Kathrin Hofmann | Technische Universität Darmstadt (original) (raw)
Papers by Kathrin Hofmann
![Research paper thumbnail of 2,5-[C4+C2] Ringtransformation of Pyrylium Salts with α-Sulfinylacetaldehydes](https://attachments.academia-assets.com/118123206/thumbnails/1.jpg)
](Molecules, Nov 13, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The Cambridge Structural Database, 2023
Zeitschrift für Kristallographie, Mar 1, 2005
Alkali metal decahydro-closo-decaborates M2[B10H10] (M = Na, Rb, Cs) were synthesised by ion-exch... more Alkali metal decahydro-closo-decaborates M2[B10H10] (M = Na, Rb, Cs) were synthesised by ion-exchange and characterised via infrared and 11B-NMR spectroscopy. The crystal structures of Na2[B10H10], K2[B10H10], and Rb2[B10H10] were determined from X-ray powder diffraction data using real-space techniques. The compounds crystallise in the monoclinic space group P21/n (no. 14) with the lattice constants: Na2[B10H10]: a = 1028.28(6) pm, b = 1302.18(5) pm, c = 667.34(3) pm, β = 93.754(3)°; K2[B10H10]: a = 1285.54(8) pm, b = 1117.84(7) pm, c = 682.27(4) pm, β = 93.357(3)°; Rb2[B10H10]: a = 1320.04(7) pm, b = 1136.88(6) pm, c = 704.23(4) pm, β = 94.158(3)°. The hydroborate anions are arranged almost hexa gonally with alkali metal cat ions in the tetrahedral interstices.
Zeitschrift für anorganische und allgemeine Chemie, May 1, 2001
Bis(tetramethylammonium) dodecahydrododecaborate, [(CH3)4N]2[B12H12], and bis(tetramethylammonium... more Bis(tetramethylammonium) dodecahydrododecaborate, [(CH3)4N]2[B12H12], and bis(tetramethylammonium) dodecahydrododecaborate acetonitrile, [(CH3)4N]2[B12H12] · CH3CN, were synthesized and characterized via Infrared, 1H and 11B NMR spectroscopy. [(CH3)4N]2[B12H12] crystallizes isopunctual to the alkali metal dodecaborates. The crystal structure of [(CH3)4N]2[B12H12] · CH3CN was determined from single crystal data and refined in the orthorhombic crystal system (Pcmn, no. 62, a = 898.68(8), b = 1312.85(9) c = 1994.5(1) pm, R(|F| , 4σ) = 5.9%, wR(F2) = 18.3%). Here, the geometry of the dodecaborate anion is that of an almost ideal icosahedron, less distorted than most other dodecaborates known. By low-temperature Guinier-Simon diffractometry phase transitions were detected for [(CH3)4N]2[B12H12] and [(CH3)4N]2[B12H12] · CH3CN at –70 and –15 °C, respectively. Synthese, Charakterisierung und Kristallstrukturbestimmung von [N(CH3)4]2[B12H12] und [N(CH3)4]2[B12H12] · CH3CN Bis(tetramethylammonium)dodecahydrododecaborat, [(CH3)4N]2[B12H12], und Bis(tetramethylammonium)dodecahydrododecaborat Acetonitril, [(CH3)4N]2 [B12H12] · CH3CN, wurden mittels Infrarotspektroskopie, 1H- und 11B-NMR-Spektroskopie charakterisiert. [(CH3)4N]2- [B12H12] kristallisiert isopunktual zu den Alkalimetalldodecaboraten. Die Kristallstruktur von [(CH3)4N]2[B12H12] · CH3CN wurde mittels Einkristallrontgenstrukturanalyse bestimmt und im orthorhombischen Kristallsystem verfeinert (Pcmn, Nr. 62, a = 898,68(8), b = 1312,85(9), c = 1994,5(1) pm, R(|F| , 4σ) = 5,9%, wR(F2) = 18,3%). In dieser Verbindung ist die Geometrie des Dodecaborat-Anions die eines nahezu idealen Ikosaeders, also weniger verzerrt als in anderen Dodecaboraten. Mittels Tieftemperatur-Guinier-SimonDiffraktometrie wurden Phasenumwandlungen fur [(CH3)4N]2- [B12H12] und [(CH3)4N]2[B12H12](CH3CN bei –70 bzw. bei –15 °C detektiert.
