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The increased affinity towards complex formation exhibited by metal ions with an unfilled d-shell is related to the crystal field stabilization of such compounds and furnishes an explanation of what is the basis of the so-called Irving-Williams rule. The orbital degeneracy of the ground term determines the symmetry of the configuration and is thus responsible for irregularities in the complexity constants. If the total spin quantum number changes during a set of consecutive complex formation steps, a sudden change of activation energies and formation constants is to be expected, as recently has been verified. The activation energies are then expected and found high only when the crystal field stabilization is large and the orbital degeneracy one. High reaction rates on the other hand are to be expected for complete or half-complete d-shells without crystal field stabilization, and for nearly complete d-shells if the orbital degeneracy is higher than one.

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).

The behaviour of the effective nuclear charge Z ∗ and the effective principal quantum number n ∗ is investigated, with special emphasis on the beginning of the 3d-, 4f-, and 5f-periods. The screening constants are seen to be so dependent on the net charge of the atom that the value of the concept is impaired. The available data on deviations from the hydrogen model, as derived from atomic spectroscopy and the absorption spectra of metal ions in solution, lead to some conclusions of chemical interest.

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.

While the effect of rubidium and caesium ions in solid salts of IrCl6 -- is a shift to lower wave-numbers, comparable to that occurring in organic solvents relative to water, the dark blue silver (I) and thallium (I) salts have a new, broad band in the red. Mixed crystals of Cs2IrCl6 and Tl2IrCl6 are prepared, and the absorption spectra are discussed in terms of a tendency to ‘ferroelectric rattling’ and strong covalent bonding of Ag and Tl. Analogous cases are pointed out in solid salts of other 5d-hexahalides.

In Schrodinger's equation, the local contribution to the kinetic energy is sometimes negative, but it allows a conservative potential in contrast to an alternative, never negative, energy proposed by Ruedenberg. The total kinetic energy evaluated in certain characteristic volumes, and in all of space, is identical in the two cases. Dirac's suggestion in 1962 of a bubble-surface representing the electron is applied in a far-reaching, but incomplete, attempt to identify external kinetic energy with a first-order relativistic effect and the internal energy constituting the difference between Schrodinger and Ruedenberg's proposals is related to oscillations of the surface. Dans l'equation de Schrodinger la contribution locale de l'energie cinetique est parfois negative. Cependant cela permet un potential conservatif ce qui n'est pas le cas avec la contribution locale de l'energie cinetique, proposee recemment par Ruedenberg. L'energie cinetique totale evaluee dans certains volumes caracteristiques et dans l'espace entire est identique dans les deux cas. Partant d'une proposition de Dirac de 1962, qui represente l'electron par une “surface de bulle”, on fait ici un essai de grande portee mais incomplet, pour identifier l'energie cinetique exterieure avec un effet relativiste du premier ordre tandis qu'on attribue l'energie interieure, qui constitue la difference entre les quantites de Schrodinger et de Ruedenberg, a des oscillations de la surface. In der Schrodingergleichung ist der lokale Beitrag der kinetischen Energie zuweilen negativ. Diese Formulierung gestattet aber ein konservatives Potential, was nicht mit der neulich von Ruedenberg vorgeschlagenen Alternative moglich ist. Die totale kinetische Energie in gewissen characteristischen Volumen und im ganzen Raum berechnet, ist in beiden Fallen dieselbe. Es wird ein von Dirac in 1962 vorgeschlagenes Modell, das das Elektron als eine “Blasenoberflache” reprasentiert, angewendet. Dieses fuhrt zu einem weitgehenden aber unvollstandigen Versuch, die aussere kinetische Energie mit einem relativistischen Effekt erster Ordnung zu identifizieren, und die innere Energie, die die Differenz zwischen Schrodinger's und Ruedenberg's Modellen ausmacht, mit der Oszillationen der Oberflache zuzuordnen.

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.

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.

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.

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...

Spectra of di-(tetra(n-butyl)ammonium)-iriduum(IV)hexabromide are measured in a variety of organic solvents. Shifts of the electron transfer bands in the visible, amounting to 2–5 per cent to lower wavenumbers, and comparable to the reflexion spectrum of the solid, are related to smaller iridium-bromine internuclear distances, compared to the aqueoous solution of IrB62−. A rough linear correlation exists between these shifts and the dielectric constant of the solvent. The variation of the shift on the six absorption bands observed is used to support previous identifications of the energy levels involved. Similar effects are observed in IrCl62−, OsBr62− and OsI62−.

