RESEARCH FRONT
Structural Characterization of Novel Ionic Salts
339
4.27 (q, J 7.3, 2H), 3.96 (s, 3H), 1.56 (t, J 7.3, 3H). m/z (ESI+)
110.9 ([C2mim]+); m/z (ESI−) 80.8 (Br−1).
C atoms. Final refinement based on 2695 reflection data con-
verged to R1 [1969 data with I > 2σ(I)] = 0.0292, wR2 = 0.0741
(all data), and goodness-of-fit on F2 = 1.004.Weighting scheme:
w = 1/[σ2(Fo2) + (0.0353P)2] where P = 1/3(Fo2 + 2F2c).
1-Propyl-1-methylpyrrolidinium Iodide ([C3mpyr][I])
1-Methylpyrrolidine (18.0 mL, 0.176 mol) was dissolved in
100 mL of ethyl acetate. Iodopropane (20.0 mL, 0.205 mol) was
added dropwise. The mixture was stirred under a nitrogen atmo-
sphere, overnight, at room temperature. The solid product was
filtered and washed with ethyl acetate. The product was dried
under vacuum for 2 days. Yield 27.4 g, 65.0%. δH (D2O) 3.57
(m, 4H), 3.34 (m, 2H), 3.07 (s, 3H), 2.25 (m, 4H), 1.92–1.76
(m, 2H), 1.02 (t, J 7.3, 3H). m/z (ESI+) 127.9 (C8H18N+); m/z
(ESI−) 126.7 (I−).
1-Ethyl-1-methylpyrrolidinium Bromide ([C2mpyr][Br])
The structure was solved using direct methods and expanded
by subsequent least-squares refinement and difference Fourier
cycles. Carbon atoms C(1), C(2), C(3), C(4), C(6), and C(7)
were modelled as disordered with two alternative positions for
each atom. The site-occupancy factors (s.o.f.s) were fixed at 0.5
after trial refinement. All non-hydrogen atoms were assigned
anisotropic temperature factors; all the hydrogen atoms were
placed in idealized positions in a riding model with Uiso(H) =
xUeq(C), where x = 1.5 for methyl and 1.2 for all other C atoms.
Full-matrix least-squares refinement, based on 2397 reflec-
tion data, converged to R1 [1840 data with I > 2σ(I)] = 0.0271,
wR2 = 0.0598 (all data), and goodness-of-fit on F2 = 1.048.
Weighting scheme: w = 1/[σ2(Fo2) + (0.0194P)2 + 0.4900P]
where P = 1/3(F2o + 2Fc2).
1-Ethyl-1-methylpyrrolidinium Tribromide
([C2mpyr][Br3])
Elemental bromine (0.5 mL, 9.76 mmol) was added dropwise
to [C2mpyr][Br] (1.24 g, 6.39 mmol). The reaction mixture was
stirred at 60◦C for 2 h. Excess elemental bromine was removed
under vacuum and the final product was crystallized at −10◦C
from acetonitrile. δH ([D6]DMSO) 1.27 (t, J 7.3, 3H), 2.05–2.18
(m, 4H), 2.96 (s, 3H), 3.37 (q, J 7.3, 2H), 3.47–3.35 (m, 4H).
1-Ethyl-1-methylpyrrolidinium Tribromide
([C2mpyr][Br3])
1-Ethyl-3-methylimidazolium Tribromide ([C2mim][Br3])
This compound was synthesized in an analogous way
to [C2mpyr][Br3], using the same relative quantities. δH
([D6]DMSO) 1.42 (t, J 7.3, 3H), 3.85 (s, 3H), 4.19 (q, J 7.3,
2H), 7.77 (s, 1H), 7.69 (s, 1H), 9.12 (s, 1H).
The structure was solved using direct methods and expanded
by subsequent least-squares refinement and difference Fourier
cycles. The atoms Br(1), Br(2), Br(3), C(1), C(2), C(7), and
N(1) were situated on a crystallographic mirror plane and the
remaining carbon atoms C(3), C(4), C(5), and C(6) were dis-
ordered over two positions (symmetry: x, y, z and x, 1/2 − y,
z). S.o.f.s were fixed at 0.5. All non-hydrogen atoms were
refined with anisotropic thermal parameters; all the hydrogen
atoms were placed in idealized positions using a riding model
(C–Hdistancesintherange0.95–1.00 ÅandUiso(H) = xUeq(C)),
where x = 1.5 for methyl and 1.2 for all other C atoms.
Full-matrix least-squares refinement, based on 1439 reflec-
tion data, converged to R1 [1090 data with I > 2σ(I)] = 0.0396,
wR2 = 0.0900 (all data), and goodness-of-fit on F2 = 1.106.
Weighting scheme: w = 1/[σ2(Fo2) + (0.0303P)2 + 3.2706P]
where P = 1/3(F2o + 2Fc2).Attempted refinement in a monoclinic
system was less satisfactory.
1-Propyl-1-methylpyrrolidinium Triiodide ([C3mpyr][I3])
X-ray-quality crystals of [C3mpyr][I3] were obtained
overnight from an electrolyte mixture containing lithium
iodide (0.0269 g, 0.201 mmol), iodine (0.0788 g, 0.310 mmol),
4-tert-butylpyridine (0.0781 g, 0.577 mmol), and 1-propyl-1-
methylpyrrolidinium iodide (0.123 g, 0.482 mmol), which was
made up to 1.00 mL with 1-propyl-1-methylpyrrolidinium
bis(trifluoromethanesulfonyl)amide.
Structure Determination and Crystal Data
General
Intensity data were collected on a Bruker X8 APEX KAPPA
CCD single crystal X-ray diffractometer (thin slice φ and ω
scans, 2θmax = 57◦, graphite-monochromated Mo-Kα X-rays,
λ = 0.71073 Å, T = 123 K). All crystals were coated in Paratone
oil (Exxon Chemical Co., TX, USA) immediately after isolation
and cooledin astreamof nitrogenvapour (15 cm3 min−1, Oxford
Cryostream cooler) on the diffractometer. Mounting of the tri-
halide crystals was particularly challenging owing to the highly
deliquescent nature of the salts. Handling of the monohalide salts
was less challenging, suggesting a lower hydrophilicity. Struc-
tures were solved and refined with the SHELX-97 software in
conjunction with the X-Seed Graphical User Interface.[26] An
empirical absorption correction was applied using SADABS.[26]
Crystal data are listed in Table 2 above.
1-Propyl-1-methylpyrrolidinium Triiodide ([C3mpyr][I3])
The structure was solved using direct methods expanded
by subsequent least-squares refinement and difference Fourier
cycles. The atoms I(1), I(2), I(3), N(1), C(1), C(2), C(5), C(6),
and C(7) were situated on a crystallographic mirror plane and the
remaining carbon atoms, C(3) and C(4), were disordered over
twopositions(symmetry: x, y, zandx, 1/2 − y, z)andrefinedwith
a fixed s.o.f. at 0.5. The atoms C(4) and C(4ꢀ) were restrained
to occupy the same coordinates and have the same atomic dis-
placement parameter and correspond to either one of the α ring
carbon atoms or the methyl group carbon atom in each disor-
der component. Additionally, the C(3)–C(4) bond distance was
restrained to a reasonable value. All non-hydrogen atoms were
refined with anisotropic thermal parameters and all the hydrogen
atoms were placed in idealized positions in a riding model (C–H
distances in the range 0.95–1.00 Å and Uiso(H) = 1.2Ueq(C)).
1-Ethyl-3-methylimidazolium Tribromide ([C2mim][Br3])
The structure was solved by direct methods and refined by
full matrix least-squares with anisotropic thermal parameters
for all non-hydrogen atoms. The hydrogen atom positions were
located in the difference Fourier map but were placed in cal-
culated positions with isotropic temperature factors assigned at
Uiso(H) = xUeq(C), where x = 1.5 for methyl and 1.2 for all other
The highest remaining electron density peak (1.02 e Å−3
)
is located at a distance of ∼0.7 Å from I(1). Full-matrix
least-squares refinement, based on 1907 reflection data, con-
verged to R1 [1534 data with I > 2σ(I)] = 0.0246, wR2 = 0.0473