elements (e.g., Pb, Ge, As, P, V); Pb concentrations are as high as 2 wt %, and Ge may reach 4000 ppm (average 900 ppm). Electron microprobe analyses and synchrotron X-ray fluorescence maps show that Zn and Ge, as well as Zn and Pb are negatively correlated, whereas Ge and Pb are positively correlated across zoned willemite crystals. In cathodoluminescence (CL) images, those areas of willemite having high trace element concentrations have no, or low CL intensities, whereas zones low in trace elements (except for P) display bright blue CL colors. X-ray absorption fine structure (XAFS) spectroscopy was used to characterize the chemical nature of Ge and Pb in willemite. Comparisons to reference spectra of natural and artificial substances points to the presence of Ge$^{4+}$ and Pb$^{2+}$ in Tres Marias willemite. No evidence for Pb$^{4+}$ was detected. Oscillatory zonation reflects trace element incorporation into willemite from the oxidation of primary Ge-bearing sphalerite and galena (PbS) by siliceous aqueous fluids

Thallium sorption by soil manganese oxides: Insights from synchrotron X-ray micro-analyses on a naturally thallium-rich soil

Thallium (Tl) is a highly toxic trace metal. It occurs mostly as soluble monovalent Tl(I) and less frequently as poorly soluble trivalent Tl(III). Laboratory studies have shown that vacancy-containing hexagonal birnessites can sorb Tl with a very high affinity via a mechanism that involves the oxidation of Tl(I) to Tl(III) and strong complexation of Tl(III), whereas other manganese (Mn) oxides bind Tl(I) non-oxidatively and with lower sorption affinity. Information on the mode of Tl uptake by natural Mn oxides in soils, on the other hand, is still limited. In this study, we characterized the association of Tl with Mn oxides and Tl (redox) speciation in a naturally Tl-rich soil using micro-focused synchrotron X-ray absorption near edge structure (XANES) spectroscopy and X-ray fluorescence (XRF) chemical imaging. The results show that most soil Tl was Tl(I) associated with micaceous clay minerals in the soil matrix. High levels of Tl in soil Mn concretions, on the other hand, were mostly identified as Tl(III), suggesting that oxidative Tl uptake by vacancy-containing hexagonal birnessite was the main process of Tl accumulation in soil Mn concretions. The spectroscopic results in combination with chemical extractions and published sorption isotherms for Tl on synthetic Mn oxides suggest that the formation and transformation of natural Mn oxides in soils and sorption competition of Tl with major and trace metal cations determine the extent and mode of Tl uptake by soil Mn oxides. Methodologically, this study compares classical micro-XRF element mapping combined with point XANES analyses for spatially-resolved element speciation with high-resolution chemical imaging of entire sample areas, which is of great interest for the geochemical community in light of diffraction-limited storage ring upgrades to many synchrotron lightsources

INCORPORATION OF Mo6+^{6+} IN FERRIHYDRITE, GOETHITE, AND HEMATITE

Among all iron oxides, hematite (α-Fe2O3), goethite (α-FeOOH), and ferrihydrite (FeOOH⋅nH2O) are the most common mineral species. While immobilization of Mo6+ by surface adsorption on ferric oxides has been studied extensively, the mechanisms of incorporation in their structure have been researched little. The objective of this study was to investigate the relation between Mo content and its structural incorporation in hematite, goethite, and six-line ferrihydrite by a combination of X-ray absorption spectroscopy (XAS), powder X-ray diffraction (pXRD), and inductively-coupled plasma optical emission spectrometry (ICP-OES). Synthesized in the presence of Mo, the hematite, goethite, and six-line ferrihydrite phases incorporated up to 8.52, 0.03, and 17.49 wt. % Mo, respectively. For hematite and goethite, pXRD analyses did not indicate the presence of separate Mo phases. Refined unit-cell parameters correlated with increasing Mo concentration in hematite and goethite. The unit-cell parameters indicated an increase in structural disorder within both phases and, therefore, supported the structural incorporation of Mo in hematite and goethite. Analysis of pXRD measurements of Mo-bearing six-line ferrihydrites revealed small amounts of coprecipitated akaganéite. X-ray absorption near edge structure (XANES) measurements at the Mo L3-edge indicated a strong distortion of the MoO6 octahedra in all three phases. Fitting of extended X-ray absorption fine structure (EXAFS) spectra of the Mo K-edge supported the presence of such distorted octahedra in a coordination environment similar to the Fe position in the investigated specimen. Incorporation of Mo6+ at the Fe3+-position for both hematite and goethite resulted in the formation of one Fe vacancy in close proximity to the newly incorporated Mo6+ and, therefore, charge balance within the hematite and goethite structures

