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George Christou - One of the best experts on this subject based on the ideXlab platform.
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synthesis structure and spectroscopic and magnetic characterization of mn12o12 o2cch2but 16 meoh 4 meoh a mn12 single molecule magnet with true Axial Symmetry
Inorganic Chemistry, 2013Co-Authors: Christos Lampropoulos, Muralee Murugesu, Andrew G Harter, Wolfgang Wernsdofer, Stephen Hill, Naresh S Dalal, A P Reyes, Philip L Kuhns, Khalil A Abboud, George ChristouAbstract:The synthesis and properties are reported of a rare example of a Mn12 single-molecule magnet (SMM) in truly Axial Symmetry (tetragonal, I4). [Mn12O12(O2CCH2But)16(MeOH)4]·MeOH (3·MeOH) was synthesized by carboxylate substitution on [Mn12O12(O2CMe)16(H2O)4]·2MeCO2H·4H2O (1). The complex was found to possess an S = 10 ground state, as is typical for the Mn12 family, and displayed both frequency-dependent out-of-phase AC susceptibility signals and hysteresis loops in single-crystal magnetization vs DC field sweeps. The loops also exhibited quantum tunneling of magnetization steps at periodic field values. Single-crystal, high-frequency electron paramagnetic resonance spectra on 3·MeOH using frequencies up to 360 GHz revealed perceptibly sharper signals than for 1. Moreover, careful studies as a function of the magnetic field orientation did not reveal any satellite peaks, as observed for 1, suggesting that the crystals of 3 are homogeneous and do not contain multiple Mn12 environments. In the single-crystal...
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the properties of the mn12o12 o2cr 16 h2o 4 single molecule magnets in truly Axial Symmetry mn12o12 o2cch2br 16 h2o 4 4ch2cl2
Journal of the American Chemical Society, 2006Co-Authors: N E Chakov, Wolfgang Wernsdorfer, Andrew G Harter, Stephen Hill, Naresh S Dalal, A P Reyes, Philip L Kuhns, Khalil A Abboud, Shengchiang Lee, George ChristouAbstract:Detailed studies are reported of a Mn(12) single-molecule magnet (SMM) in truly Axial (tetragonal) Symmetry. The complex is [Mn(12)O(12)(O(2)CCH(2)Br)(16)(H(2)O)(4)].4CH(2)Cl(2) (2.4CH(2)Cl(2) or Mn(12)-BrAc), obtained by the standard carboxylate substitution method. The complex has an S = 10 ground state, typical of the Mn(12) family, and displays frequency-dependent out-of-phase AC susceptibility signals and hysteresis in single-crystal magnetization vs applied DC field sweeps. Single-crystal high-frequency EPR spectra in frequencies up to 360 GHz exhibit narrow signals that are not overlapping multiplets, in contrast to [Mn(12)O(12)(O(2)CMe)(16)(H(2)O)(4)].2MeCO(2)H.4H(2)O (1 or Mn(12)-Ac), which also crystallizes in an Axial (tetragonal) space group but which now is recognized to consist of a mixture of six hydrogen-bonded isomers in the crystal and thus gives multiple, inhomogeneously broadened EPR signals. Similarly, single-crystal (55)Mn NMR spectra on Mn(12)-BrAc display much sharper signals than a single crystal of Mn(12)-Ac, and this allows one Mn(III) signal to show an almost baseline-resolved quintet from quadrupolar splitting ((55)Mn, I = 5/2, 100%), allowing quadrupole coupling parameters (e(2)qQ) to be determined. In addition, it was found that crushing crystals of Mn(12)-BrAc into a microcrystalline powder causes severe broadening and shifts of the NMR resonances, emphasizing the superiority of single-crystal studies. The combined results establish that Mn(12)-BrAc is far superior to Mn(12)-Ac for the study of the intrinsic properties of the Mn(12) family of SMMs in Axial Symmetry, and for the search for new phenomena such as quantum interference effects caused by higher-order (>2nd-order) transverse terms in the spin Hamiltonian.
