Salts with the [NiBr3(L)]- complex anion (L = 1-methylimidazole, 1-methylbenzimidazole, quinoline, and triphenylphosphane) and low melting points: A comparative study

Article abstract of DOI:10.1016/j.poly.2012.08.047

Four new salts with low melting points of the general formula (EMIm)[NiBr₃(L)] (EMIm = 1-ethyl-3-methyl-imidazolium) with L = N-methylimidazole (NMIm), N-methylbenzimidazole (NMBIm), quinoline (quin), and triphenylphosphane (PPh₃) were prepared and characterized by means of elemental analysis, IR, NMR, and UV-vis spectroscopy. Magnetic properties were deduced from NMR data using the EVANS method. All four compounds are paramagnetic with magnetic moments close to the spin-only values of the tetrahedrally coordinated Ni(II) ion. Molecular and crystal structures were obtained by single crystal X-ray diffraction investigations. Melting points are determined to have values between 110 °C, (EMIm)[NiBr₃(NMIm)] and 168 °C, (EMIm)[NiBr₃(PPh₃)]. They exceed the maximum temperature required to call them "Ionic Liquids". Decomposition has been found to occur above 200 °C and to depend largely on the type of organic ligand coordinated to Ni(II).

Full text of DOI:10.1016/j.poly.2012.08.047

Polyhedron 52 (2013) 482–490
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Salts with the [NiBr3(L)]ꢀ complex anion (L = 1-methylimidazole,
1-methylbenzimidazole, quinoline, and triphenylphosphane) and low melting
points: A comparative study
1
⇑
Tim Peppel , Alexander Hinz, Martin Köckerling
Institute of Chemistry, Inorganic-Solid State Chemistry Group, University of Rostock, Albert-Einstein-Str. 3a, D-18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 8 September 2012
Four new salts with low melting points of the general formula (EMIm)[NiBr3(L)] (EMIm = 1-ethyl-
3-methyl-imidazolium) with L = N-methylimidazole (NMIm), N-methylbenzimidazole (NMBIm), quino-
line (quin), and triphenylphosphane (PPh3) were prepared and characterized by means of elemental
analysis, IR, NMR, and UV–vis spectroscopy. Magnetic properties were deduced from NMR data using
the EVANS method. All four compounds are paramagnetic with magnetic moments close to the spin-only
values of the tetrahedrally coordinated Ni(II) ion. Molecular and crystal structures were obtained by
single crystal X-ray diffraction investigations. Melting points are determined to have values between
110 °C, (EMIm)[NiBr3(NMIm)] and 168 °C, (EMIm)[NiBr3(PPh3)]. They exceed the maximum temperature
required to call them ‘‘Ionic Liquids’’. Decomposition has been found to occur above 200 °C and to depend
largely on the type of organic ligand coordinated to Ni(II).
Dedicated on the Occasion of the 100th
Anniversary of the 1913 Noble Prize in
Chemistry to Alfred Werner.
Keywords:
Nickel complexes
N ligand
Bromide
X-ray structure
Thermal properties
Spectroscopy
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
low melting points. Recently, we have investigated a series of Ionic
Liquids containing the [CoBr3(quin)]ꢀ anion [9]. To get a better
Solids with low melting points have found many applications as
reaction media for the production of a wide range of materials.
Especially the so-called Ionic Liquids have been in the focus of
interest for their unique properties for more than two decades.
Characteristics are melting points below 100 °C, wide temperature
ranges wherein the salts are liquid, low vapor pressures, and high
electric conductivities [1], to name just a few. Paramagnetic com-
plex anions incorporated in Ionic Liquids result in substances with
the intriguing combination of properties of being both liquid and
responding to magnetic fields [2]. The work of Hayashi et al. on
[FeCl4]ꢀ containing Ionic Liquids [2] boosted research on transition
metal containing Ionic Liquids, because of numerous possible
applications, like transport and materials separation [2e], catalysis
[2f] or field dependent absorption [2g], to name a few. An example
of a similar paramagnetic ion is that of the general formula [MX3
(quin)]ꢀ (M = 3d-metal; X = Cl, Br, I; quin = quinoline) which is
known for Mn(II) [3], Fe(II) [4], Co(II) [5], Ni(II) [2c,6], Cu(II) [7],
and Zn(II) [8]. Preparative investigations were conducted in our
laboratories to find cation combinations with such anions with
understanding of the relation between thermal properties and so-
lid state characteristics the neutral ligand in this type of anion is
varied.
In this contribution we report on the syntheses, properties, and
structures of a series of (EMIm)[NiBr3(L)] salts (EMIm = 1-ethyl-
3-methyl-imidazolium) with L = N-methylimidazole (NMIm),
N-methylbenzimidazole (NMBIm), quinoline (quin), and triphenyl-
phospane (PPh3)).
2. Experimental
2.1. Materials and methods
N-Methylimidazole, quinoline, benzimidazole, iodomethane
and anhydrous NiBr2 were purchased from Sigma–Aldrich (>99%)
and used as received. N-Methyl-benzimidazole was synthesized
according to a known literature method [10]: Benzimidazole
(25.0 g, 211.6 mmol) is added in one portion to 100 mL of a stirred
ice-cold 50% aqueous NaOH solution. Iodomethane (33.0 g,
232.8 mmol) is added dropwise under vigorous stirring to the clear
benzimidazole solution at ambient temperature. After 1 h the solu-
tion is extracted three times with 100 mL portions of chloroform.
The combined organic phases are dried with Na2SO4 and the sol-
vent is removed under reduced pressure. The residue is distilled
⇑
Corresponding author. Tel.: +49 (0)381 4986390; fax: +49 (0)381 4986382.
E-mail address: Martin.Koeckerling@uni-rostock.de (M. Köckerling).
Present address: Leibniz Institute for Catalysis, Albert-Einstein-Str. 29a, D-18059
1
Rostock, Germany.
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.047

T. Peppel et al. / Polyhedron 52 (2013) 482–490
483
Table 1
Crystal data and structure refinement parameters for (EMIm)[NiBr3(L)], with L = NMIm, NMBIm, quin, and PPh3.
L
NMIm
NMBIm
Quin
PPh3
Formula
Formula weight
T (K)
C10H17Br3N4Ni
491.72
173(2)
C14H19Br3N4Ni
541.77
173(2)
C15H18Br3N3Ni
538.76
173(2)
C24H26Br3N2NiP
671.88
173(2)
Crystal system
Space group
monoclinic
P21/n (No. 14)
monoclinic
P21/c (No. 14)
triclinic
triclinic
P1(No. 2)
P1(No. 2)
Z
4
4
2
2
Unit cell dimensions
a (Å)
b (Å)
c (Å)
7.742(2)
14.506(3)
14.843(3)
90
92.01(3)
1665.9(6)
1.961
13.8876(4)
10.4570(3)
12.9338(3)
90
92.165(1)
1876.94(9)
1.917
7.4845(5)
8.1975(6)
15.204(1)
88.331(5)
85.297(5)
913.2(1)
10.4387(2)
11.0013(2)
13.8378(2)
79.131(1)
71.119(1)
1331.83(4)
1.675
a
(°)
b (°)
V (Å3)
qcalc. (gꢂcmꢀ3
)
1.959
7.624
l
(mmꢀ1
)
8.349
7.421
5.303
k (Å)
0.71073
164
1.021
R1 = 0.0381, wR2 = 0.0663
0.0225/1.1862
0.71073
200
1.028
R1 = 0.0223, wR2 = 0.0488
0.0220/1.0026
0.71073
200
1.052
R1 = 0.0326, R2 = 0.0714
0.0339/0.6411
0.71073
290
1.039
R1 = 0.0327, wR2 = 0.0719
0.0335/0.4157
No. parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]a,b
Weighting A/Bc
P
P
a
b
c
R1 = jjFoj ꢀ jFcjj= jFcj.
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
h
i
P
P
2
2
wR2 =
fwðF2o ꢀ Fc2Þ g= fwðF2o Þ g .
2
w = 1=½r2ðF20Þ þ ðA ꢂ PÞ þ B ꢂ Pꢃ; P ¼ ðF02 þ 2F2c Þ=3.
Scheme 1. Reaction sequence for the synthesis of (EMIm)[NiBr3(L)].
in vacuo, yielding N-methyl-benzimidazole as a colorless liquid,
which solidifies upon cooling. Yield: 21.0 g (75%), mp. 61 °C.
Elemental anal. % (calc. for C8H8N2): C, 72.50 (72.70); H, 6.19
(6.10); N, 21.18 (21.20).
(3.90); N, 4.26 (4.17). UV–vis (kmax/nm in acetonitrile, 25 °C): 378
max/cmꢀ1): 3144w, 3105w, 3084w,
3053w, 2978w, 2932w, 1584vw, 1568m, 1481m, 1462w, 1435s,
1387w, 1353vw, 1336w, 1315w, 1291w, 1267vw, 1247vw,
1185w, 1167s, 1120w, 1097s, 1073w, 1028w, 995w, 959vw,
932vw, 921vw, 837m, 795w, 756s, 745s, 709m, 693s, 647m,
(ꢁ390) , 640 (ꢁ685). IR (
m
2.2. General synthesis of (EMIm)[NiBr3(L)] (L = NMIm, NMBIm, quin,
PPh3)
617s, 594w. Magnetic data: leff
/
l
B = 3.76 (T = 25 °C, c = 2.13ꢂ10ꢀ2
-
mol/L,
m0 = 300 MHz,
v
mol = 5.93ꢂ10ꢀ3).
(EMIm)[NiBr3(quin)]: Yield: 1.5 g, 61%, mp. 124 °C. Elemental
anal. % (calc. for C15H18Br3N3Ni): C, 33.47 (33.44); H, 3.37 (3.37);
N, 7.67 (7.80). UV–vis (kmax/nm in acetonitrile, 25 °C): 372, 620,
1-Ethyl-3-methylimidazolium bromide ((EMIm)Br, 0.9 g,
4.7 mmol) and appropriate ligand L (4.7 mmol; PPh3: 1.2 g, quin:
0.6 g, NMIm: 0.4 g, NMBIm: 0.6 g) are dissolved in 25 mL of hot
1-butanol and added to a vigorously stirred boiling suspension of
NiBr2 (1.0 g, 4.6 mmol) in 25 mL of the same solvent. The resulting
mixture turns dark blue immediately and the desired product pre-
cipitates in form of crystals upon storing the solution at 0 °C over-
night. The precipitate is filtered off, washed with diethyl ether and
finally dried in vacuo at ambient temperature.
649, 700. IR
(m
max/cmꢀ1): 3144w, 3106w, 3080m, 3016vw,
2980w, 2952vw, 2882vw, 2828vw, 1622w, 1593w, 1583vw,
1570m, 1509s, 1455w, 1438w, 1397w, 1377 m, 1342w, 1311m,
1281vw, 1258w, 1234w, 1200w, 1165s, 1127w, 1097vw, 1089w,
1057w, 1026w, 991w, 957m, 866w, 848m, 813s, 779s, 754s,
733s, 708w, 645vw, 636 m, 619s, 529w. Magnetic data: leff
/
l
B = 3.76
(T = 25 °C,
c = 2.83ꢂ10ꢀ2 mol/L,
m0 = 300 MHz,
(EMIm)[NiBr3(PPh3)]: Yield: 2.5 g, 81%, mp. 168 °C. Elemental
anal. % (calc. for C24H26Br3N2NiP): C, 42.59 (42.90); H, 3.89
v
mol = 5.92ꢂ10ꢀ3).

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T. Peppel et al. / Polyhedron 52 (2013) 482–490
Table 3
Absorption maxima in the UV–vis spectra in nm for the compounds (EMIm)[NiBr3(L)]
with L = NMIm, NMBIm, quin, and PPh3.
L
NMIm
NMBIm
Quin
PPh3
kmax(1)
kmax(2)
350
621
355
602
372
649
378
640
621. IR (m
max/cmꢀ1): 3140w, 3121vw, 3105m, 2981w, 2944vw,
1699w, 1614w, 1569m, 1538w, 1524w, 1505vw, 1468w, 1454w,
1422w, 1387vw, 1342w, 1317w, 1285w, 1271vw, 1235m, 1170s,
1135vw, 1102s, 1095s, 1033vw, 1023vw, 956w, 855m, 834s,
799vw, 765m, 751s, 707w, 670w, 657m, 618s. Magnetic data: leff
/
l
v
B = 3.75
(T = 25 °C,
c = 5.66ꢂ10ꢀ2 mol/L,
m0 = 300 MHz,
mol = 5.91ꢂ10ꢀ3).
(EMIm)[NiBr3(NMBIm)]: Yield: 1.8 g, 71%, mp. 150 °C. Elemen-
tal anal. % (calc. for C14H19Br3N4Ni.0.3BuOH): C, 32.47 (32.37); H,
Fig. 1. TGA curves of (EMIm)[NiBr3(L)] in the temperature range of 30–1000 °C in
air (L is given in squared brackets).
3.74 (3.93); N, 10.16 (9.93). UV–vis (kmax/nm in acetonitrile,
25 °C): 320, 360, 602. IR (m
max/cmꢀ1): 3152vw, 3121vw, 3105w,
3078w, 3030vw, 2982vw, 2952vw, 1765w, 1732w, 1616w,
1293w, 1574w, 1567vw, 1557vw, 1538vw, 1522 m, 1485w,
1456m, 1421w, 1368w, 1339w, 1296m, 1253m, 1195vw, 1189w,
1170w, 1135w, 1095vw, 1070w, 1031vw, 1007w, 970vw, 926w,
905vw, 886vw, 869w, 848w, 775w, 761w, 738s, 667vw, 629vw,
618m, 5875w, 525w. Magnetic data: leff/lB = 3.72 (T = 25 °C,
c = 4.97ꢂ10ꢀ2 mol/L,
m0 = 300 MHz,
v
mol = 5.80ꢂ10ꢀ3).
2.3. Structure analysis and refinement
Transparent, blue single crystals of the four title compounds
were selected and separated with the aid of a microscope for the
X-ray diffraction investigations. For single crystal investigations
they were mounted on the tips of thin glass fibers. Data were col-
lected on a Bruker–Nonius Apex X8 diffractometer, equipped with
a CCD detector. Measurements were carried out using monochro-
matic Mo K
a radiation with k = 0.71073 Å. Preliminary data of
the unit cell were obtained from the reflex positions of 12 frames,
each measured in three different directions of the reciprocal space.
After completion of the data measurements the intensities were
corrected for Lorentz, polarization, and absorption effects using
Fig. 2. Isothermal TGA curves of (EMIm)[NiBr3(L)] at 200 °C in air (L is given in
squared brackets).
Table 2
Selected bond lengths in Å and angles in ° of the compounds (EMIm)[NiBr3(L)] with
L = NMIm, NMBIm, quin, and PPh3.
L
NMIm
NMBIm
Quin
PPh3
Atom distances
Ni1-Br1
Ni1-Br2
Ni1-Br3
Average Ni1-Br
Ni1-L
2.3723(3)
2.3857(3)
2.3990(3)
2.3857(3)
1.973(2)
2.3883(8)
2.3848(6)
2.3833(8)
2.3855(7)
1.974(2)
2.4035(6)
2.3837(5)
2.3795(6)
2.3899(6)
2.021(3)
2.3614(4)
2.3742(3)
2.3651(3)
2.3669(4)
2.3016(6)
Bond angles
Br1-Ni1-Br2
Br1-Ni1-Br3
Br2-Ni1-Br3
Average Br-Ni1-Br
L-Ni1-Br1
L-Ni1-Br2
L-Ni1-Br3
Average L-Ni1-Br
122.93(2)
104.82(2)
113.36(2)
113.70(2)
106.06(7)
105.50(6)
102.56(7)
104.71(7)
116.46(1)
113.63(1)
110.48(1)
113.52(2)
104.37(5)
106.89(5)
103.76(5)
105.01(5)
106.68(2)
114.66(2)
110.22(2)
110.52(2)
99.72(8)
121.41(8)
104.36(8)
108.50(8)
117.31(1)
111.79(1)
112.70(1)
113.93(1)
103.51(2)
102.78(2)
107.17(2)
104.49(2)
(EMIm)[NiBr3(NMIm)]: Yield: 1.0 g, 45%, mp. 110 °C. Elemental
anal. % (calc. for C10H17Br3N4Ni): C, 24.58 (24.43); H, 3.82 (3.49); N,
11.26 (11.40). UV–vis (kmax/nm in acetonitrile, 25 °C): 267, 350,
Fig. 3. Structure of one ion pair of (EMIm)[NiBr3(NMIm)] in the crystal (thermal
ellipsoids at 50% probability level). The dashed line shows the shortest anion–cation
contact.

T. Peppel et al. / Polyhedron 52 (2013) 482–490
485
Fig. 4. Structure of one ion pair of (EMIm)[NiBr3(NMBIm)] in the crystal (thermal ellipsoids at 50% probability level). The dashed line shows the shortest anion–cation contact.
Fig. 5. Structure of one ion pair of (EMIm)[NiBr3(quin)] in the crystal (thermal ellipsoids at 50% probability level). The dashed line shows the shortest anion–cation contact.
Fig. 6. Structure of one ion pair of (EMIm)[NiBr3(PPh3)] in the crystal (thermal ellipsoids at 50% probability level). The dashed line shows the shortest anion–cation contact.

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T. Peppel et al. / Polyhedron 52 (2013) 482–490
Fig. 7. Packing of the cations and complex anions in crystals of (EMIm)[NiBr3(NMIm)] in a view along the a axis.
Fig. 8. Packing of the cations and complex anions in crystals of (EMIm)[NiBr3(NMBIm)] in a view along the b axis.

T. Peppel et al. / Polyhedron 52 (2013) 482–490
487
the Bruker-Nonius software [11]. The structures were solved by
Direct Methods using the SHELXS-97 program and refined by least-
squares procedures on F2 with the aid of the SHELXS-97 program
[12].
All non-hydrogen atoms were refined anisotropically. H-atoms
of all the four compounds were added on idealized positions and
refined using riding models. Crystal data, data collection, and
refinement parameters are compiled in Table 1.
In the structure of 3 the EMIm cation is disordered on two posi-
tions, such that the atoms of 5-membered rings are exactly on the
same positions, but the methyl and the ethyl group are exchanged.
This situation has been treated by a split model. The two orienta-
tions are not equally occupied; one has an occupation of
39.5(7)%, and the other one of 60.5(7)%, respectively.
high yield by reacting (EMIm)Br, anhydrous NiBr2, and L in a molar
ratio of 1:1:1 in 1-butanol according to Scheme 1. All compounds
of the composition (EMIm)[NiBr3(L)] are distinguished by intensive
violet-blue to blue-green colors in crystalline form. They are non-
hygroscopic solids, which are soluble in organic solvents, espe-
cially in acetone, acetonitrile and alcohols. Suitable single crystals
of the compounds (EMIm)[NiBr3(L)] were obtained directly from
the reaction vessels by slowly cooling to ambient temperature of
saturated boiling 1-butanol solutions of the salts.
3.2. Magnetic properties
The magnetic properties at room temperature of all complex
salts were determined in solution using NMR techniques by apply-
ing the Evans method [13]. The resulting data are listed in the
Experimental Section. All complexes show similar magnetic prop-
erties: They are paramagnetic substances with effective magnetic
2.4. Analyses and spectroscopic measurements
MIR spectra (500–4000 cmꢀ1) were recorded by using the ATR
technique on a Thermo Nicolet 380 FT-IR spectrometer. Elemental
analyses for C, H, and N were obtained with a Flash EA 1112 NC
Analyzer from CE Instruments. UV–vis spectra were recorded using
a Perkin Elmer Lambda 2 spectrometer with quartz cuvettes
(SuprasilÒ, d = 10 mm). Melting points were determined by DSC
measurements using a Mettler Toledo DSC823e in the range of
20–200 °C with a heating rate of 10 °C/min (N2 atmosphere, Al cru-
cible). All melting points are peak temperatures. TG measurements
were performed on a Netzsch STA 449 F3 JupiterÒ device in the
temperature range of 30–1000 °C with a heating rate of 20 °C/
min in synthetic air atmosphere. Magnetic data were determined
by means of 1H NMR techniques (Evans method) [13]. Molar sus-
ceptibilities were corrected by applying Pascal constants [14].
moments in the range of
high-spin NiII:
eff = 2.83
those of related compounds with tetrahedral [NiX4]2ꢀ (X = Cl, Br)
complex anions, for example, (Et4N)2[NiCl4]: eff = 3.87 lB (20 °C,
[16]), (Ph3MeAs)2[NiCl4]: eff = 3.89 lB (20 °C, [16]), (Et4N)2
[NiBr4]: eff = 3.79 B (20 °C, [16]), (DBTMIm)2[NiBr4]: eff = 3.80 lB
(25 °C, [7c]), or pseudo-tetrahedral [NiBr3L]ꢀ complex anions,
for example, (Et4N)[NiBr3(PPh3)]: eff = 3.66 lB (27 °C, [17]), or
(nBu4N)[NiBr3(quin)]:
eff = 3.15–3.84 B (22 °C, [18]). These litera-
ture values show that slight deviations of leff from the spin-only
values as found also for the title compounds are found quite often
for tetrahedral complexes, as discussed for example in Ref. [25].
Because large cations separate the paramagnetic Ni(II) centers
(see below) cooperative effects are expected to be non-existent.
Therefore, we expect similar magnetic behavior in the solid state
as in solution.
l
eff = 3.72–3.76 lB at 25 °C (spin only,
l
lB). These values resemble closely
l
l
l
l
l
l
l
l
Effective magnetic moments leff/lB are given by applying the
Langevin equation [15].
3. Results and discussion
3.3. Electronic spectra
3.1. Synthesis
UV–vis spectra of 1–4 in acetonitrile show two bands in the vis-
ible wavelength regions (Table 3). These bands are characteristic
for Ni(II) in tetrahedral coordination modes.
The first band at 350 (355, 372, 378) nm can be assigned to a
charge-transfer-transition while the latter is at 621 (602, 649,
The synthesis of complexes containing the 1-ethyl-3-methyl-
imidazolium cation (EMIm) and the NiII-based anion [NiBr3(L)]ꢀ
(L = NMIm, NMBIm, quin, PPh3) can be achieved in moderate to
Fig. 9. Packing of the cations and complex anions in crystals of (EMIm)[NiBr3(quin)] in a view along the b axis.

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T. Peppel et al. / Polyhedron 52 (2013) 482–490
640) nm caused by d-d-transitions. These values compare well to
literature known ones for known [NiBr3(L)]-type complex anions
as (NEt4)[NiBr3(CH3CN)] with absorption maxima at 372.5 and
635 nm [19] and 386 and 635 nm for (NEt)4[NiBr3(PPh3)] in nitro-
methane [4].
This d-d-transition allows the integration of the used ligands
into the spectrochemical series. Thus, sorted by the extent of ligand
field splitting the order is NMBIm > NMIm > PPh3ꢁquin.
(NMBIm)] show the highest degradation temperatures (ꢁ300 °C)
suggesting liquid ranges for these two compounds of almost
200 °C. This behavior is also observable by isothermal TGA mea-
surements at 200 °C. Fig. 2 shows additional TGA curves for
(EMIm)[NiBr3(L)] for isothermal measurements in air over a longer
period of time at 200 °C (7 h). Even after 7 h at 200 °C only a mass
loss of approximately 6 % can be detected for the lowest melting
substance (EMIm)[NiBr3(NMIm)], while the highest melting salt
(EMIm)[NiBr3(PPh3)] loses more than 15% of its mass. From Figs. 1
and 2 it can be concluded, that the rate of decomposition of
(EMIm)[NiBr3(L)] is highly dependent on the chosen ligand L. This
behavior is qualitatively explained on the basis of the extended
hydrogen bonding networks and further discussed in the Crystal
Structures Section.
3.4. Thermal properties
Thermal data of the four title substances have been measured
using DSC and TGA techniques. Melting points were detected by
applying DSC measurements (20–200 °C) as endothermic peaks be-
tween 100 and 170 °C. All melting points are listed in the Experi-
mental Section and the melting point is increasing with
increasing molar mass of the ligand from 110 °C in (EMIm)[NiBr3
(NMIm)] (NMIm: M = 82.10 g/mol) to 168 °C in (EMIm)[NiBr3
(PPh3)] (PPh3: M = 262.29 g/mol). All compounds are stable in the
liquid state below 200 °C even under air before thermal degrada-
tion occurs. The decomposition curves of (EMIm)[NiBr3(L)] in air
in the temperature range of 30–1000 °C are depicted in Fig. 1. From
Fig. 1 it can be seen, that the decomposition of (EMIm)[NiBr3(L)]
follows complex pathways, while decomposition in air starts at
250–300 °C, followed by a short horizontal in the temperature
range of 450–550 °C, and further decomposition until 1000 °C leav-
ing a complex mixture of Ni and NiO. Interestingly, the lowest
melting complexes (EMIm)[NiBr3(NMIm)] and (EMIm)[NiBr3
3.5. Crystal and molecular structures
In the course of our investigations of mono-anionic transition
metal complex ions as candidates for new Ionic Liquids, we deter-
mined the single crystal X-ray structures of the four new title com-
pounds. Crystal data and parameters of the structure
determinations and refinements are listed in Table 1, and selected
bond lengths and angles in Table 2. All four compounds consist of
isolated 1-ethyl-3-methylimidazolium cations and [NiBr3(L)]ꢀ an-
ions, i.e. the compounds are to be described as salts.
The coordination geometry around the Ni atoms in 1–3 is pseu-
do-tetrahedral NiBr3N with 3 bromido ligands and 1 N ligand atom
from the corresponding aromatic organic N ligand (NMIm, NMBIm,
Fig. 10. Packing of the cations and complex anions in crystals of (EMIm)[NiBr3(PPh3)] in a view along the b axis. H atoms are omitted for clarity. Only one orientation of the
disordered EMIm cation is shown.

T. Peppel et al. / Polyhedron 52 (2013) 482–490
489
and quin). In 4, with L = PPh3 the Ni coordination is NiBr3P, respec-
tively. The average Ni–Br and the Ni–N/Ni–P bond distances fall in
their expected regions (see Table 2). In 1 and 2 with the principally
similar ligands NMIm and NMBIm the values are almost identical.
The Ni–Br distance in 3 (quin ligand) compares also well with the
ones of the former two compounds, but the Ni–N distance is
slightly longer. To the best of our knowledge crystal structure data
of nickel complex salts with ligands comparable to those of 1,2, or
3 exist in the literature so far only for (nBu4N)[NiBr3(quin)] [20].
The structural parameters of this compound compare well with
those of 3. Also, the bond lengths of the anion of 4 are in the same
range as those of (Ph4As)[NiBr3(PPh3)] [21].
In all four title compounds the average Br–Ni–Br angles are lar-
ger than the ideal tetrahedral value, whereas the average Br–Ni–N/
P angles are smaller than 109.47°, as expected from the different
atom radii (see Table 2).
The salts 1 and 2 crystallize in the monoclinic crystal system, 1
with space group P21/n and 2 with P21/c, both with four ion pairs in
the unit cell. 3 and 4 crystallize triclinic (P1) with two formula
units in the unit cell. In all four structures the atoms of the ion
pairs of the asymmetric unit are located on general positions.
Therefore, none has higher point symmetry than identity. Figs. 3–
6 show ORTEP plots of one ion pair of the four title compounds.
The arrangement of ions in the unit cells of 1–4 is shown in
Figs. 7–10.
N atoms (H at C5 (1), C9 (2), C10 (3), and C19 (4)). All these H
atoms have rather short distances to Br atoms of neighboring com-
plex anions. They range from 2.779 Å in 2 to 3.002 Å in 4. Unfortu-
nately, the trend of these increasing hydrogen bond lengths does
not reflect any reasonable trend of melting points of these
compounds.
4. Conclusion
Results of detailed investigations about new compounds with
pseudo-tetrahedral Nickel(II) complex anions of the type [NiBr3
(L)]ꢀ with L = organic ligand N ligands (three examples) and one
example with a P ligand is presented. Information about the syn-
thesis, single-crystal X-ray structures, spectroscopy, thermal
behavior and magnetic properties of (EMIm)[NiBr3(L)] with L = N-
methylimidazole, N-methylbenzimidazole, quinoline, and triphen-
ylphosphane; EMIm = 1-ethyl-3-methylimidazolim is given. They
all contain pseudo-tetrahedrally coordinated Nickel ions. The
materials are paramagnetic and thermally stable up to 200 °C. They
have relatively low melting points, and might be useful as molten
salts.
Acknowledgment
Support from the Deutsche Forschungsgemeinschaft (SPP 1191)
is gratefully acknowledged.
In crystals of 1 the cations and anions are alternatively stacked
along the crystallographic a direction in such a way that the planar
imidazolium rings, which are present in both the cation and the
anion are arranged almost parallel. Even though, the distance of
Appendix A. Supplementary data
this planar units is short at 3.87 Å,
p-stacking interactions are
not expected to be present to a larger extend, because the five-
membered ring of the cation is shifted away from that of the anion
in a direction parallel to the ring plane, see Fig. 7. Also, the ring
plane of the cation is tilted by 4° relative to that of the anion.
In the salt with the N-methylbenzimidazole ligand the arrange-
ment of ions can also be described in such a way that rows of ions
exist. But different to the arrangement in 1, where rows of alternat-
ing cations and anions exist, here rows of only cations neighboring
CCDC 878295, 878294, 878293 and 878296 contains the sup-
plementary crystallographic data for compounds 1–4. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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