Syntheses, structural variation, and characterization of a series of crystalline coordination compounds with 4-benzene-1,2,4-triazole: Polymorph, incomplete spin transition, and single crystal-to-single crystal transformation

Article abstract of DOI:10.1021/cg401141a

Based on the 4-substituted 1,2,4-triazole derivate ligand 4-benzene-1,2,4-triazole (L), a series of crystalline coordination complexes varying from mononuclear to trinuclear species, namely, [Zn(L) ₂Br₂] (1), [Zn(L)₂Br₂] (2), [Fe(L)₄(NCS)₂]₂ (3), [Fe₂(μ ₂-L)₃(L)₂(NCS)₄]·CH ₃OH·CH₃CH₂OH (4), [Fe ₂(μ₂-L)₃(L)₂(NCS) ₄]·2CH₃CH₂OH (5), [Fe ₂(μ₂-L)₃(L)₂(NCS) ₄]·2CH₃CH₂OH·1.5H₂O (6), and [Ni₃(μ₂-L)₆(L)₄(H ₂O)₂](NO₃)₆·15.5H ₂O (7), have been isolated. 1 and 2 present a temperature-induced polymorphic phenomenon of two zinc(II) coordination complexes with L. The solvent effect plays the key role for the self-assembly of these Fe(II) complexes 3-6: 3 contains mononuclear Fe(L)₄(NCS)₂ units without spin-transition behavior, whereas both 4 and 5 present binuclear Fe(II) complexes with three N₁,N₂-1,2,4-triazole bridges exhibiting incomplete spin-transition behavior. The low-temperature X-ray structural analysis (100 K) of 4 also confirms that one of the Fe(II) centers is located at the low-spin (LS) state and the other Fe(II) center is located at the high-spin (HS) state. Interestingly, when the binuclear Fe(II) complex 5 was exposed in the water atmosphere, solvent-induced single crystal-to-single crystal transformation can be observed, and the binuclear Fe(II) complex 6 exhibiting antiferromagnetic interactions can be isolated. Further, a trinuclear crystalline compound is isolated when Ni(II) salts were used to react with L. Variable-temperature magnetic susceptibility measurement (2-300 K) reveals antiferromagnetic interactions in 7. The polymorphic phenomenon (1 and 2), incomplete spin-transition phenomenon (4 and 5), and single crystal-to-single crystal transformation (from 5 to 6) also reveal great potential in the construction of these novel functional materials with L.

Full text of DOI:10.1021/cg401141a

Article
pubs.acs.org/crystal
Syntheses, Structural Variation, and Characterization of a Series of
Crystalline Coordination Compounds with 4‑Benzene-1,2,4-triazole:
Polymorph, Incomplete Spin Transition, and Single Crystal-to-Single
Crystal Transformation
Xiang Xia Wu,†,‡ You You Wang,†,‡ Pan Yang,†,‡ Yao Yao Xu,†,‡ Jian Zhong Huo,†,‡ Bin Ding,*,†,‡
Ying Wang,*,†,‡ and XiuGuang Wang†,‡
†Tianjin Key Laboratory of Structure and Performance for Functional Molecule, Tianjin Normal University, Tianjin 300071,
People’s Republic of China
‡Key Laboratory of Inorganic-Organic Hybrid Functional Material Chemistry, Tianjin Normal University, Ministry of Education,
Tianjin 300071, People’s Republic of China
S
* Supporting Information
ABSTRACT: Based on the 4-substituted 1,2,4-triazole derivate ligand 4-benzene-1,2,4-triazole (L), a series of crystalline
coordination complexes varying from mononuclear to trinuclear species, namely, [Zn(L)2Br2] (1), [Zn(L)2Br2] (2),
[Fe(L)4(NCS)2]2 (3), [Fe2(μ2-L)3(L)2(NCS)4]·CH3OH·CH3CH2OH (4), [Fe2(μ2-L)3(L)2(NCS)4]·2CH3CH2OH (5),
[Fe2(μ2-L)3(L)2(NCS)4]·2CH3CH2OH·1.5H2O (6), and [Ni3(μ2-L)6(L)4(H2O)2](NO3)6·15.5H2O (7), have been isolated. 1
and 2 present a temperature-induced polymorphic phenomenon of two zinc(II) coordination complexes with L. The solvent
effect plays the key role for the self-assembly of these Fe(II) complexes 3−6: 3 contains mononuclear Fe(L)4(NCS)2 units
without spin-transition behavior, whereas both 4 and 5 present binuclear Fe(II) complexes with three N1,N2-1,2,4-triazole
bridges exhibiting incomplete spin-transition behavior. The low-temperature X-ray structural analysis (100 K) of 4 also confirms
that one of the Fe(II) centers is located at the low-spin (LS) state and the other Fe(II) center is located at the high-spin (HS)
state. Interestingly, when the binuclear Fe(II) complex 5 was exposed in the water atmosphere, solvent-induced single crystal-to-
single crystal transformation can be observed, and the binuclear Fe(II) complex 6 exhibiting antiferromagnetic interactions can
be isolated. Further, a trinuclear crystalline compound is isolated when Ni(II) salts were used to react with L. Variable-
temperature magnetic susceptibility measurement (2−300 K) reveals antiferromagnetic interactions in 7. The polymorphic
phenomenon (1 and 2), incomplete spin-transition phenomenon (4 and 5), and single crystal-to-single crystal transformation
(from 5 to 6) also reveal great potential in the construction of these novel functional materials with L.
molecular spintronics, and high density data storage.2−5
Currently, the spin-transition (SCO) system is widely known
as molecule-based magnetic materials (such as molecule-based
INTRODUCTION
Over the past decades, the research of metal−organic
coordination frameworks has received great attention as an
■
memory devices and molecular switches, etc.). For instance,
intriguing interface between synthetic science and material
the previously reported one-dimensional Fe(II) spin-transition
chemistry, which can greatly promote the understanding of the
system with 4-R-1,2,4-triazole (R = substituted group) has been
correlation between material function and molecular struc-
ture.1 Especially, the research of these functional coordina-
tion compounds (such as single-molecule magnet systems and
spin-transition research systems) has received great interest
because of their great applications in quantum computers,
Received: July 27, 2013
Revised: November 22, 2013
© XXXX American Chemical Society
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deeply explored by Lavrenova and co-workers6 and Kahn and
co-workers.7 Further, these 1D coordination complexes can be
applied to prepare nanosized bistable magnetic materials
through the synthesis of nanopatterned films or coordination nano-
particles.8 However, iron(II) compounds with 1,2,4-triazole
derivative ligands are easy to obtain powders; hence, the powder
diffraction analysis method is often applied to explore 1D iron(II)−
triazole SCO coordination compounds.9 Only a few of these
complexes’ SCO behaviors have been analyzed by magnetic mea-
surements and single-crystal X-ray diffraction (XRD) analysis.
