New structural motifs in the aggregation of neutral gold(I) complexes: Structures and luminescence from (alkyl isocyanide)AuCN

Article abstract of DOI:10.1021/ic0206948

The preparation and X-ray crystal structures of (CyNC)Au^ICN, (n-BuNC)Au^ICN, and (i-PrNC)Au^ICN·0.5CH₂Cl₂ are reported and compared with those of (MeNC)Au^ICN and (t-BuNC)Au^ICN, which were previously described. These linear molecules are all organized through aurophilic interactions into three structural classes: simple chains ((CyNC)- Au^ICN and (t-BuNC)Au^ICN), side-by-side chains in which two strands make Au...Au contact with each other ((n-BuNC)Au^ICN), and nets in which multiple aurophilic interactions produce layers of gold(I) centers ((i-PrNC)Au^ICN and (MeNC)Au^ICN). All of these five solids dissolve to produce colorless, nonluminescent solutions with similar UV/vis spectra. However, each of the solids displays a unique luminescence with emission maxima occurring in the range 371-430 nm.

Full text of DOI:10.1021/ic0206948

Inorg. Chem. 2003, 42, 3237−3244
New Structural Motifs in the Aggregation of Neutral Gold(I) Complexes:
Structures and Luminescence from (Alkyl isocyanide)AuCN
Rochelle L. White-Morris, Matthias Stender, Dino S. Tinti, and Alan L. Balch*
Department of Chemistry, UniVersity of California, DaVis, California 95616
Daniel Rios and Saeed Attar*
Department of Chemistry, California State UniVersity, Fresno, California 93740
Received December 2, 2002
I
I
I
The preparation and X-ray crystal structures of (CyNC)AuCN, (n-BuNC)AuCN, and (i-PrNC)AuCN‚0.5CH Cl2 are
2
I
I
reported and compared with those of (MeNC)Au CN and (t-BuNC)AuCN, which were previously described. These
linear molecules are all organized through aurophilic interactions into three structural classes: simple chains ((CyNC)-
I
I
AuCN and (t-BuNC)AuCN), side-by-side chains in which two strands make Au‚‚‚Au contact with each other ((n-
I
I
BuNC)AuCN), and nets in which multiple aurophilic interactions produce layers of gold(I) centers ((i-PrNC)AuCN
and (MeNC)AuCN). All of these five solids dissolve to produce colorless, nonluminescent solutions with similar
I
UV/vis spectra. However, each of the solids displays a unique luminescence with emission maxima occurring in
the range 371−430 nm.
Introduction
quence of such aurophilic attractions, many two-coordinate
gold(I) complexes self-associate into dimers, trimers, and
extended chains that are connected exclusively through
Au‚‚‚Au contacts.
Two-coordinate gold(I) complexes typically are colorless
but may display strong luminescence in the visible region
of the spectrum depending upon the ligands present and the
state of aggregation.12-14 Patterson and co-workers have
shown that the simple [Au(CN)2]- and [Ag(CN)2]- ions
aggregate under a variety of conditions and that the ag-
gregated forms show remarkable variations in their lumines-
cence.15-17 For example, the luminescence from solutions
of K[Au(CN)2] can be “tuned” to occur from 275 to 470
nm depending upon the concentration and solvent.18
Attractive interactions between closed-shell gold(I) centers
are important in determining the structures of many gold(I)
complexes.1,2 Such aurophilic interactions are found when-
ever adjacent Au‚‚‚Au contacts are less than the van der
Waals separation of ca. 3.6 Å.3-5 Theoretical studies have
shown that this weakly bonding interaction is the result of a
combination of correlation and relativistic effects,6-9 while
experimental studies of rotational barriers have demonstrated
that the strength of this attractive interaction is comparable
to hydrogen bonding: ca. 7-11 kcal/mol.10,11 As a conse-
* Authors to whom correspondence should be addressed. E-mail:
albalch@ucdavis.edu (A.L.B.); sattar@csufresno.edu (S.A.).
(1) Jones, P. G. Gold Bull. 1986, 19, 46; 1983, 16, 114; 1981, 14, 159;
1981, 14, 102.
(2) Pathaneni, S. S.; Desiraju, G. R. J. Chem. Soc., Dalton Trans. 1993,
319.
(3) Schmidbaur, H. Gold: Progress in Chemistry, Biochemistry and
Technology; Wiley: New York, 1999.
(4) Grohmann, A.; Schmidbaur, H. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Elsevier: Oxford, 1995; Vol. 3, p 1.
