Tieftemperatur-Raman-Messungen an bewegten Proben bei 10 K am Beispiel der Isotopomeren Cs2[Pt35Cln37Cl6-n, n = 0-6 / Low-Temperature Raman Measurements on Moved Samples at 10 K Exemplified by the Isotopomers Cs2[Pt35Cln 37Cl6-n], n = 0-6

1993 ◽  
Vol 48 (12) ◽  
pp. 1737-1741 ◽  
Author(s):  
W. Preetz ◽  
E. Parzich
Keyword(s):  
Low Temperature ◽  
Ligand Exchange ◽  
Room Temperature ◽  
Valence Vibration ◽  
Closed Cycle ◽  
Exchange Reactions ◽  
Normal Coordinate ◽  
Point Groups ◽  
Isotopic Effects ◽  
Good Agreement

A technique to record Raman spectra of deeply coloured solids at low temperature (10 K) is described, using a closed cycle He-cryogenerator and moving the cell by an excentric attachment. The spectroscopic resolution is considerably enhanced as compared to room temperature or 80 K measurements. This is obvious from splittings of Raman lines observed at 10 K on the isotopomers Cs2[Pt35Cln37Cl6-n], n = 1 -5, which have been prepared by stereospecific ligand exchange reactions. As a consequence of lowered symmetry the degenerate valence vibration v2(Eg, Oh) is split into two lines for the isotopomers belonging to the point groups D4h, C4v and C2v. The isotopic effects calculated by normal coordinate analysis are in good agreement with the observed frequencies.

Darstellung, Schwingungsspektren und Normalkoordinatenanalyse von Chloro-Bromo-Rhodaten(III) / Preparation, Vibration Spectra and Normal Coordinate Analysis of Chloro-Bromo-Rhodates(III)

1989 ◽  
Vol 44 (10) ◽  
pp. 1221-1227 ◽  
Author(s):  
W. Preetz ◽  
W. Kuhr
Keyword(s):  
Exchange Chromatography ◽  
Trans Isomers ◽  
Normal Coordinate ◽  
Valence Force ◽  
Trans Influence ◽  
Diethylaminoethyl Cellulose ◽  
Point Groups ◽  
First Time ◽  
Ir And Raman ◽  
Good Agreement

The mixed chloro-bromo-rhodates(III) [RhClnBr6-n]3-, n = 1-5, have been separated for the first time by ion exchange chromatography on diethylaminoethyl-cellulose. Due to the stronger trans-effect of Br, as compared with Cl, on treatment of [RhBr6]3- with conc. HCl nearly pure cis/fac-isomers for n = 2, 3, 4 are formed. The reaction of [RhCl6]3- with conc. HBr yields mixtures of the cis/trans-isomers for n = 2, 4, which cannot be separated, but mer-[RhCl3Br3]3 is formed stereospecifically. The IR and Raman spectra of all isolated mixed ligand complexes are completely assigned according to point groups Oh, D3d, C4v, C3v and C2v, supported by normal coordinate analyses based on a general valence force field. The good agreement of calculated and observed frequencies confirms the assignments. Due to the stronger trans-influence of Br as compared to Cl, in all asymmetric Cl—Rh—Br axes the Rh—Br bonds are strengthened and the Rh—Cl bonds are weakened, indicated by valence force constants for Rh—Br approximately 14% higher, for Rh—Cl 10% lower, as compared with the values calculated for symmetric Br—Rh—Br and Cl—Rh—Cl axes, respectively.

Ligand Redistribution Equilibria in Aqueous Fluoroberyllate Solutions

1998 ◽  
Vol 53 (11) ◽  
pp. 1294-1300 ◽  
Author(s):  
Michael Schmidt ◽  
Hubert Schmidbaur
Keyword(s):  
Experimental Data ◽  
Ligand Exchange ◽  
Room Temperature ◽  
Chemical Shifts ◽  
Equilibrium Constants ◽  
Individual Species ◽  
Ph Values ◽  
Exchange Processes ◽  
The Individual ◽  
Good Agreement

The composition of aqueous fluoroberyllate solutions has been studied by 9Be and 19F NMR spectroscopy for various ratios of the beryllium and fluorine concentrations, and at different pH values. The equilibrium constants have been determined for the ligand exchange processes, which involve the species [Be(OH2)4]2+, [BeF(OH2)3]+, [BeF2(OH2)2], [BeF3(OH2)]- , and [BeF4]2-. These equilibria are shifted towards [BeF4]2- at high pH. No polynuclear fluoroberyllates have been detected. The fluoride exchange between the individual species is slow on the NMR time scale at room temperature, and separate sharp signals with the expected multiplicity are therefore recorded. Calculated 9Be chemical shifts are in good agreement with experimental data.

