Assembly structures of 1:2 nickel(II) complex of 5-methylimidazol-4-yl- methylidene-L-phenylalanine and 1:2 nickel(II) complex of its racemic ligand

Article abstract of DOI:10.1016/j.ica.2013.06.044

1:2 Nickel(II) complexes of 5-methylimidazol-4-yl-methylidene-L- phenylalanine (H₂L^L-phe) and its race-mic ligand (H ₂L^DL-phe) were synthesized and the crystal structures of the resultant [Ni(HL^L-

Full text of DOI:10.1016/j.ica.2013.06.044

Inorganica Chimica Acta 406 (2013) 59–64
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Assembly structures of 1:2 nickel(II) complex of 5-methylimidazol-4-yl-
methylidene-L-phenylalanine and 1:2 nickel(II) complex of its racemic
ligand
Seira Shintoyo a, Suguru Yamauchi a, Tomohiro Oishi b, Naohide Matsumoto a, Takeshi Fujinami a,
⇑
a Department of Chemistry, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
b The Technical Division, Faculty of Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
a r t i c l e i n f o
a b s t r a c t
-phenylalanine (H2L -phe) and its race-
L
Article history:
Received 10 May 2013
Received in revised form 24 June 2013
Accepted 25 June 2013
Available online 9 July 2013
1:2 Nickel(II) complexes of 5-methylimidazol-4-yl-methylidene-
L
DL-phe
) were synthesized and the crystal structures of the resultant [Ni(HL -phe)2]-
L
mic ligand (H2L
ÁMeOHÁ3H O (1) and [Ni(HL -phe)2]Á6H2O (2) complexes were determined. Complex 1 crystallized in an
acentrosymmetric monoclinic space group, P21 (No. 4). The nickel(II) ion is coordinated by (N2O)2 donor
2
DL
atoms from two tridentate H2L -phe ligands and has an octahedral coordination environment. In the crys-
L
tal, 1 contains only the L-isomer and forms a homochiral 2D structure through hydrogen bonding
Keywords:
between the adjacent complex molecules. In contrast, Complex 2 crystallized into a centrosymmetric
monoclinic space group, P21/c (No. 14). The nickel(II) ion is coordinated by (N2O)2 donor atoms from
Nickel(II) complex
Tridentate ligand
Phenylalanine
5-Methyl-4-formylimidazole
Chiral discrimination
Assembly process
two H2L -phe tridentate ligands. The coordination geometry around the nickel(II) ion is described as octa-
L
D-phe
L
hedral. In the crystal, 2 consists of [Ni(HL
)2] and [Ni(HL -phe)2] molecule that are related and forms a
heterochiral 3D structure via hydrogen bonding through the crystal solvents.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
In previous papers, we studied the enantioselective assembly of
a copper(II) complex with a chiral-imidazole-containing tridentate
DL-phe
The fields of crystal engineering and supramolecular chemistry
have attracted much attention during the past three decades, be-
cause a well-designed molecular building block is crucial for the
formation of a functional supramolecular assembly [1]. Self-assem-
bly involving metal ions is especially useful for the construction of
functional supramolecules; for example, metal-directed assembly
has been successfully employed to construct various supramolecu-
lar architectures such as helices [2–6], grids [7,8], boxes [9,10],
rods [11], and tubes [12], in which the assembly interactions
may involve coordination or hydrogen bonds. Such interactions
are quite strong, selective, and directional, and, in some cases, sus-
tainable [13–16]. Among the many useful building blocks for metal
complexes, imidazole-containing polydentate ligands have several
advantages for versatile assembly of different structures because of
the multitude of coordination modes available: (1) intermolecular
coordination through the imidazolate nitrogen; (2) imidaz-
oleÁ Á Áimidazolate (NHÁ Á ÁN) hydrogen bonding; and (3) imidaz-
oleÁÁÁhalogen anion (NHÁ Á ÁXÀ) hydrogen bonding [17–20].
