Synthesis and characterization of luminescent zinc(II) and cadmium(II) complexes with N,S-chelating schiff base ligands

Article abstract of DOI:10.1021/ic7020758

The reactions of zinc(II) acetate with a variety of 2-substituted benzothiazolines afforded tetrahedral mononuclear complexes with a N ₂S₂ donor set, [Zn(R-Ph-C(H)=N-C₆H ₄-S)₂]. The obtained zinc(II) complexes can be divided into three groups based on the characteristics of the absorption spectra; Group 1 (R = 2,4,6-triMe (1), 2,6-diCl (2)) showing an intense band at 250-300 nm and a weak band at 400-450 nm, Group 2 (R = 4-Cl (3), H (4), 4-Et (5), 4-OMe (6)) showing two intense bands at 250-300 nm and a weak band at 400-450 nm, and Group 3 (R = 4-NMe₂ (7), 4-NEt₂ (8)) showing an intense band at 250-300 nm and two very intense bands at 350-450 nm. The Group 2 and Group 3 complexes exhibited a strong emission on irradiating with ultraviolet light while the Group 1 complexes were not emissive at room temperature. However, all the zinc(II) complexes were luminescent in CH₂Cl₂/toluene glass at 77 K, and their emission peak energies were found to correlate with the Hammett constant of the substituent at para position of a pendent phenyl ring in each complex. Similar reactions of cadmium(II) acetate with 2-substituted benzothiazolines were also carried out to synthesize corresponding cadmium(II) complexes. While [Cd(R-Ph-C(H)=N-C₆H₄-S)₂] (R = 2,4,6-triMe (9)) with bulky substituents at ortho positions of a pendent phenyl ring had a tetrahedral mononuclear structure, other cadmium(II) complexes [Cd₂(R-Ph-C(H)=N-C₆H₄-S)₄] (R = 4-Et (10), 4-OMe (11), 4-NMe₂ (12)) possessed S-bridged dinuclear structures. These cadmium(II) complexes, which are assumed to have a mononuclear structure in solution, showed photophysical properties similar to those of the corresponding zinc(II) complexes.

Full text of DOI:10.1021/ic7020758

Inorg. Chem. 2008, 47, 3095-3104
Synthesis and Characterization of Luminescent Zinc(II) and Cadmium(II)
Complexes with N,S-Chelating Schiff Base Ligands
Tatsuya Kawamoto,*,† Masato Nishiwaki,† Yasutaka Tsunekawa,‡ Koichi Nozaki,‡ and Takumi Konno†
Department of Chemistry, Graduate School of Science, Osaka UniVersity, 1-16 Machikaneyama,
Toyonaka, Osaka 560-0043, Japan, and Department of Chemistry, Graduate School of Science
and Engineering, UniVersity of Toyama, 3190 Gofuku, Toyama, Toyama 930-8555, Japan
Received October 19, 2007
The reactions of zinc(II) acetate with a variety of 2-substituted benzothiazolines afforded tetrahedral mononuclear
complexes with a N2S2 donor set, [Zn(RsPhsC(H)dNsC6H4sS)2]. The obtained zinc(II) complexes can be divided
into three groups based on the characteristics of the absorption spectra; Group 1 (R ) 2,4,6-triMe (1), 2,6-diCl (2))
showing an intense band at 250-300 nm and a weak band at 400-450 nm, Group 2 (R ) 4-Cl (3), H (4), 4-Et
(5), 4-OMe (6)) showing two intense bands at 250-300 nm and a weak band at 400-450 nm, and Group 3 (R
) 4-NMe2 (7), 4-NEt2 (8)) showing an intense band at 250-300 nm and two very intense bands at 350-450 nm.
The Group 2 and Group 3 complexes exhibited a strong emission on irradiating with ultraviolet light while the
Group 1 complexes were not emissive at room temperature. However, all the zinc(II) complexes were luminescent
in CH2Cl2/toluene glass at 77 K, and their emission peak energies were found to correlate with the Hammett
constant of the substituent at para position of a pendent phenyl ring in each complex. Similar reactions of cadmium(II)
acetate with 2-substituted benzothiazolines were also carried out to synthesize corresponding cadmium(II) complexes.
While [Cd(RsPhsC(H)dNsC6H4sS)2] (R ) 2,4,6-triMe (9)) with bulky substituents at ortho positions of a pendent
phenyl ring had a tetrahedral mononuclear structure, other cadmium(II) complexes [Cd2(RsPhsC(H)dNsC6H4sS)4]
(R ) 4-Et (10), 4-OMe (11), 4-NMe2 (12)) possessed S-bridged dinuclear structures. These cadmium(II) complexes,
which are assumed to have a mononuclear structure in solution, showed photophysical properties similar to those
of the corresponding zinc(II) complexes.
Introduction
this report, some Schiff base zinc(II) complexes with N2O2
donor sets have been prepared to elucidate their photophysi-
Since the success of the application of tris(8-hydroxy-
quinolinato)aluminum(III) (Alq3) as an organic light-emitting
diode,1 photoluminescent metal complexes with appropriate
organic ligands have received considerable attention as
emitting materials.2,3 Previously, it has been reported that
zinc(II) complexes with Schiff bases type chelating ligands
can be used as an effective emitting layer.4 Motivated by
(3) (a) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.;
Kwong, R.; Tsyba, I.; Bortz, M.; Mui, B.; Bau, R.; Thompson, M. E.
Inorg. Chem. 2001, 40, 1704. (b) Lamansky, S.; Djurovich, P.;
Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.; Adachi, C.; Burrows, P. E.;
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(c) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.;
Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc.
2003, 125, 7377. (d) Tokito, S.; Iijima, T.; Tsuzuki, T.; Sato, F. Appl.
Phy. Lett. 2003, 83, 2459. (e) Tsuboyama, A.; Takiguchi, T.; Okada,
S.; Osawa, M.; Hoshino, M.; Ueno, K. Dalton Trans. 2004, 1115. (f)
Coppo, P.; Plummer, E. A.; De Cola, L. Chem. Commun. 2004, 1774.
(g) Kapturkiewicz, A.; Chen, T.-M.; Laskar, I. R.; Nowacki, J.
Electrochem. Commun. 2004, 6, 827. (h) Laskar, I. R.; Chen, T.-M.
Chem. Mater. 2004, 16, 111. (i) Polson, M.; Fracasso, S.; Bertolasi,
V.; Ravaglia, M.; Scandola, F. Inorg. Chem. 2004, 43, 1950. (j) Polson,
M.; Ravaglia, M.; Fracasso, S.; Garavelli, M.; Scandola, F. Inorg.
Chem. 2005, 44, 1282. (k) Hwang, F.-M.; Chen, H.-Y.; Chen, P.-S.;
Liu, C.-S.; Chi, Y.; Shu, C.-F.; Wu, F.-I.; Chou, P.-T.; Peng, S.-M.;
Lee, G.-H. Inorg. Chem. 2005, 44, 1344. (l) Li, J.; Djurovich, P. I.;
Alleyne, B. D.; Yousufuddin, M.; Ho, N. N.; Thomas, J. C.; Peter,
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* To whom correspondence should be addressed. E-mail: kaw@
ch.wani.osaka-u.ac.jp.
†
Osaka University.
University of Toyama.
‡
(1) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
(2) (a) Hopkins, T. A.; Meerholz, K.; Shaheen, S.; Anderson, M. L.;
Schmidt, A.; Kippelen, B.; Padias, A. B.; Hall, H. K., Jr.; Peygham-
barian, N.; Armstrong, N. R. Chem. Mater. 1996, 8, 344. (b) Sapochak,
L. S.; Padmaperuma, A.; Washton, N.; Endrino, F.; Schmett, G. T.;
Marshall, J.; Fogarty, D.; Burrows, P. E.; Forrest, S. R. J. Am. Chem.
Soc. 2001, 123, 6300. (c) Wang, J.; Wang, R.; Yang, J.; Zheng, Z.;
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10.1021/ic7020758 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 8, 2008 3095
Published on Web 03/18/2008

Kawamoto et al.
