Preparation and characterization of new low melting ammonium-based ionic liquids with ether functionality

Article abstract of DOI:10.1016/j.molstruc.2009.01.041

Eighteen new and three previously known but insufficiently characterized R?₃N⁺A^- and R₂?₂N⁺A^- type (R = 2-ethoxyethyl or 4-methoxybenzyl, ? = methyl, ethyl, n-propyl, n-butyl, n-

Full text of DOI:10.1016/j.molstruc.2009.01.041

Journal of Molecular Structure 922 (2009) 64–76
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Preparation and characterization of new low melting ammonium-based ionic
liquids with ether functionality
*
Minna Kärnä, Manu Lahtinen , Jussi Valkonen
Department of Chemistry, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
a r t i c l e i n f o
a b s t r a c t
+
À
+ À
´
´
Article history:
Eighteen new and three previously known but insufficiently characterized RR3N A and R2R2N A type
Received 3 November 2008
Received in revised form 19 January 2009
Accepted 20 January 2009
Available online 31 January 2009
´
(R = 2-ethoxyethyl or 4-methoxybenzyl, R = methyl, ethyl, n-propyl, n-butyl, n-pentyl or n-hexyl, A = Br,
BF4 or PF6) quaternary ammonium (QA) salts were synthesized and characterized by using 1H and 13C
NMR techniques, mass spectroscopy and elemental analysis. The bromide salts were synthesized either
by treating dimethyl formamide with an ether functionalized alkyl bromide in the presence of potassium
carbonate or by treating a tertiary amine with an ether functionalized alkyl bromide. The QA tetrafluoro-
borates and hexafluorophosphates were synthesized by metathesis reaction between a prepared QA bro-
mide and HBF4 or KPF6. The crystal structures of four compounds were determined by X-ray single crystal
diffraction and powder diffraction was used to study the crystallinity of the solid compounds and to com-
pare the structural similarities between the single crystals and the microcrystalline bulk form. Thermal
properties of all compounds were studied by using TG/DTA and DSC methods. The anion exchange had
a clear lowering effect on the melting points and enhanced the thermal stability of the BF4À and PF6À salts
compared to the analogous bromides. Most of the compounds melted clearly below 100 °C, of which four
are liquid at room temperature.
Keywords:
Quaternary ammonium bromide
Tetrafluoroborate
Hexafluorophosphate
Ionic liquid
Thermal analysis
X-ray diffraction
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
to their non-volatility, non-flammability and high ionic conductiv-
ity, among other characteristics [12]. In addition to the most stud-
The seemingly ever growing interest on room temperature ionic
liquids (RTILs) has turned the spotlight, along with many others, to
quaternary ammonium-based compounds. Ionic liquids are of
interest because of their unique characteristics, for example, low
vapor pressure and extraordinary solvent properties, which have
enabled their use in numerous applications and which have been
widely discussed in several excellent publications or reviews and
references therein [1–6].
Traditionally, the most widespread applications of ionic liquids
lie in organic synthesis as solvents and catalysts [7,8]. Ionic liquids
have in fact been described as designer solvents since their proper-
ties can be tuned by careful selection of ionic species [1,9]. They
have also various electrochemical applications: in electric double
layer capacitors (energy storage device) ionic liquids have been
used as electrolytes due to their high conductivity and some qua-
ternary ammonium-based ionic liquids have been reported to have
more potential than the traditional aromatic type ionic liquids
such as imidazolium or pyridinium due to their higher cathodic
stability [10,11]. The quest for new energy sources has also led a
great attention to dye-sensitized solar cells (DSSCs) in which ionic
liquids could be used to replace the organic liquid electrolytes due
ied imidazolium-based ionic liquids, quaternary ammonium
polyiodides have been tested as electrolytes in DSSCs [13]. Another
solar application is the use of ionic liquids as heat-transfer fluids in
electric power plants using parabolic trough solar collector tech-
nology [14–16]. Lately, some studies have suggested that ionic liq-
uids could be used as a new class of lubricants or as additives in
conventional lubricants. Certain quaternary ammonium-based io-
nic liquids have proven to be even more efficient lubricants than
conventional hydrocarbon oils in reciprocal sliding tests [17]. Some
ionic liquids containing a large amount of nitrogen are highly ener-
getic materials which may be used in industrial or military appli-
cations [18]. A large number of tested applications consider only
imidazolium-based ionic liquids which unfortunately are still
rather expensive especially for large scale industrial applications.
Quaternary ammonium and phosphonium-based ionic liquids, on
the other hand, can also be made from readily available lower cost
materials and thereby will be more applicable to industrial use if
synthesized with reasonable yields [19–22]. Furthermore, the sat-
urated quaternary ammonium cations are generally more resistant
against oxidation and reduction than 1,3-substituted imidazolium
cations that have certain degree of electrochemical instability and
have some usability limitations in organic reactions [23,24]. Intro-
ducing an oxygen-containing side chain has proven to reduce the
toxicity of imidazolium-based ionic liquids [25,26] and it might
* Corresponding author. Tel.: +358 14 2602624; fax: +358 14 2602501.
E-mail address: manu.lahtinen@jyu.fi (M. Lahtinen).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.01.041

M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
65
lead to a change of solvent properties [27,28]. Various methods to
synthesize quaternary ammonium compounds has been known for
a long time and a significant amount of publications exists [29–32].
alkyl and R is an ether-bonded alkyl or aralkyl group, have been
synthesized and characterized. In addition to these new com-
pounds, three previously known but insufficiently characterized
compounds [37–42] have been synthesized and characterized
and used as precursors for six of the new QA salts. This study
was oriented to structural characterization and thermal analysis
and therefore the performed synthesis methods were not opti-
mized. The 1H and 13C NMR spectroscopy, elemental analysis
and ESI-TOF MS measurements are used to verify the accuracy
and the purity of the compounds. Furthermore, X-ray powder dif-
fraction was used to study the crystallinity of the compounds and
to compare the consistency between the single crystal structures
and their powdery forms. The thermal properties have been ob-
served by TG/DTA and DSC and the effect of different anions on
some characteristics of the compounds have been examined by
comparing these results.
Recently, a newÀmethod was developed by our group [33] for pre-
+
´
paring R2R2N X type quaternary ammonium halides.
Relatively few studies on quaternary ammonium-based com-
pounds with ether functionality have been made so far, for exam-
ple, by Pernak [34], Das [35] and Hayamizu [36] and the number of
existing compounds still remains fairly small comparing to, e.g.,
imidazolium-based compounds, and actually almost all are based
to that cation. The number of simple acyclic non-chiral compounds
is even smaller.
The aim of our studies is to find new quaternary ammonium-
based compounds that have ionic liquid nature-compounds with
a broad liquid range, low viscosity, good electrochemical proper-
ties and low melting point combined with good thermal stability.
This is achieved by synthesizing new quaternary ammonium-
based cations, pairing them with various anions, and performing
systematic structural and thermoanalytical evaluations of the no-
vel materials. Furthermore, based on special characteristics of the
compounds potential application areas for the materials will be
sought out in further studies.
2. Experimental
2.1. Synthesis and analysis
2.1.1. General procedure
´
In this study, as a continuum to our previous ones, 18 new R2R2
All reagents and solvents were purchased from manufacturers
and used as received. Compounds 1 and 2 (Scheme 1) were pre-
pared by using the one-pot synthesis route described by Ropponen
+
N+AÀ or RR3N AÀ type quaternary ammonium (QA) salts, in which
´
´
A is bromide, tetrafluoroborate or hexafluorophosphate, R is an
A
N+
A
N+
O
O
O
O
1
8
A = Br
2
9
A = Br
A = BF4
A = BF4
15 A = PF6
16 A = PF6
A
N+
A
A
N+
N+
O
O
O
5
A = Br
6
A = Br
7
A = Br
12 A = BF4
19 A = PF6
13 A = BF4
20 A = PF6
14 A = BF4
21 A = PF6
A
N+
A
N+
O
O
3
A = Br
4
A = Br
10 A = BF4
17 A = PF6
11 A = BF4
18 A = PF6
Scheme 1. Molecular structure of the compounds 1–21.

