Search

Your search keyword '"Greer, Samuel M."' showing total 137 results
Start Over Author "Greer, Samuel M."
Sorry, I don't understand your search. ×
137 results on '"Greer, Samuel M."'

1. A Four‐Coordinate Pr4+ Imidophosphorane Complex.

Author

Boggiano, Andrew C., Chowdhury, Sabyasachi Roy, Roy, Michael D., Bernbeck, Maximilian G., Greer, Samuel M., Vlaisavljevich, Bess, and La Pierre, Henry S.

Subjects
ELECTRON paramagnetic resonance, MAGNETIC susceptibility, ELECTRONIC structure, RARE earth metals, CRYSTALS
Abstract

The imidophosphorane ligand, [NPtBu3]− (tBu=tert‐butyl), enables isolation of a pseudo‐tetrahedral, tetravalent praseodymium complex, [Pr4+(NPtBu3)4] (1‐Pr), which is characterized by a suite of physical characterization methods including single‐crystal X‐ray diffraction, electron paramagnetic resonance, and L3‐edge X‐ray near‐edge spectroscopies. Variable‐temperature direct‐current magnetic susceptibility data, supported by multiconfigurational quantum chemical calculations, demonstrate that the electronic structure diverges from the isoelectronic Ce3+ analogue, driven by increased crystal field. The four‐coordinate environment around Pr4+ in 1‐Pr, which is unparalleled in reported extended solid systems, provides a unique opportunity to study the interplay between crystal field splitting and spin‐orbit coupling in a molecular tetravalent lanthanide within a pseudo‐tetrahedral coordination geometry. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

7. Superoxide Radicals in Uranyl Peroxide Solids: Lasting Signatures Identified by Electron Paramagnetic Resonance Spectroscopy.

Author

Scherrer, Sarah K., Gates, Cassandra, Rajapaksha, Harindu, Greer, Samuel M., Stein, Benjamin W., and Forbes, Tori Z.

Subjects
ELECTRON paramagnetic resonance spectroscopy, FUEL cycle, RADICALS (Chemistry), PEROXIDES, ELECTRON paramagnetic resonance, SUPEROXIDES, REACTIVE oxygen species
Abstract

U(VI) peroxide phases (studtite and meta‐studtite) are found throughout the nuclear fuel cycle and exist as corrosion products in high radiation fields. Peroxides are part of a family of reactive oxygen species (ROS) that include hydroperoxyl and superoxide species and are produced during alpha radiolysis of water. While U(VI) peroxides have been thoroughly investigated, the incorporation and stability of ROS species within studtite have not been validated. In the current study, electron paramagnetic resonance (EPR) spectroscopy was used to identify the presence of free radicals within a series of U(VI) peroxide samples containing depleted, highly enriched, and natural uranium. Density functional theory calculations indicated that the predicted EPR signals matched well with a superoxide (O2−⋅) species incorporated into the studtite structure, confirming the presence of ROS in the material. Further analysis of samples that were synthesized between 1945 and 2023 indicated that there is a correlation between the radical signal and the product of specific activity multiplied by age of the sample. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

11. Electronic Structure of Three-Coordinate FeIIand CoIIß-Diketiminate Complexes

Author

Nagelski, Alexandra L., Ozerov, Mykhaylo, Fataftah, Majed S., Krzystek, J., Greer, Samuel M., Holland, Patrick L., and Telser, Joshua

Abstract

The ß-diketiminate supporting group, [ArNCRCHCRNAr]-, stabilizes low coordination number complexes. Four such complexes, where R = tert-butyl, Ar = 2,6-diisopropylphenyl, are studied: (nacnactBu)ML, where M = FeII, CoIIand L = Cl, CH3. These are denoted FeCl, FeCH3, CoCl, and CoCH3and have been previously reported and structurally characterized. The two FeIIcomplexes (S= 2) have also been previously characterized by Mo¨ssbauer spectroscopy, but only indirect assessment of the ligand-field splitting and zero-field splitting (zfs) parameters was available. Here, EPR spectroscopy is used, both conventional field-domain for the CoIIcomplexes (with S= 3/2) and frequency-domain, far-infrared magnetic resonance spectroscopy (FIRMS) for all four complexes. The CoIIcomplexes were also studied by magnetometry. These studies allow accurate determination of the zfs parameters. The two FeIIcomplexes are similar with nearly axial zfs and large magnitude zfs given by D= -37 ± 1 cm–1for both. The two CoIIcomplexes likewise exhibit large and nearly axial zfs, but surprisingly, CoClhas positive D= +55 cm–1while CoCH3has negative D= -49 cm–1. Theoretical methods were used to probe the electronic structures of the four complexes, which explain the experimental spectra and the zfs parameters.

