Fourth-order zero-field splitting parameters of [Mn(cyclam)Br2]Br determined by single-crystal W-band EPR (original) (raw)
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Inorganic Chemistry, 2005
The complex [Mn(dbm) 2 (py) 2 ](ClO 4 ) (dbm ) anion of 1,3-diphenyl-1,3-propanedione (dibenzoylmethane), py ) pyridine) was synthesized and characterized by X-ray crystallography. It has tetragonally distorted geometry with the axial positions occupied by the py ligands and the equatorial positions by the dbm ligands. This mononuclear complex of high-spin Mn(III) (3d 4 , S ) 2) was studied by high-frequency and -field electron paramagnetic resonance (HFEPR) both as a solid powder and in frozen dichloromethane solution. Very high quality HFEPR spectra were recorded over a wide range of frequencies. The complete dataset of resonant magnetic fields versus transition energies was analyzed using automated fitting software. This analysis yielded the following spin Hamiltonian parameters (energies in cm -1 ): D ) −4.504(2), E ) −0.425(1), B 4 0 ) −1.8(4) × 10 -4 , B 4 2 ) 7(3) × 10 -4 , B 4 4 ) 48(4) × 10 -4 , g x ) 1.993(1), g y ) 1.994(1), and g z ) 1.983(1), where the B 4 n values represent fourth-order zero-field splitting terms that are generally very difficult to extract, even from single-crystal measurements. The results here demonstrate the applicability of HFEPR at high-precision measurements, even for powder samples. The zero-field splitting parameters determined here for [Mn(dbm) 2 (py) 2 ] + are placed into the context of those determined for other mononuclear complexes of Mn(III).
Journal of the American Chemical Society, 2011
A high spin (S) compound has been synthesized whose properties straddle the interface between the classical and quantum mechanical spin descriptions. The cluster [Mn 7 O 4 (pdpm) 6 (N 3) 4 ](ClO 4) 2 (Mn 7) has an unprecedented core structure comprising an octahedral [Mn III 6 (μ 4-O)(μ 3-O) 3 (μ 3-N 3) 4 ] 6+ unit with one of its faces capped by a Mn II ion. Magnetization and susceptibility studies indicate an S = 29 / 2 ground state, the maximum possible. Variable-temperature, high-frequency electron paramagnetic resonance (HF-EPR) spectra on powder and single-crystal samples of Mn 7 exhibit sharp spectral features characteristic of a quantum spin that are well resolved in a certain temperature range but which transform to a continuum of peaks characteristic of a classical spin in another; these features have been well reproduced by computer simulations. A fast Fourier transform analysis of the sharp spectral features and the low temperature EPR spectra suggests that more than one spin state are involved.
Applied Magnetic Resonance, 2001
High-frequency and -field electron paramagnetic resonance (HFEPR) has been used to study several complexes of high-spin manganese(lIl) (3d4, S = 2): [Mn(Me,dbm)X] and [Mn(OEP)X] (X = Cl-, Br-), where Me,dbm-is the anion of 4,4' -dimethyldibenzoylmethane and OEP'-is the dianion of 2, 3,7,8,12,13,17, 18-oetaethylporphine. These non-Kramers (integer spin) systems are not EPR-active with conventional magnetic fields and microwave frequencies. However, use of fields up to 15 T in combination with multiple frequencies in the range of 95-550 GHz allows observation of richly detailed EPR spectra. Analysis of the field-and frequency-dependent HFEPR data allows accurate determination of the following spin Hamiltonian parameters for these complexes: [Mn(Me,dbm)CI], D = -2.45(3) cm-I; [Mn(Me,dbm)Br], D = -1.40(2) cm-I; [Mn(OEP)CI], D = -2.40(1) em-I; [Mn(OEP)Br], D = -1.07(1) em-I (E'" 0, and g~2.0 in all cases). Comparison of structural data with the electronic parameters for these and related complexes shows quantitatively the effects of axial and equatorial ligation on the electronic structure of Mn(lIl). These high-spin complexes can be employed as building blocks in the construction of single-molecule magnets. Thus the accurate determination and understanding of the electronic properties, best obtainable by HFEPR, of these monomeric units is important in understanding and improving the properties of the polynuclear single-molecule magnets which can be formed from them.
Inorganic Chemistry, 2008
GHz electron paramagnetic resonance experiments on a powder sample of the magnetic molecule Mn 19 with a high-spin ground state S) 83 / 2 are presented. At low temperatures, the data are well described by the simulated spectra for an isolated spin with a zero-field-splitting parameter D) 0.004 cm-1 , which is, in particular, positive. Hence, Mn 19 is not a single-molecule magnet; the previously observed magnetic hysteresis at ultralow temperatures is likely due to intermolecular dipolar interactions.
