Electron spin resonance spectra of tetragonal chromium(III) complexes.  II.  Frozen-solution and powder spectra of [CR(NH3)5X]n+.  Correlation with zero-field splittings and g factors obtained from complete d3-configuration calculations

Pedersen, Erik; Kallesoee, S.

doi:10.1021/ic50143a018

Cited by 19 publications

(3 citation statements)

References 28 publications

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“…No hyperfine coupling is resolved at the g ∥ feature, and from the width of this feature it can be concluded that the 14 N hyperfine coupling in this direction must be smaller than 25 MHz. This type of spectrum is expected for a zero-field splitting (ZFS) with axial symmetry that is significantly larger than the microwave frequency . The spectrum can be simulated with ZFS parameters D = 23 GHz and E = 0 as well as with an isotropic g value of 1.999 (ESI Figure S5).…”

Section: Resultsmentioning

confidence: 97%

“…This type of spectrum is expected for a zero-field splitting (ZFS) with axial symmetry that is significantly larger than the microwave frequency. 25 The spectrum can be simulated with ZFS parameters D = 23 GHz and E = 0 as well as with an isotropic g value of 1.999 (ESI Figure S5). Note, however, that such a large ZFS can be determined only approximately at a much smaller microwave frequency.…”

Section: ■ Resultsmentioning

confidence: 99%

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Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

et al. 2017

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Grafting molecular precursors on partially dehydroxylated silica followed by a thermal treatment yields silica-supported M(III) sites for a broad range of metals. They display unique properties such as high activity in olefin polymerization and alkane dehydrogenation (M = Cr) or efficient luminescence properties (M = Yb and Eu) essential for bioimaging. Here, we interrogate the local structure of the M(III) surface sites obtained from two molecular precursors, amides M(N(SiMe)) vs siloxides (M(OSi(OBu))·L with L = (THF) or HOSi(OBu) for M = Cr, Yb, Eu, and Y, by a combination of advanced spectroscopic techniques (EPR, IR, XAS, UV-vis, NMR, luminescence spectroscopies). For paramagnetic Cr(III), EPR (HYSCORE) spectroscopy shows hyperfine coupling to nitrogen only when the amide precursor is used, consistent with the presence of nitrogen neighbors. This changes their specific reactivity compared to Cr(III) sites in oxygen environments obtained from siloxide precursors: no coordination of CO and oligomer formation during the polymerization of ethylene due to the presence of a N-donor ligand. The presence of the N-ligand also affects the photophysical properties of Yb and Eu by decreasing their lifetime, probably due to nonradiative deactivation of excited states by N-H bonds. Both types of precursors lead to a distribution of surface sites according to reactivity for Cr, luminescence spectroscopy for Yb and Eu, and dynamic nuclear polarization surface-enhanced Y NMR spectroscopy (DNP SENS). In particular, DNP SENS provides molecular-level information about the structure of surface sites by evidencing the presence of tri-, tetra-, and pentacoordinated Y-surface sites. This study provides unprecedented evidence and tools to assess the local structure of metal surface sites in relation to their chemical and physical properties.

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Section: Resultsmentioning

confidence: 97%

Section: ■ Resultsmentioning

confidence: 99%

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

et al. 2017

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“…The D parameter has not been measured for Cr(III)−TSPP. ESR studies of six-coordinate complexes with tetragonal , and trigonal fields have given values in the range 0.03−2 cm -1 .…”

Section: Theorymentioning

confidence: 99%

NMR-Paramagnetic Relaxation Due to the High-Spin d³ Electron Configuration: Cr(III)−TSPP

Schaefle¹,

Sharp²

2005

J. Phys. Chem. A

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Sulfonated metalloporphyrins (Me-TSPP, where Me = Cr(III), Mn(III), Fe(III), and Mn(II)) comprise a well-characterized series of water-soluble paramagnetic complexes with electron spins of S = 3/2, 2, 5/2, and 5/2, respectively, which provide important model systems for mechanistic studies of paramagnetic NMR relaxation in solution. Previous studies of Mn(III), Fe(III), and Mn(II)-TSPP have uncovered relaxation mechanisms which differ qualitatively from each other and exhibit numerous unexpected features. In this study, Cr(III)-TSPP was examined as a model system for the d3 S = 3/2 electron configuration. Magnetic relaxation dispersion (MRD) profiles of the water proton R1 were measured as a function of pH between pH 1 and pH 9. In acid samples, R1 results from acid-catalyzed prototropic chemical exchange involving the Cr(III)-TSPP x 2 H2O. In neutral and basic solution, this species deprotonates, and base-catalyzed prototropic exchange becomes important. The pH 1 data were analyzed quantitatively using theory that accounts for the role of the permanent zero field splitting (zfs) tensor and for the effects of Brownian reorientation. Two levels of theory were employed: (1) spin dynamics simulation, which accurately describes the effects of Brownian reorientation on the spin wave functions, and (2) the "constant H(S)" approximation, which incorporates the effects of multiexponential electron spin relaxation and facilitates the physical interpretation of the relaxation mechanism. It was found that neither level of theory alone provides a fully satisfactory quantitative description of the data due to the fact that both reorientational modulation of the spin wave functions and multiexponential electron spin relaxation are important. The zero field splitting parameter, D = 0.27 cm(-1), is well defined by the data and was measured.

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ChemInform Abstract: ELECTRON SPIN RESONANCE SPECTRA OF TETRAGONAL CHROMIUM(III) COMPLEXES PART 2, FROZEN‐SOLUTION AND POWDER SPECTRA OF (CR(NH3)5X)(N+), A CORRELATION WITH ZERO‐FIELD SPLITTINGS AND G FACTORS OBTAINED FROM COMPLETE D(3)‐CONFIGURATION CALCULATIONS

Pedersen¹

1975

Chemischer Informationsdienst

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Electron spin resonance spectra of tetragonal chromium(III) complexes. II. Frozen-solution and powder spectra of [CR(NH3)5X]n+. Correlation with zero-field splittings and g factors obtained from complete d3-configuration calculations

Cited by 19 publications

References 28 publications

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

NMR-Paramagnetic Relaxation Due to the High-Spin d³ Electron Configuration: Cr(III)−TSPP

ChemInform Abstract: ELECTRON SPIN RESONANCE SPECTRA OF TETRAGONAL CHROMIUM(III) COMPLEXES PART 2, FROZEN‐SOLUTION AND POWDER SPECTRA OF (CR(NH3)5X)(N+), A CORRELATION WITH ZERO‐FIELD SPLITTINGS AND G FACTORS OBTAINED FROM COMPLETE D(3)‐CONFIGURATION CALCULATIONS

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Electron spin resonance spectra of tetragonal chromium(III) complexes. II. Frozen-solution and powder spectra of [CR(NH3)5X]n+. Correlation with zero-field splittings and g factors obtained from complete d3-configuration calculations

Cited by 19 publications

References 28 publications

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies

NMR-Paramagnetic Relaxation Due to the High-Spin d3 Electron Configuration: Cr(III)−TSPP

ChemInform Abstract: ELECTRON SPIN RESONANCE SPECTRA OF TETRAGONAL CHROMIUM(III) COMPLEXES PART 2, FROZEN‐SOLUTION AND POWDER SPECTRA OF (CR(NH3)5X)(N+), A CORRELATION WITH ZERO‐FIELD SPLITTINGS AND G FACTORS OBTAINED FROM COMPLETE D(3)‐CONFIGURATION CALCULATIONS

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NMR-Paramagnetic Relaxation Due to the High-Spin d³ Electron Configuration: Cr(III)−TSPP