(10) Schmidbaur, H.; Graf, W.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl.
1988, 27, 417.
(11) Harwell, D. E.; Mortimer, M. D.; Knobler, C. B.; Anet, F. A. L.;
Hawthorne, M. F. J. Am. Chem. Soc. 1996, 118, 2679.
(12) Forward, J. M.; Fackler, J. P. Jr.; Assefa, Z. In Optoelectronic
Properties of Inorganic Compounds; Roundhill, D. M., Fackler, J. P.,
Jr, Eds.; Plenum Press: New York, 1999; p 195.
(13) Yam, V. W. W.; Lo, K. K. W. Chem. Soc. ReV. 1999, 28, 323.
(14) Leung, K. H.; Phillips, D. L.; Tse, M. C.; Che, C. M.; Miskowski, V.
M. J. Am. Chem. Soc. 1999, 121, 4799.
(15) Rawashdeh-Omary, M. A.; Omary, M. A.; Patterson, H. H. J. Am.
Chem. Soc. 2000, 122, 10371.
(5) Puddephatt, R. J. In ComprehensiVe Coordination Chemistry; Wilkin-
son, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press:
Oxford, 1987; Vol. 5, p 861.
(6) Pyykko¨, P.; Runeberg, N.; Mendizabal, F. Chem. Eur. J. 1997, 3, 1451.
(7) Pyykko¨, P.; Mendizabal, F. Chem. Eur. J. 1997, 3, 1458.
(8) Pyykko¨, P. Chem. ReV. 1997, 97, 597.
(16) Rawashdeh-Omary, M. A.; Omary, M. A.; Shankle, G. E.; Patterson,
H. H. J. Phys. Chem. B 2000, 104, 6143.
(17) Omary, M. A.; Patterson, H. H. J. Am. Chem. Soc. 1998, 120, 7696.
(9) Pyykko¨, P.; Li, J.; Runeberg, N. Chem. Phys. Lett. 1994, 218, 133.
10.1021/ic0206948 CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/04/2003
Inorganic Chemistry, Vol. 42, No. 10, 2003 3237

White-Morris et al.
Table 1. Selected Interatomic Distances and Angles
(CyNC)AuCN
(t-BuNC)AuCNa
(n-BuNC)AuCN
(i-PrNC)AuCN‚0.5CH2Cl2
(MeNC)AuCNb
Au‚‚‚Au
3.426(3)
3.442(3)
3.568
3.3233(3)
3.3729(4)
3.3735(3)
3.4703(3)
3.3209(3)
3.3500(4)
3.4875(3)
3.4715(3)
3.6856(4)
3.3500(4)
3.4387(4)
3.6662(5)
1.997(6)
1.994(6)
1.987(6)
1.977(6)
1.988(6)
1.990(6)
1.139(8)
1.144(7)
1.146(8)
1.136(7)
1.132(7)
1.132(8)
67.074(8)
56.84(1)
26.59(1)
42.80(1)
150.48(1)
17.16(1)
174.8(2)
173.8(2)
178.9(3)
175.7(5)
179.1(5)
179.7(6)
174.5(5)
175.9(5)
177.7(5)
3.524(4)
3.593(3)
3.724(3)
Au(1)-C(CN)
Au(2)-C(CN)
Au(3)-C(CN)
Au(1)-C(iso)
Au(2)-C(iso)
Au(3)-C(iso)
C-N(CN)
2.01(2)
2.00(2)
1.93(3)
1.09(3)
1.21(3)
130.1
1.985(4)
1.985(4)
1.164(5)
1.133(5)
2.01(4)
1.98(5)
1.15(6)
1.18(6)
1.985(17)
1.10(3)
C-N(CN)
C-N(CN)
C-N(iso)
C-N(iso)
1.13(2)
C-N(iso)
Au‚‚‚Au‚‚‚Au
127.89(7)
62.425(8)
59.57(1)
59.4
120.6
63.1
57.5
C-Au(1)-C
178.3(8)
178(2)
178.2(8)
172(2)
175(2)
175.20(13)
177.7(3)
177.5(3)
176(2)
175(4)
179(4)
C-Au(2)-C
C-Au(3)-C
Au(1)-C-N(CN)
Au(2)-C-N(CN)
Au(3)-C-N(CN)
Au(1)-C-N(iso)
Au(2)-C-N(iso)
Au(3)-C-N(iso)
174.3(17)
a Data from ref. wr. b Data from ref. 23.
