Odd-even effect and unusual behavior of dodecyl-substituted analogue observed in the crystal structure of alkyltrimethylammonium-[Ni(dmit) 2]- salts

Article abstract of DOI:10.1246/bcsj.20100306

A series of [Ni(dmit)₂]^- (dmit: 1,3-dithiole-2- thione-4,5-dithiolato) salts of alkyltrimethylammonium (Cn: n represents the alkyl chain length; n = 3 and 518) have been prepared and analyzed by X-ray structural analysis. All complex salts have been found to be composed of alternate sheets of [Ni(dmit)₂]^- anions and sheets of cations with a pronounced interdigitation of the alkyl chains. However, molecular arrangement differed between (C3)[Ni(dmit)₂] and other (Cn)[Ni(dmit)₂] (n = 518). Adjacent cations were aligned along the long axis of [Ni(dmit)₂]^- anion in C3 complex salt, while in others (C5-C18 complex salts), they were aligned toward the short axis. Such a difference in arrangement arose from correlativity between the lengths of the long axis of cation and anion, namely CLCA. Furthermore, relative orientation between the alkyl chain of cation and [Ni(dmit)₂]^- anion differed between the odd- and even-numbered cations for C10-C18. Whereas the plane of alkyl chain for odd-numbered cation was normal to the plane of [Ni(dmit)₂]^- anion, that of even-numbered cation was parallel. It was also found that C12 analog behaved like odd-numbered cations. However, in C12 salt, the end methyl group of the dodecyl group adopted unusual end-gauche conformation.

Full text of DOI:10.1246/bcsj.20100306

312
Bull. Chem. Soc. Jpn. Vol. 84, No. 3, 312–319 (2011)
© 2011 The Chemical Society of Japan
Odd-Even Effect and Unusual Behavior of Dodecyl-Substituted
Analogue Observed in the Crystal Structure of
¹
Alkyltrimethylammonium-[Ni(dmit)2] Salts
Kotaro Dai,* Kuniharu Nomoto, Shinji Ueno, Kazuaki Tomono, and Kazuo Miyamura
Department of Chemistry, Faculty of Science, Tokyo University of Science,
1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601
Received November 2, 2010; E-mail: j1307706@ed.kagu.tus.ac.jp
¹
A series of [Ni(dmit)2] (dmit: 1,3-dithiole-2-thione-4,5-dithiolato) salts of alkyltrimethylammonium (Cn: n
represents the alkyl chain length; n = 3 and 5-18) have been prepared and analyzed by X-ray structural analysis. All
¹
complex salts have been found to be composed of alternate sheets of [Ni(dmit)2] anions and sheets of cations with a
pronounced interdigitation of the alkyl chains. However, molecular arrangement differed between (C3)[Ni(dmit)2] and
¹
other (Cn)[Ni(dmit)2] (n = 5-18). Adjacent cations were aligned along the long axis of [Ni(dmit)2] anion in C3 complex
salt, while in others (C5-C18 complex salts), they were aligned toward the short axis. Such a difference in arrangement
arose from correlativity between the lengths of the long axis of cation and anion, namely CLCA. Furthermore, relative
¹
orientation between the alkyl chain of cation and [Ni(dmit)2] anion differed between the odd- and even-numbered
¹
cations for C10-C18. Whereas the plane of alkyl chain for odd-numbered cation was normal to the plane of [Ni(dmit)2]
anion, that of even-numbered cation was parallel. It was also found that C12 analog behaved like odd-numbered cations.
However, in C12 salt, the end methyl group of the dodecyl group adopted unusual end-gauche conformation.
Alkyl chains are commonly used to promote the solubility of
organic rigid compounds such as, for example, polymers and
aromatic compounds, and octyl or dodecyl groups are usually
used because of their availability.1-8 The reason simply arises
from the fact that alkyl chains provide good solubility in
various kinds of organic solvents due to its hydrophobicity.
