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An NMR study has been made of the reactions occurring in systems which contain either the monomeric complex (π-C4H7)PdCl(Ph3As) and the dimer [(π-C4H7)PdCl]2, or only monomer and free triphenylarsine (in CDCl3). In the former case reactions were observed of Ph3As - formed by the dissociation of the monomer (reaction (a)) - with the dimer (b) and the monomer (c), respectively: In the latter case, where only monomer and Ph3As are present, two reactions were studied. The first, which was observed between -70° and -40° with a very small excess of Ph3As, and which involves the exchange of Ph3As (reaction (c)), is first-order in the arsine ligand. This reaction and the reactions in the presence of dimer were studied by measuring the rates at which the syn-protons (or the anti-protons) of the allyl group become magnetically equivalent. The second reaction, in which also exchange of Ph3As takes place, was measured between +10° and +80° with a higher excess of free Ph3As. This reaction is also first-order in Ph3As, but involves the formation of either a s-allyl intermediate or an activated state resembling the s-allyl form. The activation energies and frequency factors of the above reactions are reported. At still higher excess of Ph3As (Ph3As/Pd ∼ 2-3) an equilibrium (π-C4H7)PdCl(Ph3As) + Ph3As ⇆ [(π-C4H7)Pd(Ph3As)2]+Cl− becomes notticeable. This equilibrium moves to the right with increasing Ph3As/Pd ratio and decreasing temperature. The amount of ionic species, however, is so small that the kinetics of the above reactions are but little influenced by it.

Measurements are described of the paramagnetic susceptibilities of Co3O4, ZnCo2O4, and mixed crystals of ZnAl2O4-ZnCo2O4 and the results are given in a table of X-values and two plots of 1/X against absolute temperature. To explain the very low value of the mean Bohr magneton number, found for these compounds, the assumption is made that Co3+ in these spinel structures is situated at octahedral interstices and covalently bonded as in the other complex compounds of CoIII, thus not contributing to the paramagnetism. This assumption gives the reasonable, although somewhat high value of 4.7 μB for the Co2+ ion in Co3O4. This high value of μ for Co2+ and the weak paramagnetism of ZnCo2O4 may be caused by a slight oxygen deficiency of the compounds or a small energy difference between the diamagnetic and paramagnetic states of Co3+ in octahedra.

Enkele tientallen jaren geleden was ir. Frits Philips (1905-2005) op zakenreis aan de andere zijde van de aardbol, toen hij werd getroffen door een aanval van acute lage rugpijn. Hij bezocht daar een manueel therapeut, die hem in korte tijd van zijn klachten af hielp door manipulatie van zijn rug. En zoals Frits Philips was, verbaasde hij zich erover dat hij zoiets in Nederland nog nooit gezien en meegemaakt had. Bij terugkomst nam hij het initiatief tot het oprichten van een stichting die zich moest gaan bezighouden met het introduceren, doceren en onderzoeken van manuele behandeltechnieken: de Stichting Manuele Geneeskunde.

A systematic investigation of the systems MNbS and MTaS (M = Mn, Fe, Co, Ni) revealed the presence of the compounds MNb3S6 and MTa36. Their structures were determined from powder diagrams. They proved to have a superstructure, derived from the 2s−NbS2 type and resulting from an ordered distribution of the metal atoms M over the octahedral holes between the prismatic NbS2 layers. The magnetic susceptibilities were measured; all the compounds showed a temperature-dependent paramagnetism with a spontaneous localized moment.

The magnetic properties of Co2+ ions in tetrahedral environment are discussed in relation to published optical data. It appears that the singlet ground state 4F(Γ2)is responsible for a magnetic moment close to the spin-only value, while the 4F (Γ5) level about 4000 cm−1 above this singlet gives rise to a temperature-independent paramagnetic term of ≈ 0.5 × 10−3 erg. G−2 · mole−1. The expected departure from the Curie-Weiss law is demonstrated by susceptibility measurements on mixed crystals of CoO with ZnO, CoAl2O4 with ZnAl2O4 and CoAl2O4 with MgAl2O4 between 300° and 1200°K. The magnetic properties of Co2+ in tetrahedral interstices are compared with those of Co2+ ions in octahedral surroundings.

For reactions of the type L-O, generally called “cis-ligand insertion”, there is increasing experimental evidence that the group Q migrates. The present paper gives a theoretical analysis of this rearrangement, which is illustrated by the specific example of the growth reaction in Ziegler polymerizations of a-olefins: As a first approximation to the reaction path the angular vibrabtion of R is analysed from a quantum-mechanical point of view, showing the role that d orbitals in transition-metal compounds play in the migration of alkyl groups to π-bonded olefins. It appears that the migrating ligands finds a suitable combination of orbitals to remain bonded to the complex all along the reaction coordinate.

A mechanism for the polymerization of olefins is proposed. An essentially octahedrally coordinated ion of a transition element with empty or nearly empty t2g orbitals carrying in its coordination sphere one alkyl group and having one vacant octahedral position is supposed to be the active center. In this model the monomeric olefin is coordinated in the vacant position through a “π bond.” It is shown that theoretically one may expect the transition metal-to-carbon bond to become more susceptible to radical breaking at the very moment the π bond between metal ion and olefin is formed. Based on this theoretical argument, the proposed mechanism: involves to a first approximation an electronic rearrangement and only small nuclear displacements. This mechanism may account for the low activation energy of the propagation step. It further relates catalytic activity to the ionization potential for a d electron of the transition metal and the nature of the negative ions used in the transition metal compound. It also provides a basis for the explanation of the formation of isotactic polymers when special solid catalyst systems are used.

Normal‐coordinate calculations have been carried out for the molecules acetone, acetone‐d6, acetaldehyde, acetaldehyde‐d4, acetaldehyde‐d1, formaldehyde, and formaldehyde‐d2. Infrared and Raman spectra for acetone, acetone‐d6, and acetaldehyde‐d4 were measured and assigned. Together with experimental data and assignments taken from the literature for the other molecules, these yield an almost complete set of fundamental frequencies.These frequencies were used to derive approximate force fields for these molecules and to investigate the transferability of the force constants. Calculations were carried out with both the Urey—Bradley force field (UBFF) and the valence‐force field (VFF) with selected interaction constants. The Urey—Bradley force field is not satisfactory unless it is augmented with some valence‐force interaction constants. In the valence‐force approximation it is not possible to make an unambiguous choice of the nondiagonal constants. However, a most probable force field is indicated, which on the one hand reproduces the experimental frequencies and on the other hand shows reasonable values for diagonal and nondiagonal force constant.The CO stretching constant, KCO, and the force constants around the CO group appear to be nontransferable among these molecules. The most probable force field indicates a decrease in the value of KCO in going from formaldehyde to acetaldehyde, to acetone. It is noted that the choice of interaction constants has a great influence on the values of the diagonal force constants and on the normal coordinates. Anharmonicity effects are also found to influence the values of the force constants and may affect the resulting conclusions.

The crystal structures of the ternary compounds MNb 3 S 6 (M = Mn, Fe, Co, Ni) have been refined and their magnetic susceptibilities measured using single-crystal samples. With the values for the magnetic parameters a consistent theoretical picture of the electronic structure of MNb 3 S 6 was derived.

The magnetic properties of Co2+ ions in octahedral environment are discussed in relation to the energy-level scheme. It appears that the three low-lying levels arising from the 4F(Γ4) triplet as a consequence of spinorbit coupling are responsible for a temperature-dependent magnetic moment. The expected departure from the Curie-Weiss law is demonstrated by susceptibility measurements on mixed-crystals of CoO and MgO between 300° and 1200°k. From the experimental data the spin-orbit coupling constant for Co2+ in these compounds is estimated to be -136 cm-1.

