Recent advances in applications of multinuclear solid-state NMR to heterogeneous catalysis and inorganic materials

Nakata, Shinichi; Tanaka, Yoshinori; Asaoka, Sachio; Nakamura, Munekazu

doi:10.1016/s0022-2860(97)00259-7

Cited by 16 publications

(8 citation statements)

References 27 publications

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“…These spectra showed the presence of three signals at −67, −55, and −48 ppm. The assignments are based on previous studies of analogous systems, which involved hybrid-containing silicas and other phyllosilicates. − …”

Section: Resultsmentioning

confidence: 99%

Aminated Phyllosilicates Synthesized via a Sol−Gel Process

1999

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Three analogous phyllosilicates were synthesized via a sol−gel process from the reaction of magnesium ions with aminated trialkoxysilanes in an aqueous basic medium at 373 K. The inorganic−organic hybrids obtained, designated as SILMgx (x = 1−3) are related to [3-aminopropyl]-, [N-(2-aminoethyl)-3-aminopropyl]-, and [(10-amino)-4,7-diazanonyl]trimethoxysilane, respectively. The elemental analysis of these hybrids gave the following C/N ratios: 3.1, 2.5, and 2.4. Thermal analysis data showed 50.7, 56.2, and 58.0% weight losses for the same sequence of hybrids. However, the thermal stability decreased in the order SILMg1 > SILMg2 > SILMg3. The surface areas of these matrixes are <2.0 m2 g-1 and X-ray diffraction patterns gave lamellar distances of 1745, 2063, and 2323 pm for SILMgx (x = 1−3). The infrared data indicated the existence of a phyllosilicate structure with absorption at 540 cm-1, which is associated with vibration of the Mg−O group. 29Si NMR showed the presence of three silicon species: T1, T2, and T3 in the inorganic−organic backbone structure. The photomicrographs obtained by scanning electron microscopy showed in all cases well-formed particles that have irregular shapes and particle sizes.

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Section: Resultsmentioning

confidence: 99%

Aminated Phyllosilicates Synthesized via a Sol−Gel Process

1999

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“…The solid-state structure of a hexaniobate salt was first reported in 1980 as a 7/6 salt; meaning seven charge-balancing sodiums and six NbO 6 octahedra in the cluster. 3 Other solid-state polyoxoniobate structures include the decaniobate [Nb 10 O 28 ] 6cluster, 4 a material featuring chains of the Keggin ion, 5 [SiNb 12 O 40 ], 16-and a new heteropolyanion geometry composed of 16 NbO 6 octahedra and 2 SiO 4 tetrahedra with a central Si 2 O 7 unit. 5 In our ongoing investigations on synthesis, stability, and reactivity of polyoxoniobates, we have observed that hexaniobate can be used as a precursor for synthesis of other polyoxoniobates and that the hexaniobate cluster is sometimes an intermediate product to the formation of other polyoxoniobate geometries.…”

Section: Introductionmentioning

confidence: 99%

“…A variety of multinuclear NMR experiments have been utilized (including 17 O, 1 H, 31 P, 51 V) to investigate the role of protons in catalytically active polyoxometalates. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The majority of the solid-state 1 H magic angle spinning (MAS) NMR studies have focused on dehydrated forms of the Keggin anions. Investigations into the effect of H 2 O in the crystal lattice on protonation of polyoxometalates materials are rare.…”

Section: Introductionmentioning

confidence: 99%

Multinuclear NMR Investigations of the Oxygen, Water, and Hydroxyl Environments in Sodium Hexaniobate

