Roberto Köferstein | Martin Luther University Halle-Wittenberg (original) (raw)
Papers by Roberto Köferstein
Mater. Res. Bull. 177 (2024) 112860, 2024
Magnetoelectric (Ni x Co 1−x Fe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7 composites with a 0-3 conn... more Magnetoelectric (Ni x Co 1−x Fe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7 composites with a 0-3 connectivity and different cation stoichiometries were synthesized via a classical mixed-oxide method. XRD patterns of all ceramics show reflections of the target phases Sr y Ba 1−y Nb 2 O 6 and Ni x Co 1−x Fe 2 O 4. The influence of stoichiometry of the ferrimagnetic and ferroelectric phase on the magnetoelectric behavior was studied on composites with composition of (Ni x Co 1−x Fe 2 O 4) 0.3 −(Sr 0.5 Ba 0.5 Nb 2 O 6) 0.7 and (NiFe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7. The magnetic Curie temperature increases with nickel content. However, the saturation magnetizations as well as the Curie temperatures of the composites are always lower than the ones of bulk Ni x Co 1−x Fe 2 O 4 samples. The maximum magnetoelectric coefficient (α ME) rises with increasing nickel content from 40 (x = 0) to 180 µV Oe −1 cm −1 (x = 1) in accordance with the dynamic magnetostriction coefficient. The evolution of α ME of (NiFe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7 composites shows an increase with strontium content up to y 0.5. Higher strontium content leads to a significant reducing of α ME .
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Adv. Mater. 5 (2024) 183, 2024
In this work, we thoroughly assess the CO2 adsorption behaviour of a recently reported, pillared-... more In this work, we thoroughly assess the CO2 adsorption behaviour of a recently reported, pillared-layered Cu II ethylenediphosphonate of formula Cu2(H2O)1.7(O3P-C2H4-PO3)*1.5H2O (Cu-EtP), that features narrow channel-like pores (diameter <5 Å). Once the metal coordinated H2O molecules are removed, Cu-EtP features a very high density of open metal sites (0.0188 sites Å^-3) and can adsorb a significant amount of CO2 at saturation (2.9 mmol g^-1 , 6.9 mmol cm^-3). Most interesting, it displays a step-shaped CO2 isotherm, whereby a preliminary adsorption event takes place, followed by a step occurring at higher pressure, during which adsorption kinetics become very slow. Hysteresis in desorption suggests that structural rearrangements could be responsible for the unusual isotherm shape. Cu-EtP does not adsorb N2 , probably due to its very narrow pores, thus it displays virtually infinite CO2 /N2 selectivity. The isosteric heat of adsorption extracted using the Clausius-Clapeyron equation is in the range of 35-40 kJ mol À1 , suggesting a strong physisorptive character. This is further confirmed by CO2 adsorption microcalorimetry. In situ synchrotron powder X-ray diffraction analysis, carried out during evacuation and CO2 adsorption, proves that the MOF undergoes phase transitions during both stages, with shrinking of the interlayer spacing upon removal of water and partial reopening of the structure once CO2 is adsorbed. The phase transitions are slow, in agreement with the slow adsorption kinetics observed. In situ infrared spectroscopy suggests that CO2 interacts with the open metal sites generated after removal of strongly adsorbed water and that CO2 cannot displace H2O if this is not fully removed from the surface. NO was also used as a probe molecule to further demonstrate the existence of open metal sites, finding that it is not able to diffuse within the framework when pure, but that it can displace coordinated water. Optical spectroscopy suggests that changes in the coordination sphere of Cu take place during evacuation and CO2 adsorption. Finally, periodic density functional theory calculations were carried out to unravel the structural evolution of Cu-EtP and the energetics of interaction with H2O and CO2 , finding that the change in coordination environment of Cu is mainly responsible for the observed phase transitions.
