Square-planar N2S2NiII complexes with an extended π-conjugated system

Article abstract of DOI:10.1021/ic0618246

The reaction of a mixture of 2-(1-naphthyl)benzothiazoline (HL¹) and 2,6-diphenylbenzo[1,2-d:4,5-d′]bisthiazoline (H₃L ²) with nickel(II) acetate tetrahydrate yielded three kinds of square-planar nickel(II) complexes: one nickel(II) complex with innocent ligands ([Ni(L¹)₂] (1c)) and two nickel(II) complexes with non-innocent ligands ([Ni(L¹-L¹)] (1a) and [Ni(L ¹-L²)] (1b)). The complex 1c has two bidentate-N,S ligands, which are formed via ring opening of HL¹. On the other hand, the two complexes 1a and 1b contain a tetradentate-N₂S₂ ligand, which is created via ring opening of HL¹ and H ₃L², followed by bond formation between imino carbon atoms. Complexes 1a and 1b show very intense absorptions in the near-infrared (NIR) region, characteristic of square-planar complexes with non-innocent ligands. The third nickel(II) complex having a non-innocent tetradentate-N ₂S₂ ligand ([Ni(L²-L²)] (2)) was prepared from H₃L² and nickel(II) acetate tetrahydrate. The electronic spectrum of 2 exhibits a very intense absorption at 981 nm (ε = 3.6 × 10⁴ M^-1 cm^-1), which is significantly red-shifted compared with those of 1a (837 nm and 4.4 × 10⁴ M^-1 cm^-1) and 1b (885 nm and 4.5 × 10⁴ M^-1 cm^-1), indicating the presence of an extended π delocalization. The reaction of 2,6-bis(3,5-dichlorophenyl) benzo[1,2-d:4,5-d′]bisthiazoline (H₃L³) with nickel(II) acetate tetrahydrate also led to the formation of a nickel(II) complex with a non-innocent ligand ([Ni(L³-L³)] (3)). While complex 3 is analogous to 2, its electrical conductivity is much higher than that of 2. The molecular structures of 1b, 1c, 2, and 3 were determined by X-ray crystallography.

Full text of DOI:10.1021/ic0618246

Inorg. Chem. 2007, 46, 4239−4247
Square-Planar N2S2NiII Complexes with an Extended
System
π-Conjugated
Tatsuya Kawamoto,* Kazunori Takeda, Masato Nishiwaki, Takashi Aridomi, and Takumi Konno
Department of Chemistry, Graduate School of Science, Osaka UniVersity, 1-16 Machikaneyama,
Toyonaka, Osaka 560-0043, Japan
Received September 25, 2006
The reaction of a mixture of 2-(1-naphthyl)benzothiazoline (HL1) and 2,6-diphenylbenzo[1,2-d:4,5-d
′]bisthiazoline
(H3L2) with nickel(II) acetate tetrahydrate yielded three kinds of square-planar nickel(II) complexes: one nickel(II)
complex with innocent ligands ([Ni(L1)2] (1c)) and two nickel(II) complexes with non-innocent ligands ([Ni(L1
−
L1)]
(1a) and [Ni(L1 L2)] (1b)). The complex 1c has two bidentate-N,S ligands, which are formed via ring opening of
−
HL1. On the other hand, the two complexes 1a and 1b contain a tetradentate-N2S2 ligand, which is created via ring
opening of HL1 and H3L2, followed by bond formation between imino carbon atoms. Complexes 1a and 1b show
very intense absorptions in the near-infrared (NIR) region, characteristic of square-planar complexes with non-
innocent ligands. The third nickel(II) complex having a non-innocent tetradentate-N2S2 ligand ([Ni(L2 L2)] (2)) was
−
prepared from H3L2 and nickel(II) acetate tetrahydrate. The electronic spectrum of 2 exhibits a very intense absorption
1
at 981 nm (ꢀ ) 3.6
×
104 M- cm-1), which is significantly red-shifted compared with those of 1a (837 nm and
1
1
4.4
×
104 M- cm-1) and 1b (885 nm and 4.5
delocalization. The reaction of 2,6-bis(3,5-dichlorophenyl)benzo[1,2-d:4,5-d
tetrahydrate also led to the formation of a nickel(II) complex with a non-innocent ligand ([Ni(L3
×
104 M- cm-1), indicating the presence of an extended
π
′
]bisthiazoline (H3L3) with nickel(II) acetate
L3)] (3)). While
−
complex 3 is analogous to 2, its electrical conductivity is much higher than that of 2. The molecular structures of
1b, 1c, 2, and 3 were determined by X-ray crystallography.
Introduction
[Ni(tmdt)2] (tmdt ) trimethylenetetrathiafulvalenedithiolate),
which shows a very high conductivity.5 In addition, metal
complexes with non-innocent ligands are expected as a new
family of near-infrared (NIR)-absorbing dyes because they
tend to exhibit a very intense absorption in the NIR region.6,7
Such metal complexes, therefore, possess a great possibility
Since the early 1960s, transition-metal complexes display-
ing non-innocent redox behavior, typified by dithiolene metal
complexes, have received much attention1 because of their
attractive properties such as conductivity and magnetism.2
In particular, considerable research efforts have been centered
on the development of single-component molecular conduc-
tors,3,4 prompted by the discovery of the dithiolene complex
(4) Llusar, R.; Uriel, S.; Vicent, C.; Clemente-Juan, J. M.; Coronado, E.;
Go´mez-Garc´ıa, C. J.; Bra¨ıda, B.; Canadell, E. J. Am. Chem. Soc. 2004,
126, 12076.
* To whom correspondence should be addressed. E-mail: kaw@
ch.wani.osaka-u.ac.jp.
(5) Tanaka, H.; Okano, Y.; Kobayashi, H.; Suzuki, W.; Kobayashi, A.
Science 2001, 291, 285.
(1) (a) McCleverty, J. A. Prog. Inorg. Chem. 1968, 10, 49. (b) Schrauzer,
G. N. Acc. Chem. Res. 1969, 2, 72. (c) Holm, R. H.; O’Connor, M. J.
Prog. Inorg. Chem. 1971, 14, 241. The term “non-innocent”, which
was introduced by Jørgensen [Jørgensen, C. K. Struct. Bonding (Berlin)
1966, 1, 234], is often used for a redox-active complex. The recent
reports have suggested that non-innocent behavior in the square-planar
complexes ([M(L)2]) is provided by the ligands that consist of two
radical monoanions having antiferromagnetically coupled spins. See
ref 7. The term “innocent” is used for ligands that are not “non-
innocent”.
