Presence of edge-to-face aromatic interaction in bis[1,2-bis(4-alkylphenyl)ethanedione dioximato]nickel(II) complexes and evaluation of the fastener effect

Article abstract of DOI:10.1016/j.ica.2007.02.013

Bis[1,2-bis(4-methylphenyl)ethanedione dioximato]nickel(II), [Ni{(C₁)₂dpg}₂] (1), was found to exhibit shift in diffuse reflectance spectra from the corresponding non-methyl species. Characterization by X-ray crystal structural analysis on 1 and bis[1,2-bis(4-n-hexylphenyl)ethanedione dioximato]nickel(II), [Ni{(C₆)₂dpg}₂] (2), revealed the presence of the edge-to-face aromatic interactions caused by the electron-donating effect of the methyl and hexyl groups. The Ni(dpg)₂ units of complex 2 stack (staggered by 90°) at alternate intervals of 3.151 A? and 3.253 A?. Thus, the shift in the d-p transition of 2 was found to contain 43% of the effect of the edge-to-face aromatic interaction, together with 57% of the reported fastener effect.

Full text of DOI:10.1016/j.ica.2007.02.013

Inorganica Chimica Acta 360 (2007) 3123–3126
www.elsevier.com/locate/ica
Note
Presence of edge-to-face aromatic interaction in
bis[1,2-bis(4-alkylphenyl)ethanedione dioximato]nickel(II)
complexes and evaluation of the fastener effect
*
Yuji Soneta , Tatsuo Moritaka, Kazuo Miyamura
Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
Received 24 October 2006; received in revised form 8 February 2007; accepted 13 February 2007
Available online 21 February 2007
Abstract
Bis[1,2-bis(4-methylphenyl)ethanedione dioximato]nickel(II), [Ni{(C1)2dpg}2] (1), was found to exhibit shift in diffuse reflectance
spectra from the corresponding non-methyl species. Characterization by X-ray crystal structural analysis on 1 and bis[1,2-bis(4-n-hex-
ylphenyl)ethanedione dioximato]nickel(II), [Ni{(C6)2dpg}2] (2), revealed the presence of the edge-to-face aromatic interactions caused
by the electron-donating effect of the methyl and hexyl groups. The Ni(dpg)2 units of complex 2 stack (staggered by 90ꢀ) at alternate
˚
˚
intervals of 3.151 A and 3.253 A. Thus, the shift in the d–p transition of 2 was found to contain 43% of the effect of the edge-to-face
aromatic interaction, together with 57% of the reported fastener effect.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: Nickel complex; X-ray crystal structure; Edge-to-face; Fastener effect
1. Introduction
exhibit columnar mesophases and exhibit thermochro-
mism. These properties originate not from the individual
molecules but from their supramolecular structure. Fur-
thermore, liquid crystalline compounds are also well
known to dramatically change their supramolecular struc-
ture upon slight modification of the molecular structure.
In this paper, the structural and spectral changes of the
bis[1,2-bis(4-alkylphenyl)ethanedione dioximato]nickel(II)
complex brought about by the introduction of four methyl
groups (1) and hexyl groups (2) are reported (Chart 1).
It is well known that d8 transition metal complexes with
dioxime as a ligand have square planar configuration and
stack face to face to form one-dimensional columnar struc-
ture consisting of linear metal chains perpendicular to the
molecular plane [1,2]. These complexes exhibit piezochro-
mism in the ndz2 –ðn þ 1Þpz transition of the metal in the vis-
ible region [3,4]. The d–p transition is very sensitive to the
one-dimensional metal to metal stacking distance, so the
complex is used as a pressure indicator. Ohta et al. have
introduced long-chain-substituents into these core com-
plexes, and obtained discotic columnar liquid crystals with
such a unique chromism [5]. These columnar liquid crystals
can self-organize to show more preferable function than
the unsubstituted non-mesogenic core complexes. For
2. Experimental
2.1. Preparation of [Ni{(C1)2dpg}2] (1) and
[Ni{(C6)2dpg}2] (2)
example,
bis[1,2-bis(3,4-di-n-alkoxyphenyl)ethanedione
Hydroxylamine hydrochloride (3.83 g, 55.1 mmol) and
85% potassium hydroxide (3.83 g, 58.0 mmol) were added
to 91 ml of ethanol and the mixture was stirred vigorously
for ca. 1 h, and then filtered to remove the resulting precip-
itate of potassium chloride. 4,40-Dimethylbenzil (0.20 g,
dioximato]nickel(II) (n-alkoxy = n-C8H17O, n-C12H25O)
*
Corresponding author. Tel.: +81 3 5228 8256.
