Binary Dioxygen Complexes of Nickel, Palladium, and Platinum, M(O2) and (O2)M(O2), in Low Temperature Matrices

Abstract

The cocondensation reactions of nickel, palladium, and platinum atoms with gaseous oxygen or dilute oxygen–argon mixtures at 4.2–10 °K give rise to binary transition metal dioxygen complexes. Variable concentration and diffusion controlled warm up studies, 16O/18O isotopic substitution studies, normal coordinate and isotope intensity calculations establish the complexes to be of the types M(O2) and (O2)M(O2). Both the mono- and bisdioxygen complexes contain the dioxygen molecules coordinated to the metal atom in a side-on fashion, with a unique D2d "spiro"-type structure favored for the bis-complexes. Frequency and bond stretching force constant trends within the series of complexes are examined and suggest that the O—O and M—O values increase with increasing coordination number, and thus with an increase in partial positive charge on the metal. This trend in O—O stretching frequencies is not in accord with the evaluation of metal–dioxygen bond strengths as based on the degree of reversibility of dioxygen coordination.