(6) (a) Campbell, J.; Jackson, D. A.; Stark, W. M.; Watson, A. A. Dyes
Pigm. 1991, 15, 15. (b) Fabian, J.; Nakazumi, H.; Matsuoka, M. Chem.
ReV. 1992, 92, 1197. (c) Bigoli, F.; Cassoux, P.; Deplano, P.; Mercuri,
M. L.; Pellinghelli, M. A.; Pintus, G.; Serpe, A.; Trogu, E. F. J. Chem.
Soc., Dalton Trans. 2000, 4639. (d) Schwab, P. F. H.; Diegoli, S.;
Biancardo, M.; Bignozzi, C. A. Inorg. Chem. 2003, 42, 6613.
(7) (a) Chaudhuri, P.; Verani, C. N.; Bill, E.; Bothe, E.; Weyhermu¨ller,
T.; Wieghardt, K. J. Am. Chem. Soc. 2001, 123, 2213. (b) Herebian,
D.; Bothe, E.; Bill, E.; Weyhermu¨ller, T.; Wieghardt, K. J. Am. Chem.
Soc. 2001, 123, 10012. (c) Herebian, D.; Bothe, E.; Neese, F.;
Weyhermu¨ller, T.; Wieghardt, K. J. Am. Chem. Soc. 2003, 125, 9116.
(d) Min, K. S.; Weyhermu¨ller, T.; Bothe, E.; Wieghardt, K. Inorg.
Chem. 2004, 43, 2922. (e) Ray, K.; Weyhermu¨ller, T.; Neese, F.;
Wieghardt, K. Inorg. Chem. 2005, 44, 5345.
(2) Stiefel, E. I. Prog. Inorg. Chem. 2004, 52.
(3) Mitsumi, M.; Goto, H.; Umebayashi, S.; Ozawa, Y.; Kobayashi, M.;
Yokoyama, T.; Tanaka, H.; Kuroda, S.; Toriumi, K. Angew. Chem.,
Int. Ed. 2005, 44, 4164.
10.1021/ic0618246 CCC: $37.00
Published on Web 04/10/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 10, 2007 4239

Kawamoto et al.
Scheme 1
formed by a CV-600A apparatus (BAS) with complex concentra-
tions of 0.5 mM at 25 °C in 0.1 mol dm-3 [Bu4N]BF4/CH2Cl2 with
a glassy-carbon working electrode, a Ag/Ag+ reference electrode,
and a platinum-wire auxiliary electrode. The scan rates were 100
mV s-1. Spectroelectrochemical studies were performed by a CV-
600A apparatus (BAS) using a thin-layer quartz cell (0.5 mm light
path length) with a platinum-mesh (100 mesh) working electrode.
The computational details of the discrete variational (DV)-XR
method used in the present work have been described elsewhere.13
The atomic radius R0 for each atom was obtained from the values
determined by Slater.14 The sample points were taken up to 90 000.
Self-consistency within 0.003e was obtained for the orbital popula-
tions. Electrical resistivities of complexes 2 and 3 were measured
at room temperature for compacted pellets by the conventional two-
probe method.15 Elemental analyses were performed at Osaka
University.
to be applied as attractive multifunctional materials. How-
ever, only a few examples of metal complexes with non-
innocent ligands have been recognized to exhibit multifunc-
tional properties,8 except for those showing conductivity and
magnetism.9
Previously, we found a facile synthetic method, not
electrochemical oxidation or reduction, of d8 metal complexes
(M ) Ni, Pt) having a unique N2S2 donor set that show
intense absorptions in the range of 700-850 nm (Scheme
1).10 Furthermore, based on this synthetic method, we have
synthesized nickel(II) complexes with an extended π-con-
jugated system that show an intense absorption band at lower
energy of ca. 950 nm, although their structures and electronic
properties remained uncertain.11 Herein we report on the
synthesis and characterization of a family of nickel(II)
complexes with an extended π-conjugated system that is
regarded as a potential multifunctional material for NIR-
absorbing dye and conductor.
Synthesis of 2,6-Bis(3,5-dichlorophenyl)benzo[1,2-d:4,5-d′]-
bisthiazoline (H3L3). To a solution of NaOH (0.18 g, 4.5 mmol)
in 30 mL of hot ethanol was added 2,5-diamino-1,4-benzenethiol
dihydrochloride (0.20 g, 0.82 mmol) and 3,5-dichlorobenzaldehyde
(0.29 g, 1.6 mmol). The mixture was refluxed for 2 h and then
allowed to cool to room temperature. The light-yellow powder
precipitated was collected by filtration. The powder was dissolved
in 200 mL of THF, and insoluble NaCl was removed by filtration.
The resulting yellow solution was evaporated to dryness to afford
a yellow powder. Yield: 0.25 g, 61%. Anal. Found: C, 50.33; H,
2.88; N, 5.93. Calcd for H3L3‚0.25THF: C, 50.02; H, 2.80; N, 5.55.
1
IR (Nujol; cm-1): 3238 (νN-H). H NMR (500 MHz, DMSO-d6):
Experimental Section
δ 7.51 (s, 2H), 7.46 (d, 4H), 6.58 (d, 2H), 6.54 (br s, 2H), 6.32
(t, 2H).
