A series of luminescent Cu(i) mixed-ligand complexes containing 2,9-dimethyl-1,10-phenanthroline and simple diphosphine ligands

Article abstract of DOI:10.1039/b608641a

A series of Cu(i) mixed-ligand complexes containing dmp (2,9-dimethyl-1,10-phenanthroline) and one of simple diphosphine ligands (Ph₂P(CH₂)_nPPh₂) were prepared. Among the complexes, [Cu(dppp)(dmp)]PF₆ (n = 3) and [Cu ₂(dppb)₂(dmp)₂](PF₆)₂ (n = 4) were characterized by X-ray structure analyses. The dppp complex has been characterized as a mononuclear complex, while [Cu₂(dppb) ₂(dmp)₂]²⁺ exists as a dinuclear complex in which two dppb ligands bridge between the two Cu(i) atoms. Although the distorted tetrahedral structures around the central metals of the two complexes are similar, the P-Cu-P angles are different between the two complexes. All of the series of complexes show photoluminescence in solution, and the intensity of the luminescence increases with n (n = 2-4). The non-radiative rate constants of the complexes decrease markedly with n although radiative rate constants of the complexes are similar. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b608641a

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A series of luminescent Cu(I) mixed-ligand complexes containing
2,9-dimethyl-1,10-phenanthroline and simple diphosphine ligands†‡
Ken Saito, Takashi Arai, Naoki Takahashi, Toshiaki Tsukuda and Taro Tsubomura*
Received 19th June 2006, Accepted 10th August 2006
First published as an Advance Article on the web 18th August 2006
DOI: 10.1039/b608641a
A series of Cu(I) mixed-ligand complexes containing dmp (2,9-dimethyl-1,10-phenanthroline) and one
of simple diphosphine ligands (Ph2P(CH2)nPPh2) were prepared. Among the complexes,
[Cu(dppp)(dmp)]PF6 (n = 3) and [Cu2(dppb)2(dmp)2](PF6)2 (n = 4) were characterized by X-ray
structure analyses. The dppp complex has been characterized as a mononuclear complex, while
[Cu2(dppb)2(dmp)2]2+ exists as a dinuclear complex in which two dppb ligands bridge between the two
Cu(I) atoms. Although the distorted tetrahedral structures around the central metals of the two
complexes are similar, the P–Cu–P angles are different between the two complexes. All of the series of
complexes show photoluminescence in solution, and the intensity of the luminescence increases with n
(n = 2–4). The non-radiative rate constants of the complexes decrease markedly with n although
radiative rate constants of the complexes are similar.
Introduction
Result and discussion
There has been an increasing interest in the photophysics and
photochemistry of Cu(I) complexes in the last few decades.1
Although extensive studies on the luminescence of [Cu(diimine)2]+
type complexes have been made,2 the quantum yields (U) of
the luminescence are generally low; for example, it is 0.04%
for [Cu(dmp)2]+ (dmp = 2,9-dimethyl-1,10-phenanthroline).3 Spe-
cial structural features are required to achieve highly lumi-
nescent species for bis(diimine)Cu(I) complexes.4 The mixed-
ligand complexes of phosphines and diimines have also been
studied as interesting emitters in solution.5 In recent years, Cu(I)
complexes containing diphosphines which have a hetero atom,
e.g. DPEphos ( = bis[2-(diphenylphosphino)phenyl]ether)6 and
bis(2-(diisobutylphosphino)phenyl)amide7 have received much
attention as very strong emitters in solution. We also have
been studying the synthesis of mixed-ligand Cu(I) com-
Synthesis
The mixed-ligand complexes were prepared in a similar manner to
that described in refs. 6 and 8. Reactions of [Cu(MeCN)4]PF6
9
with dmp and diphosphine ligands with a molar ratio of 1 :
1 : 1 in CH2Cl2 gave the complexes of the empirical formula,
[Cu(Ph2P(CH2)nPPh2)(dmp)]PF6 (n = 2, 3, 4 and 5). The complexes
are obtained as orange powders and are soluble in polar organic
solvents such as dichloromethane and acetonitrile. The dppp
and dppb complexes were obtained as crystals of X-ray quality
by recrystallization (dppp = 1,3-bis(diphenylphosphino)propane),
dppb = 1,4-bis(diphenylphosphino)butane).