Therefore, most of these reported results pay less attention to
the length of alkyl chains they use. On the other hand, it is
well-known that compounds with long alkyl chains exhibit
odd-even effect depending on their chain length in various
physical properties, such as melting points, heats of fusion,
TOF-SIMS spectra and 2D molecular arrangements.9-16 This
effect on the molecular conformation in the crystal structure has
also been reported,17,18 but such structural consideration is
quite rare so far.
Chart 1.
Meanwhile, over the past two decades, an enormous amount
of research has gone into the synthesis and characterization of
transition metal-bis(dithiolato) complexes of dmit (dmit: 1,3-
dithiole-2-thione-4,5-dithiolato) and its extended ³-conjugated
derivatives.19-21 Among the vast number of studies reported
so far, a great deal of attention has been focused on the
development of electrically conductive Langmuir-Blodgett
(LB) membrane systems based on alkylammonium-[metal-
(dmit)2] (metal = Ni, Au, Pt, Pd, Zn, and Cu) salts and related
compounds.22,23 In order to understand the correlation between
the structure and the electrical properties of thin films thus
constructed, analysis of the bulk crystal structure is of
particular importance, because it can be used to predict the
local stable structure of the thin films. Some studies with
single-crystal X-ray analysis are already reported.24-26 How-
ever, systematic studies on the structural change brought about
by the change in the alkyl chain length have drawn less
attention. Since physical properties including electric conduc-
tivity of molecule-based materials depend primarily on the
molecular arrangement, systematic and thorough research on
the intra- and intermolecular interaction is required to predict
the exact structure of the material, especially in the crystalline
state, and thus their properties. From this point of view, we
¹
have been investigating the structure of [Ni(dmit)2] complex
salts of cations with long alkyl chains (Chart 1). We expected a
¹
new arrangement of [Ni(dmit)2] anions regulated by inter-
molecular interaction of long alkyl chains.27-31 As shown in our
previous report, the use of dodecyltrimethylammonium as
cation resulted in formation of characteristic cation aggregate
by hydrophobic interaction in the crystal. In this work, the
structural change in crystals of [Ni(dmit)2] complex salts
Published on the web March 4, 2011; doi:10.1246/bcsj.20100306

K. Dai et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 3 (2011)
313
depending on the alkyl chain length of alkyltrimethylammo-
nium cations is reported.
(C14)[Ni(dmit)2]; Anal. Found: C, 39.10; H, 5.25; N, 2.01%.
Calcd for C23H38NS10Ni: C, 39.02; H, 5.41; N, 1.98%. IR
¹1
¹1
(KBr): 1340 cm for ¯(C=C), 1060 cm for ¯(C=S)
.
Experimental
(C15)[Ni(dmit)2]; Anal. Found: C, 39.68; H, 5.36; N, 1.97%.
Calcd for C24H40NS10Ni: C, 39.93; H, 5.58; N, 1.94%. IR
Synthesis of Alkyltrimethylammonium (Cn) Bromide.
Trimethylamine (2.36 g, 10 mmol) and alkyl bromide (12
mmol) were stirred in acetonitrile (25 mL) for 48 h. Acetonitrile
was then evaporated to obtain a crude product. A small amount
of methanol, diethyl ether, or a mixture of these was added to
the residue to give a white powder. This powder was washed
with diethyl ether and dried in vacuo over night.
¹1
¹1
(KBr): 1346 cm for ¯(C=C), 1055 cm for ¯(C=S)
.
(C16)[Ni(dmit)2]; Anal. Found: C, 40.84; H, 5.55; N, 1.96%.
Calcd for C25H42NS10Ni: C, 40.80; H, 5.75; N, 1.90%. IR
¹1
¹1
(KBr): 1345 cm for ¯(C=C), 1059 cm for ¯(C=S)
.
