Spinning Sideband Manifolds Research Articles

Effects of polymorphic differences for sulfanilamide, as seen through 13C and 15N solid‐state NMR, together with shielding calculations

We recorded both carbon-13 and nitrogen-15 NMR spectra of the three solid forms of sulfanilamide most commonly known. This study led to an interpretation of the solid-state effects seen in cross-polarization magic angle spinning spectra. Relaxation times for the different forms were measured. These show different behaviour for the three forms, arising from mobility variations. To obtain information on local environments, static spectra and spinning sideband manifolds were recorded and analysed for the 15N resonances, using isotopically enriched samples. Shielding asymmetries and anisotropies for the two nitrogen nuclei were obtained, showing very different behaviour for the two sites. Shielding calculations were carried out for both 13C and 15N nuclei, and the results are discussed in relation to the experimental values.

Solid‐state NMR studies of 1,3‐imidazolidine‐2‐selenone and some related compounds

AbstractSolid‐state cross‐polarization magic angle spinning 13C, 77Se and 15N NMR spectra were recorded for 1,3‐imidazolidine‐2‐selenone, its N‐substituted derivatives and some related compounds. The spinning sideband manifold intensities were used to obtain principal values of 13C and 77Se chemical shift tensors. Large selenium chemical shift anisotropies were observed for these selenones. Copyright © 2003 John Wiley & Sons, Ltd.

Vanadium‐51 MAS and Static NMR Studies of the Binary V2O5—WO3 System.

Solid-state NMR spectra showing single-quantum excitation of the vanadium-51 (I = 7/2) central and six satellite transitions were obtained for polycrystalline V2O5 and x%V2O5−(100 − x%)WO3 (10 mol % ≤ x ≤ 40 mol %) solids by magic angle spinning (MAS) and static NMR spectroscopies. All MAS spectra show full spinning sideband manifolds resulting from incomplete averaging of the chemical shift and quadrupolar interaction anisotropies. Chemical shift parameters (δiso, δaniso, ηcs) and quadrupolar parameters (CQ, ηQ) were obtained by simulation of both MAS and static spectra. A single vanadium site was observed in the nominally 40 mol % V2O5−60 mol % WO3 and 30 mol % V2O5−70 mol % WO3 compositions. Interpretation of NMR spectral parameters suggests that the vanadium in this single site resides in a square pyramid-like oxygen coordination environment. Three sites were observed for the nominally 20 mol % V2O5−80 mol % WO3 and 10 mol % V2O5−90 mol % WO3 compositions. The spectral parameters for the three sites a...

Determination of nitrogen chemical shift anisotropy from the second-order cross-term in 14N MAS NMR spectroscopy

A new method for determination of nitrogen chemical shift anisotropies (CSAs) employing 14N MAS NMR spectroscopy is presented. The method utilizes the effect of the second-order cross-term between the quadrupolar coupling and chemical shift interaction in the average Hamiltonian on the lineshape for the individual resonances within the manifold of 14N spinning sidebands, as illustrated by determination of the 14N CSA for Pb(NO 3) 2. The second-order functionality for this cross-term ensures that the CSA cannot be averaged by MAS. This is illustrated by determination of the 14N CSA for Pb(NO 3) 2 spinning (12 kHz) at twice the magnitude of the 14N CSA.

Vanadium-51 MAS and Static NMR Studies of the Binary V2O5−WO3 System

Solid-state NMR spectra showing single-quantum excitation of the vanadium-51 (I = 7/2) central and six satellite transitions were obtained for polycrystalline V2O5 and x%V2O5−(100 − x%)WO3 (10 mol % ≤ x ≤ 40 mol %) solids by magic angle spinning (MAS) and static NMR spectroscopies. All MAS spectra show full spinning sideband manifolds resulting from incomplete averaging of the chemical shift and quadrupolar interaction anisotropies. Chemical shift parameters (δiso, δaniso, ηcs) and quadrupolar parameters (CQ, ηQ) were obtained by simulation of both MAS and static spectra. A single vanadium site was observed in the nominally 40 mol % V2O5−60 mol % WO3 and 30 mol % V2O5−70 mol % WO3 compositions. Interpretation of NMR spectral parameters suggests that the vanadium in this single site resides in a square pyramid-like oxygen coordination environment. Three sites were observed for the nominally 20 mol % V2O5−80 mol % WO3 and 10 mol % V2O5−90 mol % WO3 compositions. The spectral parameters for the three sites a...

