Paramagnetic Shifts Research Articles

Influence of particle size on solid solution formation and phase interfaces in Li0.5FePO4 revealed by 31P and 7Li solid state NMR spectroscopy

Here we report the observation of electron delocalization in nano-dimension xLiFePO(4):(1 - x)FePO(4) (x = 0.5) using high temperature, static, (31)P solid state NMR. The (31)P paramagnetic shift in this material shows extreme sensitivity to the oxidation state of the Fe center. At room temperature two distinct (31)P resonances arising from FePO(4) and LiFePO(4) are observed at 5800 ppm and 3800 ppm, respectively. At temperatures near 400 °C these resonances coalesce into a single narrowed peak centered around 3200 ppm caused by the averaging of the electronic environments at the phosphate centers, resulting from the delocalization of the electrons among the iron centers. (7)Li MAS NMR spectra of nanometre sized xLiFePO(4):(1 - x)FePO(4) (x = 0.5) particles at ambient temperature reveal evidence of Li residing at the phase interface between the LiFePO(4) and FePO(4) domains. Moreover, a new broad resonance is resolved at 65 ppm, and is attributed to Li adjacent to the anti-site Fe defect. This information is considered in light of the (7)Li MAS spectrum of LiMnPO(4), which despite being iso-structural with LiFePO(4) yields a remarkably different (7)Li MAS spectrum due to the different electronic states of the paramagnetic centers. For LiMnPO(4) the higher (7)Li MAS paramagnetic shift (65 ppm) and narrowed isotropic resonance (FWHM ≈ 500 Hz) is attributed to an additional unpaired electron in the t(2g) orbital as compared to LiFePO(4) which has δ(iso) = -11 ppm and a FWHM = 9500 Hz. Only the delithiated phase FePO(4) is iso-electronic and iso-structural with LiMnPO(4). This similarity is readily observed in the (7)Li MAS spectrum of xLiFePO(4):(1 - x)FePO(4) (x = 0.5) where Li sitting near Fe in the 3+ oxidation state takes on spectral features reminiscent of LiMnPO(4). Overall, these spectral features allow for better understanding of the chemical and electrochemical (de)lithiation mechanisms of LiFePO(4) and the Li-environments generated upon cycling.

Synthesis, complexation and NMR relaxation properties of Gd3+ complexes of Mes(DO3A)3

Medium sized molecules endowed with multiple Gd(3+) complexes are efficient high magnetic field MRI contrast agents. The novel ligand Mes(DO3A)(3), presenting three DO3A (1,4,7,10-tetraazacyclododecane-N,N',N''-triacetatic acid) units grafted on the methyl positions of a central mesitylene (1,3,5-trimethylbenzene), has been synthesized. Designed as an MRI contrast agent, this ligand is complexed with Gd(3+) and its efficiency is characterized by variable field (1)H-NMR and variable temperature (17)O-NMR. The evaluation of the relaxation and paramagnetic chemical shift data allowed the identification of an undesired binuclear complex which is obtained by using the classical procedure for complexation as described in the literature. An intramolecular capping mechanism appears to be responsible for the failure to introduce a third Gd(3+) ion into the ligand. A new alternative method, based on pre-complexation with Mg(2+) followed by transmetallation is described here and leads to the expected trinuclear Gd(3+) complex [Mes{Gd(DO3A)(H(2)O)(2)}(3)]. The rate constants for the water exchange (k(ex)(298) = 32 × 10(6) s(-1)) for the bi- and trinuclear complex appeared to be the same, which is surprising in relation to the difference in the charge of the complex and to the difference in the number of coordinated water molecules, one and two per Gd(3+) for the binuclear and trinuclear complex, respectively.

