FeII Complexes with Triple N1,N2-Triazole Bridge Schiff Base Ligand: Antiferromagnetic Dimer vs. Spin Conversion Trimer

Article abstract of DOI:10.1002/ejic.201800784

Based on the p-tolyl functionalized Schiff base 1,2,4-triazole ligand 4-(p-tolylidene-amino)-4H-1,2,4-triazole (toltrz), a series of three triazole-bridged Fe^II complexes have been prepared. The compounds represent a range of dinuclear and trinuclear species, with μ₂-N1,N2-triazole bridges linking the Fe^II centers. M?ssbauer spectroscopy and magnetic susceptibility measurements reveal a gradual single-step spin crossover (SCO) behavior for the trimeric compound 3 on the central Fe^II site. Single-crystal X-ray diffraction at 120 K confirms that the central Fe^II site undergoes a HS to LS transition while the peripheral Fe^II remain in HS state (HS = high spin; LS = low spin). Compounds 1 and 2 are isostructures with different terminal ligand XCN (X = S, Se), these two compounds stay in high spin state over the whole temperature range but display weak antiferromagnetic exchange coupling.

Full text of DOI:10.1002/ejic.201800784

DOI: 10.1002/ejic.201800784
Full Paper
Spin-Crossover Complexes
II
Fe Complexes with Triple N1,N2-Triazole Bridge Schiff Base
Ligand: Antiferromagnetic Dimer vs. Spin Conversion Trimer
[
a,b]
[c]
[c]
[c]
Ai-Min Li,
Tim Hochdörffer, Juliusz A. Wolny, Volker Schünemann, and
Eva Rentschler*[
a]
Abstract: Based on the p-tolyl functionalized Schiff base 1,2,4- Single-crystal X-ray diffraction at 120 K confirms that the central
II
triazole ligand 4-(p-tolylidene-amino)-4H-1,2,4-triazole (toltrz), a Fe site undergoes a HS to LS transition while the peripheral
II
II
series of three triazole-bridged Fe complexes have been pre- Fe remain in HS state (HS = high spin; LS = low spin). Com-
pared. The compounds represent a range of dinuclear and tri- pounds 1 and 2 are isostructures with different terminal ligand
II
nuclear species, with μ -N1,N2-triazole bridges linking the Fe
XCN (X = S, Se), these two compounds stay in high spin state
2
centers. Mössbauer spectroscopy and magnetic susceptibility over the whole temperature range but display weak antiferro-
measurements reveal a gradual single-step spin crossover (SCO) magnetic exchange coupling.
II
behavior for the trimeric compound 3 on the central Fe site.
[8a]
1
. Introduction
modes.[8] As summarized in the recent review by Brooker,
3
5
4
selectively functionalizing the C, C, and/or n positions of the
triazole ring gives access to a wide range of discrete Fe SCO
complexes. Similarly to the triple N1,N2-1,2,4-triazole bridged
analogues, these discrete SCO complexes provide fundamental
insights into the influence on the SCO, like counteranion effect,
supramolecular interactions and crystal packing effects, to help
us understand and synthesize the polymeric SCO systems.
Spin crossover (SCO), known as the inter-conversion between
electronic spin states in metal-organic compounds, has fasci-
nated and drawn attention for both chemist and physicist since
the discovery of the first SCO compound in 1931.
tential applications of such materials for data storage, molecular
electronics and thermosensors
mize the SCO compounds for higher T and larger hysteresis
loop areas. Among the few examples exhibiting remarkable
SCO behavior, the system based on the 1,2,4-triazole ligand still
remains the most promising material for future applications.
II
[9]
[
1–3]
The po-
[
4–6]
impel the chemists to opti-
c
4
The focus of the present study is on solely N position modi-
fied 1,2,4-triazole-based ligands. Despite the early discovery of
the first N1,N2-1,2,4-triazole bridged trinuclear Fe species in
and a continuous
endeavor on this family of compounds, the successful prepara-
tion of discrete N1,N2-1,2,4-triazole bridged SCO Fe complexes
based on exclusively N functionalized 1,2,4-triazole ligands is
still very challenging. For example, Yann Garcia et al. reported
the first such structure of a binuclear Fe complex in two differ-
ent spin states only in 2011. The three newly published ex-
amples in the last year, together with a very recent case in
II
[
10]
1
983 by the group of Prof. Jan Reedijk,
Particularly the 1D coordination polymers of general formula
–
[
Fe(Rtrz) ](X) (Rtrz = 4-subsitituted-1,2,4-triazole, X = standard
3
2
II
monoanions), display wide thermal hysteresis loops around
4
[
7]
room temperature. However, the challenge to obtain crystal-
line compounds of such coordination polymers makes it diffi-
cult to investigate the structural data at the molecular and
intermolecular scales. Alternatively, discrete polynuclear com-
plexes, i.e., dinuclear or trinuclear triazole-based complexes, in-
volving similar triple triazole bridges, are currently receiving
II
[
11]
[
12]
2
018,
indicate the lasting-hot topic in this field. A detailed
list of the reported discrete N1,N2-1,2,4-triazole bridged com-
plexes can be found in Table S1, S2, from which we can see the
vitality and creativity in this family of compounds. By introduc-
ing an electron-withdrawing and steric bulky group, p-toluyl,
the main objective in this study is to explore the different
supramolecular interactions effecting the spin transition behav-
ior. We add herein three examples to this short list of com-
plexes, enlarging the library of switchable N1,N2-1,2,4-triazole
bridged complexes for the elaboration of polynuclear architec-
tures. We report the synthesis, structure, and magnetic proper-
[
2,3]
great interest.
The versatile feature of the 1,2,4-triazole-
based ligands makes them suitable candidates for building up
discrete polynuclear complexes, with variety of coordination
[
a] Institute of Inorganic and Analytical Chemistry,
Johannes Gutenberg University Mainz,
Duesbergweg 10-14, 55128 Mainz, Germany
E-mail: rentschler@uni-mainz.de
[
[
b] Graduate School Materials Science in Mainz,
Staudingerweg 9, 55128 Mainz, Germany
c] Fachbereich Physik, Technische Universität Kaiserslautern,
Erwin-Schrödinger-Str. 46, 67663 Kaiserslautern, Germany
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201800784.
II
ties of a series of three polynuclear triazole-bridged Fe com-
plexes based on a Schiff base modified triazole ligand, i.e., 4-(p-
II
tolylidene-amino)-4H-1,2,4-triazole (toltrz): [Fe (toltrz) (SCN) ]
2
5
4
II
II
3H O (C1), [Fe (toltrz) (SeCN) ] 3H O (C2) and [Fe (toltrz) -
2
2
5
4
2
3
6
Eur. J. Inorg. Chem. 0000, 0–0
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(
H O) ] 6(BF ) 2H O 2CH CH CO CH (C3). Single X-ray diffrac- 2. Results and Discussion
2
6
4
2
3
2
2
3
tion and magnetic measurements reveal that compounds 1 and
2
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2.1 X-ray Crystal Structure Description
are isomorphous binuclear Fe complexes showing weak anti-
ferromagnetic exchange interactions, while compound 3 is a Crystallographic data for the compounds 1–3 are summarized
II
trinuclear Fe complex exhibiting a gradual spin transition be- in Table 1 and the selected bond lengths and angles are given
havior.
in Table 2 and Table S3.
Table 1. Crystallographic Data and Refinement Parameters for Compounds 1–3.
