METAL COMPLEXES OF SQUARIC ACID (DIKETOCYCLOBUTENEDIOL) IN AQUEOUS SOLUTION

Formation constants of complexes of diketocyclobutenediol (squaric acid) with several metal ions have been measured in aqueous solution at 259 and ionic strength 0.5 and found to be as follows: Fe(III), 41,000; U(VI), 1200; Al(III), 680; Cu(II), 160; Mn(II), 32; Co(II), 42; Ni(II), 30. A few measurements were made at other temperatures and ionic strengths. Spectrophotometric, Polarographie, Potentiometrie, and paper-chromatographic techniques were used. In every case, 1:1 complexes predominated over a wide concentration range. The complexes of Fe, U, and Cu are strongly colored; yellow and brown solutions were also observed with Ti(IV) and Ti(III). Sparingly soluble solid yellow complexes of U(VI) and Ti(IV) were prepared and analyzed, and the solubility of copper(II) squarate was redetermined. K2 for squaric acid was found to be 1.3 X 10-3 at 25° and ionic strength 0.5. The complexes are of special interest because of the simple aromatic character of the ligand ion. © 1969, American Chemical Society. All rights reserved.