Syntheses, structures and photophysical properties of a series of luminescent copper(I) mixed-ligand complexes

Article abstract of DOI:10.1016/j.poly.2011.12.040

The reaction of [Cu(NCCH₃)₄]ClO₄ with a chelating diimine ligand and 1,2-bis(diphenylphosphane)benzene (bdpp) in dichloromethane solution gives good yields of a series of mixed-ligand copper(I) complexes [Cu(diimine)(bdpp)]ClO₄, where the diimine ligands are 2,2′-bipyridine (bpy), 5,5′-dibromo-2,2′-bipyridine (BrbpyBr), 5,5′-diethynyl-2,2′-bipyridine (HCCbpyCCH), 1,10-phenanthroline (phen) and 3,8-dibromo-1,10-phenanthroline (BrphenBr) in complexes 1-5, respectively. All the structures are confirmed by single crystal X-ray structure analysis. A study of the HRMS results suggest that the [Cu(diimine)(bdpp)] ⁺ cations for complexes 1-5 are kinetically stable products, and [Cu(bdpp)₂]⁺ is the thermodynamically stable product in DCM solution. In the crystal structures of complexes 1-5, π...π and C-H...π interactions widely exist, among which 4·CH ₂Cl₂ shows the most striking example. The triple π...π interactions within the cation dimer and the rich C-H...π interactions among the cation dimers are suggested to be the main reasons of the high emissive quantum yield of 18.33% in the solid state under air for complex 4.

Full text of DOI:10.1016/j.poly.2011.12.040

Polyhedron 35 (2012) 47–54
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses, structures and photophysical properties of a series of
luminescent copper(I) mixed-ligand complexes
a
a
a
a
a
a
Xiu-Ling Li a,b, , Yu-Bo Ai , Bo Yang , Jie Chen , Ming Tan , Xue-Lian Xin , Yan-Hui Shi
⇑
a School of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou, Jiangsu 221116, China
b Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Xuzhou Normal University, Xuzhou, Jiangsu 221116, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of [Cu(NCCH3)4]ClO4 with a chelating diimine ligand and 1,2-bis(diphenylphosphane)ben-
zene (bdpp) in dichloromethane solution gives good yields of a series of mixed-ligand copper(I) complexes
[Cu(diimine)(bdpp)]ClO4, where the diimine ligands are 2,20-bipyridine (bpy), 5,50-dibromo-2,20-bipyri-
dine (BrbpyBr), 5,50-diethynyl-2,20-bipyridine (HC„CbpyC„CH), 1,10-phenanthroline (phen) and 3,8-
dibromo-1,10-phenanthroline (BrphenBr) in complexes 1–5, respectively. All the structures are confirmed
by single crystal X-ray structure analysis. A study of the HRMS results suggest that the [Cu(diimi-
ne)(bdpp)]+ cations for complexes 1–5 are kinetically stable products, and [Cu(bdpp)2]+ is the thermody-
Received 25 October 2011
Accepted 26 December 2011
Available online 14 January 2012
Keywords:
Copper(I)
Mixed-ligand complexes
Diimine
Diphosphane
Luminescence
namically stable product in DCM solution. In the crystal structures of complexes 1–5,
interactions widely exist, among which 4ꢀCH2Cl2 shows the most striking example. The triple
interactions among the cation dimers are suggested
p
ꢀ ꢀ ꢀ
p
and C–Hꢀ ꢀ ꢀ
p
p
ꢀ ꢀ ꢀ inter-
p
actions within the cation dimer and the rich C–Hꢀ ꢀ ꢀ
p
to be the main reasons of the high emissive quantum yield of 18.33% in the solid state under air for com-
plex 4.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
coordination shell would suppress ligand-addition reactions and
inhibit the flattening distortion in the excited state, and hence
Complexes of the Cu(I) ion have received more and more atten-
tion [1,2] in the construction of luminescent materials and for the
development of practical components for chemical sensors, display
devices and solar-energy conversion schemes due to their abun-
dant resource, comparatively low cost and non-toxic properties
compared to noble metals systems such as Re(I) [3], Ir(III) [4], Pt(II)
[5] and Au(I) [6]. Among the luminescent copper(I) systems, the
mixed-ligand copper(I) complexes [Cu(diimine)(PP)]+ (PP = chelat-
ing diphosphane ligand), which contain one diimine ligand such as
1,10-phenanthroline (phen) or 2,20-bipyridine (bpy) and one che-
lating diphosphane ligand, have been the object of intense investi-
gations due to their enhanced luminescent performance [1a,f,7]
and considerably increased lifetimes of the triplet states relative
to the corresponding [Cu(diimine)2]+ complexes [8,1f]. It is re-
ported that the [Cu(phen)(PP)]+ complexes are more similar to
the well luminescent ruthenium(II) polypyridine complexes than
to their copper(I) bis(phenanthroline) analogs when considering
the electronic and photophysical properties [7b,9].
solvent-induced quenching by an exciplex mechanism would be
impeded [7a,10] and an obvious increase in the emissive quantum
yield can be expected. Following such a consideration, most re-
ports have focused their interest on the introduction of a bulky
substituent of the phenanthroline ligand at the 2- and 9-positions
into the coordination sphere. But increasing the bulk of the substi-
tuent in the coordination sphere would also increase the repulsion
between the diimine and diphosphane ligands, and hence decrease
the stability of the Cu(I) complexes. It is well known that phospho-
rescence enhancement widely exists for the [Cu(diimine)(PP)]+
complexes in the solid state because of the
tween the diimine ligands [1c]. The bulky substituent would also
weaken the interaction and the emission in the solid state.
