Synthesis and characterization of nickel(II) schiff base complexes with methoxy or methyl groups at 2,6-positions of the pendant phenyl ring: The control of cis and trans geometries

Article abstract of DOI:10.1246/bcsj.76.127

Two nickel(II) complexes with N,S chelates were prepared by the reaction of nickel(II) acetate tetrahydrate with 2-substituted benzothiazolines. Bis[2-(2,6-dimethoxyphenylmethyleneamino)benzenethiolato]nickel(II) 1, in which the 2,6-positions of the pendant phenyl ring are occupied by methoxy groups, has an approximately square-planar geometry around a nickel atom with a cis-N₂S₂ donor atom arrangement. X-ray and variable-temperature ¹H NMR studies indicated the existence of an apical Ni...OMe interaction in 1. On the other hand, bis[2-(mesitmethyleneamino)benzenethiolato]nickel(II) 2 with methyl groups at the 2,4,6-positions of the pendant phenyl ring exhibits a perfect planar trans-N₂S₂ coordination around the nickel atom. An X-ray study revealed the existence of an intraligand CH/π interaction in 2. A difference in the geometry around -CH=N- (E and Z) was also observed between 1 and 2 (Z for 1 and E for 2).

Full text of DOI:10.1246/bcsj.76.127

c. Jpn.
© 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 127–132 (2003)
127
e Chemical
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e Chemical
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Synthesis and Characterization of Nickel(Ⅱ) Schiff Base Complexes with
Methoxy or Methyl Groups at 2,6-Positions of the Pendant Phenyl Ring:
the Control of cis and trans Geometries
Nickel(Ⅱ) Schiff Base Complexes
T. Kawamoto et al.
03
7
Tatsuya Kawamoto* and Takumi Konno
2
Department of Chemistry, Graduate School of Science, Osaka University,
1-16 Machikaneyama, Toyonaka, Osaka 560-0043
SJA8
09-2673
183
(Received July 3, 2002)
02
Two nickel(Ⅱ) complexes with N,S chelates were prepared by the reaction of nickel(Ⅱ) acetate tetrahydrate with 2-
substituted benzothiazolines. Bis[2-(2,6-dimethoxyphenylmethyleneamino)benzenethiolato]nickel(Ⅱ) 1, in which the
2,6-positions of the pendant phenyl ring are occupied by methoxy groups, has an approximately square-planar geometry
around a nickel atom with a cis-N2S2 donor atom arrangement. X-ray and variable-temperature 1H NMR studies indicat-
ed the existence of an apical Ni≥OMe interaction in 1. On the other hand, bis[2-(mesitmethyleneamino)benzenethio-
lato]nickel(Ⅱ) 2 with methyl groups at the 2,4,6-positions of the pendant phenyl ring exhibits a perfect planar trans-N2S2
coordination around the nickel atom. An X-ray study revealed the existence of an intraligand CH/π interaction in 2. A
difference in the geometry around –CHwN– (E and Z) was also observed between 1 and 2 (Z for 1 and E for 2).
