Bifunctional Fe(ii) spin crossover-complexes based on ω-(1: H -tetrazol-1-yl) carboxylic acids

Article abstract of DOI:10.1039/d0dt03315d

To increase the supramolecular cooperativity in Fe(ii) spin crossover materials based on N1-substituted tetrazoles, a series of ω-(1H-tetrazol-1-yl) carboxylic acids with chain-lengths of C2-C4 were synthesized. Structural characterization confirmed the formation of a strong hydrogen-bond network, responsible for enhanced cooperativity in the materials and thus largely complete spin-state transitions for the ligands with chain lenghts of C2 and C4. To complement the structural and magnetic investigation, electronic spectroscopy was used to investigate the spin-state transition. An initial attempt to utilize the bifunctional coordination ability of the ω-(1H-tetrazol-1-yl) carboxylic acids for preparation of mixed-metallic 3d-4f coordination polymers resulted in a novel one-dimensional gadolinium-oxo chain system with the ω-(1H-tetrazol-1-yl) carboxylic acid acting as μ2-η2:η1 chelating-bridging ligand.

Full text of DOI:10.1039/d0dt03315d

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DOI: 10.1039/D0DT03315D
ARTICLE
Bifunctional Fe(II) spin crossover-complexes based on ω-(1H-
tetrazol-1-yl) carboxylic acids
Willi Zeni,a Marco Seifried,a Christian Knoll,a Jan M. Welch,b Gerald Giester,c Berthold Stöger,d
Received 00th January 20xx,
Accepted 00th January 20xx
Werner Artner,d Michael Reissner,e Danny Müller,a* and Peter Weinbergera*
DOI: 10.1039/x0xx00000x
To increase the supramolecular cooperativity in Fe(II) spin crossover materials based on N1-substituted tetrazoles, a series
of ω-(1H-tetrazol-1-yl) carboxylic acids with chain-lengths of C2-C4 were synthesized. Structural characterization confirmed
the formation of a strong hydrogen-bond network, responsible for enhanced cooperativity in the materials and thus largely
complete spin-state transitions for the ligands with chain lenghts of C2 and C4. To complement the structural and magnetic
investigation, elctronic spectroscopy was used to investigate the spin-state transition. An initial attempt to utilize the
bifunctional coordination ability of the ω-(1H-tetrazol-1-yl) carboxylic acids for preparation of mixed-metallic 3d-4f
coordination polymers resulted in a novel one-dimensional gadolinium-oxo chain system with the ω-(1H-tetrazol-1-yl)
carboxylic acid acting as µ2-η2:η1 chelating-bridging ligand.
luminescence and fluorescence,17, 18 their sensing capacity in
form of porous switchable materials,12, 19 or their combination
with chirality20-22 have recently been reported.
Since the occurrence of SCO under ambient conditions is very
sensitive to the ligand field, it is strongly affected by the nature
of the ligand system, the presence or absence of solvates23 and
counter anions applied.24 (Substituted) azole ligands, including
Introduction
First row transition metals with 3d4-3d7 electron configurations
allow for population of their 3d-orbitals with either a maximum,
or a minimum of paired electrons. Depending on the
coordinative environment around the metal centre, the
energetic difference between these electron configurations
(high-spin (HS) and low-spin (LS) state) may be small enough to
be governed by an external stimulus such as temperature,1, 2
pressure,1-3 light4 or external electric field,5-8 among others.1
This phenomenon was first observed in the 1930s by Italian
researchers, working on iron (III) N,N-dialkyldithiocarbamates
and has since been known as spin crossover (SCO), or spin state
transition.9-11
N1-substituted tetrazoles, are
a promising platform for
systematic development of SCO-materials.1
Homoleptic hexa-coordinated Fe(II)-complexes based on N1-
substituted tetrazoles are often spin switchable, as
coordination of Fe(II) by tetrazoles results in an appropriate
ligand field strength. In this case, Fe(II) switches between a
paramagnetic HS state with S=2 and a diamagnetic LS state with
S=0.
In previous work, we have emphasized fine-tuning of the
ligands’ geometry and flexibility, shaping cooperativity and
transition temperature on a molecular scale,25, 26 as well as post
functionalization of the ligand backbone.27 Therefore, in this
work, a carboxylic acid moiety has been introduced to the ligand
system, allowing for the investigation of the SCO in [Fe(ω-(1H-
tetrazol-1-yl) carboxylic acid)6]2+-cations. Alkylcarboxylic acid
substituted tetrazoles provide three useful features: On a
molecular level the COOH-group should establish a network of
The intrinsic correlation between the bistability of SCO
materials and several of their physical properties makes them
appealing candidates for novel miniaturized sensors,12,
13
memory/storage devices,14 and
a
key technology in
spintronics.15 Today, SCO materials are primarily investigated by
an academic bottom-up approach, resulting in highly
specialized materials for devices on a nanoscale. Molecular
actuators,16 their utilization in quenching and affecting
a. Institute of Applied Synthetic Chemistry, TU Wien, Getreidemarkt 9/163-AC, 1060
Vienna, Austria
hydrogen bonds, increasing cooperativity and governing the
28-30
abruptness of the spin state transition,
the COOH-group
E-mail: danny.mueller@tuwien.ac.at; peter.e163.weinberger@tuwien.ac.at
b. Center for Labelling and Isotope Production, TRIGA Center Atominstitut, TU Wien,
Stadionallee 2, 1020 Vienna, Austria.
may act as an additional ligand allowing for the formation of
multi-metallic networks with a second transition metal, or rare-
earth element and, finally, the COOH termination of the ligand
may allow for deposition on oxide surfaces.
In this contribution, we report the ω-(1H-tetrazol-1-yl)
carboxylic acids with C2-C4 alkyl chains and the magnetic,
structural and spectroscopic characterization of their Fe(II)-SCO
c. Department of Mineralogy and Crystallography, University of Vienna,
Althanstraße 14 (UZA 2), 1090 Vienna, Austria.
d. X-Ray Center, TU Wien, Getreidemarkt 9, 1060 Vienna, Austria
e. Institute of Solid State Physics, TU Wien, Wiedner Hauptstraße 8-10/138, 1040
Vienna, Austria
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: CCDC 2024140 (4, HS),
2024142 (4, LS), 2024146 (6, HS), 2024147 (6, LS), 2024143 (7, HS), 2024141 (7, LS),
2024144 (9,HS), 2024145 (9, LS), 2024832 (10). See DOI: 10.1039/x0xx00000x
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complexes, as well as an initial attempt to prepare a multi- below 115 K is attributed to further 50 % of the Fe(II) sites
View Article Online
DOI: 10.1039/D0DT03315D
metallic 3d-4f coordination polymer.
undergoing the HS-LS transition. [Fe(3COOHTz)6](ClO4)2
(
8
)
remains all HS-state. [Fe(4COOHTz)6](ClO4)2 (9) shows by far the
completest HS-LS transition with a T of 175 K and a final χmol
T
½
of 0.66 cm3Kmol-1 at 50 K, corresponding to only
~
18 % of Fe(II)-
Results and Discussion
centres remaining in the HS state.
The spin state transition in the BF4 and ClO4 complexes of
2COOHTz, both incorporating two molecules acetonitrile, are
Synthesis
-
-
The spin crossover behaviour of Fe(II)-N1-alkyl-substituted
tetrazole complexes has been shown to be governed by the
length of the N1-alkyl substituent and the choice of weakly
coordinating anion.24, 31 Therefore, in the current study, the
length of the alkyl-skeleton was varied from C2-C4 (see scheme
overly sensitive towards loss of the solvate. 4 partially loses the
solvate already during drying in vacuum during the synthesis, or
on shelf storage. This resulted in an intermediate with
0.7 MeCN molecules incorporated (4c, determined by 1H-NMR)
and on subsequent drying in vacuum in a non-solvate (4b),
shown in figure 1b. For 0.7 MeCN molecules incorporated in 4c
the spin state transition is shifted to lower temperatures with
-
-
1) and BF4 and ClO4 were used as weakly coordinating
tetrahedral anions of comparable volume (BF4 49 Å3; ClO4
-
-
54 Å3).
The ligands 2-4COOHTz
(1-3) were prepared from the
T
1/2 at 132 K and a final χmolT of 2.75 cm3Kmol-1, corresponding
to a 25 % LS-state. The completely desolvated compound 4b is
corresponding amino-acids based on the Franke-tetrazole
synthesis,32 in analogy to the reported synthesis of (1H-tetrazol-
1-yl)-2-acetic acid (2).33-35Treatment of the resulting N1-alkyl-
substituted tetrazoles with FeX2∙6H2O (X=BF4 , ClO4 ) in
acetonitrile (MeCN) followed by subsequent washing with THF
~
spin crossover inactive, remaining in the HS-state for all
temperatures. Similarly, the desolvated ClO4 -complex 7b
-
-
-
shows no spin crossover anymore (figure 1b). This
demonstrates, how crucial the incorporated solvate molecules
are in this case additional to the H-bonding network.
All in all, the differing picture obtained from this comparison of
the SCO-behaviour is not only caused by the weak-coordinating
1
results in the desired complexes. H-NMR analysis of the bulk
samples of all prepared complexes shows that only
Fe(2COOHTz)6]2+ incorporated solvent molecules, for both
-
X=BF4 and ClO4- amounting to 2 MeCN per Fe2+ center.
anion (as obvious by comparing
4 vs. 7, or 6 vs. 9), but rather
Magnetic properties
The dependence of molar magnetic susceptibility on
temperature (10 to 300 K) was investigated for all six Fe(II)-
complexes (Figure 1a). The resulting χmolT curves show three
distinct tendencies: partial, incomplete spin crossover (
complete spin crossover (4, 6 and ) and no spin crossover
). All changes in χmolT below 50 K may be attributed to zero-
field splitting, expected for residual HS Fe(II).
molT decreases for gradually below 170 K from 3.51
cm3Kmol-1 at 300 K to 2.86 cm3Kmol-1 at 50 K. This seems to
correspond to ~25 of Fe(II) sites in LS state.
[Fe(2COOHTz)6](BF4)2∙2 MeCN ( ) shows the highest T1/2 of the
series with 227 K and decreases to a full LS-state below 180 K.
[Fe(4COOHTz)6](BF4)2 ( ) has a T of 163 K, the spin-state
transition taking place gradually from below 235 K to a final
molT of 0.98 cm3Kmol-1 at 50 K. This corresponds to
72 % of LS-
state.
Within the ClO4 compounds, [Fe(2COOHTz)6](ClO4)2∙2 MeCN (
reveals a two-step transition, featuring a kink at 170 K. Below
245 K χmolT of
decreases gradually to 2.9 cm3Kmol-1 at 170 K,
pointing to a first HS-LS transition of 18 % of the Fe(II) sites. A
sharp decrease of χmolT to a constant value of 1.2 cm3Kmol-1
5),
,
7
9
(
8
χ
5
%
a
4
6
½
χ
~
-
7
)
7
~
N
N
O
O
O
N
N
N
N
N
N
N
OH
OH
OH
N
N
N
2COOHTz
1
( )
3COOHTz
2
( )
4COOHTz
3
( )
Scheme 1. ω-(1H-tetrazol-1-yl) carboxylic acids used in this
study, the number before the name displaying the chain-
length
2 | J. Name., 2012, 00, 1-3
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attributed to a combination of different effects. Additional to
the impact of the anion, as discussed in the case of 2COOHTz
the 2 MeCN solvate makes the game. Furthermore, there is the
variation in the length of the alkyl-spacer, which for 4COOHTz
seems to be a good fit between establishing cooperativity and
preventing too much motional freedom in form of a shock-
31
absorber effect,24,
which was evidenced in the past for
increasing chain-lengths. Missing the structural characterization
of the 3COOHTz-compounds, the differing SCO-behaviour is
probably related to the odd number of C-atoms, which already
for unsubstituted alkyl-tetrazoles were found challenging in the
past.24, 31
[Fe(2COOHTz)6]2+-cations stack in layers, with three of the
ligands pointing upwards and three downwards (see figure 2) to
the adjacent layer. This arrangement is further stabilised by the
above-mentioned H-bonds (see figure 3). The Fe-atoms are
located on the Wyckoff-position 3a, alternating with an
Crystallographic analysis
Single crystals suitable for determination of the molecular
structure could be grown for
of diethyl ether (Et2O) into a concentrated MeCN-solution of the
corresponding compounds. No suitable crystals of and could
be obtained by similar means. Single crystal diffraction data
were collected at 100 and 200 K for and in order to
4, 6, 7 and 9 by vapour-diffusion
-
acetonitrile, an apex-up and an apex-down BF4- group. The BF4
5
8
4
,
6
,
7
9
determine both low- and high-spin molecular structures. In
addition variable temperature P-XRD patterns were acquired
for
4 and 7 from 100 – 300 K.
[Fe(2COOHTz)6](BF4)2∙2 MeCN (4). 4 crystallizes as MeCN
�
solvate in the trigonal R3 space group and this symmetry is
retained both at 100 K (low-spin, see figure 2) and 200 K (high-
spin). The iron-centre is octahedrally surrounded by six
2COOHTz-ligands coordinating via the exo N4-nitrogen. The Fe-
N bond lengths for all six ligands are equal (1.987 Å), typical for
a Fe(II) LS-state. At 200 K the distance increases ~9 % to 2.176
Å, characteristic for the Fe(II) HS-state (see table S1).1 The
packing in the crystal is governed – as predicted for a COOH-
group – by an H-bond network composed of infinite C(5) type
chains between the COOH-groups. Viewed along the b axis, the
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groups interact strongly with the [Fe(2COOHTz)6]2+-cations
through C–H∙∙∙F-bonds with both the tetrazolic CH and CH2-
group (see figure 4) in both the high- and low-spin states.
[Fe(2COOHTz)6](ClO4)2∙2 MeCN (7). 7 crystallizes isotypically to
4
with slightly larger cell parameters (see table 1) as an MeCN
�
solvate in the trigonal R
(2.004 Å, 100 K, LS-state; 2.184 Å, 200 K, HS-state, see table S2)
are slightly longer than in , but still compar able and
3 space group. In 7 the Fe-N distances
4
table S3). In the HS-state at 200 K the Fe-N distances increase to
characteristic for Fe(II) in the corresponding spin-state. Also, in
2.185 Å (N4), 2.182 Å (N4a) and 2.185 Å (N4b). As for
4 and 7,
-
7
both at 100 K and 200 K the ClO4 -anion is not disordered and
the supramolecular structure is governed by an H-bond network
with the COOH-groups forming a three-dimensional network of
R22(8) type ring motifs joining layers of [Fe(4COOHTz)6]2+-
cations (see figure 8). The voids between the ligand alkyl-chains
are occupied by Et2O, which also interacts with the COOH-
groups via a single H-bond. Comparing the supramolecular
stabilized through interaction with the [Fe(2COOHTz)6]2+-cation
(see figure 5).
Variable temperature P-XRD of bulk (4) and (7). Magnetic
measurements of bulk
4 and 7 show an incomplete spin
transition, whereas the Fe-N bond distances obtained from the
single crystal data suggest a largely complete transition.
Therefore, variable temperature P-XRD was used to follow any
structural changes of the bulk material during the SCO (see
figure 6). For both compounds, the calculated diffractograms
obtained from the HS and LS molecular structures are in
reasonable agreement with the powder-patterns of the bulk
arrangement of 4/7 to 6 it becomes evident, that in this case
only due to the longer alkyl-chains Et2O could be incorporated
as solvate molecule. In the former case the voids between the
cationic Fe-layers would not have been large enough to fit the
material. For both
4 (figure 6a) and 7 (figure 6b) the
temperature dependent PXRD measurements show more
pronounced changes in the powder pattern (dotted lines as a
guide) than to those just expectable from thermal contraction.
On this basis it seems clear that both bulk and single crystalline
samples are the same compound.
[Fe(4COOHTz)6](BF4)2∙Et2O (6). 6 crystallizes as an Et2O solvate,
�
1
as a result of vapour-diffusion crystallization, in the triclinic P
space group. The structure was determined at 100 K (LS-state)
and 200 K (HS-state). The asymmetric unit (see figure 7) includes
the Fe-centre with three 4COOHTz ligands, one crystallographic
-
independent BF4 -anion, as well as half of the Et2O-solvate. The
Fe-N distances of the three coordinated ligands are slightly
different (1.961 Å (N4), 1.979 Å (N4a) and 1.989 Å (N4b), see
4 | J. Name., 2012, 00, 1-3
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table S4). In
9
the [Fe(4COOHTz)6]2+-cations form layers
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connected through the H-bond network DtoOIe: 1a0c.h10o39t/hDe0rDaTn0d33t1h5De
-
ClO4 -anions.
The relevant crystallographic parameters for all Fe-containing
structures are given in table 1.
-
Et2O-molecules. Whereas at 100 K the BF4 -anions are stabilized
by the H∙∙∙F bonds similar to preventing a potential disorder,
4
at 200 K in the HS-state those interactions are no longer strong
-
enough, resulting in an apex up-down disorder of the BF4 -
groups.
Structure of [Fe(4COOHTz)6](ClO4)2∙Et2O (9). 9 crystallizes as
�
1
Et2O solvate like
6
in the triclinic P
space group but has two
-
crystallographic independent Fe-centres and two ClO4 -anions
in the asymmetric unit. Both Fe1 and Fe2 are surrounded by
each three independent 4COOHTz-ligands, which do not
interact with each other via H-bonds. The solvate molecule is
located in the cavity formed by the ligands, stabilized by an H-
bond (see figure 9). At 100 K, all Fe-N bond lengths (1.984 Å Fe1-
N4, 1.987 Å Fe1-N4a, 1.982 Å Fe1-N4b, 1.987 Å Fe2N4c, 1.987
Å Fe2-N4d, 1.984 Å Fe2-N4e) are characteristic for Fe(II) in its
low-spin state. In contrast, at 200 K the bonds extend to typical
HS distances (2.181 Å Fe1-N4, 2.178 Å Fe1-N4a, 2.173 Å Fe1-
N4b, 2.174 Å Fe2N4c, 2.185 Å Fe2-N4d, 2.178 Å Fe2-N4e, see
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Table 1. Crystallographic parameters for the crystal structures of 4, 6, 7 and 9
4∙MeCN, HS
C22H30B2F8FeN26O12
1080.19
200
4∙MeCN, LS
7∙MeCN, HS
7∙MeCN, LS
Formula
Weight [g mol-1]
T [K]
C22H30B2F8FeN26O12
1080.19
100
C22H30Cl2FeN26O20
1105.47
200
C22H30Cl2FeN26O20
1105.47
100
Colour
Shape
Crystal System
Space Group
a [Å]
white
pink
white
pink
platelet
trigonal
R-3
10.6588(7)
10.6588(7)
34.838(3)
90
platelet
trigonal
R-3
10.4735(5)
10.4735(5)
34.480(2)
90
platelet
trigonal
R-3
10.747(3)
10.747(3)
34.689(9)
90
platelet
trigonal
R-3
10.587(2)
10.587(2)
34.314(7)
90
b [Å]
c [Å]
α [°]
90
90
90
90
β [°]
120
3427.7(5)
3
1.570
0.445
120
3275.6(4)
3
1.643
0.466
120
3470(2)
3
1.587
0.543
120
3330.8(14)
3
γ [°]
V [Å3]
z
1.653
0.565
ρ
calc. [g cm-3]
µ [mm-1]
Measured Refl's.
Indep't Refl's
22250
1573
21166
1495
27060
1935
26274
1859
1421
1374
1389
1444
Refl's I≥2 σ(I)
Rint
GooF
wR2
R1
0.0308
1.068
0.0804
0.0318
2024140
0.0309
1.072
0.0673
0.0271
2024142
0.0952
1.071
0.1449
0.0569
2024146
0.0798
1.115
0.1329
0.0550
2024147
CCDC
6∙Et2O, HS
C34H58B2F8FeN24O13
1240.45
200
6∙Et2O, LS
C34H58B2F8FeN24O13
1240.45
100
9∙Et2O, HS
C34H58Cl2FeN24O21
1265.79
200
9∙Et2O, LS
C34H58Cl2FeN24O21
1265.79
100
Formula
Weight [g mol-1]
T [K]
pink
pink
platelet
triclinic
P-1
10.6120(12)
10.6186(12)
26.596(3)
95.237(3)
95.276(3)
114.758(3)
2681.9(5)
2
Colour
Shape
Crystal System
Space Group
a [Å]
white
white
platelet
triclinic
P-1
platelet
triclinic
P-1
platelet
triclinic
P-1
10.630(3)
10.971(3)
14.235(4)
74.796(6)
71.624(6)
63.563(6)
1396.1(6)
1
10.530(3)
10.576(3)
13.836(4)
75.400(8)
73.122(7)
64.974(7)
1321.2(7)
1
10.6262(13)
11.0192(13)
27.044(3)
96.080(4)
93.160(4)
116.571(3)
2797.5(6)
2
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [Å3]
z
1.512
0.377
1.665
0.396
1.503
0.459
1.567
0.479
ρ
calc. [g cm-3]
µ [mm-1]
Measured Refl's.
32025
28095
61136
53754
Indep't Refl's
6916
6513
13866
13356
2942
2733
6407
6404
Refl's I≥2 σ(I)
Rint
GooF
wR2
R1
0.1497
1.014
0.3257
0.1327
0.2107
1.002
0.1728
0.0910
0.0757
1.051
0.2197
0.0874
0.0644
1.010
0.1016
0.0596
CCDC
2024143
2024141
2024144
2024145
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Spectroscopic characterization
MIR and FIR spectroscopy. For homoleptic Fe(II)-tetrazole-
complexes IR-spectroscopy allows for confirmation of
successful SCO-complex formation, as well as gaining insight
into the spin state present, since the tetrazolic CH-vibration is
the H-bond network, transferring the volume work of the spin-
state transition. The broad absorption around 1030 cm-1
corresponds to the B-F stretching vibrations of the BF4 -anion.
-
sensitive to the N4 coordination environment.36 In figure 10, the
The CN- absorption of the MeCN solvate in
7
is very weak, and
-
is only observable in the LS-spectrum of
2250 cm-1.
7 in figure 10 around
IR spectra of 2COOHTz (
1
) and its ClO4 -complex (
7
) in the HS-
state (red) and LS-state (blue) are compared. At 3156 cm-1 the
free ligand shows its tetrazolic CH-vibration, which upon
successful coordination is split and shifted to 3159 cm-1 and
3152 cm-1. On cooling to the LS-state, at 100 K the CH-vibration
is shifted to 3164 cm-1 and 3159 cm-1, respectively. Around
1600 cm-1 the νN2=N3 stretching vibration of the tetrazole after
coordination is similarly affected by the spin-state transition,
shifting from 1612 cm-1 to 1616 cm-1 in the LS-state. The change
of the carbonyl-vibration at 1731 cm-1 on coordination and
afterwards during SCO may be attributed to interaction within
In the FIR-region of the spectra, both spin-states show the
characteristic displacement of the Fe-centre towards the
centroid of the trigonal faces of the N6-coordination
octahedron.
Those vibrations are nearly entirely decoupled from other
vibrational modes and therefore indicative of spin state. For the
HS-state, this vibration is found at 226 cm-1, for the LS-state the
characteristic vibrations are located at 470 and 443 cm-1 (see
figure 11).
UV-VIS/NIR spectroscopy. Electronic transitions are also
affected by the spin state transition. For homoleptic Fe-
tetrazole SCO complexes the HS-state absorbs around 850 nm
in the near-infrared, causing a broad and often weak absorption
5
5
in the ligand field spectrum. This T2 → E transition weakens
with cooling and spin-state transition, giving rise to two
absorptions in the visible region of the spectrum at 545 nm and
386 nm, responsible for the pink colour of the LS-state. These
absorption bands correspond to the 1A1 →1T1 transition, as well
as the 1A1 →1T2 transition. From the maxima observed in the HS
and the LS state, a ligand-field strength 10 Dq can be
estimated.37 In the case of
of 1.65 Dq is obtained.
7, measured in the solid state, a value
Towards a mixed-metallic 3d-4f coordination polymer
The functionalization of alkyl-tetrazoles with a COOH-group
introduces an H-bond donor-acceptor system thereby
enhancing supramolecular cooperativity of SCO. To take
advantage of the coordination ability of the COOH-group and
the bifunctional ligand, we attempted to prepare a multi-
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DOI: 10.1039/D0DT03315D
coordinates in an η1-fashion (see figure 14). H2O molecules
occupy the remaining coordination sites (3). The η1-interaction
of the carboxylate-ligands with the adjacent Gd-atoms is
remarkable, as the Gd-O-bond is the shortest of all three: The
η1 Gd-O interaction is 2.350 Å (Gd-O1), whereas the η2 Gd-O
bonds are with 2.432 Å (Gd-O2) and 2.685 Å (Gd-O1) 3.48 % and
14.3 % longer. The tetrazoles establish channels parallel to the
gadolinium-oxo chains. Their tetrazolic CH groups are directed to the
inner of the voids, the N2 and N3 atoms of the ring interacting with
the H2O ligands of the nearby gadolinium-oxo chain. In the voids the
Cl--anions are stabilized by a zig-zag H-bond structure, originating
from the H2O-ligands at the Gd-centre (see figure 15). The
crystallographic parameters for 10 are given in table 2.
metallic 3d-4f coordination polymer. Coronado et al. have
successfully applied such an approach to the formation of a
mixed Fe(III)-Fe(II) SCO compound using a COOH-functionalized
ligand.38
By reacting 3COOHTz (2) with Fe(ClO4)2∙6H2O and GdCl3∙6H2O in
aqueous MeOH and subsequent evaporation a slightly yellow oil
was obtained, which did not be solidify. After a few weeks at
4 °C a few colourless crystals had formed, allowing for
determination of the structure by X-ray diffraction. Instead of a
mixed-metallic coordination polymer, [Gd(3COOTz)2(H2O)3]Cl
(
10) had crystallized in the monoclinic C 2/c space group. During
Table 2. Crystallographic parameters for 10
the reaction / crystallization process the COOH-groups were
deprotonated and the resulting carboxylate groups act as
chelating, bridging ligands to the gadolinium-atoms in a µ2-η2:η1
fashion (see figure 13). Each gadolinium atom is coordinated
nine-fold by oxygen-donors as the centre of a monocapped
square antiprismatic coordination polyhedron. Due to the µ2-
η2:η1 coordination of the carboxylate-ligands one-dimensional
chains are formed, in which the Gd-atom is coordinated by four
3COOTz-ligands: Two of them coordinate as bidentate, and one
3COOTz-ligand of each adjacent Gd-centre on both sides
10
Formula
C8H16ClGdN8O7
Weight [g mol-1] 528.96
T [K]
100
Colour
Shape
Crystal System
Space Group
a [Å]
b [Å]
c [Å]
α [°]
clear colourless
plate
monoclinic
C2/c
18.0057(4)
11.2323(6)
8.0169(9)
90
β [°]
γ [°]
V [Å3]
91.838(3)
90
1620.5(2)
4
z
rcalc. [g cm-3]
m [mm-1]
2.1674
4.311
Measured Refl's. 9983
Indep't Refl's
2927
Refl's I≥2 s(I)
2505
Rint
0.0618
1.67
0.0367
0.0331
GooF
wR2
R1
8 | J. Name., 2012, 00, 1-3
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CCDC
ARTICLE
of 10 K to 300 K, measuring all 5 K with a previous thermal
2024832
View Article Online
stabilization of 5 minutes. Variable teDmOpI:e1r0a.1t0u3r9e/Dm0DidT-0r3a3n15gDe
(4000 - 450 cm-1) infrared spectra were recorded by the ATR
technique on a Perkin Elmer Spectrum 400, fitted with a
coolable/heatable PIKE Gladi ATR Unit.[25] Single crystals were
attached to a glass fiber by using perfluorinated oil and were
mounted on a Bruker KAPPA APEX II diffractometer equipped
with a CCD detector with Mo Kα radiation (Incoatec Microfocus
Source IµS: 30 W, multilayer mirror, λ=0.71073 Å). For all
measurements data were reduced to intensity values by using
40
SAINT Plus , and an absorption correction was applied by using
the multi scan method implemented by SADABS. For the
40
iron(II) complexes, protons were placed at calculated positions
and refined as riding on the parent C atoms. All non-H atoms
were refined with anisotropic displacement parameters. For
2024832 (10), a Bruker KAPPA APEX II diffractometer
equipped with a CCD detector was used and data were collected
at 100 K. The powder X-ray diffraction measurements were
carried out on a PANalytical X'Pert Pro diffractometer in Bragg-
Brentano geometry using Cu Kα1,2 radiation filtered with a BBHD
mirror and an X’Celerator linear detector. For in-situ
experiments below ambient temperature an Oxford PheniX
Cryochamber from Oxford Cryosystems was used. The powder
sample were mounted on a copper sample holder on top of a
background-free silicon support. The sample chamber was
evacuated, and all measurements were carried out under
vacuum. The actual sample temperature is directly monitored
by a thermocouple on the sample holder. The diffractograms
were evaluated using the PANalytical program suite
HighScorePlus, correcting for the background.
Figure 16 shows a comparison between the MIR spectrum of
2
and a single crystal of [Gd(3COOTz)2(H2O)3]Cl. Whereas the
tetrazolic CH-band is only slightly shifted after the coordination
to the Gd3+, the deprotonated and coordinated carbonyl-
vibration is shifted by 20 cm-1. The three coordinated H2O-
ligands appear in the MIR, resulting the OH-stretching mode at
3346 cm-1 and the OH-scissoring vibration at 1672 cm-1.
Experimental
Materials and methods
Synthesis of ligands
All operations involving Fe(II) were carried out under inert gas
atmosphere (argon 5.0). The glassware used was oven dried at
120 °C before use for at least 2 hours. All solvents for the
complexation reactions were dried before use and stored over
molecular sieve 3 Å under argon.39 Unless otherwise stated, all
starting materials were commercially obtained and used
without further purification. All NMR spectra were recorded in
dry deuterated solvents on a Bruker Avance UltraShield 400
MHz. Chemical shifts are reported in ppm; 1H and 13C shifts are
referenced against the residual solvent resonance. For the
measurement of MIR and FIR spectra, a Perkin–Elmer Spectrum
400, fitted with a coolable/heatable PIKE Gladi ATR unit was
used within the range of 4000-100 cm–1. Solid state UV/Vis/NIR
spectra were recorded with a Perkin–Elmer Lambda 900
spectrophotometer between 300 and 1600 nm in diffuse
reflectance against BaSO4. A Harrick coolable/heatable powder
sample holder in “Praying Mantis” configuration was used.
Melting points were determined by differential scanning
calorimetry, using a Netzsch STA 449 C Jupiter® with heating
rates of 2 K min-1, see figures S1-S3. The magnetic moment of
the Fe(II) complexes was measured using a Physical Property
Measurement System (PPMS®) by Quantum Design. The
Tetrazoles and their derivatives – especially in combination with
perchlorates – are potentially shock sensitive or explosive
compounds and should, therefore, be handled with great care
and with the appropriate safety precautions!
2-(1H-tetrazol-1-yl)acetic acid (2COOHTz) (1): 25 g (333 mmol, 1 eq.)
glycine and 32.4 g (499.6 mmol, 1.5 eq.) NaN3 were suspended in 97
ml (516.2 mmol, 1.55 eq.) triethylorthoformate and 250 ml acetic
acid. The suspension was heated for 18 h at 95 °C, filtrated and
evaporated to dryness. After extracting the residue with CH2Cl2, the
solvent was removed, and the resulting yellow oil refluxed for 6 h in
concentrated hydrochloric acid. After removal of all volatiles the oily
residue was adsorbed on SiO2 and was further purified by column
chromatography (MeCN:CH2Cl2=3:2) After evaporation,
1 was
obtained as beige crystalline material. Yield: 7.9 g, 18.5 %; MP:
130 °C; νCH(Tz) 3156, νCO 1731 / 1712 cm–1; 1H NMR (400 MHz, DMSO-
d6) δ= 13.43 (s, 1H, COOH), 9.38 (s, 1H, Tz), 5.43 (s, 2H, CH2) ppm;
13C{1H} NMR (101 MHz, DMSO-d6) δ= 167.94 (COOH), 144.99 (Tz),
48.52 (CH2) ppm.
3-(1H-tetrazol-1-yl)propanoic acid (3COOHTz) (2): 25 g (280.6 mmol,
1 eq.) β-alanine and 27.4 g (420.9 mmol, 1.5 eq.) NaN3 were
suspended in 81.7 ml (434.9 mmol, 1.55 eq.) triethylorthoformate
and 250 ml acetic acid. The suspension was heated for 18 h at 95 °C,
filtrated and evaporated to dryness. After extracting the residue with
CH2Cl2, the solvent was removed, and the resulting yellow oil
refluxed for 6 h in concentrated hydrochloric acid. After removal of
experimental setup consisted of
a
vibrating sample
magnetometer attachment (VSM), bearing a brass sample
holder with a quartz-glass powder container. The magnetic
moment was determined in an external field of 1 T in the range
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all volatiles the oily residue was adsorbed on SiO2 and was further stirred at 50 °C for 10 minutes, then 43.6 mg (117.27 µmol, 1 eq.)
View Article Online
DOI: 10.1039/D0DT03315D
purified by column chromatography (MeCN:CH2Cl2=3:2) After GdCl3∙6H2O was added. The mixture was further stirred for 6 h at
evaporation, 3COOHTz was obtained as off-white solid. Yield: 9.1 g, 50 °C. After evaporation of the solvent, the residual slightly yellow oil
1
22.8 %; MP: 125 °C; νCH(Tz) 3134, νCO 1709 cm–1; H NMR (400 MHz, was kept at 50 °C for 6 h under vacuum and afterwards left for 3
DMSO-d6) δ= 12.34 (s, 1H, COOH), 9.37 (s, 1H, Tz), 4.64 (t, J = 6.6 Hz, weeks at 4 °C. A few tiny colourless crystals formed.
2H, CH2), 2.98 (t, J = 6.7 Hz, 2H, CH2) ppm; 13C{1H} NMR (101 MHz,
DMSO-d6) δ= 171.72 (COOH), 144.30 (Tz), 43.74 (CH2), 33.49 (CH2).
4-(1H-tetrazol-1-yl)butanoic acid (4COOHTz) (3): 25 g (242.4 mmol,
Conclusions
1 eq.) 4-aminobutanoic acid and 23.6 g (363.7 mmol, 1.5 eq.) NaN3
were suspended in 70.6 ml (375.8 mmol, 1.55 eq.)
triethylorthoformate and 250 ml acetic acid. The suspension was
heated for 18 h at 95 °C, filtrated and evaporated to dryness. After
extracting the residue with CH2Cl2, the solvent was removed, and the
resulting yellow oil refluxed for 6 h in concentrated hydrochloric acid.
After removal of all volatiles the oily residue crystallized in the
freezer overnight. The yellow solid was adsorbed on SiO2 and further
purified by column chromatography (MeCN:CH2Cl2=3:2) After
evaporation, 4COOHTz was obtained as off-white solid. Yield: 11.24
g, 29.7 %; MP: 86 °C; νCH(Tz) 3114, νCO 1714 cm–1; 1H NMR (400 MHz,
DMSO-d6) δ= 12.21 (s, 1H, COOH), 9.41 (s, 1H, Tz), 4.48 (t, J=7.1, 2H,
CH2), 2.27 (t, J=7.3, 2H, CH2), 2.06 (p, J=7.2, 2H, CH2) ppm; 13C{1H}
NMR (101 MHz, DMSO-d6) δ= 173.52 (COOH), 143.99 (Tz), 46.91
(CH2), 30.37 (CH2), 24.72 (CH2).
Fe(II)-SCO complexes with bifunctional ω-(1H-tetrazol-1-yl)
carboxylic acids allow formation of supramolecular hydrogen
bonding networks that enhance the cooperativity of the
material. Furthermore, the COOH-group can act as anchor-
group for deposition on oxidic surfaces, or for formation of
multi-metallic coordination polymers. Three ligands bearing a
COOH-group with alkyl-chain lengths of C2-C4 were synthesized
and coordinated to Fe(II) with BF4 and ClO4 as weak-
coordinating anions. Complete and sharp spin state transitions
were observed in the cases of 4, 6, 7 and 9. An initial attempt to
prepare a 3d-4f mixed-metallic coordination polymer with Gd3+
resulted in the unexpected formation of one-dimensional Gd-
oxo chains with the 3COOHTz-ligand having been deprotonated
and coordinating to the Gd3+-atoms in a chelating-bridging µ2-
η2:η1 fashion. Future work will focus on a more suitable
synthetic approach to realise a coordination on both ligand
functional groups.
-
-
Synthesis of Fe(II)-complexes
Fe(2COOHTz)6][BF4]2∙2MeCN (4): Fe(BF4)2∙6H2O (100 mg, 296.3
µmol, 1 eq.) and 1 (231.5 mg, 1.81 mmol, 6.1 eq.) were dissolved in
10 ml MeCN and stirred at 50 °C for 18 h. After evaporation of the
solvent, the residual oil was triturated in 10 ml THF for 1 h to remove
the excess of ligand. The precipitated material was separated,
washed with further THF (10 ml) and dried in a stream of N2. Yield:
98.8 mg, 33.4 %; νCH(Tz) 3138, νCO 1744 cm–1.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
[Fe(3COOHTz)6][BF4]2 (5): Same procedure as for 4. 5 was isolated as
off-white, sticky solid. Yield: 75.7 mg, 23.6 %; νCH(Tz) 3135, νCO 1714
cm–1.
We acknowledge financial support of the Austrian Science Fund
(FWF Der Wissenschaftsfond) project P 31076-N28. The X-Ray
center (XRC) of the Vienna University of Technology provided
access to the powder X-Ray diffractometer.
[Fe(4COOHTz)6][BF4]2 (6): Same procedure as for 4. 6 was isolated
as white solid. Yield: 122 mg, 35.3 %; νCH(Tz) 3144, νCO 1733 cm–1.
[Fe(2COOHTz)6][ClO4]2∙2MeCN (7): Fe(ClO4)2∙6H2O (100 mg, 275.6
µmol, 1 eq.) was dissolved under Ar together with a tiny amount of
ascorbic acid in 2 ml MeCN and added by filtration through a syringe
filter (PTFE, 0.45 µm) to a degassed solution of 1 (215.4 mg, 1.68
mmol, 6.1 eq.) in 8 ml MeCN. The resulting mixture was stirred at
50 °C for 18 h. After evaporation of the solvent, the residual oil was
triturated in 10 ml THF for 1 h to remove the excess of ligand. The
precipitated material was separated, washed with further THF (10
ml) and dried in a stream of N2. Yield: 51.5 mg, 18.2 %; νCH(Tz) 3159 /
3152, νCO 1733 / 1715 cm–1.
[Fe(3COOHTz)6][ClO4]2 (8): Same procedure as for 7. 8 was isolated
as white sticky solid. Yield: 127.1 mg, 41.6 %; νCH(Tz) 3137, νCO 1740 /
1715 cm–1.
[Fe(4COOHTz)6][ClO4]2 (9): Same procedure as for 7. 9 was isolated
as white solid. Yield: 118.9 mg, 36.2 %; νCH(Tz) 3134, νCO 1728 cm–1.
[Gd(3COOTz)2(H2O)3]Cl (10): Fe(ClO4)2∙6H2O (42.55 mg, 117.27 µmol,
1 eq.) was dissolved under Ar together with a tiny amount of ascorbic
acid in 2 ml MeOH and added by filtration through a syringe filter
(PTFE, 0.45 µm) to a degassed solution of 2 (100 mg,703.64 mmol, 6
eq.) in 8 ml of a 1:1 mixture MeOH:H2O. The resulting mixture was
References
1.
2.
P. Gütlich and H. A. Goodwin, Journal, 2004.
P. Gütlich, Eur Inorg Chem, 2013, DOI:
J
10.1002/ejic.201300092, 581-591.
3.
H. J. Shepherd, C. Bartual-Murgui, G. Molnar, J. A. Real, M.
C. Munoz, L. Salmon and A. Bousseksou, New J Chem, 2011,
35, 1205-1210.
4.
5.
S. Decurtins, P. Gutlich, C. P. Kohler, H. Spiering and A.
Hauser, Chem Phys Lett, 1984, 105, 1-4.
A. C. Aragonès, D. Aravena, J. I. Cerdá, Z. Acís-Castillo, H. Li,
J. A. Real, F. Sanz, J. Hihath, E. Ruiz and I. Díez-Pérez, Nano
Lett, 2016, 16, 218-226.
6.
7.
C. Lefter, V. Davesne, L. Salmon, G. Molnár, P. Demont, A.
Rotaru and A. Bousseksou, Magnetochemistry, 2016, 2, 18.
C. Lefter, S. Rat, J. S. Costa, M. D. Manrique-Juárez, C. M.
Quintero, L. Salmon, I. Séguy, T. Leichle, L. Nicu, P. Demont,
A. Rotaru, G. Molnár and A. Bousseksou, Adv Mater, 2016,
28, 7508-7514.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 12
Dalton Transactions
Please do not adjust margins
Journal Name
ARTICLE
8.
C. Lefter, R. Tan, J. Dugay, S. Tricard, G. Molnár, L. Salmon, 32.
J. Carrey, W. Nicolazzi, A. Rotaru and A. Bousseksou, Chem
P. L. Franke and W. L. Groeneveld, Transit Metal Chem,
View Article Online
1981, 6, 54-56.
DOI: 10.1039/D0DT03315D
Phys Lett, 2016, 644, 138-141.
Cambi and A. Cagnasso, Atti Accad. Naz. Lincei, 1931, 13.
L. Cambi and L. Szegö, Berichte der deutschen chemischen 35.
Gesellschaft (A and B Series), 1933, 66, 656-661.
L. Cambi and L. Szegö, Berichte der deutschen chemischen
33.
34.
T. Kamiya and Y. Saito, US3767667A, 1971.
9.
10.
T. Kamiya and Y. Saito, DE2147023A1, 1971.
O. H. Jústiz, R. Fernández-Lafuente, J. M. Guisán, P. Negri,
G. Pagani, M. Pregnolato and M. Terreni, The Journal of
Organic Chemistry, 1997, 62, 9099-9106.
11.
12.
13.
14.
Gesellschaft (A and B Series), 1931, 64, 2591-2598.
M. Ohba, K. Yoneda and S. Kitagawa, Crystengcomm, 2010,
12, 159-165.
36.
37.
38.
D. Müller, C. Knoll, M. Seifried and P. Weinberger,
Vibrational Spectroscopy, 2016, 86, 198-205.
P. Gütlich, A. Hauser and H. Spiering, Angewandte Chemie
International Edition in English, 1994, 33, 2024-2054.
A. Abhervé, M. J. Recio-Carretero, M. López-Jordà, J. M.
Clemente-Juan, J. Canet-Ferrer, A. Cantarero, M.
Clemente-León and E. Coronado, Inorg Chem, 2016, 55,
9361-9367.
C.
J.
Kepert,
Chem
Commun,
2006,
DOI:
10.1039/b515713g, 695.
A. Holovchenko, J. Dugay, M. Giménez-Marqués, R. Torres-
Cavanillas, E. Coronado and H. S. J. van der Zant, Adv
Mater, 2016, 28, 7228-7233.
15.
16.
J. Dugay, M. Gimenez-Marques, T. Kozlova, H. W. 39.
Zandbergen, E. Coronado and H. S. J. van der Zant, Adv
D. D. P. W. L. F. Armarego, Butterworth-Heinemann,
Oxford, 1997.
I. Bruker Analytical X-ray Instruments, 2012.
Mater, 2015, 27, 1288-1293.
40.
H. J. Shepherd, I. y. A. Gural’skiy, C. M. Quintero, S. Tricard,
L. Salmon, G. Molnár and A. Bousseksou, Nat Commun,
2013, 4.
17.
18.
M. Matsuda, H. Isozaki and H. Tajima, Thin Solid Films,
2008, 517, 1465-1467.
C. Lochenie, K. Schötz, F. Panzer, H. Kurz, B. Maier, F.
Puchtler, S. Agarwal, A. Köhler and B. Weber, J Am Chem
Soc, 2018, 140, 700-709.
19.
C. Bartual-Murgui, A. Akou, C. Thibault, G. Molnar, C. Vieu,
L. Salmon and A. Bousseksou, J Mater Chem C, 2015, 3,
1277-1285.
20.
21.
W.-Q. Gao, Y.-S. Meng, C.-H. Liu, Y. Pan, T. Liu and Y.-Y. Zhu,
Dalton T, 2019, 48, 6323-6327.
J. Ru, F. Yu, P.-P. Shi, C.-Q. Jiao, C.-H. Li, R.-G. Xiong, T. Liu,
M. Kurmoo and J.-L. Zuo, Eur J Inorg Chem, 2017, 2017,
3144-3149.
22.
23.
24.
K. E. Burrows, S. E. McGrath, R. Kulmaczewski, O. Cespedes,
S. A. Barrett and M. A. Halcrow, Chemistry - A European
Journal, 2017, 23, 9067-9075.
I. A. Gass, S. Tewary, G. Rajaraman, M. Asadi, D. W. Lupton,
B. Moubaraki, G. Chastanet, J.-F. Létard and K. S. Murray,
Inorg Chem, 2014, 53, 5055-5066.
A. Absmeier, M. Bartel, C. Carbonera, G. N. L. Jameson, F.
Werner, M. Reissner, A. Caneschi, J. F. Letard and W. Linert,
Eur J Inorg Chem, 2007, DOI: 10.1002/ejic.200601096,
3047-3054.
25.
26.
M. Muttenthaler, M. Bartel, P. Weinberger, G. Hilscher and
W. Linert, J Mol Struct, 2005, 741, 159-169.
M. Seifried, C. Knoll, G. Giester, J. M. Welch, D. Müller and
P. Weinberger, European Journal of Organic Chemistry,
2017, 2017, 2416-2424.
27.
28.
M. Seifried, C. Knoll, G. Giester, M. Reissner, D. Müller and
P. Weinberger, Magnetochemistry, 2016, 2, 1-13.
M. Nihei, Y. Yanai, I. J. Hsu, Y. Sekine and H. Oshio,
Angewandte Chemie International Edition, 2017, 56, 591-
594.
29.
30.
31.
C. Lochenie, J. Heinz, W. Milius and B. Weber, Dalton T,
2015, 44, 18065-18077.
W. Bauer, C. Lochenie and B. Weber, Dalton Trans., 2014,
43, 1990-1999.
A. Absmeier, M. Bartel, C. Carbonera, G. N. L. Jameson, P.
Weinberger, A. Caneschi, K. Mereiter, J. F. Letard and W.
Linert, Chem-Eur J, 2006, 12, 2235-2243.
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Table of Content Entry
DOI: 10.1039/D0DT03315D
Carboxylic acid functionalized tetrazoles form Fe(II) spin crossover materials governed by H-
bonding networks.