Hence, structural information about these compounds in either
of the high-spin states or low spin-states is still poorly available.
Until recently, the existence of infinite 1D Fe(II) chains with 4-R-trz
has been confirmed by the structural analysis of [Fe(4-R-1,2,4-
triazole)3](NO3)2·2H2O (R = −NH2 group),10 which opens up the
possibility for the research of property−structure association within
these specific SCO systems.
On the other hand, there are only a few examples for
binuclear Fe(II) crystalline coordination compounds with
4-substituted 1,2,4-triazole derivates in comparison with other
triazole−metal complexes.11 For example, the first crystal
structure of a binuclear iron(II) compound with three N1,N2-
1,2,4-triazole bridges in the low-spin states and high-spin states
are reported by Yann Garcia et al. recently.12 The construction
of these binuclear crystalline iron(II) 4-R-trz-based compounds
is still an interesting and challenge work. More new binuclear
crystalline iron(II)−triazole compounds need to be synthesized
and characterized in order to deeply understand the structural−
magneto correlation of these coordination compounds and
finally to prepare interesting functional materials.
1,2,4-Triazole and its derivative are interesting multidentate
ligands since they can bridge different metal centers and
construct many novel coordination compounds that can exhibit
extraordinary structural diversity and intriguing functional
properties.13 These organic ligands play a key role in the con-
struction of novel coordination materials. In our previous
studies, we are interested in investigating these coordination
compounds using 1,2,4-triazole and its derivative ligands as the
starting materials. These multidentate ligands are employed to
prepare a series of one-, two-, and three-dimensional functional
coordination polymers; the ligand design has a direct influence
on the structure of these functional complexes as well as these
functional properties.14 For 4-benzene-1,2,4-triazole and its derivate
ligand, recently, one trinculear Fe(II) coordination complex with
4-(4′-nitrophenyl)-1,2,4-triazole and its spin-transition property
have been reported by Murugesu et al.15 As illustrated in the
previous literature, such structural fine-tuning of these magnetic
materials can lead to exciting multistep crossover behavior where an
in-depth structure−magnetism relationship can be investigated.16
However, no dincuclear iron(II) compounds with L are
investigated. In this work, 4-benzene-1,2,4-triazole (L) has been
synthesized. Based on L, a series of crystalline coordination com-
plexes varying from mononuclear to trinuclear species, namely,
[Zn(L)2Br2] (1), [Zn(L)2Br2] (2), [Fe(L)4(NCS)2]2 (3), [Fe2(μ2-
L)3(L)2(NCS)4]·CH3OH·CH3CH2OH (4), [Fe2(μ2-L)3(L)2-
(NCS)4]·2CH3CH2OH (5), [Fe2(μ2-L)3(L)2(NCS)4]·
2CH3CH2OH·1.5H2O (6), and [Ni3(μ2-L)6(L)4(H2O)2](NO3)6·
15.5H2O (7), have been isolated. The solvent effect plays the key
role for the assembly of these Fe(II) compounds 3−6. Both 4 and
5 are binuclear Fe(II) complexes with three N1,N2-1,2,4-triazole
bridges, which can exhibit incomplete spin-transition behaviors.
The low-temperature X-ray structural analysis (100 K) of 4 also
confirms that one of the Fe(II) centers is located at the low-spin
(LS) state and the other Fe(II) center is located at the high-spin
(HS) state. The polymorphic phenomenon (1 and 2), incomplete
spin-transition behaviors (4 and 5), and single crystal-to-single
crystal transformation (from 5 to 6) also reveal great potential
in the construction of these novel functional materials with L
(Scheme 1).
EXPERIMENTAL SECTION
■
Materials and Physical Techniques. The 4-benzene-1,2,4-
triazole L ligand was prepared by the literature methods.17 All the
other solvents and reagents were commercially available and used
without further purification. C, H, and N microanalyses were carried
out with a PerkinElmer 240 elemental analyzer. Powder X-ray dif-
fraction analyses were measured on a D/Max-2500 X-ray diffrac-
tometer using Cu Kα radiation. FT-IR spectra were measured from
KBr pellets in the range of 4000−400 cm−1 on a Bio-Rad FTS 135
spectrometer. The photoluminescence spectra were measured by an
MPF-4 fluorescence spectrophotometer with a xenon arc lamp as
the light source. Variable-temperature magnetic susceptibilities were
recorded on a Quantum Design MPMS-7 SQUID magnetometer. The
magnetic field used to perform magnetic measurements is 1000 Oe.
For all the constituent atoms, diamagnetic corrections can be made
with Pascal’s constants.
Synthesis of 4-Benzene-1,2,4-triazole (L). The ligand was
prepared according to a modified known synthetic strategy by first
mixing formylhydrazine (0.90 g, 15 mmol), triethylorthoformate
(3.7 mL, 25 mmol), and ethanol (40 mL) in a Synthware Glass high-
pressure vessel. The solution was stirred at 180 °C for half an hour.
The latter was cooled down to 60 °C in a warm water bath, and aniline
(2.1 g, 15 mmol) was slowly added to the solution, followed by four
drops of sulphuric acid as a catalyst. The mixed solution was heated
again at 180 °C for half an hour, resulting in a dark red solution.
While the solution was cooled, a dark yellow precipitate appeared.
The powder was filtered, washed with ethanol (3−5 mL) and ether
(3−5 mL), and dried in vacuo for 1 h. Yield, 35%.
Preparation of Complexes 1−7. [Zn(L)2Br2] (1). A solution of L
(0.146 g, 1 mmol) in 15 mL of water was warmed to 30 °C and then
slowly dripped into a solution of ZnBr2 (0.112 g, 0.5 mmol) in 15 mL
of water. Colorless solutions were isolated after stirring for ca. 6 h;
colorless block crystals with good quality can be isolated after ca. 2
weeks. Yield, 68% (based on Zn(II) salts). Anal. Calcd for C16H14-
Br2N6Zn (1): C, 37.28%; H, 2.74%; N, 16.30%. Found: C, 37.46%; H,
2.91%; N, 16.40%. FT-IR data (cm−1): 3438 (m), 3118 (m), 1658 (m),
1553 (m), 1238 (m), 863 (s), 767 (s), 692 (m), 639 (m), 514 (m).
[Zn(L)2Br2] (2). Compound 2 was synthesized by the similar method
as 1 only using a higher reaction temperature of 100 °C (boiling water
solutions). Colorless solutions were isolated after stirring for ca. 6 h;
colorless plate crystals with good quality can be isolated after ca. 2 weeks.
Yield, 55% (based on Zn(II) salts). Anal. Calcd for C16H14Br2N6Zn (2):
C, 37.28%; H, 2.74%; N, 16.30%. Found: C, 37.53%; H, 2.87%; N,
16.47%. FT-IR data (cm−1): 3431 (m), 3110 (m), 1653 (m), 1551 (m),
1233 (m), 863 (s), 766 (s), 692 (m), 638 (m), 510 (m).
