Luminescent heterometallic gold-copper alkynyl complexes stabilized by tridentate phosphine

Article abstract of DOI:10.1039/c2dt11710j

The reactions between trinuclear gold complex tppmAu₃Cl ₃ (tppm = tris(diphenylphosphino)methane), arylacetylenes HC ₂C₆H₄X and Cu⁺ under basic conditions result in formation of the heterom

Full text of DOI:10.1039/c2dt11710j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 2941
www.rsc.org/dalton
PAPER
Luminescent heterometallic gold–copper alkynyl complexes stabilized by
tridentate phosphine†
Julia R. Shakirova,a Elena V. Grachova,*a Vladislav V. Gurzhiy,a Igor O. Koshevoy,a,c Alexei S. Melnikov,b
Olga V. Sizova,a Sergey P. Tunik*a and Antonio Lagunad
Received 8th September 2011, Accepted 5th December 2011
DOI: 10.1039/c2dt11710j
The reactions between trinuclear gold complex tppmAu3Cl3 (tppm = tris(diphenylphosphino)methane),
arylacetylenes HC2C6H4X and Cu+ under basic conditions result in formation of the heterometallic
complexes [tppm(AuC2C6H4X)3Cu]+, X = H (1), COOMe (2), CN (3), OMe (4), NH2 (5). These
compounds belong to one structural motif and consist of the heterometallic {(AuC2C6H4X)3Cu} core
stabilized by the tridentate phosphine. Compounds 1–5 were characterized by polynuclear NMR and IR
spectroscopy, ESI-MS and single-crystal X-ray analysis. Luminescence properties of these complexes
have been studied and revealed a substantial red shift of the emission maxima with the increase in the
electron donicity of the alkynyl ligands substituents in the 550–680 nm range. The theoretical calculations
of the electronic structures showed that variations of the substituents on the alkynyl ligands display very
little effect on the molecular structural parameters but show appreciable influence on the orbital energies
and luminescence characteristics of the compounds under study.
paid to heteronuclear coinage metal compounds as they were
Introduction
shown to be very effective luminophores exhibiting exception-
The metal–metal interactions of the d10 ions of the coinage
metals have been intensely investigated for more than two
decades since the attraction between gold atoms was highlighted
and defined as “aurophilicity”1 which resulted in exponential
growth of the experimental2,3 and theoretical4 interest in this
topic and was particularly stimulated by the intriguing photophy-
sical properties of gold compounds.5 Development of gold(I)
polymetallic chemistry naturally resulted in expansion into the
area of gold-containing heterometallic complexes,6 due to the
successful demonstration that the presence of mixed metal–metal
interactions between the closed-shell d10 ions causes the pertur-
bation of the electronic structures and dramatic changes in the
photophysical properties.7 Therefore special attention has been
ally intense room temperature emission.8–11
One of the ways to enhance the metal–metal contacts and to
stabilize the polymetallic cluster core is to use bridging bi- or
polydentate ligands with short bite angles, which are capable of
bringing the interacting metal ions into close proximity, i.e. to
provide interatomic distances shorter than the sum of van der
Waals radii. This methodology has been widely employed in the
synthesis of numerous phosphine-containing species due to the
high Au(I) affinity toward the phosphorus donor atom. Thus, util-
ization of homo- or heterobidentate bridging phosphine ligands
in the preparation of Au(I) complexes is well documented in the
literature and exemplified by a variety of compounds of different
nuclearity – from bimetallic dimers2,12 to polymetallic clusters
and large supramolecular aggregates.6,10,13–15 Interestingly, the
coordination chemistry of gold(I) based on tri- or polydentate
phosphines is very limited,2 despite their high templating poten-
tial in the construction of the molecular multimetallic assem-
blies. For example, intense phosphorescence has been reported
for the linear chain structures16,17 built on tri- and tetrapho-
sphines; the oligoether functionalized tripodal alkynyl-phosphine
gold(I) complex serves as a photoluminescent sensor for Mg2+
ions;18 and the combination of flexible triphosphine with brid-
ging sulfide has driven the aggregation of a crown-like Au18
macrocycle.19
aSt.-Petersburg State University, Department of Chemistry,
St.-Petersburg, Russia. E-mail: stunik@inbox.ru;
Fax: +7 812 4286939; Tel: +7 812 4284028
bSt.-Petersburg State University, Department of Physics, St.-Petersburg,
Russia
cUniversity of Eastern Finland, Joensuu, 80101, Finland
dDepartamento de Quimica Inorganica, Instituto de Ciencia de
Materiales de Aragon, Universidad de Zaragoza-CSIC, E-50009
Zaragoza, Spain
†Electronic supplementary information (ESI) available: X-ray crystallo-
graphic data in CIF for 2, 3 and 4, atomic coordinates and displacement
parameters, bond lengths, and bond angles; 1H-1H COSY NMR; ESI
mass spectra; diagrams of the selected Kohn–Sham molecular orbitals
for the complexes and alkynyl ligands, contour project the deformation
of electron density, energies and Mulliken composition of frontier KS
molecular orbitals, and selected Wiberg bond indices. CCDC reference
numbers 786915, 786916 and 805993. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c2dt11710j
Recently our research efforts have focused on the synthesis
and photophysical studies of the bimetallic Au(I)–Cu(I) and
Au(I)–Ag(I) alkynyl-phosphine clusters, which showed unprece-
dented photoemissive properties, such as very high quantum
efficiency (up to 96%) and negligibly small effect of
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2941–2949 | 2941

View Article Online
phosphorescence quenching by molecular oxygen.11,20 These
complexes contain linear diphosphine ligands with spatially sep-
arated phosphorus atoms that determine the observed structural
motif – a “core” of an emissive heterometallic cluster stabilized
by an external gold(I)-phosphine “belt”. As mentioned above,
bridging diphosphines such as bis(diphenylphosphino)methane
(dppm) are also capable of supporting the polynuclear aggre-
gates, including the alkynyl ones.14,21 Surprisingly, no alkynyl
gold-containing compounds have been reported for the tridentate
relative of dppm, tris(diphenylphosphino)methane (tppm),
though a very few species (halide, dithiocarbamate) were charac-
terized.22 This prompted us to employ the tppm ligand toward
the synthesis of luminescent coinage metal complexes, in par-
ticular, toward the preparation of Au(I) containing alkynyl clus-
ters. Herein, we report on the assembly of a family of
tetranuclear Au(I)–Cu(I) tppm-based clusters from the simple
precursors, photophysical and theoretical investigations of the
novel compounds.
7.31 (d, H-ortho, 6H, JHH 7.6 Hz). ESI (m/z): 1525 (MI+), calcd
for Au3CuC61H46P3: 1525. Anal. calcd for C61H46Au3B1Cu1F4-
P3: C, 45.42; H, 2.87. Found: C, 45.36; H, 3.03.
