Photophysical properties of copper(I) and zinc(II) complexes containing phosphinoquinoline ligands

Article abstract of DOI:10.1016/j.poly.2008.08.028

Several copper(I) and zinc(II) complexes with 8-(diphenylphosphino)quinoline (PPh₂qn) or 8-diphenylphosphinoquinaldine (PPh₂qna) have been prepared. These ligands contain both imine and phosphine moieties, which can act as coordinati

Full text of DOI:10.1016/j.poly.2008.08.028

Polyhedron 28 (2009) 7–12
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Photophysical properties of copper(I) and zinc(II) complexes containing
phosphinoquinoline ligands
*
*
Toshiaki Tsukuda , Chikamine Nishigata, Kodai Arai, Taro Tsubomura
Department of Applied Chemistry, Faculty of Engineering, Seikei University, Musashino, Tokyo 180-8633, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Several copper(I) and zinc(II) complexes with 8-(diphenylphosphino)quinoline (PPh2qn) or 8-diph-
enylphosphinoquinaldine (PPh2qna) have been prepared. These ligands contain both imine and phos-
phine moieties, which can act as coordinating groups. X-ray analysis of the Cu(I) complexes reveals
that [Cu(PPh2qn)2]PF6 (Cu-1) and [Cu(PPh2qn)2]PF6 (Cu-2), coordinated by two PPh2qn and PPh2qna
ligands respectively, are obtained. In the Zn(II) complexes, a structural study shows that [ZnCl2(PPh2qn)]
(Zn-1), [ZnBr2(PPh2qn)] (Zn-2) and [ZnI2(PPh2qn)] (Zn-3) are coordinated by one PPh2qn ligand and two
of the corresponding halogeno ligands (ClÀ, BrÀ and IÀ). In the solid state Cu-1 and Cu-2 show lumines-
Received 15 May 2008
Accepted 28 August 2008
Available online 18 November 2008
Keywords:
d10 Transition metal complexes
Phosphinoquinoline ligand
X-ray crystal structures
Luminescent properties
cence which is assigned to a 3MLCT transition involving
p* of the quinoline group, as shown in the
[Cu(dmp)(diphosphine)]+ complexes; due to the reduced bulkiness of the coordination sphere around
the copper atom, no emission is observed in solution. Zn-1 shows a similar emission band to that of free
PPh2qn at both room temperature and 77 K. It suggests the emission bands should be assigned to a
ligand-centered (LC) transition. In the solid state, it is found that the emissive energy of the complexes
shift to lower energy and the energy depends on the halogeno ligands in the zinc complexes.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
of several transition metal complexes with 8-diphenylphosphino-
quinoline(PPh2qn) (Chart 1, left) have been reported [9–11]. Photo-
Much attention has been paid to emissive copper(I) complexes
containing polypyridine and/or phenanthroline ligands as candi-
dates for practical components for chemical sensors, display de-
vices and solar-energy conversion schemes [1]. In contrast to the
hitherto reported heavy metal complexes, the copper-based sys-
tem is promising due to the comparative cost advantage. Recently,
extensive studies of some mixed-ligand copper(I) complexes
involving both imines and phosphines have been reported
[2–6]. [Cu(dmp)(DPEphos)]+ (DPEphos = bis[2-(diphenylphosphino)-
phenyl]ether) exhibits an unprecedented high quantum yield and
a long lifetime in CH2Cl2 at room temperature [3,4]. Armaroli
et al. and our group have also studied the emissive properties of
the mixed-ligand [Cu(dimine)(diphosphine)]+ type complexes
coordinated by a diimine ligand such as dmp and several types
of diphosphine ligand [5,6]. As other alternatives to heavy metal
complexes, several zinc(II) complexes with quinoline groups are
potentially promising as luminescent probes and as emissive com-
pounds in electroluminescent devices [7,8].
chemical and photophysical properties of several mixed-ligand
ruthenium(II) polypyridine complexes with 8-quinolylphosphines
have been investigated [12]. It is expected that copper(I) com-
plexes containing this type of ligand can also behave as good emit-
ters, because the ligands have both diimine and phosphine
character. As a similar system, dinuclear copper(I) complexes
bridged by 2-(diphenylphosphino)pyridine (PPh2py) ligands have
been reported [13]. However, the dinuclear complexes do not keep
a rigid structure in solution due to coordination of donor solvent as
well as a PPh2py exchange process. In contrast, PPh2qn, which can
coordinate to a metal center in a chelate fashion, appears to pro-
vide discrete compounds even in solution.