[Fe(L)4(NCS)2]2 (3). A solution of L (0.073 g, 0.5 mmol) in 15 mL
of water solutions were warmed to ca. 60 °C; then the water solu-
tions were dripped into a mixture of NH4NCS (0.076 g, 1 mmol),
Fe(ClO4)2·6H2O (0.181 g, 0.5 mmol), and a small amount of ascorbic
acid in 15 mL water solutions. The resulting solutions were isolated
after stirring for ca. 5 h; colorless crystals with good quality can be
isolated after ca. 2 weeks. Yield, 61% (based on iron(II) salts). Anal.
Calcd for C34H28FeN14S2 (3): C, 54.26%; H, 3.75%; N, 26.05%.
Found: C, 54.45%; H, 3.85%; N, 26.25%. FT-IR data (cm−1): 3459
(m), 3100 (m), 2083(s), 1688 (m), 1547 (s), 1233 (m), 875 (s), 770
(s), 690 (m), 639 (m), 518 (m).
[Fe2(μ2-L)3(L)2(NCS)4]·CH3OH·CH3CH2OH (4). Compound 4 was
synthesized by the similar method as 3 only using the ethanol and
methanol (1:1) mixed solutions in place of aqua solutions. Pale yellow
crystals can be isolated after ca. 2 weeks at the low temperature of 5 °C.
It is noted that good quality of crystals of 4 cannot be isolated under the
condition of higher temperature. Yield, 39% (based on iron(II) salts).
B
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Scheme 1. Construction of Coordination Complexes 1−7 Based on L
Anal. Calcd for C47H45Fe2N19O2S4 (4): C, 49.18%; H, 3.95%; N,
23.18%. Found: C, 49.53%; H, 4.03%; N, 23.41%. FT-IR data (cm−1):
3440 (m), 3107 (m), 2071(s), 1683 (m), 1518 (s), 1238 (m), 858 (m),
753 (s), 679 (m), 644 (m), 508 (m).
[Fe2(μ2-L)3(L)2(NCS)4]·2CH3CH2OH (5). Compound 5 was synthe-
sized by the similar method as 3 only using ethanol solutions in place
of aqua solutions. Yellow needle crystals can be isolated after ca. 3
weeks at the low temperature of 5 °C. It is noted that good quality of
crystals of 5 cannot be isolated under the condition of higher
temperature. Yield, 43% (based on iron(II) salts). Anal. Calcd. for
C48H47Fe2N19O2S4 (5): C, 49.62%; H, 4.08%; N, 22.90%. Found:
C, 49.73%; H, 4.18%; N, 22.95%. FT-IR data (cm−1): 3439 (m),
C
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3106 (m), 2072 (s), 1685 (m), 1516 (s), 1238 (m), 858 (m), 753 (s),
678 (m), 644 (m), 506 (m).
interactions, listed in Table S1 (Supporting Information), also
further extend 1 and 2, forming two kinds of quite different
supramolecular architectures viewed along the crystallographic
b axis.
[Fe2(μ2-L)3(L)2(NCS)4]·2CH3CH2OH·1.5H2O (6). When 5 was ex-
posed in the water atmosphere for 24 h, the colorless crystals of 6 can
be isolated fortunately. It is noted that the crystal-to-crystal trans-
formation process is irreversible. Anal. Calcd for C48H50Fe2N19O3.5S4
(6): C, 48.49%; H, 4.24%; N, 22.38%. Found: C, 48.55%; H, 4.35%; N,
22.47%. FT-IR data (cm−1): 3444 (br), 3102 (m), 2082(s), 1692 (m),
1537 (s), 1239 (m), 862 (s), 754 (s), 686 (m), 636 (m), 520 (m).
[Ni3(μ2-L)6(L)4(H2O)2](NO3)6·15.5H2O (7). A solution of L (0.073 g,
0.5 mmol) in 15 mL of water was heated up to ca. 60 °C, and then
slowly added into a mixture of Ni(NO3)2·6H2O (0.181 g, 0.5 mmol)
dissolved in 15 mL of distilled water. A green solution was isolated
after stirring for ca. 6 h; green block crystals can be isolated after
ca. 3 weeks. Yield, 55% (based on Ni(II) salts). Anal. Calcd. for
C80H105N36Ni3O26.5 (7): C, 44.25%; H, 4.87%; N, 23.22%. Found: C,
44.61%; H, 4.96%; N, 23.39%. FT-IR data (cm−1): 3420 (br), 3110 (m),
1530 (m), 1380 (m), 1320 (m), 870 (s), 780 (s), 639 (m), 510 (m).
Caution! Perchlorate salts and complexes are potentially explosive and
should be handled in small quantities and with much care.
Crystal Structure Determination. Structure measurements of
complexes 1−7 have been performed on a computer-controlled
Bruker SMART 1000 CCD diffractometer equipped with graphite-
monochromated Mo−Kα radiation with a radiation wavelength
0.71073 Å by using the ω-scan technique. The structures have been
solved by direct methods and refined with the full-matrix least-squares
technique using the SHELXS-97 and SHELXL-97 programs.18,19
Anisotropic thermal parameters have been assigned to all non-
hydrogen atoms, and the organic hydrogen atoms have been generated
geometrically. The hydrogen atoms of the water molecules were
located from difference maps and refined with isotropic temperature
factors, analytical expressions of neutral-atom scattering factors were
employed, and anomalous dispersion corrections were incorporated.
For 4, the data have been measured on a Bruker diffractometer at 100
and 296 K, respectively.19 The crystallographic data and selected bond
lengths and angles are listed in Tables 1 and 2, respectively. CCDC
reference numbers 950197 (1), 950196 (2), 884895 (3), 950198 (4),
884898 (5), 950199 (6), and 950200 (7) contain the supplementary
crystallographic data for this article. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif (or from the Cam-
bridge Crystallographic Centre, 12 Union Road, Cambridge CB21EZ,
U.K.; Fax: (+44) 1223-336033; or deposit@ccdc.cam.ac.uk). Hydro-
gen bonds analysis was carried out using the PLATON program.20 All
the hydrogen bond distances and angles are listed in Table S1
(Supporting Information).
The coordination compounds constructed by d10 metal
centers and conjugated aromatic organic linkers are well-known
as luminescent materials with great applications such as photo-
chemistry and chemical sensors. As illustrated in the previous
literature, zinc(II) compounds as d10 transition-metal polymers
can exhibit intriguing photoluminescence properties; thus, the
preparation of Zn(II) complexes can be an efficient synthetic
strategy for obtaining new types of fluorescent materials.22
At the ambient temperature, the free ligand L in the solid state
is luminescent and shows the broad emission maximum at
410 nm (λex = 335 nm). For the L ligand, the chromospheres
are aromatic benzene rings and the observed emission is due
to π−π* transition. For 1 and 2, the comparison between
powder X-ray diffraction (PXRD) and a simulated analysis from
crystal data confirmed the pure crystal phases (Figure S1,
Supporting Information). In comparison with that of free
ligand L, upon excitation of solid samples of 1 and 2 at
335 nm (Figure 2), 1 and 2 show strong photoluminescent
emission bands with a maximum at ca. 411 nm (for 1) and ca.
