“…The EPR parameters for the pydim and pydip derivative are similar to those of related mononuclear O=V IV complexes, , , and comparable dinuclear compounds with class I valence‐isolated [OV IV (μ‐O)V V O] units , , , , . Similar valence delocalized (class II or III) behavior as found for [V 2 O 3 (pyphen) 2 ] · – has been previously reported for the radical anionic complexes [(L)OV IV (µ‐O)V V O(LO] · – with tridentate ONO 2– ligands based on hydroxy phenoxy hydrazides,, , , salenes, carboxy‐salicylaldiminates, or azophenolates,, and also the [OV IV (μ‐O oxido )(μ‐O phen )V V O] · 2+ complexes containing pentadentate (N′NONN′) 3– 2,6‐bis(phenoxymethyl‐ N , N ‐dimethylaminomethyl)aminomethyl)‐phenolates,, or complexes [(L)OV IV (µ‐O)V V O(LO] · 3+ complexes containing neutral N′NN′ ligands of the 2,6‐bis[benzimidazol‐2′‐yl]pyridine or ‐amine type, tris(2‐pyridylmethyl)amine, or 1,4,7‐triazacyclononane derivatives …”
Section: Resultssupporting
confidence: 55%
“…According to the classification for mixed-valent systems of Robin and Day, [74] the dinuclear pydim and pydip complexes represent class I complexes with a localized electron at one atom, while the pyphen derivative represents either a class III complex with a complete delocalization over both atoms or class II with easily accessible electron transfer between the two atoms of different oxidation number. The EPR parameters for the pydim and pydip derivative are similar to those of related mononuclear O=V IV complexes [59,61,63,[75][76][77][78] and comparable dinuclear compounds with class I valence-isolated [OV IV (μ-O)V V O] units. [61,62,68,77,79] Similar valence delocalized (class II or III) behavior as found for [V 2 O 3 (pyphen) 2 ] ·has been previously reported for the radical anionic complexes…”
Section: Epr and Uv/vis/nir Spectroelectrochemistry And Dft Calculationsmentioning
The coordination chemistry of three oxido‐pincer ligands 2,6‐(HOCR2)2(pyridine) (H2L) based on 2,6‐pyridinedimethanol [R = H (H2pydim), Me (H2pydip), Ph (H2pyphen)] towards vanadium(V) was explored. Reaction of NH4VO3 with the protoligands H2L gave the dinuclear complexes [(L)OV(μ‐O)VO(L)]. Mononuclear anionic species [VO2(L)]–, which were isolated as alkaline metal salts were obtained from reactions of [VO(acac)2] (acac– = acetylacetonate) and H2L under basic conditions and addition of HCl to these species allowed to isolate the unprecedented oxido chlorido complexes [VOCl(L)] for pydip and pyphen. Cyclic voltammograms of the dinuclear [V2O3(L)2] and mononuclear [VOCl(L)] complexes show reversible VV/VIV reduction waves, while corresponding waves of the anionic [VO2(L)]– are completely irreversible. The mixed‐valent VIV/VV species [V2O3(L)2]·– were characterized by EPR and UV/Vis spectroelectrochemistry revealing a delocalized system with a 15 line EPR spectrum and an intervalence charge transfer (IVCT) band for the bulky pyphen ligand but localized radicals in case of the pydim and pydip derivatives (8 line EPR, no IVCT). DFT calculated structures of the three derivatives show an V–O–V arrangement for [V2O3(pyphen)2]·– of about 145° ideally suited for delocalization, whereas for [V2O3(pydip)2]·– an angle of 128° was found.
“…The EPR parameters for the pydim and pydip derivative are similar to those of related mononuclear O=V IV complexes, , , and comparable dinuclear compounds with class I valence‐isolated [OV IV (μ‐O)V V O] units , , , , . Similar valence delocalized (class II or III) behavior as found for [V 2 O 3 (pyphen) 2 ] · – has been previously reported for the radical anionic complexes [(L)OV IV (µ‐O)V V O(LO] · – with tridentate ONO 2– ligands based on hydroxy phenoxy hydrazides,, , , salenes, carboxy‐salicylaldiminates, or azophenolates,, and also the [OV IV (μ‐O oxido )(μ‐O phen )V V O] · 2+ complexes containing pentadentate (N′NONN′) 3– 2,6‐bis(phenoxymethyl‐ N , N ‐dimethylaminomethyl)aminomethyl)‐phenolates,, or complexes [(L)OV IV (µ‐O)V V O(LO] · 3+ complexes containing neutral N′NN′ ligands of the 2,6‐bis[benzimidazol‐2′‐yl]pyridine or ‐amine type, tris(2‐pyridylmethyl)amine, or 1,4,7‐triazacyclononane derivatives …”
Section: Resultssupporting
confidence: 55%
“…According to the classification for mixed-valent systems of Robin and Day, [74] the dinuclear pydim and pydip complexes represent class I complexes with a localized electron at one atom, while the pyphen derivative represents either a class III complex with a complete delocalization over both atoms or class II with easily accessible electron transfer between the two atoms of different oxidation number. The EPR parameters for the pydim and pydip derivative are similar to those of related mononuclear O=V IV complexes [59,61,63,[75][76][77][78] and comparable dinuclear compounds with class I valence-isolated [OV IV (μ-O)V V O] units. [61,62,68,77,79] Similar valence delocalized (class II or III) behavior as found for [V 2 O 3 (pyphen) 2 ] ·has been previously reported for the radical anionic complexes…”
Section: Epr and Uv/vis/nir Spectroelectrochemistry And Dft Calculationsmentioning
The coordination chemistry of three oxido‐pincer ligands 2,6‐(HOCR2)2(pyridine) (H2L) based on 2,6‐pyridinedimethanol [R = H (H2pydim), Me (H2pydip), Ph (H2pyphen)] towards vanadium(V) was explored. Reaction of NH4VO3 with the protoligands H2L gave the dinuclear complexes [(L)OV(μ‐O)VO(L)]. Mononuclear anionic species [VO2(L)]–, which were isolated as alkaline metal salts were obtained from reactions of [VO(acac)2] (acac– = acetylacetonate) and H2L under basic conditions and addition of HCl to these species allowed to isolate the unprecedented oxido chlorido complexes [VOCl(L)] for pydip and pyphen. Cyclic voltammograms of the dinuclear [V2O3(L)2] and mononuclear [VOCl(L)] complexes show reversible VV/VIV reduction waves, while corresponding waves of the anionic [VO2(L)]– are completely irreversible. The mixed‐valent VIV/VV species [V2O3(L)2]·– were characterized by EPR and UV/Vis spectroelectrochemistry revealing a delocalized system with a 15 line EPR spectrum and an intervalence charge transfer (IVCT) band for the bulky pyphen ligand but localized radicals in case of the pydim and pydip derivatives (8 line EPR, no IVCT). DFT calculated structures of the three derivatives show an V–O–V arrangement for [V2O3(pyphen)2]·– of about 145° ideally suited for delocalization, whereas for [V2O3(pydip)2]·– an angle of 128° was found.