Because the metal complex and/or ligands are often chiral [21–
23], these complexes are useful for investigating the chiral
assembly process [24–30].
ligand, i.e., [CuIICl(HLDL-phe)], where H2L
is 5-methylimidazol-
4-yl-methylidene-DL-phenylalanine; this ligand is the 1:1 condensa-
tion product of DL-phenylalanine and 5-methyl-4-formylimidazole
[31–34]. [Cu X(HL -phe)] can function as a self-complementary
II
DL
chiral building block in the construction of assembly structures
[31–34]. As shown in Scheme 1, this CuII complex can undergo
two types of assembly processes: (1) intermolecular imidazole–
carboxylate (NHÁ Á ÁO) hydrogen bonding to form a homochiral 1D
assembly chain, or (2) intermolecular coordination bonding be-
tween a carboxylate oxygen of one molecule to a CuII ion of an
adjacent molecule (@OÀCu) to form a homochiral 1D structure. It
should be noted that such homochiral 1D assembly structures
are enantioselectively constructed from a mixture of self-comple-
D-phe
II
mentary building blocks, i.e., [CuIIX(HL
)] and [Cu X(HL -phe)].
L
To further investigate the chiral discrimination of the metal com-
plexes, we also studied the nickel(II) complexes. In contrast to
the 1:1 Cu complex, i.e., [Cu X(HL -phe)], the nickel(II) ion reacts
II
DL
to form a 1:2 complex, i.e., [Ni(HL -phe)2]. The metal
DL-phe
DL
with H2L
complex formation with the particular ligand depends predomi-
nantly on the kind of metal ion and its oxidation state. Generally
Cu(II) ion reacts with the NO-Schiff-base ligand to produce four-
or five-coordinated complex, whereas Ni(II) ion gives low-spin four
coordinated complex or high-spin six-coordinated complex. In the
present case, Cu(II) ion with the tridentate ligand forms the 1:1
⇑
Corresponding author. Tel./fax: +81 96 342 3385.
E-mail address: 124d9005@st.kumamoto-u.ac.jp (T. Fujinami).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.06.044

60
S. Shintoyo et al. / Inorganica Chimica Acta 406 (2013) 59–64
DL-phe
II
Scheme 1. [CuIIX(HLDL-phe)] and [Ni(HL
)2] and their enantioselective assembling. Homochiral 1D assembly structures of [Cu X(HL -phe)] (X = Cl, Br) constructed by
DL
intermolecular imidazoleÁ Á Ácarboxylate hydrogen bond (X = Cl), and intermolecular coordination bond between carboxylate oxygen and CuII ion (X = Br). The 1:2 complex
)2] and its assembly structure [Ni(HL -phe)2].
DL-phe
DL
[Ni(HL
Fig. 1. Molecular structures of (a) [Ni(HLL-phe)2]Á2MeOHÁH2O (1) and (b) the mononuclear unit [Ni(HL -phe)2] with the
L
isomer of the ligand of [Ni(HL -phe)2]Á7H2O (2) with the
L
DL
selected atom numbering scheme.
complex, while nickel(II) ion gives high-spin 1:2 complex. The tri-
dentate ligand plays an uninegative ligand and the 1:2 Ni(II) com-
plex with preferable six-coordination number is electronically
neutral and stable complex. Other types of chiral assemblies were
also found in the NiII complex: we report here the synthesis,
molecular structure, and chirally discriminative assembly of
2.2. Synthesis of nickel(II) complexes
II
2.2.1. Preparation of [Ni (HL -phe)2]ÁMeOHÁ3H2O (1)
L
A solution of L-phenylalanine (165 mg, 1 mmol) in 5 mL of
methanol and 5 mL of water was added to a solution of 5-
methyl-4-formylimidazole (110 mg, 1 mmol) in 5 mL of methanol,
and the mixture was stirred on a hot plate at 60 °C for 60 min. The
ligand solution was then cooled to room temperature and used for
the synthesis of the nickel(II) complex. Accordingly, a solution of
NiII(CH3COO)2Á4H2O (124 mg, 0.5 mmol) in 10 mL of methanol
was added to a solution of the H2LL-phe ligand (1 mmol). The mix-
ture was stirred at room temperature for 60 min and then filtered.