418 nm (for 2), respectively. The solid-state luminescent emission
bands of 1 and 2 should be assigned to intraligand π−π*
transitions.23 Comparing the slightly different photoluminescence
band centers and shapes, different supramolecular packing in the
polymorphic complexes 1 and 2 should be important, which can
greatly affect photoluminescence emission bands, as revealed in
the previously reported polymorphic zinc(II) compounds.24
Structure and Magnetic Property of [Fe(L)4(NCS)2]2
(3). As shown in Figure 3a, complex 3 contains two mono-
nuclear [Fe(L)4(NCS)2] structural units without solvent
molecules in the crystal lattice. Both crystallographic independent
iron(II) centers (Fe1 and Fe2) are in the octahedron geometry
and coordinated by four terminal monodentate L ligands and
two NCS− anions. All the Fe−N bond lengths (2.296(2),
2.269(2) and 2.170(5) Å) are in accordance with typical high-
spin Fe(II) central ions.25 The distortion angles (ca. 90°) around
the high-spin iron(II) centers indicate that the central iron(II)
ion lies in an ideal octahedral coordination geometry. Weak
C−H···S and C−H···N hydrogen bonds are important for the
3D supramolecular architecture of 3. No π−π stacking inter-
actions between aromatic benzene rings can be observed, which
is quite different from the 3D packing architectures of 1 and 2.
Figure 3b shows the temperature dependence of the molar
magnetic susceptibility multiplied by temperature (χMT) for 3,
where χM is the molar magnetic susceptibility and T is the temp-
erature. At room temperature, the χMT value is 3.54 cm3 mol−1 K,
which corresponds to one uncoupled octahedral Fe(II) d6 center
in the high-spin state. As the temperature is decreased, the χMT
value decreases smoothly to 3.35 cm3 mol−1 K at 35 K and then
more rapidly to reach 2.12 cm3 mol−1 K at 2 K. Fitting the magnetic
susceptibility data with the Curie−Weiss law, χM = C/(T − θ), gave
values of θ = −1.09 K and C = 2.9 cm3 K mol−1, where θ and C
represent the Weiss temperature and Curie constant, respectively.26
Though iron(II) ions have an FeN6 coordination motif in 3, they
do not present any spin-transition magnetic behavior.
RESULTS AND DISCUSSION
■
Structure and Solid-State Photoluminescent Proper-
ties of [Zn(L)2Br2] (1) and [Zn(L)2Br2] (2). Both compounds
1 and 2 crystallize in the space group P2(1)/n with a
crystallographic inversion center locating on the central zinc(II)
ion. The molecular structure is shown in Figure 1; both the
Zn(II) centers in 1 and 2 are in a tetrahedral coordination geom-
etry, which is completed by Br1, Br2, and two nitrogen atoms
(N1 and N4), forming the ZnN2Br2 donor set. Zn−Br and
Zn−N bond distances are listed in Table 2, which fall in the
normal range and are similar to those of previously reported
Zn(II) complexes. In 1 and 2, these CN double bonds of
triazole rings fall into the distance range varying from 1.295(5)
to 1.321(4) Å. These bond distances are similar to those found
in the triazole ligands between 1.2984(17) and 1.2967(17) Å,
indicating the coordination of NTriazole having little effect on the
π−π conjugation of the triazole ring.21 The minimum centroid-
to-centroid distances of aromatic benzene and triazole rings
are 3.757(3) Å for 1 and 3.616(4) Å for 2, respectively,
indicating that typical weak π···π stacking interactions exist in the
crystal structures. Interestingly, these C−H···Br hydrogen-bonding
Structure and Magnetic Property of [Fe2(μ2-L)3(L)2-
(NCS)4]·CH3OH·CH3CH2OH (4). As shown in Figure 4,
complex 4 contains the binuclear Fe(II) fundamental unit,
one CH3OH, and one CH3CH2OH solvent molecule. Its space
group is P212121. The Fe(II) ions (Fe1 and Fe2) are bridged via
D
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a
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1−7
1
Zn(1)−Br(1)
Zn(1)−N(4)
N(1)−Zn(1)−Br(2)
2.3459(8)
2.040(4)