Related studies have shown that solutions of the colorless
gold carbene complex [Au{C(NHMe)2}2](PF6)‚0.5(acetone),
which are nonluminescent at room temperature, become
luminescent upon freezing.19 The luminescence from these
frozen solutions ranges from blue to orange to nonlumines-
cent depending upon the solvent. The solid-state structures
of [Au{C(NHMe)2}2](PF6)‚0.5(acetone) and related salts
reveal that this cation can associate through Au‚‚‚Au
interactions to form extended chains or discrete dimers and
that the mode of aggregation in the solids depends upon the
anion present.19,20
Additionally, the cation in [(CyNC)2AuI](PF6) self-associ-
ates to form two crystalline polymorphs: a colorless poly-
morph with linear chains of cations and a short Au‚‚‚Au
contact (3.1822(3) Å), and a yellow polymorph with four
independent cations forming kinked, infinite chains and very
short Au‚‚‚Au contacts of 2.9800(5), 2.9784(5), 2.9652(5),
and 2.9648(5) Å.21,22 The polymorphs are both luminescent,
λmax: colorless, 424 nm; yellow, 480 nm at 298 K. Colorless
solutions of the two polymorphs have identical absorption
spectra and are nonluminescent at room temperature. How-
ever, freezing solutions of [(CyNC)2AuI](PF6) produces
intense luminescence which varies depending upon the
solvent involved. Aggregation of the cations is implicated
because the luminescence of the frozen state occurs only in
relatively concentrated solutions of the complexes.
In order to provide models for the types of aggregation
that two-coordinate gold(I) complex can undergo, we have
undertaken structural and spectroscopic studies of a series
of neutral complexes of the type (RNC)AuICN. We focused
on neutral complexes in the belief that these molecules were
more likely to self-associate than either cations or anions,
and hence a greater array of modes of association might be
observed with such compounds. Two such complexes,
(MeNC)AuICN23 and (t-BuNC)AuICN,24 have been structur-
ally characterized in earlier work, and their structures are
discussed in the context of the new structures reported here.
The UV/vis absorption spectra and the luminescence of all
of these complexes are reported here.
(18) Rawashdeh-Omary, M. A.; Omary, M. A.; Patterson, H. H.; Fackler,
J. P., Jr. J. Am. Chem. Soc. 2001, 123, 11237.
(19) White-Morris, R. L.; Olmstead, M. M.; Jiang, F.; Tinti, D. S.; Balch,
A. L. J. Am. Chem. Soc. 2002, 124, 2327.
(20) White-Morris, R. L.; Olmstead, M. M.; Jiang, F.; Balch, A. L. Inorg.
Chem. 2002, 41, 2313.
Results
(21) White-Morris, R. L.; Olmstead, M. M.; Balch, A. L. J. Am. Chem.
Soc. 2003, 125, 1033.
The new, colorless complexes, (CyNC)AuICN, (n-BuNC)-
AuICN, and (i-PrNC)AuICN, were prepared by the addition
(22) However, Schmidbaur and co-workers found that other colorless bis-
(isonitrile)gold(I) complexes, [(RNC)2AuI]X (R ) methyl, phenyl, and
mesityl, and X ) triflate or tetrafluoroborate), self-associated only
with R ) methyl, and in that one case the Au‚‚‚Au interaction is quite
long, 3.624 Å. See: Schneider, W.; Sladek, A.; Bauer, A.; Angermaier,
K.; Schmidbaur, H. Z. Naturforsch. B 1997, 52, 53.
(23) Esperås, S. Acta Chem. Scand. 1976, A 30, 527.
(24) Che, C.-M.; Yip, H.-K.; Wong, W.-T.; Lai, T.-F. Inorg. Chim. Acta
1992, 197, 177.
3238 Inorganic Chemistry, Vol. 42, No. 10, 2003

Structures and Luminescence from (Alkyl isocyanide)AuCN
Table 2. Crystallographic Data
(CyNC)AuCN
(n-BuNC)AuCN
(i-PrNC)AuCN‚0.5CH2Cl2
empirical formula
fw
C8H11AuN2
332.15
C6H9AuN2
306.12
C5.5H8AuClN2
334.55
color, habit
cryst syst
space group
colorless, needle
monoclinic
P21/c
colorless, needle
monoclinic
C2/c
colorless, block
monoclinic
P2/c
a, Å
b, Å
c, Å
6.169(7)
6.681(7)
22.27(2)
93.65(3)
916.0(16)
4
21.828(2)
10.9685(9)
6.7094(5)
103.975(3)
1558.8(2)
8
10.9649(6)
12.3442(7)
16.9844(10)
95.4050(10)
2288.7(2)
12
â, deg
V, Å3
Z
T/K
200(2)
90(2)
90(2)
λ, Å
0.71073
2.409
16.000
0.0660
0.185
0.71073
2.609
18.790
0.0187
0.0395
0.71073
2.663
19.310
0.0313
0.0808
F/g cm-1
µ/mm-1
R1a (obsd data)
wR2a (all data, F2 refinement)
a R1 ) ∑||Fo - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
Figure 1. A view of a chain of molecules in (CyNC)AuICN.
