Antiferromagnetic exchange in meta-phenylene bridged bis(tris-o-iminosemiquinonato)metal complexes

Dei, Andrea; Gatteschi, Dante; Sangregorio, Claudio; Sorace, Lorenzo; Vaz, Maria G. F.

doi:10.1016/j.jmmm.2003.12.023

Cited by 3 publications

(2 citation statements)

References 4 publications

(5 reference statements)

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“…By far the best studied spacers are m- and p- phenylene; meta - substituted diradicals possess high spin ( S = 1) ground states while para diradicals are generally low spin ( S = 0). However, the general guidelines are by no means universal as exceptions have been reported. , …”

Section: Introductionmentioning

confidence: 99%

Probing Electronic Communication in Stable Benzene-Bridged Verdazyl Diradicals

et al. 2007

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Two benzene-bridged N,N'-bis(isopropyl)6-oxoverdazyl diradicals 7a (1,4-benzene-bridged) and 7b (1,3-benzene-bridged) were prepared and studied by an array of physicochemical techniques aimed at elucidating the intramolecular electronic and magnetic coupling between verdazyl chromophores. The very high stability of these diradicals permits comprehensive investigations of their properties for the first time. The UV-vis spectra suggest negligible direct conjugative overlap involving the radical SOMOs, although significant differences in higher energy absorptions suggest that radical orbitals other than the SOMO are likely communicating via the central p-phenylene bridge in 7a. The electrochemical features of the two diradicals are nearly identical; in each derivative, both radicals are oxidized essentially independently while the reductions occur in a stepwise manner with differences of approximately 100 mV between the two reductions. EPR and magnetic susceptibility collectively indicate that the para-bridged diradical is weakly antiferromagnetically coupled while the meta analogue is weakly ferromagnetically coupled, in accord with the topology of the substitution pattern on the central benzene ring.

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Section: Introductionmentioning

confidence: 99%

Probing Electronic Communication in Stable Benzene-Bridged Verdazyl Diradicals

et al. 2007

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“…However, the overall low symmetry of these complexes as a result of the conformation of the phenyl bridge relative to the bpy rings and the potential for torsional distortions about the bpy−C 6 H 4 bonds suggest that they are likely predisposed to spin localization on the bpy orbital framework that severely attenuates both electronic and magnetic communication along the vector(s) connecting the metal centers. This exchange modulation as a function of bridging ligand conformation has been documented with semiquinone-type dinuclear complexes. − It is noteworthy that this same bridging ligand set ( m -bbb versus p -bbb) was found to engender different behavior in bimetallic Co III/II dioxolene complexes . In the Co systems the p -bbb ligand was determined to promote greater magnetic coupling than the m -bbb ligand, although the electronic interactions (as evidenced by the intervalence charge-transfer transitions) were comparable for both ligand sets.…”

Section: Discussionmentioning

confidence: 64%

Influence of Ligand Geometry in Bimetallic Ytterbocene Complexes of Bridging Bis(bipyridyl) Ligands

et al. 2007

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Two new bimetallic complexes, [Cp*2Yb]2(μ-1,3-(2,2‘-bipyridyl)-5-tBu-C6H3) (1) and [Cp*2Yb]2(μ-1,4-(2,2‘-bipyridyl)-C6H4) (2), and their corresponding two-electron oxidation products [1]2+ and [2]2+ have been synthesized with the aim of determining the impact of the bridging ligand geometry on the electronic and magnetic properties of these materials. Electrochemistry, optical spectroscopy, and bulk susceptibility measurements all support a ground-state electronic configuration of the type [(f)13-(πa*)1-(πb*)1-(f)13]. Density functional theory calculations on the uncomplexed bridging ligands as doubly reduced species also indicate that the diradical electronic configuration is the lowest lying for both meta- and para-bis(bipyridyl) systems. The electrochemical and optical spectroscopic data indicate that the electronic coupling between the metal centers mediated by the diradical bridges is weak, as evidenced by the small separation of the metal-based redox couples and the similarity of the f−f transitions of the associated dicationic complexes ([1]2+ and [2]2+) relative to those of the monometallic [Cp*2Yb(bpy)]+ analogue. The magnetic susceptibility data show no evidence for exchange coupling between the paramagnetic metal centers in the neutral complexes, but do indicate weak exchange coupling between YbIII and ligand radical spins on each of the effectively independent halves of the bimetallic complexes. These findings are in contrast to those reported recently for CoIII/II dioxolene bimetallic complexes bridged by these same bis(bipyridyl) ligands. The difference is attributed in part to the dominant singlet diradical character of the bridging ligands in the ytterbocene complexes. These experimental and theoretical results are consistent with expectations for organic diradical spin orientations for meta versus para substituents across a phenylene linker, but this effect does not induce significant longer-range superexchange or electronic interactions between the metal centers in these systems.

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Organic Radicals and Molecular Magnetism

Turek

2020

Electron Paramagnetic Resonance Spectroscopy

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Antiferromagnetic exchange in meta-phenylene bridged bis(tris-o-iminosemiquinonato)metal complexes

Cited by 3 publications

References 4 publications

Probing Electronic Communication in Stable Benzene-Bridged Verdazyl Diradicals

Probing Electronic Communication in Stable Benzene-Bridged Verdazyl Diradicals

Influence of Ligand Geometry in Bimetallic Ytterbocene Complexes of Bridging Bis(bipyridyl) Ligands

Organic Radicals and Molecular Magnetism

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