Iron(II) spin-crossover complexes with Schiff base like ligands and N-alkylimidazoles

Article abstract of DOI:10.1002/ejic.201403021

Three new iron(II) spin-crossover complexes with N₂O₂-coordinating Schiff base like equatorial ligands and alkylimidazole ligands in the axial positions were synthesised. The chain length of the alkylimidazole was varied from the previously published 1 to 5, 7 and 10 carbon atoms to investigate the influence of the alkyl chain length on the spin-transition behaviour in solution and in the solid state. The crystal structures of [1(HeptIm)₂] and [1(DecIm)₂] (1 = Fe complex with equatorial Schiff base like ligand; HeptIm = N-heptylimidazole, DecIm = N-decylimidazole) and the packing of the molecules in the crystals are discussed.

Full text of DOI:10.1002/ejic.201403021

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DOI:10.1002/ejic.201403021
Iron(II) Spin-Crossover Complexes with Schiff Base Like
Ligands and N-Alkylimidazoles
Stephan Schlamp,[a] Charles Lochenie,[a] Tobias Bauer,[a]
Rhett Kempe,[a] and Birgit Weber*[a]
Keywords: Iron / Spin crossover / Schiff base ligands / N ligands
Three new iron(II) spin-crossover complexes with N2O2-coor- behaviour in solution and in the solid state. The crystal struc-
dinating Schiff base like equatorial ligands and alkylimid-
azole ligands in the axial positions were synthesised. The
chain length of the alkylimidazole was varied from the pre-
viously published 1 to 5, 7 and 10 carbon atoms to investigate
the influence of the alkyl chain length on the spin-transition
tures of [1(HeptIm)2] and [1(DecIm)2] (1 = Fe complex with
equatorial Schiff base like ligand; HeptIm = N-heptylimid-
azole, DecIm = N-decylimidazole) and the packing of the
molecules in the crystals are discussed.
Here, we present an alternative approach for the synthe-
sis of alkyl-chain-functionalised iron(II) SCO complexes of
the ligand system used in our group. For this, N-alkylimid-
azoles were used as axial ligands. The modification of the
Schiff base like ligand resulted in amphiphilic complexes, in
which the nonpolar alkyl chains point in one direction, and
the iron centre is part of the polar head group. For the
addition of long alkyl chains to the two axial ligands, rod-
like structures of the final complex can be envisioned. Sim-
ilar structural motifs have already been realised for other
SCO systems; however, these systems all feature positively
charged complexes with counterions.[4,8] The advantage of
the ligand system presented here is that solely the influence
of the alkyl chain length can be investigated.
Introduction
Switchable molecules are important for possible applica-
tions in the thematic field of sensors, for example. Spin-
crossover (SCO) compounds are a class of molecules that
are good candidates for this, as they can be switched be-
tween the high-spin (HS) and low-spin (LS) states by vari-
ous means such as changes of temperature or pressure or
irradiation with light.[1] This switching process is ac-
companied by a change of the properties of the material
such as its magnetism or colour. The combination of this
ability with additional physical properties such as softness
can lead to multifunctional SCO complexes with additional
functionalities such as liquid crystallinity, gel formation or
nanostructuring through self-assembly.[2] To achieve this
goal, a common method is to add long alkyl chains to the
ligands of already established SCO systems.[3,4] The charac-
terisation of a variety of such SCO compounds showed that
the addition of long alkyl chains to the outer periphery
often leads to gradual spin transitions. An improved coo-
perativity with increasing alkyl chain length has only been
detected in a few cases.[5] Additionally, counterions or sol-
vent molecules that can influence SCO behaviour in an un-
predictable way are involved in most systems. We also fol-
lowed this approach by synthesising alkyl-chain-function-
alised amphiphilic Schiff base like ligands that were used for
the successful synthesis of SCO complexes.[6] In one case, a
cooperative spin transition with hysteresis was observed as
result of a highly ordered lipid-layer-like arrangement of
the molecules in the crystal packing.[7]
Results and Discussion
Synthesis and General Characterisation
Previously, we demonstrated that iron(II) complexes of
the Schiff base like ligands used in our group in combina-
tion with N-methylimidazole (MeIm) axial ligands show
SCO behaviour.[9,10] The type of spin transition (gradual or
abrupt) depends on the method of synthesis. Either the ax-
ial ligand, MeIm, was used as the solvent or the starting
iron(II) complex was heated to reflux in a mixture of MeIm
and methanol. The later strategy was used for two of the
alkylimidazole complexes discussed in this manuscript, as
the solubility of the iron(II) complex in the pure alkylimid-
azole is too high, and no solid product could be obtained.
