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A hydrogen-bonding donor-acceptor system, [Co2 Fe2 (bpy*)4 (CN)6 (tp*)2 ](PF6 )2 ⋅2ABA⋅4BN⋅2PE (1 solv ), was prepared by co-crystallization of an external stimuli-responsive cyanide-bridged tetranuclear [Co2 Fe2 ] complex and bifunctional hydrogen-bonding donors, p-aminobenzoic acid. Compound 1 solv exhibited a gradual electron-transfer-coupled spin transition (ETCST), and the removal of solvent molecules led to an abrupt thermal ETCST behavior with increased transition temperature. X-ray structural analysis revealed that the modification of ETCST was caused by a significant alteration of a hydrogen-bonding mode between the tetranuclear [Co2 Fe2 ]2+ cations and ABA molecules. Variable temperature IR measurements indicated that the desolvated form, 1 desolv , showed dynamic alteration of hydrogen-bonding interactions coupled with thermal ETCST behavior. These results suggested that the tetranuclear [Co2 Fe2 ] complex shows solid-state modulations of hydrogen-bond strengths by external stimuli.

A key part of Mossbauer (MB) spectroscopy is the selection of the resonant energy range out of a detected γ -ray spectrum. As the detection of the entire γ -ray source spectrum generates high count rates, selection of the photons having the MB transition energy requires fast processing. To achieve this goal with the MIMOS II instrument, developed and built by the group of Gostar Klingelhofer at the TU Darmstadt and JOGU Mainz, multiple sets of two comparator units, using fast operational amplifiers to define a certain energy window, are implemented in the instrument’s main electronics board. These analogue circuits use stabilized reference voltages to set the thresholds. Today’s fast microcontroller based analogue-to-digital converters (ADC), such as the Arduino Due, show better signal to noise ratio and possibilities for a two-dimensional extension of Mossbauer spectroscopy.

Nanoparticle-based voluminous 3D networks with low densities are a unique class of materials and are commonly known as aerogels. Due to the high surface-to-volume ratio, aerogels and xerogels might be suitable materials for applications in different fields, e.g. photocatalysis, catalysis, or sensing. One major difficulty in the handling of nanoparticle-based aerogels and xerogels is the defined patterning of these structures on different substrates and surfaces. The automated manufacturing of nanoparticle-based aerogel- or xerogel-coated electrodes can easily be realized via inkjet printing. The main focus of this work is the implementation of the standard nanoparticle-based gelation process in a commercial inkjet printing system. By simultaneously printing semiconductor nanoparticles and a destabilization agent, a 3D network on a conducting and transparent surface is obtained. First spectro-electrochemical measurements are recorded to investigate the charge-carrier mobility within these 3D semiconductor-based xerogel networks.

A hydrogen-bonding donor-acceptor system, [Co

A mononuclear FeII complex, prepared with a Bronsted diacid ligand, H2 L (H2 L=2-[5-phenyl-1H-pyrazole-3-yl] 6-benzimidazole pyridine), shows switchable physical properties and was isolated in five different electronic states. The spin crossover (SCO) complex, [FeII (H2 L)2 ](BF4 )2 (1A ), exhibits abrupt spin transition at T1/2 =258 K, and treatment with base yields a deprotonated analogue [FeII (HL)2 ] (1B ), which shows gradual SCO above 350 K. A range of FeIII analogues were also characterized. [FeIII (HL)(H2 L)](BF4 )Cl (1C ) has an S=5/2 spin state, while the deprotonated complexes [FeIII (L)(HL)], (1D ), and (TEA)[FeIII (L)2 ], (1E ) exist in the low-spin S=1/2 state. The electronic properties of the five complexes were fully characterized and we demonstrate in situ switching between multiple states in both solution and the solid-state. The versatility of this simple mononuclear system illustrates how proton donor/acceptor ligands can vastly increase the range of accessible states in switchable molecular devices.

Chemical modifications of the yet reported iron(II) compound [Fe(dpp)2(NCS)2]⋅Py (dpp = dipyrido[3,2a:2’3’c]phenazine, Py = pyridine) which shows abrupt spin crossover below room temperature with large hysteresis have been made. The purpose was to stabilize different spin states at room temperature as well as to adjust the spin crossover in temperature and hysteresis width. We modified the bidentate ligand dpp by substituting hydrogens at the phenazine by different functional groups. In addition, we substituted the thiocyanate monodentate ligands by NCSe−. The spin states of these compounds have been investigated by Mossbauer spectroscopy at two temperatures and temperature depending IR spectroscopy. These methods indicating that the chemical modifications are influencing the observed spin configuration of the complexes alongside the spin crossover behavior which changed to gradual and incomplete transitions. These promising results offer interesting possibilities for chemical adjustments of the shown spin crossover systems.

We synthesised a series of Iron(II)-triazole compounds and used the electrospinning procedure to incorporate spin crossover compounds (SCO) into polylactic acid polymer fibers. Composite fiber/SCO compounds of [Fe(NH2-trz)3](BF4)2 as well as [Fe(Htrz)2(trz)]BF4 were investigated via Mossbauer spectroscopy at 293 K and 77 K. The Mossbauer studies show that the spin crossover behavior is maintained in the polymer matrix.