Abstract
4,4′-(Methylenediimino)bis-1,2,5-oxadiazole-3-carboxylic acid and 4,4′-(methylenediimino)bis-1,2,5-oxadiazole-3-carboxamide have been synthesized by the acid-catalyzed condensation of 4-amino-1,2,5-oxadiazole-3-carboxylic acid and 4-amino-1,2,5-oxadiazole-3-carboxamide with formaldehyde. The crystal and molecular structures of the compounds have been determined by X-ray crystallography. 4,4′-(Methylenediimino)bis-1,2,5-oxadiazole-3-carboxylic acid crystallizes in space group C2/c, and its measured density is 1.800 g/mL, significantly above the calculated value of 1.68 g/mL. 4,4′-(Methylenediimino)bis-1,2,5-oxadiazole-3-carboxamide crystallizes in space group P21/c, and its measured density is 1.623 g/mL, in close agreement with the calculated value of 1.64 g/mL. The structure of the starting amide 4-amino-1,2,5-oxadiazole-3-carboxamide has also been determined. These data, combined with literature data, suggest that ortho-aminocarboxylic acids have unusually high densities, but the reasons for this are unclear.
Published Version
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