6298 Inorganic Chemistry, Vol. 48, No. 13, 2009
Wang et al.
Experimental and Computational Methods
Laser ablated Ti (Goodfellow), Zr, and Hf (Johnson-
Matthey) atoms were reacted with NF3 (Matheson), PF3
(PCR Research), or AsF3 (Ozark-Mahoning, vacuum dis-
tilled from dry NaF) in excess argon during condensation at
5-8 K using closed-cycle refrigerators described elsewhere.17,18
Reagent gas mixtures were typically 0.5% in argon and the
laser ablated metal atom concentrations were much lower.
After reaction, infrared spectra were recorded at a resolution
of 0.5 cm-1 using Nicolet 550 or 750 spectrometers with
Hg-Cd-Te B range detectors. Samples were later irradiated
for 15 min periods by a mercury arc street lamp (175 W) with
the globe removed using a combination of optical filters, and
then samples were annealed to allow reagent diffusion and
further reaction.
Following our work on reactions with the isoelectronic
fluoroform molecule, theoretical computations were per-
formed using the Gaussian 03 program with the B3LYP
hybrid density functional and some comparisons with the
BPW91 functional.19-21 The 6-311+G(2d) basis was used to
represent the electronic density of nitrogen, fluorine, phos-
phorus, and arsenic atoms, and SDD pseudopotentials were
used for the metal atoms.22,23 Frequencies were computed
analytically, and allenergyvaluesreportedincludezero-point
vibrational corrections. The calculation of vibrational fre-
quenciesis not an exact science, and density functional theory
(DFT) provides a very good approximation for observed
frequencies. Calculated frequencies are usually a few percent
higher than observed values,24,25 but that is not always the
case. Finally, bonding analysis was done using the natural
bond orbital method in Gaussian 03.19,26
Figure 1. Infrared spectra for group 4 metal atom reaction products
with NF3 in excess argon in the 810-530 cm-1 region. (a) Spectrum after
co-deposition of laser-ablated Ti and NF3 at 0.5% in argon at 8 K for 60
min, (b) after >220 nm irradiation for 20 min, (c) after annealing to 30 K,
and (d) spectrum after co-deposition of laser-ablated Zr and NF3 at 0.5%
in argon at 8 K for 60 min, (e) after >290 nm irradiation, and (f) after
>220 nm irradiation, and (g) spectrum after co-deposition of laser-
ablated Hf and NF3 at 0.5% in argon at 8 K for 60 min, (h) after
annealing to 20 K, and (i) after >220 nm irradiation.
binary titanium fluoride species as have the weaker bands
.
at 677.7, 674.0, and 643.6 cm-1 29,30
The latter assign-
ments were made to these products from the thermal Ti
atom reaction with argon/fluorine samples. New bands at
782.1, 705.1, and 596.7 cm-1 increase 30% on full arc
(>220 nm) irradiation, and sharpen on annealing to 30
K, spectra (b) and (c). The major Zr reaction product at
667.4 cm-1 is joined by weaker 658.2 and 553.1 cm-1
bands, which increase in concert 10% on >290 nm
irradiation and another 30% on >220 nm irradiation,
scans (d,e,f). The shoulder absorption at 668.6 cm-1 is in
agreement with the major product from an experiment
with Zr and F2 in excess argon performed in this labora-
tory and is near the 668.0 cm-1 band observed earlier for
ZrF4.31 The strongest Hf product band shifts lower to
Results and Discussion
Infrared spectra of products formed in the reactions of
laser-ablated titanium, zirconium, and hafnium atoms with
NF3, PF3, and AsF3 in excess argon during condensation at
5-8 K will be presented in turn. Density functional calcula-
tions were performed to support the identifications of new
reaction products. Bands common to experiments using
different laser ablated metals with NF3 [such as NF2 and
NF2-], with PF3 [PF2, PF5, and PF2-], and with AsF3 [AsF2
and AsF5] have been identified previously and will not be
mentioned again here.15,27,28
650.8 cm-1 just above the NF3 absorption at 648.9 cm-1
,
but this is in precise agreement with our major band for
the Hf and F2 reaction and appropriate for HfF4.31
Comparison with the zirconium experiment suggests that
there is a major product absorption at 643.9 cm-1 with
weaker associated 666.7 and 548.1 cm-1 bands that
increase together 20% on >20 K annealing and another
20% on >220 nm irradiation, spectra (g,h,i).
Infrared Spectra. Sets of infrared spectra for Ti, Zr, and
Hf reactions with NF3 are compared in Figure 1. The
strong bands at 791.8 and 740.2 cm-1 in the Ti reaction,
trace (a), have been reported previously and assigned to
(17) (a) Andrews, L. Chem. Soc. Rev. 2004, 33, 123. (b) Andrews, L.;
Citra, A. Chem. Rev. 2002, 102, 885.
(18) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040, and
references therein (Review article).
(19) Frisch, M. J., et al. Gaussian 03, Revision D.01; Gaussian, Inc.:
Pittsburgh, PA, 2004.
(20) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, Y.;
Parr, R. G. Phys. Rev. B 1988, 37, 785.
(21) Perdew, J. P.; Burke, K.; Wang, Y. Phys. Rev. B 1996, 54, 16533, and
references therein.
(22) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80, 3265.
(23) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
Theor. Chim. Acta 1990, 77, 123.
Infrared spectra for the corresponding group 4 metal
atom reactions with PF3 are illustrated in Figure 2. The
TiF3 and TiF2 bands were barely detected as PF3 is a more
stable compound than NF3. The major Ti reaction pro-
duct at 769.0 cm-1 is joined by a weaker band at 688.2
cm-1, and these two bands increase 30% on >290 nm
irradiation and reduce a like amount on subsequent >220
nm irradiation, traces (a,b,c). With Zr the strong product
(24) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.
(25) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937.
(26) (a) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735. (b) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899.
(29) Hastie, J. W.; Hauge, R. H.; Margrave, J. L. J. Chem. Phys. 1969, 51,
2648.
(30) Wilson, A. V.; Roberts, A. J.; Young, N. A. Angew. Chem., Int. Ed.
2008, 47, 1774.
::
(31) (a) Buchler, A.; Berkowitz-Mattuck, J. B.; Dugre, D. H. J. Chem.
(27) Jacox, M. E. J. Phys. Chem. Ref. Data 1994, Monograph 3; 1998, 27
Phys. 1961, 34, 2202. (b) Hauge, R. H.; Margrave, J. L. High Temp. Sci. 1973,
5, 89. (c) unpublished infrared spectra of Zr and Hf reaction products with F2
in excess argon at 5 K.
(2), 115.
(28) (a) Khider Aljibury, A. J.; Redington, R. L. J. Chem. Phys. 1970, 52,
453. (b) Brum, J. L.; Hudgens, J. W. J. Chem. Phys. 1997, 106, 485.