02
.2
It is well-known that 2-substituted benzothiazolines are suit-
able starting materials to yield Schiff base metal complexes
with N,S chelates.1,2 In fact, a variety of nickel(Ⅱ), palladi-
um(Ⅱ), and platinum(Ⅱ) complexes containing Schiff base
ligands with N,S donor atoms have been prepared by treating
M(AcO)2 with several 2-substituted benzothiazolines.3–6 One
of the most interesting features of these Schiff base complexes
is their reactivities, which are dependent on the central metal
ion. For example, it has been found that square-planar palladi-
um(Ⅱ) and platinum(Ⅱ) complexes derived from 2-(1-naphth-
yl)benzothiazoline are easily metallated at the ortho-position
of the pendant 1-naphthyl ring to yield thiolato-bridged tetra-
nuclear complexes,3 owing to C–H bond activation, which is
well observed in N-donor ligands, such as Schiff bases and
azo-derivatives.7 However, cyclometallation in the corre-
sponding nickel(Ⅱ) complexes has not yet been observed. In-
stead, we have found that a square-planar Schiff base nickel(Ⅱ)
complex with unsubstituted phenyl groups as a pendant arm is
converted into a nickel(Ⅱ) complex with a non-innocent ligand,
of which the electric structure can not be described by a com-
mon structural formula (Scheme 1).4 In addition, a nickel(Ⅱ)
complex containing chlorine atoms at the 2,6-positions of the
pendant phenyl ring was found to be converted into an octahe-
dral nickel(Ⅱ) complex with a macrocyclic ligand generated by
the activation of C–Cl bonds (Scheme 1).5 Thus, the C(aro-
matic)–R(substituent groups) bond activation in square-planar
metal complexes as well as our general interest in metal com-
plexes coordinated by mixed sulfur-nitrogen donor atoms pro-
moted us to investigate the structure and properties of Schiff
base nickel(Ⅱ) complexes with substituent groups on the pen-
dant phenyl ring. Herein we report on the synthesis and char-
acterization of two nickel(Ⅱ) complexes with the 2,6-disubsti-
Scheme 1.

128 Bull. Chem. Soc. Jpn., 76, No. 1 (2003)
Nickel(ꢀ) Schiff Base Complexes
(2H, d, J = 7.9 Hz, aryl CH), 2.24 (6H, s, CH3), and 2.00 (12H, s,
CH3). UV-vis: (CHCl3) σmax/103 cm−1 [log(ε/dm3 mol−1 cm−1)]:
14.1 (2.06) and 21.2 (3.41).
tuted pendant phenyl rings by methoxy or methyl groups.
Experimental
Thermal Reaction of 1 and 2 in Toluene. Suspensions of 1
(0.123 g) and 2 (0.094 g) in toluene (30 mL) were refluxed for 1.5
and 3 h, respectively, and the resulting solutions, which showed
one spot in TLC, were cooled to room temperature. The resulting
precipitates (0.099 g for 1 and 0.041 g for 2) were collected by fil-
tration, and analyzed by 1H NMR, showing 1 and 2.
General Procedures. All manipulations were carried out us-
ing standard Schlenk techniques under an atmosphere of argon or
nitrogen. The reagents were commercial samples, and were not
purified further.
Infrared spectra were obtained on a JASCO FT/IR-5000 Infra-
red Spectrophotometer (4000–400 cm−1) using the Nujol mulls,
NMR spectra on a JEOL EX 270 instrument using tetramethylsi-
lane as internal standard (δ 0) and UV/vis spectra on a JASCO V-
570 spectrophotometer. Elemental analyses were performed at
Osaka University.
X-ray Crystallography. X-ray measurements of complexes
1 and 2 were made on a Mac Science MXC3 diffractometer with
Mo Kα radiation (λ = 0.71073 Å) at room temperature. θ–2θ
scans were employed and empirical absorption corrections (ψ
scans) were applied. The solution and refinement procedures
were made by applying the CRYSTAN-GM package.9 The struc-
tures of complexes 1 and 2 were solved by direct methods using
PATTY in DIRDIF10 and SIR 92,11 respectively, and refined aniso-
tropically for all non-hydrogen atoms with full-matrix least-
squares calculations. All hydrogen atoms for 1 were calculated
with a C–H distance of 0.96 Å and refined isotropically. Hydro-
gen atoms for 2 were generated by difference Fourier synthesis,
except for the hydrogen atoms (H31A,B,C and H32A,B,C) for
two methyl groups which were located at the computed positions;
all hydrogen atoms were refined isotropically. Crystallographic
data for 1 and 2 are given in Table 1. Crystallographic data have
been deposited at the CCDC, 12 Union Road, Cambridge CB2
1EZ, UK and copies can be obtained on request, free of charge, by
quoting the publication citation and the deposition numbers
186593 and 186594.
Synthesis of 2-(2,6-Dimethoxyphenyl)benzothiazoline.