17O and 27Al MAS and 3QMAS NMR Study of Synthetic and Natural Layer Silicates

We report 17O and 27Al NMR results for 17O-enriched synthetic and natural layer silicates with significantly improved resolution of oxygen sites including basal and apical oxygens using 17O 3QMAS NMR spectroscopy. These oxygen sites have well-defined ranges of 17O isotropic chemical shifts (δiso) and quadrupolar coupling constants (Cq). The Cq of basal oxygen ([4]Si−O−[4]Si) range from 4.1 to 5.2 MHz for these phases, and δiso varies from 39 to 55 ppm. The δiso value of the basal oxygen sites increases with increasing Cq. The Cq and δiso values of apical oxygens ([4]Si−O−2[6]Al) are about 3.4 MHz and about 64 ppm, respectively, and are similar among the phases examined. The hydroxyl group (2[6]Al−OH) has the largest Cq (about 7 MHz) among the oxygen sites, as well as the most shielded chemical shift of about 37−44 ppm. Analysis of the 27Al MAS NMR spinning sideband manifolds yields precise NMR parameters for the [6]Al sites. 27Al MAS and 3QMAS NMR spectroscopies at 14.1 T yield excellent quantification of...

Quadrupole Coupling Parameters of Olefinic Deuterons: 2H MAS NMR Spectroscopy of Photochromic Spiropyran and Merocyanines

Three molecules with olefinic deuterons were obtained through H-D exchange of the C3 proton on the central bridging double bond of spiropyran photomerocyanines with deuterium oxide solution. Quadrupole coupling parameterswere determined by simulation of the spinning sideband manifolds in spectra obtained using solid-state deuterium MAS NMR spectroscopy. The C3-deuterated forms of the closed-ring spiropyran 1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2-indoline] (3D-6-nitro-BIPS) and the open-ring merocyanines 1',3',3'-trimethyl-6,8-dinitrospiro[2H-1-benzopyran-2,2-indoline] (3D-6,8-dinitro-BIPS) and 1',3',3'-trimethyl-6-nitro-8-bromospiro[2H-1-benzopyran-2,2-indoline] (3D-6-nitro-8-bromo-BIPS) had the same quadrupole coupling constants (QCCs) of 176 ′ 4 kHz. This value, the second reported for an olefinic deuteron, is slightly less than the QCCs known for rigid aromatic deuterons (180-185 kHz). The asymmetry parameters (η) for the latter two molecules (open rings) were 0.10 ′ 0.03, slightly larger than that observed for the closed-ring 3D-6-nitro-BIPS (0.00 ′ 0.03). This slight asymmetry of the electric field gradient around deuterium in the merocyanines is attributed to a small deviation of the C-D bond from perfect axial symmetry, probably resulting from a through-space interaction between C3-D and C9-O.

Determining the Lithium Local Environments in the Lithium Manganates LiZn0.5Mn1.5O4 and Li2MnO3 by Analysis of the 6Li MAS NMR Spinning Sideband Manifolds

Li2MnO3 and the spinel LiZn0.5Mn1.5O4 each contain a subset of lithium ions in very similar octahedral environments, in terms of the Li−O−Mn connectivities (i.e., numbers of nearby manganese ions and Li−O−Mn bond angles). We show, however, that the different geometric arrangements of the Mn ions about the lithium ions lead to very different spinning sideband manifold patterns, providing a simple method for distinguishing between the two different local environments. The dipolar coupling tensors which describe the coupling between the electron and nuclear magnetic moments are determined for the 2b site in Li2MnO3 and the octahedral site in LiZn0.5Mn1.5O4, on the basis of the crystallographic structures, and the spinning sideband patterns are calculated. Two types of axial symmetry, i.e., oblate and prolate symmetry, for the sites in Li2MnO3 and LiZn0.5Mn1.5O4, respectively, are obtained from the simulations, consistent with the experimental spectra. A good fit to the experimental spectrum was obtained, without considering the quadrupolar interaction, since the size of this interaction is small in comparison to the dipolar interaction even at the low field strengths used here (4.7 T). This study demonstrates that the 6Li MAS NMR spinning sideband manifolds are very sensitive to the arrangements of the first cation coordination sphere of Mn ions around the Li cations, providing a method for obtaining local structural information from these classes of materials.

