Reversible ring opening and closure reactions of the triazine ligands derived from 1-phenylazo-2-naphthylamine and pyridine-2-aldehyde or quinoline-2-aldehyde - Structure and reactivity of the palladium (II) complexes

Article abstract of DOI:10.1016/j.ica.2004.08.024

New ligands containing a heterocyclic ring, L¹ (1-anilino-2-(2-pyridyl)-naphth[1,2-d]imidazol-1-io-3-ide), L² (2-phenyl-3-(2-pyridyl)-3,4-dihydro-naphtho[2,1-e][1,2,4]triazin-1-io-4-ide), and L³ (1-anilino-2-(2-quinolyl)-naphth[1,2-d]imidazol-1-io-3-ide), and their palladium (II) complexes have been prepared. Structures of the ligands and the complexes were determined by X-ray crystallography. The mononuclear square-planar complexes of [PdCl₂(Lⁿ)] (n = 1 (1), n = 2 (2) and n = 3 (3)) had didentate Lⁿ (n = 1-3) ligands. The L ⁿ (n = 1-3) ligands were stable and their absorption spectra did not change in dichloromethane and methanol. On the other hand, the absorption spectrum of [PdCl₂(L²)] (2) in dichloromethane changed rapidly when methanol was added to the solution, and [PdCl(L^4b)] (5) (L^4b = N-[methoxy(2-pyridyl)methyl]-1-(phenylazo)-2-naphthylamide) was obtained from the concentrated reaction mixture. In this reaction, the dihydrotriazine ring of the didentate L² ligand in complex 2 opened and the resulting tridentate L^4b ligand coordinated to the Pd atom in complex 5. When an excess amount of (ⁿBu)₄NCl was added to complex 5 in dichloromethane, the absorption spectrum reverted to that of complex 2. Thus, the reversible ring opening and closure reactions of the coordinating dihydrotriazine ligand were observed. We also prepared [PdCl ₂(L⁵)] (9) (L⁵ = 1-(phenylazo)-N-[1-(2-pyridyl) ethylidene]-2-naphthylamine) and determined the structure. It is noted that neither the ring closure reaction nor the coordination of the azo nitrogen atom of the L⁵ ligand occurred in complex 9.

Full text of DOI:10.1016/j.ica.2004.08.024

Inorganica Chimica Acta 358 (2005) 476–488
www.elsevier.com/locate/ica
Reversible ring opening and closure reactions of the triazine ligands
derived from 1-phenylazo-2-naphthylamine and
pyridine-2-aldehyde or quinoline-2-aldehyde –
structure and reactivity of the palladium(II) complexes
a
Zhicheng Zhu , Masaaki Kojima , Kiyohiko Nakajima
b
a,
*
a
Department of Chemistry, Aichi University of Education, Kariya, Aichi 448-8542, Japan
b
Department of Chemistry, Faculty of Science, Okayama University, Tsushima, Okayama 700-8530, Japan
Received 19 March 2004; accepted 31 August 2004
Available online 28 October 2004
Abstract
New ligands containing a heterocyclic ring, L1 (1-anilino-2-(2-pyridyl)-naphth[1,2-d]imidazol-1-io-3-ide), L2 (2-phenyl-3-(2-pyr-
idyl)-3,4-dihydro-naphtho[2,1-e][1,2,4]triazin-1-io-4-ide), and L3 (1-anilino-2-(2-quinolyl)-naphth[1,2-d]imidazol-1-io-3-ide), and
their palladium (II) complexes have been prepared. Structures of the ligands and the complexes were determined by X-ray crystal-
lography. The mononuclear square-planar complexes of [PdCl2(Ln)] (n = 1 (1), n = 2 (2) and n = 3 (3)) had didentate Ln (n = 1–3)
ligands. The Ln (n = 1–3) ligands were stable and their absorption spectra did not change in dichloromethane and methanol. On
the other hand, the absorption spectrum of [PdCl2(L2)] (2) in dichloromethane changed rapidly when methanol was added to the
solution, and [PdCl(L4b)] (5) (L4b = N-[methoxy(2-pyridyl)methyl]-1-(phenylazo)-2-naphthylamide) was obtained from the concen-
trated reaction mixture. In this reaction, the dihydrotriazine ring of the didentate L2 ligand in complex 2 opened and the resulting
tridentate L4b ligand coordinated to the Pd atom in complex 5. When an excess amount of (nBu)4NCl was added to complex 5 in
dichloromethane, the absorption spectrum reverted to that of complex 2. Thus, the reversible ring opening and closure reactions of
the coordinating dihydrotriazine ligand were observed. We also prepared [PdCl2(L5)] (9) (L5 = 1-(phenylazo)-N-[1-(2-pyridyl)ethy-
lidene]-2-naphthylamine) and determined the structure. It is noted that neither the ring closure reaction nor the coordination of the
azo nitrogen atom of the L5 ligand occurred in complex 9.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Palladium (II) complex; Ring opening and closure reaction; Crystal structure; Triazine; Imidazole; Azo ligand
1. Introduction
the p–p* and n–p* bands with UV or visible light.
They are also redox active and could be reduced step-
wise to a radical anion and a hydrazido(2ꢀ) species.
Recently, transition metal complexes containing vari-
ous kinds of azo ligands have attracted increasing
attention because of their interesting electronic and
geometrical features in connection with their applica-
tion for photo-switching devices, molecular memory
storage, etc. The structure and reactivity [1], redox
chemistry [2], and photochemical properties [3] of
Azoaromatic compounds are highly colored and
have long been used as dyes and pigments. It is well
known that the azo group is photoreactive and isomer-
izes between trans and cis conformers by irradiation of
*
Corresponding author. Fax: +81 566 26 2355.
E-mail address: knakajim@auecc.aichi-edu.ac.jp (K. Nakajima).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.08.024

Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
477
various azo complexes have been reported. It is ex-
2. Experimental
pected that the reactivity and properties of azo func-
tions will be controlled in conjunction with the
electronic state of the metal ions. For example, the
trans–cis photoisomerization of azobenzene–bipyridine
ligands was controlled with the Co(III)/Co(II) [4] or
Cu(II)/Cu(I) [5] redox reactions, although the nitrogen
atom of the azo functional group does not coordinate
to metal ions in these complexes.
This work arose from our current research interest
in the preparation of photo- and thermal-responsive
metal complexes incorporating an azo functional group
whose nitrogen atom coordinates to the metal ions. We
expect that the electronic state of the metal ions would
clearly affect the properties and reactivities of the coor-
dinating azo functional group. In a previous paper, we
reported the preparation, structures, and properties of
the mono-, di-, and trinuclear palladium (II) and
platinum (II) complexes with the ligands derived from
1-phenylazo-2-naphthylamine and 2-(diphenylphosph-
ino)benzaldehyde or 2-(tert-butylthio)benzaldehyde
[6]. In this paper, the related triazine and imidazole lig-
ands were successfully isolated, and their palladium (II)
complexes were prepared (Fig. 1). We determined the
structures of the ligands and complexes, and investi-
gated the ring opening and closure reactions of the tri-
azine skeleton.
2.1. General procedures
[PdCl2(PhCN)2] was prepared according to the litera-
1
ture procedure [7]. H NMR spectra were recorded at
400 MHz on a JEOL JNM LA-400 spectrometer with
TMS as the internal reference. IR spectra were obtained
on a KBr disk using a Perkin–Elmer Spectrum 2000 spec-
trophotometer. UV–VisspectraweremeasuredonaShim-
adzu UV-2500PC or UV-1650PC spectrophotometer.
2.2. Preparations
2.2.1. L1 and L2 ligands
1-Phenylazo-2-naphthylamine (0.294 g, 1.19 mmol)
was added to the methanol solution (30 cm3) of pyri-
dine-2-aldehyde (0.129 g, 1.20 mmol). The reaction mix-
ture was refluxed for 5 h and evaporated to dryness. The
red oily residue was then dissolved in diethyl ether (2
cm3) and the solution was cooled in an ice bath for 30
min to yield a pale orange precipitate of L1, which was
filtered and washed with a small amount of hexane.
The precipitate was dissolved in a small amount of
THF and n-hexane was added slowly. The mixture
was left at room temperature for several days to yield
pale yellow crystals of L1. Yield: 0.113 g, 28.2%. Anal.
Calc. for L1 = C22H16N4: C, 78.55; H, 4.79; N, 16.66.
Found: C, 78.45; H, 4.60; N, 16.71%. 1H NMR (chloro-
form-d) d = 10.12 (s, 1H), 8.83 (m, 1H), 8.61 (m, 1H),
8.35 (d, 1H), 7.98 (m, 1H), 7.92 (d, 1H), 7.79 (m, 2H),
7.49 (m, 2H), 7.28 (m, 1H), 7.10 (m, 2H), 6.86 (m,
1H), 6.60 (dd, 2H). UV–Vis {dichloromethane, r/103
cmꢀ1 (loge/Mꢀ1 cmꢀ1)} 28.1 (4.20), 28.9 (4.21), 31.7
(4.11), 33.1 (4.14), 35.2 (4.42), 42.8 (4.56). The filtrate
and the washings were combined and evaporated. The
resulting red oily residue was dissolved in dichlorometh-
ane and charged on top of a silica gel column (20
cm · 10 mm ID). Upon elution with a 1:1 mixture of
n-hexane and diethyl ether, several bands were devel-
oped. Red crystals of L2 were obtained from the eluate
containing the red band. Yield: 0.151 g, 37.9%. Anal.
Calc. for L2 = C22H16N4: C, 78.55; H, 4.79; N, 16.66.
Found: C, 78.33; H, 4.54; N, 16.64%. 1H NMR (chloro-
form-d) d = 8.63 (m, 1H), 8.09 (m, 1H), 7.60 (m, 3H),
7.31–7.42 (m, 6H), 7.27 (s, 1H), 7.24–7.17 (m, 3H),
6.85 (d, 1H). UV–Vis {dichloromethane, r/103 cmꢀ1
(loge/Mꢀ1 cmꢀ1)} 20.1 (4.02), 26.4 (3.47), 32.3 (4.19),
40.9 (4.57).
N
N
N
N
N
N
N
N
N
N
N
H
N
H
L1
L2
L3
N
4a; R=OH
N
N
4b; R=OMe
4c; R=OEt
4d; R=OnBu
N
R
4e; R=OC(O)Me
L4a-4e
N
N
N
N
N
N
2.2.2. L3 ligand
N
N
H3C
1-Phenylazo-2-naphthylamine (0.191 g, 0.77 mmol)
was added to the methanol solution (30 cm3) of quino-
line-2-aldehyde (0.122 g, 0.78 mmol) and the reaction
mixture was refluxed for 2 h to yield a pale yellow pre-
cipitate. The precipitate was filtered and dissolved in a
L5
L6
Fig. 1. Schematic representation of the ligands.