Biferrocene Amino Acid, a Ferrocenylogoue of Ferrocene Amino Acid: Synthesis, Cross-Linking, and Redox Chemistry

Access of the novel biferrocene amino acid 7 is provided by two different routes, namely, via desymmetrization of a biferrocene and via palladium-catalyzed cross-coupling of two substituted ferrocenes. The dissymmetric biferrocene 7 is head−head coupled to ureylene-bridged bis(biferrocene) 9 and also head−tail coupled to amide-bridged bis(biferrocene) 14. The monomer 7 and the dimers 9 and 14 are oxidized to mixed-valent cations 7+, 9+, 92+, and 142+. The valencies are trapped in the solid state as shown by Mössbauer and EPR spectroscopy and by X-ray diffraction analysis of [7](I3). Paramagnetic NMR shift studies (7 → 7+) suggest that the hole is localized at the N-substituted ferrocene unit [BocNH-{III}-{II}-COOMe]+. According to DFT calculations and individual redox potentials, the dications 92+ and 142+ are best described as [MeOOC-{II}-{III}-NHCONH-{III}-{II}-COOMe]2+ and [BocNH-{III}-{II}-CONH-{III}-{II}-COOMe]2+ valence isomers, respectively. The interaction between neighboring ferrocene/ferrocenium sites in the mixed-valent systems is determined by Hush analyses of the NIR intervalence bands. The extent depends on the bridge type (direct link, amide, ureylene) and the zero-point difference of the individual redox-active units.

Predicting the 1H and 13C NMR spectra of paramagnetic Ru(III) complexes by DFT

Nuclear shieldings, including the Fermi-contact and pseudocontact terms, have been calculated with density functional theory (DFT) (nonrelativistic and relativistic) methods in several Ru(III) complexes, thereby predicting (1)H and (13)C paramagnetic shifts. A fair agreement with experimental values is observed. Structural, magnetic and dynamic parameters have also been input to the Solomon-Bloembergen equation in order to predict signal lineshapes. It is shown that DFT-predicted paramagnetic shifts can greatly aid in obtaining and understanding NMR spectra of paramagnetic Ru(III) complexes.

13C NMR study of D-pantothenic acid complexes with heavy lanthanide ions in aqueous solution

The 13C NMR study of the interaction between the trivalent lanthanide ions (from Dy to Lu) and D-pantothenic acid in aqueous solution was presented. The unambiguous resonance assignments were made on the basis of pH dependence and the analysis of molecular geometry. 13C paramagnetic shifts were separated into the contact and dipolar components by Reilley's method. The complex stability constant is 12.0 L / mol for the 1:1 ytterbium complex. An analysis of the shift data shows that heavy lanthanide ions form isostructural complexes with the substrate and the hyperfine coupling constant is independent of the ions used in the study. D-pantothenic acid is coordinated to the metal via the two oxygens of the carboxyl group with 2.25Å of Ln—O distances. The electron spin density distribution and the structural details of the complex were elucidated from the shift data. It is stated that contact contributions, while small for nuclei of several bonds away from the metal, should not be dismissed a priori.

Orientation of the axial ligands and magnetic properties of the hemes in the triheme ferricytochrome PpcA from G. sulfurreducens determined by paramagnetic NMR

The geometry of the axial ligands of the hemes in the triheme cytochrome PpcA from Geobacter sulfurreducens was determined in solution for the ferric form using the unambiguous assignment of the NMR signals of the α-substituents of the hemes. The paramagnetic 13C shifts of the hemes can be used to define the heme electronic structure, the geometry of the axial ligands, and the magnetic susceptibility tensor. The latter establishes the magnitude and geometrical dependence of the pseudocontact shifts, which are crucial to warrant reliable structural constraints for a detailed structural characterization of this paramagnetic protein in solution.