The filtrate was allowed to stand for several days, during which
[Ni(HL -phe)2]Á6H2O.
DL
2. Experimental
time light purple platelet crystals precipitated. Yield: 115 mg
2.1. General
II
(20%). Elemental Anal. Calc. for [Ni (HL -phe)2]ÁMeOHÁ3H2O = C29-
L
38
H N6O8Ni: C, 52.99; H, 5. 82; N, 12.78. Found: C, 52.78; H, 5.48;
All chemicals and solvents were obtained from Tokyo Kasei Co.,
Ltd., and Wako Pure Chemical Industries, Ltd., and were of reagent
grade and used without further purification. All the synthetic pro-
cedures were carried out in an open atmosphere.
N, 13.07%. Dry samples were used for TGA. 1 showed a 12.5%
weight loss corresponding to a calculated values of MeOHÁ3H2O
(13.1%) when heated to a temperature region lower than 120 °C.

S. Shintoyo et al. / Inorganica Chimica Acta 406 (2013) 59–64
61
In a cooling mode, a 5.2% weight increase corresponding to two
H2O molecules (5.6%) was observed.
6500 W spectrometer with the samples in KBr disks. Thermogravi-
metric analyses (TGA) were performed on a TG/DTA6200 instru-
ment (Seiko Instrument Inc.), which involved heating ꢀ2 mg of
II
2.2.2. Preparation of [Ni (HL -phe)2]Á6H2O (2)
the sample from room temperature to 210 °C at
a rate of
DL
5 °C minÀ1
.
A solution of DL-phenylalanine (165 mg, 1 mmol) in 5 mL of
methanol and 5 mL of water was added to a solution of 5-
methyl-4-formylimidazole (110 mg, 1 mmol) in 5 mL of methanol,
and the mixture was stirred on a hot plate at 60 °C for 60 min. A
2.4. X-ray crystal structure analyses
solution of NiII(CH3COO)2Á4H2O (124 mg, 0.5 mmol) in 10 mL of
Crystals of 1 and 2 were selected from the solution, mounted on
a glass rod, and quickly coated with epoxy resin; they were then
used for the X-ray diffraction study at 250 K. The X-ray diffraction
data were collected using a Rigaku RAXIS RAPID imaging plate area
DL-phe
methanol was then added to the solution of the H2L
ligand
(1 mmol). The mixture was stirred at room temperature for
60 min and then filtered. The filtrate was allowed to stand for sev-
eral days, during which time light blue platelet crystals precipi-
tated; the crystals were collected by suction filtration, washed
detector with graphite monochromated Mo
Ka radiation
(k = 0.71069 Å). The structures were resolved using direct methods
and expanded using the Fourier technique. Hydrogen atoms were
fixed at the calculated positions and refined using a riding model.
All calculations were performed using the Crystal Structure crystal-
lographic software package [35,36].
with ether, and dried. Yield: 124 mg (22%). Elemental Anal. Calc.
II
for [Ni (HL -phe)2]Á6H2O = C28H40N6O10Ni: C, 49.50; H, 5.93; N,
DL
12.37. Found: C, 49.44; H, 5.88; N, 12.32%. Dry samples were used
for TGA. 2 showed a 15.8% weight loss corresponding to the calcu-
lated values of 6H2O molecules (15.9%) when heated to a temper-
ature region lower than 120 °C. In a cooling mode, a 2.7% weight
increase corresponding to one H2O molecule (2.8%) was observed.
