Low-melting salts with the [CrIII(NCS)4(1,10- phenanthroline)]- Complex anion: Syntheses, properties, and structures

Article abstract of DOI:10.1134/S1070328412030098

Four new low melting salts, Ionic Liquids consisting of the [Cr^III(NCS)₄(Phen)]^- complex monoanion and imidazolium based cations A, with A = 1-ethyl-3-methylimidazolium (EMIm), 1-butyl-3-methylimidazolium (BMIm), 1,3-dimethyl-2,4,5-triphenylimidazolium (DML), and 1,2,3,4,5-pentamethyl-imidazolium (PMIm), were investigated. Single-crystal X-ray investigations established the structures of the four compounds. (EMIm)[Cr(NCS)₄(Phen)] (I): triclinic, P1, a = 8.1382(6), b = 10.4760(8), c = 16.003(1) A, a = 90.330(4)°, β = 94.759(4)°, y = 1 107.305(4)°, Z = 2, R1(F)/wR₂(F ²) = 0.0650/0.1770; (BMIm)[Cr(NCS)₄(Phen)] (II): triclinic, P, a = 8.5545(4), b = 9.8620(4), c = 16.6762(6) A, a = 92.503(2)°, β = 97.517(2)°, y = 91.249(2)°, Z = 2, R ₁(F)/wR₂(F²) = 0.0393/0.0848; (DML)[Cr(NCS)₄(Phen)] · C₃H₆O (III): triclinic, P1, a = 11.0475(9), b = 13.589(1), c = 14.582(1) A, a = 83.013(4)°, β = 87.116(4)°, y = 70.333(5)°, Z = 2, R1(F)/wR₂(F²) = 0.0407/0.1023; (PMIm)[Cr(NCS) ₄(Phen)] · C₃H₆O (IV): orthorhombic, Pbca, a = 17.379(1), b = 16.514(1), c = 22.304(1) A, Z = 8, R1(F)/wR ₂(F²) = 0.0460/0.1107 (in addition III and IV contain co-crystallized acetone molecules). Each compound was characterized by elemental analysis, NMR, IR, und UV - Vis spectroscopy. Magnetic properties were derived from NMR investigations (EVANS method). All four compounds are paramagnetic with effective magnetic moments of spin-only Cr^III. Melting points were obtained from DSC measurements. All melting points are higher than required for Ionic Liquids , but nevertheless low for molten salts. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070328412030098

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 3, pp. 207–218. © Pleiades Publishing, Ltd., 2012.
Dedicated to Professor Vladimir Fedorov
on the occasion of his 75th birthday
LowꢀMelting Salts with the [CrIII(NCS)4(1,10ꢀPhenanthroline)]–
Complex Anion: Syntheses, Properties, and Structures1
T. Peppela, b, P. Thielea, and M. Köckerlinga, *
a University of Rostock, Department of Chemistry, Inorganic Solid State Chemistry, Rostock, Dꢀ18059 Germany
b Leibniz Institute for Catalysis, Rostock, Dꢀ18059 Germany
*eꢀmail: Martin.Koeckerling@uniꢀrostock.de
Received September 14, 2011
Abstract
monoanion and imidazolium based cations
methylimidazolium (BMIm), 1,3ꢀdimethylꢀ2,4,5ꢀtriphenylimidazolium (DML), and 1,2,3,4,5ꢀpentamethylꢀ
imidazolium (PMIm), were investigated. Singleꢀcrystal Xꢀray investigations established the structures of the
four compounds. (EMIm)[Cr(NCS)4(Phen)] ( ): triclinic, = 8.1382(6), = 10.4760(8), = 16.003(1)
= 90.330(4) = 94.759(4) = 107.305(4)
F2) = 0.0650/0.1770;
(BMIm)[Cr(NCS)4(Phen)] (II): triclinic, = 8.5545(4),
91.249(2)
C3H6O (III): triclinic,
—
Four new low melting salts, “Ionic Liquids” consisting of the [CrIII(NCS)4(Phen)]− complex
, with = 1ꢀethylꢀ3ꢀmethylimidazolium (EMIm), 1ꢀbutylꢀ3ꢀ
A
A
I
a
b
c
Å,
P1,
α
°
,
β
°
,
γ
°
,
Z
= 2, R1
= 9.8620(4),
2, R1 )/wR2
= 11.0475(9),
(
F)/wR2
(
a
b
c
= 16.6762(6)
0.0393/0.0848;
= 14.582(1)
0.0407/0.1023;
= 22.304(1)
F2) = 0.0460/0.1107 (in addition III and IV contain coꢀcrystallized acetone molecules).
Each compound was characterized by elemental analysis, NMR, IR, und UV Vis spectroscopy. Magnetic
Å, α =
P1,
92.503(2)
(DML)[Cr(NCS)4(Phen)]
83.013(4) 87.116(4)
(PMIm)[Cr(NCS)4(Phen)] C3H6O (IV): orthorhombic, Pbca
= 8, R1 )/wR2
°
,
β
=
97.517(2)
°
,
γ
=
°
P1,
,
a
,
Z
=
(
F
(
F2
)
=
⋅
b
= 13.589(1),
2, R1 )/wR2
F2
= 17.379(1), = 16.514(1),
c
Å, α =
°
,
β
=
°
,
γ
=
70.333(5)
°
Z
=
(
F
b
( ) =
⋅
,
a
c
Å,
Z
(
F
(
⎯
properties were derived from NMR investigations (EVANS method). All four compounds are paramagnetic
with effective magnetic moments of spinꢀonly CrIII. Melting points were obtained from DSC measurements.
All melting points are higher than required for “Ionic Liquids”, but nevertheless “low” for molten salts.
DOI: 10.1134/S1070328412030098
1
INTRODUCTION
ates and derived compounds have been used for a variꢀ
ety of applications, like chemical actinometers, as
substances for quantum yield determinations, as comꢀ
pounds in charge transfer photochemistry, and in the
analysis of medicinal products [27–35].
Recently, we have reported about the syntheses,
structure determinations, and property determinations
of a series of imidazoliumꢀbased Reineckates [36].
In this contribution, we report on the synthesis,
properties, and structures of a series of imidazoliꢀ
umꢀbased salts with the Reineckateꢀanalogue anion
[Cr(NCS)4(Phen)]– (Phen = 1,10ꢀphenanthroline).
The following four new Reineckateꢀanalogue comꢀ
pounds were synthesized and investigated:
(EMIm)[Cr(NCS)4(Phen)] (EMIm = 1ꢀethylꢀ3ꢀmeꢀ
The various intriguing properties of salts with meltꢀ
ing points below 100°C have become an intensively
explored research field under the term “Ionic Liquids”
(ILs) for about the last decade. The properties of attenꢀ
tion of this class of materials include wide liquid ranges,
high electrical conductivities, large electrochemical
windows, and low vapor pressures (to name a few) [1–
8]. The number of possible anionꢀcation combinations
forming Ionic Liquids is extremely large. By no surprise
also transition metal complex anions belong to the canꢀ
didate anions of this group of materials. Besides the
other unique properties, Ionic Liquids with paramagꢀ
netic complex anions, called “Magnetic Ionic Liqꢀ
uids”, exhibit interesting magnetic behaviors [9–21].
thylimidazolium)
(BMIm = 1ꢀbutylꢀ3ꢀmethylimidazolium)
(DML)[Cr(NCS)4(Phen)] · C3H6O (DML = 1,3ꢀdimeꢀ
(
I
), (BMIm)[Cr(NCS)4(Phen)]
One appealing transition metal complex
anion with respect to ILs is the Reineckate anion,
(II),
diammineꢀtetra(isothiocyanato)
chromate(III),
[Cr(NCS)4(NH3)2]–. Salts of the Reineckate anion
thyllophinium = 1,3ꢀdimethylꢀ2,4,5ꢀtriphenylimidazoꢀ
lium) (III), and (PMIm)[Cr(NCS)4(Phen)]
(PMIm = 1,2,3,4,5ꢀpentamethylimidazolium) (IV).
Results of crystal structure determinations by means
⋅ C3H6O
are known for more than 150 years [22–26]. Reineckꢀ
1
The article is published in the original.
207

208
PEPPEL et al.
of single crystal Xꢀray diffraction, of temperature inꢀ μeff
/
μB = 3.97 (
T
= 25°C,
dependent magnetic measurements using NMR techꢀ ν0 = 300 MHz, χmol = 6.61
c
×
= 0.75
.
×
10–2 mol/L,
10–3)
niques, as well as results of elemental analyses, and
NMR measurements are reported.
Synthesis of K[Cr(NCS)4(Phen)] [41]. About
1.00 g (5.55 mmol) Phen and 3.78 g (7.30 mmol) careꢀ
fully dried K3[Cr(NCS)6] are heated under reflux in
150 mL of absolute ethanol overnight and then cooled
to room temperature. The precipitate of
K[Cr(NCS)4(Phen)] is filtered off, washed thoroughly
with ethanol and finally with diethyl ether. The resultꢀ
ing pink solid is dried overnight in a drying oven at
EXPERIMENTAL
Materials. All commercially available starting maꢀ
terials were purchased from SigmaꢀAldrich (>99%)
and were used as received. EMImBr and BMImBr
were synthesized according to known procedures [37].
60°C. The yield is 2.43 g (87%).
For EMImBr (C6H11N2Br)
calcd., %:
Found, %:
For C16H8N6CrKS4
C, 37.85;
C, 37.72;
H, 6.04;
H, 5.80;
N, 14.48.
N, 14.66.
calcd., %:
Found, %:
C, 38.16;
C, 38.67;
H, 1.60;
H, 1.54;
N, 16.69.
N, 16.23.
1
Mp. 77
1.48 (t., 3H, Me); 4.00 (s., 3H, N–Me); 4.29 (q., 2H,
N–CH2–); 7.56 (s., 2H, N–CH–CH–N); 10.17 (s.,
1H, N–CH–N). 13C NMR (CDCl3):
= 15.8 (Me); ((CH3)2CO; λmax, nm; 23
°C (77°C [38]). H NMR (CDCl3); δ, ppm):
IR (νmax, cm–1): 3092, 2085
1446, 1037, 820 (CS); 767, 666, 486, 451. UV
C): 390, 442 sh, 551.
= 0.53
10–2 mol/L,
10–3).
ν
(CN); 1609, 1600, 1467,
ν
⎯
Vis
δ
°
C,
×
36.7 (N–Me); 45.3 (N–CH2–); 122.1 (N–CH–CH–
N); 123.8 (N–CH–CH–N); 136.9 (N–CH–N).
μeff
/
μB = 3.91 (
T
= 25
°
c
×
ν0 = 300 MHz, χmol = 6.41
General synthesis of (AlkMIm)ꢀ, (PMIm)ꢀ, and
(DML)[Cr(NCS)4(Phen)]. 2.0 mmol of the appropriꢀ
ate Ionic Liquid precursor halide are added to 100 mL
of an acetonic solution of 2.0 mmol K[Cr(NCS)4L]
(L = Phen). The resulting solution is refluxed for adꢀ
ditional 2 h in order to complete cation exchange and
potassium halide precipitation. The red solution is filꢀ
tered, the solvent is evaporated and the resulting resiꢀ
due is thoroughly washed with a mixture of ethyl aceꢀ
tate–diethyl ether (1 : 1). Final drying in a drying oven
For BMImBr (C8H15N2Br)
calcd., %:
Found, %:
C, 43.98;
C, 43.85;
H, 7.01;
H, 6.90;
N, 12.98.
N, 12.78.
1
Mp. 78°C (78°C [38]). H NMR (CDCl3); δ, ppm):
0.85 (t., 3H, Me); 1.25 (m., 2H, –CH2–Me); 1.81
(m., 2H, –CH2–); 4.02 (s., 3H, N–Me); 4.24 (t., 2H,
N–CH2–); 7.48 (s., 1H, N–CH–CH–N); 7.60 (s.,
1H, N–CH–CH–N); 10.24 (s., 1H, N–CH–N). 13C
at 60
(EMIm)[Cr(NCS)4(Phen)] (I). From EMImBr.
Yield 99%; mp. 210 C.
°C leads to a ruby red solid. The yield is >90%.
NMR (CDCl3): δ = 13.5 (Me); 19.5 (CH2–Me); 32.2
(–CH2–); 36.8 (N–Me); 49.9 (N–CH2–); 122.3
(N–CH–CH–N); 123.9 (N–CH–CH–N); 137.3
(N–CH–N). 1,2,3,4,5ꢀPentamethylimidazolium ioꢀ
dide (PMImI) and 1,3ꢀdimethylꢀ2,4,5,ꢀtriphenylimidaꢀ
zolium iodide (1,3ꢀdimethyllophinium iodide, DMLI),
respectively, were synthesized according to [21, 39].
°
For C22H19N8CrS4 ⋅ 0.5H2O
calcd., %: C, 45.19; H, 3.45; N, 19.16; S, 21.94.
Found, %: C, 45.21; H, 3.14; N, 18.62; S, 20.10.
Synthesis of K3[Cr(NCS)6] [40]. A 100 mL aqueꢀ
ous solution of 5.00 g (0.01 mol) chrome alum (chroꢀ
mium(III) potassium sulfate) and 5.83 g (0.06 mol)
potassium thiocyanate is evaporated to dryness. The
residue is extracted exhaustively with ethyl acetate and
the resulting solution is evaporated to dryness again.
(The water content results from the hygroscopic naꢀ
ture and the necessity to handle the compound in air
for a short time prior to the analysis.)
IR (νmax, cm–1): 3138, 3106, 3072, 3051, 2981,
2929, 2871, 2092, 2051
1564, 1517, 1494, 1423, 1342, 1310, 1224, 1209, 1166,
1145, 1108, 1052, 1033, 959, 913, 875, 843, 831 (CS),
771, 747, 739, 718, 647, 619, 594, 560. UV Vis
((CH3)2CO; λmax, nm; 23 C): 440 sh, 543. μeff μB
3.85 ( = 25 C, = 0.57
10–2 mol/L, ν0 = 300 MHz,
χmol = 6.21
10–3).
(BMIm)[Cr(NCS)4(Phen)] (II). From BMImBr.
ν(CN), 1627, 1604, 1581,
The redꢀviolet solid is finally dried at 140
to liberate water of crystallization. The yield is 4.66 g
(90%) of a hygroscopic solid.
°C in vacuum
ν
⎯
°
/
=
For C6CrK3N6S6
calcd., %:
Found, %:
⋅ 0.5H2O
C, 13.68;
C, 13.71;
T
°
×
c
×
H, 0.19;
H, 0.17;
N, 15.95.
N, 15.98.
Yield 98%; mp. 181
°C.
(The water content results from the hygroscopic
nature and the necessity to handle the compound in
air for a short time prior to the analysis.)
For C24H23N8CrS4
calcd., %: C, 47.74; H, 3.84; N, 18.56; S, 21.24.
Found, %: C, 47.81; H, 3.63; N, 17.87; S, 22.10.
IR
(
νmax, cm–1): 2098
ν
(CN), 1698, 823
ν(CS),
C): 418, 553.
479. UV–Vis ((CH3)2CO; λmax, nm; 23
°
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 3
2012

LOWꢀMELTING SALTS WITH THE [CrIII(NCS)4(1,10ꢀPHENANTHROLINE)]–
209
IR (νmax, cm–1): 3137, 3104, 3078, 3050, 2948, 2928, 1H NMR techniques (EVANS method) [42, 43]. Molar
susceptibilities were corrected by applying PASCAL
constants [44, 45]. Effective magnetic moments
μeff μB are given by applying the Langevin equation
[46, 47].
2867, 2097, 2055
1557, 1518, 1493, 1463, 1455, 1423, 1344, 1309, 1224,
1207, 1156, 1141, 1106, 1021, 951, 877, 839 (CS),
772, 736, 727, 716, 652, 622. UV Vis ((CH3)2CO; λmax
nm; 23 C): 440 sh, 543. μeff μB = 3.78 ( = 25 C,
= 1.04
10–2 mol/L, ν0 = 300 MHz, χmol = 5.97 10–3).
ν(CN), 1682, 1629, 1603, 1581,
/
ν
⎯
,
°
×
/
T
°
Xꢀray structure analysis. Suitable single crystals for
c
×
Xꢀray measurements were obtained within a few days
by slow evaporation of the solvent off acetonic soluꢀ
tions of the salts at ambient temperature and pressure.
(PMIm)[Cr(NCS)4(Phen)] (IV). From PMImI.
Yield 98%; mp. 290°C.
Rubyꢀred crystals of A[Cr(NCS)4(Phen)]
where A = EMIm ( = 0; ), BMIm ( = 0; II), DML
= 1; III), or PMIm ( = 1; IV) were mounted on the
⋅ nC3H6O,
n
I
n
For C24H23N8CrS4
(n
n
calcd., %: C, 47.74; H, 3.84; N, 18.56; S, 21.24.
Found, %: C, 47.34; H, 3.80; N, 17.67; S, 21.82.
tips of thin glass fibers for the singleꢀcrystal Xꢀray difꢀ
fraction measurements. Data were collected on a
BrukerꢀNonius Apex X8 diffractometer equipped with
a CCD detector. Measurements were done using
IR (νmax, cm–1): 3171, 3105, 3044, 2953, 2281, 2098
monochromatic MoKα radiation (λ = 0.71073 Å).
ν
(CN), 2048, 1643, 1581, 1538, 1517, 1494, 1439,
1424, 1347, 1331, 1181, 1136, 1105, 1052, 960, 875,
851, 827 (CS), 787, 762, 738, 719, 652, 614, 569.
UV Vis ((CH3)2CO; λmax, nm): 440 sh, 543. μeff μB
3.78 (
10–2 mol/L, ν0 = 300 MHz,
χmol = 6.00
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 usꢀ
ing the BrukerꢀNonius software [48]. The structure
solutions and refinements were done with the aid of
the SHELXꢀ97 program package [49]. All nonꢀhyꢀ
drogen atoms were refined anisotropically. The hyꢀ
drogen atoms were added on idealized positions and
refined using riding models. Crystal data, data collecꢀ
tion, and refinement parameters are collected in Taꢀ
ble 1, atom distances are given in Table 2, and selected
bond angles are listed in Table 3. Crystallographic daꢀ
ta for the structural analyses have been deposited with
the Cambridge Crystallographic Data Centre (CCDC
ν
⎯
/
=
T
= 25
°
×
C,
c = 1.27 ×
10–3).
(DML)[Cr(NCS)4(Phen)] (III). From DMLI.
Yield 94%. mp. 236 C.
°
For C39H29N8CrS4 ⋅ H2O
calcd., %: C, 57.97; H, 3.87; N, 13.87; S, 15.87.
Found, %: C, 57.99; H, 3.59; N, 13.49; S, 15.92.
(The water content results from the hygroscopic
nature and the necessity to handle the compound in
air for a short time prior to the analysis.)
IR (νmax, cm–1): 3046, 2912, 2417, 2349, 2285, 2094
nos. 840095 (I), 840093 (II), 840094 (III), and
840096 (IV); deposit@ccdc.cam.ac.uk or http://www.
ccdc.cam.ac.uk).
ν
(CN), 2044, 1581, 1514, 1486, 1442, 1413, 1343,
1277, 1147, 1110, 1023, 966, 931, 876, 856, 842
(CS), 769, 760, 718, 698, 652, 560, 527. UV Vis
((CH3)2CO; λmax, nm): 440 sh, 543. μeff μB = 3.76
10–2 mol/L, ν0 = 300 MHz,
ν
⎯
RESULTS AND DISCUSSION
/
(T
= 25
°
C,
c
= 0.97
10–3).
×
The synthesis of imidazoliumꢀbased salts containing
the Reineckateꢀanalogue anion [Cr(NCS)4(Phen)]− is
facile and can be achieved easily by metathesis reacꢀ
tions between the corresponding potassium salt
K[Cr(NCS)4(Phen)] and alkylated imidazolium haꢀ
lides in high yields (>90%). The precursor potassium
salt is accessible from K3[Cr(NCS)6] [40] and Phen,
respectively, in ethanolic solution. All compounds are
distinguished by a deep rubyꢀred color in the solid
state. They are insoluble in water, but soluble in organꢀ
ic solvents, especially in acetone and acetonitrile.
χmol = 5.91
×
Analysis and spectroscopic measurements. 1H
NMR and 13C NMR spectra were recorded on a Brukꢀ
er ARX 300 spectrometer. Spectra were calibrated with
respect to the solvent signal (DMSOꢀd6: 1H
δ
= 2.50;
13C
δ
= 39.5 ppm). MIR spectra (500–4000 cm–1)
were recorded by using ATR technique on a Thermo
Nicolet 380 FTꢀIR spectrometer. Elemental analyses
for C, H, N, and S were obtained with a Flash EA 1112
NC Analyzer from CE Instruments. UV
were recorded using a PerkinElmer Lambda 2 specꢀ
trometer with quartz cuvettes (Suprasil®,
= 10 mm).
⎯Vis spectra
All four compounds consist of isolated
[Cr(NCS)4(Phen)]– anions, imidazoliumꢀbased catꢀ
d
Melting points were determined by DSC measureꢀ ions, and, in the case of III and IV, coꢀcrystallized acꢀ
etone solvent molecules. Thermal ellipsoid plots of the
ion pairs for complexes IV are shown in Fig. 1. All
ments using a Mettler Toledo DSC823e in the range of
0–400 C with a heating rate of 10 K/min (N2 atmoꢀ
sphere, Al crucible). All melting points are peak temꢀ
peratures. Magnetic data were determined by means of
I
–
°
four compounds contain the same Reineckateꢀderived
[Cr(NCS)4(Phen)]– anion, with the Cr3+ ion being
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 3
2012

210
PEPPEL et al.
Table 1. Crystallographic data and structure refinement for I–IV
Value
Parameter
I
II
III
IV
Formula
C22H19CrN8S4
575.69
C24H23CrN8S4
603.7404
173(2)
C42H35CrN8OS4
848.02
C27H29CrN8OS4
661.82
Fw
T
, K
173(2)
173(2)
173(2)
Crystal system
Space group
Triclinic
Triclinic
Triclinic
Orthorhombic
Pbca
P
1
P
1
P1
a
, Å
, Å
, Å
, deg
, de
8.1382(6)
10.4760(8)
16.003(1)
90.330(4)
94.759(4)
107.305(4)
1297.5(2); 2
1.474
8.5545(4)
9.8620(4)
16.6762(6)
92.503(2)
97.517(2)
91.249(2)
1392.9(1); 2
1.439
11.0475(9)
13.589(1)
14.582(1)
83.013(4)
87.116(4)
70.333(5)
2046.0(3); 2
1.377
17.379(1)
16.514(1)
22.304(1)
b
c
α
β
g
γ, deg
V
ρ
μ
θ
, Å3;
Z
6400.9(8); 8
1.374
, g cm–3
, mm–1
0.791
0.740
0.528
0.653
Range, deg
7.56–56.74
16490
4.72–46.40
14784
4.78–59.34
47716
7.06–56.06
48144
Collected reflections
Unique reflections (Rint
Variables
)
6196 (0.051)
316
4216 (0.045)
334
1159 (0.025)
524
12175 (0.058)
407
GOOF on F2
1.058
1.018
1.024
0.995
R1
,
,
wR2
(
I
> 2
σ
(
I
))a, b
0.0650, 0.1770
0.0836, 0.1933
0.1258, 0.3934
1.314, –0.752
0.0393, 0.0848
0.0637, 0.0946
0.0384, 0.8772
0.364, –0.286
0.0407, 0.1023
0.0618, 0.1129
0.0538, 0.8653
0.478, –0.392
0.0460, 0.1107
0.1068, 0.1357
0.0655, 0.3042
0.442, –0.425
R1
wR2 (all data)a, b
A,
Bb
Largest diff. peak and hole,
e
A–3
2 2
{w(F 2 − Fc2)2}
a
b
2
2
R
=
wR
=
w
{w(F ) };
o
= 1/[(
σ
(
Fo2) + (AP) + BP];
P
= (Fo2 + 2Fc2)/3.
F
o
− Fc
F ;
o
∑
∑
∑
∑
o
1
2
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LOWꢀMELTING SALTS WITH THE [CrIII(NCS)4(1,10ꢀPHENANTHROLINE)]–
211
Table 2. Selected bond lengths (Å) for complex anion in
I–IV and S⋅⋅⋅H contacts around the complex anion
d
, Å
Bond
I
II
III
IV
Cr(1)–NCS: Cr(1)–N(1)
Cr(1)–N(2)
1.985(3)
1.974(3)
1.990(3)
1.977(3)
1.982
2.000(3)
1.985(3)
1.982(3)
1.980(3)
1.987
1.999(2)
2.009(2)
1.999(2)
1.991(2)
2.000
1.986(2)
1.980(2)
2.015(2)
1.979(2)
1.990
Cr(1)–N(3)
Cr(1)–N(4)
Average Cr(1)–N(NCS)
Cr(1)–N(Phen): Cr(1)–N(5)
Cr(1)–N(6)
2.069(3)
2.077(3)
2.073
2.065(2)
2.077(3)
2.071
2.086(1)
2.087(1)
2.087
2.067(2)
2.068(2)
2.068
Average Cr(1)–N(Phen)
Average N–C
1.150
1.160
1.152
1.142
Average C–S
1.619
1.625
1.629
1.622
S⋅⋅⋅H contacts up to 3 Å
Number of S⋅⋅⋅H contacts
Shortest S⋅⋅⋅H contact
4
6
3
6
2.769
2.824
2.711
2.757
Table 3. Selected bond angles (deg) for the complex anion in I–IV
ω
, deg
Angle
I
II
III
IV
N(5)Cr(1)N(6)
79.4(1)
177.8(1)
178.8
79.9(1)
177.1(1)
178.4
79.19(5)
79.89(6)
NCr(1)N(NCS)*
Average NCS
178.67(6)
179.0
175.68(6)
179.1
Average Cr(1)NC
Range
166.6
174.2
165.7
174.1
158.3–171.2
172.6
169.7–178.7
172.5
159.0–176.6
171.3
172.4–176.9
172.7
Average N(Phen)CrN(NCS) (trans
)
* The NCr(1)N angle of the trans arranged NCS groups with the NCr(1)N vector perpendicular to the mean plane of the phenanthroline
moiety.
distorted octahedrally coordinated by 6N atoms. The than 90
2N atoms of the neutral Phen ligand coordinate necꢀ smaller than the ideal 180
°
, also the N(Phen)CrN(NCS) (trans) are
. Unaffected from this
ligand induced constrain the N(NCS)CrN(NCS)
trans) angle, with the N–Cr–N vector being perpenꢀ
dicular oriented to the mean plane of the atoms of the
Phen ligand, deviates much less from the ideal 180 (in
the range of 175.68(6) IV) to 178.67(6) III)). The
the coordination geometry around the Cr3+ ion deviates Cr(1)NCS angles are found in the range from 158.3
°
essarily in a cis manner to the metal ion. The other four
coordination sites are occupied by the N atoms of the
isoꢀthiocyanate ligands. Because of the fixed bite angle
of the two donor atoms of the Phen ligand, which
(
°
range from 79.19(5)° (III) to 79.9(1)° (II) (Table 3),
°
(
° (
°
from ideal octahedral. Because it is significantly smaller to 178.7°. The NCS units are almost linear, as expectꢀ
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212
PEPPEL et al.
(a)
C(14)
C(15)
C(12)
C(16)
C(11)
C(10)
S(1)
C(1)
S(2)
C(21)
N(6)
N(1)
C(2)
C(13)
C(9)
N(5)
N(2)
C(8)
C(7)
C(22)
N(8)
C(18)
C(17)
Cr(1)
C(20)
N(3)
N(7)
C(6)
C(5)
N(4)
C(4)
C(19)
C(3)
S(3)
S(4)
(b)
C(12)
C(13)
C(11)
C(10)
C(9)
C(20)
C(15)
S(1)
C(14)
N(6)
N(7)
C(17)
S(2)
C(2)
C(8)
N(2)
N(8)
C(1)
N(1)
C(16)
Cr(1)
C(19)
N(3)
C(3)
C(7)
N(5)
C(5)
C(21)
C(18)
S(3)
C(6)
N(4)
C(22)
C(23)
C(4)
S(4)
C(24)
Fig. 1. Molecular structure of the cationꢀanion pair in crystals of I (a), II (b), III (c), and IV (d) with atom labeling scheme (therꢀ
mal ellipsoids at the 50% probability level).
ed (Table 3). All these structural parameters compare plots in crystals of
I
and II
3, respectively. In crystals of the EMIm salt, the Phen
rings are separated by a distance of 4.069 , indicating
interactions. In and II, every next anion on both
sides of each Phen ligand is switched around by 180
Thereby, double layers of anions are formed extending
–IV are shown in Figs. 2 and
well with those found in compounds of the
[Cr(NCS)4(Phen)]– complex anion with other cations
[50–55]. In the crystals of the Reineckate derived anꢀ
ion with the EMIm, BMIm, and the DML cation, the
anions are arranged such that all the planar phenanꢀ
Å
π–π
I
°.
throline ligands are parallel to each other. Packing in the xyꢀplanes of the lattice. The mean planes
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LOWꢀMELTING SALTS WITH THE [CrIII(NCS)4(1,10ꢀPHENANTHROLINE)]–
213
(с)
C(25)
C(24)
C(26)
C(23)
S(4)
S(2)
C(22)
C(4)
C(2)
N(2)
N(5)
C(27)
C(5)
C(20)
N(7)
C(17)
C(6)
C(7)
N(4)
Cr(1)
C(21)
S(1)
C(19)
C(34)
N(8)
C(9)
N(6)
C(8)
C(10)
C(39)
N(1)
C(1)
C(18)
C(28)
N(3)
C(13)
C(38)
C(37)
C(35)
C(3)
C(11)
C(16)
C(12)
C(15)
C(14)
C(36)
C(30)
C(31)
S(3)
C(33)
C(32)
(d)
C(10)
C(8)
C(7)
C(11)
C(12)
C(24)
C(6)
C(5)
C(23)
C(9)
N(7)
C(14)
C(15)
C(19)
C(18)
C(13)
N(6)
N(5)
C(1)
S(1)
N(1)
C(17)
C(21)
C(20)
C(16)
N(8)
N(3)
C(22)
Cr(1)
N(2)
C(3)
S(3)
N(4)
C(2)
S(2)
C(4)
S(4)
Fig. 1. (Contd.).
through the atoms of the phenanthroline molecules scopic properties like the melting points of the comꢀ
extend in the [110] direction. Out of both sides of the
anionic double layers NCS units stick out (Fig. 2). Beꢀ
tween the anionic layers the cations are located (not
shown in Fig. 2). The arrangement of ions in IV is difꢀ
ferent from that in I, II, and III with respect to the asꢀ
sembly of the phenanthroline ligands; here two differꢀ
ent, nonꢀparallel orientations are found (Fig. 3c).
pounds. The number and distances up to
S(anion)⋅⋅⋅H(cation) contacts are listed in Table 2.
Whereas and II contain acidic protons on the imidaꢀ
zolium based cations, these are absent in III and IV
Figure 4 shows the molecular environment of one
complex anion of with the ⋅⋅⋅ contacts shorter
than Å sketched. Both compounds, and II, have the
3 Å of the
I
.
I
S H
3
I
shortest hydrogen contacts between the sulfur atoms of
the anion and the acidic H atoms of the neighboring
Another structural aspect worth mentioning are the
shortest anion⎯cation contacts with respect to the
interaction strength influencing necessarily macroꢀ cations.
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214
PEPPEL et al.
y
x
z
Cr
N
C
S
H
Fig. 2. Arrangement of the complex anions with the parallel orientation of the planar phenanthroline moieties in crystals of I.
The MIR data in the region of 4000–500 cm–1 of reported in detail in the literature [41, 60–62]. The
CN stretching frequencies ν(CN) are located between
all four compounds are listed in the Experimental Secꢀ
tion. IR spectra of imidazoliumꢀbased compounds
have been discussed extensively in the literature [56–
59]. As expected, they all show aliphatic C–H stretchꢀ
2080–2100 cm–1, the CS stretching frequencies
ν(CS)
between 820–850 cm–1, respectively, and are in accorꢀ
dance with published values [41, 60–65].
ing frequencies in the region of 3100–3000 cm–1
.
The positions of the absorption maxima in the
electronic spectra in the region from 190 to 1000 nm
for all four compounds in acetonic solution at room
temperature are given in the Experimental Section. Ocꢀ
tahedrally coordinated Cr(III) complexes exhibit two
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 the same IR region, which has
been assigned to hydrogen bonding [56–59]. With this
H atom being absent in the compounds III and IV, the
respective hydrogen bonding and the corresponding
band in the IR spectra is absent. The region 2000–
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.
The IR spectra of compounds containing the Reiꢀ
neckateꢀanalogue anions [Cr(NCS)4(Phen)]– are
spin allowed transitions, 4T2
← (F) ← ,
4A2g and 4T1 4A2
g
g g
in the Vis region. In addition, there is a third transiꢀ
tion, 4T1 4A2g, which is often interfered by
charge transfer bands. UV Vis investigations on comꢀ
(P) ←
g
⎯
pounds containing the Reineckateꢀanalogue anions
[Cr(NCS)4L]– (L = Bipy, Phen) have been reported in
the literature [41, 60–62, 66–68]. The charge transfer
band (e.g. 388 nm for K[Cr(NCS)4(Bipy)]) and the loꢀ
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LOWꢀMELTING SALTS WITH THE [CrIII(NCS)4(1,10ꢀPHENANTHROLINE)]–
215
(a)
Cr
N
C
S
H
y
z
x
(b)
Cr
N
C
S
y
H
z
x
Fig. 3. Packing of the isolated cations and anions in crystals of II (a), III (b), and IV (c).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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216
PEPPEL et al.
