89Y NMR Research Articles

ChemInform Abstract: Scandium, Yttrium, the Lanthanides

AbstractReview: literature of 2011; 116 refs.

Exploiting the Chemical Shielding Anisotropy to Probe Structure and Disorder in Ceramics: 89Y MAS NMR and First-Principles Calculations

The local structure and cation disorder in Y2(Sn,Ti)2O7 pyrochlores, materials proposed for the encapsulation of lanthanide- and actinide-bearing radioactive waste, is investigated using 89Y (I = 1/2) NMR spectroscopy and, in particular, measurement of the 89Y anisotropic shielding. Although known to be a good probe of the local environment, information on the anisotropy of the shielding interaction is removed under magic angle spinning (MAS). Here, we consider the feasibility of experimental measurement of the 89Y anisotropic shielding interaction using two-dimensional CSA-amplified PASS experiments, implemented for 89Y for the first time. Despite the challenges associated with the study of low-γ nuclei, and those resulting from long T1 relaxation times, the successful implementation of these experiments is demonstrated for the end member pyrochlores, Y2Sn2O7 and Y2Ti2O7. The accuracy and robustness of the measurement to various experimental parameters is also considered, before the approach is then applied to the disordered materials in the solid solution. The anisotropies extracted for each of the sideband manifolds are compared to those obtained using periodic first-principles calculations, and provide strong support for the assignment of the spectral resonances. The value of the span, Ω, is shown to be a sensitive probe of the next nearest neighbor (NNN) environment, i.e., the number of Sn and Ti on the six surrounding “B” (i.e., six-coordinate) sites, and also provides information on the local geometry directly, through a correlation with the average Y–O8b distance (where 8b indicates the Wyckoff position of the oxygen).

Characterization of the glass-to-vitroceramic transition in yttrium aluminum borate laser glasses using solid state NMR

The crystallization of laser glasses in the system (Y2O3)0.2{((Al2O3)x)(B2O3)0.8−x} (0.15≤x≤0.40) doped with 0.5mol% of ytterbium oxide has been investigated by x-ray powder diffraction, and various solid state NMR techniques. The crystallization process has been analyzed in a quantitative fashion by high-resolution solid state 11B, 27Al, and 89Y NMR spectroscopy as well as 11B{27Al} and 27Al{11B} rotational echo double resonance (REDOR) experiments. The homogeneous glasses undergo major phase segregation processes resulting in crystalline Al5BO9 (historically denoted as Al18B4O33), YBO3, crystalline YAl3(BO3)4, residual glassy B2O3, and an additional yet not identified crystalline phase (“X-phase”).

119Sn MAS NMR and first-principles calculations for the investigation of disorder in stannate pyrochlores

The local structure and cation disorder in Y(2)Ti(2-x)Sn(x)O(7) pyrochlores, materials proposed for the encapsulation of lanthanide- and actinide-bearing radioactive waste, is studied using (119)Sn (I = 1/2) NMR spectroscopy. NMR provides an excellent probe of disorder, as it is sensitive to the atomic scale environment without the need for any long-range periodicity. However, the complex and overlapping spectral resonances that often result can be difficult to interpret. Here, we demonstrate how (119)Sn DFT calculations can be used to aid the spectral interpretation and assignment, confirming that Sn occupies only the six-coordinate pyrochlore B site, and that the Sn chemical shift is sensitive to the number of Sn/Ti on the neighbouring B sites. Although distinct resonances are resolved experimentally when the Ti content is low, there is significant spectral overlap for Ti-rich compositions. We establish that this is a result of two competing contributions to the Sn chemical shift; an upfield shift resulting from the incorporation of the more polarizing Ti(4+) cation onto the neighbouring B sites, and a concomitant downfield shift arising from the decrease in unit cell size. Despite the considerably easier spectral acquisition, the lower resolution in the (119)Sn spectra hinders the extraction of the detailed structural information previously obtained using (89)Y NMR. However, the spectra we obtain are consistent with a random distribution of Sn/Ti on the pyrochlore B sites. Finally, we consider whether an equilibrium structure has been achieved by investigating materials that have been annealed for different durations.