We found that the [Cu(PPh2qn)2]+ complex is readily prepared
and shows emission in the solid state. In this study, the
luminescence of such copper(I) complexes with phosphinoquino-
line derivatives has been examined. In addition, treatment of zinc
8-Quinolylphosphine derivatives, which have both imine and
phosphine moieties, can act as bidentate ligands. Structural studies
* Corresponding authors. Tel.: +81 422373759; fax: +81 422373871 (T. Tsukuda),
tel.: +81 422373752; fax: +81 422373871 (T. Tsubomura).
E-mail addresses: tsukuda@st.seikei.ac.jp (T. Tsukuda), tsubomura@st.sei-
kei.ac.jp (T. Tsubomura).
PPh2
N
PPh2
N
Chart 1. PPh2qn (left) and PPh2qna (right).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.08.028

8
T. Tsukuda et al. / Polyhedron 28 (2009) 7–12
halogenide with PPh2qn readily gave the corresponding [ZnX2-
(PPh2qn)] complexes (X = Cl, Br and I). Zinc complexes coordinated
by phosphorus atoms are rare. The luminescence of these
complexes are observed in both CH2Cl2 solution and in the solid
state. In this work, the photophysical properties of the complexes
are described in detail.
2.4. X-ray measurements
X-ray crystallographic measurements were made on a Rigaku
AFC-5S (for Cu-1, Cu-2 and Zn-1 at 296 K) or a Rigaku Saturn 70
CCD area detector (for Zn-2 and Zn-3 at 123 K) with graphite-
monochromated Mo Ka radiation. Absorption corrections were
made by the numerical method. Each structure was solved by di-
rect methods (SIR92 [17]) and refined by full matrix least square
procedures (SHELXL-97 [18]). The non-hydrogen atoms were refined
anisotropically and the hydrogen atoms were fixed at calculated
positions. All calculations were carried out by CRYSTAL STRUCTURE
software.1
2. Experimental
2.1. General
8-(Diphenylphosphino)quinoline (PPh2qn) [14] and [Cu(CH3-
CN)4]PF6 [15] were prepared by the literature methods. 8-(Diphen-
ylphosphino)quinaldine (PPh2qna) (Chart 1, right) was synthesized
by a similar method to that of PPh2qn, with the use of 8-chloro-
quinaldine [16]. Each zinc halogenide was purchased from WAKO
Chemical Co. Ltd. All reactions were carried under an argon atmo-
sphere using Schlenk techniques until air-stable solid complexes
were obtained. Elemental analyses of the complexes were per-
formed on a Perkin Elmer model 2400 CHN analyzer. NMR spectra
3. Results and discussion
3.1. Preparation and characterization of the Cu(I) complexes
Since PPh2qn has both phosphine-P and imine-N donor atoms,
the coordination of two PPh2qn ligands to the copper(I) ion leads
to a similar structure to that of mixed-ligand complexes with
diphosphine and diimine ligands. The reaction of [Cu(CH3CN)4]PF6
with a two equivalent molar amount of PPh2qn in CHCl3 readily
gave a pale yellow powder of the bis-PPh2qn copper(I) complex
Cu-1. The product was identified by elemental analysis and 1H
and 31P{1H} NMR spectra. The 1H NMR spectrum of Cu-1 shows a
symmetric signal set; e.g. only one doublet assigned to the proton
in the 2-position on a quinoline ring at d 8.5 appeared The 31P NMR
spectrum of Cu-1 shows a relatively broad signal at d À16.1,
whereas the signal of free PPh2qn is sharp at d À17.0. If the signal
broadening results from a rapid exchange between the coordina-
tion and dissociation of a PPh2qn ligand in solution, lowering the
temperature may cause further broadening based on the splitting
of signals assigned to the coordinated and the free ligand. How-
ever, the measurement of the 31P NMR spectrum at À40 °C shows
a slight sharpening of the signal. So the signal broadening could re-
sult from quadrapolar relaxation arising from the copper nucleus,
which has been observed for [Cu(dmpe)]+ (dmpe = 1,2-bis(dim-
ethylphosphino)ethane) [19].