Compound
C1
C2
C3 (120 K)
C3 (173 K)
Empirical formula
Formula weight
Crystal size
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C
54
H
56Fe
2
N
24
O
3
S
4
C
54
H
56Fe
2
N
24
O
3
Se
4
C
34
H
46
B
3
F
12Fe1.5
N
12
O
6
34 46 3 12 6
C H B F12Fe1.5N O
1062.95
1329.13
1516.71
0.35 × 0.15 × 0.13
Triclinic
1062.95
0.2 × 0.14 × 0.03
Triclinic
P1¯ (No. 2)
11.7271(14)
14.1648(17)
21.415(2)
74.800(3)
75.809(3)
80.439(3)
3308.4(7)
2
1.327
0.624
1362
22926
11322 (0.1115)
834
0.44 × 0.28 × 0.04
Triclinic
P1¯ (No. 2)
12.713(3)
13.406(3)
16.821(3)
67.48(3)
84.64(3)
78.43(3)
2593.9(11)
2
1.388
0.517
1052
24183
12389 (0.0764)
742
0.57 × 0.35 × 0.15
Triclinic
P1¯ (No. 2)
12.7127(7)
13.4058(7)
16.8209(9)
67.484(2)
84.639(2)
78.432(2)
2593.9(2)
2
1.348
0.518
1068
33228
12332 (0.0804)
716
P1¯ (No. 2)
11.7281(11)
14.2238(12)
21.7330(19)
74.846(2)
75.784(2)
79.688(2)
3366.6(5)
2
1.490
2.652
1508
10413
ꢀ
[°]
γ [°]
3
V [Å ]
Z
D
calc [g/cm3]
μ(Mo-K
F(000)
α
) [mm–1
]
Reflections collected
Independent reflections
Parameters
10247 (0.0112)
825
Goodness-of-fit
0.920
0.0703
0.2274
1.025
0.0848
0.2755
1.451
0.1473
0.4542
1.050
0.0920
0.3159
[
a]
R
1
[I > 2σ(I)]
(all data)
[
b]
wR
2
= {Σ[w(F 2 2)2]/Σ [w(F ) ]}1/2.
2 2
[
a] R
1
= Σ||F | – |F ||/Σ|F |. [b] wR – F
o
c o 2 o c o
Table 2. Selected bond lengths [Å] and angles [°] of compound 3 at 173 K and 120 K.
Compound 3 at 120 K
Fe(1)–O(3 W)
Fe(1)–O(2 W)
Fe(1)–O(1 W)
Fe(1)–N(9)
2.125(7)
2.131(6)
2.152(6)
2.167(7)
89.9(3)
89.9(3)
89.8(3)
179.2(3)
90.5(3)
87.2(3)
178.4(2)
89.3(3)
90.5(2)
91.3(3)
Fe(1)–N(1)
Fe(1)–N(5)
Fe(2)–N(6)
Fe(2)–N(6)#1
2.154(7)
2.177(6)
2.161(6)
2.161(6)
89.9(3)
177.7(3)
91.0(2)
90.9(3)
89.7(2)
180.0
Fe(2)–N(2)
Fe(2)–N(2)#1
Fe(2)–N(10)
Fe(2)–N(10)#1
2.150(7)
2.150(7)
2.193(6)
2.193(6)
90.4(2)
89.6(2)
89.6(2)
90.4(2)
180.0
88.6(2)
91.4(2)
91.4(2)
88.6(2)
180.0
O(3 W)–Fe(1)–O(2 W)
O(3 W)–Fe(1)–O(1 W)
O(3 W)–Fe(1)–N(9)
O(3 W)–Fe(1)–N(1)
O(3 W)–Fe(1)–N(5)
O(2 W)–Fe(1)–O(1 W)
O(2 W)–Fe(1)–N(9)
O(2 W)–Fe(1)–N(1)
O(2 W)–Fe(1)–N(5)
O(1 W)–Fe(1)–N(9)
O(1 W)–Fe(1)–N(1)
O(1 W)–Fe(1)–N(5)
N(9)–Fe(1)–N(5)
N(1)–Fe(1)–N(9)
N(1)–Fe(1)–N(5)
N(6)#1-Fe(2)–N(6)
N(6)#1-Fe(2)–N(10)#1
N(6)–Fe(2)–N(10)#1
N(6)#1-Fe(2)–N(10)
N(6)–Fe(2)–N(10)
N(2)#1-Fe(2)–N(6)#1
N(2)–Fe(2)–N(6)#1
N(2)#1-Fe(2)–N(6)
N(2)–Fe(2)–N(6)
N(2)–Fe(2)–N(2)#1
N(2)–Fe(2)–N(10)#1
N(2)#1-Fe(2)–N(10)#1
N(2)–Fe(2)–N(10)
N(2)#1-Fe(2)–N(10)
N(10)–Fe(2)–N(10)#1
91.3(2)
88.7(2)
88.7(2)
91.3(2)
Compound 3 at 173 K
Fe(1)–O(1 W)
Fe(1)–O(2 W)
Fe(1)–O(3 W)
Fe(1)–N(1)
2.122(4)
2.116(4)
2.132(4)
2.156(4)
Fe(1)–N(5)
Fe(1)–N(9)
Fe(2)–N(2)#1
Fe(2)–N(2)
2.161(4)
2.150(4)
2.157(4)
2.157(4)
89.85(16)
89.99(16)
91.24(14)
90.13(14)
92.59(15)
180.0
Fe(2)–N(6)#1
Fe(2)–N(6)
Fe(2)–N(10)#1
Fe(2)–N(10)
2.173(3)
2.173(3)
2.193(3)
2.193(3)
91.18(13)
91.18(13)
88.82(13)
88.82(13)
180.0
88.48(13)
88.48(13)
91.52(13)
91.52(13)
180.0
O(1 W)–Fe(1)–O(3 W)
O(1 W)–Fe(1)–N(1)
O(1 W)–Fe(1)–N(5)
O(1 W)–Fe(1)–N(9)
O(2 W)–Fe(1)–O(1 W)
O(2 W)–Fe(1)–O(3 W)
O(2 W)–Fe(1)–N(1)
O(2 W)–Fe(1)–N(5)
O(2 W)–Fe(1)–N(9)
O(3 W)–Fe(1)–N(1)
89.86(17)
89.04(15)
177.56(14)
89.84(15)
88.50(16)
89.01(19)
90.84(17)
89.07(16)
178.06(14)
178.90(16)
O(3 W)–Fe(1)–N(5)
O(3 W)–Fe(1)–N(9)
N(1)–Fe(1)–N(5)
N(9)–Fe(1)–N(1)
N(9)–Fe(1)–N(5)
N(2)#1-Fe(2)–N(2)
N(2)–Fe(2)–N(6)
N(2)–Fe(2)–N(6)#1
N(2)#1-Fe(2)–N(6)#1
N(2)#1-Fe(2)–N(6)
N(2)#1-Fe(2)–N(10)#1
N(2)–Fe(2)–N(10)
N(2)#1-Fe(2)–N(10)
N(2)–Fe(2)–N(10)#1
N(6)#1-Fe(2)–N(6)
N(6)–Fe(2)–N(10)#1
N(6)#1-Fe(2)–N(10)
N(6)#1-Fe(2)–N(10)#1
N(6)–Fe(2)–N(10)
N(10)#1-Fe(2)–N(10)
90.67(14)
89.33(13)
90.67(13)
89.33(13)
Symmetry transformations used to generate equivalent atoms: #1 = –x + 1, –y + 1, –z + 1.