Magnetic properties of the geometrically frustratedS=12antiferromagnets,La2LiMoO6andBa2YMoO6, with the B-site ordered double perovskite structure: Evidence for a collective spin-singlet ground state

Two B-site ordered double perovskites, La2LiMoO6 and Ba2YMoO6, based on the S = 1/2 ion, Mo5+, have been investigated in the context of geometric magnetic frustration. Powder neutron diffraction, heat capacity, susceptibility, muon spin relaxation(_SR), and 89Y NMR- including MAS NMR- data have been collected. La2LiMoO6 deviates strongly from simple Curie-Weiss paramagnetic behavior below 150K and zero-field cooled/ field cooled (ZFC/FC)irreversibility occurs below 20K with a weak, broad susceptibility maximum near 5K in the ZFC data. A Curie-Weiss fit shows a reduced mu_eff=1.42\mu_B, (spin only = 1.73 muB) and a Weiss temperature, \theta_c, which depends strongly on the temperature range of the fit. Powder neutron diffraction, heat capacity and 7Li NMR show no evidence for long range magnetic order to 2K. On the other hand oscillations develop below 20K in muSR indicating at least short range magnetic correlations. Susceptibility data for Ba2YMoO6 also deviate strongly from the C-W law below 150K with a similarly reduced mu_eff = 1.72\mu_B and \theta_c = - 219(1)K. Heat capacity, neutron powder diffraction and muSR data show no evidence for long range order to 2K but a very broad maximum appears in the heat capacity. The 89Y NMR paramagnetic Knight shift shows a remarkable local spin susceptibility behavior below about 70K with two components from roughly equal sample volumes, one indicating a singlet state and the other a strongly fluctuating paramagnetic state. Further evidence for a singlet state comes from the behavior of the relaxation rate, 1/T1. These results are discussed and compared with those from other isostructural S = 1/2 materials and those based on S = 3/2 and S = 1.

NH NMR shifts of new structurally characterized fac-[Re(CO)3(polyamine)]n+ complexes probed via outer-sphere hydrogen-bonding interactions to anions, including the paramagnetic [Re(IV)Br6]2- anion.

fac-[Re(I)(CO)(3)L](n) complexes serve as models for short-lived fac-[(99m)Tc(I)(CO)(3)L](n) imaging tracers (L = tridentate ligands forming two five-membered chelate rings defining the L face). Dangling groups on L, needed to achieve desirable biodistribution, complicate the NMR spectra, which are not readily understood. Using less complicated L, we found that NH groups (exo-NH) projecting toward the L face sometimes showed an upfield shift attributable to steric shielding of the exo-NH group from the solvent by the chelate rings. Our goal is to advance our ability to relate these spectral features to structure and solution properties. To investigate whether exo-NH groups in six-membered rings exhibit the same effect and whether the presence of dangling groups alters the effect, we prepared new fac-[Re(CO)(3)L](n+) complexes that allow direct comparisons of exo-NH shifts for six-membered versus five-membered chelate rings. New complexes were structurally characterized with the following L: dipn [N-3-(aminopropyl)-1,3-propanediamine], N'-Medipn (3,3'-diamino-N-methyldipropylamine), N,N-Me(2)dipn (N,N-dimethyldipropylenetriamine), aepn [N-2-(aminoethyl)-1,3-propanediamine], trpn [tris-(3-aminopropyl)amine], and tren [tris-(2-aminoethyl)amine]. In DMSO-d(6), the upfield exo-NH signals were exhibited by all complexes, indicating that the rings sterically shield the exo-NH groups from bulky solvent molecules. This interpretation was supported by exo-NH signal shift changes caused by added halide and [ReBr(6)](2-) anions, consistent with outer-sphere hydrogen-bond interactions between these anions and the exo-NH groups. For fac-[Re(CO)(3)(dipn)]PF(6) in acetonitrile-d(3), the exo-NH signal shifted further downfield in the series, Cl(-) > Br(-) > I(-), and the plateau in the shift change required a lower concentration for smaller anions. These results are consistent with steric shielding of the exo-NH groups by the chelate rings. Nevertheless, despite its size, the shape and charge of [ReBr(6)](2-) allowed the dianion to induce large upfield paramagnetic shifts of the exo-NH signal of fac-[Re(CO)(3)(dipn)]PF(6). This dianion shows promise as an outer-sphere hydrogen-bonding paramagnetic shift reagent.

