June 11, 1951

Professor Worth Rodebush

Chemistry Department

University of Illinois

Urbana, Illinois

Dear Worth:

I am writing to tell you and Clausen about some new developments in the matter of hydrates.

First, I have found a reference is Fiat Review of German Science to work done by von Stacklberg and students around 1940 on various hydrates, including xenon hydrate. All of these hydrates have a cubic unit of structure considerably smaller than the one that you have proposed. Their unit is 12Å on edge.

I noticed that one of the intermetallic compound structures that we have been discussing seems to be closely related to the hydrate structure. When we replace metal atoms of one kind with water molecules, and a group of metal atoms of a second kind with xenon atoms or chlorine molecules or other similar molecules, we obtain a structure of the 46 water molecules and either 6 or 8 other molecules in the unit. This structure seems to be the structure of the various hydrates. It is somewhat similar to yours in that the hydrogen bond angles are all rather close to the tetrahedral angle. The hydrogen bond distance is close to 2.76 Å. Von Stacklberg had proposed a structure, which I am sure is wrong -it includes water molecules only about 2.4 Å from one another, and with hydrogen bond angles as small as 60º.

I do not know whether von Stacklberg has published any intensity data for his x-ray photographs, or whether these data are available only in the theses. We hope to find out before long. In any case we could easily take x-ray photographs of the hydrates here, if it is necessary.

I am writing now to say that it seems to me probably unnecessary for you to go to the work of preparing x-ray photographs of these hydrates.

Sincerely Yours,

Dictated by Linus Pauling

Signed in his absence:W