66
M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
et al. [33]. Reagents were placed in a reaction flask with an appro-
priate base and heated with continuous stirring at 65–70 °C for 96–
168 h. Reaction mixture was cooled down to room temperature,
filtered and filtrate containing the raw product was evaporated
to a minimum volume. The final product was extracted by adding
small amounts of diethyl ether or a mixture of diethyl ether and
acetone which caused the precipitation of a white or light yellow
powder. The products were recrystallized from dichloromethane
and dried in vacuo.
Compounds 3–7 (Scheme 1) were synthesized applying the pro-
cedure explained by Albadran and McMurray [42]. Reagents and sol-
vents were placed in a flask with a suitable solvent and refluxed at
70–76 °C for 24–168 h. After cooling to room temperature the mix-
tures were evaporated and the residues were washed with small
amounts of a suitable solvent, i.e., diethyl ether and dried in vacuo.
Compounds 8–21 were synthesized by metathesis between one
of the compounds 1–7 and a compound containing the desired an-
ion. The tetrafluoroborates were synthesized by dissolving the QA
bromide in a minimum volume of deionized water (further on,
water) or other suitable solvent, i.e., acetone, and adding the stoi-
chiometric amount (1:1) of 48–50 wt% solution of HBF4. The mix-
ture was stirred at room temperature for 2–30 min during which
the QA tetrafluoroborate precipitated from the solution or formed
a separate liquid layer. If other solvent than water was used, the
product was obtained by evaporating the solvent. The raw product
was filtered and washed with water until the washings were pH
neutral. The product was recrystallized from an appropriate sol-
vent, i.e., dichloromethane, and dried first in an incubator at
120 °C and then in vacuo. The liquid or waxy products were ex-
tracted with an appropriate solvent, i.e., dichloromethane, and
dried as the solid products.
C
18H24NO2Br [MÀBr]+: 286.18; found 286.14 [MÀBr]+. Elemental
analysis: calculated for C18H24NO2Br: C, 59.02; H, 6.60; N, 3.82.
Found C, 59.35; H, 6.65; N, 3.70.
2.1.4. Triethyl ethoxyethylammonium bromide (3)
Reagents: Triethylamine (10.99 ml, 79.10 mmol), 2-bromoeth-
ylethyl ether (7.40 ml, 66.00 mmol), methanol (25 ml). Reaction
temperature 70 °C and reaction time 72 h. The yield (white pow-
der) was 15.08 g (90%). 1H NMR (CDCl3, 500 MHz, ppm): 1.15
(3H, –O–CH2–CH3), 1.39 (9H, t, N–CH2–CH3), 3.49–3.57 (8H, N–
CH2–CH3, –O–CH2–CH3), 3.72–3.74 (2H, m, N–CH2–CH2–O–),
3.84–3.85 (2H, m, N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz,
ppm): 8.17 (3C, N–CH2–CH3), 14.85 (1C, –O–CH2–CH3), 54.33 (3C,
N–CH2–CH3), 57.50 (1C, N–CH2–CH2–O–), 3.89 (1C, N–CH2–CH2–
O–), 67.05 (1C, –O–CH2–CH3). ESI-TOF MS: m/z calculated for
C10H24NOBr [MÀBr]+: 174.19; found 174.18 [MÀBr]+. Elemental
analysis: calculated for C10H24NOBr: C, 47.25; H, 9.52; N, 5.51.
Found C, 46.37; H, 9.52; N, 5.57.
2.1.5. Tripropyl ethoxyethylammonium bromide (4)
Reagents: Tripropylamine (15.05 ml, 79.10 mmol), 2-bromoeth-
ylethyl ether (7.40 ml, 66.00 mmol), methanol (25 ml). Reaction
temperature 70 °C and reaction time 72 h. The yield (white pow-
der) was 11.54 g (59%). 1H NMR (CDCl3, 500 MHz, ppm): 1.00
(9H, t, N–CH2–CH2–CH3), 1.15 (3H, t, –O–CH2–CH3), 1.73–1.79
(6H, m, N–CH2–CH2–CH3), 3.33–3.37 (6H, m, N–CH2–CH2–CH3),
3.50 (2H, q, –O–CH2–CH3), 3.86 (4H, m, N–(CH2)2–O–). 13C NMR
(CDCl3, 126 MHz, ppm): 10.73 (3C, N–CH2–CH2–CH3), 14.94 (1C,
–O–CH2–CH3), 15.95 (3C, N–CH2–CH2–CH3), 59.21 (1C, N–CH2–
CH2–O), 61.44 (3C, N–CH2–CH2–CH3), 64.12 (1C, N–CH2–CH2–O),
67.06 (1C, –O–CH2–CH3). ESI–TOF MS: m/z calculated for
C13H30NOBr [MÀBr]+: 216.18; found 216.23 [MÀBr]+. Elemental
analysis: calculated for C13H30NOBr: C, 52.70; H, 10.21; N, 4.73.
Found C, 52.45; H, 9.84; N, 4.68.
The hexafluorophosphates were synthesized by dissolving the
QA bromide in a minimum volume of deionized water and adding
the stoichiometric amount (1:1) of KPF6 dissolved in a minimum
amount of water. The mixture was stirred for 30 min at room tem-
perature. The QA hexafluorophosphate precipitated from the solu-
tion or formed a separate liquid layer. The formed precipitate was
filtered, washed with water and recrystallized from an appropriate
solvent, i.e., dichloromethane and dried in vacuo. The liquid raw
products were extracted with an appropriate solvent, evaporated
and dried in vacuo.
2.1.6. Tributyl ethoxyethylammonium bromide (5)
Reagents: Tributylamine (18.84 ml, 79.10 mmol), 2-bromoeth-
ylethyl ether (7.40 ml, 66.00 mmol), methanol (25 ml). Reaction
temperature 70 °C and reaction time 144 h. The yield (white pow-
der) was 15.73 g (71%). 1H NMR (CDCl3, 500 MHz, ppm): 0.98 (9H,
t, N–CH2–CH2–CH2–CH3), 1.15 (3H, t, –O–CH2–CH3), 1.37–1.43 (6H,
m, N–CH2–CH2–CH2–CH3), 1.66–1.72 (6H, m, N–CH2–CH2–CH2–
CH3), 3.36–3.39 (6H, m, N–CH2–CH2–CH2–CH3), 3.50 (2H, q, –O–
CH2–CH3), 3.86 (4H, m, N–(CH2)2–O–). 13C NMR (CDCl3, 126 MHz,
ppm): 13.55 (3C, N–CH2–CH2–CH2–CH3), 14.91 (1C, –O–CH2–
CH3), 19.68 (3C, N–CH2–CH2–CH2–CH3), 24.17 (3C, N–CH2–CH2–
CH2–CH3), 59.24 (1C, N–CH2–CH2–O), 59.82 (3C, N–CH2–CH2–
CH2–CH3), 64.19 (1C, N–CH2–CH2–O), 67.08 (1C, –O–CH2–CH3).
ESI-TOF MS: m/z calculated for C16H36NOBr [MÀBr]+: 258.30;
found 258.30 [MÀBr]+. Elemental analysis: calculated for
C16H36NOBr: C, 56.79; H, 10.72; N, 4.14. Found C, 56.50; H,
10.85; N, 4.16.
2.1.2. Diethoxyethyldimethylammonium bromide (1)
Reagents: 2-Bromoethylethyl ether (8.35 ml, 74.02 mmol),
potassium carbonate (10.22 g, 74.02 mmol) and dimethyl formam-
ide (50 ml). Reaction temperature 70 °C and reaction time 72 h.
The yield (yellow sticky powder) was 2.76 g (28%). 1H NMR (CDCl3,
500 MHz, ppm): 1.13 (6H, t, –O–CH2–CH3), 3.41 (6H, s, N–CH3),
3.49 (4H, q, –O–CH2–CH3), 3.85–3.86 (4H, m, N–CH2–CH2–O–),
3.89–3.90 (4H, m, N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz,
ppm): 14.80 (2C, –O–CH2–CH3), 52.66 (2C, N–CH3), 64.26 (2C, N–
CH2–CH2–O), 64.74 (2C, N–CH2–CH2–O), 66.83 (2C, –O–CH2–CH3).
ESI-TOF MS: m/z calculated for C10H24NBr [MÀBr]+: 190.18; found
190.14 [MÀBr]+. Elemental analysis: calculated for C10H24NBr: C,
44.45; H, 8.95; N, 5.18. Found C, 44.16; H, 8.78; N, 4.85.
2.1.7. Tripentyl ethoxyethylammonium bromide (6)
Reagents: Tripentylamine (22.80 ml, 79.10 mmol), 2-bromoeth-
ylethyl ether (7.40 ml, 66.00 mmol), methanol (25 ml). Reaction
temperature 70 °C and reaction time 144 h. The yield (yellow
sticky powder) was 8.05 g (32%). 1H NMR (CDCl3, 500 MHz,
ppm): 0.91 (9H, t, N–CH2–CH2–CH2–CH2–CH3), 1.17 (3H, t, –O–
CH2–CH3), 1.32–1.41 (12H, m, N–CH2–CH2–(CH2)2–CH3), 1.68–
1.75 (6H, m, N–CH2–CH2–CH2–CH2–CH3), 3.35–3.39 (6H, m, N–
CH2–CH2–CH2–CH2–CH3), 3.52 (2H, q, –O–CH2–CH3), 3.89 (2H, m,
N–CH2–CH2–O–), 3.91–3.93 (2H, m, N–CH2–CH2–O–). 13C NMR
(CDCl3, 126 MHz, ppm): 13.77 (3C, N–CH2–CH2–CH2–CH2–CH3),
14.97 (1C, –O–CH2–CH3), 22.02 (3C, N–CH2–CH2–CH2–CH2–CH3),
22.15 (3C, N–CH2–CH2–CH2–CH2–CH3), 28.42 (3C, N–CH2–CH2–
2.1.3. Di-(4-methoxybenzyl)dimethylammonium bromide (2)
Reagents: 4-Methoxybenzyl bromide (5 g, 24.88 mmol), potas-
sium carbonate (3.77 g, 27.28 mmol) and dimethyl formamide
(25 ml). Reaction temperature 70 °C and reaction time 96 h. The
yield (white powder) was 1.74 g (40%). 1H NMR (CDCl3, 500 MHz,
ppm): 3.03 (6H, s, N–CH3), 3.76 (6H, s, –O–CH3), 5.03 (4H, s, N–
CH2–), 6.85 (4H, d, Ar–H), 7.56 (4H, d, Ar–H). 13C NMR (CDCl3,
126 MHz, ppm): 47.64 (2C, N–CH3), 55.38 (2C, –O–CH3), 67.01
(2C, N–CH2–), 114.48 (4C, Ar–C), 119.37 (1C, Ar–C), 134.78 (4C,
Ar–C), 161.24 (1C, Ar–C). ESI-TOF MS: m/z calculated for

