Evolution of lowest singlet and triplet excited states with transition metals in group 10-12 metallaynes containing biphenyl spacer

Article abstract of DOI:10.1016/j.jorganchem.2005.02.025

A new series of thermally stable group 10 platinum(II) and group 12 mercury(II) poly-yne polymers containing biphenyl spacer trans-[-Pt(PBu ₃)₂C≡C(p-C₆H₄) ₂C≡C-]_n and [-HgC≡C(p-C₆H ₄)₂C≡C-]_n were prepared in good yields by Hagihara's dehydrohalogenation reaction of the corresponding metal chloride precursors with 4,4′-diethynylbiphenyl HC≡C(p-C₆H ₄)₂C≡CH at room temperature. We report the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic model complexes trans-[Pt(Ph)(PEt₃)₂C≡ C(p-C₆H₄)₂C≡CPt(Ph)(PEt₃) ₂] and [MeHgC≡C(p-C₆H₄) ₂C≡CHgMe] as well as the group 11 gold(I) counterpart [(PPh₃)AuC≡C(p-C₆H₄)₂C≡ CAu(PPh₃)]. The structural properties of all model complexes have been studied by X-ray crystallography. The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and the spatial extent of lowest singlet and triplet excitons is systematically characterized. Our investigations indicate that the organic triplet emissions can be harvested by the heavy-atom effect of group 10-12 transition metals (viz., Pt, Au, and Hg) which enables efficient intersystem crossing from the Si singlet excited state to the T₁ triplet excited state.

Full text of DOI:10.1016/j.jorganchem.2005.02.025

Journal of Organometallic Chemistry 690 (2005) 5036–5048
www.elsevier.com/locate/jorganchem
Evolution of lowest singlet and triplet excited states with
transition metals in group 10–12 metallaynes
containing biphenyl spacer
a
a,
*
Li Liu a,b, Suk-Yue Poon , Wai-Yeung Wong
a
Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road,
Kowloon Tong, Hong Kong, PR China
b
Faculty of Chemistry and Material Science, Hubei University, Wuhan 430062, PR China
Received 28 January 2005; received in revised form 17 February 2005; accepted 17 February 2005
Available online 17 March 2005
Abstract
A new series of thermally stable group 10 platinum(II) and group 12 mercury(II) poly-yne polymers containing biphenyl spacer
trans-[–Pt(PBu3)2C„C(p-C6H4)2C„C–]n and [AHgC„C(p-C6H4)2C„C–]n were prepared in good yields by HagiharaÕs dehydro-
halogenation reaction of the corresponding metal chloride precursors with 4,40-diethynylbiphenyl HC„C(p-C6H4)2C„CH at room
temperature. We report the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic model com-
plexes trans-[Pt(Ph)(PEt3)2C„C(p-C6H4)2C„CPt(Ph)(PEt3)2] and [MeHgC„C(p-C6H4)2C„CHgMe] as well as the group 11
gold(I) counterpart [(PPh3)AuC„C(p-C6H4)2C„CAu(PPh3)]. The structural properties of all model complexes have been studied
by X-ray crystallography. The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and
the spatial extent of lowest singlet and triplet excitons is systematically characterized. Our investigations indicate that the organic
triplet emissions can be harvested by the heavy-atom effect of group 10–12 transition metals (viz., Pt, Au, and Hg) which enables
efficient intersystem crossing from the S1 singlet excited state to the T1 triplet excited state.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Transition metal; Acetylide; Biphenyl; Crystal structures; Triplet emission
1. Introduction
using metal-containing complexes is still one of the most
promising ways of making higher efficiency OLEDs [7].
Among these, rigid-rod organometallic poly-ynes of late
transition metals represent an important class of new
materials for basic and applied research [8]. Strong
spin–orbit coupling induced by a heavy-atom effect
mixes the singlet and triplet excited states through effi-
cient intersystem crossing (ISC) so that phosphorescence
(or triplet emission) can be measured readily using opti-
cal methods. Another attractive feature of this class of
metal-containing poly-ynes is that there is great scope
for chemical modification of the conjugated units. For
these two reasons, this family of metal poly-ynes
provides an excellent model system to study directly
the relationship between chemical structure and the
There is a continuing interest in the scientific commu-
nity in the search for new organic and metal-organic
molecular functional materials that could help to sustain
the growth of photonic research [1]. In particular, conju-
gated polymers and their metallated derivatives show a
wide domain of intriguing properties useful for the
development of optoelectronic devices such as organic
light-emitting diodes (OLEDs) [2], photovoltaic cells
[3], field-effect transistors [4], sensors [5], and nonlinear
optical systems [6]. In fact, harvesting of triplet excitons
*
Corresponding author. Tel.: +852 34117074; fax: +852 34117348.
E-mail address: rwywong@hkbu.edu.hk (W.-Y. Wong).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.025

