Synthesis, structural and spectroscopic characterization of mono- and binuclear copper(I) complexes with substituted diimine and phosphine ligands

Article abstract of DOI:10.1016/j.ica.2007.02.007

The reaction of [Cu(CH₃CN)₄]BF₄, 6-(4-methoxyl)phenyl-2,2′-bipyridine (designated as MeO-CNN), and/or tricyclohexylphosphine (PCy₃) and diimine ligands derived from 4,4′-bipyridine gave four mono- and binuclear copper(I) complexes, [Cu(MeO-CNN)₂]BF₄ (1), [Cu₂(MeO-CNN)₂(PCy₃)₂(4,4′-bipy)](BF₄)₂ · 1.5CH₂Cl₂ (2) (bipy = bipyridine), [Cu₂(MeO-CNN)₂(PCy₃)₂(bpete)](BF₄)₂ · 4CH₂Cl₂ (3) (bpete = trans-1,2-bis(4-pyridyl)ethene) and [Cu₂(MeO-CNN)₂(PCy₃)₂(4,4′-azpy)] (BF₄)₂ · 1.5CH₂Cl₂ (4) (azpy = azobispyridine). Crystallographic studies of complexes 1-4 show that each copper(I) center adopts a pseudo-tetrahedral coordination geometry. Complexes 2-4 consists of -Cu(MeO-CNN)(PCy₃) units which are linked through 4,4′-bipy, bpete and 4,4′-azpy, respectively. The UV-Vis spectra of these four complexes all exhibit intense high-energy absorptions at λ_max < 340 nm and broad visible bands in a range of 430-550 nm, ascribed to intraligand (IL π → π^*) transitions and metal-to-ligand charge-transfer (MLCT) transitions, respectively. The density functional theory calculation was used to interpret the absorption spectrum of 1, which further supports the assignment of MLCT character. The binuclear complexes 2 and 3 both display red solid-state emissions centred at 620 and 660 nm from metal-to-ligand charge-transfer excited state, respectively. Interestingly, the electron paramagnetic resonance (EPR) spectral measurements confirm copper(I) complexes oxidized to corresponding copper(II)-halide product upon excitation at 355 nm in dichloromethane solution.

Full text of DOI:10.1016/j.ica.2007.02.007

Inorganica Chimica Acta 360 (2007) 2758–2766
www.elsevier.com/locate/ica
Synthesis, structural and spectroscopic characterization
of mono- and binuclear copper(I) complexes with substituted
diimine and phosphine ligands
a,b,
a
a
b
b
a
Wen-Fu Fu
*, Xin Gan , Jian Jiao , Yong Chen , Mei Yuan , Shao-Ming Chi ,
b
c
Ming-Ming Yu , Shao-Xiang Xiong
a
College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650092, PR China
b
Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Peking 100080, PR China
Beijing Mass spectrometry Center, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China
c
Received 15 November 2006; received in revised form 9 February 2007; accepted 9 February 2007
Available online 20 February 2007
Abstract
The reaction of [Cu(CH3CN)4]BF4, 6-(4-methoxyl)phenyl-2,20-bipyridine (designated as MeO-CNN), and/or tricyclohexylphosphine
(PCy3) and diimine ligands derived from 4,40-bipyridine gave four mono- and binuclear copper(I) complexes, [Cu(MeO-CNN)2]BF4 (1),
[Cu2(MeO-CNN)2(PCy3)2(4,40-bipy)](BF4)2 Æ 1.5CH2Cl2 (2) (bipy = bipyridine), [Cu2(MeO-CNN)2(PCy3)2(bpete)](BF4)2 Æ 4CH2Cl2 (3)
(bpete = trans-1,2-bis(4-pyridyl)ethene) and [Cu2(MeO-CNN)2(PCy3)2(4,40-azpy)] (BF4)2 Æ 1.5CH2Cl2 (4) (azpy = azobispyridine). Crys-
tallographic studies of complexes 1–4 show that each copper(I) center adopts a pseudo-tetrahedral coordination geometry. Complexes
2–4 consists of –Cu(MeO-CNN)(PCy3) units which are linked through 4,40-bipy, bpete and 4,40-azpy, respectively. The UV–Vis spectra
of these four complexes all exhibit intense high-energy absorptions at kmax < 340 nm and broad visible bands in a range of 430–550 nm,
ascribed to intraligand (IL p ! p*) transitions and metal-to-ligand charge-transfer (MLCT) transitions, respectively. The density func-
tional theory calculation was used to interpret the absorption spectrum of 1, which further supports the assignment of MLCT character.
The binuclear complexes 2 and 3 both display red solid-state emissions centred at 620 and 660 nm from metal-to-ligand charge-transfer
excited state, respectively. Interestingly, the electron paramagnetic resonance (EPR) spectral measurements confirm copper(I) complexes
oxidized to corresponding copper(II)–halide product upon excitation at 355 nm in dichloromethane solution.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Copper(I) complexes; Aromatic diimine; Phosphine; Photophysical properties; Crystal structures
1. Introduction
ligand charge-transfer (MLCT or d–p*), or intraligand
excited state (IL or p–p*) can be the lowest energy elec-
tronic excited state [6–10]. A subtle change in the electronic
property of polypyridine ligand has been reported to alter
the nature of the lowest excited state in these complexes
[11,12]. In the literatures, applications of copper(I) com-
plexes containing diimine or phosphine ligands in lumines-
cent sensing and light-induced generation of hydrogen
from water have been investigated [13,14]. A remarkable
amount of work has been devoted to characterization of
the excited-state redox properties and the kinetic analysis
of excited-state electron-transfer reactions of these kinds
of complexes [15–17]
Copper(I) complexes containing diimine and/or phos-
phine ligands have been extensively studied for their photo-
physical properties, photoinduced electron-transfer
reactions and excited-state substrate-binding reactions [1–
5]. These complexes display a variety of long-lived emissive
electronic excited states. Depending on the nature of poly-
pyridine ligand, metal-centered (MC or d–d), metal-to-
*
Corresponding author. Tel.: +86 10 8254 3519; fax: +86 10 6255 4670.
E-mail address: wf_fu@yahoo.com.cn (W.-F. Fu).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.02.007

W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
2759
Complexes with 1,10-phenanthroline ligand that pos-
sesses alkyl or aryl substituent at the 2- and 9-positions
display low-energy MLCT transition and weak photolumi-
nescence in the visible region [18,19]. In general, bulky 2-
and 9-substituents of 1,10-phenanthroline ligand can lead
to an increase in emission quantum yield [20]. Although
the photophysical properties of copper(I) phenanthroline
complexes have been extensively studied, related studies
on copper(I) complexes containing bulky phosphine, such
as tricyclohexylphosphine (PCy3) substituted 2,20-bipyri-
dine and 4,40-bipyridine derivatives bridging ligands are elu-
sive [21]. Herein, we successfully designed and obtained four
mono- and binuclear copper(I) complexes in the presence of
6-(4-methoxyl)phenyl-2,20-bipyridine (MeO-CNN) [22]
and/or 4,40-bipyridine derivatives and phosphine ligands,
[Cu(MeO-CNN)2]BF4 (1), [Cu2(MeO-CNN)2(PCy3)2(4,40-
bipy)](BF4)2 Æ 1.5CH2Cl2 (2) (bipy = bipyridine), [Cu2-(MeO-
CNN)2(PCy3)2(bpete)](BF4)2 Æ 4CH2Cl2 (3) (bpete = trans-
1,2-bis(4-pyridyl)ethene) and [Cu2(MeO-CNN)2(PCy3)2-
(4,40-azpy)] (BF4)2 Æ 1.5CH2Cl2 (4) (azpy = azobispyridine).
Their structures, thermal stability and spectroscopic proper-
ties were also investigated.
0.22 mol) was added, and followed by 1 mL of concen-
trated hydrochloric acid (HCl, 37%) [25] The mixture was
refluxed for 2 h. When the solution was warm, it was
diluted by addition of acetone (100 mL), allowed to cool
slowly to room temperature, and kept overnight in the
refrigerator. A white product was collected and washed
with acetone. After dryness for 3 h at 40–50 ꢁC, the prod-
uct was obtained (7.6 g, 62%). Anal. Calc. for
C12H18ClNO2: C, 59.13; H, 7.44; N, 5.75. Found: C,
59.36; H, 7.11; N, 5.56%.
2.2.3. Synthesis of the 6-(4-methoxyphenyl)-2,20-bipyridine
To a mixture of 1-(2-pyridylcarbonylmethyl)pyridinium
iodide (6.50 g, 0.02 mol) and ammonium acetate (10 g) in
ethanol (40 mL), b-(dimethylamino)-40-methoxypropi-
ophenone hydrochloride (4.87 g, 0.02 mol) was added
[26]. The mixture was heated to reflux for 3 h. The dark
green solution was cooled and the green crude product
was filtered, washed with water and cold ethanol. The
product was purified by chromatography on silica gel col-
umn with petroleum spirit–ethyl acetate (5:1) as the eluent.
Yield: 1.5 g (29%). FT-IR (KBr disc): m 2900 (w), 1607 (m),
1582 (s), 1559 (m), 1514 (s), 1453 (s), 1421 (s), 1247 (s),
1
2. Experimental
1022 (m) cmꢀ1. H NMR (400 MHz, CDCl3): d 4.36 (s,
3H), 7.55 (d, J = 8 Hz, 2H), 7.66 (m, 1H), 7.88 (d,
J = 8 Hz, 1H), 8.01 (m, 1H), 8.14 (d, J = 8 Hz, 1H), 8.21
(m, 2H), 8.63 (d, J = 8 Hz, 1H), 8.78 (d, J = 8 Hz, 1H),
8.95 (d, J = 5 Hz, 1H). ESI-MS: m/z 262.31 [M+]. Anal.
Calc. for C17H14N2O: C, 77.84; H, 5.38; N, 10.68. Found:
C, 77.67; H, 5.16; N, 10.38%.
2.1. Materials and reagents
N-(Pyridincarbonylmethyl)pyridinium
iodide
and
[Cu(CH3CN)4]BF4 were prepared according to the pub-
lished literature [23]. 2-Acetyl pyridine (Acros, 98%), tricy-
clohexylphosphine (Acros, 98%), 1,2-bis(4-pyridyl)ethene
(Aldrich, 97%), and 4,40-bipyridine(Acros, 98%) were com-
mercially available and used as purchased without further
purification. All of the solvents obtained from commercial
sources were purified and distilled by standard procedures
prior to use.
2.2.4. Synthesis of the 4,40-azopyridine (4,40-azpy)
4,40-Azopyridine(4,40-azpy) was prepared through the
oxidative coupling of 4-aminopyridine by hypochlorite
according to published procedures [27]. Yield: 80%. Anal.
Calc. for C10H8N4: C, 65.21; H, 4.38; N, 30.42. Found:
C, 65.40; H, 4.53; N, 30.65%.
2.2. Synthesis
2.2.5. Synthesis of [Cu(MeO-CNN)2]BF4
2.2.1. Synthesis of the p-methoxyacetophenone
A mixture of [Cu(CH3CN)4]BF4 (0.157 g, 0.5 mmol) and
L (0.262 g, 1 mmol) in dichloromethane (30 mL) was stir-
red under nitrogen atmosphere at room temperature for
2 h. Then the solvents were removed and the solid residue
was afforded. Recrystallization by slow diffusion of diethyl
ether into a dichloromethane solution yielded dark crystals
suitable for X-ray diffraction. Yield: 0.277 g (82%). 1H
NMR (400 MHz, DMSO-d6): 3.61 (s, 6H, –OMe), 6.32
(s, 4H), 7.31 (s, 4H), 7.66 (m, 4H), 8.02 (t, J = 7.8, 2H),
8.20 (t, J = 7.8, 2H), 8.25 (d, J = 7.8, 2H), 8.46 (d,
J = 7.9, 2H), 8.60 (d, J = 3.1, 2H). Anal. Calc. for
C34H28BCuF4N4O2 (powders): C, 60.50; H, 4.18; N, 8.30.
Found: C, 60.83; H, 4.02; N, 8.19% [22].
To a mixture of anisole (10.8 g, 0.1 mol) and acetic
anhydride (11.3 g, 0.11 mol), iodine (0.50 g, 0.002 mol)
was added. The reaction mixture was heated to reflux for
4 h. The dark brown solution was poured into water
(50 mL) and extracted with diethyl ether (3 · 50 mL). The
diethyl ether solution was washed successively with dilute
sodium carbonate, water and dried over sodium sulfate.
After removal of the solvent and purification of the residue
under vacuum, p-methoxyacetophenone was obtained.
Yield: 10 g (67%), m.p. 36–37 ꢁC, which is comparable to
the value reported (38 ꢁC) [24].
2.2.2. Synthesis of the b-(dimethylamino)-40-
methoxypropiophenone hydrochloride
2.2.6. Synthesis of [Cu2(MeO-CNN)2(PCy3)2(4,40-bipy)]
(BF4)2 Æ 1.5CH2Cl2
To
a solution of p-methoxyacetophenone (7.5 g,
0.05 mol) and dimethylamine hydrochloride (5.27 g,
0.065 mol) in ethanol (20 mL), paraformaldehyde (2.0 g,
Under nitrogen atmosphere, a mixture of L (0.262 g,
1 mmol) and [Cu(CH3CN)4]BF4 (0.315 g, 1 mmol) in

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W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
dichloromethane (30 mL) was stirred at room temperature
for 2 h. Then tricyclohexylphosphine (0.280 g, 1 mmol) in
dichloromethane (5 mL) was dropped to the solution with
stirring followed by the addition of 4,40-bipy (0.078 g,
0.5 mmol). After stirring the resultant solution for
another 12 h, the solvents were removed and the solid res-
idue was obtained. Recrystallization by slow diffusion of
diethyl ether into a dichloromethane solution yielded yel-
low crystals suitable for X-ray diffraction. Yield: 0.602 g
(78%). 1H NMR (400 MHz, DMSO-d6): 1.02–1.14 (m,
32H, Cy), 1.47 (s, 16H, Cy), 1.60 (s, 18H, Cy), 3.83 (s,
6H, –OMe), 7.08 (s, 4H), 7.58 (s, 4H), 7.78 (s, 2H), 7.92
(s, 4H), 8.02 (s, 2H), 8.07 (s, 4H), 8.21 (t, J = 7.6, 4H),
8.46 (s, 2H), 8.57 (d, J = 7.8, 2H), 8.75 (s, 2H). 31P
(DMSO-d6): 17.46. Anal. Calc. for C80H102B2Cu2F8-
N6O2P2 (powders): C, 62.30; H, 6.67; N, 5.45. Found:
C, 62.55; H, 6.73; N, 5.47%.
2.2.8. Synthesis of [Cu2(MeO-CNN)2(PCy3)2(4,40-azpy)]
(BF4)2 Æ 1.5CH2Cl2
The preparation of complex 4 was also similar to that of
complex 2 except that 4,40-bipy was replaced by 4,40-azpy.
The dark red crystals were obtained suitable for X-ray dif-
fraction. Yield: 0.597 g (76%). 1H NMR (400 MHz,
DMSO-d6): 1.01–1.09 (m, 32H, Cy), 1.45 (s, 16H, Cy),
1.57 (s, 18H, Cy), 3.84 (s, 6H, –OMe), 7.10 (d, J = 7.0,
4H), 7.61 (s, 4H), 7.80 (s, 2H), 7.95 (s, 4H), 8.02 (d,
J = 6.4, 2H), 8.10 (d, J = 7.2, 4H), 8.22 (t, J = 7.1, 4H),
8.48 (d, J = 6.7, 2H), 8.57 (d, J = 7.5, 2H), 8.77 (s, 2H).
31P NMR (DMSO-d6): 17.45. Anal. Calc. for
C80H102B2Cu2F8N8O2P2 (powders): C, 61.19; H, 6.55; N,
7.14. Found: C, 61.37; H, 6.67; N, 7.40%.
2.3. Photophysical measurements
UV–Vis absorption spectra were recorded using Hit-
achi U-3010 spectrophotometer. Emission and excitation
spectra were performed with Hitachi F-4500 fluorescence
2.2.7. Synthesis of [Cu2(MeO-CNN)2(PCy3)2(bpete)]
(BF4)2 Æ 4CH2Cl2
1
Complex 3 was prepared in a similar way to complex 2
except that bpete was used in place of 4,40-bipy. The yellow
crystals were obtained suitable for X-ray diffraction. Yield:
spectrometer. H NMR spectra were obtained on a Bru-
ker Avance DPX-400 MHz Resonance Spectrometer.
The EPR spectra were recorded on a Bruker Electron
Spin Resonance Meter ER046 with an X band Microwave
Bridge.
1
0.565 g (72%). H NMR (400 MHz, DMSO-d6): 1.06–1.26
(m, 32H, Cy), 1.59 (s, 34H, Cy), 3.79 (s, 6H, –OMe), 7.02
(s, 4H), 7.52 (d, J = 3.5, 8H), 7.76 (t, 4H), 7.97 (s, 2H),
8.20 (t, 4H), 8.44–8.71 (m, 10H). 31P NMR (DMSO-d6):
18.11. Anal. Calc. for C82H104B2Cu2F8N6O2P2 (powders):
C, 62.80; H, 6.68; N, 5.36. Found: C, 62.57; H, 6.77; N,
5.39%.
2.4. X-ray structure determination
Crystals of complexes 1–4 suitable for X-ray structure
analysis were grown from dichloromethane solution by
Table 1
Summary of X-ray crystallographic data for complexes 1–4
Compound
1
2
3
4
Formula
C
674.95
P21/n
34H28BCuF4N4O2
C81.5H105B2Cl3Cu2F8N6O2P2
1669.70
C86H112B2Cl8Cu2F8N6O2P2
1908.06
C81.5H105B2Cl3 Cu2F8N8O2P2
1697.72
P21/n
monoclinic
9.650(10)
26.49(3)
17.001(19)
90
93.01(2)
90
4341(8)
2
Formula weight
Space group
Crystal system
ꢀ
ꢀ
P1
P1
monoclinic
15.4093(7)
11.5488(4)
17.5000(6)
90
96.514(2)
90
3094.2(2)
4
triclinic
15.050(5)
17.712(7)
18.366(9)
102.052(9)
97.512(10)
94.972(9)
4714(3)
2
triclinic
13.884(5)
14.205(5)
14.766(5)
116.176(5)
98.706(6)
108.948(5)
2318.2(14)
1
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
T (K)
293(2)
1.449
2.12–27.48
0.768
293(2)
1.176
1.92–25.00
0.629
293(2)
1.367
1.67–26.38
0.788
293(2)
1.299
2.25–25.00
0.685
qcalc (g cmꢀ3
h Range (ꢁ)
)
l (mmꢀ1
)
Observed data
7061
16368
9332
7567
Number of parameters
415
0.0467
0.0965
0.748 and ꢀ0.306
1094
0.0786
0.1904
0.800 and ꢀ0.301
617
0.0571
0.1345
0.707 and ꢀ0.422
571
a
R1
wR2
0.0806
0.1811
0.537 and ꢀ0.416
a
Maximum anꢀd3minimum
˚
peaks (e A
)
P
P
P
P
2
2
1=2
a
I > 2r(I), R1 = iFoj ꢀ jFci jFoj, wR2 ¼ f ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF o2Þ ꢁg
.

W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
2761
Table 2
slow diffusion of diethyl ether over the period of several
days. The diffraction data were collected at room temper-
ature with graphite-monochromatized Mo Ka radiation
˚
Selected bond lengths (A) and angles (ꢁ) for 1–4
Complex 1
Cu–N(1)
Cu–N(3)
N(1)–C(7)
N(3)–C(23)
2.042(3)
2.082(3)
1.355(4)
1.355(4)
Cu–N(2)
Cu–N(4)
N(2)–C(12)
N(4)–C(28)
2.040(3)
2.015(3)
1.331(4)
1.354(4)
˚
(k = 0.71073 A) on a Rigaku R-AXIS RAPID IP X-ray
diffractometer. An absorption correction was applied by
correction of symmetry-equivalent reflections using the
ABSCOR program. The structure was solved by direct
methods using the SHELXS-97 program and refined by
full-matrix least-squares on F2 using the SHELXL-97 soft-
ware [28]. The hydrogen atoms were added using ideal
geometries with a fixed C–H bond distance. The relevant
crystallographic data as well as selected bond distances
and angles for complexes 1–4 were listed in Tables 1
and 2, respectively.
N(1)–Cu–N(2)
N(3)–Cu–N(4)
N(1)–Cu–N(4)
N(1)–C(7)–C(4)
81.06(12)
81.57(12)
144.60(11)
118.3(3)
N(1)–Cu–N(3)
N(4)–Cu–N(2)
N(2)–Cu–N(3)
N(1)–C(11)–C(12)
115.74(10)
107.93(12)
136.89(11)
115.6(3)
Complex 2
Cu(1)–N(1)
Cu(1)–N(3)
C(5)–C(6)
2.125(5)
2.054(5)
1.455(9)
1.467(10)
Cu(1)–N(2)
Cu(1)–P(1)
C(10)–C(11)
2.091(5)
2.2058(17)
1.474(9)
C(20)–C(20)*
2.5. Calculational methods
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–P(1)
N(3)–Cu(1)–P(1)
C(23)–P(1)–Cu(1)
C(4)–C(5)–C(6)
N(2)–C(10)–C(11)
100.8(2)
111.72(15)
119.72(14)
116.7(2)
123.0(7)
119.0(6)
N(1)–Cu(1)–N(2)
N(2)–Cu(1)–P(1)
N(2)–Cu(1)–N(3)
N(1)–C(5)–C(6)
C(9)–C(10)–C(11)
C(19)–C(20)–C(20)*
78.5(2)
119.61(14)
115.67(19)
116.4(6)
118.8(7)
122.4(6)
The density functional theory calculation of complex 1
was carried out using the GAUSSIAN-03 suite of programs
[29], at the B3LYP level. The basis set used for C, N, O
and H atoms was 6-31G while effective core potentials with
a LanL2DZ basis set were employed for transition metals.
The contour plots of MOs were obtained with the GAUSS-
IAN-03 view program.
Complex 3
Cu(1)–N(1)
Cu(1)–N(3)
C(5)–C(6)
2.121(4)
2.066(3)
1.445(7)
1.461(5)
Cu(1)–N(2)
Cu(1)–P(1)
C(10)–C(11)
C(23)–C(23)*
2.163(4)
2.2224(12)
1.455(7)
1.301(8)
C(20)–C(23)*
3. Results and discussion
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–P(1)
N(3)–Cu(1)–P(1)
C(24)–P(1)–Cu(1)
C(4)–C(5)–C(6)
N(2)–C(10)–C(11)
100.68(13)
118.89(10)
122.58(10)
111.43(14)
123.3(6)
N(1)–Cu(1)–N(2)
N(2)–Cu(1)–P(1)
N(2)–Cu(1)–N(3)
N(1)–C(5)–C(6)
C(9)–C(10)–C(11)
C(20)–C(23)–C(23)*
78.16(16)
112.50(9)
115.21(13)
117.6(4)
118.8(5)
125.8(5)
3.1. Syntheses of ligand L and complexes
The ligand 6-(4-methoxyl)phenyl-2,20-bipyridine was
firstly synthesized according to a standard Kro¨hnke proce-
dure outlined in Scheme 1, in which the central pyridyl ring
is generated by the condensation of a 1,5-dicarbonyl inter-
mediate (obtained from the Michael reaction of N-(pyridin-
carbonylmethyl)pyridinium iodide and (b-dimethyl)
aminopropio(4-methoxy)phenone) with a large excess of
ammonium acetate [26].
120.5(4)
Complex 4
Cu(1)–N(1)
Cu(1)–N(3)
C(5)–C(6)
N(1)–C(5)
N(4)–N(4)*
2.110(3)
2.071(3)
1.450(6)
1.356(5)
1.242(5)
Cu(1)–N(2)
Cu(1)–P(1)
C(10)–C(11)
C(20)–N(4)
2.120(3)
2.220(2)
1.471(6)
1.439(4)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–P(1)
N(3)–Cu(1)–P(1)
C(23)–P(1)–Cu(1)
C(4)–C(5)–C(6)
99.27(13)
112.54(9)
123.16(9)
113.22(12)
124.8(4)
N(1)–Cu(1)–N(2)
N(2)–Cu(1)–P(1)
N(2)–Cu(1)–N(3)
N(1)–C(5)–C(6)
C(9)–C(10)–C(11)
C(19)–C(20)–N(4)
77.53(13)
119.20(9)
112.74(13)
116.2(3)
121.4(4)
116.4(3)
The reaction of
a dichloromethane solution of
[Cu(CH3CN)4]BF4 and MeO-CNN ligand in a 1:2 molar
ratio under a nitrogen atmosphere afforded mononuclear
complex 1 as a modena solid upon precipitation by diethyl
ether. By introducing tricyclohexylphosphine (PCy3) and a
series of diimine liagnds (4,40-bipy, bpete, and 4,40-azpy) in
N(2)–C(10)–C(11)
C(20)–N(4)–N(4)*
117.9(3)
112.4(4)
MeO
MeO
MeO
HN(CH3)2HCl
(CH2O)n
(CH3CO)2O
I2
N(CH3)2HCl
O
O
CH3COONH4
N
CH3CH2OH
O
N
N
O
N
N
I2
N
OMe
Scheme 1.

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W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
3.2. Crystal structures of complexes 1–4
Single-crystal X-ray analysis shows that the Cu(I) center
of mononuclear complex 1 is in a pseudo-tetrahedral geom-
etry, and the coordinated 2,20-bipyridine fragments of
MeO-CNN ligands are not coplanar with the dihedral
angles of 9.3ꢁ and 22.7ꢁ. The MeO-substituted phenyl rings
are twisted with respect to their bonded pyridine fragments
with torsion angles of 38.1ꢁ and 24.0ꢁ for two MeO-CNN
ligands, respectively. An ORTEP view with atom number-
ing for the cation is illustrated in Fig. 1. The Cu–N bond
˚
˚
lengths vary from 2.015 A to 2.082 A and the N–Cu–N
angles range from 81.06ꢁ to 144.6ꢁ (Tables 1 and 2). Inter-
estingly, interligand p–p stacking interactions in molecule
are observed between the phenyl ring and the pyridyl ring,
˚
resulting in a interplanar separation of 3.5 A. In the space
Fig. 1. Perspective drawing of [Cu(MeO-CNN)2]BF4 (1). The thermal
ellipsoids are drawn at 30% probability.
packing of 1 (Fig. S1), there exist plenty of weak hydrogen
bonds between the O(1) atꢀom of the methoxyl substituent
or F(1) atoms of the BF4 anion and the carbon atoms
of the MeO-CNN ligands, with Cꢂ ꢂ ꢂO and Cꢂ ꢂ ꢂF distances
a similar reaction manner to Cu(MeO-CNN)(CH3CN)2-
BF4, other three dinuclear copper(I) complexes 2–4 were
obtained with subtle structure changes.
˚
about 3.4 A. The relevant hydrogen-bonding distances and
angles are listed in Table (S).
Fig. 2. Perspective drawing of [Cu2(MeO-CNN)2(PCy3)2(4,40-bipy)](BF4)2 Æ 1.5CH2Cl2 (2). The thermal ellipsoids are drawn at 30% probability.
Fig. 3. Perspective drawing of [Cu2(MeO-CNN)2(PCy3)2(bpete)](BF4)2 Æ 4CH2Cl2 (3). The thermal ellipsoids are drawn at 30% probability.

W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
2763
The molecular structures of complexes 2–4 with different
bridging ligands are analogous to each other (Figs. 2–4 and
Tables 1 and 2). Each copper in all three complexes is
ligated to two nitrogen atoms of MeO-CNN, one phospho-
°
°
344.3 C
185.0 C
100
80
60
40
20
0
°
89.33%(260 C)
þ
þ
rus atom of PCy3, forming PCuN2 unit. The two PCuN2
fragments are further linked together into a binuclear form
by 4,40-bipy, bpete and 4,40-azpy for complexes 2–4,
respectively, showing a center of symmetry.
As expected, the phenyl ring is substantially twisted
away from the plane of the bipyridine segment of MeO-
CNN. The coordinated bipyridine fragments of MeO-
CNN in complexes 2–4 are not coplanar having the
dihedral angles of 5.8ꢁ for 2, 16.7ꢁ for 3, and 3.1ꢁ for 4, which
are compared with the torsion angles of 44.8ꢁ for 2, 38.6ꢁ
for 3, and 46.6ꢁ for 4 between the terminal aromatic ring
and its adjacent pyridyl ring. However, the two pyridyl
rings of the kind of bridging bipy ligands (4,40-bipy, bpete,
and 4,40-azpy) in these three complexes are almost copla-
nar. In complex 3, intermolecular C(8)ꢂ ꢂ ꢂC(21) contact of
°
19.77%(394 C)
100
200
300
400
500
°
T/ C
Fig. 5. TG curve of complex 2 in N2.
˚
3.387 A at pyridyl rings of MeO-CNN and bridging bpete
intermediate stages of decomposition were readily assigned
for these complexes. For 1 the results of TGA showed an
initial mass loss corresponding to the loss of MeO-CNN
ligands. This loss process at about 360–500 ꢁC leads to
the residue in accordance to a stoichiometry of CuBF4.
Complexes 2–4 are stable to air and moisture, but the
two-step weight loss for the complexes were observed, in
which the primary formation of intermediate (MeO-
CNN)Cu(PCy3)BF4, commencing at 185–260 ꢁC, is fol-
lowed by the subsequent formation of CuBF4 at about
344–394 ꢁC (Fig. 5). According to the above results, com-
plex 1 seems to have a higher thermal stability than com-
plexes 2–4, which also agrees well with their structural
characters that the Cu–N distances of the copper center
coordinated to two chelating MeO-CNN ligands in 1 are
significantly shorter than those of complexes 2–4 contain-
ing bridging 4,40-bipyridine derivatives.
ligands in different molecules is indicative of two pyridyl
rings of MeO-CNN ligand having larger torsion. The cop-
per center lies closer to the nitrogen atom of the bridging
˚
ligand (average bond distance at 2.064 (4) A) than it does
to those nitrogen atoms from the chelating MeO-CNN
˚
ligand (average bond distance at 2.122 (4) A). The intramo-
lecular Cu(I)ꢂ ꢂ ꢂCu(I) separations among the complexes 2–4
˚
˚
˚
are 11.194 A, 12.436 A and 13.130 A, respectively. Further-
more, similar weak hydrogen-bonding interactions to com-
plexꢀ1 are also found between the fluorine atoms of the
BF4 anion and the carbon atoms from the MeO-CNN
ligands, but the relevant Cꢂ ꢂ ꢂF distances are relatively clo-
ser than that in complex 1 (the details are listed in Table (S)
and Figs. S2–S4).
3.3. Thermogravimetric analysis
The powder samples of complexes 1–4 without solvents
were analysed using a TGA apparatus under 20 mL minꢀ1
flowing nitrogen (Figs. S5–S7). The temperature was
ramped at a rate of 20 ꢁC minꢀ1 from 40 to 500 ꢁC. The
3.4. Absorption and emission spectra
The electronic absorption spectra for complexes 1–4 all
include a series of high-energy intraligand transition and
Fig. 4. Perspective drawing of [Cu2(MeO-CNN)2(PCy3)2(4,40-azpy)](BF4)2 Æ 1.5CH2Cl2 (4). The thermal ellipsoids are drawn at 30% probability.

2764
W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
8
7
2
0.6
0.4
0.2
0.0
2
1.5
1.0
0.5
0.0
6
1
X5
1
X10
X10
5
4
4
X10
4
3
3
400
450
500
550
600
650
700
3
2
1
0
Wavelength (nm)
250
300
350
400
450
500
500
550
600
650
700
750
800
850
Wavelength (nm)
Wavelength (nm)
Fig. 6. The electronic absorption spectra of [Cu(MeO-CNN)2]BF4 (1)
(solid line), [Cu2(MeO-CNN)2(PCy3)2(4,40-bipy)](BF4)2 Æ 1.5CH2Cl2 (2)
(dash line), [Cu2(MeO-CNN)2(PCy3)2(bpete)](BF4)2 Æ 4CH2Cl2 (3) (dash
dot line), and [Cu2(MeO-CNN)2(PCy3)2(4,40-azpy)](BF4)2 Æ 1.5CH2Cl2 (4)
(dot line) in dichloromethane solution at room temperature. Inset: long
wavelength region of the electronic absorption spectra of 1–4.
Fig. 8. Room-temperature solid-state emission spectra of [Cu2(MeO-
CNN)2(PCy3)2(4,40-bipy)](BF4)2 Æ 1.5CH2Cl2 (2) (solid line) [Cu2(MeO-
CNN)2(PCy3)2(bpete)](BF4)2 Æ 4CH2Cl2 (3) (dash dot line) upon excitation
at 420 nm.
unoccupied molecular orbital (LUMO) together with the
orbital energies, are showed in the contour plots in
Fig. 7. The character of the HOMO is dominated by the
d orbital of Cu, whereas the LUMO is mainly localized
on the pyridyl rings and displays p* character. The calcula-
tions HOMO–LUMO gap 2.92 eV (425 nm) is essentially
consistent with the experimental results described as
MLCT character.
Compared with complex 2, complex 3 represents typical
spectral changes (bpete) with a shoulder peak at 312 nm,
while the characteristic spectrum (4,40-azpy) of complex 4
is not observed due to the absorption overlapping. Upon
excitation at 420 nm, complexes 2 and 3 exhibit weak pho-
toluminescence with kmax at 620 nm (i = 0.17 ls) and
660 nm (i = 0.23 ls) in the solid state at room temperature,
respectively (Fig. 8). The emission spectra of complexes 2
and 3 are extremely similar, whereas there is no significant
emission observed in the same measuring conditions for
complexes 1 and 4. With reference to the previous work,
the red emissions are assigned to the MLCT triple excited
state [1]. All complexes are non-emissive in dichlorometh-
ane or acetonitrile solutions
low-energy charge-transfer absorption (Fig. 6). Each of
these complexes shows an intense and broad band at kmax
425–550 nm, which tails beyond 650 nm in dichlorometh-
ane solution at room temperature. The intense absorptions
at kmax < 340 nm are assigned to intraligand (IL p ! p*)
transitions, which can be compared with the absorptions
of the free ligands. The low-energy absorption bands at
425 and 550 nm for the complexes are characteristic for
MLCT transition [1,30]. The density functional theory cal-
culation of complex 1 was performed to interpret the elec-
tronic character of absorption spectra. The relevant
highest-occupied molecular orbital (HOMO) and lowest-
3.5. Photoinduced electron-transfer
We observed photoinduced electron transfer reactions
of the Cu(I) complexes in dichloromethane solution at
ambient temperature, whereas no noticeable reaction was
found in pure CH3CN or (CH3)2SO solution. EPR spectra
for complexes 1–4 were recorded upon an excitation of
355 nm at 298 K in degassed dichloromethane solution.
As shown in Fig. 9, upon irradiation, the characteristic
intensity of the EPR signals at 3200–3400 G were clearly
observed in complexes 1 and 2 with methylviologen
(MV2+), indicating the formation of copper(II) species in
dichloromethane solution [31,32]. Similar EPR results have
been also found for complexes 3–4 in dichloromethane
Fig. 7. Contour plots and orbital energies of the HOMO and LUMO for
[Cu(MeO-CNN)2]BF4.

W.-F. Fu et al. / Inorganica Chimica Acta 360 (2007) 2758–2766
2765
reveal a formation of such copper(II)–halide complexes
upon excitation at 355 nm in dichloromethane solution.
a
b
Acknowledgments
The work was supported by the State Key Project (No.
2005CCA06800), the National Natural Science Founda-
tion of China (NSFC Grant Nos. 50463001 and
20671094) and Virtual Laboratory for Computational
Chemistry, CNIC, CAS. We thank the foundation
(50418010) for NSFC/RGC Joint Research.
Appendix A. Supplementary material
CCDC 615571, 615572, 615573 and 615574 contain the
supplementary crystallographic data for 1, 2, 3 and 4.
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. Supplementary data asso-
ciated with this article can be found, in the online version,
at doi:10.1016/j.ica.2007.02.007.
c
2800
3000
3200
3400
3600
3800
H (Gauss)
Fig. 9. EPR spectra of [Cu(MeOCNN)2]BF4 with methylviologen (a),
[Cu2(MeOCNN)2(PCy3)2(bipy)](BF4)2 with methylviologen (b) and
[Cu2(MeOCNN)2(PCy3)2(bipy)](BF4)2 (c) upon excitation at 355 nm at
298 K in dichloromethane solution.
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