Chr. Klixbull Jorgensen

Hypersensitive pseudoquadrupole transitions in lanthanides

It is pointed out that the absorption lines of the lanthanides that are peculiarly sensitive to changes in the ligands are consistent with the selection rules for quadrupole radiation within the 4f shell. A number of sources for this sensitivity are examined, and it is concluded that it owes its origin to the inhomogeneity of the dielectric. According to this mechanism, there is an asymmetrical distribution of the dipoles induced by the electromagnetic field in the medium surrounding a lanthanide ion. The variation across the lanthanide ion of the electric vector is very much greater than for the case of a homogeneous dielectric, and the intensities of quadrupole transitions are enormously enhanced.

The angular overlap model, an attempt to revive the ligand field approaches

A general method for the calculation of orbital energy differences within a partially filled l-shell of a central ion in an inorganic chromophore is described. The angular overlap model covers σ, π and δ anti-bonding (as well as bonding) effects, and it is shown that the consequence of the model is identical with that of a singular contact term potential acting close to each ligand nucleus. Because of this the model can also treat chromophores containing different ligands, each new ligand contributing one σ and one π (and one δ) radial parameter. In this way fewer parameters are involved than in usual ligand field approaches. Selected symmetries of chromophores, cubic, pentagonal, tetragonal, and trigonal, are used to illustrate the applications of the model.

Absorption spectra of transition group complexes of sulphur-containing ligands

Abstract Nickel(II), rhodium(III), palladium(II), iridium(III) and other central atoms are combined with diethyldithiophosphate (dtp−) diethyldithiocarbamate (dtc−) 2,2′-di(aminoethyl)sulphide (daes), thiosemicarbazide (tscaz) and other sulphur-containing ligands. The position in the spectrochemical series dtp−

Electron transfer spectra of lanthanide complexes

Moderately strong, very broad absorption bands observed in dilute lanthanide bromide solutions in nearly anhydrous ethanol are interpreted as electron transfer from the highest filled M.O. to the partly filled 4f shell in the case of Nd(III), Sm(III), Eu(III), Tm(III) and Yb(III). Good agreement is obtained with a theory taking its parameters from the internal 4f transitions. Electron transfer bands are also observed for Eu(III) and Yb(III) dialkyldithiocarbamates, and the narrow bands of similar Pr(III), Nd(III), Sm(III) and Eu(III) complexes are briefly discussed. Relatively narrow 4f→5d transitions are observed in the Ce(III), Pr(III) and Tb(III) bromide solutions and related to the same theory. As expected, no bands are observed for Gd(III), Dy(III), Ho(III), Er(III) and Lu(III).

Electron transfer spectra of hexahalide complexes

The electron transfer spectra of the chloro, bromo, and iodo complexes of Ru(III), Ru(IV), Rh(III), Pd(IV), Sn(IV), Sb(V), W(VI), Re(IV), Os(III), Os(IV), Ir(III), Ir(IV), Pt(IV), and Pb(IV) are studied and interpreted by group-theoretical methods as transitions of π (and at higher wave-numbers, σ) electrons, mainly localized in the ligands, to the available orbitals of even parity γ 5, γ 3 and γ 1, representing mainly d, d, and s electrons of the central ion. The half-widths and intensities of the bands support the identification. The remarkable similarity between the spectra of d 4 and d 5 systems with the same set of ligands is explained by the presence of only one effective excited state of the central ion. The structure expected of the group of π transfer bands as function of increasing Lande parameter ζ np of the halogen is calculated. The use of pure molecular orbital (M.O.) configurations as a convenient classification (but not a very good approximation to the wave-function) is compared to the ana...

M.O. description of diatomic molecules containing a transition group atom

The M.O. configurations of diatomic molecules MX, where M contains a partly filled 3d shell, can be related to the more usual ligand field theory. In the same way as the 3d shell of gaseous atoms generally needs one or two 4s electrons for stabilizing the ground-state, certain molecules MX can be shown to contain the number of d-like electrons characterizing M(II) and an additional σ-electron. Comparisons are made with the occurrence of metallic bonding and 5d electrons in lanthanide compounds. Some molecules, such as TiO, pose unanswered questions, and much more experimental work would be desirable.

Far ultra-violet absorption spectra of cerium(III) and europium(III) aqua ions

The far ultraviolet absorption spectra of Ce and Eu is reported and discussed. The relatively broad and weak electron transfer bands were found to have the lowest wave-number in the most oxidizing central ion, Eu(III). A solution of 0.03 M Eu(III) perchlorate in 0.1 M HClO4 shows a maximum at 188 m mu , with the molar extinction coefficient epsilon = 235 and the half- width towards smaller wave-numbers delta (--) = 5.1 kK. Other lanthanide solutions, such as Ce(III), Pr(III), and Tb(III) perchlorates, exhibit relatively narrower bands caused by 4f→5d transitions. A sixth band of Ce(III) was found at 200 m μ with epsilon = 170 and delta (+) = 1.4 kK.

Relative molecular orbital energies in tetrahedral complexes

M.O. theory is used for classifying the energy levels of tetroxo complexes, and linear relations are shown to exist between the M.O. energies (and hence the electro-negativities) and the oxidation number and electron configuration of the central ion. The extent of π-bonding effects is quantitatively studied and compared with the analogous situation in the hexahalides.

Absorption spectra of actinide compounds

From the energy levels of the gaseous ions Ac++, Th+++, and Th++, it can safely be extrapolated that the ground electron configuration of all actinide ions with ionic charges at least + 3 contains only 5f-electrons outside the emanation shells. This is further supported by the 5fn → 5fn-16d transitions observed in Pa(IV), U(III), Np(III) (though their wave numbers are too high to be measured in U(IV) and Np(IV)). The configuration f2 has a very characteristic distribution of energy levels between 3H4 and 3P2 with 1S0 as much higher, isolated level. The absorption spectra of U(IV) complexes and of PuF6 suggest interelectronic repulsion parameters ∼60 per cent of the values in the corresponding lanthanides, while the Lande factors are about twice as large. This would also explain the recent measurements of Cm(III) complexes, compared to Gd(III). The larger average radius of the 5f-shell causes larger perturbation effects from the ligands than in the lanthanides. The J-values will therefore be distributed be...

Optical electronegativities of 3d group central ions

The optical electronegativity x opt behaves in essentially the same way in the 3d group as in the 4d and 5d hexahalides though the variation differs in details. Thus, the tetrahedral complexes have considerably higher x opt than the corresponding octahedral compounds. The slope of x opt versus the number q of electrons in the partly filled shell is compared for the 3d and 4f groups, and is smaller than in the gaseous ions as are also the differences of x opt between the oxidation numbers +3 and +2 for the same q.