Odd-even effect observed in [Ni(dmit)2] complex salts of quaternary ammonium cation with both benzyl groups and ω-phenylalkyl groups

Article abstract of DOI:10.1246/bcsj.20140309

A series of [Ni(dmit)₂] (dmit: 1,3-dithiole-2-thione-4,5-dithiolate) complex salts of benzyldimethyl(ω-phenylalkyl) ammonium cation (BnCnPh: n represents the alkylene chain length; n = 14) have been prepared and characterized by X-ray crystallo

Full text of DOI:10.1246/bcsj.20140309

Odd-Even Effect Observed in [Ni(dmit)2] Complex Salts of Quaternary
Ammonium Cation with Both Benzyl Groups and ω-Phenylalkyl Groups
Masahiro Saeki,*1 Kotaro Dai,1 Shuhei Ichimura,1 Yoshinori Tamaki,1
Kazuaki Tomono,2 and Kazuo Miyamura*1
1Department of Chemical Sciences and Technology, Graduate School of Chemical Sciences and Technology,
Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601
2Department of Chemical and Biological Engineering, Ube National College of Technology,
2-14-1 Tokiwadai, Ube, Yamaguchi 755-8555
E-mail: jb112708@ed.tus.ac.jp, miyamura@rs.tus.ac.jp
Received: October 14, 2014; Accepted: November 24, 2014; Web Released: December 1, 2014
A series of [Ni(dmit)2] (dmit: 1,3-dithiole-2-thione-4,5-dithiolate) complex salts of benzyldimethyl(ω-phenyl-
alkyl)ammonium cation (BnCnPh: n represents the alkylene chain length; n = 1-4) have been prepared and characterized
by X-ray crystallographic structural analysis. All complex salts were found to be composed of alternant stacks of layers
of [Ni(dmit)2] anion dimers and cations (Layer I), and isolated cation layers (Layer II). In BnC3Ph complex salt,
ꢀ
polymorphs, P1 (α-form) and P2(1)/c (β-form) crystals are obtained from similar crystallizing conditions. One of the
biggest structural differences is the arrangement of [Ni(dmit)2] anion dimers; herringbone in α-form, while nearly parallel
in β-form. Other BnCnPh complex salts adopt herringbone structure. Interestingly, BnCnPh series (n = 1, 2, 3α, 4) exhibit
three types of pronounced odd-even effect in the crystal structures; 1. Dihedral angles between the two kinds of terminal
phenyl groups, 2. Angles between [Ni(dmit)2] anion dimers, and 3. Ni-N+ distances. Such a structural feature is a
consequence of the bulkiness of cation involving two phenyl groups. Introduction of terminal phenyl group is concluded
to have increased the steric effect and led to the formation of the novel crystal structure of [Ni(dmit)2] complex salts.
(a)
(c)
(b)
(d)
It is well-known that alkanes and alkyl derivatives often
exhibit odd-even effect with increasing carbon atoms. A vast
number of studies have been carried out in connection with the
property changes brought about by alkyl chain length, odd-
even effect is found in a variety of cases such as self-assembled
monolayers (SAMs),1-6 liquid crystals,7-14 and crystal struc-
tures,14-22 etc. As a typical example, the odd-even effect of the
melting points of n-alkane, n-alcohol, and saturated fatty acids
are noted even in high school textbooks. A plot of melting
points against the number of carbon atoms of alkyl chain
exhibits a typical zig-zag dependence.15,16 This type of odd-
even effect is typically found in the properties of condensed
phase.
(e)
(f)
Figure 1. Schematic diagram of the orientation of terminal
substituent groups in quaternary ammonium ion. (a) Even-
numbered alkyl chain, (b) odd-numbered alkyl chain,
(c) odd-numbered ω-phenylalkyl chain, (d) even-numbered
ω-phenylalkyl chain, (e) benzyl group and odd-numbered
ω-phenylalkyl chain, and (f) benzyl group and even-
numbered ω-phenylalkyl chain.
The crystal structure is also known to be affected by the
alkyl chain length. For example, most n-alkanes tend to
crystallize in two crystal systems, triclinic or orthorhombic.