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II
–
Crystal Structure of [Fe (toltrz) (SCN) ] 3H O (C1) and
[
low) The NCS anions in C1 are non-linear with the N–C–S frag-
ment showing an angle around 175°; the angle at the N-atom
coordinating to the iron atoms, Fe···N–C, is split into two groups
with the angle being around 140° and 175°. (See Table S3) In
both compounds, there is one of the bridging ligands being
disordered over the C=N bond part with a relative occupancy
of 0.5/0.5 (C18, N15).
2
5
4
2
II
Fe (toltrz) (SeCN) ] 3H O (C2)
2 5 4 2
Compounds 1 and 2 are isostructural, and the molecular struc-
tures were determined at 173(2) K. Both compounds crystallize
in triclinic space group P 1¯ . The asymmetric unit contains one
full neutral dinuclear complex plus partial six (C1) and four (C2)
lattice aqua molecules, although some of these aqua molecular
positions are partially occupied resulting in a total of 3 aqua
molecules in both structures. As shown in Figure 1, for each
compound, the two Fe centers are linked through three
μ -N1,N2-triazole bridges with a distance of 4.005(7) Å (C1),
.981(9) Å (C2), respectively. Each Fe coordination sphere is
completed by three N atoms from one terminal triazole ligand
and two thiocyanate (C1) or selenocyanate (C2) anions. The ter-
minal average Fe–N bond lengths 2.139(1) Å (C1), and
.144(1) Å (C2) are shorter than the central average Fe–N bond
lengths 2.197(1) Å (C1) and 2.191(1) Å (C2). (Table S3) In both
cases, the average bond length makes the Fe centers sitting
well in the range expected for high spin state value at 173 K,
which is further confirmed by magnetic measurement. (See be-
In compound 1, the adjacent neutral dinuclear units are in-
terconnected through π (phenyl)···π (phenyl) [centroid···cen-
troid = 3.9796(4) Å] and π (phenyl)···π (triazole) [centroid···cen-
troid = 3.8134(3) Å] stacking interactions forming a 1D chain
along c axis. (Figure 2, Table S4) This chain is further connected
through another two groups of intermolecular π···π stacking
II
2
II
3
(
Table S4) together with one set of non-classical S···π stack-
[
14]
ing
[S···centroid = 3.7232(5), c = x + 1, y, z] to form a 3D
structure. While similarly, in compound 2, a group of double
π···π stacking interactions through phenyl and triazole ring, as
2
[
14]
well as a Se···π
[Se1 centroid = 3.6503(3) Å] contact was
[
13]
found to facilitate the 1D structure along the a axis. This 1D
structure is stabilized and further extended via π···π stacking
of different directions to form a 3D supramolecular architecture.
(Figure 2, Table S4).
II
Crystal Structure of [Fe (toltrz) (H O) ] 6(BF ) 2H O
3
6
2
6
4
2
2
CH CH CO CH (C3)
3 2 2 3
II
[
Fe (toltrz) (H O) ] (BF ) 2H O 2CH CH CO CH crystallizes in
3 6 2 6 4 6 2 3 2 2 3
the triclinic space group P 1¯ . The structures at 173 and 120 K
are mutually isomorphous. The structure was found to be com-
parable to other reported trinuclear 1,2,4-triazole ana-
[
12,15]
logues.
It consists of a linear trinuclear unit, where the
central Fe2 is bridged to the exterior iron(II) atoms by three
toltrz ligands via a μ -N1,N2-donating (N2, N6, N10) mode. (Fig-
2
ure 3, this drawing corresponds to the structure obtained at
1
73 K) Both terminal coordination sites are occupied by three
II
H O molecules. The central Fe ion sits on an inversion center
2
such that there are only two unique metal centers per trinuclear
unit, Fe1 and Fe2. The central Fe2 is in an octahedral [FeN ]
6
II
coordination environment, while the outer Fe ions, Fe1 and
Fe1a (a = –x + 1, –y + 1, –z + 1), are in a [FeN O ] coordination
3
3
environment due to the coordination of the terminated aqua
molecules. Each trinuclear unit is cationic with a 6+ charge
which is balanced by six BF4– counteranions.
Figure 1. View of the dinuclear molecular structure of 1 at 173 K. Only se-
lected atoms are labeled for clarity.
Figure 2. The 1D chain connected via π···π stacking in C1 (left) and C2 (right). The dashed lines represent different π···π stacking.
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a partial spin transition is shown to occur between 200 K–50 K
gradually. (See below) The crystal structure determination was
conducted at 173 K and 120 K, right in the beginning and
middle of the SCO transition range. Although the structures at
1
75 and 120 K are similar, small, but significant differences are
observed in a number of bond lengths and angles. The compar-
ison of the coordination environment of the central ion in C3, at
1
20 and 173 K (Figure 5, Table 2), displays the typical structural
changing during a spin transition. At 120 K, the bond lengths
between the six nitrogen atoms and the central iron ion are of
2
.150(7), 2.161(6) and 2.193(6) Å for Fe2–N2, Fe2–N6 and
Fe2–N10, respectively. These values are obviously shorter than
the bond lengths measured at 173 K, which are 2.157(4),
2
.173(3) and 2.192(3) Å, respectively. (Figure 5) The decrease is
II
slightly shorter than the average values observed in Fe HS→LS
transitions for which the coordination distances are shortened
by approximately 0.15–0.20 Å. However, the gradual transition
in our compound happens from 50 K to 200 K, as such the
small changes in the coordination distances confirm that we
have a transition process from HS to LS. Moreover, the
even though small while clear bond length difference here can-
not be ascribed to purely thermal expansion, as the relative
Figure 3. View of the centrosymmetric trinuclear complex in C3 at 173 K.
Only the metal, oxygen and nitrogen atoms involved in coordination bonds
are labeled for clarity. (a = –x + 1, –y + 1, –z + 1).
[
16]
rate of thermal expansion,
α, usually lies within the range
6
–1
–6 –1
0
× 10–
K
< α < 20 × 10 K . And in our case, the relative
As shown in Figure 4, the BF – anions are involved in inten- rate of thermal expansion α at the measured two temperatures
4
sive intramolecular H-bonding with the terminated aqua mol- (120 K and 173 K) is around 2.0 × 10– K .
ecules and the bridging ligands (Table S5), which lead to a
strong binding between the counter anions and the positively
charged trimer unit. This further explains why we can isolate
the crystals in the not very polar solvent (ethyl ethylate) other
than the polar solvent like methanol. The structure also shows
at both temperatures one tolyl fragment being disordered with
a relative occupancy of 0.5/0.5 (C3 to C10 at 173 K, N4, C3 to
C10 at 120 K).
4
–1
II
Figure 5. Comparison of the coordination environment of the central Fe ion
of C3 at 120 and 173 K. Colour code: Red (Fe), Blue (N).
Supramolecular interactions play an important role in the
stabilization of the structures. Apart from the intensive intra-
molecular H-bonding involving the counteranion BF4– between
the terminated aqueous molecules and the bridging ligands as
mentioned above, other groups of intermolecular H-bonding
involving BF4– anion and adjacent C–H from triazole rings are
found, together with a group of C–H···π stacking [C11–
H11···C24a ring centroid = 3.1060(1) Å, a = –x + 2, –y + 1,
–
z + 1] and F···π stacking [F3···N5 ring centroid = 3.3033(2) Å]
–
Figure 4. Intramolecular H-bonding involved with the BF
4
anion, the sym-
to link the independent trinuclear units into a 1D chain along
a axis (Figure 6). This chain is further interconnected by a group
of C–H···π stacking interaction [C14 ring centroid···C14a ring
metrical interactions are shown as red and blue dashed lines, respectively.