[tppm(AuC2C6H4COOMe)3Cu]BF4 (2)
Triethylamine (1 ml) was added dropwise to a mixture of
methyl-4-ethynylbenzoate (22.6 mg, 0.141 mmol), [tppmAu3-
Cl3] (60.0 mg, 0.047 mmol) and [Cu(NCMe)4]BF4 (14.8 mg,
0.047 mmol) in CH2Cl2 (10 ml) under vigorous stirring. The
reaction mixture was stirred for 2 h in the absence of light. The
resulting transparent light-orange solution was reduced in
volume in vacuo and diluted with hexane to give an orange-
yellow precipitate. The precipitate was filtered off, washed with
hexane and ether, and dried in vacuo. Yield: 81 mg (96%). IR
(KBr, cm−1): ν(CuC) 2113w, ν(CvO) 1705s. 31P{1H} NMR
1
(CD2Cl2; δ): 41.7, s. H NMR (CD2Cl2; δ): phosphine: 6.57 (q,
H̲−CP3, 1H, JPH 10.2 Hz), 7.15 (dd, H-meta Ph, 12H, JHH ca.
7 Hz), 7.25 (t, H-para Ph, 6H, JHH ca. 7 Hz), 8.00 (unresolved
multiplet, H-ortho Ph, 12H), alkynyl ligands: 3.92 (s,
Experimental
COOCH
̲
3, 9H), 7.44 (d, C6H4
̲
, 6H, JHH 8.2 Hz), 7.74 (d, C6H4,
̲
6H, JHH 8.2 Hz). ESI+ (m/z): 1699 (MI+), calcd for Au3CuC67-
H52P3O6: 1699. Anal. calcd for C67H52Au3B1Cu1F4O6P3: C,
45.02; H, 2.93. Found: C, 45.07; H, 3.02. Single crystals of 2
suitable for X-ray analysis were grown from CH2Cl2 solution by
Et2O slow diffusion at +5 °C.
General comments
Phenylacetylene (Acros); 1-ethynyl-4-methoxybenzene (Alfa
Aesar); tetrahydrothiophene; tris(diphenylphosphino)methane
(tppm) (Strem Chemicals) and all solvents were used as received.
Triethylamine was distilled over KOH under a nitrogen atmos-
phere prior to use. [Au(tht)Cl] (tht = tetrahydrothiophene),23
[tppmAu3Cl3],24 [AuC2C6H4CN]n,25 methyl-4-ethynylbenzo-
ate,26 and 4-ethynylaniline27 were synthesized according to pub-
[tppm(AuC2C6H4CN)3Cu]BF4 (3)
1
1
lished procedures. The solution H, H–1H COSY and 31P{1H}
NMR spectra were recorded on a Bruker-DX300 spectrometer.
Mass spectra were determined on a Bruker micrOTOF 10223
instrument in the ESI+ mode. Theoretical isotope patterns were
calculated using the Sheffield ChemPuter program available free
of charge on-line http://winter.group.shef.ac.uk/chemputer/. The
IR and UV-Vis spectra were recorded using a Perkin Elmer
FT-IR BX spectrometer and a Shimadzu UV 3600 spectropho-
tometer, respectively.
Tppm (21.4 mg, 0.037 mmol) and [Cu(NCMe)4]BF4 (11.8 mg,
0.037 mmol) were added dropwise to a suspension of [AuC2C6-
H4CN)]n (40.0 mg, 0.113 mmol), in CH2Cl2 (10 ml) under vig-
orous stirring. The reaction mixture was stirred for 3 h in the
absence of light. The resulting transparent yellow solution was
reduced in volume in vacuo and diluted with hexane, forming a
yellow precipitate. The precipitate was filtered off, washed with
hexane and ether, and dried in vacuo. Yield: 50 mg (80%). IR
(KBr, cm−1): ν(CuC) 2114w, ν(CuN) 2226m. 31P{1H} NMR
1
(CD2Cl2; δ): 41.5, s. H NMR (CD2Cl2; δ): phosphine: 6.44 (q,
H̲−CP3, 1H, JPH 10.1 Hz), 7.16 (dd, H-meta Ph rings, 12H, JHH
[tppm(AuC2C6H5)3Cu]BF4 (1)
ca. 7 Hz), 7.26 (t, H-para Ph rings, 6H, JHH ca. 7 Hz), 7.94
(unresolved multiplet, H-ortho Ph rings, 12H), alkynyl ligands:
A solution of phenylacetylene (29.7 mg, 0.291 mmol) in
CH2Cl2 (10 ml), and triethylamine (1 ml) were added dropwise
to the suspension of [tppmAu3Cl3] (122.9 mg, 0.097 mmol) in
7.47 (s, C6H4
, 12H). ESI (m/z): 1600 (MI+), calcd for the Au3-
̲
CuC64H43P3N3: 1600. Single crystals of 3 suitable for X-ray
analysis were grown from CH2Cl2 solution by Et2O slow diffu-
sion at +5 °C.
CH2Cl2 (5 ml) under vigorous stirring.
A solution of
[Cu(NCMe)4]BF4 (30.6 mg, 0.097 mmol) in MeOH/CH2Cl2
(1 : 1) was added slowly to the reaction mixture and the colorless
suspension turned into a brilliant yellow solution. The reaction
mixture was stirred for 2 h in the absence of light. The resulting
transparent solution was reduced in volume in vacuo and diluted
with hexane to give a bright yellow precipitate. The precipitate
was filtered off, washed with hexane, and dried in vacuo. Yield:
129.3 mg (87%). IR (KBr, cm−1): ν(CuC) 2086w. 31P{1H}
[tppm(AuC2C6H4OMe)3Cu]BF4 (4)
Triethylamine (1 ml) was added dropwise to a mixture of 1-
ethynyl-4-methoxybenzene (18.6 mg, 0.141 mmol), [tppmAu3-
Cl3] (60.0 mg, 0.047 mmol), and [Cu(NCMe)4]BF4 (14.8 mg,
0.047 mmol) in CH2Cl2 (10 ml) under vigorous stirring. The
reaction mixture was stirred for 1 h in the absence of light. The
resulting transparent yellow solution was reduced in volume in
vacuo and diluted with hexane, a yellow precipitate formed. The
precipitate was filtered off, washed with hexane, and dried
in vacuo. Yield: 52.9 mg (66%). IR (KBr, cm−1): ν(CuC)
1
NMR (CDCl3; δ): 42.1, s. H NMR (CD2Cl2; δ): phosphine:
6.38 (q, H
̲−CP3, 1H, JPH 10.1 Hz), 7.14 (dd, H-meta Ph, 12H,
JHH ca. 7 Hz), 7.23 (t, H-para Ph, 6H, JHH ca. 7 Hz), 7.96 (unre-
solved multiplet, H-ortho Ph, 12H), alkynyl ligands: 7.09 (dd,
H-meta, 6H, JHH ca. 7 Hz), 7.28 (t, H-para, 3H, JHH ca. 7 Hz),
2942 | Dalton Trans., 2012, 41, 2941–2949
This journal is © The Royal Society of Chemistry 2012

View Article Online
1
2069w.31P{1H} NMR (CD2Cl2; δ): 41.5, s. H NMR (CD2Cl2;
(d, C6H4
̲
, 6H, JHH 8.2 Hz), 7.00 (d, C6H4
̲
, 6H, JHH 8.2 Hz). ESI
δ): phosphine: 6.47 (q, H−CP3, 1H, JPH 9.9 Hz), 7.14 (dd, H-
meta Ph rings, 12H, JHH ca. 7 Hz), 7.22 (t, H-para Ph rings, 6H,
JHH ca. 7 Hz), 7.99 (m, H-ortho Ph rings, 12H), alkynyl
̲
(m/z): 1570 (MI+), calcd for Au3CuC61H49P3N3: 1570.
