Synthesis and structures of cyclic gold complexes containing diphosphine ligands and luminescent properties of the high nuclearity species

Article abstract of DOI:10.1039/c2dt11722c

A mixture of cyclic gold(i) complexes [Au₂(μ-cis-dppen) ₂]X₂ (X = OTf 1, PF₆3) and [Au(cis-dppen) ₂]X (X = OTf 2, PF₆4) is obtained from the reaction of [Au(tht)₂]X (tht = tetrahydrothiophene) with one equivalent of cis-dppen [dppen = 1,2-bis(diphenylphosphino)ethylene]. The analogous reaction with trans-dppen or dppa [dppa = bis(diphenylphosphino)acetylene] affords the cyclic trinuclear [Au₃(μ-trans-dppen)₃]X₃ (X = OTf 11, PF₆12) and tetranuclear [Au₄(μ-dppa) ₄]X₄ (X = OTf 13, PF₆14, ClO₄15) gold complexes, respectively. Recrystallization of 15 from CH₂Cl ₂/MeOH yielded a crystal of the octanuclear gold cluster [Au ₈Cl₂(μ-dppa)₄](ClO₄) ₂16. Attempts to prepare dicationic binuclear gold(ii) species from the reaction of a mixture of 3 and 4 with halogens gave a mixture of products, the components of which confirmed to be acyclic binuclear gold(i) [Au ₂X₂(cis-dppen)] (X = I 5, Br 7) and cyclic mononuclear gold(iii) [AuX₂(cis-dppen)]PF₆ (X = I 6, Br 8) complexes. Complexes 11-14 reveal weak emission in butyronitrile glass at 77 K, but they are non-emissive at room temperature. Ab initio modelling was performed to determine the charge state of the gold atoms involved. Extensive structural comparisons were made to experimental data to benchmark these calculations and rationalize the conformations. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt11722c

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PAPER
Synthesis and structures of cyclic gold complexes containing diphosphine
ligands and luminescent properties of the high nuclearity species†
Suresh Bhargava,*a Kunihiko Kitadai,b Takahashi Masashi,b Daniel W. Drumm,a,c Salvy P. Russo,a,c Vivian
Wing-Wah Yam,d Terence Kwok-Ming Lee,d Jörg Waglere and Nedaossadat Mirzadeha
Received 12th September 2011, Accepted 24th January 2012
DOI: 10.1039/c2dt11722c
A mixture of cyclic gold(I) complexes [Au2(μ-cis-dppen)2]X2 (X = OTf 1, PF6 3) and [Au(cis-dppen)2]X
(X = OTf 2, PF6 4) is obtained from the reaction of [Au(tht)2]X (tht = tetrahydrothiophene) with one
equivalent of cis-dppen [dppen = 1,2-bis(diphenylphosphino)ethylene]. The analogous reaction with
trans-dppen or dppa [dppa = bis(diphenylphosphino)acetylene] affords the cyclic trinuclear [Au3(μ-trans-
dppen)3]X3 (X = OTf 11, PF6 12) and tetranuclear [Au4(μ-dppa)4]X4 (X = OTf 13, PF6 14, ClO4 15) gold
complexes, respectively. Recrystallization of 15 from CH2Cl2/MeOH yielded a crystal of the octanuclear
gold cluster [Au8Cl2(μ-dppa)4](ClO4)2 16. Attempts to prepare dicationic binuclear gold(II) species from
the reaction of a mixture of 3 and 4 with halogens gave a mixture of products, the components of which
confirmed to be acyclic binuclear gold(I) [Au2X2(cis-dppen)] (X = I 5, Br 7) and cyclic mononuclear gold
(III) [AuX2(cis-dppen)]PF6 (X = I 6, Br 8) complexes. Complexes 11–14 reveal weak emission in
butyronitrile glass at 77 K, but they are non-emissive at room temperature. Ab initio modelling was
performed to determine the charge state of the gold atoms involved. Extensive structural comparisons
were made to experimental data to benchmark these calculations and rationalize the conformations.
investigated, with one factor being the size of the ring formed.
Treating a polymeric gold acetylide complex with Ph2P
Introduction
There has been remarkable interest in the synthesis and proper-
ties of metallomacrocycles, constructed through coordination-
directed self-assembly of metal centers and multidentate ligands,
or self-assembly through non-covalent interactions. These syn-
thetic strategies have allowed the design and isolation of cate-
nanes, rotaxanes and knots.1–3 Gold chemistry has contributed a
great deal to the broad field of metallomacrocycles4–11 exhibiting
particular promise as optical materials.12–14 Linear
coordination11,15–17 and aurophilic interactions between metal
centres are two leading factors for the use of gold complexes in
the formation of complex molecular structures by self-
assembly.11,15,18–23 The factors that influence the formation of
the cyclic gold complexes and catenanes have also been
(CH2)nPPh2 (n = 2) gave a discrete cyclic species, while larger
phosphines (n = 4, 5) gave only catenanes; when n = 3, a
mixture of both species was obtained.24
Ditertiaryphosphine ligands are known to act as chelating or
bridging groups to form cyclic gold complexes11 and a number
of binuclear compounds have been prepared.25–30 The geometry
of the diphosphine ligand can also play an important role in the
formation of metal complexes. For example, treatment of a sol-
ution of sodium tetrachloroaurate with one equivalent of cis-
dppen gives the binuclear complex [Au2Cl2(cis-dppen)] in which
the diphosphine ligand bridges two metal centers. In contrast,
the analogous reaction using trans-dppen gives the mononuclear
complex [AuCl(trans-dppen)], in which only one of the phos-
phine centres is coordinated.31 Recently, the structure of
[Au2(cis-dppen)2](NO3)2 has been reported, the crystals of
which contain discrete voids capable of capturing and releasing
gas molecules.32
Polynuclear gold complexes containing diphosphine ligands
have been shown to exhibit interesting photophysical properties.