Even-numbered n-alkanes usually crystallize in triclinic,
whereas odd-numbered in orthorhombic.17-19 However, not
many reports exist because of the difficulties in crystallizing
series of alkyl-substituted compounds. Among them, the crystal
structures of alkyl α-D-glucopyranosides and their hydrates are
reported to exhibit clear odd-even effect.21 These structural
characteristics lead to the difference in packing energy which is
related to the phase transition temperatures etc. As a result, the
compounds with alkyl substituents exhibit odd-even effect in
phase transition parameters. It should be noted that the property
changes in accordance with the orientation of the terminal
methyl group of the alkyl chain. The orientation of terminal
methyl group in stable all-trans conformation changes alter-
nately as shown in Figures 1a and 1b, which is accepted as the
cause of odd-even effect.
Most of the reports on odd-even effect are concerned with
the alkyl chains whose terminal group is methyl. However, few
reports have focused on the effect of terminal group and used
phenyl groups or other aryl groups to investigate the effect of
their bulkiness in thermal properties.23-30 Gray and co-workers
358 | Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan

without further purification. Yield: 1.21 g (79%), 1.29 g (81%),
1.34 g (80%), 1.45 g (83%) for BnC1Ph-BnC4Ph bromide,
respectively.
Me
CH2 N (CH2)n
Synthesis of (BnCnPh)[Ni(dmit)2] Complex Salts. 4,5-
Di(thiobenzoyl)-1,3-dithiole-2-thione (dmit(COPh)) was syn-
thesized by a reported method.32 Obtained dmit(COPh)2
(0.50 mmol, 202 mg) was treated with an excess of sodium
methoxide in methanol (20 mL) under nitrogen at room
temperature with stirring. To the resulting dark red solution,
Ni(CH3COO)2¢4H2O (0.25 mmol, 62 mg) in methanol (10 mL)
and benzyldimethyl(ω-phenylalkyl)ammonium (BnCnPh: n =
1-4) (0.50 mmol) in methanol (10 mL) were added succes-
sively. Precipitates formed were washed with methanol. All
complex salts were obtained by oxidizing these precipitates in
acetone using I2 (1 mmol, 127 mg) and NaI (1.3 mmol, 195
mg) according to a literature procedure.32 The resultant black
crystals were collected by filtration, and purified by recrystal-
lization. Block-like single crystals for BnC1Ph-BnC3Ph(α)
and plate-like single crystal for BnC4Ph were grown by slow
evaporation from acetone, methanol and ethanol mixed solu-
tion at room temperature. Furthermore, we collected plate-
like polymorph (β-form) of BnC3Ph complex salt from
similar crystallizing condition. Yield: 1.22 g (36%), 1.11 g
(32%), 1.13 g (32%), 1.09 g (30%) for (BnC1Ph) [Ni(dmit)2]-
(BnC4Ph)[Ni(dmit)2], respectively.
Me
Benzyldimethyl(ω-phenylalkyl)ammonium
(BnCnPh: n = 1-4)
S
S
S
S
S
S
S
S
S
Ni
S
[Ni(dmit)2]-
Chart 1.
reported that transition temperatures of ω-phenylalkyl 4-(4¤-
cyanobenzylideneamino)cinnamates showed pronounced
a
odd-even effect.28,29 It was concluded that the substitution
of terminal methyl groups with more bulky phenyl groups
increased the steric effect, and led to the clear odd-even effect.
However, the extension of alkylene chain often causes decrease
of odd-even effect. Since the flexibility of alkylene chain
increases, the elongation of alkylene chain gradually enables
the terminal phenyl group to avoid possible steric effects. Thus,
it is found that short alkylene chain and bulky terminal groups
are efficient for the strong odd-even effect to appear. In order to
understand the situation, schematic diagrams of the orientation
of terminal groups in quaternary ammonium ions are shown in
Figure 1. The terminal phenyl group of ω-phenylalkyl chain
also orients to opposite directions alternately. The bulkiness of
the terminal phenyl group is expected to cause enhanced steric
effect and lead to strong odd-even effect. In fact, we reported
some types of clear odd-even effect appeared by using ω-
phenylalkyltrimethylammonium cation (Figures 1c and 1d) as
a counter cation in [Ni(dmit)2] complex salts31 (dmit is an
abbreviation of a bidentate ligand 1,3-dithiole-2-thione-4,5-
dithiolate.). In addition, substitution of methyl group with a
benzyl group is expected to lead to more increased steric effect
at both ends as shown in Figures 1e and 1f.