Crystal structures
The crystal structure of [Cu(dppe)(dmp)]PF6 was published by
Coppens et al.,10 and its distorted tetrahedral structure was clari-
fied. In the present study, the crystal structure of the mixed-ligand
complexes containing dmp and dppp or dppb have been success-
fully analyzed. The crystal structure of [Cu(dppp)(dmp)]PF6 has a
mononuclear structure similar to the dppe complex. On the other
hand, the crystal of the mixed-ligand complex containing dmp
and dppb reveals a dinuclear structure.
8
plexes, and found that [Cu(binap)(dmp)]PF6 shows emission
in CH2Cl2 solution (binap = 2,2ꢀ-bis(diphenylphosphino)-1,1ꢀ-
binaphthyl), and the quantum yield of the luminescence is
similar to that of [Cu(dppe)(dmp)]+ (U = 1%)6 (dppe = 1,2-
bis(diphenylphosphino)ethane). Recently, we studied the photo-
physical properties of the mixed-ligand complexes containing dmp
and a series of simple diphosphines, Ph2P(CH2)nPPh2 (n = 2–5).
In this article, we show that the Cu(I) mixed-ligand complexes of
the simple ligands can become good emitters.
Fig.
1 and 2 show the structure of the mononuclear
cation, [Cu(dppp)(dmp)]+, and the dinuclear cation, [Cu2(dppb)2-
(dmp)2]2+, respectively. An asymmetric unit of the crystal of the
dppp complex consists of two [Cu(dppp)(dmp)]+ cations and two
−
PF6 anions, and that of the dppb complex consists of a half
part of the [Cu2(dppb)2(dmp)2]2+ cation, one PF6 anion and two
benzene molecules. For the dppb complex, four F atoms in one
of the PF6 anions were disordered over two sites on an equato-
rial plane. Although the nuclearity of [Cu2(dppb)2(dmp)2](PF6)2
is completely different from that of [Cu(dppe)(dmp)]PF6 and
[Cu(dppp)(dmp)]PF6, the geometry around each copper atom
Department of Materials and Life Science, Seikei University, Kichijoji-
Kitamachi, Musashino, Tokyo, 1808633, Japan. E-mail: tsubomura@
st.seikei.ac.jp; Fax: +81-422-37-3871; Tel: +81-422-37-3752
† The HTML version of this article has been enhanced with colour images.
‡ Electronic supplementary information (ESI) available: Fig. S1: Absorp-
tion and corrected emission spectrum of [Cu(dmp)(Ph2P(CH2)5PPh2)]PF6.
See DOI: 10.1039/b608641a
4444 | Dalton Trans., 2006, 4444–4448
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◦
dppp chelates fall within 90 1◦ and 100 6 ,12 respectively.
Our result of [Cu(dppp)(dmp)]PF6 shows angles of 105–106◦.
On the other hand, the P–Cu–P angle in [Cu2(dppb)2(dmp)2]2+ is
126.38(5)◦. This implies that the PPh2 groups in the dppb complex
are sterically closer to the dmp ligand than in the dppe or dppp
complexes.
11
There are some close interligand C · · · C or C · · · N distances
between the dmp ligand and the phenyl groups of the diphosphine
ligands. The shortest nonbonding interaction in each of the
complex cations is shown in Fig 3. The nonbonding C · · · C or
C · · · N distances are similar in the three complex cations, which
˚
are in the range 3.34–3.35 A. However, the orientation of the
phenyl groups is markedly different between the dppp and dppb
complexes. As shown in Fig. 3, one of the phenyl groups attached
to the P1 atom in the dppb ligand is located just over the Cu atom.