The binuclear gold compound [Au2(dppm)2](ClO4)2 [dppm =
bis(diphenylphosphino)methane] shows a long-lived emission at
565 nm in acetonitrile and a number of organic halides
have been found to quench its emission in acetonitrile.33
Reaction of dppm with [Au(CuCPh)]∞ in ethanol affords
[Au3(μ2-dppm)2(CuCPh)2][Au(CuCPh)2] which is photolumi-
nescent in the solid state and in solution.34 The binuclear and tri-
nuclear gold(I) complexes containing dmpm [dmpm = bis
aAdvanced Materials & Industrial Chemistry, School of Applied
Sciences, RMIT University, GPO Box 2476V, Melbourne, Victoria3001,
Australia. E-mail: Suresh.bhargava@rmit.edu.au
bDepartment of Chemistry, Toho University, Chiba, Japan
cApplied Physics, School of Applied Sciences, RMIT University, GPO
Box 2476V, Melbourne, Victoria3001, Australia
dInstitute of Molecular Functional Materials (Areas of Excellence
Scheme, University Grants Committee (Hong Kong)), and Department
of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, PR China
eInstitut für Anorganische Chemie, Technische Universität
Bergakademie, Freiberg D-09596, Germany
†Electronic supplementary information (ESI) available. CCDC numbers
843620–843626. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt11722c
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Scheme 1 Reaction of [Au(tht)2]X (X = OTf, PF6) with one equivalent of cis-dppen.
(dimethylphosphino)methane] [Au2(dmpm)2](ClO4)2 and dmmp
[dmmp bis(dimethylphosphinomethyl)methylphosphine]
=
[Au3(dmmp)2](ClO4)3 have been reported to exhibit intriguing
emission properties.35
In view of this varied behaviour of dppen, we were interested
in further exploring its use as a ligand for the formation of gold
complexes. The use of the related alkyne analogue of dppen, bis
(diphenylphosphino)acetylene, was also investigated and the
photoluminescence behaviour of the products was studied.
Results and discussions
Cyclic mono- and binuclear gold complexes
The reaction of [Au(tht)2]OTf with one equivalent of cis-dppen
(Scheme 1) gave an air- and moisture-stable pale yellow powder,
the 31P NMR spectrum of which showed two singlet resonances
at δ 23.1 and 25.1, suggesting the presence of two species. Slow
recrystallization of this solid gave a mixture of colorless and
yellow crystals, identified by X-ray crystallography to be cyclic
binuclear gold(I) complex [Au2(μ-cis-dppen)2](OTf)2 (1) and tet-
rahedrally coordinated mononuclear gold(I) complex [Au(cis-
dppen)2]OTf (2), respectively. The molecular structure of 1,
which is analogous to [Au2(cis-dppen)2](NO3)2,32 is shown in
Fig. 1; selected bond lengths and angles are summarized in the
caption to Fig. 1. The 31P NMR spectrum of the isolated solid
resulting from the reaction of [Au(tht)2]PF6 with one equivalent
of cis-dppen showed identical resonances. By analogy to the
triflate analogues 1 and 2, these resonances were assigned to
[Au2(μ-cis-dppen)2]PF6 (3) and [Au(cis-dppen)2]PF6 (4)
(Scheme 1). Complex 4 has been previously reported by
Berners-Price et al., and was obtained as a pure compound from
the thiodiglycol reduction of Na[AuCl4] in the presence of cis-
dppen and NH4PF6.36
Fig. 1 Molecular structure of 1. Ellipsoids show 70% probability
levels. Hydrogen atoms and OTf counterion have been omitted for
clarity. Selected bond distances (Å) and angles (°) in 1. Au(1)⋯Au(1*)
2.9802(2), Au(1)–P(1) 2.2937(6), Au(1)–P(2*) 2.3172(6), P(1)–C(13)
1.812(3), P(2)–C(14) 1.810(3), C(13)–C(14) 1.333(4); C(14)–P(2)–Au
(1*) 119.17(9), C(14)–C(13)–P(1) 126.5(2), P(1)–Au(1)–Au(1*)
108.115(17), P(1)–Au(1)–P(2*) 161.95(2), P(2*)–Au(1)–Au(1*) 84.561
(16). Labels with an asterisk denote atoms at an equivalent position (−x,
1 − y, 1 − z) generated by inversion symmetry.
Å].39 The Au–P distances of 2.2937(6) Å and 2.3172(6) Å are
almost identical to the bonds in [Au2{μ-(2-C6H3-6-Me)PPh2}2]
[2.302(2) Å and 2.295(2) Å]38 and [Au2(cis-dppe)2](NO3)2
[2.303(2)–2.324(2) Å]. The P–Au–P angle [161.95(2)°] is con-
siderably distorted from linear coordination, most likely as a con-
sequence of aurophilic interaction.
Complex 1 contains two linearly coordinated gold(I) atoms
bridged by the dppen ligands, forming a ten-membered ring con-
sisting of two gold, four phosphorus and four ethylenic carbon
atoms.