Journal of The Electrochemical Society, 2008
We have investigated how secondary phases appear and disappear upon increasing europium concentra... more We have investigated how secondary phases appear and disappear upon increasing europium concentration from 1.5 to 16.2 atom % in standard strontium borophosphate phosphate phosphor, , using X-ray diffraction and photoluminescence and photoluminescence ...
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A rapid synthesis of chiral sulfoxide-functionalized meta-terphenyl derivatives by a 2,5-[C4+C2] ... more A rapid synthesis of chiral sulfoxide-functionalized meta-terphenyl derivatives by a 2,5-[C4+C2] ring transformation reaction of pyrylium salts with in-situ generated enantio-merically pure .alpha.-sulfinylacetaldehydes is described. This synthetic method demonstrates for the first time the use of .alpha.-sulfinylacetaldehydes in a reaction sequence initiated by nu-cleophilic attack of pyrylium salts by .alpha.-sulfinylcarbanions to generate chiral aromatic systems. The method presented shows broad applicability starting with various methyl sulfoxides and a number of functionalized pyrylium salts, furnishing meta-terphenyls with complex substitution patterns from readily accessible starting compounds.
Physical Review Materials, Dec 28, 2018
The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory Heusler alloys put the... more The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory Heusler alloys put them forward to use in magnetic refrigeration technology. It is associated with a first-order magnetostructural (martensitic) phase transition. We conducted a comprehensive study of the MCE for the off-stoichiometric Heusler alloy Ni 2.2 Mn 0.8 Ga in the vicinity of its first-order magnetostructural phase transition. We found a reversible MCE under repeated magnetic field cycles. The reversible behavior can be attributed to the small thermal hysteresis of the martensitic phase transition. Based on the analysis of our detailed temperature dependent X-ray diffraction data, we demonstrate the geometric compatibility of the cubic austenite and tetragonal martensite phases. This finding directly relates the reversible MCE behavior to an improved geometric compatibility condition between cubic austenite and tetragonal martensite phases. The approach will help to design shape-memory Heusler alloys with a large reversible MCE taking advantage of the first-order martensitic phase transition.
APL Materials, Jun 1, 2023
Manganese monoboride has a low- (α) and a high-temperature (β) modification, as well as a defect-... more Manganese monoboride has a low- (α) and a high-temperature (β) modification, as well as a defect-rich low-temperature variant (α′). The crystal structure (FeB-type structure, s.g. Pnma) and properties of high-temperature MnB are well-known. In this work, single crystals were grown via chemical vapor transport reactions, both of β-MnB and the low-temperature modification, α-MnB. This allowed for determining the crystal structure of defect-free α-MnB [CrB-type structure, s.g. Cmcm, a = 3.0098(6) Å, b = 7.6390(2) Å, and c = 2.94620(6) Å]. Furthermore, α′-MnB, the stacking fault-dominated CrB-variant, was obtained as crystalline powder and characterized by X-ray powder diffraction and transmission electron microscopy. Direction-resolved measurements of the magnetic properties of α-MnB revealed spin-canted magnetic behavior along c and ferromagnetism along a and b with a Curie temperature of 456 K; ferromagnetic β-MnB has a Curie temperature of 568 K.
Computational Materials Science, Sep 1, 2021
A molecular dynamics simulation approach is applied to investigate thermal expansion of the latti... more A molecular dynamics simulation approach is applied to investigate thermal expansion of the lattice parameters and heat capacities of SrMoO 3 and BaMoO 3 perovskite-type molybdates in the temperature range between 300 and 1000 K. The meaningful shape of the pairwise potential for SrMoO 3 and BaMoO 3 is achieved by fitting their lattice parameters to those of the high-purity polycrystalline powders synthesized via reduction of their respective scheelite precursors in hydrogen atmosphere at high pressure. The approach is validated by the simulated temperature dependences of the heat capacity, which follow the reported experimental data near and above the Debye temperature.
Energy technology, May 31, 2021
2015-Sustainable Industrial Processing Summit, Mar 16, 2015
The environmental impact of cement and concrete can be significantly decreased by the reduction o... more The environmental impact of cement and concrete can be significantly decreased by the reduction of the amount of Portland cement clinker. The substitution of the Portland cement clinker with substitutes like limestone powder results in a decrease of hydration products, such as calcium hydroxide. However, a minimum amount of calcium hydroxide and a high density of the hardened cement pastes are necessary to ensure sufficient alkalinity, which is necessary for the passivation of the steel reinforcement during the life cycle of a building. The development of new eco-friendly cements requires a basic understanding regarding the durability against carbonation induced corrosion of the reinforcement. We are investigating low-water limestone-rich concretes with the aim for a sufficient prediction of the carbonation resistance and hope to support the development of sustainable cements. Because of the low content of hydration products, the approved models describing the carbonation behavior of conventional concretes are not working sufficiently for the mixtures investigated here and therefore, need to be modified. For that reason, the individual phase-pure clinker phases were synthesized and after complete hydration stored under CO2 atmosphere (2 Vol %, 20 A°C, 65% humidity) for 28 days. The products of the hydration- and carbonation-reactions were investigated with X-ray powder diffraction, thermal analysis (DTA/TG), scanning electron microscopy and energy-dispersive X-ray analysis. The results are compared to analyses of conventional clinker phases.