E-mail address: j1304705@ed.kagu.tus.ac.jp (Y. Soneta).
0020-1693/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.02.013

3124
Y. Soneta et al. / Inorganica Chimica Acta 360 (2007) 3123–3126
Table 1
Selected bond lengths (A) and angles (ꢀ) in 1 and 2
˚
Compound 1
Ni1–N1
Ni1–N2
N1–O2
O1–N2
N1–C1
1.864(2)
1.868(2)
1.340(2)
1.338(2)
1.305(3)
1.300(3)
1.488(3)
N1–Ni1–N2
N1–Ni1–N2a
N1–Ni1–N1a
N2a–Ni1–N2
C1–N1–O2
C2–N2–O1
C1–N1–Ni1
C2–N2–Ni1
O1–N2–Ni1
O2–N1–Ni1
97.93(8)
82.17(8)
176.50(11)
176.52(11)
119.7(2)
N2–C2
C1–C2a
120.9(2)
117.25(16)
116.82(16)
121.76(14)
122.44(14)
Chart 1.
Compound 2
Ni1–N1
Ni1–N2
N1–O1
N2–O2
N1–C1
1.8670(19)
1.8604(18)
1.331(3)
1.333(3)
1.296(3)
1.300(3)
1.472(3)
N2–Ni1–N1
N2b–Ni1–N1
N1–Ni1–N1b
N2–Ni1–N2b
C1–N1–O1
C14–N2–O2
C1–N1–Ni1
C14–N2–Ni1
O1–N1–Ni1
O2–N2–Ni1
b
98.05(8)
81.97(8)
178.7(2)
177.9(2)
120.0(2)
120.67(19)
117.10(16)
116.80(16)
122.64(15)
122.32(15)
0.86 mmol) was added to the filtrate and the mixture was
refluxed with stirring under a nitrogen atmosphere for
14 h. Nickel(II) chloride hexahydrate (0.43 g, 1.8 mmol)
dissolved in a small amount of ethane-1,2-diol was added
to the hot reaction mixture, and immediately neutralized
with glacial acetic acid. After further refluxing for 4 h,
the reaction mixture was cooled to room temperature and
the resulting precipitate collected by filtration and dis-
solved in chloroform. The organic layer was dried over
anhydrous sodium sulfate and the solvent removed under
reduced pressure. The crude product of 1 was purified by
recrystallization from chloroform and ethanol to give crys-
tals suitable for X-ray analysis. 2 was prepared by the sim-
ilar procedure using 4,40-dihexylbenzil (0.32 g, 0.86 mmol)
instead of 4,40-dimethylbenzil. Yield, 0.025 g (10%). Anal.
Calc. for C32H30N4NiO4 (1): C, 64.47; H, 5.09; N, 9.44.
Found: C, 64.37; H, 5.01; N, 9.19%. Yield, 0.030 g (8%).
Anal. Calc. for C52H70N4NiO4 (2): C, 71.47; H, 8.07; N,
6.41 Found: C, 71.50; H, 8.07; N, 6.36%.
N2–C14
C1–C14b
a
Symmetry operation: ꢀx + 1/2, ꢀy + 3/2, z; ꢀx + 2, ꢀy + 1, z.
(I > 2r) = 0.0424, wR2(I > 2r) = 0.0979, R1 (all data) =
0.0717, wR2 (all data) = 0.1196. For 2: C52H70N4NiO4,
˚
˚
M = 873.83; a = 27.427(3) A, b = 27.427 (3) A, c = 6.4041
3
˚
˚
ꢀ
(10) A, V = 4817.6(11) A , Tetragonal, space group I4,
Z = 4, T = 173(2) K, Dcalc = 1.205 Mg/m3, l = 0.450
mmꢀ1
,
15484 reflections measured, 5541 unique
(Rint = 0.0662), GOF (on F2) = 1.010, final R1 (I > 2r) =
0.0487, wR2 (I > 2r) = 0.1327, R1 (all data) = 0.0609, wR2
(all data) = 0.1431. Selected bond lengths and angles are
shown in Table 1.
