Physical and chemical induced spin crossover

Physical spin crossover (spin transition), one of the most fascinating dynamic electronic structure phenomena occurring in coordination compounds of third row transition metal ions, mostly of iron(II), iron(III) and cobalt(II), has attracted increasing attention by many research groups. Some examples for physical and chemical induced spin crossover are discussed. Among the physical is the temperature and pressure induced switching. Novel effects observed by irradiation and magnetic and electric field will be discussed. Some chemical induced switching effects caused by solvation, ligand exchange, ligand isomerisation and bond breaking will be briefly outlined.Leibniz University of HanoverZFM/LUHLNQE/LUHDFG/SPP/1136DFG/Re 1627/1-3Fonds der chemischen Industri

Mössbauer Spectroscopic Study and Magnetic Investigation of Iron(III) Complexes on a Dendrimeric Basis

The functionalization of the molecular surface of various dendrimer generations with a phosphorous core and external amine groups is obtained by converting those amine groups into the corresponding imines of salicylaldehyde creating multiple coordination sites for the iron atoms. Treatment with iron(III) chloride yields multinuclear iron(III) complexes on a dendrimeric basis. The obtained multinuclear molecular systems exhibit extremely high total spin values. The influence of the generation growth on this type of coordination compounds is investigated by Mossbauer spectroscopy and SQUIDmagnetometry

Simulative development of the electronic component of Mössbauer spectroscopy with a focus on the controllability of a 2nd order transimpedance amplifier

In light-processing systems, light energy is converted into a photocurrent due to the photoelectric effect. This project focuses on the development of a high-precision energy-to-voltage conversion technique to optimize signal processing in light-processing systems, specifically for applications in space analytics or solid state physikcs, such as Mössbauer spectroscopy. Analog circuit development plays a vital role as downstream voltage conversion is necessary for signal processing. The objective is to enhance the signal quality and improve the signal-to-noise ratio through the design, optimization, and comparison of various circuits for voltage conversion. The development process involves the design and optimization of amplifier circuits, supplemented with the incorporation of filters and/or regulators for further improvement. A transimpedance amplifier is approximated as a second-order low-pass filter, while a state controller is designed and analyzed to efficient transient oscillation of the system towards optimal amplitude values for subsequent signal processing. The project's results contribute to the advancement of light-processing systems, enabling more precise analysis of light energy in Mössbauer spectroscopy. The findings are presented in a series of scientific publications, showcasing the effectiveness of the developed circuits and their impact on signal quality. Future work could focus on further optimization and validation of the circuits in real-world applications to confirm their performance and reliability. Overall, this project emphasizes the significance of meticulous circuit development and optimization for enhancing signal processing in light-processing systems, thus supporting their application in space analytics

Accelerated ageing of surface modified flax fiber reinforced composites

The overall aim of this study is to evaluate application-oriented potential of biocomposites made of surface-modified flax fibers for use in engineering thermoplastics. The scope of the study includes analysis of the effect of a partially bio-based epoxy-coating, a silane treatment and a combined epoxy-coating / silane treatment of the flax fibers on the mechanical behavior of biocomposites after thermo-oxidative aging. The treated flax fabrics were subjected to tensile tests as well as scanning electron microscopy (SEM) to compare their mechanical behavior and fracture surface. The natural fiber reinforced biocomposites were manufactured through film-stacking of the treated fabrics and polyamide 6 (PA6) using hot-pressing. The durability of the biocomposites after climate-change tests was confirmed via tensile and bending testing. The results show beneficial mechanical behavior of treated fabrics and corresponding biocomposites, but also negative affected durability of treated composites after climate-change tests. Treatment of the fabrics with subsequent accelerated aging leads to a similar low level of tensile and bending moduli

Competing redox reactions in Fe-containing AlO(OH) and Al2O 3 matrices: A combined investigation by Mössbauer, ESR spectroscopy and thermal analysis

The investigation of iron-doped AlO(OH)/Al2O3 systems revealed that the combined employment of Mössbauer and ESR spectroscopies together with thermal analysis yields meaningful data with complementary information. This mutual complementarity is based on the coexistence of Fe point defects with the corresponding aggregated FeOx species which has been observed even for very low Fe concentrations. Competing redox processes between the dopant, the AlOx matrix, and the gas atmosphere during the thermal treatment enable the generation of solid phases exhibiting specific chemical properties. The entire reaction process is influenced by a specific mechanical and thermal pre-treatment that affects predominantly oxydative processes in the matrix. A protecting influence of the matrix preventing further reductive attack of the Fe3+ Fe2+ ions by hydrogen has been established