The dihedral angle between the phenyl group and the dmp ligand
is 22◦. One more phenyl group attached to the P2* atom is located
near the copper atom, where the closest C · · · N distance is 3.509(8)
Fig. 1 Molecular structure of [Cu(dppp)(dmp)]+ with thermal ellipsoids
at 50% probability level. The hydrogen atoms are omitted. The data were
obtained at −150 ◦C. One of the two complex cations is shown. Selected
˚
A, although the phenyl ring is near perpendicular orientation with
respect to the dmp ligand; the dihedral angle is 75◦. Thus, the
copper atom is effectively protected by the phenyl rings on both
◦
˚
bond lengths (A) and angles ( ): Cu1–P1 2.2605(9), Cu1–P2 2.2273(9),
Cu1–N1 2.097(3), Cu1–N2 2.071(3); P1–Cu1–P2 105.42(3), N1–Cu1–N2
81.3(1). The parameters of the other complex cation are as follows:
Cu2–P3 2.2362(9), Cu2–P4 2.2620(9), Cu2–N3 2.075(3), Cu2–N4 2.073(3);
P3–Cu2–P4 105.31(3), N3–Cu2–N4 81.8(1).
Fig. 2 Molecular structure of [Cu2(dppb)2(dmp)2]2+ with thermal ellip-
soids at 50% probability level. The hydrogen atoms are omitted. The data
were obtained at 22 ◦C. An inversion centre is located at the centre of the
complex. The atoms marked with * are at equivalent positions (1 − x, −y,
◦
˚
−z). Selected bond lengths (A) and angles ( ): Cu1–P1 2.3002(14), Cu1–P2
2.256(1), Cu1–N1 2.105(4), Cu1–N2 2.117(4); P1–Cu1–P2 126.38(5),
N1–Cu1–N2 80.1(2).
in the dinuclear complex is similar to that of the mononuclear
dppp and dppe complexes. In those complexes, both Cu(I) atoms
are surrounded by P2N2 donor atoms and they form distorted
tetrahedra.
The Cu–P and Cu–N bond lengths are in the range 2.22–
˚
2.26 and 2.07–2.10 A, respectively, in both the complexes. There
are no significant differences in the bond lengths between the
dppp and dppb complexes. However, the bond angles around
the copper atoms depend largely on the diphosphines. The P–
Cu–P angles of the three complexes increase with the number
of methylene carbon atoms between the two phosphorous atoms
(n = 2–4). Literature values for the P–Cu–P angle in the dppe and
Fig. 3 Drawings of the copper complexes viewed along the two phos-
phorous atoms of the diphosphine ligands. (a), (b) The two complex
cations found in the crystal of the [Cu(dppp)(dmp]]+ complex cation. (c)
The complex cation [Cu2(dppb)2(dmp)2]2+. The closest interligand C · · · C
or C · · · N distances in each cation is shown with both-side arrows. The
˚
distances are (a) 3.340(5), (b) 3.350(4), (c) 3.346(8) A.
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Table 1 The photophysical properties of Cu complexes containing
sides of the copper centre in the dppb complex. On the other hand,
in the dppp complex, all the phenyl groups of the diphosphine
ligands are oriented away from the copper centre as shown in
Fig. 3.