Zn(1)−Br(2)
N(4)−Zn(1)−N(1)
N(4)−Zn(1)−Br(1)
2.3715(8)
100.39(16)
120.16(12)
Zn(1)−N(1)
N(4)−Zn(1)−Br(2)
N(1)−Zn(1)−Br(1)
2.059(4)
107.05(12)
106.97(11)
107.62(11)
2
3
Zn(1)−Br(1)
Zn(1)−N(4)
N(1)−Zn(1)−Br(2)
2.3819(10)
2.033(6)
Zn(1)−Br(2)
N(4)−Zn(1)−N(1)
N(4)−Zn(1)−Br(1)
2.3668(11)
106.3(2)
Zn(1)−N(1)
N(4)−Zn(1)−Br(2)
N(1)−Zn(1)−Br(1)
2.035(6)
111.53(16)
109.44(17)
105.00(16)
103.84(16)
Fe(1)−N(13)
Fe(1)−N(6A)
Fe(2)−N(14)
Fe(2)−N(7)
N(13A)−Fe(1)−N(13)
N(13A)−Fe(1)−N(3)
N(14)−Fe(2)−N(14B)
N(14)−Fe(2)−N(10)
2.123(3)
2.246(2)
2.091(3)
2.269(2)
180.0
Fe(1)−N(13A)
Fe(1)−N(3)
Fe(2)−N(14B)
Fe(2)−N(10)
N(13)−Fe(1)−N(6)
N(13)−Fe(1)−N(3)
N(14)−Fe(2)−N(7)
N(7)−Fe(2)−N(10)
4
2.123(3)
2.259(2)
2.091(3)
2.296(2)
90.24(8)
92.07(9)
87.60(8)
88.41(9)
Fe(1)−N(6)
Fe(1)−N(3A)
Fe(2)−N(7B)
Fe(2)−N(10B)
N(13)−Fe(1)−N(6A)
N(6)−Fe(1)−N(3)
N(7)−Fe(2)−N(7B)
N(7)#2−Fe(2)−N(10B)
2.246(2)
2.259(2)
2.269(2)
2.296(2)
89.76(8)
90.60(8)
180.0
87.93(9)
180.00(11)
91.59(9)
90.91(8)
296 K
Fe(1)−N(18)
Fe(1)−N(5)
Fe(2)−N(16)
Fe(2)−N(7)
N(18)−Fe(1)−N(19)
N(18)−Fe(1)−N(8)
N(5)−Fe(1)−N(11)
N(16)−Fe(2)−N(10)
2.076(7)
2.209(6)
2.077(7)
2.199(6)
92.7(3)
Fe(1)−N(19)
Fe(1)−N(8)
Fe(2)−N(17)
Fe(2)−N(1)
N(18)−Fe(1)−N(13)
N(19)−Fe(1)−N(5)
N(8)−Fe(1)−N(11)
N(16)−Fe(2)−N(7)
2.128(7)
2.217(6)
2.122(7)
2.207(6)
91.3(3)
Fe(1)−N(13)
Fe(1)−N(11)
Fe(2)−N(10)
Fe(2)−N(4)
N(19)−Fe(1)−N(13)
N(13)−Fe(1)−N(5)
N(16)−Fe(2)−N(17)
N(10)−Fe(2)−N(1)
2.179(6)
2.224(6)
2.195(6)
2.212(6)
89.9(3)
178.1(3)
88.3(2)
90.6(3)
177.4(3)
97.0(3)
90.5(2)
88.4(3)
175.6(3)
175.4(3)
100 K
Fe(1)−N(18)
Fe(1)−N(5)
Fe(2)−N(16)
Fe(2)−N(7)
N(5)−Fe(1)−N(11)
N(16)−Fe(2)−N(10)
2.019(8)
2.031(1)
2.098(8)
2.198(7)
88.9(3)
Fe(1)−N(19)
Fe(1)−N(8)
Fe(2)−N(17)
Fe(2)−N(1)
N(8)−Fe(1)−N(11)
N(16)−Fe(2)−N(7)
2.000(5)
2.021(3)
2.124(8)
2.186(7)
89.0(3)
Fe(1)−N(13)
Fe(1)−N(11)
Fe(2)−N(10)
Fe(2)−N(4)
N(16)−Fe(2)−N(17)
N(10)−Fe(2)−N(1)
2.021(1)
2.041(1)
2.211(7)
2.235(7)
94.7(3)
91.1(3)
175.2(3)
177.9(2)
5
Fe(1)−N(16)
Fe(1)−N(11)
Fe(2)−N(19)
Fe(2)−N(13)
N(16)−Fe(1)−N(17)
N(16)−Fe(1)−N(11)
N(16)−Fe(1)−N(14)
N(11)−Fe(1)−N(14)
2.093(5)
2.202(4)
2.092(5)
2.174(4)
92.02(17)
90.92(16)
178.62(17)
88.25(15)
Fe(1)−N(17)
Fe(1)−N(14)
Fe(2)−N(18)
Fe(2)−N(7)
N(16)−Fe(1)−N(2)
N(17)−Fe(1)−N(11)
N(17)−Fe(1)−N(14)
N(16)−Fe(1)−N(4)
6
2.159(5)
2.203(4)
2.113(4)
2.184(4)
91.72(16)
90.27(16)
89.09(16)
88.78(17)
Fe(1)−N(2)
Fe(1)−N(4)
Fe(2)−N(5)
Fe(2)−N(10)
N(17)−Fe(1)−N(2)
N(2)−Fe(1)−N(11)
N(2)−Fe(1)−N(14)
N(17)−Fe(1)−N(4)
2.173(4)
2.232(4)
2.169(4)
2.192(4)
89.06(16)
177.29(16)
89.12(15)
178.65(16)
Fe(1)−N(16)
Fe(1)−N(11)
Fe(2)−N(19)
Fe(2)−N(13)
N(16)−Fe(1)−N(17)
N(16)−Fe(1)−N(11)
N(19)−Fe(2)−N(7)
2.109(5)
2.192(5)
2.095(8)
2.194(6)
95.0(2)
Fe(1)−N(17)
Fe(1)−N(2)
2.124(6)
2.192(5)
2.107(5)
2.198(5)
85.4(2)
Fe(1)−N(4)
Fe(1)−N(14)
Fe(2)−N(7)
Fe(2)−N(5)
N(17)−Fe(1)−N(4)
N(19)−Fe(2)−N(18)
N(18)−Fe(2)−N(13)
2.184(6)
2.223(5)
2.161(5)
2.255(5)
175.18(19)
95.7(2)
Fe(2)−N(18)
Fe(2)−N(10)
N(16)−Fe(1)−N(4)
N(17)−Fe(1)−N(11)
N(19)−Fe(2)−N(13)
7
92.62(19)
93.3(2)
86.4(2)
172.83(19)
91.2(2)
Ni(1)−N(3)
Ni(1)−N(11)
Ni(2)−N(8)
Ni(3)−N(22)
2.060(5)
2.083(5)
2.100(4)
2.050(5)
2.067(5)
90.88(18)
89.35(18)
180.00(15)
90.1(2)
Ni(1)−N(9)
Ni(1)−N(6)
Ni(2)−N(2)
Ni(3)−N(16)
2.064(4)
2.085(5)
2.129(4)
2.060(6)
2.073(5)
178.78(16)
90.21(17)
90.19(17)
178.52(19)
89.5(2)
Ni(1)−O(1)
Ni(1)−N(14)
Ni(2)−N(2)#1
Ni(3)−O(2)
2.070(4)
2.110(4)
2.129(4)
2.067(6)
2.102(5)
90.33(17)
90.53(18)
90.5(2)
Ni(3)−N(19)
Ni(3)−N(30)
Ni(3)−N(26)
N(3)−Ni(1)−N(9)
N(3)−Ni(1)−N(11)
N(5)#1−Ni(2)−N(5)
N(22)−Ni(3)−O(2)
N(16)−Ni(3)−N(19)
N(3)−Ni(1)−O(1)
N(9)−Ni(1)−N(11)
N(5)#1−Ni(2)−N(8)#1
N(16)−Ni(3)−O(2)
O(2)−Ni(3)−N(19)
N(9)−Ni(1)−O(1)
O(1)−Ni(1)−N(11)
N(22)−Ni(3)−N(16)
N(22)−Ni(3)−N(19)
N(22)−Ni(3)−N(30)
89.81(19)
177.2(3)
91.8(2)
a
Symmetry transformations used to generate equivalent atoms: For 3: A −x + 1, −y + 1, −z + 1; B −x, −y + 1, −z + 1. For 7: A −x + 1, −y + 2, −z.
