NQR parameters of complexes and polarizability effect

Abstract

The literature data on substituent influence on the nuclear quadrupole resonance frequencies (ν), quadrupole coupling constants (e(2) Qq ⋅ h(- 1) ), and asymmetry parameters (η) for 36 series of the H-complexes, charge-transfer complexes, transition metal complexes and other donor-acceptor complexes have been considered, using the correlation analysis. Generally the ν, e(2) Qq ⋅ h(- 1) , and η values were first established to depend on the inductive, resonance, polarizability, and steric effects of substituents. The presence or otherwise of certain effects as well as relation between their contributions are determined by the type of series. The polarizability effect owes its existence to the appearance of an excess charge on the indicator centre as a result of the complexation. The contribution of this effect ranges up to 75%.

Bond dissociation energies in organometallic systems: substituent effects

“… From MacPhee et al , Galkin and Cherkasov, Egorochkin et al , Voronkov and Egorochkin, and Egorochkin et al …”

“…The polarizability effect consists in an electrostatic attraction between the excess charge q originating on the reaction (indicator) center R C and the dipole moment induced by this charge in the substituents X. The charge q is caused by chemical reaction, complexation, or electromagnetic impact . We have every reason to believe that the geometric and electronic reorganization of center R C going on in the breaking of bonds leads to the arising of the charge q and hence of the polarizability effect.…”

“…As pointed out previously, the polarizability effect is due to this charge arising from the changes in electronic structure of the center R C . Such changes result from the chemical reaction, complexation, or electromagnetic impact . Therefore, taking into account the polarizability effect is indispensable to a detailed analysis of substituent influence on the parameters of the IR, NMR, EPR, ultraviolet photoelectron, X‐ray photoelectron, NQR, and Mössbauer spectra of organometallic complexes.…”

Mössbauer parameters of organometallic compounds and polarizability effect

“…In two series (III and XIX) the contribution Pol is larger than the sum of the contributions Ind and Res. In specific series the examples of very significant contributions Pol (in brackets) are found in studies of such properties P as the ionization potentials of N-centred radical cations (55%, gaseous state) [71], frequencies in the IR spectra of transition metal complexes (57%, solution) [72], transition metal NMR chemical shifts (86%, solution) [69], EPR parameters of radical ions (92%, solution) [73], coreelectron binding energies of organoelement compounds (56%, solid state) [70], NQR parameters of complexes (75%, solid state) [79] as well as in this work (57%, solid state). As is easy to see, the contributions Ind, Res, and Pol are interdependent.…”

Reactivity of organometallic compounds and polarizability effect

“…The first evidence for this effect has come from the study of ionic gas-phase reactions involving simple organic molecules [28e30]. Further investigations demonstrated that the polarizability effect has a profound influence on the parameters of the IR [31], NMR [32,33], EPR [34], NQR [35], UVeVis electronic [36], ultraviolet photoelectron [37,38], X-ray photoelectron [39], and Mossbauer [40] spectra as well as on the bond lengths [41] and toxicity [42] of organometallic compounds. A necessary condition for arising this effect is initiation of the partial charge q on M atom and/or on bonds MÀB and MÀL.…”