Reactions with halogens
The Au⋯Au distance of 2.9802(2) Å in 1 is characteristic of
an aurophilic interaction37 and is slightly longer than the corre-
sponding separation in [Au2(cis-dppe)2](NO3)2 [2.904(2) Å],32
Au2(μ-dppm)2]Cl2 [2.962(1) Å],26 [Au2{μ-(2-C6H3-6-Me)
PPh2}2] [2.861(2) Å]38 and [Au2(μ-dppe)2](OTf)2 [2.9594(10)
There is an ever growing family of binuclear gold(II) complexes
containing metal–metal bonds being reported in literature,40
however dicationic digold(II) species are extremely rare; the only
reported examples being [Au2X2(dppam)2][ClO4]2 [X = Cl, Br;
dppam = bis(diphenylphosphino)amine], derived from reaction
4790 | Dalton Trans., 2012, 41, 4789–4798
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Scheme 2 Reaction of mixture of 3 and 4 with iodine.
Fig. 3 Molecular structure of [Au2Br2(cis-dppen)] (7). Ellipsoids show
50% probability levels. Hydrogen atoms have been omitted for clarity.
Fig. 2 The molecular structure of [AuI2(cis-dppen)]PF6 (6). Ellipsoids
show 30% probability levels. Hydrogen atoms and PF6 counterion have
been omitted for clarity. Selected bond lengths (Å) and angles (°): Au
(1)–P(1) 2.3189(12), Au(1)–P(2) 2.3273(12), Au(1)–I(1) 2.6306(4), Au
(1)–I(2) 2.6246(4); P(1)–Au(1)–I(1) 90.84(3), P(2)–Au(1)–I(2) 89.36(3),
P(1)–Au(1)–P(2) 86.60(4), I(1)–Au(1)–I(2) 93.218(15).
Table 1 Selected bond distances (Å) and angles (°) in complexes 5, 7
and 9
5 (X = I)a 5 (X = I)
7 (X = Br) 9 (X = Cl)b
Au(1)–Au(2)
Au(1)–P(1)
Au(2)–P(2)
Au(1)–X(1)
Au(2)–X(2)
C(13)–C(14)
2.9526(5) 2.9714(12) 3.0020(4)
3.05(1)
2.256(3)
2.253(2)
2.243(5)
2.231(5)
2.2065(19) 2.226(4)
2.2308(18) 2.239(5)
of [Au2(dppam)2][ClO4]2 with halogens.41 Given the structural
similarity between this gold(I) complex and [Au2(cis-dppen)2]
(PF6)2 (3), the oxidative addition reaction of halogens was
investigated.
2.5629(9) 2.5656(15) 2.4246(8)
2.5385(9) 2.5801(16) 2.4149(8)
2.299(5)
2.289(5)
1.331(18)
172.5(2)
173.3(2)
1.332(14) 1.30(3)
1.328(10)
X(1)–Au(1)–P(1) 174.80(7) 171.44(14) 171.55(6)
X(2)–Au(2)–P(2) 170.36(7) 169.37(14) 171.90(5)
Treating
a mixture of [Au2(cis-dppen)2](PF6)2 (3) and
a Data from ref. 42. b Data from ref. 44.
[Au(cis-dppen)2]PF6 (4) with I2, Br2 or PhICl2 gave air- and
moisture-stable red, yellow and pale yellow solids, respectively,
whose 31P NMR spectra showed two peaks [X = I (δ 15.6, 22.5),
Br (δ 14.1, 22.6)] or four peaks [X = Cl (δ 10.1, 12.9, 21.1,
22.5)]. Recrystallization of the red powder (X = I) from dichloro-
methane/ether at −18 °C gave a mixture of colorless and red
crystals, the identities of which were confirmed by X-ray crystal-
lography study to be [Au2I2(cis-dppen)] (5) and mononuclear
gold(III) complex [AuI2(cis-dppen)]PF6 (6), respectively
(Scheme 2). The crystal structures of [Au2I2(cis-dppen)] (5) has
been reported in literature and its photochemical conversion has
been investigated.42 By analogy to the observed trend in 31P
NMR resonances of [(AuCl)2(cis-dppen)] (δ 12.5) and [Au(cis-
dppen)2]Cl (δ 22.4) in which dppen acts as bridging and chelat-
ing ligands, respectively, the resonance at δ 15.6 was assigned to
5 and the resonance at δ 22.5 to 6.43
Complex 6, whose structure is shown in Fig. 2 (selected bond
distances and angles of 6 are shown in the caption), consists of
one gold(III) atom coordinated in a planar geometry by two
mutually cis phosphorus atoms of a dppen ligand and two iodine
atoms. The Au–P [2.323 (av.) Å] and Au–I [2.628 (av.) Å] dis-
tances are similar to the corresponding bonds in [IAu(μ-2-C6H3-
6-Me-2-PPh2)(κ2-C6H3-6-Me-2-PPh2)AuI] are 2.347(3) and
2.645(1) Å, respectively.38
Analogous reaction with Br2 has formed two species which
were tentatively assigned to complexes [Au2Br2(cis-dppen)] (7)
and [AuBr2(cis-dppen)]PF6 (8), based on their similar 31P NMR
chemical shifts (δ 14.1 and 22.6, respectively) to 5 and 6. The
structure of 7 was later confirmed by X-ray crystal structure
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Scheme 3 Reaction of [Au(tht)2]X (X = OTf, PF6) with one equivalent of trans-dppen.
determination and is shown in Fig. 3; selected bond distances in
7 are summarized in Table 1.
Reaction of the mixture of 3 and 4 with PhICl2 was more
complex than expected, and the resulting solid exhibited four 31
P
NMR resonances, two of which at δ 12.9 and 22.5 can be
assigned to [Au2Cl2(cis-dppen)] (9) [AuCl2(cis-dppen)]PF6 (10),
respectively, but the other two remain unidentified. Attempts to
separate the pale yellow mixture (X = Cl) into its components by
fractional crystallization from dichloromethane/ether at room
temperature and at −18 °C were not successful.