M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
67
CH2–CH2–CH3), 59.37 (1C, N–CH2–CH2–O–), 60.04 (1C, N–CH2–
CH2–CH2–CH2–CH3), 64.27 (1C, N–CH2–CH2–O–), 67.13 (1C, –O–
CH2–CH3). ESI-TOF MS: m/z calculated for C19H42NOBr [MÀBr]+:
300.29; found 300.33 [MÀBr]+. Elemental analysis: calculated for
C19H42NOBr: C, 59.98; H, 11.13; N, 3.68. Found C, 59.73; H,
11.28; N, 3.36.
2.1.12. Tripropyl ethoxyethylammonium tetrafluoroborate (11)
Reagents: Tripropyl ethoxyethylammonium bromide (4) (1.0 g,
3.4 mmol) and HBF4 solution (48–50 wt%). The yield (yellow wax)
was 0.8 g (82%). 1H NMR (CDCl3, 500 MHz, ppm): 0.99 (9H, t, N–
CH2–CH2–CH3), 1.17 (3H, t, –O–CH2–CH3), 1.67–1.75 (6H, m,
N–CH2–CH2–CH3), 3.21–3.24 (6H, m, N–CH2–CH2–CH3), 3.50 (2H,
q, –O–CH2–CH3), 3.52 (2H, m, N–CH2–CH2–O–), 3.78 (2H, m,
N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm): 10.51 (3C, N–
CH2–CH2–CH3), 14.91 (1C, –O–CH2–CH3), 15.49 (3C, N–CH2–CH2–
CH3), 58.48 (1C, N–CH2–CH2–O), 61.12 (3C, N–CH2–CH2–CH3),
63.71 (1C, N–CH2–CH2–O), 66.99 (1C, –O–CH2–CH3). ESI-TOF MS:
m/z calculated for C13H30NOBF4 [MÀBF4]+: 216.23; found 216.20
[MÀBF4]+. Elemental analysis: calculated for C13H30NOBF4: C,
51.50; H, 9.97; N, 4.62. Found C, 50.41; H, 10.13; N, 4.66.
2.1.8. Trihexyl ethoxyethylammonium bromide (7)
Reagents: Trihexylamine (26.70 ml, 79.10 mmol), 2-bromoeth-
ylethyl ether (7.40 ml, 66.00 mmol), methanol (25 ml). Reaction
temperature 70 °C and reaction time 168 h. The yield (white pow-
der) was 11.47 g (41%). 1H NMR (CDCl3, 500 MHz, ppm): 0.88 (9H,
t, N–CH2–CH2–CH2–CH2–CH2–CH3), 1.16 (3H, t, –O–CH2–CH3),
1.28–1.37 (18H, m, N–CH2–CH2–(CH2)3–CH3), 1.66–1.73 (6H, m,
N–CH2–CH2–CH2–CH2–CH2–CH3), 3.34–3.37 (6H, m, N–CH2–CH2–
CH2–CH2–CH2–CH3), 3.51 (2H, q, O–CH2–CH3), 3.87–3.90 (4H, m,
N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm): 13.77 (3C, N–
CH2–CH2–CH2–CH2–CH2–CH3), 14.95 (1C, –O–CH2–CH3), 22.26
(3C, N–CH2–CH2–CH2–CH2–CH2–CH3), 22.35 (3C, N–CH2–CH2–
CH2–CH2–CH2–CH3), 26.01 (3C, N–CH2–CH2–CH2–CH2–CH2–CH3),
31.20 (3C, N–CH2–CH2–CH2–CH2–CH2–CH3), 59.31 (1C, N–CH2–
CH2–O), 60.00 (3C, N–CH2–CH2–CH2–CH2–CH2–CH3), 64.25 (1C,
N–CH2–CH2–O), 67.10 (1C, O–CH2–CH3). ESI-TOF MS: m/z calcu-
lated for C22H48NOBr [MÀBr]+: 342.37; found 342.37 [MÀBr]+. Ele-
mental analysis: calculated for C22H48NOBr: C, 62.54; H, 11.45; N,
3.31. Found C, 63.03; H, 11.45; N, 3.31.
2.1.13. Tributyl ethoxyethylammonium tetrafluoroborate (12)
Reagents: Tributyl ethoxyethylammonium bromide (5) (1.0 g,
3.0 mmol) and HBF4 solution (48–50 wt%). The yield (white pow-
der) was 0.5 g (54%). 1H NMR (CDCl3, 500 MHz, ppm): 0.99 (9H, t,
N–CH2–CH2–CH2–CH3), 1.17 (3H, t, –O–CH2–CH3), 1.36–1.42 (6H,
m, N–CH2–CH2–CH2–CH3), 1.61–1.68 (6H, m, N–CH2–CH2–CH2–
CH3), 3.24–3.28 (6H, m, N–CH2–CH2–CH2–CH3), 3.50 (2H, q, –O–
CH2–CH3), 3.53–3.55 (2H, m, N–CH2–CH2–O–), 3.78 (2H, m,
N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm): 13.49 (3C, N–
CH2–CH2–CH2–CH3), 14.90 (1C, –O–CH2–CH3), 19.59 (3C, N–CH2–
CH2–CH2–CH3), 22.81 (3C, N–CH2–CH2–CH2–CH3), 58.43, (1C,
N–CH2–CH2–O), 59.48 (3C, N–CH2–CH2–CH2–CH3), 63.80 (1C, N–
CH2–CH2–O–), 67.05 (1C, –O–CH2–CH3). ESI-TOF MS: m/z calcu-
lated for C13H30NOBF4 [MÀBF4]+: 258.28; found 258.26 [MÀBF4]+.
Elemental analysis: calculated for C13H30NOBF4: C, 55.66; H,
10.51; N, 4.06. Found C, 55.30; H, 10.49; N, 3.66.
2.1.9. Diethoxyethyldimethylammonium tetrafluoroborate (8)
Reagents: Diethoxyethyldimethylammonium bromide (1)
(1.0 g, 3.7 mmol) and HBF4 solution (48–50 wt%). The yield (brown
gel) was 1.0 g (97%). 1H NMR (CDCl3, 500 MHz, ppm): 1.19 (6H, t, –
O–CH2–CH3), 3.23 (6H, s, N–CH3), 3.53 (4H, q, –O–CH2–CH3), 3.62–
3.66 (4H, m, N–CH2–CH2–O–), 3.84–3.86 (4H, m, N–CH2–CH2–O–).
13C NMR (CDCl3, 126 MHz, ppm): 14.85 (2C, –O–CH2–CH3), 52.48
(2C, N–CH3), 64.06 (2C, N–CH2–CH2–O), 64.96 (2C, N–CH2–CH2–
O), 66.89 (2C, –O–CH2–CH3). ESI-TOF MS: m/z calculated for
C10H24NBF4 [MÀBF4]+: 190.18; found 190.14 [MÀBF4]+. Elemental
analysis: calculated for C10H24NBF4: C, 43.34; H, 8.73; N, 5.05.
Found C, 41.13; H, 8.18; N, 5.15.
2.1.14. Tripentyl ethoxyethylammonium tetrafluoroborate (13)
Reagents: Tripentyl ethoxyethylammonium bromide (6) (1.0 g,
2.6 mmol) and HBF4 solution (48–50 wt%). The yield (yellow sticky
powder) was 0.8 g (75%). 1H NMR (CDCl3, 500 MHz, ppm): 0.91
(9H, t, N–CH2–CH2–CH2–CH2–CH3), 1.17 (3H, t, –O–CH2–CH3),
1.33–1.40 (12H, m, N–CH2–CH2–(CH2)2–CH3), 1.62–1.70 (6H, m,
N–CH2–CH2–CH2–CH2–CH3), 3.23–3.26 (6H, m, N–CH2–CH2–CH2–
CH2–CH3), 3.50 (2H, q, –O–CH2–CH3), 3.54–3.55 (2H, m, N–CH2–
CH2–O–), 3.76–3.77 (2H, m, N–CH2–CH2–O–). 13C NMR (CDCl3,
126 MHz, ppm): 13.72 (3C, N–CH2–CH2–CH2–CH2–CH3), 14.91
(1C, –O–CH2–CH3), 21.57 (3C, N–CH2–CH2–CH2–CH2–CH3), 23.18
(3C, N–CH2–CH2–CH2–CH2–CH3), 28.25 (3C, N–CH2–CH2–CH2–
CH2–CH3), 58.39 (1C, N–CH2–CH2–O–), 59.61 (1C, N–CH2–CH2–
CH2–CH2–CH3), 63.80 (1C, N–CH2–CH2–O–), 67.04 (1C, –O–CH2–
CH3). ESI-TOF MS: m/z calculated for C19H42NOBF4 [MÀBF4]+:
300.33; found 300.26 [MÀBF4]+. Elemental analysis: calculated
for C19H42NOBF4: C, 58.93; H, 10.93; N, 3.62. Found C, 58.66; H,
11.06; N, 3.59.
2.1.10. Di-(4-methoxybenzyl)dimethylammonium tetrafluoroborate (9)
Reagents: Di-(4-methoxybenzyl)dimethylammonium bromide
(2) (1.0 g, 2.7 mmol) and HBF4 solution (48–50 wt%). The yield
(white powder) was 0.9 g (88%). 1H NMR (CDCl3, 500 MHz, ppm):
2.85 (6H, s, N–CH3), 3.79 (6H, s, –O–CH3), 4.58 (4H, s, N–CH2–),
6.89 (4H, d, Ar–H), 7.44 (4H, d, Ar–H). 13C NMR (CDCl3, 126 MHz,
ppm): 47.41 (2C, N–CH3), 55.35 (2C, –O–CH3), 67.94 (2C, N–CH2–
), 114.62 (4C, Ar–C), 118.86 (2C, Ar–C), 134.57 (4C, Ar–C), 161.38
(2C, Ar–C). ESI-TOF MS: m/z calculated for C18H24NO2BF4
[MÀBF4]+; 286.18 found 286.11 [MÀBF4]+. Elemental analysis: cal-
culated for C18H24NO2BF4: C, 57.93; H, 6.48; N, 3.75. Found C,
58.12; H, 6.57; N, 3.44.
2.1.15. Trihexyl ethoxyethylammonium tetrafluoroborate (14)
Reagents: Trihexyl ethoxyethylammonium bromide (7) (1.0 g,
2.4 mmol) and HBF4 solution (48–50 wt%). The yield (yellow sticky
powder) was 0.9 g (85%). 1H NMR (CDCl3, 500 MHz, ppm): 0.90 (9H,
t, N–CH2–CH2–CH2–CH2–CH2–CH3), 1.18 (3H, t, –O–CH2–CH3),
1.29–1.37 (18H, m, N–CH2–CH2–(CH2)3–CH3), 1.63–1.67 (6H, m,
N–CH2–CH2–CH2–CH2–CH2–CH3), 3.23–3.26 (6H, m, N–CH2–CH2–
CH2–CH2–CH2–CH3), 3.51 (2H, q, O–CH2–CH3), 3.56–3.58 (2H, m,
N–CH2–CH2–O–), 3.78–3.79 (2H, m, N–CH2–CH2–O–). 13C NMR
(CDCl3, 126 MHz, ppm): 13.79 (3C, N–CH2–CH2–CH2–CH2–CH2–
CH3), 14.93 (1C, –O–CH2–CH3), 21.88 (3C, N–CH2–CH2–CH2–CH2–
CH2–CH3), 22.34 (3C, N–CH2–CH2–CH2–CH2–CH2–CH3), 25.89 (3C,
N–CH2–CH2–CH2–CH2–CH2–CH3), 31.09 (3C, N–CH2–CH2–CH2–
CH2–CH2–CH3), 58.48 (1C, N–CH2–CH2–O), 59.67 (3C, N–CH2–
CH2–CH2–CH2–CH2–CH3), 63.85 (1C, N–CH2–CH2–O), 67.09 (1C,
2.1.11. Triethyl ethoxyethylammonium tetrafluoroborate (10)
Reagents: Triethyl ethoxyethylammonium bromide (3) (1.0 g,
4.3 mmol) and HBF4 solution (48–50 wt%). The yield (clear color-
less gel) was 0.9 g (79%). 1H NMR (CDCl3, 500 MHz, ppm): 1.18
(3H, t, –O–CH2–CH3), 1.34 (9H, t, N–CH2–CH3), 3.41 (6H, q, N–
CH2–CH3), 3.47 (2H, m, N–CH2–CH2–O–), 3.52 (2H, q, –O–CH2–
CH3), 3.80 (2H, m, N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz,
ppm): 7.57 (3C, N–CH2–CH3), 14.86 (1C, –O–CH2–CH3), 53.96 (3C,
N–CH2–CH3), 56.91 (1C, N–CH2–CH2–O–), 63.59 (1C, N–CH2–CH2–
O–), 67.07 (1C, –O–CH2–CH3). ESI-TOF MS: m/z calculated for
C10H24NOBF4 [MÀBF4]+: 174.13; found 174.13 [MÀBF4]+. Elemen-
tal analysis: calculated for C10H24NOBF4: C, 46.00; H, 9.26; N,
5.36. Found C, 45.63; H, 10.13; N, 5.72.

