Mg(I)-Fe(-II) and Mg(0)-Mg(I) covalent bonding in the Mg n Fe(CO) 4 - ( n = 1, 2) anion complexes: an infrared photodissociation spectroscopic and theoretical study.

Heteronuclear magnesium-iron carbonyl anion complexes MgFe(CO) 4 - and Mg 2 Fe(CO) 4 - are produced in the gas phase and are detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The geometric structures and the metal-metal bonding are discussed with the aid of quantum chemical calculations. Both complexes are characterized to have a doublet electronic ground state with C 3v symmetry containing a Mg-Fe bond or a Mg-Mg-Fe bonding unit. Bonding analyses indicate that each complex involves an electron-sharing Mg(I)-Fe(-II) σ bond. The Mg 2 Fe(CO) 4 - complex involves a relatively weak covalent Mg(0)-Mg(I) σ bond.