F
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Figure 1. (a) Basic structural unit of 1. (b) 3D packing architecture for 1 viewed along the crystallographic b axis. (c) Basic structural unit of 2. (d)
3D packing architecture for 2 viewed along the crystallographic b axis (purple lines represent C−H···Br weak interactions).
one L ligand and two NCS− anions. The M···M (M = Fe)
separations across three bridging L ligands is 3.998(2) Å. The
terminal Fe−N bond lengths (2.076(7), 2.179(6), 2.207(6),
2.077(7), 2.122(7), and 2.128(7) Å) are shorter than the
central Fe−N bond lengths (2.195(6), 2.199(6), 2.212(6),
2.209(6), 2.217(6), and 2.224(6) Å), all of which indicate that
Fe1 and Fe2 are in the high-spin state at 296 K.27 In the
reaction system of L and iron(II) salts, these nonclassical
O−H···S interactions involving lattice solvent ethanol mole-
cules and these C−H···O, C−H···N, and C−H···S interactions
can be observed (Table S1, Supporting Information).
Intermolecular π−π stacking (3.586(3) Å) also can be observed
between the neighboring benzene groups. These weak
interactions further stabilize the whole framework and extend
4 into a three-dimensional supramolecular architecture.
The comparison of the coordination environment of the
central iron(II) ion in 4, at 100 and 293 K (Figure 5), displays
the structural changes occurring during the spin transition. For
4, at 100 K, the bond distances between the three ligands and
the central iron(II) ion are 2.031(1), 2.041(1), and 2.019(8) Å
Figure 2. Solid-state luminescent emission spectra of 1 and 2 recorded
at room temperature (color code: 1, green; 2, red).
for Fe1−N5, Fe1−N11, and Fe1−N8, respectively. These
values are obviously shorter than these bond distances measured at
296 K, which are 2.209(6), 2.224(6), and 2.217(6) Å, respectively.
three μ2-L ligands forming the binuclear Fe(II) structural unit.
Each central Fe(II) ion has an FeN6 donor set completed by
G
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Figure 3. (a) Basic structural unit of 3. (b) Temperature-dependent magnetic susceptibility for 3.
These decreases in the coordination lengths are consistent with
an incomplete FeII HS/LS transition for which the coordina-
tion distances are shortened by approximately 0.15−0.20 Å.
Furthermore, the volume of the central iron(II) ion decreases
by approximately 20%, which is consistent with the previously
reported data for an HS/LS transition (18−23%).28 Moreover, the
unit cell volume decreases by 395.6(1) Å3, which is also consistent
with the average change usually accompanying a spin transition.29
The variable-temperature magnetic susceptibility data of 4
have been recorded in the 300−2 K range (Figure 4b). At the
temperature of 300 K, the χMT product (7.58 cm3·K·mol−1) can
correspond to two high-spin Fe(II) ions. As the temperature is
decreased, the χMT value decreases between 202 and 50 K to
4.26 cm3·K·mol−1, which can correspond to a gradual S = 2 ↔ S = 0
spin conversion for one central Fe(II) ion, and the other iron(II)
ion still remains in its high-spin state. The T1/2 temperature is
found as 116 K (T1/2 temperature is defined when the high-spin
iron(II) and low-spin iron(II) molar fractions are both equal).
This magnetic result is also in accordance with the low-
temperature crystal structure of 4, which simultaneously contains
low-spin and high-spin iron(II) centers. The continuous decrease
for the χMT value below 50 K may be ascribed to zero-field
splitting and antiferromagnetic coupling of the remaining high-spin
Fe(II) ions. The result can be comparable with the binuclear
Fe(II) complex with 4-2-pyridine-1,2,4-triazole;30 the 4-substituent
groups (pyridine and benzene groups) may have a small effect on
H
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properties may be related to different 4-substituent groups on
the 1,2,4-triazole group (in this work, L presents 4-substituent
aromatic phenyl groups, whereas N-salicylidene-4-amino-
1,2,4-triazole presents the 4-substituted N-salicylidene-4-
amino group).30
Structure and Magnetic Properties of [Fe2(μ2-L)3(L)2-
(NCS)4]·2CH3CH2OH (5) and [Fe2(μ2-L)3(L)2(NCS)4]·
2CH3CH2OH·1.5H2O (6). The structure of complex 5 was
measured at 296 K, which crystallizes in the orthorhombic
P212121 space group. As shown in Figure 6a, the fundamental
unit of complex 5 contains a binuclear structural unit and two
ethanol molecules. Central Fe(II) ions (Fe1 and Fe2) are also
bridged via three μ2-bridging L ligands. The octahedron
geometry for each iron(II) ion is completed by one terminal L
and two NCS− anions. The nearest M···M (M = Fe) separation is
3.971(1) Å, which is slightly shorter than that of 4. The terminal
Fe−N bond lengths (2.092(6), 2.113(0), and 2.184(0) Å) are
shorter in comparison with central Fe−N distances (2.203(5),
2.159(0), and 2.232(0) Å), all of which indicate that Fe1 and Fe2
are located in the high-spin state at 296 K. In the reaction system
of L and Fe(II) salts, these nonclassical O−H···S hydrogen-
bonding interactions involving lattice solvent ethanol molecules
and C−H···O, C−H···N, and C−H···S interactions can be
observed (Table S1, Supporting Information). Intermolecular
π−π stacking (3.727(3) Å) also can be observed between two
neighboring benzene rings. These weak interactions also fur-
ther extend 5 into a three-dimensional supramolecular
framework. It is noted that N−H···O hydrogen-bonding
interactions are not observed; these nonclassical C−H···O,
C−H···N, and C−H···S interactions further extend 5 into a
3D supramolecular framework.
The variable-temperature magnetic susceptibility data of 5
have been recorded in the 300−2 K (Figure 6b). The incomplete
SCO behavior is somewhat similar to that of 4. At room
temperature of 300 K, the χMT value is ca. 7.63 cm3·K·mol−1,
which can correspond to two high-spin Fe(II) ions. As the
temperature is decreased, the χMT value decreases from 230 to
70 K (4.52 cm3·K·mol−1); the result also reveals an incomplete
SCO magnetic behavior (T1/2 = 122 K), which is slightly higher
than that of 4 and may be affected by different solvent molecules
occupied in the lattice (for 4: one methanol and one ethanol
molecule; for 5: two ethanol molecules).
Interestingly, when binuclear iron(II) complex 5 was exposed
in the water atmosphere for 24 h, solvent-induced single
crystal-to-single crystal transformation can be observed;
binuclear iron(II) complex 6 exhibiting antiferromagnetic inter-
actions can be isolated. It is noted that complex 6 crystallizes in
Figure 4. (a) Dinuclear structural unit of 4. (b) Temperature-
dependent magnetic susceptibility for 4.
the magnetic properties of these binuclear Fe(II) compounds,
though the substitute groups have an important effect in some
iron(II) spin-transition systems. It is noted that, recently, the
binuclear Fe(II) coordination compound with triple N1,N2-1,2,4-
triazole bridges has been reported as [Fe2(N-salicylidene-4-amino-
1,2,4-triazole)5(NCS)4]·4MeOH with a complete SCO mag-
netic behavior (T1/2 = 155 K).12 The different bistable magnetic
Figure 5. Comparison of FeN6 coordination environment of 4 at (a) 296 and (b) 100 K indicating that Fe2 is in the high-spin state while Fe1
changes from the high-spin state to the low-spin state, which can be in accordance with an incomplete spin-transition phenomenon.
