Synthesis, photoluminescence and electrochemical properties of a series of carbazole-functionalized ligands and their silver(I) complexes

Article abstract of DOI:10.1016/j.ica.2006.10.043

A series of carbazole-functionalized carboxylate ligands (N-carbazolylacetic acid (L1), 4-carbazol-9-yl-benzoic acid (L2), and 3-(4-carbazol-9-yl-phenyl)-acrylic acid (L3)) and their corresponding silver complexes were designed and synthesized and the str

Full text of DOI:10.1016/j.ica.2006.10.043

Inorganica Chimica Acta 360 (2007) 2083–2091
www.elsevier.com/locate/ica
Synthesis, photoluminescence and electrochemical properties of a
series of carbazole-functionalized ligands and their silver(I) complexes
a,
a
a
a
a,b,
*
Jie-Ying Wu *, Yue-Li Pan , Xuan-Jun Zhang , Tao Sun , Yu-Peng Tian
,
a
c
Jia-Xiang Yang , Zhong-Ning Chen
a
Department of Chemistry, Anhui University, Hefei, Anhui 230039, China
State Key Laboratory of Coordination Chemistry, Nanjing University, China
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, China
b
c
Received 18 May 2006; received in revised form 28 October 2006; accepted 28 October 2006
Available online 17 November 2006
Abstract
A series of carbazole-functionalized carboxylate ligands (N-carbazolylacetic acid (L1), 4-carbazol-9-yl-benzoic acid (L2), and 3-(4-car-
bazol-9-yl-phenyl)-acrylic acid (L3)) and their corresponding silver complexes were designed and synthesized and the structures were
determined by single crystal X-ray diffractions. The silver atoms in the complexes are in tetrahedral geometry coordinated with two oxy-
gen from carboxylic and two phosphorous atoms from triphenylphosphine. The complexes exhibit excellent electrochemical characters in
solution and strong photoluminescence in the solid state. The emission wavelengths of the compounds can be tuned (from ultraviolet to
visible region) by introducing of the second coordinating ligand triphenylphosphine and by elongation of the conjugation moieties.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Coordination; Crystal structure; Carbazole; Photoluminescence; Ligand
1. Introduction
troluminescence (EL) materials containing carbazole group
have been used in light emitting diodes (LEDs) devices [8,9],
most of which are pure organic compounds or polymers. We
have previously demonstrated that hybrids materials with
new emissions and enhanced thermal stability were obtained
by introducing carbazole group and second ligand such as
1,10-phenanthroline or triphenylphosphine into coordina-
tion complexes [10]. In those work, ethanoic acid group
was combined with carbazole group (Scheme 1, (L1)). The
introduce of carboxylate groups is because of it’s rich bind-
ing modes with metal ions, which can lead to complexes with
versatile molecular structures. However, the emission wave-
lengths are less than 400 nm due to the relatively little conju-
gation moiety. In this work, two new ligands (L2 and L3)
with relatively longer conjugation moieties and their corre-
sponding silver complexes emitting in the visible region have
been synthesized and characterized by single crystal X-ray
diffraction. Herein, we report the design, synthesis, crystal
structure, optical and electrochemical properties of these
three ligands and corresponding silver complexes.
Luminescent coordination compounds have been an
active research area for decades because of their various
potential applications in material science, such as electrolu-
minescent display and chemical sensors [1–4]. By carefully
selecting the organic and inorganic components new or
enhanced phenomena can arise [5]. For example, by chang-
ing metal ions or introducing second coordinating ligand,
hybrids with enhanced emissions, tunable emission wave-
lengths, or enhanced thermo stabilities can be obtained [6].
Carbazole compounds are well known to exhibit good
hole transporting properties and their charge transfer (CT)
complexes can create free carriers in the visible region
through the photocarrier generation process [7]. Several elec-
*
Corresponding authors. Address: Department of Chemistry, Anhui
University, Hefei, Anhui 230039, China. Fax: +86 551 5107342 (Y.-P.
Tian).
E-mail addresses: jywu1957@163.com (J.-Y. Wu), yptian@ahu.edu.cn
(Y.-P. Tian).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.10.043

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J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
Scheme 1.
