Tuning the Mesomorphism and Redox Response of Anionic-Ligand-Based Mixed-Valent Nickel(II) Complexes by Alkyl-Substituted Quaternary Ammonium Cations

Article abstract of DOI:10.1002/chem.201706006

The combination of the redox-active mesogenic anion [Ni^II(Bdt)(BdtSQ)]^? (Bdt=1,2-benzenedithiolato; BdtSQ=1,2-dithia-semi-benzoquinonato) with alkyl-substituted ammonium cations afforded a series of redox-active ionic complexes of the type [NR₄][Ni^II(Bdt)(BdtSQ)] [R=nC₁₆H₃₃ (NC16₄Ni) and C8,10 (NC8,10₄Ni); C8,10=6-octylhexadecyl] or [NMe₂R₂][Ni^II(Bdt)(BdtSQ)] [R=nC₁₆H₃₃ (NMe₂C16₂Ni) and C8,10 (NMe₂C8,10₂Ni)]. X-ray crystallographic analyses of NMe₂C16₂Ni and NC16₄Ni revealed the formation of cation-dependent integrated ionic layers separated by interdigittated alkyl chains. Complexes NMe₂C16₂Ni and NC16₄Ni commonly form crystalline phases at room temperature, whereas complexes NMe₂C8,10₂Ni and NC8,10₄Ni, which contain branched alkyl chains, form a metastable mesophase and an amorphous phase at the same temperature, respectively. Furthermore, complexes NMe₂C16₂Ni, NMe₂C8,10₂Ni, and NC16₄Ni commonly form a smectic A phase (SmA) at 375, 317, and 342 K, respectively. For the four complexes, well-defined cyclic voltammetry responses, derived from ligand-based oxidation and reduction, were observed in solution and the condensed phases, that is, upon casting these complexes on an indium-doped tin oxide working electrode. The present study demonstrates the tunability of the mesomorphism of ionic molecular assemblies composed of alkyl-substituted quaternary ammonium cations, while maintaining the well-defined redox responses of the anions even in the condensed phases.

Full text of DOI:10.1002/chem.201706006

DOI: 10.1002/chem.201706006
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&
Metallomesogens |Hot Paper|
Tuning the Mesomorphism and Redox Response of Anionic-
Ligand-Based Mixed-Valent Nickel(II) Complexes by Alkyl-
Substituted Quaternary Ammonium Cations
Yuichi Nakamura, Takeshi Matsumoto, Yasutaka Sakazume, Junnosuke Murata, and
[a]
Ho-Chol Chang*
Dedicated to Professor Byong-Tae Chang on the occasion of his 76th birthday
Abstract: The combination of the redox-active mesogenic
amorphous phase at the same temperature, respectively.
Furthermore, complexes NMe C16 Ni, NMe C8,10 Ni, and
II
ꢀ
anion
[Ni (Bdt)(BdtSQ)]
(Bdt=1,2-benzenedithiolato;
2
2
2
2
BdtSQ=1,2-dithia-semi-benzoquinonato) with alkyl-substitut-
NC16 Ni commonly form a smectic A phase (SmA) at 375,
4
ed ammonium cations afforded a series of redox-active ionic
317, and 342 K, respectively. For the four complexes, well-de-
fined cyclic voltammetry responses, derived from ligand-
based oxidation and reduction, were observed in solution
and the condensed phases, that is, upon casting these com-
plexes on an indium-doped tin oxide working electrode. The
present study demonstrates the tunability of the mesomor-
phism of ionic molecular assemblies composed of alkyl-sub-
stituted quaternary ammonium cations, while maintaining
the well-defined redox responses of the anions even in the
condensed phases.
II
complexes of the type [NR ][Ni (Bdt)(BdtSQ)] [R=nC H
4
16 33
(
NC16 Ni) and C8,10 (NC8,10 Ni); C8,10=6-octylhexadecyl] or
4 4
II
[NMe R ][Ni (Bdt)(BdtSQ)] [R=nC H
(NMe C16 Ni) and
2 2
2
2
16 33
C8,10 (NMe C8,10 Ni)]. X-ray crystallographic analyses of
2
2
NMe C16 Ni and NC16 Ni revealed the formation of cation-
2
2
4
dependent integrated ionic layers separated by interdigit-
tated alkyl chains. Complexes NMe C16 Ni and NC16 Ni com-
2
2
4
monly form crystalline phases at room temperature, whereas
complexes NMe C8,10 Ni and NC8,10 Ni, which contain
2
2
4
branched alkyl chains, form a metastable mesophase and an
[3]
Introduction
(
ILCs). The effective combination of the characteristics of
liquid crystals (LCs) with those of ionic compounds has paved
the way for the development of functional soft materials
based on their inherent flexibility and self-assembling nature.
Given the advantages conferred by the softness of LCs, these
assemblies respond to external stimuli such as heat, mechani-
cal stress, light, and electric and magnetic fields. In particular, a
series of LCs that respond to electrochemical and chemical
redox processes on the constituent molecules has attracted
great interest, as they should allow control of both molecular
properties and macroscopic states through precise control of
electron-transfer processes by means of exact chemistry and
Molecular ionic compounds can assemble into bulk materials
through supramolecular interactions such as hydrogen and
halogen bonds, as well as p–p interactions and coulombic in-
[
1]
teractions between cations and anions. The advantages of
these particular compounds arise from the independently tun-
able structures and functions of the oppositely charged ions,
as well as from controllable interactions between these ions.
These features have led to the development of the molecular
engineering of ionic compounds that can exhibit physico-
chemical functionality such as permanent porosity, ion trans-
[
2]
[4]
port, and ionic liquidity.
electrochemical methodologies.
Success in the construction of functional ionic crystalline
phases has prompted the integration of ionicity with meso-
morphic phases. The intended successful synergy between
these two aspects is clearly reflected in ionic liquid crystals
Our group reported a direct electrochemical response from
a hexagonal columnar ordered phase (Col ) comprising the
ho
platinum complex [Pt(Cat)(C8,10bpy)] [Cat=catecholato;
C8,10bpy=4,4’-bis-(3-octyltridecyl)-2,2’-bipyridine], which con-
tains redox-active Cat and flexible alkyl-substituted bipyri-
[5]
dine. The well-defined redox properties of this complex were
attributed to the metal-bound Cat that was able to form a
one-electron oxidized semiquinonato (SQ) form and potentially
[a] Y. Nakamura, Dr. T. Matsumoto, Y. Sakazume, J. Murata,
Prof. Dr. H.-C. Chang
Department of Applied Chemistry, Faculty of Science and Engineering
Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan)
E-mail: chang@kc.chuo-u.ac.jp
[6]
a further oxidized benzoquinone (BQ) form. The design of
the
Pt(Bdt)(C8,10bpy)] (Bdt=1,2-benzenedithiolato), wherein Bdt
coordinates through the sulfur atoms, and to
redox-active
LCs
was
further
extended
to
Supporting Information and the ORCID identification number for the
author of this article can be found under https://doi.org/10.1002/
chem.201706006.
[
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[
Pt(Htp)(C8,10bpy)] (Htp=1,2-thiophenolato), wherein Htp co-
herein the synthesis of ionic compounds with bis(hexadecyl)di-
methylammonium (NMe C16 ), bis(6-octylhexadecyl)dimethy-
[
5b]
ordinates through the sulfur and oxygen atoms,
and the
II
2
2
Colho phase was maintained. The combination of a Pt center
with dianionic Cat usually results in the formation of neutral
molecules and LC phases. On the other hand, complexes with
redox-active ligands can form several types of charged mole-
cules if two or more anionic ligands coordinate to a metal
lammonium
(NMe C8,10 ),
tetrakis(hexadecyl)ammonium
2
2
(NC164), and tetrakis(6-octylhexadecyl)ammonium (NC8,104)
cations, together with the cation-dependent mesomorphic,
thermal, and electrochemical properties of the resulting com-
plexes.
[
7]
center. For instance, well-defined redox responses of the
II
ꢀ
anionic Ni complex [Ni (Bdt)(BdtSQ)] (BdtSQ=1,2-dithia-semi-
[
7a]
benzoquinonato) were reported by Gray et al., whereas Wie- Results and Discussion
ghardt et al. reported the synthesis of the anionic Ni complex
Syntheses of NMe Ni, NMe C16 Ni, NMe C8,10 Ni, NC16 Ni,
II
ꢀ
4
2
2
2
2
4
[
Ni (DTBBdt)(DTBBdtSQ)]
(DTBBdt=3,5-di-tert-butylbenzene-
and NC8,10 Ni
4
1
,2-dithiolato; DTBBdtSQ=3,5-di-tert-butyl-1,2-dithia-semi-qui-
nonato), together with the characterization of the redox iso-
The newly designed ammonium salts with branched alkyl
groups, [NMe (C8,10) ]I and [N(C8,10) ]I, were synthesized ac-
II
2ꢀ
II
mers [Ni (DTBBdt) ]
and [Ni (DTBBdtSQ) ], which were
2
2
2
2
4
[8]
formed by ligand-centered electron-transfer processes.