General Procedures. All of the synthetic reactions were carried
out under an inert gas atmosphere using standard Schlenk tech-
niques. Workup procedures, including column chromatography,
were performed in air. The reagents were commercial samples and
were not purified further. 2-(1-Naphthyl)benzothiazoline (HL1)12
and 2,6-diphenylbenzo[1,2-d:4,5-d′]bisthiazoline (H3L2)11 were
prepared as described previously. The absorption and diffuse-
reflectance spectra were recorded with a Jasco V-570 spectropho-
tometer at room temperature. The reflectance spectra on MgSO4-
diluted samples were transformed into absorption spectra by using
the Kubelka-Munk equation. The 1H NMR spectra were recorded
with a JEOL GSX 500 spectrometer. The IR spectra in the region
of 4000-400 cm-1 were measured on a Jasco FT/IR-550 spec-
trometer by using Nujol mulls. Voltammetric studies were per-
Synthesis of [Ni(L1-L1)] (1a), [Ni(L1-L2)] (1b), and [Ni(L1)2]
(1c). To a light-yellow suspension containing HL1 (0.53 g, 2.0
mmol) and H3L2 (0.32 g, 0.92 mmol) in 60 mL of ethanol was
added nickel(II) acetate tetrahydrate (0.55 g, 2.2 mmol). The
reaction mixture was refluxed for 3 h and allowed to cool in a
refrigerator overnight. The greenish-brown powder precipitated was
collected by filtration and redissolved in 100 mL of CH2Cl2. After
filtration, the greenish-brown filtrate was concentrated to ca. 20
mL and poured onto a silica gel column. The separation with CH2-
Cl2/n-hexane (5:1) eluent gave mainly three bands. The first purple
and second green bands were collected and evaporated to dryness,
yielding 1a as a purple powder (12 mg) and 1b as a green powder
(45 mg). The green product 1b was recrystallized from CHCl3/
CH3OH in a refrigerator. The third red band was also collected
and evaporated to dryness, yielding 1c as a red-brown powder (55
mg). This red-brown product was recrystallized from CH2Cl2/n-
hexane. 1a. Anal. Found: C, 66.52; H, 5.55; N, 3.92. Calcd for
1a‚0.75CH2Cl2‚C6H14: C, 66.75; H, 5.43; N, 3.82. IR (Nujol; cm-1):
(8) (a) Smucker, B. W.; Hudson, J. M.; Omary, M. A.; Dunbar, K. R.
Inorg. Chem. 2003, 42, 4714. (b) Kobayashi, A.; Sasa, M.; Suzuki,
W.; Fujiwara, E.; Tanaka, H.; Tokumoto, M.; Okano, Y.; Fujiwara,
H.; Kobayashi, H. J. Am. Chem. Soc. 2004, 126, 426.
(9) (a) Imai, H.; Otsuka, T.; Naito, T.; Awaga, K.; Inabe, T. J. Am. Chem.
Soc. 1999, 121, 8098. (b) Aonuma, S.; Casellas, H.; Faulmann, C.;
Garreau, de Bonneval, B.; Malfant, I.; Cassoux, P.; Lacroix, P. G.;
Hosokawa, Y.; Inoue, K. J. Mater. Chem. 2001, 11, 337. (c) Mukai,
K.; Senba, N.; Hatanaka, T.; Minakuchi, H.; Ohara, K.; Taniguchi,
M.; Misaki, Y.; Hosokoshi, Y.; Inoue, K.; Azuma, N. Inorg. Chem.
2004, 43, 566.
(10) The reaction of 2-phenylbenzothiazoline with a nickel(II) ion leads
to a Schiff base nickel(II) complex via deprotonation with a ring-
opening reaction. Upon stirring of the toluene solution of the Schiff
base complex, a nickel(II) complex with a non-innocent ligand is
formed through C-C bond formation. The connected carbon atoms
are asymmetric. Both of the nickel(II) complexes, which have the same
chemical compositions, can be correlated to each other as valence
isomers. See: (a) Kawamoto, T.; Nagasawa, I.; Kuma, H.; Kushi, Y.
Inorg. Chim. Acta 1997, 265, 163. (b) Kawamoto, T.; Kuma, H.; Kushi,
Y. Bull. Chem. Soc. Jpn. 1997, 70, 1599. (c) Kawamoto, T.; Kushi,
Y. Bull. Chem. Soc. Jpn. 2004, 77, 289.
1
1595 and 1570 (νCdC). H NMR (500 MHz, CDCl3): δ 8.30 (d,
2H), 8.00 (d, 2H), 7.79 (d, 2H), 7.71 (d, 2H), 7.64 (t, 2H), 7.54 (t,
2H), 7.32 (d, 2H), 7.20 (t, 2H), 7.15 (s, 2H), 7.07 (t, 2H), 7.01 (d,
2H), 6.81 (t, 2H). UV/vis/NIR (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1
)
1143 (4.0 × 103), 985 (3.4 × 103), 837 (4.4 × 104), 353sh (6.3 ×
103). 1b. Anal. Found: C, 61.01; H, 3.72; N, 5.74. Calcd for Ni-
(L1-L2)‚0.5CHCl3‚CH3OH: C, 60.99; H, 3.92; N, 5.54. IR (Nujol;
1
cm-1): 1597 and 1570 (νCdC). H NMR (500 MHz, CDCl3): δ
8.47 (d, 1H), 8.24 (s, 1H), 8.01-7.98 (m, 3H), 7.82 (t, 1H), 7.76
(d, 1H), 7.74 (d, 1H), 7.69 (t, 1H), 7.65 (s, 1H), 7.59 (d, 2H), 7.50
(13) Adachi, H.; Tsukada, M.; Satoko, C. J. Phys. Soc. Jpn. 1978, 45, 875.
(14) Slater, J. C. Symmetry and Energy Bands in Crystals; Dover
Publications, Inc.: New York, 1972; p 55.
(15) Nakahama, A.; Nakano, M.; Matsubayashi, G. Inorg. Chim. Acta 1999,
284, 55.
(11) Kawamoto, T.; Konno, T. Mol. Cryst. Liq. Cryst. 2002, 379, 443.
(12) Kawamoto, T.; Nagasawa, I.; Kuma, H.; Kushi, Y. Inorg. Chem. 1996,
35, 2427.
4240 Inorganic Chemistry, Vol. 46, No. 10, 2007

Square-Planar N2S2NiII Complexes
Table 1. Crystallographic Data for 1b, 1c, 2, and 3
1b
1c‚CH2Cl2
2‚2CH2Cl2
3‚CH2Cl2‚DMF
empirical formula
M
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
C37H25N3NiS3
666.49
monoclinic
P21/n
11.730(8)
18.139(13)
13.679(5)
C35H26Cl2N2NiS2
668.31
monoclinic
P21/n
12.507(2)
13.842(3)
18.215(3)
C42H30Cl4N4NiS4
919.45
triclinic
P1h
11.375(8)
12.467(10)
15.068(11)
97.94(6)
109.01(5)
93.77(6)
1987(3)
2
C45H29Cl12N5NiOS4
1268.08
triclinic
P1h
11.85(3)
12.63(4)
19.59(5)
95.0(3)
102.3(2)
113.6(2)
2575(12)
2
94.60(3)
91.916(14)
2901(3)
4
3151.5(10)
4
Z
F(000)
1376
1376
940
1.537
1.006
0.0689
1276
1.635
1.204
0.0795
D
calcd/g cm-3
1.526
0.919
0.0579
0.1216
1.409
0.945
0.0451
0.1535
µ/mm-1
R1a (obsd)
wR2b (all)
0.2114
0.2467
a R1 ) ∑|(|Fo| - |Fc|)|/∑(|Fo|). b wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
2
2
2
(t, 1H), 7.44 (d, 2H), 7.38-7.31 (m, 3H), 7.18 (s, 1H), 7.15 (d,
1H), 7.12 (t, 1H), 7.02 (d, 1H), 6.91 (t, 1H), 6.85 (d, 1H), 6.32 (s,
1H). UV/vis/NIR (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1) 1229 (6.6 ×
103), 1048 (4.5 × 103), 885 (4.5 × 104), 361 (2.0 × 104). 1c. Anal.
