Anhydrous hexakis(urea-O)iron(III)]peroxydisulfate ([Fe(urea-O)6]2(S2O8)3 (compound 1), and its deuterated form were prepared and characterized with single-crystal X-ray diffraction and spectroscopic (IR, Raman, UV, and Mössbauer) methods. Six crystallographically different urea ligands coordinate via their oxygen in a propeller-like arrangement to iron(III) forming a distorted octahedral complex cation. The octahedral arrangement of the complex cation and its packing with two crystallographically different persulfate anions is stabilized by extended intramolecular (N–H⋯O = C) and intermolecular (N–H⋯O–S) hydrogen bonds. The two types of peroxydisulfate anions form different kinds and numbers of hydrogen bonds with the neighboring [hexakis(urea-O)6iron(III)]3+ cations. There are spectroscopically six kinds of urea and three kinds (2 + 1) of persulfate ions in compound 1, thus to distinguish the overlapping bands belonging to internal and external vibrational modes, deuteration of compound 1 and low-temperature Raman measurements were also carried out, and the bands belonging to the vibrational modes of urea and persulfate ions have been assigned. The thermal decomposition of compound 1 was followed by TG-MS and DSC methods in oxidative and inert atmospheres as well. The decomposition starts at 130 °C in inert atmosphere with oxidation of a small part of urea (~ 1 molecule), which supports the heat demand of the transformation of the remaining urea into ammonia and biuret/isocyanate. The next step of decomposition is the oxidation of ammonia into N2 along with the formation of SO2 (from sulfite). The main solid product proved to be (NH4)3Fe(SO4)3 in air. In inert atmosphere, some iron(II) compound also formed. The thermal decomposition of (NH4)3Fe(SO4)3 via NH4Fe(SO4)2 formation resulted in α-Fe2O3. The decomposition pathway of NH4Fe(SO4)2, however, depends on the experimental conditions. NH4Fe(SO4)2 transforms into Fe2(SO4)3, N2, H2O, and SO2 at 400 °C, thus the precursor of α-Fe2O3 is Fe2(SO4)3. Above 400 °C (at isotherm heating), however, the reduction of iron(III) centers was also observed. FeSO4 formed in 27 and 75% at 420 and 490 °C, respectively. FeSO4 also turns into α-Fe2O3 and SO2 on further heating. Graphical abstract

The multilayer of approximate structure MgO(100)/[ n fe 51 Rh 49 (63 Å)/ 57 fe 51 Rh 49 (46 Å)] 10 deposited at 200 °C is primarily of paramagnetic A1 phase and is fully converted to the magnetic B2 phase by annealing at 300 °C for 60 min. Subsequent irradiation by 120 keV Ne + ions turns the thin film completely to the paramagnetic A1 phase. Repeated annealing at 300 °C for 60 min results in 100% magnetic B2 phase, i.e. a process that appears to be reversible at least twice. The A1 → B2 transformation takes place without any plane-perpendicular diffusion while Ne + irradiation results in significant interlayer mixing. Besides the traditional "faster-smaller-cheaper" directive, a new requirement has recently arisen for the newly developed devices: the energy efficiency. The electricity consumption of information technology is expected to reach 13% of the global utilization in the next decade 1,2 , of which nearly 50% is due to unwanted heat dissipation. Therefore, the study of novel materials and developing new operation principles for energy-saving applications in information technology are essential for supporting sustainable development. From this point of view, the fine control of magnetism is a great step towards reducing energy consumption of information storage by orders of magnitude 3-11. The Fe-Rh system is an excellent playground for developing energy-efficient magnetic devices 12,13. The equilibrium phase diagram of solid Fe-Rh 14,15 includes a great variety of phases of different magnetic behaviour. The disordered bcc A2 (α or δ, prototype W) phases are, depending on temperature, ferro-or paramagnetic (PM). The ordered bcc B2 (α' or α'' , prototype CsCl) phases show ferro-, antiferro-or paramagnetism at different temperatures and concentrations. The disordered fcc A1 (γ, prototype Cu) phase is PM at all investigated temperatures. The existence of a monoclinic antiferromagnetic (AFM) ground state was predicted by DFT calculations in the equiatomic FeRh alloy in 2016 16. However, this phase could not be identified in thin films by Wolloch and co-workers 17. Using nuclear resonant inelastic X-ray scattering (NRIXS), these latter authors analysed the lattice dynamical contribution to the phase stability in FeRh and demonstrated that the AFM ground state was stabilized by phonon softening. With increasing temperature, the nearly equiatomic FeRh alloy of B2 structure undergoes a metamagnetic transition from the low-temperature AFM α'' to the high-temperature ferromagnetic (FM) α' phase close to room temperature (RT) 18-27. In the AFM phase, Fe atoms carry a magnetic moment of 3.3 μ B of alternating direction while the Rh atoms possess inconsiderable magnetic moment 22. Conversely, in the FM phase, Fe and Rh atoms carry parallel moments of 3.2 μ B and 0.9 μ B , respectively 28-30. This magnetic transition is accompanied with a reduction of the resistivity and an ~ 0.6% isotropic strain of the crystal lattice 21,31. By introducing strain in the FeRh crystal lattice, this phenomenon can be reversed and the mag...