Elemental Analyses, IR Absorptions, and UV Absorp-
tions. Elemental analyses were carried out using a Perkin-
Elmer 2400II CHN analyzer. IR absorptions (KBr pellets) were
measured using a JASCO FT/IR-4200 spectrometer, with a
resolution of 4 cm¹1. UV absorptions were measured using a
JASCO V-570 spectrometer.
(BnC1Ph)[Ni(dmit)2]; Found: C, 38.83; H, 2.79; N, 2.00%.
Calcd for C22H20S10NNi: C, 38.98; H, 2.97; N, 2.07%. IR(KBr):
¹1
¯
-
max/cm 1352 (C=C for dmit2¹) and 1054 (C=S). UV:
max(DMF)/nm 318 (¾/dm3 mol¹1 cm 2.38 © 104).
¹1
(BnC2Ph)[Ni(dmit)2]; Found: C, 40.06; H, 2.81; N, 2.01%.
Calcd for C23H22S10NNi: C, 39.93; H, 3.21; N, 2.03%. IR(KBr):
¹1
¯
-
max/cm 1352 (C=C for dmit2¹) and 1057 (C=S). UV:
max(DMF)/nm 318 (¾/dm3 mol¹1 cm 2.38 © 104).
¹1
(BnC3Ph)[Ni(dmit)2]; Found: C, 40.61; H, 3.34; N, 1.98%.
Calcd for C24H24S10NNi: C, 40.84; H, 3.43; N, 1.98%. IR(KBr):
¹1
¯
-
max/cm 1355 (C=C for dmit2¹) and 1056 (C=S). UV:
¹1
In this study, we report the crystal structures of [Ni(dmit)2]
complex salts of a series of counter cations, benzyldimethyl-
(ω-phenylalkyl)ammonium cation (BnCnPh: n represents the
alkylene chain length; n = 1-4). The chemical structures are
shown in Chart 1. In these cations, bulky and rigid phenyl
group are introduced at both ends of alkylene chain in order
to enhance the steric effect compared to terminal methyl group
in alkyl chain (Figure 1). We found three types of odd-even
effects and a new type of crystal structure.
max(DMF)/nm 318 (¾/dm3 mol¹1 cm 2.44 © 104).
(BnC4Ph)[Ni(dmit)2]; Found: C, 42.12; H, 2.81; N, 1.91%.
Calcd for C25H26S10NNi: C, 41.70; H, 3.05; N, 1.92%. IR(KBr):
¹1
¯
-
max/cm 1354 (C=C for dmit2¹) and 1048 (C=S). UV:
max(DMF)/nm 318 (¾/dm3 mol¹1 cm 2.51 © 104).
¹1
X-ray Crystallography. A single crystal was mounted
on a glass capillary, transferred to a Bruker AXS SMART
diffractometer equipped with a CCD area detector and Mo K¡
(- = 0.71073 ¡) radiation, and centered in the beam at 173 K.
The structures were solved and refined with SHELX-9733 using
the direct method and expanded using Fourier techniques.
All non-hydrogen atoms were refined anisotropically and the
hydrogen atoms were refined isotropically. The crystallo-
graphic data was deposited at Cambridge Crystallographic Data
Centre: Deposit numbers CCDC-1026020-1026024 for com-
pounds BnCnPh (n = 1-4) and BnC3Ph polymorph, respec-
tively. Copies of the data can be obtained free of charge via
Experimental
Synthesis of Benzyldimethyl(ω-phenylalkyl)ammonium
(BnCnPh) Bromide.
N,N-Dimethylbenzylamine (5 mmol)
and bromoalkylbenzene (5 mmol) were stirred in acetonitrile
(20 mL) for 48 h. Acetonitrile was then removed by evapora-
tion to obtain a crude white product. The crude product was
dried in vacuo overnight and used in the following reaction
Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan | 359

ꢀ
http://www.ccdc.cam.ac.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).
complex salt (Triclinic, P1). The selected bond lengths and
angles are listed in Table 2. [Ni(dmit)2] anion in each crystal
is almost planar (maximum deviations from the least-square
plane: BnC1Ph, 0.075(1) ¡ [S6] and 0.259(1) ¡ [S15];
BnC2Ph, 0.162(1) ¡ [S7] and 0.214(1) ¡ [S20]; BnC3Ph(α),
0.067(2) ¡ [S7], 0.220(3) ¡ [S20], 0.135(3) ¡ [S25], and
0.183(3) ¡ [S40]; BnC3Ph(β), 0.105(2) ¡ [S5] and 0.010(2) ¡
[S12]; BnC4Ph, 0.056(3) ¡ [S10] and 0.126(3) ¡ [S15]). The
cation to anion ratios are 1:1 giving the [Ni(dmit)2] unit a
Results and Discussion
Crystallographic data of (BnCnPh)[Ni(dmit)2] (n = 1-4)
complex salts are given in Table 1. Complex salts are crystal-
lized in monoclinic space group P2(1)/c except for BnC3Ph(α)
Table 1. Crystallographic Data of (BnCnPh)[Ni(dmit)2] Complex Salts
BnC1Ph
BnC2Ph
BnC3Ph(α)
BnC3Ph(β)
BnC4Ph
Formula
Formula weight
T/K
C22H20S10NNi
677.70
173
C23H22S10NNi
691.73
173
C24H24S10NNi
705.75
173
C24H24S10NNi
705.75
173
C25H26S10NNi
719.78
173
Crystal system
Space group
Unit cell
Monoclinic
P2(1)/c
20.0406(9)
17.7511(8)
16.5765(8)
Monoclinic
P2(1)/c
20.8591(13)
16.2647(10)
18.2816(12)
Triclinic
Monoclinic
P2(1)/c
22.9119(18)
13.0368(10)
22.0217(17)
Monoclinic
P2(1)/c
22.0627(19)
15.7001(14)
17.9824(16)
ꢀ
P1
a/¡
b/¡
c/¡
¡/degree
¢/degree
£/degree
16.294(4)
17.988(5)
20.185(5)
89.092(3)
88.761(3)
89.383(3)
5914(3)
8
1.585
1.046
0.0790
0.2248
110.3020(10)
111.2370(10)
115.0410(10)
102.3530(10)
Volume/¡3
5530.6(4)
8
1.628
5781.1(6)
8
1.589
5959.5(8)
8
1.573
6084.7(9)
8
1.571
Z
¹3
¤calc/Mg m
GOFa)
0.920
0.972
0.873
0.847
b)
Final R
R1
0.0336
0.0759
0.0470
0.0806
0.0481
0.1467
0.0668
0.1594
0.0594
0.1352
0.0952
0.1498
0.0580
0.1336
0.0991
0.1493
c)
Indices[I > 2σ(I)]
R indices
(all data)
wR2
R1
wR2
b)
0.1016
0.2416
c)
a) Goodness-of fit on F2. b) R1 = -««Fo« ¹ «Fc««/-«Fo«. c) wR2 = -[w(Fo ¹ Fc ) ]/-[w(Fo ) ]
.
2
2 2
2 2 1/2
Table 2. Selected Geometric Parameters
BnC1Ph
BnC2Ph
BnC3Ph(α)
BnC3Ph(β)
BnC4Ph
Ni-S distance/¡
Ni1-S
Ni2-S
Ni3-S
Ni4-S
2.1534(7)-
2.1695(7)
2.1521(7)-
2.1680(7)
2.1529(10)-
2.1709(10)
2.1560(9)-
2.1685(10)
2.1575(18)-
2.1646(19)
2.1601(19)-
2.1717(19)
2.1508(21)-
2.1779(19)
2.1591(20)-
2.1659(20)
2.1592(13)-
2.1682(11)
2.1604(10)-
2.1672(11)
2.1526(20)-
2.1662(19)
2.1567(20)-
2.1651(19)
Chelating S-Ni-S
angles/degree
S-Ni1-S 92.78(3), 93.59(2) 93.52(4), 92.77(4) 92.81(7), 92.81(7) 92.62(5), 93.30(5) 93.08(8), 93.13(7)
S-Ni2-S 93.37(3), 93.60(3) 93.04(4), 93.26(4) 92.42(7), 93.32(7) 92.61(4), 93.01(4) 93.30(7), 93.42(7)
S-Ni3-S
S-Ni4-S
S5-S10
S15-S20 14.213(1)
S25-S30
93.15(7), 93.13(7)
93.03(7), 93.14(8)
14.244(4)
14.255(4)
14.235(4)
Anion length/¡
Cation length/¡
14.244(1)
14.238(2)
14.299(2)
14.260(2)
14.258(2)
14.238(4)
14.207(4)
S35-S40
14.241(5)
10.072(4)-
[C19-C26]
10.041(4)-
11.534(8)-
[C19-C27]
11.558(6)-
[C36-C44]
12.349(14)-
[C31-C40]
12.357(13)-
[C49-C58]
8.956(12)-
12.237(7)-
[C19-C28]
8.862(6)-
13.867(15)-
[C19-C29]
6.301(7)-
[C35-C42]
[C33-C46]
[C32-C44]
[C61-C76]
8.939(11)-
[C79-C94]
360 | Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan

(b)
(a)
α-form
β-form
(c)
(d)
Layer II
Layer II
Layer II
Layer II
Layer I
Layer I
Layer I
A-type Cation
Layer I
Layer I
Layer I
A-type Cation
B-type Cation
B-type Cation
α-form
β-form
Figure 2. Crystal structures of (BnC3Ph)[Ni(dmit)2] complex salts. (a) herringbone structure of [Ni(dmit)2] anion dimers in α-form,
(b) [Ni(dmit)2] anion dimers oriented in similar direction in β-form, (c) side view of in α-form, (d) side view of in β-form. Hydrogen
atoms are omitted for clarity. Molecular arrangement in the red square is discussed in Figure 7a.
