scholarly journals Nmr Study of Cluster-Assembled Nanophase Copper

1992 ◽  
Vol 286 ◽  
Author(s):  
B. H. Suits ◽  
M. Meng ◽  
R. W. Siegel ◽  
Y. X. Liao
Keyword(s):  
Nmr Spectra ◽  
Metallic Copper ◽  
Relaxation Times ◽  
Central Peak ◽  
Copper Metal ◽  
Nmr Study ◽  
Isochronal Anneal ◽  
Average Grain Size ◽  
Line Narrowing ◽  
Spin Echoes

ABSTRACT63Cu and 65Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10nm show a broadened peak, at the normal Knight-shifted frequency for copper metal, which arises from only the central 1/2 to -1/2 transition. A very broad background is observed on either side of that peak. Some samples exhibit a second broad peak at a position normally associated with non-metallic copper. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger grained copper samples. Line shape measurements, using spin echoes, as a function of delay between rf excitation and measurement show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant, but not complete, line narrowing after an anneal at 450°C consistent with other nanophase metals which show grain growth above 40-50% of the melting temperature.

Study of cluster-assembled nanophase copper using NMR

1994 ◽  
Vol 9 (2) ◽  
pp. 336-342 ◽  
Author(s):  
B.H. Suits ◽  
M. Meng ◽  
R.W. Siegel ◽  
Y.X. Liao
Keyword(s):  
Spin Echo ◽  
Relaxation Times ◽  
Central Peak ◽  
Central Line ◽  
Internal Electric Field ◽  
Isochronal Anneal ◽  
Average Grain Size ◽  
Line Narrowing ◽  
Significant Line ◽  
Knight Shifts

Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10 nm show a broadened peak, at the normal Knight-shifted frequency for copper metal, which arises from only the central 1/2 to −1/2 transition. The broadening of the central line is associated with a distribution of Knight shifts. A very broad background is observed on either side of that peak, associated with broadening due to internal electric field gradients. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger-grained copper samples. The strain within the grains is estimated to be 0.7%. Line shape measurements as a function of spin echo delay time show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant line narrowing after an anneal at 450 °C consistent with other nanophase metals which show grain growth above 40-50% of the absolute melting temperature. The dependence of NMR linewidth on average grain diameter is estimated.

A deuterium NMR study of guest molecular dynamics of acetone in two organic inclusion compounds

1995 ◽  
Vol 73 (12) ◽  
pp. 2196-2207 ◽  
Author(s):  
Paul S. Sidhu ◽  
Jason Bell ◽  
Glenn H. Penner ◽  
Kenneth R. Jeffrey
Keyword(s):  
Molecular Dynamics ◽  
Inclusion Compounds ◽  
Nmr Spectra ◽  
Guest Molecule ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Deuterium Nmr ◽  
Spin Lattice ◽  
Nmr Study

Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times (T1) are used to investigate the dynamics of the guest molecule, acetone, in tris(5-acetyl-3-thienyl)methane (TATM) and cyclotriveratrylene (CTV) inclusion compounds. 13C CPMAS powder NMR spectra were obtained for each clathrate, to verify inclusion. In acetone: TATM, the guest molecule is undergoing twofold reorientation about the CO bond, exchanging the two methyl groups. An activation energy of 20 (± 1.4) kJ/mol, for the two-site jump motion, was found, independently, from deuterium NMR spectra an T1 measurements. Acetone in CTV performs the same type of motion as acetone in TATM. Activation energies of 25.0 (± 3.2) kJ/mol and 24.1 (± 0.5) kJ/mol were determined using the same two techniques. both inclusion compounds, the rate of methyl rotation within the acetone molecule is greater than 108 Hz even at the lowest temperature measured (84 K). Analytical expressions for the spin-lattice relaxation time (T1), for a twofold jump, were derived. Calculated values of the effective quadrupolar coupling constant and T1min for the guests agree very well with the experimental data. The 84 K spectrum of acetone:TATM unexpectedly shows some asymmetry, the origin of which is discussed. Finally, these two clathrates are compared to the recently examined acetone: tri-ortho-thymotide inclusion compound. Key words: inclusion compounds, deuterium NMR, solid state NMR spectroscopy, molecular dynamics.

