45Sc NMR Research Articles

Observing the Surface Termination of LaScO3 Perovskite Using Solid-State Nuclear Magnetic Resonance.

Materials with well-defined surfaces are drawing increased attention for the design of bespoke catalysts and nanomaterials. Gaining a detailed understanding of the surfaces of these materials is an important challenge, which is often complicated by surface polymorphism and dynamic restructuring. We introduce the use of surface-enhanced NMR spectroscopy for the observation of such surfaces, focusing on LaScO3 as an example. We show that double-resonance NMR experiments correlating surface oxygen and probe molecules to the 139La and 45Sc nuclei at the surface reveal the material to be terminated by a ScOx monolayer. Surface-selective 17O and 45Sc NMR experiments further showed the material to be hydroxyl terminated and that the surface may be prone to dynamic restructuring as a result of moisture exposure. Perhaps most interestingly, surface-selective 139La NMR experiments revealed the existence of previously undetected surface lanthanum defects, suggesting that surface-enhanced NMR may be useful as a guide in the synthesis of defect-free surfaces in the design of various nanomaterials.

Structure–Properties Correlations in the Range of Cationic Spiropyrans as Analogues of Cyanine Dyes

AbstractRecently the need for smart materials has been extremely growing, and the development of materials with appropriate characteristics has become one of the main challenges. Heptamethine cyanine dyes are widely used in theranostics and photovoltaics due to their remarkable optical properties. However, they are characterized by “rigid” non–changable properties. The main aim of the current study is to unveil correlation between structure and optical properties in the range of vinyl‐3H‐indolium substituted spiropyrans, which can be considered as the closest analogs of heptamethine cyanines with the photocontrolable optical and fluorescent properties. The effects of substitution in indoline and 2H‐chromene cycles, as well as anion change are under the study. To achieve this goal, a series of spiropyran iodides and perchlorates with methyl, methoxy substituents or fluorine atom in position 6′, as well as a conjugated vinyl‐3H‐indolium fragment in position 8′, were synthesized. The structure of the compounds was carefully studied using SC XRD, NMR, IR and mass spectroscopy. Then, studies on absorption and photoluminescence characteristics, as well as photochromic behavior were carried out.

Host-Guest Chemistry in Discrete Polyoxo-12-Palladate(II) Cubes [MO8Pd12L8]n- (M = ScIII, CoII, CuII, L = AsO43-; M = CdII, HgII, L = PhAsO32-): Structure, Magnetism, and Catalytic Hydrogenation.

A family of five host-guest assemblies comprising different metal ions inside a cuboid 12-palladium-oxo cage, [MO8Pd12L8]n- (MPd12L8, M = ScIII, CoII, CuII, L = AsO43-; M = CdII, HgII, L = PhAsO32-), was synthesized and structurally characterized in the solid state by single-crystal X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis, and their solution and gas-phase stability were validated by multinuclear NMR spectroscopy and electrospray-ionization mass spectrometry (ESI-MS). The polyoxopalladates (POPs) ScPd12As8, CoPd12As8, and CuPd12As8 represent the first three examples of the MPd12As8 archetype. The unique cubic ligand field of {MO8} allows for collecting the speciation profiles of the POPs in solution using 45Sc and 113Cd NMR techniques. Detailed magnetic and electron paramagnetic resonance (EPR) studies were performed on CuPd12As8. Catalytic studies on MPd12As8 (M = CuII and CoII) supported on SBA-15 unveiled a guest metal-dependent structure-function relationship, with CuPd12As8 being the more efficient precatalyst for the hydroconversion of o-xylene in a fixed-bed reactor.