formal charge of ¹1. There are no significant differences in
Ni-S distances and chelating S-Ni-S angles of [Ni(dmit)2]
anion in all complex salts. However, some odd-even effects
related to cation molecules are observed and their details will
be discussed later in the text. The ortep views34 and atom labels
are given in the supporting information (Figures S1 and S2).
Polymorphism is often encountered when we deal with the
complex salts, especially when they are substituted with long
alkyl chain. Thus, it should be kept in mind that the crystal
structure that has been solved is one of the stable forms in the
crystallized condition. In the case of BnC3Ph complex salts,
two kinds of polymorphs are obtained.
Figures 2c and 2d exhibit the side views of the crystal struc-
tures of α-form and β-form. It is found that the crystal structure
is composed by two different layers, Layer I and Layer II,
arranged alternately in the direction of long axis of [Ni(dmit)2].
In Layer I, one cation is sandwiched by two [Ni(dmit)2] anion
dimers. This means that the cation and anion ratios are 1:2
within a column of Layer I since half of cation is pushed out of
the Layer I to Layer II. The cation in Layer I will be referred to
as A-type cation, and the pushed out cation as B-type, hereafter.
The complex salt of [Ni(dmit)2] is intensively investigated
because of its special electronic properties, i.e. molecular con-
ductor and super conductivity. Generally, it is well known that
the crystal structure of [Ni(dmit)2] complex salts are loosely
classified into two types, “segregated stack” and “alternant
stack.” In the former type of stacking, [Ni(dmit)2] anion and
counter cation pack separately, and the anion layer and cation
layer arrange alternately. This crystal structure is often observed
in partially oxidized [Ni(dmit)2] complex salts. This segregated
type of [Ni(dmit)2] salt exhibits super conductivity.35-45 On
the other hand, in the latter case, [Ni(dmit)2] anion and counter
cation pile up alternately to form crystal of cation:anion ratio of
1:1. Good electronic properties cannot be expected in alternant
type of [Ni(dmit)2] salt, but the formation of anion dimer is
of interest.46-49
Polymorphism of (BnC3Ph)[Ni(dmit)2] Complex Salts.
Before comparing the structural characteristics of BnCnPh
complex salts (n = 1-4), polymorphism observed for BnC3Ph
is investigated. BnC3Ph complex salt crystallized in block-like
α-form and plate-like β-form single crystals in similar crys-
tallizing condition. The α-form adopts triclinic crystal system
ꢀ
and P1 space group, whereas the β-form is monoclinic and
P2(1)/c (Table 1). The basic structural difference of α-form
and β-form is the crystal packing as shown in Figure 2. In
¹
Figure 2a, dimers of [Ni(dmit)2] anions in α-form are packed
in herringbone-like manner, while in Figure 2b, all dimers in β-
form are oriented in similar direction. The angles between the
dimers are 82.60(4)° for α-form and 20.05(2)° for β-form.
Dimers in other crystals of (BnCnPh)[Ni(dmit)2] are packed in
herringbone structure. Since all other complex salts of BnCnPh
are packed in herringbone-like manner, we took α-form to
compare the crystal structures in BnCnPh series.
