Koordination Des Anions Von 2,4-Dicyanoglutaconsäurediethylester An Tripodeisen(Ii)-Einheiten. Die Entstehung Helikaler Strukturen

2001 ◽  
Vol 56 (8) ◽  
pp. 735-746 ◽  
Author(s):  
Volker Jacob ◽  
Gottfried Huttner ◽  
Elisabeth Kaifer ◽  
Peter Kircher
Keyword(s):  
Nmr Spectra ◽  
Variable Temperature ◽  
Cyano Group ◽  
Sodium Cyanide ◽  
Diethyl Ester ◽  
Bridging Ligands ◽  
Bidentate Chelate ◽  
Glutaconic Acid ◽  
Higher Temperature ◽  
Dynamic Exchange

The anion of 2,4-dicyano glutaconic acid diethyl ester, [NCC(COOEt)CHC(COOEt)CN]- (1- ), as an α,μ;-dinitrile with a three atom spacer is a highly variable ligand capable of binding in a monodentate η1-fashion, in a bidentate chelate fashion, and as a μ2-bridging entity. TripodFe(1)2, 2, [tripod = CH3C(CH2PPh2)3] contains one chelating ligand 1- and one terminally coordinated ligand 1-- . Variable temperature NMR spectroscopy shows, that, while the structure is static at 193 K, dynamic exchange of the donor functions of chelating and terminally bonded ligands occurs at higher temperature. TripodFe(1)2, 2, is obtained from a 1:1:2 mixture of tripod, Fe(II)aq (BF4)2, and Na1-2H2O . With a stoichiometry 1:1:1 of these ingredients and an additional naif equivalent of sodium cyanide, the dinuclear compound [tripodFe{μ-NCC(COOEt)CHC(COOEt)CN}2{μ-CN}Fetripod]BF4, 3 BF4, is obtained. The structure of 3+ shows a helical arrangement of the ligands 1- around the Fe···Fe axis which is a consequence of the incomensurability of the bridging ligands 1- and μ-CN. The two iron centers in 3BF4 differ by their coordination to the carbon or to the nitrogen terminus of the bridging cyano group. This difference is reflected by the NMR spectra, Mössbauer spectra and cyclovoltammograms

scholarly journals Atropisomerism of a Podophyllotoxin Derivative: Experimental and Computational Study

2018 ◽  
Vol 13 (6) ◽  
pp. 1934578X1801300
Author(s):  
Shi-Wen Zhou ◽  
Fei Jiang ◽  
Yang Yu ◽  
Xiu-Yong Huang ◽  
Yong-Heng Wang ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Nmr Spectra ◽  
Computational Study ◽  
Variable Temperature ◽  
Exchange Process ◽  
Single Bond ◽  
H Nmr ◽  
Dysosma Versipellis ◽  
Dynamic Exchange ◽  
C Nmr

Diphyllin-7′- O-β-D-glucoside, a podophyllotoxin derivative, was isolated from the roots of Dysosma versipellis. The 1H and 13C NMR spectra acquired at 300 K exhibited doubling of signals, suggesting the existence of two rotamers in solution. Variable-temperature 1H NMR experiments indicated a dynamic exchange process between the two rotamers. DFT calculations verified nearly equal energies for the two rotamers about the single bond C7′-O7.

Variable Temperature Measurement on Operating Pentacene-Based OTFT

2008 ◽  
Vol 1091 ◽  
Author(s):  
Hung-Keng Chen ◽  
Po-Tsun Liu ◽  
Ting-Chang Chang ◽  
S.-L. Shy
Keyword(s):  
Conduction Mechanism ◽  
Variable Temperature ◽  
Electrical Measurement ◽  
Isokinetic Temperature ◽  
Trap States ◽  
Band Tail ◽  
Thermally Activated ◽  
Multiple Trapping ◽  
Higher Temperature ◽  
Release Model

AbstractVariable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer¡VNeldel relationship between the activation energy and the prefactor with a Meyer¡VNeldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.

