Two new iron(II) spin-crossover complexes with N4O2 coordination sphere and spin transition around room temperature

Article abstract of DOI:10.1002/ejic.200900846

The reaction of iron(II) acetate with the tetradentate Schiff base like ligand H₂L1. {[3,3']-[4,5-dihydroxy- l,2-phenylenebis(iminomet: hylidyne)bis(2,4-pentanedion)]} leads to the formation of the complex [FeLl(MeOH)]. Reaction of this complex

Full text of DOI:10.1002/ejic.200900846

FULL PAPER
DOI: 10.1002/ejic.200900846
Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination Sphere
and Spin Transition around Room Temperature
Birgit Weber,*[a] Jaroslava Obel,[a] Dunie Henner-Vásquez,[a] and Wolfgang Bauer[a]
Keywords: Iron / Magnetic properties / Spin crossover / Schiff bases
The reaction of iron(II) acetate with the tetradentate Schiff
base like ligand H2L1 {[3,3Ј]-[4,5-dihydroxy-1,2-phenylene-
bis(iminomethylidyne)bis(2,4-pentanedion)]} leads to the for-
mation of the complex [FeL1(MeOH)]. Reaction of this com-
plex with pyridine (py) or N,NЈ-dimethylaminopyridine
(dmap) leads to the two N4O2-coordinated complexes
[FeL1(py)2]·py (1) and [FeL1(dmap)2]·MeOH·0.5dmap (2).
Both complexes are spin-crossover compounds that were
characterised by using magnetic measurements, X-ray crys-
tallography and temperature-dependent 1H NMR spec-
troscopy. Special attention was given to the role of the two
hydroxy groups on the phenyl ring in the formation of a hy-
drogen-bonding network and the influence of this network
on the spin-transition properties. Although only a gradual
spin crossover was observed for both complexes, the transi-
tion temperature was shifted to higher temperatures relative
to that of the complexes with no additional hydroxy groups
at the Schiff base like ligand. The hydrogen-bonding net-
work was responsible for this effect.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
magnetic ordering.[8] As a consequence of this finding, we
designed a new ligand based on 4,5-diaminocatechol with
two additional hydroxy groups on the phenyl ring that can
act as H-bond donors/acceptors. In Scheme 1 the general
procedure for the synthesis of the new ligand and the used
abbreviations is given. In this paper we present the synthesis
and characterisation of two octahedral iron(II) spin-cross-
over complexes of H2L1 with pyridine (py) and N,NЈ-di-
methylaminopyridine (dmap) as axial ligands. Special atten-
tion was given to the influence of the two additional hy-
Introduction
The bistability of spin-transition complexes (spin cross-
over, SCO) is one of the most promising for new electronic
devices in molecular memories and switches, as it may be
controlled by different physical perturbations as tempera-
ture, pressure or light.[1,2] Recent research activities in this
field explore the possibility to combine this SCO bistability
with additional properties (e.g., liquid crystalline proper-
ties,[3] magnetic exchange interactions[4]), resulting in multi-
functional SCO materials;[5] other research is based on the
rational design of nanostructured SCO materials and their
chemical and physical properties.[6] Of the possible types of
spin transitions (gradual, abrupt, with hysteresis, step wise,
incomplete), much of the interest is focused on the bistabil-
ity in highly cooperative systems (hysteresis or memory ef-
fect), and as such, compounds can exist in two different
electronic states depending on the history of the system.
With regard to this, we recently characterised an iron(II)
spin-crossover complex with a 70 K wide thermal hysteresis
loop around room temperature on the basis of a 2D net-
work of hydrogen bonds between the complex molecules.[7]
Systematic investigations on the magnetic properties of
iron(II) complexes of this ligand system demonstrated that
hydrogen bonds are also the foundation for long-range
[a] Center for Integrated Protein Science Munich at the Depart-
ment Chemie und Biochemie, Ludwig-Maximilians-Universität
München,
Scheme 1. General procedure for the synthesis of the new ligand
H2L1 and structures of the mononuclear complex [FeL1], [FeL2]
and the axial ligands with the used abbreviations.
