Synthesis, properties, and structures of salts with the Reineckate anion, [CrIII(NCS)4(NH3)2]-, and large organic cations

Article abstract of DOI:10.1002/zaac.201100091

A series of 9 new Reineckate salts, A[Cr^III(NCS) ₄(NH₃)₂] with various large organic cations A = tetraalkylammonium, [R₄N]⁺, R = n-butyl, n-dodecyl; 1-alkyl-3-methylimidazolium, (RMIm)

Full text of DOI:10.1002/zaac.201100091

ARTICLE
DOI: 10.1002/zaac.201100091
Synthesis, Properties, and Structures of Salts with the Reineckate Anion,
[CrIII(NCS)4(NH3)2]–, and Large Organic Cations
Tim Peppel,[a] Christin Schmidt,[a] and Martin Köckerling*[a]
Keywords: Chromium; Crystal structure; Reinecke’s salt; Imidazolium
Abstract. A series of 9 new Reineckate salts, A[CrIII(NCS)4(NH3)2] n-dodecyl-ammonium, 1-ethyl-3-methylimidazolium, and 1,2,3,4,5-
with various large organic cations A = tetraalkylammonium, [R4N]+, pentamethylimidazolium were determined by single-crystal X-ray dif-
R = n-butyl, n-dodecyl; 1-alkyl-3-methylimidazolium, (RMIm)+: R = fraction measurements: (nBu4N)[Cr(NCS)4(NH3)2]: monoclinic, C2/c
methyl, ethyl, iso-propyl, n-butyl, and n-hexyl; A = 1,3-dimethyl-2,4,5- (no. 15), a = 12.0818(8), b = 10.2425(8), c = 24.222(2) Å, β =
triphenylimidazolium and A = 1,2,3,4,5-pentamethylimidazolium was 98.324(3)°,
Z
=
4,
R1(F)/wR2(F2)
=
0.0332/0.0871;
¯
synthesized. The melting point of each compound was measured to {(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O: triclinic, P1 (no. 2), a =
see if any belongs to the group of metal-containing Ionic Liquids with 8.4049(1), b = 20.1525(4), c = 20.7908(4) Å, α = 67.487(1)°, β =
low melting points. Each compound was further characterized by ele- 81.328(1)°, γ = 78.040(1)°, Z = 2, R1(F)/wR2(F2) = 0.0533/0.1343;
mental analysis, NMR, IR, and UV/Vis spectroscopy. From NMR in- (EMIm)[Cr(NCS)4(NH3)2]: orthorhombic, Pbcm (no. 57),
a =
vestigations information about the magnetic behavior was derived 8.765(2), b = 15.888(3), c = 14.191(3) Å, Z = 4, R1(F)/wR2(F2) =
using the Evans method. It has been found that every compound is 0.0466/0.1271; (PeMIm)[Cr(NCS)4(NH3)2]: monoclinic, P21/n (no.
paramagnetic with effective magnetic moments of spin-only CrIII. The 14), a = 6.0817(2), b =13.9811(5), c = 25.2902(9) Å, β = 90.075(2)°,
structures of the Reineckates with A = tetra-n-butyl-ammonium, tetra- Z = 4, R1(F)/wR2(F2) = 0.0405/0.1111.
medicinal products.[8] Although, Łodzińska and Ali have re-
Introduction
ported about the influence of organic cations on the properties
of Reineckates,[9] until today there has been no information
The first compounds based on the Reineckate anion
[CrIII(NCS)4(NH3)2]– were reported by Morland and Reinecke
about imidazolium-based Reineckates in the literature, which
could be tested as suitable candidates for Magnetic Ionic
Liquids. In general Ionic Liquids (ILs) with melting points
below 100 °C have attracted great interest because of their spe-
cial and useful properties, such as wide liquid ranges, negligi-
ble vapor pressures, large electrochemical windows, or high
electric conductivity.[10–13] Some transition metal based Ionic
Liquids (Magnetic Ionic Liquids) exhibit interesting magnetic
properties in addition to those mentioned above. It has turned
out, that ILs containing [FeCl4]– or [CoX4]2– (X = Br, NCS)
anions are paramagnetic liquids, which show a distinct re-
sponse to magnetic fields.[14–16] In this contribution we report
on the synthesis, properties and structures of imidazolium- and
tetraalkylammonium-based Reineckates. In order to investigate
the dependence of the melting points with the length and na-
ture of the substituents in the imidazolium cations, three differ-
ent types of cations were tested: 1-alkyl-3-methylimidazolium
(alkyl = methyl, ethyl, iso-propyl, n-butyl, n-hexyl), 1,3-di-
methyl-2,4,5-triphenylimidazolium, and 1,2,3,4,5-pentamethyl-
imidazolium. Furthermore, for the reason of comparison, two
tetraalkylammonium Reineckates were synthesized as well:
tetra-n-butylammonium and tetra-n-dodecylammonium Rei-
neckate. In total 9 new Reineckates were synthesized and in-
vestigated of which 4 were characterized by means of single-
crystal X-ray diffraction.