Of the two crystallographically unique iron(II) ions, only the centroid = 3.8326(2) Å, a = –x + 1, –y + 1, –z] in bc plane, which
central one (Fe2) is in the expected coordination environment is stabilized and extended into a 3D supramolecular architec-
for SCO to occur. From magnetic susceptibility measurements, ture via different groups of H-bonding interactions (Table S5).
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Figure 6. The 1D chain formed in compound 3 along a axis.
2
.2 FT-IR Spectroscopy
the change in the geometry of the p-tolyl fragment upon com-
plex formation. The characteristic azomethine (HC=N) stretch-
The FT-IR spectra of the three compounds are very similar and
dominated by the spectral characteristics of the Schiff base li-
gand. However, some significant changes could be found due
to the coordination of the compound. The bands between
[
18]
–1
ing mode
at 1636 cm in the ligand remains unchanged in
all the compounds showing the none-coordinating character of
[
19]
the C=N groups.
The spectra for C1 and C2 are very similar
–1
with the strong C=N stretching at 2070 cm suggesting the
presence of XCN (X = S, Se) in the compounds. The 20 cm–1
hypsochromic shift as compared to the spectrum of KNCS/
–
1
–1
2800 cm and 1630–1280 cm (1609, 1531 and 1412) are at-
tributable to the C –C , and C =N stretching vibration fre-
ar ar
ar
quencies of the aromatic groups. The characteristic band for
the triazole ring at 1502 cm–1 with a strong intensity can be
–
1
KNCSe (2050 cm ) indicates the fact that XCN is coordinated
II
[20]
with Fe via the nitrogen atoms. In addition, the spectrum of
[
17]
assigned to the ω-ring vibration.
This band moves to a me-
C3 shows bands for the tetrafluoroborate counterions at
dium peak at 1531 cm–1 for all complexes, indicating the coordi-
nation of the N-donor atoms from triazole ring. The medium-
intensity doublet peaks around 1305 cm can be assigned to
–
1
1
083 cm .
–1
vibrations of the ν-triazole nucleus and stays almost the same
[
17]
2.3 Magnetic Susceptibility and Mössbauer Spectroscopy
for all the compounds.
1
In addition, the peaks at 1235 (m),
180 (m), 1065 (m), and 816 (s) cm–1 can be assigned to the
The variable-temperature magnetic susceptibility data of com-
pound 1 and 2 have been recorded in the 300–2 K range (Fig-
C–H in-plane or out-of-plane bend ring breathing, and ring de-
formation absorptions of the organic ligands. These bands can
be noticed for all the compounds. They are shifted as compared
to the ligand spectrum (Figure 7), which could be related with
ure 8). At the temperature of 300 K, the ꢀ T value of
M
3
–1
3
–1
7
.13 cm K mol (C1) and 7.86 cm K mol (C2) can be as-
II
cribed to the corresponding two high-spin Fe ions. This value
3
–1
remains almost constant at 7.10–7.14 cm K mol for com-
pound 1 from 300 K down to 60 K; below this temperature, the
ꢀMT value starts to decrease more and more abruptly to reach
3
–1
a value of 1.93 cm K mol at 2 K. For C2, ꢀ T drops to
M
3
–1
6
.71 cm K mol from 300 K down to 100 K, with a slight slope
showing a small TIP effect for the measurement. Below 100 K,
the ꢀ T value decreases more drastically all the way down to
M
3
–1
1
.53 cm K mol at 2 K. Such temperature dependence reveals
typical rather weak antiferromagnetic exchange interaction be-
II
tween two Fe ions in the high-spin state. The magnetic proper-
ties of these two compounds are thus in accordance with an
II
S = 2 HS ground state for the Fe ions throughout the whole
temperature range.
To evaluate the antiferromagnetic interaction through the
triple N1,N2-triazole bridge, the magnetic data of the entire
[
22]
Figure 7. The FT-IR spectra of ligand toltrz and compounds 1–3.
temperature range was simulated using the PHI
program
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Figure 8. The temperature-dependent magnetic susceptibility for C1 and C2 (the solid line represents the best fit curve).
with values g = 2.22 (C1) and 2.18 (C2), coupling constants
–
1
–1
J = –0.62(2) cm (C1) and –0.78(2) cm (C2), respectively. A
3
–1
TIP contribution of 0.003 cm mol was applied for the data
simulation of compound 2. (Figure 8) The values for the ex-
change coupling are small and in accordance with data for simi-
II
[5,11,12]
lar binuclear Fe analogues.
However, it is worth mention-
ing that additional zero field splitting effects might be present
which would decrease further the values of the exchange con-
[
21]
stant extracted from the fit.
The slightly increased g values
regarding to the theoretical value (2.0013) here reveals small
II
spin-orbit contribution for the high spin Fe ions.
Temperature dependent magnetic susceptibility measure-
ments on a bulk crystalline sample of compound 3 were also
made from 300 K to 2 K range. The data revealed a gradual
Figure 9. The temperature-dependent magnetic susceptibility (ꢀ
compound 3.
M
T v.s. T) for
Figure 10. Mössbauer spectra of compound 3 at 77 K, 107 K, 137 K, 167 K, 197 K and 298 K. The open circles are the experimental data, the black solid line
shows a superposition of the following components: subspectrum 1 (purple) represents the [LS] fraction of central iron (Fe2), subspectrum 2 (blue) is due to
the [HS] fraction of terminal iron (Fe1 and Fe1a), and 3 (green) is the [HS] fraction of central iron (Fe2). In addition, a minor high-spin ferric impurity species
is represented by subspectrum 4 (grey). Parameters see Table 3.
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one-step SCO (Figure 9). At 300 K, the ꢀ T values of 10.08 cm
K mol is in agreement with all Fe sites of the trinuclear unit pound 3, temperature dependent Mössbauer spectroscopy was
In order to understand the details of SCO process of com-
M
–
1
II
being in the HS state. The slightly higher value compared to performed on a bulk crystalline sample (Figure 10). The spectra
II
the expected spin-only one for three Fe ions suggests possible have been analyzed with in total 4 different subspectra. The
spin orbital contribution being involved. The value remains ap- parameters (δ: isomer shift, ΔE : quadrupole splitting, Γ: line
Q
proximately constant until 200 K when a gradual decrease in width at half maximum, A: relative spectral area) are listed in
ꢀMT values to 7.43 cm K mol–1 at 50 K is seen. The ꢀ T value at Table 3.
M
II
5
0 K indicates a SCO of one-third of the Fe sites to the LS state
As illustrated in Figure 10 and Table 3, the spectrum at 77 K
shows two distinctly different doublets. Doublet 1 (purple) has
with a transition temperature of ≈ 130 K. Again the ꢀ T values
of 7.43 cm K mol here is a bit too large for two spin only HS
Fe ions, assuming the central iron ion has a full spin transition
at this temperature. No thermal hysteresis was observed. The
SCO was further explored by Mössbauer spectroscopy (see be-
low).
M
–
1
–1
–1
δ = 0.52 mm s and ΔE = 0.20 mm s . Such a low quadrupole
Q
II
splitting is characteristic for a LS iron(II) with a half filled 3d
shell embedded in an octahedral ligand field. Doublet 2 (blue)
–1
–1
has δ = 1.25 mm s and ΔE = 3.45 mm s , values which are
Q
Table 3. 57Fe Mössbauer parameters of compound 3 as obtained from the analysis shown in Figure 10.