Retaining the cubic structure, ThO2 can accomodate large concentrations of lanthanides and the equivalent amount of oxygen vacancies. The reflection spectra are measured at 100°K of Nd(III), Sm (III) , Eu (III) , Ho (III) , Er (III) , Tm(III) and Yb(III) in such samples. The excited J-levels correspond to rather broad bands in Thi1-xMjO2-0.5x whereas Nd203 and Er203 have very detailed line groups. The visible spectra indicate a very large nephelauxetic effect in the oxide, the nephelauxetic ratio β being smaller than in the aqua ion to the extent of 0.033 for Nd(III), 0.019 for Sm (III). , 0.017 for Ho (III) , 0.016 for Er (III) and 0.013 for Tm (III) . These values are roughly five times larger than those for the anhydrous chlorides and are quite unexpected.

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.

Absorption spectra of solutions in acetonitrile of tetra (ethyl) ammonium salts of UCl6 --, UBr6 --, UI6 --, NpCl6 --, NpBr6 --, PuCl6 -- and PuBr6 -- show three types of bands arranged according to increasing half-width: (1) internal 5f q transitions showing a large nephelauxetic effect, the wavenumbers in the hexabromides being some 3–5 per cent smaller than of the corresponding hexachlorides; (2) 5f q →5f q-16d transitions indicating that the 5f→6d orbital energy differences are roughly constant as function of q in contrast to the strong increase in the aqua ions; (3) π 245f q →π 235f q+1 electron transfer bands indicating that the optical electronegativities x opt (corrected for spin-pairing energy and certain effects of L, S, J splitting) are 1·5 for U(IV), 1·75 for Np(IV) and 2·05 for Pu(IV). Further on, the charge separation effects on electron transfer bands are discussed with special regard to uranyl iodide complexes.

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 − − 3 2− is related to the number of lone-pair electrons available on the sulphur atom. The nephelauxetic effect is very conspicuous in Rh dtp 3 and Ir dtp 3 . The square-planar low-spin Ni dtp 2 and nickel(II) xanthate form high-spin pyridine addition compounds such as Ni(dtp) 2 py 2 , while Ni daes 2 2+ is high-spin. In dtp 3 and Bi dtp 3 can be precipiatated from acid solutions.

The narrow f/sup n/-bands of aqueous Dy/sup 3+/, Ho/sup 3+/, and Er/sup 3+/ perchlorates are measured in the range 800-210 m mu . The application of the theory of Slater, Condon, Shortley, and Racah to the distribution of multiplet terms is discussed. The lowest term with the total spin S one unit lower than of the groundstate often decays with fluorescence in the lanthanides and actinides. (auth)

The previous M.O. treatment of unsubstituted hexahalides has been modified, taking the results on Faraday effect obtained at the University of Virginia into account. The absorption spectra previously measured of the complexes (M=Os, Ir) trans-MCl4Br2 — and trans-MCl2 Br4 — are interpreted by a M.O. treatment for the symmetry D4h as electron transfer transitions, including a first-order relativistic (spin-orbit coupling) correction. The concept of holohedrized symmetry is sufficiently valid to allow a description of MCl5Br— and MClBr5 — as if they were tetragonal with centre of inversion and ƒac-(or cis-)MCl3Br3 — as if they were cubic. It is shown that the ligand-ligand antibonding effects have the same order of magnitude as the moderate difference in optical electronegativity between Cl- and Br-.

The inner complexes of dsep−=(C2H5O)2PSe− 2 have been prepared, involving an octahedral environment of six selenium atoms with a small trigonal distortion. The symmetry types of the M.O. formed with the corresponding symmetry D 3 are indicated. The very low value of the nephelauxetic ratio β 35 and the moderate value of β 55 in Cr dsep3 are discussed. The electron transfer bands observed are related to the concept of optical electronegativities.

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...

Absorption spectra of aqueous solutions of TcX6 - and ReX6 - (X = F, Cl, Br, I) are measured between 8 000 and ∼ 50 000 cm-1 and theoretically discussed. The electron transfer spectra indicate the optical electronegativity xopt= 2.25 for Tc (IV) and 2.05 for the less oxidizing Re (IV). The spectrochemical parameter Δ is determined to 28 400 cm-1 in TcF6 and 32 800 cm-1 in ReF6 -. The nephelauxetic effect is evaluated from the spin-forbidden intra-sub-shell transitions in all eight species, and from the two spin-allowed bands of TcF6 - The vibrational structure of the narrow absorption bands and the possible weak distortion from octahedral symmetry of Tc (IV) hexahalides are discussed.