PNNL

Abstract

Nitro-functionalized undecahalogenated closo-dodecaborates [B12X11(NO2)]2- were synthesized in high purities and characterized by NMR, IR, and Raman spectroscopy, single crystal X-diffraction, mass spectrometry, and gas-phase ion vibrational spectroscopy. The NO2 substituent leads to an enhanced electronic and electrochemical stability compared to the parent perhalogenated [B12X12]2- (X = F - I) dianions evidenced by photoelectron spectroscopy, cyclic voltammetry, and quantum-chemical calculations. The stabilizing effect decreases from X = F to X = I. Thermogravimetric measurements of the salts indicate the loss of the nitric oxide radical (NO•). The homolytic NO• elimination from the dianion under very soft collisional excitation in gas-phase ion experiments results in the formation of the radical [B12X11O]2-•. Theoretical investigations suggest that the loss of NO• proceeds via the rearrangement product [B12X11(ONO)]2-. The O-bonded nitrosooxy structure is thermodynamically more stable than the N-bonded nitro structure and its formation by radical recombination of [B12X11O]2-• and NO• is demonstrated. M.C.N is grateful for a Kekulé Fellowship from the Fonds der Chemischen Industrie. J.W. is grateful for a Freigeist Fellowship of the Volkswagen Foundation and thanks Prof. Bernd Abel for providing access to an LTQ Orbitrap-XL. K.R.A gratefully acknowledges instrumental support from the Fritz-Haber-Institute of the Max-Planck-Society. The photoelectron spectral work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, the Division of Chemical Sciences, Geosciences and Biosciences, and was performed using EMSL, a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory, which is operated by Battelle Memorial Institute for the DOE.