X-ray crystal structure determination
ligands: 3.81 (s, OCH
̲
3, 9H), 6.64 (d, C6H4, 6H, JHH 8.6 Hz),
̲
7.27 (d, C6H4
̲
, 6H, JHH 8.6 Hz). ESI (m/z): 1615 (MI+), calcd
For single crystal X-ray diffraction experiments, crystals of 2, 3
and 4 were fixed on micro mounts and placed on a Bruker Smart
Apex II diffractometer and measured at temperature 210, 150
and 170 K, respectively, using monochromated MoKα radiation.
Absorbance correction was applied according to the shape of
crystals. The structures have been solved by direct methods
using SHELX-97 program.28 Positions of H atoms were
modeled using a ‘riding’ model. Crystallographic data for 2–4
are collected in Table 1. Atomic coordinates and displacement
parameters are presented in Tables S1–S4 (S denotes Supporting
Information†) for 2, 3 and 4, respectively. Supplementary crys-
tallographic data for this paper have been deposited at the Cam-
bridge Crystallographic Data Centre (CCDC 786915, 786916
and 805993) and can be obtained free of charge via www.ccdc.
cam.ac.uk/data_request/cif.
for Au3CuC64H52P3O3: 1615. Anal. calcd for C64H52Au3B1Cu1-
F4O3P3: C, 45.13; H, 3.08. Found: C, 45.05; H, 3.09. Single
crystals of 4 suitable for X-ray analysis were grown from
CH2Cl2 solution by slow evaporation at +5 °C.
[tppm(AuC2C6H4NH2)3Cu]BF4 (5)
Triethylamine (1 ml) was added dropwise to a mixture of 4-ethy-
nylaniline (16.5 mg, 0.141 mmol), [tppmAu3Cl3] (60.0 mg,
0.047 mmol), and [Cu(NCMe)4]BF4 (14.8 mg, 0.047 mmol) in
CH2Cl2 (10 ml) under vigorous stirring. The reaction mixture
was stirred for 2 h in the absence of light and resulted in orange
precipitate formation. All volatile components were removed in
vacuo and the crystalline deposit washed with hexane, and dried
in vacuo. Yield: 69.5 mg (89%). IR (KBr, cm−1): ν(CuC)
2063w.31P{1H} NMR (CD2Cl2; δ): 41.2, s. 1H NMR
Photophysical measurements
((CD3)2SO; δ): phosphine: 6.80 (q, H
̲
All photophysical measurements were carried out in CH2Cl2,
which was distilled immediately prior to use. All solutions were
carefully degassed before lifetime and quantum yield measure-
ments. The light-emitting diode (LED, maximum emission at
7.28 (dd, H-meta Ph rings, 12H, JHH ca. 7 Hz), 7.16 (t, H-para
Ph rings, 6H, JHH ca. 7 Hz), 7.91 (unresolved multiplet, H-ortho
Ph rings, 12H), alkynyl ligands: 5.58 (s br, NH2, 6H), 6.35
Table 1 Crystallographic data for 2–4a
Compound
2
3
4
Formula
Crystal System
a/Å
b/Å
c/Å
Au3BCuC67H52F4P3O6
Trigonal
17.1354(7)
17.1354(7)
17.8646(8)
90
Au3BCuC64H43F4P3N3
Trigonal
16.9942(7)
16.9942(7)
16.6654(11)
90
Au3BCuC64H52F4P3O3
Trigonal
17.1541(8)
17.1541(8)
16.7640(8)
90
α (°)
β (°)
90
120
4542.7(3)
1787.25
R3
90
120
4168.2(4)
1688.17
R3
90
120
4272.1(3)
1703.22
R3
γ (°)
V/Å3
Molecular weight
Space group
μ/mm−1
7.735
8.417
8.215
T/K
Z
210(2)
3
1.960
150(2)
3
2.018
170(2)
3
1.986
Dc/g cm−3
Crystal size/mm
Radiation
Total reflections
Unique reflections
Angle range 2θ/°
Reflections with |Fo| ≥ 4σF
Rint
0.1 × 0.1 × 0.1
Mo-Kα
19 554
5889
3.56–59.98
4008
0.35 × 0.15 × 0.10
Mo-Kα
18 620
0.3 × 0.2 × 0.2
Mo-Kα
18 951
5509
3.66–60.00
4536
5424
3.70–59.98
4868
0.0405
0.0355
0.0306
Rσ
0.0596
0.0273
0.0436
0.0515
0.0469
−0.022(5)
0.791
0.0423
0.0231
0.0416
0.0292
0.0427
−0.019(5)
0.900
0.0366
0.0217
0.0395
0.0319
R1 (|Fo| ≥ 4σF)
wR2 (|Fo| ≥ 4σF)
R1 (all data)
wR2 (all data)
Flack parameter
S
0.0412
0.000(4)
0.857
−0.527, 0.900
ρmin, ρmax, e/Å3
−0.607, 1.075
−0.598, 1.285
2 2
2 2
2
2
2
a R1 = Σ∥Fo| − |Fc∥/Σ|Fo|; wR2 = {Σ[w(Fo2 − Fc ) ]/Σ[w(Fo ) ]}1/2; w = 1/[σ2(Fo )+(aP)2 + bP], where P = (Fo2 + 2Fc )/3; s = {Σ[w(Fo2 − Fc )]/(n −
p)}1/2 where n is the number of reflections and p is the number of refinement parameters.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2941–2949 | 2943

View Article Online
385 nm) was used to pump luminescence. The LED was used in
the continue and pulse modes (pulse width, 1–20 μs; duty of
edge ∼90 ns; repetition rate, 100 Hz to 10 kHz). A digital oscil-
loscope Tektronix TDS3014B (Tektronix, bandwidth 100 MHz),
monochromator MUM (LOMO, interval of wavelengths 10 nm)
and photomultiplier tube Hamamatsu were used for lifetime
measurements. Emission spectra were recorded using an
HR2000 spectrometer (Ocean Optics). A halogen lamp, LS-1-
CAL (Ocean Optics), and deuterium lamp, DH2000 (Ocean
Optics), were used to calibrate the absolute spectral response of
the spectral system in the 200–1100 nm range. The absolute
emission quantum yield was determined by Vavilov’s method
using LED pumping and rhodamine 6G in ethanol (Φem = 0.95
0.03) as standard with the refraction coefficients of dichloro-
methane and ethanol equal to 1.42 and 1.36, respectively.29
Results and discussion
Synthesis and characterization
The reactions of the trinuclear gold complex [tppmAu3Cl3] with
a stoichiometric amount of HC2C6H4X (X = H, COOMe, CN,
OMe, NH2) and Cu+ in the presence of a deprotonating agent
(NEt3) resulted in formation of the novel heterometallic [tppm
(AuC2C6H4X)3Cu]+ complexes 1–5 in good yields (see
−
Scheme 2), which were isolated as BF4 salts after
recrystallization.