Inorganic Chemistry Communications, 2012
The reaction of [Mn III (5-Brsalen)(MeOH)](ClO 4 ) (5-Brsalen 2− =N,N′-ethylenebis(5-bromosalicylidene-iminate)) with [Ir III (CN) 6 ] 3− yields a trinuclear, cyanide-bridged Mn III -Ir III -Mn III cluster which is a member of an isostructural series of Mn III -M III -Mn III clusters. The presence of the large, diamagnetic [Ir III (CN) 6 ] 3− bridging unit facilitates a precise determination of the Mn III zero-field splitting (zfs) parameters by the combined use of inelastic neutron scattering, high-field, high-frequency EPR spectroscopy and magnetic measurements. The single-ion axial (D) and rhombic (E) zfs parameters are found to be D=−3.72(5) cm −1 and |E|=0.21(1) cm −1 . The experimental data are consistent with a small, antiferromagnetic exchange interaction between the two Mn III ions.
Journal of Physics: Condensed Matter, 2011
Properties of the manganese-based single-molecu le magnet [Mn~I1CrIlI]3+ are studied . It contains six Mnlll ions arranged in two bowl-shaped trinuclear triplesalen building blocks linked by a hexacyanochromate and exhibits a large spin ground state of Sl = 21/2. The dominant structures in the electron emission spectra of [Mn~I1CrI1l]3+ resonantly excited at the L3 -edge are the L3M2,3M2,3, L3M2,3 V and L3 VV Auger emission groups following the decay of the primary P3/2 core hole state. Significant differences of the Auger spectra from intact and degraded [Mn~I1CrllIl3+ show up. First measurements of the electron spin polarization in the L 3 M 2 ,3 V and L3 VV Auger emission peaks from the manganese constituents in [Mn~ICrllI]3+ resonantly excited at the L3 -edge near 640 eV by circularly polarized synchrotron radiation are reported. In addition spin resolved Auger electron spectra of the reference substances MnO, Mn20 3 and Mnll (acetatehAH 2 0 are given. The applicability of spin resolved electron spectroscopy for characterizing magnetic states of constituent atoms compared to magnetic circu lar dichroism (MCD) is vcrificd: thc spin polari zati o n obtaincd from Mn ll (acetatehAH 2 0 at room temperature in the paramagnetic state compares to the MCD asymmetry revealed for a star-shaped molecule with a Mn~I06 core at 5 K in an external mag netic fi eld of 5 T.
High-frequency EPR characterization of a triangular Mn3 single-molecule magnet
Polyhedron, 2007
We present the results of a multi-high-frequency single-crystal EPR study of a recently discovered triangular trinuclear Mn complex, [Mn 3 O(O 2 CMe) 3 (mpko) 3 ](ClO 4) AE 3CH 2 Cl 2. The obtained data set confirm the findings of earlier magnetic measurements, which suggested that this complex is a single-molecule magnet with a spin ground state of S = 6. The zero-field splitting parameters obtained from the present EPR study are: D = À0.3 cm À1 , B 0 4 ¼ À3 Â 10 À5 cm À1 and g = 2.00. We also find a significant transverse anisotropy which can be parameterized by a rhombic distortion with an E value of at least 0.015 cm À1 .
Eletron-Spin Dynamics in the Two-Dimensional Compound [NH3(CH2)4NH3]MnCl4
Physica Status Solidi B-basic Solid State Physics, 1993
The two-dimensional (2D) system [NH,(CH,),NH,]MnCl, is investigated by means of electron spin resonance (ESR) at X-band over the 40 to 300 K temperature range. The linewidth, the g-factor, the spin-lattice relaxation time T I , and their thermal and angular dependences are measured. The data are characteristic of a 2D compound. The angular dependence AH(0) indicates, taking also into account the presence of a half-field line, the diffusive character of the magnetization at long time. The observed thermal dependences are consistent with an antiferromagnetic order at 40 K. The experimental data are interpreted using the Bloembergen and Wang three-reservoir model since a strong exchange interaction is present.
Physical Review B, 2002
We report the electronic structure and magnetic ordering of the single molecule magnet [Mn10O4(2,2'biphenoxide)4Br12] 4− based on first-principles all-electron density-functional calculations. We find that two of the ten core Mn atoms are coupled antiferromagnetically to the remaining eight, resulting in a ferrimagnetic ground state with total spin S = 13. The calculated magnetic anisotropy barrier is found to be 9 K in good agreement with experiment. The presence of the Br anions impact the electronic structure and therefore the magnetic properties of the 10 Mn atoms. However, the electric field due to the negative charges has no significant effect on the magnetic anisotropy.