Scheme 1
cal properties.5 In addition, it has also been shown that
zinc(II) complexes with benzothiazoles, which are oxidized
forms of benzothiazolines, are luminescent.6 On the other
hand, the luminescent properties of zinc(II) complexes
containing N,S-chelating Schiff base ligands derived from
benzothiazolines have not been investigated so far; neverthe-
less, several molecular structures of analogous zinc(II)
complexes have been reported.7 As part of our work on
transition metal complexes derived from 2-substituted ben-
zothiazolines,8 we now investigated the reactions of zinc(II)
ion or cadmium(II) ion with a variety of 2-substituted
benzothiazolines. The present paper reports the synthesis,
characterization, and photophysical properties of Schiff base
zinc(II) and cadmium(II) complexes with a N2S2 donor set
obtained by these reactions.
Results and Discussion
Synthesis. Benzothiazolines were prepared from 2-ami-
nobenzenethiol and appropriate aldehydes according to the
9
1
general procedures and characterized by IR and H NMR
spectroscopies and elemental analyses. The zinc(II) com-
plexes 1-8 and cadmium(II) complexes 9-12 were obtained
by treating the corresponding benzothiazolines with zinc(II)
acetate dihydrate or cadmium(II) acetate dihydrate (Scheme
1
1). These complexes were also characterized by IR and H
NMR spectroscopies, along with X-ray crystallography for
1, 5, 6, 7, 9, and 12, and the purity of these complexes was
confirmed by elemental analyses.
It was shown by single-crystal X-ray analyses (vide infra)
that the zinc(II) complexes 1 (R ) 2,4,6-triMe), 5 (R ) 4-Et),
6 (R ) 4-OMe), and 7 (R ) 4-NMe2) have a mononuclear
structure. As anticipated from the structures, these zinc(II)
complexes, together with the other zinc(II) complexes 2 (R
) 2,6-diCl), 3 (R ) 4-Cl), 4 (R ) H), and 8 (R ) 4-NEt2),
exhibited a well-defined single set of signals in the 1H NMR
spectra. On the other hand, the cadmium(II) complexes 9
(R ) 2,4,6-triMe) and 12 (R ) 4-NMe2) were determined
to have mononuclear and dinuclear structures, respectively,
based on X-ray analyses. In addition, it was assumed that
the other cadmium(II) complexes 10 (R ) 4-Et) and 11 (R
) 4-OMe), which have a substituent at the para position of
a pendent phenyl ring, as does 12 (R ) 4-NMe2), also adopt
(4) Hamada, Y.; Sano, T.; Fujita, M.; Fujii, T.; Nishio, Y.; Shibata, K.
Jpn. J. Appl. Phys. 1993, 32, L511.
(5) (a) Mizukami, S.; Houjou, H.; Nagawa, Y.; Kanesato, M. Chem.
Commun. 2003, 1148. (b) Chang, K.-H.; Huang, C.-C.; Liu, Y.-H.;
Hu, Y.-H.; Chou, P.-T.; Lin, Y.-C. Dalton Trans. 2004, 1731. (c) Yu,
T.; Su, W.; Li, W.; Hong, Z.; Hua, R.; Li, M.; Chu, B.; Li, B.; Zhang,
Z.; Hu, Z. Z. Inorg. Chim. Acta 2006, 359, 2246. (d) Lin, H.-C.; Huang,
C.-C.; Shi, C.-H.; Liao, Y.-H.; Chen, C.-C.; Lin, Y.-C.; Liu, Y.-H.
Dalton Trans. 2007, 781.
(6) (a) Hamada, Y.; Sano, T.; Fujii, H.; Nishio, Y.; Takahashi, H.; Shibata,
K. Jpn. J. Appl. Phys. 1996, 35, L1339. (b) Sano, T.; Nishio, Y.;
Hamada, Y.; Takahashi, H.; Usuki, T.; Shibata, K. J. Mater. Chem.
2000, 10, 157. (c) Yu, G.; Yin, S.; Liu, Y.; Shuai, Z.; Zhu, D. J. Am.
Chem. Soc. 2003, 125, 14816.
1
(7) (a) Castro, J.; Romero, J.; García-Vázquez, J. A.; Durán, M. L.;
Castiñeiras, A.; Sousa, A.; Fenton, D. E. J. Chem. Soc., Dalton Trans.
1990, 3255. (b) Brand, U.; Vahrenkamp, H. Chem. Ber. 1995, 128,
787. (c) Brand, U.; Burth, R.; Vahrenkamp, H. Inorg. Chem. 1996,
35, 1083. (d) Öztürk, S.; Ide, S.; Öztas¸, S. G.; Ancın, N.; Tüzün, M.;
Fun, H. K. Z. Kristallogr. 1999, 214, 763.
a dinuclear structure (vide infra). The H NMR spectra of
10, 11, and 12, as well as the spectrum of 9, showed only a
single set of signals, indicative of the equivalence of each
(8) (a) Kawamoto, T.; Nagasawa, I.; Kuma, H.; Kushi, Y. Inorg. Chem.
1996, 35, 2427. (b) Kawamoto, T.; Kuma, H.; Kushi, Y. Bull. Chem.
Soc. Jpn. 1997, 70, 1599. (c) Kawamoto, T.; Ohkoshi, N.; Nagasawa,
I.; Kuma, H.; Kushi, Y. Chem. Lett. 1997, 553. (d) Kawamoto, T.;
Fujimura, Y.; Konno, T. Chem. Lett. 2003, 32, 1058.
(9) (a) Goetz, F. J. J. Heterocycl. Chem. 1968, 5, 509. (b) Palmer, P. J.;
Trigg, R. B.; Warrington, J. V. J. Med. Chem. 1971, 14, 248. (c)
Chikashita, H.; Miyazaki, M.; Itoh, K. J. Chem. Soc., Perkin Trans.
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1988, 29, 5427.
3096 Inorganic Chemistry, Vol. 47, No. 8, 2008

Luminescent Zinc(II) and Cadmium(II) Complexes
Table 1. Crystallographic Data For 1, 5, 6, 7, 9, and 12
1
5
6
7
9
12
empirical formula
Mr
C32H32N2S2Zn
574.09
C30H28N2S2Zn
546.03
C28H24N2O2S4Zn
549.98
C30H30N4S2Zn
576.07
C32H32CdN2S2
621.12
C60H60Cd2N8S4
1246.20
cryst syst
space group
monoclinic
C2/c
monoclinic
P21/c
monoclinic
P21/c
orthorhombic
P212121
triclinic
P1
orthorhombic
Pbca
j
a, Å
b, Å
c, Å
9.568(3)
13.364(6)
22.457(8)
14.080(6)
13.612(6)
14.469(6)
12.908(4)
13.639(3)
14.250(5)
14.198(6)
15.037(8)
13.609(10)
8.370(6)
11.298(6)
16.018(11)
90.462(19)
101.04(2)
109.05(2)
1401.1(16)
2
16.531(4)
11.279(3)
29.569(8)
R, °
ꢀ, °
97.787(14)
108.554(14)
98.004(13)
γ, °
V, Å3
2845.0(18)
4
2629.1(19)
4
2484.2(12)
4
2905(3)
4
5513(3)
4
Z
F(000)
1200
1.340
1.034
13820
1136
1.380
1.115
22811
1136
1.471
1.186
23338
1200
1.317
1.014
3727
636
1.472
0.952
13726
2544
1.501
0.970
46009
Dc, g cm-3
µ/mm-1
reflections collected
indep. reflns (Rint
)
3258 (0.0547)
0.0382, 0.0808
0.0597, 0.0888
1.030
5870 (0.0901)
0.0555, 0.0905
0.1128, 0.1073
1.027
5654 (0.0410)
0.0304, 0.0697
0.0441, 0.0755
1.041
3727 (0.0000)
0.0425, 0.0882
0.1824, 0.1211
0.934
6312 (0.0206)
0.0259, 0.0765
0.0290, 0.0779
1.099
6274 (0.1021)
0.0503, 0.0908
0.0905, 0.1027
1.028
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
goodness-of-fit on F2
Table 2. Selected Bond Distances (Å) and Angles (°) of 1, 5, 6, and 7
2, and 3, respectively. The gross structural features of 1, 5,
6, and 7 show a ZnN2S2 coordination sphere with distorted
tetrahedral geometry, constituted by two thiolato sulfur and
two imino nitrogen atoms from two Schiff base ligands. The
1
5
6
7
Zn1-S1
Zn1-S2
Zn1-N1
Zn1-N2
2.2564(8)
2.2636(14)
2.2755(12)
2.092(3)
2.2629(8)
2.2771(8)
2.1013(15)
2.1046(16)
2.263(2)
2.271(2)
2.100(6)
2.114(7)
2.0976(17)
2.100(3)
S1-Zn1-S2 125.93(4)
S1-Zn1-N1 87.73(5)
S1-Zn1-N2 128.76(5)
S2-Zn1-N1
S2-Zn1-N2
N1-Zn1-N2 99.66(9)
120.81(5)
117.80(3)
122.11(10)
89.26(18)
121.1(2)
123.60(19)
87.86(19)
116.4(2)
89.02(8)
118.88(8)
125.07(8)
88.03(8)
89.00(4)
125.90(4)
126.71(4)
87.92(5)
118.43(10)
113.65(6)
Table 3. Selected Bond Distances (Å) and Angles (°) of 9 and 12a
9
12
Cd1-S1
Cd1-S2
Cd1-S2*
Cd1-N1
Cd1-N2
2.4376(12)
2.4232(12)
2.4721(12)
2.5231(11)
2.7496(11)
2.345(3)
Figure 1. Molecular structure of 1 with 50% probability ellipsoids.