The moderately air-stable yellow to orange complexes 1–5
were characterized by 1H, 1H–1H COSY, 31P{1H} NMR and
ESI-MS spectroscopy. The structures of 2–4 in the solid state
were determined by X-ray diffraction analysis. The molecular
views of 2–4 cations together with essential structural parameters
are given in Fig. 1; crystallographic data are summarized in
Table 1.
Computational details for DFT and TD-DFT calculations
Compounds 2–4 are isostructural and contain the {(AuC2C6-
H4X)3Cu} skeleton stabilized by coordination to the tridentate
phosphine. Three {PAuC2C6H4X} “rods” held together by the
phosphine, Cu–Au, Cu−π-CuC, and Au–Au bonding are
slightly twisted to form a distorted tetrahedral {Au3Cu}. The
symmetry of these complexes involves a threefold axis passing
through the Cu(1)–C(1)–H(1) as well as F(1)–B(1) atoms of the
Compounds 3 and 5 with different X substituents in the alkynyl
ligands were chosen to investigate and to assign the effects of
the X on the spectral and photophysical properties. The
influence of the Cu(I) ion incorporated in the central
{AuC2C6H4X}3 cluster on the spectral behavior of these com-
plexes was studied by comparison of 3 with the model system
[tppm(AuC2C6H4CN)3], 3a, which does not contain the hetero
ion. Geometry optimizations were performed on 3, 3a, and 5 in
the absence of solvent using the hybrid exchange–correlation
functional PBE0 (also known as PBE1PBE) in combination with
the SDD+DZVP basis set.30 The SDD basis set with relativistic
effective core potentials was used for the heavy metal atoms and
the all-electron DZVP basis set for hydrogen, carbon, nitrogen,
and oxygen atoms.31
Frequency analysis has shown that the optimized structures
correspond to the energy minima on the potential surface. All
TD-DFT calculations for the singlet and triplet excited states
were carried out using these optimized ground-state geometries.
The geometry of the lowest-energy triplet state of 3 and 5 was
also optimized using an unrestricted formalism (SCF approach).
The results of the calculations are summarized in Table 4.
The DFT calculations were carried out using the Gaussian 03
package.32 ChemCraft program was employed for 3D visualiza-
tion of Kohn–Sham orbitals. The contour maps of the electron
density deformation were plotted by the Chemissian program
http://www.chemissian.com. Notation of the low lying electronic
states is shown in Scheme 1 (the geometry used in the calcu-
lations is indicated in brackets).
−
BF4 anion. The Au–P distances in 2–4 are nearly identical
(2.282(1)–2.285(1) Å) and fit well with the values previously
reported for Au–P bond lengths.22,24,33 The Au–Au contacts
from 3.1843(4) to 3.2388(3) Å fall in the range typical for auro-
philic interactions in the “Au3” clusters supported by the triden-
tate phosphine,17,18,22,24,33,34 “Au4” alkynyl–phosphine cluster,35
and slightly shorter than Au–Au distances found in the other
alkynyl and alkynyl-phosphine Au(I)–Cu(I) compounds.15,36–39
The Cu–Au contacts were found to be 2.9565(9), 2.9538(7)
and 2.9278(7) Å for 2, 3 and 4, respectively, which are essen-
tially lower than the sum of the Au and Cu van der Waals radii
(3.06 Å). Due to geometrical constraints the π-CuC–Cu inter-
action is asymmetric, the Cu–C distances for a certain triple
bond differ substantially, see caption to Fig. 1. The CuC bond
lengths in 2, 3 and 4 are significantly shorter than those found
earlier in stable clusters containing effective alkynyl–copper
bonds 9,15,20,37,40,41 that evidently implies rather weak π-bonding
of the alkynyl ligands to the copper ion.
In the crystal cell the cluster cations are “head-to-tail” packed
to form infinite columns (see Fig. 2 and Fig. S1†), where the
Scheme 1
Scheme 2 Synthesis of the complexes 1–5.
2944 | Dalton Trans., 2012, 41, 2941–2949
This journal is © The Royal Society of Chemistry 2012

View Article Online
Fig. 1 Molecular views of the cations 2, 3 and 4. Selected interatomic distances (Å) for 2 are P(1)–Au(1) = 2.2816(13), Au(1)–Au(1) = 3.2388(3),
Au(1)–Cu(1) = 2.9565(9), Au(1)–C(2) = 2.007(6), Cu(1)–C(2) = 2.138(5), Cu(1)–C(3) = 2.357(5), C(2)–C(3) = 1.220(7); for 3 are P(1)–Au(1) =
2.2851(11), Au(1)–Au(1) = 3.1843(3), Au(1)–Cu(1) = 2.9538(7), Au(1)–C(2) = 2.016(5), Cu(1)–C(2) = 2.123(4), Cu(1)–C(3) = 2.376(4), C(2)–C(3)
= 1.207(6); for 4 are P(1)–Au(1) = 2.2828(10), Au(1)–Au(1) = 3.1937(3), Au(1)–Cu(1) = 2.9278(7), Au(1)–C(2) = 2.018(5), Cu(1)–C(2) = 2.130(4),
Cu(1)–C(3) = 2.453(4), C(2)–C(3) = 1.204(6).
Fig. 2 View of the infinite column structure formed in the crystalline phase of 3.
constituting units are bound to each other through hydrogen
bonds, which involve the BF4 anions.
tppm. Two clearly resolved doublets (6H per signal) in the
6.35–7.74 ppm range arise from the ortho- and meta-protons
of the alkynyl phenylene spacer, excluding 3 where these two
doublets overlap to give a singlet with 12H integral intensity.
