Ruthenium Dichloride, RuCl₂

Ruthenium Dichloride, RuCl₂, was stated by Claus to result when chlorine is passed over heated ruthenium. Repetition of the experiment by Gut bier and Trenkner in 1905 led to no definite result, varying amounts of chlorine being absorbed, but always considerably less than theory requires for the dichloride. The experiments were by no means exhaustive, and do not justify the assumption that the dichloride cannot be prepared in this way. As Gutbier points out, it is quite possible that a reversible reaction takes place between the ruthenium and chlorine, thus:

Ru + Cl₂ ⇔ RuCl₂.

In view of the catalytic activity of the metals discussed in this volume the subject is worthy of more careful investigation.

Some forty years before the discovery of ruthenium by Claus, it had been observed by VauqueJin that an azure blue colour is obtained by the action of zinc on certain solutions. This was attributed to the presence of osmium, but is now known to be a characteristic reaction for trivalent ruthenium. A similar colour is obtained by the action of hydrogen sulphide upon ruthenium trichloride, and was attributed by Claus and Joly to reduction to the dichloride. This view is supported by Howe, who, however, has not succeeded in isolating the salt, but has obtained a derivative to which he gives the formula:

3CsCl.2RuCl₂.2H₂O.

This salt is readily formed by the reduction of ruthenium trichloride in an electrolytic cell, and immediately adding a concentrated solution of cesium chloride to the blue liquid. A fine precipitate results, varying in colour from a dark greenish blue to olive green, and which oxidises with great rapidity, rendering analysis difficult.