Radical compounds and metal complexes with azobenzene chromophore

Fujino, Masahiro; Hasegawa, Satoko; Akutsu, Hiroki; Yamada, Jun−ichi; Nakatsuji, Shin’ichi

doi:10.1016/j.poly.2006.09.050

Cited by 7 publications

(5 citation statements)

References 11 publications

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“…Nitroxide N–O bond lengths are useful in assigning the ligand to the neutral radical (L • ) or anionic hydroxylamino form (L – ). For the conceptually similar ligands Tempo and Proxyl, typical free ligand nitroxide radical N–O bond lengths lie between 1.27 and 1.28 Å, coordinated nitroxide radical N–O bond lengths lie in the range of 1.261(12)–1.300(3) Å − and coordinated hydroxylamino anion or hydroxylamine groups have N–O bond lengths in the range of 1.379(5)–1.413(3) Å. − The N–O bond lengths of 1.294(4) Å in 1 suggests both ligands in 1 are in the neutral radical form (L • ), whereas the longer N–O bond lengths found in 2 of 1.401(3) Å and 1.411(3) Å suggest both ligands are in the anionic hydroxylamino form (L – ). The assignments of a Co(II) gradual spin-crossover with two neutral radical ligands (L • ) in 1 ([Co II (L • ) 2 ](NO 3 ) 2 ) and a low-spin d 6 Co(III) ion with two anionic hydroxylamino ligands (L – ) in 2 ([Co III (L – ) 2 ](BPh 4 )) have been made, not only on the basis of crystallographic data but also from interpretation of magnetic measurements, electrochemistry, EPR, and DFT calculations (vide infra).…”

Section: Resultsmentioning

confidence: 99%

Observation of Ferromagnetic Exchange, Spin Crossover, Reductively Induced Oxidation, and Field-Induced Slow Magnetic Relaxation in Monomeric Cobalt Nitroxides

et al. 2013

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The reaction of [Co(II)(NO3)2]·6H2O with the nitroxide radical, 4-dimethyl-2,2-di(2-pyridyl) oxazolidine-N-oxide (L(•)), produces the mononuclear transition-metal complex [Co(II)(L(•))2](NO3)2 (1), which has been investigated using temperature-dependent magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, electrochemistry, density functional theory (DFT) calculations, and variable-temperature X-ray structure analysis. Magnetic susceptibility measurements and X-ray diffraction (XRD) analysis reveal a central low-spin octahedral Co(2+) ion with both ligands in the neutral radical form (L(•)) forming a linear L(•)···Co(II)···L(•) arrangement. This shows a host of interesting magnetic properties including strong cobalt-radical and radical-radical intramolecular ferromagnetic interactions stabilizing a S = (3)/2 ground state, a thermally induced spin crossover transition above 200 K and field-induced slow magnetic relaxation. This is supported by variable-temperature EPR spectra, which suggest that 1 has a positive D value and nonzero E values, suggesting the possibility of a field-induced transverse anisotropy barrier. DFT calculations support the parallel alignment of the two radical π*NO orbitals with a small orbital overlap leading to radical-radical ferromagnetic interactions while the cobalt-radical interaction is computed to be strong and ferromagnetic. In the high-spin (HS) case, the DFT calculations predict a weak antiferromagnetic cobalt-radical interaction, whereas the radical-radical interaction is computed to be large and ferromagnetic. The monocationic complex [Co(III)(L(-))2](BPh4) (2) is formed by a rare, reductively induced oxidation of the Co center and has been fully characterized by X-ray structure analysis and magnetic measurements revealing a diamagnetic ground state. Electrochemical studies on 1 and 2 revealed common Co-redox intermediates and the proposed mechanism is compared and contrasted with that of the Fe analogues.