150 years ago, without any knowledge of the constitution of
their obtained salts.[1] Later, Christensen, Nordenskjöld, and
Werner, respectively, elaborated the correct constitution by
means of chemical analyses of follow reactions and decompo-
sition products.[2] The correct constitution of Reinecke’s salt
(ammonium Reineckate, (NH4)[Cr(NCS)4(NH3)]·0.66H2O)
was finally established by single-crystal X-ray diffraction tech-
niques by Takéuchi and Saito 55 years ago.[3] Since then, only
a few crystal structure determinations of compounds contain-
ing the Reineckate anion have been reported,[4] although the
chemistry of Reineckates and related substances has emerged
great interests not only in the last decades. Reineckates have
been used as chemical actinometers,[5] substances for quantum
yield determinations,[6] and as compounds in charge transfer
photochemistry.[7] Reineckates have also been used in the grav-
imetric, volumetric as well as spectrophotometric analysis of
* Prof. Dr. M. Köckerling
Fax: +49-381-498-6382
E-Mail: martin.koeckerling@uni-rostock.de
[a] Universität Rostock
Institut für Chemie
Abteilung Anorganische Festkörperchemie
Albert-Einstein-Str. 3a
18059 Rostock, Germany
1314
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 637, 1314–1321

Salts with the Reineckate Anion, [CrIII(NCS)4(NH3)2]– and Large Organic Cations
Scheme 1. Reaction sequence for the synthesis of the tetraalkylammonium- and imidazolium-based salts containing the Reineckate anion
[Cr(NCS)4(NH3)2]–.
Electronic Spectra
Results and Discussion
Octahedrally coordinated CrIII complexes exhibit two transi-
Synthesis
tions in the Vis region, which are characterized by 4T2g ← 4A2g
4
4
(lower energy) and T1g(F) ← A2g (higher energy). In addi-
tion, there is a third short-waved transition, which is often in-
The synthesis of salts with large organic cations containing the
Reineckate anion [Cr(NCS)4(NH3)2]– can be easily achieved
by metathesis reactions between the Reinecke salt
(NH4)[Cr(NCS)4(NH3)2]·0.66H2O) and alkylimidazolium or
tetraalkylammonium halides in high yields (>80 %) according
to Scheme 1. All compounds have a deep ruby-red color in
crystalline form. They are insoluble in water, but highly solu-
ble in organic solvents, especially in acetone and acetonitrile.
4
terfered by charge-transfer bands and characterized by T1g(P)
← 4A2g. Intensive UV/Vis investigations with compounds con-
taining the Reineckate anion [Cr(NCS)4(NH3)2]– are reported
in the literature.[9,18] The location of the two 4T2g ← 4A2g (526
4
4
nm) and T1g(F) ← A2g (396 nm) transitions is independent
of the choice of the cation in acetone solution and in accord-
ance with reported values.[9,18]
Infrared Spectra
Melting Points
The IR data in the region 4000–500 cm–1 of the imida-
zolium-, and tetraalkylammonium-based Reineckates are listed
Thermal data of the title compounds were measured using
in the Experimental Section. IR spectra of imidazolium-based DSC (differential scanning calorimetry) in the temperature
compounds are discussed in the literature in detail.[17] The IR range from 0–400 °C. Melting points were detected as endo-
spectra show aliphatic C–H stretching frequencies in the region thermic peaks in the DSC experiments above 100 °C, except
of 3100–3000 cm–1, as expected. Many other ILs with imida- for {(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O (C12H25
=
zolium cations, which carry an acidic hydrogen atom at the n-dodecyl, mp. 48 °C). All melting points can be found
carbon atom between the two nitrogen atoms of the imida- in the Experimental Section. The melting points decrease with
zolium ring, show a strong, broad peak in this region, increasing alkyl chain length in the imidazolium-based
which was assigned to hydrogen bonding.[17] With this hydro- cation from 201 °C in (DMIm)[Cr(NCS)4(NH3)2] to
gen atom being absent in the two compounds 122 °C in (BMIm)[Cr(NCS)4(NH3)2], see Figure 1.
(PeMIm)[Cr(NCS)4(NH3)2] and (DML)[Cr(NCS)4(NH3)2] (Pe- (HexMIm)[Cr(NCS)4(NH3)2] melts at 126 °C. This value is
MIm = 1,2,3,4,5-pentamethylimidazolium; DML = 1,3-di- slightly
higher
than
the
melting
point
of
methyl-2,4,5-triphenylimidazolium = 1,3-dimethyllophium), (BMIm)[Cr(NCS)4(NH3)2], although the alkyl chain in the cat-
the respective hydrogen bonding and the corresponding peak ion is longer than in (BMIm)[Cr(NCS)4(NH3)2]. This behavior
in the IR spectrum is absent. The region 2000–500 cm–1 is is possibly due to the energetic improved conformation of the
dominated by internal vibrations of the imidazolium ring and is n-hexyl alkyl chain (fully staggered) in the cation of
employed as the fingerprint domain for the presence of planar (HexMIm)[Cr(NCS)4(NH3)2]. Unfortunately, we have not been
imidazolium rings. The IR spectra of the Reineckate anion successful in proving this assumption by means of
[Cr(NCS)4(NH3)2]– is interpreted in detail in the literature,[9] single-crystal X-ray diffraction methods, yet. The melting
and references cited therein. The CN stretching frequencies point of compounds with higher alkylated imidazolium
(νCN) are located between 2080–2090 cm–1, the CS stretching cations like (PeMIm)[Cr(NCS)4(NH3)2] (mp. 198 °C) and
frequencies (νCS) between 820–850 cm–1, respectively, and are (DML)[Cr(NCS)4(NH3)2] (mp. 172 °C) are in the
in accordance with reported values for N-bonded thiocyanato range between 150–200 °C. None of these synthesized
complexes of 3d metals such as CrIII.[9,18]
salts can be assigned as Ionic Liquids (ILs) nor Room
Z. Anorg. Allg. Chem. 2011, 1314–1321
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 1315

T. Peppel, C. Schmidt, M. Köckerling
ARTICLE
Temperature
Ionic
Liquids
(RTILs),
except All complexes display similar magnetic properties. They are
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O. All compounds paramagnetic with effective magnetic moments in the range of
show excellent stabilities at least up to 250 °C in inert atmos- μeff = 3.83–3.90 μB at 25 °C (spin only high-spin CrIII: μeff
=
phere (N2) and neither endothermic nor exothermic decompo- 3.87 μB). These values resemble closely those of other Rei-
sition effects.