The high solubility of the final products made their isola-
tion as pure compounds difficult as washing steps always
dissolved the precipitate. Consequently, this step was
skipped; the reaction solution was simply decanted, and the
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
Universitätsstraße 30, NW 1, 95440 Bayreuth, Germany
E-mail: weber@uni-bayreuth.de
http://www.ac2-weber.uni-bayreuth.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201403021.
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Scheme 1. Final step of the synthesis of [1(PentIm)2], [1(HeptIm)2] and [1(DecIm)2].
product was dried in vacuo. As a result, alkylimidazole im- lengths and angles are observed for other LS complexes of
purities are often observed in the final products. The final this ligand type.[16]
step, the coordination of the corresponding alkylimidazole
to the precursor [1(MeOH)2], is visualised in Scheme 1. The
six-step synthesis pathway comprises adapted literature pro-
cedures for the synthesis of the alkylimidazoles[11–13] as well
as the previously described syntheses of the Schiff base like
ligand[14] and the methanol precursor complex.[15]
The imidazole rings of [1(HeptIm)2] are almost perpen-
dicular to each other with an angle of 86.4°. The C7 alkyl
chains of both axial ligands point in different directions and
span an angle of ca. 90°. Thus, the molecule does not have
the expected rodlike structure and is best described as a
bent rod. Two contacts shorter than the sum of the van der
Waals radii by 0.2 Å are observed between one molecule
and a neighbouring molecule, which is oriented upside
down. One of these two nonclassical hydrogen bonds occurs
between H29 of one imidazole ligand and the oxygen atom
O2 of the equatorial ligand directly coordinated to the cen-
tral iron ion (C29–H29···O2, 2.492 Å). The other nonclassi-
cal hydrogen bond connects oxygen atom O3 in the outer
periphery of the ligand with the first H atom, H22, of the
alkyl chain of the molecule shifted aside. In Table 2, the
geometric parameters of the nonclassical hydrogen bonds
of the molecules are listed. The angle between the imidazole
rings of [1(DecIm)2] of 76.5° is smaller and more in the
region of the angle observed for the MeIm complexes.[9,10]
In contrast to the chains in [1(HeptIm)2], the C10 alkyl
chains point in the same direction (towards O1 of the equa-
torial ligand) and are slightly bent in opposite directions.
Again, a rodlike structure is not observed, but, owing to
X-ray Structure Analysis
Single crystals suitable for X-ray structure analysis were
obtained for [1(HeptIm)2] (HeptIm = N-heptylimidazole)
and [1(DecIm)2] (DecIm = N-decylimidazole). To obtain
better datasets, the analyses were performed at 133 K.
Attempts to analyse the X-ray structure of [1(HeptIm)2] at
273 K were not successful. The molecular structures of the
two compounds are displayed in Figure 1. [1(HeptIm)2] and
¯
[1(DecIm)2] crystallise in the triclinic space group P1 with
two molecules in the unit cell. Neither compound contains
additional solvent molecules in the crystal packing. Selected
bond lengths and angles of [1(HeptIm)2] and [1(DecIm)2]
are listed in Table 1. The length of the bonds to the equato-
rially coordinated N and O atoms are all ca. 1.9 Å, and the
bond lengths to the axially coordinated nitrogen atoms of
the imidazole rings are slightly longer (ca. 2.0 Å). The data the bent alkyl chains, the structure is closer to an amphi-
were collected at 133 K, and the O–Fe–O angles of 89.4 phile. One intermolecular contact shorter than the sum of
{[1(HeptIm)2]} and 88.2° {[1(DecIm)2]} at this temperature the van der Waals radii by 0.2 Å connects two opposite
in combination with the bond lengths clearly indicate that molecules, which are again oriented upside down. Similarly
both complexes reside in the LS state, as similar bond to the short contact in [1(HeptIm)2], this contact connects
Table 1. Selected bond lengths [Å] and angles [°] within the inner coordination sphere and spin state of the complexes at 133 K discussed
in this work.
