Observation of different molecular alignments of [Ni(salphen)] substituted by a different number of octyl groups at HOPG surface

Article abstract of DOI:10.1246/bcsj.20110314

The surface adsorption structures of two Schiff-base metal complexes, [N,N'-bis(5-octylsalicylidene)-o-phenylenediaminato] nickel(II) (1) and [N,N'-bis(3,5-dioctylsalicylidene)-o-phenylenediaminato]nickel(II) (2), are imaged using scanning tunneling micro

Full text of DOI:10.1246/bcsj.20110314

592
Bull. Chem. Soc. Jpn. Vol. 85, No. 5, 592-598 (2012)
© 2012 The Chemical Society of Japan
Observation of Different Molecular Alignments of [Ni(salphen)]
Substituted by a Different Number of Octyl Groups at HOPG Surface
Yoshinori Tamaki,*1 Kazuaki Tomono,2 Yuki Hata,1 Nanami Saita,1
Takashi Yamamoto,1 and Kazuo Miyamura*1
1Department of Chemistry, Faculty of Science, Tokyo University of Science,
1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601
2Department of Material Chemistry, Graduate School of Science and Engineering,
Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611
Received October 17, 2011; E-mail: tamakiyoshinori99@yahoo.co.jp, miyamura@rs.kagu.tus.ac.jp
The surface adsorption structures of two Schiff-base metal complexes, [N,N¤-bis(5-octylsalicylidene)-o-phenyl-
enediaminato]nickel(II) (1) and [N,N¤-bis(3,5-dioctylsalicylidene)-o-phenylenediaminato]nickel(II) (2), are imaged using
scanning tunneling microscopy (STM), and compared with the dimeric structure predicted by single-crystal X-ray
diffraction and NMR analyses. STM images of 1 and 2 obtained at an o-dichlorobenzene/HOPG interface showed that
1 was adsorbed in the form of dimers, while 2 was adsorbed as monomers at HOPG surface. The surface structure of
1 was similar to that of the reported salen complex analogue. 1H NMR measurement revealed that the equilibrium
constants of dimer formation for 1 and 2 in chloroform-d were determined to be K (= [dimer]/[monomer]2) = 14.5 and
1.9 mol¹1 dm3, respectively. This decreased tendency of 2 to form dimer is concluded to be the reason why 2 did not form
dimers at HOPG surface. The crystal structure of 1 in which 1 is found to form dimers is also presented.
Compounds bearing both hydrophilic and hydrophobic
dimeric structure.36 The key technology to stabilize the surface
structure of complex is to introduce long alkyl chains. Alkyl
chains strongly adsorb on HOPG by CH-³ interaction and help
to cease the movement of the molecule at HOPG surface.
In this paper is reported the change in self-assembled struc-
tures of salphen [=bis(salicylidene)-o-phenylenediaminato]
complex analogues by the number of long alkyl chains intro-
duced. The difference between salen and salphen is that
the ethylene moiety (-CH2-CH2-) is changed to phenylene
(-C6H4-), and thus the ³-conjugated system is extended in
salphen. We have synthesized two nickel(II) complexes of
salphen substituted by two (1) and four (2) alkyl chains
(Chart 1), and observed their molecular images by STM. We
obtained totally different surface structures and also found
that the surface structure reflects the structure they adopt
in solution.
moieties within a molecule tend to gather at liquid-liquid or
liquid-solid interface, because at the interface, hydrophilic or
hydrophobic properties change discontinuously. We call this
nature the surface activity, and those amphiphilic compounds
the surfactants. At the liquid-solid interface, surfactants gather
to form self-assembled monolayers (SAMs) with characteristic
structures, which are now, frequently observed by scanning
tunnelling microscope (STM). Since SAMs exhibit a variety
of properties and are used as catalysis,1 chemical sensors,2-5
electrochemical agents,6,7 corrosion protecting materials,8-10
lubricants,11-15 adhesive and wetting materials,16-21 the relation
between the structure of SAMs and their properties is inten-
sively investigated.
