The isolobal fragments Fe(CO)3 and CpCo are predicted to form a variety of analogous car...

The isolobal fragments Fe(CO)₃ and CpCo are predicted to form a variety of analogous carbonyl complexes, for example,

In each case the cobalt compound is predicted to have a substantially shorter metal–metal bond than the analogous iron compound, even though the bond orders of the related compounds are the same. Suggest two reasons for this phenomenon. (See H. Wang, Y. Xie, R. B. King, H. F. Schaefer III, J. Am. Chem. Soc. , 2005 , 127 , 11646.)