Darstellung, Schwingungsspektren und Normalkoordinatenanalyse der Chloro-Bromo-Technetate(IV), [TcCl„Br6_n]2-, n = 0-6 / Preparation, Vibrational Spectra and Normal Coordinate Analysis of Chloro-Bromo-Technetates(IV), [TcCln Br6-n]2-, n = 0-6

1991 ◽  
Vol 46 (11) ◽  
pp. 1496-1502 ◽  
Author(s):  
W. Preetz ◽  
A. Wendt
Keyword(s):  
Exchange Chromatography ◽  
Normal Coordinate Analysis ◽  
Exchange Reactions ◽  
Normal Coordinate ◽  
Geometrical Isomers ◽  
Valence Force ◽  
Diethylaminoethyl Cellulose ◽  
Point Groups ◽  
First Time ◽  
Ir And Raman

The mixed chloro-bromo-technetates(IV), [TcClnBr6-n2-, n = 1-5, have been separated for the first time by ion exchange chromatography on diethylaminoethyl-cellulose. Due to the stronger trans-effect of Br as compared to Cl, the ligand exchange reactions of [TcBr62- with HCl and of [TcCl6]2- with HBr proceed stereospecifically, to form either cis/fac- or trans/merspecies for n = 2, 3, 4, respectively. To avoid photoisomerization the compounds have to be handled in the absence of light. The IR and Raman spectra of the ten chloro-bromo-techne-tates(IV), including the pure geometrical isomers, have been recorded at low temperature (80 K) and completely assigned to structures of point groups Oh, D4h, C4v, C3v, and C2v, supported by normal coordinate analysis based on a general valence force field. Due to the different trans-influences Cl < Br in asymmetric Cl′—Tc— Br′ axes, the Tc— Br′ bonds are strengthened and the Tc—Cl′ bonds are weakened, as indicated by valence force constants, for Tc—Br′ on average 6% higher and for Tc—Cl′ 10% lower, as compared with the values calculated for symmetric Br—Tc—Br and CI—Tc—Cl axes, respectively.

Darstellung und Charakterisierung der Chloro-Bromo-Iridate(III) und -(IV) einschließlich der Stereoisomeren / Preparation and Characterisation of Chloro-Bromo-Iridates(III) and -(IV) Including Stereoisomers

1985 ◽  
Vol 40 (6) ◽  
pp. 745-754 ◽  
Author(s):  
W. Preetz ◽  
H.-J. Steinebach
Keyword(s):  
Ligand Exchange ◽  
Redox Reactions ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Mixed Ligand ◽  
Redox Potentials ◽  
Exchange Reactions ◽  
Cyclic Voltammetric ◽  
Point Groups ◽  
Voltammetric Measurements

AbstractThe mixed chloro-bromo complexes [IrClnBr6-n]2- and [IrClnBr6-n]3-, n = 1 - 5. were separated by ion exchange chromatography on diethylaminoethylcellulose. Due to the stronger trans-effect of Br compared with Cl, on treatment of [IrBr6]2- 3- with Cl- nearly pure cis/fac-isomers and by reaction of [IrCl6]2,3- with Br- trans/mer-isomers for n = 2,3,4 were formed. The stereoselectivi­ty of successive ligand exchange reactions is better for the Ir(III) than for the Ir(IV) system. The diamagnetic Ir(III) and the paramagnetic Ir(IV) complexes can be interconverted reversibly by redox reactions at low temperature. As shown by cyclic voltammetric measurements, the redox potentials within the series [IrClnBr6-n]2- 3- are linearly dependent on n. In aqueous solution the normal potentials are in the range of Eo = 0.838 V ([IrBr6]2-,3-) to Eo = 0.908 V ([IrCl6]2-,3-). The vibrational spectra of the mixed ligand complexes are assigned according to point groups D4h, C4v, C3v and C2v. They are similar for corresponding chloro-bromo-iridates, but distinguished by a shift of 10-25 cm-1 to higher wave numbers for most of the stretching vibrations going from Ir(III) to Ir(IV).

