Highly Coordinated Heteronuclear Calcium-Iron Carbonyl Cation Complexes [CaFe(CO)n ]+ (n=5-12) with d-d Bonding.

Abstract

Heteronuclear calcium–iron carbonyl cation complexes in the form of [CaFe(CO)n]+ (n=5–12) are produced in the gas phase. Infrared photodissociation spectroscopy in conjunction with quantum chemical calculations confirm that the n=10 complex is the coordination saturated ion where a Fe(CO)4 fragment is bonded with a Ca(CO)6 fragment through two side‐on bridging carbonyl ligands. Bonding analysis indicates that it is best described by the bonding interactions between a [Ca(CO)6]2+ dication and an [Fe(CO)4]− anion forming a Fe→Ca d−d dative bond in the [(CO)6Ca–Fe(CO)4]+ structure, which enriches the pool of experimentally observed complexes of calcium that mimic transition metal compounds. The molecule is the first example of a heteronuclear carbonyl complex featuring a d−d bond between calcium and a transition metal.