(C17)[Ni(dmit)2]; Anal. Found: C, 41.61; H, 5.72; N, 1.90%.
Calcd for C26H44NS10Ni: C, 41.64; H, 5.91; N, 1.87%. IR
¹1
¹1
Synthesis of (Cn)[Ni(dmit)2] Salts. 4,5-Di(thiobenzoyl)-
1,3-dithiole-2-thione (dmit(COPH)) was synthesized by a
reported method.32 Obtained dmit(COPh)2 (920 mg, 2.25 mmol)
was treated with an excess of sodium methoxide (0.5 M) in
methanol (20 mL) under nitrogen at room temperature with
stirring. To the resulting dark red solution, NiCl2¢6H2O (238
mg, 1 mmol) in methanol (20 mL) and alkyltrimethylammonium
(Cn) bromide (2.4 mmol) in methanol (20 mL) were added
successively. The resulting precipitate was washed with meth-
anol. All complex salts were obtained by oxidizing this
precipitate in acetone using I2 and NaI according to a literature
procedure. The resultant black crystal was collected by filtra-
tion, and purified by recrystallization using a mixed solvent of
acetone and methanol. Single crystals were grown by slow
evaporation from acetone and methanol solution of complex
salt at room temperature. Unfortunately, single crystals suit-
able for X-ray crystal structural analysis were not obtained
for (C2)[Ni(dmit)2] and (C4)[Ni(dmit)2].
(KBr): 1344 cm for ¯(C=C), 1059 cm for ¯(C=S).
(C18)[Ni(dmit)2]; Anal. Found: C, 42.43; H, 5.98; N, 1.89%.
Calcd for C27H46NS10Ni: C, 42.45; H, 6.07; N, 1.83%. IR
¹1
¹1
(KBr): 1347 cm for ¯(C=C), 1059 cm for ¯(C=S)
.
Measurements. IR spectra (KBr pellets) were measured
using a JASCO FT/IR-410 spectrophotometer, with a reso-
lution of 4 cm¹1. Elemental analysis data were obtained with a
Perkin-Elmer 2400II CHN analyzer.
X-ray Crystallography. A single crystal was mounted on
a glass capillary. Intensity data were collected at 173 K with a
Bruker AXS SMART diffractometer equipped with a CCD area
detector and Mo K¡ (- = 0.71073 ¡) radiation. 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 by the full-matrix
least-square method. Some hydrogen atoms were found from
experimental data directly, and their position and isotropic
thermal parameters were refined. Selected crystallographic data
are summarized in Table 1. Crystallographic data have been
deposited at the Cambridge Crystallographic Data Centre:
Deposit numbers CCDC-796601-796610 and 796612-796616
for compounds Cn (n = 3 and 5-18) complex salts, respec-
tively. Copies of the data can be obtained free of charge via
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).
(C3)[Ni(dmit)2]; Anal. Found: C, 26.23; H, 2.64; N, 2.90%.
Calcd for C12H16NS10Ni: C, 26.03; H, 2.91; N, 2.53%. IR
¹1
¹1
(KBr): 1345 cm for ¯(C=C), 1053 cm for ¯(C=S)
.
(C5)[Ni(dmit)2]; Anal. Found: C, 29.22; H, 3.28; N, 2.43%.
Calcd for C14H20NS10Ni: C, 28.91; H, 3.47; N, 2.41%. IR
¹1
¹1
(KBr): 1349 cm for ¯(C=C), 1061 cm for ¯(C=S)
.
(C6)[Ni(dmit)2]; Anal. Found: C, 30.25; H, 4.00; N, 2.27%.
Calcd for C15H22NS10Ni: C, 30.24; H, 3.72; N, 2.35%. IR
¹1
¹1
(KBr): 1350 cm for ¯(C=C), 1059 cm for ¯(C=S)
.
(C7)[Ni(dmit)2]; Anal. Found: C, 31.88; H, 3.99; N, 2.23%.