L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
5037
evolution of singlet and triplet excitons [9]. Within this
framework, group 10 metal alkynyls and related poly-
mers have been studied extensively in view of their inter-
esting photoluminescence and electronic properties,
which depend on the transition metal, the organic li-
gand, the central spacer in the main chain and the sym-
metry of the molecules [9].
shortform of each formula, the triple bonds are abbrevi-
ated by T, and biphenyl by BP. Model monomer com-
plexes and polymers are differentiated by use of the
subscripts 1 and 1, respectively. Organic ligand [H–
T(BP)T]1 was chosen as a versatile synthon in the pres-
ent study to form a series of group 10–12 metal acetylide
complexes and polymers by adaptation of the dehydro-
halogenation procedures reported in the literature
Recently, there has been a great deal of experimental
and theoretical attention focusing on the energy levels of
singlet and triplet states in conjugated polymers. To
study the triplet excitons directly, we and others have
paid much attention to polyplatinynes and their mono-
mers to obtain a clear picture of the spatial extent of
the singlet and triplet states and their relative positions
strongly influence the ISC rate into the triplet manifold
[8,9]. For organic systems, this provides a major non-
radiative decay mechanism and reduces the lumines-
cence efficiency. Recently, the energy gap law has been
established for triplet states in Pt-containing conjugated
polymers and monomers where the intersystem crossing
rate depends exponentially on the energy gap to the
nearest triplet excited state [9a]. It would be very crucial
to understand the factors that control the spatial extent
of the singlet and triplet energy levels for the chemical
tailoring of the singlet–triplet gap. As continuation of
our research efforts in this growing field, we report here
a series of group 10–12 metal di-ynes and poly-ynes con-
taining the biphenyl spacer. The X-ray crystal structures
of the binuclear model complexes are also described.
Although there are many reports on Pt(II) poly-yne sys-
tems with a variety of organic spacers, relatively little is
known for research studies dealing with variation of me-
tal groups in metallated di-ynyl and poly-ynyl assem-
blies. Until recently, work has proliferated in the
metal-triggered phosphorescent emissions seen in some
gold(I)- and mercury(II)-containing metallaynes [10].
The aim of the present investigation is to establish in
what way the coordination of various heavy metal
groups affects the optical and electronic properties of
the metal poly-ynes. The influence of the metal on the
nature of the lowest singlet and triplet excited states will
be characterized, which is of pivotal importance for
understanding the mechanisms of LEDs based on conju-
gated polymers and thereby improving their macro-
scopic characteristics.
[9,11,12]. [Pt–T(BP)T]1 and [Pt–T(BP)T] were synthe-
1
sized by CuI-catalyzed dehydrohalogenating coupling
of trans-[PtCl2(PBu3)2] or trans-[PtCl(Ph)(PEt3)2] with
4,40-diethynylbiphenyl at room temperature (r.t.). The
feed mole ratios of the platinum chloride precursors
and the diethynyl ligand were 2:1 and 1:1 for the model
complex and polymer syntheses, respectively, and each
product was carefully purified to remove ionic impuri-
ties and catalyst residues. The diplatinum complex [Pt–
T(BP)T]1 was isolated by preparative TLC on silica.
Purification of the polymer [Pt–T(BP)T] was accom-
1
plished by silica column chromatography using CH2Cl2
as the eluent and it was obtained in high purity. Mercu-
ration of [H–T(BP)T]1 with a stoichiometric quantity of
HgCl2 using methanolic NaOH at r.t. gave an off-white
solid identified as [Hg–T(BP)T]
[10d]. Complex
1
[Hg–T(BP)T]1 was also synthesized by treatment of
[H–T(BP)T]1 with two equivalents of MeHgCl, in which
one coordination site is protected by a Me group, under
similar basic medium [11]. Likewise, we have also pre-
pared the d10 digold(I) diacetylide counterpart
[Au–T(BP)T]1, an isoelectronic and isolobal analog of
[Hg–T(BP)T]1, by reaction of Au(PPh3)Cl with
[H–T(BP)T]1 in a mole ratio of 2:1 in the presence of a
base [12]. The yields of these transformations are high
in each case. All the new complexes and polymers are
air-stable and can be stored without demanding any spe-
cial precautions. They generally exhibit good solubility
in chlorocarbons such as CH2Cl2 and CHCl3, but are
insoluble in hydrocarbons. However, we note that only
the lower molecular-weight fraction of [Hg–T(BP)T]
and [Pt–T(BP)T] can readily dissolve in chlorinated
1
1
solvents and there is always some insoluble portion left
in the solution (presumably consisting of polymer chains
of very high molecular weights) which requires filtration
prior to characterization. Estimates of the molecular
weights using gel permeation chromatography (GPC)
in THF indicate that the degrees of polymerization cal-
culated from Mn are 16 and 6 for [Pt–T(BP)T] and
1
[Hg–T(BP)T] (soluble oligomer portion), respectively.
2. Results and discussion
1
The GPC-values should be used with great care and
the GPC method does not give absolute values of molec-
ular weights but provides a measure of hydrodynamic
volume. Rod-like polymers in solution possess different
hydrodynamic properties than flexible polymers. So, cal-
ibration of the GPC with polystyrene standards is likely
to inflate the values of the molecular weights of the poly-
ynes to some extent.
2.1. Synthesis
All the metal alkynyl complexes and polymers were
obtained in good yields by the general reaction routes
described in Scheme 1. The binuclear complexes can
be considered the molecular models and the building
blocks of long chain organometallic polymers. In the