Inspired by these studies, we envisioned that the combina-
cording to Scheme 1. Bromination of 2-octyldodecanol with N-
bromosuccinimide (NBS) and PPh afforded 2-octyldodecyl bro-
3
II
ꢀ
[5a]
tion of the redox-active mesogenic anion [Ni (Bdt)(BdtSQ)]
mide, which was subsequently converted into the chain-ex-
with structurally flexible alkyl-substituted quaternary ammoni-
um cations containing a localized positive charge could furnish
a new family of ionic molecular assemblies with ambipolar
redox activity. In particular, we intended to design redox-active
tended terminal vinylic compound, 6-octylhexadecene, by a
copper-catalyzed Grignard reaction by using 1-bromomagnesi-
[9]
um-3-butene. The following hydroboration–oxidation of 6-oc-
tylhexadecene resulted in the formation of 6-octylhexadeca-
II
ꢀ
[10]
assemblies based on the [Ni (Bdt)(BdtSQ)] anion in combina-
tion with quaternary ammonium cations bearing linear and/or
branched alkyl chains, which could be controllable factors by
which the mesomorphic and redox properties of the com-
plexes could be controlled. As shown in Figure 1, we report
nol, which was subsequently converted into 6-octylhexadec-
yl bromide or iodide by the corresponding halogenation by
[5a]
[11]
using NBS and PPh3 or I and imidazole, respectively. 6-Oc-
2
tylhexadecyl bromide was converted into the primary amine,
[12]
6-octylhexadecylamine, by Gabriel amine synthesis, and was
subsequently used for the synthesis of [N(C8,10) ]I. Compound
4
[
N(C8,10) ]I was synthesized according to a method similar to
4
[13]
that reported by Kelland et al. 6-Octylhexadecyl iodide, 6-oc-
tylhexadecylamine, and K CO were heated at reflux in isobu-
2
3
tyronitrile for 96 h, which afforded symmetrically substituted
ammonium iodide [N(C8,10) ]I as a pale-yellow solid. Com-
4
pound [NMe (C8,10) ]I was synthesized according to a method
2
2
[14]
similar to that reported by Ryoo et al. by using presynthe-
sized 6-octylhexadecyl iodide. Dimethylamine and 6-octylhexa-
decyl iodide in THF were heated to reflux in the presence of
NaOH for 40 h, which resulted in the formation of the desired
unsymmetrically
substituted
ammonium
iodide,
Figure 1. Molecular structures of NMe
NC8,10 Ni.
2 2 2 2 4
C16 Ni, NMe C8,10 Ni, NC16 Ni, and
[
NMe (C8,10) ]I, as a white solid. In fact, this is the first synthet-
2
2
4
ic example of alkyl-substituted quaternary ammonium salts
Scheme 1. Synthesis of [NMe
Chem. Eur. J. 2018, 24, 1 – 13
2
(C8,10)
2 4
]I and [N(C8,10) ]I.
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with asymmetric branched long alkyl chains except
[
13]
for a salt with isohexyl chains. The presented syn-
thetic routes should be efficient for the synthesis of
new ammonium salts substituted by a variety of
long alkyl chains, in which the chain length and
branching points in the alkyl group could be modu-
II
lated. The synthetic routes to [NR ][Ni (Bdt)(BdtSQ)]
4
[
15]
[
(
[
(
R=Me (NMe Ni),
nC H (NC16 Ni), and C8,10
16 33 4
4
NC8,10 Ni); C8,10=6-octylhexadecyl] and [NMe R ]
4
2 2
II
Ni (Bdt)(BdtSQ)] [R=nC H (NMe C16 Ni) and C8,10
16
33
2
2
NMe C8,10 Ni)] are shown in Scheme 2. Complexes
2
2
NMe C16 Ni and NMe C8,10 Ni were synthesized by
2
2
2
2
the same synthetic method as that used for NMe Ni,
4
except for the use of [NMe (nC H ) ]Br and
2
16 33 2
[
NMe (C8,10) ]I. On another front, complex NC8,10 Ni
2
2
4
was synthesized by using MeOH/EtOH (1:1, v/v) as
the solvent, owing to the poor solubility of
[
N(C8,10) ]I in pure MeOH. As [N(nC H ) ]Br is not
4 16 33 4
soluble in MeOH or EtOH, complex NC16 Ni was syn-
4
thesized in water, which was inspired by the success-
[
16]
ful synthesis reported by Bꢁlombꢁ et al. All newly
synthesized Ni complexes exhibit decent stability in
solution and the condensed phases.
Scheme 2. Synthesis of NMe Ni, NMe C16 Ni, NMe C8,10 Ni, NC16 Ni, and NC8,10 Ni.
4
2
2
2
2
4
4
dent cation and anionic nickel complex per unit cell. The unit
cell of NMe C16 Ni consists of one crystallographically inde-
2
2
Molecular and assembled structures of NMe C16 Ni and
2
2
pendent cation and two anionic nickel complexes (units A and
B). All methylene groups in the ammonium cation in
NMe C16 Ni adopt the energetically favored trans conforma-
NC16 Ni
4
Complexes NMe C16 Ni and NC16 Ni yielded green single crys-
2
2
4
2
2
tals by recrystallization from CH Cl /MeOH and benzene/
tion (Figure 2a). On the other hand, the methylene groups at
2
2
MeOH, respectively. The molecular structures of NMe C16 Ni
C16, C19, C34, and C47 in NC16 Ni adopt the gauche confor-
2
2
4
and NC16 Ni are shown in Figures 2a–d, and selected bond
mation (Figure 2c).
4
lengths and angles are listed in Table 1. These complexes are
commonly composed of cations and anions in a 1:1 ratio.
The central Ni atoms in the anions of NMe C16 Ni and
2
2
NC16 Ni commonly exhibit a square-planar coordination ge-
4
Complex NC16 Ni contains one crystallographically indepen-
ometry and are coordinated by four S atoms (Figures 2b,d).
4
Figure 2. Molecular structures of a,c) the cations and b,d) the anions in NMe
are omitted for clarity. Unit A: 2ꢀx, 1ꢀy, 2ꢀz; unit B: 2ꢀx, ꢀy, 2ꢀz. The projections of the two-dimensional ionic layers of e) NMe
drogen atoms and alkyl chains are omitted for clarity; nickel and nitrogen atoms are drawn as ball-and-stick models, whereas sulfur and carbon atoms are
drawn as capped sticks. Three-dimensional packing structures of g) NMe C16 Ni and h) NC16 Ni; hydrogen atoms are omitted for clarity; nitrogen atoms and
2
C16
2
Ni and NC16
4
Ni; thermal ellipsoids set at 50% probability; hydrogen atoms
2
C16 Ni and f) NC16 Ni; hy-
2
4
2
2
4
anion units are drawn as a space-filling model, whereas the alkyl chains are drawn as capped sticks; color code: Ni=green, N=light blue, S=yellow, and
C=gray.
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ure 2 f). The shortest intermolecular N···N, Ni···Ni, and N···Ni dis-
Table 1. Selected bond lengths and angles of NMe
2 2 4
C16 Ni and NC16 Ni.
tances in NMe C16 Ni are found to be 7.108(3), 7.112(1), and
2
2
Bond lengths [ꢂ]
5.040(2) ꢂ, respectively, whereas those in NC16 Ni are 7.696(3),
4
NMe
2
C16
2
Ni
4
NC16 Ni
8.760(1), and 4.580(2) ꢂ, respectively. The anions in
Ni1ꢀS1
Ni1ꢀS2
Ni1ꢀS3
Ni1ꢀS4
Ni2ꢀS3
Ni2ꢀS4
S1ꢀC1
2.1537(7)
2.1585(8)
–
–
2.148(1)
2.1602(8)
2.1495(9)
2.154(1)
–
NMe C16 Ni are surrounded by four neighboring counterions,
2
2
whereas those in NC16 Ni are surrounded by three counterions
4
(
Figures 2e,f). Therefore, the electrostatic attractive interaction
in NMe C16 Ni is expected to be stronger than that in NC16 Ni
2.1402(7)
2
2
4
2.15106(10)
1.737(3)
1.756(2)
1.743(4)
1.742(3)
1.392(4)
1.398(4)
1.378(4)
1.403(5)
1.366(4)
1.402(3)
1.390(5)
1.395(5)
1.377(5)
1.394(6)
1.370(6)
1.410(4)
–
(see below). One plausible reason for the alternation in ionic
layered structures found in both complexes can be attributed
to the differences in the number of hexadecyl chains within
the cations: the two chains in NMe C16 Ni pack with neighbor-
1.746(3)
1.746(3)
1.735(3)
1.751(3)
1.406(3)
1.407(4)
1.374(5)
1.403(4)
1.376(4)
1.402(4)
1.392(4)
1.414(5)
1.371(6)
1.396(6)
1.379(6)
1.418(5)
S2ꢀC6
S3ꢀC7
S4ꢀC12
C1ꢀC2
C2ꢀC3
C3ꢀC4
C4ꢀC5
C5ꢀC6
C6ꢀC1
C7ꢀC8
C8ꢀC9
C9ꢀC10
C10ꢀC11
C11ꢀC12
C12ꢀC7
2
2
ing chains in the ionic layer shown in Figure 2e, whereas the
four chains in NC16 Ni would sterically hinder their closed
4
packings without changing the structure of an ionic layer to a
herringbone fashion, for which only two cations are packed
close to each other. These results therefore demonstrate that
the ordered structures of anionic nickel complexes in ionic
layers can be modulated by the number of alkyl chains.
