Symmetry, disorder, and dynamics in solid crown ether complexes: 2H NMR studies of 15-crown-5·NaI, 15-crown-5·NaClO4, and 21-crown-7·KI

2H NMR line shapes have been obtained as a function of temperature for partially deuteriated 15-crown-5·NaI, 15-crown-5·NaClO4 and 21-crown-7·KI. Sudden changes in the line shapes above 330 K correspond to phase transitions: DSC shows transitions at 338, 347 K for 15-crown-5·NaI, and 356, 374, 383 K for 15-crown-5·NaClO4. The 2H NMR line shapes for the room temperature (RT) phases show the onset of a motion of the macrocycles above 200K, which is rapid a little above room temperature. Through detailed analysis of the complicated line shapes it has been shown that the most consistent interpretation of the dynamics in these RT phases is a "merry-go-round" type of motion similar to that found for 18-crown-6 and 12-crown-4 complexes in which O-CH2-CH2 units exchange sites around the ring, simultaneously adjusting their conformation to fit the site. In the high-temperature phases of all three complexes all the ring atoms are dynamically equivalent. This can only happen through a combination of increased symmetry and disorder for which possible models have been devised.Key words: 2H NMR, crown ether complexes, dynamics, disorder.

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Chiral "basket handle" binaphthyl porphyrins: synthesis, catalytic epoxidation and NMR conformational studies

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424610002483 ◽

2010 ◽

Vol 14 (07) ◽

pp. 646-659 ◽

Cited By ~ 17

Author(s):

Eric Rose ◽

Emma Gallo ◽

Nicolas Raoul ◽

Léa Bouché ◽

Ariane Pille ◽

...

Keyword(s):

Time Scale ◽

Room Temperature ◽

Conformational Equilibrium ◽

Variable Temperature ◽

Conformational Exchange ◽

Iron Catalysts ◽

Nmr Studies ◽

Conformational Studies ◽

H Nmr ◽

Catalytic Epoxidation

Three "basket handle" porphyrins have been prepared by condensation of tetrakis-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy, -3,3′-dicarbonylchloride, -3,3′-diacetylchloride and -3,3′-dipropanoylchloride. The epoxidation of styrene with the three iron catalysts, obtained after metalation of the free porphyrins, occurs with good yields and moderate ee up to 54%. These porphyrins showed unexpected conformational differences, as revealed by NMR spectroscopy. In particular, variable temperature NMR studies showed that the methoxy group in one of them undergoes intermediate conformational exchange on the 1H NMR time scale at room temperature. Lowering the temperature to -50 °C revealed the presence of four states in slow exchange on the NMR time scale. These results evidence a dynamic conformational equilibrium of the binaphthyl handles that adopt different, asymmetric positions with respect to the porphyrin plane.

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Natural Abundance Solid State 2H NMR Studies of Phase Transitions in Rotator Phase Solids

Mendeleev Communications ◽

10.1070/mc1993v003n04abeh000264 ◽

1993 ◽

Vol 3 (4) ◽

pp. 153-155 ◽

Cited By ~ 8

Author(s):

Abil E. Alievt ◽

Kenneth D.M. Harris

Keyword(s):

Phase Transitions ◽

Solid State ◽

Natural Abundance ◽

2H Nmr ◽

Nmr Studies ◽

Rotator Phase

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Synthesis and vibrational study of a 1:1 stoichiometric complex of hydronium tetrafluoroborate and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)

Canadian Journal of Chemistry ◽

10.1139/v82-129 ◽

1982 ◽

Vol 60 (7) ◽

pp. 853-861 ◽

Cited By ~ 21

Author(s):

Robert Chênevert ◽

André Rodrigue ◽

Marie Pigeon-Gosselin ◽

Rodrigue Savoie

Keyword(s):

Aqueous Solution ◽

Transition Temperature ◽

Crown Ether ◽

Room Temperature ◽

Organic Medium ◽

Remarkable Property ◽

H Nmr ◽

Vibrational Study ◽

Raman And Ir Spectroscopy ◽

Stoichiometric Complex

The macrocyclic ether 1,4,7,10,13,16-hexaoxaoctadecane (18-crown-6) has the remarkable property of being able to transfer the hydronium (H3O+) ion from an aqueous solution to an organic medium. This property has been used to synthetize a 1:1 stoichiometric complex of this ether with hydronium tetrafluoroborate. This complex is very stable (mp 145 °C) and dissolves readily, without decomposition, in solvents such as CHCl3. The presence of the H3O+ and BF4− ions in the complex has been confirmed by chemical analysis, and by 1H nmr, Raman, and ir spectroscopy. The vibrational spectra indicate that a conformational change of the crown ether takes place in the complex over the temperature range −50 °C to −100 °C. The symmetry of the crown ether, which appears to be relatively high at room temperature, is considerably reduced below the transition temperature.