Fe–Neq
Fe–Oeq
Fe–Nax
Nax–Fe– Nax
O–Fe–O
Spin state
[1(HeptIm)2]
[1(DecIm)2]
1.870(5), 1.893(5)
1.983(2), 1.892(2)
1.947(4), 1.935(4)
1.934(1), 1.932(1)
2.010(5), 1.998(5)
2.007(2), 1.998(2)
176.06(21)
178.88(7)
89.41(15)
88.25(6)
LS
LS
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ligand. As the molecules are orientated towards each other,
this nonclassical hydrogen bond is formed.
The packing patterns of [1(HeptIm)2] and [1(DecIm)2]
are displayed in Figure 2. In the crystal packing of
[1(HeptIm)2], the alkyl chain at the top of one molecule
is arranged almost parallel to the same alkyl chain of the
neighbouring upside-down molecule. On the other hand,
the slightly bent alkyl chain on the bottom of one molecule
is arranged next to the slightly bent alkyl chain on the top
of the neighbouring upside-down molecule. Despite this
structural motif, there are no indications of van der Waals
interactions between the alkyl chains.
Figure 1. ORTEP drawings of [1(HeptIm)2] (top) and [1(DecIm)2]
(bottom). The ellipsoids are drawn at the 50% probability level.
Hydrogen atoms are omitted for clarity.
Table 2. Distances [Å] and angles [°] of the nonclassical hydrogen
bonds in the crystal structures at 133 K.
D–H···A
D– H···A
H
D···A
D–H···A
[1(HeptIm)2] C22–H22B···O3[a] 0.99 2.54 3.237(8)
C29–H29···O2[b]
0.95 2.49 3.267(8)
C33–H33A···O3[c] 0.99 2.51 3.430(3)
127
139
154
[1(DecIm)2]
[a] –x, 2 – y, 1 – z. [b] 1 – x, 2 – y, 1 – z. [c] 1 – x, 1 – y, –z.
the H atom of the first carbon atom of one alkyl chain with
the oxygen atom O3 in the outer periphery of the equatorial (bottom) [1(DecIm)2] along [010].
Figure 2. Crystal packing of (top) [1(HeptIm)2] along [010] and
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In contrast to [1(HeptIm)2], some van der Waals interac- tion of the material changes.[17] Another point is that the
tions are observed in [1(DecIm)2] between the alkyl chains spin transition occurs at comparably low temperatures;
of one molecule (C23–C31) and the second alkyl chain of thus, quenching effects are very likely at temperatures below
a neighbouring complex. Additionally, for the last part of 100 K. A similar behaviour was observed previously for
this alkyl chain, some interactions with another, third other complexes of this ligand system.[18]
neighbouring complex molecule (C37–C31) are observed.
The room-temperature χMT product of [1(DecIm)2] (χMT
In Figure 2 (bottom), the crystal packing of [1(DecIm)2] is = 2.83 cm3 Kmol–1) shows that the compound is not fully
displayed, and the closely packed alkyl chains can be seen. in the HS state at this temperature. As the temperature de-
creases, χMT decreases first gradually, then rapidly, and
then gradually again until a value of 0.54 cm3 Kmol–1 at
Magnetic Measurements
200 K is obtained. This corresponds to a LS state of the
ȇ
system with T1/2 = 254 K. Below this temperature, the
Solid samples of high enough purity and in sufficient
quantities for superconducting quantum interference device
(SQUID) magnetometry measurements were obtained for
the compounds with the C5 and C10 chains, [1(PentIm)2]
and [1(DecIm)2]. The results are plotted in Figure 3. At
300 K, the product of the molar susceptibility and tempera-
ture (χMT) of [1(PentIm)2] of 3.19 cm3 Kmol–1 is character-
istic of a HS state. As the sample is cooled to 185 K, the
χMT product slowly decreases and a plateau is observed in
the temperature range between 170 and 120 K (χMT =
2.82 cm3 Kmol–1). At 100 K, the χMT product again de-
creases to a value of 2.00 cm3 Kmol–1 and remains at this
value to 20 K, at which point it again decreases rapidly ow-
ing to zero-field splitting. The incomplete character of this
spin-transition curve could be due to the presence of dif-
ferent polymorphs in the sample, for example, with different
PentIm content (see Experimental Section). From other
SCO complexes of this ligand system, it is known that the
magnetic properties can change drastically as the composi-
χMT product decreases very gradually to 0.32 cm3 Kmol–1
at 25 K. As the temperature increases, the curve progression
of the χMT product corresponds almost exactly to the val-
ues in the cooling mode. In the more abrupt region, the
increase of the χMT product occurs at a slightly higher tem-
perature (T1/2Ȇ = 259 K), which results in a small hysteresis
of 5 K. Upon further heating to 400 K, the full HS state
(χMT = 3.06 cm3 Kmol–1) is reached. The SCO curve pro-
gression is more abrupt for [1(DecIm)2], for which a net-
work of van der Waals interactions between the alkyl chains
is observed. The complete spin transition is in good agree-
ment with the results from the X-ray structure analysis (low
spin at 133 K).