pꢀ ꢀ ꢀ
p interaction be-
pꢀ ꢀ ꢀp
To the best of our knowledge, few reports exist on the change of
the 3- and 8-positions of phen or 5- and 50-positions of bpy, but
such changes can lead to a change in the conjugacy of these dii-
mine ligands. Past work has shown that increasing delocalization
within the
p system of a diimine ligand can alter the nature of
On the other hand, it is well known that when the bulky substit-
uents are close to the donor atoms, the steric crowding in the
the lowest excited state in these complexes and enhance the life-
time [11]. Furthermore, introduction of bromine atoms into these
positions of the diimine ligands may enhance the phosphorescence
emission due to the heavy atom effect of the bromine atoms and
hence lead to a longer emission lifetime compared with the
fluorescent systems.
⇑
Corresponding author at: School of Chemistry and Chemical Engineering,
Xuzhou Normal University, Xuzhou, Jiangsu 221116, China.
E-mail address: lxl@xznu.edu.cn (X.-L. Li).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.12.040

48
X.-L. Li et al. / Polyhedron 35 (2012) 47–54
In order to reach a better understanding of the effects of the
conjugacy of the diimine ligands, the heavy atoms effect and
interactions on photophysical properties, a series of diimine
(dmp = 2,9-dimethyl-1,10-phenanthroline) was not found to be
successful, as for complexes 1–5 and those reported analogs
[Cu(dppe)(dmp)]PF6 (dppe = 1,2-bis(diphenylphosphino)ethane)
and [Cu(dppp)(dmp)]PF6 (dppp = 1,3-bis(diphenylphosphino)pro-
pane) [8c]. Layering n-hexane onto the corresponding DCM solu-
tion gave only one product as red crystals, which was identified
as [Cu(dmp)2]ClO4 by HRMS, with a cation peak at m/z 479.135.
This significant difference may arise from the repulsion between
the dmp and bdpp ligands since the two methyl groups in dmp
are close to the N donor atoms and the phenyl rings connected
to the P atoms are more crowded in bdpp than in dppp and dppe
due to the rigidity of the central phenyl ring of bdpp. On the other
hand, the failure to isolate [Cu(dmp)(bdpp)]ClO4 may also be due
to kinetic effects of crystallization since an equilibrium of different
species is likely in the solution. It is worth noting that it was
reported by Armaroli’s group that the reaction of [Cu(CH3CN)4]BF4
with a 1:1 mixture of phen and bdpp also did not give the expected
mononuclear [Cu(phen)(bdpp)]BF4 complex, instead [Cu(bdpp)2]
BF4 was obtained [13]. This difference was explained speculatively
by the different bite angles for the different chelating diphosphane
ligands. When this angle (such as in bdpp) is small enough, the me-
tal center can easily accommodate two diphosphanes ligands. In
contrast, steric factors resulting from the wider P–Cu–P angles
for the other chelating diphosphanes substantially destabilizes
the [Cu(PP)2]+ derivatives, thus preventing their formation [13].
However, here the reaction of [Cu(CH3CN)4]ClO4 with a 1:1
mixture of phen or BrphenBr and bdpp gave the corresponding
mononuclear [Cu(diimine)(bdpp)]ClO4 complexes rather than
the complex [Cu(bdpp)2]ClO4. It should be noted that when
diluted solutions of complexes 1–5, with concentrations of ca.
1.0 ꢁ 10ꢂ5 mol Lꢂ1, were left for a long enough time, such as a
pꢀ ꢀ ꢀp
ligands, by changing the substituents at the 5- and 50-positions of
bpy or 3- and 8-positions of phen, are used in this article. Here, a
series of mononuclear mixed-ligand [Cu(diimine)(bdpp)]ClO4
complexes 1–5 were obtained (diimine = bpy 1, 5,50-dibromo-
2,20-bipyridine (BrbpyBr) 2, 5,50-diethynyl-2,20-bipyridine (HC„
CbpyC„CH) 3, phen
4 and 3,8-dibromo-1,10-phenanthroline
(BrphenBr) 5, bdpp = 1,2-bis(diphenylphosphane)benzene), and
their structures and photophysical properties in the solid state
are reported.
2. Results and discussion
2.1. Syntheses
Complexes 1–5 (Scheme 1) were obtained in good yields by the
reaction of an equimolar ratio of Cu(CH3CN)4ClO4, chelating dii-
mine and bdpp ligands as a stirred dichloromethane (DCM) solu-
tion or DCM/CH3CN (1:1) solution. Complex
1 crystallizes
without any solvent. Unlike complex 1, complexes 2–5 crystallize
as their 1:1 dichloromethane solvates. All the complexes are stable
to air and moisture in the solid state. It is well accepted that the P
atom is a more soft donor than the N atom, hence it is suitable for
stabilizing the soft Lewis acid Cu(I) ion according to HSAB rules
[12]. Therefore in most cases, as a result, it was found that the sta-
ble [Cu(diimine)(PP)]+ complexes rather than their corresponding
[Cu(diimine)2]+ complexes were formed in the mixed-ligand sys-
tems. However, an effort to synthesize [Cu(dmp)(bdpp)]ClO4
Scheme 1. Synthetic routes to complexes 1–5.

