15 T, 4.2 K field-swept 27Al NMR spectroscopy

Wu, Xiao; Juban, Eric A.; Butler, Leslie G.

doi:10.1016/0009-2614(94)87017-9

Cited by 17 publications

(19 citation statements)

References 13 publications

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“…Stepped-frequency [15,17] and swept-frequency [15,18,19] techniques have been applied to acquire wideline 27 Al NMR spectra of solid materials. However, the main disadvantage of these techniques is the large number of scans, and correspondingly long time periods, required to acquire such spectra.…”

Section: H{mentioning

confidence: 99%

Ultra‐wideline ²⁷Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

et al. 2006

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Ultra-wideline 27Al NMR experiments are conducted on coordination compounds with 27Al nuclei possessing immense quadrupolar interactions that result from exceptionally nonspherical coordination environments. NMR spectra are acquired using a methodology involving frequency-stepped, piecewise acquisition of NMR spectra with Hahn-echo or quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences, which is applicable to any half-integer quadrupolar nucleus with extremely broad NMR powder patterns. Despite the large breadth of these central transition powder patterns, ranging from 250 to 700 kHz, the total experimental times are an order of magnitude less than previously reported experiments on analogous complexes with smaller quadrupolar interactions. The complexes examined feature three- or five-coordinate aluminum sites: trismesitylaluminum (AlMes3), tris(bis(trimethylsilyl)amino)aluminum (Al(NTMS2)3), bis[dimethyl tetrahydrofurfuryloxide aluminum] ([Me2-Al(mu-OTHF)]2), and bis[diethyl tetrahydrofurfuryloxide aluminum] ([Et2-Al(mu-OTHF)]2). We report some of the largest 27Al quadrupolar coupling constants measured to date, with values of C(Q)(27Al) of 48.2(1), 36.3(1), 19.9(1), and 19.6(2) MHz for AlMes3, Al(NTMS2)3, [Me2-Al(mu-OTHF)]2, and [Et2-Al(mu-OTHF)]2, respectively. X-ray crystallographic data and theoretical (Hartree-Fock and DFT) calculations of 27Al electric field gradient (EFG) tensors are utilized to examine the relationships between the quadrupolar interactions and molecular structure; in particular, the origin of the immense quadrupolar interaction in the three-coordinate species is studied via analyses of molecular orbitals.

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Section: H{mentioning

confidence: 99%

Ultra‐wideline ²⁷Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

et al. 2006

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“…Fortunately, aluminum is often found in relatively spherically symmetric environments that correspond to minor to moderate spectral broadening of the CT. [37][38][39] In instances of asymmetric local Al environments, severely broadened 27 Al SSNMR spectra have been reported. [40][41][42][43][44][45][46] The axial symmetry of the local electronic environment is described by Q , which ranges in value from 0 to 1, where a low Q value corresponds to high axial symmetry. Herein, we use a combination of thermal gravimetric analysis (TGA), powder X-ray diffraction (pXRD), and SSNMR experiments to investigate the various structural changes associated with adsorption of eight different organic guest molecules in MIL-53: acetone, diethylamine, isopropanol, isopropylamine, n-butanol, pyridine, styrene, and ethylbenzene.…”

Section: Introductionmentioning

confidence: 99%

Investigating adsorption of organic compounds in metal-organic framework MIL-53

Ibrahim

et al. 2015

Can. J. Chem.