ChemInform Abstract: Comparison of Variable-Temperature 1H NMR Spectra of Five-Coordinate High-Spin (S = 5/2) Iron(III) Porphyrins and Chlorins

ChemInform ◽  
1988 ◽  
Vol 19 (36) ◽  
Author(s):  
M. J. PAWLIK ◽  
P. K. MILLER ◽  
E. P. JUN. SULLIVAN ◽  
M. A. LEVSTIK ◽  
D. A. ALMOND ◽  
...  
Keyword(s):  
1H Nmr ◽  
High Spin ◽  
Nmr Spectra ◽  
Variable Temperature ◽  
1H Nmr Spectra

X-ray Structure and Variable Temperature NMR Spectra of [meso-Triarylcorrolato]copper(III)

2003 ◽  
Vol 42 (15) ◽  
pp. 4495-4497 ◽  
Author(s):  
Christian Brückner ◽  
Raymond P. Briñas ◽  
Jeanette A. Krause Bauer
Keyword(s):  
Nmr Spectra ◽  
Variable Temperature ◽  
X Ray ◽  
Variable Temperature Nmr Spectra

Synthesis, Characterization and Anticancer Activity of Isonicotinylhydrazide Metal Complexes

2019 ◽  
Vol 41 (1) ◽  
pp. 113-113
Author(s):  
Mansoor Ahmed Zi Ning Lei Mansoor Ahmed Zi Ning Lei ◽  
Mohsin Ali Mohsin Ali ◽  
Syed Imran Ali Syed Imran Ali ◽  
Konatsu Kojima Konatsu Kojima ◽  
Pranav Gupta Pranav Gupta ◽  
...  
Keyword(s):  
Metal Complexes ◽  
Nmr Spectra ◽  
Amorphous Materials ◽  
Physiochemical Properties ◽  
Ftir Studies ◽  
Higher Temperature ◽  
Xrd Patterns ◽  
Scanning Electron ◽  
Formation Of Complexes

This study focuses characterization of iron (II), iron (III), cobalt (II), copper (II) and nickel (II) complexes of Isoniazid (INH) and studying their spectroscopic as well as physiochemical properties. FTIR studies showed that INH binds the metal from oxygen of carbonyl group and nitrogen of amino group. The proton NMR spectra of the metal complexes confirmed the conversion of ligand molecules into their respective metal complexes. However, pattern of splitting and shapes of peaks was observed but the protons resonated in the expected region. XRD patterns may be concluded that the complexes are mostly comprised of nano-sized particles behaving like amorphous materials. Scanning electron microscopy (SEM) revealed marked changes in the morphology of complexes, and their degradation at higher temperature strengthens the hypothesis of the successful formation of complexes. The MTT cytotoxicity assay was used for the screening these complexes against four human cell lines but the results did not prove significant.

Synthesis, structure, and nonrigidity of Os4(CO)15, Os4(CO)13(PMe3)[P(OMe)3], and Os4(CO)14(CNBut)

1995 ◽  
Vol 73 (7) ◽  
pp. 1223-1235 ◽  
Author(s):  
Frederick W.B. Einstein ◽  
Victor J. Johnston ◽  
Andrew K. Ma ◽  
Roland K. Pomeroy
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nmr Spectra ◽  
Energy Exchange ◽  
Variable Temperature ◽  
Carbonyl Cluster ◽  
Space Group ◽  
Exchange Processes ◽  
Nuclear Magnetic Resonance Spectra ◽  
Osmium Carbonyl ◽  
C Nmr