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Journal of the European Ceramic Society 43 (2023) 6137–6144, 2023
Magnetoelectric (NiFe2 O 4) 0.3 −(Sr 0.5 Ba 0.5 Nb 2 O 6) 0.7 composites with addition of LiNbO 3... more Magnetoelectric (NiFe2 O 4) 0.3 −(Sr 0.5 Ba 0.5 Nb 2 O 6) 0.7 composites with addition of LiNbO 3 as sintering additive were prepared by a classical mixed-oxide method. XRD patterns of ceramics sintered between 1000 and 1200 • C show the desired Sr 0.5 Ba 0.5 Nb 2 O 6 and NiFe 2 O 4 phases. SEM investigations confirm the 0-3 connectivity of the composite ceramics. The addition of 10 and 20 mol% LiNbO 3 improves the densification of the composite ceramics and leads to an increase of the size of the Sr 0.5 Ba 0.5 Nb 2 O 6 grains. Magnetic measurements show hystereses with low coercivities. Dielectric measurements were carried out depending on temperature and frequency. The samples with the LiNbO 3 addition show significantly higher resistivity values (σ DC). Magnetoelectric measurements were carried out in dependence of the magnetic DC-field, temperature, and frequency. The maximum magnetoelectric coefficient (α ME) rises with the addition of LiNbO 3 from 180 to 803 µV Oe −1 cm −1 (@900 Hz). Temperature dependent measurements show a continuously decreasing of α ME with lower temperature.
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Ceramics International 49 (2023) 24428–24441, 2023
In this study, unique hybrid structures were constructed between a Ce-based metal-organic framewo... more In this study, unique hybrid structures were constructed between a Ce-based metal-organic framework (Ce-MOF)
and graphitic carbon nitride (g-C3N4) materials. In addition, the g-C3N4 materials used for these heterostructures
were prepared by five different methods, namely the conventional pyrolysis method, chemical exfoliation by a
strong acid, activation by an alkaline hydrothermal treatment, melamine-cyanuric acid supramolecular assembly
with a mechanochemical method, and by the solvothermally pre-treated method. The structural and morphological
properties of the resulting g-C3N4 sheets and their composites were characterized using scanning electron
microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetric
analysis-derivative thermogravimetry (TGA-DTG), diffuse reflectance UV–vis spectroscopy (UV–vis DRS) and N2
sorption-desorption isotherms (BET). Finally, the photocatalytic performance of the composites was determined
by following the photocatalytic degradation of methylene blue (MB) in an aqueous solution under UV–visible
light irradiation. It was found that the photocatalytic efficiency of the Ce-MOF/g-C3N4‒TS composite was
significantly higher than that of their counterparts (Ce-MOF or g-C3N4‒TS) for the photocatalytic degradation of
MB. When employing the composite, UV light-induced degradation of MB yielded an efficiency of 96.5% after
120 min for a dye solution containing 10 mg/L MB. This corresponds to a
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Journal of the European Ceramic Society, 2018
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Journal of the European Ceramic Society, 2017
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Journal of Materials Science, 2017
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Journal of the European Ceramic Society, 2016
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Materials Research Bulletin, 2016
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ChemInform, 2014
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Solid State Ionics, 2013
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Solid State Ionics, 2013
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Journal of Solid State Chemistry, 2014
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Materials Chemistry and Physics 278 (2022) 125616, 2022
Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot... more Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistrysynthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. =24–30 nm) which were sintered between 1050 and 1200 ◦C to ceramic bodies with relative densities up to 98%.SEM investigations confirm the formation of composite ceramics with a 0–3 connectivity and variable grain sizesfrom 0.2 to 3.6 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦C leads both to a change in themicrostructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviourwith saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe.Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both withrising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described usinga single RC circuit. Magnetoelectric meas...