Lately, in the field of coordination chemistry, the number
of reports on the observation of monolayers formed by metal
complexes is rapidly increasing. Metal complexes with large
³-conjugated system are known to easily exchange electrons
with other molecule, and by this nature, they are the good can-
didates of the above-mentioned functional materials. Phthalo-
cyanine was the first metal complex observed by STM with
a well-resolved molecular image.22 Since then, not only the
phthalocyanines,23-26 but also a variety of metal complexes
such as porphyrins,26-29 chlorophylls,30-32 and other metal com-
plexes33 have been observed by STM. We have also reported
some STM images of salen [=bis(salicylidene)ethylenedi-
aminato] complexes substituted by two alkyl side chains since
2000.34,35 The outstanding feature of this complex is that it
assembles at interface in the form of dimers. Some related
compounds imaged recently also showed the presence of
Hf
A
He
Hd
Hc
Hb
N
O
N
O
Ni
R1
B′
R1
B
R2
R2
R1 = octyl, R2 = Ha ; [Ni(2C8-salphen)] (1)
R1 = R2 = octyl ; [Ni(4C8-salphen)] (2)
Chart 1.
Published on the web May 9, 2012; doi:10.1246/bcsj.20110314

Y. Tamaki et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 5 (2012)
593
the dimension of the unit cell was 2.25 © 1.50 nm2 with acute
angle of 78°. Thus the area of unit cell was calculated to be
3.30 nm2. The parameter a and a¤, b and b¤ were the same
distance (a = a¤ = 2.25 nm, b = b¤ = 1.50 nm). Figure 2b
shows that the magnified STM image is composed of four
bright spots being brighter than the other one. Figure 2c shows a
line profile along the arrow in Figure 2c. The spot A is twice as
high as A¤. This strongly suggests the formation of dimer shown
in Figures 2d and 2e just as that observed in crystal analyzed
Results and Discussion
STM Images.
The self-assembled adlayers of 1 ([Ni-
(salphen)] substituted with two octyl groups) and 2 (1 sub-
stituted with two extra octyl groups) on solid (HOPG)-liquid
(o-dichlorobenzene; o-DCB) interface were observed, charac-
terized, and imaged with STM under ambient conditions. STM
image obtained at low bias voltage showed a hexagonal lattice
of HOPG surface, while that at high bias showed the highly
ordered self-assembled adlayer of complex molecules, indicat-
ing that the phenomenon was bias dependent.14 The molecular
orbitals calculated by DFT showed that the HOMO is located
at aromatic rings and Ni(II) as shown in Figure 1. This agrees
with the observation that the aromatic moieties of the mole-
cules are found to appear brighter than the other parts.
Figure 2a shows the STM image of the self-assembled
adlayer of complex 1 on HOPG surface, scanned at high
bias voltage; bias voltage ¹1.2 V, tunnel current 4.0 nA. This
ordered image due to adsorbed 1 at HOPG/o-DCB interface
was observed two days after the sample preparation. In
Figure 2a, ring-like structures cover the whole domain, and
Figure 1. Optimized structure and HOMO of 1 calculated
by DFT.
(a)
(d)
(b)
(e)
(c)
Figure 2. (a) Constant current STM image of 1 on HOPG. Area: 18.0 nm © 7.0 nm; Bias voltage ¹1.2 V; tunneling current 4.0 nA.
Unit cell dimensions: a = 2.25 nm, b = 1.50 nm; ¡ = 78°. (b) Magnified STM image of area shown as a rectangle in (a).
Area: 1.8 nm © 1.2 nm. (c) Line profile over an arrow indicated in figure (b). (d) Proposed adsorbed structure model viewed from
direction normal to the surface of HOPG. (e) Side view of the proposed adsorbed model of HOPG. * at right corner indicates the
three axes of underlying HOPG surface from here after. Octyl chains of ball and stick model are omitted for clarity.

594
Bull. Chem. Soc. Jpn. Vol. 85, No. 5 (2012)
Different Molecular Alignments of [Ni(salphen)] at HOPG Surface
with X-ray crystallography given later in the text. 1H NMR
study, discussed later in the text, also revealed that 1 tends to
form similar dimer. For a more quantitative representation
of the data, the distance between A and B, B and B¤ were 0.57
and 0.88 nm, respectively. B-A-B¤ and B-A¤-B¤ angles were
83 and 105°, respectively. From the results of X-ray crystallog-
raphy given later in the text, the distance between the centers
of aromatic rings A and B, B and B¤ in the scheme were 0.65
and 0.79 nm, respectively, and the angle B-A-B¤ was 75°.
By comparing the lengths and angles, the distance between
bright spots B and B¤ in Figure 2b could be assigned as B and B¤
aromatic rings of a molecule 1. However, the facts that the
distance between A and B is shorter and that the angle of
B-A-B¤ is larger than the angle from X-ray crystallographic
analysis, indicate that molecules 1 are inclined from the HOPG
surface as shown in Figure 2e. The obtained dimension of
dimer in Figure 2d agreed well with the dimension of the ring-
like structure. We also investigated the possibility of coad-
sorption of complex 1 and o-DCB. However, the distance
between the bright spots was too narrow to put o-DCB into
space. Therefore, we concluded that the ring-like structure
exhibited by 1 is of a dimer as indicated in Figure 2d and
Figure 2e, and the dimers are fixed by three-point mounting of
aromatic rings.
The alkyl groups are known to usually align along the
underlying HOPG lattice due to the stabilization caused by
CH-³ interaction. Although the alkyl chains are not imaged
clearly, we estimated that the alkyl groups are thus aligned.
In Figure 3 is given the arrangement model of Figure 2a
with van der Waals radii in accordance with the STM image.
Figure 2a shows the first adsorbed layer of complex 1 on
HOPG and the octyl chains lie along one of the three HOPG
lattice indicated in lower right corner. The metal-metal distance
along a axis corresponds to the sum of the length of a salphen
and an octyl group. This fact suggests that the alkyl chains are
aligned along one of the HOPG lattices with the octyl groups
being interdigitated as shown in Figure 2a. In Figure 2a, we
found a declination of a axis indicated by c and c¤ axes
(c = 2.02 nm and c¤ = 2.30 nm). This defect can be explained
by the difference in interdigitation as shown in Figure 3.
The fact that the ring-like bright spot shown in Figure 2b is
similar to that observed for [Ni(2C12-salen)] in which two alkyl
chains are introduced at para-orientation.35 On the other hand,
the STM image of 1 is different from that reported for salophen
in which alkyl groups are introduced at meta-orientations.34)
When four octyl groups are introduced to salphen at both ortho-
and para-positions, a totally different STM image was obtained.
Figure 4a shows a 15.0 nm © 15.0 nm STM image of 2 adsorb-
ed on HOPG surface; bias voltage ¹1.6 V, tunnel current 1.0 nA.
The obtained image of 2 is distinct from that of 1 prepared by
the same procedure and conditions. The direction of underlying
HOPG hexagonal lattice is shown by three lines at the corner.
STM image of 2 shows many bright spots with triangular
structure that can be clearly identified as salphen framework
covering the whole area. A bright spot with isosceles triangular
shape enabled us to distinguish aromatic ring A from the others.
Note that the apex of the isosceles triangular image orients
toward one of the HOPG lattices. Thus the STM image shows
that the molecules are not in the form of dimers as 1, and the
monomeric molecules are lying on the HOPG surface with the
molecular plane being parallel to the HOPG surface similarly to
other complexes reported. The lengths of the base and the height
of a triangle are 1.6 and 1.0 nm, respectively. The size is slightly
larger than the actual size of 2. When viewed along the a axis,
we can see that the orientation of each complex was inverted
alternately, and along the b axis, the orientation of every
two complexes was inverted. It gives the surface unit cell shown
by a rectangle in Figure 4a an expression of plane group p2gg,
and the unit cell parameter of 4.22 © 2.88 nm2, area per unit
cell 12.2 nm2, and area per molecule 3.04 nm2. At a surface,
achiral compounds often form chiral domains. However, the
obtained STM image of 2 showed only achiral domains.
For a more quantitative representation of the data, the line
profile along the a axis indicated by an arrow in Figure 4a has
been extracted and depicted in Figure 4b. At the center of a
single molecule, a hollow due to Ni(II) is observed. Such a
hollow is also reported in the STM image of Ni-salphen and
phthalocyanine complex.25,33 Regarding from one molecule,
there are three nearest neighbors, x = 1.93 nm (tail to tail),
y =1.73 nm (tail to head), and z = 1.70 nm (head to head),
indicated in Figure 4c. In this model, para-octyl groups of a
molecule interact by van der Waals interaction with para-octyl
groups of a neighboring molecule and edges of salphen
frameworks of other molecules in contact.
X-ray Structural Analysis. An ORTEP drawn with the
atomic numbering scheme of 1 is shown in Figure 5a. The
coordination geometry around nickel atom is square-planar
N2O2, with the ligand coordinated through nitrogen and oxygen
atoms in cis arrangement. Although the salphen framework
is almost planar (maximum deviation from the least-squares
average NiN2O2 plane is 0.1636(38) ¡ [C(10)]), three benzene
rings are twisted by 4.84(20) [A], 5.34(19)° [B], and 3.48(20)°
[B¤] to the chelate plane of [Ni(salphen)] framework. The
structure observed from ac plane in Figure 5b shows that the
complexes are stacked in the form of dimers. However, the
dimers are linked along the c axis by C(sp2)-H£O hydrogen
bonds37 and edge-to-face C(sp2)-H£³ interaction.37 The geo-
metric parameters of C(sp2)-H£O were 2.64 ¡ [H(3)£O(1) (x,
1.5 ¹ y, ¹0.5 + z)], 3.520 ¡ [C(3)£O(1)], and 157.7° [<C(3)-
Figure 3. Proposed arrangement for Figure 2a. CPK model
is for the underlying layer with adsorbing aromatic rings of
B and B¤ and ball and stick model is for layer with that
of A. Octyl chains of ball and stick model are omitted
for clarity.

Y. Tamaki et al.
(a)
Bull. Chem. Soc. Jpn. Vol. 85, No. 5 (2012)
595
(b)
(c)
Figure 4. (a) High-resolution STM image of 2 on HOPG. Image area: 15.0 nm© 15.0 nm; Bias voltage ¹1.2 V; tunneling current
2.0 nA. Unit cell is plane group p2gg with the unit cell dimensions of a = 4.22 nm, b = 2.88 nm. (b) Line profile over an arrow
indicated in (a). (c) Proposed monolayer model.
H(3)£O(1)], and the edge-to-face distance between C-H of a
ring A and the molecular plane of a ring A (1 ¹ x, 0.5 + y,
¹0.5 + z) was 2.996 ¡ (Figure 5b). Furthermore, the octyl
chains of 1 are aligned side by side to form lamellar like
structure. Such a structure is commonly observed in crystal of
compounds with long alkyl chains. When the crystal structure
of 1 is compared with that of the nonsubstituted complex
[Ni(salphen)],38 the structure of the dimer is found to be
apparently different. On the other hand, the dimer of 1 is simi-
lar to [Ni(4tBu-salphen)]39 [H2(4tBu-salphen) = 1,2-bis(3,5-
di-tert-butyl-2-hydroxybenzimino)benzene] and [Ni(3,5-Cl2-
saloph)] [H2(3,5-Cl2saloph) = N,N¤-1,2-diyl-bis(3,5-dichloro-
salicylideneimine)].40 Hydrophobic interactions between the
octyl groups that lead to form lamellar like structure might
be the reason of the difference.
(a)
(b)
The structure of a dimer of 1 is shown in Figure 6a and the
inter- and intradimer arrangements are shown in Figures 6b
and 6c, respectively. Intermolecular distance in a dimer is
3.24 ¡ while interdimer distance is 3.39 ¡. The difference is
very small, so two arrangements are considered. Four bright
spots in the STM image of 1 in Figure 2 are arranged to form
hemispherical patterns. It is clear that this pattern accords with
the top view of the dimer in Figure 6a.
Dimer Formation in Chloform-d Solution Studied by
1H NMR. 1H NMR spectra of 1 and 2 in chloroform-d were
measured with a 500 MHz spectrometer, and all peaks have been
assigned comparing them with those of the reported spectra
Figure 5. (a) Thermal ellipsoid plot (ORTEP) and atomic
numbering scheme of 1. Ellipsoids are drawn at 50%
probability level. (b) Crystal structure of 1. CH£O (dotted
line) and edge-to-face CH/³ (thin line) interactions are
also indicated. Octyl chains are omitted for clarity.
1
of the salen analogues. It is known that the H NMR peaks

596
Bull. Chem. Soc. Jpn. Vol. 85, No. 5 (2012)
Different Molecular Alignments of [Ni(salphen)] at HOPG Surface
(a)
(a)
(b)
(c)
(b)
(c)
Figure 6. Comparison of dimer and intradimer arrange-
ments. (a) Dimer; top view, (b) intradimer; top view and
(c) side view of dimer and intradimer arrangements. Light
and dark molecules of (a), and (b) were designed to
correspond with (c). H atoms of octyl groups were omitted
for clarity.
assigned to Hc and Hd of [Ni(salen)] substituted by alkyl groups
exhibit concentration dependence.41 On increasing the concen-
tration, the signals assigned to the protons Hc and Hd of 1 and 2
also exhibited clear upfield shifts. Figures 7a and 7b show the
concentration dependences of Hc and Hd for the 1 and 2. The
shifts were observed only for Hc and Hd, and neither aliphatic
protons nor the Ha and Hb protons of the benzene rings showed
observable shifts. The proposed structure for the aggregate
in chloroform-d solution is given in Figure 7c. These upfield
Figure 7. (a) Concentration dependence of Hc and (b) Hd
of 1H NMR position shift in chloroform-d solution with
calculated curve fitting and (c) proposed aggregation
structure of Ni-salphen dimer.
¹4
shifts became conspicuous above the concentration of ca. 10
mol L¹1, and shifted about a ppm upwards until the solution of
1 and 2 saturated at 40 and 200 mmol L¹1, respectively.
equation which assumes simple monomer-dimer equilibrium,
we could evaluate the equilibrium constants for 1 and 2 as 14.5
and 1.9 L mol¹1, respectively.
As is frequently discussed in the literature, NMR upfield
shifts are caused by the approach of an aromatic ring to the
protons by aggregation. Although 1 and 2 have an extra
aromatic ring A compared with the salen analogue, the fact
that the same protons exhibit upfield shifts indicates that the
structures of the aggregates of 1 and 2 are similar to that of the
1=2
¤ ¼ ¤d þ ð¤m ꢀ ¤dÞfð1 þ 8CKÞ ꢀ 1g=4CK
ð1Þ
¤, ¤m, ¤d: observed chemical shift, chemical shifts of mono-
mer and dimer, respectively, C: concentration K: equilibrium
constant of monomer-dimer equilibrium.
Note that the fitted curves given in Figure 7a agree well with
the data. Data obtained from curve fitting are summarized
in Table 1.
The results show that the K for 1 is 7 times larger than that
of 2. One reason for the difference is the solubilising effect.
The introduction of long alkyl groups increases the solubility
toward organic solvent, and the solubility of 2 is 5 times larger
1
reported salen analogue.41 As the H NMR spectra exhibit the
shifts and not the splittings, a rapid equilibrium between the
aggregate and the monomeric species is indicated. Figure 7a
shows that the peak shift of 1 (Hc and Hd) commences from
lower concentration than that of 2. Consequently, the equi-
librium constant for the aggregation equilibrium for 1 should
be larger than that of 2. By fitting the data to the following

Y. Tamaki et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 5 (2012)
597
¹1
23981 dm¹3 mol¹1 cm (383 nm). IR spectra; ¯as(C-CH3) at
Table 1. Calculated Equilibrium Constants K, and Chemical
Shifts of Monomer ¤m, and of Dimer ¤d 1 and 2
¹1
¹1
¹1
2955 cm ¯as(CH2) at 2920 cm ¯as(C=N) at 1620 cm
Synthesis of [N,N¤-Bis(3,5-dioctylsalicylidene)-o-phenyl-
enediaminato]nickel(II) (2): 2 was obtained from 3,5-
dioctylsalicylaldehyde by a similar procedure to 1 described
above. Yield was 80%. Anal. Found: C, 75.61; H, 9.59; N,
3.59%. Calcd for C36H46N2NiO2: C, 75.99; H, 9.49; N, 3.41%.
1H NMR (CDCl3): ¤ 0.88 (6H, m-, o-, p-CH3CH2-), 1.29 (20H,
m), 1.57 (4H, m-, o-, p-benzyl-CH2-CH2-), 2.50 (2H, t, J =
7.5 Hz, p-benzyl-CH2-), 2.71 (2H, t, J = 7.5 Hz, o-benzyl-
CH2-), 6.94 (1H, d, J = 1.3 Hz, Hc), 7.04 (1H, d, J = 0.9 Hz,
.
Hc
Hd
K
Complex
¹1
/mol¹1¢L
¤
m
¤
d
¤
m
¤
d
[Ni(2C8salphen)] (1)
[Ni(4C8salphen)] (2)
[Ni(2C8salen)]a)
14.5
1.9
8
7.11(6) 6.84 8.25(6) 7.98
6.95
6.81
6.47 8.22
6.00 7.47
7.44
6.25
a) [Ni(2C8salen)] = [N,N-Bis(5-octylsalicylidene)ethylenedi-
aminato]nickel(II).41
than that of 1 as mentioned previously. This effect probably
stabilizes monomeric 2 in solution, and also leads to the change
in surface adsorption behavior.
Hb), 7.20 (1H, q, J = 3.8 Hz, Hf ), 7.68 (1H, q, J = 4.4 Hz,
¹3
He), 8.21 (1H, s, Hd). UV-vis spectra (1.0 © 10¹4 mol dm
,
CHCl3); ¾
(-max) = 9483 (502 nm), 6457 (456 nm), and
max
29759 dm¹3 mol¹1 cm (387 nm). IR spectra; ¯as(C-CH3) at
¹1
Conclusion
¹1
¹1
¹1
2955 cm ¯as(CH2) at 2920 cm ¯as(C=N) at 1620 cm
.
We have observed change in the surface alignment of
[Ni(salphen)] substituted by different number of alkyl groups
on HOPG. The increase in the number of substituted long alkyl
groups is found to increase the solubility of the complex toward
organic solvent, and decrease the tendency to aggregate. This
effect is concluded as the reason why 2 with four alkyl groups
covered HOPG surface with monomers, while 1 with two alkyl
groups covered with dimers.
STM Measurements. A drop of o-DCB 1.0 mM solutions
of 1 or 2 was placed on a freshly cleaved surface of HOPG and
allowed to settle for a while. Then, this sample was measured
by Digital Instruments Nanoscope II/E STM equipment under
ambient conditions. Thus, all measurements were performed at
the liquid-solid interface. STM tips were prepared by electro-
chemically etched Pt/Ir(80/20) wire according to reported
procedures.22 STM images were obtained with a constant
current mode unless indicated. Typically a bias voltage varying
from 50 mV to ¹1.6 V (sample negative) and a tunnelling
current of 1.0-4.0 nA were employed. Obtained STM images
were manually plane-fit to account for sample tilt and then
either low-pass filtered and/or Fourier filtered. By changing the
voltage applied to the tip and the average tunnelling current
during STM imaging, it was possible to switch from the
visualization of the adsorbate layer (high voltage) to that of
the underlying HOPG substrate (low voltage). This enabled
us to correct the distorted STM image by comparison with the
equilateral-triangular lattice of HOPG. The lateral distortion
caused by the thermal drift in STM images were calibrated by
referencing distortion of underlying graphite lattice measured
prior to the molecular image of adlayer. This calibration was
carried out by WSxM software.44 To distinguish between alkyl
groups and aromatic rings, we assigned bright spots as aromatic
rings, and slightly bright area as alkyl group. In a usual STM
image, aromatic rings tend to appear brighter than alkyl chains
because of the presence of ³-electrons.
Experimental
Elemental analyses were performed with a Perkin-Elmer
2400II CHN analyzer. UV-vis-NIR spectra were recorded with
a JASCO V-570 UV/VIS/NIR spectrophotometer. IR spectra
were obtained with a JASCO FT/IR-410 spectrometer using
KBr pellets. All reagents were of reagent grade and used
without further purification.
Syntheses. 5-Octylsalicylaldehyde was synthesized by the
Reimer-Tiemann reaction42 from p-octylphenol and chloro-
form. 3,5-Dioctylsalicylaldehyde was synthesized by the Duff
reaction43 from 2,4-octylphenol obtained by the ordinary
Friedel-Crafts acylation and Clemensen reduction from p-
octylphenol and octanoyl chloride, the procedure for which
is given elsewhere.
Synthesis of [N,N¤-Bis(5-octylsalicylidene)-o-phenylene-
diaminato]nickel(II) (1): Nickel acetate tetrahydrate (0.50 g,
2 mmol) and o-phenylenediamine (0.21 g, 2 mmol) were added
to 100 mL of ethanol in a flask with stirring. After the solution
became red, 5-octylsalicylaldehyde (0.83 g, 4 mmol) was added
dropwise to the solution. The reaction mixture was then refluxed
for 3 h. Precipitates of 1 formed were filtered and recrystallized
from dichloromethane and methanol (1:1) mixed solvents. A
single crystal of 1 suitable for X-ray crystallographic analysis
was prepared by slow inter-diffusion of o-DCB/chloroform
(1:1) solution (20 mL) of 1 and ethanol (50 mL) for one week
at room temperature. Yield; 2.4 g (90%). Anal. Found: C, 72.36;
H, 7.94; N, 4.74%. Calcd for C36H46N2NiO2: C, 72.37; H, 7.76;
Theoretical Methodology.
Optimizing geometry and
obtaining orbitals of a single molecule with density function
theory (DFT) calculations were carried out using the program
package DMol3 in the Materials Studio of Accelrys Inc.45
Calculations were performed using the generalized gradient
approximation (GGA) proposed by Perdew et al.46 (PBE). A
double-numeric quality basis set with d-polarization functions
(DNP) was used.