diphosphine ligand(s) measured in CH2Cl2 solution
Diphosphine
dppea
dpppb
dppbb
kabs /nm
kem/nm
U
405
594
0.01
391
600
382
590
0.10
Spectroscopic properties
0.037
5.4
s/ls
1.33
10.8
All the mixed-ligand complexes containing Ph2P(CH2)nPPh2 (n =
2–5) show photoluminescence both in the solid state and in
degassed CH2Cl2 solution. The orange-colored complex of n = 5 is
strongly luminescent in solution, but the product has not yet been
fully characterized. Thus, the discussion about the photophysical
properties of the n = 5 complex is omitted in this paper. Absorption
and luminescence spectra of the complex are shown in ESI.‡
Fig. 4 shows the absorption spectra of the three complexes
(n = 2, 3 and 4) measured in CH2Cl2 solution. For the three
complexes, absorption bands of moderate intensities (e = 2000–
3000 M−1 cm−1) are observed in the region 350–450 nm, which
are characterized as MLCT involving the p* orbitals of the dmp
ligand of the mixed-ligand complex. The kabs of these complexes
containing dppe, dppp and dppb are 405, 391 and 382 nm,
respectively. A tendency is shown that the kabs shifts to higher
energy as the carbon chain within the diphosphine chelate becomes
longer. The correlation of the blue-shift and the geometry of the
Cu(I) mixed-ligand complexes has already been discussed.13 Small
absorption shoulders seen near 470 nm should be originated by
[Cu(dmp)2]+, which is produced by a disproportionation reaction
of the mixed-ligand complexes. However, each NMR spectrum of
kr/s−1
knr/s−1
7.5 × 103
7.6 × 103
1.1 × 104
8.1 × 104
7.4 × 105
1.8 × 105
a Cited from ref. 6. b The data were collected at 20 ◦C.
Fig.
5
Corrected emission spectra of (a) [Cu(dppe)(dmp)]+, (b)
[Cu(dppp)(dmp)]+ and (c) [Cu2(dppb)2(dmp)2]2+ measured in degassed
[Cu(dppe)(dmp)]+, [Cu(dppp)(dmp)]+ and [Cu2(dppb)2(dmp)2]2+
shows one broad signal in addition to the septet signal of PF6
CH2Cl2 ([Cu] = 5 × 10−5 M) at room temperature.
−
.
The broadening of the signal is characteristic of Cu(I) complexes.
Given the molar absorption coefficient of [Cu(dmp)2]+ is large
(7800 M−1cm−1),3 the concentration of the minor species should
be low in each solution; this accounts for the single broad NMR
signal in each spectrum.
has proved to be a strong emitter (U = 0.10). Similarly, it turned
out that the luminescence lifetime becomes longer with the length
of the carbon chain within the diphosphine ligands. Furthermore,
the values of comparatively long s suggest the involvement of
3MLCT in the luminescence of the complexes.
Table 1 summarizes the photophysical properties of the com-
plexes. The rate constants of radiative (kr) and nonradiative
processes (knr) calculated from U and s are included. The kr
values slightly increase from the dppe complex to dppb complex.
However, it turns out that the increase of the emission intensity
with the length of the carbon chain in the diphosphines is mainly
due to the marked decrease in the knr values. It is well known
that there is a close relation between the bulkiness of the ligands
around the copper centre and the intensity of the luminescence.4
The bulkiness of the ligand should prevent the complexes to distort
in the excited states. The distortion causes the increase of the
non-radiation process. Simultaneously, the bulkiness of the ligand
prevents the solvent molecule to approach to the metal centre. This
may be the reason why the increase of P–Cu–P angle results in a
marked decrease of radiationless deactivation processes.
Fig.
4
Room-temperature electronic absorption spectra of (a)
[Cu(dppe)(dmp)]+, (b) [Cu(dppp)(dmp)]+ and (c) [Cu2(dppb)2(dmp)2]2+
.
These spectra are measured in degassed CH2Cl2 The molar absorption
coefficients were calculated as the complexes were all mononuclear.
Conclusion
In conclusion, for the Cu(I) mixed-ligand complexes containing
dmp and simple diphosphine ligands (Ph2P(CH2)nPPh2), we found
that the quantum yield and lifetime of the luminescence increase
with n (from n = 2 to 4). Especially for n = 4, the complex was
found to have a dimeric structure and to be a strong emitter. The
correlation between the P–Cu–P angles and the photophysical
Fig. 5 shows the emission spectra of these complexes in CH2Cl2
solution. These spectra also show the tendency of a blue shift of
the kem with increase of the carbon chain within the diphosphine
chelates. Moreover, the intensities of the luminescence increase
with the length of the carbon chain. The dinuclear dppb complex
4446 | Dalton Trans., 2006, 4444–4448
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properties found in this system may be interpreted from the
viewpoint of the bulkiness around the metal centre.