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J. Solid State Chem., 2022
Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives we... more Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives were prepared by a soft-chemistry synthesis using polyethylene glycol. Calcination at 600 C results in nanocrystalline powders (d cryst. % 30 nm) which were sintered between 1000 and 1300 C to ceramic bodies. By addition of 10 and 20 mol % LiNbO3 , the sintering temperature was reduced by about 200 K and the activation energy of the initial stage of sintering decreases from 386 to 271 kJ mol À1. The sintering aid improves the grain growth and dense ceramic bodies were obtained after sintering at 1125 C for 1 h. A higher LiNbO3 content favors the formation of a pillarlike microstructure. XRD patterns of ceramics sintered above 1000 C show only reflections of the Sr0.5Ba0.5Nb2O6 phase indicating an incorporation of LiNbO3 in the Sr0.5Ba0.5Nb2O6 structure. Dielectric measurements reveal a diffuse phase transition and a relaxor-like behavior. The phase transition temperature (T m) depends on the sintering conditions and is between 117 and 127 C for 10 mol% LiNbO3 , which is very close to pure Sr0.5Ba0.5Nb2O6 , while addition of 20 mol% shifts T m to around 200 C and the transition becomes slightly more diffuse. The optical band gap of the samples is % 3.3 eV and depends slightly on the sintering conditions. We also tried LiF as sintering aid, but this leads to the formation of considerable amounts of secondary phases in the ceramics and relative densities of only 82%.
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Materials Chemistry and Physics 278 (2022) 125616, 2022
• Straightforward synthesis for 0-3 Sr 0.5 Ba 0.5 Nb 2 O 6-CoFe 2 O 4 composites. • Monitoring th... more • Straightforward synthesis for 0-3 Sr 0.5 Ba 0.5 Nb 2 O 6-CoFe 2 O 4 composites. • Monitoring the phase evolution during sintering to ceramics bodies. • Determination of Curie temperature. • Impedance spectroscopy up to 200 • C and 10 MHz. • Investigations of the magnetoelectric coefficient in dependence on magnetic DC field, frequency, and temperature.
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Zeitschrift für anorganische und allgemeine Chemie
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The synthesis and characterization of nano-sized MgFe2O4 by a starch-gel methodis described herei... more The synthesis and characterization of nano-sized MgFe2O4 by a starch-gel methodis described herein. A phase-pure nano-sized MgFe2O4 powder (1a) was obtained aftercalcining a (MgFe)-starch gel at 550 °C. The powder has a specific surface area of 60.6 m2/gand a crystallite size of 9 nm. TEM investigations reveal particles in the range of 7 to 15 nm.The activation energy of the crystallite growth process was calculated as 89 ± 14 kJ/mol. Theshrinkage and sintering behaviour of resulting compacts were studied. UV−VIS investigationsof the nano-sized powder 1a reveal an optical band gap of 2.38 eV, whereas calcination at1100 °C (powder 1g) leads to a crystallite size of 129 nm and a band gap of 2.16 eV.Magnetization loops at 300 K and the temperature dependence of both the field-cooled (FC) and the zero-field-cooled (ZFC) magnetization indicate a superparamagnetic behaviour. The blocking temperature for powder 1a was determined as 140 K at a field of H = 500 Oe. Wefound different saturati...
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Triclinic single crystals of Cu2[Cu(H2O)4][(CH2)4(NH3)2][C6H2(COO)4]2·4H2O have beenprepared in a... more Triclinic single crystals of Cu2[Cu(H2O)4][(CH2)4(NH3)2][C6H2(COO)4]2·4H2O have beenprepared in aqueous solution at 55 °C. Space group P-1 (no. 2), a = 799.73(7), b = 977.43(8),c = 1086.27(9) pm, α = 87.194(7), β = 84.679(7), γ = 74.744(6)°, V = 0.81540(12) nm3, Z = 1.There are two unique Cu2+ with CN 4+1 (Cu(1)) and CN 4+2 (Cu(2)), respectively. The Cu-Odistances range from 197.4(2) to 214.9(2) pm (Cu(1)) and 191.6(2) to 240.1(4) pm (Cu(2)).There is a short Cu(1)-Cu(1) contact of 267.02(6) pm. A three-dimensional coordinationpolymer with negative excess charge and channel-like voids extending parallel to [-110] ismade up by Cu2+ and [C6H2(COO)4]4-. These voids accomodate [(CH2)4(NH3)2]2+ and watermolecules, which are not coordinated to Cu2+. Thermoanalytical measurements in airindicated a step-wise loss of water of crystallization commencing at 63 °C, which is finishedat approx. 250 °C followed by an exothermic decomposition yielding CuO. The Cu(1) pairsshow anti-ferromagnetic coup...