A 15N, 13C, and 1H NMR study of reaction products from arylguanidines and chloroformate esters

1991 ◽  
Vol 56 (7) ◽  
pp. 1505-1511 ◽  
Author(s):  
Antonín Lyčka ◽  
Karel Palát
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Reaction Products ◽  
H Nmr ◽  
Nmr Study

The 15N, 13C, and 1H NMR spectra of the reaction products from arylguanidines with two mols of chloroformate esters have been measured. With application of the corresponding 15N isotopomer it has been proved that the reaction products have the structures IIIa-IIIc.

scholarly journals Trifluoroacetylation of Alcohols During NMR Study of Compounds with Bicyclo[2.2.1]heptane, Oxabicyclo[3.3.0]octane and Bicyclo[3.3.0]octane Skeleton

2021 ◽  
Vol 72 (2) ◽  
pp. 156-177
Author(s):  
Constantin I. Tanase ◽  
Anamaria Hanganu ◽  
Constantin Draghici
Keyword(s):  
Nmr Spectra ◽  
Cyclopropane Ring ◽  
Secondary Alcohol ◽  
Primary Alcohol ◽  
1H And 13C Nmr ◽  
Alcohol Group ◽  
Nmr Study ◽  
Group A ◽  
Graphical Presentation ◽  
Nmr Signals

TFA was added to a solution of a bicyclo[2.2.1]heptane azide-alcohol in CDCl3 to correctly characterize the compound, but during 24 h gave the trifluoro acetylated compound in quantitative yield. NMR spectra of the esterified compound helped us also to correctly attribute the NMR signals to the protons, and also confirmed the identification of the carbon atoms. The study was extended to other 14 compounds containing a primary alcohol group alone or with an ethylene ketal, a δ- or -lactone group, a primary and a secondary group, two primary and an alkene group and two primary and a secondary alcohol groups on scaffolds containing bicyclo[2.2.1]heptane, oxabicyclo[3.3.0]octane, bicyclo [2.2.1]heptane constrained with a cyclopropane ring and bicyclo[3.3.0]octane fragments. The esterification of all compounds was also quantitative in 24 to 72 h; this helped us to correct attribute the NMR signals to the protons and carbon atoms of the un-esterified compounds by comparison with those of the trifluoro acetylated compounds. A graphical presentation of 1H- and 13C-NMR spectra of a few un-esterified and esterified compounds are presented in the paper.

scholarly journals NMR Investigation of the Copper(II)-Ciprofloxacin System

1999 ◽  
Vol 6 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Iztok Turel ◽  
Janez Košmrlj ◽  
Bjørn Andersen ◽  
Einar Sletten
Keyword(s):  
Acidic Medium ◽  
Acidic Solution ◽  
Relaxation Times ◽  
Ring System ◽  
Proton Relaxation ◽  
X Ray ◽  
Ph Values ◽  
Nmr Study ◽  
Terminal Nitrogen Atom ◽  
Titration Data

A proton NMR study was performed on the copper(ll)-ciprofloxacin system. The proton relaxation times (T1) were determined from the titration data in acidic and basic media. In acidic medium the H5 signal is dramatically affected and it is assumed that copper is bonded to the quinolone through carbonyl and one of the carboxyl oxygens. Such bonding is in agreement with the X-ray literature data for the complex [Cu(cf)2]Cl2.6H2O isolated from the slightly acidic solution. There are additional significant changes in T1 of H3′ and H5′ atoms which suggest that the terminal nitrogen atom of the piperazine ring system-N4′ also interacts with copper in the basic conditions. Thus it is plausible that more than one species are present in the solution at high pH values.

1H and 19F NMR Study of Cation and Anion Motions in Guanidinium Fluoroantimonates

1995 ◽  
Vol 50 (8) ◽  
pp. 742-748 ◽  
Author(s):  
M. Grottel ◽  
A. Kozak ◽  
Z. Pająk
Keyword(s):  
Solid Phase ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Nmr Study ◽  
Guanidinium Cation

Abstract Proton and fluorine NMR linewidths, second moments, and spin-lattice relaxation times of polycrystalline [C(NH2)3]2SbF5 and C(NH2)3SbF6 were studied in a wide temperature range. For the pentafluoroantimonate, C3-reorientation of the guanidinium cation and C4-reorientation of the SbF5 anion were revealed and their activation parameters determined. The dynamical inequivalence of the two guanidinium cations was evidenced. For the hexafluoroantimonate, two solid-solid phase transitions were found. In the low temperature phase the guanidinium cation undergoes C3 reorien­ tation while the SbF6 anion reorients isotropically. The respective activation parameters were derived. At high temperatures new ionic plastic phases were evidenced.

Sign in / Sign up

Export Citation Format

Share Document