A re-investigation of arsenoacetic acid, (AsCH2COOH)n

• Full IR, NMR and ESI-MS data are presented for arsonoacetic acid and arsenoacetic acid.
• Arsonoacetic acid (X-ray structure) is isomorphous with phosphonoacetic acid.
• Arsenoacetic acid is a mixture of (RAs)n, n > 3, rather than a diarsene.
• The hexamer (AsCH2COOH)6 has a puckered, chair-conformation As6 ring (X-ray structure).

Detailed spectroscopic data have been obtained for arsonoacetic acid, As(CH2COOH)O3H2, and its barium and sodium salts. The X-ray crystal structure of the free acid is isomorphous with phosphonoacetic acid. Reduction gave the As(I) compound arsenoacetic acid, (AsCH2COOH)n which was shown by ESI-MS to contain cyclic species based on As–As bonds, with n mainly 3–6. The X-ray crystal structure of the hexamer was determined as the pyridine solvate and shown to have a hexacyclic As6 ring in a puckered chair conformation, with –CH2COOH groups in equatorial sites, each H-bonded to a pyridine molecule in the lattice.

Arsenoacetic acid, (AsCH2COOH)n is shown by ESI-MS to be a mixture of rings, mainly with n = 3–6; the hexameric form has been isolated as the hexa-pyridine solvate and structurally characterised by X-ray diffraction.Figure optionsDownload as PowerPoint slide