Report on Research: Supported by Rockefeller Fund, July 1, 1932- July 1, 1933
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1933-10-24 (October 24, 1933)
Original Repository: Oregon State University. Library. Ava Helen and Linus Pauling Papers
Reproduced with permission of the Ava Helen and Linus Pauling Papers. Oregon State University Library.
Medical Subject Headings (MeSH):
The Search for the Molecular Helix
Report on Research
Supported by Rockefeller Fund, July 1, 1932 -- July 1, 1933
During the year 1932-3 I have been assisted in researches carried on with the aid of the Rockefeller Fund by eleven men, of
who four were on whole-time or half-time appointment to Research Fellowships or Assistantships supported by this Fund (Dr.
J.H. Sturdivant, Dr. GW Wheland, Dr. J. Sherman, and Dr. S. Weinbaum) and even not (Dr. H.P. Klug, Dr. E. Neuman, Dr. E B
Wilson Jr, Dr. L.O. Brochway, Dr. R. Hultgren[?], Mr. BN Dickinson, and Mr -- Medlind. An account of the work is given in
the following pages. Signed, L.P.
The general problem under investigation is the experimental determination of the structure of molecules and crystals in terms
of atoms and ions or electrons and nuclei and the development of structural theories correlating and extending the results
of experimental investigation. Because of it extent, this problem is broken up into a large number of smaller investigations,
dealing with on chemical substance or a group of related substances, or with one type of structure. Since July 1, 1932 we
attached thirty or more such problems, and have carried about twenty-five investigations to completion. Papers communicating
the results of twenty of these will have been published by August 1, 1933; these titles are listed at the end of this report.
Of these papers, ten are mainly theoretical in nature, and ten experimental, indicating the essential equality of the emphasis
placed on theoretical and experimental work in our program.
The experimental investigations involve mainly the determination of the structure of crystals by x-ray diffraction of electron
waves. In addition measurements of magnetic susceptibility, heat capacity, transition points, etc are made. The
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theoretical work consists in the rigorous or approximate solution of the Schrodinger wave equation for simple atoms and molecules,
the approximate quantum-mechanical treatment of complex molecules the formulation of empirical rules compatible with quantum-mechanical
ideas by the analysis of experimental data, etc.
The discussion of the researches may be given in several parts, corresponding to different classes of substances; namely,
1. Ionic molecules and crystals, including the silicate minerals.
2. The sulfide minerals and other inorganic crystals containing covalent bonds.
3. Organic molecules and crystals. The covalent bond in general.
4. Substances containing the three-electron bond.
Ionic Molecules and Crystals.
The study of the structure of ionic molecules and crystals has led during the last five or six years to the formulation of
generally-accepted sets of ionic radii and of empirical rules regarding the stability of different structures, so that it
can be considered that the principal problems in this field of investigation have been solved. Even such a difficult and
complicated subject as the structure of the silicate minerals has been completely clarified by this work. There remain however,
a number of interesting minor problems, some of which have been treated during the last year. The relation between ionic
radii and structure for oxygen acids has been discussed, leading to the recognition of the correct formula HS [ . . . ] of
antimonic acid (1). Dr Sherman, who had
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previously written a detailed account of Madeling constants and the calculation of crystal energies, has published a note
on the Madeling constant of cuprite (2). Mr M D Shappell has discussed the cleavage of ionic minerals in relation to crystal
structure. Brochway and Professor Pauling have investigated the substances SF6, SeF6, and TeF6 by electron diffraction, the
molecules being found to be octahedral, with interatomic distances in good agreement with those predicted from ionic radii
(3). PF5 has been found to have the configuration of a square pyramid of F atoms, with the P atom nearly in the basal plane.
Crystal structure investigations of zimyite[?], Al13Si5 O20 (Ok,F)18Cl (4), RbNO3 (5), NH4HF2(6), and Na7(PO4)2F 19H20 (7)
have been carried out. Dr. Hultgren has found from powder photographs that NH4VO3 does not have the perovskite structure.
Investigations are at present under way on Hg3TeO6, (NH4)2H3IO6, Al(PO3)3, CsAlSi2O6, and other crystals.
The Sulfide Minerals and Other Inorganic Crystals.
The structural nature of the large group of sulfide minerals, which includes most of the heavy-metal ore minerals and is in
consequence of great practical importance, is not yet understood. Despite attack on the problem by a number of investigators,
only a few sulfide crystal structures have been worked out. During the last year Professor Pauling and Dr. M L Huggins have
completed the formulation of tables of atomic radii for use in crystals and molecules containing covalent bonds. With [ .
. . ] of these tables and of recently-developed theories of the covalent bond, in conjunction with experimental investiga--
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tions, it is hoped that the structural principles underlying the sulfide minerals will soon be discovered. With this end
in view, a number of crystal structure investigations have been carried out as part of our program. The correct structures
of chalcopyrite, CuFeS2 (8), and sulvanite, Cu3VS4 (9), have been published. For both of these minerals incorrect structures
had been reported by previous investigators. The structure of sulvanite is particularly interesting, inasmuch as it differs
in a remarkable way from the sphalerite structure. Dr. Hultgren has shown from powder photographs that germanite has a sphalerite-type
structure rather than the sulvanite structure. Enargite, Cu3AsS4, has been found to have a [ . . . ] structure, and bimmite[?],
Cu3AsS3, to have the same structure as tetrahedrite.
