LINUS PAULING 



electron were promoted to a p orbital, giving configuration d 5 p (with 

 one d orbital used for bonding), there might occur hybridization be- 

 tween the states 5 P 3 , 5 D 3 , and 5 F 3 , with moments 5-78, 5-19, and 4-32 

 respectively. The observed moment indicates that this hybrid does 

 represent the structure of the iron complex in ferrihaemoglobin, and 

 also the structure of the hexahydrated ferrous ion, which has reported 

 moment 5-2. 



In ferric compounds the configuration d'° leads to a 6 S 5/2 state, with 

 moment 5-92. This structure might interact with 6 P 5/2 and 6 A> /2 from 

 the configuration d*p, their moments being 5-58 and 4-90 respectively. 

 The observed moments 5-92 for the hexahydrated ferric ion, 5-90 for 

 ferrihaemoglobin fluoride, and 5-89 for the ethanol-ferrihaemoglobin 

 complex indicate that for these complexes the configuration is very 

 close to d h . For ferrihaemoglobin itself, with moment 5-77 in solutions 

 of moderate acidity and 5-46 in very acid solution, an increasing con- 

 tribution of the configuration d*p for the odd electrons is indicated by 

 the change in magnetic properties. 



The magnetic moment of ferrihaemoglobin hydroxide, 4-45, suggests 

 that there are three unpaired electrons in the complex. This situation 

 would result in case that five orbitals were used for bonds, leaving four 

 orbitals for occupancy by the five outer electrons of the ferric atom. 

 The configuration d 1 leads to 4 P 5/2 as the normal state, with moment 

 4-73. Resonance with d 7i F 5l2 (moment 3-04), or with other states 

 based on promotion of an odd electron to a p orbital, might explain 

 the observed moment. 



It is evident from the foregoing discussion that the possibilities of 

 progress in the understanding of the structure of haemoglobin through 

 the investigation of its magnetic properties have not been exhausted. 

 Haemoglobin is one of the most interesting and important of all sub- 

 stances, and even the great amount of work that would be needed for 

 a complete determination of its structure, involving the exact location 

 of each of the many thousands of atoms in its molecule, would be 

 justified. 



Received November 1948 



REFERENCES 



1 Conant, J. B. Harvey Lect. 28 (1932) 159 



2 Pauling, L. and Coryell, C. D. Proc. nat. Acad. Sci., Wash. 22 (1936) 210 



3 Coryell, C. D., Stitt, F. and Pauling, L. /. Amer. chem. Soc. 59 (1937) 633 



4 — and Stitt, F. /. Amer. chem. Soc. 62 (1940) 2942 



5 Russell, C. D. and Pauling, L. Proc. nat. Acad. Sci., Wash. 25 (1939) 517 



6 Pauling, L. Stanford Med. Bull. 6 (1948) 215 



7 — The Valences of the Transition Elements, Victor Henri Memorial Volume 

 Desoer, Liege, 1948 



64 



