NQR parameters of complexes and polarizability effect.

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%.