of the appropriate isocyanide to a suspension of AuCN in
chloroform. After all of the solid had dissolved, the product
was precipitated by the addition of petroleum ether. Exami-
nation of the crystalline solids by X-ray diffraction revealed
that the C-N-C-Au-C-N portions of the individual
molecules are all nearly linear, and there are no notable
variations in the internal distances and angles within the
molecules. Table 1 contains selected interatomic distances
and angles. The crystal data are set out in Table 2.
However, the organization of the individual molecules in
each solid differs. Broadly, the molecules organized them-
selves into three structural classes: simple chains, side-by-
side chains in which two strands made additional contacts
with each other, and nets in which multiple aurophilic
interactions produced layers of gold(I) centers.
Simple Chains: (CyNC)AuICN and (t-BuNC)AuICN.
The structure of (CyNC)AuICN reveals that there is one
molecule in the asymmetric unit which associates to form a
one-dimensional infinite chain. Figure 1 shows a drawing
of the structure. Individual molecules pack about centers of
symmetry to form a zigzag chain with an Au‚‚‚Au‚‚‚Au angle
of 127.89(7)° and two alternating Au‚‚‚Au distances of
3.426(3) and 3.442(3) Å. This zigzag chain formation is
similar to that found in (t-BuNC)AuICN which has an
Au‚‚‚Au‚‚‚Au angle of 130.1° and one slightly longer
Au‚‚‚Au distance of 3.568 Å.24
Figure 2. A drawing showing the interactions between molecules in
crystalline (n-BuNC)AuICN. Hydrogen atom positions are omitted.
Side-by-Side Chains: (n-BuNC)AuICN. The structure
of (n-BuNC)AuICN also consists of one molecule in the
asymmetric unit, but crystallographic symmetry produces a
more complex pattern of aggregation. Figure 2 shows how
these molecules are arranged. The structure can be viewed
as an arrangement of two parallel, but slightly bent, chains
Inorganic Chemistry, Vol. 42, No. 10, 2003 3239

White-Morris et al.
Figure 4. A view of the supramolecular structure of (i-PrNC)AuICN‚
0.5CH2Cl2. Hydrogen atom positions are omitted.
Figure 3. A view of the structure of crystalline (n-BuNC)AuICN which
shows how the pairs of chains are insulated from one another. Hydrogen
atom positions are omitted.
interactions running through the centers of each layer. Figure
5 shows the network of aurophilic interactions that are
present within a layer. The shortest Au‚‚‚Au contacts
(3.3209(3) and 3.3500(4) Å) are found between molecules
containing Au(1) and Au(2). Two molecules containing Au-
(2) and two molecules containing Au(1) are arranged about
a crystallographic 2-fold axis to form an aggregate with a Z
shape as seen in the bold outline in Figure 5. These figure
Z arrangements are connected through further contacts
involving, for example, Au(1A) and Au(1B) to create
extended and strongly bent chains. Molecules containing Au-
(3) are appended to edges of these chains through Au‚‚‚Au
interactions with both Au(1) (at 3.4715(3) Å) and Au(2) (at
3.4875(3) Å). Finally, molecules containing Au(3) are also
packed about crystallographic centers of symmetry to connect
the units described above. The Au‚‚‚Au separations here are
larger, 3.6662(5) Å, just at the edge where such interactions
are viewed as significantly attractive.
As reported earlier, crystalline (MeNC)AuICN also forms
a sheetlike structure.23 However, in this solid there is only
one molecule in the asymmetric unit. Each gold atom is
surrounded by six other gold ions in a roughly hexagonal
arrangement which involves Au‚‚‚Au contacts at 3.524(4),
3.593(3), and 3.724(3) Å.