Reaction Rate Acceleration of Cooperative Catalytic Systems: Metal Nanoparticles and Lewis Acids in Arene Hydrogenation

AbstractEmploying two distinct catalysts in one reaction medium synergistically is a powerful strategy for activating less reactive substrates. Although the approach has been well‐developed in homogeneous conditions, it remains challenging and rare in heterogeneous catalysis, especially under gas‐liquid‐solid multiphase reaction conditions. Here, we describe the development of cooperative and synergistic catalyst systems of heterogeneous Rh‐Pt bimetallic nanoparticle catalysts, Rh‐Pt/DMPSi‐Al2O3, and Sc(OTf)3 in the liquid phase for the hydrogenation of arenes under very mild conditions. Dramatic rate acceleration was achieved with cooperative activation. Remarkably, more challenging substrates that contained strong electron‐donating groups and sterically hindered substituents were smoothly hydrogenated. Mechanistic insights into the cooperative activation of an aromatic substrate by heterogeneous metal nanoparticles and a soluble Lewis acid was obtained by kinetic studies and by direct observation of 1H and 45Sc NMR spectra.

Reaction Rate Acceleration of Cooperative Catalytic Systems: Metal Nanoparticles and Lewis Acids in Arene Hydrogenation.

Employing two distinct catalysts in one reaction medium synergistically is a powerful strategy for activating less reactive substrates. Although the approach has been well-developed in homogeneous conditions, it remains challenging and rare in heterogeneous catalysis, especially under gas-liquid-solid multiphase reaction conditions. Here, we describe the development of cooperative and synergistic catalyst systems of heterogeneous Rh-Pt bimetallic nanoparticle catalysts, Rh-Pt/DMPSi-Al2 O3 , and Sc(OTf)3 in the liquid phase for the hydrogenation of arenes under very mild conditions. Dramatic rate acceleration was achieved with cooperative activation. Remarkably, more challenging substrates that contained strong electron-donating groups and sterically hindered substituents were smoothly hydrogenated. Mechanistic insights into the cooperative activation of an aromatic substrate by heterogeneous metal nanoparticles and a soluble Lewis acid was obtained by kinetic studies and by direct observation of 1 H and 45 Sc NMR spectra.

Pursuing the excision of carbon-centred hexanuclear scandium clusters {CSc

A multi-gram synthetic route to black solid {CSc6}I12Sc (1) was developed which comprises the reaction of scandium triiodide, ScI3, with graphite and scandium metal at 850°C. Compound 1 dissolved in N,N-dimethylacetamide (DMA) to form a red solution. Results derived from 45Sc NMR and EPR spectroscopy indicated that a scandium cluster species exists in this solution along with a complex cation [Sc(DMA)6]3+. From these solutions crystals of [Sc(DMA)6]I3 (2) and a red oily product was isolated. Compound 2 was also prepared independently by dissolving ScI3 in DMA and two polymorphs, orthorhombic 2O and monoclinic 2M were crystallised. {CSc6}I12Sc (1) also dissolved in THF yielding a red solution which contains [ScI6]3− and a scandium cluster species, as analysed by 45Sc NMR and EPR spectroscopy.

High capacity ammonia adsorption in a robust metal-organic framework mediated by reversible host-guest interactions.

To understand the exceptional adsorption of ammonia (NH3) in MFM-300(Sc) (19.5 mmol g−1 at 273 K and 1 bar without hysteresis), we report a systematic investigation of the mechanism of adsorption by a combination of in situ neutron powder diffraction, inelastic neutron scattering, synchrotron infrared microspectroscopy, and solid-state 45Sc NMR spectroscopy. These complementary techniques reveal the formation of reversible host–guest supramolecular interactions, which explains directly the observed excellent reversibility of this material over 90 adsorption–desorption cycles.

Synthesis, solid-state, solution, and theoretical characterization of an "in-cage" scandium-NOTA complex.

