The structural chemistry of iron

The only bond arrangement established for Fe(0) is the trigonal bipyramidal arrangement of five bonds, as in Fe(CO)s, and Fe(CO)3(diarsine) (d). 

The normal coordination of Fe(ii) is octahedral. Many of the ionic compounds in which Fe is surrounded by 6 X or 6 0 are isostructural with those of other metals forming similarly sized ions  

The structural similarity between these M(ii) compounds does not, however, extend to the more covalent compounds. For example, the complex cyanides formed by Fe, Co, and Ni are of quite different kinds  

The octahedral complexes of Fe(ii) are high-spin (ju 5 BM) except for those containing strong-field ligands such as Fe(CN)g and Fe(CNR)6 , which are diamagnetic. Neutral molecules include /ra s-Fe(NCS)2(py )4 (e). 

Tetrahedral coordination of Fe(ii) is comparatively rare, and in fact has not yet been directly established by a structure determination. It has been deduced from the existence of compounds isostructural with analogous compounds of Mn, Co, or Ni  

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