2.2. Measurements
The UV–Vis and diffuse reflectance spectra were
recorded with a JASCO V-570 UV/VIS/NIR spectropho-
tometer. The DSC measurements were performed by
DSC220C (Seiko Instruments). The elemental analysis
3. Results and discussion
3.1. UV–Vis absorption and diffuse reflectance spectra
were performed with
Analyzer.
a Perkin–Elmer 2400II CHN
The UV–Vis spectra of both complexes [Ni{(C1)2
dpg}2]{bis[1,2-bis(4-methylphenyl)ethanedione
dioxi-
mato]nickel(II)} (1) and [Ni{(C6)2dpg}2]{bis[1,2-bis(4-n-
hexylphenyl)ethanedione dioximato]nickel(II)} (2) mea-
sured in chloroform exhibited an intense absorption band
at 275 nm (e = 4.1 · 104 l molꢀ1 cmꢀ1) ascribed to the p–
p* transition of intra-ligand, and the absorption bands at
413 nm (e = 1.3 · 104 l molꢀ1 cmꢀ1) ascribed to the absorp-
tion of MLCT (metal to ligand charge transfer), and the
2.3. X-ray crystallography
Single crystals of 1 and 2 were mounted on a glass cap-
illary, transferred to a Bruker AXS SMART diffractometer
equipped with a CCD area detector and Mo Ka
˚
(k = 0.71073 A) radiation. The structures were solved and
absorption band at 367 nm (e = 1.0 · 104 l molꢀ1 cmꢀ1
)
refined with SHELX-97 [6] using the direct method and
expanded using Fourier techniques. All non-hydrogen
atoms were refined anisotropically and hydrogen atoms
were refined isotropically. Crystal data for C32H30N4NiO4
could not be assigned [7]. These absorption peaks exhibited
shifts to longer wavelength by the introduction of the alkyl
groups, but no apparent change was visible by the differ-
ence in alkyl groups. In the solid phase, however, an addi-
tional sharp absorption peak occurs near 515 nm, which
does not have an obvious counterpart in solution [8]. This
peak was ascribed to d–p transition which is sensitive to the
one-dimensional metal to metal stacking distance. This
˚
˚
(1), M = 593.31; a = 18.0498(14) A, b = 24.7133(18) A,
3
˚
˚
c = 6.6870(5) A; V = 2982.9(4) A , Orthorhombic, space
group Pccn, Z = 4, T = 297(2) K, Dcalc = 1.321 Mg/m3,
l = 0.693 mmꢀ1, 18627 reflections measured, 3435 unique
(Rint = 0.0726), GOF (on F2) = 0.939, final R1

Y. Soneta et al. / Inorganica Chimica Acta 360 (2007) 3123–3126
3125
Fig. 1. Diffuse reflectance spectra (R) and absorption spectra in chloro-
form (A) of 1 and 2 are represented. The d–p transition peaks were
indicated by arrows.
additional absorption of complexes 1 and 2 appeared at
542 and 582 nm, respectively as shown in Fig. 1, and they
shifted to longer wavelength compared with that of
[Ni(dpg)2]. In the previous report, the shift of the absorp-
tion band was reported as dependent on the length of the
Ni–Ni bonds due to the fastener effect of the long alkyl
or alkoxy chains [5]. However, the methyl substituent in
1 is too short to attain fastener effect. Therefore, the stack-
ing configurations of these complexes are investigated by
the X-ray crystal structural analysis.
3.2. X-ray crystal structure
Fig. 2. Crystal structures of 1 and 2 viewed along c-axis. H atoms for 2
were omitted for clarity.
Fig. 2 shows the crystal structures of complexes 1 and 2.
In complex 1, the Ni–N distances of 1.864(2) and
˚
1.868(2) A are close to the normally observed value of ca.
˚
1.85 A observed in several four-coordinate Ni(II) com-
˚
plexes. The N–C distances of 1.305(3) and 1.300(3) A and
˚
the N–O distances of 1.340(2) and 1.338(2) A in coordinat-
ing glyoxime ligand are comparable with those in non-
alkylated
species,
[Ni(dmg)2]{bis(dimethylglyoxi-
mato)nickel(II)} [9]. The benzene rings are tilted 47.3ꢀ
and 44.5ꢀ from the chelate plane. In complex 2, the Ni–N
˚
˚
˚
(1.8604(18), 1.8670(19) A), N–C (1.296(3), 1.300(3) A),
˚
N–O (1.331(3), 1.333(3) A) and O–O (2.437 A) distances
are not significantly different from those of complex 1.