In BnC3Ph complex salt, all [Ni(dmit)2] anions and half of
BnC3Ph cations pile up alternately in Layer I like “alternant
stack,” and another half of cation pack only by itself in
Layer II, just like “segregated stack.” Thus, this crystal
structure has the structural characteristics both of two types.
Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan | 361

A-type
B-type
A-type
B-type
(a)
(b)
(a)
(b)
N1+
N1+
N2+
N3+
Ni1
Ni1
N2+
(c)
(e)
(d)
(f)
N1+
N2+
N4+
Ni3
Ni1
(c)
(d)
N1+
N1+
Ni1
N2+
N2+
Ni1
Figure 3. Molecular structures and arrangements of
(BnC3Ph)[Ni(dmit)2] complex salts. (a) A-type ion pairs
in α-form, (b) isolated B-type cations in α-form, (c) A-type
ion pair in β-form, (d) isolated B-type cation in β-form.
Hydrogen atoms are omitted for clarity.
Figure 4. Molecular structures and arrangements of
(BnCnPh)[Ni(dmit)2] complex salts. A-type ion pair in
(a) BnC1Ph, (c) BnC2Ph, (e) BnC4Ph. B-type isolated
cation in (b) BnC1Ph, (d) BnC2Ph, (f) BnC4Ph. Hydrogen
atoms are omitted for clarity.
However, its electronic properties are expected to be poor
because π-electron overlaps of [Ni(dmit)2] anions are decreased
by the existence of A-type cations in between them. Due to this
reason, this type of crystal structure is usually not thoroughly
investigated. Therefore, this type of crystal structure has not
been reported. However, we focus on this and discuss its
structural aspect in later section with other BnCnPh cations.
Figure 3 shows molecular structure of an ion pair of A-type
cation and [Ni(dmit)2] anion, and B-type isolated cation in
BnC3Ph complex salt. A-type cation adopts all-trans con-
formation and aligns along planar [Ni(dmit)2] anion. Both
terminal phenyl rings orient in upper direction with respect to
anion. However, B-type cation adopted different conformation
to A-type cation. The torsion angle involving N+ is differ-
ent for the two. As a consequence, the benzyl group and ω-
phenylpropyl group orient in different direction in B-type
cation. The dihedral angles between terminal two phenyl
groups are found to have large difference in two polymorphs,
66.8(3)°, 69.3(3)° for α-form and 80.0(1)° for β-form. This
difference is simply caused by the difference in the orienta-
tion of terminal phenyl groups in Layer II, as can be seen in
Figures 2c and 2d.
BnC1Ph
BnC2Ph
BnC3Ph(α)
BnC4Ph
Figure 5. Dependence of dihedral angles between terminal
phenyl groups in A-type cations. Dotted line shows crys-
tallographic independent unit in BnC3Ph(α) complex salt.
as explained in Figure 1. Thus, dihedral angles between two
terminal phenyl rings exhibit clear odd-even effect shown in
Figure 5. The dihedral angles of odd-numbered cation tend to
be large compared to those of even-numbered cations due to the
orientations of terminal phenyl groups.
Comparison of Molecular Structures of (BnCnPh)[Ni-
(dmit)2] (n = 1, 2, 3α, 4). The molecular structures of other
(BnCnPh)[Ni(dmit)2] complex salts are shown in Figure 4.
BnC1Ph, BnC2Ph and BnC4Ph complex salts have two crys-
tallographically independent ion pair units, while BnC3Ph(α)
complex salt has four asymmetric units (Figures 3a and 3b).
The A-type cations adopt a linear structure and tend to align
along the planar [Ni(dmit)2] anion. The terminal phenyl groups
orient in upper direction with respect to [Ni(dmit)2] anion in
odd-numbered alkylene chain (BnC1Ph and BnC3Ph(α)), while
opposite direction in even-numbered (BnC2Ph and BnC4Ph),
However, B-type cations of this series do not show such
an odd-even effect. In BnC1Ph and BnC2Ph cations, B-type
cations are similar to those of A-type cations as shown in
Figures 4a-4d, whereas the structural distinction becomes clear
by elongation of alkylene chain in BnC3Ph and BnC4Ph
as shown in Figures 3a, 3c, 4e, and 4f. The torsion angles
including N+ are 178.4(2)° (C32-C31-N2-C38) for BnC1Ph,
179.6(3)° (C33-C32-N2-C39) for BnC2Ph, 62.8(8)° (C64-
C63-N3-C70) and 66.2(8)° (C82-C81-N4-C88) for BnC3Ph,
65.5(5)° (C35-C34-N2-C41) for BnC4Ph (ORTEP views with
numbering scheme of A-type and B-type cation are shown in
362 | Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan

(a)
BnC1Ph
BnC2Ph
BnC4Ph
(b)
Layer II
Layer II
Layer II
Layer II
Layer II
Layer II
Layer I
Layer I
Layer I
Layer I
Layer I
Layer I
Layer I
Layer I
Layer I
BnC1Ph
BnC2Ph
BnC4Ph
Figure 6. Crystal structures of (BnCnPh)[Ni(dmit)2] complex salts. (a) Top views showing herringbone structure, (b) side views.