Solid State Sciences, Jun 1, 2003
Black amorphous precipitates of unknown composition have been obtained from aqueous solutions of ... more Black amorphous precipitates of unknown composition have been obtained from aqueous solutions of sodium tetrahydridoborate and nickel salts. These precipitates have been analyzed by means of X-ray diffraction, electron microscopy, and electron energy loss spectroscopy, especially focussing on the energy-loss near-edge structure. By comparing the fine structure of the B K ionization edge of the nano-scalic product with that of amorphous boron and crystalline nickel boride, we show that the primary precipitate contains a metal boride formed at room temperature. The precipitate exhibits catalytic activity, e.g. for arylations of arylhalogenides. When annealed, the primary product transforms into crystalline Ni 3 B. An earlier crystal structure determination of Ni 3 B was confirmed by Rietveld refinement of highly resolved synchrotron data.
Handbook of Solid State Chemistry
The environmental impact of cement and concrete can be significantly decreased by the reduction o... more The environmental impact of cement and concrete can be significantly decreased by the reduction of the amount of Portland cement clinker. The substitution of the Portland cement clinker with substitutes like limestone powder results in a decrease of hydration products, such as calcium hydroxide. However, a minimum amount of calcium hydroxide and a high density of the hardened cement pastes are necessary to ensure sufficient alkalinity, which is necessary for the passivation of the steel reinforcement during the life cycle of a building. The development of new eco-friendly cements requires a basic understanding regarding the durability against carbonation induced corrosion of the reinforcement. We are investigating low-water limestone-rich concretes with the aim for a sufficient prediction of the carbonation resistance and hope to support the development of sustainable cements. Because of the low content of hydration products, the approved models describing the carbonation behavior o...
Molecules, Nov 13, 2023
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The Cambridge Structural Database, 2023
Zeitschrift für Kristallographie, Mar 1, 2005
Alkali metal decahydro-closo-decaborates M2[B10H10] (M = Na, Rb, Cs) were synthesised by ion-exch... more Alkali metal decahydro-closo-decaborates M2[B10H10] (M = Na, Rb, Cs) were synthesised by ion-exchange and characterised via infrared and 11B-NMR spectroscopy. The crystal structures of Na2[B10H10], K2[B10H10], and Rb2[B10H10] were determined from X-ray powder diffraction data using real-space techniques. The compounds crystallise in the monoclinic space group P21/n (no. 14) with the lattice constants: Na2[B10H10]: a = 1028.28(6) pm, b = 1302.18(5) pm, c = 667.34(3) pm, β = 93.754(3)°; K2[B10H10]: a = 1285.54(8) pm, b = 1117.84(7) pm, c = 682.27(4) pm, β = 93.357(3)°; Rb2[B10H10]: a = 1320.04(7) pm, b = 1136.88(6) pm, c = 704.23(4) pm, β = 94.158(3)°. The hydroborate anions are arranged almost hexa gonally with alkali metal cat ions in the tetrahedral interstices.
