45Sc NMR Research Articles

SOLID-STATE 13C AND 45Sc NMR STUDIES ON ENDOHEDRAL SCANDIUM-CARBIDE METALLOFULLERENES: A MOTIONAL DYNAMICS OF Sc ATOMS IN FULLERENES

Sc 2 C 2@ C 82( II ) and Sc 2 C 2@ C 82( III ) have been synthesized and chromatographically isolated and characterized by using UV-Vis-NIR absorption spectroscopy. Solid-state 13 C and 45 Sc NMR on Sc 2 C 2@ C 82 metallofullerenes provide the rotational activation energy of Sc atoms encapsulated in C 82 fullerenes which is lower than that in solution due to crystal field effects on the rate of the rotation.

Solid state NMR as a new approach for the structural characterization of rare-earth doped lead lanthanum zirconate titanate laser ceramics

To facilitate the design of laser host materials with optimized emission properties, detailed structural information at the atomic level is essential, regarding the local bonding environment of the active ions (distribution over distinct lattice sites) and their extent of local clustering as well as their population distribution over separate micro- or nanophases. The present study explores the potential of solid state NMR spectroscopy to provide such understanding for rare-earth doped lead lanthanum zirconate titanate (PLZT) ceramics. As the NMR signals of the paramagnetic dopant species cannot be observed directly, two complementary approaches are utilized: (1) direct observation of diamagnetic mimics using 45Sc NMR and (2) study of the paramagnetic interaction of the constituent host lattice nuclei with the rare-earth dopant, using 207Pb NMR lineshape analysis. 45Sc MAS NMR spectra of scandium-doped PLZT samples unambiguously reveal scandium to be six-coordinated, suggesting that this rare-earth ion substitutes in the B site. Static 207Pb spin echo NMR spectra of a series of Tm-doped PLZT samples reveal a clear influence of paramagnetic rare-earth dopant concentration on the NMR lineshape. In the latter case high-fidelity spectra can be obtained by spin echo mapping under systematic incrementation of the excitation frequency, benefiting from the signal-to-noise enhancement afforded by spin echo train Fourier transforms. Consistent with XRD data, the 207Pb NMR lineshape analysis suggests that statistical incorporation into the PLZT lattice occurs at dopant levels of up to 1 wt.% Tm 3+, while at higher levels the solubility limit is reached.

Scandium-45 NMR of pyrope-grossular garnets: Resolution of multiple scandium sites and comparison with X-ray diffraction and X-ray absorption spectroscopy

Here we present 45 Sc and 27 Al NMR results on Sc-doped pyrope (Mg 3 Al 2 Si 3 O 12 ), grossular (Ca 3 Al 2 Si 3 O 12 ), and an 80% grossular-20% pyrope garnet (grs80) that have recently been well-studied by X-ray diffraction and X-ray spectroscopies. Clearly distinct NMR peaks are observed for Sc in the eight-coordinated X site (pyrope and grs80) and in the six-coordinated Y site (grossular and grs80). X-ray and NMR data agree that only eight-coordinated Sc is present in pyrope and that six-coordinated Sc is predominant in grossular; however, the XRD results also indicated significant X and Z site (four-coordinated) Sc in the Ca-rich garnet. Possible reasons for this apparent discrepancy are discussed. We demonstrate that 45 Sc NMR is potentially a useful new method for studies of the site occupancies of Sc 3+ in oxides and silicates, at least in experimental systems where its concentration is a few percent or greater.

Solid state NMR characterization of individual compounds and solid solutions formed in Sc2O3V2O5Nb2O5Ta2O5 system

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).

Solid state NMR spectroscopy as a probe of structure and bonding in the carbides Sc 3TC 4 (T = Co, Ni, Ru, Rh, Os, Ir)

Scandium transition metal carbides having the formula Sc 3TC 4 (T = Co, Ni, Ru, Rh, Os, Ir) have been structurally characterized by solid state 13C and 45Sc nuclear magnetic resonance spectroscopy. In all the compounds investigated, well-resolved signals are observed for crystallographically distinct carbon and scandium sites, confirming the formation of superstructures in the Rh and Ir compounds at ambient temperature. 45Sc NMR spectra are dominated by anisotropic broadening due to second-order quadrupolar perturbations. The nuclear electric quadrupolar coupling parameters (the coupling constant C Q and the asymmetry parameter η) are generally found in good agreement with values calculated theoretically from the crystal structure using the WIEN2k program. Furthermore, the spectra reveal large isotropic resonance shift differences between inequivalent Sc sites in a given compound and between sites of the same type for different compounds. Altogether the results illustrate that 45Sc NMR is a sensitive method for detecting isotropic and anisotropic local electron density variations in the Sc 3TC 4 family.

