The electronic structure of decoupled graphene on SiC(0001) can be tailored by introducing atomically thin layers of germanium at the interface. The electronically inactive (6 root 3 x 6 root 3)R30 ...degrees reconstructed buffer layer on SiC(0001) is converted into quasi-free-standing monolayer graphene after Ge intercalation and shows the characteristic graphene pi bands as displayed by angle-resolved photoelectron spectroscopy. Low-energy electron microscopy (LEEM) studies reveal an unusual mechanism of the intercalation in which the initial buffer layer is first ruptured into nanoscopic domains to allow the local in-diffusion of germanium to the interface. Upon further annealing, a continuous and homogeneous quasifree graphene film develops. Two symmetrically doped (n- and p-type) phases are obtained that are characterized by different Ge coverages. They can be prepared individually by annealing a Ge film at different temperatures. In an intermediate-temperature regime, a coexistence of the two phases can be achieved. In this transition regime, n-doped islands start to grow on a 100-nm scale within p-doped graphene terraces as revealed by LEEM. Subsequently, the n islands coalesce but still adjacent terraces may display different doping. Hence, lateral p-n junctions can be generated on epitaxial graphene with their size tailored on a mesoscopic scale.
The cationic complexes of Mn(III) with the 5-Hal-sal2323 (Hal = Cl, Br) ligands and a paramagnetic doubly charged counterion ReCl62− have been synthesized: Mn(5-Cl-sal2323)2ReCl6 (1) and ...Mn(5-Br-sal2323)2ReCl6 (2). Their crystal structures and magnetic properties have been studied. These isostructural two-component ionic compounds show a thermally induced spin transition at high temperature associated with the cationic subsystem and a field-induced slow magnetic relaxation of magnetization at cryogenic temperature, associated with the anionic subsystem. The compounds are the first examples of the coexistence of spin crossover and field-induced slow magnetic relaxation in the family of known MnIII(sal2323) cationic complexes with various counterions.
Three tetraphenylborates of mononuclear Mn(III) cation complexes with hexadentate ligands, the products of the reaction between a N,N′‐bis(3‐aminopropyl)ethylenediamine and salicylaldehydes with the ...different haloid substitutions at the 5 or 3,5 positions, have been synthesized: Mn(5‐F‐sal‐N‐1,5,8,12)BPh4 (1), Mn(3,5‐diCl‐sal‐N‐1,5,8,12)BPh4 (2) and Mn(3,5‐Br,Cl‐sal‐N‐1,5,8,12)BPh4 (3). Their crystal structure, dielectric constant (ϵ) and magnetic properties have been studied. Ligand substituents have a dramatic effect on the structure and magnetic properties of the complexes. With decreasing temperature, the complex (1) shows a gradual spin crossover from the high‐spin state (HS) to the HS:LS intermediate phase, followed by an abrupt transition to the low‐spin state (LS) without changing the crystal symmetry. The complexes 2 and 3 are isostructural, but have fundamentally different properties. Complex 2 demonstrates two structural phase transitions related to sharp spin crossovers from the HS to the HS:LS intermediate phase at 137 K and from the intermediate phase to the LS at 87 K, while complex 3 exhibits only one spin transition from the HS to the HS:LS intermediate phase at 83 K.
Effect of halide substituents on spin and phase transitions in Mn(III) complexes
This article is devoted to the study of the effect of electrochemically activated water (catholyte with pH 9.3) on organic compounds of the plant matrix of brewer's spent grain in order to extract ...various compounds from it.
Brewer's spent grain was obtained from barley malt at a pilot plant by mashing the malt followed by filtration and washing of the grain in water and storing it at (0 ± 2) °C in craft bags. For the organic compound quantitative determination, instrumental methods of analysis (HPLC) were used, and the results were subjected to mathematical analysis.
The study results showed that at atmospheric pressure, the alkaline properties of the catholyte showed better results compared to aqueous extraction with respect to β-glucan, sugars, nitrogenous and phenolic compounds, and 120 min was the best period for extraction at 50 °C. The excess pressure conditions used (0.5 ÷ 1 atm) revealed an increase in the accumulation of non-starch polysaccharide and nitrogenous compounds, while the level of sugars, furan and phenolic compounds decreased with increasing treatment duration. The waste grain extract ultrasonic treatment used revealed the effectiveness of catholyte in relation to the extraction of β-glucan and nitrogenous fractions; however, sugars and phenolic compounds did not significantly accumulate. The correlation method made it possible to reveal the regularities in the formation of furan compounds under the conditions of extraction with the catholyte: Syringic acid had the greatest effect on the formation of 5-OH-methylfurfural at atmospheric pressure and 50 °C and vanillic acid under conditions of excess pressure. Regarding furfural and 5-methylfurfural, amino acids had a direct effect at excess pressure. It was shown that the content of all furan compounds depends on amino acids with thiol groups and gallic acid; the formation of 5-hydroxymethylfurfural and 5-methylfurfural is influenced by gallic and vanillic acids; the release of furfural and 5-methylfurfural is determined by amino acids and gallic acid; excess pressure conditions promote the formation of furan compounds under the action of gallic and lilac acids.