neckate compounds with isolated octahedrally coordinated
CrIII atoms, for example K[Cr(NCS)4(NH3)2] (μeff = 3.80
μB),[21a] (NH4)[Cr(NCS)4(NH3)2] (μeff = 3.86 μB),[21b,21c] or
(NH4)[Cr(NCS)4(NH3)2]·0.66H2O (μeff = 3.91 μB).[21d] There is
no indication for any cooperative magnetic interaction between
the isolated spin-only systems.
Crystal Structures
The single crystal structures of (nBu4N)[Cr(NCS)4(NH3)2],
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O,
(EMIm)[Cr(NCS)4(NH3)2], and (PeMIm)[Cr(NCS)4(NH3)2]
were established by X-ray diffraction analysis. Crystal data and
parameters of the structure determinations are given in Table 1,
and selected bond lengths as well as bond angles in Table 2
and Table 3, respectively. Suitable crystals were obtained by
slow
evaporation
of
the
solvent
(acetone)
of
Figure 1. Molar mass dependence of the melting point of the investi-
gated Reineckates.
saturated solutions at room temperature over one week. All
compounds consist of isolated tetraalkylammonium or
imidazolium-based cations, the corresponding Reineckate
anion
[Cr(NCS)4(NH3)2]–,
and
in
the
case
of
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O with 0.85 co-crystal-
lized water molecules.
Magnetic Properties
The magnetic properties of all complex salts, which contain
(nBu4N)[Cr(NCS)4(NH3)2] crystallizes in the monoclinic
the Reineckate anion [Cr(NCS)4(NH3)2]– were determined space group C2/c (no. 15) with four formula units in the unit
1
20]
using H NMR shifts by applying the Evans method.[19,
cell. Figure 2 shows the molecular structures of the tetrabutyl-
Table 1. Crystal, X-ray diffraction data, data collection and refinement parameters for (n-Bu4N)[Cr(NCS)4(NH3)2],
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O, (EMIm)[Cr(NCS)4(NH3)2], and (PeMIm)[Cr(NCS)4(NH3)2].
Compound
(n-Bu4N)-
[Cr(NCS)4(NH3)2]
{(C12H25)4N}-
[Cr(NCS)4(NH3)2]·0.85H2O
(EMIm)-
[Cr(NCS)4(NH3)2]
(PeMIm)-
[Cr(NCS)4(NH3)2]
Formula
Fw /g·mol–1
T /K
C20H42CrN7S4
560.85
C52H107.7CrN7O0.85S4
1025.00
C10H17CrN8S4
429.56
C12H21CrN8S4
457.61
173(2)
173(2)
293(2)
173(2)
Crystal system
Space group
a /Å
monoclinic
C2/c, no. 15
12.0818(8)
10.2425(8)
24.222(2)
triclinic
orthorhombic
Pbcm, no. 57
8.765(2)
15.888(3)
14.191(3)
monoclinic
P21/n, no. 14
6.0817(2)
13.9811(5)
25.2902(9)
¯
P1, no. 2
8.4049(1)
20.1525(4)
20.7908(4)
67.487(1)
81.328(1)
78.040(1)
3172.6(1), 2
1.073
b /Å
c /Å
α /°
β /°
98.324(3)
90.075(2)
γ /°
V /Å3, Z
ρ /g·cm–3
μ /mm–1
2θ range /°
Collected refl.
Unique refl., Rint
Variables
Goof on F2
2965.8(4), 4
1.256
1976.2(7), 4
1.444
2150.4(1), 4
1.413
0.688
0.349
1.010
0.933
5.24 to 57.20
13351
4.02 to 70.44
103210
5.12 to 56.96
21805
4.34 to 60.00
26938
3781, 0.0263
159
27884, 0.0259
581
2500, 0.0286
149
6262, 0.0287
250
1.063
1.018
1.043
1.069
R1, wR2 [I > 2σ(I)]a,b) 0.0333, 0.0862
0.0580, 0.1494
0.1020, 0.1846
0.0824, 1.4485
1.443, –0.993
0.0466, 0.1271
0.0622, 0.1396
0.0716, 1.5541
0.834, –0.608
0.0405, 0.1112
0.0571, 0.1248
0.0606, 1.0550
0.806, –0.452
R1, wR2 (all data)a,b)
A, Ba,b)
0.0423, 0.0898
0.0447, 1.9473
0.606, –0.447
Res. dens. /e·Å–3
a) R1 = Σ||Fo|–|Fc||/Σ|Fo|. b) wR2 = √Σ{w(Fo –Fc ) }; w = 1/[(σ2(Fo ) + (A·P)2 + B·P]; P = (Fo +2 Fc )/3.
2
2 2
2
2
2
1316 www.zaac.wiley-vch.de
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 1314–1321

Salts with the Reineckate Anion, [CrIII(NCS)4(NH3)2]– and Large Organic Cations
Table 2. Selected bond lengths /Å and angles /° for the Reineckate
anion [Cr(NCS)4(NH3)2]– in (n-Bu4N)[Cr(NCS)4(NH3)2] and
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O.
