Abstract
The dissociations of nascent Fe(CO)5++ ions created by 40.81 eV photoionization of iron pentacarbonyl have been examined using threefold and fourfold electron–ion coincidence measurements. The energies and forms of the ions have been explored by high-level calculations, revealing several new structures. The most stable form of Fe(CO)5++ has a quite different geometry from that of the neutral molecule. The dissociation pattern can be modeled as a sequence of CO evaporations followed by two-body charge separations. Each Fe(CO)n++ (n = 1–4) dication is stable in a restricted energy range; as its internal energy increases, it first ejects a neutral CO, then loses CO+ by charge separation at higher energy. In the initial stages, charge-retaining CO evaporations dominate over charge separation, but the latter become more competitive as the number of residual CO ligands decreases. At energies where ionization is mainly from the CO ligands, new Fe–C and C–C bonds are created by a mechanism which might be relevant to catalysis by Fe.
Highlights
IntroductionTransition-metal ions in the gas phase are highly reactive chemical species, often characterized by complex reaction dynamics, an in-depth understanding of which defies both theory and experiment
Transition-metal ions in the gas phase are highly reactive chemical species, often characterized by complex reaction dynamics, an in-depth understanding of which defies both theory and experiment. These ions are capable, for instance, of breaking bonds in organic compounds such as the C−C bonds of hydrocarbons by means of metal insertion reaction mechanisms[1] or, in the case of iron carbonyl or naked iron cluster cations, these ions are capable of promoting C−C bond forming reactions.[2−4] Iron pentacarbonyl is the most stable complex of those with the general formula Fem(CO)n
We explore the stabilities and structures of the major dicationic species using the most advanced available computational methods
Summary
Transition-metal ions in the gas phase are highly reactive chemical species, often characterized by complex reaction dynamics, an in-depth understanding of which defies both theory and experiment. Experimental studies of CO ligand losses in transition-metal carbonyl cations are not straightforward but can be accomplished by several techniques, such as the threefold and fourfold electron−ion coincidence or threshold collisioninduced dissociation spectroscopies Such experiments are useful as providing thermochemical data for these species and as a fundamental tool giving insights into the complex intramolecular and fragmentation dynamics of these ions. One such technique has recently been applied, for example, to the investigation of the dissociative photoionization of the chromium hexacarbonyl complex[6] for which a revised value of the formation enthalpy has been proposed
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