Structure and Magnetic Property of 2-Imidazolylnitronyl Nitroxide and Its Metal Complexes

Yoshioka, Naoki; Irisawa, Munetoshi; Aizawa, Naoyuki; Aoki, Takashi; Inoue, Hidenari; Ohba, Shigeru

doi:10.1080/10587259608042282

Cited by 5 publications

(5 citation statements)

References 9 publications

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“…This feature seems to be attracting, because, on chelate formation, the N and O bite angle of bzimNO and bzthNO might be open, being favorable for strong 3d-2p ferromagnetic coupling. Very recently, Luneau explained the spin-transition phenomenon of [CuL2(ClO4)2] (L = 2-imidazolyl-NN) [87] in terms of a magnetic coupling switch accompanied by the coordination structure modification [169]. This mechanism is quite similar to the present one and in particular to that of [Cu(phpyNO)2(H2O)2](BF4)2 (Figure 10a) [111].…”

Section: Miscellaneoussupporting

confidence: 82%

“…Thus, the relatively planar chelate indicated with the Ni-O-N-C sp 2 torsion angle of 6.3(4) • is reasonably acceptable. A quite similar synthetic strategy has been adopted to the copper(II) perchlorate and 2-imidazolyl-NN complex, which showed 2J/k B = +216 K [86,87]. The nickel(II) analogue was also reported to show ferromagnetic coupling [87].…”

Section: Magneto-structural Relationship and Molecular Designmentioning

confidence: 99%

“…A quite similar synthetic strategy has been adopted to the copper(II) perchlorate and 2-imidazolyl-NN complex, which showed 2J/k B = +216 K [86,87]. The nickel(II) analogue was also reported to show ferromagnetic coupling [87]. Another type of exception is found in the nickel(II)-2,2 -bipyridine-6,6 -diylbis(NN) complex [60].…”

Section: Magneto-structural Relationship and Molecular Designmentioning

confidence: 99%

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Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

et al. 2021

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Heterospin systems have a great advantage in frontier orbital engineering since they utilize a wide diversity of paramagnetic chromophores and almost infinite combinations and mutual geometries. Strong exchange couplings are expected in 3d–2p heterospin compounds, where the nitroxide (aminoxyl) oxygen atom has a direct coordination bond with a nickel(II) ion. Complex formation of nickel(II) salts and tert-butyl 2-pyridyl nitroxides afforded a discrete 2p–3d–2p triad. Ferromagnetic coupling is favored when the magnetic orbitals, nickel(II) dσ and radical π*, are arranged in a strictly orthogonal fashion, namely, a planar coordination structure is characterized. In contrast, a severe twist around the coordination bond gives an orbital overlap, resulting in antiferromagnetic coupling. Non-chelatable nitroxide ligands are available for highly twisted and practically diamagnetic complexes. Here, the Ni–O–N–Csp2 torsion (dihedral) angle is supposed to be a useful metric to describe the nickel ion dislocated out of the radical π* nodal plane. Spin-transition complexes exhibited a planar coordination structure in a high-temperature phase and a nonplanar structure in a low-temperature phase. The gradual spin transition is described as a spin equilibrium obeying the van’t Hoff law. Density functional theory calculation indicates that the energy level crossing of the high- and low-spin states. The optimized structures of diamagnetic and high-spin states well agreed with the experimental large and small torsions, respectively. The novel mechanism of the present spin transition lies in the ferro-/antiferromagnetic coupling switch. The entropy-driven mechanism is plausible after combining the results of the related copper(II)-nitroxide compounds. Attention must be paid to the coupling parameter J as a variable of temperature in the magnetic analysis of such spin-transition materials. For future work, the exchange coupling may be tuned by chemical modification and external stimulus, because it has been clarified that the parameter is sensitive to the coordination structure and actually varies from 2J/kB = +400 K to −1400 K.