Single crystals suitable for X-ray analysis were obtained by slow
diffusion of diethylether into an acetone solution of the complex.
The molecular structure of [Cu(PPh2qn)2]PF6 is illustrated in
Fig. 1, and detailed crystallographic data are shown in Table S1.
In this complex, the copper atom is coordinated by two bidentate
PPh2qn ligands and has a four-coordinate structure with tetrahe-
dral geometry. Selected bond lengths and angles are summarized
in Table 1. The bond lengths of Cu–P are 2.220(1) and 2.229(1) Å.
The bite angles for the chelate ring formed by the two PPh2qn li-
gands are 87.4(1)° and 86.4(1)°, which are comparable to the other
complexes containing PPh2qn [12b]. The chelate rings are almost
planar, as is evident from the torsion angles of Cu–P(1)–C(7)–
C(8) (2.4(3)°) and Cu–N(1)–C(8)–C(7) (0.3(5)°). The P–Cu–P bond
angle is 131.12(5)°, which is similar to that of [Cu(dmp)(DPE-
phos)]BF4. One quinoline ring is arranged parallel to the quinoline
ring on an adjacent molecule, and the interplanar distance be-
tween the quinoline rings is 3.6 Å.
were obtained using a JEOL
chemical shifts are referenced to tetramethylsilane (1H; as inter-
nal) or 85% H3PO4
31P{1H}; as external). Absorption and emission
K-400 spectrometer, in which the
(
spectra were measured with an Agilent 8453 spectrometer and a
Shimadzu RF-5000 fluorometer, respectively.
2.2. General procedure to prepare the Cu complexes
PPh2qn (58 mg, 0.184 mmol) or PPh2qna (60 mg, 0.183 mmol)
was added to a solution of [Cu(CH3CN)4]PF6 (34 mg, 0.092 mmol)
in CHCl3 (10 ml). The mixture was continuously stirred for 1 h,
then the solution was evaporated to a small volume. Addition of
diethyl ether to the solution afforded a pale orange precipitate.
[Cu(PPh2qn)2]PF6 (Cu-1): Yield: 51 mg (66%). Anal. Calc. for
[Cu(C21H16NP)2]PF6 C, 60.40; H, 3.86; N, 3.25. Found: C, 60.22; H,
3.70; N, 3.22%. 1H NMR (CDCl3) d 8.49 (d, 1H), 8.18 (d, 2H), 7.96
(d, 1H), 7.79 (t, 1H), 7.31–7.48 (m, 11H). 31P NMR (CDCl3): d
À16.1 (br).
[Cu(PPh2qna)2]PF6 (Cu-2): Yield: 48 mg (56%). Anal. Calc. for
[Cu(C22H18NP)2]PF6: C, 61.22; H, 4.20; N, 3.25. Found: C, 59.77;
H, 4.04; N, 3.07%. 1H NMR (CDCl3) d 8.42 (d, 1H), 8.16 (d, 1H),
7.83–7.87 (m, 1H), 7.72 (t, 1H), 7.47 (d, 1H), 7.14–7.20 (m, 10H),
2.0 (s, 3H). 31P NMR (CDCl3): d À19.2 (br).
2.3. General procedure to prepare the Zn complexes
A solution of ZnCl2, ZnBr2 or ZnI2 (1.0 mmol) in ethanol (5 ml)
was dropped into a solution of PPh2qn (0.157 g, 0.5 mmol) dis-
solved in 5 ml CHCl3. The precipitated white powder was filtered
and washed with a small amount of ethanol.
