Luminescent Au(I)/Cu(I) Alkynyl clusters with an ethynyl steroid and related aliphatic ligands: An octanuclear Au4Cu4 cluster and luminescence polymorphism in Au3Cu2 clusters

Article abstract of DOI:10.1021/ja103400e

Gold(I) bis(acetylide) complexes [PPN][AuR₂] (1-3) where PPN = bis(triphenylphosphine)iminium) and R = ethisterone (1); 1-ethynylcyclopentanol (2); 1-ethynylcyclohexanol (3) have been prepared. The reaction of 1 with [Cu(MeCN)₄][PF₆] in a 1:1 or 3:2 ratio provides the octanuclear complex [Au₄Cu₄(ethisterone)₈] (4) or pentanuclear complex [PPN][Au₃Cu₂(ethisterone) ₆] (5). Complexes 2 and 3 react with [Cu(MeCN)₄][PF ₆] to form only pentanuclear Au(I)/Cu(I) complexes [PPN][Au ₃Cu₂(1-ethynylcyclopentanol)₆] (6) and [PPN][Au₃Cu₂(1-ethynylcyclohexanol)₆] (7). X-ray crystallographic studies of 1-3 reveal nontraditional hydrogen bonding between hydroxyl groups and the acetylide units of adjacent molecules. Complexes 6 and 7 each form polymorphs in which the structures (6 a,b and 7 a,b,c) differ by Au...Au, Au...Cu, and Cu-C distances. The polymorphs exhibit different emission energies with colors ranging from blue to yellow in the solid state. In solution, pentanuclear clusters 5-7 emit with λ_max = 570-580 nm and ψ = 0.05-0.19. Complex 4 emits at 496 nm in CH ₂Cl₂ with a quantum yield of 0.65. Complex 5 exists in equilibrium with 1 and 4 in the presence of methanol, ethanol, ethyl acetate, or water. This equilibrium has been probed by X-ray crystallography, NMR spectroscopy, and luminescence experiments. DFT calculations have been performed to analyze the orbitals involved in the electronic transitions of 4, 6, and 7.

Full text of DOI:10.1021/ja103400e

Published on Web 08/12/2010
Luminescent Au(I)/Cu(I) Alkynyl Clusters with an Ethynyl
Steroid and Related Aliphatic Ligands: An Octanuclear
Au4Cu4 Cluster and Luminescence Polymorphism in Au3Cu2
Clusters
Gerald F. Manbeck,† William W. Brennessel,† Robert A. Stockland, Jr.,‡ and
Richard Eisenberg*,†
Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627, and Department
of Chemistry, Bucknell UniVersity, Lewisburg, PennsylVania 17837
Received April 21, 2010; E-mail: eisenberg@chem.rochester.edu
Abstract: Gold(I) bis(acetylide) complexes [PPN][AuR2] (1-3) where PPN ) bis(triphenylphosphine)iminium)
and R ) ethisterone (1); 1-ethynylcyclopentanol (2); 1-ethynylcyclohexanol (3) have been prepared. The
reaction of 1 with [Cu(MeCN)4][PF6] in a 1:1 or 3:2 ratio provides the octanuclear complex [Au4Cu4-
(ethisterone)8] (4) or pentanuclear complex [PPN][Au3Cu2(ethisterone)6] (5). Complexes 2 and 3 react with
[Cu(MeCN)4][PF6] to form only pentanuclear Au(I)/Cu(I) complexes [PPN][Au3Cu2(1-ethynylcyclopentanol)6]
(6) and [PPN][Au3Cu2(1-ethynylcyclohexanol)6] (7). X-ray crystallographic studies of 1-3 reveal nontraditional
hydrogen bonding between hydroxyl groups and the acetylide units of adjacent molecules. Complexes 6
and 7 each form polymorphs in which the structures (6 a,b and 7 a,b,c) differ by Au · · ·Au, Au · · ·Cu, and
Cu-C distances. The polymorphs exhibit different emission energies with colors ranging from blue to
yellow in the solid state. In solution, pentanuclear clusters 5-7 emit with λmax ) 570-580 nm and Φ
) 0.05-0.19. Complex 4 emits at 496 nm in CH2Cl2 with a quantum yield of 0.65. Complex 5 exists
in equilibrium with 1 and 4 in the presence of methanol, ethanol, ethyl acetate, or water. This equilibrium
has been probed by X-ray crystallography, NMR spectroscopy, and luminescence experiments. DFT
calculations have been performed to analyze the orbitals involved in the electronic transitions of 4, 6,
and 7.
interactions16-18 but also by the potential for Au · · ·Cu or
Au· · ·Ag interactions between these closed-shell d10 ions. One
Introduction
Among polynuclear d10 complexes,1-6 examples incorporating
Au(I) acetylide units bound to Cu(I) or Ag(I) ions in an η2
fashion have emerged as an interesting set of systems that often
exhibit intense photoluminescence.7-15 In these compounds,
emission may be modified not only by aurophilic Au · · ·Au
strategy for the preparation of such compounds is the simple
addition of Cu(I) or Ag(I) ions to dinuclear phosphine-bridged
Au(I) acetylide complexes. In this context, Yam and co-workers
have shown that (1,1′-bis(diphenylphosphino)ferrocene)Au(I)
acetylides react with [Cu(MeCN)4]PF6 or AgOTf in a 1:1 ratio
to form what was postulated as a trinuclear Au2M (M ) Ag or
Cu) complex (I).15 Weakened CtC stretching frequencies and
red-shifted emission relative to the Au(I) precursors were
consistent with η2-coordination of the acetylide ligand to Ag(I)
or Cu(I). Structural characterization was absent for these
complexes, and therefore, the exact arrangement of Au(I) and
Cu(I) ions was not known.
† University of Rochester.
‡ Bucknell University.
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A R T I C L E S
Manbeck et al.
To obtain valuable structural information regarding complexes
of this type, de la Riva, et al., prepared a dinuclear Au(I)
phenylacetylide complex of 4,6-bis(diphenylphosphino)diben-
zofuran (dbfphos).13 The rigidity of the phosphine ligand was
expected to allow for crystallographic characterization of the
complexes. Addition of Cu(MeCN)4PF6 to [Au2(phenylacetylide)2-
(µ-dbfphos)] provided a dimeric Au4Cu2 complex (II) with two
Cu· · ·Au close contacts but no Au · · ·Au contacts. Solid-state
emission of the complex (530 nm) was red-shifted from that of
the Au(I) precursor (508 nm), consistent with the observations
of Yam and co-workers.15
ethisterone47-50 that were prepared with the goal of developing
therapeutic or imaging agents having significant affinity for the
estrogen receptor. While the ethynyl group of ethisterone is often
modified for the attachment of a transition metal, a few examples
exist in which the steroid is directly coordinated to the metal
as an acetylide after deprotonation35,44,49 or through the
acetylene π system.31,48 Among them, Au(PR3)(ethynylsteroid)
complexes exemplify the same basic architecture as the gold(I)
acetylide complexes mentioned above from which luminescent
mixed-metal complexes are generated upon addition of Cu(I)
ions. Analogues incorporating ethynylestradiol derivatives dis-
play significant binding affinities toward the estrogen receptor
ligand binding domains.49 Compounds of this type could be
important considering the extensive work directed toward gold(I)
Another set of Au(I)/Cu(I) complexes that exhibit Au · · ·Cu
contacts less than the sum of van der Waal radii is composed of
pentanuclear clusters of the formula [n-Bu4N][(Au(aryl-
acetylide)2)3M2] (M ) Ag, Cu) (III) (see Chart 1 for structures of
I, II, and III). Prepared from a mixture of [n-Bu4N][Au(aryl-
acetylide)2], polymeric gold(I) acetylide and copper(I) or silver(I)
acetylides in modest yields,19,20 these complexes consist of three
gold bis(acetylide) anions bridged by two Cu(I) ions through
π-coordination to the acetylide triple bonds. Only recently have
the photophysical properties of these complexes been examined
by absorption and emission spectroscopy and electronic structure
calculations.21 The authors concluded that the emission results from
a mixture of cluster-centered and acetylide-to-cluster charge transfer
excited states. Recently, related high nuclearity mixed Au(I)/Cu(I)
complexes that contain Au(phenylacetylide)2- units and η2-
acetylide bound Cu(I) ions have been prepared by self-assembly
without prior isolation of the anionic gold(I) complexes.9,11,12
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Chart 1
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The present study focuses on new, highly luminescent Au(I)/
Cu(I) clusters in the context of potential biological interest and
application. Ethisterone (17R-ethynyltestosterone) is an ethynyl
steroid derivative shown below. The literature is rich in examples
of organic and organometallic derivatives of estradiol22-46 and
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A R T I C L E S
Figure 1. Packing diagram for PPN Au(1-ethynylcyclopentanol)2 (2). PPN cations and CH2 atoms have been omitted for clarity.
complexes as anticancer and arthritis therapy agents.51-55
Moreover, luminescent Au(I) complexes with steroid ligands
may be useful not only as hormone therapy drugs, but also for
fluorescence imaging.
ized by NMR spectroscopy, microanalyses, and X-ray
crystallography.