Solution studies of lanthanide (III) complexes based on 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and 1,10-phenanthroline Part-I: Synthesis, 1H NMR, 4 f–4 f absorption and photoluminescence

Solution studies on the complexes of the type [Ln(hfaa) 3(phen) 2] (Ln = La, Pr and Nd) and [Ln(hfaa) 3phen] (Ln = Nd, Ho, Er and Yb; hfaa stands for the anion of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and phen stands for 1,10-phenanthroline) are presented. These complexes are synthesized in high yields by an in situ method in which hfaa, ammonium hydroxide, lanthanide chlorides and phen were allowed to react in 3:3:1:1 molar ratio in ethanol. In the case of neodymium both eight- and ten-coordinate complexes are isolated. The paramagnetic shifts of the methine protons of β-diketone have their sign opposed to those of paramagnetic shifts of phen protons and the shifts are dominated by dipolar interactions. The inter- and intramolecular shift ratios have been calculated and discussed. The 4 f–4 f absorption spectra of the complexes of Pr, Nd, Ho and Er are analyzed. The eight- and ten-coordinate neodymium complexes display distinctively different band shapes of the 4G 5/2, 2G 7/2 ← 4I 9/2 hypersensitive transition. The efficient energy transfer from ligand to Pr(III) is reflected by strong red luminescence of this complex at room temperature.

Communications: Nanomagnetic shielding: High-resolution NMR in carbon allotropes

The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of (13)C high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the largest diamagnetic shifts (down to -68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.

Interaction of 6,6′′-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2′:6′,2′′-terpyridine (CyMe4-BTTP) with some trivalent ions such as lanthanide(iii) ions and americium(iii)

The new ligand 6,6''-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2':6',2''-terpyridine (CyMe4-BTTP) has been synthesized in 4 steps from 2,2':6',2''-terpyridine. Detailed NMR and mass spectrometry studies indicate that the ligand forms 1:2 complexes with lanthanide(III) perchlorates where the aliphatic rings are conformationally constrained whereas 1:1 complexes are formed with lanthanide(III) nitrates where the rings are conformationally mobile. An optimized structure of the 1:2 solution complex with Yb(III) was obtained from the relative magnitude of the induced paramagnetic shifts. X-Ray crystallographic structures of the ligand and of its 1:1 complex with Y(III) were also obtained. The NMR and mass spectra of [Pd(CyMe4-BTTP)]n(2n+) are consistent with a dinuclear double helical structure (n = 2). In the absence of a phase-modifier, CyMe4-BTTP in n-octanol showed a maximum distribution coefficient of Am(III) of 0.039 (±20%) and a maximum separation factor of Am(III) over Eu(III) of 12.0 from nitric acid. The metal(III) cations are extracted as the 1:1 complex from nitric acid. The generally low distribution coefficients observed compared with the BTBPs arise because the 1:1 complex of CyMe4-BTTP is considerably less hydrophobic than the 1:2 complexes formed by the BTBPs. In M(BTTP)(3+) complexes, there is a competition between the nitrate ions and the ligand for the complexation of the metal.

Study of Lithium Dynamics in Monoclinic Li3Fe2(PO4)3 using 6Li VT and 2D Exchange MAS NMR Spectroscopy

Details of Li-mobility in Li3Fe2(PO4)3 are elucidated using solid-state 6Li NMR. Three crystallographically unique Li sites were resolved under magic angle spinning (25 kHz) with paramagnetic shifts arising at 45 ppm, 102 ppm, and 216 ppm. These resonances were assigned to the crystallographic positions based on the degree of the Fermi-contact interaction with the paramagnetic iron center. 6Li 2D exchange NMR experiments were performed under variable temperature conditions in order to determine the activation energies for hopping between lithium sites. Activation energies ranged from 0.59 (± 0.05) eV to 0.81 (± 0.04) eV, where shorter Li internuclear distances and larger Li−O bottlenecks yielded lower activation energies. These results were compared to a previous study on the isostructural Li3V2(PO4)3, which showed similar trends of increased internuclear distance (and constricted bottlenecks) yielding larger energy barriers for Li−Li exchange. Overall, the average activation energy for lithium ion hopping in the iron-based structure is lower than the vanadium analogue, which is attributed to the more open framework of the former.