Spectroscopic Properties. The UV/vis spectra of (CyNC)-
AuICN, (n-BuNC)AuICN, and (i-PrNC)AuICN‚0.5CH2Cl2 in
acetonitrile solution are shown in Figure 6. As expected, the
presence of differing alkyl groups produces negligible
variation in these spectra, and all resemble the spectrum of
(MeNC)AuICN in solution which was reported by Chastain
and Mason.25 These authors have assigned the intense bands
in the ultraviolet to metal-to-ligand charge transfer (MLCT)
from the filled gold d orbitals. As they noted, there is no
evidence for separate MLCT to the two different types of
of gold complexes. Within each chain the gold centers are
connected through Au‚‚‚Au contacts of 3.4703(3) Å. In
Figure 2, one chain consists of Au(1C), Au(1), and Au(1D),
while the other consists of Au(1E), Au(1A), Au(1B), and
Au(1F). Au(1) is transformed into Au(1C) or into Au(1D)
through crystallographic centers of symmetry. Within these
chains the angle Au‚‚‚Au‚‚‚Au is 150.3(1)°. These two chains
are connected to one another through additional aurophilic
interactions. These Au‚‚‚Au contacts are shorter than the
contacts within the chains. Thus, Au(1) is transformed into
Au(1A) by a crystallographic center of inversion to produce
a Au‚‚‚Au contact of 3.3233(3) Å, while Au(1) is trans-
formed into Au(1B) by a crystallographic 2-fold axis to
produce a Au‚‚‚Au contact of 3.3735(3) Å. As a result of
these aurophilic interactions, each gold ion in (n-BuNC)-
AuICN is connected to four other gold(I) ions through
Au‚‚‚Au contacts that are shorter than 3.6 Å.
Figure 3 shows a view of the structure of (n-BuNC)-
AuICN that reveals that the side-by-side chains are isolated
from each other. The n-Bu groups protrude away from the
chains and effectively insulate one chain from its neighbors.
There is disorder in the positions of the γ and δ carbon atoms
of the butyl group. The two alternative positions for each of
these carbon atoms have 0.50 site occupancy. Only one of
these sites is shown in Figures 2 and 3.
Nets: (i-PrNC)AuICN‚0.5CH2Cl2 and (MeNC)AuICN.
Unlike the compounds considered previously, the solid-state
structure of (i-PrNC)AuICN‚0.5CH2Cl2 involves three crys-
tallographically different molecules in the asymmetric unit.
As noted above, however, the three molecules show only
minor variations in their geometric parameters. Figures 4 and
5 show how these three different molecules interact with one
another. The molecules are arranged in layers with aurophilic
(25) Chastain, S. K.; Mason, W. R. Inorg. Chem. 1982, 21, 3717.
3240 Inorganic Chemistry, Vol. 42, No. 10, 2003

Structures and Luminescence from (Alkyl isocyanide)AuCN
Figure 5. A projection of the layered structure of (i-PrNC)AuICN‚0.5CH2Cl2 which shows the aurophilic interactions. Hydrogen atom positions are omitted.
dashed line in Figure 7 shows the emission spectrum with
excitation at 315 nm, which produces an emission maximum
at 413 nm. The excitation profile shown was obtained while
emission was monitored at 413 nm. Excitation at longer
wavelengths produces a shoulder at ca. 460 nm. The solid
line in the top panel of Figure 7 shows the emission spectrum
obtained with excitation at 360 nm. For (t-BuNC)AuICN two
different sets of emission and excitation spectra are shown
in Figure 7. The emission spectra are dependent upon the
excitation wavelength. The first set of spectra show the
emission generated by excitation at 293 nm and the excitation
profile for the emission at 371 nm. The second set of spectra
show the emission obtained by excitation at 341 nm and the
emission profile for the emission at 456 nm. Interestingly,
the two solids that show changes in their emission as a
function of excitation wavelength belong to the same
structural class with simple zigzag chains.
Despite the similarity in the absorption spectra of these
complexes, the solid-state luminescence of each shows
unique features. The emission maxima range from 371 nm
for (t-BuNC)AuICN to 430 nm for (i-PrNC)AuICN, and the
excitation maxima range from 293 nm for (t-BuNC)AuICN
and (n-BuNC)AuICN to 353 nm for (i-PrNC)AuICN‚0.5CH2-
Cl2 and (MeNC)AuICN. Moreover, the spectra of (CyNC)-
AuICN and (t-BuNC)AuICN show two emission bands. The
observation that the excitation maxima occur at lower
energies than any of the MLCT absorption features seen in
the solution phase spectra shown in Figure 6 indicates that
Figure 6. The absorption spectra of 0.18 mM acetonitrile solutions of
(A) (CyNC)AuICN), (B) (n-BuNC)AuICN; and (C) (i-PrNC)AuICN‚0.5CH2-
the absorption and emission properties of the solid are
supramolecular in nature and that the aurophilic interactions
are crucial for the observation of luminescence.