X.-L. Li et al. / Polyhedron 35 (2012) 47–54
49
Table 2
month, the color of the solutions were found to become nearly col-
orless and [Cu(bdpp)2]+ ions were found to be the main species
Crystallographic data and select refinement details for 4ꢀCH2Cl2 and 5ꢀCH2Cl2.
identified by the HRMS results, with
a cation peak at m/z
4ꢀCH2Cl2
C43H34Cl3CuN2O4P2
874.55
293(2)
0.71073
5ꢀCH2Cl2
C43H32Br2Cl3CuN2O4P2
1032.36
293(2)
0.71073
955.200, suggesting that the [Cu(diimine)(bdpp)]+ cations for com-
plexes 1–5 are kinetically stable products and [Cu(bdpp)2]+ is the
thermodynamically stable product in DCM solution.
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
triclinic
monoclinic
P2(1)/c
ꢀ
P1
2.2. Crystallographic studies
12.497(3)
13.396(3)
15.054(3)
73.95(3)
68.54(3)
63.46(3)
2078.8(7)
2
1.397
0.839
896
16298
9422
12.931(3)
18.021(4)
18.568(4)
b (Å)
c (Å)
The crystal structures of all the complexes have been deter-
mined by single crystal X-ray diffraction. Complexes 1, 2ꢀCH2Cl2,
3ꢀCH2Cl2 and 5ꢀCH2Cl2 crystallize in the monoclinic system with
the space group P2(1)/c, while 4ꢀCH2Cl2 crystallizes in the triclinic
a
(°)
b (°)
101.84(3)
c
(°)
V (Å3)
4234.9(15)
4
1.619
2.712
2064
24050
9626
6948
ꢀ
system with the space group P1. The crystal data and select refine-
Z
ment details of complexes 1, 2ꢀCH2Cl2, 3ꢀCH2Cl2, 4ꢀCH2Cl2 and
5ꢀCH2Cl2 are presented in Tables 1 and 2. The ORTEP drawings of
the cations and some weak interactions in the crystal structures
for 1, 2ꢀCH2Cl2, 3ꢀCH2Cl2, 4ꢀCH2Cl2 and 5ꢀCH2Cl2 are depicted in
Figs. 1–5, respectively.
Dcalc (Mg mꢂ3
)
l
(mmꢂ1
)
F(000)
Reflections collected
Independent reflections
Reflections with [I > 2
r
(I)]
4928
The X-ray structural analysis shows that all the complexes 1–5
have a mononuclear structure, similar to those reported before
[1,7]. The copper(I) ion in each complex adopts a distorted tetrahe-
dral coordinated geometry and is coordinated by two nitrogen
atoms from chelating diimine ligands and two phosphorus atoms
from the chelating bdpp moiety. The distortion is mainly induced
by the N1–Cu1–N2 and P1–Cu1–P2 bite angles which are restricted
by the chelating diimine and bdpp ligands. The N1–Cu1–N2 angles
are 81.0(1)°, 80.7(2)°, 80.5(2)°, 81.0(2)° and 81.9(2)° for 1, 2ꢀCH2Cl2,
3ꢀCH2Cl2, 4ꢀCH2Cl2 and 5ꢀCH2Cl2, respectively, whereas the corre-
sponding P1–Cu1–P2 angles are 92.5(1)°, 90.7(1)°, 90.4(1)°,
87.0(1)° and 91.0(1)°, respectively. The dihedral angles between
the planes Cu1–P1–P2 and Cu1–N1–N2 are 79.6°, 91.6°, 92.9°,
92.0° and 89.6°, respectively, in complexes 1–5. The Cu–N and
Cu–P bond lengths are in the ranges 2.007(6)–2.092(5) and
2.216(1)–2.281(2) Å, respectively, which are in good agreement
with the lengths in analogous systems [1b,1e].
Data/restraints/parameters
9422/0/496
0.950
0.0778
0.2153
0.1320
0.2653
9626/0/515
1.140
0.0885
0.1833
0.1228
0.2020
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
wR2 [I > 2 (I)]
r
R indices (all data)
wR2 (all data)
2.2.1. Weak interactions
In the crystal structure of complex 1, as shown in Fig. 1, one cat-
interactions
ion links another two on both sides through C–Hꢀ ꢀ ꢀ
p
between C33–H33A of the pyridine ring at the 4-position and the
central phenyl ring of bdpp at the x, 0.5 ꢂ y, ꢂ0.5 + z position
(dC33ꢀ ꢀ ꢀX1 = 3.596 Å, C33–H33Aꢀ ꢀ ꢀX1 = 144°, and X1 denotes the
centroid of the central phenyl ring of bdpp at the x, 0.5 ꢂ y,
ꢂ0.5 + z position), leading to a 1-D chain structure along the c axis.
The 1-D chain structures of the cations are further connected to
Table 1
Crystallographic data and select refinement details for 1, 2ꢀCH2Cl2 and 3ꢀCH2Cl2.
