COMPLEX COMPOUNDS OF BIPOSITIVE SILVER WITH PYRIDINE CARBOXYLIC ACIDS. PART II. ARGENTIC COMPOUNDS OF PYRIDINE DICARBOXYLIC ACIDS

In continuation of our previous work on bipositive silver complexes of pyridine monocarboxylic acids, we have now been able to prepare the argentic complexes of all the dicarboxylic acids of pyridine with the exception of that of dinicotinic acid, which is not at hand for the present.

Argentic complexes of quinolinic, cinchomeronic, Isocinchomieronic, lutidinic and dipicolinic acids are formed by the oxidation of silver nitrate in presence of the corresponding acid by alkali persuI­phate in aqueous medium. They form red to dark red, finely divided crystals, more or less sparingly Soluble in water. The argentic complex of dipicolinic acid has, however, been obtained in two different colours —dark red and green, the last we being produced at a lower temperature. The com­position or all these complexes is given by the general formula Ag(XH)₂ (where XH₂=one molecule of the pyridine dicarboxylic acid). With the exception of cinchomerunic acid (3 : 4), all the complexes may be represented by a monomeric structure like that of the argentic picolinate. The structure of the argentic cinchomeronate resembles possibly that of nicotinic or isonicotinic acid, being either dimeric, or polymeric with the formation of unending two-dimensional sheets and layer A, The complexes are all decomposed by acids and alkalies.

All these argentic complexes are paramagnetic and give moment values of approximately 1.73 pc. X-ray powder photographs show that the green and chocolate modifications of the argentic complex dipicolinic acid differ in their crystal structure. Cupric and argentic quiuolinates crystallise with different water molecules and hence show, as might be expected, different X-ray patterns.