The Au–Au distances in 5, 7 and 9 decrease in the order Cl >
Br > I. The gold(I) atoms in 5, 7 and 9 are coordinated almost
linearly by the phosphine and halogen atoms [∠X–Au–P ca.
170°]. The X–Au–P angle increases in the order I < Br < Cl, pre-
sumably due to the increasing size of halide.
Fig. 4 Molecular structure of [Au3(μ-trans-dppen)3](OTf)3 11. Ellip-
soids show 30% probability levels. OTf counterions have been omitted
for clarity and only the ipso carbons of the PPh2 groups are shown.
Cyclic tri- and tetranuclear gold complexes
The reaction of [Au(tht)2]X (X = OTf, PF6) with one equivalent
of trans-dppen gave the cyclic trinuclear gold complexes
[Au3(μ-trans-dppen)3]X3 (X = OTf 11, PF6 12) (Scheme 3), as
white powders in high yields. The 31P NMR spectra of 11 and
12 each showed a single resonance at δ 41 ppm and the FAB
mass spectra showed a peak at m/z 594. Elemental analyses were
consistent with the empirical formula [Au(dppen)]X. The struc-
ture of 11 has been confirmed by single crystal X-ray diffraction
(Fig. 4) and shown to be an energetic minimum by ab initio cal-
culations. A comparison of selected bond lengths and angles is
shown in Table 2. To aid in obtaining a chemically intuitive
understanding of the structure, the charge state of the Au atoms
was also calculated, and found to be neutral. Analysis of the
electronic density of states showed a bandgap in the meV range,
well under the onset of the visible spectrum near 1.77 eV.
The cyclic trication is generated by a crystallographic three-
fold axis, and thus has a three-fold symmetric structure. Two of
the three corresponding triflate ions are located on three-fold
axes, surrounded with phenyl groups; the third triflate anion was
heavily disordered and could not be located. Almost all of the
known cyclic trinuclear gold(I) complexes reported in the litera-
ture contain bidentate N,N or C,N donor ligands; examples
include [Au3(CH3NvCOCH3)3] A,45 [Au3(pz)3] (pz = 3,5-
diphenylpyrazolato anion) B46 and [Au3(NC5H4)3] C.47 The
Table 2 Selected bond distances (Å) and angles (°) in complex 11
XRD
DFT
Au(1)–P(1)
Au(1)–P(2)
P(1)–C(13)
2.2923(11)
2.3054(11)
1.786(4)
2.30
2.30
1.77
P(2)–C(14)
1.816(4)
1.77
P(1)–Au(1)–P(2)
C(13)–P(1)–Au(1)
C(14)–P(2)–Au(1)
174.20(4)
113.64(16)
112.83(14)
176.53
114.25
113.17
only reported cyclic trinuclear gold(I) complex containing a
diphosphine ligand is [Au3(PAnP)3](ClO4)3 [PAnP = 9,10-bis-
(diphenylphosphino)anthracene].48 While the conformations of
the neutral complexes A, B and C are planar, those of 11 and
[Au3(PAnP)3](ClO4)3 have a cyclohexane-like chair confor-
mation. The Au–P distances in 11 [2.2923(11) and 2.3054(11)
Å] are similar to those in 1 [2.2937(6) and 2.3172(6) Å] and
[Au3(PAnP)3](ClO4)3 [2.294(3)–2.312(3) Å]. The gold atoms are
almost linearly coordinated by two phosphorus atoms [P(1)–Au
(1)–P(2) 174.20(4)°].
4792 | Dalton Trans., 2012, 41, 4789–4798
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Scheme 4 Reaction of [Au(tht)2]X with an equimolar amount of dppa.
Table 3 Selected bond distances (Å) and angles (°) in complex 14
XRD
DFT
Au(1)–P(1)
Au(1)–P(2)
P(2)–C(25)
C(25)–C(26)
P(1)–Au(1)–P(2)
C(25)–P(2)–Au(1)
C(26)–C(25)–P(2)
2.278(2)
2.295(2)
1.698(9)
1.239(16)
177.85(7)
114.2(5)
175.3(16)
2.28
2.27
1.73
1.23
177.67
105.86
169.46
S-bridged [{Au2(C6H4S2-1,2)(PEt3)}2].52 The XRD data for 14
was used to build a stable ab initio model without the structural
disorder seen in the anions and phenyl groups; a comparison of
selected bond lengths (Å) and angles (°) is shown in Table 3.
Analysis of the electronic density of states showed a bandgap in
the meV range (∼80 meV), with energies far less than those of
photons in the visible spectrum. The charge state of the Au
atoms was evaluated as neutral.
Interestingly, recrystallization of 15 from CH2Cl2/MeOH gave
orange crystals which were shown by X-ray crystallography to
be the octanuclear gold cluster [Au8Cl2(μ-dppa)4](ClO4)2 16; all
attempts to isolate 16 in a pure form failed. The structure of 16 is
shown in Fig. 6 and selected bond lengths and angles are sum-
marized in Tables 4 and 5, respectively. This structure has been
modeled with ab initio techniques, and analysis of the electronic
density of states gave a bandgap of 2.05 eV, corresponding to a
photon of wavelength 605 nm which matches well with the
observation of orange (∼590 nm) crystals.
