Mg(i)–Fe(–ii) and Mg(0)–Mg(i) covalent bonding in the MgnFe(CO)4− (n = 1, 2) anion complexes: an infrared photodissociation spectroscopic and theoretical study

Abstract

Heteronuclear magnesium–iron carbonyl anion complexes MgFe(CO)₄⁻ and Mg₂Fe(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 Mg₂Fe(CO)₄⁻ complex involves a relatively weak covalent Mg(0)–Mg(I) σ bond.