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Section: Resultsmentioning

confidence: 99%

Observation of Ferromagnetic Exchange, Spin Crossover, Reductively Induced Oxidation, and Field-Induced Slow Magnetic Relaxation in Monomeric Cobalt Nitroxides

et al. 2013

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“…The corresponding nitrosonium cation found in [NITPh](ClO 4 ) has an average N−O bond length of 1.225(4) Å consistent with values expected for an NO bond while N−O bond lengths of 1.333(4), 1.367(3), and 1.342(4) Å are found in a series of Fe 2+ complexes involving the reduced form of the IM2py radical . A more fitting comparison with L would be with transition metal complexes of the Tempo and Proxyl radicals (See Figure ) which have two sp 3 carbons adjacent to the nitroxide N−O in a similar way to L. For both Tempo and Proxyl 3d transition metal complexes the N−O bond length in the coordinated radical species is in the range 1.261(12)−1.300(3) Å − while for Tempo the equivalent coordinated hydroxylamino anion or hydroxylamine groups have N−O bond lengths in the range 1.379(5)−1.413(3)Å. − A recent paper on Cu(II) t -butyl-2-pyridyl-nitroxide (2pyNO) bis-chelates (with 5-membered CuONCN(py) rings) has presented similar arguments concerning N−O bond lengths and the redox state of the bidentate pyridyl-nitroxide . The N−O bond lengths from the two cations in complex 1 of 1.317(3) and 1.314(3) Å suggest that the ligand is in the neutral coordinated radical form (L • ) with bond order 1.5.…”

Section: Resultsmentioning

confidence: 99%

Anion Dependent Redox Changes in Iron Bis-terdentate Nitroxide {NNO} Chelates

Gass¹,

Gartshore²,

Lupton³

et al. 2011

Inorg. Chem.

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The reaction of [Fe(II)(BF(4))(2)]·6H(2)O with the nitroxide radical, 4,4-dimethyl-2,2-di(2-pyridyl) oxazolidine-N-oxide (L(•)), produces the mononuclear transition metal complex [Fe(II)(L(•))(2)](BF(4))(2) (1) which has been investigated using temperature dependent susceptibility, Mössbauer spectroscopy, electrochemistry, density functional theory (DFT) calculations, and X-ray structure analysis. Single crystal X-ray diffraction analysis and Mössbauer measurements reveal an octahedral low spin Fe(2+) environment where the pyridyl donors from L(•) coordinate equatorially while the oxygen containing the radical from L(•) coordinates axially forming a linear O(•)··Fe(II)··O(•) arrangement. Magnetic susceptibility measurements show a strong radical-radical intramolecular antiferromagnetic interaction mediated by the diamagnetic Fe(2+) center. This is supported by DFT calculations which show a mutual spatial overlap of 0.24 and a spin density population analysis which highlights the antiparallel spin alignment between the two ligands. Similarly the monocationic complex [Fe(III)(L(-))(2)](BPh(4))·0.5H(2)O (2) has been fully characterized with Fe-ligand and N-O bond length changes in the X-ray structure analysis, magnetic measurements revealing a Curie-like S = 1/2 ground state, electron paramagnetic resonance (EPR) spectra, DFT calculations, and electrochemistry measurements all consistent with assignment of Fe in the (III) state and both ligands in the L(-) form. 2 is formed by a rare, reductively induced oxidation of the Fe center, and all physical data are self-consistent. The electrochemical studies were undertaken for both 1 and 2, thus allowing common Fe-ligand redox intermediates to be identified and the results interpreted in terms of square reaction schemes.

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“…The interactions between these chains proceed through C-HÁ Á Á contacts involving the C8-C13 ring and the terminal atom C11 (Table 1) 4. Database survey A search in the Cambridge Structural Database (Version 5.39 with one update, Groom et al, 2016) returned 101 entries for unsubstituted azobenzene, including the dynamic disorder study of Harada & Ogawa (2004); five entries for O-paraphenylazobenzoyl monoesters (Fitjer et al, 1984;Fujino et al, 2007;Nakatsuji et al, 2007, Park et al, 2015; and only two entries for 3-oxy-substituted 2-pyrrolidone (Clark et al, 2006). A partial view of the crystal packing of the title compound.…”

Section: Supramolecular Featuresmentioning

confidence: 99%