2. Experimental
(8.40 g, 50 mmol), fresh potassium tert-butoxide (5.60 g,
50 m mol) and anhydrous dmf (200 mL) were mixed in a
flask fitted with a magnetic stirrer and condenser. The mix-
ture was heated at 110 ꢁC for 0.5 h, 4-fluorobenzaldehyde
(6.20 g, 50 mmol) was added dropwise into it with stirring
for 36 h. The mixture was cooled to room temperature, and
poured into ice water. After 30 min of stirring, the mixture
was filtered, and evaporated. The crude residue was re-
crystallized by acetone/water (10:1). Pale yellow powder
was obtained (9.49 g, 70%). Mp 163 ꢁC. Anal. Calc. for
C19H13ON: C, 84.13; H, 4.80; N, 5.17. Found: C, 84.40;
H, 4.77; N, 5.12%. IR (KBr, pellet, cmꢀ1) 3419 (s), 3056
(w), 1597 (s), 1509 (m), 1480 (w), 1448 (s), 1360 (m), 1337
(m), 1220 (m), 1158 (m), 1125 (m), 830 (m) 753 (s). UV–
Vis (dmf solution). k/nm (loge): 265.5 (4.13), 292.0 (4.35),
326.2 (3.70), 341.1 (3.40).
2.1. Materials
All chemicals and solvents were dried and purified by
usual methods. The ligand N-carbazolylacetic acid (L1)
was synthesized by the method as we had reported [10].
Elemental analyses were performed with a Perkin–Elmer
240 instrument. IR spectra were recorded with a Nicolet
FT-IR 170SX instrument (KBr discs) in the 4000–
400 cmꢀ1 region. UV–Vis spectra were recorded with a
UV-265 spectrophotometer and corrected by subtracting
solvent backgrounds. TGA analyses were recorded with a
Perkin–Elmer Pris-1 DMDA-V1 analyzer in a atmosphere
of nitrogen at a heating rate of 5 ꢁC minꢀ1. The lumines-
cence spectra were recorded on a Perkin–Elmer LS50B
spectrofluorimeter. Electrospray mass spectra (ES-MS)
were determined with a Finnigan LCQ mass spectrograph;
3.2. 4-Carbazol-9-yl-benzoic acid (L2)
the concentration of the samples was about 1.0 mmol Lꢀ1
.
The diluted solution was electrosprayed at a flow rate of
5 · 10ꢀ6 L minꢀ1 with a needle voltage of 4.5 kV. The
mobile phase was an aqueous solution of methanol (1:1,
v/v). The samples were run in the positive-ion mode.
Cyclic voltammograms were obtained on an EG&G
PAR 283 potentiostat at 20 ꢁC, using acetonitrile as solvent
for the ligands and DMF for complexes, 0.1 M Bu4NClO4
as supporting electrolyte. The potentials were referred to
an Ag–AgCl electrode separated from the solution by a
medium-porosity fritted disk. A platinum-wire auxiliary
electrode was used in conjunction with a platinum-disk-
working electrode cyclic voltammograms of a freshly pre-
pared (1 mM) solution of all compounds in solution
recorded at 0.05 V sꢀ1 in the ꢀ1.5 to 2.0 V range, and the
values of compounds and a measured potentials were after-
ward referred to Ag–AgCl.
4-Carbazol-9-ylbenzaldehyde (2.71 g, 10 mmol), H2O2
(11.32 mL) and NaOH (0.4 g, 10 mmol) were solved in
the mixed solvent of dioxane (5 mL), the mixture was stir-
red at 0 ꢁC for 2 h, then was heated to reflux overnight and
filtered. The filtration was adjusted to pH = 2 with HCl
solution, filtered again. The crude residue was re-crystal-
lized in acetone/water (5:1) and dried in vacuum. Yield
was 71% (2.04 g). Anal. Calc. for C19H13O2N: C, 79.14;
H, 4.38; N, 4.69. Found: C, 79.44; H, 4.53; N, 4.87%.
ES-MS, m/z 286.3. IR (KBr, pellet, cmꢀ1) 3450 (s), 3076
(w), 1687 (s), 1600 (s), 1524 (m), 1483 (w), 1448 (s), 1421
(s), 1356 (m), 1287 (s), 1222 (m), 1165 (m), 1127 (w), 753
(s). UV–Vis (dmf solution). k/nm (loge): 265.5 (4.21),
292.0 (4.48), 326.2 (3.90), 341.1 (3.71). Weight loss at:
330 ꢁC.