PbO / PbF2 Flux Growth of YScO3 and LaScO3 Single Crystals – Structure and Solid-State NMR Spectroscopy

Well-shaped small single crystals of the orthorhombic perovskites YScO3 and LaScO3 were grown from mixtures of the corresponding sesquioxides RE2O3 in PbO/PbF2 fluxes. Both structures were refined from single-crystal diffractometer data: GdFeO3-type, Pnma, a = 570.68(7), b = 789.3(1), c = 542.44(7) pm, wR2 = 0.0363, 448 F2 values for Y0.96ScO2.94, and a = 579.68(9), b = 810.3(2), c = 568.3(1) pm, wR2 = 0.0387, 513 F2 values for La0.94ScO2.91, with 32 variables per refinement. The 4c rare-earth sites of both perovskites show small defects which are charge-compensated by defects on both oxygen sites, leading to the compositions La0.94ScO2.91 and Y0.96ScO2.94 for the investigated crystals. The rare-earth sites have been characterized by 89Y and 45Sc magic-angle spinning (MAS) NMR. The 45Sc quadrupolar interaction parameters extracted from these spectra by simulations are found to be in good agreement with those obtained from DFT calculations of the electric field gradient.

Glass-to-Vitroceramic Transition in the Yttrium Aluminoborate System: Structural Studies by Solid-State NMR

The crystallization of laser glasses in the system (B2O3)0.6{(Al2O3)0.4−y(Y2O3)y} (0.1 ≤ y ≤ 0.25) doped with different levels of ytterbium oxide has been investigated by X-ray powder diffraction, differential thermal analysis, and various solid-state NMR techniques. The homogeneous glasses undergo major phase segregation processes resulting in crystalline YBO3, crystalline YAl3(BO3)4, and residual glassy B2O3 as the major products. This process can be analyzed in a quantitative fashion by solid-state 11B, 27Al, and 89Y NMR spectroscopies as well as 11B{27Al} rotational echo double resonance (REDOR) experiments. The Yb dopants end up in both of the crystalline components, producing increased line widths of the corresponding 11B, 27Al, and 89Y NMR resonances that depend linearly on the Yb/Y substitution ratio. A preliminary analysis of the composition dependence suggests that the Yb3+ dopant is not perfectly equipartitioned between both crystalline phases, suggesting a moderate preference of Yb to substitu...

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.

Kinetics of Yttrium−Ligand Complexation Monitored Using Hyperpolarized 89Y as a Model for Gadolinium in Contrast Agents

Hyperpolarization by dissolution dynamic nuclear polarization (DNP) enhances (89)Y spin magnetization by 3 to 4 orders of magnitude and provides a way to monitor yttrium-ligand complexation "on the fly" by means of (89)Y NMR. In this communication, we show an example of free yttrium Y(3+) being complexed with 1,4,7,10-tetrakis(acetamido)-1,4,7,10-tetraazacyclododecane (DOTAM) to form [Y(DOTAM)(H(2)O)](3+) as a model for gadolinium in contrast agents.

Structural Characterization of Rare-Earth Doped Yttrium Aluminoborate Laser Glasses Using Solid State NMR

The structure of laser glasses in the system (B2O3)0.6{(Al2O3)0.4−x(Y2O3)x} (0.1 ≤ x ≤ 0.25) has been investigated by means of 11B, 27Al, and 89Y solid state NMR as well as Y-3d core-level X-ray photoelectron spectroscopy. 11B magic-angle spinning (MAS) NMR spectra reveal that the majority of the boron atoms are three-coordinated, and a slight increase of four-coordinated boron content with increasing x can be noticed. 27Al MAS NMR spectra show that the alumina species are present in the coordination states four, five and six. All of them are in intimate contact with both the three- and the four-coordinate boron species and vice versa, as indicated by 11B/27Al rotational echo double resonance (REDOR) data. These results are consistent with the formation of a homogeneous, nonsegregated glass structure. For the first time, 89Y solid state NMR has been used to probe the local environment of Y3+ ions in a glass-forming system. The intrinsic sensitivity problem associated with 89Y NMR has been overcome by combining the benefits of paramagnetic doping with those of signal accumulation via Carr-Purcell spin echo trains. Both the 89Y chemical shifts and the Y-3d core level binding energies are found to be rather sensitive to the yttrium bonding state and reveal that the bonding properties of the yttrium atoms in these glasses are similar to those found in the model compounds YBO3 and YAl3(BO3)4. Based on charge balance considerations as well as 11B NMR line shape analyses, the dominant borate species are concluded to be meta- and pyroborate anions.

