106 



P. George, J. Beetlestone and J. S. Griffith 



compounds in which the bonding of OH" is unequivocal (see Basolo and 

 Pearson, 1958), e.g. 



Fe(H20)6+++ ^ Fe(Hp)50H++ + H+, ^K = 2-2 (2) 



Co(NH3)5H20+++ ^ Co(NH3)50H++ + H+, p^ = 5-7 (3) 



rra«^Co(en)2N02 • H2O++ ^ transCo(Qn)^N02 • OH+ + H+, ipK = 6-4 (4) 



Secondly, the changes in spectrum and magnetic susceptibility when the ferri- 

 haemoproteins ionize are similar to those which accompany the formation of 

 complexes where other ligands such as F~ CN~ N3-, HS", etc., are bonded 

 to the iron. Yet the remote possibiUty that these changes originate in the 

 ionization of a group distant from the iron, but, for instance, connected to it 

 via a conjugated system of double and single bonds, cannot be excluded. 



Following the general practice it will be assumed that hydroxides are 

 produced, although the correlation developed in Section IV between spectro- 

 scopic and magnetic properties is equally valid provided that the same 

 structural feature is present in the alkaline forms of all the ferrihaemoproteins 

 upon which the calculations are based. 



THE INTERPRETATION OF THE MAGNETIC MOMENTS OF THE 

 HYDROXIDES ACCORDING TO VARIOUS THEORIES OF THE 

 ELECTRONIC STRUCTURE OF CO-ORDINATION COMPLEXES 



Coryell, Stitt and Pauling (1937) were the first to measure the magnetic 

 moment of one of these hydroxides, and obtained 4-47 Bohr magnetons for 

 the ferrihaemoglobin derivative. This value differed in a striking manner, not 

 only from the values found for acidic ferrihaemoglobin and the F~ complex, 

 5-80 and 5-92 B.M., but also from those for the CN~ and SH~ complexes, 

 2-50 and 2-26 B.M. These other moments were in close agreement with 

 the theoretical values calculated from the contribution of five and one 

 unpaired electrons respectively. For five unpaired electrons the electronic 

 configuration corresponds to ^S of the free ion, and therefore one expects a 

 magneton number very close to the free spin value of 5-92 (see Table 2) as, 



Table 2. Spin magnetic moments for metal comple xes conta ining 

 from one to five unpaired electrons, /< = v n{n + 2) 



Unpaired electrons, n 

 /<, Bohr magneton 



1 



1-73 



2 

 2-83 



3 

 3-87 



4 

 4-90 



5 

 5-92 



for example, in (NH4)3FeF6. For one unpaired electron there is a spatial 

 degeneracy of three, and associated with this a considerable orbital magnetic 

 moment. The observed magneton number for K3Fe(CN)6 is 2-33 compared 

 with the spin-only value of 1-73, and the large diff'erence is due to the orbital 

 moment combined with effects of the spin-orbit coupling (Howard, 1935; 