(nBu4N)[Cr(NCS)4(NH3)2]{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O
atoms
bond
length
atoms
bond
length
atoms
bond
length
Cr1–N1
Cr1–N2
Cr1–N3
N1–C1
N2–C2
C1–S1
C2–S2
1.989(1)
1.986(1)
2.072(2)
1.159(2)
1.164(2)
1.622(2)
1.621(2)
Cr1–N1
Cr1–N2
Cr1–N5
N1–C1
N2–C2
C1–S1
C2–S2
1.983(2) Cr2–N3
1.999(1) Cr2–N4
2.072(2) Cr2–N6
1.164(2) N3–C3
1.160(2) N4–C4
1.614(2) C3–S3
1.624(2) C4–S4
1.989(2)
1.989(2)
2.056(4)
1.154(4)
1.146(3)
1.619(3)
1.614(3)
atoms
bond
angle
atoms
bond
angle
atoms
bond
angle
N1–Cr1–N2 90.21(6)
N1–Cr1–N3 91.40(6)
N2–Cr1–N3 88.48(6)
N1–Cr1– 90.18(6) N3–Cr2– 90.20(9)
N2 N4
N1–Cr1– 89.86(6) N3–Cr2– 89.9(1)
N5 N6
N2–Cr1– 91.64(6) N4–Cr2– 91.9(1)
N5 N6
Figure 2. View of the molecular structures of the (n-Bu4N)+ cation and
of the Reineckate anion [Cr(NCS)4(NH3)2]– in crystals of (n-
Bu4N)[Cr(NCS)4(NH3)2] with atom numbering scheme. Atomic dis-
placement ellipsoids are shown at the 50 % probability level. C–H···S
hydrogen contacts, which are shorter than 2.95 Å, are shown as dashed
lines.
Cr1–N1–C1 173.3(1)
Cr1–N2–C2 177.3(1)
Cr1–N1– 171.9(2) Cr2–N3– 172.6(3)
C1 C3
Cr1–N2– 176.4(2) Cr2–N4– 165.0(3)
C2 C4
lengths are 1.621(2) for C2–S2 and 1.622(2) Å for C1–S1, re-
ammonium cation and the Reineckate anion as well as hydro- spectively. The averaged Cr–N–C bond angle is 175.3° and
gen bond contacts. Selected bond lengths and bond angles of slightly lower than 180° for an expected end-on coordination
the anion can be found in Table 2. The Cr–N bonds within the of the thiocyanate ligand. This behavior is in accordance with
anion range from 1.986(1) to 2.072(2) Å. The latter is the dis- published data.[4] Hydrogen bonding interactions are com-
tance between the CrIII atom and the nitrogen atom of the NH3 monly found in Ionic Liquids as well as in known transition
ligand. In all four compounds, which have been investigated metal-based ILs.[14–17] The shortest H···S contact is formed in
by means of X-ray techniques, the Cr–N(H3) bond is slightly between two different Reineckate anions: N–H2···S1 with
longer than the Cr–N(CS) bond. This can be also found in 2.661 Å. The longer H···S contact is formed between a
comparable Reineckates known from the literature.[4] The N– methylene group and the Reineckate anion: C5–H5B···S2 with
C bond lengths in the thiocyanate ligands are 1.159(2) for N1– 2.904 Å. Bond lengths between atoms of the cation are within
C1 and 1.164(2) Å for N2–C2, the corresponding C–S bond expected ranges.
Table 3. Selected bond lengths /Å and angles /° for (EMIm)[Cr(NCS)4(NH3)2] and (PeMIm)[Cr(NCS)4(NH3)2].
(EMIm)[Cr(NCS)4(NH3)2]
(PeMIm)[Cr(NCS)4(NH3)2]
Anion
atoms
Cation
atoms
Anion
atoms
Cation
atoms
bond length
bond length
bond length
bond length
averaged
Cr–N(NCS)
averaged
Cr–N(NH3)
averaged
N–C
1.99
2.08
1.15
1.62
C4–N6
C5–C6
C4–N7
N6–C5
N7–C6
1.358(6)
1.282(8)
1.303(8)
1.358(6)
1.35(1)
averaged
Cr–N(NCS)
averaged
Cr–N(NH3)
averaged
N–C
2.00
2.07
1.16
1.62
C5–N7
C5–N8
N7–C6
N8–C7
C6–C7
1.359(3)
1.351(3)
1.370(3)
1.366(3)
1.356(3)
averaged
C–S
averaged
C–S
atoms
bond angle
atoms
bond angle
atoms
bond angle
atoms
bond angle
Cr1–N1–C1
Cr1–N2–C2
Cr1–N3–C3
177.4(3)
167.7(2)
175.0(4)
N6–C4–N7
C4–N6–C5
C4–N7–C6
N6–C5–C6
N7–C6–C5
104.6(5)
108.0(3)
111.1(5)
108.5(4)
106.8(5)
Cr–N1–C1
Cr–N2–C2
Cr–N3–C3
Cr–N4–C4
170.8(2)
172.3(2)
172.9(2)
174.8(2)
N7–C5–N8
C5–N7–C6
C5–N8–C7
N7–C6–C7
N8–C7–C6
107.7(2)
108.6(2)
108.4(2)
107.1(2)
108.2(2)
Z. Anorg. Allg. Chem. 2011, 1314–1321
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1317

T. Peppel, C. Schmidt, M. Köckerling
ARTICLE
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O crystallizes in the
¯
triclinic space group P1 (no. 2) with two formula units in the
unit cell. Figure 3 shows the molecular structures of both the
cation and Reineckate anion. Selected bond lengths and bond
angles of the anion are given in Table 2. The averaged Cr–
N(CS) bond length is 1.99 Å, the averaged Cr–N(H3) bond
length 2.06 Å. This is similar to the values found in
(nBu4N)[Cr(NCS)4(NH3)2]. Interestingly, only one of the four
dodecyl chains in the cation shows the most favorable stag-
gered conformation for all carbon atoms within the alkyl chain
(C29 to C40). This could be an important hint towards the
question, why no liquid crystalline behavior is present in
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O.