The abnormally low value of the magnetic susceptibility of Co 3 O 4 and ZnCo 2 O 4 and the uncertainty about the valence of the cobalt ions in these spinels has led to the investigation of mixed crystals of CoO and ZnO . The magnetic susceptibility of the ( Co , Zn ) O mixed crystals, measured up to 1200°K, could be represented by ζ = α + C T − θ with a fairly large temperature-independent paramagnetism (α = 0.5 × 10 −3 e.m.u.) and a magnetic moment for the Co 2 + ions in tetrahedral interstices of 4.05 μ β . The susceptibility measurements on several samples of ZnCo 2 O 4 indicated that Co 3 + ions are present in the octahedral holes. They showed only a small temperature-independent paramagnetism of 0.1 × 10 −3 e.m.u. It appears that in this spinel tervalent cobalt behaves in a similar way as in the numerous six-coordinated complex compounds. The temperature dependence of the molar susceptibility of Co 3 O 4 : ζ m = α + C T − θ with α = 0.7 × 10 −3 e.m.u. and μ = 4.14μ β is now easily explained on the assumption that this compound is a normal 2–3 spinel. The tervalent cobalt ions in the octahedral interstices do not exhibit a permanent moment, which explains the low susceptibility values. The Co 3 + ions in the octahedral of the perowskite LaCoO 3 seem to be normally paramagnetic. This difference in behaviour of tervalent cobalt in the octahedra of various oxygen lattices and the behaviour of divalent cobalt in tetrahedra can be qualitatively understood with the aid of the ⪡crystal field⪢ theory.

It is shown that in π-allylpalladium complexes, e.g. (π-C4H7)PdClL (L = AsPh3, PPh3) and substituted π-methallyl compounds, so called “πσ” reactions may occur, i.e. reversible interconversions from the π-allyl to a short-lived σ-allyl form with interchange of the syn- and anti-protons. These interchanges are caused either by reactions of the monomeric complex with excess free ligand L or by reactions of the complex with dimeric π-allylpalladium chloride compounds. In the case of these dimer-dependent “πσ” reactions it was found that at low temperatures syn- and anti-protons interchange on one side of the allyl group, whereas at higher temperatures interchange occurs on both sides of the allyl group of the monometer. The interchange on one side was studied in particular for various phosphine compounds. It proved to be first order in the monomer and first order in the dimer complex for L =P(n-C4H9)3. Additional information about “πσ” reactions in general was further obtained for dimethyl-substituted π-methallylpalladium compounds. Also included are the results of NMR measurements on the formation and ligand exchange reactions of ionic complexes [(π-C4H7)Pd(PR3)2]+Cl− for various phosphines.

The stereospecificity of the polymerization of propene under the influence of α-TiCl 3 and alkyl aluminum compounds is explained. The explanation rests exclusively on quantum chemical principles and the crystal chemistry of transition metal trichloride layer structures, subjects described in two preceding papers. The active centers formed by alkylation of titanium ions at those faces of the surface where chlorine vacancies are available are shown to possess the asymmetry necessary for the appropriate orientation of the α olefin in the π complex with the exposed titanium. The nonequivalence of the crystallographic sites of vacancy and alkyl group at the active center ensures that the growing alkyl group will move back to its original position after each incorporation of a new monomer. Thus the polymerization consists of a sequence of sterically identical steps which leads to isotacticity of the product.

The surface chemistry of Cr5+ complexes in chromia/silica catalysts for the polymerization of ethene is investigated. To this end not only the chromia/silica system is studied, but also the related combinations chromia/alumina, vanadia/silica and vanadia/alumina. Electron spin resonance spectra are used to follow the rearrangements in the co-ordination of the Cr5+ and V4+ ions, caused by contact with a number of different gases of vapours: H2O, air, CO, C2H4, HCI and NH3. It is found that the atomic arrangement at the surface of some of the systems studied is very flexible and easily influenced by, for instance, contact at room temperature with H2O, HCl or NH3. It is suggested that such a flexibility—encountered especially in chromia/silica—is a prerequisite for the catalytic activity. The active species in the fresh catalyst is Cr5+ in tetrahedral co-ordination. A mechanism is proposed according to which in the initiation step of the polymerization the co-ordination number is increased from four to five. An empty sixth co-ordination site may then be available to accommodate ethene monomers.