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1H nuclear magnetic resonance, differential scanning calorimetry, and electrical conductivity studies on the phase transitions of pentylammonium chloride and the cationic self-diffusion in its rotator phase

Canadian Journal of Chemistry ◽

10.1139/v88-316 ◽

1988 ◽

Vol 66 (8) ◽

pp. 1961-1969 ◽

Cited By ~ 10

Author(s):

Shigehiko Iwai ◽

Ryuichi Ikeda ◽

Daiyu Nakamura

Keyword(s):

Phase Transition ◽

Electrical Conductivity ◽

Differential Scanning Calorimetry ◽

Room Temperature ◽

Stable Phase ◽

Scanning Calorimetry ◽

Nmr Studies ◽

Self Diffusion ◽

H Nmr ◽

Rotator Phase

Measurements of 1H nmr, differential thermal analysis, and differential scanning calorimetry have revealed that solid pentylammonium chloride, cooled rapidly from room temperature, forms a mixture of the stable and metastable low-temperature phases below the phase transition temperature, Ttr (238 K). The sample annealed just below Ttr for 3 h was shown to consist of a single stable phase down to about 100 K, indicating the existence of a time-consuming phase transition taking place successively just below the normal transition. In the rotator phase obtainable above Ttr (257 K), 1H nmr studies proved the presence of axial rotation of the whole cation about the long axis, similar to n-paraffins in their rotator phase. Above room temperature, the onset of the translational self-diffusion of the cations within 2D planes in the layer structure of the rotator phase was detected by measuring the temperature dependence of electrical conductivity as well as 1H T1 and T1p. 2D self-diffusion constants and diffusional correlation times evaluated from the electrical conductivity observed between room and the melting temperatures indicate that the 2D cationic diffusion near the melting point is as fast as 3D self-diffusion in usual plastic crystals. Cationic motions in the two different rotator phases α and α′ are compared.

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Structural Phase Transitions and Ionic Motions in Pyridinium Hexachlorotellurate(IV),Hexachlorostannate(IV), and Hexabromostannate(IV) Crystals as Studied by 1H NMR

Zeitschrift für Naturforschung A ◽

10.1515/zna-1989-0409 ◽

1989 ◽

Vol 44 (4) ◽

pp. 300-306 ◽

Cited By ~ 4

Author(s):

Yutaka Tai ◽

Tetsuo Asaji ◽

Ryuichi Ikeda ◽

Daiyu Nakamura

Keyword(s):

Phase Transitions ◽

High Temperature ◽

Structural Phase ◽

Lattice Relaxation ◽

Relaxation Mechanism ◽

Lattice Relaxation Time ◽

Spin Lattice Relaxation ◽

Scanning Calorimetry ◽

Spin Lattice ◽

H Nmr

Abstract The 1H NMR second moment M2 and the spin-lattice relaxation time T1 are determined for pyridinium hexachlorotellurate(IV), hexachlorostannate(IV), and hexabromostannate(IV) at various temperatures above ca. 140 K. The phase transition temperatures already reported from halogen NQR experiments are determined as 272, 331, and 285 K, respectively, by differential thermal analysis (DTA). The DTA as well as differential scanning calorimetry measurements show that the above phase transitions are of second-order. For pyridinium hexachlorotellurate(IV) and hexa-bromostannate(I V), a sharp 1H T1 dip was observed at the transition temperature. This is interpreted in terms of a phenomenon related to the critical fluctuation of an order parameter. From the measurements of 1H M2, 60° two-site jumps (60° flips) around the pseudo C6 axis of the cation are suggested to occur in the high temperature phases of the complexes. Modulation of X...1H (X = CI, Br) magnetic dipolar interactions due to the reorientational motion of the complex anions is considered as a possible relaxation mechanism in the high temperature phases.