Figure 4. View of the molecular structures of the (EMIm)+ cation and
the [Cr(NCS)4(NH3)2]– anion in crystals of (EMIm)[Cr(NCS)4(NH3)2]
with atom numbering scheme. Atomic displacement ellipsoids are
shown at the 50 % probability level.
Figure 5. View of the unit cell content of (PeMIm)[Cr(NCS)4(NH3)2]
with all C–H···S contacts, which are shorter than 2.90 Å in a view
along the crystallographic a direction. Atomic displacement ellipsoids
are shown at the 50 % probability level.
Figure 3. View of the molecular structures of the {(C12H25)4N}+ cation
and of the two symmetry independent [Cr(NCS)4(NH3)2]– anions in
crystals of {(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O with atom num-
bering scheme. Atomic displacement ellipsoids are shown at the 50 %
probability level.
Experimental Section
Figure 4 shows the molecular structures of the cation
and the anion in the imidazolium-based Reineckate
(EMIm)[Cr(NCS)4(NH3)2]. Selected bond lengths and bond
angles can be found in Table 3, which also has the values for
(PeMIm)[Cr(NCS)4(NH3)2]. The correct assignment of the
orientation with respect to the allocation of the nitrogen atoms
in the 1,2,3,4,5-pentamethylimidazolium cation in crystals of
(PeMIm)[Cr(NCS)4(NH3)2] can be difficult due to possible dis-
order. Such disorder is known for example with the isoelec-
Analysis and Spectroscopic Measurements
1H NMR, and 13C NMR spectra were recorded with a Bruker ARX
300 spectrometer. Spectra were calibrated with respect to the solvent
signal ([D6]DMSO: 1H δ = 2.50; 13C δ = 39.5 ppm). MIR spectra
(500–4000 cm–1) were recorded by using ATR technique with a
Thermo Nicolet 380 FT-IR spectrometer. Elemental analyses for C, H,
N, and S were obtained with a Flash EA 1112 NC Analyzer from CE
Instruments (error 0.5). UV/Vis spectra were recorded using a
Perkin–Elmer Lambda 2 spectrometer with quartz cuvettes (Suprasil®,
d = 10 mm). Melting points were determined by DSC measurements
using a Mettler Toledo DSC823e in the range of 0–400 °C with a heat-
ing rate of 10 K·min–1 (Ar atmosphere, Al crucible). All melting points
are peak temperatures. Magnetic data were determined by means of
1H NMR techniques (Evans method).[19,20] Molar susceptibilities were
corrected by applying Pascal constants.[25] Effective magnetic
moments μeff/μB are given by applying the Langevin equation.[26]
– [22]
tronic fragment C5Me5 . The correct assignment was estab-
lished by applying known models from the literature.[23,24]
Bond lengths and bond angles for the EMIm+ cation and the
PeMIm+ cation are in accordance with published values for
similar ILs. Figure 5 shows the arrangement of the molecular
ions in (PeMIm)[Cr(NCS)4(NH3)2] with all H···S contacts,
which are shorter than 2.90 Å. The shortest H···S contact is
formed between N6–H5···S2 with 2.661 Å. From Figure 5 it
can be seen that H···S contacts are not only present between the
(PeMIm)+ cation and the Reineckate anion, but also between
different Reineckate anions themselves (e.g. N5–H3···S2···H5–
N). This can be found also in the other three compounds.
X-ray Structure Analysis
Ruby-red crystals of (nBu4N)[Cr(NCS)4(NH3)2] (nBu = n-butyl),
{(C12H25)4N}[Cr(NCS)4(NH3)2]·H2O
(C12H25
=
n-dodecyl),
1318
www.zaac.wiley-vch.de
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 1314–1321

Salts with the Reineckate Anion, [CrIII(NCS)4(NH3)2]– and Large Organic Cations
(EMIm)[Cr(NCS)4(NH3)2] (EMIm = 1-ethyl-3-methylimidazolium), The suspension was filtered, and the resulting filtrate was evaporated
and (PeMIm)[Cr(NCS)4(NH3)2] (PeMIm = 1,2,3,4,5-pentamethylimid- in vacuo, yielding an off-white powder. Yield 1.4 g (92 %), mp.
azolium) were mounted on the tips of thin glass fibers for the single-
272 °C (lit.[31] 266 °C). C23H21N2I % (calcd.): C 60.9 (61.1); H 4.6
1
crystal X-ray diffraction measurements. Data were collected on a (4.7); N 6.0 (6.2). H NMR ([D6]DMSO): δ = 7.48–7.94 (m, 15 H,
Bruker–Nonius Apex X8 diffractometer equipped with a CCD detector. phenyl), 3.53 (s, 6 H, N–Me). 13C NMR ([D6]DMSO): δ = 121.9–
Measurements were done using monochromatic Mo-Kα radiation (λ = 132.4 (Cphenyl, Me–N–C=C–N), 144.1 (Me–N–C=N), 34.5 (N–Me).
