Strategies to model corrosion protection mechanisms

14 Molecular structure of [CeFejIbpyljifTj-OHfr-Djifr-LhDjfLH) (HjOljl-O.Bibpyl-THjO (LH = 2-hydroxyacetate) viewed approximately perpendicular to the CeFe i/ -O) plane. 

The key features present in the complex are (1) a CeFe2(//3-0) core (2) the heterometallic bridging bidentate carboxylates (3) the glycolate oxo bridging between Fe and Ce and (4) the oxo-carboxyl chelation of the double deprotonated glycolate to Fe. These motifs demonstrate that Ce cations may be able to bind to an iron-oxide surface in the presence of suitable carboxylate groups. 

Subsequent woik focused on the preparation of model componnds containing cerium, iron and the sahcylate ligand. Initial work involved the reaction of CeCl3, FeClj and Na(salH) in various mole ratios over a pH range. Use of mole ratios of 1 1 6 and 1 2 4 at pH 7 gave dark red-brown precipitates (AandB respectively), which resembled the colour of cerium salicylate-treated iron coupons. More importantly, ATR-FTIR spectra of these precipitates closely resembled the spectrum of a cerium salicylate treated coupon after 24-hour exposure to cerium salicylate in a 0.1M NaCl solutioa 

The basic stractural units of (1) and (2) consist of octahedral Fe (sal)2(bpy) moieties, each with one chelating bpy ligand and two doubly deprotonated salicylic acid residues chelated to the iron through the phenolate and one caiboxylate oxygen atom (Fig. 1.16(a)), whereas the Ce sites are surrounded by nine oxygen atoms (Fig. 1.16(b)). 

15 The polymeric complex cation of [ FeisaDjIbpy CejdHjO) ] [salHlj.EtOH. SHjO (2). The solid-state structure shows the two complete environments and connectivity to neighbouring Reproduced by permission of the Royal Society of Chemistry from Chem. Commun., 2002, 2820 (doi 10.1089/B207722A).  

---