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Zeitschrift für anorganische und allgemeine Chemie
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Mater. Res. Bull. 177 (2024) 112860, 2024
Magnetoelectric (Ni x Co 1−x Fe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7 composites with a 0-3 conn... more Magnetoelectric (Ni x Co 1−x Fe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7 composites with a 0-3 connectivity and different cation stoichiometries were synthesized via a classical mixed-oxide method. XRD patterns of all ceramics show reflections of the target phases Sr y Ba 1−y Nb 2 O 6 and Ni x Co 1−x Fe 2 O 4. The influence of stoichiometry of the ferrimagnetic and ferroelectric phase on the magnetoelectric behavior was studied on composites with composition of (Ni x Co 1−x Fe 2 O 4) 0.3 −(Sr 0.5 Ba 0.5 Nb 2 O 6) 0.7 and (NiFe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7. The magnetic Curie temperature increases with nickel content. However, the saturation magnetizations as well as the Curie temperatures of the composites are always lower than the ones of bulk Ni x Co 1−x Fe 2 O 4 samples. The maximum magnetoelectric coefficient (α ME) rises with increasing nickel content from 40 (x = 0) to 180 µV Oe −1 cm −1 (x = 1) in accordance with the dynamic magnetostriction coefficient. The evolution of α ME of (NiFe 2 O 4) 0.3 −(Sr y Ba 1−y Nb 2 O 6) 0.7 composites shows an increase with strontium content up to y 0.5. Higher strontium content leads to a significant reducing of α ME .
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Adv. Mater. 5 (2024) 183, 2024
In this work, we thoroughly assess the CO2 adsorption behaviour of a recently reported, pillared-... more In this work, we thoroughly assess the CO2 adsorption behaviour of a recently reported, pillared-layered Cu II ethylenediphosphonate of formula Cu2(H2O)1.7(O3P-C2H4-PO3)*1.5H2O (Cu-EtP), that features narrow channel-like pores (diameter <5 Å). Once the metal coordinated H2O molecules are removed, Cu-EtP features a very high density of open metal sites (0.0188 sites Å^-3) and can adsorb a significant amount of CO2 at saturation (2.9 mmol g^-1 , 6.9 mmol cm^-3). Most interesting, it displays a step-shaped CO2 isotherm, whereby a preliminary adsorption event takes place, followed by a step occurring at higher pressure, during which adsorption kinetics become very slow. Hysteresis in desorption suggests that structural rearrangements could be responsible for the unusual isotherm shape. Cu-EtP does not adsorb N2 , probably due to its very narrow pores, thus it displays virtually infinite CO2 /N2 selectivity. The isosteric heat of adsorption extracted using the Clausius-Clapeyron equation is in the range of 35-40 kJ mol À1 , suggesting a strong physisorptive character. This is further confirmed by CO2 adsorption microcalorimetry. In situ synchrotron powder X-ray diffraction analysis, carried out during evacuation and CO2 adsorption, proves that the MOF undergoes phase transitions during both stages, with shrinking of the interlayer spacing upon removal of water and partial reopening of the structure once CO2 is adsorbed. The phase transitions are slow, in agreement with the slow adsorption kinetics observed. In situ infrared spectroscopy suggests that CO2 interacts with the open metal sites generated after removal of strongly adsorbed water and that CO2 cannot displace H2O if this is not fully removed from the surface. NO was also used as a probe molecule to further demonstrate the existence of open metal sites, finding that it is not able to diffuse within the framework when pure, but that it can displace coordinated water. Optical spectroscopy suggests that changes in the coordination sphere of Cu take place during evacuation and CO2 adsorption. Finally, periodic density functional theory calculations were carried out to unravel the structural evolution of Cu-EtP and the energetics of interaction with H2O and CO2 , finding that the change in coordination environment of Cu is mainly responsible for the observed phase transitions.