2-
(2,6-Dimethoxyphenyl)benzothiazoline was prepared according to
a literature procedure for 2-substituted benzothiazolines.8 To a so-
lution of 2,6-dimethoxybenzaldehyde (0.25 g, 1.5 mmol) in etha-
nol (20 mL) was added 2-aminothiophenol (0.20 g, 1.6 mmol); the
solution was then heated under reflux for 30 min. The resulting
solution was allowed to cool in a refrigerator overnight. Pale yel-
low crystals were collected by filtration and dried in vacuo. Yield:
0.27 g, 66%. Found: C, 65.77; H, 5.59; N, 5.12%. Calcd for
C15H15NO2S: C, 65.91; H, 5.53; N, 5.12%. IR (Nujol) νmax/cm−1
3310 (NH). 1H NMR (270 MHz, CDCl3, r.t.) δ 7.24 (1H, t, J =
8.4 Hz, aryl CH), 7.14 (1H, d, J = 7.3 Hz, aryl CH), 6.97 (1H, s,
2-CH), 6.93 (1H, dd, J = 8.8 and 1.7 Hz, aryl CH), 6.84 (2H, t, J
= 7.5 Hz, aryl CH), 6.57 (2H, d, J = 8.6 Hz, aryl CH), and 3.78
(6H, s, OCH3).
Synthesis of Bis[2-(2,6-dimethoxyphenylmethyleneamino)-
benzenethiolato]nickel(Ⅱ) 1.
2-(2,6-Dimethoxyphenyl)benzo-
Results and Discussion
thiazoline (0.23 g, 0.84 mmol) and nickel(Ⅱ) acetate tetrahydrate
(0.11 g, 0.44 mmol) were refluxed in ethanol (20 mL) for 1.5 h.
Brown microcrystals precipitated upon cooling to room tempera-
ture were collected by filtration. Yield: 0.17 g, 64%. Crystals of
complex 1 suitable for a structure determination were grown by
the slow diffusion of diethyl ether into a CH2Cl2 solution of 1.
Found: C, 59.48; H, 4.77; N, 4.59%. Calcd for C30H28N2NiO4S2:
C, 59.72; H, 4.68; N, 4.64%. IR (Nujol) νmax/cm−1 1603 (CwN).
1H NMR (270 MHz, CDCl3, −50 °C) δ 7.86 (2H, s, CHwN), 7.42
(2H, t, J = 8.2 Hz, aryl CH), 7.33 (2H, d, J = 6.9 Hz, aryl CH),
6.94 (2H, t, J = 7.4 Hz, aryl CH), 6.68 (2H, t, J = 7.1 Hz, aryl
CH), 6.52 (2H, d, J = 8.2 Hz, aryl CH), 6.32 (2H, d, J = 7.9 Hz,
aryl CH), 6.30 (2H, d, J = 8.6 Hz, aryl CH), 3.96 (6H, s, OCH3),
and 3.79 (6H, s, OCH3). UV-vis: (CHCl3) σmax/103 cm−1 [log(ε/
dm3 mol−1 cm−1)]: 16.0(sh) (2.59) and 22.2 (3.61).
Synthesis of Bis[2-(mesitmethyleneamino)benzenethiolato]-
nickel(Ⅱ) 2. A solution of mesitaldehyde (0.24 g, 1.62 mmol)
and 2-aminothiophenol (0.21 g, 1.67 mmol) in ethanol (20 mL)
was refluxed for 1 h. After the resulting solution was cooled to
room temperature, nickel(Ⅱ) acetate tetrahydrate (0.20 g, 0.80
mmol) was added [2-(mesit)benzothiazoline was not isolated].
The mixture was refluxed for 20 min and cooled to room tempara-
ture. Precipitated brown powder was collected by filtration and
recrystallized from CHCl3. Yield: 0.25 g, 53%. Crystals of com-
plex 2 suitable for a structure determination were grown by the
slow diffusion of diethyl ether into a CHCl3 solution of 2. Found:
C, 65.71; H, 5.55; N, 4.89%. Calcd for C32H32N2NiS2•0.2CHCl3:
C, 65.41; H, 5.49; N, 4.74%. IR (Nujol) νmax/cm−1 1597 (CwN).