The [Ni(dpg)2] units of 1 stack (staggered by 90ꢀ) at
Fig. 3. Edge-to-face aromatic interaction of 1 viewed along a-axis.
˚
intervals of 3.344 A. The Ni–Ni distance in 1 is thus
˚
˚
0.20 A shorter than that of [Ni(dpg)2] (3.547 A). When
the geometric structure of 1 was compared with the non-
substituted complex [Ni(dpg)2], no apparent difference in
molecular structure that leads to the decrease in Ni–Ni dis-
tance could be found. Itoh et al. reported the preparation
of the diphenylglyoxime complex substituted with hydroxyl
or amino group, and found that these crystal structures
were strongly controlled by the hydrogen bond [10], but
no such interactions with neighboring columns were
observed in the crystal of 1. However, the edge-to-face aro-
matic interactions reported elsewhere, especially in the field
of structural biology, were present [11]. As is seen in Fig. 3,
the edge-to-face distance between C–H and the plane of p-
˚
system was 2.751 and 2.810 A shorter than the mean dis-
2
˚
tance (ca. 2.86 A) of the sp -CHꢁ ꢁ ꢁp reported by Suezawa
et al. [12]. This is an evidence for the edge-to-face aromatic
interaction. In the case of complex 1, the Ni(dpg)2 moieties
attract each other by the edge-to-face aromatic interac-
tions, may be due to increase in the electrostatic potential
brought about by the introduction of the methyl groups,
since the electron-donating groups (NH2, OH and CH3)
and electron-withdrawing groups (NO2 and CN) increase

3126
Y. Soneta et al. / Inorganica Chimica Acta 360 (2007) 3123–3126
˚
˚
and decrease, respectively, the negative electrostatic poten-
tial on the p-electron system of the aromatic ring. No such
interaction could be observed in the crystal structure of
non-substituted [Ni(dpg)2]. A similar situation can also
be seen in 2.
(staggered by 90ꢀ) at intervals of 3.151 A and 3.253 A. In
the case of 2, the Ni(dpg)2 moieties attracted each other
by the edge-to-face aromatic interactions and fastener
effect. Therefore, the evaluation of the edge-to-face interac-
tion and fastener effect could be calculated by the spectral
shift.
To investigate the mesomorphic properties of 2, the
phase transition temperatures and enthalpy changes were
measured by DSC. When 2 was heated to 121.2 ꢀC
(6.8 kJ/mol), the crystalline phase transformed into a meso-
phase. On further heating, the mesophase changed into an
isotropic liquid phase at 198.7 ꢀC (12.25 kJ/mol). It is
known that disk-like molecules substituted with four alk-
oxychains tend to show disk-like lamellar mesophases,
while those with eight alkoxychains tend to show columnar
phase [13]. However, Ohta et al. reported that the columnar
mesophases are observed although the [Ni{(C12)2dpg}2]
complex has only four long chains and this behavior may
be attributable to the dimerization by which a disk unit
(dimer) can apparently possess eight long chains [5]. The
structural feature of 2, where the [Ni(dpg)2] units of 2 stack
Appendix A. Supplementary material
CCDC 615018 and 615019 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.ica.2007.02.013.
References
˚
˚
(staggered by 90ꢀ) at intervals of 3.151 A and 3.253 A is
consistent with this report. In 2, one hexyl group adopted
an all-trans conformation with a slight distortion. This dis-
tortion was due to the steric repulsion between the
approached hexyl groups. This is an evidence for the fas-
tener effect proposed by Ohta et al. [5]. However, the contri-
bution of the fastener effect to the spectroscopic change in
d–p transition is not as high as they predicted. Since the
methyl substituted analogue 1 exhibited a shift of
970 cmꢀ1, the 43% of the peak shift, 2240 cmꢀ1, of hexyl-
substituted analogue 2 should be attributed to the edge-
to-face interaction and the rest (57%) to the fastener effect.