Butenandtstr. 5-13 (Haus F), 81377 München, Germany
Fax: +49-89-2180-77407
E-mail: bwmch@cup.uni-muenchen.de
Eur. J. Inorg. Chem. 2009, 5527–5534
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B. Weber, J. Obel, D. Henner-Vásquez, W. Bauer
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droxy groups on the spin-crossover properties. For this pur-
pose, the properties of the two newly prepared complexes
are compared with the previously published analogue com-
plexes [FeL2(py)2] and [FeL2(dmap)2] with no additional
hydroxy groups on the phenylene ring.[9] Those two com-
plexes both show a cooperative spin transition with an ap-
proximate 9 K-wide thermal hysteresis loop in the case of
the dmap adduct (T1/2 = 179 K) and an approximate 2 K-
wide thermal hysteresis loop in the case of the py adduct
(T1/2 = 190 K). In both cases, the hysteresis is due to elastic
interactions with several short van der Waals contacts,
which are more pronounced in the case of the dmap ad-
duct.[9]
Figure 1. ORTEP drawing of the asymmetric unit of 1 with the
atom numbering scheme. Hydrogen atoms are omitted for clarity.
Thermal ellipsoids are shown at the 50% probability level.
Results and Discussion
Synthesis and General Characterisation
ures 1 and 2 the asymmetric units of the two complexes are
displayed. Selected bond lengths and angles within the first
coordination sphere are summarised in Table 1.
In Scheme 1 the general structure of the mononuclear
iron complexes [FeL1/2] and the used axial ligands is given.
Starting point for the synthesis of the new ligand H2L1 is
4,5-diaminocatechol, which was prepared as described pre-
viously by Rosa et al.[10] starting with commercially avail-
able veratrol. Condensation with two equivalents of the
keto–enol ether (compound A[11]) resulted in the formation
of the desired ligand, which was characterised by elemental
analysis and IR, mass and NMR spectroscopy. Conversion
of the ligand with iron(II) acetate (1.3 equiv.) in methanol
gave the iron(II) complex [FeL1(MeOH)]. The desired octa-
hedral complexes [FeL1(py)2]·py (1) and [FeL1(dmap)2]·
MeOH·0.5dmap (2) were obtained by reaction of [FeL1]
with pyridine or dmap followed by slow crystallisation.
Both complexes were fully characterised by elemental
analysis and mass spectroscopy as well as temperature-de-
pendent magnetic susceptibility measurements, X-ray struc-
ture analysis and temperature-dependent 1H NMR spec-
troscopy in the case of 1.
Figure 2. ORTEP drawing of the asymmetric unit of 2 with the
atom numbering scheme. Hydrogen atoms and additional solvent
molecules are omitted for clarity. Thermal ellipsoids are shown at
the 50% probability level.
Description of the X-ray Structures
Crystals suitable for X-ray structure analysis were ob-
tained for the two octahedral complexes. The crystallo-
graphic data are summarised in Table 5. The quality of the
In both complexes, the iron centre is located in a dis-
data of 2 was inferior and problems occurred with the re- torted octahedral coordination sphere with a N4O2 sur-
finement of the strongly disordered dmap and methanol rounding. The bond lengths and angles within the first co-
solvent molecules. Therefore, those atoms were not refined ordination sphere are within the region reported for low-
anisotropically. We will only be publishing the conforma- spin (LS) iron(II) complexes of the same ligand type.[12] The
tion of the complex and the crystallographic data. In Fig- average bond lengths are 1.90 (Fe–Neq), 1.94 (Fe–Oeq) and
Table 1. Selected bond lengths [Å] and angles [°] within the first coordination spheres of the complexes discussed in this work.