Hydrogen atoms are omitted for clarity. Molecular arrangements in the red squares are discussed in Figure 7a.
Supporting Information, Figure S1 and Figure S2). Thus, it is
(a)
recognized that clear structural change related to B-type cations
occurs between BnC2Ph and BnC3Ph. This reason may be the
steric effects of phenyl groups around N+. In BnC1Ph and
BnC2Ph cations, the alkylene chain is too short and not easy to
change the conformation. In addition, the steric effects around
the N+ increase by bulky terminal phenyl groups. Thus, the
torsion angles adopt nearly 180° so as to keep the terminal
phenyl groups from approaching. On the other hand, in
BnC3Ph and BnC4Ph cations, the alkylene chains are relatively
long and flexibility of the ω-phenylalkyl group enables the
cation to change its conformation. Furthermore, when A-type
cation length elongates, terminal phenyl groups slightly pro-
trude from Layer I, and stick out into Layer II. As a result, the
cations adopt different structures shown in Figures 3b and 4f to
avoid the steric repulsion.
Crystal Structures of (BnCnPh)[Ni(dmit)2] Complex
Salts (n = 1, 2, 3α, 4). The crystal structures of BnCnPh
complex salts (n = 1, 2, 4) are given in Figure 6. Anion dimers
in these crystals are packed in herringbone structure like
BnC3Ph(α) dimer shown in Figure 2a. Interestingly, it is found
that the angles between [Ni(dmit)2] anion dimers in herring-
bone structure (ª in Figure 7a) exhibit clear odd-even effect as
shown in Figure 7b. Even-numbered ones are larger than right
angle, while those of odd-numbered are nearly vertical.
Furthermore, Ni-N+ distances exhibit odd-even effect
shown in Figure 8. As for the molecules in red squares in
Figure 2a and Figure 6a, one A-type cation can be regarded
as sitting on a different two [Ni(dmit)2] anions (Anion1 and
Anion2). This situation is illustrated schematically in Figure 7a.
The distances between Ni1-N1+ and Ni2-N1+ exhibit odd-
even effect with opposite dependence. In odd-numbered cations,
the N1+ tends to approach Ni1 compared to Ni2. However, in
even-numbered, the difference is smaller than those of odd-
numbered cations. Although BnC3Ph cations have two crys-
tallographically independent A-type cations, this tendency is
maintained.
A-type BnC1Ph cation
A-type BnC2Ph cation
Ni1-N1+
Ni2-N1+
Ni1-N1+
Anion 1
Ni2-N1+
θ
θ
Anion 2
Anion 1
Anion 2
A-type BnC3Ph(α) cation
A-type BnC4Ph cation
Ni1-N1+
Ni2-N1+
Anion 2
Ni1-N1+
Anion 1
Ni2-N1+
θ
θ
Anion 1
Anion 2
(b)
BnC1Ph
BnC2Ph
BnC3Ph(α)
BnC4Ph
Figure 7. (a) Molecular arrangements of A-type BnCnPh
cation sitting on two crystallographic independent [Ni-
(dmit)2] anions. (b) Dependence of dihedral angles ª
between [Ni(dmit)2] anions in herringbone structure.
Dotted line shows crystallographic independent unit of
BnC3Ph(α).
Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan | 363

(a)
(b)
Ni2-N1+
(c)
(d)
(e)
Ni1-N1+
BnC1Ph
BnC2Ph
BnC3Ph(α)
BnC4Ph
Figure 8. Dependence of Ni-N+ distances in (BnCnPh)-
[Ni(dmit)2] complex salts. Circle ( ) and square ( ) are for
Ni1-N1+ distances and Ni2-N1+ distances, respectively.
