Some aspects of quantum chemical calculations for the study of Schiff base corrosion inhibitors on copper in NaCl solutions

The inhibiting effect of some Schiff bases-N,N'-o-phenylen-bis(3 -methoxy-salicylidenimine) (V-oph-V), N-2-hydroxyphenyl-(3-methoxy-salicylidenimine) (V-psd), N,N'-phenylcarbazide-(3-methoxy-saricylidenimine) (V-psd) N,N'-o-phenylenhis(salicylidenimine) (S-oph-S), N,N'-p-phenylen-bis(salicylidenimine) (S-pph-S), N-4-phenylcarbazide-(salicylidenimine) (S-psd) on the corrosion of copper in 1.0 M NaCl solutions, under various conditions, has been studied by means of the potentiostatic polarization method and the AC impedance technique. In order to study the ability of quantum chemistry to select corrosion inhibitors, quantum chemical calculations have been applied to the six kinds of Schiff base. The corresponding structures have been optimized and the energies and coefficients of their molecular orbitals have been calculated using the semi-empirical MINDO/3 method. The theoretical results obtained have been compared with the experimental data and the relations between the inhibition efficiency and quantum parameters (such as HOMO energy and LUMO energy) have been discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.