Synthesis and Structural Characterization of the Yttrium Containing Isopolytungstate [YW10O36]9−

AbstractThe yttrium containing isopolytungstate [YW10O36]9− (1) has been synthesized and isolated in the form of its hydrated sodium salt Na9[YW10O36]·35H2O (Na‐1). The title compound has been structurally characterized in the solid state by single‐crystal X‐ray crystallography, IR spectroscopy, thermogravimetric analysis and in solution by 183W and 89Y NMR spectroscopy. The X‐ray analysis shows that Na‐1 crystallizes in the triclinic system, space group $P{\bar 1}$, with a = 12.7625(9), b = 13.0825(10), c = 20.496(2) Å, α = 82.856(5), β = 74.520(4), γ = 88.822(4)°, V = 3272.1(4) Å3 and Z = 2. Solution 183W NMR shows the expected 2 lines at –1.3 ppm and –14.3 ppm, respectively, with an intensity ratio of 1:4, and 89Y NMR shows a singlet at –12.9 ppm.

Five‐ and Four‐Coordinate 1,3‐Diaza‐2‐yttria‐ and 1,3‐Diaza‐2‐scandia‐[3]ferrocenophanes

Abstract2‐Chloro‐1,3‐bis(trimethylsilyl)‐1,3‐diaza‐2‐metalla‐[3]ferrocenophanes with M = Y (3) and Sc (4) have been prepared as the dipyridine adducts, starting from YCl3 and ScCl3, respectively, and N,N′‐dilithio‐N,N′‐bis(trimethylsilyl)‐1,1′‐diaminoferrocene (2). The reaction of 3 with sodium pentamethylcyclopentadienide (NaCp*) gave the complex 5, in which the yttrium atom is four‐coordinate, bearing the diamido ligand, Cp* and one pyridine ligand. An ate complex of four‐coordinate yttrium (6) was obtained, when YCl3 was treated with 2 equiv. of 2. In 6a, the lithium atom is threefold coordinated by two of the four amido nitrogen atoms and by pyridine, and addition of an excess of pyridine gave the separated ion pairs (6b) in solution. The molecular structures of 3, 5 and 6a were determined by X‐ray structural analysis, and the solution‐state structures were deduced from consistent NMR spectroscopic data sets (1H, 13C, 29Si, 89Y NMR). The 89Y nuclear magnetic shielding of amido complexes appears to increase with the coordination number (3, 4, 5) of yttrium.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Vacancy and Cation Distribution in Yttria-Doped Ceria: An 89Y and 17O MAS NMR Study

The local structure and dynamics of oxide ions in yttria-doped ceria (YDC, 5 to 30% Y2O3) were studied using high-resolution 89Y and 17O MAS NMR spectroscopy at ambient temperature and high temperatures to 500 °C. Eight-, seven-, and six-coordinated yttrium cations are clearly resolved in 89Y MAS NMR spectra, and their relative populations were measured. The derived average coordination number of yttrium is smaller than that for a random distribution of oxygen vacancies, suggesting that there is strong association between yttrium cations and vacancies and there is the possibility of pairing of two yttrium cations with one vacancy. In the 17O MAS NMR spectra, resonances for oxygens with different coordination environments are resolved and are assigned to oxygens with different numbers of yttrium cations in the first coordination sphere. The relative intensities of the 17O resonances also deviate from those expected from a random distribution, again indicating possible pairing of yttrium cations. High-tempe...