3. Results and discussion
3.1. Synthesis and characterization of nickel(II) complexes
2.3. Physical measurements
Tridentate ligands, i.e., H2LL-phe and H2L -phe, were prepared via
DL
Elemental C, H, and N analyses were performed at the Center for
Instrumental Analysis of Kumamoto University, Japan. Infrared
spectra were recorded at room temperature using a JEOL JIR-
a 1:1 condensation reaction of 5-methyl-4-formylimidazole and
either L-phenylalanine or DL-phenylalanine in a mixed solvent com-
prising methanol and H2O (2:1 by volume); the resulting ligand
solution was used for the synthesis of the metal complex without
isolating the ligand. The nickel(II) complexes, i.e., [Ni (HL -phe)2]-
II
L
Table 1
II
ÁMeOHÁ3H O (1) and [Ni (HL -phe)2]Á6H2O (2), were prepared by
2
DL
Crystallographic data of nickel(II) complexes [Ni(HLL-phe)2]Á2MeOHÁH2O and [Ni(HL -phe)2]Á
DL
mixing NiII(CH3COO)2Á4H2O with H2LL-phe and H2L -phe, respec-
DL
7H2O.
tively, in a 1:2 M ratio in the mixed solvent. After slow crystalliza-
tion at room temperature, complexes 1 and 2 were obtained as
light purple platelet and light blue platelet crystals, respectively.
The relatively low yields (ꢀ20%) were probably due to the high
solubility of the complex in the crystallization solvent. C, H, and
Complex
[Ni(HL -phe)2]Á2MeOHÁH2O
[Ni(HL -phe)2] Á7H2O
L
DL
Formula
Formula weight
Crystal system
Space group
a (Å)
C
30H38N6O7Ni
C28H42N6O11Ni
697.37
653.37
monoclinic
P21 (No. 4)
10.389(1)
12.096(2)
13.439(2)
100.530(4)
1660.4(4)
2
monoclinic
P21/c (No. 14)
12.2143(9)
11.4255(7)
24.292(2)
95.427(2)
3374.9(4)
4
b (Å)
c (Å)
Table 3
Relevant coordination bond and hydrogen bond distances of [Ni(HL -phe)2]Á7H2O.
DL
b (°)
V (Å3)
DL
Complex
[Ni(HL -phe)2]Á7H2O
Z
T (K)
250
1.307
0.0753, 0.1712
0.07(3)
250
1.372
0.0751, 0.1992
Coordination bond distances (Å)
NiÀN1 (imidazole)
NiÀN3 (imine)
Dcalcd (g cmÀ1
R, Rw
)
2.093(5)
2.012(4)
2.107(5)
2.006(4)
2.107(4)
2.089(4)
Flack parameter
NiÀN4 (imidazole)
NiÀN6 (imine)
NiÀO1 (carboxylate)
NiÀO3 (carboxylate)
Table 2
Hydrogen bond distances (Å)
O1 (carboxylate)Á Á ÁO6⁄1 (water)
O2 (carboxylate)Á Á ÁO7⁄2 (water)
O2 (carboxylate)Á Á ÁO9⁄2 (water)
O3 (carboxylate)Á Á ÁO11⁄3 (water)
O4 (carboxylate)Á Á ÁO5⁄4 (water)
O4 (carboxylate)Á Á ÁO8⁄3 (water)
O5 (water)Á Á ÁO6 (water)
Relevant coordination bond and hydrogen bond distances of [Ni(HL -phe)2]Á2
L
2.719(6)
2.874(6)
2.724(6)
2.762(6)
2.722(6)
2.807(6)
2.737(6)
2.734(6)
2.882(7)
2.901(6)
2.873(6)
2.886(7)
2.908(7)
2.771(7)
2.808(7)
2.766(7)
MeOHÁH2O.