2.346(2)
2.347(2)
2.766(3)
S1-Cd1-S2
S1-Cd1-S2*
S1-Cd1-N1
S1-Cd1-N2
S2-Cd1-S2*
S2-Cd1-N1
S2-Cd1-N2
S2*-Cd1-N1
S2*-Cd1-N2
N1-Cd1-N2
Cd1-S2-Cd1*
144.29(3)
122.52(4)
110.97(4)
81.57(8)
115.86(7)
87.30(4)
154.18(8)
70.66(7)
92.45(8)
133.06(7)
91.26(10)
92.70(4)
79.38(5)
124.92(6)
119.09(6)
81.89(6)
105.46(7)
a An asterisk refers to the following equivalence positions relative to
Figure 2. Molecular structure of 6 with 50% probability ellipsoids.
the x, y, z set: -x, -y, -z.
ligand. Thus, it is considered that these dicadmium(II)
complexes also have a mononuclear structure in solution.
Molecular Structures of Zinc(II) Complexes. The crystal
structures of the zinc(II) complexes, 1, 5, 6, and 7, along
with the cadmium(II) complexes 9 and 12 (vide infra), were
determined by X-ray crystallography. Table 1 gives crystal-
lographic data, and Tables 2 and 3 summarize selected bond
distances and angles of these complexes. Oak Ridge thermal
ellipsoid plot (ORTEP) diagrams for 1 (R ) 2,4,6-triMe), 5
(R ) 4-Et), 6 (R ) 4-OMe), and 7 (R ) 4-NMe2) are
illustrated in Figures 1, Supporting Information Figure S1,
Figure 3. Molecular structure of 7 with 50% probability ellipsoids.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3097

Kawamoto et al.
Scheme 2
Zn-S and Zn-N bond lengths in 1, 5, 6, and 7 are very
similar to one another (2.2564(8) Å and 2.0976(17) Å in 1,
2.2636(14) and 2.2755(12) Å and 2.092(3) and 2.100(3) Å
in 5, 2.2629(8) and 2.2771(8) Å and 2.1013(15) and
2.1046(16) Å in 6, and 2.263(2) and 2.271(2) Å and 2.100(6)
and 2.114(7) Å in 7) and lie within the range observed for
the analogues.7 A comparison of the dihedral angles between
pendent phenyl rings and azomethine moieties, which refer
to the twisting around the azomethine carbon atom in each
complex, is informative. The mean values of the dihedral
angles in 1, 5, 6, and 7 decrease in the order 1 (78.1(2)°; the
dihedralanglebetweenthemeanplanesofC7-C8-C9-C10-
C11-C12-C13 and N1-C7-C8), 5 (av. 27.9°; the dihedral
angles between the mean planes of C7-C8-C9-C10-C11-
C12-C13andN1-C7-C8, betweenthemeanplanesofC22-
C23-C24-C25-C26-C27-C28 and N2-C22-C23, and
between the mean planes of C22-C23-C24-C25′-C26′-
C27′-C28′ and N2-C22-C23 are 22.3(4)°, 27.9(8)°, and
33.5(8)°), 6 (av. 23.8°; the dihedral angles between the mean
planesofC7-C8-C9-C10-C11-C12-C13andN1-C7-C8
andbetweenthemeanplanesofC21-C22-C23-C24-C25-
C26-C27 and N2-C21-C22 are 25.9(2)° and 21.6(2)°), and
7 (av. 20.2°; the dihedral angles between the mean planes
of C7-C8-C9-C10-C11-C12-C13 and N1-C7-C8
andbetweenthemeanplanesofC22-C23-C24-C25-C26-
C27-C28 and N2-C22-C23 are 15.1(6)° and 25.3(8)°).
The extremely large angle for 1 induces a highly distorted
tetrahedral structure; the dihedral angle between the ZnNS
trigonal planes in 1 (72.90(5)°) is much smaller than the
corresponding angles in 5 (88.07(8)°), 6 (80.59(4)°), and 7
(87.2(2)°). In complex 7 (R ) 4-NMe2) with the smallest
angle (20.2°), the quinoid type distortion is observed for two
pendent phenyl rings. That is, two shorter aromatic C-C
bonds (av. 1.370(10) Å for C9-C10 and C12-C13, av.
1.344(12) Å for C24-C25 and C27-C28) and four longer
aromatic C-C bonds (av. 1.407(12) Å for C8-C9, C8-C13,
C10-C11, and C11-C12, av. 1.412(13) Å for C23-C24,
C23-C28, C25-C26, and C26-C27) are found in the six
C-C distances of the pendent phenyl part. The azomethine
CdN bond distances (av. 1.298(9) Å) in 7 are relatively long
as a CdN double bond. On the other hand, the bond distances
(av. 1.358(11) Å) between the nitrogen atom of the di-
methylamino group and the aromatic carbon atom are
relatively short as a C-N single bond, and the sum of the
angles around each nitrogen atom is close to 360° (358.8°
for N3 and 359.2° for N4). Therefore, the resonance
contribution is considered to the ligand structure in 7
Figure 4. Molecular structure of 9 with 50% probability ellipsoids.
(Scheme 2). In addition, 7 crystallizes in the orthorhombic
space group P212121, indicating that 7 is subject to spontane-
ous resolution. The ∆ and Λ absolute configurations are
possible for this structure with respect to the substantial C2
axis of the molecule.10 Refinement of the Flack enantiopole
parameter [0.00(3)] implies that the crystal used for the X-ray
analysis contains only the ∆ enantiomer of the molecule.
The lack of optical activity of this crystal in CH2Cl2 is
suggestive of the racemization in solution.
In 1 (R ) 2,4,6-triMe), there exist two intramolecular face-
to-face interactions between the chelating aromatic and the
pendent aromatic rings; the centroid · · · centroid distance is
3.789 Å (Figure 1). On the other hand, in 5 (R ) 4-Et), 6
(R ) 4-OMe), and 7 (R ) 4-NMe2), there are no noteworthy
intra and intermolecular interactions or short contacts.
Molecular Structures of Cadmium(II) Complexes.
ORTEP diagram of complex 9 (R ) 2,4,6-triMe) is shown
in Figure 4. The cadmium(II) ion adopts a distorted
tetrahedral coordination geometry bonded by two five-
membered N,S chelate rings. The dihedral angle between
the CdN1S1 and the CdN2S2 trigonal planes is 86.35(6)°.
The Cd-S bond distances (2.4376(12) and 2.4232(12) Å)
are shorter and the Cd-N bond distances (2.346(2) and
2.347(2) Å) are longer than those of the related four-
coordinate cadmium(II) complexes.11 In addition, this com-
plex has unsymmetrical structure in the chelate ligands as
observed in the twisting around the azomethine carbon atoms
(the dihedral angles between C7-C8-C9-C10-C11-
C12-C13andN1-C7-C8andC23-C24-C25-C26-C27-
C28-C29 and N2-C23-C24 are 79.3(2)° and 46.7(2)°,
respectively). This structural feature is different from that
of the corresponding zinc(II) complex 1, in which metal
center is located on a crystallographic 2-fold axis. An
intramolecular face-to-face interaction between the chelated
aromatic ring and the pendent aromatic ring is observed; the
centroid · · · centroid distance is 3.707 Å.
(10) von Zelewsky, A. Stereochemistry of Coordination Compounds; John
Wiley & Sons: Chichester, 1996.
