Magnetic properties and electronic structure of manganese(III) porphyrins

“…Such information can in principle also be obtained by magnetic susceptibility, as was done with several Mn(III) porphyrin complexes [26,27,31]. The advantage of HFEPR is that this resonance technique provides higher precision and accuracy in the g tensor and D, including the sign of D, than do bulk magnetic measurements.…”

Section: Hfepr Spectroscopy and Analysismentioning

confidence: 99%

“…The relation of ligand field to zfs in Mn(III) porphyrins was first pointed out by Dugad et al [31], who semiquantitatively evaluated the contributions to D. We employed their method in our earlier studies of [Mn(TPP)Cl] [20] and [MnCor] [14]. Briefly, for an axially elongated (e.g., square-pyramidal) system, as is the case here for both the Me2dbm-and OEP2-complexes of Mn(III), the zfs is expected to be negative (D < 0) [31].…”

Section: Relation Of Structure To Spin Hamiltonian Parametersmentioning

confidence: 99%

“…Briefly, for an axially elongated (e.g., square-pyramidal) system, as is the case here for both the Me2dbm-and OEP2-complexes of Mn(III), the zfs is expected to be negative (D < 0) [31]. As for the magnitude of ID1, the equatorial ligand field determines the value of zl, the d-d2_2 energy separation, and the axial ligand determines the value of 8, the dxy d,, Yz energy separation.…”

Section: Relation Of Structure To Spin Hamiltonian Parametersmentioning

confidence: 99%

“…These in turn determine the energy splittings between the ground state (5B, in C4v symmetry) and the excited 5 B2 state (d = E(5B2) -E(5B 1 )) and s E state (A -S, = E(SE) -E( S B,)). Spin-orbit coupling with these excited states combines to give D 22 [-4/A + 1/(d -8,)], where A> 5, and A is the spin-orbit coupling constant [20,31]. Thus for a constant equatorial ligand field, such as is the case among a series of porphyrins (or even among different porphyrins, since the organic substituents of the ligand have little effect), variation in the axial ligand field will strongly affect D, so that as S, increases (the axial field weakens), the magnitude of I DI will decrease due to diminished coupling with the excited 5E state.…”

Section: Relation Of Structure To Spin Hamiltonian Parametersmentioning

confidence: 99%

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High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in axially symmetric coordination complexes

Krzystek¹,

Telser²,

Knapp³

et al. 2001

Appl. Magn. Reson.

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High-frequency and -field electron paramagnetic resonance (HFEPR) has been used to study several complexes of high-spin manganese(III) (3d4, S = 2): [Mn(Me2dbm)X] and [Mn(OEP)X] (X = Cl-, Br -), where Meidbm-is the anion of 4,4'-dimethyldibenzoylmethane and OEP 2-is the dianion of 2,3,7,8,12,13,17,18-octaethylporphine. 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)Cl], D = -2.45(3) cm'; [Mn(Me2dbm)Br], D = -1.40(2) cm'; [Mn(OEP)Cl], D = -2.40(1) cm'; [Mn(OEP)Br], D = -1.07 (1) cm -' (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(III). 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. IntroductoinPolynuclear transition metal clusters that possess large ground-state spins (S > 4) are of significant interest for use as magnetic materials. In particular, high-spin molecules with large-magnitude, negative zero-field splitting (zfs) (D < 0) exhibit magnetic hysteresis effects resembling nanomagnets and are termed single-molecule magnets (SMMs) [1][2][3][4][5][6][7][8][9]. The resultant zfs of a polynuclear complex reflects * Present address:

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An Unusual Stable Mononuclear Mn^III Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation and Theoretical Study

Romain

Duboc

Neese

et al. 2009

Chemistry A European J

103

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The mononuclear manganese bis-terpyridine complex [Mn(tolyl-terpy)(2)](X)(3) (1(X)(3); X=BF(4), ClO(4), PF(6); tolyl-terpy=4'-(4-methylphenyl)-2,2':6',2"-terpyridine), containing Mn in the unusual +III oxidation state, has been isolated and characterised. The 1(3+) ion is a rare example of a mononuclear Mn(III) complex stabilised solely by neutral N ligands. Complex 1(3+) is obtained by electrochemical oxidation of the corresponding Mn(II) compound 1(2+) in anhydrous acetonitrile. Under these conditions the cyclic voltammogram of 1(2+) exhibits not only the well-known Mn(II)/Mn(III) oxidation at E(1/2)=+0.91 V versus Ag/Ag(+) (+1.21 V vs. SCE) but also a second metal-based oxidation process corresponding to Mn(III)/Mn(IV) at E(1/2)=+1.63 V (+1.93 V vs. SCE). Single crystals of 1(PF(6))(3)2 CH(3)CN were obtained by an electrocrystallisation procedure. X-ray analysis unambiguously revealed its tetragonally compressed octahedral geometry and high-spin character. The electronic properties of 1(3+) were investigated in detail by magnetic measurements and theoretical calculations, from which a D value of +4.82 cm(-1) was precisely determined. Density functional and complete active space self consistent field ab initio calculations both correctly predict a positive sign of D, in agreement with the compressed tetragonal distortion observed in the X-ray structure of 1(PF(6))(3)2 CH(3)CN. The different contributions to D were calculated, and the results show that 1) the spin-orbit coupling part (+2.593 cm(-1)) is predominant compared to the spin-spin interaction (+1.075 cm(-1)) and 2) the excited triplet states make the dominant contribution to the total D value.

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Magnetic properties and electronic structure of manganese(III) porphyrins

Cited by 46 publications

References 11 publications

Magnetic Parameters and Magnetic Functions in Mononuclear Complexes Beyond the Spin-Hamiltonian Formalism

Magnetic Parameters and Magnetic Functions in Mononuclear Complexes Beyond the Spin-Hamiltonian Formalism

High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in axially symmetric coordination complexes

An Unusual Stable Mononuclear Mn^III Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation and Theoretical Study

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Magnetic properties and electronic structure of manganese(III) porphyrins

Cited by 46 publications

References 11 publications

Magnetic Parameters and Magnetic Functions in Mononuclear Complexes Beyond the Spin-Hamiltonian Formalism

Magnetic Parameters and Magnetic Functions in Mononuclear Complexes Beyond the Spin-Hamiltonian Formalism

High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in axially symmetric coordination complexes

An Unusual Stable Mononuclear MnIII Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation and Theoretical Study

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An Unusual Stable Mononuclear Mn^III Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation and Theoretical Study