et al. 2004

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Solid-state (1)H, (17)O MAS NMR, (1)H-(93)Nb TRAPDOR NMR, and (1)H double quantum 2D MAS NMR experiments were used to characterize the oxygen, water, and hydroxyl environments in the monoprotonated hexaniobate material, Na(7)[HNb(6)O(19)].15H(2)O. These solid-state NMR experiments demonstrate that the proton is located on the bridging oxygen of the [Nb(6)O(19)](8-) cluster. The solid-state NMR results also show that the NbOH protons are spatially isolated from similar protons, but undergo proton exchange with the water species located in the crystal lattice. On the basis of double quantum (1)H MAS NMR measurements, it was determined that the water species in the crystal lattice have restricted motional dynamics. Two-dimensional (1)H-(17)O MAS NMR correlation experiments show that these restricted waters are preferentially associated with the bridging oxygen. Solution (17)O NMR experiments show that the hydroxyl proton is also attached to the bridging oxygen for the compound in solution. In addition, solution (17)O NMR kinetic studies for the hexaniobate allowed the measurement of relative oxygen exchange rates between the bridging, terminal, and hydroxyl oxygen and the oxygen of the solvent as a function of pH and temperature. These NMR experiments are some of the first investigations into the proton location, oxygen and proton exchange processes, and water dynamics for a base stable polyoxoniobate material, and they provide insight into the chemistry and reactivity of these materials.

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“…Solid-state NMR experiments can yield quantitative site-specific information for amorphous and crystalline solids, in the bulk, on surfaces, and at the interfaces . Multinuclear solid-state NMR has been applied to probe various aspects of the structure and reactivity of heteropoly systems, − but the potential of solids NMR for the analysis of POMs has not been fully realized. In particular, 51 V solid-state NMR spectroscopy is rapidly emerging as a technique for the analysis of vanadium-containing systems.…”

Section: Introductionmentioning

confidence: 99%

⁵¹V Magic Angle Spinning NMR Spectroscopy of Six-Coordinate Lindqvist Oxoanions: A Sensitive Probe for the Electronic Environment in Vanadium-Containing Polyoxometalates. Counterions Dictate the ⁵¹V Fine Structure Constants in Polyoxometalate Solids

et al. 2003

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Geometric and electronic environments of vanadium have been addressed by (51)V magic angle spinning NMR spectroscopy of six-coordinated polyoxometalate solids. (C(4)H(9))(4)N(+) and mixed Na(+)/Cs(+) salts of the Lindqvist-type mono- and divanadium-substituted oxotungstates, [VW(5)O(19)](3-) and [V(2)W(4)O(19)](4-), have been prepared as microcrystalline and crystalline solids. The solid-state NMR spectra reflect the details of the local environment of the vanadium site in these hexametalate solids via the anisotropic quadrupolar and chemical shielding interactions. Remarkably, these (51)V fine structure constants in the solid state are dictated by the nature and geometry of the countercations. Electrostatic calculations of the electric field gradients at the vanadium atoms have been performed. Experimental trends are well reproduced with the simple electrostatic model, and explain the sensitivity of the anisotropic NMR parameters to the changes in the cationic environment at the vanadium site.

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Recent advances in applications of multinuclear solid-state NMR to heterogeneous catalysis and inorganic materials

Cited by 16 publications

References 27 publications

Aminated Phyllosilicates Synthesized via a Sol−Gel Process

Aminated Phyllosilicates Synthesized via a Sol−Gel Process

Multinuclear NMR Investigations of the Oxygen, Water, and Hydroxyl Environments in Sodium Hexaniobate

⁵¹V Magic Angle Spinning NMR Spectroscopy of Six-Coordinate Lindqvist Oxoanions: A Sensitive Probe for the Electronic Environment in Vanadium-Containing Polyoxometalates. Counterions Dictate the ⁵¹V Fine Structure Constants in Polyoxometalate Solids

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Recent advances in applications of multinuclear solid-state NMR to heterogeneous catalysis and inorganic materials

Cited by 16 publications

References 27 publications

Aminated Phyllosilicates Synthesized via a Sol−Gel Process

Aminated Phyllosilicates Synthesized via a Sol−Gel Process

Multinuclear NMR Investigations of the Oxygen, Water, and Hydroxyl Environments in Sodium Hexaniobate

51V Magic Angle Spinning NMR Spectroscopy of Six-Coordinate Lindqvist Oxoanions: A Sensitive Probe for the Electronic Environment in Vanadium-Containing Polyoxometalates. Counterions Dictate the 51V Fine Structure Constants in Polyoxometalate Solids

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⁵¹V Magic Angle Spinning NMR Spectroscopy of Six-Coordinate Lindqvist Oxoanions: A Sensitive Probe for the Electronic Environment in Vanadium-Containing Polyoxometalates. Counterions Dictate the ⁵¹V Fine Structure Constants in Polyoxometalate Solids