Multinuclear Solid-State NMR Spectroscopy of Doped Lanthanum Fluoride Nanoparticles

Multinuclear solid-state NMR spectroscopy and powder X-ray diffraction (XRD) experiments are applied to comprehensively characterize a series of pure and lanthanide-doped LaF3 nanoparticles (NPs) that are capped with di-n-octadectyldithiophosphate ligands (Ln3+ = diamagnetic Y3+ and Sc3+ and paramagnetic Yb3+ ions), as well as correlated bulk microcrystalline materials (LaF3, YF3, and ScF3). Solid-state 139La and 19F NMR spectroscopy of bulk LaF3 and the LaF3 NPs reveal that the inorganic core of the NP retains the LaF3 structure at the molecular level; however, inhomogeneous broadening of the NMR powder patterns arises from distributions of 139La and 19F NMR interactions, confirming a gradual change in the La and F site environments from the NP core to the surface. 139La and 19F NMR experiments also indicate that low levels (5 and 10 mol %) of Ln3+ doping do not significantly change the LaF3 structure in the NP core. Similar doping levels of paramagnetic Yb3+ ions severely broaden 19F resonances, but only marginally effect 139La powder patterns, suggesting that the dopant ions are uniformly distributed throughout the NP core and occupy vacant La sites. Measurements of 139La T1 and T2 relaxation constants are seen to vary between the bulk material and NPs and between samples with diamagnetic and paramagnetic dopants. 45Sc NMR experiments confirm that the dopants are integrated into the La sites of the LaF3 core. Solid-state 1H and 31P magic-angle spinning (MAS) NMR spectra aid in probing the nature of the capping ligands and their interactions at the NP surface. 31P cross-polarization (CP)/MAS NMR experiments identify not only the dithiophosphate head groups but also thiophosphate and phosphate species which may form during NP synthesis. Finally, 19F-31P CP/MAS and 1H MAS experiments confirm that ligands are coordinated to the NP surface.

Entrapped Bonded Hydrogen in a Fullerene: the Five‐Atom Cluster Sc3CH in C80

The synthesis and characterisation of the new endohedral cluster fullerene Sc(3)CH@C(80) is reported. The encapsulation of the first hydrocarbon cluster inside a fullerene was achieved by the arc burning method in a reactive CH(4) atmosphere. The extensive characterisation by mass spectrometry (MS), high- pressure liquid chromatography (HPLC), (45)Sc NMR, electron spin resonance (ESR), UV/Vis-NIR and Raman spectroscopy provided the experimental evidence for the caging of the five-atom Sc(3)CH cluster inside the C(80) cage isomer with icosahedral symmetry. The proposed new structure was confirmed by DFT calculations, which gave a closed shell and large energy gap structure. Thus a pyramidal Sc(3)CH cluster and the I(h)-C(80) cage were shown to be the most stable configuration for Sc(3)CH@C(80) whereas alternative structures give a smaller bonding energy as well as a smaller energy gap.

New Stannide ScAgSn: Determination of the Superstructure via Two-Dimensional 45Sc Solid State NMR