5038
L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
i
Scheme 1. (i) trans-[PtPh(Cl)(PEt3)2], CuI, Pr2NH, r.t.; (ii) trans-[PtCl2(PBu3)2CuI, Pr2NH, r.t.; (iii) MeHgCl, NaOH/MeOH, r.t.; (iv) HgCl2,
i
NaOH/MeOH, r.t.; (v) Au(PPh3)Cl, NaOH/MeOH, r.t.
2.2. Spectroscopic properties
case, the crystal structure consists of discrete binuclear
molecules in which two terminal organometallic groups
are linked by the biphenyl-spaced bis(acetylide) moiety
to afford the expected rod-like skeleton. There are two
independent molecules per asymmetric unit in the unit
cell of [Pt–T(BP)T]1 and the mean dihedral angle be-
tween the two central phenyl planes is ca. 21.5ꢁ. For
each of [Au–T(BP)T]1 and [Hg–T(BP)T]1, the molecule
sits on a crystallographic center of symmetry at the
mid-point of the C–C bond between the two planar phe-
nyl rings, resulting in a perfectly coplanar biphenyl unit
in the solid-state favorable for p-conjugation. The coor-
dination geometry is square-planar at platinum with the
two PEt3 groups trans to each other and linear about the
gold and mercury centers. The C„C bond lengths in the
The IR, NMR (1H, 13C and 31P) and MS data of our
compounds shown in Section 4 agree with their chemical
structures. The solution IR spectra are each character-
ized by a single sharp m(C„C) absorption band at ca.
2098–2144 cmꢀ1. The insoluble component of [Hg–
T(BP)T] also exhibits a characteristic solid-state IR
1
m(C„C) band, similar to that for the soluble portion.
The IR spectrum of each compound shows no band in
the range 3200–3300 cmꢀ1, characteristic of „CAH
stretching vibration, thus confirming that the [H–
T(BP)T]1 is capped by metal groups via r bonds. The
single 31P{1H} NMR signals flanked by platinum satel-
lites for [Pt–T(BP)T] and [Pt–T(BP)T]1 are consistent
1
with a trans geometry of the square-planar Pt unit.
1
The JP–Pt values in [Pt–T(BP)T] and [Pt–T(BP)T]1
˚
˚
ethynyl bridge [1.179(11)–1.193(11) A for Pt, 1.198(8) A
˚
for Au, and 1.233(16) A for Hg] are fairly typical of me-
1
are typical of those for related trans-PtP2 systems [13].
The room-temperature 31P NMR spectrum of [Au–
T(BP)T]1 displays a sharp singlet at d 44.04, indicating
a symmetrical arrangement of PAuC„C groups in solu-
tal–alkynyl r-bonding. The bond angles for the metal–
C„C units are close to linearity and conform to the
rigid-rod nature of these model compounds. By virtue
of the fact that [MeHg]+ is isoelectronic and isolobal
with the [(PPh3)Au]+ fragment, both [Au–T(BP)T]1
and [Hg–T(BP)T]1 have similar structural motifs, remi-
niscent of other reported examples. The Hg–C (alkyne)
bond in [Hg–T(BP)T]1 is slightly longer than the Au–C
(alkyne) bond in [Au–T(BP)T]1, but comparable to
those in other Hg(II) acetylide compounds [14]. The
1
tion. H NMR resonances arising from the protons of
the organic moieties were observed. The low solubility
of [Hg–T(BP)T] and [Pt–T(BP)T] led to some diffi-
1
1
culties for their complete 13C NMR characterization
but the higher solubility of the model compounds al-
lowed their full 13C NMR spectra to be interpreted.
The formulas of the model complexes [Pt–T(BP)T]1,
[Hg–T(BP)T]1 and [Au–T(BP)T]1 were successfully
established by the presence of intense molecular ion
peaks in their respective positive FAB mass spectra.
˚
Hg–CH3 bond (ca. 2.063(12) A) appears to be shorter
than those observed in some methylmercury complexes
with thiol ligands [15]. No apparent short intermolecular
contacts or p-stacking interactions are observed in our
Pt complex. In contrast to many Au(I) compounds,
where there frequently exist short Auꢁ ꢁ ꢁAu contacts,
aurophilicity is absent in [Au–T(BP)T]1 and the closest
intermolecular non-bonded contact is due to an
2.3. Crystal structure analyses
The three-dimensional molecular structures of [Pt–
T(BP)T]1, [Au–T(BP)T]1 and [Hg–T(BP)T]1 were ana-
lyzed by X-ray crystallography. Perspective views of
their structures are shown in Figs. 1–3. Pertinent bond
distances and angles are given in Tables 1–3. In each
˚
Au(1)ꢁ ꢁ ꢁH(26B) interaction (3.097 A). However, exami-
nation of the crystal packing diagram for the Hg(II)
counterpart reveals the involvement of ligand-unsup-
ported mercurophilicity in its structure. Remarkably,

L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
5039
Fig. 1. A perspective drawing of [Pt–T(BP)T]1 with the thermal ellipsoids drawn at the 25% probability level.
Fig. 2. A perspective drawing of [Au–T(BP)T]1 with the thermal ellipsoids drawn at the 25% probability level.
Fig. 3. A perspective drawing of [Hg–T(BP)T]1 with the thermal ellipsoids drawn at the 25% probability level.
there is a strong tendency for the molecules to aggregate
together and the whole lattice structure is fully sup-
ported and stabilized by extensive non-covalent
d10–d10 Hgꢁ ꢁ ꢁHg interactive vectors (ca. 3.833, 4.222
actions in the present system. In fact, the van der Waals
radius of mercury has been the subject of much debate
˚
and a value of up to 2.2 A has been proposed recently
[18], which appears to be a better estimate than the value
quoted by Bondi in 1964 [19]. So, the observed Hgꢁ ꢁ ꢁHg
˚
and 4.506 A) that link up the individual molecules in
˚
separations can be compared to those of 3.71–4.25 A for
an organized 3D polymeric network (Fig. 4). Although
alkynylgold(I) complexes exhibiting Auꢁ ꢁ ꢁAu interac-
tions are numerous [16], literature reports showing
Hgꢁ ꢁ ꢁHg bonding interactions are, to our knowledge,
comparatively very limited [17]. While the Hgꢁ ꢁ ꢁHg con-
tacts here indicate that each of the individual interac-
tions is relatively weak in nature, it is the large
number of them that play a supramolecular role and
generate a significant driving force for the observation
of solid-state aggregation. We conceive that such mer-
curophilic forces are more than just van der Waals inter-
mononuclear [Hg(C„CR)2] (R = Ph, SiMe3) [17a],
˚
3.738–4.183 A for binuclear [MeHgC„CRC„CHgMe]
(R = 9,9-dioctylfluorenediyl and oligothienyl) [11a] and
˚
4.077 and 4.449 A computed for molecular (HgH2)n
clusters (n = 2, 3) [17c] and are toward the upper limit
of those accepted as representing metallophilic interac-
tions. As shown in Fig. 4, the lattice is characterized
by infinite linear chains of Hg atoms between adjacent
molecules (e.g., Hg(1B)ꢁ ꢁ ꢁHg(1D)ꢁ ꢁ ꢁHg(1H)ꢁ ꢁ ꢁHg(1L)
and Hg(1E)ꢁ ꢁ ꢁHg(1I)ꢁ ꢁ ꢁHg(1M)ꢁ ꢁ ꢁHg(1O)) with the