(11) (a) Swenson, D.; Baenziger, N. C.; Coucouvanis, D. J. Am. Chem.
Soc. 1978, 100, 1932. (b) Ueyama, N.; Sugawara, T.; Sasaki, K.;
Nakamura, A.; Yamashita, S.; Wakatsuki, Y.; Yamazaki, H.; Yasuoka,
N. Inorg. Chem. 1988, 27, 741. (c) Tarafder, M. T. H.; Jin, K. T.;
Crouse, K. A.; Ali, A. M.; Yamin, B. M.; Fun, H.-K. Polyhedron
2002, 21, 2547. (d) Tarafder, M. T. H.; Khoo, T.-J.; Crouse, K. A.;
Ali, A. M.; Yamin, B. M.; Fun, H.-K. Polyhedron 2002, 21, 2691.
3098 Inorganic Chemistry, Vol. 47, No. 8, 2008

Luminescent Zinc(II) and Cadmium(II) Complexes
Scheme 3
Figure 5. Molecular structure of 12 with 50% probability ellipsoids.
UV/vis Absorption Spectra. The present zinc(II) com-
plexes [Zn(RsPhsC(H)dNsC6H4sS)2] are classified into
three groups on the basis of the position and intensity of the
absorption bands. That is, the Group 1 complexes (R ) 2,4,6-
triMe (1), 2,6-diCl (2)) show an intense band at 250-300
nm and a weak band at 400-450 nm, the Group 2 complexes
(R ) 4-Cl (3), H (4), 4-Et (5), 4-OMe (6)) show two intense
bands at 250-300 nm and a weak band at 400-450 nm,
and the Group 3 complexes (R ) 4-NMe2 (7), 4-NEt2 (8))
show an intense band at 250-300 nm and two very intense
bands at 350-450 nm (Table 4, Supporting Information
Figure S2); the representative absorption spectra of each
group are shown in Figure 6. Similarly, the cadmium(II)
complexes [Cd(RsPhsC(H)dNsC6H4sS)2] can also be
classified into three groups; Group 1 (R ) 2,4,6-triMe (9)),
Group 2 (R ) 4-Et (10), 4-OMe (11)), and Group 3 (R )
4-NMe2 (12)) (Table 5, Supporting Information Figure S3).
To elucidate the origin of the very intense absorption bands
observed for the Group 3 complexes, DFT calculations were
carried out using the X-ray structural data of 7. Frontier
molecular orbitals obtained at the B3LYP/LAN2DZ level
are shown in Figure 7. The highest occupied molecular
orbital (HOMO), HOMO-1, and HOMO-4 possess a large
contribution from the 3p orbitals on the thiolato sulfur atoms
and π orbitals on N,S-benzene moieties. The HOMO-2 and
HOMO-3 are dominated by the π orbitals delocalized over
the conjugated RsPhsC(H)dN (R ) 4-NMe2) moiety,
while the lowest unoccupied molecular orbital (LUMO) and
the LUMO+1 are dominated by the π* orbitals on the
conjugated RsPhsC(H)dN moiety. Time-dependent DFT
calculation indicates that the lowest-energy excitation occurs
from HOMO f LUMO which is characterized by a charge
transfer transition from the thiolato sulfur atoms to the
conjugated RsPhsC(H)dN moiety. The strongly allowed
transitions corresponding to the intense band at 384 nm
involve several one-electron transitions: HOMO-2 f LU-
MO+1, HOMO-4 f LUMO, and HOMO-4 f LUMO+1.
Because the LUMO (or LUMO+1) has no contribution from
the sulfur 3p orbitals, the transition dipole moment for
HOMO-4 f LUMO (or LUMO+1) is considered to be
small. Thus, the origin of the intense 384 nm band is
ascribable to HOMO-2 f LUMO+1, π-π* transition
within the RsPhsC(H)dN moiety. Such very large batho-
chromic shifts of π-π* absorption bands in Group 3
complexes can be explained on the basis of the valence-
Complex 12 (R ) 4-NMe2) crystallizes in the orthorhom-
bic space group Pbca with four formula units in the unit
cell, and the asymmetric unit consists of one-half of the
complex molecule. The ORTEP diagram of 12 is shown in
Figure 5. There is a crystallographic inversion center at the
midpoint of the Cd1 · · · Cd1* vector. Two cadmium(II) ions
are bridged by two thiolato sulfur atoms from two Schiff
base ligands, and each cadmium(II) center has a five-
coordinate geometry formed by two nitrogen and two sulfur
atoms from two N,S-chelate ligands and one sulfur atom from
one bridging ligand. A long Cd1 · · · Cd1* separation of
3.8185(9) Å is indicative of the absence of a Cd · · · Cd
interaction. To estimate the relative geometry about each
cadmium atom in the five-coordinated environment, the
angular parameter ꢁ was calculated.12 The ꢁ value (0.53)
suggests that each cadmium(II) center resides in a coordina-
tion geometry just between trigonal bipyramid and square-
pyramid. While the Cd-S2* bond distance (2.7496(11) Å)
is longer than the Cd-S1 (2.4721(12) Å) and Cd-S2
(2.5231(11) Å) distances, these values fall in the range found
for dimeric five-coordinate cadmium(II) complexes.13 The
Cd-N1 bond distance (2.345(3) Å) agrees with those found
in cadmium(II) complexes with a five-coordinated environ-
ment,14 but the Cd-N2 bond (2.766(3) Å) is considerably
longer than the sum of the covalent radii of cadmium and
nitrogen atoms (2.15 Å).15
Molecular model examination revealed that a serious steric
repulsion arises between the N,S-chelating benzene moiety
and a substituent at the ortho position of a pendent phenyl
ring in the S-bridged dinuclear structure (Scheme 3). In fact,
the related cadmium(II) complex 9 that has methyl groups
at ortho positions adopts a mononuclear structure. Because
the other cadmium(II) complexes 10 (R ) 4-Et) and 11 (R
) 4-OMe) have no substituent at ortho positions, as does
12 (R ) 4-NMe2), it is likely that these complexes also adopt
a dinuclear structure.
(12) Konno, T.; Tokuda, K.; Sakurai, J.; Okamoto, K. Bull. Chem. Soc.
Jpn. 2000, 73, 2767.
(13) (a) Bochmann, M.; Webb, K.; Harman, M.; Hursthouse, M. B. Angew.
Chem., Int. Ed. Engl. 1990, 29, 638. (b) Pérez-Lourido, P.; Romero,
J.; García-Vázquez, J. A.; Sousa, A.; Maresca, K. P.; Zubieta, J. Inorg.
Chem. 1999, 38, 3709. (c) Kötte, S.; Stelzig, L.; Wonnemann, R.;
Krebs, B.; Steiner, A. Z. Anorg. Allg. Chem. 2000, 626, 1575.
(14) (a) Vallina, A. T.; Stoeckli-Evans, H. Polyhedron 2002, 21, 1177. (b)
Fan, R.-Q.; Zhu, D.-S.; Mu, Y.; Li, G.-H.; Yang, Y.-L.; Su, Q.; Feng,
S.-H. Eur. J. Inorg. Chem. 2004, 4891.
(15) Lee, J. D. Concise Inorganic Chemistry; Chapman & Hall: London,
1996.
(16) Christie, R. M. Colour Chemistry; The Royal Society of Chemistry:
Cambridge, 2001.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3099

Kawamoto et al.
Table 4. Photophysical Properties of Zinc(II) Complexes
λ
max,em, nma
(CH2Cl2/
λmax,em,
λ
max,abs, nm (ε, M-1 cm-1
)
nma
lifetime,
quantum yield,
complex
(CH2Cl2, r.t., 1 × 10-5 to 3 × 10-4 M)
toluene, 77 K) (solid, r.t.)
nsc (solid, r.t.)
Φe (solid, r.t.)