[ZnCl2(PPh2qn)] (Zn-1): Yield 0.15 g (67%). Anal. Calc. for
[ZnCl2(C21H16NP)]: C, 56.10; H, 3.59; N, 3.12. Found: C, 55.30; H,
3.34; N, 2.96%. 1H NMR (CDCl3) d 9.21 (d, 1H), 8.54 (d, 1H), 8.16
(d, 1H), 7.99 (t, 1H), 7.80 (br, 2H), 7.66–7.70 (m, 4H), 7.47–7.53
(m, 6H). 31P NMR (CDCl3): d À34.3
The reaction of PPh2qna instead of PPh2qn with [Cu(CH3-
CN)4]PF6 gave Cu-2. This product was also identified by elemental
analysis and 1H and 31P{1H} NMR spectra. Just as the case of Cu-1, a
symmetrical signal set for Cu-2 in the 1H NMR spectrum was ob-
tained. A methyl singlet of Cu-2 was observed at d 2.00, which is
shifted to higher field compared to that of free PPh2qna (d 2.57)
[ZnBr2(PPh2qn)] (Zn-2): Yield 0.18 g (67%). Anal. Calc. for
[ZnBr2(C21H16NP)]: C, 46.84; H, 2.99; N, 2.60. Found: C, 55.30; H,
3.34; N, 2.96%. 1H NMR (CDCl3) d 9.23 (d, 1H), 8.54 (d, 1H), 8.17
(d, 1H), 7.99 (t, 1H), 7.79–7.83 (m, 2H), 7.66–7.70 (m, 4H), 7.46–
7.53 (m, 6H). 31P NMR (CDCl3): d À36.0.
[ZnI2(PPh2qn)] (Zn-3): Yield 0.12 g (38%). Anal. Calc. for
[ZnI2(C21H16NP)]: C, 39.88; H, 2.55; N, 2.21. Found: C, 55.30; H,
3.34; N, 2.96%. 1H NMR (CDCl3): d 9.29 (d, 1H), 8.55 (d, 1H), 8.18
(d, 1H), 7.98 (t, 1H), 7.81–7.84 (m, 2H), 7.65–7.70 (m, 4H), 7.45–
7.53 (m, 6H). 31P NMR (CDCl3): d À37.3.
1
CrystalStructure, ver.3.60: Single Crystal Structure Analysis Software, Molecular
Structure Corporation.

T. Tsukuda et al. / Polyhedron 28 (2009) 7–12
9
Table 2
Selected bond lengths (Å) and angles (°) for Zn-1, Zn-2 and Zn-3.
Zn-1 (X = Cl)
Zn-2 (X = Br)
Zn-3 (X = I)
Zn–X(1)
Zn–X(2)
Zn–P
2.218(2)
2.201(2)
2.395(2)
2.104(5)
2.3601(8)
2.3377(6)
2.395(1)
2.096(5)
2.5388(6)
2.5509(6)
2.390(1)
2.094(3)
Zn–N
X(1)–Zn–X(2)
P(1)–Zn–N(1)
P(1)–Zn–X(1)
P(1)–Zn–X(2)
N(1)–Zn–X(1)
N(1)–Zn–X(2)
116.53(6)
82.0(1)
112.71(6)
122.95(5)
106.9(1)
108.5(1)
115.17(3)
82.4(1)
113.03(4)
123.98(4)
106.8(1)
108.7(1)
11.9.92(2)
83.30(9)
112.53(3)
117.7(4)
114.0(1)
102.6(1)
Fig. 1. ORTEP structure of Cu-1.
only one PPh2qn ligand is coordinated to the zinc(II) ion in these
complexes. Attempts to prepare [Zn(PPh2qn)2] by treatment of
Zn(PF6)2 without halides failed. Preparation of the [ZnF2(PPh2qn)]
complex by treatment with ZnF2 was also unsuccessful. The prod-
ucts were identified by elemental analysis and 1H and 31P{1H} NMR
spectra. In the 31P NMR spectra of the complexes, a sharp singlet
signal was observed between d À34 and À39, which shifted to
higher field on coordination. Such higher field shifts are hardly ever
observed in other Zn(II) complexes containing phosphines [20]. It
suggests that the electron density around the phosphorus atom
is considerably increased by either the zinc atom or the coordi-
nated halides.
