Investigation of in situ oxalate formation from 2,3-pyrazinedicarboxylate under hydrothermal conditions using nuclear magnetic resonance spectroscopy.

We have investigated the assembly of a two-dimensional coordination polymer, Nd(2)(C(6)H(2)N(2)O(4))(2)(C(2)O(4))(H(2)O)(2), that has been prepared from the hydrothermal reaction of Nd(NO(3))(3)·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 (1)H and (13)C nuclear magnetic resonance spectroscopy, and a pathway for C(2)O(4)(2-) anion formation under hydrothermal conditions has been elucidated. The oxalate ligands found in Nd(2)(C(6)H(2)N(2)O(4))(2)(C(2)O(4))(H(2)O)(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.