Fe–Neq
Fe–Oeq
Fe–Nax
O1–Fe–O2
Lax–Fe–Lax
1
2
1.885(2), 1.899(2)
1.910(4), 1.912(3)
1.928(2), 1.929(1)
1.934(3), 1.952(3)
1.991(2), 1.996(2)
2.017(4), 2.032(4)
87.51(6)
91.01(12)
178.49(7)
176.25(15)
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Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination
2.01 Å (Fe–Nax). A characteristic tool for the determination
of the spin state of these types of iron(II) complexes is the
O–Fe–O angle, which changes from about 110° in the high-
spin (HS) state to about 90° in the LS state.[13] For the com-
plexes reported here, the angle is 89°, which is clearly in the
region typical for the LS state. The bond lengths observed
for 2 are all slightly longer than the bond lengths of 1, indi-
cating an already started spin transition with a small frac-
tion of HS molecules. The bond lengths within the
FeOCCCN chelate six-membered ring of the equatorial li-
gand cannot be assigned to single and double bonds, indi-
cating the delocalisation of the negative charge of the ligand
over the chelating ring.
As already pointed out in the introduction, intermo-
lecular interactions can play a crucial role for the obtained
magnetic properties. They are not only relevant for cooper-
ative interactions in spin-transition complexes[7,13a,14,15] or
long-range magnetic ordering,[8,13b] as it is also known that
H-bonds can influence the ligand field strength and by this
the spin state of the iron complexes.[16] In Table 2 selected
intermolecular distances of 1 are summarised, and in Fig-
ure 3 the packing of the molecules of 1 in the crystal is
displayed.
Figure 3. Packing of the molecules of 1 in the crystal. Hydrogen
atoms not involved in the H-bonding network are omitted for clar-
ity.
two hydroxy groups of the phenylene ring are involved as
H-bond donors in two hydrogen bonds, both linking two
complex molecules. One of the two donor contacts (H5A)
links the molecules over the OCMe group (O4) of the neigh-
bouring complex in a similar fashion as that observed for
Table 2. Selected intermolecular distances [Å] and angles [°] of 1
resulting in a 1D chain with the base vector [0 1 0]. Only contacts
shorter than the sum of the van der Waals radii –0.2 Å were consid-
ered.
D–H
H···A
A···D
D–H···A
Table 3. Selected intermolecular distances [Å] and angles [°] of 2.
O5–H5···O4[a]
O6–H6···N5[b]
C26–H26···O6[b]
H25···H25Ј[c]
H28···C6[d]
0.82
0.82
0.93
1.81
1.95
2.46
2.20
2.57
2.21
2.627(2)
2.693(3)
3.163(3)
174.5
149.6
132.2
D–H
H···A
A···D
D–H···A
O5–H5A···O4[a]
O6–H6···O5[b]
C5–H5···O4[b]
0.82
0.82
0.93
1.77
2.02
2.58
2.58
2.71
3.22
169
143
127
H23···H23Ј[e]
[a] 1/2 + x, 1/2 – y, 1/2 + z. [b] 1 – x, 1 – y, 1 – z.
[a] x, 1 + y, z. [b] 1 – x, –y, –z. [c] 1 – x, –y, 1 – z. [d] 1 + x, y, z.
[e] –x, –y, 1 – z.
The two hydroxy groups at the phenylene ring give rise
to a 1D chain of H-bond-linked molecules along the base
vector [0 1 0]. Both OH groups act as H-bond donors. One
of the two donor contacts (H5) links directly two complex
molecules over the OCMe group (O4) of the neighbouring
molecule. The second OH group (H6) forms a hydrogen
bond to the nitrogen (N5) atom of the additional pyridine
molecule included in the crystal packing and does thus not
participate in the 1D chain of linked molecules. This chain,
however, is further supported by a weak hydrogen bond be-
tween the aromatic CH hydrogen atom of a coordinated
pyridine molecule (H26), involving the second hydroxy
group as a H-bond acceptor (O6) and three further short
van der Waals contacts (Table 2). In the case of 2, a com-
plete analysis of the intermolecular interactions is pre-
cluded because of the low quality of the X-ray structure
and the strong disorder of the included solvent molecules.