Published
2024
Full Text
View/download PDF

13. Extreme g-Tensor Anisotropy and Its Insensitivity to Structural Distortions in a Family of Linear Two-Coordinate Ni(I) Bis-N-heterocyclic Carbene Complexes

Author

Blackaby, William J. M., primary, Harriman, Katie L. M., additional, Greer, Samuel M., additional, Folli, Andrea, additional, Hill, Stephen, additional, Krewald, Vera, additional, Mahon, Mary F., additional, Murphy, Damien M., additional, Murugesu, Muralee, additional, Richards, Emma, additional, Suturina, Elizaveta, additional, and Whittlesey, Michael K., additional

Published
2022
Full Text
View/download PDF

14. Synthesis, solid-state, solution, and theoretical characterization of an “in-cage” scandium-NOTA complex

Author

Aldrich, Kelly E., primary, Popov, Ivan A., additional, Root, Harrison D., additional, Batista, Enrique R., additional, Greer, Samuel M., additional, Kozimor, Stosh A., additional, Lilley, Laura M., additional, Livshits, Maksim Y., additional, Mocko, Veronika, additional, Janicke, Michael T., additional, Scott, Brian L., additional, Stein, Benjamin W., additional, and Yang, Ping, additional

Published
2022
Full Text
View/download PDF

16. Understanding the Photochemical Properties of Polythiophene Polyelectrolyte Soft Aggregates with Sodium Dodecyl Sulfate for Antimicrobial Activity

Author

Livshits, Maksim Y., primary, Yang, Jianzhong, additional, Maghsoodi, Fahimeh, additional, Scheberl, Andrea, additional, Greer, Samuel M., additional, Khalil, Mohammed I., additional, Strach, Edward, additional, Brown, Dylan, additional, Stein, Benjamin W., additional, Reimhult, Erik, additional, Rack, Jeffrey J., additional, Chi, Eva, additional, and Whitten, David G., additional

Published
2021
Full Text
View/download PDF

20. Applying Unconventional Spectroscopies to the Single‐Molecule Magnets, Co(PPh 3 ) 2 X 2 (X=Cl, Br, I): Unveiling Magnetic Transitions and Spin‐Phonon Coupling

Author

Bone, Alexandria N., primary, Widener, Chelsea N., additional, Moseley, Duncan H., additional, Liu, Zhiming, additional, Lu, Zhengguang, additional, Cheng, Yongqiang, additional, Daemen, Luke L., additional, Ozerov, Mykhaylo, additional, Telser, Joshua, additional, Thirunavukkuarasu, Komalavalli, additional, Smirnov, Dmitry, additional, Greer, Samuel M., additional, Hill, Stephen, additional, Krzystek, J., additional, Holldack, Karsten, additional, Aliabadi, Azar, additional, Schnegg, Alexander, additional, Dunbar, Kim R., additional, and Xue, Zi‐Ling, additional

Published
2021
Full Text
View/download PDF

21. Spectroscopic Investigation of a Metal–Metal-Bonded Fe6 Single-Molecule Magnet with an Isolated S = 19/2 Giant-Spin Ground State

Author

Nehrkorn, Joscha, primary, Greer, Samuel M., additional, Malbrecht, Brian J., additional, Anderton, Kevin J., additional, Aliabadi, Azar, additional, Krzystek, J., additional, Schnegg, Alexander, additional, Holldack, Karsten, additional, Herrmann, Carmen, additional, Betley, Theodore A., additional, Stoll, Stefan, additional, and Hill, Stephen, additional

