Coordination Chemistry of Chromium☆

Lay, Peter A.; Levina, Aviva

doi:10.1016/b978-0-12-409547-2.11126-6

Cited by 2 publications

(1 citation statement)

References 597 publications

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“…We, therefore, initiated an investigation to test the redox activity of the coordinated macrocyclic ligand L-N 4 Me 2 in reduced chromium complexes because the chemistry of chromium(II) ions, in particular, is characterized by their pronounced reducing power. [6] In a groundbreaking publication, Wieghardt et al could unambiguously demonstrate by structural and spectroscopic methods as well as by theoretical calculations that, for a series of chromium complexes with derivatized reduced tris(2,2'-bipyridyI) ligands [Cr( t bipy) 3 ] n (with n = 0, 1 + , 2 + ; t bipy = 4,4'di(tert.-butyl)-2,2'-bipyridine), the chromium ion is not reduced to oxidation states from + II down to 0 for an increasing number of electrons. Instead the electronic structure was determined to have arisen from a chromium(III) ion and, depending on n, one to three coordinated radical anion ligands ( t bipy) *À .…”

Section: Introductionmentioning

confidence: 99%

Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units

Krämer,

Schmitz,

Kelm

et al. 2023

Chemistry A European J

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In the tetraazamacrocyclic ligand N,N’‐dimethyl‐2,11‐diaza‐[3.3](2,6)pyridinophane (L‐N4Me2), the two pyridine units are separated from each other by sp3‐hybridized triatomic bridges. Such electronically isolated pyridine moieties are considerably less prone to reductions than di‐ or triimines. A detailed structural, magnetic, and spectroscopic investigation of the complexes [Cr(L‐N4Me2)(OAc)2] and [Cr(L‐N4Me2)(OAc)2](PF6), in combination with theoretical calculations, reveals that the reduced complex must be described as a chromium(III) ion coordinated to the anionic radical ligand (L‐N4Me2)⋅− rather than a low‐spin chromium(II) ion bound to closed‐shell ligands. Thus, it is, to the best of our knowledge, only the second example of a stable and structurally characterized metal complex containing a reduced isolated pyridine unit. The stability is attributed to the delocalization of the unpaired electron across the two pyridine units, mediated by their interaction to the metal ion.

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Section: Introductionmentioning

confidence: 99%

Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units

Krämer,

Schmitz,

Kelm

et al. 2023

Chemistry A European J

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Solid-State Structural Studies of Chromium(III) Nicotinato Nutritional Supplements

et al. 2014

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While Cr(III) dietary supplements are widely consumed, some commercial supplements have yet to be structurally characterized. X-ray absorption spectroscopy and other spectroscopic methods were used to characterize Cr(III) nicotinato nutritional supplements that have long been used in complementary medicine. Different ratios of nicotinic acid and CrCl3·6H2O (trans-[CrCl2(OH2)4]Cl·2H2O) at different pH values gave a range of products. The local structures of Cr(III) nicotinato complexes obtained at pH 7 and of the patented complex were characterized by performing multiple-scattering analysis of their EXAFS spectra as well as EPR, UV-vis, and IR spectroscopies. For the first time, these complexes have been definitively characterized as nicotinato-bridged polymers of dihydroxido-bridged dinuclear Cr(III) cores. In the patented complex used in commercial preparations, each Cr is octahedral with an additional terminal O-bound nicotinato ligand, two bridging nicotinato (one O and one N bound), and an aqua ligand. The other species also have two or three bridging nicotinato ligands and an aqua and, in some cases, a terminal hydroxido ligand, which is dependent upon the stoichiometry of the reactants and the pH value of the solution in which they are prepared.

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Coordination Chemistry of Chromium☆

Cited by 2 publications

References 597 publications

Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units

Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units

Solid-State Structural Studies of Chromium(III) Nicotinato Nutritional Supplements

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