The strong-field singlets at 3.92, 3.81 and 5.58 ppm for 2 (9H),
4 (9H) and 5 (6H), respectively, correspond to the protons of
the X substituent. The low-field multiplets (7.14–8.00 ppm,
see Experimental), which display correlations in the corre-
sponding COSY spectra, Figs. S7–S9†, are evidently generated
by the protons of the phosphine phenyl rings. It is worth
noting that the chemical shifts of these signals are nearly
identical for all clusters studied. This observation together
with the relative intensity and multiplicity of the signals
clearly supports the suggested assignment. The solid-state IR
spectra of 1–5 expectedly show a low frequency shift of CuC
stretching bands (in the range from 2063 to 2226 cm−1) as a
result of coordination of the CuC triple bonds to the metal
ions. These spectroscopic data obtained show that the general
structural motif found in the solid state remains unchanged in
solution.
Complexes 1 and 5 didn’t give single crystals suitable for X-
ray analysis and their structures have been established on the
basis of spectroscopic data. The ESI mass spectra of the com-
pounds studied (Figs. S2–S6†) display signals of the singly
charged [tppm(AuC2C6H4X)3Cu]+ molecular ions, the m/z
values and isotopic patterns of which completely match the
calculated ones. The 31P{1H} NMR spectra of 1–5 display
singlet resonances at ca. 41 ppm that corresponds to all equiv-
alent phosphorus atoms of the triphosphine ligand and is com-
patible with the presence of the threefold axis in the molecules
1
under study. The number of signals in the H NMR spectra of
1–5 and their relative intensities fit well the structural patterns
shown in Scheme 2, as well as the solid state structures
1
revealed for 2–4. Assignment of the signals observed in the H
NMR spectra of 1, 4, and 5 was additionally supported by
1H–1H COSY spectra because the aromatic resonances were
1
not clearly resolved in 1D H NMR. The high-field quartet at
6.5 ppm (JPH ca. 10 Hz, 1H) corresponds to the CH group of
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2941–2949 | 2945

View Article Online
Table 2 Photophysical properties of the complexes 1–5 in CH2Cl2 solution, 25 °C, λex = 385 nm
Q.Y., %
τobs, μs
knonrad, 10−6 −1
s
krad, 10−6 −1
s
Hammett λabs, nm
λex,b
nm
λem
,
constanta (ε×10−3, cm−1M−1
)
nm Degassed Aerated Degassed
Aerated
1.45 0.08 0.35
Degassed Aerated Degassed Aerated
1
2
0
270sh (32); 319sh (12);
390 (1)
270; 309; 560 1.7 0.2 1.4 0.2 2.8 0.1
0.68
0.35
0.006
0.006
0.009
0.004
390
0.45
256 (101); 268sh (92);
300sh (42); 341 (18);
387 (3)
293; 345; 560 4.0 0.6 1.0 0.2 7.0 0.4
387w
2.8 0.1
0.14
3
0.66
290 (56); 305 (54);
326sh (38);
270; 305; 550 5.2 0.8 3.1 0.5 6.8 0.4
390
2.8 0.1
0.14
0.35
0.008
0.011
390 (5); 484 (1)
258 (95); 287sh (58);
342 (16); 404 (3)
271 (26); 314sh (16);
338 (13); 357sh (11);
424w (3)
4
5
−0.27
−0.66
270; 302; 580 1.9 0.3 1.2 0.2 0.95 0.05 0.63 0.04 1.0
339; 396
309; 342; 680 0.6 0.1 0.4 0.1 0.44 0.02 0.30 0.02 2.2
365; 424
1.6
3.3
0.02
0.02
0.02
0.01
a Hammett constants of the X substituent.43 b The maximum of bands in the excitation spectra.
Fig. 3 The UV-Vis absorption and emission spectra of 1–5.
Fig. 4 The correlations between Hammett constants of the X substitu-
ent and emission wavelength, luminescence lifetime, and quantum yield
for 1–5; ■ emission band maxima; ◆ quantum yield; ▼ lifetime.
Photophysical properties
The photophysical and spectroscopic data for complexes 1–5 are
summarized in Table 2, the UV-Vis absorption and emission
spectra in dichloromethane are shown in Fig. 3. The absorption
spectra of the compounds are essentially similar. The broad
higher-energy absorptions below 290 nm can be ascribed to the
intra-ligand π→π* transitions of the alkynyl {C2C6H4X} moi-
eties and phosphine ligand rings. This assignment is consistent
with the previous reports on the related alkynyl–phosphine com-
plexes, for which the prevalent absorption in the spectral range
250–300 nm, in general, is ascribed to the characteristic bands of
the alkynyl and phosphine ligands.11,15,38,42 As for the lower
energy absorption bands, the TD-DFT calculations have been
used to interpret these electronic transitions, vide infra.
luminescence lifetime and quantum yield, Fig. 4. A similar trend
was observed earlier for the Au(I)–Cu(I) “rods-in-belt” clusters,41
where variations of luminescence wavelength were rationally
ascribed to the changes in the energy of ground state orbitals
involved in the emission. Similar to related heterometallic gold–
copper alkynyl phosphine complexes11,15,37–39,42 the excited
state lifetimes for 1–5 fall in the microsecond domain that point
to the triplet origin of the emission. It is worth mentioning that
emission quantum yield and lifetime for all the complexes show
nearly no luminescence quenching by molecular oxygen, which
is an indication of effective shielding of the chromophoric center
by external ligand environment.
All compounds studied exhibit room temperature lumines-
cence in solution (Fig. 3, Table 2). Variation of the para-substitu-
ents in the alkynyl groups from the electron-withdrawing CN to
the electron-donating NH2 allowed for the monitoring of the
ligands’ electronic effect onto the photophysical characteristics
of these complexes. Emission band maxima fall in 550–680 nm
range and display a systematic red shift with the increase in X
substituent donicity together with the related decrease of
Computational studies
Structural and electronic properties of the complexes under study
were elucidated by density functional calculations (see the
Experimental for notation and computational details). Selected
calculated structural parameters of the ground and excited triplet
states for 3, 5 and the model compound 3a (without Cu(I) ion)
2946 | Dalton Trans., 2012, 41, 2941–2949
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 3 Selected interatomic distances (Å) and Au–C(2)–C(3) angles (deg) for 3, 5, and 3a
3
5
3a
Exper.