Found: C, 63.02; H, 4.04; N, 4.27. Calcd for 1c‚CH2Cl2: C, 62.90;
H, 3.92; N, 4.19. IR (Nujol; cm-1): 1593 and 1574 (νCdN and νCd
and 3‚CH2Cl2‚DMF were made on a Rigaku RAXIS RAPID image-
plate diffractometer at 200 K and that for 1c‚CH2Cl2 on a Rigaku
AFC5R four-cycle diffractometer using graphite-monochromated
Mo KR radiation at room temperature. Crystallographic data are
summarized in Table 1. A total of 44 oscillation images for 1b
and 2‚2CH2Cl2 and a total of 74 oscillation images for 3‚CH2Cl2‚
DMF were collected. A sweep of data for 1b and 2‚2CH2Cl2 was
done using ω scans from 130.0 to 190.0° in 5.0° steps, at ø )
45.0° and φ ) 0.0°. That for 3‚CH2Cl2‚DMF was done using ω
scans from 130.0 to 190.0° in 3.0° steps, at ø ) 45.0° and φ )
30.0°. The exposure rate for 1b and 3‚CH2Cl2‚DMF was 300.0
s/deg, and that for 2‚2CH2Cl2 was 258.0 s/deg. The intensity data
of 1c‚CH2Cl2 were collected by the ω-2θ scan mode up to 2θ )
55.0°. An empirical absorption correction was applied for each
complex. The 23 871, 7555, 6648, and 10 088 independent reflec-
tions with I > 2σ(I) of the measured 48 680, 7874, 13 532, and
20 230 reflections for 1b, 1c‚CH2Cl2, 2‚2CH2Cl2, and 3‚CH2Cl2‚
DMF, respectively, were considered as “observed” and used for
the structure determination. All of the structures were solved by
direct methods and expanded using Fourier techniques. All non-
hydrogen atoms were refined anisotropically by full-matrix least-
squares methods. Hydrogen atoms for 1b and 1c were generated
by difference Fourier synthesis and refined isotropically, while those
for 2 and 3 were included in calculated positions and refined using
a riding model. All calculations were performed using the SHELXL-
97 program.16
1
C). H NMR (500 MHz, CDCl3): δ 10.73 (d, 2H), 8.19 (s, 2H),
7.95 (d, 2H), 7.84 (d, 2H), 7.60 (t, 2H), 7.41 (d, 2H), 7.39 (t, 2H),
7.16 (t, 2H), 7.03 (d, 2H), 7.01 (t, 2H), 6.59 (t, 2H), 5.89 (d, 2H).
UV/vis/NIR (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1) 513sh (3.3 × 103),
467 (3.9 × 103), 344 (1.3 × 103).
Synthesis of 1c (Direct Synthetic Method). A suspension of
HL1 (0.11 g, 0.42 mmol) and nickel(II) acetate tetrahydrate (0.06
g, 0.24 mmol) in 20 mL of ethanol was heated to reflux for 30
min. A dark-red precipitate was collected by filtration. Yield: 0.07
g, 57%.
Synthesis of [Ni(L2-L2)] (2). To a light-yellow suspension of
H3L2 (0.32 g, 0.92 mmol) in 30 mL of ethanol was added nickel-
(II) acetate tetrahydrate (0.30 g, 1.2 mmol). The reaction mixture
was refluxed for 2 h and allowed to cool in a refrigerator overnight.
The resulting green powder was collected by filtration and
redissolved in 50 mL of CH2Cl2. After filtration, the green product
was dried in vacuo and recrystallized from dimethylformamide
(DMF)/CH2Cl2. Yield: 0.07 g, 17%. Anal. Found: C, 56.59; H,
3.85; N, 7.03. Calcd for 2‚0.5DMF‚1.5CH2Cl2: C, 56.53; H, 3.59;
N, 6.90. IR (Nujol; cm-1): 1601, 1584, and 1572 (νCdN and νCd
C). UV/vis/NIR (DMF): λmax/nm (ꢀ/M-1 cm-1) 1559 (4.4 × 103),
981 (3.6 × 104), 572 (1.4 × 104), 514 (1.3 × 104), 404 (4.5 ×
Results and Discussion
104). Electrical conductivity (S cm-1): 5.9 × 10-8
.
Synthesis, Structures, and Properties of 1a-1c. The
three nickel(II) complexes 1a-1c were obtained in a ratio
of roughly 1a:1b:1c ) 1:3:5 from the reaction of a mixture
of HL1 and H3L2 with nickel(II) acetate tetrahydrate in
ethanol (Scheme 2). These nickel(II) complexes were
Synthesis of [Ni(L3-L3)] (3). To a yellow suspension of H3L3
(0.47 g, 0.93 mmol) in 30 mL of ethanol was added nickel(II)
acetate tetrahydrate (0.30 g, 1.2 mmol). The reaction mixture was
refluxed for 3 h and allowed to cool in a refrigerator overnight.
The resulting green powder was collected by filtration and
redissolved in 50 mL of CH2Cl2. After filtration, the dark-green
product was dried in vacuo and recrystallized from DMF/CH2Cl2.
Yield: 0.17 g, 30%. Anal. Found: C, 45.25; H, 2.69; N, 6.14. Calcd
for 3‚1.5DMF‚0.75CH2Cl2: C, 45.35; H, 2.52; N, 6.43. IR (Nujol;
1
characterized by elemental analyses, UV/vis/NIR and H
NMR spectroscopies, and cyclic voltammetry, besides X-ray
crystallography for 1b and 1c. While 1c was also prepared
by the reaction of HL1 and nickel(II) acetate tetrahydrate,
attempts to prepare 1a upon heating 1c in toluene, according
to the previously reported procedure (Scheme 1), were
unsuccessful. This indicates that the intramolecular C-C
cm-1): 1568 (νCdN). UV/vis/NIR (DMF): λmax/nm (ꢀ/M-1 cm-1
)
1574 (5.3 × 103), 995 (3.7 × 104), 626 (1.6 × 104), 523 (1.6 ×
104), 434 (4.1 × 104). Electrical conductivity (S cm-1): 1.5 × 10-5
.
