444 IRON-CONTAINING PROTEINS AND ENZYMES
orbital forming aσ bonding interaction; and (2) the peroxide π v orbital
donates electron density into the dxy Fe III orbital, forming a δ - bonding
interaction. The peroxide π σ orbital ’ s interaction with both the half - occupied
dz^2 Cu II orbital ( η^1 ) and the dxz Fe III orbital ( η^2 ) forms a “ superexchange ”
pathway for strong antiferromagnetic coupling between the metal centers.
The two highest - occupied orbitals of the peroxide ion would normally be
the degenerate π orbitals, but these split under the infl uence of the
metal centers. The π σ orbital resides in the Fe – O 2 – Cu plane, while the π *v
orbital is perpendicular to this plane. The DFT calculations were also used to
determine bond distances and angles for fully optimized and constrained
(.)[()()()]Fe =−− 37 Å III^22 −+II model structures. Data are Cu P Fe O Cu TMPA
reported in Table 7.9.
The [( 82 ) III−−(^2 −+) II( )] F TPP Fe complex was also studied using O Cu TMPA
Cu and Fe K - edge extended X - ray absorption - fi ne structure (EXAFS) spec-
troscopy in the solid state and in acetonitrile solution by reference 153 authors.
The data were fi t with a Fe · · · Cu distance of ∼ 3.72 Å. Very little change
in bond distances or angles were found between the solid versus solution
EXAFS results. In general, there is good agreement between the found
X - ray crystallographic bond distances and angles (for Naruta ’ s tethered
[(TMP)FeIII−−() (O^22 −+CuII 5 MeTPA)] complex, reference 155 ) and those
found for the EXAFS experiments as well as the calculated values from DFT
calculations. Differences are noted in the Fe – Cu distances, with the fully opti-
mized DFT calculated structure (Fe – Cu = 4.006 Å ) agreeing better with the
Figure 7.46 Crystal structure of tethered [( ) III−−( 22 −+) II( 5 ] TMP Fe. O Cu MeTPA)
(Reprinted with permission from Figure 7 of reference 138. Copyright 2004 American
Chemical Society.)
CuO(3) O(2)Fe