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Structural Phase Transitions and Cationic Motions in Pvridinium Dichloroiodate(I) as Studied by 1H NMR, Differential Thermal Analysis, and Powder X-Ray Diffraction

Zeitschrift für Naturforschung A ◽

10.1515/zna-1989-1112 ◽

1989 ◽

Vol 44 (11) ◽

pp. 1111-1115 ◽

Cited By ~ 2

Author(s):

Reiko Watanabe ◽

Tetsuo Asaji ◽

Yoshihiro Furukawa ◽

Daiyu Nakamura ◽

Ryuichi Ikeda

Keyword(s):

Thermal Analysis ◽

Differential Thermal Analysis ◽

Phase Transitions ◽

Room Temperature ◽

Structural Phase ◽

Spin Lattice Relaxation ◽

Growth Time ◽

Stable Phase ◽

Temperature Phase ◽

H Nmr

For crystals of pyridinium dichloroiodate (I), (pyH)ICl2, the temperature dependences of the 1H NMR spin-lattice relaxation time T1 and the 1H second moment M2 were determined. M2 was found to be small (~ 1 G2) above room temperature, indicating that the cations perform rapid reorientational motion about their pseudohexad axis perpendicular to the cationic plane. 1H T1 at its minimum was unusually long, indicating this motion occurring in the low symmetry local environments. Phase transitions between stable solid phases were revealed at 282 and 373 K by the 1H NMR measurements and differential thermal analysis. The highest-temperature phase was easily supercooled and transformed reversibly into another metastable phase and back on cooling and warming at almost the same temperature of 138 K. The kinetics of the phase transition from the supercooled to the stable phase at room temperature was analyzed using an Avrami type relation. The growth time of the stable phase was estimated to be about 14 h at room temperature

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Room temperature crystal structure and high temperature structural and magnetic phase transitions in Sr(Fe0.5Nb0.5)O3 ceramic

Journal of Applied Physics ◽

10.1063/1.5091551 ◽

2019 ◽

Vol 125 (17) ◽

pp. 174102 ◽

Cited By ~ 3

Author(s):

Sushil Kumar ◽

Akhilesh Kumar Singh

Keyword(s):

Crystal Structure ◽

Phase Transitions ◽

High Temperature ◽

Room Temperature ◽

Magnetic Phase ◽

Magnetic Phase Transitions

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Trihapto cycloheptatrienyl molybdenum and tungsten dicarbonyl compounds incorporating tridentate chelating dimethyl(1-pyrazolyl)(ethanolamine)gallate ligands

Canadian Journal of Chemistry ◽

10.1139/v80-366 ◽

1980 ◽

Vol 58 (21) ◽

pp. 2278-2285 ◽

Cited By ~ 8

Author(s):

Kenneth S. Chong ◽

Alan Storr

Keyword(s):

Nitrogen Atom ◽

Low Temperature ◽

Physical Properties ◽

Nmr Spectra ◽

Room Temperature ◽

Amino Nitrogen ◽

Nmr Studies ◽

Dicarbonyl Compounds ◽

H Nmr ◽

And Tungsten

The synthesis and physical properties of a series of cycloheptatrienyl molybdenum and tungsten dicarbonyl compounds incorporating dimethyl(1-pyrazolyl)(ethanolamine)gallate ligands have been investigated. The monomeric, pseudo octahedral, complexes have the organogallate ligand occupying a set of facial positions with the cycloheptatrienyl ring situated opposite to the amino nitrogen atom. Proton nmr studies have shown the η3-C7H7 ligand of the complexes to be fluxional in solution at room temperature. In the low temperature limiting 1H nmr spectra of the complexes in solution, however, it is possible to distinguish ail seven protons of the static η3-C7H7 ring owing to the asymmetric nature of the octahedral molecules.

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Observation of a Hydrogen Doublet Site in High Defect Density As-Grown a-Si:H by 1H NMR

MRS Proceedings ◽

10.1557/proc-862-a13.5 ◽

2005 ◽

Vol 862 ◽

Author(s):

D. Bobela ◽

T. Su ◽

P. C. Taylor ◽

G. Ganguly

Keyword(s):

Defect Density ◽

Hydrogen Separation ◽

Vibrational Modes ◽

Nmr Studies ◽

Temperature Range ◽

H Nmr ◽

Line Shapes ◽

Line Shape Analysis ◽

Doublet Line ◽

Hydrogenated Amorphous

Abstract1H NMR studies of hydrogenated amorphous silicon (a-Si:H) with ˜1017 cm-3 defects grown by PECVD with a rate of 5 Å/s show the existence of a hydrogen doublet for both asgrown and light-soaked samples. We observe the doublet over the temperature range from 5 to 20 K in a sample where no light soaking has occurred. The doublet line shapes display no narrowing over this temperature range. Vibrational modes characteristic of SiH2 wagging and scissor modes are seen from infrared spectroscopy. These results suggest that the doublet is due to SiH2 that occurs at a density of approximately 1 at. % in this sample. From line shape analysis, we estimate a lower limit of 1.8 ˜ for the hydrogen-to-hydrogen separation.

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