Multistep redox series of the tris(o-semiquinone)chromium(III) complexes

Downs, Hartley H.; Buchanan, Robert M.; Pierpont, Cortlandt G.

doi:10.1021/ic50197a003

Cited by 72 publications

(54 citation statements)

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“…The semiquinone complexes of iron have been of interest as molecules that show relatively strong metal−radical magnetic exchange. Electrochemical activity at both the metal and quinone ligands has been investigated for members of the Cr(SQ) 3 series but not for the related complexes of iron. 3,6-Di- tert -butyl-1,2-benzoquinone reacts with Fe(CO) 5 to give Fe(3,6-DBSQ) 3 .…”

Section: Resultsmentioning

confidence: 99%

Iron−Semiquinone, Semiquinone−Semiquinone, and Iron−Iron Magnetic Exchange in Monomeric and Dimeric Ferric Complexes Containing the 3,6-Di-tert-butyl-1,2-semiquinonate Ligand

et al. 1996

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Fe(3,6-DBSQ)(3) has been prepared by reacting 3,6-di-tert-butyl-1,2-benzoquinone with Fe(CO)(5). The complex has been characterized structurally [orthorhombic, Pbca, a = 18.277(5) Å, b = 11.634(3) Å, c = 39.903(10) Å, V = 8485(4) Å(3), Z = 8, R = 0.063], electrochemically, and magnetically. Ligand-based redox couples are observed in electrochemical experiments that consist of reversible or quasireversible Cat/SQ steps at negative potentials and irreversible SQ/BQ oxidations at positive potentials. Magnetic measurements show temperature dependence that arises from antiferromagnetic exchange. Data have been fit to an expression that includes the effects of both Fe-SQ and SQ-SQ exchange with the result that J(SQ-SQ) is larger in magnitude than J(Fe-SQ). In methanol, the complex undergoes solvolysis to form [Fe(3,6-DBSQ)(2)(&mgr;-OMe)](2). Structural characterization [triclinic, P&onemacr;, a = 11.441(2) Å, b = 11.514(2) Å, c = 14.552(2) Å, alpha = 67.86(1) degrees, beta = 70.51(1) degrees, gamma = 72.79(1) degrees, V = 1641.8(5) Å(3), Z = 1, R = 0.048] has shown that the molecule is a centrosymmetric dimer with no close intermolecular contacts. The temperature dependence of magnetic measurements has been fit to a model consisting of two interacting S = (3)/(2) centers that arise from strong Fe-SQ exchange with J(Fe-Fe) = -22.4 cm(-1).

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Section: Resultsmentioning

confidence: 99%

Iron−Semiquinone, Semiquinone−Semiquinone, and Iron−Iron Magnetic Exchange in Monomeric and Dimeric Ferric Complexes Containing the 3,6-Di-tert-butyl-1,2-semiquinonate Ligand

et al. 1996

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“…If we replace C104" by the much bulkier anion BPh4" in order to dilute the trinuclear units in the crystal lattice, we obtain much the same magnetic behavior, which suggests that the weak interaction is largely intramolecular. An upper limit of the singlet-triplet energy gap in 2 and 3 arising from the interaction between the terminal magnetic ions may then be obtained by fitting the magnetic data with the theoretical law for a pair of copper(II) ions: 2jv/jyr / ; \ i-1 µ = -^-[3 + exp^--Jj (l-p) + Cp (7) where the eventual presence of a small proportion p of uncoupled impurity is taken into account. The upper limit was found as j = -1.6 cm"1 with g = 2.18.…”

Section: Description Of the Structuresmentioning

confidence: 99%

Interactions in CuIICuIICuII, CuIIZnIICuII, and CuIINiIICuII trinuclear species. Crystal structure of bis(N,N'-bis(3-aminopropyl)oxamido)tricopper(II) perchlorate

Journaux¹,

Sletten²,

Kahn³

1986

Inorg. Chem.

130

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“…Due to the high stability of the d 3 electron configuration for Cr III in octahedral ligand fields, chromium complexes have played a key role in the identification of redox activity for several ligand systems. Multimembered redox series with ligand-centered redox events are known for many classic redox-active ligands including catechols, − dithiolenes, − bipyridine, , terpyridine, − and pyridine diimine . Herein, we report the synthesis and characterization of the two redox series [Cr( Me PDP) 2 ] z ( z = 1–, 2–, 3−) and [Mo( Me PDP) 2 ] z ( z = 0, 1–, 2–, 3−) and provide experimental and computational evidence for the redox activity of the PDP ligand under reductive conditions.…”

Section: Introductionmentioning

confidence: 99%

Redox Chemistry of Bis(pyrrolyl)pyridine Chromium and Molybdenum Complexes: An Experimental and Density Functional Theoretical Study

2018

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The three- and four-membered redox series [Cr(PDP)] (z = 1-, 2-, 3-) and [Mo(PDP)] (z = 0, 1-, 2-, 3-) were synthesized to study the redox properties of the pincer ligand PDP (HPDP = 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine). The monoanionic complexes were characterized by X-ray crystallography, UV/vis/NIR spectroscopy, and magnetic susceptibility measurements. Experimental and density functional theory (DFT) studies are consistent with closed-shell PDP ligands and +III oxidation states (d, S = 3/2) for the central metal ions. Cyclic voltammetry established multiple reversible redox processes for [M(PDP)] (M = Cr, Mo), which were further investigated via chemical oxidation and reduction. For molybdenum, one-electron oxidation yielded Mo(PDP) which was characterized by X-ray crystallography, UV/vis/NIR, and magnetic susceptibility measurements. The experimental and computational data indicate metal-centered oxidation to a Mo complex (d, S = 1) with two PDP ligands. In contrast, one- and two-electron reductions were found to be ligand centered resulting in the formation of PDP radicals, in which the unpaired electron is predominantly located on the central pyridine ring of the ligand. The presence of ligand radicals was established experimentally by observation of ligand-to-ligand intervalence charge transfer (LLIVCT) bands in the UV/vis/NIR spectra of the dianionic and trianionic complexes and further supported by broken-symmetry DFT calculations. X-ray crystallographic analyses of the one-electron-reduced species [M(PDP)] (S = 1, M = Cr, Mo) established structural indicators for pincer reduction and showed localization of the radical on one of the two pincer ligands. The two-electron-reduced, trianionic complexes (S = 1/2) were characterized by UV/vis/NIR spectroscopy, magnetic susceptibility measurements, and EPR spectroscopy. The electronic structures of the reduced complexes are best described as containing +III metal ions (d) antiferromagnetically coupled to one and two radical ligands for the dianionic and trianionic species, respectively.

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Multistep redox series of the tris(o-semiquinone)chromium(III) complexes

Cited by 72 publications

References 3 publications

Iron−Semiquinone, Semiquinone−Semiquinone, and Iron−Iron Magnetic Exchange in Monomeric and Dimeric Ferric Complexes Containing the 3,6-Di-tert-butyl-1,2-semiquinonate Ligand

Iron−Semiquinone, Semiquinone−Semiquinone, and Iron−Iron Magnetic Exchange in Monomeric and Dimeric Ferric Complexes Containing the 3,6-Di-tert-butyl-1,2-semiquinonate Ligand

Interactions in CuIICuIICuII, CuIIZnIICuII, and CuIINiIICuII trinuclear species. Crystal structure of bis(N,N'-bis(3-aminopropyl)oxamido)tricopper(II) perchlorate

Redox Chemistry of Bis(pyrrolyl)pyridine Chromium and Molybdenum Complexes: An Experimental and Density Functional Theoretical Study

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