Developing chelators that strongly and selectively bind rare-earth elements (Sc, Y, La, and lanthanides) represents a longstanding fundamental challenge in inorganic chemistry. Solving these challenges is becoming more important because of increasing use of rare-earth elements in numerous technologies, ranging from paramagnets to luminescent materials. Within this context, we interrogated the complexation chemistry of the scandium(III) (Sc3+) trication with the hexadentate 1,4,7-triazacyclononane-1,4,7-triacetic acid (H3NOTA) chelator. This H3NOTA chelator is often regarded as an underperformer for complexing Sc3+. A common assumption is that metalation does not fully encapsulate Sc3+ within the NOTA3- macrocycle, leaving Sc3+ on the periphery of the chelate and susceptible to demetalation. Herein, we developed a synthetic approach that contradicted those assumptions. We confirmed that our procedure forced Sc3+ into the NOTA3- binding pocket by using single crystal X-ray diffraction to determine the Na[Sc(NOTA)(OOCCH3)] structure. Density functional theory (DFT) and 45Sc nuclear magnetic resonance (NMR) spectroscopy showed Sc3+ encapsulation was retained when the crystals were dissolved. Solution-phase and DFT studies revealed that [Sc(NOTA)(OOCCH3)]1- could accommodate an additional H2O capping ligand. Thermodynamic properties associated with the Sc-OOCCH3 and Sc-H2O capping ligand interactions demonstrated that these capping ligands occupied critical roles in stabilizing the [Sc(NOTA)] chelation complex.

Solvation coordination compounds of scandium chloride from the dehydration of scandium chloride hexahydrate

Attempts to dehydrate [Sc(H2O)6]3[Cl]•(H2O) using simple organic solvents led to the isolation of [ScCl3(THF)3] (1) from the addition of thionyl chloride (O = SCl2) to the hydrate, slurried in tetrahydrofuran (THF). Modification of 1 by a variety of solvents yielded the crystallographically characterized compounds: [ScCl3(MeCN)3]•MeCN (2), [ScCl3(py)3]•py (3), [ScCl2(MeOH)4][X] (X = Cl 4; X = Br 4a), and [ScCl2(HOPri)4][Cl] (5) (where MeCN = acetonitrile; py = pyridine; MeOH = methanol, HOPri = isopropanol). The heating of 3 resulted in the formation of [py-H-py][ScCl4(py)2]•(py)1/2 referred to as 6•py1/2. Attempts to dehydrate [Sc(H2O)6]3[Cl]•(H2O) with the same set of organic solvents did not lead to full exchange; however, direct dehydration was readily observed for Zwitterionic species, including: triphenylphosphine oxide (O=PPh3), diphenylsulfoxide (O=SPh2), urea (O=C(NH2)2), dimethylformamide (OC(H)N(Me)2), diphenylformamide (O=C(H)N(Ph)2) which formed [ScCl2(O=PPh3)4][Cl]•2HOEt (7), [ScCl3(O=SPh2)3] (8), [Sc(OC(NH2)2)6]3[Cl] (9), [ScCl3(O=C(H)N(Me)2)3] (10), [ScCl3(OC(H)N(Ph)2)3] (11), respectively. Interestingly, the use of propylene carbonate (PC) resulted in the reduction of the modifier forming [Sc(κ2(O,O’)PD)(μ, κ 2(O,O’)H-PD)(H2O)2]22[Cl] (12) where H2-PD = propane-1,2 diol. All compounds were identified using single crystal X-ray and solution 45Sc NMR.

Synthesis of the scandium chloride hydrates ScCl3·3H2O and Sc2Cl4(OH)2·12H2O and their characterisation by X-ray diffraction, 45Sc NMR spectroscopy and DFT calculations

Abstract The compounds ScCl3·3H2O (SCTH) and [{Sc(H2O)5(μ-OH)}2]Cl4·2H2O (SCOH), have been synthesised and characterised by single-crystal XRD, 45Sc NMR spectroscopy and DFT calculations, with the crystal structure of SCTH reported here for the first time. From 45Sc NMR measurements under static and MAS conditions, both chemical shift and quadrupolar coupling parameters have been determined. The quadrupolar coupling constants χ for the octahedrally coordinated scandium sites in SCTH are 2.0 ± 0.1 MHz for Sc(1) and 3.81 ± 0.05 MHz for Sc(2). For SCOH, where the hepta-coordination of the single scandium site constitutes a less symmetric electronic environment, 14.68 ± 0.05 MHz was found. DFT calculations for the static SCTH structure consistently overestimate the quadrupolar coupling constants, indicating the possible presence of crystal water dynamics on the NMR time scale.

