Über die Hydrolyse von Eisen(III)Salzlösungen. I. Die Hydrolyse der Lösungen von Eisen(III)chlorid

When a very diluted iron(III)chloride solution is slowly alkalified by a weak base, the deprotonation of [Fe(H2O)6]3+ proceeds in a first stage to form mono‐ and dinuclear hydroxoaquo‐complexes. In a second stage 4 dimers condense around a chloride ion to form an eight membered ring, an embryon, which grows fast to very small crystals of the composition Fe4O3(OH)5Cl and the structure of the β‐FeOOH. These crystalline micells remain colloidally dissolved. If the pH is raised above approximately 3.4 the Cl−‐ are exchanged against OH−‐ions and flocculation occurs. This shows that Pauli, assuming the micells of such sols to be polynuclear complex ions, is basically correct, and it follows that micells can also be micro‐crystals. When an iron(III)chloride solution is neutralized fast with a strong base, an ‘amorphous’ precipitation is obtained which gives with MoKα‐X‐rays only two broad reflections, showing that the iron oxide hydroxide octahedra are condensed in a highly disordered way. The coherently scattering areas of this precipitate are probably tetramers. Small amounts of primarily formed amorphous iron(III)hydroxide are transformed into β‐FeOOH.