Ligand-Field Calculations on Pseudo-Tetragonal High-Spin Fe(II) Compounds

1977 ◽  
Vol 32 (12) ◽  
pp. 1404-1418
Author(s):  
A. Vermaas ◽  
W. L. Groeneveld ◽  
J. Reedijk
Keyword(s):  
Experimental Data ◽  
Magnetic Susceptibility ◽  
Room Temperature ◽  
Point Group ◽  
Point Symmetry ◽  
Ligand Field ◽  
Ligand Field Theory ◽  
State Splitting ◽  
Ligand Field Spectra ◽  
Theoretical Results

Abstract The compounds Fe(pz)4X2 and Fe(mpz)4X2, where pz stands for pyrazole, mpz for 5-methyl-pyrazole and X means Cl, Br or I, have been investigated by magnetic susceptibility, magnetic saturation and Mössbauer spectroscopy. The experimental temperatures vary from 2K to room temperature for the magnetic susceptibility measurements and from 4K to room temperature for the Mössbauer measurements. Mössbauer spectra in an applied magnetic field are also reported. The results of both types of measurements and ligand-field spectra are interpreted using a ligand-field theory. The tetragonal ground-state splitting parameters have been determined using the ligand-field spectra. For the pyrazole compounds, the experimental data nicely agree with theoretical results. The quadrupole splitting and the magnetic properties of these com­ pounds can be completely described within the used model, assuming a tetragonal molecular point symmetry. For the 5-methylpyrazole compounds, the measurements show that the point symmetry is lower than tetragonal. The agreement between the experimental data and the theoretical results for a point group Ci is less fair, especially concerning the Vzz and η values. Besides the Vzz values of Fe(mpz)4X2 differ significantly from those of the corresponding Fe(pz)4X2 compounds.

The ligand field spectra of trinuclear chromium(III) and iron(III) basic acetates

1969 ◽  
Vol 22 (4) ◽  
pp. 701 ◽  
Author(s):  
L Dubicki ◽  
RL Martin
Keyword(s):  
Field Theory ◽  
Ligand Field ◽  
Ligand Field Theory ◽  
Visible Spectra ◽  
Ligand Field Spectra

The visible spectra of trinuclear chromium(III) acetates [Cr3O(CH3CO2)6R2]+ can be successfully analysed by means of the ligand field theory for tetragonal fields. The ligands R (R = H2O, NH3, py, DMSO) are relatively labile and may be replaced by several ligands of varying donor strength. The spectra of trinuclear iron(III) acetates [Fe3O(CH3CO2)6R3]+ are poorly resolved but can be interpreted on the basis of a d5 configuration in octahedral fields.

Copper(II) complexes with 1-phenyl-4,6-dimethylpyrimidine-2-thione. Chemical, spectroscopic, magnetic, conductivity and polarographic studies

1990 ◽  
Vol 55 (9) ◽  
pp. 2199-2215 ◽  
Author(s):  
Raffaele Battistuzzi ◽  
Marco Borsari
Keyword(s):  
Room Temperature ◽  
Copper Ions ◽  
Magnetic Moments ◽  
Thermal Analyses ◽  
Ligand Field ◽  
L System ◽  
Counter Ions ◽  
Ligand Field Spectra ◽  
Ir Bands ◽  
Magnetic Conductivity

New copper(II) complexes of general composition: CuLX2.nH2O (X = Cl-, n = 0.25; X = NO3-, n = 0.5), Cu2L3Cl4.2H2O, CuL2X2.H2O (X = ClO4-, BF4- and NO3-) and Cu2L7X4 (X = ClO4-, BF4- and NO3-), where L = 1-phenyl-4,6-dimethylpyrimidine-2-thione, have been isolated. Chemical and thermal analyses, conductivity, magnetic susceptibility, infrared and ligand field spectroscopic data and, for the perchlorate complexes also polarographic studies, are reported. Diagnostic IR bands frequencies of counter-ions, χ(Cu-X) modes and ligand field spectra for the mono-and bis-ligand compounds, having an equatorial [CuNSCl2], [CuNSO2] and [CuN2S2] microsymmetry, indicate a coordinating character of some anions, suggesting an elongated octahedral geometry for these complexes. For the [Cu2L7]X4 (X = ClO4-, BF4- and NO3-) complexes, which exhibit at room temperature subnormal magnetic moments, a polynuclear structure with the copper(II) in a roughly square-pyramidal environment, is proposed. Polarographic data for the perchlorate complexes and for the Cu(ClO4)2-L system at various ligand concentrations, have shown that in DMF solution the prevailing species are [CuL2]2+, [CuL3]2+ and [Cu2L7]4+ confirming the oxidation state II for the copper ions in the [Cu2L7]X4 complexes.