Reduced Arene Complexes of Scandium

Alkali metal naphthalenide or anthracenide reacted with scandium(III) anilides [Sc(X){N(tBu)Xy}2(thf)] (X=N(tBu)Xy (1); X=Cl (2); Xy=C6H3‐3,5‐Me2) to give scandium complexes [M(thf)n][Sc{N(tBu)Xy}2(RA)] (M=Li–K; n=1–6; RA=C10H8 2− (3‐Naph‐K) and C14H10 2− (3‐Anth‐M)) containing a reduced arene ligand. Single‐crystal X‐ray diffraction revealed the scandium(III) center bonded to the naphthalene dianion in a σ2:π‐coordination mode, whereas the anthracene dianion is symmetrically attached to the scandium(III) center in a σ2‐fashion. All compounds have been characterized by multinuclear, including 45Sc NMR spectroscopy. Quantum chemical calculations of these intensely colored arene complexes confirm scandium to be in the oxidation state +3. The intense absorptions observed in the UV/Vis spectra are due to ligand‐to‐metal charge transfers. Whereas nitriles underwent C−C coupling reaction with the reduced arene ligand, the reaction with one equivalent of [NEt3H][BPh4] led to the mono‐protonation of the reduced arene ligand.

Scandium bis(trimethylsilyl)methyl complexes revisited: extending the 45Sc NMR chemical shift range and a new structural motif of Li[CH(SiMe3)2

Depending on the molar ratio employed, the reaction of ScCl3(thf)3 with Li[CH(SiMe3)2] afforded the bis and tris(alkyl) ate complexes [Sc{CH(SiMe3)2}2(μ-Cl)2Li(thf)2]2 and Sc[CH(SiMe3)2]3(μ-Cl)Li(thf)3, respectively, in moderate yields. Treatment of these mixed alkyl/chlorido complexes with MeLi gave the mixed alkyl complexes [Sc{CH(SiMe3)2}2(μ-Me)2Li(thf)2]2 and Sc[CH(SiMe3)2]3(μ-Me)Li(thf)3. Aiming at homoleptic {Sc[CH(SiMe3)2]3} both of the mixed [CH(SiMe3)2]/Me complexes were treated with AlMe3. Although LiAlMe4 separation occurred, aluminium complex Al[CH(SiMe3)2]Me2(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe3)2}2(μ-Me)2Li(thf)2]2 and [Sc(CH2SiMe3)4][Li(thf)4] revealed the maximum downfield 45Sc NMR chemical shifts of 888.0 and 933.4 ppm, respectively, reported to date. The synthesis of putative {Sc[CH(SiMe3)2]3} was also attempted via the aryloxide route applying complexes Sc(OC6H2tBu2-2,6-Me-4)3 and [Sc(OC6H3iPr2-2,6)3]2 along with Li[CH(SiMe3)2] but the outcome was inconclusive. Instead, a cyclic octamer was found for Li[CH(SiMe3)2] in the solid state.

Trimethylscandium.

The hitherto unknown homoleptic tetramethylaluminate complex [Sc(AlMe4)3] could be obtained by reacting the ate complex [Li3ScMe6(thf)1.2] with AlMe3 in the cold. It cocrystallizes with AlMe3 as [Sc(AlMe4)3(Al2Me6)0.5] and decomposes at ambient temperature in n-pentane via multiple C-H bond activations to the mixed methyl/methylidene complex [Sc3(μ3-CH2)2(μ2-CH3)3(AlMe4)2(AlMe3)2]. Donor-induced methylaluminate cleavage of [Sc(AlMe4)3(Al2Me6)0.5] produced [ScMe3]n in good yield, which could be derivatized with trimethyltriazacyclononane (Me3TACN) to form the structurally characterizable [(Me3TACN)ScMe3]. Additionally, half-sandwich complex [Cp*Sc(AlMe4)2] and sandwich complex [Cp*2Sc(AlMe4)] were accessible by salt metathesis reactions from [Sc(AlMe4)3(Al2Me6)0.5] and KCp* (Cp* = C5Me5). 45Sc NMR spectroscopy was applied as a significant probe to evidence the existence of [ScMe3]n. Compounds [(Me3TACN)ScMe3] (+624.6 ppm) and [ScMe3(thf)x] (+601.7 ppm) gave large 45Sc NMR shifts, revealing the strong deshielding effect of the σ-bonded alkyl ligands on the scandium nuclei. Ultimately, cationized [Sc(AlMe4)3(Al2Me6)0.5] was employed in isoprene polymerization, leading to polymers in high yields (>95%) and with high (>90%) cis-1,4-polyisoprene content.

