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21.
Dr. Markus Hiller Thomas Sittel Prof. Dr. Hubert Wadepohl Prof. Dr. Markus Enders 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10668-10677
Combination of three radical anionic Ph-BIAN ligands (Ph-BIAN=bis-(phenylimino)-acenaphthenequinone) with lanthanoid ions leads to a series of homoleptic, six-coordinate complexes of the type Ln(Ph-BIAN)3. Magnetic coupling data were measured by paramagnetic solution NMR spectroscopy. Combining 1H NMR with 2H NMR of partially deuterated compounds allowed a detailed study of the magnetic susceptibility anisotropies over a large temperature range. The observed chemical shifts were separated into ligand- and metal-centered contributions by comparison with the Y analogue (diamagnetic at the metal). The metal-centered contributions of the complexes with the paramagnetic ions could then be separated into pseudocontact and Fermi contact shifts. The latter is large within the Ph-BIAN scaffold, which shows that magnetic coupling is significant between the lanthanide ion and the radical ligand. Pseudocontact shifts were further correlated to structural data obtained from X-ray diffraction experiments. Ligand-field parameters were determined by fitting the temperature dependence of the observed magnetic susceptibility anisotropies. The electronic structure determined by this approach shows, that the Er and Tm analogues are candidates for single molecule magnets (SMM). These results demonstrate the possibilities for the application of NMR spectroscopy in investigations of paramagnetic systems in general and single molecule magnets in particular. 相似文献
22.
Caleb J. Hiller Dr. Chi Chung Lee Dr. Martin T. Stiebritz Lee A. Rettberg Prof. Dr. Yilin Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2389-2395
Nitrogenase utilizes an ATP-dependent reductase to deliver electrons to its catalytic component to enable two important reactions: the reduction of N2 to NH4+, and the reduction of CO to hydrocarbons. The two nitrogenase-based reactions parallel the industrial Haber–Bosch and Fischer–Tropsch processes, yet they occur under ambient conditions. As such, understanding the enzymatic mechanism of nitrogenase is crucial for the future development of biomimetic strategies for energy-efficient production of valuable chemical commodities. Mechanistic investigations of nitrogenase has long been hampered by the difficulty to trap substrates and intermediates relevant to the nitrogenase reactions. Recently, we have successfully captured CO on the Azotobacter vinelandii V-nitrogenase via two approaches that alter the electron fluxes in a controlled manner: one approach utilizes an artificial electron donor to trap CO on the catalytic component of V-nitrogenase in the resting state; whereas the other employs a mismatched reductase component to reduce the electron flux through the system and consequently accumulate CO on the catalytic component of V-nitrogenase. Here we summarize the major outcome of these recent studies, which not only clarified the catalytic relevance of the one-CO (lo-CO) and multi-CO (hi-CO) bound states of nitrogenase, but also pointed to a potential competition between N2 and CO for binding to the same pair of reactive Fe sites across the sulfur belt of the cofactor. Together, these results highlight the utility of these strategies in poising the cofactor at a well-defined state for substrate- or intermediate-trapping via controlled alteration of electron fluxes, which could prove beneficial for further elucidation of the mechanistic details of nitrogenase-catalyzed reactions. 相似文献
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Dr. Gregorio Guisado‐Barrios Joanna Hiller Prof. Eduardo Peris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10405-10411
Two new palladium complexes with a pyracene‐linked bis‐imidazolylidene (pyrabim) group have been obtained and fully characterized. The related monometallic analogues were obtained from the coordination of an acetanaphthene‐supported N‐heterocyclic carbene (NHC). The catalytic properties of all complexes were studied in the acylation of aryl halides with hydrocinnamaldehyde, and in the Suzuki–Miyaura coupling of aryl halides and aryl boronic acids. The results show that the presence of a second metal in the dimetallic complexes induces some benefits in the catalytic behavior of the complexes. This effect is more pronounced in the Suzuki–Miyaura coupling, for which the dimetallic complexes exhibit significantly higher activity than their monometallic counterparts. 相似文献
26.
Dr. Sonja Pullen Dr. Alexander Hegmans Prof. Wolf G. Hiller André Platzek Prof. Eva Freisinger Prof. Bernhard Lippert 《ChemistryOpen》2021,10(1):28-45
The conversion of the 1 : 1-complex of Cisplatin with 1-methyluracil (1MeUH), cis-[Pt(NH3)2(1MeU-N3)Cl] ( 1 a ) to the aqua species cis-[Pt(NH3)2(1MeU-N3)(OH2)]+ ( 1 b ), achieved by reaction of 1 a with AgNO3 in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH3 ligands. In dilute aqueous solution, 1 a , and dinuclear compounds cis-[(NH3)2(1MeU-N3)Pt(μ-OH)Pt(1MeU-N3)(NH3)2]+( 3 ) as well as head-tail cis-[Pt2(NH3)4(μ-1MeU-N3,O4)2]2+ ( 4 ) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of 1H NMR and ESI-MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ-OH, μ-1MeU, and μ-NH2 bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N2 complex, [Pt(NH3)(1MeU)(N2)]+ appears to be formed in gas phase during the ESI-MS experiment. In the presence of Na+ ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non-metalated uracil quartets found in tetrastranded RNA. 相似文献
27.