5040
L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) for [Pt–T(BP)T]1
Molecule 1
Molecule 2
Molecule 1
Molecule 2
Pt(1)–P(1)
Pt(1)–C(1)
Pt(2)–P(3)
Pt(2)–C(34)
C(19)–C(20)
2.281 (2)
2.081(8)
2.273(3)
2.027(9)
1.193(11)
2.271(3)
2.056(7)
2.270(3)
2.046(9)
1.192(11)
Pt(1)–P(2)
Pt(1)–C(19)
Pt(2)–P(4)
Pt(2)–C(47)
C(33)–C(34)
2.274(2)
2.009(8)
2.267(3)
2.069(8)
1.179(11)
2.279(3)
1.998(8)
2.279(3)
2.072(8)
1.182(11)
P(1)–Pt(1)–P(2)
176.63(8)
88.7(2)
90.8(3)
176.64(10)
93.2(3)
88.9(2)
P(1)–Pt(1)–C(19)
P(3)–Pt(2)–P(4)
89.7(2)
175.89(10)
88.7(3)
87.0(3)
176.50(10)
87.7(2)
P(2)–Pt(1)–C(19)
P(3)–Pt(2)–C(34)
Pt(1)–C(19)–C(20)
Pt(2)–C(34)–C(33)
P(4)–Pt(2)–C(34)
C(19)–C(20)–C(21)
C(30)–C(33)–C(34)
179.8(9)
175.2(8)
177.5(9)
178.3(9)
175.0(9)
178.6(9)
174.7(10)
177.1(10)
Table 2
former is similar to that found for the prototypical poly-
mer trans-[–Pt(PBu3)2C„C(p-C6H4)C„C–]n (abbrevi-
˚
Selected bond lengths (A) and angles (ꢁ) for [Au–T(BP)T]1
Au(1)–P(1)
C(19)–C(20)
2.2818(16) Au(1)–C(19)
1.198(8)
1.996(6)
ated as [Pt–T(P)T] ) [21], it is slightly higher than
1
those observed for the related platinum(II) poly-ynes
bridged by bipyridyl (274 and 287 ꢁC) [9c] or bithienyl
(275 ꢁC) [3b] spacers. The onset of decomposition for
P(1)–Au(1)–C(19) 174.68(19)
Au(1)–C(19)–C(20) 171.3(6)
[Hg–T(BP)T] takes place at a higher temperature than
1
Table 3
Selected bond lengths (A) and angles (ꢁ) for [Hg–T(BP)T]1
those for Hg-containing poly(ethynylenefluorenylene)
copolymers (200–280 ꢁC) [10d]. We observe a sharp
weight loss of 37% between 295 and 420 ꢁC for [Pt–
˚
Hg(1)–C(1)
C(2)–C(3)
2.063(12)
1.233(16)
Hg(1)–C(2)
2.031(12)
T(BP)T] , whereas 36% of the weight was lost for
1
[Hg–T(BP)T] as the temperature rose from 330 to
C(1)–Hg(1)–C(2)
Hg(1)–C(2)–C(3)
178.7(4)
170.8(12)
C(2)–C(3)–C(4)
178.7(11)
1
400 ꢁC. The decomposition step is ascribed to the
removal of six butyl groups from [Pt–T(BP)T] and
1
the loss of one –C„C-(p-C6H4)2– group from [Hg–
Hg–Hg–Hg bond angle of 180ꢁ. Aggregation of each
stack of these molecules also persists throughout the en-
tire crystal lattice in a 3D space via weak Hgꢁ ꢁ ꢁHg
attractive interactions (e.g., Hg(1A)ꢁ ꢁ ꢁHg(1J) 3.833
T(BP)T] .
1
2.5. Electronic absorption and luminescent spectra
˚
and Hg(1A)ꢁ ꢁ ꢁHg(1F) 4.222 A) to form another zigzag
The photophysical data of the new compounds mea-
sured in both solution and solid state are shown in Table
4. All the metal alkynyls display similar structured
absorption bands in the near UV region. The lowest en-
ergy transitions are predominantly intraligand in nature
chains of Hg centers with the Hg(1A)–Hg(1J)–Hg(1C)
and Hg(1C)–Hg(1A)–Hg(1J) angles of 67.8ꢁ and 60.2ꢁ,
respectively. We also locate minor short intermolecular
contacts involving the Hg atoms and methyl hydrogen
˚
atoms (Hg(1)ꢁ ꢁ ꢁH(1B) 3.399 A) as well as phenyl pro-
1
˚
consisting of both acetylenic and aromatic (pp*) char-
tons (Hg(1)ꢁ ꢁ ꢁHA 3.164 A) that make only little contri-
acter, possibly mixed with some admixture of metal
orbitals. The 0–0 absorption peak is assigned as the
S0 ! S1 transition from the highest occupied molecular
orbital (HOMO) to the lowest unoccupied molecular
orbital (LUMO), which are mainly delocalized p and
p* orbitals [9]. Coordination of each of the metal entities
to the organic system results in enhanced p ! p* transi-
tions for the aryleneethynylene moiety. As compared to
the band at 289 nm in CH2Cl2 for [H–T(BP)T]1, we find
that the position of the lowest energy absorption band is
red-shifted after the inclusion of metal fragment in all
the metal alkynyls. This reveals that p-conjugation is
preserved through the metal site by mixing of the fron-
tier orbitals of metal and the ligand. In energy terms,
the experimentally determined HOMO–LUMO energy
gaps (Eg) as measured from the onset wavelength in so-
lid film state are also tabulated in Table 4. The transition
bution to the overall molecular packing. This structure
is unique in that no apparent weak Hgꢁ ꢁ ꢁg2–C„C inter-
actions are observed which have been shown to be an
important driving force for the solid-state aggregation
process to take place in alkynyl complexes of Cu(I),
Ag(I) and Hg(II) [17b,20].
2.4. Thermal analysis
The thermal properties of the polymers were
examined by thermal gravimetry (TG) under nitrogen.
Analysis of the TG trace (heating rate 20 ꢁC/min) for
[Pt–T(BP)T] and [Hg–T(BP)T] shows that they exhi-
bit good thermal stability. Decomposition commences
at 297 and 330 ꢁC for [Pt–T(BP)T] and [Hg–T(BP)T] ,
1
1
1
1
respectively, and decomposition onset was defined as a
mass loss of 2%. While the onset temperature for the