T = 77 K
III
Subspectra
HS Fe1
LS Fe2
HS Fe1a
HS Fe2
Fe -oxides
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
Rel. Area [%]
1.25 ± 0.03
3.45 ± 0.50
0.35 ± 0.02
65.00 ± 1.10
0.52 ± 0.04
0.20 ± 0.05
0.30 ± 0.05
32.50 ± 1.30
–
–
–
0
–
–
–
0
0.56 ± 0.15
0.70 ± 0.17
0.30 ± 0.10
2.40 ± 1.20
T = 107 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
1.22 ± 0.02
3.45 ± 0.04
0.40 ± 0.02
49.10 ± 1.60
0.52 ± 0.03
0.10 ± 0.02
0.28 ± 0.03
23.50 ± 1.5
1.19 ± 0.02
3.60 ± 0.03
0.30 ± 0.02
17.10 ± 0.80
1.34 ± 0.03
3.30 ± 0.04
0.30 ± 0.05
8.50 ± 2.10
0.56 ± 0.16
0.70 ± 0.05
0.30 ± 0.03
1.70 ± 1.90
Rel. Area [%]
T = 137 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
1.20 ± 0.05
3.32 ± 0.04
0.40 ± 0.04
39.7 ± 1.40
0.52 ± 0.04
0.10 ± 0.02
0.28 ± 0.03
19.9 ± 0.90
1.17 ± 0.04
3.60 ± 0.03
0.30 ± 0.04
24.8 ± 1.20
1.32 ± 0.03
3.20 ± 0.04
0.30 ± 0.04
12.4 ± 1.60
0.56 ± 0.04
0.70 ± 0.05
0.30 ± 0.05
3.17 ± 1.70
Rel. Area [%]
T = 167 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
1.20 ± 0.03
3.25 ± 0.05
0.40 ± 0.03
34.50 ± 0.90
0.52 ± 0.04
0.10 ± 0.03
0.28 ± 0.04
17.3 ± 1.10
1.13 ± 0.03
3.30 ± 0.04
0.30 ± 0.03
27.6 ± 1.40
1.28 ± 0.05
3.10 ± 0.04
0.30 ± 0.04
13.8 ± 1.20
0.52 ± 0.04
0.70 ± 0.05
0.30 ± 0.08
6.90 ± 1.80
Rel. Area [%]
T = 197 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
1.15 ± 0.03
3.10 ± 0.05
0.40 ± 0.03
17.20 ± 1.00
0.52 ± 0.04
0.10 ± 0.03
0.28 ± 0.04
7.30 ± 1.90
1.13 ± 0.04
3.30 ± 0.04
0.30 ± 0.03
43.1 ± 0.50
1.28 ± 0.05
3.10 ± 0.05
0.30 ± 0.03
21.6 ± 0.90
0.46 ± 0.03
0.70 ± 0.05
0.30 ± 0.04
10.77 ± 1.60
Rel. Area [%]
T = 227 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
1.15 ± 0.04
3.10 ± 0.05
0.40 ± 0.03
12.70 ± 0.80
0.52 ± 0.04
0.10 ± 0.02
0.28 ± 0.05
6.40 ± 1.80
1.11 ± 0.02
3.15 ± 0.04
0.30 ± 0.03
44.40 ± 1.20
1.28 ± 0.03
3.10 ± 0.03
0.30 ± 0.04
22.60 ± 0.90
0.46 ± 0.02
0.70 ± 0.04
0.30 ± 0.02
14.00 ± 1.10
Rel. Area [%]
T = 257 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
1.13 ± 0.03
3.10 ± 0.04
0.40 ± 0.02
8.54 ± 1.20
0.52 ± 0.04
0.10 ± 0.03
0.28 ± 0.04
4.30 ± 1.90
1.10 ± 0.03
2.90 ± 0.05
0.30 ± 0.03
42.7 ± 0.80
1.24 ±0.05
2.90 ± 0.05
0.30 ± 0.04
21.30 ± 1.20
0.43 ± 0.03
0.70 ± 0.04
0.30 ± 0.05
23.10 ± 0.70
Rel. Area [%]
T = 298 K
δ [mm/s]
ΔE [mm/s]
0
Γ [mm/s]
–
–
–
0
–
–
–
0
1.08 ± 0.02
2.85 ± 0.03
0.30 ± 0.04
47.00 ± 1.50
1.18 ± 0.03
2.90 ± 0.04
0.30 ± 0.02
23.50 ± 1.60
0.43 ± 0.03
0.70 ± 0.04
0.30 ± 0.03
29.40 ± 1.20
Rel. Area [%]
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typical fingerprints of a high-spin iron(II) species in an octahe-
[
23]
dral N/O ligand environment.
The relative intensity ratio of
1:2 between these two doublets indicates that the central
iron(II) is in its low spin state, i.e., for complex 3 a HS-LS-HS state
is stabilized at 77 K, which is in accordance with the magnetic
susceptibility results discussed above. With increasing tempera-
ture, the intensity of doublet 1 representing the central LS
iron(II) decreases while a new doublet 3 (green) emerges which
–
1
II
has δ > 1 mm s , an isomer shift typical for Fe HS. Neverthe-
less, the parameters of doublet 3 are clearly distinct from those
of 2. Thus, doublet 3 can, without any doubts, be assigned to
originate from the central Fe site. The SCO of this central Fe is
reflected in the Mössbauer spectra displayed in Figure 9 by an
intensity increase of the green doublet 3 which is on the ex-
pense of the decreasing intensity of the purple doublet 1 repre-
senting the central iron in its LS state. At 298 K, doublet 1 van-
ishes, and the approximate 2:1 relative area ratio of the HS dou-
blet 2 and the HS doublet 3 reflects the SCO transition of com-
plex 3 from a HS-LS-HS state to a HS-HS-HS state. At 167 K, the
relative HS and LS ratio reaches 1:2, which gives us the hint of
the transition temperature around 170 K. The gradual character
of this spin transition made it difficult to spot the exact transi-
Figure 11. Plot of reduced magnetization (M/Nꢀ) vs. H for compound 3 in the
2
–10 K range. The solid lines are just for the guidance of the eye, does not
represent any simulated results.
the molecules are sufficient to stabilize the 3D supramolecular
architecture and initiate the spin transition, it is obviously not
strong enough to trigger an abrupt transition. The weak com-
munication between the SCO units can also be explained by the
tion temperature, while a derivative plot of the ꢀ T vs. T curve
M
(
Figure S2) helps us to identify the T1/2 at 180 K. This is in good
“
dilution/separation effect” of the bulky aromatic substituents,
agreement with the Mössbauer data discussed above.
[
15]
which has been noticed and reported in several articles.
–1
Subspectrum 4 has an isomer shift of δ ≈ 0.56 mm s and a
–
1
quadruple splitting of ΔE ≈ 0.7 mm s which are characteristic
Q
III
[23]
parameters for Fe -oxide/hydroxides.
(Figure 10, Table 3).
3
. Conclusion
Since this component accounts only for 2 to 3 % of the total
spectral area at 77 K, it represents clearly a small impurity frac-
tion. The increasing of the relative area of this component (30 %
at 298 K) is caused by the large Lamb–Mössbauer factor of
The work described herein represents three new examples of
II
discrete polynuclear Fe complexes from a 4-substituted 1,2,4-
triazole. Based on the ligand 4-(p-tolylidene-amino)-4H-1,2,4-tri-
II
III
II
azole (toltrz), a series of crystalline coordination Fe complexes,
Fe -oxide/hydroxide nanoparticles compared to that of Fe in a
relatively soft complex environment. A further confirmation for
only a very small impurity of the sample is provided by the
magnetization measurements.