Homoleptic Rare‐Earth Metal(III) Tetramethylaluminates: Structural Chemistry, Reactivity, and Performance in Isoprene Polymerization

The complexes [Ln(AlMe4)3] (Ln=Y, La, Ce, Pr, Nd, Sm, Ho, Lu) have been synthesized by an amide elimination route and the structures of [Lu{(micro-Me)2AlMe2}3], [Sm{(micro-Me)2AlMe2}3], [Pr{(micro-Me)2AlMe2}3], and [La{(micro-Me)2AlMe2}2{(micro-Me)3AlMe}] determined by X-ray crystallography. These structures reveal a distinct Ln3+ cation size-dependency. A comprehensive insight into the intrinsic properties and solution coordination phenomena of [Ln(AlMe4)3] complexes has been gained from extended dynamic 1H and 13C NMR spectroscopic studies, as well as 1D 89Y, 2D 1H/89Y, and 27Al NMR spectroscopic investigations. [Ce(AlMe4)3] and [Pr(AlMe4)3] have been used as alkyl precursors for the synthesis of heterobimetallic alkylated rare-earth metal complexes. Both carboxylate and siloxide ligands can be introduced by methane elimination reactions that give the heterobimetallic complexes [Ln{(O2CAriPr)2(micro-AlMe2)}2(AlMe4)(C6H14)n] and [Ln{OSi(OtBu)3}(AlMe3)(AlMe4)2], respectively. [Pr{OSi(OtBu)3}(AlMe3)(AlMe4)2] has been characterized by X-ray structure analysis. All of the cerium and praseodymium complexes are used as precatalysts in the stereospecific polymerization of isoprene (1-3 equivalents of Et2AlCl as co-catalyst) and compared to the corresponding neodymium-based initiators reported previously. The superior catalytic performance of the homoleptic complexes leads to quantitative yields of high-cis-1,4-polyisoprene (>98%) in almost all of the polymerization experiments. In the case of the binary catalyst mixtures derived from carboxylate or siloxide precatalysts quantitative formation of polyisoprene is only observed for nLn:nCl=1:2. The influence of the metal size is illustrated for the heterobimetallic lanthanum, cerium, praseodymium, neodymium, and gadolinium carboxylate complexes, and the highest activities are observed for praseodymium as a metal center in the presence of one equivalent of Et2AlCl.

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.

Prediction of 89Y NMR Chemical Shifts in Organometallic Complexes with Density Functional Theory

Organometallic and coordination compounds containing yttrium are usefully characterized with 89Y NMR spectroscopy (I = −1/2, 100% nat. abund.). Even though the qualitative contributions of various ligand groups to the yttrium NMR chemical shift have been known for some time, attempts to predict the shifts quantitatively have been limited. In the present work, a variety of organoyttrium complexes containing cyclopentadienyl, alkyl, hydride, and aryloxide ligands have been optimized with density functional theory methods. The optimized structures were used with the gauge-including atomic orbital (GIAO) method to calculate the corresponding 89Y NMR magnetic shielding values (σcalc); the latter were linearly scaled to adjust the fit with observed chemical shifts. Agreement between predicted and experimental 89Y NMR shifts is typically within ±70 ppm (∼5% of the ca. 1300 ppm shift range). 89Y NMR calculations were used to provide supporting evidence for the existence of the bulky triallyl complex Y[1,3-(SiMe3)2C3H3]3.

89Y Magic-Angle Spinning NMR of Y2Ti2-xSnxO7 Pyrochlores

The yttrium local environment in the series of pyrochlores Y2Ti2-xSnxO7 was studied using 89Y NMR. Oxides with the pyrochlore structure exhibit a range of interesting physical and chemical properties, resulting in many technological applications, including the encapsulation of lanthanide- and actinide-bearing radioactive waste. The use of the nonradioactive Y3+ cation provides a sensitive probe for any changes in the local structure and ordering with solid solution composition, through 89Y (I = 1/2) NMR. We confirm that a single pyrochlore phase is formed over the entire compositional range, with Y found only on the eight-coordinated A site. A significant (approximately 15 ppm) chemical shift is observed for each Sn substituted into the Y second neighbor coordination environment. The spectral signal intensities of the possible combinations of Sn/Ti neighbors match those predicted statistically assuming a random distribution of Sn4+/Ti4+ on the six-coordinated pyrochlore B site.

Local structure analysis of YSZ by Y-89 MAS-NMR

The local coordination structure around Yttrium ions in yttria stabilized zirconia (YSZ) has been investigated by 89Y MAS-NMR. The NMR spectrum showed multiple peaks corresponding to yttrium ions in different coordination numbers. The compositional dependence of spectra was observed. Yttrium ions of different oxygen coordination number were quantified. The oxygen vacancy concentration around the cations was determined. It was found that the vacancies were distributed around Zirconium ions in lower Y 2O 3 concentrations, and the vacancy concentration located to Yttrium began increasing at concentrations above 10 mol% Y 2O 3. The local structure change was able to be directly observed by 89Y NMR measurements.

Relaxometric and solution NMR structural studies on ditopic lanthanide(iii) complexes of a phosphinate analogue of DOTA with a fast rate of water exchange

A novel "ditopic" ligand containing two monophosphinate triacetate DOTA-like units linked by a thiourea bridge has been synthesized and its complexes with Ln3+ ions (Ln = Y, Eu, Gd, Dy) investigated by NMR spectroscopy and relaxometry. The presence of one water molecule in the first coordination sphere has been determined by the measurement of the dysprosium(III)-induced 17O NMR shifts. The 1H and 31P NMR spectra of the Eu(III) derivative indicate a higher abundance of the fast-exchanging twisted square antiprismatic (m) isomer than the isomeric square antiprismatic (M; m/M = 3:2) complex. The analysis of the 89Y and 13C T1 NMR relaxation times in the Gd(III)/Y(III) mixed complex have provided useful structural information. Values of ca. 6.3 and 8.2 A for the Gd...Y and Gd...C distances, respectively, have been estimated which indicate a rather compact solution structure. This result finds support in the value of the relaxivity whose increase (at 20 MHz and 298 K) on passing from the monomeric (5.7 s(-1) mM(-1)) to the ditopic complex (8.2 s(-1) mM(-1)) can be attributed to the doubling of the inner-sphere term following the doubling of the molecular size. The structural and dynamic relaxivity-controlling parameters were assessed by a simultaneous fitting of the variable temperature 17O NMR and 1H NMRD relaxometric data. The mean water residence lifetime (298tauM) has been found to be 53 ns, one of the shortest values reported for ditopic complexes. The reorientational correlation time is two times longer (298tauR = 183 ps) than the corresponding value of the parent monomeric Gd(III) complex, thus supporting the view of a limited degree of internal rotation. The possible influence of magnetic Gd-Gd coupling has been excluded by a comparison of the 1H NMRD profiles of the homodinuclear Gd(III)/Gd(III) and the heterodinuclear Gd(III)/Y(III) complexes.

Revisiting Y 2Si 2O 7 and Y 2SiO 5 polymorphic structures by 89Y MAS-NMR spectroscopy

This paper describes the 89Y MAS-NMR spectra for all the established polymorphs of Y 2Si 2O 7 ( y, α, β, γ and δ) and Y 2SiO 5 ( X1 and X2). The combination of our spectroscopic data with the structural information published up to now from diffraction data permits the revision and correction of mistakes which appear in the literature. Finally, the influence of different structural factors, such as yttrium coordination number and Y–O distances on the 89Y NMR isotropic chemical shift is analyzed.

Molecular structure of [Y4(μ3,η2-OR)3(μ,η2-OR)2(η1-OR)4 (μ,η1-OR)3]2 R=C2H4OPri, an homoleptic alkoxide with three different coordination numbers

The reaction between yttrium chips or Y5O(OPri)13 and 2-isopropoxyethanol afforded the title compound. It has been characterized in the solid state by X-ray diffraction and in solution by 1H and 89Y NMR spectroscopy.