[1] L.E. Godycki, R.E. Rundle, Acta Crystallogr. 6 (1953) 487.
[2] M.S. Hussain, B.E.V. Salinas, E.O. Schlemper, Acta Crystallogr. B
35 (1979) 628.
[3] J.C. Zahner, H.G. Drickamer, J. Chem. Phys. 33 (1965) 1625.
[4] M. Tkacz, H.G. Drickamer, J. Chem. Phys. 85 (1986) 184.
[5] (a) K. Ohta, H. Hasebe, M. Moriya, T. Fujimoto, I. Yamamoto,
Mol. Cryst. Liq. Crystallogr. 208 (1991) 43;
(b) K. Ohta, H. Hasebe, M. Moriya, T. Fujimoto, I. Yamamoto, J.
Mater. Chem. 1 (1991) 831;
(c) K. Ohta, M. Moriya, M. Ikejima, H. Hasebe, T. Fujimoto, I.
Yamamoto, Bull. Chem. Soc. Jpn. 66 (1993) 3553;
(d) K. Ohta, M. Moriya, M. Ikejima, H. Hasebe, T. Fujimoto, I.
Yamamoto, Bull. Chem. Soc. Jpn. 66 (1993) 3559;
(e) K. Ohta, R. Higashi, M. Ikejima, I. Yamamoto, N. Kobayashi, J.
Mater. Chem. 8 (1998) 1979;
4. Conclusion
(f) K. Ohta, Y. Inagaki-Oka, H. Hasebe, I. Yamamoto, Polyhedron
19 (2000) 267.
Bis[1,2-bis(4-alkylphenyl)ethanedione dioximato] nickel
(II) {alkyl = methyl; [Ni{(C1)2dpg}2] (1) and alkyl = n-
hexyl; [Ni{(C6)2dpg}2] (2)} have been prepared and ana-
lyzed by diffuse reflectance spectra. The absorption peaks
ascribed to d–p transition exhibited shifts to longer wave-
length by the introduction of the alkyl groups compared
with that of no substituted [Ni(dpg)2] in solid state. There-
fore, the stacking configurations of these complexes were
investigated by the X-ray crystal structural analysis. The
[Ni(dpg)2] units of 1 stacked (staggered by 90ꢀ) at intervals
[6] G. M. Sheldrick, SHELXS-97 and SHELXS-97, Program for the Solution
of Crystal Structures, University of Go¨ttingen, Germany, 1997.
[7] Y. Ohashi, I. Hanazaki, S. Nagakura, Inorg. Chem. 9 (1970) 2551.
[8] C.V. Banks, D.W. Barnum, J. Am. Chem. Soc. 80 (1958) 4767.
[9] D.E. Williams, G. Wohlauer, R.E. Rundle, J. Am. Chem. Soc. 81
(1959) 755.
[10] T. Itoh, K. Iijima, J. Toyoda, K. Nakasuji, Mol. Crystallogr.. Liq.
Crystallogr. 285 (1996) 287.
[11] E. Kim, S. Paliwal, C.S. Wilcox, J. Am. Chem. Soc. 120 (1998) 11192.
[12] H. Suezawa, T. Yoshida, Y. Umezawa, S. Tsuboyama, M. Nishio,
Eur. J. Inorg. Chem. (2002) 3148.
˚
˚
[13] (a) K. Ohta, H. Muroki, A. Takagi, K. Hatada, H. Ema, I.
Yamamoto, K. Matsuzaki, Mol. Crystallogr. Liq. Crystallogr. 140
(1986) 131;
of 3.344 A, and the Ni–Ni distance in 1 was 0.20 A shorter
˚
than that of [Ni(dpg)2] (3.547 A). In the case of complex 1,
the Ni(dpg)2 moieties attracted each other by the edge-to-
face aromatic interactions, may be due to increase in the
electrostatic potential brought about by the introduction
of the methyl groups. The [Ni(dpg)2] units of 2 stacked
(b) Y. Shimizu, M. Miya, A. Nagata, K. Ohta, A. Matsumura, I.
Yamamoto, S. Kusabayashi, Chem. Lett. (1991) 25;
(c) K. Ohta, Y. Morizumi, H. Ema, T. Fujimoto, I. Yamamoto,
Mol. Crystallogr. Liq. Crystallogr. 208 (1991) 55.