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Section: Miscellaneoussupporting

confidence: 82%

Section: Magneto-structural Relationship and Molecular Designmentioning

confidence: 99%

Section: Magneto-structural Relationship and Molecular Designmentioning

confidence: 99%

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Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

et al. 2021

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“…Regardless of the structural similarities, the overall magnetic behaviors of 1 and 2 are quite different as shown in Figure . − As predicted, χ T per dinitroxide is ca. 0.75 emu·K/mol at 300 K for both 1 and 2 , consistent with weakly coupled biradicals.…”

mentioning

confidence: 76%

Observation of a Hysteretic Phase Transition in a Crystalline Dinitroxide Biradical That Leads to Magnetic Bistability

et al. 2001

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“…1,3-Bis{2-(1-oxyl-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene ( 1 ) and 1,3-bis{2-(1-oxyl-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene ( 2 ) were designed and synthesized in this work. NN- and IN-imidazole groups in 1 and 2 , respectively, are expected to serve as bidentate ligands and interact magnetically to each other through bonds and/or space. We wish to describe the analyses of their crystal structures and the measurements of their magnetic properties by means of EPR spectroscopy and SQUID magneto/susceptometry.…”

mentioning

confidence: 99%

Crystal Structures and Magnetic Properties of m-Phenylenebis(imidazole) Derivatives Having Two Nitronyl Nitroxide or Iminyl Nitroxide Radicals. The Two Kinds of Antiferromagnetic Interaction Alternating along One-Dimensional Chains

Akabane¹,

Tanaka²,

Matsuo³

et al. 1997

J. Org. Chem.

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1,3-Bis{2-(1-oxyl-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene (1), 1,3-bis{2-(1oxyl-4,4,5,5-tetramethylimidazolin-2-yl)imidazol-1-yl}benzene (2), and their chloro derivatives (3 and 4) were prepared. Both diradicals 1, 2 and 3, 4 crystallized in orthorhombic, space group Pbcn and in monoclinic, space group P2 1 /c, respectively. The molecular structures of diradicals 1 and 2 were similar to each other and had C 2 symmetry. Intra-and intermolecular average distances between the two NO groups of the nitronyl nitroxide (NN) moieties in 1 and those of the N-N and NO-NO of the iminyl nitroxide (IN) moieties in 2 were found to be 4.26 and 3.49 Å for 1 and 4.38 and 3.54 Å for 2, respectively, suggesting the formation of magnetically linear chain structures along the c axis. An alternating antiferromagnetic one-dimensional chain model (H ) -2J Σ{S A2i S A2i-1 + RS A2i S A2i+1 }) was applied to the spin systems 1 and 2 and a theoretical equation derived therefrom was fitted to the observed χ mol T vs T plots to give the exchange coupling parameters, J/k B ) -158 ( 2 and -239 ( 8 K and R ) 0.22 ( 0.02 and 0.11 ( 0.04, respectively. The molecular structures of 3 and 4 were also similar to each other, in which two NN and IN groups are far away from each other by the nearest intramolecular average distance between radical centers being 4.54 and 4.72 Å for 3 and 4, respectively. One of the latter has a disorder with respect to the position of the oxygen atom in IN. One of the two NNs and INs in both diradicals had intermolecular short distances between the radical centers in the neighboring molecules; average distances 3.56 Å for 3 and 3.82 Å for 4, to form magnetic dimer structures. The exchange coupling parameters for 3 and 4 were determined to be J/k B ) -4.85 ( 0.15 and -37.3 ( 0.3 K (one triplet species for the singlet-triplet model; H ) -2JS 1 S 2 , and isolated two doublets in a ratio of 1:1), respectively.

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Structure and Magnetic Property of 2-Imidazolylnitronyl Nitroxide and Its Metal Complexes

Cited by 5 publications

References 9 publications

Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

Observation of a Hysteretic Phase Transition in a Crystalline Dinitroxide Biradical That Leads to Magnetic Bistability

Crystal Structures and Magnetic Properties of m-Phenylenebis(imidazole) Derivatives Having Two Nitronyl Nitroxide or Iminyl Nitroxide Radicals. The Two Kinds of Antiferromagnetic Interaction Alternating along One-Dimensional Chains

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