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Metal-organic frameworks (MOFs) are versatile materials that incorporate metal centers along with organic linkers in highly ordered, intricate structures. MIL-53 is a MOF that exhibits a "breathing effect," where the pore size and MOF topology are profoundly influenced by the identity and binding mechanism of guest molecules. This phenomenon renders MIL-53 a promising candidate for sensing applications. In this report, the adsorption of various organic compounds within MIL-53 is investigated using a combination of complementary techniques. Thermal gravimetric analysis experiments confirm loading of the guest molecules and yield insight into adsorption interactions and strengths. Significant guest-induced changes in the crystal structure of MIL-53 are revealed by powder X-ray diffraction experiments; specific unique phases of MIL-53 are related to the identity of the guest molecule and its binding mechanism to the framework. 27 Al and 13 C solid-state NMR experiments probe the interaction between guest molecules and MIL-53. The relationship between the nature of the guest, the structure of MIL-53, and 27 Al NMR parameters is explored. 27 Al NMR parameters are sensitive to the host-guest binding mechanism (i.e., hydrogenbonding or -stacking interactions) and yield valuable information regarding the influence of the adsorbates on the local aluminum environment. This combination of physical characterization techniques is a useful probe of guest adsorption and the breathing effect within MIL-53 and should prove useful for investigation of related MOFs. Résumé: Les réseaux métallo-organiques (MOF, acronyme anglais pour Metal-Organic Frameworks) sont des matériaux polyvalents où des centres métalliques sont incorporés dans un réseau organique formant des structures complexes et hautement ordonnées. Le MIL-53 est un réseau métallo-organique présentant un « effet de respiration », dont la taille des pores et la topologie du réseau métallo-organique dépendent fortement de l'identité et du mécanisme de liaison des molécules invitées. Ce phénomène fait du MIL-53 un candidat prometteur pour des applications dans le domaine des capteurs. Dans les présents travaux, nous avons étudié l'adsorption de divers composés organiques au MIL-53 à l'aide d'un ensemble de techniques complémentaires. Des analyses thermogravimétriques confirment la charge de molécules invitées et fournissent un aperçu des interactions et des forces d'adsorption. Des expériences de diffraction des rayons X sur poudre ont permis de révéler des modifications importantes de la structure cristalline du MIL-53 induites par l'invité; des phases uniques propres au MIL-53 sont liées à l'identité de l'invité et à son mécanisme de liaison au réseau. Des expériences de RMN 27 Al et 13 C à l'état solide ont permis d'explorer les interactions entre les molécules invitées et le MIL-53. Nous avons étudié la relation entre la nature de l'invité, la structure du MIL-53 et les paramètres RMN 27 Al. Ces derniers sont sensibles au mécanisme de liaison hôte-invité (c.-à -d. les l...

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“…29 Recently, methods designed to access the full, quadrupolar-broadened line-shape have returned. [30][31][32][33] In these methods, either the field or the frequency is adjusted as the spectrum is acquired piecewise over an unlimited spectral range.…”

Section: Introductionmentioning

confidence: 99%

Structural Characterization of MAO and Related Aluminum Complexes. 1. Solid-State ²⁷Al NMR with Comparison to EFG Tensors from ab Initio Molecular Orbital Calculations

et al. 2001

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Experimental and ab initio molecular orbital techniques are developed for study of aluminum species with large quadrupole coupling constants to test structural models for methylaluminoxanes (MAO). The techniques are applied to nitrogen- and oxygen-containing complexes of aluminum and to solid MAO isolated from active commercial MAO preparations. (Aminato)- and (propanolato)aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three (27)Al NMR techniques optimized for large (27)Al quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. Four-membered (aminato)aluminum complexes with AlN(4) coordination yield slightly smaller C(q) values than similar AlN(2)C(2) sites: 12.2 vs 15.8 MHz. Planar 3-coordinate AlN(2)C sites have the largest C(q) values, 37 MHz. In all cases, molecular orbital calculations of the electric field gradient tensors yields C(q) and eta values that match with experiment, even for a large hexameric (aminato)aluminum cage. A D(3d) symmetry hexaaluminum oxane cluster, postulated as a model for MAO, yields a calculated C(q) of -23.7 MHz, eta = 0.7474, and predicts a spectrum that is too broad to match the field-swept NMR of methylaluminoxane, which shows at least three sites, all with C(q) values greater than 15 MHz but less than 21 MHz. Thus, the proposed hexaaluminum cluster, with its strained four-membered rings, is not a major component of MAO. However, calculations for dimers of the cage complex, either edge-bridged or face-bridged, show a much closer match to experiment. Also, MAO preparations differ, with a gel form of MAO having significantly larger (27)Al C(q) values than a nongel form, a conclusion reached on the basis of (27)Al NMR line widths in field-swept NMR spectra acquired from 13 to 24 T.

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15 T, 4.2 K field-swept 27Al NMR spectroscopy

Cited by 17 publications

References 13 publications

Ultra‐wideline ²⁷Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Ultra‐wideline ²⁷Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Investigating adsorption of organic compounds in metal-organic framework MIL-53

Structural Characterization of MAO and Related Aluminum Complexes. 1. Solid-State ²⁷Al NMR with Comparison to EFG Tensors from ab Initio Molecular Orbital Calculations

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15 T, 4.2 K field-swept 27Al NMR spectroscopy

Cited by 17 publications

References 13 publications

Ultra‐wideline 27Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Ultra‐wideline 27Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Investigating adsorption of organic compounds in metal-organic framework MIL-53

Structural Characterization of MAO and Related Aluminum Complexes. 1. Solid-State 27Al NMR with Comparison to EFG Tensors from ab Initio Molecular Orbital Calculations

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Ultra‐wideline ²⁷Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Ultra‐wideline ²⁷Al NMR Investigation of Three‐ and Five‐Coordinate Aluminum Environments

Structural Characterization of MAO and Related Aluminum Complexes. 1. Solid-State ²⁷Al NMR with Comparison to EFG Tensors from ab Initio Molecular Orbital Calculations