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resonant tunneling in truly Axial Symmetry mn 12 single molecule magnets sharp crossover between thermally assisted and pure quantum tunneling
Physical Review Letters, 2006Co-Authors: Wolfgang Wernsdorfer, Muralee Murugesu, George ChristouAbstract:Magnetization measurements of a truly Axial Symmetry ${\mathrm{Mn}}_{12}\mathrm{\text{\ensuremath{-}}}t\mathrm{BuAc}$ molecular nanomagnet with a spin ground state of $S=10$ show resonant tunneling. This compound has the same magnetic anisotropy as ${\mathrm{Mn}}_{12}\mathrm{\text{\ensuremath{-}}}\mathrm{Ac}$ but the molecules are better isolated and the crystals have less disorder and a higher Symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The results establish a sharp crossover between thermally assisted and pure quantum tunneling, as had been previously predicted.
Michael Manuel - One of the best experts on this subject based on the ideXlab platform.
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phylogeny and evolution of calcareous sponges monophyly of calcinea and calcaronea high level of morphological homoplasy and the primitive nature of Axial Symmetry
Systematic Biology, 2003Co-Authors: Michael Manuel, Carole Borchiellini, Eliane Alivon, Yannick Le Parco, Jean Vacelet, Nicole BouryesnaultAbstract:Because calcareous sponges are triggering renewed interest with respect to basal metazoan evolution, a phyloge- netic framework of their internal relationships is needed to clarify the evolutionary history of key morphological characters. Morphological variation was scored at the suprageneric level within Calcispongia, but little phylogenetic information could be retrieved from morphological characters. For the main subdivision of Calcispongia, the analysis of morphological data weakly supports a classification based upon cytological and embryological characters (Calcinea/Calcaronea) rather than the older classification scheme based upon the aquiferous system (Homocoela/Heterocoela). The 18S ribosomal RNA data were then analyzed, both alone and in combination with morphological characters. The monophyly of Calcispongia is highly supported, but the position of this group with respect to other sponge lineages and to eumetazoan taxa is not resolved. The monophyly of both Calcinea and Calcaronea is retrieved, and the data strongly rejected the competing Homo- coela/Heterocoela hypothesis. The phylogeny implies that characters of the skeleton architecture are highly homoplastic, as are characters of the aquiferous system. However, Axial Symmetry seems to be primitive for all Calcispongia, a conclusion that has potentially far-reaching implications for hypotheses of early body plan evolution in Metazoa. (Axial Symmetry; Calcarea; Calcispongia; evolution; Metazoa; phylogeny; Porifera; 18S rRNA.)
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phylogeny and evolution of calcareous sponges monophyly of calcinea and calcaronea high level of morphological homoplasy and the primitive nature of Axial Symmetry
Systematic Biology, 2003Co-Authors: Michael Manuel, Carole Borchiellini, Eliane Alivon, Yannick Le Parco, Jean Vacelet, Nicole BouryesnaultAbstract:Because calcareous sponges are triggering renewed interest with respect to basal metazoan evolution, a phylogenetic framework of their internal relationships is needed to clarify the evolutionary history of key morphological characters. Morphological variation was scored at the suprageneric level within Calcispongia, but little phylogenetic information could be retrieved from morphological characters. For the main subdivision of Calcispongia, the analysis of morphological data weakly supports a classification based upon cytological and embryological characters (Calcinea/Calcaronea) rather than the older classification scheme based upon the aquiferous system (Homocoela/Heterocoela). The 18S ribosomal RNA data were then analyzed, both alone and in combination with morphological characters. The monophyly of Calcispongia is highly supported, but the position of this group with respect to other sponge lineages and to eumetazoan taxa is not resolved. The monophyly of both Calcinea and Calcaronea is retrieved, and the data strongly rejected the competing Homocoela/Heterocoela hypothesis. The phylogeny implies that characters of the skeleton architecture are highly homoplastic, as are characters of the aquiferous system. However, Axial Symmetry seems to be primitive for all Calcispongia, a conclusion that has potentially far-reaching implications for hypotheses of early body plan evolution in Metazoa.
Nicole Bouryesnault - One of the best experts on this subject based on the ideXlab platform.
