Hexakis(benzotriazolato)tetrakis(2,4‐pentanedionato)pentacopper(II): A Model for Corrosion Inhibition

Abstract

The importance of fit in the recognition reaction and the subsequent hydrolysis can be demonstrated by variation of the "receptor" of the barbituric acid (by methylation of the pyrimidine nitrogen atoms; lipid 2). At pH 3, TAP is inserted into the monolayer of lipid 2 significantly more slowly than into that of lipid 1 (slow disappearance of the aggregation band) due to steric hindrance caused by the space-demanding methyl groups. The rate of the hydrolysis of lipid 2 on a TAP-containing subphase at pH 6.5 is linked to the rate of the insertion (Fig. 6). The aggregation band is observed until the hydrolysis is complete. 0.61 250 300 350 400 450 500 550 600 A [nm) -Fig. 6. UVjVIS reflection spectra of lipid 2 on a 1 0 -4~ TAP subphase at pH 6.5. Slow insertion (slow disappearance of the aggregation hand) followed by hydrolytic cleavage of the C=C bond (see Fig. 2b).This experiment particularly emphasizes the importance of the organization of lipids at the gas-water interface. AIthough lipid 2 does not associate with TAP in CDCI, according to 'H NMR spectra, ['] it does at the gas-water interface even though the solvent is changed from an aprotic to a protic one. The preorientation of the recognition structure by the lipid monolayer ensures that the complex, otherwise weak in solution, is stabilized by this arrangement. In this system the formation of the complex is the rate-determining step.The importance of molecular recognition is underlined by the investigation of the interaction of the pyrazolidine-3,sdione lipid 3 with TAP at the gas-water interface. In this case the aggregation band of the chromophore is not interrupted by TAP, because the five-and six-membered ring structures of lipid 3 and TAP do not fit together well enough. The monolayer of lipid 3 is stable on a TAP-containing subphase at pH 3 and pH 6.5 (no changes at all in the UV/VIS reflection spectra).Preliminary experiments with subphases containing nucleobases indicate a defined interaction, for example, between cytosine and lipid 1, which is only possible via the enol form of the base. In addition, the reverse systems-water-soluble barbituric acid derivatives and monolayers of amphiphilic triaminopyrimidine and melamine derivatives-are currently under investigation.

Surface Coordination Chemistry: Corrosion Inhibition by Tetranuclear Cluster Formation of Iron with Salicylaldoxime

“…[22] Iron ions must be available for the formation of such species, and the efficiency of P50 is therefore enhanced by treatment of an oxidized iron surface with a mild acid. The results reported here provide evidence, in addition to the information obtained on the nature of the interaction of oxidized Cu surfaces with benzotriazole, [23] that corrosion inhibition at a metal surface can involve the production of metal clusters. The low ligand/metal ratio which arises for a ligand in immediate contact with an oxidized metal surface means that polyfunctional ligands have advantages over monofunctional ligands as corrosion inhibitors.…”

Combined Studies on the Surface Coordination Chemistry of Benzotriazole at the Copper Electrode by Direct Electrochemical Synthesis and Surface‐Enhanced Raman Spectroscopy

“…For example, the introduction of ligands such as β-diketonate, acetylacetone, and triphenylphosphane (PPh 3 ) can result in remarkable differences in the structures of metal complexes with BTAH, specifically, the transformation of single metal nuclear to multinuclear complexes. [1,[44][45][46][47][48][49] Therefore, it is worth investigating the inhibition of BTAH in nonaqueous solutions containing some organic molecules that might play an important role in the formation of surface complex films. In contrast, it is highly desirable to extend SERS studies directly to wider applications in surface science, not only for the various processes of corrosion and inhibition, but also for the surface coordination chemistry of BTAH together with other ligands.…”

“…[1][2][3][4][5] For example, some organic molecules adsorbed on particular metal surfaces form a compact complex layer that can inhibit the corrosion of the surface effectively. [6][7][8][9][10][11][12] Despite the importance of special organic inhibitors, little attention has been paid to the investigation of how they bind or coordinate to the metal surfaces or as to why seemingly minor modifications in the structures of the active organic compounds can have a profound effect on their efficiency.…”

Raman spectroscopic studies on surface coordination mechanism of benzotriazole and triphenylphosphine with metals

“…So far, there are lots of reports on the Cu complexes with BTAH and other ligands, it was mainly due to the high corrosion inhibition of BTAH with Cu and its alloys [4]. Handley et al synthesized a copper(II) complex of BTAH and acac with the structure of hexakis(benzotriazolato) tetrakis-(2,4-pentanedionato)pentacopper [Cu 5 (B-TA) 6 (acac) 4 ], which could be used as the model of corrosion inhibition [5]. However, most of the relevant investigation was focused on the Cu complexes with BTAH and another ligands, and there were no reports on the preparation of single crystal of Cu complexes only with BTAH.…”

“…The coordination chemistry of benzotriazole (BTAH) and its ring substituted derivatives has attracted considerable attention due to the effective inhibition for transition metals, particularly for Cu and its alloys [1][2][3][4][5][6]. Since the pioneering work of Cotton and coworkers [1,2], the adsorption/coordination behavior and bonding configuration between BTAH and Cu substrates have been extensively studied by many scientists using various techniques, such as electrochemical, surface analytical and spectroscopic techniques [7][8][9][10][11][12][13][14].…”