1H NMR (270 MHz, CDCl3, r.t.) δ 9.19 (2H, s, CHwN), 7.33 (2H,
dd, J = 7.8 and 1.2 Hz, aryl CH), 6.85 (2H, t, J = 7.6 Hz, aryl
CH), 6.75 (4H, s, aryl CH), 6.32 (2H, t, J = 7.8 Hz, aryl CH), 6.02
Syntheses and Properties. 2-(2,6-Dimethoxyphenyl)ben-
zothiazoline was prepared by a reaction of 2-aminothiophenol
with 2,6-dimethoxybenzaldehyde in ethanol. This compound
was isolated as pale yellow crystals, and characterized by IR
and NMR spectroscopies, besides elemental analysis. Because
2-(mesit)benzothiazoline, which was prepared from 2-amino-
thiophenol and mesitaldehyde, is a liquid at room temperature,
it was used for the reaction without isolation. The reactions of
nickel(Ⅱ) acetate tetrahydrate with 2-(2,6-dimethoxyphen-
yl)benzothiazoline or 2-(mesit)benzothiazoline proceeded
smoothly in ethanol to produce 1 and 2 (Scheme 2), which
were determined by X-ray analyses to be bis(bidentate-N,S)-
type square-planar nickel(Ⅱ) complexes, cis-isomer for 1 and
trans-isomer for 2 (vide infra). Complexes 1 and 2 are fairly
stable in solution, and no subsequent reaction occurred even
after refluxing for a few hours in toluene. This is in contrast to
the case of a nickel(Ⅱ) complex with unsubstituted phenyl
groups as a pendant arm, which is converted into a nickel(Ⅱ)
complex with a non-innocent ligand through carbon–carbon
bond formation (Scheme 1).4 In addition, the activation of
C(aromatic)–OCH3 or C(aromatic)–CH3 bonds was also not
recognized for 1 and 2, while it has been shown that heating
the nickel(Ⅱ) complex with chlorine atoms at 2,6-positions of
the pendant phenyl ring in toluene gives a distorted octahedral
nickel(Ⅱ) complex by C(aromatic)–Cl bond activation
(Scheme 1).5 The stability of 2 can be explained by the trans
arrangement, which prevents contact of the two azomethine
groups required for carbon–carbon bond formation, besides
the contact between the metal center and the methyl carbon

T. Kawamoto et al.
Table 1. Crystallographic Data for 1 and 2 Complexes
Bull. Chem. Soc. Jpn., 76, No. 1 (2003) 129
1
2
Formula
M
C30H28N2NiO4S2•CH2Cl2
688.32
C32H32N2NiS2
567.44
Crystal system
Space group
Monoclinic
P21/a
Triclinic
P1
a/Å
b/Å
c/Å
13.598(6)
21.225(9)
11.056(5)
10.21(1)
14.738(9)
9.80(1)
90.92(7)
103.30(8)
100.49(6)
1409(2)
2
α/°
β/°
99.79(4)
γ /°
V/Å3
3144(2)
4
0.955
4490
Z
µ/mm−1
0.856
5496
No. unique reflections measured
No. reflections in refinement
R
2780 (I > 2.0σ(I))
0.063
4551 (I > 2.0σ(I))
0.056
Rw
0.062
0.062
R = Σ||Fo| − |Fc||/Σ|Fo|, Rw = [Σw(|Fo| − |Fc|)2/Σw(Fo)2]1/2
,
2
Weighting scheme: 1/[σ2(Fo) + 0.001Fo ].
Scheme 2.
atom for the activation of C(aromatic)–CH3 bond. On the oth-
er hand, 1 is possibly stabilized by the existence of the apical
Ni≥OMe interaction, as evidenced by an X-ray analysis,
which would prevent any further reaction.
recognized for the related cis-N2S2 type nickel(Ⅱ) complex-
es,4,5 this spectral feature may be used for the discrimination of
cis and trans isomers.
In the 1H NMR spectrum at 25 °C in CDCl3, 1 exhibited one
broad resonance for ortho-methoxy groups (Fig. 2). As the
temperature was lowered from 25 to −50 °C, however, this
resonance became two separate signals (δ 3.79 and 3.96 at
−50 °C), one of which is located considerably downfield of δ
3.96 compared with the corresponding signal for 2-(2,6-
dimethoxyphenyl)benzothiazoline (δ 3.78). Furthermore, the
spectrum of 1 at −50 °C gave two doublets centered at δ 6.30
and 6.52 due to inequivalent meta protons of the pendant phen-
yl ring,13 which appeared as a broad signal at 25 °C. Thus, it is
assumed that the rotation about the CH–C6H3(OMe)2 moiety
of 1, which occurs on the NMR time scale at room tempera-
The electronic spectra of 1 and 2 in the visible region con-
sist of two absorption components (Fig. 1). The weak band at
lower energy (ca. 15 × 103 cm−1) and the intense band at high-
er energy (ca. 20 × 103 cm−1) for each complex are assigned
as a ligand field (LF) and ligand-to-metal charge transfer
(LMCT) transitions, respectively.12 The LF transition for 2,
which has a trans coordination geometry, occurs as a well-
defined band at 14.1 × 103 cm−1, while the absorption spec-
trum of 1, having a cis geometry, gives a LF transition shoulder
at a higher energy of 16.0 × 103 cm−1. Because similar ab-
sorption shoulders due to LF transitions have been commonly

130 Bull. Chem. Soc. Jpn., 76, No. 1 (2003)
Nickel(ꢀ) Schiff Base Complexes
Fig. 1. Electronic absorption spectra of 1 (solid line) and 2
(broken line) in CHCl3.
Fig. 3. Molecular structure of 1 with 50% probability ellip-
soids. H atoms and the included solvent molecule are
omitted for clarity.
ture, is restricted at low temperature in solution, because of the
existence of the intramolecular Ni≥OMe interaction.14 Con-
trary to the broad resonances for 1 at 25 °C, sharp resonances
were observed in the 1H NMR spectrum of 2 at room tempera-
ture: one singlet at δ 9.19 due to azomethine protons, four sig-
nals at δ 6.02, 6.32, 6.85, and 7.33 due to 2-iminothiophenol
moieties, one singlet at δ 6.75 due to pendant phenyl rings, and
two singlets at δ 2.00 and 2.24 with intensities 12H:6H due to
methyl groups. These signals for 2 correspond to a half-set of
protons, consistent with the C2-symmetrical structure. It is
noteworthy that the azomethine signal for 2 shows a significant
downfield shift (δ 9.19) compared with that for 1 (δ 7.86 at
−50 °C). This downfield shift for 2 may be related to the in-
tramolecular C–H≥S interaction due to the short contact be-
tween the azomethine proton and the coordinated sulfur atom
of the other chelate.15
Molecular Structure of Complex 1.
The molecular
structure of 1, together with the atomic labeling scheme, is
shown in Fig. 3. Selected bond lengths and angles are listed in
Table 2. Complex 1•CH2Cl2 crystallizes in the monoclinic
space group P21/a. The asymmetric unit of 1•CH2Cl2 consists
of one nickel center and one dichloromethane. The coordina-
tion geometry around the nickel atom is an approximately
square-planar, having a cis-N2S2 coordination mode. The di-
hedral angle between the two S–Ni–N planes is 12(3)°. The
Fig. 2. Variable-temperature 1H NMR spectra of 1 in CDCl3
from +25 °C to −50 °C.

T. Kawamoto et al.
Bull. Chem. Soc. Jpn., 76, No. 1 (2003) 131
Table 2. Selected Bond Distances (Å) and Angles (deg) of 1
and 2 Complexes
1
2
Ni1–S1
Ni1–S2
Ni1–N1
Ni1–N2
Ni2–S2
Ni2–N2
S1–C1
S2–C16
S2–C17
N1–C2
N1–C7
N2–C17
N2–C22
N2–C18
N2–C23
2.184(4)
2.172(4)
1.913(9)
1.928(9)
2.204(13)
1.893(12)
2.198(2)
1.900(3)
1.747(4)
1.754(13)
1.763(13)
1.754(4)
1.446(5)
1.292(5)
1.450(15)
1.278(14)
1.444(15)
1.281(15)
1.437(4)
1.283(5)
S1–Ni1–S2
S1–Ni1–N1
S1–Ni1–N1*
S2–Ni1–N2
N1–Ni1–N2
S2–Ni2–N2
S2–Ni2–N2*
90.2(2)
87.2(3)
86.5(5)
93.5(6)
Fig. 4. One of the crystallographically independent mole-
cules of 2 with 50% probability ellipsoids. H atoms are
omitted for clarity.
87.4(3)
96.3(4)
85.2(1)
94.8(1)
Ni–S (average 2.178 Å) and Ni–N (average 1.921 Å) bond dis-
tances are quite normal.2,4,5 Axial intramolecular Ni≥OMe
contacts of 2.630(9) Å for Ni(1)≥O(1) and 2.709(9) Å for
Ni(1)≥O(3) in 1 should be noted. These contacts are signifi-
cantly shorter than the sum of their van der Waals distances
(3.15 Å).16 A similar interaction has been observed between
the metal center and the methoxy-oxygen atom for nickel(Ⅱ) or
palladium(Ⅱ) complexes with aromatic phosphines.17 The ox-
ygen atoms of the methoxy groups may therefore be consid-
ered to coordinate weakly to the nickel atom, or at least to have
an attractive interaction with the nickel one.18
Scheme 3.
served between 2 and trans-[Pt(fabt)2]. That is, 2 has an E ge-
ometry about the CwN double bond, while the pendant arms of
trans-[Pt(fabt)2] is restricted to have a Z geometry. In addition,
2 adopts a stepped conformation with respect to the metal-con-
taining 2-iminothiophenol moieties, which is different from an
umbrella conformation for trans-[Pt(fabt)2] (Scheme 4).6 In 2,
the Ni–S bond distances (average 2.201 Å) are longer, while
the Ni–N bond distances (average 1.897 Å) are in the shorter
region, compared with the values found in the related square-
planar nickel(Ⅱ) complexes having a cis-N2S2 coordination
mode.2,4,5 This would be a reflection of the mutual trans influ-
ence due to coordinated sulfur atoms. The azomethine hydro-
gen atoms and the coordinated sulfur atoms show short con-
tacts of C(7)–H(7)≥S(1)* 2.48(4) and C(23)–H(23)≥S(2)*
2.55(3) Å, accompanying the E geometry about CwN double
Molecular Structure of Complex 2.
The molecular
structure of 2, together with the atomic labeling scheme, is
shown in Fig. 4. Selected bond lengths and angles are listed in
Table 2. Complex 2 crystallizes in the triclinic space group
P1. There are two crystallographically independent molecules
of 2 in the asymmetric unit which are almost the same as each
other. Each molecule lies on an inversion center, the two Ni
atoms being situated at (0, 0, 0) and (0.5, 0.5, 0.5). Thus, 2
adopts a perfect planar geometry around the nickel atom with a
trans-N2S2 donor atom arrangement. A rough consideration
based on molecular models suggests that the trans isomer was
formed preferentially due to a less severe steric repulsion
among the methyl groups of the pendant arms and the Ni cen-
ter. Such a trans coordination geometry is unusual for bis-
chelate N2S2 metal complexes with Schiff base ligands.19 The
only example of a trans isomer for N2S2 Schiff base complexes
derived from 2-substituted benzethiazolines is trans-[Pt(fabt)2]
(fabt = 2-(ferrocenylmethyleneamino)benzenethiolato) con-
taining ferrocenyl groups as a pendant arm.6 However, a
marked difference in another geometrical isomerism (E or Z)
due to the restricted –CwN– double bond (Scheme 3)20 is ob-
Scheme 4.

132 Bull. Chem. Soc. Jpn., 76, No. 1 (2003)
Nickel(ꢀ) Schiff Base Complexes
Kiefer, Chem. Rev., 86, 451 (1986). d) I. Omae, Coord. Chem.
