Outer-sphere complexation oxalate

This interpretation has been supported by a study of oxalate sorption on corundum modelled by the CD-MUSIC model involving ATR-IR spedroscopy (Johnson et al., 2004). A mononuclear bidentate complex was found up to 14 pmol/m, whereupon oxalate additionally adsorbed as an outer-sphere complex. Sorption of oxalate has also been studied on boehmite and corundum by Yoon et al. (2004) The peaks assigned to the inner-sphere complex in previous works (near 1286,1418,1700 and 1720 cmi) were claimed to arise from the presence of several species. Evidence for this phenomenon comes from the observation that peaks at 1286 and 1418 cm-i are shifted to 1297 and 1408 cm-i as the oxalate surface coverage increases. The authors finally postulated the existence of two species species "A" at 1286 and 1418 cmi, and species "B" at 1297 and 1408 cm-i, respectively, which were... 

Although somewhat more stable than its hexaammine relative, the air-sensitive [Co(en)3]2+ is still substitutionally labile and racemizes rapidly in solution. Chiral discrimination in its (racemic) solutions has been observed in outer sphere electron transfer reactions with optically active oxidants including [Coin(EDTA)], 209,210 [Cr(ox)3]3-,211,212 Co111 oxalate, malonate, and acetylacetonate (acac) complexes.213... 

On hematite (Duckworth and Martin, 2001), the spectra of sorbed oxalate are similar to the above discussed surface complex on an aluminum oxy-hydroxide and consequently a 5-member bidentate complex was proposed. The effect of pH on the sorption of oxalate on goethite has also been studied (Persson and Axe, 2001). An outer-sphere surface complex and a 5-member ring inner-sphere surface complex were inferred from spectra of the goethite/ oxalate system and the aqueous Fe(lll)-oxalate complex. At low pH, the presence of outer-sphere surface complexes (COOH)2 was ruled out because of the absence of a band corresponding to these species in aqueous solutions (around 1735 and 1233 cmi). 

Eigen-Tamm-Wilkins mechanism for complex formation.The same mechanism is thought to operate in the formation of the oxalate complex from cis-[Co(en)2(NH3)(OH2)]. Again all three forms of the ligand, ox , oxH", and 0XH2, react with the aquo complex. The outer-sphere association constant for the oxH" anion is 1.5, for the ox anion 5.8 dm mol ° The kinetic results here are compared with those established several years ago for the reaction of [Co(NH3)5(OH2)] with oxalate.The formation of the sulfito complex [Co(NH3)5(S03)] is mentioned in Section 5.7.7. below. 

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