59Co Chemical Shift Anisotropy and Quadrupole Coupling for K3Co(CN)6 from MQMAS and MAS NMR Spectroscopy

59Co triple-quantum (3Q) MAS and single-pulse MAS NMR spectra of K3Co(CN)6 have been obtained at 14.1 T and used in a comparison of these methods for determination of small chemical shift anisotropies for spin I=7/2 nuclei. From the 3QMAS NMR spectrum a spinning sideband manifold in the isotropic dimension with high resolution is reconstructed from the intensities of all spinning sidebands in the 3QMAS spectrum. The chemical shift anisotropy (CSA) parameters determined from this spectrum are compared with those obtained from MAS NMR spectra of (i) the complete manifold of spinning sidebands for the central and satellite transitions and of (ii) the second-order quadrupolar lineshapes for the centerband and spinning sidebands from the central transition. A good agreement between the three data sets, all of high precision, is obtained for the shift anisotropy (δσ=δiso−δzz) whereas minor deviations are observed for the CSA asymmetry parameter (ησ). The temperature dependence of the isotropic 59Co chemical shift has been studied over a temperature range from −28 to +76°C. A linear and positive temperature dependence of 0.97 ppm/°C is observed.

Solid-state NMR spectroscopy of paramagnetic metallocenes.

The paramagnetic metallocenes and decamethylmetallocenes (C(5)H(5))(2)M and (C(5)Me(5))(2)M with M=V (S=3/2), Mn (S=5/2 or 1/2), Co (S=1/2), and Ni (S=1) were studied by (1)H and (13)C solid-state MAS NMR spectroscopy. Near room temperature spinning sideband manifolds cover ranges of up to 1100 and 3500 ppm, and isotropic signal shifts appear between -260 and 300 ppm and between -600 and 1640 ppm for (1)H and (13)C NMR spectra, respectively. The isotropic paramagnetic signal shifts, which are related to the spin densities in the s orbital of ligand atoms, were discussed. A Herzfeld--Berger spinning sideband analysis of the ring carbon signals yielded the principal values of the paramagnetic shift tensors, and for metallocenes with a small g-factor anisotropy the electron spin density in the ligand pi system was determined from the chemical shift anisotropy. The unusual features of the (1)H and (13)C solid-state NMR spectra of manganocene were related to its chain structure while temperature-dependent (1)H MAS NMR studies reflected antiferromagnetic interaction between the spin centers.

207Pb NMR chemical shifts of lead tetracarboxylates

207Pb NMR spectroscopy was used to investigate 20 lead(IV) tetracarboxylates both in solution and in the solid state by cross-polarization magic angle spinning (CP/MAS) NMR. There is generally good correlation between isotropic chemical shifts in the solid state and those in solution. Multiple CP/MAS NMR isotropic resonances are observed for three of the compounds and are interpreted in terms of multiple molecules in the crystallographic asymmetric unit. From an analysis of the range of, and trends in, the NMR chemical shifts, circumstantial evidence is presented for augmentary coordination by Lewis basic ortho-aromatic substituents of the carboxylate groups. The 207Pb chemical shift anisotropy (CSA) parameters were extracted from analysis of the spinning sideband manifolds of the CP/MAS spectra. The CSA spreads are small in comparison with others reported for 207Pb, and all have positive skew, in contrast to the typical case for lead(II) compounds. Thirteen of the 20 CSA analyses performed show effectively axial CSA tensors. A simple shielding model which rationalizes this typical CSA pattern is presented, based on an analysis of geometric information derived from the two known single-crystal x-ray structures of lead(IV) carboxylates. Copyright © 2001 John Wiley & Sons, Ltd.