Calc. S0(S0)
Calc. T1(T1)
Calc. S0(S0)
Calc. T1(T1)
Calc. S0(S0)
Cu–Au
Au–Au
Au–P
Au–C(2)
Cu–C(2)
Cu–C(3)
CuC
Cu–C(1)
Au–C(2) –C(3)
2.954
3.184
2.285
2.016
2.123
2.376
1.207
5.183
175.0
2.982
3.264
2.334
2.010
2.129
2.456
1.234
5.188
176.4
2.971
3.263
2.335
2.000
2.130
2.203
1.232
5.379
171.7
2.955
3.292
2.328
2.006
2.137
2.434
1.237
5.135
176.9
2.964
3.161
2.326
2.005
2.109
2.301
1.251
5.245
173.0
—
3.364
2.327
1.986
—
—
1.226
—
175.5
are given in Table 3. All of the studied complexes retain the
structural motif (Fig. 1 and Scheme 2) during the geometry
optimization, and the changes in structural parameters are fairly
small. However, it is worth noting that the calculated Au–Au,
Au–C, and Au–P distances are markedly longer than those
found in the solid state structures. It was also found that in 3 and
5 the bond order indices are quite similar for the atoms related to
the {Au3Cu} cluster core (see Table S8†). The observed appreci-
able Stokes shifts are indicative of distinguishable structural
changes associated with the intersystem crossing and formation
of the emissive triplet state. In the T1 excited state a decrease in
the Au–CuC angles results in a shortening of the Cu–C(2) dis-
tances in the triplet excited states as compared to the ground
states (Table 3). In addition, in the T1 state the Wiberg indices of
the Cu–(CuC) bonds increase, and the indices of the CuC
bonds decrease.44 These changes are caused by the distortion of
the geometry of these complexes.
As the symmetry of the {Au3Cu} metal core is close to C3v,
many Kohn–Sham (KS) orbitals including the frontier ones are
pseudo-degenerated, and the orbitals shown in Fig. 5 are dis-
torted due to the mixing of two components. The energies of the
frontier KS molecular orbitals of 3 and 5 are essentially different,
which evidently reflects the effect of the alkynyl ligand substitu-
ents:
Fig. 5 Frontier KS molecular orbitals of 3, 5 and 3a (top = LUMO,
bottom = HOMO), 0.03 isosurface value.
behavior of the heterometallic complexes. It was also found that
the energy and the composition of the HOMOs depend on the
nature of the X substituent. The contribution of the alkynyl
-C6H4- fragment to the HOMO in 5 (with the donor X) is
appreciably higher than in 3 (with acceptor X) while the percen-
tage of Cu(I) orbitals is higher in 3 compared to 5 (see Figs.
S10–13 and Table S7†). Thus, the replacement of the CN substi-
tuent for NH2 results in a reduction of the HOMO/LUMO gap
due to a larger increment of the HOMO energy in comparison to
that of the LUMO. This observation is completely in line with
the observed variations of luminescence parameters of the com-
plexes under study where the increase in electron-donor ability
of the X group shifts the emission energy to lower values.
For compounds 3 and 5, the HOMO’s are mainly located at
the alkynyl {C2C6H4X} moieties and the Cu(I) center. In the
model complex 3a the HOMO orbital is mostly centered at the
alkynyl ligand with a small contribution from the gold centers.
The LUMO’s of 3, 5 and 3a are mainly located on the tppm
ligand with some admixture of the Au(I) atomic orbitals.
The major contribution into the two lowest almost degenerated
singlet–singlet transitions is related to the HOMO→LUMO exci-
tation. Thus, the absorption in the 300–360 nm range (com-
plexes 3, 5) can be assigned to the electronic transitions from the
[{Cu}, {C2C6H4}] fragments to the {Au3} skeleton and empty
antibonding orbitals of the phosphine ligand. On the contrary,
the low energy transitions in the model complex 3a correspond
to the inter-ligand transfer {C6H4}→{PPh2}, that is indicative of
a significant influence of the copper center on the spectral
Only the lowest spin-forbidden transition was modeled, since
phosphorescence usually occurs from the lowest triplet (T1)
excited state. For 5 the calculated energy of T1 is lower than that
for 3 as well as the energy of S1 and the HOMO/LUMO gap.
However, the results of the TD-DFT calculations give markedly
overestimated values of the emission energies for both com-
plexes (Table 4). Additionally, the TD-DFT approach didn’t
reveal a dominant configuration of the triplet state for 3, there-
fore the description of this state on the basis of the ground state
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2941–2949 | 2947

View Article Online
Table 4 DFT energies (eV) of the lowest singlet and triplet states of 3
and 5 and the HOMO/LUMO gap (for notation see Scheme 1)
core, stabilized by tripodal phosphine ligand and alkynyl groups.
All the compounds studied exhibit phosphorescence in solution
at room temperature with emission maxima in the range
550–680 nm. Luminescence properties of these clusters depend
on the electron donor properties of the aromatic alkynyl ligands,
which were varied via changing the X substituents in the para
positions of the -C6H4- groups; increase in basicity of X causes a
bathochromic shift of the emission maxima. The latter is clearly
exemplified by the correlation of emission parameters with the
corresponding Hammett constants. Quantum chemical calcu-
lations provide a deeper insight into the structural, electronic and
spectroscopic properties of this novel family of gold–copper
alkynyl–phosphine complexes and show that the observed long-
wavelength phosphorescence is associated with metal centered
triplet emission within the heterometallic alkynyl cluster.
3
5
HOMO/LUMO gap, S0(S0)
S0(S0)
S0(T1)
S1(S0) TD-DFT
T1(S0) SCF
T1(S0) TD-DFT
T1(T1)
3.80
0.00
0.39
2.93
2.81
2.62
2.26
1.87
2.25
3.09
0.00
0.34
2.47
2.39
2.28
2.09
1.76
1.82
T1(T1) – S0(T1)
Eem(exper.)
Acknowledgements
The authors greatly appreciate the financial support of Saint-
Petersburg State University research grant 12.37.132.2011, the
University of Eastern Finland (Russian–Finnish collaborative
project), the Russian Foundation for Basic Research grants 11-
03-00974, 11-03-00541, and 11-03-92010. The work was
carried out using the equipment of the Resource Center “Analyti-
cal centre of nano- and bio-technology of SPbSPU”. We also
would like to thank Prof. V. I. Baranovskii and Dr. L. V. Scripni-
kov for fruitful discussions of theoretical results.
Fig. 6 Isosurfaces of the natural orbitals based on the electron density
difference (S0–T1) for the complexes 3 with optimized S0 geometry: the
orbital, from which the electron is excited (left), and the orbital, to
which the electron is transferred (right).
Notes and references
frontier orbital analysis should be done with caution. Presum-
ably, it is more appropriate to draw conclusions on the electronic
structure of the lowest triplet from the orbitals of the optimized
excited state (SCF scheme). Within the framework of the SCF
1 F. Scherbaum, A. Grohmann, B. Huber, C. Kruger and H. Schmidbaur,
Angew. Chem., Int. Ed. Engl., 1988, 27, 1544–1546; H. Schmidbaur,
Gold Bull., 1990, 23, 11–21; H. Schmidbaur and A. Schier, Chem. Soc.