3.3. 3-(4-Carbazol-9-yl-phenyl)-acrylic acid (L3)
3. Preparations
4-Carbazol-9-ylbenzaldehyde (2.71 g, 10 mmol), malonic
acid malonic acid (2.16 g, 0.03 mol), in pyridine were mixed
with four drops of piperidine. The reaction was stirred at
90 ꢁC for 2 h, followed by adjustment of pH = 2 with HCl
solution. A yellow crude product was obtained and re-crys-
3.1. 4-Carbazol-9-ylbenzaldehyde (a)
The compound was prepared by modification of the pre-
viously reported method in a high yield [11]. Carbazole

J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
2085
tallized with toluene and dried in vacuum. Yield was 95%
(2.97 g). Anal. Calc. for C21H15O2N: C, 80.51; H, 4.791; N,
4.47. Found: C, 80.43; H, 4.8; N, 4.50%. ES-MS, m/z
312.0. IR (KBr, pellet, cmꢀ1) 3449 (s), 3056 (w), 1686 (s),
1628 (s), 1599 (s), 1514 (s), 1449 (s), 1424 (m), 1361 (w),
1313 (m), 1223 (s), 1169 (m), 753 (s). UV–Vis (dmf solution).
k/nm (loge): 265.5 (4.83), 292.0 (4.65), 326.2 (3.70), 341.1
(3.40). Weight loss at: 344 ꢁC.
AgL1: N-Carbazolylacetic acid (0.45 g, 2 mmol) was
added into a solution of NaOH (0.08 g, 2 mmol) in water
(80 mL). The mixture was stirred for 30 min and filtered.
To the filtration silver nitrate (0.34 g, 2 mmol) in water
(10 mL) was added with vigorous stirring. The white pre-
cipitate was filtered and washed exhaustively with water
and ethanol and air-dried. Yield was 92% (0.66 g). Anal.
Calc. for AgC14H10O2N: C, 50.60; H, 3.01; N, 4.22. Found:
C, 50.42; H, 2.95; N 4.11%.
AgL2: To a solution of NaOH (0.08 g, 2 mmol) in water
(10 mL), 2 (0.58 g, 2 mmol) was added, the mixture was
stirred for 30 min and filtered. To the filtration silver
nitrate (0.34 g, 2 mmol) in water (10 mL) was added with
vigorous stirring. The white precipitate was filtered and
washed exhaustively with water and ethanol and air-dried.
Yield was 90% (0.71 g). Anal. Calc. for AgC19H12O2N: C,
57.87; H, 3.05; N, 3.55. Found: C, 57.65; H, 3.12; N, 3.73%.
AgL3: Acid 3 (0.63 g, 2 mmol) in ethanol (10 mL) was
added to a solution of NaOH (0.08 g, 2 mmol) in ethanol
(10 mL), the mixture was stirred for 30 min and filtered.
To the filtration silver nitrate (0.34 g, 2 mmol) in ethanol
(10 mL) was added with vigorous stirring. The white pre-
cipitate was filtered and washed exhaustively with water
and ethanol and air-dried. Yield was 87% (0.73 g). Anal.
Calc. for AgC21H14O2N: C, 60.24; H, 3.33; N, 3.33. Found:
C, 60.00; H, 3.31; N, 3.45%.
ture was heated to 100 ꢁC for 10 min. A colorless solution
was filtered and stood at room temperature. After 10 h col-
orless crystals were formed. Yield was 78% (0.67 g). Anal.
Calc. for AgC50H40O2NP2: C, 70.09; H, 4.67; N, 1.64.
Found: C, 69.82; H, 4.92; N, 1.58%. IR (KBr, pellet,
cmꢀ1) 3076 (w), 1581 (s), 1481 (m), 1462 (m), 1429 (s),
1385 (m), 1350 (m), 1304 (w), 1261 (w), 1097 (m), 744 (s).