Published
2021
Full Text
View/download PDF

23. Characterizing Polyoxovanadate‐Alkoxide Clusters Using Vanadium K‐Edge X‐Ray Absorption Spectroscopy

Author

Meyer, Rachel L., primary, Greer, Samuel M., additional, Blake, Anastasia V., additional, Cary, Samantha K., additional, Ditter, Alexander S., additional, Daly, Scott R., additional, Li, Feng, additional, Kozimor, Stosh A., additional, Matson, Ellen M., additional, Mocko, Veronika, additional, Seidler, Gerald T., additional, Stein, Benjamin W., additional, and Weinstein, Samuel D., additional

Published
2020
Full Text
View/download PDF

27. Access to Heteroleptic Fluorido‐Cyanido Complexes with a Large Magnetic Anisotropy by Fluoride Abstraction

Author

Liu, Jun‐Liang, primary, Pedersen, Kasper S., additional, Greer, Samuel M., additional, Oyarzabal, Itziar, additional, Mondal, Abhishake, additional, Hill, Stephen, additional, Wilhelm, Fabrice, additional, Rogalev, Andrei, additional, Tressaud, Alain, additional, Durand, Etienne, additional, Long, Jeffrey R., additional, and Clérac, Rodolphe, additional

Published
2020
Full Text
View/download PDF

28. Spectroscopic and electrochemical characterization of a Pr4+ imidophosphorane complex and the redox chemistry of Nd3+ and Dy3+ complexes.

Author

Rice, Natalie T., Popov, Ivan A., Carlson, Rebecca K., Greer, Samuel M., Boggiano, Andrew C., Stein, Benjamin W., Bacsa, John, Batista, Enrique R., Yang, Ping, and La Pierre, Henry S.

Subjects
COMPLEX compounds, ELECTRON paramagnetic resonance spectroscopy, EINSTEIN-Podolsky-Rosen experiment, ELECTROCHEMICAL analysis, OXIDATION states
Abstract

The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr3+(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (1-Pr(NP*)) with AgI at −35 °C. The Pr4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln3+(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*). The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex. [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

29. Access to Heteroleptic Fluorido-Cyanido Complexes with a Large Magnetic Anisotropy by Fluoride Abstraction

Author

Liu, Jun-Liang, Pedersen, Kasper Steen, Greer, Samuel M, Oyarzabal, Itziar, Mondal, Abhishake, Hill, Stephen, Wilhelm, Fabrice, Rogalev, Andrei, Tressaud, Alain, Durand, Etienne, Long, Jeffrey R, Clérac, Rodolphe, Liu, Jun-Liang, Pedersen, Kasper Steen, Greer, Samuel M, Oyarzabal, Itziar, Mondal, Abhishake, Hill, Stephen, Wilhelm, Fabrice, Rogalev, Andrei, Tressaud, Alain, Durand, Etienne, Long, Jeffrey R, and Clérac, Rodolphe

Abstract

Silicon-mediated fluoride abstraction is demonstrated as a means of generating the first fluorido-cyanido transition metal complexes. This new synthetic approach is exemplified by the synthesis and characterization of the heteroleptic complexes, trans-[MIV F4 (CN)2 ]2- (M=Re, Os), obtained from their homoleptic [MIV F6 ]2- parents. As shown by combined high-field electron paramagnetic resonance spectroscopy and magnetization measurements, the partial substitution of fluoride by cyanide ligands leads to a marked increase in the magnetic anisotropy of trans-[ReF4 (CN)2 ]2- as compared to [ReF6 ]2- , reflecting the severe departure from an ideal octahedral (Oh point group) ligand field. This methodology paves the way toward the realization of new heteroleptic transition metal complexes that may be used as highly anisotropic building-blocks for the design of high-performance molecule-based magnetic materials.

Published
2020

30. Radical Dimerization in a Plastic Organic Crystal Leads to Structural and Magnetic Bistability with Wide Thermal Hysteresis

Author

Dragulescu-Andrasi, Alina, primary, Filatov, Alexander S., additional, Oakley, Richard T., additional, Li, Xiang, additional, Lekin, Kristina, additional, Huq, Ashfia, additional, Pak, Chongin, additional, Greer, Samuel M., additional, McKay, Johannes, additional, Jo, Minyoung, additional, Lengyel, Jeff, additional, Hung, Ivan, additional, Maradzike, Elvis, additional, DePrince, A. Eugene, additional, Stoian, Sebastian A., additional, Hill, Stephen, additional, Hu, Yan-Yan, additional, and Shatruk, Michael, additional

Published
2019
Full Text
View/download PDF

32. Applying Unconventional Spectroscopies to the Single‐Molecule Magnets, Co(PPh3)2X2 (X=Cl, Br, I): Unveiling Magnetic Transitions and Spin‐Phonon Coupling.