L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
5041
Fig. 4. Crystal packing diagram for [Hg–T(BP)T]1 showing the linear and zigzag chains of Hg atoms aggregated through Hgꢁ ꢁ ꢁHg intermolecular
contacts and all hydrogen atoms are omitted for clarity.
Table 4
Photophysical data for the model complexes and polymers
kmax (nm)a
Eg (eV)b
kem (nm)c
CH2Cl2
Film
352
CH2Cl2 (290 K)d
Frozen CH2Cl2 (77 K)e
[Pt–T(BP)T]1
[Pt–T(BP)T]
305 (3.7)
349 (11.4)
3.17
391
408* (2.2, 2.0)
383*
407*
542 (0.34)
582*
418*
304
372
362
374
3.10
3.31
369*
1
409 (6.0, 2.4)
556*
367
549 (0.12)
592*
395*
[Hg–T(BP)T]1
309 (11.7)
310
382* (6.0, 2.2)
420*
464
526 (6.7)f
543*
[Hg–T(BP)T]
310
308
342
3.27
3.24
371 (3.0, 2.2)
405br
523 (3.9)f
551
1
[Au–T(BP)T]1
326 (53.7)
365*
383 (1.6, 1.0)
376*
396*
529 (0.10)
568*
[H–T(BP)T]1
289 (3.8)
270
3.50
a
Extinction coefficients (104 Mꢀ1 cmꢀ1) are shown in parentheses.
b
c
d
e
f
Estimated from the onset wavelength of the solid-state optical absorption.
Asterisks indicate that emission peaks appear as shoulders or weak bands.
Fluorescence quantum yields (%) and lifetimes (ns) shown in parentheses (UF, sF) are measured in CH2Cl2 relative to anthracene.
Phosphorescence lifetimes sP (ls) at 20 K for the peak maxima are shown in parentheses.
sP (ls) was measured at 77 K; br = broad.
energies of the long-chain polymer [Pt–T(BP)T] are
At 290 K, all of the complexes in CH2Cl2 solution
emit purple-blue 1(pp*) fluorescence (S1 ! S0) peak near
400 nm that is characterized by the small Stokes shift be-
tween the bands in the absorption and the emission
spectra. At 77 K, the principal emission peak occurs
1
lowered with respect to those of [Pt–T(BP)T]1, suggest-
ing a well-extended singlet excited state in the Pt(II)
polymer. According to the type of the metal groups,
the optical energy gaps of the poly-ynes follow the
experimental order [Hg–T(BP)]T] > [Pt–T(BP)T]
at ca. 549 and 523 nm for [Pt–T(BP)T]
[Hg–T(BP)T] , and at ca. 542, 529 and 526 nm for
and
1
1
1
and those of the model compounds [Hg–T(BP)T]1 >
[Au–T(BP)T]1 > [Pt–T(BP)T]1.
1
[Pt–T(BP)T]1, [Au–T(BP)T]1 and [Hg–T(BP)T]1,

5042
L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
respectively. The large Stokes shifts of these lower-lying
emission peaks from the dipole-allowed absorptions
(1.08–1.66 eV, see Figs. 5–9), plus the long emission life-
times (sP) in the microsecond regime are indicative of
their triplet parentage, and they are thus assigned to
3
the (pp*) excited states of the 4,40-diethynylbiphenyl
core (i.e., T1 ! S0 emission). Such assignment can be
further supported by the observed temperature depen-
dence of the emission data for [Pt–T(BP)T] (see Fig.
1
10), in accordance with earlier work on platinum(II)
poly-ynes [9]. From 290 to 20 K, the singlet emission
peak intensity increases only by a factor of 3.8 but the
intensity of the lower-lying triplet emission increases
by a factor of 61.2 which is accompanied by a well-re-
solved vibronic structure, and such an increase in inten-
sity indicates a long-lived triplet excited state that is
more sensitive to thermally activated non-radiative de-
cay mechanisms. For [Hg–T(BP)T]1, an emission band
also appears at 464 nm presumably due to the formation
of solid-state aggregates in frozen CH2Cl2 [10d,22] and
this corroborates well with the results from X-ray struc-
tural analysis (vide supra). The observation of a broad
band centered at ꢂ405 nm (spanning up to ꢂ500 nm)
Fig. 6. Room temperature optical absorption spectrum and photolu-
minescence spectrum (77 K) of [Pt–T(BP)T] in CH2Cl2.
1
in the photoluminescence spectrum of [Hg–T(BP)T]
1
is also a manifestation of the solid-state aggregation
effect.
Based on the absorption and photoluminescence
data, we can obtain experimental values of the lower-ly-
ing excitations (Table 5) and construct an energy scheme
as shown in Fig. 11 for the polymers and the model com-
plexes that allows thorough investigation of the spatial
extent of the singlet and triplet excitons. The energy val-
ues are absolute values with respect to the S0 ground
state. Values of DE(S0 ꢀ T1) (energy gap between S0
and T1) were compiled to be 2.26–2.36 eV for all the me-
tal di-ynes and poly-ynes. The measured DE(S1 ꢀ T1)
values are 0.76, 0.71, 0.76, 0.70 and 0.79 eV for [Pt–
T(BP)T]1, [Pt–T(BP)T] , [Hg–T(BP)T]1, [Hg–T(BP)T]
Fig. 7. Room temperature optical absorption spectrum and photolu-
minescence spectrum (77 K) of [Au–T(BP)T]1 in CH2Cl2.
1
1
Fig. 5. Room temperature optical absorption spectrum and photolu-
minescence spectrum (77 K) of [Pt–T(BP)T]1 in CH2Cl2.
Fig. 8. Room temperature optical absorption spectrum and photolu-
minescence spectrum (77 K) of [Hg–T(BP)T]1 in CH2Cl2.