0.71073 Å). Preliminary data of the unit cell were obtained from the IR: ν
= 3053, 3021, 2992, 2947, 1651, 1644, 1604, 1592, 1512,
˜
max
reflex positions of 36 frames, measured in different directions of the 1485, 1443, 1415, 1392, 1365, 1280, 1179, 1167, 1153, 1074, 1057,
reciprocal space. After completion of the data measurements the inten- 1023, 995, 983, 940, 931, 859, 768, 753, 698, 668, 653 cm–1.
sities were corrected for Lorentz, polarization, and absorption effects
using the Bruker–Nonius software.[27] The structure solutions and re-
finements were done with the aid of the SHELX-97 program
package.[28] All non-hydrogen 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 analy-
ses have been deposited with the Cambridge Crystallographic Data
Centre, CCDC-790229 for (n-Bu4N)[Cr(NCS)4(NH3)2], CCDC-
790230 for {(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O, CCDC-790231
Synthesis of (R4N)[Cr(NCS)4(NH3)2] (R = n-Butylammo-
nium, n-Dodecylammonium)
An aqueous solution of (NH4)[Cr(NCS)4(NH3)2]·H2O (Reinecke’s salt,
8 mmol in 100 mL water) was given to a stirred aqueous solution of
the corresponding tetraalkylammonium precursor (8 mmol in 100 mL
water). A pink solid precipitated immediately, which was filtered off,
washed with water, diethyl ether and finally dried in air. Yield >80 %.
for
(EMIm)[Cr(NCS)4(NH3)2],
and
CCDC-809956
for
(n-Bu4N)[Cr(NCS)4(NH3)2]: Yield 84 %. mp. 155 °C. C20H42CrN7S4
(PeMIm)[Cr(NCS)4(NH3)2]. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; Fax:
+44-1223-336-033; or E-Mail: deposit@ccdc.cam.ac.uk.
(calcd.): C 42.9 (42.8); H 7.8 (7.6); N 17.0 (17.5). IR: ν
= 3382,
˜
max
3342, 3254, 3168, 2963, 2871, 2064 (νCN), 1603, 1487, 1464, 1377,
1243, 1179, 1151, 1107, 1029, 881, 848 (νCS), 804, 741, 649 cm–1.
UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.89 (lit. μeff /μB
=
3.80–3.95,[21] spin only: μeff /μB = 3.88, T = 25 °C, c = 3.21·10–2
mol·l–1, ν0 = 300 MHz, χmol = 6.35·10–3)
Materials
{(C12H25)4N}[Cr(NCS)4(NH3)2]·0.85H2O: Yield 88 %. mp. 48 °C.
Reinecke’s salt, (NH4)[Cr(NCS)4(NH3)2·H2O], was synthesized ac-
cording to known procedures.[1,29] The Ionic Liquid precursors RMImX
(RMIm = 1-alkyl-3-methylimidazolium, X = Cl, Br, I) were also pre-
pared by applying published procedures.[32–34] 1,2,3,4,5-pentamethyl-
imidazolium iodide (PeMImI) was synthesized according to ref.[23]
Tetra-n-butylammonium bromide (nBu4NBr, Fluka, >99 %), tetra-n-
dodecylammonium bromide ((C12H25)4NBr, Aldrich, >99 %), benzil
(Aldrich, >98 %), benzaldehyde (Aldrich, >99.5 %), NH4OAc (Al-
drich, >98 %), KOH (VWR, >86 %), K2CO3 (Aldrich >99 %), and
iodomethane (Aldrich, >99 %) were used as received without any fur-
ther purification.
C52H106CrN7S4·H2O (calcd.): C 60.6 (60.8); H 10.8 (10.6); N 9.0 (9.5).
IR: ν
= 3289, 3150, 2953, 2920, 2851, 2119, 2069 (νCN), 1600,
1482, 1465, 1402, 1377, 1259, 1235, 1184, 1092, 1026, 961, 915, 869,
˜
max
836 (νCS), 802, 720, 674 cm–1. UV/Vis (acetone): λmax = 396, 526 nm.
μ
eff /μB = 3.85 (T = 25 °C, c = 0.13·10–2 mol·l–1, ν0 = 300 MHz, χmol
=
6.22·10–3)
General Synthesis of (AlkMIm)-, (PeMIm)-, and
(DML)[Cr(NCS)4(NH3)2] (AlkMIm = 1-Alkyl-3-methylimida-
zolium, PeMIm = 1,2,3,4,5-Pentamethylimidazolium,
DML = 1,3-Dimethyllophinium)
Synthesis of Lophine (2,4,5-Triphenyl-1H-imidazole)
An aqueous solution of (NH4)[Cr(NCS)4(NH3)2]·H2O (Reinecke’s salt,
8 mmol in 100 mL water) was given to a stirred aqueous solution of
the corresponding IL precursor (8 mmol in 100 mL water). A pink
solid precipitated immediately, which was filtered off, washed with
water and finally dried in air. Yield >90 %.
