Synthesis, characterization and crystal structure of Iridium(III)bis(2-p- tolyl-benzothiazolato-N,C2)(acetylacetonate)

Article abstract of DOI:10.1007/s10870-008-9452-5

A novel thiazole-based iridium (III) complex (iridium(III)bis(2-p-tolyl- benzothiazolato-N,C²)(acetylacetonate)) has been prepared and fully characterized by EA, IR, ¹H-NMR and MS. The molecular structure of the complex has been dete

Full text of DOI:10.1007/s10870-008-9452-5

J Chem Crystallogr (2009) 39:241–245
DOI 10.1007/s10870-008-9452-5
ORIGINAL PAPER
Synthesis, Characterization and Crystal Structure
of Iridium(III)bis(2-p-tolyl-benzothiazolato-N,C2)
(acetylacetonate)
Lianqing Chen Æ Xingyu Qu
Received: 5 September 2006 / Accepted: 10 July 2008 / Published online: 16 October 2008
Ó Springer Science+Business Media, LLC 2008
Abstract A novel thiazole-based iridium (III) complex
(iridium(III)bis(2-p-tolyl-benzothiazolato-N,C2)(acetylace-
tonate)) has been prepared and fully characterized by EA,
IR, 1H-NMR and MS. The molecular structure of the
complex has been determined by single crystal X-ray dif-
fraction analysis. The iridium (III) center adopts a distorted
octahedral geometry with cis-O–O, cis-C–C, and trans-N–
N chelate disposition. The complex crystallizes in the
orthorhombic Pbca space group with cell parameters a =
the heterocyclic ligands [3]. The emission frequency of the
iridium complexes can usually be tuned by the introduction
of different heterocyclic ligands [4]. However, there is very
little work to study iridium (III) complexes with thiazole-
based heterocyclic ligands [5].
Herein we report the synthesis, characterization and
crystal structure analysis of a novel thiazole-based iridium
(III) complex (iridium(III)bis(2-p-tolyl-benzothiazolato-
N,C2)(acetylacetonate)). The absorption and emission
spectra of this complex will be presented.
˚
˚
˚
10.1388(7) A, b = 18.3565(12) A, c = 31.021(2) A,
a = b = c = 90 ° and Z = 8. The electronic absorption and
emission spectra of this complex have been investigated.
Experimental
Keywords Iridium complex Á Iridium(III)bis
(2-p-tolyl-benzothiazolato-N,C2)(acetylacetonate) Á
Crystal structure Á Photophysical properties
General Information
The reactions and manipulations involving iridium (III)
complexes were carried out under argon atmosphere.
Chemicals were used without further purification unless
otherwise stated. Elemental analysis of carbon, hydrogen,
and nitrogen was performed on a Carlorerba-1106 micro-
analyzer. Infrared spectra were obtained on a Nicolet SX
Fourier transform spectrometer. Mass Spectra (FAB-MS)
was determined by VJ-ZAB-3F Mass Spectrometer. 1H
NMR spectra were recorded on Varian Mercury VX-
300 MHz spectrometer. UV–Vis absorption spectra were
recorded on Schimadzu 160A UV–Vis recording spectro-
photometer. PL spectra were performed on Perkin-Elmer
LS 55 luminescence spectrophotometer.
Introduction
Recently the long lived excited state and highly efficient
solid-state emissions of d6 and d8 metal complexes have
made them of interest as potential components in organic
light emitting diodes (OLEDs) [1]. Especially, the iridium
(III) complexes with cyclometalated ligands show intense
phosphorescence at room temperature and behavior as very
promising phosphor dye in OLEDs [2].
Generally, both the luminescent efficiency and emission
wavelength of iridium complexes are greatly affected by
Synthesis of 2-p-tolyl-benzothiazole (TBT)
L. Chen (&) Á X. Qu
Key Laboratory of Catalysis and Materials Science of the State
Ethnic Affairs Commission & Ministry of Education,
South-Central University for Nationalities,
Wuhan 430074, China
2-Aminothiophenol (1.25 g, 10 mmol) and 4-methyl-
benzaldehyde (1.20 g, 10 mmol) were dissolved to
20 mL of DMSO under argon atmosphere. The mixture
e-mail: lqchen@mail.scuec.edu.cn
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J Chem Crystallogr (2009) 39:241–245
was heated at 200 °C for 0.5 h. After cooling, the
solution was poured into ice water, and then adjusted the
solution to pH 8–9 with 1 N NaHCO3 solution. The
precipitate was filtered, washed with a great deal of
water several times. After dried under vacuum, the crude
product was recrystallized with ethanol. White crystal,
parameters were determined from a least-squares fit of
4977 carefully centred reflections (2.62° \ 2h \ 56.56°).