Rev., 83, 137 (1988). e) A. D. Ryabov, Chem. Rev., 90, 403
(1990).
bond in 2. Furthermore, it should be noted that the methyl
groups of the pendant phenyl rings contact with 2-imino-
thiophenol moieties (C(2)≥C(14) 3.079(6) and C(18)≥C(30)
3.105(6) Å), indicative of the existence of an intraligand CH/π
interaction.21 As a result, the pendant phenyl rings approach to
the 2-iminothiophenol moieties having tilting angles of 58(3)°
for Ni(1) and 58(4)° for Ni(2) between the pendant phenyl
rings and the 2-iminothiophenol moieties.
8
P. J. Palmer, R. B. Trigg, and J. V. Warrington, J. Med.
Chem., 14, 248 (1971).
9
CRYSTAN-GM, A Computer Program for the Solution and
Refinement of Crystal Structures for X-ray Diffraction Data,
MAC Science Corporation, Yokohama, 1994.
10 “DIRDIF”: P. T. Beurskens, G. Admiraal, G. Beurskens, W.
P. Bosman, S. Garcia-Granda, R. O. Gould, J. M. M. Smits, and C.
Smykalla, Technical report of the Crystallography Laboratory,
University of Nijmegen, Nijimegen, The Netherlands, 1994.
11 “SIR 92”: A. Altomare, G. Cascarano, C. Giacovazzo, and
A. Guagliardi, J. Appl. Crystallogr., 26, 343 (1993).
12 H. Frydendahl, H. Toftlund, J. Becher, J. C. Dutton, K. S.
Murray, L. F. Taylor, O. P. Anderson, and E. R. T. Tiekink, Inorg.
Chem., 34, 4467 (1995).
Conclusion
We have synthesized and characterized two Schiff base
nickel(Ⅱ) complexes with different substituents on the pendant
phenyl ring. The nickel(Ⅱ) complex bearing the methoxy
groups at the 2,6-positions of the pendant phenyl ring (1)
shows an approximately square-planar geometry with a cis-
N2S2 donor atom arrangement. The existence of the apical
Ni≥OMe interaction in the cis complex 1 has been established
based on an X-ray analysis, together with variable-temperature
1H NMR studies. On the other hand, the nickel(Ⅱ) complex
with methyl groups as a substituent group (2) exhibits a perfect
planar trans-N2S2 coordination. These results suggest that the
geometry of nickel(Ⅱ) complexes of this type is successfully
controlled by changing the substituent on the pendant phenyl
ring. In addition, no further reactivity has been observed for
both complexes, which is ascribed to the existence of the api-
cal Ni≥OMe interaction for 1 and to the trans arrangement for
2. We are currently investigating the structure and reactivity of
other metal complexes containing the same ligands employed
in this work.
13 Assignments for the 1H NMR were supported by selective
homonuclear decoupling at −50 °C.
1
14 Line shape analysis of the variable-temperature H NMR
spectra of 1 yields ∆H‡ = 66.6 0.3 kJ mol−1 and ∆S‡ = 22.7
0.8 J mol−1 K−1 for the exchange of the two methoxy groups
about the CH–C6H3(OMe)2 moiety.
15 a) W.-Y. Sun, X.-F. Shi, L. Zhang, J. Hu, and J.-H. Wei, J.
Inorg. Biochem., 76, 259 (1999). b) Y. Tang, Y. Yao, L. Wu, Y.
Qin, Y. Kang, and Z. Li, Chem. Lett., 2001, 542.
16 A. Bondi, J. Phys. Chem., 68, 441 (1964).
17 a) K. R. Dunbar, J.-S. Sun, and A. Quillevere, Inorg.
Chem., 33, 3598 (1994). b) K. R. Dunbar and J.-S. Sun, J. Chem.
Soc., Chem. Commun., 1994, 2387. c) J.-F. Ma, Y. Kojima, and Y.
Yamamoto, J. Organomet. Chem., 616, 149 (2000).
18 The Ni(1)≥C(14) (3.511(19) Å) and Ni(1)≥C(29)
(3.569(16) Å) distances in 1 suggest that there is no Ni≥H–C
interaction.
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