Detection of Free Monomeric AgCN and AuCN
A R T I C L E S
Figure 1. Crystal structures of AgCN (left) and AuCN (right) determined
5
,6
by neutron diffraction.
Figure 2. A typical spectral line of 107AgCN and AuCN in the ground
vibrational states generated by a sputtering reaction of a silver and gold
sheet, respectively. The integration time is approximately 10 s for each
spectrum.
1
1
AgCN, albeit in an even more highly disordered form.
However, the structures of R-CuCN/AgCN and AuCN differ
in the way the chains are packed together (Figure 1). In AuCN,
gold atoms are arranged in layers, whereas in R-CuCN/AgCN,
copper/silver atoms in neighboring chains are displaced along
the chain axis by one-third of the chain repeat distance. It is
thought that AuCN adopts this chain arrangement to mini-
mize the Au-Au distance and to enhance an aurophilic
4
interaction. This interaction is thought to result from electron
correlation of the closed-shell component, somewhat similarly
to van der Waals interactions, but it is unusually strong as a
1
4,15
result of relativistic effects.
Recently, Pyykk o¨ and co-
workers have theoretically predicted that CuCN, AgCN, and
AuCN may have an alternative sheet structure with energy
1
6,17
comparable to that of the chain structure.
1
3
109
13
In contrast, there have been very few studies on monomeric
silver and gold monocyanides, AgCN and AuCN. Monomeric
copper monocyanide, CuCN, has been experimentally detected
Figure 3. Spectral lines of Au CN and Ag CN near 399.7 GHz, J )
63-62, generated by a sputtering reaction of gold and silver sheets with
1
3
CH CN. The integration time is approximately 10 s. Experimental
conditions were not optimized to save the C-enriched precursor.
1
3
1
8
by microwave spectroscopy. Five theoretical studies have so
far been reported on AgCN and AuCN. In 1993, Veldkamp and
1
9
This Article reports on the first preparation of free silver and
gold monocyanides, AgCN/AuCN, and the observation of their
rotational spectra. The AgCN/AuCN molecules have been
generated by the sputtering reaction of Ag/Au sheets placed on
Frenking predicted that the ground electronic states of AgCN
1
+
and AuCN were the closed-shell Σ states. In 1999, Seminario
20
et al. carried out density-functional-theory (DFT) calculations
on several gold-bearing species including AuCN. Later, Dietz
2
1
3
a stainless steel cathode in the presence of acetonitrile (CH CN)
et al. concluded that the cyanide forms, MCN, of the group
-
1
vapor. Accurate bond lengths in both species have been determined
from the isotopic data. Reliability of various theoretical calculations
has been assessed for the first time through a comparison between
experimental and theoretical results.
1
1 metals (Cu, Ag, and Au) were several thousand cm more
stable than the isocyanide forms, MNC, of these metals. Lee et
2
2
al. extensively studied the group 1 (Li, Na, K, Rb, Cs, and
Fr) and group 11 (Cu, Ag, and Au) monocyanides and discussed
the stability of their linear-MCN, linear-MNC, and triangular
Experimental Details and Data Analysis
2
3
isomers. Recently, Zaleski-Ejgierd et al. carried out high-
precision calculations on MCN (M ) Cu, Ag, Au, and Rg) at
the CCSD(T) level with the latest pseudopotentials and basis
sets up to cc-pVQZ. However, experimental evidence for
monomeric AgCN and AuCN is considerably scarce. The
The present experiments were carried out using a source-
modulation microwave spectrometer with a free space discharge
cell. A multiplier following an OKI klystron was employed as
the microwave source. The radiation transmitted through the cell
was detected by an InSb detector cooled by liquid He. The accuracy
of observed transition frequencies was better than 30 kHz.
The AgCN and AuCN species were generated in the free space
25
2
4
photoelectron spectroscopy of AgCN (and also CuCN) is the
sole experimental study on the subject.
3
cell by a sputtering reaction. Vapor of CH CN entrained in argon
gas was continuously introduced into the cell. Silver and/or gold
sheets lining the inner surface of the stainless steel cathode were
sputtered by a dc glow discharge with a current of 300 mA in the
(
(
(
(
14) Schmidbaur, H. Chem. Soc. ReV. 1995, 24, 391.
15) Schmidbaur, H. Gold Bull. 2000, 33, 3.
16) Hakala, M. O.; Pyykk o¨ , P. Chem. Commun. 2006, 2890.
17) Zaleski-Ejgierd, P.; Hakala, M.; Pyykk o¨ , P. Phys. ReV. B 2007, 76,
presence of 1 mTorr of CH
3
CN vapor and 4 mTorr of Ar gas. For
0
94104.
13
15
observing the C or N isotopic species, we used, instead of normal
(
18) Grotjahn, D. B.; Brewster, M. A.; Ziurys, L. M. J. Am. Chem. Soc.
1
2
14
13
15
3 3 3
CH C N species, CH CN or CH C N as the precursor. The
2
002, 124, 5895.
cell was cooled to approximately 150 K by circulating liquid
nitrogen. Under these conditions, the AgCN and AuCN lines were
strong enough to be observed without data accumulation. The
typical spectra obtained are shown in Figures 2 and 3. The AgCN
and AuCN lines showed diamagnetic properties, and they rapidly
disappeared when the discharge current was turned off. This
behavior indicated that the carriers were singlet transient species.
(
19) Veldkamp, A.; Frenking, G. Organometallics 1993, 12, 4613.
(20) Seminario, J. M.; Zacarias, A. G.; Tour, J. M. J. Am. Chem. Soc. 1999,
1
21, 411.
(
(
21) Dietz, O.; Ray o´ n, V. M.; Frenking, G. Inorg. Chem. 2003, 42, 4977.
22) Lee, D.; Lim, I. S.; Lee, Y. S.; Hagebaum-Reignier, D.; Jeung, G.-H.
J. Chem. Phys. 2007, 126, 244313.
(
(
23) Zaleski-Ejgierd, P.; Patzschke, M.; Pyykk o¨ , P. J. Chem. Phys. 2008,
1
28, 224303.
24) Boldyrev, A. I.; Li, X.; Wang, L.-S. J. Chem. Phys. 2000, 112, 3627.
2
Weaker transitions were also observed in the ν (bend) vibrational
J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009 11713