The coordinating ability of the antibiotic cycloserine towards transition metal halides

1980 ◽  
Vol 33 (1) ◽  
pp. 57 ◽  
Author(s):  
C Preti ◽  
G Tosi
Keyword(s):  
Field Theory ◽  
Magnetic Properties ◽  
Ring Opening ◽  
Isotope Exchange ◽  
Room Temperature ◽  
Manganese Complexes ◽  
Chemical Analyses ◽  
Conductivity Measurements ◽  
Crystal Field Theory ◽  
Experimental Conditions

A series of cycloserine complexes of chromium(III), manganese(II), rhodium(III) and iridium(III) halides has been prepared and characterized by chemical analyses, conductivity measurements, room temperature magnetic moment studies, electronic, i.r. and far-i.r. spectra and isotope exchange (deuteration) experiments. From the magnetic properties it was concluded that the above ligand forms high- spin complexes with chromium(III) and manganese(II) and low-spin complexes with rhodium(III) and iridium(III). The position and multiplicity of the metal-halogen stretching modes in the far-i.r. region have been extensively investigated, the results being particularly useful in distinguishing between the mer and fac isomers in the ML3X3-type octahedral complexes. The ligand behaves as monodentate O-bonded. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of the crystal field theory and the various parameters have been calculated. The calculated Dq parameters are in accord with the presence of CrO6, CrN3X3, RhO3X3 and IrO3X3 chromophores according to the infrared results. The values of B and C obtained for the manganese complexes are significantly lower than the corresponding values for the free gaseous ion. Under our experimental conditions no metal-induced ring opening of the ligand was observed.

Reinvestigation of the Reaction of (NH4)2[Ce(N03)6] with Triphenylphosphine Oxide; the Crystal Structure and Magnetic Properties of mer-Ce(NO3)3(OPPh3)3 • 2 (CH3)2CO

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1241-1247 ◽  
Author(s):  
Jianhua Lin ◽  
Evamarie Hey-Hawkins ◽  
Hans Georg von Schnering
Keyword(s):  
Crystal Structure ◽  
Field Theory ◽  
Magnetic Properties ◽  
Reaction Time ◽  
Low Temperature ◽  
Triphenylphosphine Oxide ◽  
High Yield ◽  
Crystal Data ◽  
Crystal Field Theory

AbstractThe reaction of (NH4)2[Ce(NO3)6 ] with two equivalents of OPPh3(Ph = C6H5 ) in acetonitrile yields Ce(NO3 ) 4(OPPh3 )2 (1) in high yield, whereas using acetone as solvent affords mer- Ce(NO3 )3(OPPh3)3 • 2(CH3)2CO (2), the yield of which is dependent on the reaction time. A crystal structure determination of 2 shows that the Ce atom is coordinated with three bidentate nitrato groups and three OPPh3 ligands, thus achieving a coordination number of nine. Eight non-coordinating acetone molecules are present in the unit cell. Crystal data (292 K): space group P21/n (no. 14), 0=12.438(2), b = 25.532(4), c = 20.379 (4) Å, β = 96.33(2)°, V = 6432(1) , Z = 4, dcalc = 1.318 g em 3. Due to poor crystal quality the refinement converges at R = 0.11, Rw = 0.09. 2 is paramagnetic, but it does not follow the Curie-Weiss law at low temperature. Therefore crystal field theory was used in order to explain these findings.

Enhancement of Photoluminescence in BaSi2O2N2:Eu2+ by Partial Ge4+ Substitution for Si4+

2016 ◽  
Vol 16 (4) ◽  
pp. 3608-3612 ◽  
Author(s):  
Baochen Wang ◽  
Jian Chen ◽  
Yufei Xia ◽  
Yangai Liu
Keyword(s):  
Field Theory ◽  
Emission Intensity ◽  
Room Temperature ◽  
Solid State Reaction Method ◽  
Initial Value ◽  
Crystal Field Theory ◽  
Light Emitting ◽  
Reaction Method ◽  
White Light Emitting Diodes ◽  
Thermal Stability Of

Ge4+-doped BaSi2O2N2:Eu2+ phosphors were prepared by a high temperature solid-state reaction method. The phase structure, photoluminescence (PL) properties and PL thermal stability of the as-synthesized samples were investigated. The emission intensity of the Ba(Si0.99Ge0.01)2O2N2: 0.05Eu2+ phosphor was 41.7% greater than that of BaSi2O2N2:0.05Eu2+. When the temperature increased to 150 °C, the emission intensity of Ba(Si0.99Ge0.01)2O2N2:0.05Eu2+ phosphor was 67.0% of the initial value at room temperature. This value was 22.9% greater than that of BaSi2O2N2:0.05Eu2+. The related mechanism has also been explained through the crystal field theory. All these results indicated that the Ge4+-doped BaSi2O2N2:0.05Eu2+ phosphor is a promising material for application in white light emitting diodes.