Darstellung und Schwingungsspektren von Chloro-Bromo-Platinaten(IV) einschließlich der Stereoisomeren / Preparation and Vibrational Spectra of Chloro-Bromo-Platinates(IV) Including Stereoisomers

1982 ◽  
Vol 37 (5) ◽  
pp. 579-586 ◽  
Author(s):  
W. Preetz ◽  
G. Rimkus
Keyword(s):  
Vibrational Spectra ◽  
Ligand Exchange ◽  
Critical Discussion ◽  
Exchange Chromatography ◽  
Mixed Ligand ◽  
Mixed Ligand Complexes ◽  
Exchange Reactions ◽  
Separation Processes ◽  
Point Groups ◽  
Better Than

The mixed chloro-bromo complexes [PtClnBr6-n]2-, n = 1-5, are separated by ion exchange chromatography on diethylaminoethylcellulose. The separation of corresponding stereoisomers for n = 2, 3, 4 is not possible. Due to the stronger trans-effect of Br compared with Cl, on treatment of [PtBrß]2- with Cl- in the presence of Br2 nearly pure cis-isomers, and by reaction of [PtClsBr]2- and cis-fPtC^Bro]2- with Br~/Br2 completely pure transisomers are formed. The stereoselectivity of the successive ligand exchange reactions is better than in corresponding series of Re, Os and Ir. The highly resolved vibrational spectra allow the distinction of the mixed ligand complexes as well as the estimation of purity of the isomers. All allowed stretching frequencies are observed and assigned according to point groups D4h, C4V, C3V and C2V. Especially in the ν(Pt-Br) region it is possible to distinguish bands arising either from symmetric Br-Pt-Br or asymmetric Cl-Pt-Br axes. The UV/VIS spectra exhibit systematic hypsochromic shifts on the successive exchange of Br-ligands by Cl. A critical discussion of the literature concerning chloro-bromo-platinates- (IV) shows the importance of effective separation processes for the isolation of pure mixed ligand complexes

Phosphorus-31, mercury-199 and selenium-77 n.m.r. studies of ligand exchange reactions in mercury(II) halide complexes

1980 ◽  
Vol 33 (7) ◽  
pp. 1463 ◽  
Author(s):  
R Colton ◽  
D Dakternieks
Keyword(s):  
Time Scale ◽  
Ligand Exchange ◽  
Room Temperature ◽  
Mixed Ligand ◽  
Mixed Ligand Complexes ◽  
Exchange Reactions ◽  
Halogen Exchange ◽  
Redistribution Reactions ◽  
Halide Complexes

Mercury(II) halide complexes of tris(4-methoxyphenyl)phosphine have been investigated by 31P and 199Hg n.m.r. spectroscopy of CH2Cl2 solutions. At room temperature the phosphine exchanges at an appreciable rate and halogen exchange is fast. At -50°C both phosphine and halogen exchange are slow on the n.m.r. time scale and halogen redistribution reactions are observed. ��� Mercury(II) halide complexes with tributylphosphine selenide have been investigated by 31P, 199Hg and 77Se n.m.r. methods. This ligand is labile and exchanges rapidly on the n.m.r. time scale at room temperature, although the exchange can be slowed down at about -100°C. Halogen exchange is also fast at room temperature. ��� Ligand exchange reactions between tributylphosphine and either tris(4-methoxyphenyl)phosphine or tributylphosphine selenide were investigated and redistribution reactions to give mixed ligand complexes were observed.