Calcd for C16H24NS10Ni: C, 31.52; H, 3.97; N, 2.30%. IR
Results and Discussion
¹1
¹1
(KBr): 1351 cm for ¯(C=C), 1059 cm for ¯(C=S)
.
Fifteen single crystals of alkyltrimethylammonium-
[Ni(dmit)2] salts were obtained from acetone and methanol
solutions. The crystal data are shown in Table 1. Measured
temperatures of X-ray crystallographic analysis were 173 K,
except for C17 complex salt (297 K).
Crystal Structures of the Complex Salts. Table 1 shows
that C3 complex salt crystallized in monoclinic space group
C2/c, while other complex salts adopted triclinic space group
(C8)[Ni(dmit)2]; Anal. Found: C, 32.91; H, 4.10; N, 2.30%.
Calcd for C17H26NS10Ni: C, 32.73; H, 4.20; N, 2.25%. IR
¹1
¹1
(KBr): 1351 cm for ¯(C=C), 1059 cm for ¯(C=S)
.
(C9)[Ni(dmit)2]; Anal. Found: C, 33.89; H, 4.26; N, 2.51%.
Calcd for C18H28NS10Ni: C, 33.90; H, 4.43; N, 2.20%. IR
¹1
¹1
(KBr): 1340 cm for ¯(C=C), 1060 cm for ¯(C=S)
.
(C10)[Ni(dmit)2]; Anal. Found: C, 35.12; H, 4.53; N, 2.16%.
Calcd for C19H30NS10Ni: C, 35.01; H, 4.64; N, 2.15%. IR
ꢀ
P1. The number of molecules in a unit cell (Z) is essentially
¹1
¹1
(KBr): 1342 cm for ¯(C=C), 1060 cm for ¯(C=S)
.
equal to 2 in C5-C18 complex salts, but in C8 complex salt, it is
4. In the case of C8 complex salt, the asymmetric unit consists
of two cation/anion pairs. Thus, the crystal of C8 complex salt
might be a different polymorph form from the others, but only
single crystals with the observed lattice parameters could be
obtained. The densities of crystals calculated from X-ray data
tend to decrease with an increase of the carbon number.
However, the density of C12 complex salt, 1.512 mg cm¹3, is
larger than those of C11 and C13 complex salts, 1.502 and
1.481 mg cm¹3, respectively. As will be described in more detail
(C11)[Ni(dmit)2]; Anal. Found: C, 35.97; H, 4.74; N, 2.35%.
Calcd for C20H32NS10Ni: C, 36.08; H, 4.84; N, 2.10%. IR
¹1
¹1
(KBr): 1341 cm for ¯(C=C), 1061 cm for ¯(C=S)
.
(C12)[Ni(dmit)2]; Anal. Found: C, 37.34; H, 4.73; N, 2.02%.
Calcd for C21H34NS10Ni: C, 37.10; H, 5.04; N, 2.06%. IR
¹1
¹1
(KBr): 1345 cm for ¯(C=C), 1061 cm for ¯(C=S)
.
(C13)[Ni(dmit)2]; Anal. Found: C, 37.89; H, 4.94; N, 2.04%.
Calcd for C22H36NS10Ni: C, 38.08; H, 5.23; N, 2.02%. IR
¹1
¹1
(KBr): 1344 cm for ¯(C=C), 1062 cm for ¯(C=S)
.