II
II
that is, two binuclear [Fe (toltrz) (SCN) ] 3H O (C1), [Fe -
(
2
5
4
2
2
II
toltrz) (SeCN) ] 3H O (C2) and one trinuclear [Fe (toltrz) -
5 4 2 3 6
(
H O) ] 6(BF ) 2H O 2CH CH CO CH (C3) have been synthe-
2
6
4
2
3
2
2
3
sized and structurally as well as magnetically characterized. A
gradual spin transition was found for compound 3, while the
isostructural complexes C1 and C2 showed a similar weak anti-
As shown in Figure 11, the variable field isotherms measure-
ments were performed in the range 2–10 K under external mag-
netic fields up to 70 kOe. The maximum value of 5.99 Nꢀ at
II
ferromagnetic exchange coupling between the linked Fe cen-
7
0 kOe (2 K) matches perfectly with the theoretical saturation
ters. As there are still only a few examples for these binuclear
II
magnetization value of Fe ion (6.00 Nꢀ), suggesting good ho-
mogeneous character of the sample. In addition, the reduced
magnetization plots (M vs. H/T) exhibit significant separations
between the isofield curves, confirming the existence of zero
II
Fe crystalline complexes, the successful preparation and analy-
sis of these compounds is still a challenge and interesting work.
More related crystalline coordination materials with 4-subsiti-
tuted-1,2,4-triazole derivatives also need to be synthesized and
characterized in order to deeply understand the structural–
magneto correlation of these coordination compounds and
provide some fundamental trends for the SCO field.
field splitting, which possibly explains the dropping of ꢀ T val-
M
ues below 30 K (Figure S2, S3). In conclusion the temperature
dependent Mössbauer spectra displayed in Figure 9 clearly
show that the central iron(II) in complex 3 is able to undergo
SCO starting at around 100 K and completing at room tempera-
ture in accordance with the magnetic susceptibility data shown
in Figure 8.
4
. Experimental Section
4.1 General Methods and Materials: All commercially purchased
The overall gradual SCO behavior of this compound suggests
relatively weak cooperativity between the molecules in the lat-
tice. This is in accordance with the fact that the dominating
supramolecular interaction in the structure is the multiple intra-
chemicals and solvents were used without further purification. Mag-
netic susceptibility data were collected with a Quantum Design
SQUID magnetometer MPMS XL-7 in a temperature range of
2
–300 K with an applied field of 1 kOe. Samples were prepared in
molecular H-bonding interactions via the BF4– counteranions. gelatin capsules and held in plastic straws for insertion into the
Even though the H-bonding and π···π stacking found between magnetometer. Magnetic susceptibility values were corrected for
Eur. J. Inorg. Chem. 0000, 0–0
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[
24a]
the diamagnetic susceptibility according to Pascal's constants.
4.3 Syntheses
57
Fe Mössbauer spectra were recorded in transmission geometry
using a constant acceleration spectrometer operated in conjunction
with a 512-channel analyzer in the time-scale mode (WissEl GmbH).
The source contained Co diffused in Rh with an activity of 1.4 GBq.
The spectrometer was calibrated against α-iron at room tempera-
ture (r.t.). Variable temperature measurements were performed with
Synthesis of the Ligand
The ligand 4-(p-tolylidene-amino)-4H-1,2,4-triazole (toltrz) (Fig-
5
7
ure 12) was prepared via a modified procedure from the reported
[
30a]
article.
To avoid the possible by-product, we choose ethanol as
the reaction solvent. 4-Amino-1,2,4-triazole (1.68 g, 0.02 mol,
1.0 equiv.) and 4-methylbenzaldehyde (2.65 g, 0.022 mol, 1.1 equiv.)
were dissolved in ethanol with the addition of few drops of H SO ,
DN
a continuous flow cryostat (Optistat , Oxford Instruments). Spec-
tral data were transferred from the multi-channel analyzer to a PC
2
4
acting as acidic catalyst. The reaction mixture was slowly heated up
to 80 °C until it started to boil, then refluxed at this temperature
for 10 h. When cooled down to room temp., the excess of the sol-
vent was removed by rotary evaporator at 35 °C. The product such
obtained was washed with small amounts of cold ethanol and di-
ethyl ether, and then dried in the desiccator with phosphorus
pentoxide as dry agent. A white powder with intense smelling was
obtained. Yield: 3.53 g (94.85 %), m.p.137–163 °C. IR (KBr): ν˜ = 1608
for further analysis employing the public domain program Vinda
running on an Excel 2003® platform.[
24b]
The spectra were analyzed
by least-squares fits using Lorentzian line shapes, Γ. Elemental anal-
ysis (C, H, and N) was measured at the microanalytical laboratories
of the Johannes Gutenberg University Mainz. Infrared spectra
(
FT-IR) were recorded as potassium bromide pellets in the range
–
1
from 4000 to 400 cm with a JASCO FT/IR-4200 at the Johannes
Gutenberg-University Mainz.
–
1 1
(
(
H–C=N), 3101 (Ar, C H-stretch.); 817, 2918 (Ar-CH ) cm . H NMR
3
4
.2 Single Crystal X-ray Diffraction: Single-crystal X-ray diffraction
Figure S1) (CD OD): δ = 7.35–7.82 (dd, 4 H, Ar–H), 8.94 (s, 1 H,
3
data (C1 and C2 at 173 K) were collected on a Bruker Smart APEX
II CCD diffractometer, operating at 45 kV and 35 mA using Mo-Kα
radiation (λ = 0.71073 Å). The diffractometer was equipped with a
nitrogen cold stream operating at 173(2) K. The crystal of C3 (at
H–C=N), 9.05(s, 2 H, triazole), 2.43(s, 3 H, p-CH ) ppm.
3
Synthesis of the Complex
Synthesis of [FeII (toltrz) (SCN) ] 3H O (C1): To a stirring solution
2
5
4
2
of toltrz (150 mg, 0.8 mmol) in methanol (5 mL) was added an
1
20 K and 173 K) was measured on a Stoe IPDS II diffractometer
aqueous solution of FeSO 7H O (90 mg, ≈ 0.3 mmol) and NH SCN
operating with a Mo-K (λ = 0.71073 Å) X-ray tube with a graphite
4
2
4
α
(50 mg, ≈ 0.6 mmol). The solution turned from colorless to light
monochromator. Data reduction was performed using the SMART
and SAINT software[
applied using the SADABS program.
by direct methods and refined by full-matrix least-squares on F
using the SHELXTL program package, and the Olex2 program.