Other inorganic crystals containing covalent bonds whose structures have been determined or are under investigation are K2SeBr6
(10), by Dr. Hoard and Mr. Dickinson, KSCN (11), by Dr. Klug, Pol(NH3)4Cl2 H20, by Mr. Dickinson, rhombic sulfur and monoclinic
selenium, by Dr. Klug, and CaB6, by Professor Pauling. Dr. Hultgren has also been studying the system Ce[?] -- Ru by x-ray
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Organic Molecules and Crystals. The Covalent Bond.
As a preliminary step to the discussion of the structure of molecules, Dr. Wilson has been solving the Schrodinger wave equation
for light atoms. After a study of the helium problem, he has found a reasonably accurate wave function involving four parameters
for normal lithium (12). The extension of this treatment to normal beryllium, however, has not been very successful, and
he hopes to improve the treatment greatly by introducing the inter-electronic distances in the wave functions. Mr. Dickinson
has applied the Rosen treatment to the hydrogen molecule-ion (13) and Dr. Weinbaum has discussed the normal hydrogen molecule,
with especial reference to the contribution of ionic structures (14).
As a result of the discovery of a simple method of calculating matrix elements for various electronic structures of molecules
(15), Professor Pauling, Dr Wheland, and Dr Sherman have made great strides in the application of quantum mechanics to organic
chemistry. The discussion of benzene and naphthalene has led to a quantitative knowledge of the contribution of various electronic
structures to the normal states of these molecules, completely answering the old question as to the nature of aromatic nuclei
(16). A similar treatment of hydrocarbon free radicals has provided an understanding not only of the general mechanism of
stabilization of the radicals, through resonance of the odd electron among several positions, but also of the varying relative
efficacy of different groups in producing stable radicals. An
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analysis of empirical data on heats of combustion of organic substances has provided strong evidence that many molecules are
resonating among several electronic structures, and has permitted the tabulation of resonance energies (17). The theoretical
study of resonance in conjugated systems of double bonds and aromatic nuclei, including the dihydronaphthalenes and dihydronaphthracenes[?],
phenylethylene, stilbene, iso-stilbene, O, M, and P diphenylbenzene, and 1, 3, 5 -- triphenylbenzene, has led to an understanding
of many properties of organic molecules such as for example, the relative ease of addition at different positions in naphthalene
and anthracene. This work is now being extended to heterocyclic compounds, chromophore groups, etc.
On the experimental side, the determination of the atomic configuration and the deduction of the resonating electronic structures
for methyl azide, cyanogens, diacetylene, and carbon suboxide have been carried out by Dr. Brochway and Professor Pauling.
Dr. Klug is studying organic crystals by x-ray methods including ortho-iodobnzoic acid (18), C2H4I2, C2H2I2, C2I2, etc.
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The Three-Electron Bond
Since the discovery of the three-electron bond in 1931, a number of molecules have been shown to contain it as an essential
part of the electronic structure. The theoretical treatment of the simplest molecule in which this bond occurs, He2, has
led to a thorough understanding of its [ . . . ] [ . . . ] (19). Electron-diffraction photographs made by Dr Brochway have
shown the existence of this bond in Clo2 (20). Moreover, the possibility that "potassium tetroxide, K2O4", might
actually be KO2, containing the ion [ . . . ], was investigated and verified by Dr Neuman by the determination of its magnetic
susceptibility. Dr. Neuman also found that potassium superoxide (as the substance may well be named) shows a transition at
about 150[degrees]A., correspondingly probably to the transition of the [ . . . ] ions to the lower of the two levels of the
doublet. Dr. Neuman is also studying the crystal structure of this substance. Polarographic experiments on solutions of
KO2 in bn KOH kindly indicate the presence of the superoxide ion in solution and further indicate that molecular oxygen and
peroxide ions react to form superoxide ions.
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Plans for 1933-4
During the next year it is planned to continue research in the fields discussed above, with especial emphasis on applications
to organic chemistry, with the hope that ultimately such problems as the structure of alkaloids, proteins, hemoglobin, etc.
can be solved. In addition a number of investigations are planned to be carried out with the aid of the new ionization spectrometer,
designed by Dr Sturdwant which is now completed and will soon be in operation.
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Published Papers, 1932-3
1. The Formulas of Antimonic Acid and the Antimonates. Linus Pauling, J.A.C.S. 55, 1895-1900 (1933).
2. Madeling[?] Constant Sherman Phil Mag.
3. SF6 etc Brockway and P Not Acad
4. Zunyite P. Z Krist
5. RbNO3 P. and Sherman ZK
6. NH4HF2 P ZK
7. Na7 (PO4)2 F 19H2O Neuman ZK
8. Chalcopyrite P and B. ZK
9. Sulvanite, P and Hultgren ZK
10. K2SeBr6, Hoard and Dick. ZK
11. KSCN Klug ZK
12. Li Wilson J.C.P.
13. H2+ Dickinson JCP
14. H2 Weinbaum JCP
15. Matrix elements P. JCP
16. Arom. Sub. And Free Rad. P and Wheland JCP.
17. Res. Energies P and Sh. JCP
18. O- iodobenzoic acid Klug JACS
19. He2+ P. J.C.P.
20. ClO2 Brockway P.N.A.
Give titles etc as for 1.
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October 24, 1933.
Warren Weaver suggests sending in a request for extension of the fund immediately, action to be taken December 14th.
He says their policy is to support a definite biological program*. Atomic physics is definitely out. My work may be included
because of its bearing on biological problems, though ordinary work in organic chemistry would not be.
* Especially quantitative work in biology
In addition he has a small emergency fund which can be used for other problems. This is apportioned in December. I may come
in under it.