The three-dimensional packing structures of NMe C16 Ni
2
2
and NC16 Ni (Figures 2g,h) are similar to those of previously
4
[19]
reported alkylammonium and alkylpyridinium salts. The as-
sembled structures of these complexes consist of ionic layers
composed of anionic nickel complexes and cationic nitrogen
atoms separated by interdigitated alkyl chains. The spacings
between each layer in NMe C16 Ni and NC16 Ni are 22.196(4)
Bond angles [8]
S1ꢀNi1ꢀS2
S1ꢀNi1ꢀS3
S3ꢀNi1ꢀS4
S4ꢀNi1ꢀS2
S1ꢀNi1ꢀS2*
S3ꢀNi2ꢀS4
S3ꢀNi2ꢀS4*
91.59(3)
–
–
–
88.41(3)
91.89(3)
88.11(3)
91.96(3)
87.76(3)
91.83(3)
90.62(3)
–
–
–
2
2
4
and 24.856(4) ꢂ, respectively. The shorter spacing in
NMe C16 Ni is probably due to the contraction of alkyl layers
[
[
a]
2
2
b]
upon decreasing the alkyl chains.
[
1
a] Symmetry transformations used to generate equivalent atoms: 2ꢀx,
ꢀy, 2ꢀz. [b] Symmetry transformations used to generate equivalent
Thermal phase-transition behavior
atoms: 2ꢀx, ꢀy, 2ꢀz.
As complex NMe Ni was reported by Sellmann et al. to form a
4
[15]
crystalline phase at room temperature, it should be interest-
ing to examine the effects of long alkyl-substituted cations on
the structures and thermal properties of the resulting com-
plexes. Initially, we examined the assembled phases of
NMe C16 Ni, NMe C8,10 Ni, NC16 Ni, and NC8,10 Ni at room
The NiꢀS, CꢀS, and CꢀC distances in the anions of these com-
plexes fall in the ranges of 2.1402(7)–2.1602(8), 1.735(3)–
1
.756(2), and 1.370(6)–1.418(5) ꢂ, respectively, all of which are
II
ꢀ
close to those of the previously reported [Ni (Bdt)(BdtSQ)]
2
2
2
2
4
4
[
17]
anion. The CꢀC bonds of the six-membered rings display
two alternating shorter and four longer CꢀC bonds, which re-
temperature by using polarizing optical microscopy (POM) and
X-ray diffraction (XRD) measurements (Figure 3). Complexes
NMe C16 Ni and NC16 Ni commonly exhibit optical anisotropy
[
18]
sults in quinoid-like distortion.
The similarities between
2
2
4
these structural parameters and those found in the monoanion
under crossed polarizers at room temperature (Figures 3b,e).
The XRD pattern of NMe C16 Ni at the same temperature
II
ꢀ
[
Ni (DTBBdt)(DTBBdtSQ)] , which was reported by Wieghardt
2
2
[
8]
et al., are consistent with the formulation of the anions as
shows a strong small-angle diffraction corresponding to the
(001) and (002) reflections derived from a highly ordered la-
mellar structure (Figure 3b and Table S1 in the Supporting In-
formation). A set of intense peaks in the wide-angle region
suggests a high degree of structural order in three dimensions.
II
ꢀ
[Ni (Bdt)(BdtSQ)] in NMe C16 Ni and NC16 Ni.
2 2 4
The two-dimensionally assembled structures of NMe C16 Ni
2
2
and NC16 Ni are shown in Figures 2e,f. These complexes com-
4
monly form two-dimensional ionic layers composed of anionic
nickel complexes and cationic nitrogen atoms. The anionic
nickel complexes in NMe C16 Ni show a side-by-side arrange-
Similar tendencies are also observed in the case of NC16 Ni
4
(Figure 3e). The similarity of the observed XRD patterns with
those simulated on the basis of the single-crystal structural
data acquired at 223 and 123 K for NMe C16 Ni and NC16 Ni,
2
2
[17a]
ment to form a one-dimensional order along the b axis.
These anionic arrays alternatively arrange with the cationic ni-
2
2
4
trogen atoms of NMe C16 within the ab plane (Figure 2e). In
respectively (Figures 3a,d), represents compelling evidence
that both complexes form a crystalline phase and that phase
transitions do not occur between room temperature and the
temperature at which the single-crystal diffraction data were
2
2
contrast to the case of NMe C16 Ni, the anionic nickel com-
2
2
plexes in NC16 Ni pack in a herringbone fashion within the bc
4
[
17c]
plane to form a two-dimensional structure,
wherein two cat-
[20]
ionic nitrogen atoms of NC16 lie within the anionic cage (Fig-
collected.
4
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Figure 4. DSC curves of a) NMe
4 2 2 2 2
Ni, b) NMe C16 Ni, c) NMe C8,10 Ni,
ꢀ
1
d) NC16 Ni, and e) NC8,10 Ni at a scan rate of 5 Kmin .
4
4
Figure 3. Simulated XRD patterns based on the single-crystal X-ray diffrac-
tion data of a) NMe C16 Ni at 223 K and d) NC16 Ni at 123 K and the XRD
patterns and polarized optical microscopy images of b) NMe C16 Ni,
c) NMe C8,10 Ni, e) NC16 Ni, and f) NC8,10 Ni at room temperature.
2
2
4
2
2
transition prior to decomposition (Figures 4a,e). In contrast,
NMe C16 Ni, NMe C8,10 Ni, and NC16 Ni show six, two, and
2
2
4
4
2
2
2
2
4
four consecutive endothermic peaks during each heating pro-
cess, respectively (Figures 4b–d). The phase transition temper-
atures and their associated enthalpy changes are summarized
in Table 2. Complex NMe C16 Ni shows optical anisotropy after
In contrast to NMe C16 Ni and NC16 Ni, complex
2
2
4
NMe C8,10 Ni with branched alkyl chains affords an optical ani-
2
2
sotropic state with small domains at room temperature (Fig-
ure 3c). The XRD pattern of NMe C8,10 Ni at this temperature
2
2
four endothermic peaks at T=323, 330, 346, and 367 K, which
is consistent with the crystalline morphology and the diffrac-
tions results (Figure 5a). The XRD patterns measured at T=
327, 338, 358, and 368 K commonly show strong small-angle
diffraction peaks corresponding to highly ordered lamellar
structures. Accordingly, the four endothermic peaks should be
assigned to crystal–crystal phase transitions. A typical focal
conic texture was formed after an exothermic peak at T=
2
2
shows strong small-angle diffraction peaks corresponding to a
highly ordered lamellar structure. On the other hand, no sharp
diffraction is observed in the wide-angle region, which indi-
cates mesomorphic properties of NMe C8,10 Ni at room tem-
2
2
perature. On the other hand, complex NC8,10 Ni with four
4
branched tails shows an amorphous phase with no optical ani-
sotropy and diffraction at room temperature (Figure 3 f). Fur-
thermore, the IR spectra of NMe C8,10 Ni and NC8,10 Ni with
2
2
4
branched tails show upwards shifts for the vibrational modes
of the alkyl chains relative to those of NMe C16 Ni and
4 2 2 2 2 4
Table 2. Phase diagrams of NMe Ni, NMe C16 Ni, NMe C8,10 Ni, NC16 Ni,
2
2
[
a]
4
and NC8,10 Ni.
NC16 Ni (Figure S2). These results indicate that the bulky
4
branched alkyl chains in NMe C8,10 Ni and NC8,10 Ni increase
ꢀ1
2
21]
2
4
Complex
Phase (K [kJmol ])
[
the conformational disorder.
4
NMe Ni
K 480 decomp.
The phase-transition behavior of NMe Ni, NMe C16 Ni,
4
2
2
NMe C16 Ni K1 323 (15.0) K2 330 (10.5) K3 346 (5.0) K4 367 (8.5) K5
2
2
NMe C8,10 Ni, NC16 Ni, and NC8,10 Ni was investigated by
375 (34.9) SmA 410 (7.5) IL
2
2
4
4
NMe
NC16
NC8,10
2
C8,10
2
Ni M 317 (19.6) SmA 345 (3.0) IL
K1 332 (2.5) K2 336 (0.3) K3 342 (72.0) SmA 348 (7.0) IL
amorphous 506 decomp.
thermogravimetric differential thermal analysis (TG-DTA), POM,
differential scanning calorimetry (DSC), and temperature-de-
pendent XRD measurements. The TG-DTA (Figure S3) and DSC
4
Ni
Ni
4
[
a] K=crystal, SmA=smectic A liquid crystal, IL=isotropic liquid, M=
(Figure 4 and Table S2) measurements reveal that complexes
metastable mesophase.
