The Stability of the Cobaltammines.

Abstract

The marked tendency of the cobaltic ion to combine with ammonia and similar unsaturated molecules is evidently responsible for the existence of the numerous, variegated and frequently very stable cobaltammines. It appeared to us of interest to determine the actual magnitude of this tendency toward complex formation and to examine how it varies among the different ammines. b r AT'direct and elegant method of accomplishing this purpose, since we can be sure that the concentration of the simple cobaltic ions is minute undeiany experimental conditions, is to determine the ratio of the cobaltic and cobaltous ion concentrations by measurements of the oxidation potentials of solutions containing known concentrations of cobaltous ions and of the cobaltammines. From these ratios we at once know the actual cobaltic ion concentrations, and these in turn are an inverse measure of the stabilities, since evidently the more stable the complex ion the less the equilibrium concentration of the cobaltic ion in its solutions.This method has entailed certain subsidiary determinations. Thus, it has been necessary to determine the cobaltous ion concentrations in ammoniacal solutions of cobalt salts; also since the existing data on the normal oxidation potential of the cobaltic-cobaltous electrode are very meager, additional determinations of this potential in solutions containing known concentrations of the respective ions have been required.Attempts were first made to measure the oxidation potential in neutral and slightly acid solutions of the ammines, but definite and reproducible results could not be obtained under these conditions. Satisfactory results were, however, obtained in concentrated ammoniacal solutions, the observed potentials varying normally with changes in the cobaltic-cobaltous ion concentrations. Nevertheless, the use of such solutions involved much inconvenience since they had to be scrupulously protected from contact with the air.Preparation of Ammines.The 6 ammines studied were prepared and carefully purified by the most recent methods of J6rgensen11 and were in general used promptly after preparation. These precautions as to purity and freshness are necessary, since it was found that with certain ammines small amounts of impurities have a noticeable effect on the potential, while with other ammines, and in particular the aquo-tetrammine chloride, changes occur on standing even in the dry state which produce marked effects on the potential.

Complex Compounds of Biguanides and Guanylureas with Metallic Elements.

“…From determinations of the equilibrium constants of the decomposition reactions of cobalt(III) tris(biguanide) and cobalt(III) tris(phenylbiguanide) complexes with acids and of the concentration of The instability constants, kh k¡, and k3, for each stage (unibiguanide to tris(biguanide)), as well as the overall constant K = ki-k^-ki at 33°C., are given above (36). The K value for hexamminecobalt (III), however, is only of the order of 10~34 (81).…”

Quantum Yields and Kinetics of a Photosensitized Production of Reducing Sugars from Sucrose in Aqueous Solutions of Uranyl Sulfate by Visible and Ultraviolet Light

“…The independence of upon the pH in Expts. 4 and 6, and 21 and 22, shows that the catalytic effect of the hydrogen ions is replaced by the activated uranyl salts.…”

“…In combination with a zinc spark, the energies at 208, 254 and 280 µ transmitted by the exit slit were about the same as those obtained elsewhere with similar apparatus. 4 Two reaction cells were used with the monochromator ensemble. One was rectangular, 20 mm.…”

“…Analytical.-The light flux entering the actinic systems was measured with the uranyl oxalate solutions recommended for use as actinometers.3•7 The oxalate content of the solutions was determined by electrometric titration with permanganate after proof that the method gave the same values of as titration to a color end-point. The (4) Forbes and Brackett, ibid., 53, 3973 (1931).…”

The Acid-Base Properties of Complex Ions.

“…I think it is fair to say now that the special form of the theory has no particular appeal, while many of its substantial ideas are wholly consistent with present views. With Larson in 1920, Lamb (26) determined the relative stabilities of several cobaltic ammines, finding that the dissociation into simple cobaltic ions, ammonia, and other products decreased in the order shown in table 2. The concentration dissociation constants are very small (Kc = 2.2 X 10"34 in the case of the hexammine), as is indicated by the well-known stability of these groups in ordinary chemical operations.…”