The complex 16 has −1 symmetry and contains eight gold
atoms, six of which form two edge-shared tetrahedra with Au–
Au distances in the range of 2.6–2.8 Å. Coordinated to the two
gold atoms of the Au6 core, sitting in the vertices of the shared
edges of two tetrahedra, are two dppa ligands, which also coordi-
nate from the other side to the terminal univalent gold atoms,
bonded to chlorine groups and phosphorus atoms of bridging bis
(diphenylphosphino)acetylene; these gold atoms exhibit linear
Fig. 5 Molecular structure of [Au4(μ-dppa)4](PF6)4 14. Ellipsoids
show 20% probability levels. Only the ipso carbons of the PPh2 groups
are shown.
Tetranuclear gold(I) complexes [Au4(μ-dppa)4]X4 (X = OTf
13, PF6 14, ClO4 15), shown in Scheme 4, were prepared from
the reaction of [Au(tht)2]X with an equimolar amount of dppa.
Complexes 13–15 each show a singlet at ca. δ 17 ppm in their
31P NMR spectra and a parent ion peak in their FAB mass
spectra. The structure of 14, shown in Fig. 5, has been confirmed
by X-ray crystallography from crystals grown from CH2Cl2/
ether.
The XRD structure of [Au4(μ-dppa)4](PF6)4 14 was of poor
quality, and only used for confirming the overall structure.
Several complexes containing Au4L4 type structure have been
reported in the literature including P-bridged [{Au(PMes2)}4]
(Mes = 2,4,6-Me3C6H2),49 N-bridged [{Au(μ-3,5-tBu-pz)}4]
(pz
=
pyrazolato anion),50 [{Au[μ-N(SiMe3)2]}4]51 and
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coordination (ca. 177°). The other four gold atoms in the Au6
core are coordinated by two dppa ligands to generate a 12-mem-
bered ring in which the gold atoms display almost linear geome-
try (ca. 175°). The structure is comprised of the twelve-
membered ring and an S-shaped chain; the two fragments are
held together by aurophilic interactions. The shortest gold–gold
distances in 16 are between Au(2) and Au(2*) [2.6192(7) Å] and
Au(3) and Au(4) [2.6205(6) Å], slightly shorter than those
reported for the Au5 cluster [Au5(C6H4PPh2)4]CF3SO3 (2-OTf)
[2.709(2) and 2.701(2) Å] obtained by the reaction of
[Au2(C6H4PPh2)2] with trifluoromethanesulfonate at −78 °C.53
The gold–gold distances in 16 [ca. 2.6–3 Å] are typical of gold–
phosphine clusters, [Au8(PPh3)8](aliz)2 (aliz = alizarinsulpho-
nate) [2.587(5)–2.878 Å],54 [Au8(PPh3)8](PF6)2] [2.635(8)–
2.896(8) Å],55 [Au5(dppmH)3(dppm)](NO3)2 [dppm
=
(Ph2PCHPPh2)−] (2.70–3.01 Å),56 [Au9{P(C6H4-p-Me)3}8]
(PF6)3 2.689(3)–2.868(3) Å,57 and [Au8(PPh3)7](NO3)2 [2.629
(5)–2.942(6) Å].58
Fig. 6 Molecular structure of 16. Ellipsoids show 50% probability
levels. The phenyl rings of the PPh2 groups only show the ipso carbons.
Atoms with an * in the atom labels are at equivalent position (2 − x, 1 −
y, −z) generated by inversion symmetry.
Photophysical studies
The electronic absorption data of the cyclic gold(I) complexes
[Au3(μ-trans-dppen)3]X3 (X
[Au4(μ-dppa)4]X4 (X = OTf 13, PF6 14) in dichloromethane at
=
OTf 11, PF6 12) and
Table 4 Selected bond lengths (Å) in 16
Bond
XRD
DFT Bond
XRD
DFT
Au(1)–Au(4)
Au(2)–Au(4)
Au(3)–Au(4)
Au(1)–Au(3)
Au(2)–Au(2*) 2.6192(7) 2.69 Au(3)–P(3)
Au(2)–Au(3*) 2.7887(5) 2.85 Au(4)–P(4)
Au(2)–Au(4*) 2.7989(6) 2.83 Au(1)–Cl(1)
2.9738(6) 3.06
2.8144(6) 2.89 Au(3)–Au(2) 2.8403(5) 2.87
2.6205(6) 2.67 Au(1)–P(1)
3.0522(6) 3.00 Au(2)–P(2)
—
—
—
Table 6 Electronic absorption data for complexes 11–14 in
dichloromethane at ambient temperature
2.245(3)
2.276(2)
2.297(3)
2.294(3)
2.313(2)
2.28
2.31
2.32
2.32
2.35
Compound
λabs/nm (ε/dm3 mol−1 cm−1
)
11
12
13
14
268 sh (34 505), 278 sh (24 245)
268 sh (33 595), 278 sh (23 710)
272 sh (27 740), 278 sh (22 070)
272 sh (26 190), 280 sh (18 200)
Asterisks denote atoms generated by symmetry.
