Binding Motifs of Doubly and Singly Charged Proton-Bound Clusters of B ₁₂ F ₁₂ ^2– and Diaminoalkanes

The complexation of perfluorinated dodecaborate, B₁₂F₁₂^2-, with protonated diaminoalkanes, [H₂N(CH₂)<i>_n</i>H₂N] (<i>n=</i> 2 - 12), is studied with a combination of infrared multiple photon dissociation (IRMPD) action spectroscopy and ion mobility spectrometry. Singly charged clusters of the form [B₁₂F₁₂ + H₂N(CH₂)<i>_n</i>H₂N + H]^- (<i>n =</i> 2-12) and doubly charged clusters of the form [2B₁₂F₁₂ + H₂N(CH₂)<i>_n</i>H₂N + 2H]^2- (<i>n =</i> 2-12) are observed and characterized experimentally and computationally. For the singly charged clusters, low-energy structural motifs associated with monodentate and bidentate binding motifs of the diaminoalkane are computed via a combination of CREST conformer exploration and density functional theory. For the doubly charged clusters, the doubly protonated diaminoalkane acts as a tether between two B₁₂F₁₂^2- cages. Major product channels of the singly charged and doubly charged species are found to be the formation of HB₁₂F₁₂^- via proton transfer and the loss of B₁₂F₁₂^2-. The fragmentation of HB₁₂F₁₂^- leads to several secondary products, including [B₁₂F₁₁ + N₂]^-. Collision cross sections (CCSs) for the singly charged clusters are reported, and the major subpopulation of the gas phase ensemble for the different singly charged species is the bidentate conformation.