X-ray Crystallography. Crystals were grown from CHCl3/CH3-
OH (1b), CH2Cl2/n-hexane (1c), and DMF/CH2Cl2 (2 and 3).
Single-crystal X-ray diffraction measurements for 1b, 2‚2CH2Cl2,
(16) Sheldrick, G. M. SHELXL-97. A Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 46, No. 10, 2007 4241

Kawamoto et al.
Figure 1. Absorption spectra of 1a (dotted line), 1b (dashed-dotted line),
and 1c (solid line) in CH2Cl2.
Scheme 2
Figure 2. Molecular structure of 1b.
Figure 3. Molecular structure of 1c.
bond formation reaction in 1c is inhibited by the steric
hindrance between two 1-naphthyl groups.
absorption spectrum with that of H3L2.17 On the other hand,
the absorption spectrum of 1c shows a visible band at 467
nm (ꢀ ) 3.9 × 103 M-1 cm-1) with a shoulder on the lower
energy side, and no intense absorption band is observed in
the NIR region.
The sharp N-H stretching bands found in the IR spectra
of free HL1 and H3L2 (3334 cm-1 for HL1 and 3242 cm-1
for H3L2) were not recognized in the spectra of 1a-1c, in
agreement with the formation of N,S-type chelates via ring
opening of benzothiazolines. The UV/vis/NIR absorption
spectra of 1a-1c are shown in Figure 1. Complex 1a, which
is a deep-violet color in CH2Cl2, gives a very intense
absorption band at 837 nm (ꢀ ) 4.4 × 104 M-1 cm-1). This
absorption band is characteristic of square-planar d8 metal
complexes with non-innocent ligands,7 including nickel(II)
and platinum(II) complexes derived from 2-substituted
benzothiazolines through C-C bond formation.10 The ab-
sorption spectrum of 1b, which is a green color in CH2Cl2,
is similar to that of 1a in terms of the overall shape. However,
1
The H NMR spectra of 1a-1c are shown in Figure S1
1
in the Supporting Information. The H NMR spectrum of
1a shows one singlet at δ 7.15 assignable to the protons on
asymmetric carbon atoms, besides six doublets and five
triplets in the aromatic region. These signals correspond to
a half-set of protons for 1a. This result, along with the
elemental analysis, indicates that 1a has a symmetrical
structure with a tetradentate ligand that is generated by the
C-C bond formation between two bidentate-N,S ligands L1.
1
Of particular note for the H NMR spectrum of 1b are the
λ
max in the vis/NIR absorption spectrum of 1b (885 nm and
characteristic four singlet resonances due to two protons on
asymmetric carbon atoms (δ 7.18 and 6.32) and two protons
of the N2S2-benzene ring (δ 8.24 and 7.65). In addition, the
ꢀ ) 4.5 × 104 M-1 cm-1) appears at lower energy than that
of 1a, indicative of more extensive π delocalization in 1b.
In addition, 1b displays an intense π-π* transition based
mainly on thiazole at 361 nm (ꢀ ) 2.0 × 104 M-1 cm-1),
the assignment of which is made by the comparison of its
(17) Roberts, M. F.; Jenekhe, S. A.; Cameron, A.; McMillan, M.; Perlstein,
J. Chem. Mater. 1994, 6, 658.
4242 Inorganic Chemistry, Vol. 46, No. 10, 2007

Square-Planar N2S2NiII Complexes
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1b
Ni1-S1
Ni1-S2
Ni1-N1
Ni1-N2
S1-C1
S2-C21
N1-C2
N2-C22
2.1006(14)
2.1229(16)
1.801(3)
1.806(4)
1.711(4)
1.702(4)
1.337(5)
1.335(5)
N1-C7
N2-C27
C7-C27
S3-C4
S3-C14
N3-C5
N3-C14
1.486(5)
1.487(5)
1.538(6)
1.732(4)
1.754(4)
1.357(5)
1.294(5)
S1-Ni1-S2
N1-Ni1-N2
93.50(6)
85.87(15)
S1-Ni1-N1
S2-Ni1-N2
90.23(11)
90.43(12)
Table 3. Selected Bond Distances (Å) and Angles (deg) for 1c‚CH2Cl2
Figure 4. Molecular orbitals of 1b and 2 based on the DV-XR calculation.
Ni1-S1
Ni1-S2
Ni1-N1
Ni1-N2
S1-C1
2.1628(14)
2.1650(14)
1.916(3)
1.936(3)
1.749(5)
1.744(5)
N1-C2
N2-C19
N1-C7
N2-C24
1.421(5)
1.432(5)
1.278(5)
1.280(5)
S2-C18
S1-Ni1-S2
N1-Ni1-N2
91.62(6)
96.86(13)
S1-Ni1-N1
S2-Ni1-N2
87.55(11)
87.79(10)
integration and coupling patterns of the remainder of the
aromatic signals confirms that 1b has an unsymmetrical
structure composed of L1 and L2 ligands. This result, along
with the elemental analysis, suggests that 1b contains an
unsymmetrical tetradentate ligand derived from the bidentate-
N,S ligands L1 and L2. The 1H NMR spectrum of 1c permits
an easier assignment; a singlet at δ 8.19 and a doublet at δ
10.73 can be assigned to azomethine protons and ortho
protons of naphthyl groups, respectively. The resonance for
ortho protons of naphthyl groups in 1c appears significantly
downfield compared with those of 1a (δ 8.30) and 1b (δ
8.47), indicative of a strong metal-ligand interaction.12 This
result, along with the elemental analysis, indicates that 1c
has a symmetrical structure with azomethine groups. The
1H NMR spectral change of 1a was monitored as a function
of time, which indicates that 1a changes to 1c with time in
CDCl3 (Figure S2 in the Supporting Information). It is seen
from this result that 1a has the same composition as 1c, and
hence 1a and 1c are correlated to each other as valence
isomers.10b
Figure 5. Cyclic voltammograms of 1a (solid line) and 1b (dotted line)
in CH2Cl2 (0.10 M [(n-Bu)4N]BF4) with a scan rate of 0.1 V s-1
.