Author

Bone, Alexandria N., Widener, Chelsea N., Moseley, Duncan H., Liu, Zhiming, Lu, Zhengguang, Cheng, Yongqiang, Daemen, Luke L., Ozerov, Mykhaylo, Telser, Joshua, Thirunavukkuarasu, Komalavalli, Smirnov, Dmitry, Greer, Samuel M., Hill, Stephen, Krzystek, J., Holldack, Karsten, Aliabadi, Azar, Schnegg, Alexander, Dunbar, Kim R., and Xue, Zi‐Ling

Subjects
SINGLE molecule magnets, MAGNETIC transitions, INELASTIC neutron scattering, MAGNETIC relaxation, ELECTRONIC spectra, QUANTUM coherence, EXCITATION spectrum
Abstract

Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single‐molecule magnets (SMMs). Spin‐phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin‐phonon coupling in molecules is challenging. We have found that far‐IR magnetic spectra (FIRMS) of Co(PPh3)2X2 (Co‐X; X=Cl, Br, I) reveal rarely observed spin‐phonon coupling as avoided crossings between magnetic and u‐symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero‐field split (ZFS) levels of the S=3/2 electronic ground state were probed by INS, high‐frequency and ‐field EPR (HFEPR), FIRMS, and frequency‐domain FT terahertz EPR (FD‐FT THz‐EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) and g values. Ligand‐field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities in Co‐X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin‐phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling. [ABSTRACT FROM AUTHOR]

Published
2021
Full Text
View/download PDF

34. Characterizing Polyoxovanadate‐Alkoxide Clusters Using Vanadium K‐Edge X‐Ray Absorption Spectroscopy.

Author

Meyer, Rachel L., Greer, Samuel M., Blake, Anastasia V., Cary, Samantha K., Ditter, Alexander S., Daly, Scott R., Li, Feng, Kozimor, Stosh A., Matson, Ellen M., Mocko, Veronika, Seidler, Gerald T., Stein, Benjamin W., and Weinstein, Samuel D.

Subjects
*X-ray absorption, *X-ray spectroscopy, *VANADIUM, *COUPLING schemes, *METAL compounds
Abstract

A number of technologies would benefit from developing inorganic compounds and materials with specific electronic and magnetic exchange properties. Unfortunately, designing compounds with these properties is difficult because metal⋅⋅⋅metal coupling schemes are hard to predict and control. Fully characterizing communication between metals in existing compounds that exhibit interesting properties could provide valuable insight and advance those predictive capabilities. One such class of molecules are the series of Lindqvist iron‐functionalized and hexavanadium polyoxovanadate‐alkoxide clusters, which we characterized here using V K‐edge X‐ray absorption spectroscopy. Substantial changes in the pre‐edge peak intensities were observed that tracked with the V 3d‐electron count. The data also suggested substantial delocalization between the vanadium cations. Meanwhile, the FeIII cations were electronically isolated from the polyoxovanadate core. [ABSTRACT FROM AUTHOR]

Published
2021
Full Text
View/download PDF

36. High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopic Analysis of Metal–Ligand Covalency in a 4f7Valence Series (Eu2+, Gd3+, and Tb4+)

Author

Gompa, Thaige P., Greer, Samuel M., Rice, Natalie T., Jiang, Ningxin, Telser, Joshua, Ozarowski, Andrew, Stein, Benjamin W., and La Pierre, Henry S.

Abstract

The recent isolation of molecular tetravalent lanthanide complexes has enabled renewed exploration of the effect of oxidation state on the single-ion properties of the lanthanide ions. Despite the isotropic nature of the 8S ground state in a tetravalent terbium complex, [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4], preliminary X-band electron paramagnetic resonance (EPR) measurements on tetravalent terbium complexes show rich spectra with broad resonances. The complexity of these spectra highlights the limits of conventional X-band EPR for even qualitative determination of zero-field splitting (ZFS) in these complexes. Therefore, we report the synthesis and characterization of a novel valence series of 4f7molecular complexes spanning three oxidation states (Eu2+, Gd3+, and Tb4+) featuring a weak-field imidophosphorane ligand system, and employ high-frequency and -field electron paramagnetic resonance (HFEPR) to obtain quantitative values for ZFS across this valence series. The series was designed to minimize deviation in the first coordination sphere from the pseudotetrahedral geometry in order to directly interrogate the role of metal identity and charge on the complexes’ electronic structures. These HFEPR studies are supported by crystallographic analysis and quantum-chemical calculations to assess the relative covalent interactions in each member of this valence series and the effect of the oxidation state on the splitting of the ground state and first excited state.