25]
yellow immediately. One spatula-amount (≈ 35 mg) of ascorbic acid
was added to prevent possible oxidation process. The reaction mix-
ture was then stirred for 3–4 hours before filtered with rapid filter
paper. The obtained clear light reddish solution was kept in a small
vial and left stand still to evaporate the solvent slowly. After one
week, light yellow plate-like crystals of C1 were deposited at the
bottom of the vial. After removing the mother liquid, the single
crystals were quickly dried in an argon stream, and stored under
argon. The crystalline sample changed to light-yellow powder after
the drying process and was used for SQUID measurements without
further modification. Yield: 62.3 mg (47.15 % based on Fe). Anal.
and an empirical absorption correction was
[26]
All structures were solved
2
[27]
[28]
The ordered non-hydrogen atoms in each structure were refined
with anisotropic displacement parameters, while the hydrogen
atoms were placed in idealized positions and allowed to ride on
their parent atoms. In compound 1 and 2, the N18 and C35 atoms
are respectively disordered over two positions with a ratio of 1:1. In
compound 3, there is a disordering over one p-tolyl fragment (C3
to C10) with a ratio of 1:1 at both temperatures. While the refine-
ment of the reflection data yielded poorly resolved structural re-
sults: there is one more N4 (connected with the disordered p-tolyl
ring) disordering, plus the ethyl ethylate solvent molecule was also
disordered at the carbonyl group C33=O1 over three positions with
a ratio of 0.5:0.25:0.25. Even though, the structure of C3 at 120 K
Calcd (Found) for C H N O S Fe : C 49.06 (49.17); H 3.74 (4.03);
54 56 24
3
4
2
N 25.43 (25.38). IR (KBr): ν˜ = 3104 (w), 2976 (m), 2920 (w), 2072 (s),
607 (vs), 1121 (vs), 1062 (m), 817 (m), 620 (vs), 505 (m), 396 (w)
1
–
1
cm .
Synthesis of [FeII (toltrz) (SeCN) ] 3H O (C2): The preparation of
2
5
4
2
got a poor reflection data with the final R [I > 2σ(I)] value of 0.1473,
compound 2 is almost the same as the procedure for compound 1,
1
the major part of the structure is still reliable and gives us valuable
data for the structure and property investigation (see in the main
text). In all the structures, the lattice water molecules were refined
with anisotropic displacement parameters, while the hydrogen
atoms were not defined. Thus, in the discussion in the main text,
all the lattice water molecules or the disordered parts were not
except for changing of NH SCN (50 mg, ≈ 0.6 mmol) to KSeCN
4
(47 mg, ≈ 0.6 mmol). The light-yellow crystals collected from the
mother liquid were quickly dried in an argon stream, and used for
SQUID measurements without further modification. As the selenium
compound is slightly light sensitive, all the procedures here (reac-
tion, evaporation, ...) were performed in a rather dark environment.
included. The crystallographic data and refinement parameters of Yield: 63.4 mg (41.97 % based on Fe). Anal. Calcd (Found) for
C1, C2, C3 (173 K) and C3 (120 K) are listed in Table 1. All structure
C H N O Se Fe : C 42.93 (42.48); H 3.34 (3.48); N 22.25 (21.46).
54 56 24 3 4 2
figures are generated with DIAMOND-3.[
29]
IR (KBr): ν = 3217 (w), 3108 (m), 2975 (w), 2854 (m), 2070 (s), 1607
˜
(
(
vs), 1524 (s), 1369 (m), 1179 (m), 1115 (vs), 1063 (m), 881 (m), 817
CCDC 1587514 (for C1), 1587515 (for C2), 1587516 (for C3 at 173 K),
and 1587517 (for C3 at 120 K) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.
–
1
m), 755 (m), 622 (vs), 509 (m), 443 (w) cm .
Synthesis of [FeII (toltrz) (H O) ] (BF ) 2H O 2CH CH CO CH
3
6
2
6
4 6
2
3
2
2
3
(C3): To the dissolved Fe(BF ) 6H O (135 mg, 0.4 mmol) in 10 mL
4
2
2
Figure 12. Synthetic Scheme to prepare the toltrz ligand.
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9
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Full Paper
of ethyl acetate, one spatula amount (≈ 35 mg) of ascorbic acid
added to prevent possible oxidation process. After the complete-
ness of dissolving the iron salt, a solution of toltrz (150 mg,
A. S. Barltrop, N. G. White, H. L. Feltham, S. Brooker, Inorg. Chem. 2018,
5
5
7, 6266–6282; d) S. Rodríguez-Jiménez, S. Brooker, Inorg. Chem. 2017,
6, 13697–13708.
[
[
[
10] G. Vos, R. A. Le Febre, R. A. De Graaff, J. G. Haasnoot, J. Reedijk, J. Am.
0
.8 mmol) dissolved in ethyl acetate (5 ≈ 10 mL) was slowly added
Chem. Soc. 1983, 105, 1682–1683.
11] Y. Garcia, F. Robert, A. D. Naik, G. Y. Zhou, B. Tinant, K. Robeyns, S. Mi-
chotte, L. Piraux, J. Am. Chem. Soc. 2011, 133, 15850–15853.
12] a) J. L. Wang, Q. Liu, Y. S. Meng, H. Zheng, H. L. Zhu, Q. Shi, T. Liu, Inorg.
Chem. 2017, 56, 10674–10680; b) W. B. Chen, J. D. Leng, Z. Z. Wang, Y. C.
Chen, Y. Miao, M. L. Tong, W. Dong, Chem. Commun. 2017, 53, 7820–
7823; c) N. Pittala, F. Thétiot, C. Charles, S. Triki, K. Boukheddaden, G.
Chastanet, M. Marchivie, Chem. Commun. 2017, 53, 8356–8359; d) W. B.
Chen, Y. C. Chen, M. Yang, M. L. Tong, W. Dong, Dalton Trans. 2018, 47,
to the above solution. This reaction solution was then stirred for
around 3–4 hours before filtered with rapid filter paper. The ob-
tained almost colorless solution was kept in a small vial and left
stand still to evaporate the solvent slowly. After five days, light-
green block crystals of C3 were deposited at the bottom of the vial.
After removing the mother liquid, the single crystals were quickly
dried in an argon stream, and stored under argon. After the drying
process, the crystalline sample was found to change color from light
green to pale-green. The same sample powder such obtained was
used for SQUID and Mössbauer measurements without further
modification. Yield: 61.26 mg (58.18 % based on Fe). Anal. Calcd
4
307–4314.
[
13] P. Chakraborty, A. Tissot, L. Peterhans, L. Guenee, C. Besnard, P. Pattison,
A. Hauser, Phys. Rev. B 2013, 87, 2143.
14] a) A. Bauzá, T. J. Mooibroek, A. Frontera, CrystEngComm 2016, 18, 10–23;
b) G. A. Senchyk, A. B. Lysenko, D. Y. Naumov, V. P. Fedin, H. Krautscheid,
K. V. Domasevitch, Inorg. Chem. Commun. 2010, 13, 1576–1579.
[15] a) Y. M. Klein, N. F. Sciortino, C. E. Housecroft, C. J. Kepert, S. M. Neville,
Magnetochemistry 2016, 2–8; b) D. Savard, C. Cook, G. D. Enright, I. Kor-
obkov, T. J. Burchell, M. Murugesu, CrystEngComm 2011, 13, 5190–5197;
c) H. Z. Scott, T. M. Ross, B. Moubaraki, K. S. Murray, S. M. Neville, Eur. J.
Inorg. Chem. 2013, 803–812.
[
(
Found) for solvent-free C H N O B F Fe1.5: C 35.02 (34.74);
30 44 12 7 3 12
H 4.31 (4.03); N 16.34 (16.43). IR (KBr): ν˜ = 3132 (m), 3032 (m), 2975
(
(
(
w), 2921 (w), 2859 (m), 1606 (vs), 1567 (s), 1532 (s), 1307 (m), 1181
m), 1084 (vs), 1073 (vs), 1037 (vs), 993 (m), 889 (w), 817 (m), 726
m), 627 (s), 533 (m), 522 (m), 397 (w) cm .