478
Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
small amount of dichloromethane. n-Hexane was added
slowly to the solution, which was left at room tempera-
ture for several days to yield pale yellow crystals of L3.
Yield: 0.218 g, 73.0%. Anal. Calc. for L3 = C26H18N4: C,
80.81; H, 4.69; N, 14.50. Found: C, 80.37; H, 4.41; N,
14.40%. The triazine ligand corresponding to L2 could
be in the filtrate but was not isolated. 1H NMR (chloro-
form-d) d = 10.53 (s, 1H), 8.88 (m, 1H), 8.51 (d, 1H),
8.26 (d, 1H), 8.13 (d, 1H), 8.00 (m, 1H), 7.96 (d, 1H),
7.84–7.75 (m, 3H), 7.60–7.47 (m, 3H), 7.09 (dd, 2H),
6.83 (t, 1H), 6.70 (d, 2H). UV–Vis {dichloromethane,
r/103 cmꢀ1 (loge/Mꢀ1 cmꢀ1)} 26.9 (4.48), 30.9 (4.09),
36.2 (4.68).
yield a yellow precipitate, which was filtered and air-
dried. Yield: 0.030 g, 92.4%. Anal. Calc. for
[PdCl2(L3)] = C26H17Cl2N4Pd: C, 55.49; H, 3.04; N,
1
9.96. Found: C, 55.32; H, 2.94; N, 9.86%. H NMR
(chloroform-d) d = 10.36 (s, 1H), 8.86 (m, 1H), 8.49
(d, 1H), 8.41 (d, 1H), 8.16–8.09 (m, 2H), 8.01–7.95 (m,
2H), 7.89–7.80 (m, 2H), 7.65 (td, 1H), 7.58–7.55 (m,
2H), 7.11 (t, 2H), 6.75 (t, 1H), 6.63 (d, 2H). UV–Vis
{dichloromethane, r/103 cmꢀ1 (loge/Mꢀ1 cmꢀ1)} 23.5
(3.70 sh), 24.8 (3.74), 32.6 (3.57 sh), 36.2 (4.07).
2.2.6. [PdCl(L4a)] (4)
Complex 2 (0.030 g, 0.059 mmol) was suspended in
dichloromethane (30 cm3)–acetone (20 cm3) and water
(4 cm3) was added. The reaction mixture was stirred
for 10 min. and evaporated to dryness. The residue
was dissolved in a small amount of dichloromethane.
n-Hexane was added slowly to the solution, which was
left at room temperature for several days to yield brown
crystals. Yield: 0.014 g, 47.9%. Anal. Calc. for
[PdCl(L4a)] = C22H17ClN4OPd: C, 53.35; H, 3.46; N,
2.2.3. [PdCl2(L1)] (1)
An acetonitrile solution (10 cm3) of [PdCl2(PhCN)2]
(0.016 g, 0.042 mmol) was added to dichloromethane–
acetonitrile (1:4 v/v) solution (25 cm3) of L1 (0.014 g,
0.042 mmol) with stirring. The reaction mixture was
warmed at 60 ꢁC in an oil bath for 2 h to yield a yellow
precipitate, which was filtered and air-dried. Yield: 0.018
g, 83.6%. Anal. Calc. for [PdCl2(L1)] = C22H16Cl2N4Pd:
C, 51.44; H, 3.14; N, 10.91. Found: C, 51.15; H, 2.73; N,
10.87%. The complex is almost insoluble in common or-
ganic solvents.
1
11.31. Found: C, 53.67; H, 3.48; N, 11.17%. H NMR
(chloroform-d) d = 9.26 (dd, 1H), 8.40 (d, 1H), 7.95
(m, 1H), 7.80 (d, 1H), 7.74 (d, 1H), 7.61 (m, 4H),
7.54–7.41 (m, 2H), 7.40–7.28 (m, 4H), 6.60 (d, 1H),
2.96 (d, 1H). UV–Vis {dichloromethane, r/103 cmꢀ1
(loge/Mꢀ1 cmꢀ1)} 18.5 (3.88), 20.0 (3.62 sh), 26.4
(3.97), 31.3 (4.13 sh), 33.8 (4.26 sh), 39.6 (4.68).
2.2.4. [PdCl2(L2)] (2)
Method A: [PdCl2(PhCN)2] (0.033 g, 0.086 mmol)
was added to a dichloromethane solution of L2 (0.032
g, 0.096 mmol). The reaction mixture was refluxed for
7 h and evaporated to 5 cm3. n-Hexane (20 cm3) was
added slowly and the solution was left overnight to yield
dark red crystals. Yield: 0.037 g, 83.4%. Anal. Calc. for
2.2.7. [PdCl(L4b)] (5), [PdCl(L4c)] (6), and [PdCl-
(L4d)] (7)
The following procedure is described for [PdCl(L4b)]
(5), as an example.
[PdCl2(L2)]Æ0.67CH2Cl2 = C22.66H17.33Cl3.33N4Pd:
C,
Method A: Methanol (20 cm3) was added to a suspen-
sion of complex 2 (0.101 g, 0.197 mmol) in dichloro-
methane (20 cm3). After the reaction mixture was
stirred for several minutes, the reddish purple solution
was filtered and evaporated to dryness. The residue
was dissolved in a small amount of dichloromethane.
Methanol was added slowly to the solution, which was
left at room temperature for several days to yield red-
dish-purple crystals. Yield: 0.086 g, 85.7%. Anal. Calc.
for [PdCl(L4b)] = C23H19ClN4OPd: C, 54.24; H, 3.76;
N, 11.00. Found: C, 54.10; H, 3.64; N, 10.91%. 1H
NMR (chloroform-d) d = 9.36 (dd, 1H), 8.43 (d, 1H),
7.97 (td, 1H), 7.78 (d, 1H), 7.70 (d, 1H), 7.66–7.60 (m,
4H), 7.49 (m, 1H), 7.46–7.41 (m, 3H), 7.33 (m, 2H),
6.70 (s, 1H), 3.18 (s, 3H). UV–Vis {dichloromethane,
r/103 cmꢀ1 (loge/Mꢀ1 cmꢀ1)} 18.5 (3.74), 20.0 (3.51
sh), 26.4 (3.85), 31.3 (4.03 sh), 33.8 (4.16 sh), 39.9
(4.58). Alternatively, the complex was also conveniently
prepared according to the following procedure.
Method B: The methanol solution (40 cm3) of pyri-
dine-2-aldehyde (0.034 g, 0.321 mmol) and 1-phenyl-
azo-2-naphthylamine (0.078 g, 0.317 mmol) was
refluxed for 2 h. [PdCl2(PhCN)2] (0.113 g, 0.293 mmol)
47.72; H, 3.06; N, 9.82. Found: C, 47.94; H, 2.91; N,
9.77%. Alternatively, the complex was also conveniently
prepared according to the following procedure.
Method B: The methanol solution (40 cm3) of pyri-
dine-2-aldehyde (0.090 g, 0.842 mmol) and 1-phenyl-
azo-2-naphthylamine (0.205 g, 0.828 mmol) was
refluxed for 2.5 h, and evaporated to dryness. The dark
red residue was dissolved in dichloromethane (40 cm3)
and [PdCl2(PhCN)2] (0.303 g, 0.789 mmol) was added.
The reaction mixture was refluxed for 9 h, filtered, and
evaporated to a small amount. n-Hexane (20 cm3) was
added slowly and the solution was left overnight to yield
dark red crystals. Yield: 0.307 g, 75.6%. 1H NMR (chlo-
roform-d) d = 9.24 (d, 1H), 8.14 (d, 1H), 7.95 (d, 1H),
7.90 (td, 1H), 7.55–7.30 (m, 12H). UV–Vis {dichloro-
methane, r/103 cmꢀ1 (loge/Mꢀ1 cmꢀ1)} 17.6 (3.82),
22.4 (3.94), 32.3 (4.11), 41.1 (4.69).
2.2.5. [PdCl2(L3)] (3)
[PdCl2(PhCN)2] (0.022 g, 0.058 mmol) was added to a
dichloromethane solution (10 cm3) of L3 (0.023 g, 0.060
mmol). The reaction mixture was refluxed for 2 h to

Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
479
was then added to the solution, which was refluxed for 8
h to yield fine reddish-purple crystals. The crystals were
filtered, washed with a small amount of diethyl ether,
and air-dried. Yield: 0.120 g, 80.3%.
52.53; H, 3.49; N, 10.21. Found: C, 52.39; H, 3.20; N,
10.58%. UV–Vis {dichloromethane, r/103 cmꢀ1 (loge/
M
(4.62). The complex is almost insoluble in common or-
ganic solvents.
ꢀ1 cmꢀ1)} 16.9 (3.91), 24.8 (3.83), 30.3 (4.23), 38.4
A similar procedure (Method A) was also applied for
the synthesis of [PdCl(L4c)] (Yield: 79.8%. Anal. Calc.
for [PdCl(L4c)] = C24H21ClN4OPd: C, 55.08; H, 4.04;
N, 10.71. Found: C, 54.91; H, 3.89; N, 10.66%. 1H
NMR (chloroform-d) d = 9.67 (d, 1H), 8.43 (d, 1H),
8.00–7.94 (m, 2H), 7.72 (d, 1H), 7.64 (d, 1H), 7.54–
7.28 (m, 9H), 6.76 (s, 1H), 3.75–3.66 (m, 1H), 3.12–
3.04 (m, 1H), 1.94 (s, 3H). UV–Vis {dichloromethane,
r/103 cmꢀ1 (loge/Mꢀ1 cmꢀ1)} 18.5 (3.86), 20.0 (3.63
sh), 26.4 (3.95), 29.8 (4.03 sh), 31.5 (4.11), 39.5 (4.66).)
and [PdCl(L4d)] (Yield: 46.2%. Anal. Calc. for
[PdCl(L4d)] = C26H25ClN4OPd: C, 56.64; H, 4.57; N,
2.3. X-ray crystallography
Crystallographic data and experimental details for lig-
ands Ln (n = 1–3) and complexes 2, 3, 4, 5, 8, and 9 are
summarized in Table 1. Each single crystal of the com-
plexes except complex 4 was glued on a glass fiber, while
that of complex 4 was sealed in a glass capillary with the
mother liquor to prevent loss of the water of crystalliza-
tion. X-ray diffraction data were collected on a Rigaku
AFC7S diffractometer using graphite-monochromated
1
n
˚
10.16. Found: C, 56.36; H, 4.40; N, 10.09%. H NMR
Cu Ka radiation (k = 1.54178 A) for ligands L (n = 1–
3), a RAXIS–RAPID diffractometer using graphite-
(chloroform-d) d = 9.35 (dd, 1H), 8.43 (d, 1H), 7.96
(td, 1H), 7.77 (d, 1H), 7.71–7.60 (m, 5H), 7.52–7.40
(m, 4H), 7.32 (m, 2H), 6.70 (s, 1H), 3.74–3.67 (m, 1H),
3.14–3.07 (m, 1H), 1.42 (m, 2H), 1.22 (m, 2H), 0.75 (t,
3H). UV–Vis {dichloromethane, r/103 cmꢀ1 (loge/
˚
monochromated Mo Ka radiation (k = 0.71069 A) for
complexes 2, 4, 5, and 9, and an MSC Mercury CCD
diffractometer using graphite-monochromated Mo Ka
˚
radiation (k = 0.71069 A) for complexes 3 and 8. A
M
29.9 (3.98 sh), 31.4 (4.04), 39.5 (4.59).) using EtOH
ꢀ1 cmꢀ1)} 18.5 (3.79), 20.0 (3.56 sh), 26.4 (3.87),
numerical absorption correction using the program
NUMABS [8] was applied to the intensity data. The struc-
tures were solved by direct methods (SIR92 [9]) and ex-
panded using Fourier techniques (DIRDIF94 [10]). The
structures were refined by full-matrix least-squares
based on F (Ln, n = 1–3 and 2, 4, 5, and 9) and F2 (3
and 8) with anisotropic displacement parameters for
all non-hydrogen atoms. Hydrogen atoms were placed
at idealized positions and included in the refinement
but were not refined. All calculations were performed
using the teXsan [11] crystallographic software package
of Molecular Structure Corporation.
n
and BuOH, respectively, instead of MeOH.
2.2.8. [PdCl(L4e)] (8)
Complex 2 (0.030 g, 0.058 mmol) was dissolved in
acetone (100 cm3) and the solution was left in the dark
at room temperature for 20 days. After the solution
was filtered, the filtrate was evaporated to dryness.
The brown residue was dissolved in THF (1 cm3) and
n-hexane (20 cm3) was added slowly to yield fine red-
dish-purple crystals, which were filtered and air-dried.
Yield: 0.014 g, 45.2%. Anal. Calc. for [PdCl(L4e)] =
C25H21ClN4OPd: C, 56.09; H, 3.95; N, 10.47. Found:
1
C, 56.01; H, 3.79; N, 10.40%. H NMR (chloroform-
3. Results and discussion
d) d = 9.33 (ddd, 1H), 8.41 (d, 1H), 7.83 (td, 1H),
7.72–7.64 (m, 4H), 7.56 (d, 1H), 7.48 (m, 1H), 7.42 (m,
2H), 7.35 (m, 1H), 7.32–7.27 (m, 2H), 7.18 (d, 1H),
6.13 (dd, 1H), 3.28 (dd, 1H), 3.06 (dd, 1H), 2.18 (s,
3H). UV–Vis {dichloromethane, r/103 cmꢀ1 (loge/
3.1. Structures of ligands L1, L2, and L3
Ligands L1 and L2 were obtained from the reaction of
1-phenylazo-2-naphthylamine with pyridine-2-aldehyde.
1-Phenylazo-2-naphthylamine was added to the metha-
nol solution of pyridine-2-aldehyde and the reaction
mixture was evaporated to dryness. The residue was dis-
solved in ether and pale orange crystals of the L1 ligand
were isolated from the solution. When chromatographic
separation of the reaction mixture was carried out on a
column of silica gel, several eluates of the products were
obtained. However, only the L1 and L2 ligands were iso-
lated as major products, and other minor components
were not isolated. Although we expected that the reac-
tion of 1-phenylazo-2-naphthylamine with pyridine-2-al-
dehyde would produce a tridentate Schiff base ligand
M
29.6 (4.12), 31.0 (4.09 sh), 38.8 (4.66).
ꢀ1 cmꢀ1)} 18.3 (3.88), 20.0 (3.65 sh), 26.3 (3.91 sh),
2.2.9. [PdCl2(L5)] (9)
2-Acetylpyridine (0.041 g, 0.338 mmol) and 1-phenyl-
azo-2-naphthylamine (0.080 g, 0.322 mmol) were dis-
solved in acetonitrile (30 cm3), and the solution was
refluxed for 2 h. The acetonitrile solution (20 cm3) of
[PdCl2(PhCN)2] (0.130 g, 0.340 mmol) was added and
the reaction mixture was evaporated to about 15 cm3.
After the solution was left at room temperature for
one day, the red crystals were filtered, washed with
diethyl ether, and air-dried. Yield: 0.065 g, 34.8%. Anal.
Calc. for [PdCl2(L5)]Æ0.5H2O = C24H19Cl2N4O0.5Pd: C,
(L6)
(L6 = 1-(phenylazo)-N-(2-pyridylmethylidene)-2-
naphthylamine), the L6 ligand was not identified. We

Table 1
Crystallographic data and experimental details
Compound
L1
L2
L3
2
3
4Æ2.5H2O
5
8
9
Formula
M
C
336.40
22H16N4
C22H16N4
336.40
orthorhombic triclinic
C26H18N4
386.45
C22H16Cl2N4Pd C26H18Cl2N4Pd C22H16ClN4O3.5Pd C23H19ClN4OPd C25H21ClN4OPd C23H18N4Cl2Pd
535.32
513.70
monoclinic
P21/c
563.76
orthorhombic
Pbca
534.25
orthorhombic
Pccn
509.28
monoclinic
P21/c
527.73
monoclinic
P21/c
Crystal system
Space group
monoclinic
Pa
monoclinic
P21/n
ꢀ
Pbca
P1
˚
a (A)
31.061(2)
11.474(1)
9.859(1)
10.1427(8)
10.3580(9)
9.418(1)
112.745(6)
101.636(7)
70.531(6)
857.3(1)
2
20.341(2)
13.445(1)
7.1923(6)
10.8969(3)
13.9359(3)
13.8534(3)
10.609(3)
16.408(4)
25.862(7)
13.991(1)
16.801(1)
20.438(1)
13.1173 (5)
10.3936(5)
15.5499(7)
12.203(2)
8.909(2)
20.694(4)
11.4571(5)
12.3142(4)
15.7677(6)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
98.172(6)
108.827(1)
103.953(1)
93.062(5)
92.773(1)
3
˚
V (A )
3513(1)
8
1947.0(3)
4
1991.19(8)
4
4501(1)
8
4804.1(9)
8
2057.5(2)
4
2246.4(7)
4
2222.0(2)
4
Z
l (cmꢀ1
)
6.10 (Cu Ka)
6.26 (Cu Ka)
6.25 (Cu Ka)
Transmission factor 0.8195–0.8985 0.9236–0.9998 0.9765–0.9997 0.7130–0.9312
12.17 Mo Ka
10.85 Mo Ka
0.8594–0.9759
orange
9.15 Mo Ka
0.9504–0.9614
red
10.55 Mo Ka
0.6475–0.7799
purple
9.71 Mo Ka
0.8335–0.9774
orange
10.93 Mo Ka
0.7531–0.8926
brown
prism
Crystal color
Crystal habit
Crystal size (mm3)
colorless
prism
red
colorless
prism
purple
plate
prism
0.25 · 0.40
· 0.40
1.303
140.0
0.048
0.082c
1.99
needle
prism
prism
needle
0.20 · 0.30
· 0.40
1.272
0.20 · 0.30
· 0.40
1.318
0.06 · 0.30
· 0.30
1.713
0.03 · 0.03
· 0.20
1.663
0.20 · 0.20
· 0.30
1.477
0.30 · 0.30
· 0.30
1.644
0.05 · 0.07
· 0.50
1.583
0.10 · 0.20
· 0.40
1.577
Dcalc (g cmꢀ3
2hmax (ꢁ)
R1(R)a
Rw
)
140.0
0.064
0.074b
1.97
140.0
0.042
0.051b
1.53
55.0
0.028
0.038b
1.12
55.0
55.0
0.060
0.088b
1.47
55.0
0.031
0.050b
1.57
55.0
55.0
0.034
0.047b
1.27
0.118 (0.180)
0.182
1.10
0.075 (0.092)
0.170b
1.36
Sd
P
P
P
a
R1 = jjFoj ꢀ jFcjj/ jFoj, R is obtained for all observed data.
P
P
b
c
2 1/2
Rw = [ w(jFoj ꢀ jFcj)2/ wjFoj ]
.
P
P
2
2 2
2 2 1/2
Rw = [ w(jFoj ꢀ jFcj ) / w(jFoj ) ]
.
S = [ w(jFoj ꢀ jFcj)2/(m ꢀ n)]1/2 (m is the no. of used reflections, n is the no. of refined parameters).
d

Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
481
presume that the L6 ligand could be unstable and con-
Table 2
n
˚
verted into the L1 and L2 ligands rapidly in the course
of the reaction in methanol. The L3 ligand was also ob-
tained in a similar manner by the reaction of 1-phenyl-
Selected bond distances (A) and angles (ꢁ) for the L (n = 1–3) ligands
L1
N(2)–C(6)
N(2)–C(7)
N(3)–N(4)
1.313(3)
1.380(3)
1.396(3)
N(3)–C(6)
N(3)–C(16)
C(7)–C(16)
1.377(3)
1.387(3)
1.379(3)
azo-2-naphthylamine
with
quinoline-2-aldehyde;
however, a ligand containing the six-membered ring of
dihydrotriazine, the analogous compound with L2, was
not obtained. We determined the structures of the L1,
L2, and L3 ligands by X-ray crystallography (Fig. 2).
These ligands had a six-membered ring of dihydrotria-
zine in L2, and a five-membered ring of imidazole in
L1 and L3. The selected bond distances and angles of
the ligands are summarized in Table 2.
In the L1 ligand, the N(3) atom is attached to the C(6)
atom, and an imidazole ring composed of C(6), N(2),
C(7), C(16), and N(3) atoms is formed. The naphthoim-
idazole ring {N(2), N(3), and C(6)–C(16)} makes a dihe-
dral angle of 25.75(9)ꢁ with the pyridine ring {N(1) and
C(1)–C(5)}. The benzene ring {C(17)–C(22)} and the
naphthoimidazole ring are almost perpendicular to each
other (88.62(8)ꢁ). It is notable that a hydrogen atom is
attached to N(4) and the bond length of N(3)–N(4)
C(6)–N(2)–C(7)
N(4)–N(3)–C(6)
N(4)–N(3)–C(16)
C(6)–N(3)–C(16)
N(3)–N(4)–C(17)
105.2(2)
127.6(2)
124.3(2)
107.3(2)
116.0(2)
N(2)–C(6)–N(3)
N(2)–C(6)–C(5)
N(3)–C(6)–C(5)
N(2)–C(7)–C(16)
N(3)–C(16)–C(7)
111.7(2)
124.6(2)
123.7(2)
111.3(2)
104.4(2)
L2
N(2)–C(6)
N(2)–C(7)
N(3)–N(4)
1.445(2)
1.296(2)
1.335(1)
N(3)–C(16)
N(4)–C(6)
C(7)–C(16)
1.311(2)
1.482(2)
1.464(2)
C(6)–N(2)–C(7)
N(4)–N(3)–C(16)
N(3)–N(4)–C(6)
N(3)–N(4)–C(17)
C(6)–N(4)–C(17)
113.9(1)
116.8(1)
119.1(1)
116.9(1)
123.7(1)
N(2)–C(6)–N(4)
N(2)–C(6)–C(5)
N(4)–C(6)–C(5)
N(2)–C(7)–C(16)
N(3)–C(16)–C(7)
110.5(1)
113.0(1)
110.2(1)
122.3(1)
119.4(1)
L3
N(2)–C(10)
N(2)–C(11)
N(3)–N(4)
1.307(5)
1.355(5)
1.406(4)
N(3)–C(10)
N(3)–C(20)
C(11)–C(20)
1.377(5)
1.379(4)
1.396(5)
˚
(1.396(3) A) indicates an N–N single bond. Accordingly,
C(10)–N(2)–C(11)
N(4)–N(3)–C(10)
N(4)–N(3)–C(20)
C(10)–N(3)–C(20)
N(3)–N(4)–C(21)
107.6(3)
127.2(3)
124.8(3)
107.9(3)
115.7(3)
N(2)–C(10)–N(3)
N(2)–C(10)–C(9)
N(3)–C(10)–C(9)
N(2)–C(11)–C(20)
N(3)–C(20)–C(11)
110.2(3)
124.0(3)
125.7(3)
110.0(3)
104.3(3)
the double bond character of the azo moiety of 1-phe-
nylazo-2-naphthylamine was lost in the L1 ligand.
In the L2 ligand, on the other hand, the N(4) atom is
attached to the C(6) atom, and a dihydrotriazine ring
composed of C(6), N(2), C(7), C(16), N(3), and N(4)
atoms is formed. The bond lengths of N(2)–C(6)
˚
˚
˚
character. The bond length of N(3)–N(4) (1.335(1) A)
is longer than those of uncoordinated N@N double
bonds (the average N@N bond length of azo
(1.445(2) A), N(4)–C(6) (1.482(2) A), and C(5)–C(6)
˚
(1.532(2) A) are in the range of common single bond
˚
lengths, and those of N(2)–C(7) (1.296(2) A) and
N(3)–C(16) (1.311(2) A) indicate C@N double bond
˚
˚
compounds; 1.25 A [12]), however, the bond angles
Fig. 2. ORTEP drawings of ligands L1–L3 with the atom labeling scheme. All non-hydrogen atoms are represented by their thermal displacement
vibrational ellipsoids at 30% probability.