In the X-ray structures of 1-3, nontraditional hydrogen
bonding is observed in which hydroxylic protons are directed
at the acetylide π systems of neighboring anions forming
infinite chains of the Au(I) bis(acetylide) anions (Figure 1).
While the geometry at gold is nearly linear in each structure,
Au1-C1-C2 and Au2-C3-C4 bond angles are somewhat
less than the 180° expected for sp-hybridized carbons. The
effect is a curvature that is particularly noticeable in 3 where
the Au1-C1-C2 and Au2-C3-C4 angles are 173.7(3)° and
167.1(4)°, respectively. The unconventional OH · · · π type of
hydrogen bonding seen for 1-3 has been reported in the
organometallic complex [Ni(Cp)PPh3(2-methyl-3-butyn-2-ol)]
in which spiral columns were formed in the extended
π-bonded structure.58
In light of the relative ease of synthesizing Au(I) bis(acetyl-
ide) complexes,56 the rich photophysical properties that have
been obtained by the reaction of these Au(I) acetylide anions
with Cu(I) ions, and the importance of transition metal
complexes incorporating steroid units, we chose to prepare
a mononuclear anionic Au(I) bis-ethisterone complex and
examine its reaction with [Cu(MeCN)4][PF6] to form new
highly luminescent complexes. In addition, we have prepared
model Au(I) bis-acetylide complexes incorporating 1-ethy-
nylcyclopentanol and 1-ethynylcyclohexanol in place of
ethisterone. These simpler ethynyl alcohols were chosen for
their resemblance to the steroid D-ring and the opportunity
to elucidate the effect of H-bonding and steroid structure on
the structural and photophysical properties of the mixed-metal
Au(I)/Cu(I) ethisterone complexes. The resultant systems
include an unprecedented octanuclear Au4Cu4 cluster and a
case of luminescence polymorphism in Au3Cu2 clusters in
which subtle differences in intramolecular Au · · · Au distances
appear to strongly influence solid-state emission energy.
Addition of [Cu(MeCN)4](PF6) to 1 in an equimolar ratio
provides an octanuclear complex, [{Au(ethisterone)2}4Cu4]
(4), which possesses a novel Au4Cu4 core as described below.
In contrast, when the ratio of Au:Cu in the reaction solution
is changed to 3:2, a pentanuclear complex is obtained as the
PPN+ salt, [PPN][{Au(ethisterone)2}3Cu2] (5). While complex
5 was the major product of this reaction, small amounts of
compound 4 were always present. Thus, the identity of 5
was confirmed by NMR spectroscopy and by comparison of
its photophysical properties to those of analogous penta-
nuclear complexes with 1-ethynylcyclopentanol and 1-eth-
ynylcyclohexanol ligands, [PPN][{Au(R)2}3Cu2] 6 and 7 (6,
R ) 1-ethynylcyclopentanol; 7, R ) 1-ethynylcyclohexanol).
These were prepared by the reaction of Au(I) complexes 2
and 3 with [Cu(MeCN)4][PF6] in a 3:1 ratio. Octanuclear
Au4Cu4 complexes with the 1-ethynylcyclohexanol and
1-ethynylcyclopentanol ligands were unobtainable. Room
Results and Discussion
Synthesis and Crystallography. Mononuclear gold(I) bis(acetyl-
ide) salts [PPN][Au(R)2] (PPN ) bis(triphenylphosphine)-
iminium) 1-3 (1, R ) ethisterone; 2, R ) 1-ethynylcyclo-
pentanol; 3, R ) 1-ethynylcyclohexanol) were prepared Via
the “acac method”57 from [PPN][Au(acac)2] and a slight
excess of alkyne. The complexes were crystallized by vapor
diffusion of ether into CH2Cl2 solutions and were character-
1
temperature H NMR spectra of 4-7 were complicated by
the presence of aliphatic resonances, and therefore, 13C NMR
spectroscopy proved essential for characterization of the
clusters. No resonances were observed for the alkyne carbons
coordinated to Cu(I) ions in 4, 6, or 7, but weak signals were
seen in 5. The pentanuclear complexes 5-7 (Chart 2)
exhibited a single set of ligand resonances in the 13C NMR
spectrum, suggesting C3 symmetry in solution. On the other
hand, two distinct sets of ligand resonances were clearly
visible for diagnostic protons (vinyl CH, OH, CH3) in the
1H NMR spectrum and for several resonances in the 13C NMR
spectrum of the Au4Cu4 complex 4 (see Supporting Informa-
tion).
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A R T I C L E S
Manbeck et al.
Figure 2. Perspective views of complex 4 displaying the (a) full structure, and the [Au(acetylide)2]4 Cu4 core from (b) a side view, (c) end-on.
Chart 2
approximately 26° while the C3-Au2-Au3-C5 dihedral angle
between the Au· · ·Au linked [{Au(ethisterone)2}2Cu2] units is
nearly 81°. The packing of complex 4 contains large channels
parallel to the a- and b-axes (see cif in Supporting Information).
Recently, somewhat similar coordination has been reported for
vapochromic [Au2Ag2(4-C6F4I)4] which can exist as a monomer
or a polymer.59 In the absence of acetylide donors, the Ag ions
are coordinated only to the Au(I) ions.
Crystallization of clusters 6, [PPN][{Au(ethynylcyclopentanol)2}3-
Cu2], and 7, [PPN][(Au{ethynylcyclohexanol)2}3Cu2], from mix-
tures of CH2Cl2 and ether at -15 °C provided two different types
of crystals of complex 6 and three different crystalline forms for
complex 7. Both forms of 6 were morphologically similar but were
distinguishable by their blue (6a) or yellow-green (6b) solid-state
emission (Figure 3). The three forms of cluster 7 were morphologi-
cally distinct with stacked blocks (blue emission, 7a), needles
(yellow-green emission, 7b), and large blocks (yellow emission,
7c). Form 7b was the major product when the crystals were grown
from CH2Cl2/ether in the freezer, while 7a was present to the extent
of ∼20% of the crystals, and 7c existed as a small minority.
Polymorph 7b was obtained exclusively by slow evaporation of
dichloromethane or by storing a solution of the complex in CH2Cl2
and hexanes (1:1 V:V) at -15 °C. Vapor diffusion of pentane into
concentrated THF solutions yielded only crystals of 7c. Recrys-
tallization of isolated forms of 6 or 7 provided mixtures of each
crystalline form. The complexes do not exhibit any luminescence
mechanochromism or vapochromism.
Complex 4, [{Au(ethisterone)2}4Cu4], crystallizes in the chiral
space group P41212 as a dimer of [{Au(ethisterone)2}2Cu2] units
connected by an unsupported Au · · ·Au interaction having an
exceptionally close contact of 2.927(1) Å which approaches the
2.889(1) Å Au · · ·Au distance found in metallic gold. Within
each Au2Cu2 unit, the Cu(I) ions bridge adjacent Au(I)
bis(acetylide) anions by coordination to the acetylenic π bonds
(Figure 2). The Cu-C distances in 4 range from 1.97(2) to
2.19(2) Å and Cu · · ·Au separations range from 2.948(2) to
2.955(2) Å. Longer metal-metal separations of 3.919 and 3.870
Å are found between Au1 · · ·Au2 and Au3 · · ·Au4, indicative
of the absence of any attractive interactions between these pairs
of Au(I) ions. The linear orientation of the four Au(I) atoms
and the relative positions of the acetylides are shown in Figure
2b. Dihedral angles between adjacent acetylides within each
[{Au(ethisterone)2}2Cu2] unit (i.e., C1-Au1-Au2-C3) are
(59) Laguna, A.; Lasanta, T.; Lopez-de-Luzuriaga, J. M.; Monge, M.;
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A R T I C L E S
bipyramid of metal ions (Figure 4). Intramolecular Au · · ·Au
distances range from 3.2913(3) to 3.5917(3) Å, while Cu · · ·Au
distances span a minimum of 2.7876(7) Å to a maximum of
3.0502(7) Å with the smaller distances being somewhat shorter
than the sum of van der Waals radii (3.06 Å) for Cu and Au.
The extended structure exhibits intermolecular hydrogen bond-
ing among -OH groups of the acetylide ligands. These
complexes should be considered pseudopolymorphs as a variety
of cocrystallized solvent molecules were found. Complex 6a is
solvent-free, but 6b cocrystallized with four molecules of
CH2Cl2, one of which is disordered with a PPN phenyl ring.
For complex 7a and 7b each contains disordered CH2Cl2 and
diethyl ether molecules, and 7c contains two solvents per
asymmetric unit. Detailed discussion regarding the treatment
of disordered solvent molecules is described in the Experimental
Section.
Significant differences between the polymorphic forms of 6
and 7 that appear to have spectroscopic consequences are found
upon close examination of the Au · · · Au, Au · · · Cu, and
Cu-C(acetylide) distances (Table 1). In 6a the Au1 · · ·Au2
distance is 3.2913(1) Å, while the Au1 · · ·Au3 and Au2 · · ·Au3
distances are significantly longer (∼3.55-3.59 Å). Conversely,
in 6b a narrow distribution of Au · · ·Au distances was found
(3.4145(3)-3.4822(4) Å). For 7a there are two Au · · ·Au
distances near 3.43 Å and one near 3.55 Å, while 7b and 7c
exhibit one short and two long or two short and one long
metal-metal distances, respectively. Smaller deviations among
Au· · ·Cu distances are found. The average Au · · ·Cu distance
in 6a is slightly greater than that of 6b, while 7c exhibits the
shortest and 7b exhibits the longest average Au · · ·Cu distances
among the polymorphs of 7. There are no significant differences
in the sets of Au-C and alkynyl C-C distances between
polymorphs of the same complex. In each complex, the distances
between copper atoms and gold-bound carbon atoms (CR) are
somewhat shorter than the Cu-Cꢀ distances, reflecting asym-
metric coordination of the Cu(I) ions to the acetylide π system.
This asymmetric coordination might be related to attractive
forces between Cu and Au ions.
Figure 3. Photographs of crystals of (a) isolated 6a (left), 6b with two
crystals of 6a grown together (right), (b) 7a on the left, and a mixture of
7b (green) and 7c (yellow) on the right, (c) isolated 7c under ambient light
(left) and UV irradiation (right). Slight differences in color between identical
polymorphs are an artifact of brightness and focus.
The structural results represent a rare example of lumines-
cence polymorphism in which the same compound exhibits
different color emissions based solely on differences in in-
tramolecular bond lengths. The only intermolecular interactions
are hydrogen bonds between -OH groups of the acetylide
ligands, but the influence of intermolecular hydrogen bonding
on intramolecular metal-metal distances can not be quantified
easily. Importantly, the aliphatic portions of the acetylide ligands
are not expected to be involved in the excited state. There is no
interaction with the PPN cation or cocrystallized solvent in any
of the pseudopolymorphs suggested here. Thus, different bond
Figure 4. ORTEP diagram for 6a with 40% thermal ellipsoids. Hydrogen
atoms have been omitted.
The structures of 6a, 6b, 7a, 7b, and 7c were determined
crystallographically and each was found to adopt a geometry
similar to those of aryl acetylide analogues reported in the
literature.19,21 Three Au(I) ions form a nearly equilateral triangle
that is capped on both faces by Cu(I) ions to give a trigonal
Table 1. Selected Bond Lengths (Å) in Structures of 6 and 7
6a
6b
7a
7b
7c
Au1-Au2
3.2913 (3)
3.5462 (3)
3.5917 (3)
2.8873 (5)
2.9951 (5)
3.0080 (5)
2.9981 (5)
2.9694 (5)
2.9312 (5)
2.9648
3.4273 (3)
3.4145 (3)
3.4822 (4)
3.0495 (7)
2.9140 (7)
2.9635 (7)
3.0205 (7)
2.9545 (7)
2.8137 (7)
2.9526
3.4206 (5)
3.5496 (5)
3.4383 (5)
3.0127 (8)
2.9118 (7)
2.9511 (7)
3.0127 (8)
2.9119 (7)
2.9511 (7)
2.9585
3.3728 (3)
3.5177 (3)
3.5123 (3)
3.0502 (7)
2.9280 (6)
2.8969 (6)
2.9459 (6)
2.9528 (6)
3.0493 (6)
2.9705
3.3541 (3)
3.3330 (3)
3.5683 (3)
2.7873 (6)
3.0058 (6)
2.9894 (6)
2.9017 (6)
3.0157 (7)
2.8508 (7)
2.9251
Au1-Au3
Au2-Au3
Cu1-Au1
Cu1-Au2
Cu1-Au3
Cu2-Au1
Cu2-Au2
Cu2-Au3
average Cu · · ·Au
average Cu-CR
average Cu-Cꢀ
2.142
2.333
2.129
2.414
2.147
2.359
2.135
2.403
2.130
2.443
9
J. AM. CHEM. SOC. VOL. 132, NO. 35, 2010 12311

A R T I C L E S
Manbeck et al.
Table 2. Summary of Photoluminescence Data
complex
absorptions/nm (ε/M-1 cm-1
)
medium (T/K)
emission λem/nm (τ/µs)
Φ
4
230 (29,790), 305 (5,410)
390 (5,703)
CH2Cl2 (298)
solid (298)
solid (77)
CH2Cl2
solid (298)
496 (1.5)
490 (1.1)
495 (1.9)
570 (3.0)
499 (14)
516 (27)
580 (8.9)
504 (7.0)
515 (11)
530 (29)
540 (84)
580 (21)
505 (14)
526 (36)
548 (39)
562 (58)
555 (14)
578 (57)
0.65
5
6
250, 274, 297, 320a
0.06b
0.05
solid (77)
235 (45,580), 269 (16,540)
276 (14,440), 295 (12,440)
320 (9,810)
CH2Cl2 (298)
6a solid (298)
6a solid (77)
6b solid (298)
6b solid (77)
CH2Cl2 (298)
7a solid (298)
7a solid (77)
7b solid (298)
7b solid (77)
7c solid (298)
7c solid (77)
7
235 (76,420), 269 (21,890)
276 (20,320), 295 (16,840)
320 (12,210)
0.19
a Extinction coefficients are unknown as 5 was never completely void of small amounts of 4 and 1 (see below). b Approximate value.
lengths in the pseudopolymorphs of 6 and 7, particularly
Au· · ·Au distances, are presumed responsible for the markedly
different emissions from identical molecules.
In a reported example, [Au{cyclohexyl isocyanide}2][PF6]
forms two different types of linear chains which are true
polymorphs and differ by their Au · · ·Au distances and emission
color.60,61 More typically, luminescence polymorphism arises
from varying packing arrangements which may be accompanied
by differing degrees of intermolecular interactions (i.e.,
metal-metal interactions or π stacking) which perturb the
excited state.62-70 In some cases, Au(I) cationic complexes
which differ only by the anion or incorporation of different
solvate molecules exhibit different emission properties related
to the solid-state packing.71,72 Balch and co-workers have shown
that hexagold(I) complexes exhibit a phase change to a different
polymorph that results in appreciable changes in aurophilic
interactions and consequently drastically different emission at
Figure 5. Absorption, excitation, and normalized emission spectra for
complex 4, [Au(ethisterone)2]4Cu4, in CH2Cl2 (1 × 10-5 M) and in the solid
state. Inset: Photographs of crystalline 4 under ambient light and UV
irradiation at room temperature.
298 K vs 77 K.73
Absorption and Emission Spectroscopy. Absorption and
emission spectra of the Au4Cu4 cluster 4 are presented in Figure
5 and summarized in Table 2. The absorption spectrum is
characterized by an intense band at 230 nm and two strong bands
at 305 and 390 nm. The electronic spectra of the Au3Cu2
pentanuclear clusters 5-7 are characterized by strong absorp-
tions at 230 nm and less intense shoulders ranging from 270 to
320 nm that decrease in intensity up to 350 nm (see Supporting
Information). Spacings between the shoulders from 275 to 320
nm are on the order of 2300-2800 cm-1, which may indicate
vibronic structure in the optical transitions. Notably, the low-
energy transitions in 5-7 are higher in energy than those
reported for similar Au3Cu2 clusters.21 High energy absorptions
in other Au(I) acetylide complexes have been assigned as
1(π-π*) transitions of the acetylide ligand.6,21,74,75 In consid-
eration of the vibronic structure in the absorptions of 5-7, a
1(π-π*) acetylide transition is plausible for these complexes
as well. The weak absorptions at ∼350 nm extending toward
the visible region may arise from cluster-centered (CC) or
ligand-to-metal charge transfer (LMCT) contributions as their
extinction coefficients drop substantially compared to the
absorptions bands at λ < 320 nm and no particular maxima are
apparent.
(60) White-Morris, R. L.; Olmstead, M. M.; Balch, A. L. J. Am. Chem.
Soc. 2003, 125, 1033.
(61) Balch, A. L. Gold Bull. 2004, 37, 45.
(62) Zhang, G.; Lu, J.; Sabat, M.; Fraser, C. L. J. Am. Chem. Soc. 2010,
132, 2160.
(63) Zhang, H.; Zhang, Z.; Ye, K.; Zhang, J.; Wang, Y. AdV. Mater. 2006,
18, 2369.
(64) Mizukami, S.; Houjou, H.; Sugaya, K.; Koyama, E.; Tokuhisa, H.;
Sasaki, T.; Kanesato, M. Chem. Mater. 2005, 17, 50.
(65) Gussenhoven, E. M.; Olmstead, M. M.; Fettinger, J. C.; Balch, A. L.
Inorg. Chem. 2008, 47, 4570.
(66) White-Morris, R. L.; Olmstead, M. M.; Attar, S.; Balch, A. L. Inorg.
Chem. 2005, 44, 5021.
(67) Toronto, D. V.; Weissbart, B.; Tinti, D. S.; Balch, A. L. Inorg. Chem.
1996, 35, 2484.
(68) Weissbart, B.; Toronto, D. V.; Balch, A. L.; Tinti, D. S. Inorg. Chem.
1996, 35, 2490.
(69) Kohmoto, S.; Tsuyuki, R.; Masu, H.; Azumaya, I.; Kishikawa, K.
Tetrahedron Lett. 2008, 49, 39.
(70) Lu, W.; Zhu, N. Y.; Che, C. M. J. Am. Chem. Soc. 2003, 125, 16081.
(71) Rios, D.; Olmstead, M. M.; Balch, A. L. Inorg. Chem. 2009, 48, 5279.
(72) Rios, D.; Olmstead, M. M.; Balch, A. L. Dalton. Trans. 2008, 4157.
(73) Gussenhoven, E. M.; Fettinger, J. C.; Pham, D. M.; Malwitz, M. M.;
Balch, A. L. J. Am. Chem. Soc. 2005, 127, 10838.
(74) Yam, V. W. W.; Choi, S. W. K.; Cheung, K. K. Organometallics
1996, 15, 1734.
(75) Lu, W.; Xiang, H. F.; Zhu, N. Y.; Che, C. M. Organometallics 2002,
21, 2343.
9
12312 J. AM. CHEM. SOC. VOL. 132, NO. 35, 2010

Luminescent Au(I)/Cu(I) Alkynyl Clusters
A R T I C L E S
Table 3. Calculated Energies, Oscillator Strengths (f), and Participating Orbitals for Complexes 4-C5,4-Me, and the Polymorphs of 6, and 7
complex
states
λcalculated
energy (cm-1
)
f
major orbitals
4-C5
T1
S1
S2
T1
S1
S2
402.4
361.0
338.3
391.1
350.9
332.1
24849
27702
29556
25184
28501
30115
0
HOMOfLUMO (100%)
HOMOfLUMO (87%)
HOMO-1fLUMO (85%)
HOMOfLUMO (102%)
HOMOfLUMO (84%)
HOMO-2fLUMO (33%)
HOMO-1fLUMO (59%)
HOMOfLUMO (98%)
HOMOfLUMO (96%)
HOMOfLUMO (96%)
HOMOfLUMO (93%)
HOMOfLUMO (98%)
HOMOfLUMO (96%)
HOMOfLUMO (96%)
HOMOfLUMO (96%)
HOMOfLUMO (78%),
HOMO-1fLUMO (19%)
HOMOfLUMO (83%)
HOMO-1fLUMO (13%)
0.5599
0.1016
0
0.6903
0.0041
4-Me
6a
6b
7a
7b
7c
T1
S1
T1
S1
T1
S1
T1
S1
T1
391.8
373.8
390.9
370.4
393.1
372.9
408.9
387.0
379.0
25521
26750
25580
26995
25436
26816
24453
25841
26383
0
0.0013
0
0.0014
0
0.0002
0
0.0008
0
S1
359.8
27796
0.0015
Upon excitation into either absorption band of complex 4 in
fluid CH2Cl2, emission at 496 nm (Φ ) 0.65, τ ) 1.5 µs) is
observed. While the lifetime of 1.5 µs is suggestive of a triplet
excited state, the emission of 4 is not quenched by oxygen. In
dichloromethane, the pentanuclear clusters emit at 570 nm (5)
and 580 nm (6 and 7) with quantum yields in the range of
(0.05-0.19) and lifetimes of several microseconds (see Sup-
porting Information for emission spectra). The similarity of
solution emission energies for complexes 6 and 7 suggests that
the saturated cyclopentyl and cyclohexyl rings are not involved
in the excited state. Unlike complex 4, the emission intensities
of 5-7 are strongly attenuated in the presence of O2.
All complexes exhibit bright solid-state emission at room
temperature and at 77 K. For complex 4 a slight red shift from
490 to 495 nm is observed upon cooling from 298 to 77 K,
while larger red shifts of 10-20 nm occur for the pentanuclear
clusters 5-7. Lifetimes at 77 K are somewhat longer than at
room temperature. As shown in Figure 6, emission maxima for
polymorphs 6a and 6b at 298 K differ by 26 nm (973 cm-1),
and polymorphs 7a and 7b exhibit emission maxima differing
by 43 nm (1554 cm-1). The energy difference is more subtle
between 7b and 7c (7 nm, 230 cm-1).
and the oscillator strength for the two lowest energy singlet states
(S1, S2) and the lowest-energy triplet state (T1) are listed in Table
3. All calculated transitions as well as the predicted absorption
spectrum are provided as Supporting Information. From Figure
7 it can be seen that the highest occupied molecular orbital
(HOMO) is composed mainly of Au and Cu d-orbitals with
greater contributions from the Au2 and Au3 atoms that are
connected by an unsupported aurophilic interaction along with
some contribution from the acetylide πb orbitals as well. The
Au2· · ·Au3 interaction in the HOMO is antibonding. The lowest
unoccupied molecular orbital (LUMO), on the other hand, is
composed principally of acetylide π* functions and Au and Cu
s and p orbitals. HOMO-1 consists of Au and Cu d-orbitals
but is localized on only one of the two Au2Cu2 moieties.
Inspection of HOMO-2 to HOMO-6 (Supporting Information)
reveals nearly identical compositions for HOMO-1 and HO-
MO-2 with similar pairings of HOMO-3/-4 and HOMO-5/
-6.
We viewed the asymmetry in the HOMO-1/-2 pair of
orbitals with some suspicion and were puzzled as to whether
this might have been an artifact of the calculation. To probe
this further, the structure was simplified to a methyl group set
in place of the 1-cyclopentanol moiety to give [{Au-
(methyl acetylide)2}4Cu4] (4-Me). While the orbital composi-
tions and calculated transition energies remained similar to 4-C5
(Figure 8), HOMO-1 and HOMO-2 are properly matched and
are nearly degenerate (-6.19 and -6.20 eV). By matched, we
mean that HOMO-1 is primarily located on the left half of the
dimer, while HOMO-2 is nearly its mirror image. Likewise,
HOMO-3/-4 and HOMO-5/-6 are paired spatially although
energies are slightly different.
Electronic Structure Calculations. Time-dependent density
functional (TD-DFT) calculations at the B3LYP/6-31G(d) level
were performed on a simplified octanuclear complex [{Au-
(1-ethynylcyclopentanol)2}4Cu4] (4-C5) using the crystallo-
graphically determined geometry for complex 4. This simplified
model was used to reduce computational expense. The calculated
parameters including the energy gap in wavenumbers and nm
The calculated absorption spectrum of 4-Me (Figure S24,
Supporting Information) qualitatively matches the experimental
absorption spectrum with the two lowest energy singlet absorp-
tions attributed to the (1) HOMOfLUMO and (2) (HOMO-1
fLUMO) + (HOMO-2 fLUMO) transitions. Contributions
from both HOMO-2 and HOMO-1 in the second excited state
can be understood in terms of configuration mixing for these
nearly degenerate orbitals. The similarity between experimental
and calculated spectra supports the use of 4-Me as a model for
4, and implies orbitals of the steroid ligand are not involved in
the lowest excited states. The orbital identities suggest an
Figure 6. Solid-state emission spectra of the polymorphic forms of
complexes 6 and 7 at room temperature.
3
assignment of the excited state in 4 as cluster-centered (CC)
9
J. AM. CHEM. SOC. VOL. 132, NO. 35, 2010 12313

A R T I C L E S
Manbeck et al.
Figure 7. Calculated frontier orbitals and energies for complex 4-C5.
Figure 9. Frontier orbitals of the T1 state of 4-Me with the higher SOMO
(-1.41 eV) on the left and the lower SOMO (-3.77 eV) on the right.
Figure 10. Calculated (a) HOMO (-2.7 eV) and (b) LUMO (1.41 eV) of
polymorph 6a [PPN][(Au(ethynylcyclopentanol)2)]3Cu2.
would occur in the solid state. As shown in Figure 9, the singly
occupied orbitals (SOMOs) of T1 are nearly identical in
composition to the HOMO and LUMO of the singlet ground
state, further supporting the excited-state assignment.
Figure 8. Frontier orbitals for complex 4-Me. Isovalue ) 0.025.
3
possibly mixed with some intraligand (π-π*) states. This
Time-dependent DFT calculations for the pentanuclear clusters
6 and 7 indicate that the lowest-energy S0fS1 and S0fT1
transitions in these Au3Cu2 complexes are largely HOMOfLUMO
in nature although slight mixing of HOMO-1fLUMO occurs to
a modest extent in several of the compounds. Similar frontier
orbitals were calculated for each polymorph of 6 and 7. The HOMO
is composed of gold and copper d orbitals and πb-orbitals of the
acetylide ligands, while the LUMO consists of gold sp-hybridized
orbitals mixed with π* orbitals of the acetylides (Figure 10). This
description agrees with the reported electronic structure of [{Au(4-
tolylacetylide)2}3M2] (M ) Cu, Ag) in which analysis of the frontier
orbitals was used to explain the difference in emission energy
assignment, in conjunction with a space-filling model of the
complex (Figure S5, Supporting Information), offers a possible
explanation for the absence of emission quenching by molecular
oxygen in solution. Since the emissive core of the molecule is
highly shielded by the eight steroid ligands, interaction of the
luminophore with a quenching O2 molecule is precluded.
A single point energy calculation of the lowest energy triplet
state (T1) was performed to model the electronic structure upon
promotion of an electron from the highest occupied orbital to
the LUMO. The ground state geometry was used for the
calculation with the assumption that negligible geometry changes
9
12314 J. AM. CHEM. SOC. VOL. 132, NO. 35, 2010

Luminescent Au(I)/Cu(I) Alkynyl Clusters
A R T I C L E S
Figure 11. (a) Titration of 5 with methanol. Complex 5 emits at 570 nm, while complex 4 emits at 490 nm. λexc ) 390 nm. (b) Ratio of the emission
intensity at 490 to 570 during the titration of complex 5 with CH3OH or CD3OD.
between Ag(I) and Cu(I) congeners.21 However, in the present
work, analysis of the calculated HOMO/LUMO gaps does not
clearly model the experimentally observed trends regarding solid-
state emission energies between the polymorphs of 6 and 7 (6a >
6b and 7a > 7b > 7c). For complex 6, only a difference of 161
cm-1 was calculated between the HOMO/LUMO gaps of the two
polymorphs with a larger gap for 6b. The HOMO/LUMO gap of
7c, which exhibits yellow emission, is calculated to be 1,855 cm-1
higher in energy than that of the green emitting form, 7b. Similar
results were obtained using a simplified form of each complex
[PPN][Au3Cu2(CtCCH3)6] with the core geometry of the parent
compound. Analysis of the time-dependent calculations does not
resolve the issue. As seen in Table 3, calculated T1 and S1 energies
suggest very similar energy transitions for 6b and 6a. For complex
7 polymorphs, the calculations predict emission energies in the
order: 7c > 7a > 7b. The lowest-energy triplet states were calculated
for the propyne models, Au3Cu2(CtCCH3)6 to examine the singly
occupied molecular orbitals. For complex 6a, the triplet calculation
did not converge; however in all other examples, the higher SOMO
is identical to the ground state LUMO while the lower SOMO of
T1 is similar in composition to the ground state HOMO (Figures
S33-S36, Supporting Information).
While the luminescence polymorphism in these complexes
arises from ligand-to-cluster charge transfer (LCCT) states in
3
triangular Au3 cores, the assignment differs from that in other
+
polymorphic Au(I) complexes in which linear AuR2 cations
are linked into chains by aurophilic interactions.60 Complexes
differing by the counteranion or cocrystallized solvent form
extended structures in similar ways.71,72 The aurophilic bonding
2
in these types of aggregates arises from overlap of gold 5dz
orbitals to produce filled σb and σ* MOs stabilized by config-
uration interaction with collinear empty pz orbitals. The pz
orbitals form a similar but empty set of MOs. Excitation
b
2
promotes an electron from the 5dz σ* band to the 6pz σ band
and therefore it would be anticipated that different Au · · ·Au
separations would affect the energy of this transition. In the
present work on triangular AuI3 complexes, acetylide π-functions
contribute strongly to the HOMO, while metal-metal antibond-
ing contributions are small. Most similar to the Au(I) chains
found in the literature is complex 4 with a linear arrangement
of four Au(I) ions, two of which are quite close. In this case,
the calculated highest occupied molecular orbital is indeed
Au-Au anti-bonding with respect to the closely interacting
Au(I) ions and the σb MO containing overlapping Au2-Au3
2
Although the HOMO/LUMO gaps or calculated absorption
energies do not correlate with observed emission energies among
polymorphs of clusters 6 and 7, the DFT calculations provide
insight in assigning the nature of the excited state as primarily
5dz orbitals, which was found to be MO number 114, (-9.37
eV, Figure S37, Supporting Information) is much lower in
energy than the HOMO.
Equilibrium Between Complexes 4 and 5. During the prepa-
ration of crystallization solutions of [PPN][{Au(ethisterone)2}3-
Cu2] (5), it was noticed that the addition of some solvents
(MeOH, EtOH, EtOAc, H2O) to CH2Cl2 solutions of this
pentanuclear complex resulted in a change in emission from
yellow to the blue color characteristic of [{Au(ethister-
one)2}4Cu4] (4). The yellow emission persisted in the presence
of THF, pentane, hexanes, or ether. The process is reversible:
if a few drops of MeOH are added, followed by dilution with
CH2Cl2, the emission returns to yellow. Addition of more
methanol results in blue emission again.
3
3(CC) in 4 and as ligand-to-cluster charge transfer (LCCT) in
5-7. The contribution of the acetylides to the excited state is
evident in the experimental absorption spectra of 5-7 which
show some vibronic structure whereas the absorption in 4
exhibits broad bands.
In complexes 6 and 7, Au· · ·Au distances range from
3.2913(3) Å to 3.5917(3) Å with the latter generally believed
to be outside the range of significant interactions. The variety
in Au · · ·Au distances is most likely responsible for the distinct
differences in emission energy although subtle differences in
Au· · ·Cu distances may play a role. In light of the calculated
nature of the HOMO and LUMO (i.e., metal-metal antibonding
in the HOMO and metal-metal bonding character of the
LUMO), closer Au · · ·Au distances would be predicted to raise
the HOMO and lower the LUMO although the extent of each
effect is difficult to judge. This influence on the LUMO energy
was found computationally with the exception of 7c. The variety
of Au · · ·Au distances within each Au3 triangle of a single
complex compromises the ability to predict emission energy
from crystallographic data.
The 13C NMR spectrum of 5 in CD2Cl2 displays major and
minor components for some resonances in an approximate 10:1
ratio. Addition of CD3OD (1:1 V/V with CD2Cl2) results in an
increase of the minor component (Supporting Information).
Upon standing overnight, the NMR solution provided crystals
of 4. Crystals of mononuclear 1 grew during slow evaporation
of the remaining mother liquor.
A solution of 5 in dichloromethane was titrated with methanol
and the emission spectra were recorded (Figure 11). With an
increase in MeOH, the emission at 570 nm from complex 5
9
J. AM. CHEM. SOC. VOL. 132, NO. 35, 2010 12315

A R T I C L E S
Manbeck et al.
decreases while the emission at 495 nm from complex 4
increases. A nearly isoemissive point occurs at 535 nm during
the titration. The titration and 13C NMR results may be explained
by an equilibrium between complexes 5 and 4 + 1 (eq 1 where
ethist ) ethisterone). Formation of 4 thus appears to be favored
in the presence of polar solvents capable of hydrogen-bonding
either as H-bond donors or acceptors. To test this theory,
methanol was added to yellow-emitting solution of 5 in CH2Cl2
to provide blue-emitting 4. Complex 1 was then added to perturb
the equilibrium and the yellow emission of 5 returned. The
process was repeated by further addition of methanol then
complex 1 to the same result. Addition of 1 to a pure solution
of 4 resulted in formation of 5 as well.
In the solid state, Au3Cu2 complexes with 1-cyclopentanol
or 1-cyclohexanol alkynyl units exhibit an interesting example
of luminescence polymorphism in which the color of emission
varies, depending on the intramolecular atomic distances in the
core of the clusters. The variety in distances may be influenced
by a combination of attractive forces among closed-shell d10
Au(I) and Cu(I) ions and by intermolecular hydrogen-bonding
schemes which were found to link the Au3Cu2R6 complex anions
into infinite chains in the solid state. Absorption and emission
spectroscopy and lifetime measurements in conjunction with
DFT calculations have led to an assignment of the excited state
3
as (acetylide π-to-Au3Cu2 cluster) charge transfer. With this
assignment, different emission among polymorphs of the same
complex can be understood as arising from some perturbation
of the frontier orbitals evidenced by the different intramolecular
d10-d10 M· · ·M distances observed.
2[PPN][{Au(ethist)2}3Cu2] h
5
[{Au(ethist)2}4Cu4] + 2[PPN][Au(ethist)2] (1)
4
1
Experimental Section
The single set of impurity resonances in the 13C NMR
spectrum of 5 is likely an averaged signal resulting from rapid
exchange between 4 and 1. Otherwise, the impurity should be
General Considerations. NMR spectra were obtained using
1
Bruker Avance 400 and 500 MHz spectrometers with H and 13C
NMR chemical shifts referenced to residual solvent peaks in CDCl3,
CD2Cl2, or DMSO-d6. 31P{1H} NMR data are referenced to external
85% H3PO4. Mass spectra of bis(acetylide) gold(I) ions were
measured on a Shimadzu 2010 series liquid chromatography mass
spectrometer (LC/MS) under negative mode electrospray ionization
(ESI). Absorption spectra were measured on a Hitachi U-2000
UV-vis spectrometer. Steady-state excitation and emission spectra
were obtained using a Spex Fluoromax-P fluorometer. Solution
emission measurements were performed in quartz cuvettes equipped
with screw-cap lids and septa, and samples were deoxygenated by
purging with N2 for at least 15 min prior to obtaining spectra. For
titration experiments, deoxygenated methanol was added via 10 µL
syringe to a deoxygenated CH2Cl2 solution of complex 4 through
the septum. Solid-state emission samples were prepared by packing
a capillary tube with the emissive complex in a matrix of KBr (∼1%
by wt). For low temperature measurements, the capillary was held
in a vacuum dewar filled with liquid nitrogen. Lifetime measure-
ments were performed using a model LN203C nitrogen laser (Laser
Photonics Inc.) with λ ) 337.1 nm and a 0.1 nm spectral width
pulsed at 1 pulse/second. Signals were detected by a silicon
photodiode and photomultiplier tube (1P28 type) with a 2 ns rise
time and viewed with a Hewlett-Packard 54510-B oscilloscope
connected to a computer Via a GPIB interface. No less than five
decay curves were averaged data fitting.
characterized by two resonances from pure 4 and one signal
-
from free Au(ethist)2
.
Considering the nature of solvents that promote the formation
of 4 and 1 from 5, the response could result from a dielectric
effect, a hydrogen-bonding driven process, or a combination
of both. To probe the influence of hydrogen bonding, the titration
of 5 in CH2Cl2 was performed with CH3OH and CD3OD in
order to examine the extent to which complex 4 is formed from
5 in the presence of either solvent. The titration was carried
out at 5 × 10-6 M, and the emission of the mixture was
monitored using 390 nm as the excitation wavelength. To
elucidate the effects of CH3OH vs CD3OD, the ratio of emission
intensity at 490 nm (complex 4) to the intensity at 570 nm (5)
was plotted vs titrant volume.
The data from both titrations have been fit to sigmoidal curves
(Figure 10b). For the MeOH titration, the maximum ratio of
intensities at 490-570 nm is 35.9 ( 0.8 with half equivalence
occurring at 150 µL of added methanol. When titrated with
methanol-d4, half equivalence is reached after 93 µL and the
maximum ratio of intensities is calculated as 9.7 ( 0.1.
Evidently, equilibrium (1) lies further to the right in the presence
of protonated methanol relative to that in methanol-d4. This
observation is consistent with an equilibrium isotope effect in
which H-bonding of 4 + 1 with solvent is more favorable for
O-H than O-D relatiVe to the zero-point energies of O-H
and O-D in 5.
Syntheses were carried out under at atmosphere of N2 using
standard Schlenk conditions. Dichloromethane for reactions and
photophysical measurements was dried by passage through an
alumina solvent system. 1-ethynyl-1-cyclopentanol, 1-ethynyl-1-
cyclohexanol, and ethisterone were purchased from Aldrich chemi-
cal company and used as received. [PPN][Au(acac)2] was prepared
according to the literature.76
Crystal Structure Determinations. Each crystal was placed onto
the tip of a glass fiber using Paratone and mounted on a Bruker
SMART Platform diffractometer equipped with an APEX II CCD
area detector. All data were collected at 100.0(1) K using Mo KR
radiation (graphite monochromator).77 For each sample, a set of
preliminary cell constants and an orientation matrix were determined
from reflections harvested from three orthogonal wedges of
reciprocal space. Full data collections were carried out with frame
exposure times of 45 (1, 6a, 6b, 7b, and 7c), 60 (2, 3, 7a) or 90
(4) seconds at detector distances of 4 cm for 1-3, 6a, 6b, and
7a-7c or 6 cm for complex 4. Randomly oriented regions of
reciprocal space were surveyed for each sample: four major sections
Conclusions
Pentanuclear Au3Cu2 complexes with hydroxyl-aliphatic
acetylide ligands can be prepared as PPN salts directly from
Au(I) bis(acetylide) precursors and a Cu(I) source. When the
acetylide is ethisterone, Au3Cu2 and Au4Cu4 clusters are
obtained. The latter is a brightly emissive dimer exhibiting an
unsupported aurophilic interaction between the central Au(I)
atoms. [PPN][{Au(ethisterone)2}3Cu2] (5) is not particularly
stable in solution and converts to the octanuclear complex (4)
and the Au(I) bis(ethisterone) precursor (1) in a hydrogen-
bonding assisted equilibrium which was probed by luminescence
titration experiments. The octanuclear excited state is assigned
as cluster-centered with particularly strong contribution from
an anti-bonding Au2 · · ·Au3 interaction to the HOMO.
(76) Vicente, J.; Chicote, M. T.; Saurallamas, I.; Lagunas, M. C. J. Chem.
Soc., Chem. Commun. 1992, 915.
(77) Saint Bruker AXS, Madison WI, 2008.
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Luminescent Au(I)/Cu(I) Alkynyl Clusters
A R T I C L E S
of frames were collected with 0.50° steps in ω at four different
settings and a detector position of -38° in 2θ. The intensity data
were corrected for absorption,78 and final cell constants were
calculated from the xyz centroids of approximately 4000 strong
reflections from the actual data collection after integration.77
Structures were solved using SIR9779 and refined using SHELXL-
97.80 Space groups were determined on the basis of systematic
absences and intensity statistics. For complex 1, a Paterson method
solution was calculated which provided the location of the gold
atoms from the E-map. For all other complexes, direct-methods
solutions were calculated which provided most non-hydrogen atoms
from the difference Fourier map. Full-matrix least-squares (on F2)/
difference Fourier cycles were performed which located the
remaining non-hydrogen atoms which were refined with anisotropic
displacement parameters. Absolute configurations for structures in
chiral (1, 4, 6b) and noncentrosymmetric (7b) space groups were
determined by anomalous dispersion effects. For complexes 1, 2,
6a, and 7b, hydroxide hydrogen atoms were found from the
difference map and then refined as riding atoms with relative
isotropic displacement parameters. For 6b, 7a, and 7c, hydroxide
hydrogen atoms could not be found and were placed in reasonable
hydrogen-bonding positions on the basis of precedent in 6a and
7b. For 3, all hydrogen atoms, and all nonhydroxide hydrogen atoms
of all other structures were placed in ideal positions and refined as
riding atoms with relative isotropic thermal parameters. For complex
4, hydroxide hydrogen atoms were placed on the basis of residual
peaks in the difference Fourier map prior to application of
SQUEEZE;81 one set is directed at the neighboring hydroxide
oxygen atom, while the other is directed out into the solvent. Alkyne
C-C bond lengths were restrained to be similar.
The cation and anion in 7a are modeled as disordered over
crystallographic mirror planes. One cocrystallized diethyl ether
molecule is modeled as disordered over a mirror plane as well.
Complex 7b packs with a disordered combination of cocrystallized
dichloromethane and diethyl ether molecules in channels parallel
to the c-axis. One solvent site is modeled as a 45:55 disorder of
one ether molecule and two dichloromethane molecules while the
other site is modeled as 83:17 disorder of one diethyl ether molecule
and one dichloromethane molecule. In 4 highly disordered cocrys-
tallized solvent was found in channels parallel the a- and b-axes.
In 7c highly disordered solvent was found in four sites, each
occupied by two solvent molecules. Reflection contributions from
this solvent in 4 and 7c were removed using the function SQUEEZE
in the program PLATON which determined there to be 2097
electrons in 3975 Å3 removed per unit cell in 4 and 355 electrons
in 3975 Å3 removed per unit cell in 7c. Minor merohedral inversion
twinning in 4 was refined to a mass ratio of 94:06.
performed on structures for which 1-cyclopentanol and 1-cyclo-
hexanol moieties were replaced with methyl groups (6a-Methyl,
6b-Methyl, etc.) Triplet calculations were performed using the
restricted open shell method (roB3LYP) which forces R ) ꢀ. For
the octanuclear complex, 4, ethisterone ligands were reduced to
1-ethynylcyclopentanol (4-C5) then further simplified to methyl
acetylide (4-Me) in each case using the X-ray geometry for the
core. TD-DFT was used to calculate the six lowest singlet and triplet
energy absorptions from the S0 state.
[PPN][Au(ethisterone)2] (1). A mixture of [PPN][Au(acac)2]
(0.232 g, 0.25 mmol) and ethisterone (0.194 g, 0.62 mmol) was
stirred in CH2Cl2 (15 mL) for 3 h covered with foil. The solution
was filtered through Celite, concentrated to 1-2 mL, and added
dropwise to 100 mL of rapidly stirring ether. The white precipitate
was collected and dried to yield 0.310 g of 1 in 92% yield. X-ray-
quality crystals were obtained by diffusion of diethyl ether into a
1
CH2Cl2 solution of the complex. H NMR (DMSO-d6, 25 °C): δ
7.70-7.68 (m, 6H, PPN), 7.58-7.54 (m, 24H, PPN), 5.60 (s, 2H,
dCH-), 4.39 (s, 2H, -OH), 2.39-2.34 (m, 4H, -CH-, -CH2-),
2.22-2.11 (m, 4H -CH-, -CH2-), 1.95-1.07 (m, 26H, -CH-,
-CH2-), 1.12 (s, 6H, -CH3), 0.92-0.76 (m, 4H, -CH-,
-CH2-), 0.68 (s, 6H, CH3). 13C{1H} NMR (CD2Cl2, 25 °C): δ
199.5 (s, quat), 172.4 (s, quat), 134.3 (s, Ar-CH), 132.7 (m,
Ar-CH), 130.0 (m, Ar-CH), 127.6 (d, J ) 108), 127.6 (s, tC-),
124.0 (s, -CH-, vinyl), 105.1 (s, tC-), 80.7 (s, quat), 53.7 (s,
-CH-), 50.0 (s, -CH-), 46.8 (s, quat), 40.2 (s, -CH2-), 39.2
(s, quat), 37.0 (s, -CH-), 36.1 (s, -CH2-), 34.5 (s, -CH2-),
33.5 (s, -CH2-), 33.2 (s, -CH2), 32.0 (s, -CH2-), 23.6 (s,
-CH2-), 21.5 (s, -CH2), 17.9 (s, -CH3), 13.2 (s, -CH3). 31P{1H}
NMR (DMSO-d6, 25 °C): δ 21.9 (s, PPN) MS (ESI negative)
819.15. Anal. Calc for C78H84AuNO4P2 · CH2Cl2: C, 67.30; H, 6.12;
N, 1.00. Found: C, 67.61; H, 6.23.
[PPN][[Au(1-ethynyl-cyclopentanol)2] (2). To a CH2Cl2 (10
mL) solution of [PPN][Au(acac)2] (0.163 g, 0.175 mmol) was added
a CH2Cl2 (5 mL) solution of 1-ethynylcyclopentanol (0.059 g, 0.54
mmol). The reaction was covered with aluminum foil and stirred
for 5 h. A white precipitate was collected and washed with CH2Cl2
(3 mL) and diethyl ether (50 mL) to provide 0.140 g of the title
compound in 84% yield. Analytically pure, X-ray-quality crystals
were grown by diffusion of diethyl ether into a dilute dichlo-
1
romethane solution of the complex. H NMR (DMSO-d6, 25 °C):
δ 7.71-7.69 (m, 6H, PPN), 7.60-7.53 (m, 24H, PPN), 4.42 (s,
2H, -OH), 1.63-1.53 (m, 16H, -CH2-). 13C{1H} NMR (DMSO-
d6, 25 °C): δ 133.7 (s, PPN), 132.0 (m, PPN), 129.5 (m, PPN),
126.8 (d, J ) 106, PPN), 125.1 (s, tC-), 106.0 (s, tC-), 73.1
(s, quat), 42.8 (s, -CH2-), 23.1 (s, -CH2-). 31P{1H} NMR
(DMSO-d6, 25 °C): δ 21.9 (s, PPN). MS (ESI negative) 414.95.
Anal. Calc for C50H48AuNO2P2: C, 62.96; H, 5.07; N, 1.47. Found:
C, 62.67; H, 4.91; N, 1.53.
Theoretical Calculations. DFT and time-dependent density
functional (TD-DFT) calculations were carried out using the
B3LYP82,83 method as implemented by Gaussian 03.84 The
LANL2DZ85-88 effective core potential was used for Au and Cu,
while the 6-31G(d) basis set was applied for C, H, and O atoms.
For the [Au3Cu2] anionic polymorphs of complexes 6 and 7, full
geometries from the X-ray experiments were used. Additional single
point calculations of the singlet (S0) and triplet (T1) states were
[PPN][Au(1-ethynyl-cyclohexanol)2] (3). A mixture of [PPN]
[Au(acac)2] (0.244 g, 0.262 mmol) and 1-ethynylcyclohexanol
(0.097 g, 0.79 mmol) was stirred in CH2Cl2 (10 mL) for 4 h covered
with foil The solution was filtered through Celite, concentrated to
1-2 mL, and added to 75 mL of rapidly stirred ether to provide a
fine white precipitate which was triturated for 1 h and collected by
vacuum filtration to provide 0.200 g of product in 80% yield. X-ray-
quality crystals were obtained by diffusion of diethyl ether into a
(78) APEX2 Bruker AXS: Madison, WI, 2009.
(79) Altomare, A. B., M.C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. Istituto
di Cristallografio, CNR: Bari, Italy, 1999.
(80) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(81) Spek, A. L.; PLATON: A Multipurpose Crystallographic Tool, version
300106; Utrecht University: Utrecht, The Netherlands, 2006.
(82) Becke, A. D. J. Chem. Phys. 1993, 98, 5652.
(83) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(84) Frisch, M. J. T.; et al.; Gaussian 03, revision C.02; Gaussian, Inc.:
Wallingford CT, 2004.
(85) Dunning, T. H. , Jr.; Hay, P. J. In Modern Theoretical Chemistry;
Schaefer, H. F., III., Ed.; Plenum: New York, 1976; Vol. 3, pp 1-28.
(86) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270.
(87) Hadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(88) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
1
CH2Cl2 solution of the complex. H NMR (DMSO-d6, 25 °C): δ
7.70-7.68 (m, 6H, PPN), 7.60-7.53 (m, 24H, PPN) 4.48 (s, 2H,
-OH), 2.51-1.37 (m, 12H, -CH2-), 1.36-1.28 (m, 6H, -CH2-),
1.11-1.08 (m, 2H, -CH2-). 13C{1H} NMR (DMSO-d6, 25 °C):
δ 133.6 (s, PPN), 131.9 (m, PPN), 129.5 (m, PPN), 126.8 (d, J )
107, PPN), 125.9 (s, tC-), 105.7 (s, tC-), 66.9 (s, quat), 41.1
(s, -CH2-), 25.3 (s, -CH2-), 23.0 (s, -CH2-). 31P{1H} NMR
(DMSO-d6, 25 °C): δ 21.9 (s, PPN). MS (ESI negative) 443.00.
Anal. Calc for C52H52AuNO2P2: C, 63.61; H, 5.34. Found: C, 63.05;
H, 5.33.
[{Au(ethisterone)2}4Cu4] (4). A mixture of 1 (0.100 g, 0.074
mmol) and [Cu(MeCN)4][PF6] (0.024 g, 0.074 mmol) was stirred
9
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A R T I C L E S
Manbeck et al.
for 3 h in 5 mL of CH2Cl2. The entire solution was set up for
crystallization by vapor diffusion of ether into the CH2Cl2. After
several days at room temperature, white flaky crystals were collected
(0.055 g, 85%); however, NMR analysis revealed contamination
by [PPN][PF6]. Pure samples were obtained by vapor diffusion of
(s, 6H, -OH), 1.84-1.80 (m, 24H, -CH2-), 1.66-1.59 (m, 24H,
-CH2-) 13C{1H} NMR (CD2Cl2, 25 °C): δ 133.8 (s, PPN), 132.2
(m, PPN), 129.5 (m, PPN), 127.0 (d, J ) 107, PPN), 75.9 (s, quat),
43.4 (s, -CH2-), 23.5 (s, -CH2-). 31P{1H} NMR (CD2Cl2, 25
°C): δ 22.4 (s, PPN). Anal. Calc for C78H84Au3Cu2NO6P2: C, 49.01;
H, 4.43. Found: C, 48.84; H, 4.43.
1
ether into a solution of the complex in 1:1 V/V MeOH/CH2Cl2. H
NMR and microanalyses revealed the presence of ∼4 water
[PPN][{Au(1-ethynyl-cyclohexanol)2}3Cu2] (7). Complex 3
(0.045 g, 0.046 mmol) and [Cu(MeCN)4][PF6] (0.0099 g, 0.031
mmol) were stirred for 4 h in 5 mL of CH2Cl2, diluted with 10 mL
of ether and filtered through a glass frit. The filtrate was stored in
the freezer to provide a mixture of 7a, 7b, and 7c which were
collected by centrifugation and washed with diethyl ether to yield
0.026 g (85% yield) of complex 7 as a mixture of polymorphs.
Individual polymorphs were obtained as described in the synthesis
molecules per complex in the crystals. This agrees with the presence
1
of unknown solvent in the X-ray structure. H NMR (CD2Cl2, 25
°C, 400 MHz): δ 5.94 (s, 4H, dCH-), 5.69 (s, 4H, dCH-), 4.49
(s, 4H, -OH), 3.82 (s, 4H, -OH), 2.65-1.25 (m, 136 H, -CH-,
-CH2-), 1.10-0.85 (m, 16H, -CH-, -CH2-), 1.20 (s, 12H,
-CH3), 1.13 (s, 12H, -CH3), 0.89 (s, 12H, -CH3), 0.86 (s, 12H,
-CH3). 13C{1H} NMR (CD2Cl2, 25 °C, 400 MHz): δ 202.8 (s,
quat), 199.6 (s, quat), 172.2 (s, quat), 171.2 (s, quat), 125.4 (s,
-CH-, vinyl), 124.1 (s, -CH-, vinyl), 81.5 (s, quat), 80.9 (s,
quat), ∼53.7 (s, -CH-, (overlapped with CD2Cl2), 50.5 (s,
-CH-), 49.1 (s, -CH-), 48.2 (s, quat), 46.6 (s, quat) 42.2, 41.8,
39.5, 39.0, 36.9, 36.5, 36.2, 34.5, 34.3, 33.1, 32.3 (s, -CH2-),
23.9 (s, -CH2-), 23.6 (s, -CH2-), 21.3 (s, -CH2), 21.1 (s,
-CH2-), 17.7 (s, -CH3), 13.3 (s, -CH3). 31P{1H} NMR (CD2Cl2,
25 °C): δ 22.3 (s, PPN). Anal. Calc for C168H216Au4Cu4O16 ·4H2O:
C, 55.96; H, 6.26. Found: C, 55.90; H, 6.32.
1
section. H NMR (CD2Cl2, 25 °C): δ 7.67-7.58 (m, 6H, PPN),
7.51-7.43 (m, 24H, PPN), 1.98-1.90 (m, 12H, -CH2-), 1.57-1.16
(m, 42H, -CH2-), 1.16-1.13 (m, 6H, -CH2-). 1H NMR (DMSO-
d6, 25 °C): δ 7.70-7.57 (m, 6H, PPN), 7.57-7.54 (m, 24H, PPN),
5.41 (br, 6H, -OH), 1.78 (m, 10H, -CH2-), 1.52-1.15 (m, 42H,
-CH2-), 1.14-1.07 (m, 8H, -CH2-). 13C{1H} NMR (CD2Cl2,
25 °C): δ 133.7 (s, PPN), 132.1 (m, PPN), 129.5 (m, PPN), 127.0
(d, J ) 108, PPN), 69.4 (s, quat), 40.4 (s, -CH2-), 25.5 (s,
-CH2-), 23.5 (s, -CH2-). 31P{1H} NMR (CD2Cl2, 25 °C): δ 22.4
(s, PPN). Anal. Calc for C84H96Au3Cu2NO6P2: C, 50.56; H, 4.85.
Found: C, 50.35; H, 5.04.
[PPN][{Au(ethisterone)2}3Cu2] (5). A mixture of 1 (0.185 g,
0.14 mmol) and [Cu(MeCN)4][PF6] (0.030 g, 0.092 mmol) was
stirred for 4 h in 5 mL of CH2Cl2. The volume was reduced to 2
mL, and diethyl ether was added to precipitate complex 5 and
1
Acknowledgment. Professor Tom Cundari (U. of North Texas)
and Dr. Theresa McCormick are gratefully acknowledged for fruitful
discussions concerning DFT calculations. We thank Christopher
M. Evans for assistance with lifetime measurements and crystal
photographs, and the National Science Foundation GOALI program
(Grant CHE-0616782) for support of this research.
[PPN][PF6] for a total of 0.194 g (97% for 5 · 2 [PPN]PF6) H
NMR (CD2Cl2, 25 °C): δ 7.68-7.65 (m, 6H, PPN), 7.51-7.47 (m,
24H, PPN), 5.61 (s, 6H, dCH-), 4.47 (s, 6H, -OH), 2.60-2.25
(m, 30 H, -CH-, -CH2-), 2.00-1.26, (m, 60 H, -CH-,
-CH2-), 1.19-1.02 (m, 12H, -CH-, -CH2-), 1.15 (s, 18H,
-CH3), 0.82 (s, 18H, -CH3). 13C{1H} NMR (CD2Cl2, 25 °C): δ
199.4 (s, quat), 172.1 (s, quat), 134.3 (s, Ar-CH), 132.7 (m,
Ar-CH), 130.0 (m, Ar-CH), 127.6 (d, J ) 107), 124.0 (s, -CH-,
vinyl), 115.3 (s, tC-), 111.8 (s, tC-), 81.3 (s, quat), 53.7 (s,
-CH-), 50.1 (s, -CH-), 47.6 (s, quat), 39.2 (s, -CH2-), 39.0
(s, quat), 37.1 (s, -CH-), 36.1 (s, -CH2-), 34.5 (s, -CH2-),
33.5 (s, -CH2-), 33.0 (s, -CH2), 32.0 (s, -CH2-), 23.6 (s,
-CH2-), 21.4 (s, -CH2), 17.8 (s, -CH3), 13.5 (s, -CH3). 31P{1H}
NMR (CD2Cl2, 25 °C): δ 22.3 (s, PPN).
Supporting Information Available: Complete reference 84,
ORTEP diagrams, refinement parameters, and packing diagrams
for 1, 2, 4, 6a, 6b, 7a, 7b, 7c, space filling diagram for 4,
crystallographic data in cif format, absorption, excitation,
emission for 4, 5, 6, 7, calculated absorption spectra and
transition lists for 4-C5 and 4-Me, triplet orbitals for 4-Me,
frontier orbital diagrams and tables of all calculated transitions
for 6a, 6b, 7a, 7b, 7c, orbital diagrams for S0 and T1 of
[PPN][{Au(1-ethynyl-cyclopentanol)2}3Cu2] (6). Complex 2
(0.115 g, 0.121 mmol) and [Cu(MeCN)4][PF6] (0.026 g, 0.080
mmol) were stirred for 4 h in 6 mL of CH2Cl2. Ten milliliters of
ether was added, and the mixture was filtered through a fine glass
frit. The filtrate was left stored in the freezer whereupon crystals
of 6a (32 mg) and 6b (32 mg) formed and were separated carefully
by hand for a total of 64 mg (84% yield). 1H NMR (DMSO-d6, 25
°C): δ 7.71-7.60 (m, 6H, PPN), 7.60-7.52 (m, 24H, PPN), 5.20
1
simplified 6a, 6b, 7a, 7b, 7c, H and 13C NMR of complexes
with ethisterone (1, 4, 5) This material is available free of charge
via the Internet at http://pubs.acs.org.
JA103400E
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12318 J. AM. CHEM. SOC. VOL. 132, NO. 35, 2010