I
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2Nβ2g2
kT
χMD
=
[exp(J/kT) + 5 exp(3J/kT)
+ 14 exp(6J/kT)
+ 30 exp(10J/kT)]/[1 + 3 exp(J/kT)
+ 5 exp(3J/kT) + 7 exp(6J/kT) + 9 exp(10J/kT)]
in which the symbols g and J have their usual meanings. These
symbols can be determined by minimizing R = ∑(χoMbsd − χMcalcd)2/
Σ(χoMbsd)2; the best fit result is J = −1.19 cm−1 and g = 2.16, and R =
2.5 × 10−3. The solvent effect should be key for the spin-transition
magnetic behaviors in 4 and 5, which also induces different
crystalline space groups for 4, 5 (P2 2 2 ), and 6 (P1). For 4−6,
̅
1
1 1
the χMT values are slightly higher than the theoretical values, which
is likely the result of an orbital contribution to the paramagnetic
susceptibility, as illustrated in the previous literature.32 A similar
comparable χMT value (7.46 cm3 K mol−1) also can be observed in
the binuclear Fe(II) complex [Fe2(N-salicylidene-4-amino-1,2,4-
triazole)5(NCS)4]·4MeOH.12
Structure and Magnetic Property of [Ni3(μ2-L)6(L)4-
(H2O)2](NO3)6·15.5H2O (7). As shown in Figure 8, complex 7
has the linear trinuclear cation [Ni3(L)6(H2O)6]6+ structural
unit, six free nitrate anions, and 15.5 free aqua solvent
molecules. The three nickel(II) ions are linked by six bridging
triazole ligands. For each terminal nickel(II) ion, its octahedral
geometry is completed by three aqua ligands. It is noted that
all the nickel(II) ions lie in a nearly ideal octahedral geometry.
The central Ni(II)−N bond distances are slight longer in com-
parison with the terminal Ni−N bond distances; the selected
bond distances and angles are listed in Table 2, which all fall in
the normal range.33
The variable-temperature magnetic susceptibility measure-
ment for the linear trinuclear complex 7 has been investigated
in the temperature range of 2−300 K. The magnetic plots of 7
are shown in Figure 8. The χMT value is 3.21 cm3 mol−1 K at
300 K, which is close to the spin-only value for a trinickel(II)
coordination compound. As the temperature is decreased,
χMT values gradually decrease to 1.15 cm3 mol−1 K at 2 K; the
result also reveals typical antiferromagnetic interactions
between neighboring nickel(II) ions.33 In general, the magnetic
exchange interactions in centrosymmetric linear trimers can
be illustrated by the isotropic Hamiltonian H = −2J[(S1·S2) +
(S2·S3)] − 2J13(S1·S3), where J13 and J are the exchange
constants between terminal and neighboring metal ions, re-
spectively. The Zeeman part of the Hamiltonian (gμBH(S1 +
S2 + S3)), illustrating the magnetic interactions of the spin system
with the magnetic field applied, is ignored. The spectroscopic
splitting constant g was assumed to be equal for all the individual
ions, and intercluster interactions and zero-field splitting were
assumed to be negligible. In the absence of a clearly defined
exchange pathway between the terminal nickel(II) ions, J13 was
assumed as zero. Under these conditions, the variable-temperature
magnetic susceptibility per mole of nickel(II) ions is calculated as34
Figure 6. (a) Binuclear structural unit of 5. (b) Temperature-
dependent magnetic susceptibility for 5.
the triclinic P1 space group different from that of 5. As shown in
̅
Figure 7a, complex 6 also contains a binuclear iron(II) basic
structural unit, two ethanol solvent molecules, and 1.5 water solvent
molecules. These Fe(II) ions are linked via three μ2-bridging L
ligands forming binuclear structures. The octahedron geometry for
each Fe(II) ion is completed by one L and two NCS− anions. The
Fe1···Fe2 separations across three bridging L ligands is 3.963(6) Å.
The Fe−N bond distances (2.108(7), 2.125(7), 2.185(7), 2.198(5),
2.194(7), and 2.255(7) Å) indicate both Fe1 and Fe2 are in a high-
spin state. Intermolecular π−π stacking (3.709(5) Å) can be
observed between two neighboring benzene rings of L. N−H···O
and O−H···O interactions and C−H···O interactions involving
lattice solvent water molecules extend 6 into a three-dimensional
supramolecular framework (Figure 7b).
2N g2μ 2
3kT
3 + 42e4x + 18e−2x + 15e2x + 3e−6x
A
B
χ =
The χMT vs T plots of 6 are shown in Figure 7c. The χMT
value of 7.59 cm3 mol−1 K at 300 K decreases upon cooling down;
the result also reveals typical antiferromagnetic magnetic behaviors
between two iron(II) ions in the high-spin state. To illustrate the
magnetic behavior of 6, the expression for the magnetic
3 + 7e4x + 8e−2x + 5e2x + 3e−6x + e−4x
where NA is Avogadro’s number, μB is the Bohr magneton, and
χ = J/kT. The variable-temperature magnetic susceptibility can
be fitted using least-squares methods to the theoretical expressions
resulting from the above equation. The best fitting result gives
J = −7.65 cm−1 and g = 2.13. The agreement factor R =
∑(χobsd − χ′cacld)2/∑(χobsd)2 is 1.3 × 10−3. In Figure 8b, the
D
susceptibility χM for a pair of local spin quintets is used. The
̂
̂
expression is deduced from the spin Hamiltonian H = −JSA·SB +
30,31
̂
̂
⃗
gβ(SA + SB)·H, and the expression is
J
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Figure 7. (a) Binuclear structural unit of 6 containing two solvent ethanol molecules and 1.5 lattice solvent water molecules. (b) The 3D hydrogen-
bonded framework of 6 (red lines represent weak interactions involving free solvent ethanol and water molecules). (c) The temperature-dependent
magnetic susceptibility for 6 (the solid line represents the best fit curve).
theoretical prediction of χMT is shown as the solid curve. The
change in slope in the region 1.5 < kT/|J| < 2 (for S = 1) is typical
of linear trimers with an antiferromagnetic exchange interaction
between nearest neighbors.
ca. 2100 cm−1 can be ascribed to the existence of terminal
thiocyanate ligands. Previous examples also reveal that ligand-
directed self-assembly is an effective synthetic strategy to tune
these coordination framework architectures and modify their
functional properties.35 In this work, as shown in Scheme 2 and
listed in Table 3, various different torsion angles between
triazole and aromatic benzene rings can be observed, which also
shows that L can adopt the flexible spatial coordination
geometries and greatly influence the structures and luminescent
or magnetic properties of these zinc(II), iron(II), and nickel(II)
complexes.