This study showed that a catholyte allows for efficient extraction of carbohydrate, nitrogenous and monophenolic compounds under pressure conditions, while flavonoids require a reduction in extraction time under pressure conditions.
A coordination compound with the composition CoLCl
2
·H
2
O (
L
= bis-condensation product of diacetyl and 2-hydrazinyl-4,6-dimethylpyrimidine) was synthesized, in which the Co(
ii
) ion was ...hexacoordinated. Under applied DC fields, this compound exhibited single-ion magnet behavior. Two relaxation processes were observed when increasing the applied magnetic field from 1000 to 3200 Oe. The first relaxation (high-frequency) was observed both at 1000 Oe and 3200 Oe, while the second relaxation was only registered under a field of 3200 Oe at low frequencies (<1 Hz) and low temperatures (<5 K). Modeling of the magnetic DC properties using the Griffith Hamiltonian accompanied by quantum chemical calculations revealed easy-axis-type magnetic anisotropy with weak rhombic contributions.
This study presents the novel hexacoordinated Co(
ii
) mononuclear complex with SIM behavior.
A new hexacoordinate Co(II) complex with the general formula CoL(NCS)2·DMSO (1) (L = biscondensation product of diacetyl and 2-hydrazinyl-4,6-dimethylpyrimidine, DMSO = dimethylsulfoxide) ...exhibiting field-induced single-ion magnet (SIM) behavior has been obtained and characterized. To explain such field-induced SIM behavior, we have performed the analysis of the observed direct current (DC) magnetic properties based on the Griffiths Hamiltonian in combination with the high-level quantum-chemical calculations of the crystal field parameters. The complex has been shown to exhibit strong easy-axis-type magnetic anisotropy arising from a large negative value Δax = −1538.0 cm–1 of the axial crystal parameter, which is accompanied by a weak rhombic contribution with |Δrh| = 219.3 cm–1. Magnetic properties of 1 have been compared with the previously studied field-induced SIM compound CoLCl2·H2O (2). Introduction of a thiocyanide anion in 1 (instead of chloride in 2) in the Co(II) coordination sphere resulted in improvement of uniaxial magnetic anisotropy and switch of the relaxation process from the combination of direct and Raman mechanisms in 2 to Orbach-type one in complex 1. Effects of substitution of acidoligands in the Co(II) coordination sphere on the crystalline structure, DC magnetic properties, magnetic anisotropy, and magnetization relaxation processes have been rationalized.
New nitrosonium manganese(II) nitrate, (NO)Mn
(NO
)
, has been synthesized and structurally characterized. In the temperature range of 45-298 K, the crystal is hexagonal (centrosymmetric sp. gr.
6
/
...). Mn
ions are assembled into tubes along axis
with both NO
filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature
= 190 K, a structural phase transition related to the libration of the intertube NO
group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn
(NO
)
allow suggesting that ordering of NO
units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at
= 12.0 K and
= 8.4 K.
New nitrosonium manganese(II) nitrate, (NO)Mn6(NO3)13, has been synthesized and structurally characterized. In the temperature range of 45–298 K, the crystal is hexagonal (centrosymmetric sp. gr. ...P63/m). Mn2+ ions are assembled into tubes along axis c with both NO3 – filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature T S1 = 190 K, a structural phase transition related to the libration of the intertube NO3 group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn6(NO3)13 allow suggesting that ordering of NO+ units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at T N1 = 12.0 K and T N2 = 8.4 K.
The homogeneous high-entropy wolframite-type solid solution (Mn1/5Co1/5Ni1/5Cu1/5Cd1/5)WO4 was prepared by solid-state reaction at 1000 °C. Elongated “crystals” were grown from the Na2WO4 flux, but ...their strongly broadened powder X-ray diffraction patterns indicated partial dissolution. Nevertheless, successive annealing of the homogeneous solid solution for 3–4 h at 800, 700, and 600 °C did not bring any sign of dissolution. Thus, the material is kinetically stable at low temperatures although thermodynamically unstable. The long-range antiferromagnetic order was established at T N ∼ 24.8 K. Based on magnetization and specific heat measurements, a magnetic phase diagram was built, demonstrating the presence of an additional field-induced phase. In contrast to the parent MnWO4, no dielectric anomaly has been found down to 2 K.
The homogeneous high-entropy wolframite-type solid solution (Mn
Co
Ni
Cu
Cd
)WO
was prepared by solid-state reaction at 1000 °C. Elongated "crystals" were grown from the Na
WO
flux, but their ...strongly broadened powder X-ray diffraction patterns indicated partial dissolution. Nevertheless, successive annealing of the homogeneous solid solution for 3-4 h at 800, 700, and 600 °C did not bring any sign of dissolution. Thus, the material is kinetically stable at low temperatures although thermodynamically unstable. The long-range antiferromagnetic order was established at
∼ 24.8 K. Based on magnetization and specific heat measurements, a magnetic phase diagram was built, demonstrating the presence of an additional field-induced phase. In contrast to the parent MnWO
, no dielectric anomaly has been found down to 2 K.