X-ray Crystallography. A single crystal of 1 was mounted
on a glass capillary. Intensity data were collected at 300(1) K by
a Bruker AXS SMART diffractometer equipped with CCD area
detector and Mo K¡ (- = 0.71073 ¡) radiation. The structure of
1 was solved and refined with the SHELX-9747 software using
direct method and expanded using Fourier techniques. All non-
hydrogen atoms were refined anisotropically by the full-matrix
least-squares method. Some hydrogen atoms were found from
1
N, 4.69%. H NMR (CDCl3): ¤ 0.88 (3H, t, CH3CH2-, J =
6.7 Hz), 1.28 (10H, m), 1.57 (2H, m, benzyl-CH2-CH2), 2.51
(2H, t, J = 7.6 Hz, benzyl-CH2), 7.08 (1H, d, J = 1.4 Hz, Hc),
7.10 (1H, d, J = 9.2 Hz, Ha), 7.15 (1H, dd, J = 9.2 and 1.0 Hz,
Hb), 7.23 (1H, q, J = 4.0 Hz, Hf ), 7.70 (1H, q, J = 4.0 Hz,
¹3
He) 8.22 (1H, s, Hd). UV-vis spectra (1.0 © 10¹4 mol dm
,
CHCl3): ¾
(-max) = 7768 (493 nm), 5117 (445 nm), and
max

598
Bull. Chem. Soc. Jpn. Vol. 85, No. 5 (2012)
Different Molecular Alignments of [Ni(salphen)] at HOPG Surface
16 M. K. Chaudhury, G. M. Whitesides, Science 1992, 255,
1230.
17 G. M. Whitesides, P. E. Laibinis, Langmuir 1990, 6, 87.
18 C. D. Bain, G. M. Whitesides, Angew. Chem., Int. Ed. Engl.
1989, 28, 506.
19 P. E. Laibinis, R. G. Nuzzo, G. M. Whitesides, J. Phys.
Chem. 1992, 96, 5097.
20 R. K. Smith, P. A. Lewis, P. S. Weiss, Prog. Surf. Sci. 2004,
75, 1.
21 A. Ulman, Thin Solid Films 1996, 273, 48.
22 R. H. Lippel, R. J. Wilson, M. D. Miller, Ch. Wöll, S.
Chiang, Phys. Rev. Lett. 1989, 62, 171.
23 P. Sautet, C. Joachim, Surf. Sci. 1992, 271, 387.
24 X. Lu, K. W. Hipps, X. D. Wang, U. Mazur, J. Am. Chem.
Soc. 1996, 118, 7197.
25 X. Lu, K. W. Hipps, J. Phys. Chem. B 1997, 101, 5391.
26 X. Qiu, C. Wang, Q. Zeng, B. Xu, S. Yin, H. Wang, S. Xu,
C. Bai, J. Am. Chem. Soc. 2000, 122, 5550.
27 A. Ogunrinde, K. W. Hipps, L. Scudiero, Langmuir 2006,
22, 5697.
28 S.-L. Yau, Y.-G. Kim, K. Itaya, J. Phys. Chem. B 1997, 101,
3547.
29 T. Ikeda, M. Asakawa, M. Goto, K. Miyake, T. Ishida, T.
Shimizu, Langmuir 2004, 20, 5454.
30 R. K. Naqvi, T. B. Melø, B. B. Raju, T. Jávorfi, I. Simidjiev,
G. Garab, Spectrochim. Acta, Part A 1997, 53, 2659.
31 Y. Kureishi, H. Shiraishi, H. Tamiaki, J. Electroanal.
Chem. 2001, 496, 13.
32 H. Kirchhoff, H.-J. Hinz, J. Rösgen, Biochim. Biophys.
Acta, Bioenerg. 2003, 1606, 105.
experimental data directly, and their position and isotropic
thermal parameters were refined. Crystallographic data have
been deposited at Cambridge Crystallographic Data Centre:
Deposit number CCDC-842634 for compound 1. Copies of the
data can be obtained free of charge via http://www.ccdc.cam.uk/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge, CB2 1EZ, U.K.;
FAX: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
Crystal data for 1; Mr = 597.46; red rectangular block,
0.39 © 0.10 © 0.05 mm3; monoclinic, P2(1)/c; a = 18.867(2)
¡, b = 9.0908(11) ¡, c = 18.433(2) ¡, £ = 94.508(2)°, V =
3151.7(6) ¡3, Dcalcd = 1.259 Mg m¹3, 2ªmax = 55.02°, 18841
reflections collected, 4318 uniques [R(int) = 0.0780]; final
GOF = 1.034, R1 = 0.0813, wR2 = 0.1319, R indices based
¹1
on 7104 reflections with I > 2·(I), ® = 0.649 mm
.
1H NMR Measurements. Concentration dependence of
1H NMR spectra were measured at 25 °C using a lambda
spectrometer JEOL JNM-LA500 FT-NMR system. Chloro-
form-d containing 1% TMS as inner reference supplied from
Kantoh Chemical Co., was used as a solvent. 5 and 10 mL
measuring flasks were used to prepare the sample solution. The
solutions of different concentration were prepared stepwise,
adding the complex in small portions each time after the
measurement had been completed.
Supporting Information
Figure of STM image of large area of 2 on HOPG. This
material is available free of charge on the Web at: http://www.
csj.jp/journals/bcsj/.
33 M. T. Räisänen, F. Mögele, S. Feodorow, B. Rieger, U.
Ziener, M. Leskelä, T. Repo, Eur. J. Inorg. Chem. 2007, 4028.
34 T. Fujii, K. Miyamura, Bull. Chem. Soc. Jpn. 2000, 73, 365.
35 I. Sakata, K. Miyamura, Chem. Commun. 2003, 156.
36 J. A. A. W. Elemans, S. J. Wezenberg, M. J. J. Coenen,
E. C. Escudero-Adán, J. Benet-Buchholz, D. den Boer, S. Speller,
A. W. Kleij, S. De Feyter, Chem. Commun. 2010, 46, 2548.
37 G. R. Desiraju, Acc. Chem. Res. 1996, 29, 441.
38 A. Radha, M. Seshasayee, K. Ramalingam, G.
Aravamudan, Acta Crystallogr., Sect. C 1985, 41, 1169.
39 O. Rotthaus, O. Jarjayes, F. Thomas, C. Philouze, C. P.
Del Valle, E. Saint-Aman, J.-L. Pierre, Chem.®Eur. J. 2006, 12,
2293.
40 F. Azevedo, M. A. A. F. de C. T. Carrondo, B. de Castro,
M. Convery, D. Domingues, C. Freire, M. T. Duarte, K. Nielsen,
I. C. Santos, Inorg. Chim. Acta 1994, 219, 43.
41 K. Miyamura, K. Satoh, Y. Gohshi, Bull. Chem. Soc. Jpn.
1989, 62, 45.
42 I. Fells, E. A. Moelwyn-Hughes, J. Chem. Soc. 1959, 398.
43 L. N. Ferguson, Chem. Rev. 1946, 38, 227, and references
cited therein.
References
1
G. A. Somorjai, Chemistry in Two Dimensions: Surfaces,
Cornell University Press, Ithaca NY, 1981.
R. Izumi, K. Hayama, K. Hayashi, K. Toko, Chem. Senses
2004, 20, 50.
2
3
J. Ladd, C. Boozer, Q. Yu, S. Chen, J. Homola, S. Jiang,
Langmuir 2004, 20, 8090.
4
5
S. Huan, G. Shen, R. Yu, Electroanalysis 2004, 16, 1019.
F. Maya, A. K. Flatt, M. P. Stewart, D. E. Shen, J. M. Tour,
Chem. Mater. 2004, 16, 2987.
S. Flink, B. A. Boukamp, A. van den Berg, F. C. J. M.
van Veggel, D. N. Reinhoudt, J. Am. Chem. Soc. 1998, 120, 4652.
C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K.
6
7
Beverly, J. Sampaio, F. M. Raymo, J. F. Stoddart, J. R. Heath,
Science 2000, 289, 1172.
8
C. M. Whelan, M. Kinsella, H. M. Ho, K. Maex,
J. Electrochem. Soc. 2004, 151, B33.
Z. Quan, S. Chen, X. Cui, Y. Li, Corrosion (Houston, TX,
9
U. S.) 2002, 58, 248.
10 S. Ramachandran, B.-L. Tsai, M. Blanco, H. Chen, Y. Tang,
W. A. Goddard, III, Langmuir 1996, 12, 6419.
11 G. P. Lopez, M. W. Albers, S. L. Schreiber, R. Carroll, E.
Peralta, G. M. Whitesides, J. Am. Chem. Soc. 1993, 115, 5877.
12 Q. Zhang, L. A. Archer, J. Phys. Chem. B 2003, 107,
13123.
13 A. Lio, D. H. Charych, M. Salmeron, J. Phys. Chem. B
1997, 101, 3800.
14 V. V. Tsukruk, Adv. Mater. 2001, 13, 95.
15 Y.-S. Shon, S. Lee, R. Colorado, Jr., S. S. Perry, T. R. Lee,
J. Am. Chem. Soc. 2000, 122, 7556.
44 I. Horcas, R. Fernández, J. M. Gómez-Rodríguez, J.
Colchero, J. Gómez-Herrero, A. M. Baro, Rev. Sci. Instrum.
2007, 78, 013705.
45 Materials Studio, version 4.4, Accelrys Inc., San Diego,
CA, 2006.
46 J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996,
77, 3865.
47 G. M. Sheldrick, SHELX-97 and SHELXL-97, Program
for the Solution of Crystal Structures, University of Göttingen,
Germany, 1997.