1
2
3
265 (3.15 × 104), 308sh (1.34 × 104), 405 (4.46 × 103)
615
649
632
b
b
633
d
f
f
265 (2.88 × 104), 423 (3.42 × 103)
<0.2
260 (3.54 × 104), 281 (3.29 × 104), 309sh (2.31 × 104),
447 (5.62 × 103)
0.37 ( 0.05
0.009
4
5
6
7
8
259 (3.48 × 104), 279 (3.32 × 104), 307sh (1.87 × 104),
441 (5.34 × 103)
620
613
605
578
572
627
606
600
584
591
<0.2
f
261 (3.20 × 104), 283 (3.28 × 104), 309sh (2.48 × 104),
438 (6.20 × 103)
0.42 ( 0.05
0.56 ( 0.05
0.014
0.021
260 (2.48 × 104), 282 (2.33 × 104), 325 (3.09 × 104),
432 (6.93 × 103)
255 (3.20 × 104), 280sh (2.08 × 104), 317 (7.25 × 103),
384 (5.33 × 104), 424 (3.52 × 104)
0.38 ( 0.1(80%) 1.1 ( 0.1(20%)
0.23 ( 0.1(80%) 0.78 ( 0.1(20%)
0.062
0.088
256 (2.79 × 104), 282sh (1.98 × 104), 318 (6.53 × 103),
389 (5.34 × 104), 429 (4.01 × 104)
a The excitation wavelength was set to 355 nm. b Not observed. c Determined for solid-state sample with excitation at 473nm. A value in parenthesis
denotes the fraction of each component in dual exponential decay. d The emission was too weak for lifetime measurements. e Error ( 10%. f Less than 0.001.
the twisting around the azomethine carbon atom; the highly
twisted structure observed in the Group 1 complexes,
compared with the other Group 2 and 3 complexes, results
in the obvious decrease of emission intensity. The emission
lifetimes of the Group 2 complexes were very short, less
than 0.6 ns. The Group 3 complexes showed dual exponential
decays with a long lifetime component of about 1 ns. Such
multiple exponential decays are often observed for emissive
crystalline samples, probably because of quenching of
migrating excitons by defects inside or at the surface of
crystals. All the zinc(II) complexes were luminescent in
CH2Cl2/toluene glass at 77 K though they are almost
nonemissive in the fluid solution probably because of the
rapid nonradiative transition induced by solvent interactions.
Among the various substituted complexes, 7 and 8, having
the strongest electron-donating groups, exhibit emissions at
much shorter wavelengths (λem, max) than those of the other
complexes (Table 4, Figure 9). In addition, 3, having a chloro
group, exhibits an emission at a slightly longer wavelength
than does 4, which has an unsubstituted phenyl group. Thus,
the emission peaks for the monosubstituted zinc(II) com-
plexes, including 4, show the hypsochromic shift as the
substituent becomes more electron-donating, and the emis-
sion maxima for the zinc(II) complexes are linearly related
to the Hammett constants (Figure 10).17 A similar relation
holds for the cadmium(II) complexes (Table 5, Supporting
Information Figure S4). This tendency is in contrast to the
fact that Alq3 derivatives with electron-donating substituents
show the bathochromic shifts.18 The relationship between
the emission wavelength and the properties of substituents
for the present complexes is rationalized on the basis of the
distribution of the frontier orbitals (HOMO and LUMO)
involved in the emission. That is, the HOMO is localized
on the thiolato sulfur atoms with a high nucleophilic property,
whereas the LUMO is delocalized over the ligands (Figure
7). Thus, the LUMO energy rises to give a wide HOMO-
LUMO gap as the electron-donating ability of the substituents
Figure 6. Absorption spectra of 1 (dotted line), 6 (dashed-dotted line),
and 7 (solid line) in CH2Cl2. (concentrations: 1 × 10-5 to 2 × 10-4 M).
bond (resonance) approach as shown in the X-ray analysis
of 7 (Scheme 2).16
Photoluminescence Properties. The emission spectral
data in the solid state for all the zinc(II) complexes were
recorded with excitation at 355 nm. As summarized in Table
4, 1 (R ) 2,4,6-triMe) and 2 (R ) 2,6-diCl), which belong
to Group 1, did not show emission while a moderately strong
emission and a considerably strong orange emission were
observed for the Group 2 complexes (R ) 4-Cl (3), H (4),
4-Et (5), 4-OMe (6)) and the Group 3 complexes (R )
4-NMe2 (7), 4-NEt2 (8)), respectively, in the region of
584-633 nm at room temperature. Typical examples of
emission spectra for each group are shown in Figure 8, and
the quantum yields for the Zn(II) and Cd(II) complexes in
the solid state are summarized in Tables 4 and 5. The
quantum yields of the new emissive compounds are not high
compared with those of the zinc(II) complexes with N,O-
chelating Schiff base ligands.5 However, the Group 3
complexes show a quantum efficiency higher than those of
the other complexes. Thus, the substituent positions on the
pendent phenyl rings substantially affect the emission in the
solid state. This behavior can be mainly correlated to
(17) Hansch, C.; Leo, A.; Taft, R. W. Chem. ReV. 1991, 91, 165.
(18) Pohl, R.; Montes, V. A.; Shinar, J.; Anzenbacher, P., Jr. J. Org. Chem.
2004, 69, 1723.
3100 Inorganic Chemistry, Vol. 47, No. 8, 2008

Luminescent Zinc(II) and Cadmium(II) Complexes
Table 5. Photophysical Properties of Cadmium(II) Complexes
λ
max,abs, nm (ε, M-1 cm-1
)
λ
max,em, nma
λmax,em
,
quantum yield,
complex
(CH2Cl2, r.t., 4 × 10-5 to 2 × 10-4 M)
(CH2Cl2/toluene, 77 K) nma (solid, r.t.)
lifetime, nsc (solid, r.t.)
Φe (solid, r.t.)
9
10
11
273 (3.50 × 104), 394 (4.29 × 103)
285 (3.97 × 104), 422 (5.84 × 103)
287 (3.19 × 104), 322 (3.40 × 104),
415 (7.38 × 103)
601
610
594
b
574
566
d
f
0.33 ( 0.05
0.38 ( 0.05
0.012
0.015
12
262 (3.36 × 104), 379 (4.66 × 104), 419sh
(3.22 × 104)
561
548
0.36 ( 0.1(80%) 1.1 ( 0.1(20%)
0.049
a The excitation wavelength was set to 355 nm. b Not observed. c Determined for solid-state sample with excitation at 473nm. A value in parenthesis
denotes the fraction of each component in dual exponential decay. d The emission was too weak for lifetime measurements. e Error ( 10%. f Less than 0.001.
Figure 8. Emission spectra of 6 (dashed-dotted line) and 7 (solid line) in
the solid state at room temperature.
Figure 7. Molecular orbitals of 7 based on the DFT calculations.
increases, which results in the emission shift to the shorter
wavelength side.
Figure 9. Emission spectra of 4 (dotted line), 6 (dashed-dotted line), and
7 (solid line) in CH2Cl2/toluene glass at 77 K.
It has been well-known that the oxidation species of
benzothiazolines are luminescent.19 However, the benzothia-
zolines themselves, which are the starting material in this
study, virtually do not possess the luminescent property.
Therefore, the origin of the present luminescence observed
for the zinc(II) and cadmium(II) complexes is based on the
Schiff base ligands newly formed via the ring opening of
benzothiazolines; that is, the formation of N2S2-Schiff base
ligands in zinc(II) and cadmium(II) complexes results in the
obvious luminescent property.
Conclusion
A series of Schiff base zinc(II) complexes with various
substituents on the pendent phenyl rings ([Zn(RsPhs
C(H)dNsC6H4sS)2], R ) 2,4,6-triMe (1), 2,6-diCl (2), 4-Cl
(3), H (4), 4-Et (5), 4-OMe (6), 4-NMe2 (7), 4-NEt2 (8))
have been newly synthesized and characterized. X-ray
analyses revealed that they have a mononuclear structure with
(19) (a) Dey, J.; Dogra, S. K. J. Phys. Chem. 1994, 98, 3638. (b) Mathis,
C. A.; Bacskai, B. J.; Kajdasz, S. T.; McLellan, M. E.; Frosch, M. P.;
Hyman, B. T.; Holt, D. P.; Wang, Y.; Huang, G.-F.; Debnath, M. L.;
Klunk, W. E. Bioorg. Med. Chem. Lett. 2002, 12, 295. (c) Mathis,
C. A.; Wang, Y.; Holt, D. P.; Huang, G.-F.; Debnath, M. L.; Klunk,
W. E. J. Med. Chem. 2003, 46, 2740. (d) Alagille, D.; Baldwin, R. M.;
Tamagnan, G. D. Tetrahedron Lett. 2005, 46, 1349.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3101

Kawamoto et al.
cell (1 mm inner diameter) and a liquid-nitrogen Dewar flask.