NMe Ni and NC8,10 Ni do not engage in any thermal phase
4
4
Chem. Eur. J. 2018, 24, 1 – 13
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Figure 5. a) Simulated XRD pattern of NMe
XRD pattern of NC16
NMe C8,10 Ni at 298, 318, and 363 K together with the corresponding polarized optical microscopy images.
2
C16
2
Ni at 223 K and XRD patterns (first heating process) at 298, 327, 338, 358, 368, 378, and 418 K; b) simulated
4
Ni at 123 K and XRD patterns (first heating process) at 298, 335, 339, 342, and 353 K; and c) XRD patterns (first heating process) of
2
2
369 K followed by an endothermic peak at T=375 K (Fig-
that complexes NMe C16 Ni, NMe C8,10 Ni, and NC16 Ni melt
2 2 2 2 4
ure 5a). At T=378 K, an intense (001) reflection at 2q=3.628,
corresponding to a layer distance of d=24.39 ꢂ, and a broad
halo at 2qꢁ208 as an indication of liquid-like order of the ali-
phatic chains were observed. The distance between layers (d=
into IL phases at T=410, 345, and 348 K, respectively, demon-
strates that the stability of the SmA phases is significantly
modulated by the type and quantity of alkyl chains present in
the cations. The comparable melting points of NMe C8,10 Ni
2
2
24.39 ꢂ at T=378 K) is longer than that in the crystalline phase
(T=345 K) and NC16 Ni (T=348 K) suggest that the arrange-
4
(
d=21.42 ꢂ at T=298 K), suggesting thermal expansion of the
ments of the anionic nickel complexes and cationic nitrogen
atoms in the ionic layers in the SmA phases might be similar.
The melting point of NMe C16 Ni is higher than those of the
interlayer distance (Table S1). On the basis of the POM and
XRD data, the mesophase was tentatively assigned to a smec-
2
2
[
19c,22]
tic A phase (SmA).
Heating the SmA phase beyond the
other two complexes, indicating the formation of more stable
ionic layers, which is consistent with the results of the crystal-
lographic assessment (Figure 2).
exothermic peak at T=410 K led to melting into an isotropic
liquid (IL), for which no optical anisotropy or XRD pattern was
observed (Figure 5a). Complex NC16 Ni also shows a SmA
4
phase with typical focal conic texture at T=342 K following a
two-step crystal-phase transition and a final melt to an IL at
T=348 K (Figure 5b). The temperature-dependent XRD study
on NMe C8,10 Ni also demonstrated the formation of a SmA
Spectroscopic and electrochemical properties
The UV/Vis absorption spectra of NMe Ni, NMe C16 Ni,
4
2
2
NMe C8,10 Ni, NC16 Ni, and NC8,10 Ni in THF and the con-
2
2
2
2
4
4
phase with a focal conic texture at T=317 K, which melts into
an IL at T=345 K (Figure 5c).
densed phase are shown in Figure 6, and the relevant data are
summarized in Table 3. These complexes exhibit similar spectra
in solution and in the condensed phases, which is indicative of
insignificant changes in the electronic structures of the anionic
chromophores. The absorption spectra in THF exhibit intense
absorption bands in the near-infrared (NIR) region with
maxima at lꢁ860 nm in addition to three absorption bands in
the UV region. The absorption bands in the visible region
should be attributed to a intervalence charge-transfer (IVCT)
A comparison of the melting points of NMe C16 Ni (T=
2
2
3
75 K) and NC16 Ni (T=342 K) suggests that the stabilities of
4
the crystalline phases are modulated by the number of alkyl
chains in the cations. Complex NMe C16 Ni forms a more
2
2
stable crystalline phase than NC16 Ni, which is possibly due to
4
an increase in interchain interactions as a result of the closely
packed alkyl chains. On the other hand, the formation of a
mesophase of NMe C8,10 Ni at room temperature suggests
[8]
band, which is a typical absorption band for metal complexes
with mixed-valence Bdt/BdtSQ ligands.
2
2
the induction of disorder in the branched alkyl chains. These
results indicate that the introduction of branched alkyl chains
effectively destabilizes crystalline phases. Furthermore, the fact
The cyclic voltammetry (CV) curves of NMe Ni, NMe C16 Ni,
4
2
2
NMe C8,10 Ni, NC16 Ni, and NC8,10 Ni in THF are shown in
2
2
4
4
&
&
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Figure 7. a) Cyclic voltammograms of NMe
4
Ni (black), NMe
Ni (blue) and NC8,10 Ni (purple) in THF (1 mm,
, 100 mVs ). b) Spectroelectrochemistry of NMe C8,10 Ni
2 2
C16 Ni (red),
NMe
2
C8,10
2
Ni (green), NC16
4
4
ꢀ
1
0.1m nBu
4
PF
6
2
2
during reduction at ꢀ1.0 V and c) oxidation at rest potential in THF (0.5 mm,
0
.1m nBu PF ). Absorption spectra corresponding to the initial (green), re-
4
6
duced state (red), and intermediate state (gray).
new bands emerged at lꢁ400 nm. The presence of isosbestic
points clearly demonstrates that the electrochemical reduction
involves two species that are interconverted by chemically re-
versible processes. In contrast to the reduction, the electro-
chemical oxidation led, in all cases, to the formation of strong-
ly colored precipitates. The oxidized product synthesized by
chemical oxidation of NMe Ni by using I does not contain any
Figure 6. UV/Vis absorption spectra of a) NMe
4 2 2
Ni, b) NMe C16 Ni,
c) NMe C8,10 Ni, d) NC16 Ni, and e) NC8,10 Ni in THF (1.0 mm, black line)
2
2
4
4
and in the condensed phases (KBr disk, red line).
4 2 2
Table 3. Electronic absorption spectral data of NMe Ni, NMe C16 Ni,
[
a]
NMe
2 2 4 4
C8,10 Ni, NC16 Ni, and NC8,10 Ni in 1 mm THF.
4
2
ammonium cation, as is evident from IR and UV/Vis absorption
spectroscopy (Figure S6), which indicates homovalency of the
ꢀ
1
ꢀ1
Complex
l
max [nm] (e [m cm ])
II
ꢀ [8]
NMe
NMe
NMe
4
2
2
Ni
246 (26600), 311 (17500), 361 (6600), 666sh (1030), 720 sh
1670), 810 sh (5350), 866 (8300)
Ni 246 (38800), 312 (28100), 362 (10800), 669 sh (1420), 721
sh (2530), 810 sh (8830), 869 (14200)
Ni 247 (38000), 312 (27900), 362 (10700), 663 sh (1320), 729
sh (2690), 810 sh (8690), 868 (14000)
ligands, as in the case of [Ni (DTBBdtSQ) ] . These results are
2
(
thus consistent with the ligand-based redox behavior of the
complexes: one-electron reduction processes should provide a
C16
2
II
2ꢀ
[8,23]
C8,10
Ni
NC8,10 Ni
2
dianionic [Ni (Bdt) ] species,
2
whereas one-electron oxida-
II
tion processes should provide a neutral [Ni (BdtSQ) ] species,
2
NC16
4
247 (38200), 312 (27200), 362 (10500), 667 sh (1290), 725
sh (2490), 810 sh (8540), 866 (13800)
248 (37900), 312 (27800), 362 (10700), 666 sh (1300), 728
sh (2600), 810 sh (8660), 866 (14000)
[8,24]
as shown in Scheme 3.
The cation-dependent assembled phases of NMe C16 Ni,
2
2
4
NMe C8,10 Ni, NC16 Ni, and NC8,10 Ni with their well-defined
2
2
4
4
electrochemical activity in solution prompted us to examine
the corresponding redox behavior in the condensed phases.
For direct electrochemical studies on their condensed phases,
we immobilized NMe C16 Ni, NMe C8,10 Ni, NC16 Ni, and
[a] sh=shoulder.
2
2
2
2
4
Figures 7a and S4 (the relevant data are listed in Table S3). All
of these complexes display reversible one-electron reduction
NC8,10 Ni on an indium-doped tin oxide (ITO) electrode by
4
using a dropcasting method. Casting 10 mm CH Cl solutions
2
2
and oxidation waves at nearly identical redox potentials at Eꢁ
onto ITO working electrodes, followed by evaporation of the
solvents led to the formation of green condensed phases, as
+
ꢀ
0.90 and 0.09 V (vs. Ag/Ag ) independent of the cations,
which is similar to the case of the previously reported mono-
II
ꢀ [8]
anion [Ni (DTBBdt)(DTBBdtSQ)] . Figures 7b,c depict changes
in the absorption spectra during the reversible electrochemical
reduction of NMe C8,10 Ni in THF at E=ꢀ1.0 V (for other com-
2
2
plexes, see Figure S5) During the electrochemical reduction,
II
nꢀ
Scheme 3. Redox scheme for the [Ni (Bdt)
n
(BdtSQ)2ꢀn
]
4
moieties of NMe Ni,
the IVCT bands at lꢁ860 nm commonly disappeared, whereas
NMe C16 Ni, NMe C8,10 Ni, NC16 Ni, and NC8,10
2
2
2
2
4
4
Ni.