N-[(2-Chloro-6-methylquinolin-3-yl)methyl]aniline

Quinolinyl amines are important organic compounds which possess a variety of pharmacological activities such as antimalarial, antifungal, hypotensive and antidepressant activity.

Overexpression, characterization, and crystallization of the functional domain of cytochrome c z from Chlorobium tepidum

Cytochrome c(z) is found in green sulfur photosynthetic bacteria, and is considered to be the only electron donor to the special pair P840 of the reaction center. It consists of an N-terminal transmembrane domain and a C-terminal soluble domain that binds a single heme group. Large scale expression of the C-terminal functional domain of the cytochrome c(z) (C-cyt c(z)) from the thermophilic bacterium Chlorobium tepidum has been achieved using the Escherichia coli expression system. The C-cyt c(z) expressed has been highly purified, and is stable at room temperature over 10 days of incubation for both reduced and oxidized forms. Spectroscopic measurements indicate that the heme iron in C-cyt c(z) is in a low-spin state and this does not change with the redox state. (1)H-NMR spectra of the oxidized C-cyt c(z) exhibited unusually large paramagnetic chemical shifts for the heme methyl protons in comparison with those of other Class I ferric cytochromes c. Differences in the (1)H-NMR linewidth were observed for some resonances, indicating different dynamic environments for these protons. Crystals of the oxidized C-cyt c(z) were obtained using ammonium sulfate as a precipitant. The crystals diffracted X-rays to a maximum resolution of 1.2 A, and the diffraction data were collected to 1.3 A resolution.

Approaches for the measurement of solvent exposure in proteins by 19F NMR

Fluorine NMR is a useful tool to probe protein folding, conformation and local topology owing to the sensitivity of the chemical shift to the local electrostatic environment. As an example we make use of (19)F NMR and 3-fluorotyrosine to evaluate the conformation and topology of the tyrosine residues (Tyr-99 and Tyr-138) within the EF-hand motif of the C-terminal domain of calmodulin (CaM) in both the calcium-loaded and calcium-free states. We critically compare approaches to assess topology and solvent exposure via solvent isotope shifts, (19)F spin-lattice relaxation rates, (1)H-(19)F nuclear Overhauser effects, and paramagnetic shifts and relaxation rates from dissolved oxygen. Both the solvent isotope shifts and paramagnetic shifts from dissolved oxygen sensitively reflect solvent exposed surface areas.

Predicting the NMR Spectra of Paramagnetic Molecules by DFT: Application to Organic Free Radicals and Transition‐Metal Complexes

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.

Electron Paramagnetic Resonance Line Shifts and Line Shape Changes Due to Spin Exchange of Nitroxide Free Radicals in Liquids. 7. Singly Charged Surfactant Nitroxide