Chromium(III), manganese(II) and iron(III) O,O'-bonded complexes of the para- and meta-substituted benzeneseleninic acids

1980 ◽  
Vol 33 (6) ◽  
pp. 1203 ◽  
Author(s):  
C Preti ◽  
G Tosi
Keyword(s):  
Field Theory ◽  
Spectral Data ◽  
Crystal Field ◽  
Electronic Spectra ◽  
Conductivity Measurements ◽  
Crystal Field Theory ◽  
Metal Ligand ◽  
Bonded Complexes

A number of complexes of chromium(III), manganese(II) and iron(III) with para- and meta-substituted benzeneseleninic acids, XC6H4SeO2H (X = H, p-Cl, m-Cl, p-Br, m-Br, p-Me), are reported. The newly prepared compounds are characterized on the basis of near-i.r. and far-i.r. spectroscopy, electronic spectra and conductivity measurements, as well as by magnetochemical evidence. The wavelengths of the principal absorption peaks have been accounted for quantitatively in terms of the crystal field theory for chromium(III) and manganese(II) derivatives. The nephelauxetic parameters are all indicative of an appreciable metal-ligand covalency. The i.r. spectral data suggest that the ligands act as bidentate in seleninato-O,O' complexes and we can propose octahedral geometries with D3 symmetry for the chromium(III) and iron(III) derivatives and octahedral geometries, distorted towards D4h, for the manganese(II) complexes, in which the water has been shown to be coordinated to the metal.

Osmium(III) Halide Complexes with para-and meta-Substituted Benzeneseleninato Ligands

1985 ◽  
Vol 38 (11) ◽  
pp. 1675 ◽  
Author(s):  
G Graziosi ◽  
C Preti ◽  
G Tosi ◽  
P Zannini
Keyword(s):  
Field Theory ◽  
Molar Ratio ◽  
Spectroscopic Techniques ◽  
Conductivity Measurements ◽  
Crystal Field Theory ◽  
Halide Complexes ◽  
Thermogravimetric Studies ◽  
Q Values ◽  
Metal Ligand ◽  
Octahedral Configuration

New complexes of osmium(III) with para - and meta-substituted benzeneseleninic acids of the type XC6H4SeO2H (X = H, p- Cl , m- Cl , p-Br, m-Br, p-Me) are reported. The compounds, of the type Os(XC6H4SeO2)3, Os(XC6H4SeO2)2Y, Os(XC6H4SeO2)Y2 and Os2(XC6H4SeO2)3Y3 (Y = Cl , Br), have been studied through spectroscopic techniques ( i.r ., far- i.r .and electronic spectra), magnetic susceptibility measurements, thermogravimetric studies and conductivity measurements. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of the crystal-field theory; the nephelauxetic parameter is indicative of an appreciable metal- ligand covalency. It is worth noting that among the present complexes the highest q values are related to the Os(XC6H4SeO2)3 derivatives in which OsO6 chromophores are present; the Dq values decrease on passing to the 1 : 2, 1 : 1.5 and 1 : 1 metal/ ligand molar ratio complexes according to the presence of chlorine- and bromine-containing chromophores . The i.r . data point to a seleninato -O,O′ coordination for all the complexes; in particular, the presence of three SeO bands with the irreducible representation A2 + 2E in the i.r . spectra of the tris derivatives suggests an octahedral configuration with D3 symmetry. All the halo complexes are polymeric octahedral with bridging halide atoms. The magnetic moment values lie in the expected range for the trisbenzeneseleninato derivatives, and they decrease on passing to the halo complexes.

Synchrotron X-ray analysis of the electron density in CoF2 and ZnF2

2001 ◽  
Vol 57 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Nicholas J. O'Toole ◽  
Victor A. Streltsov
Keyword(s):  
Field Theory ◽  
Transition Metal ◽  
Electron Density ◽  
Crystal Field ◽  
Room Temperature ◽  
Crystal Field Theory ◽  
X Ray ◽  
Structure Factors ◽  
Small Crystals ◽  
Multipole Refinement

Accurate structure factors for small crystals of the rutile-type structures CoF2, cobalt difluoride, and ZnF2, zinc difluoride, have been measured with focused λ = 0.8400 (2) Å synchrotron X-radiation at room temperature. Phenomenological structural trends across the full series of rutile-type transition metal difluorides are analysed, showing the importance of the metal atom in the degree of distortion of the metal–F6 octahedra in these structures. Multipole models reveal strong asphericities in the electron density surrounding the transition metals, which are consistent with expectations from crystal field theory and the structural trends in these compounds. Transition metal 3d-orbital populations were computed from the multipole refinement parameters, showing significant repopulation of orbitals compared with the free atom, particularly for CoF2.

STRUCTURAL CHARACTERIZATION, PREPARATION AND MAGNETIC PROPERTIES OF SEVERAL ROOM-TEMPERATURE MAGNETIC OXIDES WITH THE PEROVSKITE-LIKE STRUCTURE

1977 ◽  
Vol 38 (C1) ◽  
pp. C1-95-C1-101 ◽  
Author(s):  
B. BOCHU ◽  
M. N. DESCHIZEAUX ◽  
J. C. JOUBERT ◽  
J. CHENAVAS ◽  
A. COLLOMB ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Structural Characterization ◽  
Room Temperature ◽  
Magnetic Oxides

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

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