Chem. Eur. J. 2018, 24, 1 – 13
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shown in Figure 8. Each part of the figure also depicts the CV
to the transfer of the electrochemically generated oxidized and
reduced species into the electrolyte phase (Figure S9). The oxi-
dation could involve the transfer of the NMe C8,10 cation into
curves of the cast films of the complexes immersed in a 0.1m
LiBF /MeOH solution, in which the complexes do not dissolve
4
2
2
II
at the rest potentials. All films show redox responses during in-
dependent positive and negative potential scans with suffi-
the electrolyte phase to generate a neutral [Ni (BdtSQ) ] spe-
2
cies, and on the other hand, the reduction could be accompa-
nied by the transfer of cations between the condensed and
electrolyte phases to compensate the additional anionic charg-
es generated by the one-electron reduction of the mixed-
[8,23,24]
valent Ni core (Scheme 3).
Conclusions
In summary, this study revealed that the combination of a
II
ꢀ
redox-active mesogenic anion, [Ni (Bdt)(BdtSQ)] (Bdt=1,2-
benzenedithiolato; BdtSQ=1,2-dithia-semi-benzoquinonato),
with structurally flexible alkyl-substituted quaternary ammoni-
um cations afforded a series of redox-active ionic complexes,
II
that is, [NMe R ][Ni (Bdt)(BdtSQ)] [R=nC H (NMe C16 Ni) and
2
2
16 33
2
2
II
C8,10 (NMe C8,10 Ni)] and [NR ][Ni (Bdt)(BdtSQ)] [R=nC H
16 33
2
2
4
(
NC16 Ni) and C8,10 (NC8,10 Ni); C8,10=6-octylhexadecyl]. X-
4 4
ray crystallographic analyses coupled with IR and UV/Vis–near-
infrared spectroscopy studies indicated that all of these com-
II
ꢀ
plexes contain mixed-valence [Ni (Bdt)(BdtSQ)] anions both in
solution and in the condensed phases. Complexes [NMe ]
4
II
[
Ni (Bdt)(BdtSQ)] (NMe Ni), NMe C16 Ni, and NC16 Ni common-
4
2
2
4
ly form crystalline phases at room temperature, whereas com-
plexes NMe C8,10 Ni and NC8,10 Ni with branched alkyl chains
2
2
4
exhibit a metastable mesophase and amorphous phase at the
same temperature, respectively. This study also found that
complexes NMe C16 Ni, NMe C8,10 Ni, and NC16 Ni are able
2
2
2
2
4
to form smectic A phases, whereby the individual melting
points could be modulated by the cations. These results dem-
onstrated that the assembled structures at room temperature
and their phase-transition behavior could be controlled either
by increasing the chain length of the alkyl substituents or by
introducing branched alkyl chains. We also examined the po-
tential redox activity of these complexes in the condensed
phase. Interestingly, we observed ambipolar redox activity in-
dependent of the type of cation. The present investigation on
the combination of ionic, redox-active mesogens with tunable
alkyl-chain-functionalized ammonium cations should offer val-
uable design guidelines for electrochemically active molecular
assemblies.
Figure 8. Cyclic voltammograms and microphotographs of a) NMe2C162Ni,
b) NMe2C8,102Ni, c) NC164Ni, and d) NC8,104Ni cast on an ITO electrode
ꢀ
1
(0.1m LiBF
4
in MeOH, 100 mVs , RT). The images were taken under parallel
(left) and crossed polarizers (right) at rest potentials.
cient reproducibility (Figure S7). The observed voltammetric re-
sponses of the complexes demonstrate their redox activity
even in the condensed phases, whereas these voltammograms
also involve relatively large peak separations between the
anodic and cathodic peaks, suggesting the presence of slow ki-
[25]
netics associated with electron- and ion-transfer processes.
To assess the redox responses of the condensed phases in Experimental Section
detail, NMe C8,10 Ni was chosen as a typical example owing to
2
2
General procedures
its voltammetric response, which is the largest in this series.
The complex shows two visible anodic and cathodic peaks
All synthetic operations were performed under an atmosphere of
N by using Schlenk-line techniques. Dichloromethane (CH Cl ), n-
2 2 2
hexane, tetrahydrofuran (THF), diethyl ether (Et O), diglyme, metha-
nol (MeOH), chloroform (CHCl ), toluene, HCl, sodium chloride
ꢀ1
during a positive scan at 100 mVs , whereas a virtually single
set response is observed during an independent negative
scan. The voltammograms also demonstrate a significant scan-
rate dependency (Figure S8). A decrease in a scan rate leads to
an increase in peak-to-peak separation, and simultaneously,
the voltammograms become progressively more asymmetric.
The decreases in cathodic and anodic currents during the re-
peated positive and negative scans, respectively, are attributed
2
3
(NaCl), sodium borohydride (NaBH ), and sodium metabisulfite
4
were purchased from Kanto Chemical Industry Co., Ltd. (Japan).
Ethyl acetate (EtOAc), N,N-dimethylformamide (DMF), ethanol
(EtOH), acetone, [D]chloroform (CDCl ), copper dichloride (CuCl ),
3
2
1-phenyl-1-propyne, magnesium (Mg), hydrogen peroxide (H O )
2
2
(30% in H O), sodium hydroxide (NaOH), sodium hydrogen carbon-
2
&
&
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Full Paper
ate (NaHCO ), potassium phthalimide, potassium hydroxide (KOH),
was purified by column chromatography (silica gel, n-hexane/
3
ammonium chloride (NH Cl), potassium carbonate (K CO ), and hy-
EtOAc=8:1, v/v; R =0.25) to afford 6-octylhexadecanol as a color-
4
2
3
f
1
drazine monohydrate (N H ·H O) were purchased from Wako Pure
less oil (8.13 g, 22.9 mmol, 41%): H NMR (500 MHz, CDCl ): d=
2
4
2
3
3
3
3
Chemical Industries Inc. (Japan). Isobutyronitrile, 4-bromo-1-
butene, magnesium sulfate (MgSO4), boron trifluoride–diethyl
ether (BF ·OEt ), imidazole, iodine (I ), 1,2-benzenedithiol (BdtH ),
3.64 (t, J =6.7 Hz, 2H), 1.57 (dd, J =6.7 Hz, J =6.7 Hz, 2H),
1.40–1.20 (m, 39H), 0.88 ppm (t, JH,H =6.9 Hz, 6H); C NMR
(126 MHz, CDCl ): d=63.07 (HOCH -), 37.35 (HOCH CH -), 33.65,
H,H
H,H
3
H,H
13
3
2
2
2
3
2
2
2
tetramethylammonium bromide ([NMe ]Br), and bis(hexadecyl)di-
32.85, 31.93, 30.15, 29.72, 29.68, 29.66, 29.37, 26.69, 26.51, 26.21,
4
methylammonium bromide ([NMe (nC H ) ]Br) were purchased
from Tokyo Chemical Industry Co., Ltd. (Japan). 2-Octyldodecanol,
22.69, 14.11 ppm (CH CH ); IR (ATR): n˜ =3325 (m), 2920 (s), 2852 (s),
1464 (m), 1377 (w), 1055 (w), 721 cm (w).
2
16 33 2
2
3
ꢀ1
triphenylphosphine (PPh ), dimethylamine (NHMe ) (2.0m in THF),
6-Octylhexadecyl iodide: 6-Octylhexadecanol (5.98 g, 16.9 mmol),
imidazole (1.38 g, 20.3 mmol), and triphenylphosphine (5.34 g,
20.4 mmol) were dissolved in CH Cl (30 mL) and cooled to 273 K.
3
2
and tetrakis(hexadecyl)ammonium bromide ([N(nC H ) ]Br) were
16
33 4
purchased from Aldrich Chemical Co. Ltd. (Japan). N-Bromosuccin-
imide (NBS) was purchased from Nacalai Tesque, Inc. (Japan).