Dotted lines show crystallographic independent units of
BnC3Ph(α).
Figure 9. Classifications of crystal structure of [Ni(dmit)2]
complex salts. (a) Segregated stack, (b) alternant stack,
(c) (3,7-bis(dialkylamino)phenothiazin-5-ium)[Ni(dmit)2]
(Ref. 49), (d) (BnCnPh)[Ni(dmit)2] (n = 1, 2, 3α, 4),
(e) (BnC3Ph(β))[Ni(dmit)2]. Characters of a and c repre-
sent the anion and cation, respectively.
The odd-even effects are caused by the steric effect of
terminal phenyl rings. Figure S3 shows the arrangement of A-
type cation and [Ni(dmit)2] anion including Ni2 (Anion2). The
terminal phenyl rings in odd-numbered cation are placed over
the Anion2 so as to cover the anion plane, while in even-
numbered cations, terminal phenyl rings stand perpendicular to
the anion plane. Considering the arrangement between A-type
cation and Anion1 shown in Figures 3a and 4a, it is recognized
that the contact of terminal phenyl groups to Anion2 (and
Anion4) increases in odd-numbered cations. Thus, Ni2-N1+
distances become relatively longer than those of Ni1-N1+
distances. On the other hand, in even-numbered cation, the
terminal phenyl rings orient in the similar direction against
Anion1 and Anion2 as shown in Figures 4c, 4e, S3b, and S3d.
Thus, the steric effects by the terminal phenyl groups are
similar and as a consequence, the differences between Ni1-
N1+ and Ni2-N1+ distances are small. It is found that the
difference the orientation of terminal phenyl group of A-type
cation leads to the difference in Ni1-N1+ and Ni2-N1+
distances, cation-anion arrangement (Figure 7a), and odd-even
effect in dihedral angle ª.
Conclusion
We have prepared four 1:1 complex salts composed of
[Ni(dmit)2] anion and BnCnPh cations (BnCnPh = benzyldi-
methyl(ω-phenylalkyl)ammonium, n = 1-4) to examine the
effects of bulky terminal phenyl groups on the crystal structures
of transition metal complex salts.
Interestingly, a novel type of crystal structure in [M(dmit)2]
complex salts is found using BnCnPh cation. All crystal
structures are composed by Layer I and Layer II. The linear A-
type cation and [Ni(dmit)2] anion stacks perpendicular to the
[Ni(dmit)2] anion plane in Layer I, whereas only isolated B-
type cation is aggregated in Layer II. Furthermore, three types
of odd-even effects are found. i.e. 1. Dihedral angles between
the two kinds of terminal phenyl groups, 2. Angles between
[Ni(dmit)2] anion dimers, 3. Ni-N+ distances. It is concluded
that the introduction of bulky terminal phenyl groups leads to
the crystal structure changes and clear odd-even effect.
In the BnCnPh series, a new type of crystal structure, which
has both segregated stack (Figure 9a) and alternant stack
(Figure 9b) characteristics, is found. This type of crystal is
also reported in (3,7-Bis(dialkylamino)phenothiazin-5-ium)-
[Ni(dmit)2] complex salts.49 The packing is destabilized by the
elongation of alkyl chain which increases the bulkiness of the
cation, and [Ni(dmit)2] anion is reported to be pushed out of the
piled column of cations and anions by elongation (Figure 9c).
However, in (BnCnPh)[Ni(dmit)2] complex salts, the molecule
that is pushed out of the column is not [Ni(dmit)2] anions but
BnCnPh cations (Figures 9d and 9e). One reason that gave this
structural difference is the difference in planarity of the cations.
Dye cations are planar and they have tendency to stack and
aggregate. Therefore, the species that are pushed out to avoid
the steric repulsion are not dye cations but [Ni(dmit)2] anions.
A second reason is the presence of π-π and CH-π interaction
present between BnCnPh cations, in Layer II. By this inter-
action, BnCnPh tends to form a layer by itself. Packing in
Layer II is given in Figure S4.
Supporting Information
ORTEP views together with numbering scheme of BnCnPh
complex salts, molecular structures of BnCnPh complex salts,
and crystal structures of Layer II. This material is available
electronically on J-STAGE.
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Bull. Chem. Soc. Jpn. 2015, 88, 358–365 | doi:10.1246/bcsj.20140309
© 2014 The Chemical Society of Japan | 365