The new stannide ScAgSn was synthesized by induction melting of the elements in a sealed tantalum tube and subsequent annealing. ScAgSn crystallizes with a pronounced subcell structure: ZrNiAl type, P2m, a = 708.2(2) pm, c = 433.9(1) pm, wR2 = 0.1264, 321 F2 values, and 14 variables. The Guinier powder pattern reveals weak superstructure reflections pointing to a TiFeSi-type structural arrangement: I2cm, a = 708.1(1) pm, b = 1225.2(2) pm, c = 869.9(1) pm, wR2 = 0.0787, 5556 F2 values, and 49 variables. So far the growth of high-quality single crystals failed. Determination of the superstructure was partly based on merohedral triplet X-ray data augmented by 119Sn Mössbauer spectroscopy and 119Sn and 45Sc solid-state NMR data. In particular, the observation of three crystallographically inequivalent sites in 45Sc NMR triple quantum magic-angle spinning (TQ-MAS) NMR spectra provided unambiguous proof of the superstructure proposed. The ScAgSn structure consists of a three-dimensional [AgSn] network (with Ag-Sn distances between 273 and 280 pm) in which the scandium atoms are located in distorted hexagonal channels, each having five tin and two silver nearest neighbors. Both crystallographically independent tin sites have a tricapped trigonal prismatic coordination, that is, [Sn1Sc6Ag3] and [Sn2Ag6Sc3] environments, which are well distinguished in the 119Sn NMR and Mössbauer spectra because of their different site symmetries.

Scandium, yttrium, the lanthanides

Evans reports the synthesis of the highly congested [Cp*3Ln] (Ln = Gd, Y), in the most striking of a number of important contributions from his laboratories. Other publications feature the first homoleptic CeIV amide and important clarification of the scandium aqua ion, whilst there is significant interest in 45Sc, 89Y and 139La NMR.

Experimental and Theoretical Studies of 45Sc NMR Interactions in Solids

Solid-state 45Sc NMR spectroscopy, ab initio calculations, and X-ray crystallography are applied to examine the relationships between 45Sc NMR interactions and molecular structure and symmetry. Solid-state 45Sc (I = 7/2) magic-angle spinning (MAS) and static NMR spectra of powdered samples of Sc(acac)3, Sc(TMHD)3, Sc(NO3)3.5H2O, Sc(OAc)3, ScCl3.6H2O, ScCl3.3THF, and ScCp3 have been acquired. These systems provide a variety of scandium coordination environments yielding an array of distinct 45Sc chemical shielding (CS) and electric field gradient (EFG) tensor parameters. Acquisition of spectra at two distinct magnetic fields allows for the first observations of scandium chemical shielding anisotropy (CSA). 45Sc quadrupolar coupling constants (CQ) range from 3.9 to 13.1 MHz and correlate directly with the symmetry of the scandium coordination environment. Single-crystal X-ray structures were determined for Sc(TMHD)3, ScCl3.6H2O, and Sc(NO3)3.5H2O to establish the hitherto unknown scandium coordination environments. A comprehensive series of ab initio calculations of EFG and CS tensor parameters are in excellent agreement with the observed parameters. Theoretically determined orientations of the NMR interaction tensors allow for correlations between NMR tensor characteristics and scandium environments. Solid-state 45Sc, 13C, and 19F NMR experiments are also applied to characterize the structures of the microcrystalline Lewis acid catalyst Sc(OTf)3 (for which the crystal structure is unknown) and a noncrystalline, microencapsulated, polystyrene-supported form of the compound.

Scandium Coordination in Solid Oxides and Stabilized Zirconia: 45Sc NMR

45Sc NMR isotropic chemical shifts and quadrupole coupling constants of several scandium-containing solid oxides have been measured. Both parameters prove to be sensitive to local structure. In particular, in these materials the 45Sc isotropic chemical shift appears to be dominated by the first neighbor coordination environment, i.e., the coordination number. The difference in the isotropic shifts between six-coordinated and eight-coordinated scandium is more than 150 ppm, suggesting that this parameter may be especially useful in studying the scandium coordination in oxide materials, disordered solids in particular. Quadrupole coupling constants are sensitive to the nature of the second coordination cation, although many other structural details may play a role. The chemical shift correlation was applied to scandia-stabilized zirconia, (ZrO2)0.92(Sc2O3)0.08, and the mean coordination number obtained appears to be close to seven, which suggests the possibility of two scandium cations pairing with one vacancy.

Preparation and Structure of CeSc2N@C80: An Icosahedral Carbon Cage Enclosing an Acentric CeSc2N Unit with Buried f Electron Spin

Herein, we report the preparation, purification, and characterization of a mixed trimetallic nitride endohedral metallofullerene, CeSc(2)N@C(80). Single-crystal X-ray diffraction shows that CeSc(2)N@C(80) consists of a four-atom asymmetric top (CeSc(2)N) inside a C(80) (I(h)()) carbon cage. Unlike the situation in most endohedrals of the M(3)N@C(2)(n)() type, the nitride ion is not located at the center of the carbon cage but is offset by 0.36 A in order to accommodate the large Ce(III) ion. The cage carbon atoms near the endohedral Ce and Sc atoms exhibit significantly larger pyramidal angles than the other carbon atoms on the C(80) cage. Surprisingly, at ambient temperature, the (13)C NMR spectrum exhibits isotropic motional averaging yielding only two signals (3 to 1 intensity ratio) for the icosahedral C(80) cage carbons. At the same temperature, the (45)Sc NMR exhibits a relatively narrow, symmetric signal (2700 Hz) with a small temperature-dependent Curie shift. A rotation energy barrier (E(a) = 79 meV) was derived from the (45)Sc NMR line-width analysis. Finally, the XPS spectrum for CeSc(2)N@C(80) confirms a +3 oxidation state for cerium, Ce(3+)(4f(1)5d(0)). This oxidation state and the Curie shift are consistent with a weakly paramagnetic system with a single buried f electron spin.

Hydrogen-Bonded Aggregates of Scandium(III) Complexes

The influence of the concentration of halide ions and concentration of an organic component (Solv) in solutions on the composition, coordination number, and structure of the scandium(III) complexes in solutions and in crystal is studied. The 45Sc NMR data show that the main factor determining Cl– coordination in the Sc3+–Cl––H2O–Solv systems is the Solv concentration. According to the X-ray diffraction analysis data, at the molar ratios of X– : Sc3+ < 3 (X– = Cl, Br), the [Sc(OH)(H2O)5]2X4 · 2H2O salts with a coordination number of Sc 7 are isolated from solutions in H2O and alcohols (coordination core is ScO7 and X– ions are not involved in coordination). Supramolecular H-bonded aggregates containing the ScCl3(H2O)3 molecular complex with coordination number of Sc 6 and meridianal arrangement of analogous ligands are isolated from solutions with the Cl– : Sc3+ molar ratios from 3 to 20 (in concentrated HCl) using macrocyclic molecules (1,4,7,10,13,16-hexaoxocyclooctadecane (18C6) and 1,4,10,13-tetraoxo-7,16-diazacyclooctadecane (DA18C6)).

Application of amplitude-modulated radiofrequency fields to the magic-angle spinning NMR of spin- [formula omitted] nuclei

We report pulse sequences for the sensitivity enhancement of magic-angle spinning and multiple-quantum magic-angle spinning spectra of spin- 7 2 systems. Sensitivity enhancement is obtained with the use of fast amplitude-modulated (FAM) radiofrequency pulses. In one-dimensional magic-angle spinning experiments, signal enhancement of 3 is obtained by a FAM pulse followed by a soft 90° pulse. In two-dimensional multiple-quantum magic-angle spinning experiments, FAM pulses are used for both the excitation of multiple-quantum coherences and for their conversion into observable single-quantum coherences. The observed signal enhancements are 2.2 in 3Q experiments, 3.1 in 5Q experiments, and 4.1 in 7Q experiments, compared to the conventional two-pulse scheme. The pulse schemes are demonstrated on the 45Sc NMR of Sc 2(SO 4) 3 · 5H 2O and the 139La NMR of LaAlO 3. We also demonstrate the generation of FAM pulses by double-frequency irradiation.

Primary and secondary coordination of crown ethers to scandium(iii). Synthesis, properties and structures of the reaction products of ScCl3(thf)3, ScCl3·6H2O and Sc(NO3)3·5H2O with crown ethers

The synthesis and spectroscopic characterisation of [ScCl(15-crown-5)(MeCN)][SbCl6]2, [ScCl2(18-crown-6)][FeCl4] and [ScCl2([15]aneS2O3)][FeCl4] ([15]aneS2O3 = 1,4-dithia-7,10,13-trioxacyclopentadecane) are reported, the last containing the first example of thioether-scandium(III) coordination. The structure of [ScCl(15-crown-5)(MeCN)][SbCl6]2 reveals a pentagonal bipyramidal cation with axial Cl and MeCN, whilst [ScCl2(18-crown-6)][FeCl4] is also pentagonal bipyramidal with axial Cl ligands. 1H and 45Sc NMR spectroscopies have been used to study the speciation in the ScCl3/18-crown-6 system in the presence of the Lewis acids SbCl5 and FeCl3 in anhydrous MeCN. Hydrolysis of any of the above complexes and of [Sc(12-crown-4)2]3+ (formed from ScCl3(thf)3, crown and SbCl5), results in the formation of [ScCl3(H2O)3]·crown, the solution NMR spectra of which show a common scandium species and uncomplexed crown ether. The structure of [ScCl3(H2O)3]·18-crown-6 reveals a mer octahedral scandium species which is hydrogen bonded via the scandium-coordinated water to the 18-crown-6 (secondary coordination) leading to infinite chains. Similar complexes have been isolated directly from reaction of ScCl3·6H2O and the crown ethers in absolute ethanol, including [ScCl3(H2O)3]n·(crown) (n = 1 or 2, crown = 18-crown-6; n = 2, crown = 15-crown-5 or 12-crown-4). Hydrated scandium nitrate and the crown ethers react in ethanol solution to form a surprisingly diverse range of structural types containing the crown ethers hydrogen bonded to the scandium-aquo-nitrato or scandium-aquo-hydroxo-nitrato complexes. X-Ray crystal structures are reported for [Sc(H2O)2(NO3)3]·(12-crown-4)2, [Sc(H2O)4(NO3)2]NO3·15-crown-5 and [Sc2(NO3)2(H2O)6(OH)2](NO3)2·12-crown-4. However, in the related [Sc2(NO3)4(H2O)4(OH)2][Na(12-crown-4)2](NO3)·(H2O)3 the hydrogen bonding occurs between the lattice water and the scandium dimer unit.

Scandium halide complexes of phosphine- and arsine-oxides: synthesis, structures and 45Sc NMR studies

The reactions of ScCl 3·6H 2O, ScBr 3·6H 2O and ScI 3·8H 2O with Ph 3PO, Ph 3AsO, Ph 2MePO, Me 3PO and Me 3AsO have been examined in EtOH or Me 2CO solution. The new complexes [ScCl(Me 3PO) 5]Cl 2, [Sc(Me 3PO) 6]X 3 (X=Br or I), [ScX 2(Ph 3PO) 4]X (X=Cl, Br or I), [ScX 2(Ph 3AsO) 4]X, [Sc(Me 3AsO) 6]X 3 (X=Cl, Br or I), [ScCl 3(Ph 2MePO) 3] and [ScBr 2(Ph 2MePO) 4]Br were isolated as solids and were characterised by analysis, IR and multinuclear ( 1H, 31P{ 1H} and 45Sc) NMR spectroscopy and conductance measurements. The crystal structures of [ScBr 2(Ph 3PO) 4]Br·1/2Et 2O, [ScCl 2(Ph 3AsO) 4]Cl and [Sc(Me 3AsO) 6]Br 3 are also reported. The solution speciation (in CH 2Cl 2 or MeNO 2) in the various systems was examined by multinuclear NMR spectroscopy. The 45Sc NMR chemical shifts and line widths show systematic trends with donor set and symmetry, which are described. No reaction between these ligands and ScF 3·1/2H 2O was observed.

Scandium, yttrium and lanthanum nitrate complexes of tertiary arsine oxides: synthesis and multinuclear spectroscopic studies. X-ray structures of [M(Me 3AsO) 6](NO 3) 3 (M=Sc or Y), [Sc(Ph 3AsO) 3(NO 3) 2]NO 3, [M″(Ph 3AsO) 4(NO 3) 2]NO 3 (M″=Y or La) and [La(Ph 3AsO) 2(EtOH)(NO 3) 3

