Application of gas phase cryogenic vibrational spectroscopy to characterize the CO2, CO, N2 and N2O interactions with the open coordination site on a Ni(I) macrocycle using dual cryogenic ion traps

Abstract

Recent advances in gas phase ion chemistry, coupled with cryogenic ion vibrational predissociation spectroscopy, provide a powerful way to characterize the structures of small molecules bound to open coordination sites of organometallic compounds. Here we extend our previous measurements on the relatively weakly interacting CO2 molecule with a Ni(I) tetraaza-macrocyclic compound to enable the characterization of more strongly interacting substrates. We first confirm the calculated η2–C,O binding motif of CO2 using isotopic labeling by direct, one photon vibrational predissociation of the Ni(I)-CO2 complex. We then apply this approach to study complexation of N2 at the active site. The generality of the method is then expanded to include application to more strongly bound systems that cannot be photodissociated with one IR photon. This involves implementation of a recently developed scheme (Marsh et al., 2015) involving two temperature-controlled ion traps. The first is optimized to complex the substrate molecule to the active site and the second is cooled to around 10K to enable condensation of weakly bound “tag” molecules onto the target complex so as to enable its characterization by linear vibrational predissociation spectroscopy. We demonstrate this capability by applying it to the coordination of CO to the active Ni(I) site, as well as to elucidate the nature of the products that are formed upon reaction with N2O.