Recrystallization of the zinc complexes did not give single crys-
tals available for X-ray analysis, whereas they were directly ob-
tained by slowly mixing both solutions of PPh2qn in CHCl3 and
ZnX2 in CH3OH. The molecular structures of Zn-1, Zn-2 and Zn-3
are illustrated in Fig. 3. It was found that the PPh2qn ligand coordi-
nates to the zinc center with two halide ions. Selected bond lengths
and angles are summarized in Table 2. and crystallographic data
are described in Table S2. The Zn–P bond lengths in these com-
plexes range from 2.390(1) to 2.395(1) Å. Especially, Zn-3 has the
shortest bond length of the reported zinc complexes containing
aryl phosphine derivatives [21–23]. The Zn–X bond lengths in-
crease in the order of the following halide ions, Cl, Br and I, how-
ever there are no notable differences in the other bond lengths
(e.g. Zn–N bonds) and bond angles in the three complexes. So the
three complexes have a similar coordination environment with re-
gard to PPh2qn.
Table 1
Selected bond lengths (Å) and angles (°) for Cu-1 and Cu-2.
Cu-1
Cu-2
Cu–P(1)
Cu–P(2)
Cu–N(1)
Cu–N(2)
2.220 (1)
2.229 (1)
2.071 (4)
2.073 (4)
Cu–P(1)
2.227 (2)
2.081 (3)
Cu–N(1)
*
*
P(1)–Cu–P(2)
N(1)–Cu–N(2)
P(1)–Cu–N(1)
P(2)–Cu–N(2)
P(1)–Cu–N(2)
P(2)–Cu–N(1)
131.12 (5)
112.1 (1)
125.4 (1)
116.2 (1)
87.4 (1)
P(1)–Cu–P(1)
N(1)–Cu–N(1)
P(1)–Cu–N(1)
118.27 (8)
112.7 (2)
87.7 (1)
*
P(1)–Cu–N(1)
127.5(1)
86.4 (1)
on coordination. The 31P NMR spectrum of Cu-2 shows a relatively
broad signal at d À19.23.
The crystals of Cu-2 for X-ray analysis were obtained by slow
diffusion of diethylether into a chloroform solution of the complex.
The structure of [Cu(PPh2qna)2]PF6 is illustrated in Fig. 2. Just as in
the case of Cu-1, the copper atom coordinated by two PPh2qna li-
gands has a four-coordinate structure with a tetrahedral geometry,
however the crystal of Cu-2 has different space group, C2/c, com-
pared to P21/c for Cu-1, as shown in Table 1. A twofold axis goes
through the copper atom. Selected bond lengths and angles are
summarized in Table 2. The Cu–P and Cu–N bond lengths are
2.227(2) and 2.081(3) Å, respectively, which are similar to those
of Cu-1. The P–Cu–P bond angle is 118.27(8)°.
3.3. Photophysical properties of the complexes containing
phosphinoquinoline ligands
3.2. Preparation and characterization of the Zn(II) complexes
The absorption spectra of Cu-1 and Cu-2 in CH2Cl2 are shown in
Fig. 4. Each complex shows an absorption ranging from 380 to
450 nm, which is not observed for the corresponding free phosph-
inoquinoline ligand. The Cu–diimine MLCT bands are known to be
observed in the region 400–360 nm, with an absorption coefficient
of the order of 1.0 Â 103 molÀ1 dm3 cmÀ1 for mononuclear Cu–
P2N2 complexes [3–6]. It suggests that the absorption bands of
Cu-1 and Cu-2 are assigned to the MLCT transition from the Cu(I)
center to the quinoline moiety. The enhancement of the absorption
intensity in the region from 300 to 340 nm for each complex stems
from the coordination of the two ligands in one complex molecule.