1
2ꢀCH2Cl2
3ꢀCH2Cl2
Empirical formula
Formula weight
T (K)
C40H32ClCuN2O4P2
765.61
173(2)
C41H32Br2Cl3CuN2O4P2
1008.34
293(2)
C45H34Cl3CuN2O4P2
898.57
298(2)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
P2(1)/c
0.71073
monoclinic
P2(1)/c
0.71073
monoclinic
P2(1)/c
16.426(2)
10.893(1)
20.777(3)
12.423(3)
18.374(4)
18.817(4)
12.536(3)
18.746(4)
18.984(4)
b (Å)
c (Å)
a
(°)
b (°)
103.859(7)
104.98(3)
105.62(3)
c
(°)
V (Å3)
3609.2(7)
4
1.409
4149.2(14)
4
1.614
4296.4(15)
4
1.389
Z
Dcalc (Mg mꢂ3
)
l
(mmꢂ1
)
0.812
2.766
0.814
F(000)
1576
2016
1840
Reflections collected
Independent reflections
29432
6342
34011
7287
21259
7531
Reflections with I > 2
r(I)
4879
6574
3463
Data/restraints/parameters
6342/0/451
1.055
7287/0/497
1.144
7531/74/570
1.067
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
wR2 [I > 2 (I)]
R indices (all data)
wR2 (all data)
r(I)]
0.0537
0.1205
0.0747
0.1322
0.0643
0.1415
0.0734
0.1467
0.0694
0.1739
0.1705
0.2583
r

50
X.-L. Li et al. / Polyhedron 35 (2012) 47–54
Fig. 1. ORTEP drawing of the chain structure of the cation in the crystal structure of complex 1 along the c axis, with the atom labeling scheme, showing 30% thermal
ellipsoids. Most hydrogen atoms are omitted for clarity. Selected bond parameters: Cu1–N1 = 2.031(3), Cu1–N2 = 2.015(3), Cu1–P1 = 2.216(1) and Cu1–P2 = 2.237(1) Å; N1–
Cu1–N2 = 81.0(1)°, N1–Cu1–P1 = 129.0(1)°, N1–Cu1–P2 = 108.7(1)°, P1–Cu1–P2 = 92.5(1)°, N2–Cu1–P1 = 124.1(7)° and N2–Cu1–P2 = 124.6(1)°.
Fig. 2. ORTEP drawing of the cation dimer of 2ꢀCH2Cl2 with the atom-labeling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms are omitted for clarity. Selected
bond parameters: Cu1–N1 = 2.069(4), Cu1–N2 = 2.011(4), Cu1–P1 = 2.241(2) and Cu1–P2 = 2.241(1) Å; N1–Cu1–N2 = 80.7(2)°, N1–Cu1–P1 = 111.7(1)°, N1–Cu1–
P2 = 116.1(1)°, P1–Cu1–P2 = 90.7(1)°, N2–Cu1–P1 = 127.7(1)° and N2–Cu1–P2 = 130.7(1)° (symmetry code for C: ꢂx + 1, ꢂy + 1, ꢂz + 2).
Fig. 3. ORTEP drawing of the cation dimer of 3ꢀCH2Cl2 with the atom-labeling scheme, showing 30% thermal ellipsoids. Most hydrogen atoms are omitted for clarity. Selected
bond parameters: Cu1–N1 = 2.074(6), Cu1–N2 = 2.007(6), Cu1–P1 = 2.245(2) and Cu1–P2 = 2.242(2) Å; N1–Cu1–N2 = 80.5(2)°, N1–Cu1–P1 = 117.9(2)°, N1–Cu1–
P2 = 110.9(2)°, P1–Cu1–P2 = 90.4(1)°, N2–Cu1–P1 = 130.9(2)° and N2–Cu1–P2 = 127.2(2)°.
each other through C–Hꢀ ꢀ ꢀO hydrogen bonds (see Table S1) into a
3-D network.
rings – the ring consisting of C6, C7, C8, C9, C10 and N2 atoms
and its symmetric ring at the ꢂx + 1, ꢂy + 1, ꢂz + 2 position (inter-
centroid distance 3.609 Å, perpendicular distance 3.474 Å, offset
0.981 Å), and the latter occurs between C8–H8A at the 4-position
of BrbpyBr and one of the side phenyl rings of bdpp connected to
In the crystal structure of complex 2ꢀCH2Cl2, a cation dimer is
formed through
Fig. 2). The former occurs between two exactly parallel pyridine
p
ꢀ ꢀ ꢀ
p
and double C–Hꢀ ꢀ ꢀ
p interactions (see

X.-L. Li et al. / Polyhedron 35 (2012) 47–54
51
In the crystal structure of complex 3ꢀCH2Cl2, as shown in
Fig. 3, the cation dimer is also formed through and double
ꢀ ꢀ ꢀ
C–Hꢀ ꢀ ꢀ interactions, which are very similar to those found for
complex 2ꢀCH2Cl2 (see Tables S2 and S3). Every cation dimer is
p
p
p
further linked with another four cation dimers through C–Hꢀ ꢀ ꢀ
p
interactions between one of the side phenyl rings of bdpp
connected to P2 and C25–H25A, leading to 2-D network (see
Table S2 and Fig. S2). The 2-D networks are further linked
through C–Hꢀ ꢀ ꢀO hydrogen bonds (see Table S1) into a 3-D
framework.