Emission quantum yields of the complexes in the solid state were
determined in a similar way to that described by Islam et al.20 Dilute
samples of 5% Zn(II) or Cd(II) complexes in MgO were prepared
by homogeneously mixing sample powder and commercial grade
MgO powder and were packed into a 1 mm quartz cell. A powder
of pure MgO packed in another 1 mm quartz cell was used as a
reference. A monochromated light of a 150 W xenon lamp was
irradiated onto the surface of the sample or the reference, and a
part of the scattered light or emission was measured by the grating
monochromator with the CCD image sensor. The difference in
reflectance between the sample and reference was less than 1.5%
when irradiated with the light at 600 nm where the complexes have
no absorption. The quantum yield of emission (Φ) was calculated
by eq 1.
Ds
Φ )
(1)
(Dr - Ds ′ ) ⁄ F
where Ds is integrated intensity of the emission spectrum. Ds′ and
Dr are the integrated intensity of the reflected excitation light for
the sample and the reference, respectively. F is the absolute
reflectance of MgO (0.9). For the determination of emission
lifetimes, the sample was photoexcited using a Q-switched DPSS
laser (µFLARE, 473 nm, 1 ns, 3 kHz, 3 mW, Lumanova GmbH).
The emission from the sample was focused into a grating mono-
chromator (H-10, Jobin Yvon) with a Si avalanche photodiode (Si-
APD, S5139, Hamamatsu). The photocurrent from the Si-APD was
amplified through a wide-band amplifier (DC-500 MHz, CLC110)
and accumulated on a digitizing oscilloscope (HP 54520 Hewlett-
Packard) to get the decay-profile of the emission intensity, which
was fitted to single or double exponential function with convolution
of the instrumental response function of the measuring system. The
Figure 10. Relationship between the emission maxima and the Hammett
substituent constants in zinc(II) complexes.
a distorted tetrahedral geometry. It has been found that the
electronic property of the substituents, as well as their
positions on the pendent phenyl rings of the Schiff base
ligands, affects the electronic absorption spectra of the
complexes. All the complexes were luminescent in CH2Cl2/
toluene glass at 77 K, and the emission wavelengths were
correlated with the Hammett constant of the substituents on
the pendent phenyl rings. The analogous cadmium(II)
complexes ([Cd(RsPhsC(H)dNsC6H4sS)2], R ) 2,4,6-
triMe (9) and [Cd2(RsPhsC(H)dNsC6H4sS)4], R ) 4-Et
(10), 4-OMe (11), 4-NMe2 (12)) were synthesized, but they
have a dinuclear structure in the solid state, except 9. The
cadmium(II) complexes also gave emission spectra in the
CH2Cl2/toluene glass at 77 K. These zinc(II) and cadmium(II)
complexes with N2S2-Schiff base ligands are a new class
of luminescent compounds, and the careful derivatization of
the substituents on the pendent phenyl rings permits a fine-
tuning of the emission wavelength.
1
time resolution of the system was 0.2 ns. The H NMR spectra
were recorded with a JEOL GSX 500 spectrometer. The IR spectra
in the region of 4000-400 cm-1 were recorded as KBr pellets on
a JASCO FT/IR-550 spectrometer. Elemental analyses were
performed at Osaka University. Calculations using density func-
tional theory (DFT) were performed by with the GAUSSIAN 03
software.21 The basis functions used in the computations were the
Dunning-Hay split valence double-ꢂ for the C, H, and N atoms
(D95) and the Hay-Wadt double-ꢂ with the Los Alamos relativistic
effective core potential for heavy atoms (LANL2DZ).22,23 Becke’s
style three-parameter hybrid functional of B3LYP was employed.24
Experimental Section
General Procedures. All of the synthetic reactions were carried
out under an atmosphere of argon or nitrogen using standard
Schlenk techniques. Workup procedures were performed in air. The
reagents were commercial samples and not purified further.
The 2-(2,4-dichlorophenyl)benzothiazoline,9a 2-(4-chlorophenyl)-
(20) Islam, A.; Ikeda, N.; Nozaki, K.; Ohno, T. J. Chem. Phys. 1998, 109,
4900.
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene,
M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala,
P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,revision
D.02; Gaussian, Inc.: Wallingford, CT, 2004.
benzothiazoline,9c 2-phenylbenzothiazoline,8b 2-(4-methoxyphenyl)-
8 c
b e n z o t h i a z o l i n e ,
a n d
2 - ( 4 -
dimethylaminophenyl)benzothiazoline9dwere prepared as described
previously. The absorption spectra were recorded with a JASCO
V-570 spectrophotometer at room temperature. The emission spectra
in the solid state were obtained using a JASCO FP-6600 lumines-
cent spectrometer with the slits of 5 nm at room temperature.
Measurements of low-temperature emission spectra were carried
out using a grating monochromator with the entrance slit of 4 nm
(Triax 1900, Jobin Yvon) equipped with a CCD image sensor
(S7031, Hamamatsu) of which the spectral sensitivity was corrected
using a bromine lamp (IPD 100V 500WCS, Ushio). A sample in a
1-mm quartz cell was excited using an LD-excited solid-state Nd:
YAG laser (355 nm, 440 ps, 13 kHz, 6 mW, JDS Uniphase). The
measurements at 77 K were performed using a cylindrical quartz
(22) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry;
Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3.
(23) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. 284, 299.
(24) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
3102 Inorganic Chemistry, Vol. 47, No. 8, 2008

Luminescent Zinc(II) and Cadmium(II) Complexes
The drawing of molecular orbitals was performed using
MOLEKEL.25,26
mL) was added zinc(II) acetate dihydrate (0.34 g, 1.5 mmol). The
reaction mixture was refluxed for 30 min and then cooled to room
temperature. The resulting orange powder was collected by filtration.
Yield: 0.33 g, 34%. Anal. Calcd for C26H16Cl4N2S2Zn: C, 49.75;
H, 2.57; N, 4.46. Found. C, 49.91; H, 2.55; N, 4.48. IR (KBr; cm-1):
1611 (νCdN). 1H NMR (500 MHz, CDCl3): δ 8.69 (2H, s, CH)N),
7.20 (2H, d, J ) 7.3, benzene), 7.15 (2H, d, J ) 7.6, benzene),
7.13 (2H, t, J ) 7.9, benzene), 7.00 (2H, d, J ) 7.9, benzene),
6.97 (2H, d, J ) 7.3, benzene).
Synthesis of 2-(Mesit)benzothiazoline. To a solution of 2-ami-
nobenzenethiol (4.09 g, 32.7 mmol) in ethanol (40 mL) was added
mesitbenzaldehyde (4.84 g, 32.7 mmol). The mixture was refluxed
for 30 min and then cooled to room temperature. The resulting
yellow solution was evaporated to dryness. The pale yellow solid
was dissolved in CH2Cl2 (2 mL), and n-hexane (20 mL) was added
to the pale yellow solution. The precipitated white powder was
collected by filtration and dried in vacuo. Yield: 3.85 g, 46.2%.
Anal. Calcd for C16H17NS: C, 75.25; H, 6.71; N, 5.48. Found. C,
Synthesis of 3. To a light yellow suspension of 2-(4-chlorophe-
nyl)benzothiazoline (0.61 g, 2.5 mmol) in ethanol (20 mL) was
added zinc(II) acetate dihydrate (0.27 g, 1.2 mmol). The reaction
mixture was refluxed for 30 min and then cooled to room
temperature. The resulting reddish orange powder was collected
by filtration. Yield: 0.47 g, 68%. Anal. Calcd for C26H18Cl2N2S2Zn:
C, 55.88; H, 3.25; N, 5.01. Found. C, 55.78; H, 3.24; N, 5.00. IR
1
75.13; H, 6.69; N, 5.48. IR (KBr; cm-1): 3356 (νN-H). H NMR
(500 MHz, CDCl3): δ 7.09 (1H, s, 2-CH), 7.03 (1H, d, J ) 7.9,
benzene), 6.91 (1H, t, J ) 7.6, benzene), 6.86 (2H, s, benzene),
6.71 (1H, t, J ) 7.6, benzene), 6.57 (1H, d, J ) 7.9, benzene),
4.05 (1H, s, NH), 2.49 (6H, s, CH3), 2.27 (3H, s, CH3).