The reaction of Ph 3AsO with Sc(NO 3) 3·5H 2O, Y(NO 3) 3·6H 2O or La(NO 3) 3·6H 2O in acetone gave [Sc(Ph 3AsO) 2(NO 3) 3], [Y(Ph 3AsO) 4(NO 3) 2]NO 3, [La(Ph 3AsO) 4(NO 3) 2]NO 3, and [La(Ph 3AsO) 3(NO 3) 3], whilst from ethanol solution [Sc(Ph 3AsO) 3(NO 3) 2]NO 3, [Y(Ph 3AsO) 2(EtOH)(NO 3) 3] and [La(Ph 3AsO) 2(EtOH)(NO 3) 3] were produced. Similar reactions using Me 3AsO produced [M(Me 3AsO) 6](NO 3) 3 (M=Sc, Y or La) and [La(Me 3AsO) 2(H 2O)(NO 3) 3]. All complexes were characterised by analysis, IR and 1H, 45Sc or 89Y NMR spectroscopy, and conductance measurements. The solution speciation and interconversions of the Sc and Y complexes have been probed by 45Sc and 89Y NMR spectroscopy. X-Ray crystal structures are reported for the 6-coordinate [M(Me 3AsO) 6](NO 3) 3 (M=Sc or Y), seven-coordinate [Sc(Ph 3AsO) 3(NO 3) 2]NO 3, eight-coordinate [M″(Ph 3AsO) 4(NO 3) 2]NO 3 (M″=Y or La), and nine-coordinate [La(Ph 3AsO) 2(EtOH)(NO 3) 3].

Structure-function relationships in novel peptide dodecamerswith broad-spectrum bactericidal and endotoxin-neutralizing activities.

A series of designed peptide 33-mers (betapep peptides) areknown to be bactericidal [Mayo, Haseman, Ilyina and Gray (1998)Biochim. Biophys. Acta 1425, 81-92]. Here dodecapeptides (SC-1-SC-8), which 'walk through' the sequence ofbetapep-25, were investigated for their ability to kill Gram-negativeand -positive bacteria and to neutralize endotoxin. SC-4 (KLFKRHLKWKI I-NH(2); the -NH(2) at the right of each sequenceindicates amidation of the C-terminal carboxylate group) is the mosteffective, more so than betapep-25, at killing Gram-negative bacteriawith nanomolar LD(50) values. Against Gram-positive bacteria,SC-4 also shows good activity with submicromolar LD(50)values. Leakage studies indicate rapid bacterial membrane permeability,with t(1/2) valuesof 10-15 min. SC-4 in the micromolar range also effectivelyneutralizes endotoxin and is not haemolytic below 10(-4)M. For all SC peptides, CD and NMR data indicate the presence of both 3(10)- and alpha-helix. For SC-4, nuclear-Overhauser-effect-based computational modelling yields an amphipathic helix with K1, K4,R5, and K8 arrayed on the same face (K is lysine, R is arginine). Activity differences among SC peptides and single-site variants of SC-4allow some structure-function relationships to be deduced. Relative to other known bactericidal peptides in the linear peptide,helix-forming category, SC-4 is the most potent broad-spectrumantibacterial identified to date. The present study contributes to thedevelopment of agents involved in combating the ever-recurring problemof drug-resistant micro-organisms.

NMR study of Sc 1− xU xPd 3 under non-fermi liquid state

We have performed 45Sc NMR measurements on the Sc 1− x U x Pd 3 system, which exhibits an unconventional Kondo effect with a non-Fermi liquid character at low temperatures for the samples with x⩽0.3. The relaxation rates, 1/ T 1, for the x=0.3 and 0.25 samples are strongly enhanced by magnetic fluctuations below 30 K in low magnetic field, where other macroscopic properties show typical NFL behavior. Since the x=0.2 samples show Korringa ( T 1 T=const.) behavior, this enhancement in the x=0.3 and 0.25 samples may be associated with an unusual electronic state near the quantum critical point. Below 1 K , T 1 in the x=0.3 sample seems to obey a 1/ T 1∝ T relation. This behavior may be associated with the enhanced Korringa relation in the vicinity of the quantum critical point.

45Sc and 93Nb NMR in relaxors

The narrow components in the 93Nb(I = 9/2) and 45Sc(I = 7/2) NMR spectra of single crystalline PMN and disordered single crystalline PST are due to the 1/2 → -1/2 NMR transition whereas the broad background components are due to satellite transitions. The macroscopic cubic symmetry is locally broken on the NMR time scale. From the NMR point of view, the structure is homogeneous and there is no need to invoke the existence of “pinned” chemical clusters. The observed NMR spectra in PMN and PST can be described in terms of reorientable dynamic polar nanoclusters-mainly due to Pb2+ site disorder-as invoked by the spherical random bond-random field model.