Angewandte
Chemie
DOI: 10.1002/anie.201205072
Gold Fluorides
Investigation of Gold Fluorides and Noble Gas Complexes by Matrix-
Isolation Spectroscopy and Quantum-Chemical Calculations**
Xuefeng Wang, Lester Andrews, Knut Willmann, Felix Brosi, and Sebastian Riedel*
Gold fluorides have long been known, ever since Moissan, the
discoverer of the element fluorine, reported the first reaction
of fluorine with gold in 1889.[1] Despite the early synthesis of
AuF3, the chemistry of gold fluorides has been explored less
over the years when compared with its heavier homologues
chlorine, bromine, and iodine. This is probably due to
difficulties in the practical handling of the element fluorine.
The most prominent oxidation state in gold chemistry is
+ III, as represented by AuF3 and higher oligomers Au2F6 and
Au3F9, which have been extensively investigated experimen-
tally[2–5] and theoretically.[6,7] Gas-phase electron diffraction
(GED) experiments of the monomer have shown that this
compound forms an almost T-shaped structure, owing to first-
order Jahn–Teller distortion,[2] whereas a helical structure was
determined for its crystal.[3,8] The planar dimer structure
Au2F6 with two bridging fluorine atoms was also studied in the
gas phase.[2,6] Similar bridging of fluorine has been observed
in the dimerization and trimerization of AuF5 to form
[Au2F10][9,10] and [Au3F15].[10,11] This unusually high oxidation
state of + V, when compared with its lighter homologues
silver and copper, is due to the relativistic maximum of
gold.[12–14]
copy is limited because of the 100% occurrence of the natural
isotopes 197Au and 19F.
The stability of AuF was first predicted by Schwerdt-
feger[17,18] and afterwards experimentally confirmed by mass
spectrometry[19,20] and microwave spectroscopy.[21] The latter
method was successfully used for the discovery of the heavy
=
noble-gas gold fluoride compounds such as NgAuF (Ng Ar,
Kr, Xe),[22–24] which have also been investigated computa-
tionally.[25,26] The corresponding neon species NeAuF has only
been explored by quantum-chemical calculations,[27–29] which
indicate that the bonding nature is more electrostatic and its
dissociation energy is extrapolated to be 10 kJmolꢀ1 [29]
.
The abovementioned gold fluorides AuF, AuF3, and AuF5
are closed-shell species (for complete overviews, see
Pyykkç[30–32] and Mohr[33]). To the best of our knowledge, no
binary open-shell gold fluorides such as AuF2, AuF4, or even
AuF6 have been experimentally observed. The oxidation state
AuII is only known if stabilized by, for example, SbF6 as in
ꢀ
[Au(SbF6)2][34] or by its polymeric mixed-valence gold(II)/
gold(III) compounds [Au3F8](SbF5)2 and [Au3F7](SbF5)3.[35]
However, AuH2 has been characterized by matrix IR spectra
and electronic structure computations.[36]
To date no higher oxidation state for gold has been
Herein we report IR spectra and quantum-chemical
calculations of the products of laser-ablated gold atom
reactions with fluorine in excess argon and neon during
condensation at 4 K. New gold fluoride species were prepared
by co-deposition of gold atoms with F2/Ne or F2/Ar mixtures
onto a CsI window at 4 K[37–39] in Virginia and Freiburg. IR
experimentally observed, as the previous claims of AuVIIF7
[15]
have been shown by quantum-chemical calculations to be
erroneously assigned[11] and they most likely correspond to
AuF5···F2.[16] Such quantum-chemical calculations, which con-
sider relativistic effects as well as electron correlation, are
powerful methods, especially because vibrational spectros-
ꢀ
spectra in the Au F stretching frequency region produced by
Au atom reactions with 3, 6, 12, and 24% F2 in argon are
shown in Figure 1.
The spectra show seven major bands in the region from
730 to 470 cmꢀ1. New bands at 575.1 and 640.1 cmꢀ1 decrease
upon sample annealing up to 40 K, while a band at 646 cmꢀ1
gives way to a nearby feature increasing at 655 cmꢀ1 during
annealing of the sample, along with a band at 489 cmꢀ1.
Broader bands at 690 and 708 cmꢀ1 also increase during
annealing. The spectra in Figure 1 clearly show increasing
higher frequency band intensities with increasing F2 concen-
tration and on sample annealing to successively higher matrix
temperatures. Another 6% F2 matrix was co-deposited with
double the laser energy as estimated from the target plume
intensity, and the 655 and 489 cmꢀ1 bands were stronger
relative to the other product absorptions, which suggests that
the latter bands are due to a species with more gold atoms
than the others. Finally, argon matrix spectra recorded at
Virginia (Supporting Information, Figure S1) are in agree-
ment with these results, except for a broad band at 720 cmꢀ1
for the highest frequency product absorption.
[*] Prof. X. Wang
Department of Chemistry
Tongji University, Shanghai 200092 (China)
Prof. X. Wang, Prof. Dr. L. Andrews
Department of Chemistry, University of Virginia
Charlottesville, Virginia 22904-4319 (USA)
Prof. Dr. L. Andrews, K. Willmann, Dipl.-Chem. F. Brosi, Dr. S. Riedel
Institut fꢀr Anorganische und Analytische Chemie
Albert-Ludwigs-Universitꢁt Freiburg
Albertstrasse 21, 79104 Freiburg im Breisgau (Deutschland)
E-mail: sebastian.riedel@psichem.de
[**] Financial support from the NSF (Grant CHE 03-52487), a DAAD
Research Visit to Freiburg for L.A., and an NSFC Grant (20973126)
to X.W. is acknowledged. S.R. thanks the DFG project HA 5639/3-
1 and the Fonds der Chemischen Industrie for financial support, the
BWGrid cluster for computational resources, and Prof. I. Krossing
and Prof. H. Hillebrecht for their generous and continuous support.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!
Wang, Xuefeng