1
(KBr; cm-1): 1599 (νCdN). H NMR (500 MHz, CDCl3): δ 8.57
Synthesis of 2-(4-Ethylphenyl)benzothiazoline. To a solution
of 2-aminobenzenethiol (1.43 g, 11.4 mmol) in ethanol (20 mL)
was added 4-ethylbenzaldehyde (1.53 g, 11.4 mmol). The mixture
was heated under reflux for 30 min. The resulting solution was
evaporated to approximately one-half of the initial volume and then
allowed to cool in a freezer overnight. White powder was collected
by filtration and dried in vacuo. Yield: 1.49 g, 54.1%. Anal. Calcd
for C15H15NS: C, 74.65; H, 6.26; N, 5.80. Found. C, 74.39; H, 6.15;
N, 5.88. IR (KBr; cm-1): 3314 (νN-H). 1H NMR (500 MHz, CDCl3):
δ 7.46 (2H, d, J ) 8.0, benzene), 7.19 (2H, d, J ) 7.5, benzene),
7.04 (1H, d, J ) 7.5, benzene), 6.94 (1H, t, J ) 7.7, ben-
zene), 6.76 (1H, t, J ) 7.5, benzene), 6.65 (1H, d, J ) 8.0, benzene),
6.36 (1H, s, 2-CH), 4.33 (1H, s, NH), 2.65 (2H, q, J ) 7.5, CH2),
1.23 (3H, t, J ) 7.5, CH3).
Synthesis of 2-(4-Diethylaminophenyl)benzothiazoline. To a
solution of 2-aminobenzenethiol (1.44 g, 11.5 mmol) in ethanol
(20 mL) was added 4-diethylaminobenzaldehyde (1.36 g, 7.67
mmol). The mixture was heated under reflux for 1 h. The resulting
solution was evaporated to approximately one-half of the initial
volume and then allowed to cool in a freezer for 4 days. Dark yellow
powder was collected by filtration and dried in vacuo. Yield: 1.64 g,
75.1%. Anal. Calcd for C17H20N2S: C, 71.79; H, 7.09; N, 9.85.
Found. C, 72.24; H, 7.37; N, 9.41. IR (KBr; cm-1): 3334 (νN-H).
1H NMR (500 MHz, CDCl3): δ 7.39 (2H, d, J ) 8.6, benzene),
7.03 (1H, d, J ) 7.5, benzene), 6.92 (1H, t, J ) 7.7, benzene),
6.73 (1H, t, J ) 7.7, benzene), 6.62 (3H, m, benzene), 6.33 (1H, s,
2-CH), 4.23 (1H, s, NH), 3.34 (4H, q, J ) 6.9, CH2), 1.15 (6H, t,
J ) 6.9, CH3).
(2H, s, CH)N), 7.64 (4H, d, J ) 7.9, benzene), 7.55 (2H, d, J )
7.3, benzene), 7.20 (2H, t, J ) 6.9, benzene), 7.02 (8H, m, benzene).
Synthesis of 4. To a light yellow suspension of 2-phenylben-
zothiazoline (0.60 g, 2.8 mmol) in ethanol (20 mL) was added
zinc(II) acetate dihydrate (0.31 g, 1.4 mmol). The reaction mixture
was refluxed for 30 min and then cooled to room temperature. The
resulting orange powder was collected by filtration. Yield: 0.38 g,
56%. Anal. Calcd for C26H20N2S2Zn: C, 63.73; H, 4.11; N, 5.72.
Found. C, 63.42; H, 4.10; N, 5.74. IR (KBr; cm-1): 1593 (νCdN).
1H NMR (500 MHz, CDCl3): δ 8.46 (2H, s, CH)N), 7.76 (4H, d,
J ) 7.3, benzene), 7.58 (2H, d, J ) 7.9, benzene), 7.36 (2H, t, J )
7.6, benzene), 7.15 (2H, d, J ) 7.3, benzene), 7.09 (4H, d, J )
7.6, benzene), 7.00 (2H, d, J ) 7.6, benzene), 6.97 (2H, t, J ) 7.6,
benzene).
Synthesis of 5. To a light yellow suspension of 2-(4-ethylphe-
nyl)benzothiazoline (0.72 g, 3.0 mmol) in ethanol (20 mL) was
added zinc(II) acetate dihydrate (0.33 g, 1.5 mmol). The reaction
mixture was refluxed for 30 min and then cooled to room
temperature. The resulting orange powder 5 was collected by
filtration. Yield: 0.69 g, 85%. Anal. Calcd for C30H28N2S2Zn: C,
65.98; H, 5.17; N, 5.13. Found. C, 65.54; H, 5.18; N, 5.10. IR
1
(KBr; cm-1): 1597 (νCdN). H NMR (500 MHz, CDCl3): δ 8.44
(2H, s, CH)N), 7.67 (4H, d, J ) 7.6, benzene), 7.57 (2H, d, J )
7.9, benzene), 7.14 (2H, t, J ) 7.3, benzene), 7.00 (2H, d, J ) 7.6,
benzene), 6.96 (2H, t, J ) 7.5, benzene), 6.88 (2H, d, J ) 7.3,
benzene), 2.56 (4H, q, J ) 7.6, CH2), 1.14 (6H, t, J ) 7.6, CH3).
Synthesis of 6. To a light yellow suspension of 2-(4-methoxy-
phenyl)benzothiazoline (1.37 g, 5.63 mmol) in ethanol (20 mL)
was added zinc(II) acetate dihydrate (0.61 g, 2.8 mmol). The
reaction mixture was refluxed for 30 min and then cooled to room
temperature. The resulting orange powder was collected by filtration.
Yield: 1.03 g, 66%. Crystals of complex 6 suitable for a structure
determination were grown by the slow diffusion of diethyl ether
into a CH2Cl2 solution of 6. Anal. Calcd for C28.1H24.2Cl0.2N2O2S2Zn:
C, 60.43; H, 4.37; N, 5.02. Found. C, 60.44; H, 4.32; N, 5.11. IR
(KBr; cm-1): 1593 (νCdN). 1H NMR (500 MHz, DMSO-d6): δ 8.78
(2H, s, CH)N), 7.81 (4H, d, J ) 8.5, benzene), 7.40 (2H, d, J )
7.9, benzene), 7.32 (2H, d, J ) 7.9, benzene), 7.14 (2H, t, J ) 7.6,
benzene), 7.02 (2H, t, J ) 7.6, benzene), 6.57 (4H, d, J ) 8.5,
benzene), 3.71 (6H, s, CH3).
Synthesis of 1. To a light yellow suspension of 2-(mesit)ben-
zothiazoline (0.83 g, 3.3 mmol) in ethanol (20 mL) was added
zinc(II) acetate dihydrate (0.36 g, 1.6 mmol). The reaction mixture
was refluxed for 30 min and then cooled to room temperature. The
resulting yellow powder was collected by filtration. Yield: 0.78 g,
84%. Crystals of 1 suitable for a structure determination were grown
by slow evaporation of a CH2Cl2-ethanol mixed solution of 1. Anal.
Calcd for C32H32N2S2Zn: C, 66.94; H, 5.62; N, 4.88. Found. C,
1
66.64; H, 5.49; N, 4.91. IR (KBr; cm-1): 1615 (νCdN). H NMR
(500 MHz, CDCl3): δ 8.84 (2H, s, CH)N), 7.13 (2H, d, J ) 7.9,
benzene), 7.03 (2H, d, J ) 7.9, benzene), 7.01 (2H, t, J ) 7.9,
benzene), 6.93 (2H, t, J ) 7.3, benzene), 6.58 (4H, s, benzene),
2.23 (6H, s, CH3), 2.08 (12H, s, CH3).
Synthesis of 2. To a light yellow suspension of 2-(2,6-
dichlorophenyl)benzothiazoline (0.87 g, 3.1 mmol) in ethanol (20
Synthesis of 7. To a light yellow suspension of 2-(4-dimethyl-
aminophenyl)benzothiazoline (1.24 g, 4.86 mmol) in ethanol (20
mL) was added zinc(II) acetate dihydrate (0.53 g, 2.4 mmol). The
reaction mixture was refluxed for 30 min and then cooled to room
temperature. The resulting orange powder was collected by filtration.
Yield: 1.12 g, 79%. Crystals of complex 7 suitable for a structure
(25) Flukiger, P.; Luthi, H. P.; Portmann, S.; Weber, J. Swiss Center for
Scientific Computing; Manno, 2000–2002.