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Journal of the European Ceramic Society 43 (2023) 6137–6144, 2023
Magnetoelectric (NiFe2 O 4) 0.3 −(Sr 0.5 Ba 0.5 Nb 2 O 6) 0.7 composites with addition of LiNbO 3... more Magnetoelectric (NiFe2 O 4) 0.3 −(Sr 0.5 Ba 0.5 Nb 2 O 6) 0.7 composites with addition of LiNbO 3 as sintering additive were prepared by a classical mixed-oxide method. XRD patterns of ceramics sintered between 1000 and 1200 • C show the desired Sr 0.5 Ba 0.5 Nb 2 O 6 and NiFe 2 O 4 phases. SEM investigations confirm the 0-3 connectivity of the composite ceramics. The addition of 10 and 20 mol% LiNbO 3 improves the densification of the composite ceramics and leads to an increase of the size of the Sr 0.5 Ba 0.5 Nb 2 O 6 grains. Magnetic measurements show hystereses with low coercivities. Dielectric measurements were carried out depending on temperature and frequency. The samples with the LiNbO 3 addition show significantly higher resistivity values (σ DC). Magnetoelectric measurements were carried out in dependence of the magnetic DC-field, temperature, and frequency. The maximum magnetoelectric coefficient (α ME) rises with the addition of LiNbO 3 from 180 to 803 µV Oe −1 cm −1 (@900 Hz). Temperature dependent measurements show a continuously decreasing of α ME with lower temperature.
Bookmarks Related papers MentionsView impact
Ceramics International 49 (2023) 24428–24441, 2023
In this study, unique hybrid structures were constructed between a Ce-based metal-organic framewo... more In this study, unique hybrid structures were constructed between a Ce-based metal-organic framework (Ce-MOF)
and graphitic carbon nitride (g-C3N4) materials. In addition, the g-C3N4 materials used for these heterostructures
were prepared by five different methods, namely the conventional pyrolysis method, chemical exfoliation by a
strong acid, activation by an alkaline hydrothermal treatment, melamine-cyanuric acid supramolecular assembly
with a mechanochemical method, and by the solvothermally pre-treated method. The structural and morphological
properties of the resulting g-C3N4 sheets and their composites were characterized using scanning electron
microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetric
analysis-derivative thermogravimetry (TGA-DTG), diffuse reflectance UV–vis spectroscopy (UV–vis DRS) and N2
sorption-desorption isotherms (BET). Finally, the photocatalytic performance of the composites was determined
by following the photocatalytic degradation of methylene blue (MB) in an aqueous solution under UV–visible
light irradiation. It was found that the photocatalytic efficiency of the Ce-MOF/g-C3N4‒TS composite was
significantly higher than that of their counterparts (Ce-MOF or g-C3N4‒TS) for the photocatalytic degradation of
MB. When employing the composite, UV light-induced degradation of MB yielded an efficiency of 96.5% after
120 min for a dye solution containing 10 mg/L MB. This corresponds to a
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Journal of the European Ceramic Society, 2018
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Journal of the European Ceramic Society, 2017
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Journal of Materials Science, 2017
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Journal of the European Ceramic Society, 2016
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Materials Research Bulletin, 2016
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ChemInform, 2014
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Solid State Ionics, 2013
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Solid State Ionics, 2013
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Journal of Solid State Chemistry, 2014
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Materials Chemistry and Physics 278 (2022) 125616, 2022
Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot... more Magnetoelectric (Sr0.5Ba0.5Nb2O6)1x(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistrysynthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. =24–30 nm) which were sintered between 1050 and 1200 ◦C to ceramic bodies with relative densities up to 98%.SEM investigations confirm the formation of composite ceramics with a 0–3 connectivity and variable grain sizesfrom 0.2 to 3.6 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦C leads both to a change in themicrostructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviourwith saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe.Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both withrising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described usinga single RC circuit. Magnetoelectric meas...