The treatment of ZnCl2, ZnBr2 and ZnI2 with PPh2qn readily
afforded Zn-1, Zn-2 and Zn-3, respectively. Unlike [Cu(PPh2qn)2]+,
The bands are assigned to the quinoline-based intraligand
p–p*
transition, as reported for the ruthenium(II) complexes containing
PPh2qn [12].
Cu-1 and Cu-2 show emission in the solid state as shown in
Fig. 5. The emission maximum of Cu-1 is located at ca. 640 nm.
The emission lifetime is estimated at 0.33 ls from the emission
decay curve fitted with a single exponential function. The lumines-
cent properties, which are comparable to that of [Cu(dmp)-
(diphosphine)]+, suggests that the emission band is assigned to
Fig. 2. ORTEP structure of Cu-2.

10
T. Tsukuda et al. / Polyhedron 28 (2009) 7–12
Fig. 3. ORTEP structures of Zn-1 (left), Zn-2 (middle) and Zn-3 (right).
one in solution. The emission maximum of Cu-2 is similar to that
of Cu-1. However, the emission lifetime of Cu-2 is ca. 1.0 s, which
10
l
is three times longer than that of Cu-1. In the case of copper(I)
complexes containing dmp, it has already been shown that the ste-
ric effect of methyl-substituted groups usually results in a higher
quantum yield and a longer emission lifetime [2–5]. However, as
described in the X-ray structure, the coordination sphere around
copper in Cu-2 is not bulky enough to inhibit quenching of the ex-
cited states to emit in solution, even in the presence of the methyl-
substituted group in PPh2qna.
5
The absorption spectra of the zinc complexes are shown in
Fig. 6. All the zinc complexes show similar absorption spectra.
Although the free PPh2qn ligand has an absorption band ranging
from 330 to 370 nm, the zinc complexes show smaller intensity
ε
in this region. It suggests that the band is assigned to the n–p*
charge transfer transition from the lone pair on the phosphorus
atom to the quinoline ring. This type of transition for some metal
complexes was reported to have character similar to a protonated
aryl phosphine, involving a shift to higher energies compared to
the free phosphine [24].
0
300
400
500
Wavelength /nm
Among the three Zn complexes, only Zn-1 shows luminescence
in CH2Cl2 solution at room temperature. As shown in Fig. 7, the
emission spectrum of Zn-1 is similar to that of free PPh2qn. There-
fore, the emission bands are assigned to the ligand-centered (LC)
transition. Dissociation of PPh2qn from Zn-1 is not suggested be-
cause the 31P NMR spectrum of Zn-1 shows a sharp singlet, as de-
scribed above. The emission lifetime of Zn-1 is too short to be
measured (<20 ns). It suggests that the emission is fluorescent.
The emission spectra in frozen CH2Cl2 at 77 K of Zn-1 and free
PPh2qn show emission maxima at 535 and 530 nm, respectively
(Fig. 7). The spectra were independent of the excitation wave-
Fig. 4. Absorption spectra of Cu-1 (solid line), Cu-2 (dotted line), PPh2qn (dashed
line) and PPh2qna (dashed-dotted line) in CH2Cl2.
1
500
600
Wavelength / nm
700
800
Fig. 5. Emission spectra (uncorrected) of Cu-1 (solid line) and Cu-2 (dotted line) in
the solid state.
ε
3MLCT transition involving
p* of the quinoline group. The assign-
0
ment is consistent with the suggestion that no emission is ob-
served in solution because of the lower bulkiness of the
coordination sphere around the copper atom in the complex struc-
ture, facilitating a tetragonal flattening distortion of the excited
luminophore and/or attack of solvent molecules to the excited
250
300
350
400
Wavelength / nm
Fig. 6. Absorption spectra of PPh2qn (bold solid line), Zn-1 (solid line), Zn-2 (dotted
line) and Zn-3 (dashed line) in CH2Cl2 solution.

