Investigations on a Series of Ionic Liquids Containing the [CoIIBr3quin

ARTICLE pubs.acs.org/crystal

Investigations on a Series of Ionic Liquids Containing the [CoIIBr3quin]
Anion (quin = quinoline) Tim Peppel†,‡ and Martin K€ockerling*,† †

University of Rostock, Department of Chemistry, Inorganic Solid State Chemistry, Albert-Einstein-Strasse 3a, D-18059 Rostock, Germany ‡ Leibniz Institute for Catalysis, Albert-Einstein-Strasse 29a, D-18059 Rostock, Germany ABSTRACT: A series of eight new 1-alkyl-3-methylimidazolium derived salts with the pseudotetrahedral CoII-based complex anion, [CoIIBr 3 quin]
, quin = quinoline, and 1-alkyl-3-methylimidazolium cations, AlkMIm, Alk = ethyl, n-butyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, allyl, and propargyl; M = methyl, was synthesized. The melting point of each compound was measured to see if they are designated as metal-containing ionic liquids (magnetic ionic liquids). Each compound was further characterized by elemental analysis, NMR, IR, and UV/vis spectroscopy. From NMR investigations, information about the magnetic behavior was derived using the EVANS method. It has been found that every compound is paramagnetic with effective magnetic moments of spin-only CoII. The solid state structures of the compounds (AlkMIm)[CoIIBr3quin] with Alk = ethyl, n-butyl, n-hexyl, and n-nonyl were established by single-crystal X-ray diffraction techniques with regard to finding correlations between thermal and structural properties: (EMIm)[CoBr3quin]: triclinic, P1 (No. 2), a = 7.4889(3) Å, b = 8.2056(3) Å, c = 15.2471(6) Å, α = 88.453(2)°, β = 85.457(2)°, γ = 79.531(2)°, Z = 2, R1(F)/wR2(F2) = 0.0248/0.0569; (BMIm)[CoBr3quin]: triclinic, P1 (No. 2), a = 8.2915(4) Å, b = 10.2560(4) Å, c = 12.3943(5) Å, α = 91.877(2)°, β = 95.427(2)°, γ = 101.826(2)°, Z = 2, R1(F)/wR2(F2) = 0.028057/0.0592; (HexMIm)[CoBr3quin]: monoclinic, P21/c (No. 14), a = 8.0375(2) Å, b = 25.7514(5) Å, c = 11.3451(3) Å, β = 105.449(1)°, Z = 4, R1(F)/wR2(F2) = 0.0263/0.0554; (NonMIm)[CoBr3quin]: monoclinic, P21/c (No. 14), a = 13.1727(5) Å, b = 12.1438(5) Å, c = 17.2612(6) Å, β = 111.321(2)°, Z = 4, R1(F)/wR2(F2) = 0.0288/0.0588.

’ INTRODUCTION Salts containing singly charged anions of the formula [MeX3quin]
(Me = 3d-metal; X = Cl, Br, I; quin = quinoline) have been reported in the literature for MnII,1 FeII,2 CoII,3 NiII,3c,4 CuII,5 and ZnII,6 respectively. These compounds have been studied using electron spin resonance (ESR) spectroscopy and polarized electron spectroscopy. Their magnetic and structural properties have been investigated. Recently, we reported on a series of imidazolium-based transition metal containing salts in order to investigate their ability as ionic liquids (ILs).7 ILs with melting points below 100 °C have attracted great scientific and industrial interest because of their special and useful properties, such as wide liquid ranges, large electrochemical windows, or high electric conductivities and very low vapor pressures.8 Transition metal based ILs with paramagnetic complex anions (magnetic ionic liquids) exhibit interesting magnetic properties in addition to the ones mentioned above.7,9 But on imidazoliumbased compounds bearing the [MeX3quin]
anion there has been no investigation up to now. In order to get a better understanding of the thermal and solid state properties of these salts, it is necessary to investigate their crystal and molecular structures. Single crystal X-ray structures of compounds consisting of the [MeX3quin]
anion are rare and are only known for the combinations [MeCl3quin]
(Me = Co,3e Ni,4d Cu5) and [MeBr3quin]
r 2011 American Chemical Society

(Me = Ni4a). In this contribution, we report on the synthesis, IR, UV/vis, and thermal and magnetic properties, as well as on the crystal and molecular structures of a series of imidazolium-based ionic liquids with the [CoIIBr3quin]
anion with regard to obtaining structure
property relationships. In total eight new compounds were synthesized and investigated: (AlkMIm)[CoBr3quin] (AlkMIm = 1-Alkyl-3-methylimidazolium; Alk = ethyl, n-butyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, allyl, propargyl). Crystallization experiments led to suitable single crystals for X-ray determinations of four of these substances: AlkMIm = EMIm, BMIm, HexMIm, NonMIm.

’ EXPERIMENTAL SECTION Analysis and Spectroscopic Measurements. Mid infrared (MIR) spectra (500
4000 cm
1) were recorded by using the attenuated total reflectance (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 (Suprasil, d = 10 mm). Melting points were determined by Received: August 10, 2011 Revised: October 2, 2011 Published: October 04, 2011 5461

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Table 1. Crystal, X-ray Diffraction Data, Data Collection and Refinement Parameters for (AlkMIm)[CoBr3quin] (AlkMIm = EMIm, BMIm, HexMIm, NonMIm) compound

(BMIm)[CoBr3quin]

(HexMIm)[CoBr3quin]

(NonMIm)[CoBr3quin]

formula

C15H18Br3CoN3

C17H22Br3CoN3

C19H26Br3CoN3

C22H32Br3CoN3

Fw /g 3 mol
1 T /K

538.98 173(2)

567.04 173(2)

595.09 173(2)

637.17 173(2)

crystal system

triclinic

triclinic

monoclinic

monoclinic

space group

P1, No. 2

P1, No. 2

P21/c, No. 14

P21/c, No. 14

a /Å

7.4889(3)

8.2915(4)

8.0375(2)

13.1727(5)

b /Å

8.2056(3)

10.2560(4)

25.7514(5)

12.1438(5)

c /Å

15.2471(6)

12.3943(5)

11.3451(3)

17.2612(6)

105.449(1)

111.321(2)

α /°

88.453(2)

91.877(2)

β /° γ /°

85.457(2) 79.531(2)

95.427(2) 101.826(2)

V /Å3, Z

918.38(6), 2

1025.51(8), 2

2263.33(9), 4

2572.2(2), 4

F /g 3 cm
3

1.949

1.836

1.746

1.645

μ /mm
1

7.459

6.685

6.062

5.340

2θ range /°

5.04
56.68

5.10
62.84

5.49
56.61

4.72
59.34

collected refl

12788

22928

20085

34748

unique refl, Rint

4527, 0.0176

6778, 0.0317

5527, 0.0283

7378, 0.0433

variables GOF on F2

199 1.023

217 1.041

235 1.032

262 1.021

R1, wR2 [I > 2σ(I)]a,b

0.0248, 0.0569

0.0280, 0.0592

0.0263, 0.0554

0.0288, 0.0588

R1, wR2 (all data)a,b

0.0339, 0.0599

0.0396, 0.0627

0.0387, 0.0598

0.0485, 0.0640

A, Bb

0.0272, 0.7072

0.0231, 0.6117

0.0214, 2.0225

0.0266, 0.5565

res dens/e 3 Å
3

1.125,
0.311

0.849,
0.860

0.805,
0.403

0.574,
0.734

)

R1 = ∑ Fo|
|Fc /∑ |Fo|. b wR2 = (∑{w(Fo2
Fc2)2}/∑{w(Fo2)2})1/2; w = 1/[(σ2(Fo2) + (A 3 P)2 + B 3 P]; P = (Fo2 + 2 Fc2)/3. )

a

(EMIm)[CoBr3quin]

differential scanning calorimetry (DSC) measurements using a Mettler Toledo DSC823e in the range of
50 to 300 °C with a heating rate of 10 °C/min (N2 atmosphere, Al crucible). All melting points are peak temperatures. Thermogravimetric (TG) measurements were performed on a Netzsch STA 449 F3 Jupiter device in the temperature range of 30
1000 °C with a heating rate of 10 °C/min in air and nitrogen atmosphere. Magnetic data were determined by means of 1H NMR techniques (EVANS method).10 Molar susceptibilities were corrected by applying PASCAL constants.11 Effective magnetic moments μeff/μB are given by applying the LANGEVIN equation.12 X-ray Structure Analysis. Light blue crystals of (AlkMIm)[CoBr3quin] (AlkMIm = EMIm, BMIm, HexMIm, NonMIm; quin = quinoline) were mounted on the tips of thin glass fibers for the single crystal X-ray diffraction measurements. Data were collected on a BrukerNonius Apex X8 diffractometer equipped with a CCD detector. Measurements were done using monochromatic MoKα radiation (λ = 0.71073 Å). Preliminary data of the unit cell were obtained from the reflex positions of 36 frames, measured in different directions of the reciprocal space. After completion of the data measurements, the intensities were corrected for Lorentz, polarization, and absorption effects using the Bruker-Nonius software.13 The structure solutions and refinements were done with the aid of the SHELX-97 program package.14 All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were added on idealized positions and refined using riding models. Crystal data, data collection, and refinement parameters are collected in Table 1. Crystallographic data for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre, CCDC-835126 for (EMIm)[CoBr3quin], CCDC-835128 for (BMIm)[CoBr3quin], CCDC-835129 for (HexMIm)[CoBr3quin], and CCDC-835130 for (NonMIm)[CoBr3quin]. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk or from the Cambridge Crystallographic

Data Centre, 12 Union Road, Cambridge CB21EZ, UK; Fax: (+44) 1223-336-033; or e-mail: [email protected]. Materials. All commercially available starting materials were purchased from Sigma-Aldrich (>99%) and were used without further purification or drying. Ionic liquid precursors (AlkMIm)Br (AlkMIm = 1-alkyl3-methylimidazolium; Alk = ethyl, n-butyl, n-hexyl, n-heptyl, n-octyl, nnonyl, allyl, propargyl) were synthesized according to known procedures.15 General Synthesis of (AlkMIm)[CoBr3quin]. 5.0 mmol of (AlkMIm)Br and 5.0 mmol of quinoline are dissolved in 25 mL of 1-butanol. This solution is added to a hot solution of 5.0 mmol of CoBr2 in 25 mL of the same solvent. Immediately, the resulting solution turns dark blue and a precipitate is formed, which is soluble in the boiling solvent. The butanolic solution is kept at 0 °C overnight and the precipitate is filtered off. The blue powder is finally washed with diethyl ether and dried in vacuo. Yield > 95%. (EMIm)[CoBr3quin]. Yield: 95%. mp. 137 °C. Elemental analysis for C15H18N3CoBr3 % (calc.): C 33.07 (33.43); H 3.30 (3.37); N 7.68 (7.80). IR (νmax /cm
1): 3150, 3107, 3082, 2980, 2950, 2881, 1621, 1592, 1570, 1508, 1455, 1438, 1397, 1377, 1341, 1310, 1258, 1234, 1200, 1164, 1126, 1088, 1055, 1025, 991, 956, 867, 848, 814, 780, 755, 733, 708, 635, 619, 529. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.42 (T = 25 °C, c = 5.16  10
3 mol/L, ν0 = 300 MHz, χmol = 8.19  10
3). (BMIm)[CoBr3quin]. Yield: 96%. mp. 105 °C. Elemental analysis for C17H22N3CoBr3 % (calc.): C 36.25 (36.01); H 3.84 (3.91); N 7.24 (7.41). IR (νmax /cm
1): 3142, 3117, 3097, 3078, 2956, 2931, 2871, 1623, 1568, 1559, 1510, 1462, 1450, 1402, 1374, 1311, 1238, 1161, 1133, 1091, 1056, 1021, 957, 845, 801, 778, 764, 749, 735, 700, 649, 623, 597. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.50 (T = 25 °C, c = 9.76  10
3 mol/L, ν0 = 300 MHz, χmol = 8.48  10
3). 5462

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(HexMIm)[CoBr3quin]. Yield: 97%. mp. 67 °C. Elemental analysis for C19H26N3CoBr3 3 0.25H2O % (calc.): C 37.95 (38.06); H 4.41 (4.45); N 6.96 (7.01). IR (νmax /cm
1): 3137, 3101, 3074, 2952, 2927, 2856, 1620, 1593, 1582, 1567, 1563, 1508, 1463, 1438, 1400, 1375, 1336, 1311, 1236, 1161, 1130, 1102, 1091, 1054, 1021, 955, 810, 782, 773, 736, 648, 633, 618, 528. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.48 (T = 25 °C, c = 11.85  10
3 mol/L, ν0 = 300 MHz, χmol = 8.41  10
3). (HeptMIm)[CoBr3quin]. Yield: 97%. mp. 90 °C. Elemental analysis for C20H28N3CoBr3 3 0.25H2O % (calc.): C 39.12 (39.15); H 4.49 (4.68); N 6.81 (6.85). IR (νmax /cm
1): 3152, 3101, 3072, 2948, 2925, 2864, 2846, 1620, 1592, 1568, 1509, 1464, 1453, 1397, 1374, 1335, 1313, 1266, 1236, 1163, 1130, 1090, 1054, 1023, 995, 973, 957, 849, 811, 780, 762, 736, 651, 634, 624, 528. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.48 (T = 25 °C, c = 7.36  10
3 mol/L, ν0 = 300 MHz, χmol = 8.41  10
3). (OctMIm)[CoBr3quin]. Yield: 96%. mp. 91 °C. Elemental analysis for C21H30N3CoBr3 3 0.5H2O % (calc.): C 39.92 (39.90); H 5.00 (4.94); N 6.70 (6.65). IR (νmax /cm
1): 3138, 3096, 3065, 2950, 2923, 2852, 1620, 1592, 1567, 1509, 1452, 1397, 1374, 1336, 1312, 1235, 1161, 1129, 1089, 1055, 1022, 995, 973, 956, 848, 811, 780, 759, 736, 652, 633, 622, 528. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.60 (T = 25 °C, c = 7.19  10
3 mol/L, ν0 = 300 MHz, χmol = 8.86  10
3). (NonMIm)[CoBr3quin]. Yield: 95%. mp. 115 °C. Elemental analysis for C22H32N3CoBr3 % (calc.): C 41.25 (41.47); H 5.06 (5.06); N 6.75 (6.59). IR (νmax /cm
1): 3133, 3093, 3068, 2922, 2855, 1620, 1594, 1562, 1506, 1470, 1462, 1437, 1423, 1377, 1358, 1314, 1239, 1203, 1162, 1129, 1103, 1090, 1055, 1021, 979, 958, 865, 820, 776, 757, 739, 694, 649, 635, 622, 600, 529. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.44 (T = 25 °C, c = 4.84  10
3 mol/L, ν0 = 300 MHz, χmol = 8.27  10
3). (AllylMIm)[CoBr3quin]. Yield: 99%. mp. 117 °C. Elemental analysis for C16H18N3CoBr3 % (calc.): C 33.64 (34.88); H 3.26 (3.29); N 7.68 (7.63). IR (νmax /cm
1): 3159, 3127, 3102, 3058, 2950, 1593, 1582, 1558, 1505, 1441, 1421, 1396, 1385, 1375, 1312, 1283, 1235, 1199, 1159, 1126, 1103, 1024, 1001, 971, 958, 912, 847, 817, 784, 745, 734, 678, 634, 624, 619, 565, 528. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.48 (T = 25 °C, c = 6.17  10
3 mol/L, ν0 = 300 MHz, χmol = 8.41  10
3).

(PropargylMIm)[CoBr3quin]. Yield: 96%. mp. 136 °C. Elemental analysis for C16H16N3CoBr3 3 0.25H2O % (calc.): C 34.64 (34.72); H 2.84 (3.00); N 7.62 (7.59). IR (νmax /cm
1): 3258, 3149, 3095, 2943, 2918, 1620, 1592, 1570, 1508, 1461, 1436, 1415, 1398, 1374, 1343, 1312, 1236, 1162, 1145, 1128, 1107, 1056, 1024, 975, 956, 863, 843, 808, 780, 752, 740, 678, 635, 614, 528. UV/vis (λmax /nm in acetonitrile, 25 °C): 204, 263, 300, 312, 618, 633, 693. μeff/μB = 4.54 (T = 25 °C, c = 6.68  10
3 mol/L, ν0 = 300 MHz, χmol = 8.63  10
3).

’ RESULTS AND DISCUSSION Synthesis. The synthesis of ionic liquids containing the CoII-

based anion [CoBr3quin]
(quin = quinoline) can be easily achieved by reacting imidazolium-based precursor ionic liquid halides, anhydrous CoBr2, and quinoline in a molar ratio of 1:1:1 according to Scheme 1. The IL precursors are accessible in short reaction times and mild reaction conditions, for example, under ultrasound or microwave irradiation in the alkylation reactions of N-methylimidazole.15 All compounds of the composition (AlkMIm)[CoBr3quin] (AlkMIm = 1-alkyl-3-methylimidazolium) are distinguished by a intensive blue color in crystalline form. They are non-hygroscopic solids, which are soluble in organic solvents, especially in acetone and acetonitrile. Suitable single crystals of the compounds (AlkMIm)[CoBr3quin] (AlkMIm = EMIm, BMIm, HexMIm, NonMIm) were obtained within a few days by slow evaporation of the solvent from acetonic solutions of the salts at ambient temperature and pressure. Crystal Structures. The single crystal structures of (AlkMIm)[CoBr3quin] (AlkMIm = EMIm, BMIm, HexMIm, NonMIm) have been established by X-ray diffraction analysis. Crystal data and parameters of the structure determinations are given in Table 1, and selected bond lengths of the complex anions as well as bond angles are in Tables 2 and 3, respectively. All compounds consist of isolated imidazolium-based cations and the [CoBr3quin]
anion. (EMIm)[CoBr3quin] crystallizes in the triclinic space group P1 (No. 2) with 2 formula units in the unit cell. Table 2 shows that the averaged Co
Br bond length equals 2.401 Å, which is comparable to the Ni
Br bond length found in the related compound (nBu4N)[NiBr3quin] (2.375 Å), which is the only previously known structurally investigated substance containing the [MeBr3quin]
anion.4a The measured values of the Co
Br bond lengths are in general 0.02 Å shorter than the ones, which can be found, for example, in the salt (DBTMIm)2[CoBr4] with tetrahedrally structured complex anions.7b The Co
N bond length equals 2.058(2) Å, which is in accordance with the analogue bond length, which is found in (nBu4N)[NiBr3quin] (2.029(3) Å). Bond lengths and angles within the quinoline ligand as well as in the (EMIm)+ cation are in compliance with

Scheme 1. Reaction Sequence for the Synthesis of (AlkMIm)[CoBr3quin]

Table 2. Selected Bond Lengths (Å) for the Complex Anion in (AlkMIm)[CoBr3quin] (AlkMIm = EMIm, BMIm, HexMIm, NonMIm) bond length (EMIm)[CoBr3quin]

(BMIm)[CoBr3quin]

(HexMIm)[CoBr3quin]

(NonMIm)[CoBr3quin]

Co
Br1

2.3875(4)

2.4022(3)

2.4054(4)

2.4068(3)

Co
Br2 Co
Br3

2.4157(4) 2.3990(4)

2.3916(3) 2.4078(3)

2.4062(4) 2.4043(4)

2.3781(4) 2.4059(3)

atoms

aver Co
Br

2.400

2.401

2.405

2.397

Co
N1

2.058(2)

2.055(2)

2.077(2)

2.041(2)

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Table 3. Selected Bond Angles (°) for the Complex Anion in (AlkMIm)[CoBr3quin] (AlkMIm = EMIm, BMIm, HexMIm, NonMIm) bond angle atoms

(EMIm)[CoBr3quin]

(BMIm)[CoBr3quin]

(HexMIm)[CoBr3quin]

(NonMIm)[CoBr3quin]

Br1
Co
Br2

112.97(2)

110.64(1)

109.48(1)

116.39(1)

Br1
Co
Br3

108.99(2)

107.02(1)

113.78(2)

105.52(1)

Br2
Co
Br3 aver Br
Co
Br

106.55(2) 109.5

111.35(1) 109.7

108.06(2) 110.4

110.38(1) 110.8

N1
Co
Br1

103.64(6)

106.11(5)

105.15(6)

109.15(5)

N1
Co
Br2

106.19(6)

107.27(5)

117.22(5)

107.30(5)

N1
Co
Br3

118.68(6)

114.35(5)

103.23(5)

107.84(5)

aver N
Co
Br

109.5

109.2

108.5

108.1

Figure 1. Packing of the cations and complex anions in crystals of (EMIm)[CoBr3quin] with three dimensionally connecting C
H 3 3 3 Br contacts. Viewing direction along the crystallographic b-axis.

Figure 2. Surrounding of the complex anion in crystals of (EMIm)[CoBr3quin] with all C
H 3 3 3 Br contacts shorter than 3.0 Å shown as dashed lines. Thermal ellipsoids are shown at the 50% probability level.

reported values.4a,16b In (EMIm)[CoBr3quin] the arrangement of the quinoline ligand shows a similar structural behavior to the situation, which is present in the structure of (nBu4N)[NiBr3quin]: Two of the three Br atoms, all the atoms of the quinoline ligand, and the non-hydrogen atoms of the cation are arranged in layers. Every third Br atom of each anion is located in the neighboring layer, thereby the anions bridge between the layers. The metal atoms are located slightly below and above, respectively, these layers. This atom arrangement is also found in other complexes bearing [MeX3quin]
anions.3e,4d,5 Figure 1 shows this ion packing in crystals of (EMIm)[CoBr3quin] along the crystallographic b-axis and also the three dimensionally connecting C
H 3 3 3 Br hydrogen bonds (dashed lines). Apparently, the phenomenon of hydrogen bonding in ionic liquids is present and certainly contributes to the structure formation.7,16 Furthermore, Figure 1 shows that C
H 3 3 3 Br bonds, which are parallel oriented to the crystallographic a-axis, are connecting the layers within the crystals of (EMIm)[CoBr3quin]. Table 2 summarizes the C
H 3 3 3 Br bond lengths, which are shorter than 3.0 Å. Figure 2 depicts the C
H 3 3 3 Br hydrogen bonds in (EMIm)[CoBr3quin] (dashed lines). The shortest C
H 3 3 3 Br bond is built between the most acidic hydrogen atom of the (EMIm)+ cation and one of the three bromido ligands (C
H10A 3 3 3 Br1: 2.794 Å). From Figure 2, it can be seen that not only C
H 3 3 3 Br bonds between the complex anion and the (EMIm)+ cation are present, but also interestingly two additional intramolecular C
H 3 3 3 Br bonds between the bromido- and quinoline ligands (e.g., C
H6A 3 3 3 Br3: 2.846 Å).

(BMIm)[CoBr3quin] crystallizes as (EMIm)[CoBr3quin] in the triclinic space group P1 with 2 formula units in the unit cell. Similar to the structure of (EMIm)[CoBr3quin], the planar quinoline ligands are arranged parallel to each other. Contrary to (EMIm)[CoBr3quin], the atoms of the butyl group of the BMIm unit are not located as those of the ethyl group of EMIm within these layers. Figure 3 shows the ion arrangement of crystals of (BMIm)[CoBr3quin] and the intermolecular, three dimensionally bridging C
H 3 3 3 Br hydrogen bonds, respectively. Selected bond lengths and angles of the anion are given in Tables 2 and 3. The bond lengths and angles of the complex anion in (BMIm)[CoBr3quin] are comparable to the values, which were determined for (EMIm)[CoBr3quin]. Structural information about the (HexMIm)+ cation in the literature is so far limited to compounds containing lanthanideor uranium-based complex anions.20,21 (HexMIm)[CoBr3quin] crystallizes in the monoclinic space group P21/c (No. 14) with Z = 4 formula units in the unit cell. Selected bond lengths and angles of the anion are given in Tables 2 and 3. The Co
Br bond lengths range from 2.4043(4) to 2.4062(4) Å and are in accordance with values found in (EMIm)[CoBr3quin] or (BMIm)[CoBr3quin]. Figure 4 shows the packing of the molecular ions in crystals of (HexMIm)[CoBr3quin] in a view along the crystallographic a-axis. Similar to the EMIm and the BMIm salts, the quinoline ligands of the complex anion are arranged parallel to each other. These layers are penetrated by (HexMIm)+ cations, in which the conformation of the n-hexyl chain is shaped in such a 5464

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Figure 3. Packing of the molecular ions in crystals of (BMIm)[CoBr3quin] with three dimensionally connecting C
H 3 3 3 Br contacts drawn as dashed lines. Thermal ellipsoids are shown at the 50% probability level.

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Figure 5. Surrounding of the complex anion in crystals of (HexMIm)[CoBr3quin] with all C
H 3 3 3 Br contacts shorter than 3.0 Å shown as dashed lines. Thermal ellipsoids are shown at the 50% probability level.

Figure 4. Layering of the molecular ions in crystals of (HexMIm)[CoBr3quin] with three dimensionally connecting C
H 3 3 3 Br contacts shown as dashed lines. Viewing direction along the crystallographic a-axis.

way that the alkyl chain is parallel orientated to the layers built from the quinoline ligands and complex anions. The occurrence of hydrogen bonding is also present in crystals of (HexMIm)[CoBr3quin], but only Br3 is involved in the hydrogen network between cations and complex anions (see Figure 5). Br2 is involved in intramolecular hydrogen bonding, whereas Br1 is involved in neither intra- nor intermolecular hydrogen bonding. It is interesting to note that none of the hydrogen atoms of the imidazolium ring interact in hydrogen bonding; only hydrogen atoms of the n-hexyl side chain are building up a hydrogen bonding network with contacts shorter than 3.0 Å. This feature probably contributes to the low melting point of (HexMIm)[CoBr3quin] (mp. 67 °C), although the n-hexyl chain is in a favorable fully staggered conformation. This assumption is additionally confirmed by the higher melting points of (EMIm)[CoBr3quin] (mp. 137 °C), (BMIm)[CoBr3quin] (mp. 105 °C) or (NonMIm)[CoBr3quin] (mp. 115 °C), respectively. On the other hand, in certain classes of ILs hydrogen bonding is responsible for lower melting points because they disturb the otherwise regular Coulomb system.23 The report about the crystal structure determination of (NonMIm)[CoBr3quin] is the first one of a solid state structure, which contains the (NonMIm)+ cation. (NonMIm)[CoBr3quin] crystallizes as (HexMIm)[CoBr3quin] in the monoclinic space group P21/c (No. 14) with Z = 4 formula units in the unit cell. Selected bond lengths and angles of the anion are given in Tables 2 and 3. The asymmetric unit is shown in Figure 6, and the extended hydrogen bonding network is in Figure 7, respectively.

Figure 6. The ion pair of the asymmetric unit in crystals of (NonMIm)[CoBr3quin] (ellipsoids at the 50% probability level).

As depicted in Figure 6, it is obvious that the n-nonyl side chain is in a favorable fully staggered conformation (C15
C22). Figure 7 shows that two of the bromido ligands of the complex anion (Br1 and Br3) are involved in the hydrogen bonding network, whereas Br2 is involved neither in intra- nor intermolecular hydrogen bonding. The shortest C
H 3 3 3 Br bond is found between the most acidic hydrogen atom of the (NonMIm)+ cation and Br3 (C
H1A 3 3 3 Br3: 2.821 Å). This is in accordance with the behavior found in (EMIm)[CoBr3quin] and (BMIm)[CoBr3quin]. Infrared Spectra. The IR data in the region 4000 to 500 cm
1 of all compounds are listed in the Experimental Section. IR spectra of imidazolium-based compounds are discussed in the literature in detail.16 The IR spectra show aliphatic C
H stretching frequencies in the region of 3100 to 3000 cm
1, as expected. Many other ILs with imidazolium cations, which carry an acidic hydrogen atom on the C atom between the two nitrogen atoms of the imidazolium ring, show a strong, broad peak in this region, which has been assigned to hydrogen bonding.16 The region 2000 to 500 cm
1 is dominated by internal vibrations of the imidazolium ring and is employed as the fingerprint domain for the presence of planar imidazolium rings. Electronic Spectra. Data from electronic spectra in the region 190
1100 nm for all compounds in acetonitrile solution at 25 °C are given in the Experimental Section. The UV and Vis spectra of (OctMIm)[CoBr3quin] are shown exemplarily in Figure 8. The spectra are designated by several absorption maxima in the 5465

dx.doi.org/10.1021/cg2010419 |Cryst. Growth Des. 2011, 11, 5461–5468

Crystal Growth & Design

Figure 7. Surrounding of the complex anion in crystals of (NonMIm)[CoBr3quin] with all C
H 3 3 3 Br contacts, which are shorter than 3.0 Å shown as dashed lines (C and H atoms of the alkyl side chains are omitted for clarity).

ARTICLE

Figure 9. Molar mass dependence of the melting points of (AlkMIm)[CoBr3quin].

Figure 8. UV- (dashed line, highly diluted solution