Benzil (4.2 g, 20.0 mmol), NH4OAc (5.4 g, 70.0 mmol) and freshly
distilled benzaldehyde (2.2 g, 20.0 mmol) were mixed in a PTFE ves-
sel and heated in a microwave oven over a period of 5 min at 800 W
(Tmax = 120 °C). The resulting solid was suspended in methanol, trans-
ferred to a mortar and well ground. The powder was finally recrystal-
lized from methanol/acetone (2:1, 150 mL), yielding a slightly yellow
solid. Yield: 5.4 g (87 %), mp. 273–275 °C (lit.[30] 276–277 °C).
C21H16N2 % (calcd.): C 85.1 (85.1); H 5.6 (5.4); N 9.3 (9.5). 1H NMR
([D6]DMSO): δ = 7.27–8.06 (m, 15 H, phenyl), 12.48 (s, 1 H, NH).
13C NMR ([D6]DMSO): δ = 125.0–131.0 (Cphenyl), 135.0, 137.0 (NH–
(DMIm)[Cr(NCS)4(NH3)2] (DMIm = 1,3-Dimethylimidazolium):
From DMImI.[32] Yield 93 %. mp. 201 °C. C9H15N8CrS4 (calcd.): C
25.8 (26.0); H 3.5 (3.6); N 26.6 (27.0) %. IR: ν
= 3312, 3230,
˜
max
3153, 2082 (νCN), 1602, 1572, 1260, 1170, 822 (νCS), 699, 620,
491 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.88 (T =
25 °C, c = 2.17·10–2 mol·l–1, ν0 = 300 MHz, χmol = 6.26·10–3)
C=C–N), 145.4 (NH–C=N). IR: νmax = 3164, 3079, 3059, 3040, 2988,
˜
2966, 2869, 2866, 2810, 2784, 2731, 1602, 1588, 1504, 1489, 1462,
1446, 1442, 1412, 1397, 1129, 1071, 966, 917, 843, 777, 766, 736,
713, 706, 698, 691, 674, 606 cm–1.
(EMIm)[Cr(NCS)4(NH3)2] (EMIm
=
1-Ethyl-3-methylimida-
zolium): From EMImBr.[33] Yield 91 %. mp. 186 °C. C10H17N8CrS4
(calcd.): C 27.6 (28.0); H 4.0 (4.0); N 25.9 (26.1) %. IR: νmax = 3313,
˜
3229, 3150, 2090 (νCN), 1602, 1567, 1260, 1166, 825 (νCS), 701,
493 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.84 (T =
25 °C, c = 3.23·10–2 mol·l–1, ν0 = 300 MHz, χmol = 6.41·10–3)
Synthesis of DMLI (DML = 1,3-Dimethyllophinium = 1,3-
Dimethyl-2,4,5-triphenylimidazolium)
Lophine (1.0 g, 3.4 mmol), K2CO3 (1.4 g, 10.1 mmol) and 50 mL io- (i-PMIm)[Cr(NCS)4(NH3)2] (i-PMIm = 1-Methyl-3-isopropylimid-
domethane were heated to reflux in actonitrile (150 mL) overnight. azolium): From i-PMImI.[33] Yield 91 %. mp. 159 °C. C11H19N8CrS4
Z. Anorg. Allg. Chem. 2011, 1314–1321
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1319

T. Peppel, C. Schmidt, M. Köckerling
ARTICLE
[2] a) O. T. Christensen, J. Prakt. Chem. 1892, 45, 213–222; b) O.
Nordenskjöld, Z. Anorg. Chem. 1892, 1, 126–143; c) A. Werner,
Z. Anorg. Chem. 1897, 15, 243–277.
(calcd.): C 29.7 (29.8); H 4.2 (4.3); N 25.0 (25.3) %. IR: νmax = 3303,
˜
3226, 3151, 2083 (νCN), 1553, 1266, 1151, 828 (νCS), 764, 698,
492 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.85 (T =
25 °C, c = 4.21·10–2 mol·l–1, ν0 = 300 MHz, χmol = 6.22·10–3)
[3] Y. Takéuchi, Y. Saito, Bull. Chem. Soc. Jpn. 1957, 30, 319–325.
[4] a) H. M. Colquhoun, K. Henrick, J. Chem. Soc., Chem. Commun.
1981, 85–87; b) R. Ciechanowski, A. Grodzicki, E. Szlyk, Z.
Zhang, G. J. Palenik, J. Cryst. Spectrosc. Chem. 1993, 23, 649–
655; c) C. J. Kepert, M. Kurmoo, M. R. Truter, P. Day, J. Chem.
Soc., Dalton Trans. 1997, 607–613; d) K.-L. Zhang, W. Chen, Y.
Xu, Z. Wang, Z. J. Zhong, X.-Z. You, Polyhedron 2001, 20,
2033–2036; e) T. G. Cherkasova, I. P. Goryunova, Russ. J. Inorg.
Chem. 2003, 48, 528–532; f) T. G. Cherkasova, I. P. Goryunova,
Russ. J. Inorg. Chem. 2004, 49, 22–24; g) A. Cucos, N. Avarvari,
M. Andruh, Y. Journaux, A. Müller, M. Schmidtmann, Eur. J.
Inorg. Chem. 2006, 903–907; h) V. M. Nikitina, O. V. Nesterova,
V. N. Kokozay, E. A. Goreshnik, J. Jezierska, Polyhedron 2008,
27, 2426–2430; i) V. M. Nikitina, O. V. Nesterova, V. N. Kok-
ozay, V. V. Dyakonenko, O. V. Shishkin, J. Jezierska, Polyhedron
2009, 28, 1265–1272; j) V. M. Nikitina, O. V. Nesterova, V. N.