The binary carbonyl Os4(CO)15, 1, has been prepared by the addition of Os(CO)5 to Os3(CO)10(cyclooctene)2 at −15 °C. The related clusters Os4(CO)13(PMe3)[P(OMe)3], 2, and Os4(CO)14(CNBu′), 3, have been synthesized from Os4(CO)13(PMe3) and Os4(CO)15(CNBu′), respectively. The crystal structures of 1, 2, and 3 reveal similar planar metal skeletons with short (2.774 (1) − 2.793 (2) Å) and long (2.978 (2) − 3.019 (2) Å) peripheral Os—Os bonds; the hinge Os—Os bond in 1–3 ranges in length from 2.936 (2) to 2.948 (1) Å. The variable temperature 13C nuclear magnetic resonance spectra of 1 and 3 show that both are highly nonrigid in solution even at −120 °C. The mechanism of nonrigidity is believed to be an all-equatorial, merry-go-round carbonyl exchange. The variable temperature 13C nmr spectra of 2 indicate it is rigid on the nmr time scale in solution at −45 °C. Carbonyl exchange is, however, observed in the spectrum at −6 °C. From the mode of collapse of the signals it is believed that the lowest energy exchange processes in 3 involve axial-equatorial, merry-go-round CO exchanges in the two planes that each contain a short Os—Os bond. Crystallographic data for compound 1: space group C2/c; a = 12.802 (3) Å, b = 10.217 (3) Å, c = 16.380 (5) Å, β = 91.39 (2)°; R = 0.044, 1204 observed reflections. For compound 2: space group P21/c; a = 11.106 (7) Å, b = 16.931 (5) Å, c = 16.481 (5) Å, β = 97.71 (5)°; R = 0.051, 2117 observed reflections. For compound 3: space group P21/n; a = 11.747 (3) Å, b = 18.009 (5) Å, c = 12.448 (2) Å, β = 92.65 (2)°; R = 0.054, 2131 observed reflections. Keywords: osmium, carbonyl, cluster, nonrigidity.

Nuclear magnetic resonance studies of the methylammonium hexahalotellurates

1992 ◽  
Vol 70 (3) ◽  
pp. 849-855 ◽  
Author(s):  
Mark R. MacIntosh ◽  
Marco L. H. Gruwel ◽  
Katherine N. Robertson ◽  
Roderick E. Wasylishen
Keyword(s):  
Line Shape ◽  
Nmr Spectra ◽  
Room Temperature ◽  
Solid Phase ◽  
Variable Temperature ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
H Nmr ◽  
Nmr Study ◽  
Correlated Motion

A 2H and 14N NMR study of the solid methylammonium hexahalotellurates, (MA)2TeX6 (MA = CH3ND3+ or CD3NH3+, X = Cl, Br, and I), has been undertaken to characterize the dynamics of the methylammonium (MA) ion as a function of temperature. At room temperature, the MA ion in the hexachlorotellurate (solid II) is confined to C3 jumps about the C—N axis while a small angle libration of the C—N axis is occurring. In the room temperature phase, solid I, of (MA)2TeBr6 and (MA)2TeI6 the MA ions are performing overall reorientations on the ps time scale, averaging the 2H nuclear quadrupolar interactions to zero. Variable temperature 2H NMR spin-lattice relaxation times, T1, indicate an activation energy, EA, for "isotropic" reorientations of the CH3ND3+ ion of 5.2 ± 0.5 and 2.6 ± 0.3 kJ mol−1 for X = Br and I, respectively. Deuterium T1 values for C-deuterated MA ion in the hexaiodotellurate indicate an EA for whole-ion reorientation of 3.1 ± 0.3 kJ mol−1. At any given temperature, the correlation time, τc, derived from the T1 results was found to be the same for the two deuterium-labelled hexaiodotellurates. The similarity of both the EA and the τc values implies correlated motion of the methyl and ammonium groups. The 14N T1 results for solid I of (MA)2TeI6 indicate that C—N axis motions, with an EA = 5.6 ± 0.6 kJ mol−1, are more hindered than N—D or C—D bond dynamics. The 2H NMR spectra for (MA)2TeI6 (solid II) and (MA)2TeBr6 (solids II, III, and IV) are characterized by a Pake doublet line shape. The measured peak-to-peak splittings are less than what is predicted by C3 motion about the molecular symmetry axis. It is possible to model these line shapes by postulating that C3 rotations of the methyl and ammonium groups occur as the C—N axis librates in an effective cone about the position of the static molecular axis. For (CH3ND3)2TeBr6 and (CD3NH3)3TeBr6 the peak-to-peak splittings in the 2H NMR spectra were measured as a function of temperature in solid phases II, III, and IV and were found to be similar. Finally, the 2H NMR line shape relaxation for (MA)2TeBr6 (solid III) displays an orientation dependence indicating that rotations about the C—N axis are discrete rather than diffusive in nature. For solid phase II of (MA)2TeCl6, the line shape is observed to relax isotropically, implying that continuous C3 rotations are taking place. Keywords: 2H and 14N NMR, methylammonium hexahalotellurates, molecular motion.

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