Only hydrogen bonds directly linking two complex mole-
cules were considered. In Table 3 selected intermolecular
distances are summarised, and in Figure 4 an excerpt of the
Figure 4. Packing of the molecules of 2 in the crystal. Hydrogen
atoms not involved in the H-bonding network and additional sol-
packing of the molecules of 2 in the crystal is given. The vent molecules are omitted for clarity.
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B. Weber, J. Obel, D. Henner-Vásquez, W. Bauer
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1. The second OH group (H6) forms a hydrogen bond to undergoes a gradual spin transition with T1/2 = 229 K.
the oxygen (O5) atom of the hydroxy group of a neighbour- Upon heating, the transition curve differs slightly from the
ing molecule. Those two hydrogen bonds give rise to a 2D cooling curve and a small hysteresis is observed in the high-
network of linked complex molecules along the plane (1 0 temperature region (T1/2 = 231 K). Further heating of the
–1).
complex to 320 K leads to a further increase in the χMT
product to a value of 3.35 cm3 K/mol expected for an
iron(II) complex in the HS state. In the second cooling cy-
cle, the transition temperature is shifted to lower tempera-
tures (T1/2 = 212 K) and this curve progression is obtained
for all further heating and cooling cycles. The observed be-
haviour can be explained with a (partial) loss of the meth-
anol molecules included in the crystal packing in the first
heating cycle. A good agreement is obtained between the
outcomes from the magnetic measurements and the results
from X-ray crystallography. In contrast to the two parent
compounds [FeL2(py)2] and [FeL2(dmap)2] with no ad-
ditional hydroxy groups on the phenylene ring, no coopera-
tive spin transition was obtained for 1 and 2. The reason is
most likely the inclusion of solvent molecules in the crystal
packing, which reduces the number of direct short
van der Waals contacts between the complex molecules.
However, a positive effect of the introduced hydroxy groups
is a shift in the transition temperature of the complexes to
higher temperatures, and this temperature is in a region that
is closer to room temperature.
Magnetic Susceptibility Data
Magnetic susceptibility measurements were performed in
the temperature range from 350 to 10 K for both complexes
by using a Quantum design MPMSR2-SQUID magnetom-
eter. Figure 5 displays the thermal dependence of the χMT
product (with χM being the molar susceptibility and T the
temperature) at 0.05 T for both compounds. For complex
1, the room-temperature value is with 0.22 cm3 K/mol in the
region expected for a complex essentially in the LS state.
Upon cooling, the value decreases further to 0.03 cm3 K/
mol at 100 K Ϫ a value typical for diamagnetic iron(II)
complexes. Upon heating the complex above room tempera-
ture, the χMT product increases rapidly and reaches a value
of 1.24 cm3 K/mol at 350 K. This increase in the magnetic
moment can be associated with a spin transition of the
complex above room temperature that is still not complete
at 350 K. The system was not heated any further to avoid
loss of the pyridine molecules included in the crystal pack-
ing.
1H NMR Spectroscopy
We recently reported the possibility to follow a spin tran-
sition in solution by interpretation of the temperature de-
pendence of the 1H NMR chemical shifts of the com-
pounds.[17] In order to investigate the influence of the ad-
ditional hydroxy groups on the spin transition in more de-
tail, 1 was dissolved in a mixture of [D5]pyridine/[D8]tolu-
ene (50:50). The iron centre was assumed to retain its octa-
hedral coordination sphere; however, all hydrogen bonds
observed in the crystal packing and any additional intermo-
lecular interactions were disabled. This allowed us to evalu-
ate the influence of packing effects on the transition curve
of 1. Figure 6Ͻyigr6 pos="x11"Ͼ shows the 1H NMR spec-
trum of 1 at 65 °C with the signal assignment to the right.
The assignment was accomplished by spectral comparison
with previously published spectra[17] and by taking the dif-
ferent line widths and relative intensities into consideration.
The position of the signals of protons A, B and C with the
relative intensities of 3 (A and B) and 1 (C) is comparable
to those of the previously published complex [FeL2(py)2] in
a pyridine/toluene mixture (50:50). The signals were there-
fore assigned to the CH3 groups (A, B) of the substituents
of the equatorial ligand. The signal with a relative intensity
of 1 was assigned to proton C of the phenylene ring. Of the
two remaining protons, the signal of the OH proton D is
Figure 5. Plots of χMT product (filled squares) vs. T for compounds
1 (top) and 2 (bottom) at 0.05 T. The open circles correspond to
the temperature dependence of the χMT product of 2 after heating
to 320 K.
In the case of 2, the room-temperature value of the χMT observed in the 9 ppm region of the spectrum. The signal
product is 3.12 cm3 K/mol, which is in the region expected of the last proton was not assigned. Considering the NMR
for an iron(II) complex essentially in the HS state. Upon spectra of these types of complexes in pyridine,[17] the HC-
cooling, the magnetic moment decreases gradually and N proton should be in the 400–500 ppm region of the spec-
reaches a value of 0.29 cm3 K/mol at 100 K. Compound 2 trum but is very broad and therefore difficult to detect.
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Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination
were fit by taking an extended Curie law into account with
different Curie constants (or spin densities) for the ground
and exited states:
con
δn = (F/T){W1C2n1 = +W2C2n2e–∆E/kT}/{W1 + W2e–∆E/kT
}
(1)
where W1 and W2 are the weighting factors for the ground
and excited states [S(S+1) in each case], Cn1 and Cn2 are
the orbital coefficients (spin densities) for the ground state
and exited state, F is the Curie constant, ∆E is the energy
difference between the ground state and the first exited state
and k is the Boltzmann constant. Because the most likely
excited state is that in which the formerly t2g electrons are
rearranged between the dxy and dyz orbitals, both the
ground state and the first exited state were assumed to exhi-
bit a total spin S = 2. Other possible spin states were also
tried but produced no reliable fits. The fit obtained with the
TDF (temperature-dependent fitting) program written by
Shokhirev and Walker[18] (solid lines) simulates the tem-
perature dependence of the isotropic shift very well. The
Figure 6. 1H NMR spectrum of 1 in a [D5]pyridine/[D8]toluene
(50:50) at 65 °C. The signal assignment is given at the right. S de-
notes the solvent toluene/pyridine and * denotes the impurities.
The temperature dependence of the NMR parameters of
1 (isotropic shifts plotted vs. 1/T) is given in Figure 7 (top).
Above 15 °C (288.15 K; 1/T = 3.5 1000/K) the behaviour is
similar to those expected for pure HS complexes. At lower
temperatures, the isotropic shifts move rapidly towards zero
as reported previously for these types of spin-transition
complexes.[17] The paramagnetic shift of the pure HS com-
plex above 15 °C does not follow the ideal Curie law
straight line. This is most probably due to thermally access-
ible exited states. The experimental data in Figure 7 (top)
best-fit parameters are: E1(GS)
=
2
[(dxy)2-
(dxz,dyz)2(dz2)1(dx2–y2)1], E1(ES) = 2 [(dxy)1(dxz,dyz)3(dz2
)
1(dx2–y2)1], ∆E1,2 = 744 cm–1, MSD (mean standard devia-
tion) = 0.073, spin densities 1: –0.013(a), 0.006(b), 0.005(c);
2: –0.022(a), 0.005(b), 0.001(c). The calculated isotropic
shifts of the pure HS complex at lower temperature can now
be used to determine the HS molar fraction (γHS) of the
complex as a function of temperature:
γHS = [δcon(measured)T]/[δcon(calculated)T]
(2)
In Figure 7 (bottom), the average of the spin transition
curves for the different protons is given (dots). The data
were fitted using the expression:
–RTln[γHS/(1 – γHS)] = ∆HHL – T∆SHL
(3)
where ∆HHL and ∆SHL are the thermodynamic enthalpy
and entropy values associated with the spin transition (solid
line). The obtained fitting parameters are ∆HHL
=
25.1Ϯ1.1 kJ/mol and ∆SHL = 124.5Ϯ5.3 J/Kmol with a
transition temperature of T1/2 = 201 K. The obtained en-
tropy change is quite high (about three times the expected
value), indicating that either cooperative interactions are
not totally negligible or there are some dynamics in the
compound. The transition temperature obtained in solution
is significantly lower than the transition temperature in the
solid state and the solid-state properties are clearly influ-
enced by the crystal packing.