Darstellung und spektroskopische Charakterisierung der Oxorhenate(V), [ReOI4]–und [ReO(SCF3)4]–/ Preparation and Spectroscopic C haracterization of the Oxorhenates(V), [ReOI4]–and [ReO(SCF3)4]–

1993 ◽  
Vol 48 (1) ◽  
pp. 44-47 ◽  
Author(s):  
W. Preetz
Keyword(s):  
Force Field ◽  
Vibrational Spectra ◽  
Ligand Exchange ◽  
Nmr Spectra ◽  
Point Group ◽  
Exchange Reactions ◽  
Normal Coordinate ◽  
Valence Force ◽  
Valence Force Field ◽  
First Time

By ligand exchange reactions of (n-Bu4N )[ReOBr4] with NaI dissolved in acetone pure (n-Bu4N )[ReOI4], and with AgSCF3 suspended in dichloromethane (n-Bu4N )[ReO(SCF3)4] have been prepared for the first time. The vibrational spectra of both complexes are assigned according to point group C4v, supported by normal coordinate analysis based on a general valence force field. 13C and ,19F NMR spectra provide evidence for the equivalence o f the SCF3 groups.

Schwingungsspektren und Normalkoordinatenanalyse der Bromo-Iodo-Osmate(IV), [OsBrnI6-n]2-, n = 0-6 / Vibrational Spectra and Normal Coordinate Analysis of Bromo-Iodo-Osmates(IV), [OsBrnI6-n]2-, n = 0-6

1992 ◽  
Vol 47 (12) ◽  
pp. 1667-1672 ◽  
Author(s):  
W. Preetz ◽  
M. Manthey
Keyword(s):  
Low Temperature ◽  
Force Field ◽  
Raman Spectra ◽  
Vibrational Spectra ◽  
Normal Coordinate ◽  
Geometrical Isomers ◽  
Valence Force ◽  
Valence Force Field ◽  
Point Groups ◽  
Ir And Raman

The IR and Raman spectra of the ten bromo-iodo-osmates(IV) [OsBrnI6-n]2-, n = 0-6, including the geometrical isomers for n = 2, 3, 4, have been recorded at low temperature. The vibrational spectra are completely assigned according to point groups Oh, D4h, C4v, C3v, and C2v, as supported by normal coordinate analyses based on a general valence force field. Due to the different trans-influences Br<I in asymmetric axes Br′–Os–I′, the Os–I′ bonds are strengthened and the Os–Br′ bonds are weakened, as indicated by valence force constants, for Os–I′ on average 4% higher and for Os–Br′ 4% lower, as compared with the values calculated for symmetric I–Os–I and Br–Os–Br axes, respectively.

Tem and Computer Image Simulation Studies on the Dissociation of Superdislocations in Ll2 Al3Ti Alloy

1994 ◽  
Vol 364 ◽  
Author(s):  
Yonghua Rong ◽  
Xiaohua Wu ◽  
Xiaofu Chen ◽  
Shipu Chen ◽  
Gengxiang Hu
Keyword(s):  
Flow Stress ◽  
Low Temperature ◽  
Computer Image ◽  
Room Temperature ◽  
Dislocation Core ◽  
Simulation Studies ◽  
Image Simulation ◽  
Dislocation Core Structure ◽  
Image Simulations ◽  
Good Agreement

AbstractTEM investigation associated with computer image simulations were conducted to determine the dislocation core structure in the Ll2 Al67MnsTi25 alloy deformed at room temperature. It is identified that the a<110> superdislocations dissociated into pairs of a/3<112> superpartials with SISF between them. The theoretical and experimental micrographs are in good agreement under various diffraction conditions. The unusual temperature dependence of flow stress at low temperature can be related to the SISF-type dissociation.

Low temperature crystal structure of TbAsO4 and DyAsO4

1977 ◽  
Vol 55 (18) ◽  
pp. 1633-1640 ◽  
Author(s):  
F. G. Long ◽  
C. V. Stager
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Low Temperature ◽  
Phase Transition Temperature ◽  
Room Temperature ◽  
X Rays ◽  
Single Crystal Diffraction ◽  
Low Temperature Crystal Structure ◽  
Jahn Teller ◽  
Good Agreement

The crystal structures of TbAsO4 and DyAsO4 have been determined by X rays, using single crystal diffraction techniques. The structures have been determined both above and below the co-operative Jahn–Teller phase transition temperature. The structures at room temperature are in good agreement with previous results. The low temperature structures, below the phase transition temperature, are compared to the theory of Elliott, Harley, Hayes, and Smith.

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