T. Tsukuda et al. / Polyhedron 28 (2009) 7–12
11
The emission spectra of the zinc complexes and the free ligand
have been obtained in the solid state and are shown in Fig. 8. The
emission band of Zn-1 at ca. 500 nm is shifted to lower energy than
that in solution, whereas the lifetime is very short (<20 ns). The
emission maxima of Zn-1 and Zn-2 are slightly shifted to higher
energy compared to that of the free PPh2qn, whereas that of Zn-
3 is observed in the lower energy region and involves vibrational
structure; thus the heavier the halogen in the zinc complex, the
lower the energy of the emission. The emission energy dependence
on the coordinated halogenide ions and structural similarity
involving the Zn-PPh2qn moiety between the complexes suggest
that the halogen-to-ligand charge transfer (XLCT) from halogenide
to quinoline ring may contribute to the emissive excited states.
However, it should be noted that the absorption bands ranging
from 300 to 330 nm hardly show any dependence on the haloge-
nide ion, so the character of the excited states associated with
the absorption, which may be p–p* of the quinoline ring, may dif-
fer from that of the emissive excited states.
350
450
550
650
700
wavelength / nm
4. Conclusion
Fig. 7. Emission spectra (uncorrected) of Zn-1 and PPh2qn in CH2Cl2; Zn-1 at 298 K
(solid line), PPh2qn at 298 K (bold solid line), Zn-1 at 77 K (dashed line) and PPh2qn
at 77 K (dotted line).
The utilization of PPh2qn or PPh2qna, containing both imine and
phosphine moieties, successfully gives the new copper complexes
Cu-1 and Cu-2, respectively. Both complexes have similar struc-
tures to those of mixed-ligand complexes with a P2N2 donor set.
In the solid state, both Cu(I) complexes show an emission assigned
to 3MLCT. However, no emission is observed in solution, even for
Cu-2 coordinated by PPh2qna which has a bulkier group than
PPh2qn. The bulkiness in the coordination sphere around the cop-
per atom should be smaller than that of the reported mixed-ligand
[Cu(dmp)(diphosphine)]-type complexes.
Meanwhile, a series of Zn(II) complexes coordinated by only one
PPh2qn ligand and two halogenide ions was also prepared. All the
complexes are stable in solution, and each sharp singlet signal was
shifted to amazingly higher field on coordination. Structural char-
acterization shows the similarity of the coordination environment
around the PPh2qn ligand for the three complexes. Zn-1 shows a
similar emission band to that of free PPh2qn at both room temper-
ature and 77 K. It suggests the emission bands are assigned to a li-
gand-centered (LC) transition. In the solid state, it is found that the
emissive energy of the complex is shifted to lower energy for the
series, ClÀ > BrÀ > IÀ. A contribution of the halogenide orbitals in
the emissive states is suggested Chart 1.
400
500
600
700
Wavelength / nm
Appendix A. Supplementary data
Fig. 8. Emission spectra of PPh2qn (bold solid line) Zn-1 (solid line), Zn-2 (dotted
line), Zn-3 (dashed line) in the solid state at room temperature.
CCDC 683537, 683538, 683539, 683540 and 683541 contain the
supplementary crystallographic data for Cu-1, Cu-2, Zn-1, Zn-2
and Zn-3. 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, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
X-ray crystallographic data of the Cu(I) and Zn(II) complexes are
shown in Figs. S1 and S2, respectively. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.poly.2008.08.028.
length, over the range 330–350 nm. Fife et al. have reported that
the emission spectrum of [ZnCl2(PPh2Me)] in diethylether–isopen-
tane–ethanol glass at 77 K show a slightly higher energy emission
maximum, at ca. 420 nm, than that of free PPh2Me [24]. The emis-
sion band of Zn-1 is also similar to that of [Ru(bpy)2(PPh2qn)] ob-
served in EtOH/MeOH glass at 77 K, which is assigned to a
quinoline based 3(
p–p*) transition [12]. In the case of zinc(II) com-
plexes, a high promotion energy does not result in low-energy
MLCT excited states [24]. Thus unlike the Cu(I) complexes, the
emission band is assigned to not a metal-to-ligand but to a li-
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