(с)
Cr
N
C
S
H
z
y
x
Fig. 3. (Contd.).
cation of the two 4T2
←
4A2 (540–550 nm) and
g
in (EMIm)[Cr(NCS)4(Phen)] to 181
°
C
in
g
4T1 4A2g (440–445 nm) transitions, respectively,
(F) ←
g
(BMIm)[Cr(NCS)4(Phen)]. It is obvious that these
compounds have high melting points, which lie far
above the limit for “Ionic Liquids”. It is interesting to
note, that in the case when the most acidic hydrogen
atom in the imidazolium ring between the two nitroꢀ
gen atoms is exchanged by either methyl or phenyl
substituents in the compounds (PMIm)ꢀ or
(DML)[Cr(NCS)4(Phen)], the melting points are not
decreasing. This behavior supports the finding, that
often directed hydrogen contacts disturb the otherꢀ
wise more symmetrical coulomb system and leads to
lower melting points [39, 69]. The highest melting
point can be found for the compound
(PMIm)[Cr(NCS)4(Phen)] due to the high symmetry
of the 1,2,3,4,5ꢀpentamethylimidazolium cation.
This behavior can be also found in other known
PMImꢀcontaining systems [39, 69].
are nearly independent of the choice of the cation in
acetonic solution and are in accordance with values
found for the four title compounds.
In order to see if the title compounds can be conꢀ
sidered to belong to the chemical subclass of “Ionic
Liquids”, thermal data have been measured using
DSC techniques in the temperature range from 0–
400°C. Melting points were detected as endothermic
peaks in the DSC experiments above 100
°C. All meltꢀ
ing points are listed in the Experimental section. All
detected melting points are higher than the melting
points in the corresponding imidazoliumꢀbased Reiꢀ
neckates A[Cr(NCS)4(NH3)2] (A = EMIm, BMIm,
PMIm, DML) [36]. The melting point is slightly deꢀ
creasing with increasing alkyl chain length from ethyl
to butyl in the imidazoliumꢀbased cation from 210°C
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2012

LOWꢀMELTING SALTS WITH THE [CrIII(NCS)4(1,10ꢀPHENANTHROLINE)]–
217
2.972
Å
2.769
Å
Cr
N
C
2.924
Å
S
2.941
Å
H
Fig. 4. Molecular environment of each complex anion in crystals of (EMIm)[Cr(NCS) (Phen)] with the S⋅⋅⋅H contacts shorter
4
than 3
Å shown as dashed lines.
5. Weingärtner, H., Angew. Chem., 2008, vol. 120, p. 664.
6. Buzzero, M.C., Evans, R.G., and Compton, R.G.,
Chem. Phys. Chem., 2004, vol. 5, p. 1106.
7. Marsh, K.N., Boxal, J.A., and Lichtenthaler, R., Fluid
Phase Equilib., 2004, vol. 219, p. 93.
The magnetic properties at room temperature of all
investigated complex salts were determined in solution
using NMR techniques applying the Evans method
[42, 43]. All complexes display similar magnetic propꢀ
erties. They are paramagnetic with effective magnetic
moments in the range of μeff = 3.76–3.93 μB at 25°C
8. Endres, F. and Abedin, S.Z.E., Phys. Chem. Chem.
Phys., 2006, vol. 8, p. 2101.
9. Hayashi, S. and Hamaguchi, H., Chem. Lett., 2004,
vol. 33, p. 1590.
10. Hayashi, S., Saha, S., and Hamaguchi, H., IEEE
Trans. Magn., 2006, vol. 42, p. 12.
(spin only highꢀspin Cr3+: μeff = 3.87 μB). These values
resemble closely those of related compounds, for examꢀ
ple K[Cr(NCS)4(Phen)] (μeff = 4.10 μB) [70],
[Ce(Phen)4][Cr(NCS)4(Phen)] (μeff = 3.77 μB) [60–
62], or (Ph3Ge)[Cr(NCS)4(Phen)] (μeff = 3.73 μB
300 K) [66–68].
,
11. Zhang, Q.ꢀG., Yang, J.ꢀZ., Lu, X.ꢀM., et al., Fluid
Phase Equilibria, 2004, vol. 226, p. 207.
12. Zhong, C., Sasaki, T., JimboꢀKobayashi, A., et al., Bull.
Chem. Soc. Jpn., 2007, vol. 80, p. 2365.
13. Kozlova, S.A., Verevkin, S.P., Heintz, A., et al.,
ACKNOWLEDGMENTS
Support from the DFG (SPP 1191–Ionic Liquids,
KO–1616/4ꢀ1 and 1616/4ꢀ2) is gratefully acknowlꢀ
edged. The authors also thank Dr. K. Neubauer,
C. Schmidt, and J. Bronkal for their support.
J. Chem. Eng. Data, 2009, vol. 54, p. 1524.
14. Peppel, T
2010, vol. 636, p. 2439.
15. Peppel, T., K ckerling, M., GeppertꢀRybczy
et al., Angew. Chem., 2010, vol. 122, p. 7270.
16. Yoshida, Y and Saito, G., Phys. Chem. Chem. Phys.
2010, vol. 12, p. 1675.
.
and K
ö
ckerling, M., Z. Anorg. Allg. Chem.
,
'
ö
n
ska, M.,
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