[Ni(HL -phe)2]Á2MeOHÁH2O
L
Complex
Coordination bond distances (Å)
NiÀN1 (imidazole)
NiÀN3 (imine)
2.118(5)
1.994(7)
2.102(8)
1.995(8)
2.122(5)
2.111(7)
NiÀN4 (imidazole)
NiÀN6 (imine)
O5 (water)Á Á ÁN5 (imidazole)
O6 (water)Á Á ÁO10⁄8 (water)
O7 (water)Á Á ÁO8 (water)
NiÀO1 (carboxylate)
NiÀO3 (carboxylate)
O7 (water)Á Á ÁO11 (water)
Hydrogen bond distances (Å)
O7 (water)Á Á ÁN2 (imidazole)
O8 (water)Á Á ÁO9 (water)
O1 (carboxylate)Á Á ÁO5⁄1 (water)
O2 (carboxylate)Á Á ÁN2⁄2 (imidazole)
O3 (carboxylate)Á Á ÁO7⁄3 (methanol)
O4 (carboxylate)Á Á ÁO5⁄3 (water)
O4 (carboxylate)Á Á ÁO6⁄3 (methanol)
O5 (water)Á Á ÁN5 (imidazole)
2.771(7)
2.652(8)
2.840(18)
2.735(10)
2.82(4)
O9 (water)Á Á ÁO10 (water)
O10 (water)Á Á ÁO11 (water)
O10 (water)Á Á ÁO11⁄13 (water)
Symmetry operations:
2.732(10)
(⁄1), Àx + 1,Ày + 2,Àz + 1; (⁄2), x,Ày + 3/2,z À 1/2;
(⁄3), Àx + 2,y À 1/2,Àz + 3/2; (⁄4), x + 1,y,z;
(⁄8), x À 1,Ày + 5/2,z À 1/2; (⁄13), Àx + 2,Ày + 2,Àz + 2.
Symmetry operations:
(⁄1), Àx + 2,y À 1/2,Àz + 2; (⁄2), x + 1,y,z; (⁄3), x,y À 1,z.

62
S. Shintoyo et al. / Inorganica Chimica Acta 406 (2013) 59–64
N elemental analyses of 1 and 2 agreed with the chemical formulae
Ni–N(3) (imine) = 1.994(7) Å; Ni–O(1) (carboxylate) = 2.122(5) Å;
Ni–N(4)(imidazole) = 2102(8) Å; Ni–N(6) (imine) = 1.995(8) Å;
and Ni–O(3) (carboxylate) = 2.111(7) Å. The Ni–N (imine) distance
is shorter than the Ni–N (imidazole) and Ni–O (carboxylate)
distances.
II
II
[Ni (HL -phe)2]ÁMeOHÁ3H2O
and
[Ni (HL -phe)2]Á6H2O,
L
DL
of
respectively.
3.2. Crystal structure of nickel(II) complexes
Complex 2 crystallized into a centrosymmetric monoclinic
space group, P21/c (No. 14), with the formula of [Ni(HL -phe)2]Á7H2O.
DL
The crystal structures of 1 and 2 were determined by sin-
gle-crystal X-ray diffraction analyses at 250 K. The molecular
structures of 1 and 2 are shown in Fig. 1, while Table 1 shows
the crystallographic data; Tables 2 and 3 list the relevant bond
lengths and hydrogen bond distances.
-
DL
The number of the crystal solvents is not compatible with [Ni(HL
phe)2]Á6H2O by the elemental analyses. The same products used as
samples for the X-ray diffraction and elemental analyses. Crystals
for X-ray diffraction analyses were selected from the solution,
whereas crystals for the elemental analyses were kept in open
atmosphere. Therefore, it suggested that water molecules of the
crystal solvents are eliminated. The crystal structure consists of
Complex 1 crystallized into an acentrosymmetric monoclinic
space group, P21 (No. 4), with Z = 2 and the formula of
[Ni(HL -phe)2]Á2MeOHÁH2O. The number of the crystal solvents is
L
D-phe
[Ni(HL
)2] and [Ni(HL -phe)2] molecules that are related by
not compatible with [Ni(HL -phe)2]ÁMeOHÁ3H2O by the elemental
L
L
inversion because the P21/c space group has an inversion center.
analyses. The samples used for the X-ray and elemental analyses
are same products. Crystals for X-ray diffraction analyses were se-
lected from the solution, whereas crystals for the elemental analy-
ses were kept in open atmosphere. Therefore, it suggested that the
crystal solvents are eliminated and absorbed. The Flack parameter
was refined to nearly zero, which is consistent with the chirality of
Fig. 1(b) shows the molecular structure of [Ni(HL -phe)2], where
L
two tridentate ligands coordinated to the NiII ion have the same
chirality but two H2L -phe ligands differ with respect to the orienta-
L
tion of the phenyl group. The nickel(II) ion is coordinated by (N2O)2
donor atoms from two H2L -phe tridentate ligands. The coordination
L
geometry around the nickel(II) ion is described as octahedral; the
coordination bond distances are as follows: Ni–N(1) (imidaz-
ole) = 2.093(5) Å; Ni–N(3) (imine) = 2.012(4) Å; Ni–O(1) (carboxyl-
ate) = 2.107(4) Å; Ni–N(4) (imidazole) = 2.107(5) Å; Ni–N(6)
L
-phenylalanine used forthe synthesis. The nickel(II) ion is coordi-
nated by (N2O)2 donor atoms from two tridentate H2LL-phe ligands
and has an octahedral coordination environment; the coordination
bond distances are as follows: Ni–N(1) (imidazole) = 2.118(5) Å;
Fig. 2. (a) Homochiral 2D network structure of [Ni(HL -phe)2]Á2MeOHÁH2O (1) constructed by intermolecular imidazoleÁ Á Ácarboxylate hydrogen bond of O(2)Á Á ÁN(2) and two
L
hydrogen bonds via water molecule O(5). Green-colored molecule represents an enantiomer consisting of L-phenylalanine moiety. (b) A view of double layer projected onto
the layer. Adjacent 2D layers related by 21 symmetry operation along the b-axis are linked by a water molecule O(5) via hydrogen bonds, forming a double layer. (c) Side view
of two double layers. The double layers are stacked along the c-axis. Two methanol molecules are hydrogen bonded to carboxylate groups and occupy the void between the
double layers. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

S. Shintoyo et al. / Inorganica Chimica Acta 406 (2013) 59–64
63
b-transformation (x,1 + y,z), with
a
distance (O(5)Á Á ÁO(4)⁄) of
2.735(10) Å. The 1D chains running along the a-axis are linked
via an oxygen atom of the water molecule, O(5), through two
hydrogen bonds, i.e., N(5)Á Á ÁO(5) and O(5)Á Á ÁO(4)⁄, to give a 2D
layer structure, as shown in Fig. 2(a). The adjacent 2D layer is gen-
erated by a 21 symmetry operation along the b-axis and is stacked
along the c-axis. The adjacent 2D layers are linked by O(5)Á Á ÁO(1)
(carboxylate) andO(5)Á Á ÁO(4)⁄ (carboxylate) hydrogen bonds to
form a double-layer structure; the hydrogen bond distances of
O(5)Á Á ÁO(1) and O(5)Á Á ÁO(4)⁄ are 2.771(7) and 2.735(10) Å, respec-
tively. The oxygen atom of the water molecule, O(5), of [Ni(HL -phe)2]Á
L
2MeOHÁH2O (1) forms three hydrogen bonds to the three neighbor-
ing [Ni(HL -phe)2] and functions a connector to form the double-
L
layer structure. Fig. 2(b) shows the double-layer structure viewed
perpendicular to the 2D layer, i.e., along the c-axis. Fig. 2(c) shows
a side view of the double layers, which are stacked along the c-axis.
Two molecules of methanol crystal solvent are hydrogenbonded to
carboxylate groups and occupy the void between the double layers.
The assembly structure of 2 is shown in Fig. 3(a) and (b). One of
the two imidazole nitrogen atoms, N(5), of a NiII complex is hydro-
gen bonded to an oxygen atom of a water molecule, O(5), with a
distance (N(5)Á Á ÁO(5)) of 2.734(6) Å; O(5) is further hydrogen
bonded to a carboxylate oxygen atom, O(4)⁄, of an adjacent NiII
complex that is related by an a-transformation (1 + x,y,z) with
O(5)Á Á ÁO(4)⁄ = 2.722(6) Å. Two hydrogen bonds to an oxygen atom
in a water molecule, O(5), i.e., N(5)Á Á ÁO(5) and O(5)Á Á ÁO(4)⁄, are re-
peated along the a-axis to form a 1D chain. A nitrogen atom from
the second imidazole group, N(2), of the NiII complex is hydrogen
bonded to an oxygen atom of a water molecule, O(7), with a dis-
tance of 2.886(7) Å; the water molecule is further hydrogen
bonded through O(7) to a carboxylate oxygen atom, O(2)⁄, of the
adjacent NiII complex, which is related by inversion (Àx,Ày,Àz),
with a distance of 2.874(6) Å. The 1D chains running along the c-
axis are linked via an oxygen atoms of a water molecule, O(7),
through two hydrogen bonds, i.e., N(2)Á Á ÁO(7) and O(7)Á Á ÁO(2)⁄,
to provide the 2D layer structure, as shown in Fig. 3(a). The 2D
layer structure contains D-isomer (red) or L-isomer (green) chains
bonded by two hydrogen bonds to an oxygen atom of a water mol-
ecule, O(5), i.e., N(5)Á Á ÁO(5) and O(5)Á Á ÁO(4)⁄, which run along the
a-axis. The adjacent chains with opposite chirality are linked by
two hydrogen bonds to an oxygen atom of a water molecule,
O(7), i.e., N(2)Á Á ÁO(7) and O(7)Á Á ÁO(2)⁄, to give a heterochiral 2D
layer structure. Because the phenyl groups are present on the same
side, the layer is hydrophobic. The water clusters are present at the
opposite sides of the hydrophobic layer formed by the phenyl
group. The adjacent 2D layer is generated by a 21 symmetry oper-
ation along the a-axis and is stacked along the b-axis; the layers are
connected via hydrogen bonds of the water clusters. As a result,
complex 2 features a heterochiral 3D structure, as shown in
Fig. 3. (a) Heterochiral 2D network structure of [Ni(HL -phe)2]Á7H2O (2) constructed
DL
by the hydrogen bonds to a water molecule O(5) and O(7), where green- and red-
colored molecules represent two enantiomers consisting of L- and D-phenylalanine
moieties, respectively. (b) The 2D layers are stacked along the b-axis and the
adjacent a heterochiral 2D layer is linked by the hydrogen bonds through the water
clusters to forms a heterochiral 3D structure.
Fig. 3(b). The O(5) and O(7) atoms of water molecules in [Ni(HL -phe)2]Á
DL
7H2O (2) are hydrogen bonded to water clusters and function as
connectors to form the 3D structure [37,38]. Table 3 summarizes
the hydrogen bond OÁ Á ÁO distances.
(imine) = 2.006(4) Å; and Ni–O(3) (carboxylate) = 2.089(4) Å. The
Ni–N (imine) distance is shorter than the Ni–N (imidazole) and
Ni–O (carboxylate) distances.
The assembly structure of 1 is shown in Fig. 2(a–c). One of the
two imidazole nitrogen atoms, N(2), in each nickel(II) complex is
hydrogen bonded to a carboxylate oxygen atom, O(2)⁄, of the adja-
cent NiII complex, which is related by an a-transformation
4. Concluding remarks
The 1:2 nickel(II) complex, [Ni(HL -phe)2]ÁMeOHÁ3H2O (1) was
L
synthesized using an optically pure ligand of N-[(5-methylimida-
(1 + x,y,z), with
a
hydrogen bond distance (N(2)Á Á ÁO(2)⁄) of
zol-4-yl)methylidene]-L-phenylalanine. Complex 1 contains only
2.652(8) Å. The intermolecular N(2)Á Á ÁO(2)⁄ hydrogen bond repeats
along the a-axis to give a 1D chain. Another imidazole nitrogen
atom, N(5), of a NiII complex is hydrogen bonded to an oxygen
the -isomer and crystallized into an acentrosymmetric monoclinic
L
space group, P21 (No. 4). The crystal structure formed a homochiral
2D structure through hydrogen bonds between the adjacent
complexes. To investigated from the perspective of enantioselec-
tive assembly into crystal lattices, the 1:2 nickle(II) complex
atom of
a
water molecule, O(5), with
a
distance of
2.732(10) Å;O(5) is further hydrogen bonded to a carboxylate oxy-
gen atom, O(4)⁄, of the adjacent NiII complex, which is related by a
[Ni(HL -phe)2]Á6H2O (2) was synthesized using racemic ligand of
DL

64
S. Shintoyo et al. / Inorganica Chimica Acta 406 (2013) 59–64
[10] E. Leize, A.V. Dorsselaer, R. Kramer, J.M. Lehn, J. Chem. Soc., Chem. Commun.
N-[(5-methylimidazol-4-yl)methylidene]-D-phenylalanine and N-
(1993) 990.
[(5-methylimidazol-4-yl)methylidene]-L-phenylalanine. In the 1:2
[11] X. Delaigue, M.W. Hosseini, E. Leize, S. Kieffer, A.V. Doreeslaer, Tetrahedron
Lett. 34 (1993) 7561.
nickle(II) complex, [Ni(HLD-phe)2], [Ni(HLL-phe)2] and [Ni(HL
)
D-phe
(HL -phe)] are three probable isomers. Complex
2 contains
L
[12] R. Fuchs, N. Habermann, P. Klufers, Angew. Chem., Int. Ed. Engl. 32 (1993) 852.
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D-phe
)2] and [Ni(HL -phe)2] molecules that are related by
L
[Ni(HL
inversion because 2 crystallized into a centrosymmetric mono-
clinic space group, P21/c (No. 14). The crystal structure formed a
heterochiral 3D structure via hydrogen bonds through the crystal
solvents. The different assembly structures were formed by chiral
aggregation and the presence of hydrogen-bonded solvent
molecules.
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5720.
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(1998) 197.
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Acknowledgment
T. Fujinami was supported by the Research Fellowship for
Young Scientists of the Japan Society for the Promotion of Science,
KAKENHI 00248556.
[23] S. Takahashi, S. Hashimoto, Y. Shimogori, N. Matsumoto, T. Nakashima, M.
Tsuchimoto, Polyhedron 30 (2011) 2026.
Appendix A. Supplementary material
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43 (2004) 6168.
CCDC 933581 and 933582 contains the supplementary
crystallographic data for [Ni(HL -phe)2]Á2MeOHÁH2O (1) and
L
[Ni(HL -phe)2]Á7H2O (2) at 250 K. These data can be obtained free
DL
of charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.ica.2013.06.044.
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Polyhedron 33 (2012) 209.
[34] S. Yamauchi, T. Hashibe, M. Murase, H. Hagiwara, N. Matsumoto, M.
Tsuchimoto, Polyhedron 49 (2013) 105.
[35] CrystalStructure 3.7.0, Crystal Structure Analysis Package, Rigaku and Rigaku/
MSC, 9009 New Trails Dr., The Woodlands, TX 77381, USA, 2000–2005.
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