X-RAY-ABSORPTION PRE-EDGE STUDIES OF HIGH-SPIN IRON(II) COMPLEXES

Fe K-edge X-ray absorption spectroscopy is utilized to study a series of 22 synthetic high-spin iron(II) complexes. The 1s --> 3d pre-edge p eak of each complex is quantitated and compared with the others in ord er to explore its correction with the coordination number and symmetry of the iron center. Like the high-spin iron(III) complexes (Roe,A.L,; Schneider,D.J.; Mayer,R.J.; Pyrz,J.W. Que,L.,Jr. J. Am. Chem. Soc. 19 84, 106, 1676-1681), the iron(ll) complexes can be grouped on the basi s of their normalized pre-edge peak intensities: the six-coordinate co mplexes have pre-edge areas from 4 to 6 units, the five-coordinate fro m 8 to 13 units, and the tetrahedral 16 to 21 units. Three six-coordin ate ''iron(II)'' nitrosyl complexes examined have pre-edge areas compa rable to those of normal iron(II) five-coordinate complexes due to the ir highly distorted geometry. The information obtained here can be use d to deter;niiie the coordination number of the high-spin iron(lI) cen ters in iron(II)-containing proteins and other model complexes and to complement analyses based on extended X-ray absorption fine structure (EXAFS).