Synthesis, Electronic Properties and Reactivity of [B12X11(NO2)]2− (X=F–I) Dianions

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. © 2020 The Authors. Published by Wiley-VCH GmbH