Additionally, we determined the temperature-dependent
magnetic susceptibilities of the iron complex 1 bearing axi-
ally coordinated alkylimidazole ligands with different alkyl
chain lengths of 1, 5, 7 and 10 carbon atoms in methanol/
alkylimidazole solutions. This allowed us to study the influ-
ence of the alkyl chain length and packing effects on the
spin-transition properties. The concentrations of the com-
plexes in the solutions were ca. 38–55 mg/mL (methylimid-
azole to decylimidazole). The presence of the octahedral
complexes in solution was confirmed by colour changes
upon cooling owing to the spin transition (see Supporting
Information, Figure S1). The results are plotted in Figure 4.
The spin-transition behaviour for all complexes is identical.
The gradual progression is typical of SCO in solution, in
which all of the cooperative effects that are responsible for
a rapid switch of the spin state are switched off. This proves
Figure 4. SQUID measurements of solutions of [1(MeIm)2] (open
squares), [1(PentIm)2] (circles), [1(HeptIm)2] (triangles) and [1-
(DecIm)2] (open triangles).
Figure 3. SQUID measurements of [1(PentIm)2] (top) and [1-
(DecIm)2] (bottom).
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over 3.5 h. After cooling to room temp., the two-phase mixture was
separated from the solid, and the solvent was evaporated. Chloro-
form (100 mL) was added slowly, and the solution was filtered at
room temp. The product was dried over Na2SO4 overnight and
distilled at 155 °C and 3ϫ10–4 bar, yield 28.3 g (57%). MS (DEI+):
that packing effects (e.g., different orientations of the axial
ligand, short contacts) are responsible for the differences in
the SCO behaviour of the solids.
1
m/z (%) = 166 (36) [M]+. H NMR (CDCl3, 399.8 MHz): δ = 0.81
Conclusions
(t, CH3), 1.22 [m, (CH2)4], 1.70 (q, NCH2CH2), 3.85 (t, NCH2),
6.84 [s, (Im)NCHCHN], 6.98 [s, (Im)NCHCHN], 7.39 [s, (Im)
NCHN] ppm.
In this article, we present a new class of iron(II) spin-
crossover coordination compounds with Schiff base like
equatorial ligands and alkylimidazoles with different chain
lengths as axial ligands. The alkyl chain lengths were varied
from 1 to 5, 7 and 10 carbon atoms. The crystal structures
of [1(HeptIm)2] and [1(DecIm)2] were obtained, and the
molecules show a very similar crystal packing. Pairs of mol-
ecules oriented upside down relative to each other are
strongly connected by nonclassical hydrogen bonds. In
contrast to those in [1(HeptIm)2], the alkyl chains in
N-Decylimidazole: Imidazole (34.04 g, 0.5 mol) was dissolved in
methanol (45 mL), and an aqueous KOH solution (50%, 100 mL)
was added. The mixture was heated to 90 °C, and 1-bromodecane
(110.59 g, 0.5 mol) was added dropwise under vigorous stirring
over 4 h. After cooling to room temp., the two-phase mixture was
separated from the solid, and the solvent was evaporated. Chloro-
form (300 mL) was added slowly, and the solution was filtered at
room temp. The product was dried over Na2SO4 overnight and
distilled twice at 145 °C and 3.5ϫ10–4 bar, yield 82.97 g (80%). 1H
[1(DecIm)2] interact with each other and are, therefore, ar- NMR (CDCl3, 399.8 MHz): δ = 0.89 (t, CH3), 1.20 [m, (CH2)2],
1.71 (q, NCH2CH2), 3.87 (t, NCH2), 6.85 [s, (Im)NCHCHN], 6.99
[s, (Im)NCHCHN], 7.41 [s, (Im)NCHN] ppm.