Conclusions
Two new spin-crossover complexes were prepared with
an N2O2 coordinating Schiff base like ligand that was al-
tered by introduction of two additional hydroxy groups
with the idea to provide better preconditions for the forma-
tion of a hydrogen-bonding network. The aim of this modi-
fication was to synthesise more examples of H-bond-linked
spin-crossover complexes similar to our previous complex
with a 70 K-wide thermal hysteresis loop[7] to provide a bet-
Figure 7. Top: Isotropic shifts of 1 plotted vs. 1/T (dots). The solid
lines represent the calculated shifts of the pure HS complex by
using the extended Curie law [Equation (1)]. The fitting parameters
are given in the text. Bottom: HS mol fraction (γHS) of 1 obtained
by interpretation of the isotropic shifts by using the extended Curie
law. The solid line corresponds to fitted data by using the regular
solution model with the parameters given in the text.
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B. Weber, J. Obel, D. Henner-Vásquez, W. Bauer
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ter understanding about the suitability of hydrogen bonds involves the OH group of the neighbouring molecule as a
to transmit cooperative interactions during the spin transi- H-bond acceptor. This probably compensates the effects de-
tion. In this work, we present that the new modification was scribed above and the influence of the H-bond network on
only partly successful. The outcomes from X-ray structure the ligand field strength is less pronounced compared to that
analysis clearly demonstrate that, as requested, the intro- in 1, in agreement with the outcome of the magnetic mea-
duced hydroxy groups give rise to the formation of a net- surements.
work of H-bond-linked molecules. However, in contrast to
the two parent compounds [FeL2(py)2] and [FeL2-
(dmap)2] additional solvent molecules are included in the
crystal packing. As a consequence, only gradual spin transi-
tions are observed for these two complexes. In order to in-
vestigate the influence of the H-bonding network on coop-
erative interactions during the spin transition, it will be nec-
essary to prepare complexes with no included solvent mole-
cules.
Experimental Section
Synthesis: All syntheses were carried out under an atmosphere of
argon by using Schlenk tube techniques. All solvents were purified
as described in the literature[19] and distilled under an atmosphere
of argon. The synthesis of 4,5-diaminocatechol,[10] compound A[11]
and iron(II)acetate[20] is described in literature.
