Density Functional Theory Investigations for the ... - Sciensage.info

M Lebrini et al. have studied the inhibiting effects of some
oxadiazole derivatives on the corrosion of mild steel in
perchloric acid solution [21]. Joseph Raj et al. have investigated
the effect of some oxadiazole derivatives on the corrosion
inhibition of brass in natural seawater [22]. A new class of
corrosion inhibitors of mild steel in acidic media on the
substituted 1,3,4-oxadiazoles was studied by bentiss et al. [23].
Although experimental work of M. Benabdellah, et al. [24]
provide valuable information on the corrosion inhibition
efficiency of 2,5-Bis(4-methylphenyl)-1,3,4-oxadiazole (Inh-I)
and 2,5-bis(4-methoxyphenyl)-1,3,4-oxadiazole (Inh-II), a
deep understanding of the inhibition property remain unclear.
To date, however, no study has been performed to investigate
the corrosion inhibition efficiency of Inh-II >Inh-I by using
quantum chemical calculations. The aim of the present work is
to correlate the clear relationship between the experimentally
determined inhibition efficiencies with the quantum chemical
parameters of the investigated inhibitors.
The analyzed inhibitive properties are the molecular
structure, the dipole moment, E HOMO , E LUMO , energy gap (ΔE),
and those parameters that give valuable information about the
reactive behavior: electronegativity (χ), global hardness (η)
and the fraction of electrons transferred from the inhibitor
molecule to the metallic atom (ΔN) and the back-donation
(ΔE Back-donation ). The local reactivity has been analyzed by means
of the Fukui indices, since they indicate the reactive regions, in
the form of the nucleophilic and electrophilic behavior of each
atom in the molecule. Results obtained showed that the
inhibition efficiency of Inh-II > Inh-1. It is well correlated with
the experimental results. From the calculations we have
explained which adsorption site is favoured to bind to the
metal surface.
2. MATERIAL AND METHODS
2.1. Quantum-chemical calculation
P. Udhayakala et al, J Adv Sci Res, 2012, 3(3): 67-74 68
is considered a very useful technique to probe the
inhibitor/surface interaction as well as to analyze the
experimental data. The results of the geometry optimization of
the compounds Inh-I and Inh-II are presented in Figure 1.
2,5-bis(4-methylphenyl)-1,3,4-oxadiazole (Inh-I)
2,5-bis(4-methoxyphenyl)-1,3,4-oxadiazole (Inh-II)
Inh-I
Among quantum chemical methods for evaluation of
corrosion inhibitors, density functional theory (DFT) has
shown significant promise and appears to be adequate for
pointing out the changes in electronic structure responsible for
inhibitory action [25]. In order to explore the theoreticalexperimental
consistency, quantum chemical calculations were
performed with complete geometry optimizations using
standard Gaussian-03 software package [26]. Geometry
optimization were carried out by B3LYP functional at the 6-
31G (d,p) basis set [27]. This basis set provided accurate
geometry and electronic properties of a wide range of organic
compounds [28]. Recently, Density functional theory (DFT)
has been used to analyze the characteristics of the inhibitor/
surface mechanism and to describe the structural nature of the
inhibitor in the corrosion process [29, 30]. Furthermore, DFT
Inh-II
Figure 1. Optimized molecular structure of Inh-I and Inh-II by
B3LYP/6-31G (d,p)
Density functional theory (DFT) has become an attractive
theoretical method because it gives exact basic vital parameters
for even huge complex molecules at low cost [31, 32]. It has
been quite successful in providing theoretical basis for popular
qualitative chemical concepts like electronegativity (χ),
Journal of Advanced Scientific Research, 2012, 3(3)