Thorium Fluorides ThF, ThF2, ThF3, ThF4, ThF3(F2), and ThF5– Characterized by Infrared Spectra in Solid Argon and Electronic Structure and Vibrational Frequency Calculations

Abstract

Reactions of laser-ablated Th atoms with F2 produce ThF4 as the major product based on agreement with matrix spectra recorded of the vapor from the solid at 800-850 °C. Weaker higher-frequency bands at (567.2, 564.8), (575.9, 575.1), and (531.0, 528.4) cm(-1) in argon are assigned to ThF, ThF2 and ThF3, ThF3(F2) on the basis of their chemical behavior upon increasing reagent concentrations, annealing, and irradiation, the use of NF3, OF2, and HF as F-atom sources, and a comparison with frequencies calculated at the DFT/B3LYP and CCSD(T) levels with a large segmented + ECP basis set on Th and the aug-cc-pVTZ basis set on F. An additional broader band at 460 cm(-1) is assigned to the ThF5(-) anion. The trigonal-bipyramidal ThF5(-) anion (calculated electron detachment energy of 7.17 eV) increases at the expense of ThF3(F2) and F3(-) on full mercury arc irradiation. [ThF3(+)][F2(-)] is shown by calculations to be an ionic complex with a side-bound F2(-) subunit. This paper reports the first evidence for novel pentacoordinated thorium species including the unique [ThF3(+)][F2(-)] ionic radical-ion pair molecule and its electron-capture product, the very stable ThF5(-) anion.