Kokozay, V. V. Dyakonenko, O. V. Shishkin, J. Jezierska, Inorg.
Chem. Commun. 2009, 12, 101–104.
(BMIm)[Cr(NCS)4(NH3)2] (BMIm
=
1-Butyl-3-methylimida-
zolium): From BMImCl.[34] Yield 91 %. mp. 122 °C. C12H21N8CrS4
(calcd.): C 31.3 (31.5); H 4.6 (4.6); N 24.1 (24.5) %. IR: νmax = 3309,
˜
3227, 3150, 2926, 2082 (νCN), 1560, 1262, 1158, 822 (νCS), 743, 693,
488 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.83 (T =
25 °C, c = 2.75·10–2 mol·l–1, ν0 = 300 MHz, χmol = 6.14·10–3)
(HexMIm)[Cr(NCS)4(NH3)2] (HexMIm = 1-Hexyl-3-methylimida-
zolium): From HexMImBr.[33] Yield 93 %. mp. 126 °C. C14H25N8CrS4
(calcd.): C 34.4 (34.6); H 5.1 (5.2); N 23.0 (23.1) %. IR: νmax = 3372,
˜
3302, 3231, 3154, 2928, 2080 (νCN), 1259, 1164, 823 (νCS), 690,
489 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.90 (T =
25 °C, c = 0.79·10–2 mol·l–1, ν0 = 250 MHz, χmol = 6.36·10–3)
(PeMIm)[Cr(NCS)4(NH3)2] (PeMIm = 1,2,3,4,5-Pentamethylimida-
zolium): From PeMImI.[23] Yield 95 %. mp. 198 °C. C12H21N8CrS4
[5] E. E. Wegner, A. W. Adamson, J. Am. Chem. Soc. 1966, 88, 394–
404.
[6] a) Concepts of Inorganic Photochemistry (Eds.: A. W. Adamson,
P. D. Fleischhauer), Wiley, New York, 1975; b) V. Balzani, V.
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[7] a) B. Mainusch, F. Wasgestian, Z. Stasicka, A. Karocki, J. Inf.
Rec. Mats. 1994, 21, 687–689; b) B. Mainusch, A. Karocki,
D. M. Guldi, Z. Stasicka, F. Wasgestian, Inorg. Chim. Acta 1997,
255, 87–93.
(calcd.): C 31.3 (31.5); H 4.6 (4.6); N 24.5 (24.5) %. IR: νmax = 3305,
˜
3280, 3228, 3193, 3152, 2956, 2924, 2469, 2424, 2298, 2071 (νCN),
1650, 1601, 1544, 1439, 1390, 1369, 1252, 1073, 1033, 972, 830 (νCS),
704, 650, 578, 562 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff
μB = 3.85 (T = 25 °C, c = 2.99·10–2 mol·l–1, ν0 = 300 MHz, χmol
6.22·10–3)
/
=
(DML)[Cr(NCS)4(NH3)2] (DML = 1,3-Dimethyllophinium): From
DMLI. Yield 95 %. mp. 172 °C. C27H27N8CrS4 (calcd.): C 50.2 (50.4);
[8] a) I. Gănescu, M. Preda, Pharmazie 1990, 45, 438–439; b) G.
Bratulescu, I. Ganescu, S. Braz. J. Chem. 2007, 15, 49–57;
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H 4.2 (4.2); N 17.5 (17.4); S 19.9 (19.9) %. IR: ν
= 3368, 3350,
˜
max
3320, 3232, 3219, 3187, 3139, 3054, 3029, 2951, 2912, 2056 (νCN),
1500, 1591, 1509, 1485, 1441, 1409, 1392, 1350, 1273, 1237, 1179,
1158, 1076, 1052, 1021, 963, 937, 926, 855 (νCS), 786, 770, 759, 697,
671 cm–1. UV/Vis (acetone): λmax = 396, 526 nm. μeff /μB = 3.85 (T =
25 °C, c = 1.47·10–2 mol·l–1, ν0 = 300 MHz, χmol = 6.21·10–3)
[11] P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 2000, 39, 3772–
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Conclusions
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M. Grätzel, Inorg. Chem. 1996, 35, 1168–1178.
A series of 9 different complex compounds with the
[Cr(NCS)4(NH3)2]– Reineckate anion and large organic cations
was synthesized. Looking for the possibility to use such com-
pounds as metal-containing Ionic Liquids the melting points
were measured using the DSC technique. It turned out that all
Reineckates with imidazolium based cations have melting
points higher than 100 °C. Only the tetra-n-dodecylammonium
Reineckate melts below 100 °C at 48 °C and can be consid-
ered an “Ionic Liquid”. Single crystal X-ray structures of 4
selected compounds show that most likely H···S and H···N hy-
drogen bonds contribute to the relative high melting points of
the imidazolium based Reineckates.
[14] a) S. Hayashi, H. Hamaguchi, Chem. Lett. 2004, 33, 1590–1591;
b) Q.-G. Zhang, J.-Z. Yang, X.-M. Lu, J.-S. Gui, M. Huang, Fluid
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Hamaguchi, IEEE Trans. Magn. 2006, 42, 12–14; C. Zhong, T.
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Acknowledgement
Support from the Deutsche Forschungsgemeinschaft (DFG) (SPP
1191-Ionic Liquids, KO-1616/4–1 and 1616/4–2) is gratefully ac-
knowledged. We thank Elias Reiter for his help with the drawings of
this manuscript.
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: February 22, 2011
Published Online: May 31, 2011
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