Nickel dichloride hexahydrate (NiCl ·6H O) was purchased from
2
2
After the addition of iodine (4.94 g, 19.5 mmol), the solution was
stirred at 273 K for 15 min, before it was warmed to room temper-
ature and stirred for 12 h. The reaction was quenched by adding
an excess amount of sodium metabisulfite, and the mixture was
then extracted with CH Cl . The combined pale-yellow organic
2
2
Kishida Chemical Co., Ltd. (Japan). All solvents that were used
under anaerobic conditions were thoroughly degassed by three
freeze–pump–thaw cycles immediately prior to use. Flash column
chromatography was performed on Kanto Chemical silica gel neu-
2
2
phase was washed with water and brine, dried (MgSO ), and fil-
4
[5a]
tral (spherical, 50 mm). 2-Octyldodecyl bromide, 1-bromomagne-
tered before CH Cl was removed under reduced pressure. The ob-
2
2
[26]
II
sium-3-butene,
benzenedithiolato,
and
[NMe ][Ni (Bdt)(BdtSQ)]
(Bdt=1,2-
tained crude product was purified by column chromatography
4
[27]
BdtSQ=1,2-dithia-semi-benzoquinonato)
(silica gel, n-hexane; R =0.8) to afford 6-octylhexadecyl iodide as a
f
1
were synthesized according to literature procedures.
colorless oil (5.24 g, 11.3 mmol, 67%): H NMR (500 MHz, CDCl ):
d=3.19 (t, J =7.1 Hz, 2H), 1.83 (dd, J =7.1 Hz, J =6.7 Hz,
H), 1.40–1.20 (m, 39H), 0.88 ppm (t, J =6.9 Hz, 6H); C NMR
H,H
3
3
3
3
H,H
H,H
H,H
3
13
2
Syntheses
(126 MHz, CDCl ): d=37.31 (ICH -), 33.62, 33.46, 31.93, 31.00, 30.14,
3 2
6
-Octylhexadecene: 1-Bromo-2-octyldodecane (27.1 g, 75.0 mmol),
CuCl2 (313 mg, 2.33 mmol), and 1-phenyl-1-propyne (8.73 g,
5.2 mmol) were mixed in THF (60 mL). The resulting pale-yellow
29.72, 29.68, 29.37, 26.68, 25.65, 22.70, 14.13, 7.23 ppm (CH
CH ); IR
2 3
(ATR): n˜ =2920 (s), 2851 (s), 1463 (m), 1377 (w), 1203 (w),
ꢀ
1
7
1167 cm (w).
suspension was treated at ambient temperature with 1-bromo-
magnesium-3-butene (1.7m in THF, 88 mL, 150 mmol), and the
mixture was stirred at 298 K for 40 h. The reaction was quenched
6-Octylhexadecyl
14.6 mmol) and PPh
bromide:
6-Octylhexadecanol
(5.17 g,
Cl
(7.65 g, 29.2 mmol) were dissolved in CH
3
2
2
(14 mL) and cooled to 273 K. The mixture was slowly treated with
NBS (3.93 g, 22.1 mmol) and stirred at room temperature for 24 h
to afford an orange suspension. After removal of the solvent under
reduced pressure, the resulting colorless oil was dissolved in n-
hexane. Purification by column chromatography (silica gel, n-
by adding 1m aq. HCl, and the products were extracted with Et O.
2
The organic phase was washed with water and brine. The resulting
solution was dried (anhydrous MgSO ) and filtered, and Et O was
4
2
evaporated to afford a pale-yellow crude oil. Purification of the
crude product by column chromatography (silica gel, n-hexane;
Rf =0.93) afford 6-octylhexadecene as a colorless oil of less than
absolute purity. Yield: 18.6 g. The formation of the target molecule
hexane; R
=0.8) yielded 6-octylhexadecyl bromide as a colorless
f
1
oil (5.17 g, 12.4 mmol, 85%): H NMR (500 MHz, CDCl
): d=3.41 (t,
H,H =6.9 Hz, 2H), 1.86 (dd, JH,H =6.9 Hz, JH,H =6.7 Hz, 2H), 1.40–
3
3
3
3
J
1
3
13
was confirmed by the following techniques: H NMR (500 MHz,
1.20 (m, 39H), 0.88 ppm (t, JH,H =6.8 Hz, 6H); C NMR (126 MHz,
CDCl ): d=37.32 (BrCH -), 34.00, 33.63, 33.48, 32.90, 31.94, 30.15,
29.72, 29.68, 29.38, 28.67, 26.68, 25.89, 22.70, 14.12 ppm (CH CH );
2
CDCl ): d=5.86–5.78 (m, 1H), 5.00 (d, J =17.0 Hz, 1H), 4.94 (d,
3
2
3
H,H
3
3
3
JH,H =10.0 Hz, 1H), 2.02 (dt, J =0.89 Hz, J =6.7 Hz, 2H), 1.40–
.20 (m, 37H), 0.89 ppm (t, J =6.7 Hz, 6H); C NMR (126 MHz,
H,H
H,H
2
3
ꢀ1
3
13
1
IR (ATR): n˜ =2921 (s), 2852 (s), 1463 (m), 722 (w), 648 (w), 566 cm
H,H
CDCl ): d=139.29 (H C=CH), 114.10 (H C=CH-), 37.32, 37.12, 34.29,
(w).
3
2
2
3
2
1
3.67, 33.21, 32.77, 31.95, 30.17, 30.16, 30.06, 29.76, 29.74, 29.72,
9.70, 29.69, 29.40, 29.39, 27.11, 26.71, 26.08, 22.71, 19.73,
4.12 ppm (CH CH ); IR (ATR): n˜ =2921 (s), 2852 (s), 1641 (w), 1460
N-(6-Octylhexadecyl)phthalimide:
6-Octylhexadecyl
bromide
(1.50 g, 3.60 mmol) and potassium phthalimide (732 mg,
3.95 mmol) were dissolved in DMF (6.0 mL) and stirred at 363 K for
12 h. After cooling the mixture to room temperature, it was
poured into water (50 mL) and extracted with CH Cl . The com-
2
3
ꢀ
1
(
m), 1377 (w), 991 (w), 909 (m), 721 cm (w). Although resonances
derived from other minor impurities were also found in the spec-
trum, the compound was used for the next reaction without fur-
ther purification.
2
2
bined organic layer was washed with 0.10% aq. KOH, water, and
saturated aq. NH Cl before the solvents were removed under re-
4
6
-Octylhexadecanol: NaBH (962 mg, 25.4 mmol) was added to a
duced pressure. The residue was suspended in n-hexane, and an
insoluble inorganic byproduct was filtered off. Subsequently, the
solvent was removed under reduced pressure to yield N-(6-octyl-
4
solution of 6-octylhexadecene (18.62 g, 55.3 mmol) in diglyme
45 mL), and the mixture was stirred at room temperature until
(
most of NaBH4 was dissolved. BF ·OEt2 (3.69 g, 26.0 mmol) was
added dropwise to this suspension at 273 K. The resulting white
mixture was stirred at room temperature for 3 h, before water
hexadecyl)phthalimide as a colorless oil (1.52 g, 3.14 mmol, 87%):
3
1
H NMR (500 MHz, CDCl ): d=7.85–7.82 (m, 2H), 7.73–7.69 (m, 2H),
3
3
3.67 (t, J =7.3 Hz, 2H), 1.70–1.67 (m, 2H), 1.40–1.20 (m, 39H),
0.88 ppm (t, JH,H =6.9 Hz, 6H); C NMR (126 MHz, CDCl ): d=
H,H
3
13
(
(
3 mL) was added to quench the reaction, followed by aq. NaOH
3
5m, 15.0 mL, 75.0 mmol) and aq. H O (30%, 25.1 g, 221 mmol).
168.43 (C=O), 133.79 (CC=O), 132.18 (CHCHCC=O), 123.11 (CHCCO),
38.10 (NCH ), 37.33 (NCH CH ), 33.59, 33.50, 31.91, 30.13, 29.67,
2
2
After stirring the resulting mixture at room temperature for 12 h, it
was poured into water (70 mL). The mixture was extracted with
2
2
2
29.65, 29.35, 28.64, 27.37, 26.65, 26.64, 26.27, 22.67, 14.10 ppm
Et O, and the combined organic phase was washed with saturated
(CH CH ); IR (ATR): n˜ =2921 (s), 2852 (s), 1774 (m), 1713 (s), 1466
(m), 1394 (s), 1369 (m), 1040 (w), 791 cm (w).
2
2
3
ꢀ
1
aq. NaHCO and brine to remove most of the diglyme. The result-
3
ing solution was dried (anhydrous MgSO ) and filtered, and Et O
was evaporated to afford a colorless crude oil. The crude product
6-Octylhexadecylamine: A solution of N-(6-octylhexadecyl)phthal-
imide (1.51 mg, 3.13 mmol) in MeOH (18 mL) was treated with
4
2
Chem. Eur. J. 2018, 24, 1 – 13
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II
N H ·H O (479 mg, 9.57 mmol). After the mixture was heated to
[NMe (nC H ) ][Ni (Bdt)(BdtSQ)] (NMe C16 Ni): BdtH (171 mg,
2 16 33 2 2 2 2
2
4
2
reflux for 12 h, it was cooled to room temperature and MeOH was
removed under reduced pressure. The residue was dissolved in
CH Cl and washed with 10 wt% aq. KOH and brine. After drying
1.20 mmol) and NaOH (200 mg, 5.00 mmol) were dissolved in
MeOH (5 mL). This pale-yellow solution was treated with a pale-
green solution of NiCl ·6H O (143 mg, 0.60 mmol) in MeOH
2
2
2
2
the organic fraction (anhydrous MgSO ) and filtering, the filtrate
(13 mL), which induced a color change of the solution to reddish
brown. After stirring the mixture for 30 min under air, a solution of
[NMe C16 ]Br (345 mg, 0.60 mmol) in MeOH (7 mL) was added to
4
was concentrated under reduced pressure to give 6-octylhexadecyl
1
amine as a colorless oil (902 mg, 2.55 mmol, 81%): H NMR
2
2
3
(
1
500 MHz, CDCl ): d=2.67 (d, J =7.0 Hz, 2H), 1.46–1.40 (m, 2H),
afford a dark-green solid. The solid was filtered, washed with
MeOH, and dried under reduced pressure. The crude product was
purified by flash column chromatography (silica gel, CH Cl /
3
H,H
3
13
.40–1.20 (m, 39H), 0.87 ppm (t, JH,H =6.6 Hz, 6H); C NMR
(
126 MHz, CDCl ): d=42.16 (H NCH ), 37.35 (H NCH CH ), 33.68,
3 2 2 2 2 2
2
2
3
2
1
3.64, 31.91, 30.14, 29.70, 29.66, 29.65, 29.35, 27.35, 26.67, 26.55,
MeOH=20:1, v/v; R =0.6), and green single crystals of NMe C16 Ni
f 2 2
2.67, 14.10 ppm (CH CH ); IR (ATR): n˜ =3271 (w), 2920 (s), 2851 (s),
suitable for X-ray crystallographic analysis were obtained by recrys-
tallization from CH Cl /MeOH (179 mg, 0.21 mmol, 36%): IR (ATR):
2
3
ꢀ1
464 (m), 1377 (w), 1309 (m), 1040 cm (w).
2
2
Bis(6-octylhexadecyl)dimethylammonium iodide ([NMe C8,10 ]I):
n˜ =3080 (w), 3036 (w), 2950 (w), 2916 (s), 2847 (s), 1537 (w), 1485
2
2
Dimethylamine (2.0m in THF, 0.54 mL, 1.08 mmol), 6-octylhexadecyl
iodide (1.00 g, 2.15 mmol), and NaOH (51.9 mg, 1.30 mmol) were
heated to reflux in THF (2.0 mL) for 43 h. After the mixture was
cooled to room temperature, it was poured into water (10 mL) and
(w), 1456 (s), 1417 (m), 1373 (w), 1291 (m), 1235 (w), 1130 (w), 1083
ꢀ
1
(m), 965 (w), 870 (w), 740 (s), 671 (w), 435 cm (w); elemental anal-
ysis calcd (%) for C H NS Ni (834.08): C 66.24, H 9.67, N 1.68;
4
6
80
4
ꢀ
1
found: C 66.38, H 9.93, N 1.69; c T =0.395 emuKmol .
[NMe (C8,10) ][Ni (Bdt)(BdtSQ)] (NMe C8,10 Ni): BdtH (67.1 mg,
2 2 2 2 2
M
100K
II
extracted with Et O. The combined organic layer was washed with
2
water, dried (anhydrous MgSO ), and filtered, and the volatiles
were removed under reduced pressure. The crude product was pu-
rified by column chromatography (silica gel, n-hexane/EtOAc=8:1,
0.47 mmol) and NaOH (75.5 mg, 1.89 mmol) were dissolved in
MeOH (7 mL). This pale-yellow solution was treated with a pale-
green solution of NiCl ·6H O (56.2 mg, 0.24 mmol) in MeOH (5 mL),
4
2
2
v/v; R =0.5) to afford N,N-di(6-octylhexadecyl)-N,N-dimethylammo-
nium iodide as a white solid (428 mg, 0.51 mmol, 47%): H NMR
which induced a color change of the solution to reddish brown.
After stirring the mixture for 30 min under air, a solution of
[NMe C8,10 ]I (199 mg, 0.24 mmol) in MeOH (10 mL) was added to
f
1
(
4
500 MHz, CDCl ): d=3.53–3.50 (m, 4H), 3.40 (s, 6H), 1.74–1.71 (m,
3
2
2
3
13
H), 1.40–1.20 (m, 78H), 0.88 ppm (t, J =6.6 Hz, 12H); C NMR
precipitate a dark-green solid. The solid was filtered, washed with
MeOH, and dried under reduced pressure. The crude product was
purified by flash column chromatography (silica gel, n-hexane/
EtOAc=5:1, v/v; R =0.5) to afford NMe C8,10 Ni as a dark-green
H,H
(
126 MHz, CDCl ): d=63.99 (NCH ), 51.50 (NCH ), 37.28 (NCH CH ),
3 2 3 2 2
3
2
3.47, 33.45, 33.43, 31.84, 30.08, 30.07, 29.66, 29.65, 29.60, 29.59,
9.30, 29.28, 26.61, 26.60, 26.41, 22.83, 22.60, 14.04 ppm (CH CH );
2
3
f
2
2
ꢀ
1
IR (ATR): n˜ =2920 (s), 2852 (s), 1464 (m), 1377 (w), 902 cm (w).
solid (145 mg, 0.14 mmol, 58%): IR (ATR) n˜ =3035 (w), 2920 (s),
Tetrakis(6-octylhexadecyl)ammonium iodide ([NC8,10 ]I): 6-Octyl-
hexadecyl amine (254 mg, 0.72 mmol), 6-octylhexadecyl iodide
2851 (s), 1536 (w), 1500 (m), 1418 (w), 1377 (w), 1292 (m), 1235
4
ꢀ1
(w), 1082 (w), 743 (s), 670 (w), 435 cm (w); elemental analysis
calcd (%) for C H NS Ni (1058.51): C 70.35, H 10.67, N 1.32;
(
990 mg, 2.13 mmol), and K CO (198 mg, 1.44 mmol) in isobutyro-
2 3
62 112
4
ꢀ1
nitrile (2.5 mL) were heated to reflux for 4 days. After the mixture
was cooled to room temperature, it was poured into water (10 mL)
found: C 70.23, H 10.66, N 1.27; c T =0.374 emuKmol .
M 100K
[N(nC H ) ][Ni (Bdt)(BdtSQ)] (NC16 Ni): An aqueous solution of
II
1
6
33
4
4
and extracted with CHCl . The combined organic layer was washed
BdtH (73.25 mg, 0.5150 mmol) and NaOH (73.25 mg, 0.5150 mmol)
3
2
with water, dried (anhydrous MgSO ), and filtered. The filtrate was
was added to an aqueous suspension of [NC16 ]Br (248.82 mg,
4
4
concentrated under reduced pressure, and the crude product was
purified by flash column chromatography (silica gel, n-hexane/
0.24991 mmol, 125 mL), which was subsequently heated to 808C.
This mixture was treated with a pale-green aqueous solution of
NiCl ·6H O (59.48 mg, 0.2502 mmol), and the mixture was stirred
EtOAc=10:1, v/v; R =0.7) to afford tetra(6-octylhexadecyl)ammoni-
f
2
2
um iodide as a pale-yellow solid (606 mg, 0.41 mmol, 57%):
for 2 h. The resulting green suspension was extracted with toluene.
The combined organic layer was washed with water, dried (anhy-
1
H NMR (500 MHz, CDCl ): d=3.38–3.35 (m, 8H), 1.72–1.66 (m, 8H),
3
3
13
1
.40–1.20 (m, 156H), 0.88 ppm (t, JH,H =6.6 Hz, 24H); C NMR
drous MgSO ), and filtered, and toluene was removed under re-
4
(
126 MHz, CDCl ): d=59.41 (NCH ), 37.32 (NCH CH ), 33.52, 33.50,
duced pressure. The crude product was purified by flash column
3
2
2
2
3
2
3.48, 31.88, 30.12, 30.11, 29.71, 29.70, 29.65, 29.63, 29.34, 29.33,
6.85, 26.66, 26.65, 26.36, 22.64, 22.49, 14.06 ppm (CH CH ); IR
chromatography (silica gel, CH Cl /MeOH=10:1, v/v; R =0.9) and
2
2
f
green single crystals of NC16 Ni suitable for X-ray crystallographic
2
3
4
ꢀ1
(
ATR): n˜ =2918 (s), 2850 (s), 1467 (m), 1377 (w), 890 cm (w).
analysis were obtained by recrystallization from CH Cl /MeOH
2
2
II
[NMe ][Ni (Bdt)(BdtSQ)] (NMe Ni): Whereas Mrkvovꢃ et al. already
(47.9 mg, 0.04 mmol, 15%): IR (ATR): n˜ =3040 (w), 2953 (m), 2917
4
4
[27]
reported the synthesis of this complex, we used the following
modified procedure in this study: BdtH (284 mg, 2.00 mmol) and
NaOH (350 mg, 8.75 mmol) were dissolved in MeOH (30 mL). This
pale-yellow solution was treated with a pale-green MeOH (5 mL)
solution of NiCl ·6H O (238 mg, 1.00 mmol), which induced a color
(s), 2849 (s), 1467 (m), 1417 (w), 1377 (w), 1293 (m), 1233 (w), 1083
ꢀ
1
(w), 746 (s), 671 (w), 435 cm (w); elemental analysis calcd (%) for
C H NS Ni (1254.88): C 72.74, H 11.25, N 1.12; found: C 72.62, H
2
7
6
140
4
ꢀ
1
11.25, N 0.88; c T =0.392 emuKmol
[N(C8,10) ][Ni (Bdt)(BdtSQ)]
.
M
100K
II
(NC8,10 Ni):
BdtH2
(57.0 mg,
2
2
4
4
change of the solution to reddish brown. After stirring the mixture
0.40 mmol) and NaOH (65.0 mg, 1.63 mmol) were dissolved in
MeOH (5 mL). This pale-yellow solution was treated with a pale-
green solution of NiCl ·6H O (47.6 mg, 0.20 mmol) in MeOH (5 mL),
for 30 min under air, a MeOH (5 mL) solution of [NMe ]Br (154 mg,
4
1
.00 mmol) was added to give a dark-green solid, which was isolat-
2
2
ed by filtration, washed with MeOH, and dried under reduced pres-
which induced a color change of the solution to reddish brown.
