The hexadecafluorophthalocyanine-iron complex FePcF 16 was recently shown to convert olefins into ketones in the presence of stoichiometric amounts of triethylsilane in ethanol at room temperature under an oxygen atmosphere. Herein, we describe an extensive mechanistic investigation for the conversion of 2-vinylnaphthalene into 2-acetylnaphthalene as model reaction. A variety of studies including deuterium-and 18 O 2 -labeling experiments, ESI-MS, and 57 Fe Mössbauer spectroscopy were performed to identify the intermediates involved in the catalytic cycle of the oxidation process. Finally, a detailed and well-supported reaction mechanism for the FePcF 16 -catalyzed Wacker-type oxidation is proposed.
We present a systematic 57 Fe Mössbauer study on highly diluted Fe centers in Li 2 (Li 1−x Fe x )N single crystals as a function of temperature and magnetic field applied transverse and longitudinal with respect to the single-ion anisotropy axis. Below 30 K, the Fe centers exhibit a giant magnetic hyperfine field of BA = 70.25(2) T parallel to the axis of strongest electric field gradient Vzz = −154.0(1) V/Å 2 . Fluctuations of the magnetic hyperfine field are observed between 50 and 300 K and described by the Blume two-level relaxation model. From the temperature dependence of the fluctuation rate, an Orbach spin-lattice relaxation process is deduced. An Arrhenius analysis yields a single thermal activation barrier of ĒA = 570(6) K and an attempt frequency ν0 = 309(10) GHz. Mössbauer spectroscopy studies with applied transverse magnetic fields up to 5 T reveal a large increase of the fluctuation rate by more than one order of magnitude. In longitudinal magnetic fields, a splitting of the fluctuation rate into two branches is observed consistent with a Zeeman induced modification of the energy levels. The experimental observations are qualitatively reproduced by a single-ion effective spin Hamiltonian analysis assuming a Fe 1+ d 7 charge state with the unquenched orbital moment and a J = 7/2 ground state. It is demonstrated that a weak axial single-ion anisotropy D of the order of a few Kelvin can cause a two orders of magnitude larger energy barrier for longitudinal spin fluctuations.
The trinuclear high-spin iron(III) complex [Fe3Cl3(saltagBr)(py)6]ClO4 {H5saltagBr = 1,2,3-tris[(5-bromo-salicylidene)amino]guanidine} was synthesized and characterized by several experimental and theoretical methods. The iron(III) complex exhibits molecular 3-fold symmetry imposed by the rigid ligand backbone and crystallizes in trigonal space group P3̅ with the complex cation lying on a crystallographic C 3 axis. The high-spin states (S = 5/2) of the individual iron(III) ions were determined by Mößbauer spectroscopy and confirmed by CASSCF/CASPT2 ab initio calculations. Magnetic measurements show an antiferromagnetic exchange between the iron(III) ions leading to a geometrically spin-frustrated ground state. This was complemented by high-field magnetization experiments up to 60 T, which confirm the isotropic nature of the magnetic exchange and negligible single-ion anisotropy for the iron(III) ions. Muon-spin relaxation experiments were performed and further prove the isotropic nature of the coupled spin ground state and the presence of isolated paramagnetic molecular systems with negligible intermolecular interactions down to 20 mK. Broken-symmetry density functional theory calculations are consistent with the antiferromagnetic exchange between the iron(III) ions within the presented trinuclear high-spin iron(III) complex. Ab initio calculations further support the absence of appreciable magnetic anisotropy (D = 0.086, and E = 0.010 cm–1) and the absence of significant contributions from antisymmetric exchange, as the two Kramers doublets are virtually degenerate (ΔE = 0.005 cm–1). Therefore, this trinuclear high-spin iron(III) complex should be an ideal candidate for further investigations of spin-electric effects arising exclusively from the spin chirality of a geometrically frustrated S = 1/2 spin ground state of the molecular system.
Besides the well-known hard magnetic materials Nd 2 Fe 14 B [1][2][3][4] and SmCo 5 [5][6][7] also intermetallics, such as RE 2 Fe 4 Sb 5 (RE = La-Nd and Sm), YMn 12−x Fe x and Eu 14 MnSb 11 , have been investigated for exotic magnetic properties, namely spinglass behavior, giant tunable exchange bias, or colossal magnetoresistance. [8][9][10] RE-TM-antimonides, in particular, have received considerable attention from a more fundamental perspective due to their interesting magnetic properties and rich phase diagrams. [11][12][13] The 3d electrons of the TM are usually a source of strong exchange interactions and the RE 4f electrons provide a large magnetocrystalline anisotropy due to strong spin-orbit coupling (SOC). A strong exchange interaction between TM and RE atoms transfers the large anisotropy to the TM atoms. The RE and TM magnetic moments are usually coupled parallel for the light RE and antiparallel for the heavy RE. [12,[14][15][16][17][18][19][20] In 2010, Nasir et al. reported a novel compound, Nd 3 Fe 3 Sb 7 , with a unique hexagonal structure type (P6 3 /m, a = 13.180(2) Å, c = 4.1843(7) Å at T = 293 K). [21] Magnetization measurements on powder samples of Nd 3 Fe 3 Sb 7 showed a pronounced Consolidating a microscopic understanding of magnetic properties is crucial for a rational design of magnetic materials with tailored characteristics. The interplay of 3d and 4f magnetism in rare-earth transition metal antimonides is an ideal platform to search for such complex behavior. Here the synthesis, crystal growth, structure, and complex magnetic properties are reported of the new compound Pr 3 Fe 3 Sb 7 as studied by magnetization and electrical transport measurements in static and pulsed magnetic fields up to 56 T, powder neutron diffraction, and Mößbauer spectroscopy. On cooling without external magnetic field, Pr 3 Fe 3 Sb 7 shows spontaneous magnetization, indicating a symmetry breaking without a compensating domain structure. The Fe substructure exhibits noncollinear ferromagnetic order below the Curie temperature T C ≈ 380 K. Two spin orientations exist, which approximately align along the Fe-Fe bond directions, one parallel to the ab plane and a second one with the moments canting away from the c axis. The Pr substructure orders below 40 K, leading to a spin-reorientation transition (SRT) of the iron substructure. In low fields, the Fe and Pr magnetic moments order antiparallel to each other, which gives rise to a magnetization antiparallel to the external field. At 1.4 K, the magnetization approaches saturation above 40 T. The compound exhibits metallic resistivity along the c axis, with a small anomaly at the SRT.
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