Study of the NaF-ScF3 system as a molten bath for production of Sc alloys: A combination of NMR and molecular dynamics simulations

In situ high temperature NMR spectroscopy was used to characterize the NaF-ScF3 melt over a wide range of compositions. 19F, 23Na, and 45Sc NMR spectra were acquired in NaF-ScF3 melts of up to 70 mol% of ScF3. The interpretation of all experimental results obtained in situ in the melt is significantly enhanced by the contribution of Molecular Dynamics (MD) calculations. A new interatomic potential for the molten NaF-ScF3 system was developed by using a Polarizable Ion Model (PIM). The potential parameters were obtained by force-fitting to density functional theory (DFT) reference data. MD simulations were combined with further DFT calculations to determine NMR chemical shifts for 19F, 23Na, and 45Sc. The agreement between the experimental NMR data and the corresponding calculated data from our applied computational protocol indicated the polymerization and network formation in the melt. Additionally, the density and the electrical conductivity in the molten state were calculated from the statistical analysis of ionic trajectories obtained through MD simulations.

Synthesis, 45Sc NMR characterization, and interconversion of structurally diverse scandium chloride hydrates

The dissolution of scandium metal (Sc°) in concentrated hydrochloric acid was found to generate a wide variety of products based on the reaction/processing conditions. The compounds [Sc(H2O)6]3[Cl] (1) and [ScCl2(H2O)4][Cl]·H2O (2) were isolated from the above reaction when an ice bath is used. If the reaction was allowed to warm uncontrolled during synthesis, [Sc(μ-OH)(H2O)5]24[Cl]·2H2O (termedOH) was produced. If 1 or 2 were heated (130 °C) in toluene or H2O, [ScCl2(H2O)4][ScCl4(H2O)2] (3) crystallized. Interconversion of the various hydrates and OH structure were studied via 45Sc NMR spectroscopy studies. Efforts to easily dehydrate 2 through the addition of a Lewis base led to the characterization of monohydrate solvates: [ScCl3(THF)2(H2O)]·THF (4·THF) or [ScCl3(κ2-DME)(H2O)] (5) where THF = tetrahydrofuran and DME = dimethoxyethane. In contrast, the use of pyridine formed [Sc(μ-OH)(Cl)2(py)2]2·py (6) where py = pyridine. The formation of the OH moiety is attributed to the higher reaction temperatures achieved using py as the solvent. These compounds were also characterized using 45Sc NMR spectroscopy and compared to commercial ScCl3 dissolved in the parent solvent.

Mixed Dimetallic Cluster Fullerenes: ScGdO@ C3v(8)-C82 and ScGdC2@ C2v(9)-C82.

Mixed-metal cluster fullerenes have been extensively studied in recent years for their rich structural variability of the encaged clusters and have shown great potential in applied studies such as biomedicine and molecular electronic devices. However, the studies in this field have mostly concentrated on the nitride cluster fullerene, and very few other types of mixed-metal cluster fullerenes have been reported so far. Herein, we report the synthesis and isolation of the first mixed-metal oxide cluster fullerene, ScGdO@C82, and a novel mixed dimetallic carbide cluster fullerene, ScGdC2@C82. Spectroscopic and electrochemical studies combined with density functional theory (DFT) calculations assigned the molecular structure of the two cluster fullerenes (CFs) to ScGdO@ C3v(8)-C82 and ScGdC2@ C2v(9)-C82, respectively. DFT calculations also suggested that these two mixed-metal clusters are likely to be found in any of the three isolated pentagon rule Cs(6)-C82, C3v(8)-C82 and/or C2v(9)-C82 cages. The electrochemical studies show that the electrochemical gap of ScGdO@ C3v(8)-C82 and ScGdC2@ C2v(9)-C82 are 1.49 and 1.08 V. Moreover, comparative studies of ScGdO@ C3v(8)-C82 and Sc2O@ C3v(8)-C82, ScGdC2@ C2v(9)-C82 and Sc2C2@ C2v(9)-C82 showed that, despite their close structural resemblance, the replacement of one Sc ion by a Gd ion resulted in notable changes in their electrochemical behaviors as well as their 45Sc NMR spectra.