In the crystal structure of complex 4ꢀCH2Cl2, the cation dimer is
formed through triple
pꢀ ꢀ ꢀp stacking interactions occurring be-
tween two exactly parallel rings – the ring consisting of C4, C5,
C6, C7, C11 and C12 and its symmetric ring at the ꢂx + 2, ꢂy,
ꢂz + 1 position (intercentroid distance 3.768 Å, perpendicular dis-
tance 3.522 Å, offset 1.338 Å), and between two six-membered
rings consisting of N1, C1, C2, C3, C4 and C11, and N2, C7, C8, C9,
C10 and C12 at the ꢂx + 2, ꢂy, ꢂz + 1 position (intercentroid dis-
tance 3.682 Å, perpendicular distance 3.423 and 3.464 Å) with a
dihedral angle 4.87° (see Fig. 4), and also between the other two
corresponding six-membered rings consisting of N2, C7, C8, C9,
C10 and C12, and N1, C1, C2, C3, C4 and C11 at the ꢂx + 2, ꢂy,
ꢂz + 1 position. Every cation dimer further links with another four
through two C–Hꢀ ꢀ ꢀ
p interactions (see Table S2) leading to a 2-D
network in the ab plane (see Fig. S3).
Fig. 4. ORTEP drawing of the cation dimer of 4ꢀCH2Cl2 with the atom-labeling
scheme, showing 30% thermal ellipsoids. The hydrogen atoms are omitted for
clarity. Selected bond parameters: Cu1–N1 = 2.059(4), Cu1–N2 = 2.062(4),
Cu1–P1 = 2.260(2) and Cu1–P2 = 2.281(2) Å; N1–Cu1–N2 = 81.0(2)°, N1–Cu1–
P1 = 127.9(1)°, N1–Cu1–P2 = 122.7(1)°, P1–Cu1–P2 = 87.0(1)°, N2–Cu1–P1 =
125.6(1)° and N2–Cu1–P2 = 117.1(1)°.
In the crystal structure of 5ꢀCH2Cl2, a cation dimer is also
formed through a
p p stacking interaction occurring between
ꢀ ꢀ ꢀ
two exactly parallel six-membered rings (see Table S3 and
Fig. 5). Every cation dimmer is further linked with another six cat-
ion dimers through two C–Hꢀ ꢀ ꢀ interactions leading to a 2-D net-
work in the bc plane (see Table S2 and Fig. S4). The anions are
connected with cations and the solvent DCM molecules through
electrostatic attractions and rich C–Hꢀ ꢀ ꢀO intramolecular hydrogen
bonds (see Table S1).
P1 (dC8ꢀ ꢀ ꢀX2 = 3.682 Å, C8–H8Aꢀ ꢀ ꢀX2 = 149°, X2 is the centroid of the
phenyl ring of C29C–C34C. C: ꢂx + 1, ꢂy + 1, ꢂz + 2). The cation di-
mers link each other through another C–Hꢀ ꢀ ꢀ
p interaction into a 1-
In summary,
crystal structures of complexes 1–5. It is interesting to note that all
the stacking interactions occur between diimine ligands,
ꢀ ꢀ ꢀ
p
ꢀ ꢀ ꢀ
p
and C–Hꢀ ꢀ ꢀ
p interactions widely exist in the
D chain structure (see Fig. S1 and Table S2). These 1-D chains are
further linked through C–Hꢀ ꢀ ꢀO hydrogen bonds (dCꢀ ꢀ ꢀO = 3.279–
3.470 Å, C–Hꢀ ꢀ ꢀO = 131–178°, see Table S1) into a 3-D framework.
p
p
Fig. 5. ORTEP drawing of the cation dimer of complex 5 with the atom-labeling scheme, showing 30% thermal ellipsoids. The hydrogen atoms are omitted for clarity
(symmetry code for A: 2 ꢂ x, 1 ꢂ y, 1 ꢂ z). Selected bond parameters: Cu1–N1 = 2.020(5), Cu1–N2 = 2.092(5), Cu1–P1 = 2.234(2) and Cu1–P2 = 2.239(2) Å; N1–Cu1–
N2 = 81.9(2)°, N1–Cu1–P1 = 129.1(2)°, N1–Cu1–P2 = 131.2(1)°, P1–Cu1–P2 = 91.0(1)°, N2–Cu1–P1 = 110.5(1)° and N2–Cu1–P2 = 112.0(2)°.

52
X.-L. Li et al. / Polyhedron 35 (2012) 47–54
among which the triple
complex 4 is the most striking example.
p
ꢀ ꢀ ꢀ
p
interaction in the cation dimer of
sion for complexes 1–3 may arise from intramolecular
gand-centered transitions and the low energy bands for 1–5 are
assigned to the
(Cu) ? p⁄(diimine) (3MLCT) excited state
p ?
p⁄ li-
d
p
[1d,13,15]. The long lifetimes of the lower energy bands in the
microsecond range further support such a triple excited state
assignment. The double exponential character of the low energy
bands for complexes 2 and 4 indicates they may be mixed with
some intermolecular ligand to ligand charge transfer (LLCT) char-
2.3. Photophysical properties
2.3.1. Infrared spectra
All the complexes 1–5 exhibit typical
m
(ClO4ꢂ) modes at about
(C„C)
1090 cmꢂ1 in their IR spectra. Complex 3 also displays a
m
mode at 2112 cmꢂ1 and two
m(C–H) bands of C„C–H units at
acter due to the widely existing
p
ꢀ ꢀ ꢀ
p
and C–Hꢀ ꢀ ꢀ
p interactions.