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phylogeny and evolution of calcareous sponges monophyly of calcinea and calcaronea high level of morphological homoplasy and the primitive nature of Axial Symmetry
Systematic Biology, 2003Co-Authors: Michael Manuel, Carole Borchiellini, Eliane Alivon, Yannick Le Parco, Jean Vacelet, Nicole BouryesnaultAbstract:Because calcareous sponges are triggering renewed interest with respect to basal metazoan evolution, a phyloge- netic framework of their internal relationships is needed to clarify the evolutionary history of key morphological characters. Morphological variation was scored at the suprageneric level within Calcispongia, but little phylogenetic information could be retrieved from morphological characters. For the main subdivision of Calcispongia, the analysis of morphological data weakly supports a classification based upon cytological and embryological characters (Calcinea/Calcaronea) rather than the older classification scheme based upon the aquiferous system (Homocoela/Heterocoela). The 18S ribosomal RNA data were then analyzed, both alone and in combination with morphological characters. The monophyly of Calcispongia is highly supported, but the position of this group with respect to other sponge lineages and to eumetazoan taxa is not resolved. The monophyly of both Calcinea and Calcaronea is retrieved, and the data strongly rejected the competing Homo- coela/Heterocoela hypothesis. The phylogeny implies that characters of the skeleton architecture are highly homoplastic, as are characters of the aquiferous system. However, Axial Symmetry seems to be primitive for all Calcispongia, a conclusion that has potentially far-reaching implications for hypotheses of early body plan evolution in Metazoa. (Axial Symmetry; Calcarea; Calcispongia; evolution; Metazoa; phylogeny; Porifera; 18S rRNA.)
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phylogeny and evolution of calcareous sponges monophyly of calcinea and calcaronea high level of morphological homoplasy and the primitive nature of Axial Symmetry
Systematic Biology, 2003Co-Authors: Michael Manuel, Carole Borchiellini, Eliane Alivon, Yannick Le Parco, Jean Vacelet, Nicole BouryesnaultAbstract:Because calcareous sponges are triggering renewed interest with respect to basal metazoan evolution, a phylogenetic framework of their internal relationships is needed to clarify the evolutionary history of key morphological characters. Morphological variation was scored at the suprageneric level within Calcispongia, but little phylogenetic information could be retrieved from morphological characters. For the main subdivision of Calcispongia, the analysis of morphological data weakly supports a classification based upon cytological and embryological characters (Calcinea/Calcaronea) rather than the older classification scheme based upon the aquiferous system (Homocoela/Heterocoela). The 18S ribosomal RNA data were then analyzed, both alone and in combination with morphological characters. The monophyly of Calcispongia is highly supported, but the position of this group with respect to other sponge lineages and to eumetazoan taxa is not resolved. The monophyly of both Calcinea and Calcaronea is retrieved, and the data strongly rejected the competing Homocoela/Heterocoela hypothesis. The phylogeny implies that characters of the skeleton architecture are highly homoplastic, as are characters of the aquiferous system. However, Axial Symmetry seems to be primitive for all Calcispongia, a conclusion that has potentially far-reaching implications for hypotheses of early body plan evolution in Metazoa.
P J Diamond - One of the best experts on this subject based on the ideXlab platform.
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Axial Symmetry and rotation in the sio maser shell of ik tauri
arXiv: Astrophysics, 2005Co-Authors: D A Boboltz, P J DiamondAbstract:We observed v=1, J=1-0 43-GHz SiO maser emission toward the Mira variable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 x 32 mas with an Axial ratio of 1.8:1. The major axis of this elliptical distribution is oriented at position angle of ~59 deg. The line-of-sight velocity structure of the SiO masers has an apparent axis of Symmetry consistent with the elongation axis of the maser distribution. Relative to the assumed stellar velocity of 35 km/s, the blue- and red-shifted masers were found to lie to the northwest and southeast of this Symmetry axis respectively. This velocity structure suggests a NW-SE rotation of the SiO maser shell with an equatorial velocity, which we determine to be ~3.6 km/s. Such a NW-SE rotation is in agreement with a circumstellar envelope geometry invoked to explain previous water and OH maser observations. In this geometry, water and OH masers are preferentially created in a region of enhanced density along the NE-SW equator orthogonal to the rotation/polar axis suggested by the SiO maser velocities.
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Axial Symmetry and rotation in the sio maser shell of ik tauri
The Astrophysical Journal, 2005Co-Authors: D A Boboltz, P J DiamondAbstract:We observed v = 1, J = 1-0 43 GHz SiO maser emission toward the Mira variable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 × 32 mas with an Axial ratio of 1.8 : 1. The major axis of this elliptical distribution is oriented at a position angle of ~59°. The line-of-sight velocity structure of the SiO masers has an apparent axis of Symmetry consistent with the elongation axis of the maser distribution. Relative to the assumed stellar velocity of 35 km s-1, the blue- and redshifted masers were found to lie to the northwest and southeast of this Symmetry axis, respectively. This velocity structure suggests a northwest-southeast (NW-SE) rotation of the SiO maser shell with an equatorial velocity, which we determine to be ~3.6 km s-1. Such a NW-SE rotation is in agreement with a circumstellar envelope geometry invoked to explain previous H2O and OH maser observations. In this geometry, H2O and OH masers are preferentially created in a region of enhanced density along the NE-SW equator orthogonal to the rotation/polar axis suggested by the SiO maser velocities.