ranged parallel to each other. [1(PentIm)2] shows a rather
gradual and stepwise incomplete spin transition with pla-
teaus, whereas [1(DecIm)2] exhibits a relatively abrupt spin
crossover with 5 K wide hysteresis, centred at 257 K. Thus,
with increasing alkyl chain length, increased cooperative in-
teractions between the spin-crossover centres are observed
owing to the improvement in conditions for van der Waals
interactions. This observation is in excellent agreement with
the results obtained for related complexes with amphiphilic
Schiff base like ligands.[6c,7] Magnetic measurements of the
complexes in solution with alkylimidazoles bearing dif-
ferent alkyl chain lengths prove the absence of cooperative
effects in solution, and almost identical behaviour is ob-
served for all complexes.
[1(DecIm)2]: [1(MeOH)2] (0.62 g, 1.40 mmol) and DecIm (2.5 mL)
were heated to reflux in methanol (4 mL) for 70 min. The reddish-
black solution was stored at –28 °C. The solution was then de-
canted at –27 °C from the black blocklike crystals. C44H66FeN6O4·
0.75DecIm·1.5MeOH (1003.20): calcd. C 66.15, H 9.04, N 10.47;
found C 66.32, H 8.53, N 10.64. IR: ν = 2923 (vs, CH ), 2854 (s,
˜
2
CH2), 1635 (m, CO), 1560 (vs, CO), 1393 (s), 1274 (s), 1228 (s),
1076 (s) cm–1.
[1(PentIm)2]: [1(MeOH)2] (0.55 g, 1.23 mmol) and PentIm (2.0 mL)
were heated to reflux in methanol (4 mL) for 3 h 15 min. The red-
dish-black solution was stored at –28 °C. The solution was then
decanted at –27 °C from the black precipitate. C34H46FeN6O4·
3PentIm·MeOH (1105.28): calcd. C 64.11, H 8.39, N 15.21; found
C 63.86, H 8.05, N 15.52. IR: ν = 2931 (s, CH ), 2861 (m, CH ),
˜
2
2
1627 (s, CO), 1556 (vs, CO), 1382 (vs), 1271 (vs), 1229 (s), 1079 (s)
cm–1.
Experimental Section
[1(HeptIm)2]: [1(MeOH)2] (1.58 g, 4.13 mmol) and HeptIm
(10.0 mL) were heated to 90 °C for 6 h. After several cycles of stor-
ing at 5 and 25 °C, a black precipitate could be isolated. In the
remaining solution, black needles crystallised at –30 °C.
C38H54FeN6O4·6HeptIm (1712.13): calcd. C 68.74, H 9.54,
General: The syntheses of the iron complexes were performed under
an argon atmosphere by Schlenk techniques. The solvents were
purified and distilled under an atmosphere of argon.[19] The alkyl
bromides were commercial products (Sigma–Aldrich) and used as
received. The syntheses of the precursors ethoxymethyleneacetyl-
acetone[20] and iron(II) acetate[21] have been described previously.
For the synthesis of the alkylimidazoles, slightly modified literature
procedures were used.[11–13]
N 14.72; found C 68.59, H 9.76, N 16.75. IR: ν = 2925 (s, CH ),
˜
2
2857 (m, CH2), 1652 (s, CO), 1563 (s, CO), 1391 (vs), 1271 (m),
1225 (vs), 1075 (vs) cm–1.
Preparation of the Solutions: [1(MeOH)2] (0.202 g, 0.45 mmol) was
dissolved in the different alkylimidazoles (methylimidazole, pentyl-
imidazole, heptylimidazole and decylimidazole; 2.5 mL), and the
red solutions were heated to 150 °C for 1 h. The solutions were
cooled to room temperature, and methanol (4 mL) was added. For
the SQUID samples, 0.05 mL of each solution was used.