Polarisations-absorptionsspektrometrische Untersuchungen zur elektronischen und geometrischen Struktur der Oktacyanokomplexe des Molybdäns und Wolframs, I Das Mo(CN)8 -Ion in K4Mo(CN)8 · 2 H2O / Polarization-Absorption Spectrometric Studies of the Electronic and Geometrical Structure of the Octacyano Complexes of Molybdenum and Tungsten, I The Mo(CN)8 Ion in K4Mo(CN)8 · 2 H2O

1976 ◽  
Vol 31 (9) ◽  
pp. 1224-1237 ◽  
Author(s):  
P. Morys ◽  
G. Gliemann
Keyword(s):  
Room Temperature ◽  
Geometrical Structure ◽  
Ligand Field ◽  
Complex Ions ◽  
Ligand Field Theory ◽  
X Ray ◽  
Structure Determinations ◽  
Exact Symmetry ◽  
Region 10 ◽  
The Ideal

Polarized absorption spectra of the ions Mo(CN)84- and W(CN)84- were measured on single crystals of the compounds K4Mo(CN)8 · 2 H2O and K4W(CN)8 · 2 H2O over the spectral region 10-47 kK and at temperatures from 300°K to 4.2°K. The results obtained were interpreted on the basis of the ligand field theory.According to their d → d-spectrum, these complex ions in the crystalline state have a quasi-dodecahedral coordination structure with the exact symmetry D2. The deviation from the ideal dodecahedral structure is appreciably smaller at low temperatures than at room temperature.Contrary to the results of earlier X-ray structure determinations, the only space group which can be assigned to the crystals of K4Mo(CN)8 · 2 H2O and K4W(CN)8 · 2 H2O is C92v.

Donor properties of 2-aminothiazole and 2-acetylaminothiazole towards cobalt(II) halides

1974 ◽  
Vol 27 (3) ◽  
pp. 509 ◽  
Author(s):  
PP Singh ◽  
AK Srivastava
Keyword(s):  
Magnetic Susceptibility ◽  
Infrared Spectra ◽  
Electronic Spectra ◽  
Point Group ◽  
Carbonyl Oxygen ◽  
Ligand Field ◽  
Tetrahedral Configuration ◽  
X Ray ◽  
Ligand Field Parameters

Molecular addition complexes of the type CoL2X2 (X = Cl, Br, I and L = 2-aminothiazole and 2-acetylaminothiazole) have been prepared and studied by infrared spectra, electronic spectra, magnetic susceptibility and X-ray powder data. Infrared and electronic spectra suggest coordination through exocyclic nitrogen in 2-aminothiazole and through carbonyl oxygen in 2-acetylaminothiazole. The complexes have tetrahedral configuration and belong to the C2" point group. Ligand field parameters Dq, B' and β show more covalency in 2-aminothiazole complexes than in 2-acetylamino-thiazole complexes and suggest a weak ligand field for both the ligands.

The Nephelauxetic Effect — Calculation and Accuracy of the Interelectronic Repulsion Parameters

1972 ◽  
Vol 27 (1) ◽  
pp. 1-6 ◽  
Author(s):  
E. König
Keyword(s):  
Field Theory ◽  
Experimental Data ◽  
Low Temperature ◽  
Sufficient Accuracy ◽  
Ligand Field ◽  
Electron Systems ◽  
Ligand Field Theory ◽  
Transition Energies ◽  
Semi Empirical ◽  
Complex Ion

Expressions are reviewed which may be used to determine 10 Dq and B from the spin-allowed bands in the optical spectra of d3 and d7 electron systems within octahedral and tetrahedral sym metry. Application to low-temperature single crystal spectra demonstrates that (i) the semi-empirical ligand field theory reproduces transition energies with sufficient accuracy; (ii) differences in the values of 10 Dq and B observed with different fitting methods may be attributed to the inaccuracy of experimental data; (iii) there are generally valid values of B35 and β35 for each complex ion.

Evidence for ordered Fe3Ni

1987 ◽  
Vol 45 ◽  
pp. 216-217
Author(s):  
K.B. Reuter ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Experimental Data ◽  
Martensitic Transformation ◽  
Electron Diffraction ◽  
Room Temperature ◽  
Direct Evidence ◽  
Transformation Product ◽  
Iron Meteorites ◽  
X Ray ◽  
Ni Content ◽  
Temperature Transformation

In the Fe-Ni system, although ordered FeNi and ordered Ni3Fe are experimentally well established, direct evidence for ordered Fe3Ni is unconvincing. Little experimental data for Fe3Ni exists because diffusion is sluggish at temperatures below 400°C and because alloys containing less than 29 wt% Ni undergo a martensitic transformation at room temperature. Fe-Ni phases in iron meteorites were examined in this study because iron meteorites have cooled at slow rates of about 10°C/106 years, allowing phase transformations below 400°C to occur. One low temperature transformation product, called clear taenite 2 (CT2), was of particular interest because it contains less than 30 wtZ Ni and is not martensitic. Because CT2 is only a few microns in size, the structure and Ni content were determined through electron diffraction and x-ray microanalysis. A Philips EM400T operated at 120 kV, equipped with a Tracor Northern 2000 multichannel analyzer, was used.

