Photochemistry of chloro-, bromo-, and iodo-pentacarbonylmanganese in frozen gas matrices at 12 K. Infrared spectroscopic evidence for tetracarbonylhalogenomanganese species with a C2ν trigonal-bipyramidal structure

Abstract

Infrared spectroscopic evidence, including ¹³CO labelling and energy-factored force-field fitting for [Mn(CO)₅Cl] and [Mn(CO)₄Cl], is presented to show that on photolysis of [Mn(CO)₅X](X = Cl, Br, or I) complexes at high dilutions in Ar and CH₄ matrices at 12 K new species [Mn(CO)₄X], with the X ligand occupying an equatorial position in a trigonal-bipyramidal structure and having C_2v symmetry, are produced. The observations of CO ejection, the formation of a co-ordinatively unsaturated species, and the reversibility of the reaction (i) are interpreted as [Mn(CO)₅X] [graphic omitted] [Mn(CO)₄X]+ CO (i) confirming the existence of a co-ordinatively unsaturated species as the intermediate in the substitution reactions of [Mn(CO)₅X] complexes; i.e. the reaction follows the dissociative path proposed from previous kinetic studies.