Table 5 Selected bond angles (°) in 16
Bond angle
XRD
DFT
Bond angle
XRD
DFT
Au(2*)–Au(2)–Au(3)
Au(2*)–Au(2)–Au(3*)
Au(2*)–Au(2)–Au(4)
Au(2*)–Au(2)–Au(4*)
Au(2)–Au(3)–Au(1)
Au(2*)–Au(3)–Au(1)
Au(2*)–Au(3)–Au(2)
Au(3)–Au(4)–Au(2*)
Au(3)–Au(4)–Au(2)
Au(4)–Au(1)–Au(3)
Au(4)–Au(3)–Au(1)
Au(4)–Au(3)–Au(2)
Au(4)–Au(3)–Au(2*)
P(1)–Au(1)–Au(4)
P(2)–Au(2)–Au(2*)
P(2)–Au(2)–Au(3*)
P(2)–Au(2)–Au(4*)
P(3)–Au(3)–Au(2)
P(3)–Au(3)–Au(4)
P(4)–Au(4)–Au(2)
P(4)–Au(4)–Au(3)
61.275(16)
63.274(16)
61.886(16)
62.487(17)
109.853(16)
122.060(17)
55.451(15)
61.834(14)
62.893(14)
51.535(13)
62.689(14)
61.891(14)
62.228(14)
103.83(7)
170.11(7)
125.86(7)
124.61(7)
120.95(7)
176.02(7)
118.96(7)
175.21(7)
61.54
62.37
60.92
63.14
111.15
124.12
56.09
62.16
61.89
52.27
65.02
Au(2)–Au(4)–Au(1)
Au(2*)–Au(4)–Au(1)
Au(2*)–Au(4)–Au(2)
Au(3*)–Au(2)–Au(3)
Au(3*)–Au(2)–Au(4*)
Au(3*)–Au(2)–Au(4)
Au(3)–Au(4)–Au(1)
Au(4)–Au(2)–Au(3)
Au(4*)–Au(2)–Au(3)
Au(4*)–Au(2)–Au(4)
Cl(1)–Au(1)–Au(3)
Cl(1)–Au(1)–Au(4)
P(1)–Au(1)–Au(3)
P(1)–Au(1)–Cl(1)
P(2)–Au(2)–Au(3)
P(2)–Au(2)–Au(4)
P(3)–Au(3)–Au(1)
P(3)–Au(3)–Au(2*)
P(4)–Au(4)–Au(1)
P(4)–Au(4)–Au(2*)
—
112.874(17)
124.594(17)
55.627(16)
124.549(15)
55.938(13)
97.959(17)
65.776(15)
55.215(14)
97.118(16)
124.373(16)
74.92(7)
108.78
122.36
55.95
123.91
56.14
96.61
62.70
55.28
97.45
124.05
79.54
74.88
104.33
176.05
111.12
109.91
111.34
122.37
113.96
121.14
—
62.83
61.70
78.68(7)
105.71(7)
177.26(10)
109.47(7)
110.60(7)
113.33(7)
121.50(7)
109.75(7)
122.95(7)
—
106.76
170.23
124.55
125.93
118.07
175.83
120.07
176.64
Asterisks denote atoms generated by symmetry.
4794 | Dalton Trans., 2012, 41, 4789–4798
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Fig. 7 (a) Electronic absorption spectra of complexes 11–14 in dichloromethane at ambient temperature; (b) normalized emission spectra of com-
plexes 11–14 in butyronitrile glass at 77 K.
ambient temperature are summarized in Table 6 and the absorp-
tion spectra are shown in Fig. 7a. All complexes display spin-
allowed intraligand 1IL and metal-perturbed intraligand 1IL
shoulders at 268–280 nm.59–61 The complexes are non-emissive
at room temperature. Upon photo-excitation in butyronitrile glass
at 77 K, the complexes reveal weak emission (Fig. 7b).
With reference to the previous reports on the photophysical
studies of gold(I)–phosphine complexes,59–61 the high-energy
emission bands are tentatively assigned to originate from spin-
forbidden metal-perturbed intraligand 3IL (phosphine) exited
states. The slightly higher emission energy of 11 and 12 than 13
and 14 is consistent with the higher intraligand (phosphine)
exited state energy of Ph2PCHvCHPPh2 than the more conju-
gated Ph2PCuCPPh2. The lack of emissive properties at room
temperature is probably due to the floppy nature of the metalla-
macrocyclic ring structure of the complexes.
complex [AuX2(cis-dppen)]PF6 (X = I 6, Br 8, Cl 10). In con-
trast to the cis-isomer, the reaction of trans-dppen with [Au-
(tht)2]X gives the cyclic trinuclear complexes [Au3(μ-trans-
dppen)3]X3 (X = OTf 11, PF6 12). Effect of geometry of ligand
has been shown to be an important factor in the reaction of
dppen with tetrachloroaurate.31 When dppa used, reaction pro-
ceeded in a different direction to give high nuclearity species,
tetranuclear gold complexes [Au4(μ-dppa)4]X4 (X = OTf 13, PF6
14, ClO4 15); recrystallization of the last of three from CH2Cl2/
MeOH gave orange crystals which proved to be an octanuclear
gold cluster by X-ray crystallography.
Experimental section
General comments
1H NMR and 31P NMR spectra were recorded on a JEOL
JNM-ECP 400 or Varian Gemini 300 NMR spectrometer as
CDCl3 solutions, referenced to residual solvent peaks; 31P NMR
spectra were obtained as proton-decoupled. FAB-mass spectra
were measured on a JEOL JMS-600H spectrometer in positive
ion mode. Elemental analyses were carried out in-house on a
Perkin-Elmer 2400 analyzer or at the Microanalytical Laboratory
of the Research School of Chemistry, Australian National Uni-
versity. Crystals suitable for single-crystal X-ray diffraction were
obtained by layering a dichloromethane solution of the complex
with hexane.