After stirring the mixture for 30 min under air, a solution of
sure. The green solid (NMe Ni) was reprecipitated from acetone/n-
4
hexane to give the title compound (119 mg, 0.29 mmol, 29%): IR
[NC8,10 ]I (300 mg, 0.20 mmol) in EtOH (10 mL) was added to give
4
(
(
4
ATR): n˜ =3021 (m), 1531 (w), 1486 (m), 1403 (w), 1290 (w), 1235
a dark-green oil. The oil was washed with MeOH/EtOH (1:1, v/v)
and dried under reduced pressure. The crude product was purified
by flash column chromatography (silica gel, n-hexane/EtOAc=
10:1, v/v; R =0.6) to afford NC8,10 Ni as a dark-green oil (243 mg,
w), 1153 (w), 1130 (w), 1084 (w), 958 (s), 758 (m), 669 (w),
ꢀ1
35 cm (w); elemental analysis calcd (%) for C H NS Ni (413.29):
16 20 4
C 46.50, H 4.88, N 3.39; found: C 46.26, H 4.88, N 3.36; c T
0
=
M
100K
f
4
ꢀ
1
.377 emuKmol .
0.14 mmol, 71%): IR (ATR): n˜ =3040 (w), 2920 (s), 2851 (s), 1464
&
&
Chem. Eur. J. 2018, 24, 1 – 13
www.chemeurj.org
10
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
(
4
m), 1417 (w), 1377 (w), 1293 (m), 1233 (w), 1082 (w), 738 (s),
ꢀ1
Table 4. Crystallographic data of NMe
2
2
C16 Ni and NC16
4
Ni.
34 cm
(w); elemental analysis calcd (%) for C108H204NS Ni
4
(
1703.73): C 76.14, H 12.07, N 0.82; found: C 76.20, H 12.11, N 0.92.
NMe C16
2
2
Ni
NC16
4
Ni
ꢀ1
c T =0.380 emuKmol
.
M
100K
formula
C
46
H
80NNiS
4
76 4
C H140NNiS
Fw
834.08
0.30ꢄ0.20ꢄ0.10
triclinic
1254.89
0.18ꢄ0.15ꢄ0.08
monoclinic
3
crystal size [mm ]
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
b [8]
g [8]
V [ꢂ ]
Physical measurements
P 1¯ (No. 2)
1
P2 /c (No. 14)
1
13
7.9254(16)
14.223(2)
22.196(4)
73.720(6)
87.801(8)
85.110(7)
2392.7(8)
223
24.856(4)
16.509(3)
19.411(3)
90
107.912(2)
90
H NMR and C NMR (500 and 126 MHz) spectra were measured
with a JEOL EX-500 (and JEOL A-500) spectrometer. Flash column
chromatography was performed with a Biotage Isolera apparatus.
Elemental analyses were performed with a PerkinElmer 2400 II
CHN analyzer (Flash EA 1112 series, Thermo Finnigan Instruments).
Absorption spectra in solution were recorded with a Hitachi U-
3
7579(2)
123
4
100 (U-3500) spectrophotometer at T=296 K (l=200–3300 nm).
T [K]
Z
D
2
4
Infrared (IR) spectra were recorded with a Nicolet 6700 FTIR spec-
trometer equipped with a Smart-Orbit (Diamond) ATR (attenuated
total reflection) accessory. Thermogravimetric and differential ther-
mal analyses (TG-DTA) were performed with a Rigaku Thermoplus
EVO TG-DTA8120 machine. Differential scanning calorimetry (DSC)
measurements were conducted with a METTLER DSC822e. For TG-
DTA and DSC measurements, an Al pan was used under a flow of
ꢀ
3
calcd [gcm
]
1.158
910.00
6.099
19560
10581
22.42
1.100
2780.00
4.052
61526
17060
23.09
F (000)
m(MoKa) [cm
measured reflns
unique reflns
refined parameters
GOF on F
ꢀ
1
]
2
1.044
1.087
N . Variable-temperature X-ray powder diffraction measurements
were performed by using CuKa radiation with a Rigaku RINT-2000
diffractometer with Al sample pans. Polarized optical microscopy
R
R
1
wR
0.0413
0.0588
0.1472
0.0665
0.0658
0.1661
2
int
[
a]
[
2
b]
(all data)
=SkF jꢀkF
(
POM) images were recorded with an Olympus BX51 polarizing mi-
2
2
2
2 2 1/2
[
a] R
1
o
c
k/SjF
o
j. [b] wR
2
={[Sw(F
o
ꢀF
c o
) ]/[Sw(F ) ]} .
croscope equipped with a DP70 digital camera. Samples were
cooled and heated with a Linkam THM600 hot stage with a pro-
grammable temperature controller. Magnetic susceptibilities were
recorded over 100 K at 1 T with a superconducting quantum inter-
ference device MPMS XL (Quantum Design) at Tohoku University.
All values were corrected for diamagnetism using Pascal’s con-
Acknowledgements
[28]
stants. Electrochemical measurements were performed with an
ALS model 650A electrochemical analyzer. A standard three-elec-
The authors are grateful to Prof. Tamejiro Hiyama and Dr. Yasu-
nori Minami (Chuo University) for their support regarding the
crystallographic and mass spectrometry measurements, as well
as Prof. Youichi Ishii (Chuo University) for his support with the
elemental analyses. The authors also gratefully acknowledge
Prof. Hitoshi Miyasaka and Dr. Wataru Kosaka (Tohoku Universi-
ty) for their support with the magnetic susceptibility measure-
ments. This work was supported financially by Ministry of Edu-
cation, Culture, Sports, Science and Technology (MEXT) KAKEN-
HI grant 17H05382 (Coordination Asymmetry), as well as by
Japan Society for the Promotion of Science (JSPS) KAKENHI
grants 16H04123, 16K13967, and 17H04871 and the Science
Research Promotion Fund from the Promotion and Mutual Aid
Corporation for Private Schools of Japan. This work was fur-
thermore supported by the Inter-University Cooperative Re-
search Program of the Institute for Materials Research, Tohoku
University (Proposal No.17K0091).
trode system (glassy carbon working electrode, platinum-wire
+
counter electrode, and Ag/Ag /CH CN reference electrode) was
3
used for the electrochemical studies in solution. Cyclic voltamme-
try (CV) and bulk electrolysis in the condensed phase were per-
formed by using an indium-doped tin oxide (ITO) working elec-
+
trode, platinum-wire counter electrode, and Ag/Ag /CH CN refer-
3
ence electrode. CH Cl solutions (3 mL, 10 mm) were cast on ITO
2
2
electrodes followed by evaporation of the solvents under reduced
pressure.
Crystallographic data collection and structure refinement
Single-crystal X-ray diffraction measurements of NMe C16 Ni and
2
2
NC16 Ni were performed with a Rigaku VariMax with Saturn equip-
4
ment by using graphite-monochromated MoKa radiation (l=
0
.71075 ꢂ). Single crystals of suitable size and quality were selected
under paraffin oil, mounted onto a MicroMounts (MiTeGen), and
cooled by an N -flow-type temperature controller. Molecular struc-
2
Conflict of interest
[29]
tures were solved by direct methods (SIR2004), which allowed
the successful location of all non-hydrogen atoms within the unit
cell. All calculations were performed by using the CrystalStructure
The authors declare no conflict of interest.
[30]
crystallographic software package, except for refinement calcula-
[31]
tions, which were performed by using SHELXL-97. A summary of
the crystallographic data of NMe C16 Ni and NC16 Ni is shown in
Keywords: cations · ligand effects · metallomesogens · nickel ·
redox chemistry
2
2
4
Table 4. CCDC 1589632 (NMe C16 Ni) and 1589633 (NC16 Ni) con-
2
2
4
tain the supplementary crystallographic data for this paper. These
data are provided free of charge by The Cambridge Crystallograph-
ic Data Centre.
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Manuscript received: December 19, 2017
Accepted manuscript online: March 5, 2018
Version of record online: && &&, 0000
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&
&
Chem. Eur. J. 2018, 24, 1 – 13
www.chemeurj.org
12
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
&
Metallomesogens
Y. Nakamura, T. Matsumoto, Y. Sakazume,
J. Murata, H.-C. Chang*
&& – &&
Tuning the Mesomorphism and Redox
Response of Anionic-Ligand-Based
Mixed-Valent Nickel(II) Complexes by
Alkyl-Substituted Quaternary
Ammonium Cations
In tune: This study demonstrates the
in the condensed phases is also exam-
ined. The results should provide valu-
able guidelines for the design of elec-
trochemically active molecular assem-
blies.
tunability of the mesomorphism of
II
anionic-ligand-based mixed-valent Ni
complexes through alkyl-substituted
quaternary ammonium cations. The po-
tential redox activity of these complexes
Chem. Eur. J. 2018, 24, 1 – 13
www.chemeurj.org
13
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