F.F. Roelandt

Normal coordinate analysis of α-FeOOH - a molecular approach

Abstract The infrared spectra of α-FeOOH and the deuteratad analogue have been interpreted by a normal coordinate analysis. The assumption was made of partial covalent bond formation between the oxy and hydroxy oxygen and iron. Frequencies and force constants involving the motion of the hydrogen atom and the Fe-OH bond are evaluated in a distorted Fe3OH tetrahedron. The Fe-O parameters are separately derived in a quasi planar trigonal Fe3O geometry.

CNDO/2 study of 29Si NMR chemical shifts

Abstract A CNDO-2 study of 29 Si NMR chemical shifts for compounds of the type (CH 3 ) n SiX 4- n (X = H, F, Cl) is reported. The paramagnetic screening constants σ p are given. The general variation in σ p with n agrees fairly well with the variation of the observed chemical shifts for X = H and F, but the correlation is not so good for X = Cl.

Ab initio study of the electronic structure of compounds with a double-bonded silicon atom: Part II. HNSi

Abstract Ab initio LCAOMOSCF calculations have been carried out on HNSi, with a number of different basis sets. The geometry of this molecule was optimised: R (SiN) = 1.557 A, R (NH) = 0.997 A and ∠HNSi = 180°. Using a harmonic force field, the force constants and vibrational frequencies are calculated and compared with the experimental values. The electron distribution is studied in terms of a Mulliken population analysis, and the electrical dipole moment is discussed.

Ab initio study of the electronic structure of compounds with a double bonded silicon atom: Si2H4

Abstract Ab initio LCAO-MO-SCF calculations have been performed on the compound disilene, Si2H4. The calculations indicate for the SiSi bond length an optimized value of 2.15 ». The electronic structure of the molecule is discussed in terms of a Mulliken population analysis, and it is shown that the 3d orbitals on silicon do not make a substantial contribution to the bonding.Abstract Ab initio LCAO-MO-SCF calculations have been performed on the compound disilene, Si 2 H 4 . The calculations indicate for the SiSi bond length an optimized value of 2.15 ». The electronic structure of the molecule is discussed in terms of a Mulliken population analysis, and it is shown that the 3 d orbitals on silicon do not make a substantial contribution to the bonding.

Theoretical study of the barriers to internal rotation in dimethyl ether, methoxysilane and disiloxane

Abstract The barriers to internal rotation have been computed by ab initio methods for CH3OCH3, CH3OSiH3 and SiH3OSiH3. It is shown that minimal basis set results agree fairly well with experimental results for CH3OCH3 and to a lesser extent for SiH3OSiH3. To predict a correct ordering of the CH3 and SiH3 rotation barriers in CH3OSiH3, a split valence basis set has to be used. Attention is also paid to the influence of geometry optimization on the barriers to internal rotation.

Charge-transfer spectra of organometallic complexes. I: Formation constants for complexes of trialkyltiniodides with iodine in carbon tetrachloride solutions

Abstract A charge-transfer complex is formed as reaction intermediate in the iodinolysis of R 3 SnI (R = CH 3 , C 2 H 5 , n -C 3 H 7 , iso -C 3 H 7 , n -C 4 H 9 , iso -C 4 H 9 and sec -C 4 H 9 ) in CCl 4 solutions. By means of the spectrophotometric molar ratio method and by the detection of an isosbestic point at 510 nm, the complex species was identified as a 1 : 1 molecular adduct between the alkyltiniodide and iodine. Formation constants of the complex were calculated using a non-linear regression analysis of absorbancy measurements on the perturbed iodine band. With the aid of these constants, the maxima of the charge-transfer peaks (u.v. region) and blue shifted iodine peaks (visible region) could be accurately determined.

Vibrational study of diphenylphosphorus halides Ph2PX (X Cl, Br, I)

Abstract The Raman and i.r. spectra of diphenylphosphorus halides, Ph2PX (X  Cl, Br, I), have been measured and concerted assignments have been made confirmed by an approximate normal coordinate analysis for the skeletal vibrations of Ph2PCl using a three mass model for the phenyl group.