Wolfgang Wernsdorfer - One of the best experts on this subject based on the ideXlab platform.
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the solvent effect in an Axially symmetric fe 4 iii single molecule magnet
Chemical Communications, 2014Co-Authors: Wolfgang Wernsdorfer, Yuanyuan Zhu, Tingting Yin, Shangda Jiang, Annelaure Barra, Petr Neugebauer, Raphael Marx, Maria DorfelAbstract:A pair of enantiopure FeIII4 SMMs with Axial Symmetry was synthesized and characterized by magnetization and high-frequency electron paramagnetic resonance methods. The results reveal that the Axial Symmetry of the structure is broken by the interaction of FeIII4 with the disordered solvent molecules.
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the properties of the mn12o12 o2cr 16 h2o 4 single molecule magnets in truly Axial Symmetry mn12o12 o2cch2br 16 h2o 4 4ch2cl2
Journal of the American Chemical Society, 2006Co-Authors: N E Chakov, Wolfgang Wernsdorfer, Andrew G Harter, Stephen Hill, Naresh S Dalal, A P Reyes, Philip L Kuhns, Khalil A Abboud, Shengchiang Lee, George ChristouAbstract:Detailed studies are reported of a Mn(12) single-molecule magnet (SMM) in truly Axial (tetragonal) Symmetry. The complex is [Mn(12)O(12)(O(2)CCH(2)Br)(16)(H(2)O)(4)].4CH(2)Cl(2) (2.4CH(2)Cl(2) or Mn(12)-BrAc), obtained by the standard carboxylate substitution method. The complex has an S = 10 ground state, typical of the Mn(12) family, and displays frequency-dependent out-of-phase AC susceptibility signals and hysteresis in single-crystal magnetization vs applied DC field sweeps. Single-crystal high-frequency EPR spectra in frequencies up to 360 GHz exhibit narrow signals that are not overlapping multiplets, in contrast to [Mn(12)O(12)(O(2)CMe)(16)(H(2)O)(4)].2MeCO(2)H.4H(2)O (1 or Mn(12)-Ac), which also crystallizes in an Axial (tetragonal) space group but which now is recognized to consist of a mixture of six hydrogen-bonded isomers in the crystal and thus gives multiple, inhomogeneously broadened EPR signals. Similarly, single-crystal (55)Mn NMR spectra on Mn(12)-BrAc display much sharper signals than a single crystal of Mn(12)-Ac, and this allows one Mn(III) signal to show an almost baseline-resolved quintet from quadrupolar splitting ((55)Mn, I = 5/2, 100%), allowing quadrupole coupling parameters (e(2)qQ) to be determined. In addition, it was found that crushing crystals of Mn(12)-BrAc into a microcrystalline powder causes severe broadening and shifts of the NMR resonances, emphasizing the superiority of single-crystal studies. The combined results establish that Mn(12)-BrAc is far superior to Mn(12)-Ac for the study of the intrinsic properties of the Mn(12) family of SMMs in Axial Symmetry, and for the search for new phenomena such as quantum interference effects caused by higher-order (>2nd-order) transverse terms in the spin Hamiltonian.
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resonant tunneling in truly Axial Symmetry mn 12 single molecule magnets sharp crossover between thermally assisted and pure quantum tunneling
Physical Review Letters, 2006Co-Authors: Wolfgang Wernsdorfer, Muralee Murugesu, George ChristouAbstract:Magnetization measurements of a truly Axial Symmetry ${\mathrm{Mn}}_{12}\mathrm{\text{\ensuremath{-}}}t\mathrm{BuAc}$ molecular nanomagnet with a spin ground state of $S=10$ show resonant tunneling. This compound has the same magnetic anisotropy as ${\mathrm{Mn}}_{12}\mathrm{\text{\ensuremath{-}}}\mathrm{Ac}$ but the molecules are better isolated and the crystals have less disorder and a higher Symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The results establish a sharp crossover between thermally assisted and pure quantum tunneling, as had been previously predicted.