However, comparative studies in solution and in the solid
state clearly demonstrate an effect of the H-bonding net-
work on the transition temperature, as summarised in
Table 4. In solution, the effect of the introduction of a hy-
droxy group on the phenylene ring of the Schiff base like
ligand is marginal, and nearly the same transition tempera-
tures are obtained for complexes 1 and [FeL2(py)2]. In con-
trast to this, a difference of about 150 K is obtained for the
transition temperatures in the solid state and the only pos-
sible reason is the observed H-bonding network in the case
of 1. Systematic investigations on about 20 octahedral mo-
nonuclear iron(II) complexes of this ligand system with N-
heterocycles as axial ligands revealed an systematic effect of
the substituents at the Schiff base like ligand on the overall
ligand field strength.[13] Substituents with a negative meso-
meric effect [(–)-M] at the OCCCN chelating six-membered
ring of the ligand lead to a reduction in the electron density
at the donor atoms and a reduced ligand field strength.[13]
In the crystal packing of 1 and 2 a hydrogen bond between
the OH group and the COMe substituent at the chelating
six-membered ring is observed. However, this hydrogen
bond should increase the (–)-M effect of this substituent and
thus lead to a reduction in the ligand field strength. A more
likely explanation is that due to the hydrogen bonds, the
electron density at the hydroxy oxygen atom is increased to
such an extent that instead of a negative inductive [(–)-I] and
a (+)-M effect of an OH group, a (+)-I and a (+)-M effect
is observed, similar to an O– substituent. This results in an
increase in the electron density at the nitrogen donor atom
in the para-position and an increase in the overall ligand
field strength. Thus, the spin transition is shifted to higher
temperatures. In the case of complex 2, one hydrogen bond
H2L1: To
(4.60 g, 15.23 mmol) and sodium methoxide (1.66 g, 30.73 mmol)
in methanol (120 mL) was added compound (4.80 g,
30.73 mmol) in methanol (20 mL) in one portion. The solution was
stirred for 16 h at room temperature. After this time the precipitate
was filtered off, recrystallised from ethanol and dried in vacuo.
Yield: 5.38 g (98%). C18H20N2O6 (360.36): calcd. C 59.99, H 5.59,
a solution of 4,5-diaminocatechol dihydrobromide
A
N 7.77; found C 58.78, H 5.60, N 7.57. IR (nujol): ν = 1603 (C=O,
˜
COMe), 3101 (br., OH) cm–1. MS (FAB+): m/z (%) = 361 (20)
1
[H2L1 + H]+. H NMR (270 MHz, CDCl3): δ = 2.25 (s, 6 H, CO-
CH3), 2.34 (s, 6 H, CO-CH3), 6.94 (s, 2 H, CH-phenylene), 8.16 (d,
2 H, CH=C), 9.5 (s, 2 H, OH), 12.58 (d, 2 H, NH) ppm.
[FeL1(MeOH)]: A suspension of iron(II)acetate (3.05 g, 17.5 mmol)
and H2L1 (4.86 g, 13.51 mmol) in methanol (150 mL) was heated
at reflux for 2 h. After cooling, a red brown precipitate was ob-
tained that was collected, washed with methanol (2ϫ20 mL) and
dried in vacuo. Yield: 3.22 g (65%). C19H22FeN2O7 (446.23): calcd.
C 51.14, H 4.97, N 6.28; found C 50.89, H 5.15, N 6.28. MS
(DEI+): m/z (%) = 31 (100) [MeOH]+, 414 (5) [FeL1]+. IR (nujol):
ν = 1606 (C=O, COMe), 3300 (br., OH) cm–1.
˜
[FeL1(py)2](py) (1): A solution of [FeL1(MeOH)] (0.40 g, 0.89 mmol)
in pyridine (15 mL) was heated at reflux for 30 min. After this time,
oxygen-free water (15 mL) was added. Cooling the mixture to 4 °C
yielded a fine crystalline black precipitate of 1 that was collected and
dried in vacuo. Yield: 0.30 g (50%). C33H33FeN5O6 (651.49): calcd.
C 60.84, H 5.11, N 10.75; found C 60.81, H 5.09, N 10.85. MS
(FAB+): m/z (%) = 79 (100) [py]+, 414 (35) [FeL1]+. IR (nujol): ν =
˜
1652 (C=O, COMe), 3070 (br. OH) cm–1.
[FeL1(dmap)2](MeOH)(dmap)0.5 (2): A solution of [FeL1(MeOH)]
(0.50 g, 1.30 mmol) and dmap (6.35 g, 51.99 mmol) in methanol
(90 mL) was heated at reflux for 1.5 h. Cooling the mixture to 4 °C
yielded a fine crystalline black precipitate of 2 that was collected,
washed with methanol (5 mL) and dried in vacuo. Yield: 0.30 g
(33%). C36.5H48FeN7O7.5 (760.66): calcd. C 57.63, H 6.36, N 12.89;
found C 57.50, H 6.11, N 12.86. MS (FAB+): m/z (%) = 123 (100)
[dmap], 413 (25) [FeL1]+. IR (nujol): ν = 1610 (C=O, COMe), 3444
Table 4. Comparison of the transition temperatures of the four
complexes 1, 2, [FeL2(py)2] and [FeL2(dmap)2] discussed in this
work in solution and in the solid state.