Published
2021
Full Text
View/download PDF

38. Spin crossover in Fe(II) complexes with N4S2 coordination

Author

Arroyave, Alejandra, Lennartson, Anders, Dragulescu-Andrasi, Alina, Pedersen, Kasper Steen, Piligkos, Stergios, Stoian, Sebastian A., Greer, Samuel M., Pak, Chongin, Hietsoi, Oleksandr, Hoa Phan, Hill, Stephen, McKenzie, Christine J., Shatruk, Michael, Arroyave, Alejandra, Lennartson, Anders, Dragulescu-Andrasi, Alina, Pedersen, Kasper Steen, Piligkos, Stergios, Stoian, Sebastian A., Greer, Samuel M., Pak, Chongin, Hietsoi, Oleksandr, Hoa Phan, Hill, Stephen, McKenzie, Christine J., and Shatruk, Michael

Published
2016

39. Spin Crossover in Fe(II) Complexes with N4S2 Coordination

Author

Arroyave, Alejandra, primary, Lennartson, Anders, additional, Dragulescu-Andrasi, Alina, additional, Pedersen, Kasper S., additional, Piligkos, Stergios, additional, Stoian, Sebastian A., additional, Greer, Samuel M., additional, Pak, Chongin, additional, Hietsoi, Oleksandr, additional, Phan, Hoa, additional, Hill, Stephen, additional, McKenzie, Christine J., additional, and Shatruk, Michael, additional

Published
2016
Full Text
View/download PDF

42. A Dimeric Hydride-Bridged Complex with Geometrically Distinct Iron Centers Giving Rise to an S= 3 Ground State

Author

Hickey, Anne K., Greer, Samuel M., Valdez-Moreira, Juan A., Lutz, Sean A., Pink, Maren, DeGayner, Jordan A., Harris, T. David, Hill, Stephen, Telser, Joshua, and Smith, Jeremy M.

Abstract

Structural and spectroscopic characterization of the dimeric iron hydride complex [Ph2B(tBuIm)2FeH]2reveals an unusual structure in which a tetrahedral iron(II) site (S= 2) is connected to a square planar iron(II) site (S= 1) by two bridging hydride ligands. Magnetic susceptibility reveals strong ferromagnetic coupling between iron centers, with a coupling constant of J= +110(12) cm–1, to give an S= 3 ground state. High-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy confirms this model. A qualitative molecular orbital analysis of the electronic structure, as supported by electronic structure calculations, reveals that the observed spin configuration results from the orthogonal alignment of two geometrically distinct four-coordinate iron fragments held together by highly covalent hydride ligands.

Published
2019
Full Text
View/download PDF

45. Intercalation of Coordinatively Unsaturated FeIII Ion within Interpenetrated Metal-Organic Framework MOF-5.

Author

Holmberg, Rebecca J., Burns, Thomas, Greer, Samuel M., Kobera, Libor, Stoian, Sebastian A., Korobkov, Ilia, Hill, Stephen, Bryce, David L., Woo, Tom K., and Murugesu, Muralee

Subjects
INTERCALATION reactions, COORDINATE covalent bond, IRON ions, METAL-organic frameworks, CHEMICAL structure, SINGLE crystals
Abstract

Coordinatively unsaturated FeIII metal sites were successfully incorporated into the iconic MOF-5 framework. This new structure, FeIII-iMOF-5, is the first example of an interpenetrated MOF linked through intercalated metal ions. Structural characterization was performed with single-crystal and powder XRD, followed by extensive analysis by spectroscopic methods and solid-state NMR, which reveals the paramagnetic ion through its interaction with the framework. EPR and Mössbauer spectroscopy confirmed that the intercalated ions were indeed FeIII, whereas DFT calculations were employed to ascertain the unique pentacoordinate architecture around the FeIII ion. Interestingly, this is also the first crystallographic evidence of pentacoordinate ZnII within the MOF-5 SBU. This new MOF structure displays the potential for metal-site addition as a framework connector, thus creating further opportunity for the innovative development of new MOF materials. [ABSTRACT FROM AUTHOR]

