Complexation of Oxobisperoxovanadate by Multidentate Heteroligands

There is evidence from Raman studies that oxalate coordinates in a bidentate manner without elimination of a peroxo group [6], Possibly here, as for the picolinate complex, the question of the coordination could be more definitively answered by observation of 13C coordination-induced NMR chemical shifts. The x-ray structure for the oxalate complex shows that the two V0ox bond distances are very different. The VO distance to the equatorial oxalato oxygen is 2.060(4) A compared to 2.251(4) A to the apical oxygen [15], Similarly long distances are found in the picolinato complex (VOpic 2.290 A [16]) and other complexes [20], These distances are indicative of relatively weak bonds to the apical oxygens, and dissociation of that bond 

A number of x-ray structures of monoperoxoheteroligand complexes of vanadate have been reported. The heteroligands have included picolinate, dipicolinate, dipeptides, and a number of a-hydroxycarboxylate. Solution NMR studies have been carried out for several of these systems, and various solution products described. Table 6.4 gives the 51V NMR chemical shifts for a number of products that have been studied. This table covers a variety of types of complexes, and the chemical shifts range over about 100 ppm, from about -580 to -680 ppm. 

Dipeptides complex in a trident fashion to form oxoperoxodipeptido products. The rate of complexation by these ligands is quite slow. Even the vanadium-catalyzed disproportionation of hydrogen peroxide occurs quickly when compared to the rate of complexation by dipeptides. The formation of the dipeptide complex is interesting, in the sense that the ligand is tridentate, and complex formation involves loss of a 

51V NMR Chemical Shifts of Selected Aqueous Oxoperoxovanadate Heteroligand (V L X) Complexes 

Chelate complexation through both amine and carboxylate 

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