Zeitschrift für anorganische und allgemeine Chemie, May 1, 2001
Bis(tetramethylammonium) dodecahydrododecaborate, [(CH3)4N]2[B12H12], and bis(tetramethylammonium... more Bis(tetramethylammonium) dodecahydrododecaborate, [(CH3)4N]2[B12H12], and bis(tetramethylammonium) dodecahydrododecaborate acetonitrile, [(CH3)4N]2[B12H12] · CH3CN, were synthesized and characterized via Infrared, 1H and 11B NMR spectroscopy. [(CH3)4N]2[B12H12] crystallizes isopunctual to the alkali metal dodecaborates. The crystal structure of [(CH3)4N]2[B12H12] · CH3CN was determined from single crystal data and refined in the orthorhombic crystal system (Pcmn, no. 62, a = 898.68(8), b = 1312.85(9) c = 1994.5(1) pm, R(|F| , 4σ) = 5.9%, wR(F2) = 18.3%). Here, the geometry of the dodecaborate anion is that of an almost ideal icosahedron, less distorted than most other dodecaborates known. By low-temperature Guinier-Simon diffractometry phase transitions were detected for [(CH3)4N]2[B12H12] and [(CH3)4N]2[B12H12] · CH3CN at –70 and –15 °C, respectively. Synthese, Charakterisierung und Kristallstrukturbestimmung von [N(CH3)4]2[B12H12] und [N(CH3)4]2[B12H12] · CH3CN Bis(tetramethylammonium)dodecahydrododecaborat, [(CH3)4N]2[B12H12], und Bis(tetramethylammonium)dodecahydrododecaborat Acetonitril, [(CH3)4N]2 [B12H12] · CH3CN, wurden mittels Infrarotspektroskopie, 1H- und 11B-NMR-Spektroskopie charakterisiert. [(CH3)4N]2- [B12H12] kristallisiert isopunktual zu den Alkalimetalldodecaboraten. Die Kristallstruktur von [(CH3)4N]2[B12H12] · CH3CN wurde mittels Einkristallrontgenstrukturanalyse bestimmt und im orthorhombischen Kristallsystem verfeinert (Pcmn, Nr. 62, a = 898,68(8), b = 1312,85(9), c = 1994,5(1) pm, R(|F| , 4σ) = 5,9%, wR(F2) = 18,3%). In dieser Verbindung ist die Geometrie des Dodecaborat-Anions die eines nahezu idealen Ikosaeders, also weniger verzerrt als in anderen Dodecaboraten. Mittels Tieftemperatur-Guinier-SimonDiffraktometrie wurden Phasenumwandlungen fur [(CH3)4N]2- [B12H12] und [(CH3)4N]2[B12H12](CH3CN bei –70 bzw. bei –15 °C detektiert.
Journal of The Electrochemical Society, 2008
We have investigated how secondary phases appear and disappear upon increasing europium concentra... more We have investigated how secondary phases appear and disappear upon increasing europium concentration from 1.5 to 16.2 atom % in standard strontium borophosphate phosphate phosphor, , using X-ray diffraction and photoluminescence and photoluminescence ...
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A rapid synthesis of chiral sulfoxide-functionalized meta-terphenyl derivatives by a 2,5-[C4+C2] ... more A rapid synthesis of chiral sulfoxide-functionalized meta-terphenyl derivatives by a 2,5-[C4+C2] ring transformation reaction of pyrylium salts with in-situ generated enantio-merically pure .alpha.-sulfinylacetaldehydes is described. This synthetic method demonstrates for the first time the use of .alpha.-sulfinylacetaldehydes in a reaction sequence initiated by nu-cleophilic attack of pyrylium salts by .alpha.-sulfinylcarbanions to generate chiral aromatic systems. The method presented shows broad applicability starting with various methyl sulfoxides and a number of functionalized pyrylium salts, furnishing meta-terphenyls with complex substitution patterns from readily accessible starting compounds.
Physical Review Materials, Dec 28, 2018
The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory Heusler alloys put the... more The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory Heusler alloys put them forward to use in magnetic refrigeration technology. It is associated with a first-order magnetostructural (martensitic) phase transition. We conducted a comprehensive study of the MCE for the off-stoichiometric Heusler alloy Ni 2.2 Mn 0.8 Ga in the vicinity of its first-order magnetostructural phase transition. We found a reversible MCE under repeated magnetic field cycles. The reversible behavior can be attributed to the small thermal hysteresis of the martensitic phase transition. Based on the analysis of our detailed temperature dependent X-ray diffraction data, we demonstrate the geometric compatibility of the cubic austenite and tetragonal martensite phases. This finding directly relates the reversible MCE behavior to an improved geometric compatibility condition between cubic austenite and tetragonal martensite phases. The approach will help to design shape-memory Heusler alloys with a large reversible MCE taking advantage of the first-order martensitic phase transition.
