Complexes of lithium cation with nitrogen trifluoride: a computational investigation on the structure and stability of Li~+-(NF_3) isomers

摘要

The structure and stability of the still experimentally unknown Li~+-(NF_3) ions have been theoretically investigated at the B3LYP, QCISD, QCISD(T), and CCSD(T) levels of theory in conjunction with the 6-311G(d), 6-311+G(2d), and 6-311+G(3df) basis sets. Irrespective of the employed theoretical level, it was found that the ligation of Li~+ to the F atoms of NF_3 may occur in two distinct ways, leading to the formation of the monocoordinated isomer 2 and the dicoordinated isomer . These two isomeric ions are practically degenerate and more stable than the nitrogen-coordinated isomer 1 by ca. 6 kcal - mol~(-1). In addition, the optimized geometries of the Li~+-(NF_3) isomers 1, 2, and 3 and the analysis of their chemical bonding indicate the formation of ion-dipole complexes between Li~+ and NF_3. The Li~+ ion affinity of NF_3 at 298.15 K is computed as 15.6 kcal mol~(-1) at the B3LYP/6-311+G(3df) level of theory, 13.3 kcal mol~(-1) at the QCISD(T)/6-311+G(2d) level of theory, and 12.8 kcal mol~(-1) at the B3LYP/6-311+G(3df) level of theory, 13.3 kcal mol~(-1) at the QCISD(T)/6-311+G(2d) level of theory, and 12.8 kcal mol~(-1) at the CCSD(T)/6-31+G(2d) level of theory. These values are large enough to suggest the possibility that lithiated NF_3 could be actually observed as a stable species in the gas phase. From the applied pint of view, this finding supports the proposal that Li~+ ion attachment mass spectrometry, recently proposed by Fujii [J. Phys. Chem. A 104 (2000) 9613] as a conceivable technique to quantify the emissions of the greenhouse gases CF_4, C_2F_6, C_4F_8, and SF_6 from the electronic industry, could be also employed to quantify the emissions of NF_3, one of the perfluorocompounds most extensively used in semiconductor technology.