(26) Portmann, S.; Luthi, H. P. MOLEKEL: An Interactive Molecular
Graphics Tool. Chimia, 2000, 54, 766.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3103

Kawamoto et al.
determination were grown by the slow diffusion of diethyl ether
into a CHCl3 solution of 7. Anal. Calcd for C30.1H30.2Cl0.2N4S2Zn:
C, 61.84; H, 5.21; N, 9.58. Found. C, 62.09; H, 5.22; N, 9.65. IR
89%. Anal. Calcd for C56H48Cd2N4O4S4: C, 56.33; H, 4.05; N, 4.69.
Found. C, 56.08; H, 4.14; N, 4.70. IR (KBr; cm-1): 1593 (νCdN).
1H NMR (500 MHz, CDCl3): δ 8.35 (2H, s, CH)N), 7.66 (6H, d,
J ) 9.1, benzene), 7.14 (2H, t, J ) 7.6, benzene), 7.01 (2H, t, J )
7.6, benzene), 6.92 (2H, d, J ) 6.7, benzene), 6.52 (4H, d, J )
8.5, benzene), 3.71 (6H, s, CH3).
Synthesis of 12. To a light yellow suspension of 2-(4-dimethyl-
aminophenyl)benzothiazoline (0.59 g, 2.3 mmol) in ethanol (20 mL)
was added cadmium(II) acetate dihydrate (0.31 g, 1.2 mmol). The
reaction mixture was refluxed for 30 min and then cooled to room
temperature. The resulting yellow powder was collected by filtration.
Crystals of suitable for a structure determination were grown by
the slow diffusion of diethyl ether into a CH2ClCH2Cl solution of
12. Yield: 0.55 g, 76%. Anal. Calcd for C60H60Cd2N8S4: C, 57.83;
H, 4.85; N, 8.99. Found. C, 57.34; H, 4.81; N, 8.92. IR (KBr; cm-1):
1609 (νCdN). 1H NMR (500 MHz, CDCl3): δ 8.25 (2H, s, CH)N),
7.66 (2H, d, J ) 7.9, benzene), 7.57 (4H, d, J ) 9.1, benzene),
7.08 (2H, t, J ) 7.6, benzene), 6.99 (2H, t, J ) 7.3, benzene), 6.93
(2H, d, J ) 7.9, benzene), 6.16 (4H, d, J ) 8.5, benzene), 2.92
(12H, s, CH3).
X-ray Crystallography. X-ray crystallographic data for com-
plexes 1, 5, 6, 9, and 12 were collected with the ω scan technique
on a Rigaku RAXIS-RAPID image plate diffractometer with
graphite monochromated Mo KR (λ ) 0.71073 Å) radiation at 200
K. Empirical absorption corrections were applied. Complex 7 was
measured on a Rigaku AFC5R diffractometer with Mo KR radiation
at room temperature. θ-2θ scans were employed; no significant
decomposition of the crystal occurred during the data collection.
The solution and refinement procedures were made with the
CrystalStructure software package. The structures of complexes 1,
5, 6, 7, 9, and 12 were solved by direct methods using SIR 92 and
refined anisotropically for all nonhydrogen atoms with full-matrix
least-squares calculations. Hydrogen atoms were placed at calculated
positions and refined isotropically. A part of one pendent phenyl
group (C25-C30) in 5 was found to be disordered and was split
on two positions in a ratio of 50:50.
1
(KBr; cm-1): 1609 (νCdN). H NMR (500 MHz, CDCl3): δ 8.19
(2H, s, CH)N), 7.65 (4H, d, J ) 8.5, benzene), 7.60 (2H, d, J )
7.3, benzene), 7.05 (2H, t, J ) 7.3, benzene), 6.95 (2H, d, J ) 7.6,
benzene), 6.93 (2H, t, J ) 7.3, benzene), 6.18 (4H, d, J ) 8.5,
benzene), 2.92 (12H, s, CH3).
Synthesis of 8. To a light yellow suspension of 2-(4-diethyl-
aminophenyl)benzothiazoline (1.27 g, 4.47 mmol) in ethanol (20
mL) was added zinc(II) acetate dihydrate (0.47 g, 2.1 mmol). The
reaction mixture was refluxed for 30 min and then cooled to room
temperature. The resulting orange powder was collected by filtration.
Yield: 1.09 g, 80%. Anal. Calcd for C34H38N4S2Zn: C, 64.59; H,
6.06; N, 8.86. Found. C, 64.28; H, 6.02; N, 8.84. IR (KBr; cm-1):
1607 (νCdN). 1H NMR (500 MHz, CDCl3): δ 8.11 (2H, s, CH)N),
7.66 (4H, d, J ) 8.5, benzene), 7.62 (2H, d, J ) 7.9, benzene),
7.03 (2H, t, J ) 7.3, benzene), 6.95 (2H, d, J ) 7.6, ben-
zene), 6.91 (2H, t, J ) 7.3, benzene), 6.19 (4H, d, J ) 9.1, benzene),
3.26 (8H, q, J ) 7.3, CH2), 1.08 (12H, d, J ) 7.0, CH3).
Synthesis of 9. To a light yellow suspension of 2-(mesit)ben-
zothiazoline (0.55 g, 2.2 mmol) in ethanol (20 mL) was added
cadmium(II) acetate dihydrate (0.29 g, 1.1 mmol). The reaction
mixture was stirred at room temperature for 2 h. The resulting
yellow powder was collected by filtration. Crystals suitable for a
structure determination were grown by the slow evaporation of
CHCl3-ethanol-n-hexane mixed solution of 9. Yield: 0.57 g, 84%.
Anal. Calcd for C32H32CdN2S2: C, 61.88; H, 5.19; N, 4.51. Found.
C, 61.67; H, 5.25; N, 4.60. IR (KBr; cm-1): 1613 (νCdN). 1H NMR
(500 MHz, CDCl3): δ 8.73 (2H, s, CH)N), 7.39 (2H, d, J ) 7.9,
benzene), 7.08 (2H, t, J ) 7.6, benzene), 6.98 (2H, d, J ) 7.9,
benzene), 6.93 (2H, t, J ) 8.0, benzene), 6.62 (4H, s, benzene),
2.24 (6H, s, CH3), 2.14 (12H, s, CH3).
Synthesis of 10. To a light yellow suspension of 2-(4-ethylphe-
nyl)benzothiazoline (0.51 g, 2.1 mmol) in ethanol (20 mL) was
added cadmium(II) acetate dihydrate (0.28 g, 1.1 mmol). The
reaction mixture was stirred at room temperature for 1 h. The
resulting orange powder was collected by filtration. Yield: 0.52 g,
83%. Anal. Calcd for C60H56Cd2N4S4: C, 60.75; H, 4.76; N, 4.72.
Found. C, 60.76; H, 4.73; N, 4.78. IR (KBr; cm-1): 1603 (νCdN).
1H NMR (500 MHz, CDCl3): δ 8.40 (2H, s, CH)N), 7.65 (2H, d,
J ) 7.9, benzene), 7.61 (4H, d, J ) 7.9, benzene), 7.15 (2H, t, J )
7.6, benzene), 7.00 (2H, t, J ) 7.6, benzene), 6.90 (2H, d, J ) 7.9,
benzene), 6.88 (4H, d, J ) 7.9, benzene), 2.56 (4H, q, J ) 7.5,
CH2), 1.15 (6H, t, J ) 7.6, CH3).
Acknowledgment. K.N. gratefully acknowledges financial
support from the Ministry of Education, Science, Sports, and
Culture for a Grant-in-Aid for Scientific Research (18550054).
Supporting Information Available: X-ray crystallographic files
in CIF format for the structures in this work, molecular structure
of 5 (Figure S1), absorption spectra of zinc(II) and cadmium(II)
complexes (Figures S2 and S3), and relationship between the
emission maxima and the Hammett substituent constants in cad-
mium(II) complexes (Figure S4, PDF). This material is available
free of charge via the Internet at http://pubs.acs.org.
Synthesis of 11. To a light yellow suspension of 2-(4-methoxy-
phenyl)benzothiazoline (0.40 g, 1.7 mmol) in ethanol (20 mL) was
added cadmium(II) acetate dihydrate (0.22 g, 0.83 mmol). The
reaction mixture was stirred at room temperature for 1 h. The
resulting yellow powder was collected by filtration. Yield: 0.44 g,
IC7020758
3104 Inorganic Chemistry, Vol. 47, No. 8, 2008