Table 1. Crystal Data of Complex Salts
Compound
(C3)[Ni(dmit)2]
12H16NNiS10
553.57
(C5)[Ni(dmit)2]
(C6)[Ni(dmit)2]
(C7)[Ni(dmit)2]
(C8)[Ni(dmit)2]
(C9)[Ni(dmit)2]
(C10)[Ni(dmit)2]
Formula
Fw
C
C14H20NNiS10
581.62
C15H22NNiS10
595.65
C16H24NNiS10
609.67
C17H26NNiS10
623.70
C18H28NNiS10
637.72
C19H30NNiS10
651.75
T/K
173
173
173
173
173
173
173
Crystal system
Space group
Unit cell
Monoclinic
C2/c
19.235(2)
17.615(2)
14.240(2)
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a/¡
b/¡
c/¡
¡/deg
¢/deg
£/deg
8.0755(7)
12.0608(11)
12.7621(11)
80.153(2)
76.702(10)
81.257(2)
1167.87(18)
2
1.654
0.896
0.0275
0.0627
8.2667(8)
12.0965(12)
12.7074(13)
78.155(2)
77.511(2)
80.636(2)
1185.4(2)
2
1.669
0.878
0.0305
0.0720
8.1401(6)
12.2681(10)
13.0992(10)
76.3220(10)
73.5060(10)
89.1520(10)
1216.81(16)
2
1.664
0.814
0.0279
0.0921
13.720(4)
13.787(4)
15.842(4)
66.707(3)
79.470(4)
69.680(3)
2577.6(12)
4
1.607
0.837
0.0385
0.1076
8.150(4)
12.772(6)
14.082(6)
71.647(5)
80.628(6)
81.246(6)
1340.0(10)
2
1.581
0.913
0.0567
0.1332
8.1143(9)
12.2084(13)
15.8379(17)
69.290(2)
75.866(2)
78.928(2)
1413.4(3)
2
1.531
1.081
0.0491
0.1096
61.142(2)
Volume/¡3
4225.8(9)
8
1.740
Z
¹3
¤
calcd/Mg m
GOFa)
0.868
Final R
R1b)
0.03106
0.0600
0.0614
0.0661
Indices [I > 2·(I)]
R indices
(all data)
wR2c)
R1b)
0.0383
0.0652
0.0425
0.0752
0.0316
0.0986
0.0675
0.1364
0.1580
0.1974
0.0585
0.1148
wR2c)
Continued on next column:
Table 1. Continued:
Compound
(C11)[Ni(dmit)2]
(C12)[Ni(dmit)2]
(C13)[Ni(dmit)2]
(C14)[Ni(dmit)2]
(C15)[Ni(dmit)2]
(C16)[Ni(dmit)2]
(C17)[Ni(dmit)2]
(C18)[Ni(dmit)2]
Formula
Fw
T/K
C
20H32NNiS10
C21H34NNiS10
679.80
173
C22H36NNiS10
693.83
173
C23H38NNiS10
707.85
173
C24H40NNiS10
721.88
173
C25H42NNiS10
735.91
173
C26H44NNiS10
749.93
297
C27H46NNiS10
763.96
173
665.78
173
Crystal system
Space group
Unit cell
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a/¡
b/¡
c/¡
¡/deg
¢/deg
£/deg
9.6430(8)
10.0712(8)
16.4924(14)
73.7090(10)
88.9310(10)
73.7170(10)
1472.6(2)
2
1.502
0.665
0.0266
0.0810
9.569(2)
10.061(2)
16.780(4)
74.960(3)
88.565(3)
73.382(3)
1493.0(6)
2
1.512
0.758
0.0329
0.0945
9.752(2)
10.000(2)
16.923(3)
79.468(3)
84.896(2)
73.675(2)
1556.0(6)
2
1.481
1.074
0.0483
0.1569
8.0131(11)
12.2226(17)
16.985(2)
86.841(3)
79.046(3)
78.755(2)
1601.6(4)
2
1.468
0.0739
0.0470
0.0886
9.744(2)
10.003(2)
17.929(4)
84.721(4)
80.195(3)
73.365(3)
1648.2(7)
2
1.455
0.799
0.0449
0.1145
7.7999(15)
12.296(2)
18.473(4)
86.853(3)
79.371(3)
78.733(3)
1700.1(6)
2
1.438
0.868
0.0372
0.1049
9.8139(8)
10.1853(8)
19.5086(16)
87.385(2)
76.070(2)
72.839(2)
1807.7(3)
2
1.378
0.818
0.0445
0.0948
7.747(3)
12.320(5)
19.877(7)
80.534(5)
80.819(4)
78.468(5)
1796.8(11)
2
1.412
0.829
0.0412
0.1087
Volume/¡3
Z
¹3
¤
calcd/Mg m
GOFa)
Final R
R1b)
Indices [I > 2·(I)]
R indices
(all data)
wR2c)
R1b)
0.0315
0.0898
0.0400
0.1046
0.0603
0.1716
0.1259
0.1363
0.0956
0.1508
0.0549
0.1280
0.0984
0.1222
0.0751
0.1414
wR2c)
2
a) Goodness-of fit on F2. b) R1 = ∑««Fo« ¹ «Fc««/∑«Fo«. c) wR2 = ∑[w(Fo ¹ Fc2)2]/∑[w(Fo2)2]1/2
.

K. Dai et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 3 (2011)
315
Figure 1. Crystal packing structures of (C3)[Ni(dmit)2], (C5)[Ni(dmit)2], (C6)[Ni(dmit)2], and (C12)[Ni(dmit)2]. Cations and
anions are distinguished by white and gray, respectively.
Figure 2. Schematic diagram of stacking structures I and
II. Characters a and c represent anion and cation,
respectively.
later in the text, the crystal packing of C12 complex salt became
denser because of the end-gauche conformation of the dodecyl
group present only in this complex salt.
The crystal packing structures in Figure 1 show that the
¹
layers of [Ni(dmit)2] anions and the layers of cations are
alternately piled up, and the anions formed dimers by stacking.
Figure 3. ORTEP III view of (a) an ion pair with
numbering scheme and (b) crystal structure of (C10)[Ni-
(dmit)2]. Hydrogen atoms are omitted for clarity. Displace-
ment ellipsoids are drawn at the 50% probability level,
hereafter.
This structural characteristic is commonly observed in all
crystals. However, stacking structure clearly differed between
C3 and other complex salts. Adjacent cations were aligned
¹
along the long axis of [Ni(dmit)2] anion in C3 complex salt,
while those of other salts were aligned toward the short axis of
¹
[Ni(dmit)2] anion. The lengths of cations were 4.8828(42)
(C9£C12 distance), 7.4615(39) (C9£C14 distance), 8.7631(44)
(C9£C15 distance), and 14.5729(40) ¡ (C8£C21 distance) for
C3, C5, C6, and C12 complex salts, respectively, and the
length of anion was about 14.2 ¡ (S5-S10 distance) for all
complex salts. These data indicate that the length of cation in
complex salt shown in Figure 3 as an example. ORTEP plot of
an ion pair shown in Figure 3a with the atomic numbering
scheme exhibits a close contact of N+ in ammonium cation and
¹
thiolate S in the dmit moiety of the anion. This suggests the
presence of strong electrostatic interaction in the crystal. Alkyl
chain nestles along the anion in the direction of long molecular
¹
C3 complex salt is shorter than half the length of [Ni(dmit)2]
¹
anion, while that of other complex salt with longer alkyl chain
is longer. This difference led to the difference in crystal
structure as schematically shown in Figure 2. Thus the crystal
structures can be classified into two categories, structures I and
II. C3 complex salt adopted structure I, because the length of
axis of [Ni(dmit)2] anion. On the other hand, the crystal
packing in Figure 3b shows that two anions face each other to
form a dimer by ³-³ interaction, and two cations are in contact
with each other to form a dimer by hydrophobic interaction
between the alkyl groups.
¹
the cation is shorter than half the length of [Ni(dmit)2] anion.
In addition, structural characteristics of C5-C10 complex
salts are found to be fundamentally similar, while structural
characteristics in Cn complex salts with n exceeding 10 exhibit
notable differences between odd- and even-numbered Cn
complex salts. It is generally accepted that the hydrophobic
interaction between long alkyl chains becomes enhanced by
elongation of the chain length n, and it often predominates
other intermolecular interactions when n exceeds ca. 10. This
effect leads to the characteristic nature of the compound with
long alkyl groups, such as surfactants, lipids, greasy oils, etc.
Thus, the observed difference between short and long alkyl
substituted analogs can be attributed to this effect.
By adopting this structure I, cations can attain closer contact
with the anions. These results indicate that different stacking
structures arose from “correlativity in the lengths of long axis
of cation and anion” principle, namely CLCA. It is well-known
that the matching of the sizes of counter ions is important in the
crystallization process.34,35 CLCA can be regarded as a special
case of this principle for the salts of ions with relatively
elongated molecular shape. The feature of CLCA principle will
be discussed later in the text.
Commonly observed structural characteristics of complex
salts are described below using the crystal structure of C10

¹
316
Bull. Chem. Soc. Jpn. Vol. 84, No. 3 (2011)
Odd-Even Effect in Alkylammonium-[Ni(dmit)2]
Figure 4. Two types of orientation for alkyl chain; (a) vertical and (b) parallel orientations relative to the molecular plane of anion.
¹
Odd-Even Effect in the Crystal Structure of C10-C18
Complex Salts. When the structures of ion pairs in crystals
are thoroughly investigated, we found an interesting odd-even
effect in their structures. It is well known that the alkyl chains
tend to adopt the most stable all-trans conformation. In all the
crystals investigated, alkyl chains adopted all-trans conforma-
tion with the exception of C12 complex salt in which the end
methyl group of dodecyl chain adopted gauche conformation,
i.e., the end-gauche conformation. We concluded that the
crystal structure of C12 complex salt is exceptional, thus we
decided to discuss separately later in the text. As can be seen in
Figure 3, the plane of decyl chain extends parallel to the plane
With regard to the intermolecular interactions, [Ni(dmit)2]
anions in the case of even-numbered Cn complex salts
(excluding C12) are dimerized by a face-to-face stack with
sulfur-sulfur contacts (3.5631(1)-3.679(2) ¡) shorter than the
sum of the van der Waals radii. The dimer is found to form
further sulfur-sulfur contacts with adjacent dimers by side-by-
side interaction (3.5962(17)-3.695(2) ¡). In the case of odd-
numbered Cn complex salts, anions form dimers but with
no sulfur-sulfur contact. However, sulfur-sulfur contacts of
dimers by side-by-side interaction (3.4903(14)-3.694(2) ¡) are
also present, in this case. As noted previously, all complex salts
¹
are found to be composed of alternate layers of [Ni(dmit)2]
¹
of [Ni(dmit)2] anion. Note that the C7 methyl group sticks out
anions and cations (Figure 3b). Ni-N+ distances were
4.569(3)-4.624(3) and 4.716(3)-4.741(2) ¡ for even and odd
numbered Cn complex salts, respectively. Therefore, the
distances in even-numbered Cn complex salts with parallel
orientation tend to be shorter than the distances in odd-
numbered Cn complex salts with vertical orientation. Ni-N+
distances versus the number of carbon atoms in the alkyl chain
for Cn complex salts are given in Figure 5. As is evident in
Figure 5, Ni-N+ distances in the case of C10-C18 complex
salts also exhibit a clear odd-even effect.
Crystal data in Table 1 also exhibit odd-even effect. When
the number of carbon atoms in alkyl chain is odd, the values of
a axis tends to be longer while that of b axis shorter, and the
angle ¡ tends to be smaller than those in the case of even-
numbered complex salts with the exception of C12 complex
salt. As previously pointed out, C12 complex salt is excep-
tional and its lattice parameters are similar to those of odd-
numbered complex salts.
¹
normal to the plane of [Ni(dmit)2] anion. However, in C11-
C13, C15, and C17 complex salts, the direction is inverted as
shown in Figure 4. With the exception of C12 complex salt,
the crystal structure exhibited a clear odd-even effect.
In order to elucidate the structural difference between two
crystal packing structures, structural parameters were thor-
oughly investigated. In the cations, all alkyl chains except for
C12 complex salt adopted all-trans conformation with dihedral
angles, C-C bond lengths and C-C-C bond angles of the
alkyl chains being within the region of 171.5(5)-179.9(3)°,
1.469(7)-1.529(5) ¡ and 109.0(3)-119.6(7)°, respectively.
These data are in close agreement with the values previously
reported for long alkyl chains of related compounds.36,37 In
¹
[Ni(dmit)2] anions, the bond length of C=C of dmit moieties
are 1.347(7)-1.363(2) ¡, indicating that the complex is mono-
valent.38 Coordination geometries of [Ni(dmit)2] were essen-
tially square-planar, and the Ni-S distances were 2.1471(16)-
2.1654(6) ¡, and cis-S-Ni-S angles were 86.67(2)-93.30(2)°,
which are also normal values for the monovalent complex.
Crystal packing along the a axis shown in Figure 6 for C11
complex salt shows that the structure of C11 complex salt with

K. Dai et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 3 (2011)
317
Figure 5. Dependence of Ni-N+ distance on the number of
carbon atoms.
Figure 7. Molecular packings of (C10)[Ni(dmit)2] and
(C11)[Ni(dmit)2] along b axis. Hydrogen atoms are omitted
for clarity.
Figure 6. Molecular packing of (C11)[Ni(dmit)2]. Hydro-
gen atoms are omitted for clarity.
Figure 8. View along molecular axis (a, c) and side view (b, d) of neighboring cations for (C10)[Ni(dmit)2] (a, b) and
(C11)[Ni(dmit)2] (c, d).
an odd-numbered alkyl chain is similar to the structure of
C10 complex salt with even-numbered alkyl chain given in
Figure 3b as a whole. However, views along the b axis given in
Figure 7 show clear difference between them. The values of a
and b axes are 8.1143(9) and 12.2084(13) ¡ for C10 complex
salt, and 9.6430(8) and 10.0712(8) ¡ for C11 complex salt,
respectively. This difference reflects parallel or vertical
orientation of ion pairs in Figure 4.
Relative arrangement of the nearest neighboring cations is
given in Figure 8. View along molecular axis (a, c) and side

¹
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Bull. Chem. Soc. Jpn. Vol. 84, No. 3 (2011)
Odd-Even Effect in Alkylammonium-[Ni(dmit)2]
view (b, d) clearly exhibit the difference between the structures
of C10 and C11 complex salts. Two N-methyl groups (C7) of
neighboring cations are facing each other in C10 complex salt,
while those in C11 complex salt are oriented in opposite
direction. When the carbon number of the alkyl chain is even
(C10), the end-methyl group is located close to the ¢-carbon of
the neighboring alkyl chain. Thus, N-methyl groups (C7) have
enough space to adopt face-to-face arrangement, which leads to
a closer packing. In contrast, when the carbon number is odd
(C11), the end-methyl group is located close to the ¡-carbon
of the neighboring alkyl chain. This structural feature, as a
consequence, does not provide enough space for N-methyl
group (C7) to adopt face-to-face arrangement. Accordingly, N-
methyl group (C7) is distantly positioned from the end-methyl
group to avoid steric hinderance between them. The difference
in the arrangement of N-methyl groups resulted in the structural
difference of ion pair (Figure 4).
Supporting Information
¹
Data of geometric parameters, lengths of [Ni(dmit)] anion
and cation, Ni-N+ distance in ion pair and distances/¡ of
sulfur-sulfur interactions. This material is available free of
charge on the web at http://www.csj.jp/journals/bcsj/.
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