The molecular structures of 1b and 1c, determined by
single-crystal X-ray analyses, are shown in Figures 2 and 3,
respectively. The selected bond distances and angles are listed
in Tables 2 and 3. As shown in Figure 2, 1b is a mononuclear
nickel(II) complex having a square-planar configuration, in
which a dihedral angle between the two S-Ni-N planes is
1.9°. The C-C bond (C7-C27) is formed between L1 and
L2 to give the tetradentate ligand L1-L2. The L2 moiety in
1b contains a thiazole ring [N3-C5 ) 1.357(5) Å; N3-
C14 ) 1.294(5) Å]. This implies that H3L2 is easily oxidized
to thiazole, as described in a previous paper.11 The Ni-S
[2.1006(14) and 2.1229(6) Å] and Ni-N [1.806(4) and
1.801(3) Å] bond distances are shorter than the normal values
of Ni-thiolato and Ni-imino distances10 but are comparable
to those reported for nickel(II) complexes with non-innocent
ligands.7,10 The C-S [1.711(4) and 1.702(4) Å] and C-N
[1.337(5) and 1.335(5) Å] bond distances are typical for other
Figure 6. Absorption spectra of 1b (solid line) and its electrochemi-
cally generated monoanion (dashed line) and dianion (dotted line) in
CH2Cl2.
non-innocent ligands.7,10 From these results, it is obvious that
1b has a non-innocent ligand.
Complex 1c consists of two bidentate-N,S ligands to form
a distorted square-planar structure with a dihedral angle
between the S-Ni-N planes of 21.5°. The coordination
environment has a cis geometry with a N2S2 donor set (Figure
3). The Ni-S [2.1628(14) and 2.1650(14) Å] and Ni-N
[1.916(3) and 1.936(3) Å] bond distances, which are longer
than those of 1b, are normal for four-coordinate imino-
thiolato nickel(II) complexes.10 Complex 1c shows a mo-
lecular helicity with crossing of two pendant naphthyl groups,
which is analogous to that found in [Ni(phbt)2].10
Inorganic Chemistry, Vol. 46, No. 10, 2007 4243

Kawamoto et al.
Table 4. Selected Bond Distances (Å) and Angles (deg) for 2‚2CH2Cl2
Ni1-S1
Ni1-S2
Ni1-N1
Ni1-N2
S1-C1
S2-C21
N1-C2
N2-C22
2.112(2)
2.1129(18)
1.802(4)
1.798(4)
1.723(5)
1.716(5)
1.350(6)
1.354(6)
N1-C7
N2-C27
C7-C27
S3-C4
S3-C14
N3-C5
N3-C14
S4-C24
S4-C34
N4-C25
N4-C34
1.464(5)
1.469(5)
1.536(6)
1.719(5)
1.743(5)
1.363(6)
1.274(6)
1.721(5)
1.756(5)
1.380(6)
1.283(6)
S1-Ni1-S2
N1-Ni1-N2
95.11(7)
86.72(17)
S1-Ni1-N1
S2-Ni1-N2
88.97(13)
89.19(13)
91 mV) and E21/2 ) -0.448 V (Epc - Epa ) 84 mV) for 1b
(Figure 5). The effect of the extension of conjugation in 1b
is clearly reflected in the observed redox potentials; 1b is
more easily reduced by 130 mV for E11/2 and by 76 mV for
E21/2 than 1a. In addition, one oxidative wave is also
observed for 1a and 1b at E31/2 ) 0.780 V (Epc - Epa ) 134
mV) and E31/2 ) 0.756 V (Epc - Epa ) 91 mV), respectively.
They are quasi-reversible and oxidative in nature.
Figure 7. Absorption spectra of 2 (dotted line) and 3 (solid line) in DMF.
The absorption spectra of the electrochemically generated
mono- and dianions of 1b are shown in Figure 6. While a
drastic decrease in the absorbance is observed for electro-
chemically reduced species (1b- and 1b2-), the HOMO_1
f LUMO transition for monoanion species 1b- is still
observed in the electronic spectrum, which shifts to lower
energy upon the reduction from the neutral material (885
nm for 1b and 937 nm for 1b-). On the other hand, in the
dianionic species 1b2-, the corresponding transition is made
impossible and the absorption band does not appear in the
NIR region. This behavior is similar to those of reduced
forms of square-planar bis(benzene-1,2-dithiolato)metal com-
plexes [M(L)2]0.7e The absorption intensity for the charge-
transfer transition in the NIR region of neutral complexes
with non-innocent ligands is generally weakened upon
oxidation or reduction,7 and hence it is hard to apply ionic
complexes with non-innocent ligands as a favorable NIR-
absorbing dye.
Figure 8. Molecular structure of 2.
To gain insight into the electronic structure of 1b, a
computational study was performed by using the DV-XR
molecular orbital calculation based on the X-ray structural
data. The DV-XR calculation suggests that the intense
absorption band at 885 nm is assigned to a HOMO_1(ψ171
)
Synthesis, Structure, and Properties of 2. Treatment of
H3L2 with nickel(II) acetate tetrahydrate in ethanol led to
the formation of 2. This nickel(II) complex was characterized
by elemental analysis and UV/vis/NIR spectroscopy, besides
X-ray crystallography. The low solubility of 2 in common
solvents precluded measurements of NMR spectra and cyclic
voltammograms, but UV/vis/NIR spectra could be recorded
in DMF.19
f LUMO(ψ173) transition (Figure 4). This calculation also
shows that not only the N2S2-benzene moieties but also the
nickel(II) center are involved in the NIR absorption band,18
whereas the contribution of the thiazole moiety is small and
the pendant naphthyl and phenyl groups are not involved.
The absorption band at 1229 nm in the NIR region is
assignable as arising from the HOMO(ψ172) f LUMO(ψ173
transition (Figure S3 in the Supporting Information).
)
The IR bands attributed to N-H stretching vibrations were
not observed in the IR spectrum of 2. The UV/vis/NIR
absorption spectrum of 2 gives an intense absorption band
at 981 nm (Figure 7), which is fairly red-shifted compared
with those of 1a and 1b with a slight reduction in ꢀmax (3.6
× 104 M-1 cm-1 for 2, 4.4 × 104 M-1 cm-1 for 1a, and 4.5
× 104 M-1 cm-1 for 1b). This is in agreement with the
extension of π conjugation in 2. In addition, the presence of
The electrochemistry of 1a and 1b was studied by cyclic
voltammetry and spectroelectrochemistry. In the cyclic
voltammetric studies, each complex displays two quasi-
reversible reductive waves at peak potentials of E11/2
)
-1.368 V (Epc - Epa ) 92 mV) and E2 ) -0.524 V (Epc
1/2
- Epa ) 98 mV) for 1a and E1 ) -1.238 V (Epc - Epa
)
1/2
(18) In a preliminary experiment, the characteristic NIR absorption band
in the cobalt(II) complex, [Co(L1-L2)], showed a pronounced blue
shift (705 nm) compared with that of the corresponding nickel(II)
complex (1b).
