Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Metal carbonyl wikipedia , lookup
Hydroformylation wikipedia , lookup
Fischer–Tropsch process wikipedia , lookup
Jahn–Teller effect wikipedia , lookup
Stability constants of complexes wikipedia , lookup
Coordination complex wikipedia , lookup
Metalloprotein wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Practical application of Mössbauer Iron spectroscopy By: Udo Bauer, Jan Hufschmidt, Daniel Malko, Marius Piermeier, Florian Späth and Patrick Uffinger Table of Contents • Mössbauer Spectroscopy in Fischer Tropsch catalysis • Mössbauer Spectroscopy in Metal-Organic-Frameworks • Spincrossover control via Mössbauer Spectroscopy • Mössbauer studies on the oxidationstate • Mössbauer studies on the geometry • Mössbauer Spectroscopy in material science Mössbauer Spectroscopy (MöS) in Catalysis • In the Fischer Tropsch process all sorts row 8 – 10 metal catalysts are used • Iron has the advantage to be cheap and very active if used right • Different preparation methods lead different activities of the catalysts • This is dependents on the pH and the additions in your solution Measurements of fresh Catalysts Changes during the Reaction • Kinetic measurements show that high amount of α-Fe increase the catalytic activity as does Iron carbide as 8.0 AH is most reactive • This increased reactivity leads, however to reduced selectivity • MöS was able to identify active species and helped tuning the catalyst to enhance reactivity or selectivity Another look an FT-Catalysts U n r e d u c e d R e d u c e d Another look at FT-Catalysts • In the reduced form we now have two species in different amounts • We have a lower signal to noise ratio at the lower temperature • At 4 K the spectra looks very different • This is due to low intensity, hyperfine-splitting and because the material is amorphous, meaning it has only a chaotic order in the long distance MöS in Metal-Organic Freameworks (MOF) • MOFs may be used as catalyst carrier, as chirality inducing agents, as spin crossover systems and in nonlinear optics • Its behaviors depend on many parameters during formation (pH, heat, [Fe], solvent) Differences in the formation • One can see that the Fe-Ions have a different surrounding and very broad lines due to randomly scattered Iron concentrations within the polymer • Overall not very strong effects • MöS turned out to be not that helpful Spincrossover studies via MöS • Spincrossover, no matter how it is induced always is affiliated to a chance in bondlength and thus MöS is ideal to study it • The figure to the side shows the frank condon principle for spin transition Light-induced excited spin state trapping (LIESST) I.S. = 0,11 mms-1 Q.S.= 3,08 mms-1 I.S. = 0,44 mms-1 Q.S. = 1,14 mms-1 • A spincrossover can be observed via MöS. I.S. tells us that the bonds are indeed longer in the HS state and Q.S. tells us that we have a more symmetrical electron distribution around the core in HS • Two Iron centers, which seem to be independent form each other in switching behavior • Left: HS: grey; LS: dark grey • Although this is now a Liquid Crystal system and the shift form HS to LS is more steady, MöS look the same as most of the time [Fe(L)2](PF6) Spincrossover studies via MöS • dinuclear Fe(II)-compound: [Fe(NCSe)(py)]2(bpypz)2 • magnetic measurements and Mössbauer spectra to learn more about the behavior of that compound • unfilled circles show the μeff-value plotted vs. T: T1/2 = 109 K, μeff = 5,3 ( for 300 - 150 K) • and μeff = ~1,5 (for 100 – 25 K) • abrupt HS-HS to LS-LS transition • Mössbauer spectra of [Fe(NCSe)(py)]2(bpypz)2]: a) b) δ / mm s-1 1,00 ΔEQ / mm s-1 1,99 0,58 0,54 0,49 3,71 1,15 0,33 • a) quite normal values for such compounds • b) unusual lineshape, fitted to a sum of three lines • δ-values lower → LS-LS state (since no change in oxidation number), no antibonding orbitals filled, shorter bonds lead to lower values • further work is needed to understand the whole mechanism Dinitrosyl iron complexes (DNIC) with imidazole bridging ligands • • • • • • compound 1: [(imidazole)-Fe(NO)2]4 compound 2: [(2-isopropylimidazole)Fe(NO)2]4 compound 3: [(benzimidazole)Fe(NO)2]4 compounds forming tetramers biological implication of DNICs measurement of MöS of the complexes and of some reference complexes compound 1: Fe (orange), O (red), N(blue), C (black) tetramers • isomer shifts nearly the same for all 3 compounds → nearly same oxidation state for all iron centers [ Fe(III), S=1/2, low spin] → also nearly the same bond distances of imidazolenitrogens to iron centers • quadrupole splitting parameters also nearly the same for all 3 complexes → all 3 complexes low spin d5 with nearly the same noncubic electron distribution • A and C are reduced, B and D oxidized forms, whereas D is most similar to the tetramers • A has two strongly σ-donating NHC ligands, in comparison C has one CO as weaker σ-donor but stronger π-acceptor → shorter bond of CO to Fe center → lower isomer shift than A • D has highest δ due to strong σ- and πdonating ligands • interesting here: A and C have lower isomer shifts than B and D although they have the lower oxidation state this is due to greater π-backbonding in A and C (3d orbitals of Fe in reduced DNIC energetically close to NO π* orbitals) • all in all: tetramers have much higher δvalues since NHCs as bridging ligands have less σ-donating ability than ligands in D reference complexes Mössbauer study of Fe(Dioximato)nL2] mixed coordination compounds • Important in Biochemistry and Analytical Chemistry • Two families: One Octahedral and one Planar • The strong donor– acceptor interactions between the metal and ligand ions • empty 4s and 3d orbitals of iron serve as the main acceptors • N-donated 4s electron density increases the total s electron density and thus reducing δ Octahedral Planar • As expected the quasi Octahedral Structure is more Symmetric than the Planar one 1-5 Octahedral 6-8 Planar Metallurgical behavior of iron in brass studied using MöS • brass = Cu / Zn – alloy • α-Fe (bcc structure, stable below 910 °C, ferromagnetic) • γ-Fe (fcc structure, stable between 910 °C 1390 °C, weakly antiferromagnetic) • γ-Fe undergoes transition to α-Fe due to plastic deformation or aging thus meaning a change in the properties of the brass material • The amount of Fe is proportional to the peaksize • Fe atoms with only Cu / Zn neighbours • Fe with one Fe atom as nearest neighbour • Fe with mostly Fe atoms as neighbours Tuning material properties with MÖS • Different annealing procedures lead to differently ordered Fe impurities in our Brass and thus to different mechanical and electrical properties • For specific applications of your brass you want certain annealing processes Conclusion • MöS is a very versatile spectroscopy and applicable in a wide field • MöS spectra may be easy to interpret on the first look, may, however, get more complicated if you dive deeper in the use • It is used to identify Spins, Oxidationstats, Ligandsurroundings, Crystalstructure and the composition of your material