Oxalate dianion

Vanadium(V) oxide is amphoteric, dissolving in alkali to give salts of tetrahedral VO " anion, and in acid to give V02. The latter cation is almost certainly cis-[V02(H20)4]+, as in [V02(ox)2]3- and [V02(edta)]3 (ox = oxalate dianion edta = ethylenediamine tetraacetate tetraanion). All dioxo complexes of d° metals have cis configurations, an arrangement that maximizes dji-pjt interactions. 

The coordination of oxalate dianion to nickel(II) has been studied in aqueous solution.1773,1774 A number of oxalato complexes including the simple... 

C.-K. Lam and T. C. W. Mak, Carbonate and oxalate dianions as prolific hydrogen-bond acceptors in supramolecular assembly. Chem. Commun., 2660-61 (2003). 

Oxalate viologen ion pair complexes have been examined in detail under pulsed laser flash and continuous photolysis [205], As the photolysis leads to the oxidation of oxalate dianion, the strongly reducing CO 2"is formed after decarboxylation and a second MV2 + is reduced, generating another equivalent of MV +. Malonate, succinate, glutarate, polyacrylate and polymethacrylate were also tested and found to be effective as CTC donors for MV + formation. In the case of malonate, decomposition of the carboxylate was not accompanied by MV2 + consumption. This was attributed to the efficiency of a back electron transfer step following immediately the decarboxylation [206]. 

Carbon dioxide is more easily reduced than CO, and reductive activation may be chemical [113,114], enzymatic [115], electrochemical or photochemical [116,117], proceeding by one-, two-, four-, six- or even eight-electron steps. Two-electron processes are the most common and are known to produce salts of formate, oxo, carbonate, and oxalate dianions, and carbon monoxide [118]. 

Oxalate dianion 1,2-Dithiolene Acetylacetate Diethylentriamine (dien) 1,3,5-Triaminocyclohexane (tach) 1,4,7-Triazacyclononane (tacn) 3,3 -Iminobispropylamine (dpt) 2,2 -Bipyridyl Triethylentetramine (trien)... 

Of these the in-phase combination of the two M28 orbitals with the oxalate n orbital, XI, is by far the most important. (The filled CO2 k bonding orbitals lie several eV below the energy of the M28 orbitals). Effectively, the fQled M28 orbitals back-bond to the oxalate tt system and stabilize the planar O2CCO2 unit by placing electron density in an orbital which has C-C it bonding character. The free oxalate dianion has the twisted D2d geometry which minimizes oxygen lone pair repulsions. 

Formation of oxalate radical anion from oxalate dianion)... 

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