Given the structural similarities between [Au2(μ-cis-dppen)2]X-
(X = OTf 1, PF6 3) and previously reported luminescent gold com-
plexes,62 one would expect these compounds to be prospective
candidate for photophysical study. The initial investigation was
carried out by exposing the mixtures of [Au2(μ-cis-dppen)2]X
(X = OTf 1, PF6 3) and [Au(cis-dppen)2]X (X = OTf 2, PF6 4) to
UV radiation. As the mixtures did not appear to be luminescent
under UV light at room temperature, and several attempts to separate
the components of mixtures were failed, this was not pursued further.
Conclusion
Diphosphine ligands have been used to prepare mono, di, tri and
tetranuclear cyclic complexes. The reaction of cis-dppen with
[Au(tht)2]X failed to give a pure product, but rather a mixture of
[Au2(μ-cis-dppen)2]X (X = OTf2 1, PF6 3) and [Au(cis-dppen)2]
X (X = OTf 2, PF6 4). The mixture of 3 and 4 reacted with halo-
gens to give a mixture of acyclic binuclear gold(I) [Au2X2 (cis-
dppen)] (X = I 5, Br 7, Cl 9) and cyclic mononuclear gold(III)
X-ray crystallography
All diffraction data were collected on a Bruker SMART CCD area
detector diffractometer with graphite monochromated Mo-Kα
radiation (λ = 0.71073 Å). Geometric and intensity data were col-
lected using SMART software.63 The data were processed using
SAINT,64 and corrections for absorption were applied using
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 4789–4798 | 4795

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Table 7 Crystal data and details of data collection and structure refinement for complexes 1, 5–7, 11, 14 and 16
Compound
1
5
6
7
Formula
FW
C54H44Au2F6O6P4S2
1484.82
C26H22Au2I2P2
1044.12
C26H22AuF6I2P3
992.11
C26H22Au2Br2P2
950.12
Crystal system
Space group
a (Å), b (Å), c (Å)
Triclinic
P1
10.8043(6), 10.9164(6),
11.7847(6)
Monoclinic
Cc
13.340(4), 12.988(4),
16.396(5)
Monoclinic
P2(1)/c
17.6151(8), 9.3424(4),
19.5736(9)
Monoclinic
Cc
13.2194(7), 12.9069(7),
15.6042(8)
ˉ
α (°), β (°), γ (°)
76.473(1), 82.956(1), 73.340
(1)
1292.35(12)
1
1.908
5.947
90(2)
90, 103.629(6), 90
90, 111.3970(10), 90
90, 101.7360(10), 90
V (Å3)
2760.9(14)
4
2.512
12.980
173(2)
2999.2(2)
4
2.197
7.177
298(2)
2606.8(2)
4
2.421
14.444
173(2)
Z
Dcalc (mg m−3
)
μ (mm−1
T (K)
)
Crystal dimensions (mm)
θ range (°)
Reflections collected
Unique (Rint) [χ Flack]
Data/restrains/parameters
0.46 × 0.22 × 0.14
1.78–28.30
9611
6330 (0.0179)
6330/0/334
0.30 × 0.098 × 0.093
2.22–28.30
9041
4731 (0.0496) [0.00(1)]
4731/2/289
R1 = 0.0554, wR2 =
0.1360
0.28 × 0.096 × 0.064
2.24–28.34
21 835
7463 (0.0251)
7463/0/343
0.36 × 0.26 × 0.22
2.23–28.31
9391
4834 (0.0249) [0.00(1)]
4834/2/289
Final R indices [I > 2σ(I)] R1 = 0.0217, wR2 = 0.0583
R1 = 0.0338, wR2 = 0.0889 R1 = 0.0259, wR2 = 0.0624
R indices (all data)
R1 = 0.0221, wR2 = 0.0586
1.881 and −2.224
R1 = 0.0651, wR2 =
0.1427
3.867 and −4.442
R1 = 0.0425, wR2 = 0.0942 R1 = 0.0265, wR2 = 0.0626
Largest diff. peak and
1.621 and −1.270
1.229 and −1.005
hole (e Å−3
)
Compound
11
14
16
Formula
FW
Crystal system
Space group
C88H80Au3Cl14F9O9P6S3
2821.71
Trigonal
R3c
C108.50H89Au4Cl9F24P12
C106H82Au8Cl10O8P8
3661.71
3327.35
Tetragonal
P4/ncc
Triclinic
ˉ
P1
a (Å), b (Å), c (Å)
19.9108(2), 19.9108(2), 39.4563
(7)
19.2584(2), 19.2584(2), 32.3309
(5)
12.6200(11), 13.6183(11), 16.8190
(14)
α (°), β (°), γ (°)
90, 90, 120
13 546.4(3)
90, 90, 90
11 991.1(3)
72.088(2), 73.716(2), 82.431(2)
2636.8(4)
V (Å3)
Z
D
6
4
1
calc (mg m−3
)
2.075
5.531
100(2)
1.843
5.323
150(2)
2.306
11.513
90(2)
μ (mm−1
T (K)
)
Crystal dimensions (mm)
θ range (°)
Reflections collected
Unique (Rint) [χ Flack]
Data/restrains/parameters
Final R indices [I > 2σ(I)]
R indices (all data)
0.25 × 0.18 × 0.12
2.57–28.00
77 102
7265(0.0555) [0.00(8)]
7265/1/311
R1 = 0.0256, wR2 = 0.0618
R1 = 0.0276, wR2 = 0.0626
0.730 and −0.401
0.22 × 0.18 × 0.12
1.96–25.00
49 276
5283(0.0542)
5283/13/275
R1 = 0.0468, wR2 = 0.1484
R1 = 0.0703, wR2 = 0.1586
1.289 and −1.250
0.16 × 0.063 × 0.044
1.57–28.34
19 687
12 955(0.0395)
12 955/0/631
R1 = 0.0555, wR2 = 0.1194
R1 = 0.0783, wR2 = 0.1291
4.114 and −1.551
Largest diff. peak and hole
(e Å−3
)
SADABS.65 The data sets of 1, 6, 7, 10, 11 were further treated
with an Xabs2 absorption correction as implemented in WinGX.66
All structures were solved by direct methods using the
SHELX-TL package.67 Crystallographic data are summarized in
Table 7. The structure of 13 contains heavily disordered anions
and solvent molecules. After an initial refinement, which revealed
three sites in the asymmetric unit accessible to solvent molecules,
the data set was treated with SQUEEZE as implemented in
WinGX PLATON.68 CCDC reference numbers 843620–843626
refer to the crystals structures reported in this paper.