Heavy-atom method was employed to locate Ir atom and
the remaining non-hydrogen atoms were refined by full-
matrix least squares on F2 using SHELXL-97 program [7].
An empirical absorption correction using the program
SADABS [8] was applied. All non-hydrogen atoms were
described with anisotropic thermal parameters. Hydrogen
atoms were introduced at calculated positions. All figures
were prepared using the program ORTEP-3 for windows
[9]. A summary of the refinement details for the complex
are given in Table 1.
1
yield: 89%. H NMR (CDCl3, 300 MHz) d: 8.02 (d, J =
8.1 Hz, 1H), 7.95 (d, J = 8.1 Hz, 2H), 7.85 (d, J =
8.1 Hz, 1H), 7.45 (t, J = 7.5 Hz, 1H), 7.33 (t,
J = 7.2 Hz, 1H) 7.26 (d, J = 8.1 Hz, 2H), 2.42 (s, 3H).
mp = 85–86 °C. Anal.Calcd for C14H11NS: C, 74.63; H,
4.92; N, 6.22. Found: C, 74.55; H, 4.87; N, 6.24%. MS
(FAB): m/e, 225 (M?).
Results and Discussion
Synthesis of Ir(III) Complexes
Synthesis and Characterization
Cyclometalated chloride-bridged dimer: iridium trichloride
hydrate (0.352 g, 1.0 mmol), combined with 2-p-tolyl-
benzothiazole (0.563 g, 2.5 mmol), were dissolved in a
mixture of 2-ethoxyethanol (30 mL) and water (10 mL),
and then refluxed for 24 h. The solution was cooled to
room temperature, and the resulting orange red precipitate
was collected on by filtration and washed with water and
ethanol. After dried, the crude product was directly used
for next step without further purification [6].
Iridium(III)bis(2-p-tolyl-benzothiazolato-N,C2)(acetyl-
acetonate) Ir(TBT)2(acac): 0.1 mmol of chloride-bridged
dimer, 0.25 mmol of acetylacetone and 1.0 mmol anhydrous
sodium carbonate were dissolved in 2-ethoxyethanol. The
solution was refluxed under argon for 15 h. After cooling to
room temperature, small quantity water was added. The
resulting orange precipitate was collected by filtration,
washed with water, ethanol and hexane, and dried in vacuum.
The crude product was purified by column chromatography
on silica gel with CH2Cl2/petroleum ether (1:1–1:3) as elu-
ent. Orange powders, yield: 88%. IR (KBr, cm-1): 3030,
2987, 1720, 1604, 1503, 852. 1H NMR (CDCl3, 300 MHz): d
(ppm) 8.02 (m, 2H), 7.86 (m, 2H), 7.54 (d, J = 7.5 Hz, 2H),
7.39 (m, J = 4.5 Hz, 4H), 6.65 (d, J = 7.8 Hz, 2H), 6.20 (s,
2H), 5.09 (s, 1H), 2.01 (s, 6H), 1.74 (s, 6H). Anal. Calcd for
C33H27O2N2S2Ir: C, 53.57; H, 3.79; N, 3.68. Found: C,
53.53; H, 3.74; N, 3.65%. MS (FAB): m/e, 740 (M?).