Results and Discussion. In summmary, the work
described herein represents a series of new examples of
crystalline zinc(II), iron(II), and Ni(II) complexes with the
4-R-1,2,4-triazole research system. Complexes 1−7 varying
from mononuclear to trinuclear species have been prepared
in H2O/methanol/ethanol mixed-solvent systems with the
4-benzene-1,2,4-triazole organic ligand (L). For the L ligand,
mono- and binuclear iron(II) complexes were isolated in
the presence of thiocyanate; the anion ligand shows medium
coordination ability similar with nitrogen atoms in tri-
azole ligands. For 3−6, the strong FT-IR bands located at
The solvent effect plays the key roles in the self-assembly of
these crystalline Fe(II) coordination compounds. For instance,
Kepert et al. illustrate a nanoporous material,36 in which the
removal of guest solvent molecules can dramatically change the
K
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Figure 8. (a) ORTEP view of the linear trinuclear nickel(II) unit in 7 showing the inversion symmetry. (b) χMT (Δ) versus T plot for 7; the solid
line represents the best fit.
Table 3. Variable Dihedral Angles (deg) between Triazole
and Aromatic Benzene Rings of L for Compounds 1−7
their magnetic behaviors from weak antiferromagnetic inter-
actions to spin transition.
On the other hand, though 5 and 6 share the similar
binuclear iron(II) coordination motifs, as for the magnetic
behaviors, antiferromagnetic interactions and a weak coopera-
tive spin-transition magnetic property can be observed for 6
and 5, respectively. The presence of intermolecular interactions
by hydrogen bonding in 6 (Figure 7c) involving solvent water
molecules may not have a favorable effect on the cooperativity
developed by such binuclear systems. While without water
molecules in the crystal packing in 5, it is possible that the
network was assumed to be more flexible than that in 6 so that
the structural change during SCO can happen. The binuclear
unit in 4−6 can be considered as a suitably basic structural
model of the 1D 1,2,4-triazole-iron(II) SCO coordination
polymers. The spin-transition magnetic behaviors in 4 and 5 may
be due to intra- and intermolecular interactions mediated by 1,2,4-
triazole together with supramolecular interactions existing in the
complex
variable torsion angles of L
17.8 and 43
1
2
3
4
29.3 and 55.1
13.5 and 30.2
296 K
100 K
7.8, 20.6, 29.9 (for μ2-L) and 28.6, 41.2 (for L)
9.6, 18.4, 24.6 (for μ2-L) and 19.0, 31.7 (for L)
8.0, 18.3, 24.6 (for μ2-L) and 29.3, 43.3 (for L)
3.8, 6.9, 29.7 (for μ2-L) and 10.6, 33.2 (for L)
27.8, 29.7, 41.8 (for μ2-L) and 46.9, 65.6 (for L)
5
6
7
magnetic properties. In this study, we found that the
coordination motifs of iron(II) can be tuned from mononuclear
in 3 to binuclear in 4 and 5 by a simple change of reaction
solvents from water to ethanol or a methanol/ethanol mixed-
solvent system. A further such structural difference also leads to
L
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compounds is still a challenge and interesting work; more related
crystalline coordination materials with 4-benzene-1,2,4-triazole
derivates also need to be synthesized and characterized in order
to deeply understand the structural−magneto correlation of these
coordination compounds and finally to prepare interesting
functional materials. We are currently extending this family of
iron(II) complexes and their homologues such as other metal(II)
coordination compounds with L to include different counteranions,
ligand types, solvents of crystallization, and other nuclearity.
Scheme 2. Variable Torsion Angles between Triazole and
Aromatic Benzene Rings of L in 1−7
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic files (CIF) for 1−7, and selected
hydrogen bond lengths [Å] and angles [deg] for 1−7 is listed
in Table S1. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: qsdingbin@aliyun.com (B.D.).
*E-mail: hxxwy@mail.tjnu.edu.cn (Y.W.).
Notes
crystal lattice. We believed that fine-tuning of these type of ligands,
using the appropriate functionalized aromatic groups on the 1,2,4-
triazole-based ligand, could result in a deliberate tuning of SCO
magnetic behaviors and supramolecular organizations of these
molecules and ultimately can allow one to deeply understand the
structural−magneto correlation of these coordination compounds
and finally to prepare interesting functional materials.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Young Scientist Fund (Grant
Nos. 21301128 and 21001080), the Natural Science
Foundation of Tianjin (Grant No. 11JCYBJC03600), and
Tianjin Normal University (Grant No. 5RL090).
CONCLUSIONS AND PERSPECTIVES
■
REFERENCES
In summary, based on the 4-substituted 1,2,4-triazole derivate
ligand 4-benzene-1,2,4-triazole (L), a series of crystalline coordina-
tion complexes varying from mononuclear to trinuclear species,
namely, [Zn(L)2Br2] (1), [Zn(L)2Br2] (2), [Fe(L)4(NCS)2]2 (3),
[Fe2(μ2-L)3(L)2(NCS)4]·CH3OH·CH3CH2OH (4), [Fe2(μ2-L)3-
(L)2(NCS)4]·2CH3CH2OH (5), [Fe2(μ2-L)3(L)2(NCS)4]·
2CH3CH2OH·1.5H2O (6), and [Ni3(μ2-L)6(L)4(H2O)2](NO3)6·
15.5H2O (7), have been isolated. 1 and 2 present temperature-
induced polymorphic phenomenon of two zinc(II) coordination
complexes with L. The solvent effect plays the key role in the self-
assembly of these Fe(II) compounds 3−6: 3 contains mononuclear
Fe(L)4(NCS)2 units without spin-transition behavior, whereas
both 4 and 5 present binuclear iron(II) complexes with three
N1,N2-1,2,4-triazole bridges exhibiting incomplete spin-transition
behavior. The low-temperature X-ray structural analysis (100 K) of
4 also reveals that one of the Fe(II) centers is located at the low-
spin (LS) state and the other Fe(II) center is located at the high-
spin (HS) state. Interestingly, when binuclear iron(II) complex 5
was exposed in the solvent water atmosphere, solvent-induced single
crystal-to-single crystal transformation can be observed; binuclear
iron(II) complex 6 exhibiting antiferromagnetic interactions was
isolated. Further, a trinuclear nickel(II) compound can be isolated
when nickel(II) salts were used to react with L. Variable-
temperature magnetic susceptibility measurement (2−300 K)
reveals antiferromagnetic interactions in 7. The polymorphic
phenomenon (1 and 2), incomplete spin-transition phenomenon
(4 and 5), and single crystal-to-single crystal transformation (from 5
to 6) also reveal great potential in the construction of these novel
functional materials with L. Because there are still a few examples for
these binuclear Fe(II) crystalline complexes with 4-R-trz-based
organic ligands, the construction of these Fe(II) crystallization
■
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