482
Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
Table 3
around the N(4) atom (116.9–123.7ꢁ) suggest that the
N(4) atom is sp2-hybridized. Such a resonance hybrid
of the ligand structure has been reported previously in
the relevant Pd complexes [6]. The dihydrotriazine ring
is not planar, and the plane 1 {N(2), C(7), C(16),
N(3), and N(4) atoms} makes a dihedral angle of
40.91(4)ꢁ with the plane 2 {N(2), N(4), and C(6) atoms}.
˚
Selected bond distances (A) and angles (ꢁ) for complexes 2 and 3
Complex 2
Pd(1)–Cl(1)
Pd(1)–Cl(2)
Pd(1)–N(1)
Pd(1)–N(2)
N(2)–C(6)
2.2800(9)
2.2887(8)
2.053(2)
2.027(3)
1.468(3)
N(2)–C(7)
N(3)–N(4)
N(3)–C(16)
N(4)–C(6)
C(7)–C(16)
1.301(4)
1.334(3)
1.309(4)
1.471(4)
1.450(4)
˚
The C(6) atom is 0.563(2) A out of the plane 1. The ben-
Cl(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(2)
Cl(2)–Pd(1)–N(1)
Cl(2)–Pd(1)–N(2)
N(1)–Pd(1)–N(2)
C(6)–N(2)–C(7)
N(4)–N(3)–C(16)
91.41(3)
92.87(7)
170.57(6)
175.09(7)
97.27(6)
78.63(9)
119.7(2)
118.9(2)
N(3)–N(4)–C(6)
N(3)–N(4)–C(17)
C(6)–N(4)–C(17)
N(2)–C(6)–N(4)
N(2)–C(6)–C(5)
N(4)–C(6)–C(5)
N(2)–C(7)–C(16)
N(3)–C(16)–C(7)
121.9(2)
116.1(2)
122.0(2)
111.6(2)
106.4(2)
114.8(2)
120.2(2)
121.5(3)
zene ring {C(17)–C(22)} and the plane 1 make a dihe-
dral angle of 39.85(5)ꢁ.
The L3 ligand has a naphthoimidazole ring {N(2),
N(3), and C(10)–C(20)}, which makes a small dihedral
angle of 6.14(9)ꢁ with the quinoline ring {N(1) and
C(1)–C(9)}. Thus, the two aromatic rings are conjugated
˚
and the bond length of C(9)–C(10) (1.486(5) A) indicates
some double bond character.
Complex 3
Pd(1)–Cl(1)
Pd(1)–Cl(2)
Pd(1)–N(1)
Pd(1)–N(2)
N(2)–C(10)
2.308(3)
2.272(3)
2.107(7)
2.034(9)
1.34(1)
N(2)–C(11)
N(3)–N(4)
N(3)–C(10)
N(3)–C(20)
C(11)–C(20)
1.38(1)
1.40(1)
1.36(1)
1.40(1)
1.36(2)
3.2. Structures of the complexes
Complexes 1, 2, and 3 were prepared by treating
[PdCl2(PhCN)2] with ligands L1, L2, and L3 in dichloro-
methane or acetonitrile–dichloromethane. Complex 2
was also prepared in good yield by the reaction of
[PdCl2(PhCN)2] with the reaction mixture of 1-phenyl-
azo-2-naphthylamine and pyridine-2-aldehyde in dichlo-
romethane, which suggests that the L1 ligand should be
produced in preference to the L2 ligand. Complex 1
could not be recrystallized because the complex was al-
most insoluble in common organic solvents; however,
complexes 2 and 3 were successfully recrystallized and
good single crystals were obtained. We carried out the
X-ray structure determination for complexes 2 and 3.
The selected bond distances and angles of those com-
plexes are summarized in Table 3.
Cl(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(2)
Cl(2)–Pd(1)–N(1)
Cl(2)–Pd(1)–N(2)
N(1)–Pd(1)–N(2)
C(10)–N(2)–C(11)
N(4)–N(3)–C(10)
85.6(1)
N(4)–N(3)–C(20)
C(10)–N(3)–C(20)
N(3)–N(4)–C(21)
N(2)–C(10)–N(3)
N(2)–C(10)–C(9)
N(3)–C(10)–C(9)
N(2)–C(11)–C(20)
N(3)–C(20)–C(11)
127.6(9)
107.4(9)
116.5(8)
111.0(9)
119(1)
100.0(3)
165.5(3)
173.4(2)
95.2(2)
80.3(3)
105.2(9)
124.9(8)
129.9(9)
111.4(9)
105(1)
Fig. 3 shows a perspective view of complex 2. The
coordination geometry around the palladium atom is
square planar. The difference in bond lengths in the
dihydrotriazine ring was hardly discernible between
the free L2 ligand and that of complex 2. However, the
˚
C(6) atom is 0.337(4) A out of the plane 1 {N(2),
C(7), C(16), N(3), and N(4) atoms}, and the dihedral an-
gle (23.61(9)ꢁ) between the plane 1 and the plane 2
{N(2), N(4), and C(6) atoms} is considerably smaller
than that of the free L2 ligand. The benzene ring
{C(17)–C(22)} and the plane 1 show a small dihedral an-
gle of 18.0(1)ꢁ. Accordingly, the naphthalene and ben-
zene rings are conjugated via N(3) and N(4) atoms in
complex 2. It seems that the coordinating L2 ligand
has a longer conjugated system than the corresponding
free L2 ligand. The conjugated plane, however, makes
a large dihedral angle of 64.5(1)ꢁ with the coordination
plane {Pd(1), Cl(1), Cl(2), N(1), and N(2)}.
Fig. 3. An ORTEP drawing of [PdCl2(L2)] (2) with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability.
Fig. 4 shows a perspective view of complex 3. The
naphthoimidazole ring {N(2), N(3), and C(10)–C(20)}
and the quinoline ring {N(1) and C(1)–C(9)} were al-
most in the same plane, and the chelate ring {N(1),
N(2), C(9), and C(10)} has a small dihedral angle of
17.9(2)ꢁ with the plane defined by Pd(1), Cl(1), and
Cl(2). Thus, the coordination plane around the Pd atom

Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
483
Cl
Cl
Pd
N
N
N
Pd
Cl
Cl
N
N
N
N
N
Cl
Cl
Pd
N
N
Pd
Cl
Cl
N
N
N
N
N
N
H
H
Fig. 5. A resonance hybrid of the two structures for [PdCl2(L2)] (2)
and [PdCl2(L3)] (3).
Fig. 4. An ORTEP drawing of [PdCl2(L3)] (3) with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability.
was slightly twisted towards tetrahedral, and close ap-
proaches between Cl(1) and the hydrogen atom H(1) at-
tached to C(2), and between Cl(2) and H(7) attached to
C(12) could be avoided. The calculated distances {2.50
˚
˚
A for Cl(1)–H(1) and 2.60 A for Cl(2)–H(7)} are, never-
theless, shorter than the sum of the van der Waals radii
˚
of 3.00 A {1.20(H) + 1.80(Cl) A}. The bond length of
˚
˚
N(3)–N(4) (1.40(1) A) is similar to that of the N(3)–
N(4) single bond in ligand L3. A hydrogen atom
attached to N(4) could not be observed by X-ray crystal-
lography, but was confirmed by a measurement of the
IR spectrum (vide infra). The most reasonable represen-
tation of complexes 2 and 3 is a resonance hybrid of the
two structures, respectively (Fig. 5).
Figs. 6–8 show perspective views of complexes 4, 5,
and 8, and selected bond distances and angles are sum-
marized in Table 4. A tridentate ligand coordinates to
the Pd atom with three nitrogen atoms (N(1), N(2),
and N(4)) in each complex, and OHꢀꢀ (complex 4),
CH3Oꢀ (complex 5) and CH3COCH2 (complex 8)
groups are attached to the sp3-C(6) atom. The bond
length of N(2)–C(6) (1.48(1) (complex 4), 1.467(4) (com-
Fig. 6. An ORTEP drawing of complex [PdCl(L4a)] (4) with the atom
labeling scheme. All non-hydrogen atoms are represented by their
thermal displacement vibrational ellipsoids at 30% probability.
form. However, the bond lengths of N(2)–C(7) (1.32(1)
˚
˚
(complex 4), 1.330(4) (complex 5), and 1.318(7) A (com-
plex 8)) and N(3)–C(16) (1.35(1) (complex 4), 1.359(4)
˚
(complex 5), and 1.296(7) A (complex 8)) are considera-
plex 5), and 1.482(6) A (complex 8)) indicates an N–C
single bond, and the bond length of N(3)–N(4)
(1.28(1) (complex 4), 1.268(4) (complex 5), and
˚
1.287(7) A (complex 8)) indicates an N–N double bond
bly shorter than those of N–C single bonds. Accord-
ingly, a resonance hybrid of the two structures (a) and
(b) should be the most reasonable representation of
the complexes, and the negative charge of the ligand is
character of the azo moiety. These results are consistent
with those of the expected structure, which is illustrated
in Fig. 9(a). The coordinating azo group has the trans-

484
Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
Table 4
Selected bond distances (A) and angles (ꢁ) for complexes 4, 5, and 8
˚
Complex 4
Pd(1)–Cl(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(4)
O(1)–C(6)
N(2)–C(6)
2.325(3)
2.055(7)
1.975(7)
1.991(7)
1.39(1)
N(2)–C(7)
N(3)–N(4)
N(3)–C(16)
C(5)–C(6)
C(7)–C(16)
1.32(1)
1.275(9)
1.35(1)
1.50(1)
1.44(1)
1.48(1)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(2)
Cl(1)–Pd(1)–N(4)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(4)
N(2)–Pd(1)–N(4)
C(6)–N(2)–C(7)
92.5(3)
173.5(2)
94.9(2)
82.0(3)
172.6(3)
90.7(3)
119.5(8)
N(4)–N(3)–C(16)
O(1)–C(6)–N(2)
O(1)–C(6)–C(5)
N(2)–C(6)–C(5)
N(2)–C(7)–C(16)
N(3)–C(16)–C(7)
125.7(8)
111.2(7)
112.9(9)
110.3(8)
122.4(8)
126.3(8)
Complex 5
Pd(1)–Cl(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(4)
O(1)–C(6)
N(2)–C(6)
2.3392(7)
2.038(2)
1.979(2)
1.995(2)
1.408(4)
1.467(4)
N(2)–C(7)
N(3)–N(4)
N(3)–C(16)
C(5)–C(6)
C(7)–C(16)
1.330(4)
1.268(4)
1.359(4)
1.511(4)
1.441(4)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(2)
Cl(1)–Pd(1)–N(4)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(4)
N(2)–Pd(1)–N(4)
C(6)–N(2)–C(7)
93.09(7)
168.65(7)
94.83(7)
82.5(1)
N(4)–N(3)–C(16)
O(1)–C(6)–N(2)
O(1)–C(6)–C(5)
N(2)–C(6)–C(5)
N(2)–C(7)–C(16)
N(3)–C(16)–C(7)
124.9(2)
114.0(3)
111.3(3)
110.3(2)
122.8(3)
125.9(3)
Fig. 7. An ORTEP drawing of [PdCl(L4b)] (5) with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability.
171.10(9)
90.5(1)
118.3(2)
Complex 8
Pd(1)–Cl(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(4)
N(2)–C(6)
N(2)–C(7)
2.317(2)
2.046(5)
1.973(5)
1.978(5)
1.482(6)
1.318(7)
N(3)–N(4)
N(3)–C(16)
C(5)–C(6)
C(6)–C(23)
C(7)–C(16)
1.287(7)
1.296(7)
1.511(8)
1.521(8)
1.447(7)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(2)
Cl(1)–Pd(1)–N(4)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–N(4)
N(2)–Pd(1)–N(4)
C(6)–N(2)–C(7)
92.1(1)
174.3(1)
93.6(1)
82.9(2)
174.2(2)
91.3(2)
118.8(5)
N(4)–N(3)–C(16)
N(2)–C(6)–C(5)
N(2)–C(6)–C(23)
C(5)–C(6)–C(23)
N(2)–C(7)–C(16)
N(3)–C(16)–C(7)
127.7(5)
110.6(4)
109.9(4)
110.4(5)
121.2(5)
127.1(5)
ligand L5, whose azo group has the trans-form and
the azo nitrogen atoms (N(3) and N(4)) are not
coordinated to the Pd atom. The bond length of
˚
N(3)–N(4) (1.228(5) A) is in the range of the common
N–N double bond lengths and shorter than those of
complexes 1, 3–5 and 8. The chelate ring {Pd(1),
N(1), N(2), C(5), and C(6)} has a dihedral angle of
75.49(9)ꢁ with the naphthalene ring {C(8)–C(17)}.
We suppose that these two rings could not be copla-
nar to each other because of the steric hindrance be-
tween the methyl protons attached to the C(7) atom
and the aromatic proton attached to the C(9) atom.
Therefore, coordination of the azo nitrogen atoms to
the Pd atom did not occur.
Fig. 8. An ORTEP drawing of [PdCl(L4e)] (8) with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability.
regarded as being spread over the conjugated system (c)
(Fig. 9).
Fig. 10 shows a perspective view of complex 9. The
selected bond distances and angles are summarized in
Table 5. The complex contains a didentate Schiff base

Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
485
3.3. IR and UV–Vis spectra of the ligands and complexes
Cl
Pd
Cl
Pd
N
N
It has been reported that the mN@N of 2-(phenyl-
azo)aniline (H2L) is observed at 1460 cmꢀ1, while that
of Pd(HL)2 is shifted to a lower wave number (1340
cmꢀ1) [13]. In the L2 ligand, a strong band was observed
at 1382 cmꢀ1, while the corresponding band was not de-
tected in the L1 and L3 ligands. Accordingly, we as-
signed the band at 1382 cmꢀ1 as the mN@N. On the
other hand, the L1 and L3 ligands displayed a single
band at 3303 and 3317 cmꢀ1, characteristic of the NH
group, respectively. These data are consistent with the
structures of the L1 and L3 ligands that were determined
by X-ray methods; that is, a hydrogen atom is attached
to the N(4) atom and the N(3)–N(4) bond has a single
bond character (Fig. 1). The mN@N of complexes 2, 4,
5, 8, and 9 was not assigned because the spectra were
complicated with many bands in the 1200–1400 cmꢀ1 re-
gion. The complicated spectral aspect of this region is
similar to those of palladium (II) and platinum (II)
complexes with the ligands derived from 1-phenylazo-
2-naphthylamine and 2-(diphenylphosphino)benzalde-
hyde or 2-(tert-butylthio)benzaldehyde that we reported
in a previous paper [6]. Complexes 1 and 3 showed a
broad stretching vibration band at 3240 and 3222
cmꢀ1, respectively, and it was confirmed that a hydrogen
remains attached to the N(4) atom.
N
N
N
N
N
N
RO
RO
(a)
(b)
Cl
Pd
N
N
N
N
RO
(c)
Fig. 9. A resonance hybrid of the two structures ((a) and (b)) for
[PdCl(L4a)] (4), [PdCl(L4b)] (5) and [PdCl(L4e)] (8), where the negative
charge is spread over the conjugated system (c).
Figs. 11 and 12 show the absorption spectra of the Ln
(n = 1–3) ligands and complexes 2, 6, 8, and 9 in
dichloromethane. The L2 ligand has an N@N chromo-
phore and the red solution of the L2 ligand exhibits an
absorption band at 498 nm, while each solution of the
L1 and L3 ligands is nearly colorless and no absorption
band was observed in the visible region. The purple
solution of complex 2 in dichloromethane exhibits an
Fig. 10. An ORTEP drawing of [PdCl2(L5)] (9) with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability.
Table 5
˚
Selected bond distances (A) and angles (ꢁ) for complex 9
Pd(1)–Cl(1)
Pd(1)–Cl(2)
Pd(1)–N(1)
Pd(1)–N(2)
N(2)–C(6)
2.280(1)
2.298(1)
2.024(3)
2.021(3)
1.285(5)
N(2)–C(8)
N(3)–N(4)
N(3)–C(17)
C(5)–C(6)
C(8)–C(17)
1.435(5)
1.228(5)
1.407(5)
1.471(5)
1.382(5)
Cl(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(2)
Cl(2)–Pd(1)–N(1)
Cl(2)–Pd(1)–N(2)
N(1)–Pd(1)–N(2)
C(6)–N(2)–C(8)
92.23(4)
172.5(1)
94.05(9)
94.0(1)
N(4)–N(3)–C(17)
N(2)–C(6)–C(5)
N(2)–C(6)–C(7)
C(5)–C(6)–C(7)
N(2)–C(8)–C(17)
N(3)–C(17)–C(8)
117.1(3)
115.9(4)
124.4(4)
119.7(3)
121.6(3)
126.7(4)
171.9(1)
80.1(1)
119.3(3)
Fig. 11. Absorption spectra of ligands L1 (–––), L2 (–––) and
L3 (––Æ––) in dichloromethane.

486
Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
Fig. 12. Absorption spectra of complexes [PdCl2(L2)] (2) (–––),
[PdCl(L4c)] (6) (–––), [PdCl(L4e)] (8) (––Æ––) and [PdCl2(L5)] (9)
(––ÆÆ––) in dichloromethane.
Fig. 13. The change in absorption spectrum of [PdCl2(L2)] (2) (25 ꢁC)
in dichloromethane–ethanol (2:1 v/v) at 27 s intervals.
dichloromethane–ethanol (2:1 v/v) at regular time inter-
vals. The absorption bands at 570 and 446 nm dimin-
ished with time, and new absorption bands at 541 and
379 nm grew. The converged spectrum was identical
with that of complex 6. Complex 2 underwent a similar
absorption band at 570 nm. Thus, the absorption band
of the visible region of complex 2 is shifted to a longer
wavelength relative to the L2 ligand. The absorption
bands of complexes 6 and 8 appeared at 541 and 546
nm, respectively, and the spectral patterns were similar
to each other in the wavelength region of 230–700 nm.
The absorption spectral pattern of complexes 4, 5, and
7 also closely resembles these bands. On the other hand,
the absorption band of complex 9 was observed at 592
nm. Unfortunately, the absorption spectra of pale yel-
low complexes 1 and 3 could not be measured quantita-
tively because of their poor solubility in common
organic solvents; however, no absorption band was ob-
served in the visible region. Accordingly, the absorption
bands which were observed at 541–592 nm for com-
plexes 2 and 4–9 could be identified as p–p *or n–p*
transitions on the N@N chromophore.
n
reaction with water and BuOH to yield complexes 4
and 7, respectively. It is notable that complex 2 also re-
acted with acetone to yield complex 8, although the
reaction was relatively slow at room temperature.
Accordingly, alcohols and acetone undergo addition
reactions for complex 2, and the ring opening reaction
of the triazine skeleton occurs to produce the complexes
containing azo ligands (Fig. 14).
On the other hand, the absorption spectrum of com-
plex 5 (solid line) in dichloromethane changed as shown
by the dashed line by an addition of excess amount of
(nBu)4NCl (Fig. 15). The absorption spectra of the prod-
uct were exactly similar to that of complex 2. Complex 2
was recovered from the concentrated solution. Thus, it
has become apparent that coordination of the Clꢀ lig-
and occurred and the triazine ring was formed by the
subsequent ring closure to yield complex 2.
3.4. Reactivity of the ligands and complexes
The absorption spectrum of ligand L2 remained un-
changed for at least one day in dichloromethane or
methanol, and those of ligands L1 and L3, which were
insoluble in methanol, were also invariant in
dichloromethane.
The absorption spectrum of complex 2 in dichloro-
methane was invariant; however, the color of the solu-
tion changed from purple to reddish-purple rapidly
when several drops of methanol or ethanol were added
to the solution. The reaction of complex 2 with metha-
nol proceeds faster than that with ethanol. Complexes
5 and 6 were obtained as reddish-purple crystals from
each concentrated solution (vide supra, Method A for
the preparation of complexes 5–7). Fig. 13 shows the
change in the absorption spectrum of complex 2 in
Cl
Cl
Pd
N
Pd
N
_
Cl
N
X
N
N
N
N
N
X
X = OH, OMe, OEt, OnBu, CH2COCH3
Fig. 14. Schematic representation of a triazine ring opening reaction
for [PdCl2(L2)] (2).

Z. Zhu et al. / Inorganica Chimica Acta 358 (2005) 476–488
487
4. Supplementary material
Tables of non-hydrogen atom coordinates and aniso-
tropic thermal parameters, coordinates of the hydrogen
atoms, and bond lengths and angles have been deposited
as CIF files (Nos. 246824–246832 for ligands Ln (n = 1–
3) and complexes 2, 3, 4, 5, 8, and 9) at the Cambridge
Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk).
Acknowledgments
The present work was supported by a Grant-in-Aid
for Scientific Research Nos. 13640557 and 15550048
from the Ministry of Education, Culture, Sports, Sci-
ence and Technology. We thank the Institute for Molec-
ular Science (Okazaki) for the use of X-ray facilities.
Fig. 15. An addition of (nBu)4NCl caused the change in absorption
spectrum of [PdCl(L4b)] (5) (–––) in dichloromethane and the spectrum
represented by the dashed line was obtained.
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closure reactions of the triazine ligand can be under-
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