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 ] À anion forming a Fe!Ca dÀd dative bond in the [(CO) 6 Ca-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 À d bond between calcium and a transition metal.