PATROS—A New MAS Exchange Method Using Sideband Separation: Application to Poly(n-butylmethacrylate)

The tr-ODESSA method (Reichert et al., J. Magn. Reson. 125, 245 (1997)), which is a 1D MAS experiment designed to monitor spin exchange involving both equivalent and inequivalent sites, is extended to situations where the spectrum consists of several spinning side band (ssb) manifolds with small chemical shift anisotropies. To increase the spectral resolution in such situations, the tr-ODESSA sequence is combined with that of PASS to a single experiment, which we term PATROS. In this hybrid experiment, magnetization transfer is monitored by the tr-ODESSA part, while the increase in resolution is provided by the separation of the ssb according to their order, during the PASS part. We demonstrate the feasibility of the method on a standard solid dimethylsulfone (DMS) sample and then apply it to monitor separately the ultraslow motions of the main- and side-chains in the polymer poly(n-butylmethacrylate). Theoretical expressions for the ssb intensities in PATROS experiments are derived and the merits and limitations of the method are discussed. Copyright 2000 Academic Press.

Initial conditions for carbon-13 MAS NMR 1D exchange involving chemically equivalent and inequivalent nuclei

A major problem in dynamic 1D (13)C MAS NMR concerns the exchange between magnetically inequivalent, but chemically equivalent sites, whose signals are not resolved in the regular 1D spectrum. This difficulty may be overcome by properly preparing the initial nonequilibrium state of the spin system in the exchange experiments. In the present paper we discuss the advantages and limitations of several such experiments already in use and propose a new sequence, which we term SELDOM-ODESSA. Unlike the other 1D-exchange methods, this experiment yields pure absorption spectra that can more readily be analyzed quantitatively. The experiment is a hybrid comprising a SELDOM sequence, for selective excitation of one of the spinning sideband manifolds in the spectrum, followed by the ODESSA sequence, which induces alternate polarization in the excited sideband manifold. The evolution of the spectrum following this sequence provides information on both the exchange between congruent sites belonging to the same group of equivalent nuclei, and the exchange between inequivalent sites. Results are presented for a tropolone sample specifically enriched in carbon-13 at the carbonyl and hydroxyl sites. The dominant exchange mechanism in this sample involves spin diffusion. The various spin exchange processes in this sample, in the presence and absence of proton decoupling during the mixing time, are measured and discussed. Copyright 2000 Academic Press.

Carbon-13 and Fluorine-19 NMR Spectroscopy of the Supramolecular Solid p-tert-Butylcalix[4]arene ·α,α,α-trifluorotoluene

The supramolecular 1:1 host–guest inclusion compound, p-tert-butylcalix[4]arene·α,α,α-trifluorotoluene, 1, is characterized by 19F and 13C solid-state NMR spectroscopy. Whereas the 13C NMR spectra are easily interpreted in the context of earlier work on similar host–guest compounds, the 19F NMR spectra of solid 1 are, initially, more difficult to understand. The 19F{1H} NMR spectrum obtained under cross-polarization and magic-angle spinning conditions shows a single isotropic resonance with a significant spinning sideband manifold. The static 19F{1H} CP NMR spectrum consists of a powder pattern dominated by the contributions of the anisotropic chemical shift and the homonuclear dipolar interactions. The 19F MREV-8 experiment, which minimizes the 19F–19F dipolar contribution, helps to identify the chemical shift contribution as an axial lineshape. The full static 19F{1H} CP NMR spectrum is analysed using subspectral analysis and subsequently simulated as a function of the 19F–19F internuclear distance (DFF=2.25±0.01 Å) of the rapidly rotating CF3 group without including contributions from additional libration motions and the anisotropy in the scalar tensor. The shielding span is found to be 56 ppm. The width of the centerband in the 19F{1H} sample-spinning CP NMR spectrum is very sensitive to the angle between the rotor and the magnetic field. Compound 1 is thus an attractive standard for setting the magic angle for NMR probes containing a fluorine channel with a proton-decoupling facility.