EPR spectra of aqueous solutions of the singly charged surfactant nitroxide 4-[N,N-dimethyl-N-(ndodecyl) ammonium]-2,2,6,6-tetramethylpiperidinyl-N-oxy bromide-d16 (DCAT12) are studied as functions of the molar concentration, c = 0.1-8 mM, and the temperature from 273 to 353 K. This concentration range is below the critical micelle concentration, cmc, at which DCAT12 forms micelles. Spin-spin broadening of the EPR lines averaged over the three lines is separated into contributions due to spin exchange, <Be>, and dipolar, <Bdip>, interactions yielding values of the fractional broadening by spin exchange, Omega(T), that vary from near unity at 353 K to approximately 50% at 273 K. This compares with a variation from unity to approximately 77% for a neutral spin probe perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (PDT) over the same range. Unlike PDT and the Stokes-Einstein prediction, the broadening constant by spin exchange, d<Be>/dc, is not linear with T/eta, where eta is the shear viscosity, instead following a quadratic dependence. Nevertheless, d<Be>/dc is remarkably close to a hydrodynamic prediction using the Stokes-Einstein equation modified to take the spin probe charge into account. Compared with PDT, values of d<Be>/dc are decreased and d<Bdip>/dc increased at all temperatures, while the values of the re-encounter rate, tau(RE)(-1), deduced from line shifts, are reduced. Interestingly, values of d<Bdip>/dc, Omega(T), and tau(RE)(-1) are comparable for PDT and DCAT12 when compared at the same rotational diffusion rates.

On the contribution of deoxy-hemoglobin to MRI gray–white matter phase contrast at high field

High field (≥7 T) MRI studies based on signal phase have been used to improve visualization of the fine structure of the brain, most notably the major white matter fiber bundles, the gray–white matter subdivision, and the laminar cortical architecture. The observed contrast has been attributed in part to local variations in magnetic susceptibility arising from iron in storage proteins and tissue lipid. Another contribution could come from the paramagnetic blood constituent deoxy-hemoglobin, the tissue concentration of which may vary through local variations in vascular density. To investigate this possibility, we examined phase contrast between gray and white matter in rats after intravenous administration of a superparamagnetic contrast agent at various dosages. At the maximum dosage (3 mg Fe/kg), which resulted in an estimated paramagnetic susceptibility shift 4–8 times larger than deoxy-hemoglobin, we observed a negligible increase in phase contrast between gray and white matter. This result suggests that endogenous deoxy-hemoglobin has no significant contribution to phase contrast between gray and white matter.

Ammonia Vapor Removal by Cu3(BTC)2 and Its Characterization by MAS NMR

Adsorption equilibria and NMR experiments were performed to study the adsorption and interactions of ammonia with metal-organic framework (MOF) HKUST-1, or Cu(3)(BTC)(2) (BTC = 1,3,5-benzenetricarboxylate). Ammonia capacities determined from chemical breakthrough measurements show significantly higher uptake capacities than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the Cu(3)(BTC)(2) framework. Indeed, (1)H MAS NMR reveals that a major disruption of the relatively simple spectrum of Cu(3)(BTC)(2) occurs to generate a composite spectrum consistent with Cu(OH)(2) and (NH(4))(3)BTC species under humid conditions-the anticipated products of a copper(II) carboxylate reacted with limited ammonia. These species are not detected under dry conditions; however, reaction stoichiometry combined with XRD results suggests the partial formation of an indeterminate diammine copper (II) complex with some residual Cu(3)(BTC)(2) structure retained. Cu(II)-induced paramagnetic shifts exhibited by various species in (1)H and (13)C MAS NMR spectra are consistent with model compounds and previous literature. Although results show extensive ammonia capacity of Cu(3)(BTC)(2), much of the capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.

Anisotropic Magnetic Behavior of Anionic Ce@C82 Carbene Adducts

Derivatives of Ce@C(82)(C(2v)) have been synthesized and fully characterized, and their anisotropic magnetism has been observed as paramagnetic shifts in NMR measurements. Carbene addition by photochemical reaction afforded two isomers of Ce@C(82)(C(2v))Ad (Ad = adamantylidene), 2a and 2b, demonstrating high regioselectivity. The two isomers were characterized using MALDI-TOF mass spectrometry, vis-NIR absorption spectroscopy, (1)H and (13)C NMR spectroscopy, and electrochemistry. The structure of the minor isomer (2b) was elucidated by single-crystal X-ray structural analysis. (13)C and (1)H NMR measurements revealed the characteristic anisotropic interaction between the f electron on the Ce atom and nuclear spins of the carbon atoms of the cage and the protons of the Ad group, respectively.