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J. Solid State Chem., 2022
Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives we... more Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives were prepared by a soft-chemistry synthesis using polyethylene glycol. Calcination at 600 C results in nanocrystalline powders (d cryst. % 30 nm) which were sintered between 1000 and 1300 C to ceramic bodies. By addition of 10 and 20 mol % LiNbO3 , the sintering temperature was reduced by about 200 K and the activation energy of the initial stage of sintering decreases from 386 to 271 kJ mol À1. The sintering aid improves the grain growth and dense ceramic bodies were obtained after sintering at 1125 C for 1 h. A higher LiNbO3 content favors the formation of a pillarlike microstructure. XRD patterns of ceramics sintered above 1000 C show only reflections of the Sr0.5Ba0.5Nb2O6 phase indicating an incorporation of LiNbO3 in the Sr0.5Ba0.5Nb2O6 structure. Dielectric measurements reveal a diffuse phase transition and a relaxor-like behavior. The phase transition temperature (T m) depends on the sintering conditions and is between 117 and 127 C for 10 mol% LiNbO3 , which is very close to pure Sr0.5Ba0.5Nb2O6 , while addition of 20 mol% shifts T m to around 200 C and the transition becomes slightly more diffuse. The optical band gap of the samples is % 3.3 eV and depends slightly on the sintering conditions. We also tried LiF as sintering aid, but this leads to the formation of considerable amounts of secondary phases in the ceramics and relative densities of only 82%.
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Materials Chemistry and Physics 278 (2022) 125616, 2022
• Straightforward synthesis for 0-3 Sr 0.5 Ba 0.5 Nb 2 O 6-CoFe 2 O 4 composites. • Monitoring th... more • Straightforward synthesis for 0-3 Sr 0.5 Ba 0.5 Nb 2 O 6-CoFe 2 O 4 composites. • Monitoring the phase evolution during sintering to ceramics bodies. • Determination of Curie temperature. • Impedance spectroscopy up to 200 • C and 10 MHz. • Investigations of the magnetoelectric coefficient in dependence on magnetic DC field, frequency, and temperature.
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Zeitschrift für anorganische und allgemeine Chemie
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The synthesis and characterization of nano-sized MgFe2O4 by a starch-gel methodis described herei... more The synthesis and characterization of nano-sized MgFe2O4 by a starch-gel methodis described herein. A phase-pure nano-sized MgFe2O4 powder (1a) was obtained aftercalcining a (MgFe)-starch gel at 550 °C. The powder has a specific surface area of 60.6 m2/gand a crystallite size of 9 nm. TEM investigations reveal particles in the range of 7 to 15 nm.The activation energy of the crystallite growth process was calculated as 89 ± 14 kJ/mol. Theshrinkage and sintering behaviour of resulting compacts were studied. UV−VIS investigationsof the nano-sized powder 1a reveal an optical band gap of 2.38 eV, whereas calcination at1100 °C (powder 1g) leads to a crystallite size of 129 nm and a band gap of 2.16 eV.Magnetization loops at 300 K and the temperature dependence of both the field-cooled (FC) and the zero-field-cooled (ZFC) magnetization indicate a superparamagnetic behaviour. The blocking temperature for powder 1a was determined as 140 K at a field of H = 500 Oe. Wefound different saturati...
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Triclinic single crystals of Cu2[Cu(H2O)4][(CH2)4(NH3)2][C6H2(COO)4]2·4H2O have beenprepared in a... more Triclinic single crystals of Cu2[Cu(H2O)4][(CH2)4(NH3)2][C6H2(COO)4]2·4H2O have beenprepared in aqueous solution at 55 °C. Space group P-1 (no. 2), a = 799.73(7), b = 977.43(8),c = 1086.27(9) pm, α = 87.194(7), β = 84.679(7), γ = 74.744(6)°, V = 0.81540(12) nm3, Z = 1.There are two unique Cu2+ with CN 4+1 (Cu(1)) and CN 4+2 (Cu(2)), respectively. The Cu-Odistances range from 197.4(2) to 214.9(2) pm (Cu(1)) and 191.6(2) to 240.1(4) pm (Cu(2)).There is a short Cu(1)-Cu(1) contact of 267.02(6) pm. A three-dimensional coordinationpolymer with negative excess charge and channel-like voids extending parallel to [-110] ismade up by Cu2+ and [C6H2(COO)4]4-. These voids accomodate [(CH2)4(NH3)2]2+ and watermolecules, which are not coordinated to Cu2+. Thermoanalytical measurements in airindicated a step-wise loss of water of crystallization commencing at 63 °C, which is finishedat approx. 250 °C followed by an exothermic decomposition yielding CuO. The Cu(1) pairsshow anti-ferromagnetic coup...
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Zeitschrift für anorganische und allgemeine Chemie
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