Molecular switching in iron complexes bridged via tin-cyanides observed by Mössbauer and ESR spectroscopy

The precursor [FeIII(L)Cl] (LH2 N,N'-bis(2'-hydroxy- 3'-X-benzyliden)-1,6-diamino-3-N-hexane) is a high-spin (S 5/2) complex (with X -CH3, -O-CH3). This precursor is combined with the bridging unit [SnIV(CN)4] to yield star-shaped pentanuclear clusters, [(L-X-FeIII)4Sn(CN) 4]Cl4 57Fe-Mössbauer, 119mSn- Mössbauer, and ESR spectroscopy are used to study our samples. For X -CH3 the 57Fe-Mössbauer data show a multiple spin transition between iron(III) in the high-spin and low-spin state. Changing the functional group from X -CH3 to X -O-CH3 turns the switchability off

Preliminary Investigation of Possible Biochar Use as Carbon Source in Polyacrylonitrile Electrospun Fiber Production

Electrospinning with consequent thermal treatment consists in a carbon fiber production method that spins a polymer solution to create fibers with diameters around a few hundred nanome-ters. The thermal treatments are used for the cyclization and then carbonization of the material at 1700◦C for one hour. The unique structure of micro-and nano-carbon fibers makes them a promis-ing material for various applications ranging from future battery designs to filtration. This work investigated the possibility of using milled gasification biochar, derived from a 20 kW fixed-bed gasifier fueled with vine pruning pellets, as an addictive in the preparation of electrospinning solu-tions. This study outlined that solvent cleaning and the consequent wet-milling and 32 µm sifting are fundamental passages for biochar preparation. Four different polyacrylonitrile-biochar shares were tested ranging from pure polymer to 50–50% solutions. The resulting fibers were analyzed via scanning electron microscopy, and energy-dispersive X-ray and infrared spectroscopy. Results from the morphological analysis showed that biochar grains dispersed themselves well among the fiber mat in all the proposed shares. All the tested solutions, once carbonized, exceeded 97%wt. of carbon content. At higher carbonization temperatures, the inorganic compounds naturally showing in biochar such as potassium and calcium disappeared, resulting in an almost carbon-pure fiber matrix with biochar grains in between. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

A rectangular Ni-Fe cluster with unusual cyanide bridges

An asymmetric polycyanide iron complex, K2[Fe III(L1)(CN)4](MeOH) (HL1 = 2,2′-(1H-pyrazole-3,5- diyl)bis-pyridine), was synthesized and its complexation compatibility with nickel ions was examined. Two kinds of enantiomeric nickel-iron squares were obtained in the presence of a chiral bidentate capping ligand. The compounds display unusual cyanide bridge geometry and have ferromagnetic interactions between nickel and iron ions. © 2013 The Royal Society of Chemistry

Structural, Magnetic, and Electrochemical Characterization of Iron(III) and Cobalt Complexes with Penta-N3O2-dentate Ligands

Six new mononuclear [FeIII(LBr,Cl)X]-complexes (LBr,Cl is the dianionic penta-N3O2-dentate Schiff base ligand N,N′-bis(2’-hydroxy-3-bromo-5-chlorobenzylidene)-1,6-diamino-3-azahexane; X: Cl−, N3−, NCO−, NCS−, NCSe−, CN−) were synthesized and their structures, magnetic and electrochemical properties studied. Structure analysis and magnetic measurements showed that [FeIII(LBr,Cl)CN] is in the low spin state and the other five complexes are in high spin states. Furthermore, the trinuclear mixed valent cobalt complex {[CoIII(LH,H)CN]2[CoII(1-methylimidazole)3(H2O)]} was prepared and its magnetic behavior studied. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH Gmb

Iron(III) Complexes on a Dendrimeric Basis and Various Amine Core Investigated by Mössbauer Spectroscopy

Dendrimers of various generations were synthesized by the divergent method. Starting from various amine cores (G(0a), G(0b), G(0c)) the generations were built by reaction of the amine with acrylnitrile followed by hydrogenation with DIBAL-H. Treatment with salicylaldehyde creates a fivefold coordination sphere for iron in the molecular periphery. The resulting multinuclear coordination compounds are investigated by Mossbauer spectroscopy