The β‐Agostic Structure in (C5Me5)2Sc(CH2CH3): Solid‐State NMR Studies of (C5Me5)2Sc−R (R=Me, Ph, Et)

AbstractMultinuclear solid‐state NMR studies of Cp*2Sc−R (Cp*=pentamethylcyclopentadienyl; R=Me, Ph, Et) and DFT calculations show that the Sc−Et complex contains a β‐CH agostic interaction. The static central transition 45Sc NMR spectra show that the quadrupolar coupling constants (Cq) follow the trend of Ph≈Me>Et, indicating that the Sc−R bond is different in Cp*2Sc−Et compared to the methyl and phenyl complexes. Analysis of the chemical shift tensor (CST) shows that the deshielding experienced by Cβ in Sc−CH2CH3 is related to coupling between the filled σC‐C orbital and the vacant orbital.

The β-Agostic Structure in (C5 Me5 )2 Sc(CH2 CH3 ): Solid-State NMR Studies of (C5 Me5 )2 Sc-R (R=Me, Ph, Et).

Multinuclear solid-state NMR studies of Cp*2 Sc-R (Cp*=pentamethylcyclopentadienyl; R=Me, Ph, Et) and DFT calculations show that the Sc-Et complex contains a β-CH agostic interaction. The static central transition 45 Sc NMR spectra show that the quadrupolar coupling constants (Cq ) follow the trend of Ph≈Me>Et, indicating that the Sc-R bond is different in Cp*2 Sc-Et compared to the methyl and phenyl complexes. Analysis of the chemical shift tensor (CST) shows that the deshielding experienced by Cβ in Sc-CH2 CH3 is related to coupling between the filled σC-C orbital and the vacant πSc⋯HC* orbital.

Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X-ray Diffraction, and Density Functional Theory Calculations.

The structures of several fluoroscandate compounds are presented here using a characterization approach combining powder X-ray diffraction and solid-state NMR. The structure of K5Sc3F14 was fully determined from Rietveld refinement performed on powder X-ray diffraction data. Moreover, the local structures of NaScF4, Li3ScF6, KSc2F7, and Na3ScF6 compounds were studied in detail from solid-state 19F and 45Sc NMR experiments. The 45Sc chemical shift ranges for six- and seven-coordinated scandium environments were defined. The 19F chemical shift ranges for bridging and terminal fluorine atoms were also determined. First-principles calculations of the 19F and 45Sc NMR parameters were carried out using plane-wave basis sets and periodic boundary conditions (CASTEP), and the results were compared with the experimental data. A good agreement between the calculated shielding constants and experimental chemical shifts was obtained. This demonstrates the good potential of computational methods in spectroscopic assignments of solid-state 45Sc NMR spectroscopy.

Solid-state 45Sc NMR studies of Cp*2Sc-X and Cp*2ScX(THF).

Cp*2Sc-X, where X is a halide, were synthesized and studied by solid-state 45Sc NMR to determine how the Sc-X bond affects quadrupolar NMR parameters. The experimental quadrupolar coupling constants (CQ) show that the fluoride has the largest coupling constant and that the iodide has the smallest coupling constant. DFT analysis of this data indicates that the CQ of these compounds is related to core scandium and halide orbitals, which is related to polarizability of the halide and the Sc-X distance. Cp*2ScX(THF) were also investigated by solid-state 45Sc NMR spectroscopy, and have much smaller CQ values than the base-free halides. This is related to the change in structure of the THF adduct and occupation of orbitals of π-symmetry that reduce CQ.