CrystalStructure17 crystallographic software package except for
refinement, which was performed using SHELXL-97.18
[Cu(dppp)(dmp)]PF6: C41H38CuN2P3F6, Mr = 829.19, mon-
oclinic, space group = P21/a (no. 14), a = 17.2378(9), b =
Experimental
◦
3
˚
˚
15.4342(7), c = 28.742(1) A, b = 102.727(1) , V = 7459.1(6) A ,
l = 7.8 cm−1, Z = 8, Dc = 1.477 g cm−3, No. of unique reflections
(2h <55◦) = 16446, R1 = 0.067 (I > 2r(I)), wR2 = 0.142 (all data),
GOF = 1.22. Highest peak and deepest hole in the last difference
General
The preparation of the mixed-ligand complexes was conducted
under an Ar atmosphere using standard Schlenk tube techniques
although the products are stable in air. CHN analyses of the
complexes were performed on the Perkin-Elmer model 2400.
NMR spectra were obtained using JEOL K-400 spectrometer.
−3
˚
Fourier map were 0.72 and −0.53 e A , respectively.
[Cu2(dppb)2(dmp)2](PF6)2. The single crystals for X-ray struc-
tural analysis were obtained by slow diffusion of benzene into
an acetone solution of the complex. Data were collected on
an automated Rigaku AFC5S diffractometer using graphite-
Synthetic procedure and characterization
◦
˚
The mixed-ligand complexes, [Cu(dmp)(Ph2P(CH2)nPPh2)]PF6
(n = 2, 3, 4 and 5), were prepared by reaction of [Cu(MeCN)4]PF6
with 2,9-dimethyl-1,10-phenanthroline and Ph2P(CH2)nPPh2 (n =
2–5). [Cu(dppe)(dmp)]PF6.6 [Cu(CH3CN)4]PF69 (0.37 g, 1 mmol),
dmp (2,9-dimethyl-1,10-phenanthroline) (0.22 g, 1 mmol) and
dppe (0.40 g, 1 mmol) were dissolved in CH2Cl2 (15 ml). After
stirring for 90 min at room temperature, the addition of diethyl
ether to the solution of the complex gave a yellow powder of
the mixed-ligand complex, [Cu(dppe)(dmp)]PF6. The complex was
obtained by filtration, and dried in vacuo. Yield, 85%.
monochromated Mo-Karadiation (k = 0.71069 A) at 23 C. Three
standard reflections were measured in every 150 reflections. An
empirical absorption correction based on azimuthal scans of
several reflections was applied. Calculations were carried out by
using teXsan.19 The structures were solved by a direct method and
refined by full-matrix least-squares methods.18 Hydrogen atoms
were placed at the idealized positions, and the coordinates and the
isotropic temperature factors were fixed. Anisotropic temperature
factors were used for all non-hydrogen atoms except for the atoms
shown below. Drawings were generated by ORTEP III.20
Other mixed-ligand complexes were prepared from
[Cu(MeCN)4]PF6, dmp and diphosphine in CH2Cl2 in a similar
manner to that described above, dppp, dppb and 1,5-dppp
(1,5-bis(diphenylphosphino)pentane) were used as diphosphine
ligands.
[Cu2(dppb)2(dmp)2](PF6)2·4C6H6: C108H106Cu2N4P6F12, Mr
=
¯
1998.87, triclinic, space group P1, a = 13.380(5), b = 17.163(3),
◦
˚
c = 11.366(2) A, a = 101.27(2), b = 91.44(2), c = 79.57(2) , V =
3
−1
−3
˚
2517(1) A , l = 5.9 cm , Z = 1, Dc = 1.32 g cm , x–2h scan
method, No. of unique reflections (2h < 50◦) = 8853, R1 = 0.063
(I > 2r(I)), wR2 = 0.164 (all data), GOF = 1.017. Highest peak
and deepest hole in the last difference Fourier map were 0.51 and
[Cu(dppp)(dmp)]PF6·Et2O. Yield, 84%. Anal. Calc. for
C45H48CuF6N2OP3: C, 59.83; H, 5.36; N, 3.10. Found: C, 60.02;
−3
˚
−0.43 e A , respectively.