Microdiffraction analysis of precipitate crystallography and morphology in Al alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 954-955
Author(s):  
B.C. Muddle ◽  
G.R. Hugo
Keyword(s):  
Point Group ◽  
Hexagonal Lattice ◽  
Intersection Point ◽  
Saed Pattern ◽  
Point Symmetry ◽  
Hexagonal Symmetry ◽  
Precipitate Crystal ◽  
The Matrix ◽  
The Subject ◽  
Electron Microdiffraction

Electron microdiffraction has been used to determine the crystallography of precipitation in Al-Cu-Mg-Ag and Al-Ge alloys for individual precipitates with dimensions down to 10 nm. The crystallography has been related to the morphology of the precipitates using an analysis based on the intersection point symmetry. This analysis requires that the precipitate form be consistent with the intersection point group, defined as those point symmetry elements common to precipitate and matrix crystals when the precipitate crystal is in its observed orientation relationship with the matrix.In Al-Cu-Mg-Ag alloys with high Cu:Mg ratios and containing trace amounts of silver, a phase designated Ω readily precipitates as thin, hexagonal-shaped plates on matrix {111}α planes. Examples of these precipitates are shown in Fig. 1. The structure of this phase has been the subject of some controversy. An SAED pattern, Fig. 2, recorded from matrix and precipitates parallel to a <11l>α axis is suggestive of hexagonal symmetry and a hexagonal lattice has been proposed on the basis of such patterns.

Clustering-Triggered Efficient Room Temperature Phosphorescence from Nonconventional Luminophores

2019 ◽  
Author(s):  
Shuyuan Zheng ◽  
Taiping Hu ◽  
Xin Bin ◽  
Yunzhong Wang ◽  
Yuanping Yi ◽  
...  
Keyword(s):  
Room Temperature ◽  
High Efficiency ◽  
Spin Orbit Coupling ◽  
Design Rationale ◽  
Emission Mechanism ◽  
Room Temperature Phosphorescence ◽  
Electronic Interactions ◽  
Energy Gaps ◽  
Theoretical Results

Pure organic room temperature phosphorescence (RTP) and luminescence from nonconventional luminophores have gained increasing attention. However, it remains challenging to achieve efficient RTP from unorthodox luminophores, on account of the unsophisticated understanding of the emission mechanism. Here we propose a strategy to realize efficient RTP in nonconventional luminophores through incorporation of lone pairs together with clustering and effective electronic interactions. The former promotes spin-orbit coupling and boost the consequent intersystem crossing, whereas the latter narrows energy gaps and stabilizes the triplets, thus synergistically affording remarkable RTP. Experimental and theoretical results of urea and its derivatives verify the design rationale. Remarkably, RTP from thiourea solids with unprecedentedly high efficiency of up to 24.5% is obtained. Further control experiments testify the crucial role of through-space delocalization on the emission. These results would spur the future fabrication of nonconventional phosphors, and moreover should advance understanding of the underlying emission mechanism.<br>

Niobocene Dichloride and Niobocene Diiodide: Electronic Absorption Spectra and Electron Spin Resonance

1998 ◽  
Vol 63 (5) ◽  
pp. 628-635 ◽  
Author(s):  
Jana Holubová ◽  
Zdeněk Černošek ◽  
Ivan Pavlík
Keyword(s):  
Absorption Spectra ◽  
Electronic Absorption ◽  
Electronic Absorption Spectra ◽  
Point Group ◽  
Esr Spectra ◽  
Ligand Field ◽  
Orbital Interaction ◽  
Symmetry Point Group ◽  
Spin Orbital ◽  
Halide Ligands

The effect of the halide ligand on the bonding of niobium in niobocene dichloride and niobocene diiodide was investigated. The electronic absorption spectra of the two compounds in the range of d-d transitions were resolved into four bands corresponding to transitions of the d1 electron between five frontier orbitals in a molecule of symmetry point group C2v. The energies of the frontier molecular orbitals were determined relatively to the energy of the orbitals in the spherically symmetric ligand field formed by the appropriate halide ligands. The effect of the halide ligands on the spin-orbital interaction of the HOMO orbital is discussed qualitatively on the basis the ESR spectra.

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