September 21, 1936
Dr. Egon Wiberg
Technischen Hochschule Krlsruhe
Karlsruhe, Germany
Dear Dr. Wiberg:
I am glad to inform you that we have finally obtained a little more direct evidence regarding the nature of the boron hydrides. Dr. Bauer and I have completed the electron diffraction investigation of B5H9, which was found to have the structure shown below.
[diagram of structure]
The whole molecule is coplanar, the boron-boron distances being about 1.76 A., which is only slightly smaller than the single bond separation, and the boron-hydrogen distance being about 1.18 A., the single bond valence. Our paper will be published in the Journal of the American Chemical Society in a couple of months. I am not sure as to what the electronic structure corresponding to this atomic configuration is, but a reasonable structure can be written in which each boron is attached to other borons by electron pair bonds and to hydrogen atoms by either electron pair bonds or one electron bonds, there being four of the latter.
Sincerely yours
Linus Pauling
LP:ml
September
21, 1936