1
H, 5.25; N, 3.32%. 31P{ H} NMR (CDCl3) d −8 (br).
CCDC reference numbers 602727 and 611492.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b608641a
[Cu2(dppb)2(dmp)2](PF6)2. Yield, 80%. Anal. Calc. for
C84H80Cu2F12N4P6: C, 59.68; H, 5.01; N, 3.31. Found: C, 60.13;
1
H, 4.69; N, 3.35%. 31P{ H} NMR (CDCl3) d −18 (br).
[Cu(dmp)(PPh2(CH2)5PPh2)]PF6. Yield, 83%. Anal. Calc. for
C43H42CuF6N2P3 : C, 60.25; H, 4.94; N, 3.27. Found: C, 59.77; H,
Optical spectroscopy
1
4.96; N, 3.18%. 31P{ H} NMR (CDCl3) d −16 (br).
The absorption and luminescence spectroscopy of the mixed-
ligand complexes in CH2Cl2 solution were measured using a quartz
cell connected to a glass tube and a Teflon stop-cock. All samples
were thoroughly deoxygenated by successive freeze–pump–thaw
cycles. Absorption and luminescence spectra were measured with
a Shimadzu UV-2100 spectrophotometer and a Shimadzu RF-
5000 fluorometer, respectively. Luminescence decay curves were
measured on a laboratory-made apparatus; the sample was excited
using a nitrogen laser (USHO AN-200) and the emission light
was focused into a Jobin-Yvon H-20 monochromator equipped
with a Hamamatsu R955 photomultiplier. The output of the
photomultiplier was digitized by a Iwatsu–Lecroy DS4262 digital
oscilloscope and then downloaded to a PC.
Emission quantum yields, U, were measured in a deaerated
(freeze–pump–thaw cycles) CH2Cl2 solution at 20 1 ◦C with the
use of [Ru(bpy)3](PF6)2 in CH3CN as a standard (U = 0.09).21
The emission spectra were corrected with a calibration function
that was made with the use of N,Nꢀ-dimethyl-3-nitroaniline and
4-dimethyl-4ꢀ-nitrostylbene as standard substances.22
Data collection and reduction for X-ray crystallographic analyses
[Cu(dppp)(dmp)]PF6. The single crystals for X-ray structural
analysis were obtained by slow diffusion of n-heptane into a
CH2Cl2 solution of the complex. All measurements were made on a
Rigaku Saturn CCD area detector with graphite-monochromated
Mo-Ka radiation. The crystal-to-detector distance was 54.90 mm.
The data were collected at a temperature of −150
1
◦C to a
maximum 2h value of 55.0◦. 1800 oscillation images were collected.
Of the 67721 reflections that were collected, 16446 were unique
(Rint = 0.048); equivalent reflections were merged. Data were col-
lected and processed using CrystalClear (Rigaku).14 A numerical
absorption correction was applied which resulted in transmission
factors ranging from 0.86 to 0.94. The structure was solved by
direct methods15 and was expanded using Fourier techniques.16
The non-hydrogen atoms were refined anisotropically. Some
hydrogen atoms were refined isotropically and the rest were refined
using the riding model. All calculations were performed using the
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P. E. Fanwick, D. R. McMillin and R. A. Walton, J. Am. Chem. Soc.,
2002, 124, 7.
Acknowledgements
7 Seth B. Harkins and Jonas C. Peter, J. Am. Chem. Soc., 2005, 127, 2030.
8 K. Saito, T. Tsukuda and T. Tsubomura, Bull. Chem. Soc. Jpn., 2006,
79, 437.
This work was financially supported by the Promotion and Mutual
Aid Corporation for Private Schools of Japan through the Science
Research Promotion Fund and through the High-tech Research
Center project.
9 G. J. Kubas, Inorg. Synth., 1979, 19, 90.
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