Multiple-Rotor-Cycle 2D PASS Experiments with Applications to 207Pb NMR Spectroscopy

Thetwo-dimensional phase-adjusted spinning sidebands (2D PASS) experiment is a useful technique for simplifying magic-angle spinning (MAS) NMR spectra that contain overlapping or complicated spinning sideband manifolds. The pulse sequence separates spinning sidebands by their order in a two-dimensional experiment. The result is an isotropic/anisotropic correlation experiment, in which a sheared projection of the 2D spectrum effectively yields an isotropic spectrum with no sidebands. The original 2D PASS experiment works best at lower MAS speeds (1–5 kHz). At higher spinning speeds (8–12 kHz) the experiment requires higher RF power levels so that the pulses do not overlap. In the case of nuclei such as 207Pb, a large chemical shift anisotropy often yields too many spinning sidebands to be handled by a reasonable 2D PASS experiment unless higher spinning speeds are used. Performing the experiment at these speeds requires fewer 2D rows and a correspondingly shorter experimental time. Therefore, we have implemented PASS pulse sequences that occupy multiple MAS rotor cycles, thereby avoiding pulse overlap. These multiple-rotor-cycle 2D PASS sequences are intended for use in high-speed MAS situations such as those required by 207Pb. A version of the multiple-rotor-cycle 2D PASS sequence that uses composite pulses to suppress spectral artifacts is also presented. These sequences are demonstrated on 207Pb test samples, including lead zirconate, a perovskite-phase compound that is representative of a large class of interesting materials.

Separation of 2H MAS NMR Spectra by Two-Dimensional Spectroscopy

New methods for optimum separation of 2H MAS NMR spectra are presented. The approach is based on hypercomplex spectroscopy that is useful for sign discrimination and phase separation. A new theoretical formalism is developed for the description of hypercomplex experiments. This exploits the properties of Lie algebras and hypercomplex numbers to obtain a solution to the Liouville–von Neumann equation. The solution is expressed in terms of coherence transfer functions that describe the allowed coherence transfer pathways in the system. The theoretical formalism is essential in order to understand all the features of hypercomplex experiments. The method is applied to the development of two-dimensional quadrupole-resolved 2H MAS NMR spectroscopy. The important features of this technique are discussed and two different versions are presented with widely different characteristics. An improved version of two-dimensional double-quantum 2H MAS NMR spectroscopy is developed. The conditions under which the double-quantum experiment is useful are discussed and its performance is compared with that observed for the quadrupole-resolved experiments. A general method is presented for evaluating the optimum pulse sequence parameters consistent with maximum sensitivity and resolution. This approach improves the performance of the experiments and is essential for any further development of the techniques. The effects of finite pulse width and hypercomplex data processing may lead to both intensity and phase distortions in the spectra. These effects are analyzed and general correction procedures are suggested. The techniques are applied to polycrystalline malonic-acid-2H4 for which the spinning sideband manifolds from the carboxyl and methylene deuterons are separated. The spinning sideband manifolds are simulated to determine the quadrupole parameters. The values are consistent with previous results, indicating that the techniques are both accurate and reliable.

H MAS and 1H/27Al TRAPDOR NMR Studies of Oxygen−Zeolite Interactions at Low Temperatures: Probing Bronsted Acid Site Accessibility

Sorption of oxygen in the pores of zeolite HY and 1H MAS NMR has been used to determine which Bronsted acid sites are accessible to oxygen. Large increases in the 1H spinning-sideband manifolds are observed at low temperatures for the supercage protons that can directly interact with the oxygen molecules; a much smaller increase in sideband intensity is seen for the sodalite protons. Dramatic reductions of the T1's of all the protons, of approximately 2 orders of magnitude, are observed at −150 °C, in comparison to T1 measurements made in air at room temperature, or at −150 °C for samples with adsorbed N2. The T1's of the supercage protons are, however, shorter than those measured for the sodalite protons. Both the decrease in the T1's, and the large sideband manifolds, are due to the dipolar coupling interactions with the unpaired electrons present on the O2 molecules. Second moment (M2) analysis is used to quantify the increase in the width of the 1H spinning sideband manifolds, in samples of zeolites H...