68
M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
O–CH2–CH3). ESI-TOF MS: m/z calculated for C22H48NOBF4
[MÀBF4]+: 342.37; found 342.35 [MÀBF4]+. Elemental analysis: cal-
culated for C22H48NOBF4: C, 61.53; H, 11.27; N, 3.26. Found C,
61.41; H, 11.27; N, 2.96.
N–CH2–CH2–CH2–CH3), 1.60–1.66 (6H, m, N–CH2–CH2–CH2–CH3),
3.31–3.25 (6H, m, N–CH2–CH2–CH2–CH3), 3.48–3.53 (4H, m, N–
CH2–CH2–O–CH2–CH3), 3.76–3.77 (2H, m, N–CH2–CH2–O–). 13C
NMR (CDCl3, 126 MHz, ppm): 13.45 (3C, N–CH2–CH2–CH2–CH3),
14.87 (1C, –O–CH2–CH3), 19.55 (3C, N–CH2–CH2–CH2–CH3), 23.78
(3C, N–CH2–CH2–CH2–CH3), 58.42 (1C, N–CH2–CH2–O), 59.52 (3C,
N–CH2–CH2–CH2–CH3), 63.68 (1C, N–CH2–CH2–O–), 67.14 (1C,
–O–CH2–CH3). ESI-TOF MS: m/z calculated for C16H36NOPF6
[MÀPF6]+: 258.28; found 258.26 [MÀPF6]+. Elemental analysis: cal-
culated for C16H36NOPF6: C, 47.63; H, 8.99; N, 3.47. Found C, 47.93;
H, 9.20; N, 3.48.
2.1.16. Diethoxyethyldimethylammonium hexafluorophosphate (15)
Reagents: Diethoxyethyldimethylammonium bromide (1)
(1.0 g, 3.7 mmol) and KPF6 (0.68 g, 3.7 mmol). The yield (yellow
gel) was 0.8 g (64%). 1H NMR (CDCl3, 500 MHz, ppm): 1.1 (6H, t,
–O–CH2–CH3), 3.19 (6H, s, N–CH3), 3.52 (4H, q, –O–CH2–CH3),
3.57–3.59 (4H, m, N–CH2–CH2–O–), 3.81–3.83 (4H, m, N–CH2–
CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm): 14.79 (2C, –O–CH2–
CH3), 52.51 (2C, N–CH3), 63.91 (2C, N–CH2–CH2–O), 65.01 (2C,
N–CH2–CH2–O), 66.87 (2C, –O–CH2–CH3). ESI-TOF MS: m/z calcu-
lated for C10H24NO2PF6 [MÀPF6]+: 190.18; found 190.17 [MÀPF6]+.
Elemental analysis: calculated for C10H24NO2PF6: C, 35.82; H, 7.22;
N, 4.18. Found C, 35.85; H, 7.04; N, 4.04.
2.1.21. Tripentyl ethoxyethylammonium hexafluorophosphate (20)
Reagents: Tripentyl ethoxyethylammonium bromide (6) (1.0 g,
2.6 mmol) and KPF6 (0.48 g, 2.6 mmol). The yield (white powder)
was 1.0 g (85%). 1H NMR (CDCl3, 500 MHz, ppm): 0.92 (9H, t, N–
CH2–CH2–CH2–CH2–CH3), 1.18 (3H, t, O–CH2–CH3), 1.31–1.41
(12H, m, N–CH2–CH2–(CH2)2–CH3), 1.61–1.67 (6H, m, N–CH2–
CH2–CH2–CH2–CH3), 3.20–3.24 (6H, m, N–CH2–CH2–CH2–CH2–
CH3), 3.48–3.53 (4H, m, N–CH2–CH2–O–CH2–CH3), 3.75–3.76 (2H,
m, N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm): 13.71 (3C,
N–CH2–CH2–CH2–CH2–CH3), 14.89 (1C, O–CH2–CH3), 21.55 (3C,
N–CH2–CH2–CH2–CH2–CH3), 22.07 (3C, N–CH2–CH2–CH2–CH2–
CH3), 28.20 (3C, N–CH2–CH2–CH2–CH2–CH3), 58.38 (1C, N–CH2–
CH2–O–), 59.66 (3C, N–CH2–CH2–CH2–CH2–CH3), 63.69 (1C,
N–CH2–CH2–O–), 67.14 (1C, O–CH2–CH3). ESI-TOF MS: m/z calcu-
lated for C19H42NOPF6 [MÀPF6]+: 300.32; found 300.32 [MÀPF6]+.
Elemental analysis: calculated for C19H42NOPF6: C, 51.22; H, 9.50;
N, 3.14. Found C, 51.60; H, 9.78; N, 3.18.
2.1.17. Di-(4-methoxybenzyl)dimethylammonium
hexafluorophosphate (16)
Reagents: Di-(4-methoxybenzyl)dimethylammonium bromide
(2) (1.0 g, 2.7 mmol) and KPF6 (0.50 g, 2.7 mmol). The yield (white
crystals) was 0.7 g (63%). 1H NMR (DMSO, 500 MHz, ppm): 2.78
(6H, s, N–CH3), 3.81 (6H, s, –O–CH3), 4.47 (4H, s, N–CH2–), 7.06
(4H, d, Ar–H), 7.49 (4H, d, Ar–H). 13C NMR (DMSO, 126 MHz,
ppm): 47.57 (2C, N–CH3), 55.23 (2C, –O–CH3), 66.67 (2C, N–CH2–
), 114.28 (4C, Ar–C), 119.67 (1C, Ar–C), 134.44 (4C, Ar–C), 160.60
(1C, Ar–C). ESI-TOF MS: m/z calculated for C18H24NO2PF6 [MÀPF6]+:
286.13: found 286.13 [MÀPF6]+. Elemental analysis: calculated for
C18H24NO2PF6: C, 50.12; H, 5.61; N, 3.25. Found C, 50.43; H, 5.65; N,
2.74.
2.1.22. Trihexyl ethoxyethylammonium hexafluorophosphate (21)
Reagents: Trihexyl ethoxyethylammonium bromide (7) (1.0 g,
2.4 mmol) and KPF6 (0.44 g, 2.4 mmol). The yield (white powder)
was 1.0 g (89%). 1H NMR (CDCl3, 500 MHz, ppm): 0.89 (9H, t, N–
CH2–CH2–CH2–CH2–CH2–CH3), 1.18 (3H, t, O–CH2–CH3), 1.32–1.37
(18H, m, N–CH2–CH2–(CH2)3–CH3), 1.60–1.65 (6H, m, N–CH2–
CH2–CH2–CH2–CH2–CH3), 3.20–3.23 (6H, m, N–CH2–CH2–CH2–
CH2–CH2–CH3), 3.48–3.53 (4H, m, N–CH2–CH2–O–CH2–CH3),
3.75–3.76 (2H, m, N–CH2–CH2–O–CH2–CH3). 13C NMR (CDCl3,
126 MHz, ppm): 13.77 (3C, N–CH2–CH2–CH2–CH2–CH2–CH3),
14.90 (1C, O–CH2–CH3), 21.82 (3C, N–CH2–CH2–CH2–CH2–CH2–
CH3), 22.33 (3C, N–CH2–CH2–CH2–CH2–CH2–CH3), 25.81 (3C,
N–CH2–CH2–CH2–CH2–CH2–CH3), 31.04 (3C, N–CH2–CH2–CH2–
CH2–CH2–CH3), 58.39 (1C, N–CH2–CH2–O–), 59.68 (3C, N–CH2–
CH2–CH2–CH2–CH2–CH3), 63.70 (1C, N–CH2–CH2–O–), 67.15 (1C,
O–CH2–CH3). ESI-TOF MS: m/z calculated for C22H48NOPF6
[MÀPF6]+: 342.37; found 342.32 [MÀPF6]+. Elemental analysis: cal-
culatedforC22H48NOPF6:C, 54.19;H, 9.92;N, 2.87. FoundC, 54.47;H,
10.01; N, 2.50.
2.1.18. Triethyl ethoxyethylammonium hexafluorophosphate (17)
Reagents: Triethyl ethoxyethylammonium bromide (3) (1.0 g,
4.3 mmol) and KPF6 (0.80 g, 4.3 mmol). The yield (yellow gel)
was 1.1 g (81%). 1H NMR (CDCl3, 500 MHz, ppm): 1.18 (3H, t, –O–
CH2–CH3), 1.34 (9H, t, N–CH2–CH3), 3.36 (6H, q, N–CH2–CH3),
3.40–3.42 (2H, m, N–CH2–CH2–O–), 3.52 (2H, q, –O–CH2–CH3),
3.77 (2H, m, N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm):
7.44 (3C, N–CH2–CH3), 14.81 (1C, –O–CH2–CH3), 53.97 (3C, N–
CH2–CH3), 56.87 (1C, N–CH2–CH2–O–), 63.44 (1C, N–CH2–CH2–O–
), 67.09 (1C, –O–CH2–CH3). ESI-TOF MS: m/z calculated for
C10H24NOPF6 [MÀPF6]+: 174.19; found 174.15 [MÀPF6]+. Elemental
analysis: calculated for C10H24NOPF6: C, 37.62; H, 7.58; N, 4.39.
Found C, 37.39; H, 7.37; N, 4.42.
2.1.19. Tripropyl ethoxyethylammonium hexafluorophosphate (18)
Reagents: Tripropyl ethoxyethylammonium bromide (4) (1.0 g,
3.4 mmol) and KPF6 (0.62 g, 3.4 mmol). The yield (white powder)
was 0.9 g (77%). 1H NMR (CDCl3, 500 MHz, ppm): 0.99 (9H, t, N–
CH2–CH2–CH3), 1.18 (3H, t, –O–CH2–CH3), 1.66–1.74 (6H, m, N–
CH2–CH2–CH3), 3.18–3.21 (6H, m, N–CH2–CH2–CH3), 3.46–3.47
(2H, m, N–CH2–CH2–O–), 3.50 (2H, q, –O–CH2–CH3), 3.76 (2H, m,
N–CH2–CH2–O–). 13C NMR (CDCl3, 126 MHz, ppm): 10.42 (3C, N–
CH2–CH2–CH3), 14.88 (1C, –O–CH2–CH3), 15.43 (3C, N–CH2–CH2–
CH3), 58.47 (1C, N–CH2–CH2–O), 61.14 (3C, N–CH2–CH2–CH3),
63.56 (1C, N–CH2–CH2–O), 67.04 (1C, –O–CH2–CH3). ESI-TOF MS:
m/z calculated for C13H30NOPF6 [MÀPF6]+: 216.23; found 216.22
[MÀPF6]+. Elemental analysis: calculated for C13H30NOPF6: C,
43.21; H, 8.37; N, 3.88. Found C, 43.25; H, 8.67; N, 3.92.
2.2. Characterization in the liquid state
The formation of the desired products was confirmed by 1H and
13C NMR spectroscopy and ESI-TOF mass spectroscopy. Elemental
analysis was used to verify the purity of the formed compounds.
1H and 13C NMR spectra were measured in CDCl3 (or appropriate
solvent) at 30 °C by using a Bruker Avance DRX 500 NMR spec-
trometer operating at 500 MHz for 1H and at 126 MHz for 13C. Mass
spectra were obtained by using the Micromass LCT time of flight
(TOF) mass spectrometer with electrospray ionization (ESI). The
measurements were made by using the positive ion mode with a
sample concentration of 25 mg/l in a methanol solution. When
necessary, the absence of the bromide-ion was confirmed by using
the negative ion mode. The elemental analyses were carried out
with Vario EL III CHN elemental analyzer by using sample weights
of 2–8 mg.
2.1.20. Tributyl ethoxyethylammonium hexafluorophosphate (19)
Reagents: Tributyl ethoxyethylammonium bromide (5) (1.0 g,
3.0 mmol) and KPF6 (0.54 g, 3.0 mmol). The yield (white powder)
was 1.0 g (77%). 1H NMR (CDCl3, 500 MHz, ppm): 0.99 (9H, t, N–
CH2–CH2–CH2–CH3), 1.18 (3H, t, –O–CH2–CH3), 1.38–1.42 (6H, m,

M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
69
2.3. X-ray single crystal diffraction structures
was carried out using melting points of five reference materials
(In, Sn, Zn, Al, Au) at given heating rate. The weight balance was
calibrated by measuring a standard weight at room temperature.
The sample weights used in the measurements were about 5–
20 mg.
The thermal transitions of the QA salts were examined on a
power compensation type Perkin Elmer Pyris 1 DSC. DSC measure-
ments were carried out under nitrogen atmosphere (flow rate
The crystal structures for compounds 2, 3, 9 and 16 were deter-
mined by single crystal X-ray diffraction. Colorless single crystals
were obtained from mixture of dichloromethane and ethyl acetate
or from slow evaporation of dichloromethane in dry air atmo-
sphere. Some of the compounds remained as gels or waxes despite
of continuous efforts to solidify them.
The crystallographic data were recorded with a Kappa APEX II
diffractometer at À120 °C using graphite monochromatized Mo
50 ml/min) using 50
made by using a 30
l
l sealed aluminum pans. The sealing was
l
l aluminum pan with pinholes to ascertain
Ka
(k = 0.71073 Å) radiation. The data were processed with Den-
good thermal contact between the sample and a pan, and to min-
imize the free volume inside the pan. The temperature calibration
was made by using two standard materials (n-decane and In) and
the energy calibrations by an indium standard (28.45 J gÀ1). The
samples were heated at the heating rate of 5 °C/min either from
À60 or À50 °C to a temperature close to the decomposition tem-
perature of each compound and then cooled at the heating rate
of 5 °C/min back to the starting temperature. The cycle was re-
peated twice. The sample weights used were about 2–20 mg.
zo-SMN v0.95.373 [43,44] and the absorption correction for all
compounds was performed using SADABS [45]. The structures
were solved by using direct methods (SHELXS-97 [46] or SIR2004
[47] and refined on F2 by full matrix least squares techniques
(SHELXL-97 [48]) by using anisotropic displacement parameters
for non-hydrogen atoms. All hydrogen atoms were calculated to
their ideal positions as riding atoms by using isotropic displace-
ment parameters. The isotropic displacement parameters were
fixed to be 20–50% larger than those of the attached non-hydrogen
atom. The programs Diamond [49] and Mercury [50] were used for
depicting the crystal structures.
2.6. Solid state NMR
13C CP/MAS NMR spectrum was measured to work out the mor-
phology of compound 2. The spectrum was measured with Bruker
Avance 400 spectrometer equipped with 4 mm standard bore CD/
MAS probe-head using 4 mm diameter zirconia rotor and Kel-F
caps at ambient temperature. The contact time was 2 ms.
2.4. X-ray powder diffraction analyses
The X-ray powder diffraction data was measured with PANalyt-
´
ical XPert PRO diffractometer in Bragg–Brentano geometry using
Johansson monochromator ( 1 setup) to produce pure Cu K 1 radi-
a
a
ation (1.5406 Å; 40 kV, 30 mA) and step-scan technique in 2h range
of 4–70°. The data was collected by XCelerator detector in contin-
3. Results and discussion
´
uous scanning mode with a step size of 0.0167° and using counting
time of 40–100 s per step. Programmable divergence slit (PDS) was
used to set irradiated length on sample to 10 mm together with 10
or 15 mm incident beam mask. Soller slits of 0.02° rad were used
both on incident and diffracted beam side together with anti-scat-
ter slits (4° and 8.7 mm, respectively). The diffraction data was
converted from automatic slit mode (ADS) to a fixed slit mode
(FDS) data in Highscore Plus v. 2.2c software package before fur-
ther analyses by the same program package. Powder samples were
prepared either on standard steel plate holders (having 10 or
16 mm radius cavity) or on a silicon-made zero-background holder
(petrolatum jelly was used as an adhesive). The simulated powder
diffraction patterns were calculated by the program Mercury [50]
from the CIF-files of the compounds under investigation.
3.1. Characterization in liquid and solid state
According to the 1H, 13C NMR spectra and mass spectra, all of
the synthesized QA salts succeeded with rational yields for our
purposes (the optimization of preparing methods were out of
scope in this study) and appeared to be pure and free of reaction
solvents. In case of compounds 8–21 the absence of the bromide-
ion was confirmed by mass spectra. However, compounds 3, 10
and 17 are exceptions containing, according to the NMR-studies
traces of triethylamine hydrobromide, a side product from the syn-
thesis. The low melting and waxy tetrafluoroborates are somewhat
hygroscopic and in these circumstances the elemental analysis of
these compounds is challenging. The bromide and tetrafluorobo-
rate salts were soluble in water, and the hexafluorophosphates
were insoluble in water, as expected. All compounds were also sol-
uble in dichloromethane, chloroform and acetone but insoluble in
diethyl ether and hexane. The hexafluorophosphates with longer
alkyl chains dissolved in acetone but the rest of the compounds
were insoluble.
2.5. Thermal properties
The thermal decomposition paths of compounds 1–21 were ob-
tained with Perkin Elmer Diamond TG/DTA. Measurements were
carried out using 45 ll open platinum pans under air atmosphere
(135 ml/min) at a temperature range of 25–900 °C. To increase
temperature resolution, heating rate was controlled automatically
(auto-step mode) by monitoring the weight loss gradient using 25
3.2. X-ray single crystal diffraction structure analysis
After a successful crystallization four crystal structures were
solved. The crystallographic data of compounds 2, 3, 9 and 16 are
presented in Table 1 and the selected bond angles and distances
in Table 2. The structure determination from the powder diffrac-
tion data was also tested for some of the more crystalline salts such
as 4 and 18. However, either unambiguous cell candidates were
not found, or in case of found cells the quality of the powder dif-
fraction data was not adequate for successful determination of
the powder structure.
Compound 2 crystallizes in the orthorhombic space group
P212121 having one cation in a slightly distorted W-conformation
and one BrÀ anion in the asymmetric unit as can be seen in
Fig. 1. The W-conformation resembles the packing of two similar
compounds, dimethyldi-(4-methylbenzyl)ammonium bromide
and 175 lg/min thresholds with 20 s heating/cooling rate update
interval to slow down from, or speed up to the nominal heating
rate of 10 °C/min. In practice, primary decomposition of a sample
occurred at isothermal conditions readily after the first initiation
of the weight loss over 175
for the heating rate back to nominal rate was set as low as
25
lg/min as the speeding up threshold
l
g/min. The observed isothermal steps were ꢀ20 min, at short-
est, prolonging to ꢀ90 min on some of the QA salts. By this heating
method, more precise decomposition temperatures can be ac-
quired as the onset is less affected by the overshoot, that constant
and relatively fast heating rates may cause, due to slow kinetics
and low heat conductivities; property of many ionic liquids
[51,52]. The temperature calibration of the TG/DTA equipment

70
M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
Table 1
Crystallographic data for compounds 2, 3, 9 and 16.
Compound
2
3
9
16
Formula
Mr (g/mol)
Crystal system
Space group
a (Å)
[C18H24NO2]Br
366.29
[C10H24NO]Br Á1/8 H2O
256.46
[C18H24NO2]BF4
373.19
[C18H24NO2]PF6
431.35
Orthorhombic
P212121 (No. 19)
8.8971(18)
9.3222(19)
21.026(4)
90
1743.9(6)
4
1.395
Monoclinic
P21/n (No. 14)
8.7740(18)
9.0660(18)
33.063(7)
97.18(3)
2609.4(9)
8
1.304
Orthorhombic
Pna21 (No. 33)
20.527(4)
8.1957(16)
11.164(2)
90
1878.2(6)
4
1.320
Monoclinic
P21/c (No. 14)
8.5580(17)
21.159(4)
10.806(2)
92.66(3)
1954.6(6)
4
b (Å)
c (Å)
b (°)
V (Å3)
Z
qcalcd (g/cm3)
1.466
0.210
l
(mmÀ1
)
2.364
3.123
0.111
F(000)
760
1080
784
896
Crystal size (mm3)
h range (degree)
Reflections collected
Independent reflections
Data/restraints/parameters
GooF
0.1 Â 0.5 Â 0.1
0.2 Â 0.4 Â 0.6
2.34–28.64
13,294
5390
5390/0/246
1.021
0.1 Â 0.3 Â 0.6
2.68–28.85
19,278
2506
2506/1/239
1.103
0.2 Â 0.2 Â 0.2
2.39–29
2.57–29
27,894
4496
4496/0/203
1.044
31,531
4990
4990/0/257
1.125
R (int)
0.055
0.0593
0.0819
0.092
Final R indices [I > 2
r
(I)]
R1 = 0.0327,
wR2 = 0.0607
R1 = 0.0479,
wR2 = 0.0649
0.25 and À0.32
0.065(9)
R1 = 0.0619,
wR2 = 0.1082
R1 = 0.1344,
wR2 = 0.1279
0.88 and À0.93
–
R1 = 0.0782,
wR2 = 0.1271
R1 = 0.1476,
wR2 = 0.1461
0.25 and À0.31
–
R1 = 0.0890,
wR2 = 0.2202
R1 = 0.1324,
wR2 = 0.2390
0.83 and À0.36
–
R indices (all data)
Largest diff. peak/hole (e/Å3)
Flack parameter
3.00(1) Å and a third cation with a bond distance of 2.98(1) Å.
There is also a weak C–HÁ Á ÁBr bond between the anion and an adja-
cent methyl group, bond length is 2.93(1) Å. The bond angles vary
between 135° and 176°. Cations are also packed via intermolecular
Table 2
Selected bond lengths (Å) and bond angles (degrees) with e.s.d.s for compounds 2, 3, 9
and 16.
Compound
2
3
9
16
edge to face
seen in Fig. 2b.
p–p interactions between the phenyl groups as can be
N(1)–C(11)
N(1)–C(21)
N(1)–C(31)
N(1)–C(41)
C(11)–N(1)–C(21)
C(11)–N(1)–C(31)
C(11)–N(1)–C(41)
C(21)–N(1)–C(31)
C(21)–N(1)–C(41)
C(31)–N(1)–C(41)
1.537(5)
1.530(5)
1.495(6)
1.499(6)
106.4(3)
110.1(3)
110.6(3)
109.7(3)
110.2(3)
109.8(4)
1.519(6)
1.534(6)
1.522(6)
1.513(6)
109.0(4)
108.0(4)
111.7(4)
110.3(4)
108.5(4)
109.4(4)
1.503(7)
1.527(8)
1.481(8)
1.503(8)
106.9(5)
110.4(5)
109.8(5)
111.1(5)
110.0(5)
108.7(6)
1.534(5)
1.528(5)
1.504(5)
1.496(5)
109.4(3)
110.4(3)
110.9(3)
106.3(3)
110.7(3)
109.0(3)
Compound 3 crystallizes in the monoclinic space group P21/n.
The ion-pair ordering and the crystal packing are presented in Figs.
3 and 4. The asymmetric unit is composed of two cations and two
Br-anions together with one quarter of a water molecule (Fig. 3).
The cations pack in a tail-to-tail and head-to-head conformations
forming layers along the crystallographic a-axis, as can be seen
in Fig. 4. The water molecule, along with the second bromine atom
in asymmetric unit, is found inside a pocket formed by the cations.
Within the pocket there are two possible locations for the water
molecule and there are two pockets in the unit cell. The water mol-
ecule can be located randomly at each of the four possible posi-
tions. Based on a quick search of CSD database [55], compounds
with a similar geometrical ordering between bromine and water
molecule have also been reported earlier [56]. The packing is fur-
ther stabilized by weak hydrogen bonds between the cations and
anions. Each bromine atom has a C–HÁ Á ÁBrÀ (<3.0 Å) bond to four
cations, bond distances for Br1 are 2.81(1)–2.88(4) Å and for Br2
2.86(4)–2.98(1) Å. There are also interactions between the water
and the BrÀ anion although only the Br2-signed bromine atom in
the asymmetric unit forms hydrogen bonds with the water mole-
cule. Each water molecule is connected to two bromine atoms with
a bond angle of 129.7° and the distances between the water oxygen
and the bromine atoms being 2.79(3) and 3.53(4) Å, respectively.
Due to low site occupancy of the oxygen, water-hydrogens could
not be found from the electron density map. The shortest distance
between the bromine and the nitrogen atom is 4.53(4) Å. The other
bromine atom is located inside the layer and has a minimum
distance of 4.52(4) Å to the nitrogen atom.
Fig. 1. The molecular structure and labeling scheme of compound 2.
and analogous chloride.[53,54] The observed distortion is caused
by different orientation of the methoxy group compared to the
methyl group at the para position of the phenyl group. The packing
(Fig. 2a) is affected by Coulombic interactions between the cations
and anions, the shortest distance between the nitrogen and bro-
mine atoms being 4.13(1) Å.
Compound 9 crystallizes in the orthorhombic space group
Pna21. It differs from the analogous bromide (2) by the orientation
of the methyls on methoxy groups, which point at the opposite
directions. The asymmetric unit is presented in Fig. 5, showing
one cation in a slightly distorted W-conformation together with
Each cation is connected to the BrÀ anion by a weak C–HÁ Á ÁBr
bond (<3.0 Å), with a bond distance of 2.77(1) Å between H and
Br. The same BrÀ anion is connected to a second cation with two
C–HÁ Á ÁBrÀ bonds, bond distances varying from 2.91(1) to

M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
71
Fig. 2. (a) The packing of compound 2 viewed along the crystallographic a-axis. The weak hydrogen bonds are shown as dashed lines. (b) Edge to face
p–
p
interactions
forming the network of connections between cations. Some of the cations and anions have been removed for clarity.
anion. The packing is stabilized by Coulombic interactions and
C–HÁ Á ÁF hydrogen bonds (<2.65 Å) can also be observed inside
the crystal lattice. The shortest distance between the nitrogen
and phosphorous atom is 4.86 Å and between nitrogen and fluorine
3.73 Å. Each anion forms 14 hydrogen bonds, six of which are
bifurcated, with the six nearest cations as can be seen in Fig. 9a.
The length of the C–HÁ Á ÁF bonds varies between 2.43(1) and
2.65(3) Å and bond angles between 131° and 168°. Weak intermo-
lecular edge to face p–p interactions connects the cations to each
other causing the formation of chain-like structures along the crys-
tallographic c-axis (Fig. 9b). The residual electron density is located
close (ꢀ1 Å) to the phosphorous atom.
3.3. X-ray powder diffraction analysis
The experimental powder diffraction data for compounds 2, 3
and 16 are presented in Fig. 10 together with the simulated pat-
terns obtained from the single crystal structure parameters. The
simulated data were obtained by Mercury [50]. The similarities be-
tween the bulk composition and the single crystals are obvious for
compounds 3 and 16 as can be seen in Fig. 10. Compound 2 forms
two different polymorphs in microcrystalline bulk form, which was
also confirmed by the solid state NMR measurements. Based on the
powder diffraction data, the first polymorph is consistent with the
single crystal data. Considering the fact that the result of the ele-
mental analysis is exact and the NMR spectra are unambiguous,
the existence of a second polymorph is confirmed. Additionally, a
shoulder in the DSC scan can be observed suggesting that the
two polymorphs have melting points very close to each other.
However, the structure of the second polymorph remained un-
known since the indexing of a second polymorph from a mixture
cannot be made unambiguously due to the peak overlap with the
dominating peaks of the main component.
Fig. 3. The molecular structure and labeling scheme of compound 3.
À
one BF4 anion. The packing (Fig. 6) is affected by Coulombic inter-
actions; the shortest distance between a fluorine atom and the
nitrogen atom being F1Á Á ÁN1 3.81(1) Å. Each anion also share ten
C–HÁ Á ÁF hydrogen bonds (<2.65 Å) with six nearest cations. The
C–HÁ Á ÁF bond distance varies between 2.37(1) and 2.64(1) Å with
bond angles from 115° to 162°.
Compound 16 crystallizes in a monoclinic space group P21/c
deviating also from the analogous bromide salt (2). The ion-pair
ordering and the crystal packing are presented in Figs. 7 and 8.
The asymmetric unit consists of one cation, in which the two phe-
À
nyl groups are strongly turned towards each other, and one PF6

72
M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
Fig. 4. The packing of compound 3 viewed along the crystallographic b-axis. The hydrogens have been removed for clarity.
Compounds 4, 9 and 12 were crystalline or semi-crystalline (see
in Table 3. The results on the second heating scans are also in-
cluded in the Table 3 to emphasize the tendency for crystallization
when compounds are cooled from a liquid state and reheated
again. Many of the ionic liquids including some of the salts re-
ported in this study can form glassy states via a supercooled liquid
state and thus these compounds can be cooled down without ini-
tiation of crystallization [23]. Some of the ionic liquid salts in
glassy state can be recrystallized via a cold crystallization when
heated above the glass transition temperature, whereas some of
the salts will enter to a supercooled liquid state and simply form
new glassy state when cooled again below the glass forming
temperature.
supplementary material Fig. S1) but did not form single crystals
suitable for measurements. For the compounds 16 and 18–21 the
crystallinity of the compounds decreases as the alkyl chain length
increases (Fig. S2). Due to the platy crystals, especially on com-
pounds 3, 4, 12 and 18–21 (microscopy studies revealed the crys-
tals to be nearly two-dimensional and stacked on piles), few
diffraction peaks at low 2h-angle range showed significant pre-
ferred orientation, which in part caused the powder structure
determinations being unsuccessful. For the semisolids (waxes,
gels) powder diffraction measurements were not made.
3.4. Thermal properties
All the tabulated temperature values from the DSC measure-
ments were taken at peak maximum because rather broad melting
The summarized results of the DSC measurements together
with the decomposition temperatures (by TG/DTA) are presented
Fig. 5. The molecular structure and labeling scheme of compound 9.
Fig. 7. The molecular structure and labeling scheme of compound 16.
Fig. 6. The packing of compound 9 viewed along the crystallographic b-axis.

M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
73
Fig. 8. The packing of compound 16 viewed along the crystallographic c-axis.
Fig. 9. (a) The weak C–HÁ Á ÁF hydrogen bonds (dashed lines) of compound 16. (b) Edge to face
p–p interactions forming the network of connections between cations. Some of
the cations and anions have been removed for clarity.
ranges were observed. Typical DSC scans are exemplified in Fig. 11
and the TG curves for compounds 1–21 are presented in Fig. 12.
The differences and similarities between the first and the second
heating scans (DSC) together with their decomposition onsets are
also presented graphically in Fig. 13 (results being arranged both
by similarity of anion and cation) and the liquid ranges together
with start and end temperatures are gathered to Table 4.
All the compounds, except 8 and 15, exhibited a melting transi-
À
À
tion on first heating scan. Compounds 8 (BF4 salt) and 15 (PF6
salt) are viscous liquids at room temperature and showed no ther-
mal events on either of the two heating scans. Occasionally a
shoulder in the melting transition occurred for compound 2 sug-
gesting that it crystallizes as a mixture of polymorphs, as men-
À
tioned earlier. In addition, one of the bromide (7) and PF6 (18)
salts exhibited a solid–solid phase transition before melting at
À32.4 and 46.5 °C, respectively. These phase transitions were
repeatable as transitions were observed also on a second heating.
By inspecting the melting temperatures as a function of the anion,
it can be noted that the melting points of the bromide salts varied
À
in the range 80–176 °C and similarly for BF4 À salts in the range of
17–153 °C. The melting temperatures of BF4 salts were typically
clearly lower than that of their bromide analogies; the temperature
difference between two salt analogies varying ꢀ18–73 °C. By
À
changing the anion to PF6 higher melting temperatures (varying
in the range of 25–166 °C) were observed when compared to the
À
corresponding BF4 salts but still 10–30 °C below the melting tem-
peratures of analogous bromides (see Table 4). Compounds 8 and
15 are exceptions to the above-mentioned as they remained as vis-
cous liquids at least till À60 °C, which is the lowest temperature
reached by our DSC. In addition, compounds 10 (BF4À) and 17
(PF6À) exhibited also low melting temperatures, those being ꢀ17
and 25 °C, respectively.
Fig. 10. Experimental powder diffraction patterns of 2, 3 and 16 compared with
simulated data which were obtained from the single crystal structure parameters.
Some of the stronger diffraction peaks corresponding to the second polymorph of
compound 2 are marked by Ã.

74
M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
Table 3
Thermal properties for compounds 1–21.
Compound 1st Heating scan
2nd Heating scan
Tg and Cp Tm and
Decomp.
Ts–s and
D
H
Tm and
D
H
D
D
H
Td
BrÀ
1
2
–
–
79.7 (62.9)
175.5
À48.1 [033]
80.4 (60.1)a 203
50.8 [0.42]
–
195
(69.6)
3
4
–
–
89.6 (82.2)
102.6
(92.0)
86.0 (55.7)
107.9
–
–
89.6 (81.1)
92.2 (51.6)
102.9 (6.9)
193
183
5
6
–
–
–25.8 [0.22]
–
85.5 (46.6)a 178
106.8 (54.7)
184
(57.6)
7
À32.4
92.1 (33.9)
–
91.9 (37.1)
184
(12.8)
À
BF4
8
–
–
<À60b
–
–
–
283
238
9
152.6
22.3 [0.32]
Fig. 11. DSC curves of compounds 5, 7, 11, 12, 16 and 19 measured under nitrogen
(67.5)
with a heating rate of 10 °C/min. Tg, glass transition; Tc, cold crystallization; Ts–s
solid–solid phase transition; Tm, melting.
,
10
11
12
13
14
–
–
–
–
–
16.9 (19.0)
50.3 (57.1)
68.1 (72.3)
41.9 (15.5)
45.8 (23.9)
–
17.6 (19.9)
48.5 (2.8)a
267
207
À47.6 [0.32]
À46.6 [0.19]
À54.3 [0.09]
–
67.1 (65.3)a 201
33.7 (13.8)a 199
55.2 (16.0)
230
À
PF4
15
16
–
–
<À60b
–
–
–
305
253
166.0
20.8 [0.33]
(82.9)
17
18
19
20
21
–
24.9 (32.6)
73.8 (58.6)
83.6 (58.0)
80.6 (33.4)
95.4 (39.4)
–
–
25.1 (33.9)
74.9 (49.6)
83.3 (58.9)
82.0 (29.8)
90.8 (25.0)
315
320
319
311
293
46.5 (9.6)
–
–
–
–
–
Ts–s, solid–solid transition temperature (°C); Tm, melting temperature; Tg, glass
transitions temperature;
D DCp heat capacity
H, enthalpy of a transition (J gÀ1),
change (J gÀ1 °CÀ1); Td, decomposition onset by TG/DTA.
a
Exhibits cold crystallization (crystallization on heating) between a glass tran-
sition and melting.
b
See text.
Fig. 12. TG curves of compounds 1–21 measured under air with a heating rate of
10 °C/min.
Further on, the thermal behavior of the prepared QA salts (apart
from compounds 8 and 15) can roughly be divided into three
groups based on the observations on the second heating scans.
Compounds 3, 4, 6, 7, 10, 14 and 17–21 crystallized from a melt
while cooled, and re-melted on the second heating similarly as
found on first melting (Table 3). Both melting temperatures and
their enthalpies observed on the second heating correspond suffi-
ciently to those on the first heating, indicating that the samples
have been recrystallized more or less in the same extent. It can
be noted, though, that compound 10 was weakly crystalline al-
ready from the start as the observed enthalpies were low
(ꢀ19 J gÀ1) on both heating scans. Slightly reduced melting enthal-
pies were observed also for compounds 4 and 21 on the second
heating. The compounds forming the second group (1, 5, 11–13)
supercooled on cooling and turned to a glass as glass transitions
were observed at very low temperatures (from ꢀÀ55 to À25 °C).
However, on reheating cold crystallization transition was observed
above the glass transition which was followed by a remelting at
similar temperatures as those found on the first heating scan. Most
of the compounds regained the initial extent of crystallinity on cold
crystallization but particularly for compound 11 seemingly lesser
fraction of the sample recrystallized as the melting enthalpy was
Fig. 13. The Td and Tm (or Tg) temperatures for compounds 1–21 arranged by same
type of the anion (top) and the cation (bottom). In case of the second heating scans,
only the melting point is taken account if both glass and melting transitions were
observed.
significantly smaller than that found on the first heating (reduced
from 57 to 2.8 J gÀ1). The compounds in the third group (2, 9, 16;
compounds having a dimethyldi-(4-methoxybenzyl)dimethylam-
monium cation) also showed a tendency to form glassy states by
supercooling but instead of cold crystallizing the reheated samples
remained as supercooled liquids as only glass transitions were

M. Kärnä et al. / Journal of Molecular Structure 922 (2009) 64–76
75
Table 4
tures of four compounds (2, 3, 9 and 16) could be determined after
recrystallization by X-ray single crystal diffraction, one of which
had two different polymorphs according to the powder diffraction
data and solid state NMR spectrum.
Liquid ranges for compounds 1–21.
À
À
Comp.
Bromides (°C)
Comp.
BF4 salts (°C)
Comp.
PF6 salts (°C)
1
2
3
4
5
6
7
80–203 (123)
176–195 (19)
90–193 (103)
103–183 (80)
86–178 (92)
108–184 (76)
92–184 (92)
8
9
À60–283 (343)
153–238 (85)
17–267 (250)
50–207 (157)
68–201 (133)
41–199 (158)
46–230 (184)
15
16
17
18
19
20
21
À60–305 (365)
160–253 (93)
25–315 (290)
73–320 (247)
84–319 (235)
81–311 (230)
96–293 (197)
Comparing analogous compounds with a same cation, decompo-
sition temperatures increases in the following order: BrÀ
10
11
12
13
14
À
< BF4 < PF6À. The decomposition temperatures of the hexafluoro-
phosphates were about 20–100 °C higher than that of the tetra-
fluoroborates and 70–140 °C higher than that of the bromides.
Four compounds: 8, 10, 15 and 17 are liquid at room temperature
and have liquid ranges of 224–365 °C thus enabling their possible
use as ionic liquids in the future. Several of the other synthesized
compounds are liquid under 100 °C and have a broad liquid range
and therefore can also be categorized as ionic liquids. The aromatic
compounds 2, 9 and 16 [all three having dimethyldi-(4-methoxy-
benzyl)ammonium cation] differed clearly from the other studied
compounds. Their decomposition temperatures were significantly
lower compared to the aliphatic compounds and the liquid ranges
were narrower. When comparing compounds 2, 9 and 16 to the pre-
viously published results of similar but non-ether functionalized
compounds, it can be observed that introducing an ether group have
only a slight effect on the thermal behavior. For the rest of the pre-
pared QA salts, comparison of thermal properties to other similar
non-ether functionalized compounds could not be made since this
information is yet not available.
observed on second heating scans; the bromide having the highest
(50.8 °C) and both BF4 and PF6 salts having a lower glass transi-
tion temperatures at ꢀ22 and 21 °C, respectively.
À
À
The decomposition of the bromides occurred mainly in one sin-
gle stage without identifiable cleavages except for the aralkyl
substituted bromide (2), as can be seen in Fig. 12. The decomposi-
tion started at temperatures 178–203 °C and the compounds
decomposed mainly in one stage. Compound 2 decomposed in
three stages starting from 195 °C and based on the DSC and TG/
DTA measurements the decomposition started during or even be-
fore melting. Compared to previously published results for a simi-
lar compound, dimethyldi-(4-methylbenzyl)ammonium bromide
[53], the decomposition of compound 2 started at a similar tem-
perature, but occurred in several steps. The decomposition of tetra-
fluoroborates was slightly more complicated than that of the
bromides. The decompositions occurred typically in 2–4 steps
and compound 9, analogous to compound 2, had a decomposition
path differing clearly from others (Fig. 12). The decompositions of
tetrafluoroborates (8–14) started at temperature range 194–
283 °C. The decomposition temperatures of all compounds were
about 15–80 °C higher than that of the analogous bromides. The
thermal decomposition of the hexafluorophosphates (15–21)
resembled those of the bromides, only the decomposition temper-
atures were 60–140 °C higher than that of the bromides and 15–
120 °C higher than that of the tetrafluoroborates. The decomposi-
tion of compound 16 started at 253 °C and for compounds 15
and 17–21 between 293 and 320 °C. Yet again, compound 16 (anal-
ogous to compounds 2 and 9) decomposed having several cleav-
ages, which on the other hand is expected for all three due to
their more aromatic nature (phenyl groups). A comparison of these
three salts to the structurally similar but non-ether functionalized
QA salts (dimethyldi-(4-methylbenzyl)ammonium cation with a
same anions) [53,57] reveals that introducing an ether group have
only a slight effect on the decomposition temperatures but due to
lower melting points, the liquid ranges of the now reported salts
are somewhat broader. For the rest of the prepared compounds,
comparison of thermal properties to other similar non-ether func-
tionalized salts could not be made as similar compounds either
does not exists or they are insufficiently characterized.
Acknowledgements
We thank Ms. Elina Hautakangas for the elemental analyses,
Mr. Reijo Kauppinen for the NMR-measurements and Ms. Mirja
Lahtiperä for the ESI-TOF MS-measurements. M.K. gratefully
acknowledges the financial support of the Inorganic Materials
Chemistry Graduate Program.
Appendix A. Supplementary data
CCDC 678519–678522 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.01.041.
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