Rev., 2008, 37, 1931–1951.
2 O. Crespo, in Modern Supramolecular Gold Chemistry, Wiley-VCH
Verlag GmbH & Co. KGaA, 2008, pp. 65–129.
approach the emission energies were estimated as Eem
=
E(T1(T1)) – E(S0(T1)) to take into account the geometrical relax-
ation of the emitting T1 state and the distortion of geometry from
S0(S0) to S0(T1). In general, the emission energy obtained by
this method is underestimated compared to the experimental
data, especially for complex 3. According to these results the
major contribution to the T1→S0 transition is made by the elec-
tronic density redistribution inside the {(CuC–Au)3Cu} core
fragment; this type of emissive transition can be described as
“intracore” charge transfer, see Fig. 6 and S14†. It is worth
noting that the copper ion in the complexes under study deter-
mines the nature and properties of the lowest triplet electronic
structure. For the complexes 1–5 the intra-ligand π–π and charge
transfer transitions are also responsible for the observed
emission.
3 R. J. Puddephatt, Chem. Soc. Rev., 2008, 37, 2012–2027;
E. R. T. Tiekink and J.-G. Kang, Coord. Chem. Rev., 2009, 253, 1627–
1648.
4 P. Pyykko, Chem. Soc. Rev., 2008, 37, 1967–1997.
5 V. W.-W. Yam, E. C.-C. Cheng, Chem. Soc. Rev., 2008, 37, 1806–1813;
C.-M. Che, S.-W. Lai, in Gold Chemistry, ed. F. Mohr, Wiley-VCH,
Weinheim, 2009, pp. 249–282; X. He, V. W.-W. Yam, Coord. Chem. Rev.,
2011, 255, 2111–2123; W. Lu, W.-M. Kwok, C. Ma, C. T.-L. Chan, M.-
X. Zhu, C.-M. Che, J. Am. Chem. Soc., 2011, 133, 14120–14135.
6 C. Silvestru, in Modern Supramolecular Gold Chemistry, Wiley-VCH
Verlag GmbH & Co. KGaA, 2008, pp. 181–293.
7 V. W.-W. Yam, K.-L. Cheung, E. C.-C. Cheng, N. Zhu and K.-
K. Cheung, Dalton Trans., 2003, 1830–1835.
8 E. J. Fernandez, A. Laguna and J. M. Lopez-de-Luzuriaga, Dalton
Trans., 2007, 1969–1981; A. Laguna, T. Lasanta, J. M. Lopez-de-Luzur-
iaga, M. Monge, P. Naumov and M. E. Olmos, J. Am. Chem. Soc., 2010,
132, 456–457; C. E. Strasser and V. J. Catalano, J. Am. Chem. Soc.,
2010, 132, 10009–10011.
9 G. F. Manbeck, W. W. Brennessel, R. A. Stockland and R. Eisenberg, J.
Am. Chem. Soc., 2010, 132, 12307–12318.
10 J.-H. Jia and Q.-M. Wang, J. Am. Chem. Soc., 2009, 131, 16634–16635;
M. C. Gimeno and A. Laguna, Chem. Soc. Rev., 2008, 37, 1952–1966.
11 I. O. Koshevoy, Y.-C. Lin, A. J. Karttunen, P.-T. Chou, P. Vainiotalo,
S. P. Tunik, M. Haukka and T. A. Pakkanen, Inorg. Chem., 2009, 48,
2094–2102.
12 V. J. Catalano and S. J. Horner, Inorg. Chem., 2003, 42, 8430–8438; S.-
K. Yip, W. H. Lam, N. Zhu and V. W.-W. Yam, Inorg. Chim. Acta, 2006,
359, 3639–3648; P. C. Kunz, M. U. Kassack, A. Hamacher and
B. Spingler, Dalton Trans., 2009, 7741–7747; M. A. Bennett, S.
K. Bhargava, D. C. R. Hockless, L. L. Welling and A. C. Willis, J. Am.
Conclusions
In summary, a new family of tetranuclear Au(I)–Cu(I) alkynyl
clusters supported by a tridentate phosphine ligand (tppm) has
been synthesized using a self-assembly reaction of simple pre-
cursors under basic conditions. The complexes [tppm(AuC2C6-
H4X)3Cu]+ (X = H, COOMe, CN, OMe, NH2) display a general
structural motif which contains heteronuclear {Au3Cu} cluster
2948 | Dalton Trans., 2012, 41, 2941–2949
This journal is © The Royal Society of Chemistry 2012

View Article Online
Chem. Soc., 1996, 118, 10469–10478; C. Khin, A. S. K. Hashmi and
F. Rominger, Eur. J. Inorg. Chem., 2010, 1063–1069.
32 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin,
J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. Ochterski, P. Y. Ayala, K. Morokuma,
G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-
Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. G. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople,
GAUSSIAN 03 (Revision B.05), Gaussian, Inc., Wallingford, CT, 2004
33 C.-M. Che, H.-K. Yip, V. W.-W. Yam, P.-Y. Cheung, T.-F. Lai, S.-J. Shieh
and S.-M. Peng, J. Chem. Soc., Dalton Trans., 1992, 427–433.
34 M. Bardaji, A. Laguna, P. G. Jones and A. K. Fischer, Inorg. Chem.,
2000, 39, 3560–3566.
13 E. J. Fernandez, J. M. Lopez-de-Luzuriaga, M. Monge, M. A. Rodriguez,
O. Crespo, M. C. Gimeno, A. Laguna and P. G. Jones, Chem.–Eur. J.,
2000, 6, 636–644; L. Hao, M. A. Mansour, R. J. Lachicotte,
H. J. Gysling and R. Eisenberg, Inorg. Chem., 2000, 39, 5520–5529; S.-
Y. Yu, Z.-X. Zhang, E. C.-C. Cheng, Y.-Z. Li, V. W.-W. Yam, H.-
P. Huang and R. Zhang, J. Am. Chem. Soc., 2005, 127, 17994–17995;
M. J. Calhorda, C. Ceamanos, O. Crespo, M. C. Gimeno, A. Laguna,
C. Larraz, P. D. Vaz and M. D. Villacampa, Inorg. Chem., 2010, 49,
8255–8269; A. Burini, R. Galassi, S. Ricci, F. Bachechi, A. A. Mohamed
and J. P. Fackler Jr., Inorg. Chem., 2010, 49, 513–518.