Evaluationsbericht der Erziehungswissenschaftlichen Lehr- und Forschungswerkstatt (ELF) der Technischen Universität Dresden: Auswertung der Teilnehmendenevaluationen aus dem Zeitraum Wintersemester 2013/14 bis Sommersemester 2018

Die Erziehungswissenschaftliche Lehr- und Forschungswerkstatt (ELF) ist ein Projekt, das an den Arbeitsbereich der Professur Schulpädagogik: Schulforschung des Instituts für Erziehungswissenschaft an der Technischen Universität Dresden angebunden ist und seit dem Wintersemester 2013/2014 Lehrveranstaltungen anbietet. Die ELF bietet engagierten Studierenden Raum, sich wissenschaftsbasiert in Team- und Kooperationsfähigkeit, Selbständigkeit und kritischer Selbstreflexion zu üben. Mit den Angeboten „Kollegiale Fallberatung“, „Blocktrainings zu sozialen und personalen Kompetenzen im Lehrer*innenberuf“ (kurz auch „Kompetenztrainings“ oder „Trainings“ genannt) und „Tutor*innentraining 1 und 2“ werden pädagogische Kompetenzen der Studierenden gestärkt, die bereits in der Organisation und Bewältigung des Studienalltags höchste Relevanz haben (Themen der Trainings sind bspw. Stress-/Zeitmanagement und Kommunikation) und auch im späteren Berufsalltag eine erhebliche Rolle spielen. Im Zuge dieser Lehrerfahrungen werden die Studierenden intensiv, individuell und prozessbezogen in ihren Lern- und Entwicklungsprozessen im Sinne eines Peer-Coaching von studentischen Mitarbeiter*innen der ELF begleitet. Die Reflexion dieser Selbsterfahrung als Lehrperson im Studium ist ein bedeutsamer Faktor für erfolgreiches pädagogisches Handeln im späteren Berufsleben, da die Handlungs- und Reflexionsfähigkeit der Teilnehmenden maßgeblich erweitert werden. Die Vermittlung der Lehrinhalte im Rahmen der ELF folgt darüber hinaus dem Prinzip eines Multiplikatorensystems. Die Teilnehmer*innen aller Lehrveranstaltungen der ELF erhalten mit der letzten Sitzung der Kollegialen Fallberatung, am Ende des zweiten Trainingstages der Kompetenztrainings und zum Abschluss des Tutor*innenprogrammes einen auf das jeweilige Format der Lehrveranstaltung zugeschnittenen Evaluationsbogen. Der Evaluationsbogen erhebt neben personenbezogenen Daten auch subjektive Einstellungen zu dem Format und der Durchführung des jeweiligen Lehrangebotes sowie der Leitung dessen durch die Peer-Leiter*innen, Einstellungen bezüglich der ELF und deren Wahrnehmung sowie die Einschätzung der individuellen Kompetenzentwicklung. Im vorliegenden Bericht werden die Ergebnisse der durchgeführten Evaluationen im Zeitraum vom Wintersemester 2013/14 bis zum Sommersemester 2018 dargestellt und erörtert.:1 Einführung 2 Methodik 3 Kollegiale Fallberatung (KFB) 4 Kompetenztrainings 5 Tutor*innentraining 1 6 Tutor*innentraining 2 7 Auswertung offene Fragen 8 Ausblick 9 Literatu

Np(V) Retention at the Illite du Puy Surface

In this study, Np(V) retention on Illite du Puy (IdP) was investigated since it is essential for understanding the migration behavior of Np in argillaceous environments. The presence of structural Fe(III) and Fe(II) in IdP was confirmed by Fe K-edge X-ray absorption near-edge structure (XANES) and $^{57}$Fe Mössbauer spectroscopy. In batch sorption experiments, a higher Np sorption affinity to IdP was found than to Wyoming smectite or iron-free synthetic montmorillonite. An increase of the relative Np(IV) ratio sorbed onto IdP with decreasing pH was observed by solvent extraction (up to (24 ± 2)% at pH 5, c$_0$(Np) = 10$^{–6}$ mol/L). Furthermore, up to (33 ± 5)% Np(IV) could be detected in IdP diffusion samples at pH 5. Respective Np M$_5$-edge high-energy resolution (HR-) XANES spectra suggested the presence of Np(IV/V) mixtures and weakened axial bond covalency of the NpO$_2$$^+$ species sorbed onto IdP. Np L$_3$-edge extended X-ray absorption fine structure (EXAFS) analysis showed that significant fractions of Np were coordinated to Fe─O entities at pH 9. This highlights the potential role of Fe(II/III) clay edge sites as a strong Np(V) surface complex partner and points to the partial reduction of sorbed Np(V) to Np(IV) via structural Fe(II)