APL Materials, Jun 1, 2023
Manganese monoboride has a low- (α) and a high-temperature (β) modification, as well as a defect-... more Manganese monoboride has a low- (α) and a high-temperature (β) modification, as well as a defect-rich low-temperature variant (α′). The crystal structure (FeB-type structure, s.g. Pnma) and properties of high-temperature MnB are well-known. In this work, single crystals were grown via chemical vapor transport reactions, both of β-MnB and the low-temperature modification, α-MnB. This allowed for determining the crystal structure of defect-free α-MnB [CrB-type structure, s.g. Cmcm, a = 3.0098(6) Å, b = 7.6390(2) Å, and c = 2.94620(6) Å]. Furthermore, α′-MnB, the stacking fault-dominated CrB-variant, was obtained as crystalline powder and characterized by X-ray powder diffraction and transmission electron microscopy. Direction-resolved measurements of the magnetic properties of α-MnB revealed spin-canted magnetic behavior along c and ferromagnetism along a and b with a Curie temperature of 456 K; ferromagnetic β-MnB has a Curie temperature of 568 K.
Computational Materials Science, Sep 1, 2021
A molecular dynamics simulation approach is applied to investigate thermal expansion of the latti... more A molecular dynamics simulation approach is applied to investigate thermal expansion of the lattice parameters and heat capacities of SrMoO 3 and BaMoO 3 perovskite-type molybdates in the temperature range between 300 and 1000 K. The meaningful shape of the pairwise potential for SrMoO 3 and BaMoO 3 is achieved by fitting their lattice parameters to those of the high-purity polycrystalline powders synthesized via reduction of their respective scheelite precursors in hydrogen atmosphere at high pressure. The approach is validated by the simulated temperature dependences of the heat capacity, which follow the reported experimental data near and above the Debye temperature.
Energy technology, May 31, 2021
2015-Sustainable Industrial Processing Summit, Mar 16, 2015
The environmental impact of cement and concrete can be significantly decreased by the reduction o... more The environmental impact of cement and concrete can be significantly decreased by the reduction of the amount of Portland cement clinker. The substitution of the Portland cement clinker with substitutes like limestone powder results in a decrease of hydration products, such as calcium hydroxide. However, a minimum amount of calcium hydroxide and a high density of the hardened cement pastes are necessary to ensure sufficient alkalinity, which is necessary for the passivation of the steel reinforcement during the life cycle of a building. The development of new eco-friendly cements requires a basic understanding regarding the durability against carbonation induced corrosion of the reinforcement. We are investigating low-water limestone-rich concretes with the aim for a sufficient prediction of the carbonation resistance and hope to support the development of sustainable cements. Because of the low content of hydration products, the approved models describing the carbonation behavior of conventional concretes are not working sufficiently for the mixtures investigated here and therefore, need to be modified. For that reason, the individual phase-pure clinker phases were synthesized and after complete hydration stored under CO2 atmosphere (2 Vol %, 20 A°C, 65% humidity) for 28 days. The products of the hydration- and carbonation-reactions were investigated with X-ray powder diffraction, thermal analysis (DTA/TG), scanning electron microscopy and energy-dispersive X-ray analysis. The results are compared to analyses of conventional clinker phases.
Solid State Sciences, Jun 1, 2003
Black amorphous precipitates of unknown composition have been obtained from aqueous solutions of ... more Black amorphous precipitates of unknown composition have been obtained from aqueous solutions of sodium tetrahydridoborate and nickel salts. These precipitates have been analyzed by means of X-ray diffraction, electron microscopy, and electron energy loss spectroscopy, especially focussing on the energy-loss near-edge structure. By comparing the fine structure of the B K ionization edge of the nano-scalic product with that of amorphous boron and crystalline nickel boride, we show that the primary precipitate contains a metal boride formed at room temperature. The precipitate exhibits catalytic activity, e.g. for arylations of arylhalogenides. When annealed, the primary product transforms into crystalline Ni 3 B. An earlier crystal structure determination of Ni 3 B was confirmed by Rietveld refinement of highly resolved synchrotron data.
Handbook of Solid State Chemistry
The environmental impact of cement and concrete can be significantly decreased by the reduction o... more The environmental impact of cement and concrete can be significantly decreased by the reduction of the amount of Portland cement clinker. The substitution of the Portland cement clinker with substitutes like limestone powder results in a decrease of hydration products, such as calcium hydroxide. However, a minimum amount of calcium hydroxide and a high density of the hardened cement pastes are necessary to ensure sufficient alkalinity, which is necessary for the passivation of the steel reinforcement during the life cycle of a building. The development of new eco-friendly cements requires a basic understanding regarding the durability against carbonation induced corrosion of the reinforcement. We are investigating low-water limestone-rich concretes with the aim for a sufficient prediction of the carbonation resistance and hope to support the development of sustainable cements. Because of the low content of hydration products, the approved models describing the carbonation behavior o...