N-Pentylimidazole: Imidazole (34.04 g, 0.5 mol) was dissolved in
methanol (45 mL), and an aqueous KOH solution (50%, 100 mL)
was added. The mixture was heated to 85 °C, and 1-bromopentane
(75.52 g, 0.5 mol) was added dropwise under vigorous stirring over
4 h. After cooling to room temp., the two-phase mixture was sepa-
rated from the solid, and the solvent was evaporated. Chloroform
(300 mL) was added slowly, and the solution was filtered at room
temp. The product was dried over Na2SO4 overnight and distilled
at 100 °C and 5ϫ10–4 bar, yield 35.6 g (52%). MS (DEI+): m/z (%)
= 138 (72) [M]+. 1H NMR (CDCl3, 399.8 MHz): δ = 0.89 (t, CH3),
1.30 [m, (CH2)2], 1.77 (q, NCH2CH2), 3.92 (t, NCH2), 6.90 [s, (Im)
NCHCHN], 7.04 [s, (Im)NCHCHN], 7.45 [s, (Im)NCHN] ppm.
Magnetic Susceptibilities: The data for [1(PentIm)2] and
[1(DecIm)2] were collected with a Quantum Design MPMS-XL5
SQUID magnetometer under an applied field of 0.05 T over 10–
400 K in the sweep mode. All samples were placed in gelatine cap-
sules held within plastic straws. The data were corrected for the
diamagnetic magnetisation of the ligands, which were estimated
from Pascal’s constants, and the sample holder. The outcomes from
elemental analysis were used to determine the exact molecular
weight per iron centre. For the measurements in solution, the sam-
ples were sealed in the plastic straws and measured in the settle
N-Heptylimidazole: Imidazole (20.42 g, 0.3 mol) was dissolved in
methanol (32 mL), and an aqueous KOH solution (50%, 65 mL)
was added. The mixture was heated to 100 °C, and 1-bromohept-
ane (43.73 g, 0.3 mol) was added dropwise under vigorous stirring
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mode with an applied field of 0.2 T. The raw data were corrected
for the diamagnetism of the solution and the diamagnetism of the
organic ligand by using tabulated Pascal’s constants.
X-ray Diffraction: The intensity data of [1(HeptIm)2] and
[1(DecIm)2] were collected with a Stoe IPDS II diffractometer at
133 K with graphite-monochromated Mo-Kα radiation. The data
were corrected for Lorentz and polarisation effects. The structures
were solved by direct methods {Sir2011[22] for [1(HeptIm)2],
Sir97[23] for [1(DecIm)2]} and refined by full-matrix least-square
techniques against F02 (SHELXL-97).[24] The hydrogen atoms were
included at calculated positions with fixed displacement param-
eters. All non-hydrogen atoms were refined anisotropically.
ORTEP-III[25] was used to prepare the structure representation,
and Schakal-99[26] and Mercury[27] were used to prepare the repre-
sentations of the molecule packing.
CCDC-1016502 {for [1(HeptIm)2]} and -1016503 {for
[1(DecIm)2]} contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Elemental Analysis: Elemental analysis was performed with a
VarioEL III CHN instrument and tin boats purchased from Ele-
mentar, and acetanilide (Merck) were used as the standard.
Acknowledgments
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Support from the University of Bayreuth, the Deutsche For-
schungsgemeinschaft (DFG) (WE 3546_4-1) and the Fonds der
Chemischen Industrie is gratefully acknowledged.
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Received: October 27, 2014
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I43021
/KAP1
Date: 15-12-14 13:08:27
Pages: 7
www.eurjic.org
FULL PAPER
Spin-Crossover Complexes
S. Schlamp, C. Lochenie, T. Bauer,
R. Kempe, B. Weber* ........................ 1–7
Iron(II) spin-crossover complexes with
Schiff base like equatorial ligands and
alkylimidazole axial ligands are syn-
thesised. The alkyl chain length is varied
from 5 to 7 and 10 carbon atoms. The crys-
tal structures of the C7 and C10 compounds
are described. There is an increased coop-
erativity in spin-crossover behaviour for the
compound with the longer C10 alkyl chain
than for the C5 compound.
Iron(II) Spin-Crossover Complexes with
Schiff Base Like Ligands and N-Alkyl-
imidazoles
Keywords: Iron / Spin crossover / Schiff
base ligands / N ligands
Eur. J. Inorg. Chem. 0000, 0–0
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim