G. N. Dolenko

Electron density redistribution on complexation in non-transition element complexes

Abstract Complexes of tin, antimony, silicon, germanium, iodine, boron and titanium halogenides with organic ligands were investigated using nuclear quadrupole resonance (NQR) and X-ray fluorescence spectroscopies, and Mossbauer effect and quantum-chemical calculations. A discussion of results which we obtained previously as well as literature data is included. The correlations between 35 Cl NQR and ClKα line shifts in SnCl 4 L 2 , SbCl 5 L and TiCl 4 L 2 complexes were obtained. The geometry of the acceptor was found to influence the value of effective charge on the chlorine atom ( q Cl ) in SnCl 4 L 2 complexes, but not to influence the chlorine atom in TiCl 4 L 2 complexes. Values of q Sn and q Sb were calculated from Mossbauer isomer shifts in the SnCl 4 L 2 and SbCl 5 L complexes. Electron-density transfer from the ligand to the vacant d orbital of the central atom on complexation was observed.

X-ray investigation of electron density redistribution on complexation

Abstract The shirts of the kα lines for P, S and Cl atoms were studied as functions of the effective charges on these atoms obtained using CNDO/S, CNDO/2, INDO, MINDO/3 and MNDO methods for model compounds. The best correlation for all three elements was obtained by the INDO method in a minimal basis set. The problem of electron density redistribution on complexation was investigated from the “viewpoint” of a ligand, taking AlBr3L complexes (L=PCl3,P(C6H5)3,SPCl3, OPCl3) as examples. Significant transfer of electron density from a ligand to the acceptor does not occur on complexation with AlBr3, but there is a significant increase in the PCl bond ionicity. The PS bond ionicity does not change on complexation.

Investigation of the electronic structure of SnCl4L2, TiCl4L2 and SbCl5L complexes by X-ray fluorescence spectroscopy

Abstract The electronic structure of SbCl 5 L complexes has been analyzed on the basis of the fluorescence spectra of the sulfur and chlorine atoms as well as quantum chemical XαDV and PM3 calculations. The results have been compared with the corresponding data for SnCl 4 L 2 and TiCl 4 L 2 complexes. An increase in electron density on the chlorine atoms accompanied by a decrease on the central metal atom has been observed for the complexes arranged according to their stability. The arrangement of Sn, Sb, and Ti complexes with dimethyl sulfide according to their increasing stability is in disagreement with the order of the complexes with respect to electron density on the sulfur atom.

Distinctive features of the electronic structure of tetrachloride titanium complexes

Abstract The paper reports results of measurements of the ClKα shifts in the X-ray fluorescence spectra and 35Cl-NQR frequency for a group of tetrachloride titanium complexes. The experimental ClKα shifts were correlated with the parameters describing donor properties of ligands such as ligand strength (DN), ionisation potential (IP) or parameters of influence (P). Analysis of the correlation dependencies has indicated that changes in the electronic density on the chloride atom of the acceptor, taking place upon complexation, are determined by the polarisation effects.

Changes in electron density distribution resulting from formation of antimony pentachloride complexes studied by X-ray fluorescence spectroscopy

Abstract Changes in the electronic structure of SbCl 5 L complexes during their formation have been studied and compared with corresponding earlier data for SnCl 4 L 2 and TiCl 4 L 2 complexes. Analysis of the results of X-ray structural studies, against data on the heat of complex formation, the Mossbauer effect, results of PM3 quantum chemical calculations, derivatographic data and the frequencies of valence vibrations, permitted assessment of the complex stability against different factors and determination of the enthalpies of complex formation, and proved that the transfer of electron density from donor to acceptor was small. The charge of the donor is proved to affect mainly the polarization of the acceptor bonds.

Investigation of chlorine valence electron density in SnCl4L2, SbCl5L and TiCl4L2 complexes

Abstract The electron density on valence orbitals of chlorine atoms in SnCl 4 L 2 , SbCl 5 L and TiCl 4 L 2 complexes has been investigated by NQR and X-ray fluorescence spectroscopy. It has been established that the increase in the negative charge on the chlorine atoms in the acceptor part of the complex can be explained only when changes in the acceptor geometry are taken into account.

Study of charges on heteroatoms in organic compounds of the second-row elements by X-ray fluorescence spectroscopy

The characteristic features of the electronic structure of SbCl5L complexes has been studied in comparison with those of the SnCl4L2 and TiCl4L2 complexes. The results of X-ray structural analysis were correlated with the heats of complexation, the data of Mössbauer spectroscopy, derivatography, quantum-chemical PM3 calculations, and stretching frequencies of the donor-acceptor bonds. Based on these data, the contributions of different effects to the stabilities of complexes were determined, complexation enthalpies previously unknown were calculated, and a conclusion was drawn that the electron density transfer from the donor to the acceptor is small. The charge effect of the donor consists primarily in polarization of the acceptor bonds; this polarization decreases as a result of (he change in the geometry of the acceptor upon complexation. The relative stabilities of the complexes with dimethyl sulfide were determined using a unique internal standard technique.

Investigation of the charge state of heteroatoms in organic compounds of third-row elements by x-ray fluorescence spectroscopy 11. Redistribution of electron density in simple phosphorus-containing molecules upon complexation with AlBr3

The electron density on the atom in the ligands PCl3, PPH3, SPCl3, and OPCl3 by means of which they are coordinated to a metal atom, decreases upon coordination with AlBr3 twice as much as does the total electron density of the ligands, and the ionicity of the PCl bonds in the ligands increases appreciably upon complexation.

X-ray fluorescence spectroscopy study of the charge state of hetero atoms in organic compounds of row III elements. 9. Compounds containing P=S and P-S fragments

The dependences of the shift of the Kα line of sulfur on the effective charge on the S atom, calculated by the CNDO/S method, are decomposed into two linear dependences: one for a compound of thione sulfur, the other for the rest of sulfur-containing systems. The dependences of the shift of the Kα line of P on the effective charge on the P atom, calculated by the CNDO/S method, are also decomposed into two linear dependences; one for compounds of three-coordinate P, the other for compounds of P with coordination number >3. In thiophosphoryl compounds, the electron density on the S atom varies symbatically with that for the P atom. In systems containing the P-S bond, the magnitudes of the effective charge on the S atom remain virtually constant.

X-ray fluorescent spectroscopy study of the charge state of heteroatoms in organic compounds of third row elements. 7. Thiocyanates and isothiocyanates

We propose an x-ray spectral criterion as a characteristic of organic and inorganic thiocyanates and isothiocyanates. We establish the lack of interaction between the level of the unshared electron pair of sulfur and the πc≡C-orbitals in thiocyanates.