Solid-state NMR studies of fluorinated diazadiphosphetidines

A solid-state NMR study of three diazadiphosphetidines with fluorine substituents has been carried out in order to obtain information on structural and dynamic properties. The 19F and 31P spectra are discussed in relation to X-ray results. The NMR data depend on the substituents at both the phosphorus and nitrogen positions, and motional properties observed in solution-state NMR are slowed in the solid state, but can still be investigated. Axial and equatorial fluorine positions have been distinguished by (fluorine) chemical shift, effective shielding anisotropies and isotropic (JPF) coupling for (PhF2PNMe)2 at ambient probe temperature. Axial ⇆ equatorial exchange is also shown to be slowed on the NMR timescale for (F3PNPh)2 at low temperature. Analysis of spinning sideband manifolds has yielded data on effective shielding anisotropies for both 31P and 19F spectra. Triple resonance 31P-{19F, 1H} experiments have allowed the determination of true shielding tensor parameters. For (Ph2FPNMe)2 a triple-fit procedure has provided additional data, though not to high accuracy. Static 19F and 31P spectra, MAS 13C and 15N spectra and some relaxation times are also reported and discussed.

A 6Li, 7Li and 59Co MAS NMR study of rock salt type Li xCoO 2 (0.48≤ x≤1.05)

Low temperature (LT, 400°C) and high temperature (HT, 900°C) Li x CoO 2 samples were synthesised with Li/Co ratios between 0.8 and 1.05. These samples were characterised by XRD, chemical analysis, 6Li, 7Li and 59Co MAS NMR. 7Li MAS NMR of the Li x CoO 2-T 400 samples (LT) showed a single resonance line at −0.9 ppm, characteristic of lithium in an octahedral coordination. A somewhat narrower resonance at the same position was observed in the 7Li MAS NMR spectra of the Li x CoO 2-T 900 samples synthesised with a Li/Co ratio ≤0.95. The Li x CoO 2-T 900 samples synthesised with a Li/Co ratio >0.95 showed several new lithium resonances, containing up to 35% of the signal intensity. The resonance positions of these new resonances indicate the presence of a paramagnetic cobalt species in the material. The 59Co MAS NMR spectra of the Li x CoO 2-T 900 samples revealed a spinning sideband manifold centred at ≈14 250 ppm for x ≤0.95 and three overlapping spinning sideband manifolds at ≈14 285, ≈14 260 and ≈14 230 ppm for Li/Co ratios >0.95. Compared to the Li x CoO 2-T 900 samples the Li x CoO 2-T 400 samples all showed one resonance with an increased line width. These resonance positions are typical for Co 3+ octahedrally coordinated by oxygen. No quadrupole induced shift is observed as a function of the external field (measurements performed at 14.1 and 7.05 T), indicating an undistorted octahedral coordination of cobalt in the materials studied. Chemical extraction of lithium with H 2SO 4 leads to the formation of lithium that can not be detected with NMR. Electrochemical extraction of lithium, on the other hand, leads to a low field shift of the lithium resonance of 60–120 ppm, depending on the amount of lithium removed. Electrochemical intercalation (discharging) of the samples results in the reappearance of the original lithium spectra, showing the excellent reversibility of the charge/discharge process. Partly charged samples are characterised by signals in the range of 120–60 ppm and a signal at −0.9 ppm, indicating that part of the lithium remains in an unchanged environment. The dependence of the chemical shift on the amount of lithium removed is due to an rapid exchange process.

171Yb Cross-Polarization Magic Angle Spinning NMR Spectroscopic Studies of Organometallic Compounds: Bis(cyclopentadienyl) Derivatives

A series of nine Yb(II) bis(cyclopentadienyl) complexes have been studied by 171Yb CP MAS (cross polarization magic angle spinning) NMR spectroscopy. The optimization of the cross polarization conditions are described. The proton T1ρ values have been determined. The spinning side band manifold for each compound has been analyzed. The derived chemical shift tensor data are discussed with respect to molecular structure elucidation.