˜
(br., OH) cm–1.
Magnetic Measurements: Magnetic measurements of the fine crys-
Complex
T1/2 [K],
solid state
T1/2 [K],
solution
Ref.
talline samples were performed with
a Quantum-Design-
MPMSR2-SQUID-Magnetometer in a temperature range from 10
to 350 K. The measurements were carried out at 0.05 T in the settle
mode. The data were corrected for the magnetisation of the sample
holder and diamagnetic corrections were made by using tabulated
Pascal’s constants.
1
Ͼ350
230
190
201
this work
2
this work
[5,13]
[FeL2(py)2]
[FeL2(dmap)2]
211
[5]
179
5532
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5527–5534

Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination
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X-ray Crystallography: The intensity data of 2 were collected with
a Nonius KappaCCD diffractometer by using graphite-monochro-
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an Oxford XCalibur diffractometer by using graphite-monochro-
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[2]
risation effects. The structure was solved by direct methods
(SIR97[21]) and refined by full-matrix least-square techniques
against F0 (SHELXL-97[22]). The hydrogen atoms were included
2
at calculated positions with fixed thermal parameters. ORTEP-III
was used for structure representation.[23] Crystallographic data are
summarised in Table 5. Selected distances and angles are presented
in Table 1. CCDC-744753 (for 1) and -744754 (for 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.
[3]
Table 5. Crystallographic data of the octahedral complexes dis-
cussed in this work.
[4]
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1
2
Empirical formula
Formula weight
Temperature [K]
Crystal size [mm]
Crystal system
Space group
λ [Å]
a [Å]
b [Å]
c [Å]
α [°]
C33H33FeN5O6
651.49
200
0.30ϫ0.21ϫ0.13
triclinic
P1
0.71073
8.709(4)
11.767(3)
16.660(2)
104.894(16)
94.73(2)
105.38(3)
1569.9(9)
2
1.378
0.533
680
3.74–26.25
–10/10
–14/14
–20/20
25475
C36.5H48FeN7O7.5
760.66
200
0.24ϫ0.21ϫ0.024
monoclinic
P21/n
0.71073
16.2330(5)
12.6390(4)
19.2770(5)
90
106.548(2)
90
3791.23(19)
4
1.3221
0.455
1584
3.13–24.11
–18/18
–14/14
–22/22
20985
6008
6008/0/476
0.0525 (0.0706)
0.1392 (0.1510)
1.029
¯
[7]
[8]
β [°]
γ [°]
V [Å3]
Z
ρcalcd. [g/cm3]
µ [1/mm]
F(000)
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[10]
Θ range [°]
Index ranges
[11]
[12]
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Reflections collected
Reflections unique
6388
Data/restrains/parameters 6388/0/415
R1 (all)
wR2
GooF
0.0347 (0.0686)
0.0701 (0.0791)
0.931
Acknowledgments
[13]
[14]
[15]
This work has been supported financially by the Deutsche For-
schungsgemeinschaft (SPP 1137) the Fonds der Chemischen Indus-
trie, the Center for Integrated Protein Science Munich (CIPSM)
and the University of Munich. The authors thank P. Mayer for
acquisition of the crystallographic data of 2.
[16]
A. P. Summerton, A. A. Diamantis, M. R. Snow, Inorg. Chim.
Acta 1978, 27, 123–128.
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Eur. J. Inorg. Chem. 2009, 5527–5534
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5533

B. Weber, J. Obel, D. Henner-Vásquez, W. Bauer
FULL PAPER
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Received: August 27, 2009
Published Online: November 4, 2009
5534
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 5527–5534