(19) The absorption spectra of 1a and 1b in DMF display intense bands at
833 and 887 nm, respectively.
4244 Inorganic Chemistry, Vol. 46, No. 10, 2007

Square-Planar N2S2NiII Complexes
Figure 9. Crystal structure of 2 showing intermolecular contacts (top) and its space-filling form showing the stacking perpendicular to the molecular
planes (bottom).
Scheme 3
two thiazole moieties in 2 is reflected in the intensity of the
absorption band at 404 nm (ꢀ ) 4.5 × 104 M-1 cm-1), which
is about 2 times that of 1b (ꢀ ) 2.0 × 104 M-1 cm-1) having
one thiazole moiety.
From DV-XR calculation based on the X-ray structural
data of 2 (vide infra), the absorption band at 981 nm is
assigned to a HOMO_1(ψ192) f LUMO(ψ194) transition
(Figure 4). This calculation also indicates that the ex-
tended π system containing a thiazole ring of 2 is pro-
foundly involved in the NIR absorption band. The absorp-
tion band for the HOMO(ψ193) f LUMO(ψ194) transition
is observed at 1559 nm (Figure S3 in the Supporting
Information).
The molecular structure of 2 is shown in Figure 8, and
the selected bond distances and angles are listed in Table 4.
Complex 2 consists of a tetradentate ligand, which was
generated by C-C bond formation (C7-C27) between the
two L2 ligands, accompanied by partial oxidation to form
thiazole rings. The geometry around the nickel(II) center is
square-planar with a dihedral angle between the S-Ni-N
planes of 0.8°. The Ni-S [2.112(2) and 2.1129(18) Å] and
Ni-N [1.802(4) and 1.798(4) Å] bond distances are typical
values found for other complexes with non-innocent ligands
and so are the C-S [1.723(5) and 1.716(5) Å] and C-N
[1.350(6) and 1.354(6) Å] bond distances.7,10 Thus, 2 is
regarded as a complex with a non-innocent ligand, which
has extended coplanar planes, with the two terminal carbon
atoms (C18 and C38) being separated by 22.883(9) Å. The
packing structure of 2 is shown in Figure 9. Each molecule
is surrounded by four neighboring molecules to form a 2-D
sheet structure interpenetrated to each other, aided by eight
edge-to-face interactions between the pendant phenyl groups
and the basal planes of molecules [C-C contacts (Å): C1‚
‚‚C30 ) 3.533(7), C6‚‚‚C31 ) 3.518(7), C10‚‚‚C18 ) 3.732-
(8), C11‚‚‚C21 ) 3.573(7), C30‚‚‚C38 ) 3.67(1)]. The
interplanar angles between benzene rings showing short
contacts are 92.5-96.8°. The shortest Ni‚‚‚Ni distance is
8.1394(8) Å.
Inorganic Chemistry, Vol. 46, No. 10, 2007 4245

Kawamoto et al.
Table 5. Selected Bond Distances (Å) and Angles (deg) for
3‚CH2Cl2‚DMF
Ni1-S1
Ni1-S2
Ni1-N1
Ni1-N2
S1-C1
S2-C21
N1-C2
N2-C22
2.126(10)
2.132(5)
1.815(7)
1.818(10)
1.712(9)
1.711(11)
1.339(11)
1.353(10)
N1-C7
N2-C27
C7-C27
S3-C4
S3-C14
N3-C5
N3-C14
S4-C24
S4-C34
N4-C25
N4-C34
1.464(11)
1.467(10)
1.515(12)
1.727(9)
1.748(12)
1.389(11)
1.295(10)
1.710(11)
1.763(9)
1.379(10)
1.279(11)
S1-Ni1-S2
N1-Ni1-N2
94.9(3)
85.6(4)
S1-Ni1-N1
S2-Ni1-N2
89.7(3)
89.7(3)
As mentioned above, there are CH/π interactions between
the protons of pendant phenyl groups and the N2S2-benzene
moieties of neighboring molecules in the crystal structure
of 2. It is expected that such intermolecular interactions
produce conduction paths to induce appreciable conductivity.
However, a room-temperature electrical conductivity of 2
in a compressed powder pellet was only 5.9 × 10-8 S cm-1.
Thus, in the solid phase of 2, the intermolecular contact due
to CH/π interactions seems to be inadequate to form effective
electron conduction pathways.
Figure 10. Molecular structure of 3.
the two partly oxidized L3 ligands. A consideration of the
Ni-S [2.126(10) and 2.132(5) Å], Ni-N [1.815(7) and
1.818(10) Å], C-S [1.712(9) and 1.711(11) Å], and C-N
[1.339(11) and 1.353(10) Å] bond distances, which are
similar to those observed in complexes with non-innocent
ligands,7,10 supports that 3, as well as 2, is a complex with
a non-innocent ligand. The π-conjugated system of 3 is as
large as that of 2 with the C18‚‚‚C38 distance of 22.92(2)
Å. The packing structure of 3 is shown in Figure 11. In 3,
each molecule is surrounded by five neighboring molecules
to form a 2-D sheet structure, stacked perpendicularly to the
molecular plane. The crystallization solvents are among the
2-D sheets, and no transverse interaction between the 2-D
sheets is found. The shortest Ni‚‚‚Ni distance is 7.150(2) Å.
The most interesting feature of the crystal structure in 3 is
that there exist face-to-face interactions [C-S contact (Å),
S1‚‚‚C5 ) 3.454(8); C-C contacts, C1‚‚‚C1 ) 3.40(1), C26‚
‚‚C39 ) 3.39(1) Å], which are not observed in 2, besides
three edge-to-face interactions between the pendant phenyl
groups and the basal planes of complexes [C10‚‚‚C18 )
3.76(2) Å, C11‚‚‚C35 ) 3.69(1) Å, and C11‚‚‚C36 ) 3.55-
(1) Å]. The corresponding interplanar angles in the face-to-
face and edge-to-face interactions are 0.0-1.4° and 87.7-
96.3°, respectively. In addition, two weak CH‚‚‚N hydrogen
bonds are observed between the pendant phenyl groups and
the thiazole rings of the basal planes [C29‚‚‚N3 ) 3.40(1)
Å; C-H‚‚‚N ) 157.1°].20 Although 3 has chlorine atoms in
the pendant phenyl ring and thus is expected to be more
sterically crowded compared with 2, the molecule of 3
aggregates in a more compact manner (Dcalcd ) 1.537 g cm-3
for 2 and 1.635 g cm-3 for 3) via several intermolecular
interactions containing face-to-face interactions as depicted
in Figure 11.