Cl2.
ligands present in these complexes. None of the solutions
used to obtain the spectra shown in Figure 6 are luminescent.
However, as solids each of these complexes is luminescent
at room temperature. Figure 7 shows the emission and
excitation spectra of polycrystalline samples of (CyNC)-
AuICN, (t-BuNC)AuICN, (n-BuNC)AuICN, (i-PrNC)AuICN‚
0.5CH2Cl2, and (MeNC)AuICN. For (n-BuNC)AuICN, (i-
PrNC)AuICN‚0.5CH2Cl2, and (MeNC)AuICN the emission
is independent of excitation wavelength. However, for
(CyNC)AuICN and (t-BuNC)AuICN there is a wavelength
dependence of the emission. Thus, for (CyNC)AuICN the
The luminescence decays of the solids were recorded at
room temperature following pulsed excitation at 337 nm with
a N2 laser. The decays could be analyzed as a sum of two
exponential components, but the shorter-lived component had
a small amplitude and significant error in all cases. Its origin
is unclear. We present the lifetimes only for the longer-lived
component. This component has a lifetime of 140 ns in
(MeNC)AuCN. The long-lived components have longer
lifetimes in the other solids. For both (n-BuNC)AuCN and
(CyNC)AuCN the lifetimes are 0.70 µs, and for both
(t-BuNC)AuCN and (i-PrNC)AuCN the lifetimes are 1.2 µs.
Inorganic Chemistry, Vol. 42, No. 10, 2003 3241

White-Morris et al.
150 ns delay (with 337 nm excitation) agree with the data
in Figure 7 for (MeNC)AuCN, (n-BuNC)AuCN, and (i-
PrNC)AuCN‚0.5CH2Cl2. For (CyNC)AuCN and (t-BuNC)-
AuCN, the spectra at a delay of 150 ns are shifted to longer
wavelengths relative to the spectra taken at 0 ns. This shift
is more pronounced for (t-BuNC)AuCN where the emission
maximum shifts from 420 at 0 ns delay to 460 nm at 150 ns
delay. In (CyNC)AuCN the emission maximum remains at
405 nm, but a distinct shoulder appears at 460 nm in the
spectra at 150 ns delay. These variations are consistent with
the differences seen in the effects of excitation wavelength
on the emission of (t-BuNC)AuCN and (CyNC)AuCN.
Interestingly, the two solids that show changes in their time-
resolved spectra also belong to the same structural class with
simple zigzag chains.
In agreement with the proposition that the spectroscopic
properties of the solids are a result of the supramolecular
structures present in the crystals, the UV/vis absorption
spectra of the solids also differ from those of the solutions.
Relevant data are reported in Figure 8, which shows
absorption spectra of the complexes recorded as dispersions
in KBr.
Infrared spectra of the new complexes, which show clearly
differentiated ν(cyanide) and ν(isocyanide) bands, are re-
ported in the Experimental Section.
Discussion
The structural data reported here demonstrate that the
neutral molecules, (RNC)AuICN, can self-associate through
aurophilic interactions into a range of different solid-state
structures. However, it is interesting to note that none of the
close Au‚‚‚Au separations seen in these neutral molecules
are as short as those observed between the chains of cations
in [Au{C(NHMe)2}2](PF6)‚0.5(acetone) (Au‚‚‚Au, 3.1882-
(1) Å) and in the two polymorphs of [(CyNC)2AuI](PF6)
(colorless, Au‚‚‚Au, 3.1822(3) Å; yellow, Au‚‚‚Au, 2.9803-
(6), 2.9790(6), 2.9651(6), and 2.9643(6) Å). On the other
hand, these neutral rodlike complexes do show interesting
variations in their modes of aggregation, which can involve
additional aurophilic interactions beyond those seen in chain
structures. For example, in (i-PrNC)AuICN‚0.5CH2Cl2 each
of the three crystallographically different gold ions interacts
with three neighboring gold ions, whereas in chain aggregates
there are, of course, only two neighboring gold ions. In (n-
BuNC)AuICN, each gold ion interacts with four other gold
ions in the side-by-side chains. In (MeNC)AuICN, each gold
ion interacts with six others in a hexagonal net but the
Au‚‚‚Au distances are longer.
Figure 7. The emission (right) and excitation (left) spectra of crystalline
samples of (CyNC)AuICN, (t-BuNC)AuICN, (n-BuNC)AuICN, (i-PrNC)-
AuICN‚0.5CH2Cl2, and (MeNC)AuICN obtained at 25 °C. For (CyNC)-
AuICN the dashed line shows emission with excitation at 315 nm and the
excitation profile was obtained while emission was monitored at 413 nm.
The solid line shows the emission spectrum obtained with excitation at 360
nm. For (t-BuNC)AuICN the first set of spectra show the emission generated
by excitation at 293 nm and the excitation profile for the emission at 371
nm, while the second set of spectra show the emission obtained by excitation
at 341 nm and the emission profile for the emission at 456 nm.
The crystalline forms of all five complexes ((CyNC)-
AuICN, (t-BuNC)AuICN, (n-BuNC)AuICN, (i-PrNC)AuICN‚
0.5CH2Cl2, and (MeNC)AuICN) are luminescent at room
temperature, but their solutions are nonluminescent. Conse-
quently, the luminescence of the solids is attributed to the
presence of aurophilic interactions in the solid state. The
differences seen in the excitation profiles and the absorption
spectra of these complexes reinforce the notion that the
luminescence arises from the unique intermolecular inter-
actions present in the solid. The luminescent features (λmax
All reported lifetimes have relative uncertainties of (10%.
These lifetimes suggest that the corresponding components
of the emission represent phosphorescence.
The time-resolved emission spectra at 0 ns delay (with
337 nm excitation) agree with the CW emission spectra
shown in Figure 7 for (n-BuNC)AuICN, (i-PrNC)AuICN‚
0.5CH2Cl2, and (MeNC)AuICN and with the CW emission
spectra of (CyNC)AuICN (band at 403 nm, exclusively) and
(t-BuNC)AuICN with excitation at 341 nm. The spectra at
3242 Inorganic Chemistry, Vol. 42, No. 10, 2003

Structures and Luminescence from (Alkyl isocyanide)AuCN
(dbm is 1,8-diisocyano-p-menthane).26 In this complex the
bridging dmb ligand facilitates the aurophilic interaction. The
intramolecular Au‚‚‚Au separation in the solid state is 3.54-
(1) Å. This binuclear complex is luminescent in solution (λmax
) 458 nm in dichloromethane), since the bridging ligand
can maintain the aurophilic interaction upon dissolution.
Isoelectronic acetylide complexes of the type RNCAuCCR
are also luminescent. However, the examples presently
known involve arene substituents, and the luminescence from
such complexes is likely to arise from ligand π-π* states.27
Experimental Section
Materials. Gold(I) cyanide, n-butyl isocyanide, and i-propyl
isocyanide were obtained from Strem Chemicals. Cyclohexyl
isocyanide was purchased from Aldrich. All chemicals were used
as received.
Preparation of (RNC)AuICN. All compounds were obtained
through the same synthetic procedure. Gold cyanide (110 mg, 0.49
mmol) was suspended in 12 mL of chloroform. The respective
isocyanide (0.56 mmol) was added to the suspension, and it was
stirred for 1 h. During this time, the yellow suspension dissolved
to produce a colorless solution. The solution was then filtered, and
its volume was reduced to 4 mL under a vacuum. Petroleum ether
(ca. 20 mL) was added to the concentrated solution to producing a
colorless solid. The solid was collected by filtration, washed with
petroleum ether, and dried under a vacuum. The yields of the
products were (CyNC)AuCN, 69%; (i-PrNC)AuCN, 79%; and (n-
BuNC)AuCN, 76%.
Figure 8. The absorption spectra of crystalline samples of (CyNC)AuI-
CN, (t-BuNC)AuICN, (n-BuNC)AuICN, (i-PrNC)AuICN‚0.5CH2Cl2, and
(MeNC)AuICN dispersed in a potassium bromide pellet at 25 °C.
Crystals of (CyNC)AuCN were obtained from slow evaporation
of a dichloromethane solution of the complex, while crystals of
(i-PrNC)AuCN and (n-BuNC)AuCN were grown through liquid
diffusion of diethyl ether into a dichloromethane solution of the
respective complex.
excitation and λmax emission) of each crystalline solid are
different, whereas the solution UV/vis spectra of these
complexes are nearly identical. Moreover, the two examples
((CyNC)AuCN and (t-BuNC)AuCN) from the structural class
with simple zigzag chains show similar features in that there
are dual emissions that are time-resolved and that show
dependence on excitation wavelength.
The aurophilic attractions in these crystals allow overlap
of the occupied gold 5d orbitals to produce a filled band of
orbitals, while overlap of the empty gold 6p orbitals produces
a corresponding band of unoccupied orbitals. Excitation of
an electron from the filled 5d band to the empty 6p band
strengthens the bonding along these chains by removing what
is effectively an antibonding electron from the 5d band and
transferring that electron to the bonding 6p band. Emission
results from the reverse process, transfer of an excited
electron from the 6p band back to the 5d band.
Infrared Spectra. (CyNC)AuCN: 2943.8, 2918.6, 2856.3,
2256.1 (ν(cyanide)), 2157. 3 (ν(isocyanide)), 1448.4, 1366.2, 894.3
cm-1. (i-PrNC)AuCN: 2980.8, 2941.7, 2870.0, 2263.8 (ν(cyanide)),
2156.5 (ν(isocyanide)), 1446.5, 1341.0, 908.2 cm-1. (n-BuNC)-
AuCN: 2960.5, 2923.0, 2868.9, 2277.7 (ν(cyanide)), 2155.9 (ν-
(isocyanide)), 1423.0, 1377.6, 931.2 cm-1. (MeNC)AuCN: 3014.9,
2291.2 (ν(cyanide)), 2155.3 (ν(isocyanide)), 1434.5, 1398.3, 970.2
cm-1
.
Physical Measurements. Infrared spectra were recorded as
pressed KBr pellets on a Matteson Galaxie Series FTIR 3000
spectrometer. Electronic absorption spectra were recorded using a
Hewlett-Packard 8450A diode array spectrophotometer. Conven-
(26) Che, C. M.; Wong, W. T.; Lai, T. F.; Kwong, H. L. J. Chem. Soc.,
Chem. Commun. 1989, 243.
(27) Irwin, M. J.; Vittal, J. J.; Puddephatt, R. J. Organometallics 1997, 16,
3541. Jia, G.; Payne, N. C.; Vittal, J. J.; Puddephatt, R. J. Organo-
metallics 1993, 12, 4771.
It is interesting to compare the results reported here to
those reported for the binuclear complex, 1 (µ-dmb){AuCN}2
Inorganic Chemistry, Vol. 42, No. 10, 2003 3243

White-Morris et al.
tional fluorescence excitation and emission spectra were recorded
on a Perkin-Elmer LS50B luminescence spectrophotometer. These
spectra were collected at room temperature (298 K) on poly-
crystalline samples that were examined microscopically to determine
that the samples contained crystals of uniform morphology and ones
that produced uniform luminescence.
Pulsed excitation for the luminescence decay measurements and
the time-resolved spectra was provided by a N2 laser (337 nm, e10
ns pulse width). The luminescence intensity following the pulsed
excitation was monitored by a 1 m spectrometer with a RCA
C31034 photomultiplier. The spectrometer output was processed
by a Tektronix TDS 724C digitizing oscilloscope for the decay
measurements and a Stanford Research Systems SR250 gated
integrator and boxcar averager for the time-resolved spectra. The
digitized decay data were analyzed by a least-squares fitting
procedure.
X-ray Crystallography and Data Collection. The crystals were
removed from the glass tubes in which they were grown together
with a small amount of mother liquor and immediately coated with
a hydrocarbon oil on the microscope slide. Suitable crystals were
mounted on glass fibers with silicone grease and placed in the cold
dinitrogen stream of a Bruker SMART CCD with graphite-
monochromated Mo KR radiation at 90(2) K. Crystals of (CyNC)-
AuCN cracked upon cooling to 90 K, and hence the data for this
compound were obtained at 200 K. No decay was observed in 50
duplicate frames at the end of each data collection. Crystal data
are given in Table 2.
The structures were solved by direct methods and refined using
all data (based on F2) using the software of SHELXTL 5.1. A
semiempirical method utilizing equivalents was employed to correct
for absorption.28 Hydrogen atoms were added geometrically and
refined with a riding model.
Acknowledgment. We thank the Petroleum Research
Fund (Grant 37056-AC) for support. The Bruker SMART
1000 diffractometer was funded in part by NSF instrumenta-
tion grant CHE-9808259.
Supporting Information Available: X-ray crystallographic files
in CIF format for (CyNC)AuICN, (n-BuNC)AuICN, and (i-PrNC)-
AuICN‚0.5CH2Cl2. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0206948
(28) SADABS 2.0, Sheldrick, G. M. based on a method of Blessing, R. H.
Acta Crystallogr., Sect. A 1995, A51, 33.
3244 Inorganic Chemistry, Vol. 42, No. 10, 2003