Solid‐State NMR Investigation of Ligand Mobility and Reactivity in Transition Metal Complexes

Chierotti, Michele R.; Gobetto, Roberto

doi:10.1002/ejic.200801205

Cited by 19 publications

(17 citation statements)

References 158 publications

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“…Indeed the small shifts observed, in particular those related to the carbonyl group resonance (3 CdO: from 188.5 to 191.4 ppm) and to peripheral C atoms of the aromatic rings (6 CH: from 134.6 to 138.3 ppm), are indicative of an intervened inclusion of the dye with the presence of weak interactions between the host and the guest. 83,84 The detected variations are consistent, although less evident, with those reported in previous works: most pronounced shifts, in fact, are known to appear at higher indigo content (11.5 wt %) and temperature (g280°C). 25 A lesser indigo amount (2 wt %) coupled with a less intense heating treatment (190°C), which are consistent with those typical of the original Mayan artifact, therefore justifies the observed decrease in the magnitude of the detected variations.…”

Section: Resultssupporting

confidence: 92%

Host/Guest Interactions in a Sepiolite-Based Maya Blue Pigment: A Spectroscopic Study

et al. 2011

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Maya Blue pigment forms through heating-induced encapsulation and bonding of indigo in microporous clays, namely, palygorskite or sepiolite. Stabilizing host/guest interactions in a sepiolite-based Maya Blue were investigated by means of vibrational and NMR spectroscopies and proved to be H-bonds formed between indigo reactive groups and the clay structural OH2. Indigo sorption inhibits sepiolite structural folding induced by partial OH2 loss with temperature rise, but despite this, no direct Mg/indigo bonding was detected. Encapsulation is favored by breaking of intermolecular bonds, allowing dye diffusion inside the clay microtunnels. H-bond formation involves both CO/N–H indigo groups, its molecule undergoing distortion and partial oxidation to dehydroindigo. Both the strength and number of sepiolite/indigo interactions are less marked than those occurring in a palygorskite-based composite. In the wider sepiolite channels, H-bonds can form only on one side of the guest molecule, whereas both sides are involved in palygorskite. Halving in bond number undermines the stability of the resulting adduct.

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Section: Resultssupporting

confidence: 92%

Host/Guest Interactions in a Sepiolite-Based Maya Blue Pigment: A Spectroscopic Study

et al. 2011

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“…These motions can cover a wide range of correlation times from very fast processes that occur in nanoseconds down to very slow motions of the order of seconds. 58 Since the aim of the dynamic investigation is the quantification of the time scale of the motion and the geometric interpretation of the molecular process, the type and the correlation time of dynamics determine the choice of experiments and techniques. The SSNMR represents a powerful tool for the investigation of molecular dynamics due to the possibility offered by the use of different parameters to cover a wide timescale of a fluxional process from 10 2 to 10 −10 s. When the motion occurs it determines variations in the NMR spectra that are dependent from the strength of the interaction tensors, the correlation time of the motion and the orientation of the interaction tensors with respect to the external magnetic field.…”

Section: Dynamics In Supramolecular Systemsmentioning

confidence: 99%

Solid‐State NMR Studies on Supramolecular Chemistry

Chierotti

Gobetto

2012

Supramolecular Chemistry

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Solid‐state NMR (SSNMR) methods provide new insights in the investigation of the structure and dynamics of condensed phases. Advances in commercial solid‐state hardware and the developments of new pulse sequences have been of paramount importance for overcoming the earlier resolution problems and yield spectra sensitive to intra‐ and intermolecular hydrogen‐bonding and π–π interactions. This chapter aims to provide an overview of the recent development of the technique for the study of the structure and dynamics of supramolecular systems paying particular attention to the role of the weak interactions such as hydrogen bonds through NMR chemical shift as well as the through‐space dipolar coupling SSNMR investigations.

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“…[5] Depending on the complexity of the system investigated, the results obtained can consist of the determination of a generic "degree of mobility", useful in comparing similar systems, or of more detailed parameters characteristic of specific motions, such as the "geometry" of the motion, correlation times, and activation energies. The nuclear properties exploited to obtain these results include different types of relaxation times (T 1 , T 2 , T 11 ), chemical shift anisotropy, residual dipolar coupling, and quadrupolar interaction.…”

Section: Introductionmentioning

confidence: 99%

Detailed Characterization of the Dynamics of Ibuprofen in the Solid State by a Multi‐Technique NMR Approach

2011

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The internal rotations and interconformational jumps of ibuprofen in the solid state are fully characterized by the simultaneous analysis of a variety of low- and high-resolution NMR experiments for the measurement of several (13)C and (1)H spectral and relaxation properties, performed at different temperatures and, in some cases, frequencies. The results are first qualitatively analyzed to identify the motions of the different molecular fragments and to assign them to specific frequency ranges (slow, <10(3) Hz; intermediate, 10(3)-10(6) Hz; and fast, >10(6) Hz). In a second step, a simultaneous fit of the experimental data sets most sensitive to each frequency range is performed by means of suitable motional models to obtain, for each motion, values of correlation times and activation energies. The rotations of the three methyl groups around their ternary symmetry axes, which occur in the fast regime, are characterized by slightly different activation energies. Thanks to the simultaneous analysis of (1)H and (13)C data, the π-flip of the dimeric structure made by the acidic groups is also identified and seen to occur in the fast regime. On the contrary, the π-flip of the phenyl ring is found to occur in the slow motional regime, while the rotations of the isobutyl and propionic groups are frozen. The approach used appears to be of general applicability for studying the dynamics of small organic molecules.

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Solid‐State NMR Investigation of Ligand Mobility and Reactivity in Transition Metal Complexes

Cited by 19 publications

References 158 publications

Host/Guest Interactions in a Sepiolite-Based Maya Blue Pigment: A Spectroscopic Study

Host/Guest Interactions in a Sepiolite-Based Maya Blue Pigment: A Spectroscopic Study

Solid‐State NMR Studies on Supramolecular Chemistry

Detailed Characterization of the Dynamics of Ibuprofen in the Solid State by a Multi‐Technique NMR Approach

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