L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
5043
[9d]. From the S1 energy levels obtained by absorption
studies, it is clear that the S1 states are notably lower
for the d8 Pt(II) species than those for the d10 Au(I)
and Hg(II) congeners. The order of p-delocalization
through the metal chromophore is Pt(II) > Au(I) >
Hg(II). For the Pt(II) and Hg(II) systems, the lowest
T1 state remains strongly localized, as can be inferred
from the small energy difference between triplet emis-
sions in the metal di-ynes and in the poly-ynes. Previous
calculations carried out for [Pt–T(P)T] also indicated
1
the triplet to be confined onto the phenylene ring [24].
Substitution of the metal groups does not seem to alter
this strong confinement. We observe that the energy lev-
els for the Pt di-yne and poly-yne are red-shifted relative
to [Pt–T(P)T]1 and [Pt–T(P)T] (P = p-phenylene) in
1
Fig. 9. Room temperature optical absorption spectrum and photolu-
minescence spectrum (77 K) of [Hg–T(BP)T] in CH2Cl2.
which the presence of two phenyl rings in the former
cases was shown to increase the p-conjugation length
and can shift the phosphorescence to the red by 0.10
and 0.12 eV, respectively. The energy of the T1 ! S0
transition also varies with the organometallic groups.
Apparently, the T1 levels for the Au(I) and Hg(II) com-
pounds are slightly higher than those for the corre-
sponding Pt(II) congeners in the present system. We
note that the order of S1 ! T1 crossover efficiency is
[Au–T(BP)T]1 > [Pt–T(BP)T]1, since the energy of the
T1 state is higher for the former, resulting in a faster
phosphorescence radiative decay rate. This also agrees
with the results obtained from the peak height ratio
from triplet emission to singlet emission at 77 K,
DE(T1 ! S0, S1 ! S0) (Table 5), which has been
adopted previously as a good parameter to evaluate
the relative ISC efficiency [9e,9f,9i]. An order of ISC effi-
1
ciency [Pt–T(BP)T] > [Pt–T(BP)T]1 is observed, simi-
Fig. 10. Temperature dependence of the photoluminescence of [Pt–
T(BP)T]
1
.
lar to the Pt system with a single phenyl ring. Based
on the work by others that the ISC efficiency is close
to unity for third row transition metal chromophores
[25], the radiative (kr) and non-radiative (knr) decay rates
are related to the measured lifetime of triplet emission
(sP) and the phosphorescence quantum yield (UP) by
the following expressions:
1
and [Au–T(BP)T]1, respectively, and they correspond
well with the S1 ꢀ T1 energy gap of 0.7 0. l eV for sim-
ilar p-conjugated Pt(II), Au(I) and Hg(II) poly-ynes
[9a,10a,10d], and are close to the gaps estimated for a
series of related organic conjugated polymers [23]. We
attribute such a constant DE(S1 ꢀ T1) value to the ex-
change energy and possibly some additional constant
contribution due to the admixture of the metal orbitals
knr ¼ ð1 ꢀ UPÞ=sP;
kr ¼ UP=sP:
Table 5
Experimental values of various transition energies among the S0, S1 and T1 levels and intersystem crossing efficiencies of platinum(II), gold(I) and
mercury(II) di-ynes and poly-ynes containing biphenyl groups
Energy (eV)
[Pt–T(BP)T]1
[Pt–T(BP)T]
[Hg–T(BP)T]1
[Hg–T(BP)T]
[Au–T(BP)T]1
1
1
S0 ! S1
3.55
3.05
2.29
0.76
6.0
3.33
2.97
2.26
0.71
18.9
4.01
3.12
2.36
4.00
3.06
2.36
3.80
3.13
2.34
0.79
9.1
S1 ! S0
T1 ! S0
S1 ! T1
0.76
b
0.70
b
DE(T1 ! S0, S1 ! S0)a
a
Ratio of the intensities of triplet emission to singlet emission at 77 K.
b
Cannot be accurately determined due to the presence of broad aggregate emission band.

5044
L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
Fig. 11. Electronic energy level diagram of biphenyl-linked metal alkynyls determined from absorption and emission data. Dashed lines represent the
levels for [Pt–T(P)T]1 and [Pt–T(P)T] and the data were taken from Ref. [9e]. The S0 levels are arbitrarily shown to be of equal energy.
1
Table 6
The measured phosphorescence quantum yields, lifetimes, and radia-
groups anchored on the alkynyl unit, we were able to
build up polymeric mercury(II) acetylide system in the
tive and non-radiative decay rates of [Pt–T(BP)T]1, [Pt–T(BP)T] and
1
[Au–T(BP)T]1 at 20 K
solid state aggregated through Hgꢁ ꢁ ꢁHg secondary inter-
actions. All the compounds were analytically and spec-
UP (%)
sP (ls)
(knr)P
(sꢀ1
)
(kr)P (sꢀ1
)
troscopically characterized to possess a well-defined
size and structure. The materials are solution-process-
able and thermally stable. All the three transition metals
(viz., Pt, Au, and Hg) can exert heavy-atom effects in the
enhancement of ISC rate and a discussion was made on
the relation between the T1 energy state and the kr value
for the triplet emission. It is envisioned that a structure–
property–function relationship can be established and
valuable insight into the photophysical nature of
(–C„C–Ar–C„C–)n conjugated materials can be sub-
sequently derived. Future work in this direction should
elucidate a direct evaluation of the role of a metal center
on the properties of conjugated compounds and such an
investigation is desirable for optoelectronic applications
that utilize the T1 state for light emission through light-
harvesting techniques.
[Pt–T(BP)T]1
[Pt–T(BP)T]
[Au–T(BP)T]1
26.4
23.9
18.6
0.34
0.12
0.10
2.2 · 106
6.6 · 106
7.8 · 106
7.8 · 105
2.1 · 106
1.8 · 106
1
The measured UP and sP values for [Pt–T(BP)T]1 are
0.26 and 0.34 ls at 20 K, respectively, and those for
[Au–T(BP)T]1 are 0.19 and 0.10 ls. The values calcu-
lated for knr and kr at 20 K for both Pt and Au di-ynes
are given in Table 6. For phosphorescence in aromatic
hydrocarbon molecules, kr lies typically between 0.1
and 1 sꢀ1 [26]. So, the heavy-atom effect of Pt and Au
can speed up the radiative decay rate for the triplet emis-
sion by 5–6 orders of magnitude and the phosphores-
cence decay rate for [Au–T(BP)T]1 (kr ꢂ 1.8 · 106 sꢀ1
)
is about twice that of [Pt–T(BP)T]1 (kr ꢂ 7.8 · 105 sꢀ1).
However, for the sake of accuracy, no attempts were
made to compare the results with [Hg–T(BP)T]1 because
of the aggregate emission band that is present which
would provide another possible radiative decay
pathway.
4. Experimental
4.1. General procedures
All reactions were carried out under a nitrogen atmo-
sphere using standard Schlenk techniques, but no special
precautions were taken to exclude oxygen during work-
up. Solvents were predried and distilled from appropri-
ate drying agents. All reagents and chemicals, unless
otherwise stated, were purchased from commercial
sources and used without further purification. Prepara-
tive TLC was performed on 0.7 mm silica plates (Merck
3. Concluding remarks
This report demonstrated that 4,40-diethynylbiphenyl
is a useful precursor to afford a new series of lumines-
cent bimetallic and organometallic poly-yne materials
of group 10–12 transition metals. On the structural as-
pect, depending on the steric properties of the end

