Fe-X bonds

The broken bonds (boldface = dissociated fragment) BDEs (boldface = recommended data reference in parentheses) Methods (reference in parentheses)  

Fe(CO)2(dmpe)-CO, dmpe = l,2-bis (dimethyl-phosphino)ethane 36.1 151 PAC 1993NAY/BUR 

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The dependence of Fe—X bond length on the nature of the halide X and on the oxidation state and coordination number of the iron in about 300 species containing FeX units has been documented. 

If, however, covalent Fe—X bonds are formed with use of two of the 3d orbitals (as well as some of the other orbitals—see Chap. 5), as in the ferricyanide ion, [(Fe(CN) ]", then the five unshared 3d electrons of the iron atom must crowd into the remaining three 3d orbitals, with formation of two pairs. This complex contains only one unpaired electron, whereas the complexes of the first kind contain five unpaired electrons. Transition between these structures cannot be continuous. 

It is proposed that these complexes decompose by homolytic cleavage of the Fe-X bond (355). 

The inner-shell barrier for reduction of high-spin iron (III) porphyrins consists of contributions from both metal atom out-of-plane displacement and axial ligand bond stretching. The influence of the latter term can be assessed by comparing the rate of Fe (111) /Fe (II) reduction with the strength of the Fe-X bond. The force constant for... 

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