Dr. Irán Rojas-León Gelen Gómez-Jaimes Dr. Pedro Montes-Tolentino Prof. Dr. Wolf Hiller Dr. Hazem Alnasr Prof. Dr. Braulio Rodríguez-Molina Dr. Irán F. Hernández-Ahuactzi Prof. Dr. Hiram Beltrán Prof. Dr. Klaus Jurkschat Prof. Dr. Herbert Höpfl 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(48):12276-12283
Hydrolysis reactions of di- and trinuclear organotin halides yielded large novel cage compounds containing Sn−O−Sn bridges. The molecular structures of two octanuclear tetraorganodistannoxanes showing double-ladder motifs, viz., [{Me3SiCH2(Cl)SnCH2YCH2Sn(OH)CH2SiMe3}2(μ-O)2]2 [ 1 , Y=p-(Me)2SiC6H4-C6H4Si(Me)2] and [{Me3SiCH2(I)SnCH2YCH2Sn(OH)CH2SiMe3}2(μ-O)2]2 ⋅ 0.48 I2 [ 2⋅ 0.48 I2, Y=p-(Me)2SiC6H4-C6H4Si(Me)2], and the hexanuclear cage-compound 1,3,6-C6H3(p-C6H4Si(Me)2CH2Sn(R)2OSn(R)2CH2Si(Me)2C6H4-p)3C6H3-1,3,6 ( 3 , R=CH2SiMe3) are reported. Of these, the co-crystal 2⋅ 0.48 I2 exhibits the largest spacing of 16.7 Å reported to date for distannoxane-based double ladders. DFT calculations for the hexanuclear cage and a related octanuclear congener accompany the experimental work. 相似文献
28.
Henry W. Orton Dr. Jan Stanek Dr. Tobias Schubeis Dylan Foucaudeau Claire Ollier Dr. Adrian W. Draney Dr. Tanguy Le Marchand Dr. Diane Cala-De Paepe Prof. Dr. Isabella C. Felli Prof. Dr. Roberta Pierattelli Prof. Dr. Sebastian Hiller Dr. Wolfgang Bermel Dr. Guido Pintacuda 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(6):2400-2405
29.
Dipl.-Ing. H. Bartels Priv. Doz. Dr.-Ing. habil. M. Hiller 《Archive of Applied Mechanics (Ingenieur Archiv)》1982,52(1-2):47-61
Übersicht Für ein allgemeines räumliches Gelenkviereck, das in vielen technischen Anwendungen als Antriebselement oder Übertragungsglied auftritt, werden mit Hilfe von Impuls- und Drallsätzen die Bewegungsgleichungen aufgestellt, um so gleichzeitig die praktisch interessierenden Lager- und Gelenkreaktionen mit zu erfassen. Dabei hängt das dynamische Verhalten des Gelenkviereckes wesentlich von der technischen Ausführung der gelenkigen Verbindungen ab. Die Arbeitsweise des zur Lösung der Bewegungsgleichungen entwickelten numerischen Verfahrens wird an einem Beispiel demonstriert.
Analysis ot the dynamical behaviour of spatial four-bar mechanisms
Summary The equations of motion for the general spatial four-bar mechanism which appears in many technical applications, are derived by means of the theorems of momentum and moment of momentum. Thus, the reaction forces in the bearings and the combining hinges can be calculated simultaneously. Furthermore, the dynamical behaviour of the four-bar mechanism depends on the technical realization of the hinged articulations. The equations of motion are solved numerically, and the procedure is demonstrated by an example.相似文献
30.
Ground-state hyperfine splittings in hydrogen and muonium are very well measured. Their difference, after correcting for magnetic moment and reduced mass effects, is due solely to proton structure-the large QED contributions for a pointlike nucleus essentially cancel. The rescaled hyperfine difference depends on the Zemach radius, a fundamental measure of the proton, computed as an integral over a product of electric and magnetic proton form factors. The determination of the Zemach radius, (1.019+/-0.016) fm, from atomic physics tightly constrains fits to accelerator measurements of proton form factors. Conversely, we can use muonium data to extract an experimental value for QED corrections to hydrogenic hyperfine data. There is a significant discrepancy between measurement and theory, in the same direction as a corresponding discrepancy in positronium. 相似文献