UV–Vis (dmf solution). k/nm (loge): 265.5 (4.03), 292.0
(4.25), 326.2 (3.53), 341.1 (3.27). Weight loss at 271 ꢁC.
Complex 5: To a solution of AgL2 (0.39 g, 1 mmol) in dmf
(10 mL) PPh3 (0.52 g, 2 mmol) was added. The mixture was
heated to 100 ꢁC for 10 min and then a colorless solution
appeared, which was filtered and stood at room temperature.
After 10 h colorless crystals were formed. Yield was 82%
(0.75 g). Anal. Calc. for AgC55H42O2NP2: C, 71.90; H,
4.58; N, 1.53. Found: C, 71.87; H, 4.54; N, 1.55%. IR
(KBr, pellet, cmꢀ1) 3076 (w), 1637 (m), 1591 (m), 1537 (s),
1516 (m), 1450 (m), 1381 (s), 1168 (m), 742 (s). UV–Vis
(dmf solution). k/nm (loge): 265.1 (4.49), 290.3 (4.63),
323.0 (3.46), 339.5 (3.76). Weight loss at 280 ꢁC.
Complex 6: To a solution of AgL3 (0.42 g, 1 mmol) in
dmf (10 mL) PPh3 (0.52 g, 2 mmol) was added. The mixture
was heated to 100 ꢁC for 10 min, a colorless solution
appeared, which was filtered and stood at room tempera-
ture. After 8 h colorless crystals were formed. Yield was
90% (0.85 g). Anal. Calc. for AgC57H44O2NP2: C, 72.46;
H, 4.66; N, 1.48. Found: C, 72.31; H, 4.70; N, 1.51%. IR
(KBr, pellet, cmꢀ1) 3076 (w), 1632 (m), 1593 (s), 1539 (m),
1483 (m), 1439 (m), 1379 (s), 1165 (m), 1099 (w), 742 (s).
UV–Vis (dmf solution). k/nm (loge): 271.4 (4.91), 295.3
(4.83), 322.0 (3.95), 338.5 (3.73). Weight loss at 286 ꢁC.
3.4. X-ray crystal structure determinations
Complex 4: To a solution of AgL1 (0.33 g, 1 mmol) in
dmf (10 mL), PPh3 (0.52 g, 2 mmol) was added. The mix-
The crystallographic data for ligands and their silver
complexes were collected on a Bruker Smart 1000 CCD
Table 1
The crystal data and parameters of the ligands and complexes
Compounds
L2
L3
4
5
6
Formula
C
19H13NO2
C28H23NO2
405.47
monoclinic
P21/c
8.555(4)
34.440(15)
7.884(4)
90
104.282(8)
90
2251.1(17)
4
C50H40AgNO2P2
856.64
triclinic
C55H42AgNO2P2
918.71
triclinic
C57H44AgNO2P2
944.74
triclinic
Formula weight
Crystal system
Space group
287.30
monoclinic
P21/c
5.0955(5)
24.613(2)
11.5320(11)
90
90.818(2)
90
1446.1(2)
4
ꢀ
ꢀ
ꢀ
P1
P1
P1
˚
a (A)
12.3268(2)
13.6246(2)
14.2818(3)
110.873(1)
91.914(1)
110.198(1)
2069.63(6)
2
10.638(2)
11.818(2)
18.712(3)
79.261(4)
89.388(4)
80.157(3)
2276.8(7)
2
10.502(8)
13.226(10)
17.198(13)
96.072(11)
93.687(12)
98.614(11)
2341(3)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
l (mmꢀ1
)
0.086
1.320
600
0.075
1.196
856
0.605
1.375
880
0.555
1.340
944
0.542
1.340
972
Dcalc (g cmꢀ3
F(000)
)
Unique reflections
2482
3950
7941
7933
8178
Reflections observed
4264
11394
12741
12019
12350
R
Rw
0.0666
0.1455
0.172, ꢀ0.258
0.0627
0.1429
0.239, ꢀ0.173
0.0589
0.1516
1.271, ꢀ2.312
0.0265
0.0663
0.333, ꢀ0.196
0.0379
0.0596
0.493, ꢀ0.320
ꢀ3
˚
Dqmax,min (e A
)

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J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
Table 2
8.2 ppm, which are characters of carbazolyl ring. The
chemical shift above 10 ppm is a character of –COOH.
Thermogravimetric analysis (TGA) was used to study
the thermal stabilities of the five compounds on the powder
sample. All the compounds display high thermal stability
since there was no weight loss below the temperature of
250 ꢁC.
˚
Selected bond distances (A) and angles (ꢁ) for the six compounds
Compound 2
O(1)–C(17)
O(2)–C(17)
C(22)–N(1)–C(14)
C(32)–N(1)–C(14)
C(15)–C(14)–N(1)
1.274(4)
1.261(4)
125.9(3)
125.8(3)
119.0(3)
N(1)–C(22)
N(1)–C(32)
C(13)–C(14)–N(1)
O(2)–C(17)–O(1)
O(2)–C(17)–C(11)
1.403(4)
1.407(4)
120.9(3)
122.9(3)
119.2(3)
The main absorption peaks in the IR spectra of the six
compounds are given in synthetic section. The difference
between mas(COO) and ms(COO) (Dm) of the complexes com-
pared to the corresponding carboxylates is currently
employed to determine the coordination mode of carboxyl-
ate group [13,14]. The frequency differences between the
asymmetric COO stretching and the symmetric stretching
are 196 cmꢀ1, 210 cmꢀ1 and 214 cmꢀ1 for (4), (5) and (6),
respectively. It suggests that the carboxylate group in the
three complexes is coordinated to a silver atom via a biden-
tate mode, which agree well with the crystal structures
analysis. For all of the three ligands, there is a shift of their
stretching band towards lower frequency after the carbox-
ylic group bonding to the metal ion.
Compound 3
O(2)–C(1)
O(1)–C(1)
O(2)–C(1)–O(1)
O(1)–C(1)–C(2)
C(2)–C(3)–C(4)
1.256(4)
1.265(4)
123.1(3)
117.8(3)
128.5(3)
N(1)–C(10)
N(1)–C(21)
O(2)–C(1)–C(2)
C(3)–C(2)–C(1)
C(8)–C(7)–N(1)
1.403(4)
1.380(4)
119.1(3)
123.4(3)
119.6(3)
Compound 4
Ag(1)–O(2)
O(1)–C(37)
P(2)–Ag(1)–O(2)
P(2)–Ag(1)–O(1)
O(1)–C(37)–O(2)
C(37)–O(1)–Ag(1)
2.419(3)
Ag(1)–O(1)
O(2)–C(37)
O(2)–Ag(1)–P(1)
P(1)–Ag(1)–O(1)
O(2)–Ag(1)–O(1)
C(37)–O(2)–Ag(1)
2.448(3)
1.215(5)
109.20(8)
119.49(8)
126.2(4)
89.8(3)
1.265(5)
115.18(8)
105.99(8)
54.06(9)
90.0(2)
Compound 5
Ag(1)–O(1)
O(1)–C(1)
2.421(15)
1.256(2)
Ag(1)–O(2)
O(2)–C(1)
2.490(14)
1.255(2)
O(1)–Ag(1)–P(1)
O(1)–Ag(1)–P(2)
O(2)–C(1)–O(1)
C(1)–O(1)–Ag(1)
105.51(5)
117.08(5)
123.63(18)
92.96(12)
P(2)–Ag(1)–O(2)
P(1)–Ag(1)–O(2)
O(1)–Ag(1)–O(2)
C(1)–O(2)–Ag(1)
109.69(4)
112.92(4)
53.55(5)
4.2. Crystal structural description
In ligand L1, carbazolyl ring and –COO were linked
though –CH2– group. Ligand L2 (Fig. 1) has an extended
p-delocalization through phenyl group. In ligand L3
(Fig. 2) the p-delocalization was further extended through
a phenylethylene group. There are p–p stacking interac-
tions in crystal of L2. The centroid-centroid distance
89.81(11)
Compound 6
Ag(1)–O(2)
O(2)–C(1)
P(1)–Ag(1)–O(1)
O(1)–Ag(1)–P(2)
O(1)–C(1)–O(2)
C(1)–O(1)–Ag(1)
2.400(2)
1.258(3)
117.10(5)
110.90(5)
123.6(2)
Ag(1)–O(1)
O(1)–C(1)
O(2)–Ag(1)–P(2)
O(2)–Ag(1)–P(1)
O(2)–Ag(1)–O(1)
C(1)–O(2)–Ag(1)
2.440(2)
1.247(3)
112.29(7)
121.96(7)
54.25(6)
˚
between the carbazolyl rings is 3.679 A. A classical O-
90.13(16)
91.71(16)
Hꢁ ꢁ ꢁO hydrogen bond [O(1)–H(1 A)ꢁ ꢁ ꢁO(2)a 2.6233 A,
˚
172.66ꢁ; symmetry code: 1 ꢀ x, 1 ꢀ y, 1 ꢀ z] exists between
neighboring carboxylic acid. In the crystal of L3, O–Hꢁ ꢁ ꢁO
area detector diffractometer. Equipped with Mo Ka
(k = 0.71073 A) radiation using w-scan mode. Empirical
a
˚
˚
hydrogen bonds [O(1)–H(1 A)ꢁ ꢁ ꢁO(2) 2.6473 A, 166.28ꢁ;
absorption correction was applied to the data. The struc-
tures were solved by direct methods and refined by full-
matrix least-squares methods on F [2]. All non-hydrogen
atoms were located from the trial structure and then refined
anisotropically. All hydrogen atoms were generated in ide-
alized positions. All calculations were performed with the
SHELXL-97 programs [12]. Other relevant parameters of
the crystal structure are listed in Table 1. Selected bond
lengths and angles are given in Table 2. CCDC reference
numbers 245219–245223. See http://www.rsc.org/supp-
data/nj/b2/b203334h/ for crystallographic data in CIF or
other electronic format.
symmetry code: ꢀx, ꢀy, 3 ꢀ z also exists between neigh-
boring carboxylic acid. The two carboxylic groups from
are connected by hydrogen bonds to form dimer unit.
In the crystals of the complex 4, 5 and 6 (Fig. 3), each
Ag(I) atoms are in a distorted tetrahedral AgO2P2 environ-
ments coordinated by two oxygen atoms from one ligand
and phosphorus atoms from two different PPh3, respec-
tively. Each carboxylate ligand adopts bidentate chelating
coordination mode. Upon closer examination of the struc-
tures, none of the ligands are planar. The average dihedral
angles between the carbazolyl ring planes and the N-
replacement plane are 79.1ꢁ, 46.1ꢁ and 54.4ꢁ for L1–L3;
67.3ꢁ, 59.9ꢁ and 67.0ꢁ for 4–6, respectively. In complex 4,
the C(37)–O(1) bond length and C(37)–O(2) bond length
4. Results and discussion
˚
are 1.2155 and 1.2655 A, respectively. The O(1)–Ag(1)–
4.1. Synthesis and characterization
P(1) and O(2)–Ag(1)–P(2) bond angles are 105.99ꢁ and
109.21ꢁ, respectively, indicating a slight distorted tetrahe-
dral coordination environment. C37, O1, O2 and Ag1
atoms are almost in one plane (the largest deviation:
The three ligands were prepared in high yields. The
structures of L2, L3 and three silver complexes 4, 5, and
1
˚
6 have been confirmed by H NMR, IR spectra and ele-
0.0017 A) that forms a dihedral angle of 81.3ꢁ with the
1
mental analyses. The H NMR spectra of compounds L2
carbazole ring. In complex 5, the C(1)–O(1) bond length
˚
and L3 display well resolved peaks, ranging from 7.3 to
and C(1)–O(2) bond length is 1.2562 and 1.2552 A, respec-

J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
2087
Fig. 1. Molecular structure of L2.
Fig. 2. Molecular structure of L3. Solvent molecules have been omitted.
˚
tively, which is slightly shorter than 1.2614 and 1.2744 A of
the C–O bond length in corresponding ligand L2. The
O(1)–Ag(1)–P(1) and O(2)–Ag(1)–P(2) bond angles are
105.51ꢁ and 109.69ꢁ, respectively, indicating a slight distor-
tion. All of the coordination environments were summa-
rized in Table 3. Although the formation of a four-
member Ag–O–C–O ring, with the high angular strains
involved, is not expected to be energetically favorable, this
type of structure is more stable than the one in which carb-
oxylato group adopts monodentate mode with three bulky
triphenylphosphine ligands to complete four-coordination
geometry of the Ag(I) ion.
There are a number of C–Hꢁ ꢁ ꢁO interactions in com-
plexes 4–6. In complex 4, there is a weak interaction
between the carboxyl O(1) and H(18) on a adjacent PPh3
˚
ring (C(18)–O(1) 3.432(1) A, 149.72ꢁ) and a slightly stron-
ger interaction between the carboxyl O(2) and H(38) on a
˚
adjacent vinyl chain (C(18)–O(1) 3.377 A, 164.23ꢁ). As
well, there is a interaction between the carboxyl O(2) and
H(40) on the adjacent carbazolyl ring (C(40)–O(2)

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J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
Table 3
Structural comparison of the ligands and their complexes
Compounds \P–Ag–P \AgO2 Dihedral \CO2(ꢁ) Ag–O
C@O
˚
(ꢁ)
(ꢁ)
angle (ꢁ)
(CO2/
(A)
C–O
˚
Dd (A)
carbazol)
1
79.1
46.1
54.4
125.1
122.9
117.8
1.193(3)
1.323(3)
0.13
2
1.261(4)
1.274(4)
0.013
3
1.256(4)
1.265(4)
0.009
4/Da
5/Da
6/Da
129.37
132.08
121.59
54.06
53.55
54.25
67.3/11.8 126.2
2.419(3) 1.215(5)
2.448(3) 1.265(5)
0.05
59.9/
ꢀ13.8
123.63 2.421(1) 1.255(2)
2.490(14) 1.256(2)
0.001
67/ꢀ12.6 123.6
2.400
2.440
1.247(3)
1.258(3)
0.011
Da: Dihedral angle change comparing with its free ligand.
Dd: Differences of the bond lengths between C@O and C–O bond in
carboxylato group.
4.4. Solution photoluminescence
The single-photon fluorescence spectra for the ligands
and their complexes were measured in different solvents.
The emission maxima at k = 352, 388 and 416 nm for
L1–L3 and 353, 389 and 514 nm for 4–6 in dmf, respec-
tively. There is a distinct red shift (36 nm) of the emission
energy from compound L1 to L2, and there is a ca.
64 nm red shift from L1 to L3, which is due to the extended
conjugation of the molecules. This phenomenon also exists
in the corresponding complexes. As well, the fluorescent
spectra of all the ligands and complexes show sensitivity
to the polarity of the environments. The PL intensity is
weak in acetonitrile compared with those in other solvents.
In The represent fluorescent peak at 370–390 nm in hexane,
Fig. 3. ORTEP drawing of the complex 4, 5, and 6. The thermal ellipsoids
are drawn at the 50% probability.
˚
3.291(8) A, 171.97ꢁ). In complex 5 and 6, there are also a
number of C–Hꢁ ꢁ ꢁO interactions forming supramolecules.
4.3. UV–Vis absorbance
UV–Vis absorbance spectra was shown in Fig. 4. All of
the compounds show similar peak position but the com-
plexes showed relatively stronger absorbance than the
ligands.
Fig. 4. UV–Vis spectra of ligands 1–3 and complexes 4–6 in DMF.

J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
2089
the least polar solvent. However, there were two peaks in
DMF, chloroform, and ethyl acetate ranging from 330 to
370 nm and 450 to 500 nm, respectively. The long wave-
length emissions were probably resulted from exciplex
between these compounds with solvents. The excitation
spectra of 6 in different solvents and PL spectra with differ-
ent concentrations were shown in Fig. 5.
4.5. Solid state photoluminescence
The fluorescent emission spectrum of six compounds
were also measured in the solid state at room temperature.
The maximum emission peaks for ligands L1–L3 are at ca.
423, 460 and 465 nm, respectively (Fig. 6). For lumines-
cence of compound 4, two peaks of emissions are shown
in Fig. 7. The maximum is at 377 nm, which can be
assigned to the intraligand p–p charge transfer similarly
to the emission of carbazole in dmf solution. The other
emission is at 418 nm with a shoulder at 439 nm, which
can be assigned to the excimeric emissions due to the weak
ligand–ligand interactions between the molecules in solid
state. For the luminescence of 5, the emission of 377 nm
disappears due to the delocalization of the benzene ring
and carbazole group. Excimeric emissions at 412 and
Fig. 5. The PL and excitation spectra of complex 6: (a) PL in different
solvents, (b) excitation spectra in different solvents, (c) PL spectra in DMF
with different concentrations.
Fig. 7. Emission spectra of 4–6 in the solid state at room temperature.
10
0
-10
c
-20
b
-30
a
-40
2.0
1.8
1.6
1.4
1.2
1.0
0.8
E(V)
Fig. 6. The emission spectra of L1–L3 in solid state at room temperature.
Fig. 8. Cyclic voltammograms for (a) ligand L1; (b) ligand L2; (c) ligand L3.

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J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
435 nm were also observed. The luminescence of 6 is simi-
lar to that of 5, with some red shifts due to further elonga-
tion of the delocalization.
conjugation of these ligands. Different oxidation wave of
ligand L2 in different time are shown in Fig. 9. The oxida-
tion route can be explained in Scheme 2, which indicates
that the cation radical is unstable and produce dicarbazyl
easily. The site 1 and site 8 carbons are somewhat sterically
hindered due to the rather rigid structure of the N-substi-
tuted derivatives. Therefore, the formation of 1,10-dica-
rbazyl from resonance form C seems unlikely and in fact,
has not been observed. The 3,30-dicarbazyl is more easily
oxidized than before and loses two electrons (anodic peak
at 1.50 V) to yield a moderately stable dication with exten-
sive conjugation.
The reason of shift from L1 to L3 and 4 to 6 is similar to
the solution fluorescence spectra. Here, we observed that
the emission spectra of the complexes are remarkable
blue-shifted compared to corresponding free ligands. This
is reasonable according to their crystal structures. In these
complexes, the two bulky PPh3 ligands with six benzene
rings almost perpendicular to one another significantly
decrease the symmetry of the molecule. The strong emis-
sion at short wavelength is caused by the energy increase
resulting from the symmetry decrease of 4, 5 and 6 com-
pared to the free ligand and the high angular strain of
the four-number chelating ring [10].
The cyclic voltammogram of the three complexes in
DMF are similar and are related with the carbazole and
Table 4
4.6. Electrochemical studies
The oxidation–reduction peak data for 4–6
Compound
Ag(I) ! Ag(II)
Ag(II) ! Ag(I)
Ag(I) ! Ag(0)
The cyclic voltammogram of the ligands in MeCN was
shown in Fig. 8. The initial oxidation wave of the three
ligands is at +1.39, 1.36 and 1.31 V for ligand L1 to ligand
L3, respectively, which appears to be the formation of cat-
ion radicals. The different oxidation wave is related to the
(v)
(v)
(v)
4
5
6
0.232
0.155
0.218
ꢀ0.452
ꢀ0.300
ꢀ0.316
ꢀ0.926
ꢀ1.009
ꢀ0.968
10
0
-10
b
-20
-30
-40
d
e
-50
2.0
1.8
1.6
1.4
E(v)
1.2
1.0
0.8
Fig. 9. Cyclic voltammograms for ligand L2 (b), 10 min later (d), 30 min
later (e) in CH3CN/Bu4NClO4/Pt vs. SCE at 20 ꢁC, scan rate =
Fig. 10. Cyclic voltammogram for complex 4 in dmf/Bu4NClO4/Pt vs.
SCE at 20 ꢁC, scan rate = 50 mV sꢀ1
.
50 mV sꢀ1
.
B
C
A
-1e
6
3
+1e
N
R
N
R
N
R
8
1
N
R
D
+
2H
2B
D
N
R
N
R
-2e
N
R
N
R
Scheme 2. Oxidation process of the ligands.

J.-Y. Wu et al. / Inorganica Chimica Acta 360 (2007) 2083–2091
2091
COOꢀ groups (Table 4). The cyclic voltammogram
References
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This work was supported by a grant for the National Nat-
ure Science Foundation of China (50532030, 50335050, and
50325311). Team for Scientific Innovation Foundation of
Anhui Province (2006KJ007TD). Doctoral Program Foun-
dation of the Ministry of Education of China.