“…In addition, the integrities of the [V IV (cat) 3 ] 2- , [V IV (dtbc) 3 ] 2- , and [V IV (tcc) 3 ] 2- species in solutions generated by bulk electrolysis were confirmed by EPR spectroscopy (Figure S4 in the Supporting Information). The EPR spectral parameters observed for these solutions ( g iso ≈ 1.950, A iso ( 51 V) ≈ 7.5 × 10 -3 cm -1 , Figure S4 in the Supporting Information) were characteristic for V(IV) triscatecholato complexes, whereas typical V(IV) oxo complexes (such as [V IV O(acac) 2 ] or [V IV O(OH 2 ) 5 ] 2+ , Figure S4 in the Supporting Information) possess significantly higher g iso and A iso values. , 3 Typical changes in UV−vis spectra during the bulk electrolysis of Cr or V catecholato complexes (10 mM) in DMF (a and b) or MeCN (c−e) solutions in the presence of ( n Bu 4 N)BF 4 (0.10 M) and the corresponding catechols (20 mM, b−d only) at 22 °C. Samples of the reaction solutions (30 μL) were diluted 100-fold with the corresponding solvent (Ar-saturated).…”
Transition-metal complexes with redox-active catecholato ligands are of interest as models of bioinorganic systems and as potential molecular materials. This work expands our recent X-ray absorption spectroscopic (XAS) studies of Cr(V/IV/III) triscatecholato complexes (Levina, A.; Foran, G. J.; Pattison, D. I.; Lay, P. A. Angew. Chem., Int. Ed. 2004, 43, 462-465) to a Cr(III) monocatecholato complex, [Cr(tren)(cat)]+ (tren = tris(2-aminoethyl)amine, cat = catecholato2-), and its oxidized analogue, as well as to a series of V(V/IV/III) triscatecholato complexes ([VL3]n-, where L = cat, 3,5-di-tert-butylcatecholato2-, or tetrachlorocatecholato2-, and n = 1-3). Various oxidation states of these complexes in solutions were generated by bulk electrolysis directly in the XAS cell. Increases in the edge energies and pre-edge absorbance intensities in XANES spectra, as well as decreases in the average M-O bond lengths (M = Cr or V) revealed by XAFS data analyses, are consistent with predominantly metal-based oxidations in both the Cr(V/IV/III) and V(V/IV/III) triscatecholato series, but the degree of electron delocalization between the metal ion and the ligands was higher in the case of Cr complexes. By contrast, oxidation of [Cr(III)(tren)(cat)]+ was mainly ligand-based and led to [Cr(III)(tren)(sq)]2+ (sq = semiquinonato-), as shown by the absence of significant changes in the pre-edge and edge features and by an increase in the average Cr-O bond length. The observed differences in electron-density distribution in various oxidation states of Cr and V mono- and triscatecholato complexes have been discussed on the basis of the results of density functional calculations. A crystal and molecular structure of (Et3NH)2[V(IV)(cat)3] has been determined at 25 K and the same complex with an acetonitrile of crystallization at 150 K.
Nuclear shieldings, including the Fermi contact and pseudocontact terms, have been calculated with DFT methods in a variety of open-shell molecules (nitroxides, aryloxyl and various transition-metal complexes), thereby predicting (1)H and (13)C chemical shifts. In general, when experimental data are reliable a good agreement with experimental values is observed, thus demonstrating the predictive power of DFT also in this context. However, the general accuracy is lower than that for closed-shell species. A few inconsistencies in literature values are reconciled by reassigning some shifts. Structural, magnetic, and dynamic parameters have also been put into the Solomon-Bloembergen equations to predict signal line shapes, in particular those of signals that are difficult to locate or are undetectable. Guidelines are provided to predict the order of magnitude of relaxation rates. It is shown that DFT-predicted paramagnetic shifts can greatly assist in obtaining and understanding the NMR spectra of paramagnetic molecules, which generally require different experimental strategies and exhibit problems in detection and assignment.
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