To the best of our knowledge, for [Cu(diimine)(PP)]+ complexes,
only limited examples, such as [Cu(Mepypm)(DPEphos)]BF4 (Me-
pypm = 4-methyl-2-(20-pyridyl) pyrimidine, DPEphos = bis[2-
(diphenylphosphino)phenyl]ether) and [Cu(ABPQ)(DPEphos)]BF4
(ABPQ = acenaphtho[1,2-b]bipyrido[2,3-h:3,2-f]quinoxaline), dis-
played dual emission [1a,16]. The dual emission of
[Cu(Mepypm)(DPEphos)]BF4 was due to its geometric bistability
based on inversion of the pyrimidine [1a], and those of
3238 and 3299 cmꢂ1, respectively, indicating the presence of
HC„CbpyC„CH.
2.3.2. Absorption spectra
UV–Vis absorption data of 1–5 in DCM solution at room temper-
ature are summarized in Table 3, while the corresponding elec-
tronic absorption spectra are depicted in Fig. S5. All the
complexes 1–5 display two distinct absorption regions, a high en-
ergy region with wavelengths shorter than ca. 360 nm and a low
energy band with wavelengths longer than ca. 360 nm. By compar-
ison with the absorptions of bdpp and the corresponding diimine
ligands, along with those of the reported [Cu(bdpp)2]+ and the
[Cu(diimine)(PP)]+ analogs [1c,1d,7a,7c,8c,9,10,11b,14], the high-
[Cu(ABPQ)(DPEphos)]BF4 in CHCl3 solution at ca. 470 and 600 nm
1
were also assigned to
(p ?
p⁄) ligand-centered transitions and
the 3MLCT excited state, respectively [16]. The lifetimes of the
3MLCT excited state for complexes 1–3 are shorter than those of
complexes 4 and 5, which may be due to the free rotation of the
C–C bond between the pyridine rings and the less rigid character
of the bpy units.
er-energy intense bands are assigned to
transitions of bdpp and the corresponding diimine ligands, while
p ?
p⁄ ligand-centered
In order to get quantitative data and explore the factors affect-
ing the luminescence, the emission quantum yields of complexes 4
and 5 in the solid state were measured under air (see Table 3). The
solid state emission quantum yield of complex 4 is 0.1833, which is
much higher than those of Cu(I) complexes of the bi-phen system
under nitrogen [17], and very close to those of the highly emissive
the latter lower-energy, new weak and broad bands, should be as-
signed to metal-to-ligand charge transfer dp
(Cu) ? p⁄(diimine)
(MLCT) transitions. The absorption maximum wavelengths of the
MLCT bands, kabs(MLCT), in complexes 1–5 are 414, 442, 465,
422 and 449 nm, respectively. There is the tendency for kabs(MLCT)
to shift to lower energy as the conjugated degree of the diimine li-
gands becomes larger, which can be observed from complex 1 to
complex 3, and from complex 4 to complex 5.
[Cu(POP)(dmp)]tfpb
(POP = bis[2-(diphenylphosphino)phenyl]
ether), tfpb = tetrakis(bis-3,5-trifluoromethylphenylborate) and
[Cu(xantphos)(dipp)]tfpb (xantphos = 4,5-bis(diphenylphosphino)
-9,9-dimethylxanthene, dipp = 2,9-diisopropyl-1,10-phenanthro-
line) complexes, 0.19 and 0.22, respectively, under oxygen [18].
Mann and co-workers has reported that the highly emissive [Cu
(diimine)(PP)]+ complexes [Cu(POP)(dmp)]tfpb, [Cu(xantphos)
(dmp)]tfpb, [Cu(xantphos)(dipp)]tfpb and [Cu(xantphos)(dipp)]
pftpb (pftpb = tetrakis(pentfluorophenyl)borate) are oxygen sen-
sors [18]. Oxygen can quench their luminescence. The sensing abil-
ity correlates with the amount of void space calculated from the
crystal structures, but the void space is only a necessary, not a suf-
ficient condition for oxygen sensing in this type of compound [18].
Here the void space in the crystal structure of 4ꢀCH2Cl2 is 3.8%, and
no residual solvent accessible void is found for complex 5ꢀCH2Cl2
using PLATON/VOID [19,20]. The emission quantum yield of com-
plex 4 under air, 0.1833, is ca. five times of that of complex 5,
0.0358, furthering suggesting the void space is a necessary but
not sufficient condition for oxygen sensing. It is suggested that
the high solid state emissive quantum yield of complex 4 may be
2.3.3. Luminescence
The solid-state emission spectra of complexes 1–5 in the crys-
talline state were investigated at room temperature upon excita-
tion with k = 300–350 nm for complexes 1–3 and with k = 300–
430 nm for complexes 4 and 5 (see Fig. S6), and the spectral data,
including emission wavelength, emission lifetimes and the solid-
state photoluminescence quantum yields of complexes 4 and 5,
are summarized in Table 3. Complexes 1–3 display dual emission
bands with kmax = 399 and 539, 425 and 564, and 495 and
603 nm, respectively, while complexes 4 and 5 show single broad
emission bands with kmax = 553 and 570 nm, respectively. As
shown in Table 3 and Fig. S6, the emission bands show an obvious
red shift in the same series when the conjugated degree of the dii-
mine ligands becomes larger from bpy to HC„CbpyC„CH, and
from phen to BrphenBr. The use of single crystals, obtained from
repeated recrystallization, for luminescence determination rules
out the possibility that the high energy emission comes from a
minor contamination of the free ligand, so the higher energy emis-
related to the triple
p
ꢀ ꢀ ꢀ
p stacking interactions in the cation dimer
and rich C–Hꢀ ꢀ ꢀ interactions in the crystal structure, since these
p
weak interactions could enhance the phosphorescence emission
[1c]. The phosphorescence enhancement accompanies an obvious
emission blue shift and a longer excited-state lifetime on going
from complex 5 to complex 4.
