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Table 1 Calculated and observed vibrational frequencies of HUF in cmÀ1 (intensities in km molÀ1) compared with UH2 and UF2 and calculated thermochemistry of
HUF in kJ molÀ1
Stretching
mode
B3LYP RSC/
aVTZa
B3LYP RSC/
aVTZb
CCSD(T) RSC/
aVTZa
CCSD(T) RSC/
aVTZc
B3LYP RSC/
aVTZ
Ar
544.6e
Reaction
HUFd
DUF
UH2
UD2
UF2
U–F
U–H
U–F
U–D
U–H sym.
U–H asym.
U–D sym.
U–D asym.
U–F sym.
U–F asym.
548.3 (148)
1426.4 (401)
546.1 (132)
1011.5 (201)
1452.4 (339)
1395.6 (651)
1029.0 (171)
989.9 (329)
552.6 (87)
543.8
1349.6
541.0
972.1
1393.3
1329.7
999.2
956.6
547.0
518.0
568.7 (150)
1454.4 (406)
567.7
564.2
1377.6
562.6
HUF - U +HF
345
229
1383.1e
542.6
988.3
1406.17
1370.77
1003.57
978.77
—
HUF - UF + H
HUF - UH + F
UF - U + F
U + HF - UF + H
U + HF - UH + F
UF + HF - HUF2
HUF + F - HUF2
HUF + H - FUH2
2HUF - UH2 + UF2
626
1031.3
992.2
673 f,g
À115
281
1480.0 (411)
1438.0 (460)
1050.4
1021.8
567.5 (104)
513.5 (114)
1420.1
1372.1
1020.6
988.5
561.9
504.8
À300
À628
À267
10
526.7 (152)
—
a
b
c
d
Harmonic frequencies. Anharmonic frequencies. Anharmonicity calculated at DFT level. CASPT(2) harmonic frequencies are U–F 563.9 cmÀ1
(191) and U–H 1490.1 cmÀ1 (677). Neon: 555.5/1402.8 cmÀ1, Krypton: 537.5/1371.6 cmÀ1
. .
Experimental value from ref. 19: 648 kJ molÀ1
e
f
g
Computed value at B3LYP level of ref. 20: 673 kJ molÀ1
.
found in the ESI.† The quintet ground state structure is shown 30–41 K range could be due to reaction (2), and possible evidence
in Fig. 4: the triplet state is 20 kJ molÀ1 higher in energy.
is found only for the strongest calculated modes for H2UF2
Table 1 compares calculated and observed frequencies for (antisymmetric U–H2 modes calculated at 1523 and 1528 cmÀ1
)
some species of interest. The harmonic frequencies, cmÀ1 in a weak doublet band observed at 1487.5–1485.7 cmÀ1 (not
(intensities, km molÀ1) calculated for HUF are 1426.4(401), shown). This is very close to the 1483.6–1481.7 cmÀ1 doublet
548.3(148), 308.4(63) and for DUF are 1011.5(201), 546.1(132), observed for UH4 in solid argon.7
225.5(33). The 1426.4/1011.5 ratio, 1.410, is larger than our
We gratefully acknowledge financial support from DOE
observed 1.400 ratio owing to a small cubic anharmonicity in Grant No. DE-SC0001034 to LA. SR thanks the Fonds der
the U–H stretching mode. Including anharmonicity based on Chemischen Industrie (FCI) for financial support. We are grate-
B3LYP calculations the computed ratio is 1.388. The calculated ful to Prof. Ingo Krossing and Prof. Harald Hillebrecht for their
543.8 cmÀ1 U–F stretching frequency is fortunately close to the generous and continuous support. The authors are also grateful
544.6 cmÀ1 observed argon matrix value, and the calculated to Dr. Florian Kraus for the donation of uranium metal.
DUF shift of 2.2 cmÀ1 for this mode matches our observed shift,
which helps to characterize this new molecule and first uranium References
hydride fluoride. Several calculated energies are of interest. First, for
1 D. Fishlock, Chem. World, 2004, 1, 46–49.
the primary reaction, ignoring spin orbit coupling for U, the energy
is exothermic 345 kJ molÀ1 at DFT level. The addition of a second
HF is also favorable, but the addition of another HF is slightly
endothermic. Additional thermochemistry data is given in Table 1.
