Journal of the American Chemical Society
COMMUNICATION
Computing Grant CHE07-0004N, fluorine from J. Thrasher, and
helpful suggestions from D. A. Dixon.
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Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937. The
Ga-F stretching frequencies computed using the BPW91 functional are
30 cm-1 lower than the values obtained using B3LYP.
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Figure 4. Calculated structure of (F2)GaF2. B3LYP values using the
aug-cc-pVTZ basis set for F and Ga are in normal type, and CCSD(T)
values using the 6-311þG(3df) basis set for F and the SDD (large core)
set for Ga are in bold type.
The observation of the Tl(III) molecule TlF3 is important in
its own right. Although the decreasing stability of trivalent
fluorides from B to Tl is well-known, quadratic configuration-
interaction calculations of the TlF3 f TlF þ F2 reaction energy
predicted stability for the TlF3 molecule.20
The interesting group 13 chemistry trend here should be noted:
the observed antisymmetric and symmetric modes for (F2)BF2 are
just a little higher than the same modes for BF2 but much lower than
the antisymmetric B-F mode for BF3. However, for the heavier
metals, the terminal M-F modes for (F2)MF2 increase relative to
that for the MF3 molecule. Finally, the strong mode for (F2)TlF2 is
located at a higher wavenumber than the antisymmetric Tl-Fmode
for TlF3, suggesting the participation of electron-occupied d orbitals
for Tl in charge transfer, which allows the Tl-F bonds to be more
polarized. The calculated Mulliken atomic charges range from þ1
for the B product to þ2 for the Tl product.
Electron-deficient group 13 metals react with electron-rich F2 to
give the compounds MF2, which further combine with F2 to form
the very high electron affinity neutral adduct molecules (F2)MF2 in
reactions that are exothermic by amounts ranging from 128 kcal/
mol for AlF2 þ F2 to 49 kcal/mol for TlF2 þ F2 (Table 1). These
(F2)MF2 molecules are unique: the two longer M-F bonds in
(F2)MF2 include the weak F F interaction using three-elec-
3 3 3
tron-three-center bonds, which is substantiated by a natural bond
orbital analysis of the DFT-computed molecular orbitals. The
computed structure of (F2)GaF2 is given in Figure 4. Notably,
the F F bond length is near that calculated for one-electron-
3 3 3
-
bonded F2 and the calculated F0-F0 stretching frequencies
(Table 1) are in the range of those measured for the alkali metal
(Mþ)(F2-) species.12,21 However, this weak F F bond is
3 3 3
cleaved upon electron attachment to give the very stable tetrahedral
anion MF4-. The electron affinities calculated with CCSD(T) fall
between 7.8 eV for (F2)AlF2 and 7.0 eV for (F2)TlF2 (Table 1) for
this new class of very high electron affinity molecules.
’ ASSOCIATED CONTENT
S
Supporting Information. Complete ref 6, calculated
b
GaFx product frequencies and Mulliken atomic charges, and
additional IR spectra. This material is available free of charge via
(19) Hassanzadeh, P.; Citra, A.; Andrews, L.; Neurock, M. J. Phys.
Chem. 1996, 100, 7317.
’ AUTHOR INFORMATION
(20) (a) Schwerdtfeger, P.; Heath, G. A.; Dolg, M.; Bennett, M. A.
J. Am. Chem. Soc. 1992, 114, 7518 and references therein. (b) Schwerdtfeger,
P.; Ischtwan, J. J. Comput. Chem. 1993, 14, 913.
Corresponding Author
(21) Howard, W. F., Jr.; Andrews, L. J. Am. Chem. Soc. 1973,
95, 3045.
’ ACKNOWLEDGMENT
(22) Hassanzadeh, P.; Andrews, L. J. Phys. Chem. 1993, 97, 4910.
We gratefully acknowledge financial support from NSF Grant
CHE 03-52487 to L.A., NSFC Grant 20973126 to X.W., and NCSA
3771
dx.doi.org/10.1021/ja1110442 |J. Am. Chem. Soc. 2011, 133, 3768–3771