Characterization and Separation of Some of the Coordination Compounds of Chromium and Aluminon

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Abstract
Chromic nitrate and aluminon (ATA) react to form highly colored lakes. Examination of these lakes by the Vosburgh and Cooper method has led to the identification of a pigment [(ATA)Cr(H2O)x] which is insoluble in water and absolute alcohol, a deep red anionic component [(ATA)BCr(H2O)x]−y, and a purplish-red cationic component [(ATA)Cr4(H2O)x]+y. These components of the lake have been isolated and separated in the dry form. The anionic compound is apparently a simple coordination compound and can be used as a cytoplasmic stain while the cationic component is a chelate and can be used as a rather selective nuclear stain. In addition to these components, a number of other components were also found. Not only the ratio between chromium and aluminon but also the concentration of the reactants influences the formation of these different components. The amount of pigment formed is maximal with a molar ratio of 1 and a concentration of 10−2 M or 10−1 M. The anionic component is maximal with a molar ratio of 1 Cr to 6 aluminon at the 10−1 M concentration, the cationic component is maximal with a molar ratio of 4 chromium to 1 aluminon at the 10−1 M concentration. None of these are formed at the 10−4 M concentration but only a deep redpurple soluble compound at the 1 : 1 ratio, which was not further investigated.