Calculations were performed using the PBE GGA correlation-
exchange functional,70 and projector augmented-wave (PAW)71
potentials for all atoms. The plane-wave cutoff was set at 400 eV
for all calculations. A 2 × 2 × 2 Monkhorst-Pack k-point mesh
was used. All calculations were performed by constructing a
supercell from the XRD data. For compound 14, some atoms
with fractional occupancies in the XRD data were omitted
(though their counterparts were retained). In performing the geo-
metry optimization, relaxation was alternately applied to the
ionic coordinates and the cell parameters, before allowing both
to vary. Final stresses on the supercell were less than 3 kB in
magnitude. Charge analysis was performed using the Bader
method,72 as implemented in ref. 73–75. Bandgap comparisons
were performed in the manner of Chilukuri and Cundari,76 who
used the HOMO–LUMO gap derived from the electronic density
of states (eDOS) as a fundamental predictor of several effects.
Computational details
Ab initio calculations were performed using the Vienna ab initio
simulation package (VASP) developed at the Universität Wien.69
4796 | Dalton Trans., 2012, 41, 4789–4798
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1
Due to the size of the primitive cells (several hundred atoms),
this is currently the limit to which theory can be used to predict
optical properties of these crystals. Techniques such as time-
dependent density functional theory, which also take account of
the excited states of systems, are simply not computationally
tractable in these cases.
12: Yield: 196 mg, 79%. H NMR (CDCl3): δ 7.19–7.55 (m,
aromatics). 31P NMR (CDCl3): δ 40.7. FAB-MS (m/z): 594
[Au3(dppen)3]+3, Anal. Calcd for C81H66Au3F9O9P6S3: C 43.68,
H 2.99. Found: C 43.36, H 2.70.
[Au4(μ-dppa)4]X4 (X = OTf 13, PF6 14, ClO4 15). In an analo-
gous reaction to that described above, treatment of a dichloro-
methane solution of [Au(tht)2]X (X = OTf, PF6, ClO4)
(0.34 mmol) with an equimolar amount of bis(diphenylpho-
sphino)acetylene gave the title products.
Photophysical measurements and instrumentation
The electronic absorption spectra were recorded on a Hewlett-
Packard 8452A diode array spectrophotometer. Steady-state
emission spectra recorded at room temperature and at 77 K were
measured on a Spex Fluorolog-3 Model FL3-211 fluorescence
spectrofluorometer equipped with a R2658P PMT detector. Low-
temperature butyronitrile glass photophysical measurements
were carried out with the sample in a quartz tube inside a quartz-
walled Dewar flask with liquid nitrogen.
1
13: Yield: 213 mg, 86%. H NMR (CDCl3): δ 7.19–7.80 (m,
aromatics). 31P NMR (CDCl3): δ 17.0. FAB-MS (m/z): 592
[Au4(dppa)4 + H]+4, Anal. Calcd for C108H80Au4F12O12P8S4: C
43.80, H 2.72. Found: C 44.12, H 2.89.
1
14: Yield: 241 mg, 98%. H NMR (CDCl3): δ 7.13–7.73 (m,
aromatics). 31P NMR (CDCl3): δ 17.1. FAB-MS (m/z): 592
[Au4(dppa)4 + H]+4, Anal. Calcd for C104H80Au4F24P12: C
42.41, H 2.74. Found: C 42.51, H 2.76.
1
15: Yield: 208 mg, 90%. H NMR (CDCl3): δ 7.16–7.79 (m,
aromatics). 31P NMR (CDCl3): δ 18.3. FAB-MS (m/z): 592
Syntheses
[Au4(dppa)4 + H]+4.
[Au2(μ-cis-dppen)2]X2 (X = OTf 1, PF6 3) and [Au(cis-
dppen)2]X (X = OTf 2, PF6 4). To a stirred solution of [Au(tht)2]
X (X = OTf, PF6) (0.334 mmol) in dichloromethane (30 mL)
was added an equimolar amount of cis-dppen (0.334 mmol) at
room temperature. The mixture was stirred for 30 min and then
was filtered through Celite. The volume of the solution was
reduced to half under reduced pressure and ether was added, pre-
cipitating out the product.
Acknowledgements
VWWY acknowledges support from the Areas of Excellence
Scheme of the University Grants Committee of Hong Kong
(AoE/P-03/08).
1H NMR(CDCl3): δ 7.09–7.58 (m, aromatics). 31P NMR
(CDCl3): δ 23.1, 25.1. FAB-MS (m/z): 1338 [Au2(dppen)2OTf +
H]+, 1334 [Au2(dppen)2PF6 + H]+, 1187 [Au2(dppen)2 + H]+.
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11 Yield: 229 mg, 93%. H NMR (CDCl3): δ 7.05–7.73 (m,
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This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 4789–4798 | 4797

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