14 J. Chen, A. A. Mohamed, H. E. Abdou, J. A. Krause Bauer, J. P. Fackler
Jr., A. E. Bruce and M. R. M. Bruce, Chem. Commun., 2005, 1575–
1577; Q.-H. Wei, L.-Y. Zhang, G.-Q. Yin, L.-X. Shi and Z.-N. Chen,
J. Am. Chem. Soc., 2004, 126, 9940–9941.
15 H. de la Riva, M. Nieuwhuyzen, C. Mendicute Fierro, P. R. Raithby,
L. Male and M. C. Lagunas, Inorg. Chem., 2006, 45, 1418–1420.
16 Y. Takemura, H. Takenaka, T. Nakajima and T. Tanase, Angew. Chem.,
Int. Ed., 2009, 48, 2157–2161.
17 G. S. M. Tong, S. C. F. Kui, H.-Y. Chao, N. Zhu and C.-M. Che, Chem.–
Eur. J., 2009, 15, 10777–10789.
18 X. He, E. C.-C. Cheng, N. Zhu and V. W.-W. Yam, Chem. Commun.,
2009, 4016–4018.
19 T. K.-M. Lee, N. Zhu and V. W.-W. Yam, J. Am. Chem. Soc., 2010, 132,
17646–17648.
35 M. I. Bruce, M. Jevric, B. W. Skelton, A. H. White and N. N. Zaitseva,
J. Organomet. Chem., 2010, 695, 1906–1910.
36 O. M. Abu-Salah, A.-R. A. Al-Ohaly and C. B. Knobler, J. Chem. Soc.,
Chem. Commun., 1985, 1502–1503; M. Sakhawat Hussain, M. Ul-Haque
and O. M. Abu-Salah, J. Cluster Sci., 1996, 7, 167–177.
20 I. O. Koshevoy, Y.-C. Lin, Y.-C. Chen, A. J. Karttunen, M. Haukka, P.-
T. Chou, S. P. Tunik and T. A. Pakkanen, Chem. Commun., 2010, 46,
1440–1442; I. O. Koshevoy, A. J. Karttunen, J. R. Shakirova, A.
S. Melnikov, M. Haukka, S. P. Tunik and T. A. Pakkanen, Angew. Chem.,
Int. Ed., 2010, 49, 8864–8866.
37 S.-K. Yip, C.-L. Chan, W. H. Lam, K.-K. Cheung and V. W.-W. Yam,
Photochem. Photobiol. Sci., 2007, 6, 365–371.
38 I. Koshevoy, L. Koskinen, M. Haukka, S. Tunik, P. Serdobintsev,
A. Melnikov and T. Pakkanen, Angew. Chem., Int. Ed., 2008, 47, 3942–
3945; I. O. Koshevoy, A. J. Karttunen, S. P. Tunik, M. Haukka, S.
I. Selivanov, A. S. Melnikov, P. Y. Serdobintsev, M. A. Khodorkovskiy
and T. A. Pakkanen, Inorg. Chem., 2008, 47, 9478–9488.
21 Q.-H. Wei, G.-Q. Yin, L.-Y. Zhang, L.-X. Shi, Z.-W. Mao and Z.-
N. Chen, Inorg. Chem., 2004, 43, 3484–3491.
22 H. Xiao, Y.-X. Weng, W.-T. Wong, T. C. W. Mak and C.-M. Che,
J. Chem. Soc., Dalton Trans., 1997, 221–226; E. J. Fernandez, J. Lopez-
de-Luzuriaga, M. Monge, E. Olmos, A. Laguna, M. D. Villacampa and
P. G. Jones, J. Cluster Sci., 2000, 11, 153–167.
23 R. Uson, A. Laguna, M. Laguna, D. A. Briggs, H. H. Murray and
J. P. Fackler Jr, Inorg. Synth., 2007, 26, 85–91.
24 A. Stutzer, P. Bissinger and H. Schmidbaur, Chem. Ber., 1992, 125, 367–
372.
25 G. E. Coates and C. Parkin, J. Chem. Soc., 1962, 3220–3226.
26 W. B. Austin, N. Bilow, W. J. Kelleghan and K. S. Y. Lau, J. Org. Chem.,
1981, 46, 2280–2286.
27 A. J. Deeming, G. Hogarth, M.-y. V. Lee, M. Saha, S. P. Redmond, H.
T. Phetmung and A. G. Orpen, Inorg. Chim. Acta, 2000, 309, 109–122.
28 G. M. Sheldrick SHELXTL: Program for Crystal Structure Refinement,
version 3.1; Universitat Gottingen, Gottingen, 1997
29 G. A. Crosby and J. N. Demas, J. Phys. Chem., 1971, 75, 991–1024.
30 C. Adamo and V. Barone, J. Chem. Phys., 1999, 110, 6158–6170;
J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77,
3865–3868.
39 I. O. Koshevoy, E. S. Smirnova, A. Domenech, A. J. Karttunen,
M. Haukka, S. P. Tunik and T. A. Pakkanen, Dalton Trans., 2009, 8392–
8398.
40 S. S. Y. Chui, M. F. Y. Ng and C.-M. Che, Chem.–Eur. J., 2005, 11,
1739–1749; I. O. Koshevoy, Y.-C. Lin, A. J. Karttunen, M. Haukka, P.-
T. Chou, S. P. Tunik and T. A. Pakkanen, Chem. Commun., 2009, 2860–
2862; I. O. Koshevoy, A. J. Karttunen, S. P. Tunik, M. Haukka, S.
I. Selivanov, A. S. Melnikov, P. Y. Serdobintsev and T. A. Pakkanen,
Organometallics, 2009, 28, 1369–1376; I. O. Koshevoy, P. V. Ostrova, A.
J. Karttunen, A. S. Melnikov, M. A. Khodorkovskiy, M. Haukka, J. Janis,
S. P. Tunik and T. A. Pakkanen, Dalton Trans., 2010, 39, 9022–9031;
F. Olbrich, J. Kopf and E. Weiss, Angew. Chem., Int. Ed. Engl., 1993, 32,
1077–1079.
41 I. O. Koshevoy, Y.-C. Lin, A. J. Karttunen, P.-T. Chou, P. Vainiotalo,
S. P. Tunik, M. Haukka and T. A. Pakkanen, Inorg. Chem., 2009, 48,
2094–2102.
42 I. O. Koshevoy, A. J. Karttunen, S. P. Tunik, J. Janis, M. Haukka, A.
S. Melnikov, P. Y. Serdobintsev and T. A. Pakkanen, Dalton Trans., 2010,
39, 2676–2683.
31 M. Dolg, H. Stoll, H. Preuss and R. M. Pitzer, J. Phys. Chem., 1993, 97,
5852–5859; N. Godbout, D. R. Salahub, J. Andzelm and E. Wimmer,
Can. J. Chem., 1992, 70, 560–571.
43 C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165–195.
44 K. B. Wiberg, Tetrahedron, 1968, 24, 1083–1096; E. D. Glendening and
F. Weinhold, J. Comput. Chem., 1998, 19, 610–627.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2941–2949 | 2949