O. Kh. Poleshchuk

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.

Donor–Acceptor Bond in Nontransition and Transition Element Complexes: Studies with Natural Bonding Orbital Approach

Electronic structures of tin, antimony, titanium, and niobium chloride complexes were analyzed using density functional theory. Parameters of nuclear quadrupole resonance spectra calculated using pseudopotential and all-electron basis states were compared with the experimental values. It was shown that the use of the central atom pseudopotential leads to a significant deviation of the atomic quadrupole coupling constants from their experimental values. The bonding in complexes was analyzed by making use of the natural orbitals of metal–chlorine and metal–ligand bonds. Donor–aceptor interactions in complexes of main group elements are described within the framework of sp-hybridization, while those in the transition element complexes, within the sd-hybridization framework.

The asymmetry parameter of the electric field gradient tensor of TiCl4 and its complexes studied by NQR nutation spectroscopy

Abstract Nuclear Quadrupole Resonance (NQR) Nutation Spectroscopy studies and INDO calculations of the electronic structure of TiCl 4 and its complexes have been performed. An explanation of the changes of the NQR frequencies and asymmetry parameters upon complex formation have been proposed. The populations of the TiCl 4 orbitals have been estimated for different crystallographic structures and compared with the population of the TiCl 4 ·2CH 3 CN orbitals. The values of the experimental 35 Cl NQR frequencies correlated with the calculated ones. Moreover, there is good agreement between the experimentally determined and calculated nutation spectra asymmetry parameter for TiCl 4 . The results of the INDO calculations showed that the Ti–Cl bond order decreases upon complex formation and consequently the 35 Cl NQR frequencies decrease and the asymmetry parameter increases. On the basis of the results of the quantum chemical calculations the population of the 3p π chlorine orbital decreases when the molecular structure changes from TiCl 4 (T d ) to TiCl 4 (D 4 h ). The electron density transfer from the p π orbital of the chlorine atom to the d π orbital of the Ti atom decreases due to complex formation. It was found that the INDO method is suitable for determining the electron distribution in TiCl 4 and its complexes.

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.

Quantum chemical study of the structure and properties of isotopically pure lead chalcogenides

In the present work the theoretical methods B3LYP/SDD, GGA and BP86/TZ2P were used for quantum-chemical calculations of lead chalcogenides. It is shown that these levels of theory are applicable for assessment of their geometric parameters, Raman and IR spectra and thermodynamic characteristics. It is shown that there are correlations between the experimental and calculated characteristics of lead sulphide, selenide and telluride. The influence of different isotopes of lead, sulphur, selenium and tellurium on the thermodynamic parameters and the Raman spectra for the lead chalcogenides is shown.

New chemical markers based on phthaleins

New chemical markers based on mixtures of individual phthaleins were developed. These markers are characterized by high level of secrecy in use, good transferability to contacting persons, enhanced retention on the objects marked, and reliable identification of phthaleins by expert investigation. The experimental studies of the markers obtained show that the synthesized mixture of three phthalein homologs contains the previously unknown phthalein with unsymmetrical phenolic substituents, o-cresolphenolphthalein [3-(3′-methyl-4′-hydroxyphenyl)-3-(4″-hydroxyphenyl)phthalide], which decreases the probability of the marker falsification. Quantum-chemical calculations of the reaction of the o-cresolphthalein synthesis show that the overall reaction is characterized by small positive changes in the enthalpy and Gibbs free energy, and the second and third steps occur with negative changes in the Gibbs energy. The optimum structure of the transition state was calculated.

Bonding in Halide and Interhalide Complexes with Ammonia: Studies by Microwave Spectroscopy and Density Functional Theory

Electron density redistribution and quadrupole coupling constants (QCC) in XY···NH3 complexes were analyzed. Data on bond lengths and QCC calculated by the BHandHLYP/aug-cc-pVTZ were used to compare the results obtained with experimental data of rotational spectroscopy. Analysis of QCC values and of the results of approximation of the natural bonding orbitals reveals prevailing electrostatic nature of intermolecular interaction.

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.