L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
5045
Kieselgel 60 GF254) prepared in our laboratory. The
compounds [H–T(BP)T]1 [27], trans-[PtCl(Ph)(PEt3)2]
[28] and trans-[PtCl2(PBu3)2] [29] were prepared by liter-
ature methods. Infrared spectra were recorded as
CH2Cl2 solutions or KBr pellets using a Perkin–Elmer
Paragon 1000 PC or Nicolet Magna 550 Series II FTIR
spectrometer. NMR spectra were measured in CDCl3 on
a Jeol EX270 or a Varian Inova 400 MHz FT NMR
spectrometer, with 1H and 13C NMR chemical shifts
quoted relative to TMS and 31P chemical shifts relative
to an 85% H3PO4 external standard. Fast atom bom-
bardment (FAB) mass spectra were recorded on a Finn-
igan MAT SSQ710 mass spectrometer. Electronic
absorption spectra were obtained with a HP 8453 UV–
vis spectrometer. For solid-state emission spectral mea-
surements, the 325 nm line of a He–Cd laser was used as
an excitation source. The luminescence spectra were
analyzed by a 0.25 m focal length double monochroma-
tor with a Peltier cooled photomultiplier tube and pro-
P(CH2)2CH2CH3) and 0.94 (m, 18H, CH3) ppm.
31P{1H} NMR (CDCl3): d 4.12 (1JPt–P = 2356 Hz)
ppm. Anal. Found: C, 59.82; H, 7.68. Calc. for
(C40H62PtP2)n: C, 60.06; H, 7.81%. GPC (THF as elu-
ent): Mw = 14770, Mn = 13060, polydispersity = 1.13.
4.2.2. Synthesis of [Pt–T(BP)T]1
A solution of [H–T(BP)T]1 (9.1 mg, 0.045 mmol)
and two molar equivalents of trans-[PtCl(Ph)(PEt3)2]
(48.9 mg, 0.090 mmol) in iPr2NH/CH2Cl2 (10 cm3,
1:1, v/v) was charged into a 50 mL Schlenk flask
and a small amount of CuI (3.0 mg) was then added.
The resulting mixture was stirred at r.t. over a period
of 15 h, after which all the volatile components were
evaporated to dryness. The residue was redissolved
in CH2Cl2 and the solution was purified on prepara-
tive TLC plates eluting with hexane/CH2Cl2 (3:2, v/v,
Rf = 0.55) to give the title complex as an off-white
crystalline solid with an isolated yield of 67%
cessed with
a
lock-in-amplifier. For the low
(36.7 mg). IR (CH2Cl2): m(C„C) 2098 cmꢀ1 1H
.
temperature experiments, samples were mounted in a
closed-cycle cryostat (Oxford CC1104) in which the tem-
perature can be adjusted from 10 to 330 K. The solution
emission spectra at 290 and 77 K were measured on a
PTI Fluorescence Master Series QM1 spectrophotome-
ter. The fluorescence quantum yields (UF) were deter-
mined in CH2Cl2 at 290 K against the anthracene
standard (UF = 0.27). Phosphorescence quantum yields
UP were measured in solid thin films at 20 K relative
to the prototypical polymer trans-[–Pt(PBu3)2C„C(p-
C6H4)C„C–]n (UP = 0.30 at 20 K) [9a]. The molecular
weights of the polymers were determined by GPC (HP
1050 series HPLC with visible wavelength and fluores-
cent detectors) using polystyrene standards and thermal
analyses were performed with a Perkin–Elmer TGA6
thermal analyzer.
NMR (CDCl3): d 7.37 (d, J = 7.8 Hz, 4H, Ar), 7.28–
7.18 (m, 8H, Ar + Hortho of Ph–Pt), 6.89 (t,
J = 7.6 Hz, 4H, Hmeta of Ph–Pt), 6.74 (t, J = 7.6 Hz,
2H, Hpara of Ph–Pt), 1.71 (m, 24 H, CH2CH3) and
1.03 (m, 36H, CH2CH3) ppm. 13C NMR (CDCl3): d
156.28, 139.05, 137.09, 131.02, 127.94, 127.16, 126.08,
121.09 (Ar), 114.18, 110.06 (C„C), 15.19 and 8.14
(Et) ppm. 31P{1H} NMR (CDCl3): d 11.67 (1JPt–P
=
2628 Hz) ppm. FAB-MS: m/z 1217 [M+]. Anal.
Found: C, 51.02; H, 6.50. Calc. for C52H78Pt2P4: C,
51.31; H, 6.46%.
4.2.3. Synthesis of [Hg–T(BP)T]
1
A solution of HgCl2 (25.6 mg, 0.094 mmol) in MeOH
(10 cm3) was mixed with [H–T(BP)T]1 (19.1 mg,
0.094 mmol) in MeOH (10 cm3). To this mixture,
1.9 cm3 of 0.20 M basic MeOH (0.38 mmol, prepared
by dissolving 0.40 g of NaOH in 50 cm3 of MeOH)
was added. Within several minutes, an off-white solid
precipitated from the homogeneous solution. The reac-
tion was complete after stirring for 12 h and the solid
was collected by filtration, washed with MeOH
(2 · 20 cm3), and air-dried to furnish the polymer in
4.2. Preparations of complexes
4.2.1. Synthesis of [Pt–T(BP)T]
A mixture of 4,40-diethynylbiphenyl, [H–T(BP)T]1,
1
(11.0 mg,
0.054 mmol)
and
trans-[PtCl2(PBu3)2]
i
(36.5 mg, 0.054 mmol) in a 1:1 molar ratio in Pr2NH/
CH2Cl2 (10 cm3, 1:1, v/v) was allowed to react in the
presence of CuI (3.0 mg). The solution was stirred at
r.t. for 15 h, after which all volatile components were re-
moved under reduced pressure. The residue was taken
up in CH2Cl2 and filtered through a silica gel column
using the same solvent as the eluent to give a yellow
solution. Upon removal of solvent, the product was then
reprecipitated twice from a CH2Cl2/MeOH mixture fol-
lowed by washing with MeOH to afford a light yellow
powder in 65% yield (28.3 mg). IR (CH2Cl2): m(C„C)
80% yield (30.3 mg). IR (CH2Cl2): m(C„C) 2138 cmꢀ1
.
1H NMR (CDCl3): d 7.56 (t, J = 8.6 Hz, 4H, Ar) and
6.93 (d, J = 8.6 Hz, 4H, Ar) ppm. Anal. Found: C,
47.65; H, 1.88. Calc. for (C16H8Hg)n: C, 47.94; H,
2.01%. GPC (THF as eluent): Mw = 2390, Mn = 2200,
polydispersity = 1.09.
4.2.4. Synthesis of [Hg–T(BP)T]1
The organic di-yne [H–T(BP)T]1 (13.0 mg,
0.064 mmol) in MeOH (10 cm3) was first combined with
MeHgCl (37.1 mg, 0.15 mmol) in MeOH (10 cm3).
0.20 M basic MeOH (1.3 mL, 0.26 mmol) was subse-
quently added to produce a pale yellow suspension.
1
2101 cmꢀ1. H NMR (CDCl3): d 7.45 (d, J = 6.8 Hz,
4H, Ar), 7.29 (d, J = 6.8 Hz, 4H, Ar), 2.18 (m, 12H,
PCH2), 1.61 (m, 12H, PCH2CH2), 1.46 (m, 12H,