2 H. A. Wilhelm, J. Chem. Educ., 1960, 37, 56–68.
3 C. D. R. Harrington and A. E. Ruehle, Uranium Production Technology,
Van Nostrand, Princeton, NJ, 1959.
4 L. R. Morss, N. M. Edelstein, J. Fuger and J. J. Katz, The Chemistry of
the Actinide and Transactinide Elements, Springer, Heidelberg, 2006.
5 G. T. Seaborg, ‘‘Uranium’’. The Encylcopedia of the Chemical Elements,
Rienhold Book Corporation, Skokie, IL, 1968.
6 G. T. Seaborg and J. J. Katz, The Actinide Elements, McGraw-Hill Book
Company, New York, NY, 1954.
U + HF - HUF DE = À345 kJ molÀ1
HUF + HF - H2UF2 DE = À278 kJ molÀ1
H2UF2 + HF - H3UF3 DE = 28 kJ molÀ1
(1)
(2)
(3)
7 P. F. Souter, G. P. Kushto, L. Andrews and M. Neurock, J. Am. Chem.
Soc., 1997, 119, 1682–1687.
8 J. Raab, R. H. Lindh, X. Wang, L. Andrews and L. Gagliardi, J. Phys.
Chem. A, 2007, 111, 6383–6387.
The CCSD(T) U–H distance of 203.1 is close enough to the
sum of recently reported single-bond covalent radii, 170 + 32 =
202 pm. In contrast, the U–F bond length of 204.3 is between
9 R. D. Hunt, C. Thompson, P. Hassanzadeh and L. Andrews, Inorg.
Chem., 1994, 33, 388–391. The absorptions at 400 and 446 cmÀ1 that
increase on annealing are due to (HF)2 and (HF)3. see ref. 12.
the sum of the single-bond radii, 170 + 64 = 234 pm,17 and the 10 P. F. Souter and L. Andrews, J. Mol. Struct., 1997, 412, 161–167.
sum of the double-bond radii, 134 + 59 = 193 pm.18 Our
intermediate U–F distance might indicate some p bonding,
11 L. Andrews, Chem. Soc. Rev., 2004, 33, 123–132.
12 (a) L. Andrews and G. L. Johnson, J. Phys. Chem., 1984, 88, 425–432;
(b) L. Andrews, J. Phys. Chem., 1984, 88, 2940–2949; (c) L. Andrews,
but the B3LYP orbitals instead suggested considerable ionic
character for the U–F bond (NPA charges U: 1.24, F: À0.71).
Based on our extensive work with laser ablated U reacting
S. R. Davis and R. D. Hunt, Mol. Phys., 1992, 77, 993–1003.
13 S. A. McDonald and L. Andrews, J. Chem. Phys., 1979, 70, 3134–3136.
¨
14 S. Riedel, T. Kochner, X. Wang and L. Andrews, Inorg. Chem., 2010,
49, 7156–7164.
with F2 and H2,7–10 we expect laser ablated U atoms to react 15 I. O. Antonov and M. C. Heaven, J. Phys. Chem. A, 2013, DOI:
10.1021/jp312362e.
16 Y. Gong, X. Wang, L. Andrews, T. Schloder and S. Riedel, Inorg.
with HF during condensation in excess argon, and the new
¨
1383 and 544 cmÀ1 product bands support this conclusion. It is
Chem., 2012, 51, 6983–6991.
¨
interesting to note that further reaction occurs on annealing into 17 P. Pyykko and M. Atsumi, Chem.–Eur. J., 2009, 15, 186–197.
¨
18 P. Pyykko and M. Atsumi, Chem.–Eur. J., 2009, 15, 12770–12779.
the 20–29 K range and these product bands increase and sharpen.
Hence reaction (1) proceeds with little or no activation energy.
The demise of these product bands on annealing into the
19 D. L. Hildenbrand and K. H. Lau, J. Chem. Phys., 1991, 94, 1420–1425.
20 E. R. Batista, R. L. Martin and P. J. Hay, J. Chem. Phys., 2004, 121,
11104–11111.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 3863--3865 3865