Synthesis, Structure, and Properties of 3. To improve
the electrical conductivity of 2, we employed H3L3 as a
starting material, which is expected to form a packing
structure different from that of 2 by replacing the hydrogen
atoms of the pendant phenyl rings in H3L2 with chlorine
atoms (Scheme 3). This starting reagent H3L3 was synthe-
sized according to the procedures for H3L2 and characterized
by elemental analysis and IR and 1H NMR spectroscopies.11
Treatment of H3L3 with nickel(II) acetate tetrahydrate in
ethanol led to the formation of 3. This nickel(II) complex
was characterized by elemental analysis and UV/vis/NIR
spectroscopy, besides X-ray crystallography.
The UV/vis/NIR absorption spectrum of 3 (Figure 7) gives
an intense NIR band at 995 nm (ꢀ ) 3.7 × 104 M-1 cm-1),
besides an intense visible band at 434 nm (ꢀ ) 4.1 × 104
M-1 cm-1). The NIR absorption band of 3 is slightly red-
shifted compared with that of 2. In addition, diffuse-
reflectance spectra of 2 and 3 reveal two broad bands at 990
and 1324 nm and at 1004 and 1358 nm, respectively (Figure
S4 in the Supporting Information).
From the DV-XR calculation on 3, it is suggested that
the absorption bands at 995 and 1574 nm are assigned to
HOMO-1(ψ256) f LUMO(ψ258) and HOMO(ψ257) f LUMO-
(ψ258) transitions, respectively (Figure S5 in the Supporting
Information). This result indicates that the extended π system
composed of the N2S2-benzene and thiazole moieties con-
taining the nickel(II) center exerts a great influence on NIR
absorption.
The structure of 3 was also determined by single-crystal
X-ray analysis. The selected bond distances and angles are
listed in Table 5. As shown in Figure 10, 3 has a square-
planar configuration as 2 does. The dihedral angle between
the S-Ni-N planes is 2.9°. The tetradentate-N2S2 ligand is
formed through C-C bond formation (C7-C27) between
(20) (a) Alekseyeva, E. S.; Batsanov, A. S.; Boyd, L. A.; Fox, M. A.;
Hibbert, T. G.; Howard, J. A. K.; MacBride, J. A. H.; Mackinnon,
A.; Wade, K. Dalton Trans. 2003, 475. (b) Cappelli, A.; Giorgi, G.;
Anzini, M.; Vomero, S.; Ristori, S.; Rossi, C.; Donati, A. Chem.s
Eur. J. 2004, 10, 3177.
4246 Inorganic Chemistry, Vol. 46, No. 10, 2007

Square-Planar N2S2NiII Complexes
Figure 11. Crystal structure of 3 showing intermolecular contacts (top) and its space-filling form showing the stacking perpendicular to the molecular
planes (bottom).
A pressed pellet of powdered 3 displays a room-temper-
ature electrical conductivity of 1.5 × 10-5 S cm-1. This
conductivity, while not especially high relative to those for
the reported single-component molecular conductors,3-5,21 is
noteworthy for the solid sample that has neither S‚‚‚S
contacts nor M‚‚‚M interactions.3 The electrical conductivity
of 3 is presumably due to the presence of partially filled
HOMO and LUMO bands, which is introduced by the large
intermolecular overlap and the small HOMO_LUMO energy
gap owing to an extended π-conjugated system, as indicated
by the reflectance spectrum. Judging from the electrical
a very intense absorption band at lower energy than those
of 1a and 1b, reflecting the more extended conjugate system.
The corresponding reaction with H3L3 gave [Ni(L3-L3)] (3),
which shows a very intense absorption band at the lowest
energy for the nickel(II) complexes with non-innocent ligands
in the present work. These results indicate that the fine
control of the NIR absorption is possible through the
adjustment of π-conjugated systems. Note that 3 shows an
electrical conductivity of 1.5 × 10-5 S cm-1, which is
significantly higher than that of 2 (5.9 × 10-8 S cm-1). This
behavior may be correlated to the difference in packing
structures, in which edge-to-face and face-to-face intermo-
lecular interactions are mainly observed for 2 and 3,
respectively. Finally, the present results indicate that mul-
tifunctional nickel(II) complexes available as both NIR-
absorbing dyes and semiconductors could be prepared
through the subtle changes of the π-conjugated ligands.
Further studies to construct 3-D assemblies with transverse
interactions are in progress in our laboratory.
conductivities (1.5 × 10-5 S cm-1 for 3 and 5.9 × 10-8
S
cm-1 for 2), it may be considered that the molecular array
with face-to-face interactions, which can form a dense
stacking structure, is more suitable for the construction of
electron-conduction pathways than that with edge-to-face
interactions.
Conclusion
The three kinds of nickel(II) complexes, [Ni(L1-L1)] (1a),
[Ni(L1-L2)] (1b), and [Ni(L1)2] (1c), were prepared by
treating nickel(II) acetate with a mixture of HL1 and H3L2.
Treatment of nickel(II) acetate with H3L2 afforded [Ni(L2-
L2)] (2) having a π-conjugated system. Complex 2 exhibits
Acknowledgment. We gratefully thank Dr. Motohiro
Nakano for the electrical resistivity measurements.
Supporting Information Available: Figures S1-S5 and X-ray
crystallographic files in CIF format for the structures in this work.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(21) (a) Belo, D.; Alves, H.; Lopes, E. B.; Duarte, M. T.; Gama, V.;
Henriques, R. T.; Almeida, M.; Pe´rez-Ben´ıtez, A.; Rovira, C.; Veciana,
J. A. Chem.sEur. J. 2001, 7, 511. (b) Itkis, M. E.; Chi, X.; Cordes,
A. W.; Haddon, R. C. Science 2002, 296, 1443.
IC0618246
Inorganic Chemistry, Vol. 46, No. 10, 2007 4247