Published
2016
Full Text
View/download PDF

48. Crowded bis ligand complexes of TtzPh,Me with first row transition metals rearrange due to ligand field effects: structural and electronic characterization (TtzPh,Me = tris(3-phenyl-5-methyl-1,2,4-triazolyl)borate)

Author

Oseback, Shannon N., primary, Shim, Sarah W., additional, Kumar, Mukesh, additional, Greer, Samuel M., additional, Gardner, Sean R., additional, Lemar, Keisha M., additional, DeGregory, Paul R., additional, Papish, Elizabeth T., additional, Tierney, David L., additional, Zeller, Matthias, additional, and Yap, Glenn P. A., additional

Published
2012
Full Text
View/download PDF

49. Photoinitiated Dioxygenase-Type Reactivity of Open-Shell 3d Divalent Metal Flavonolato Complexes.

Author

Grubel, Katarzyna, Marts, Amy R., Greer, Samuel M., Tierney, David L., Allpress, Caleb J., Anderson, Stacey N., Laughlin, Brynna J., Smith, Rhett C., Arif, Atta M., and Berreau, Lisa M.

Subjects
METAL complexes, FLAVONOLS, IRRADIATION, REACTIVITY (Chemistry), CATALYSTS, PHOTOCHEMICAL research
Abstract

Irradiation of 3-hydroxyflavonolato (3-Hfl) complexes of MnII, CoII, NiII and CuII ( 1- 4) at 300 nm under aerobic conditions results in dioxygenase-type reactivity and the formation of the corresponding divalent metal O-benzoylsalicylato ( O-bs) complexes 8- 11 and CO. The latter were characterized by using multiple methods, including elemental analysis, X-ray crystallography, NMR and/or EPR spectroscopy, mass spectrometry and IR spectroscopy. Compounds 1- 4 serve as catalysts for the photoinduced reactivity of 3-hydroxyflavonol (3-HflH) to produce O-benzoylsalicylic acid as the major product. Spectroscopic studies (UV/Vis and 1H NMR) show that each O-benzoylsalicylato complex 8- 11 reacts with one equiv. of 3-hydroxyflavonol to regenerate 1- 4 and enable turnover reactivity. Unlike what is observed for free 3-HflH, photoinduced reactions involving 1- 4 and excess flavonol show only minor amounts of flavonol isomerization reactivity. These results indicate that the presence of a metal ion, whether under stoichiometric or catalytic conditions, facilitates the photoinduced degradation of 3-HflH to produce a carboxylic acid and CO as products. [ABSTRACT FROM AUTHOR]

Published
2012
Full Text
View/download PDF

50. Spectroscopic Investigation of a Metal–Metal-Bonded Fe6Single-Molecule Magnet with an Isolated S= 19/2Giant-Spin Ground State

Author

Nehrkorn, Joscha, Greer, Samuel M., Malbrecht, Brian J., Anderton, Kevin J., Aliabadi, Azar, Krzystek, J., Schnegg, Alexander, Holldack, Karsten, Herrmann, Carmen, Betley, Theodore A., Stoll, Stefan, and Hill, Stephen

Abstract

The metal–metal-bonded molecule [Bu4N][(HL)2Fe6(dmf)2] (Fe6) was previously shown to possess a thermally isolated spin S= 19/2ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [J. Am. Chem. Soc.2015, 137, 13949–13956]. Here, we present a comprehensive spectroscopic investigation of this unique single-molecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequency-domain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe6. Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin–spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn12-acetate. The combined high-resolution measurements on both powder samples and an oriented single crystal provide a quantitative measure of the isolated nature of the spin ground state in the Fe6molecule, as well as additional microscopic insights into factors that govern the quantum tunneling of its magnetization. This work suggests strategies for improving the performance of polynuclear SMMs featuring direct metal–metal bonds and strong ferromagnetic spin–spin (exchange) interactions.

Published
2021
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results