Table 3
Photophysical data of 1–5 at 298 K.
b
Compound
k [nm] (CH2Cl2)
kem [nm] (sem
[l
s])a (solid)
Uem (solid)
1
231, 294, 414
399
539 (0.406)
425
564 (0.456, 2.436)
495
603 (0.211)
553 (2.147, 7.418)
570 (3.401)
3. Summary
2
3
238, 308, 442
A
series of mixed-ligand copper(I) complexes, [Cu(diimi-
229, 274, 315,
325, 342, 465
237, 293, 422
237, 300, 449
ne)(bdpp)]ClO4, were synthesized and characterized. Their struc-
tures and photophysical properties have been studied. In the
crystal structures of the complexes,
ꢀ ꢀ ꢀ
widely exist, and all the stacking interactions occur between
the diimine ligands in the cation dimers. The bpy series of
4
5
0.1833
0.0358
p
ꢀ ꢀ ꢀ
p
and C–Hꢀ ꢀ ꢀ
p interactions
a
p
p
Solid state emission lifetimes were determined under air.
Solid-state quantum yields were determined under air.
b

X.-L. Li et al. / Polyhedron 35 (2012) 47–54
53
complexes display dual emissions in the solid state, while the phen
series exhibit a single emission. The most significant example of
weak intermolecular interactions is observed for complex 4, which
in 51.9% yield (45.3 mg). Anal. Calc. for C42H32ClCuN2O4P2ꢀCH2Cl2:
C, 59.17; H, 3.93; N, 3.21. Found: C, 59.08; H, 3.86; N, 3.22%. HRMS
(m/z): 689.1337 [MꢂClO4]+ (calcd. 689.1337). IR (KBr, cmꢂ1):
1094vs (ClO4ꢂ).
displays triple
p
ꢀ ꢀ ꢀ
p interactions between the phen ligands and
rich C–Hꢀ ꢀ ꢀ
p
interactions among the cation dimers. These weak
interactions are suggested to be the main reasons for the high
emissive quantum yield of 18.33% in the solid state for complex 4.
4.2.5. [Cu(BrphenBr)(bdpp)]ClO4ꢀCH2Cl2 (5ꢀCH2Cl2)
This complex was prepared by the same procedure as that of 1
except for the use of BrphenBr instead of bpy. Layering n-hexane
onto the DCM solution gave the product as orange prismatic crys-
4. Experimental
tals in 65.4% yield (67.2 mg). Anal. Calc. for
C42H30Br2ClCu-
4.1. Materials and reagents
N2O4P2ꢀCH2Cl2: C, 50.20; H, 3.14; N, 2.72. Found: C, 50.27; H,
3.17; N, 2.79%. HRMS (m/z): 844.962 [MꢂClO4]+ (calcd. 844.954).
IR (KBr, cmꢂ1): 1094vs (ClO4ꢂ).
The reagents bpy, phen and bdpp were commercially available
and were used without further purification. BrbpyBr, BrphenBr,
HC„CbpyC„CH and [Cu(CH3CN)4][ClO4] were prepared by the
published methods [21–24]. All solvents were purified and dis-
tilled by standard procedures before use, except those for spectro-
scopic measurements, which were of spectroscopic grade. All other
reagents were of analytical grade and were used as received.
4.3. Crystal structure determination
Crystals suitable for X-ray diffraction studies for 1, 2ꢀCH2Cl2,
3ꢀCH2Cl2, 4ꢀCH2Cl2 and 5ꢀCH2Cl2 were obtained by layering n-hex-
ane onto the corresponding DCM solutions in the absence of light.
They were measured on RIGAKU SCXmini, Bruker Smart APEX CCD
4.2. Preparation of the complexes
and RIGAKU MERCURY CCD diffractometers, respectively, by the
scan technique at room temperature with graphite-monochromat-
ed MoK radiation (k = 0.71073 Å). The CrystalClear software
x
All reactions were carried out under anhydrous and anaerobic
conditions using standard Schlenk techniques under an atmo-
sphere of dry argon at room temperature.
a
package 2005 [25], Bruker SAINT [26] and the CrystalClear soft-
ware package 2007 [27] were used for data reduction and empiri-
cal absorption corrections, respectively. The structures were solved
by the direct method. The heavy atoms were located from the
E-map, and the remaining non-hydrogen atoms were found in sub-
sequent Fourier maps. The non-hydrogen atoms were refined
anisotropically, whereas the hydrogen atoms were generated
geometrically with isotropic thermal parameters. The structures
were refined on F2 by full-matrix least-squares methods using
the SHELXTL-97 program package [28].