Redox-active iron minerals can act as energy sources or electron-transferring mediators in microbial syntrophic associations, being important means of interspecies metabolic cooperation in sedimentary environments. Alkaline conditions alter the thermodynamic stability of iron minerals, influencing their availability for interspecies syntrophic interactions. We have modeled anaerobic alkaliphilic microbial associations in ethanol-oxidizing co-culture of an obligate syntroph Candidatus “Contubernalis alkalaceticum” and a facultative lithotroph Geoalkalibacter ferrihydriticus, which is capable of dissimilatory Fe(III) reduction and homoacetogenic oxidation of Fe(II) with CO2. The co-cultures were cultivated with thermodynamically metastable ferric-containing ferrihydrite, or ferrous-containing siderite, or without minerals. Mössbauer spectral analysis revealed the transformation of both minerals to the stable magnetite. In the presence of ferrihydrite, G. ferrihydriticus firstly reduced Fe(III) with ethanol and then switched to syntrophic homoacetogenesis, providing the growth of obligate syntroph on ethanol. The ability of G. ferrihydriticus to accept hydrogen from its syntrophic partner and produce extra acetate from carbonate during ethanol oxidation was confirmed by co-culture growth without minerals. In the presence of siderite, G. ferrihydriticus performed homoacetogenesis using two electron donors simultaneously— siderite and hydrogen. Pieces of evidence for direct and indirect hydrogen-mediated electron exchange between partner organisms were obtained. Relative abundancies of partner organisms and the rate of acetate production by their co-cultures were strongly determined by thermodynamic benefits, which G. ferrihydriticus got from redox transformations of iron minerals. Even the minor growth of G. ferrihydriticus sustained the growth of the syntroph. Accordingly, microbe-to-mineral interactions could represent underestimated drivers of syntrophic interactions in alkaline sedimentary environments.

Iron (Fe) is an essential cofactor for all livings. Although Fe membrane transport mechanisms often utilize FeII, uncoordinated or deliberated ferrous ions can initiate Fenton reactions. FeIII citrate complexes are among the most important complexed forms of FeIII especially in plants that, indeed, can undergo photoreduction. Since leaves as photosynthetic organs of higher plants are generally exposed to illumination in daytime, photoreaction of ferric species may have biological relevance in iron metabolism, the relevance of which is poorly understood. In present work FeIII citrate transformation during the photodegradation in solution and after foliar application on leaves was studied by Mössbauer analysis directly. To obtain irradiation time dependence of the speciation of iron in solutions, four model solutions of different pH values (1.5, 3.3, 5.5, and 7.0) with Fe to citrate molar ratio 1:1.1 were exposed to light. Highly acidic conditions led to a complete reduction of Fe together with the formation of FeII citrate and hexaaqua complexes in equal concentration. At higher pH, the only product of the photodegradation was FeII citrate, which was later reoxidized and polymerized, resulting in the formation of polynuclear stable ferric compound. To test biological relevance, leaves of cabbage were treated with FeIII citrate solution. X-ray fluorescence imaging indicated the accumulation of Fe in the treated leaf parts. Mössbauer analysis revealed the presence of several ferric species incorporated into the biological structure. The Fe speciation observed should be considered in biological systems where FeIII citrate has a ubiquitous role in Fe acquisition and homeostasis. Graphical abstract