Gas‐phase Ion Stereochemistry of Iron Complexes probed by Mass Spectrometric Techniques

Abstract

Modern mass spectrometry (MS) evolved into a ‘complete chemical laboratory’, enabling studies to be performed on structure and reactivity of ionic species under environment‐free conditions. The advent of theoretical methods as a supplement to experimental MS data has expanded gas‐phase ion chemistry to include the stereochemical perspective. In the last decade IRMPD (infrared multiple‐photon dissociation) and IRSPD (infrared single‐photon dissociation) spectroscopy methods have been increasingly employed to directly probe the 3D structures of mass‐selected ions. This chapter aims to provide an overview (139 references) of gas‐phase ion stereochemistry of metal complexes as exemplified by Fe‐containing species, with a special emphasis on combined experimental/theoretical approaches and the advantages that this prolific partnership brought to the field. A survey of literature has revealed that circa 100 three‐dimensional structures of ionic Fe‐containing species have been characterized to date by both MS techniques and computational methods. These include coordinatively unsaturated organoiron species with various hydrocarbons, Fe complexes with homogeneous and heterogeneous conjugated cyclic hydrocarbons (including PAHs of astrophysical interest), anionic and cationic iron carbonyls, Fe complexes of N‐, O‐ and S‐donor ligands providing classical Werner‐type coordination sites. Some of these gaseous species adopt only a single stable structure, while others generate multiple conformers. In most cases, the reactivity of Fe‐containing species is oxidation‐state dependent. The nature of the ligands in a complex clearly influences the reactivity. With a decrease in the number of available coordination sites on the metal center, the gas‐phase reactivity decreases as well, with a concomitant increase in selectivity.