The synthetic route of the complex was outlined in
Scheme 1. The heterocyclic ligand was prepared by the
Table 1 Crystal data and structure refinement for Ir(TBT)2(acac)
complex
Empirical formula
CCDC deposit no
Color/shape
Formula weight
Crystal system
space group
a
C33H27O2N2S2Ir
CCDC-271360
Orange, block
739.89
Orthorhombic
Pbca
˚
10.1388(7) A
˚
18.3565(12) A
b
˚
31.021(2) A
c
a = b = c
Volume
90°
5773.4(7) A
3
˚
Z
8
Calculated density
Temperature
Wavelength (Mo-Ka)
Theta range
Limiting indices
1.702 Mg/m3
293(2) K
˚
0.71073 A
1.31° \ h \ 28.00°
-13 B h B 9, -23 B k B 24,
-39 B l B 40
Crystal size
0.20 9 0.20 9 0.06 mm
4.803 mm-1
Absorption coefficient
F(000)
2,912
X-ray Crystallography Analysis
Completeness to h = 28.28
Reflections collected/unique
Goodness-of-fit on F2
Final R indices [I [ 2sigma(I)]
R indices (F2)
99.2%
39,926/6,923 [R(int) = 0.0841]
An orange-red crystal of Ir(TBT)2(acac) (dimensions
0.20 9 0.20 9 0.06 mm3) suitable for X-ray diffraction
studies was mounted in inert oil on a glass fiber for the cell
determination, and data was collected using a Bruker
SMART CCD detector diffractometer with graphite-mono
1.191
R1 = 0.0658a, wR2 = 0.1248b
R1 = 0.1006a, wR2 = 0.1413b
P
P
a
R1 = [|Fo|-|Fc|]/ |Fo|
P
P
b
˚
wR2 = { [w(Fo2 - Fc2)]/ (wFo2)}1/2
chromatic Mo Ka (0.71073 A) radiation. The unit cell
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J Chem Crystallogr (2009) 39:241–245
243
Scheme 1 Synthesis of
Ir(TBT)2(acac) complex
NH2
SH
O
S
DMSO
HC
CH3
CH3
CH3
200°C
N
CH3
CH3
CH3
O
O
Cl
Cl
C5H8O2
Na2CO3
Ir
Ir
IrCl33H2O
Ir
N
S
S
N
S
N
S
N
2
2
2
cyclomerization reaction of o-aminobenzenethiol with 4-
methylbenzaldehyde. Cyclometalated Ir (III) l-chloro-
bridged dimer was synthesized by iridium trichloride
hydrate with heterocyclic ligands according to the similar
method reported by Nonoyama [10]. The chloride-bridged
diiridium complex can be converted to mononuclear irid-
ium complexes by replacing the two bridging chlorides
with bidentate monoanionic acetylacetone ligand in high
yield.
chemical shift in the aromatic region appears at 6.20 ppm,
assigned for the proton ortho to the metalated carbon atom.
The chemical shift for –CH– moiety in acac ancillary ligand
is 5.09 ppm, which is similar to other analogues [5].
˚
Table 2 Selected bond lengths (A) and angles (°) for Ir(TBT)2(acac)
complex
˚
Bond lengths (A)
Bond angles (°)
Elemental analysis of the complex is consistent with the
expected formulation of their structures. The mass spectra of
complex give corresponding molecular ion peak at 740. In
addition, the mass spectra all show a peak at 641 for the
Ir(1)–C(6)
Ir(1)–C(20)
Ir(1)–N(1)
Ir(1)–N(2)
Ir(1)–O(1)
Ir(1)–O(2)
O(1)–C(30)
O(2)–C(32)
1.998(8)
1.998(7)
2.053(6)
2.053(6)
2.163(5)
2.139(5)
1.272(9)
1.296(10)
C(6)–Ir(1)–C(20)
C(6)–Ir(1)–N(2)
C(20)–Ir(1)–N(2)
C(6)–Ir(1)–N(1)
C(20)–Ir(1)–N(1)
N(2)–Ir(1)–N(1)
C(6)–Ir(1)–O(2)
C(20)–Ir(1)–O(2)
N(2)–Ir(1)–O(2)
N(1)–Ir(1)–O(2)
C(6)–Ir(1)–O(1)
O(2)–Ir(1)–O(1)
92.1(3)
95.6(3)
80.3(3)
80.4(3)
95.1(3)
173.9(2)
87.5(3)
179.0(3)
98.8(2)
85.7(2)
175.2(3)
87.7(2)
1
complex, which arises from the Ir(TBT)2 fragment. The
FIT-IR spectrum (KBr) of this complex exhibits a sharp
intense absorption peaks at 1,720 cm-1 are corresponding to
the stretch vibration of C=O group, which belongs to the
1
characteristic absorption bonds of ketone group. H-NMR
spectrum shows well-resolved multiplets for the cyclometa-
lated ligand parts of the complex. The maximum high-field
1.0
0.8
0.6
0.4
0.2
PL
UV-vis
0.0
200
300
400
500
600
700
Wavelength(nm)
Fig. 1 ORTEP diagram of Ir(TBT)2(acac) with the thermal ellip-
soids representing at 30% probability level. Hydrogen atoms are
omitted for clarity
Fig. 2 Absorption and PL spectra of Ir(TBT)2(acac) complex in
CH2Cl2 solution at 298 K
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J Chem Crystallogr (2009) 39:241–245
Table 3 Photophysical data for Ir(TBT)2(acac) complex
Complex
kmax Abs(loge) nm
kmax Em (nm)
Ufc (%)
solutiona
Filmb
Solutiona
Filmb
Ir(TBT)2(acac)
245(3.9), 335(4.0), 412(3.2)
449(3.2), 479(3.1), 534(2.3)
256, 339, 398
450, 483, 535
555, 586
558, 590
39.6
a
In CH2Cl2 solution at 298 K
b
c
In PMMA film (5% weight ratio)
Quantum yield was measured in CH2Cl2 solution relative to quinine bisulfate (10-5 M in 1.0 N H2SO4)
Crystal Structure of Ir(TBT)2(acac)
UV-light at ambient temperature. As shown in Fig. 2, the
complex displays a broad emission at 555 nm, which has
good fluorescence quantum yield, and large Stoke’s shifts
(Table 3). The vibronic fine structures in the PL spectra
imply that the emissions result predominantly from the
Single crystal of Ir(TBT)2(acac) suitable for X-ray dif-
fraction studies was obtained by slow diffusion of
diethylether to a dilute dichloromethane solution of the
complex. The ORTEP drawing of Ir(TBT)2(acac) is
3
ligand-based p–p* transitions [12].
˚
shown in Fig. 1. The selected bond lengths (A) and angles
(deg) are collected in Table 2.
In general, the iridium (III) center adopts a distorted
octahedral geometry with cis-O–O, cis-C–C, and trans-N–
N chelate disposition. The bond distances of Ir-C (1.998(8),
˚
1.998(7) A) are shorter than the Ir–N bond distances
˚
(2.053(6), 2.053(6) A). These values are very similar to
Conclusions
In summary, we have presented the synthesis and detailed
characterization of a novel thiazole-based iridium (III)
complex (iridium(III)bis(2-p-tolyl-benzothiazolato-N,C2)
(acetylacetonate)) based on analytical, spectrometric,
spectroscopic and X-ray diffraction methods. The elec-
tronic absorption and emission spectra of this complex
have been investigated. This provides some clue to design
and develop new phosphorescent materials.
those in the analogous complexes reported [11]. The Ir–O
˚
˚
bond distances of 2.163(5) A for O(1) and 2.139(5) A for
O(2) indicate a slight structural trans effect of the phenyl
groups, while the similarity of O(1)–C(30) and O(2)–C(32)
bond lengths indicate that the -1 charge of the acetylace-
tone is delocalized over both oxygen atoms. The C–Ir–C
angle for the complex is 92.1(3)° and the N–Ir–N angle is
173.9(2)°, which are almost equal to the idealized value and
well accorded with their cis-C–C and trans-N–N disposi-
tions, respectively. The acac chelate results in O(1)–Ir(1)–
O(2) bond angle of 87.7(2)° appreciably less than the ide-
alized 90° value. The benzothiazole and phenyl moieties in
the same cyclometalated ligand are approximately coplanar.
Supplementary Material
CCDC-271360 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.
html (or from the Cambridge Crystallographic Data Centre
(CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax:
?44 (0)1223–336033; email: deposit@ccdc.cam.ac.uk).
Absorption and Photoluminescent Spectra
Acknowledgments We are grateful for financial support from the
National Natural Science Foundation of China (Project Nos.
20702064) and Natural Science Foundation of South-Central Uni-
versity for Nationalities (grant Nos. YZZ07007).
Figure 2 shows the absorption and emission spectra of
complex Ir(TBT)2(acac) in CH2Cl2 solution. As shown in
Fig. 2, intense absorptions between 250 and 350 nm can be
assigned to the spin allowed p–p* transitions from cyclo-
metalated ligands. The weaker absorption bands in the
range of 350–450 nm were clearly resolved, ascribing to a
spin-allowed metal-to-ligand charge transfer (1MLCT)
transition. The long tail extended to lower energies (in the
range of 420–550 nm) can be likely associated with both
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