We have investigated the assembly of a two-dimensional coordination polymer, Nd-2(C6H2N2O4)(2)(C2O4)-(H2O)(2), that has been prepared from the hydrothermal reaction of Nd(NO3)(3)center dot 6H(2)O and 2,3-pyrazinedicarboxylic acid (H(2)pzdc). In situ oxalate formation as observed in this system has been been investigated using H-1 and C-13 nuclear magnetic resonance spectroscopy, and a pathway for C2O42- anion formation under hydrothermal conditions has been elucidated. The oxalate ligands found in Nd-2(C6H2N2O4)(2)(C2O4)(H2O)(2) result from the oxidation of H(2)pzdc, which proceeds through intermediates, such as 2-pyrazinecarboxylic acid (2-pzca), 2-hydroxyacetamide, 3-amino-2-hydroxy-3-oxopropanoic acid, 2-hydroxymalonic acid, 2-oxoacetic acid (glyoxylic acid), and glycolic acid. The species are generated through a ring-opening that occurs via cleavage of the C-N bond of the pyrazine ring, followed by hydrolysis/oxidation of the resulting species.