4.2.1. [Cu(bpy)(bdpp)]ClO4 (1)
[Cu(CH3CN)4][ClO4] (32.6 mg, 0.100 mmol) was added to a de-
gassed DCM solution (10 mL) of bpy (15.6 mg, 0.100 mmol) and
bdpp (45.5 mg, 98%, 0.100 mmol). The color of the solution gradu-
ally changed to yellow. The solution was then stirred for 1 day at
room temperature. After filtration, layering n-hexane onto the
DCM solution gave the product as yellow crystals in 71% yield
(54.0 mg). Anal. Calc. for C40H32ClCuN2O4P2: C, 62.82; H, 4.22; N,
3.67. Found: C, 62.57; H, 3.95; N, 3.69%. HRMS (m/z): 665.1331
ꢂ +
[MꢂClO4
]
(calcd. 665.1337). IR (KBr, cmꢂ1): 1095vs (ClO4ꢂ).
4.4. Physical measurements
4.2.2. [Cu(BrbpyBr)(bdpp)]ClO4ꢀCH2Cl2 (2ꢀCH2Cl2)
This complex was prepared by the same procedure as that of 1
except for the use of BrbpyBr instead of bpy. Layering n-hexane
onto the DCM solution gave the product as orange-yellow crystals
Infrared (IR) spectra were obtained from KBr pellets using a
Bruker Optics TENSOR 27 FT-IR spectrophotometer. UV–Vis
absorption spectra were recorded on a Purkinje General TU-1901
UV–Vis spectrophotometer. Elemental analyses (C, H, N) were car-
ried out on a Perkin–Elmer model 240C elemental analyzer. HRMS
analyses were carried out with a Bruker-micro-TOFQ-MS analyzer
using a DCM/methanol mixture as the mobile phase. Steady-state
emission spectra were recorded with a Hitachi F4500 fluorescence
spectrophotometer. Emission lifetimes were determined on an
Edinburgh Analytical Instrument (F900 fluorescence spectrometer)
under air and the resulting emission was detected by a thermo-
electrically cooled Hamamatsu R3809 photomultiplier tube. The
photoluminescence yield in the solid state under air at room tem-
perature is defined as the number of photons emitted for per pho-
ton absorbed by the system and was measured under air on an
Edinburgh Analytical Instrument FLS920 with an integrating
sphere established by Wrighton et al. [29].
in 78.2% yield (78.5 mg). Anal. Calc. for
C40H30Br2ClCu-
N2O4P2ꢀCH2Cl2: C, 49.01; H, 3.21; N, 2.79. Found: C, 48.96; H,
ꢂ +
3.25; N, 2.73%. HRMS (m/z): 820.9547 [MꢂClO4
]
(calcd.
820.9547). IR (KBr, cmꢂ1): 1094vs (ClO4ꢂ).
4.2.3. [Cu(HC„CbpyC„CH)(bdpp)]ClO4ꢀCH2Cl2. (3ꢀCH2Cl2)
[Cu(CH3CN)4][ClO4] (32.6 mg, 0.100 mmol) was added to a
20 mL degassed DCM–acetonitrile (v/v = 1:1) solution of
HC„CbpyC„CH (20.4 mg, 0.100 mmol) and bdpp (45.5 mg, 98%,
0.100 mmol). The color of the mixture gradually changed to or-
ange-red. The solution was then stirred for 1 day at room temper-
ature, after which the solvent was removed under reduced
pressure and DCM was added. After filtration, layering n-hexane
onto the filtrate gave the product as orange-red crystals in 54.8%
yield (49.1 mg). Anal. Calc. for
C
44H32ClCuN2O4P2ꢀCH2Cl2: C,
60.27; H, 3.82; N, 3.13. Found: C, 60.36; H, 3.87; N, 3.27%. HRMS
(m/z): 713.1277 [MꢂClO4]+ (calcd. 713.1377). IR (KBr, cmꢂ1):
Acknowledgments
1091vs [
(C„C)].
m m(C„CH)], 3238m [m(C„CH)], 2112m
(ClO4ꢂ)], 3299m [
[
m
This work was supported financially by the National Natural
Science Foundation of China (NSFC) (20801047 and 21071121),
the Major Basic Research Project of Natural Science Foundation
of the Jiangsu Higher Education Institutions (11KJA430009), PAPD
of Jiangsu Higher Education Institutions and the QingLan Project
08QLT001.
4.2.4. [Cu(phen)(bdpp)]ClO4ꢀCH2Cl2 (4ꢀCH2Cl2)
This complex was prepared by the same procedure as that of 2
except for the use of phen instead of HC„CbpyC„CH. Layering n-
hexane onto the DCM solution gave the product as yellow crystals

54
X.-L. Li et al. / Polyhedron 35 (2012) 47–54
(c) J. Ni, L.Y. Zhang, H.M. Wen, Z.N. Chen, Chem. Commun. (2009) 3801;
Appendix A. Supplementary data
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CCDC 826032, 826033, 826034, 826035 and 826036 contain the
supplementary crystallographic data for 1, 2ꢀCH2Cl2, 3ꢀCH2Cl2,
4ꢀCH2Cl2 and 5ꢀCH2Cl2. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
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