5046
L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
The solvent was then decanted and the light yellow solid
(32.5 mg, 80%) was washed with MeOH (2 · 10 cm3)
5. Crystallography
and air-dried. IR (CH2Cl2): m(C„C) 2138 cmꢀ1
.
1H
Single crystals of [Pt–T(BP)T]1, [Au–T(BP)T]1 and
[Hg–T(BP)T]1 suitable for X-ray crystallographic analy-
ses were grown by slow evaporation of their respective
solutions in CH2Cl2–hexane at r.t. The crystals were
chosen and mounted on a glass fiber using epoxy resin.
Crystal data, data collection parameters and results of
the analyses are listed in Table 7. The diffraction exper-
iments were carried out at r.t. on a Bruker Axs SMART
1000 CCD area-detector diffractometer using graphite-
2
NMR (CDCl3): d 7.52 (m, 8H, Ar) and 0.71 (s, J(Hg–
H) = 147 Hz, 6H, CH3) ppm. 13C NMR (CDCl3): d
144.18, 140.06, 132.82, 127.03 (Ar), 105.25 (C„C) and
7.35 (CH3) ppm. FAB-MS: m/z 631 [M+]. Anal. Found:
C, 34.02; H, 2.10. Calc. for C18H14Hg2: C, 34.24; H,
2.23%.
4.2.5. Synthesis of [Au–T(BP)T]1
˚
To the solution of [H–T(BP)T]1 (8.2 mg, 0.041 mmol)
in MeOH (10 cm3) was added two molar equivalents of
Au(PPh3)Cl (43.1 mg, 0.087 mmol), followed by a solu-
tion of NaOMe/MeOH (0.20 M, 0.16 mmol, 0.8 cm3).
The mixture was stirred at r.t. overnight and the pale
yellow powdery solid was then collected by decantation
which was washed with MeOH (2 · 10 cm3) and air-
dried to give 44.4 mg (97%) of the pure product. IR
monochromated Mo Ka radiation (k = 0.71073 A).
The raw intensity data frames were integrated with the
SAINT+ program using a narrow-frame integration
algorithm [30]. Corrections for Lorentz and polarization
effects were also applied by SAINT. For each analysis,
an empirical absorption correction based on the multi-
ple measurement of equivalent reflections was applied
by using the program SADABS [31]. The structures were
solved by direct methods and expanded by difference
Fourier syntheses using the software SHELTXL [32]. Struc-
ture refinements were made on F2 by the full-matrix
least-squares technique. In each case, all the non-hydro-
gen atoms were refined with anisotropic displacement
parameters. The hydrogen atoms were placed in their
ideal positions but not refined.
(CH2Cl2): m(C„C) 2144 cmꢀ1 1H NMR (CDCl3): d
.
7.50 (m, 38H, Ar) ppm. 13C NMR (CDCl3): d 139.12,
134.63, 134.49, 132.99, 131.80, 130.24, 129.45, 129.33,
126.64, 123.98 (Ar), 104.52 (C„C) ppm. 31P{1H}
NMR (CDCl3): d 44.04 ppm. FAB-MS: m/z 1119
[M+]. Anal. Found: C, 55.58; H, 3.35. Calc. for
C52H38Au2P2: C, 55.83; H, 3.42%.
Table 7
Summary of crystal structure data for [Pt–T(BP)T]1, [Au–T(BP)T]1 and [Hg–T(BP)T]1
[Pt–T(BP)T]1
[Au–T(BP)T]1
[Hg–T(BP)T]1
Empirical formula
Molecular weight
Crystal size (mm)
Crystal system
C52H78P4Pt2
1217.20
C52H38Au2P2
1118.70
C18H14Hg2
631.47
0.30 · 0.22 · 0.20
Triclinic
0.20 · 0.10 · 0.08
Triclinic
0.22 · 0.16 · 0.10
Triclinic
ꢀ
ꢀ
ꢀ
Space group
˚
P1
P1
P1
a (A)
˚
9.476(6)
17.300(11)
34.13(2)
76.951(12)
86.479(12)
84.269(12)
5419(6)
1.492
6.7962(6)
10.6022(9)
14.8133(13)
100.380(2)
102.077(2)
90.032(2)
1025.85(15)
1.811
4.5058(6)
8.8672(11)
10.0227(12)
96.419(2)
96.422(2)
97.915(2)
390.84(9)
2.683
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
U (A )
Dcalc (g cmꢀ3
)
Z
4
5.306
2424
1
7.257
538
1
19.603
282
l(Mo Ka) (mmꢀ1
F(000)
)
h angle (ꢁ)
0.61–23.32
45235
15605
1.95–24.99
5132
3548
2.06–25.00
1657
1200
Reflections collected
Unique reflections
Rint
0.0638
10750
1045
0.0259
2951
253
0.0278
1118
92
Observed reflections [I > 2r(I)]
No. of parameters
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
Goodness-of-fit on F2
0.0600, 0.1237
0.0919, 0.1356
1.108
0.0329, 0.0676
0.0469, 0.0731
1.024
0.0371, 0.0984
0.0390, 0.1001
1.047
ꢀ3
˚
Residual extrema in final difference map (e A
)
1.278 to ꢀ1.416
0.716 to ꢀ0.654
1.731 to ꢀ1.053

L. Liu et al. / Journal of Organometallic Chemistry 690 (2005) 5036–5048
5047
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6. Supplementary material
Crystallographic data (comprising hydrogen atom
coordinates, thermal parameters and full tables of bond
lengths and angles) for the structural analysis have been
deposited with the Cambridge Crystallographic Centre
(Deposition Nos. 261310–261312). Copies of this infor-
mation may be obtained free of charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: + 44 1223 336 033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
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Financial support from a CERG Grant from the
Hong Kong Research Grants Council of the Hong
Kong SAR, PR China (Project No. HKBU2048/01P)
is gratefully acknowledged. We also thank Dr. K.-W.
Cheah for the access of the facilities for variable temper-
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