–
1
Acknowledgments
[16] a) R. S. Krishnan, R. Srinivasan, S. Devanarayanan, Thermal Expansion of
Crystals, Pergamon, 1979; b) T. H. K. Barron, G. K. White, Heat Capacity
and Thermal Expansion at Low Temperatures, Kluwer Academic, 1999; c)
K. Takenaka, Sci. Technol. Adv. Mater. 2012, 13, 013001; d) B. R. Mullaney,
L. Goux-Capes, D. J. Price, G. Chastanet, J. F. Létard, C. J. Kepert, Nat.
Commun. 2017, 8, 1053.
We kindly thank Dr. Dieter Schollmeyer and Regine Jung-Poth-
mann (Johannes Gutenberg University, Mainz) are kindly ac-
knowledged for collecting the crystal structural data. A. M. L.
acknowledges the financial support from Graduate School
Mainz and is a recipient of a Deutsche Forschungsgemeinschaft
[
[
17] E. Borello, A. Zecchina, Spectrochim. Acta 1963, 19, 1703–1715.
18] Y. Prashanthi, S. Raj, J. Sci. Res. 2010, 2, 114–126.
(
DFG) fellowship through the Excellence Initiative by the
[19] S. H. Sumrra, Z. H. Chohan, Spectrochim. Acta Part A 2012, 98, 53–61.
[20] a) A. A. Salaudeen, C. A. Kilner, M. A. Halcrow, Polyhedron 2008, 27, 2569–
Graduate School Materials Science in Mainz (DFG/GSC 266). E. R.
and V. S. also acknowledge the support of the German Research
Foundation (DFG) through the Transregional Collaborative Re-
search Center SFB/TRR173 Spin+X, Projects A04 and A09.
2
576; b) K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds Part B (5th ed.) Wiley Interscience, New York, 1997,
p. 116.
[
21] a) J. S. Sun, H. H. Zhao, O. Y. Xiang, R. Clerac, J. A. Smith, J. M. Clemente-
Juan, C. Gomez-Garcia, E. Coronado, K. R. Dunbar, Inorg. Chem. 1999, 38,
5
841–5855; b) G. DeMunno, M. Julve, J. A. Real, F. Lloret, R. Scopelliti,
Keywords: Spin crossover · Iron(II) · Trinuclear ·
Binuclear · 1,2,4-Triazole · Schiff bases
Inorg. Chim. Acta 1996, 250, 81–85; c) P. Albores, E. Rentschler, Inorg.
Chem. 2010, 49, 8953–8961; d) S. Konar, E. Zangrando, M. G. B. Drew, T.
Mallah, J. Ribas, N. R. Chaudhuri, Inorg. Chem. 2003, 42, 5966–5973.
22] N. F. Chilton, R. P. Anderson, L. D. Turner, A. Soncini, K. S. Murray, J.
Comput. Chem. 2013, 34, 1164.
23] V. Schünemann, H. Winkler, Rep. Prog. Phys. 2000, 63, 263–353.
24] a) G. A. Bain, J. F. Berry, J. Chem. Educ. 2008, 85, 532; b) H. P. Gunnlaugs-
son, Hyperfine Interact. 2016, 237, 79.
[
[
1] a) L. Cambi, L. Szegö, Ber. Dtsch. Chem. Ges. 1931, 64, 2591–2598; b) L.
Cambi, L. Szegö, Ber. Dtsch. Chem. Ges. 1933, 66, 656–661; c) L. Cambi,
L. Malatesta, Ber. Dtsch. Chem. Ges. 1937, 70, 2067–2078.
[
[
[
2] a) H. A. Goodwin, Coord. Chem. Rev. 1976, 18, 293–325; b) E. Konig, R.
Gerhard, S. K. Kulshreshtha, Chem. Rev. 1985, 85, 219–234.
[
25] SMART 5.0 and SAINT 4.0 for Windows NT, Area Detector Control and
Integration Software, Bruker Analytical X-ray Systems Inc., Madison, WI,
[
3] a) P. Gütlich, G. Yann, A. G. Harold, Chem. Soc. Rev. 2000, 29, 419–427; b)
M. A. Halcrow, Chem. Soc. Rev. 2011, 40, 4119–4142; c) E. Coronado, M. E.
Guillermo, Chem. Soc. Rev. 2013, 42, 1525–1539.
1
998.
[
26] G. M. Sheldrick, SADABS: Program for Empirical Absorption Correction of
Area Detector Data, University of Göttingen, Göttingen, Germany, 1996.
27] a) G. M. Sheldrick, Acta Crystallogr., Sect. C 2015, 71, 3–8; b) G. M. Shel-
drick, SHELXTL 5.1 for Windows NT: Structure Determination Software Pro-
grams, Bruker Analytical X-ray Systems, Inc., Madison, WI, 1997.
28] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. J.
Puschmann, Appl. Crystallogr. 2009, 42, 339–341.
29] Diamond – Crystal and Molecular Structure Visualization Crystal Impact –
Dr. H. Putz & Dr. K. Brandenburg GbR, Kreuzherrenstr. 102, 53227 Bonn,
Germany.
[
[
[
[
4] a) O. Kahn, J. Kröber, C. Jay, Adv. Mater. 1992, 4, 718–728; b) P. Gütlich,
Y. Garcia, H. A. Goodwin, Chem. Soc. Rev. 2000, 29, 419–427.
5] a) R. N. Muller, V. Elst, S. Laurent, J. Am. Chem. Soc. 2003, 125, 8405–
[
8407; b) J. F. Letard, O. Nguyen, N. Daro, Patent, 2007, FR2894581.
6] a) M. Matsuda, H. Isozaki, H. Tajima, Chem. Lett. 2008, 37, 374–375; b) S.
Kanegawa, S. Kang, O. Sato, Eur. J. Inorg. Chem. 2013, 2013, 725–729.
7] a) O. Kahn, M. C. Jay, Science 1998, 279, 44–48; b) J. G. Haasnoot, Coord.
Chem. Rev. 2000, 131, 200–201; c) O. Roubeau, Chem. Eur. J. 2012, 18,
[
[
15230–15244.
[
8] a) H. L. C. Feltham, A. S. Barltrop, S. Brooker, Coord. Chem. Rev. 2017, 344,
[
30] a) T. Khan, R. Yadav, Heterocycl. Lett. 2016, 6, 757–766; b) A. Kwiecień, M.
Barys, Z. Ciunik, Molecules 2014, 19, 11160–11177.
2
1
6–53; b) M. H. Klingele, S. Brooker, Coord. Chem. Rev. 2003, 241, 119–
32; c) J. A. Kitchen, S. Brooker, Coord. Chem. Rev. 2008, 252, 2072–2092.
[
9] a) H. L. Feltham, K. Dankhoff, C. J. Meledandri, S. Brooker, ChemPlusChem
018, 83, 1–9; b) H. L. Feltham, M. G. Cowan, J. A. Kitchen, G. N. Jameson,
S. Brooker, Supramol. Chem. 2018, 30, 296–304; c) S. Rodríguez-Jiménez,
2
Received: June 22, 2018
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Spin-Crossover Complexes
A.-M. Li, T. Hochdörffer,
J. A. Wolny, V. Schünemann,
E. Rentschler* ................................... 1–11
II
Fe Complexes with Triple N1,N2-Tri-
azole Bridge Schiff Base Ligand:
Antiferromagnetic Dimer vs. Spin
Conversion Trimer
II
A series of linear Fe complexes with characterized. A gradual spin transition
-(p-tolylidene-amino)-4H-1,2,4-tri- was found on the central Fe site of the
4
azole ligand were synthesized and trinuclear complex.
DOI: 10.1002/ejic.201800784
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
11
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim