Synthesis, crystal structures, and magnetic properties of three iron(II) complexes with 3-(p -bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2,4-triazole

Article abstract of DOI:10.1080/00958972.2013.877585

Three iron(II) complexes with 3-(p-bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2, 4-triazole (L), trans-[FeL₂(NCS)₂] (1), trans-[FeL ₂(NCS)₂]·2MeOH (1·2MeOH), and trans-[FeL₂(NCSe)₂] (2), have been synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and single crystal X-ray crystallography. Crystallographic studies reveal that all the complexes contain a distorted octahedral [FeN₆] core with two trans NCS(Se)^- ions. Each L adopts a chelating bidentate coordination via one N of pyridyl and one N of triazole. Magnetic susceptibility measurement indicated that both 1 and 1·2MeOH are in a high-spin state from 2 to 300 K. 2014

Full text of DOI:10.1080/00958972.2013.877585

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Synthesis, crystal structures, and
magnetic properties of three iron(II)
complexes with 3-(p-bromophenyl)-4-
phenyl-5-(2-pyridyl)-1,2,4-triazole
Xin Hea, Dong-Yong Caoa, Jing-Jing Jianga, Xuan Shena & Dun-Ru
Zhua
a State Key Laboratory of Materials-oriented Chemical
Engineering, College of Chemistry and Chemical Engineering,
Nanjing Tech University, Nanjing, PR China
Accepted author version posted online: 23 Dec 2013.Published
Click for updates
online: 20 Jan 2014.
To cite this article: Xin He, Dong-Yong Cao, Jing-Jing Jiang, Xuan Shen & Dun-Ru Zhu (2014)
Synthesis, crystal structures, and magnetic properties of three iron(II) complexes with 3-(p-
bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2,4-triazole, Journal of Coordination Chemistry, 67:2,
227-235, DOI: 10.1080/00958972.2013.877585
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Journal of Coordination Chemistry, 2014
Vol. 67, No. 2, 227–235, http://dx.doi.org/10.1080/00958972.2013.877585
Synthesis, crystal structures, and magnetic properties of three
iron(II) complexes with 3-(p-bromophenyl)-4-phenyl-5-(2-
pyridyl)-1,2,4-triazole
XIN HE, DONG-YONG CAO, JING-JING JIANG, XUAN SHEN and DUN-RU ZHU*
State Key Laboratory of Materials-oriented Chemical Engineering, College of Chemistry and
Chemical Engineering, Nanjing Tech University, Nanjing, PR China
(Received 8 October 2013; accepted 5 December 2013)
Three iron(II) complexes with an asymmetrically 3,4,5-triarylsubstituted 1,2,4-triazole, [FeL2(NCS)2]
(1),[FeL2(NCS)2]∙2MeOH (1∙2MeOH) and [FeL2(NCSe)2](2), have been synthesized and character-
ized by singlecrystal X-ray crystallography.
Three iron(II) complexes with 3-(p-bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2,4-triazole (L),
trans-[FeL2(NCS)2] (1), trans-[FeL2(NCS)2]·2MeOH (1·2MeOH), and trans-[FeL2(NCSe)2] (2),
have been synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and single crystal
X-ray crystallography. Crystallographic studies reveal that all the complexes contain a distorted octa-
hedral [FeN6] core with two trans NCS(Se)− ions. Each L adopts a chelating bidentate coordination
via one N of pyridyl and one N of triazole. Magnetic susceptibility measurement indicated that both
1 and 1·2MeOH are in a high-spin state from 2 to 300 K.
Keywords: Synthesis; Triazole; Crystal structure; Iron(II) complex
*Corresponding author. Email: zhudr@njtech.edu.cn
© 2014 Taylor & Francis

228
X. He et al.
1. Introduction
Over the past decade, coordination of triaryltriazoles and related ligands has attracted
attention due to versatile structures and the intriguing magnetic properties of their resulting
transition metal complexes [1–3]. Some iron(II) complexes with triaryltriazole ligands show
interesting spin crossover (SCO) properties which can be applied in molecular electronics,
memory devices, information storage, and switching materials [4, 5].
Recently, some 4-arylsubstituted 3,5-di(2-pyridyl)-1,2,4-triazoles and their metal
complexes have been prepared [6–12]. However, complexes with asymmetrically 3,4,5-
triarylsubstituted 1,2,4-triazole have been little studied [13]. As a continuation of our inves-
tigation of asymmetrically substituted triaryltriazole [14–19], we present here the synthesis
of three iron(II) complexes, [FeL2(NCS)2] (1), [FeL2(NCS)2]·2MeOH (1·2MeOH), and
[FeL2(NCSe)2] (2) with 3-(p-bromophenyl)-4-phenyl-5-(2-pyridyl)-1,2,4-triazole (L) [20].
Their molecular structures were investigated by single-crystal X-ray diffraction and their
magnetic properties were explored by variable-temperature magnetic susceptibility. The
influence of the solvent, the different co-ligands, and intermolecular interactions on the
crystal packing and magnetic behavior are also discussed. All the complexes contain a simi-
lar [FeN6] octahedral geometry with two trans NCS(Se)− groups. Compared to 1, complex
1·2MeOH contains two MeOH molecules, whereas complex 2 has two different co-ligands.
2. Experimental
2.1. Materials and measurements
All chemicals used were of analytical grade. Solvents were purified by conventional
methods. L was synthesized using a modified method [20]. Elemental analyses were carried
out with a Thermo Finnigan Flash 1112A elemental analyzer. IR spectra were recorded on a
Nicolet Avatar 380 FT-IR instrument with KBr pellets from 4000 to 400 cm−1. Electrospray
ionization mass spectra (ESI-MS) were recorded with a LCQ ADVANTAGE MAX mass
spectrometer, with MeOH on the mobile phase; the flow rate of the mobile phase was
0.2 cm3 min−1. The spray voltage was 4 kV and the capillary voltage was 40 V. The temper-
ature dependence of the magnetic susceptibility for 1 and 1·2MeOH were measured on a
Quantum Design MPMS-7 SQUID magnetometer from 2 to 300 K under 2000 Oe of
external field. Diamagnetic correction was made with Pascal’s constants.
2.2. Syntheses and characterization of 1 and 2
To a solution of KSCN (0.8 mmol) in anhydrous MeOH (4 mL) was added a solution of
FeSO4·7H2O (0.4 mmol) in MeOH (3 mL). The mixture was stirred for 30 min, the K2SO4
precipitate was filtered off and then washed with 3 mL of anhydrous MeOH. The methano-
lic fractions containing Fe(SCN)2 were collected and then were poured into a methanol
solution of L (0.8 mmol). The resulting solution was stirred for 1.5 h during which an
orange precipitate formed, which was isolated by filtration, washed with H2O, and dried
thoroughly in vacuo to give [FeL2(NCS)2] (318.7 mg, 86%) as an orange powder.
Complex 1. Red single crystals suitable for X-ray diffraction were obtained by evapora-
tion from an acetone and n-butyl alcohol (1 : 1) solution of [FeL2(NCS)2] under argon.

Iron(II) triazole complex
229
Anal. Calcd for C40H26Br2FeN10S2 (%): C, 51.85; H, 2.83; N, 15.12; S, 6.92. Found (%):
C, 51.73; H, 2.67; N, 15.01; S, 7.11. FT-IR (cm−1): 2061(s), 1600(m), 1570(m), 1497(m),
1476(m), 1460(m), 1396(m), 1076(m), 837(m), 795(m), 737(w). ESI-MS: m/z = 868.2,
777.4, 379.2.
Complex 1·2MeOH. Orange single crystals suitable for X-ray diffraction were obtained
by evaporation from a methanol solution of [FeL2(NCS)2] under argon. Anal. Calcd for
C42H34Br2FeN10O2S2 (%): C, 50.93; H, 3.46; N, 14.14; S, 6.47. Found (%): C, 50.74; H,
3.27; N, 14.32; S, 6.64. FT-IR (cm−1): 3426(m,b), 2920(w), 2848(w), 2060(s), 1598(m),
1572(m), 1496(m), 1477(m), 1463(m), 1395(m), 1076(m), 838(m), 794(m), 741(w).
ESI-MS: m/z = 868.2, 777.4, 379.2.
Complex 2. The complex was obtained following the same method as for 1 except
replacing KSCN with KSeCN. An orange powder of 2 was obtained in a yield of 88.2%.
Single crystals suitable for X-ray diffraction were obtained by evaporation from a methanol
solution under argon. Anal. Calcd for C40H26Br2FeN10Se2 (%): C, 47.09; H, 2.57; N, 13.73.
Found (%): C, 47.28; H, 2.37; N, 13.42. FT-IR (cm−1): 2065(s), 1598(m), 1496(m), 1476
(m), 1395(m), 1075(m), 838(m), 795(m), 742(m). ESI-MS: m/z = 915.2, 777.2, 401.3, 379.4.
2.3. Crystal structure determination
Crystals of 1, 1·2MeOH and 2 were selected for lattice parameter determination and
collection of intensity data at 296 K on a Bruker Smart APEX II CCD diffractometer with
monochromated Mo Kα radiation (λ = 0.71073 Å) using a ϕ‒ω scan mode. The structures
were solved by direct methods and refined on F2 by full matrix least-squares using
SHELXTL [21]. All non-hydrogen atoms were refined anisotropically. Hydrogens for C−H
were placed in calculated positions and allowed to ride on the parent to which they are
attached. The contribution of these hydrogens was included in the structure factor
Table 1. Crystal data and structure refinements for 1–2.
Complex
1
1·2MeOH
2
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C40H26Br2FeN10S2
926.50
Monoclinic
P21/c
9.917(5)
8.546(4)
23.555(11)
90.551(7)
1996.1(17)
2
1.541
2.527
C42H34Br2FeN10O2S2
990.58
Monoclinic
P21/c
9.311(18)
16.18(3)
14.44(3)
102.54(3)
2122(7)
2
1.550
2.386
C40H26Br2FeN10Se2
1020.30
Monoclinic
P21/c
11.0863(13)
8.1863(10)
22.494(3)
95.302(2)
2032.7(4)
2
b (Å)
c (Å)
β (°)
V (Å3)
Z
DCalcd (g cm−3
)
1.667
4.170
1000
μ (mm−1
F (000)
)
928
1000
Crystal size (mm)
θ Range
0.16×0.13×0.10
1.73−25.00
13,764
3518 [Rint =0.057]
2346
3518/12/250
0.975
0.0377/0.0715
0.0735/0.0788
0.293, −0.387
0.18×0.14×0.12
1.9−25.00
14,439
3737 [Rint =0.0897]
2332
3737/6/271
1.000
0.0577/0.1456
0.1013/0.1664
0.635, −0.593
0.13×0.10×0.08
1.82−25.00
14,027
3580 [Rint =0.0619]
2191
3580/0/250
1.009
0.0451/0.1014
0.0920/0.1154
0.654, −0.786
Reflections collected
Independent reflections
Reflections observed [I >2σ(I)]
Data/restraints/parameters
Goodness-of-fit on F2
R/wR [I >2σ(I)]
R/wR (all data)
Max., Min. Δρ (e·Å−3
)

230
X. He et al.
Table 2. Selected bond distances (Å) and angles (°) for 1–2.
Complex
1
1·2MeOH
2
Fe1‒N1
Fe1‒N2
Fe1‒N5
N5‒C20
C20‒S1(Se1)
Br1‒C11
2.214(3)
2.134(3)
2.137(3)
1.156(4)
1.621(4)
1.896(3)
2.163(5)
2.137(5)
2.118(6)
1.143(6)
1.617(6)
1.865(6)
2.208(4)
2.131(4)
2.144(5)
1.132(6)
1.799(7)
1.898(5)
N1‒Fe1‒N2
N1‒Fe1‒N5
N2‒Fe1‒N5
N5‒C20‒S1(Se1)
Fe1‒N5‒C20
74.80(10)
86.21(11)
84.27(11)
179.2(4)
74.9(2)
90.80(19)
95.09(19)
177.8(5)
154.3(5)
75.21(15)
87.41(16)
87.33(16)
177.3(5)
148.5(3)
150.6(5)
calculations. Crystallographic data are summarized in table 1. Selected bond lengths and
angles for 1, 1·2MeOH and 2 are listed in table 2.
3. Results and discussion
3.1. Synthesis
L reacts with iron(II) and KNCS(Se) in molar ratio 2 : 1 : 2 to form three mononuclear iron
(II) complexes, trans-[FeL2(NCX)2], 1 (X = S), 1·2MeOH (X = S), and 2 (X = Se), which
are stable in air. The elemental analyses were satisfactory and indicate that all the
complexes contain one iron(II), two triazole ligands and two NCS(Se)– except 1·2MeOH
has two MeOH molecules.
3.2. Crystal structures of 1, 1·2MeOH, and 2
The crystal structures of 1, 1·2MeOH, and 2 were determined by X-ray crystallography,
and all the complexes crystallize in the monoclinic space group P21/c and have similar
mononuclear structure (figure 1). There is an inversion center at iron(II). Each Fe(II) is
coordinated by four nitrogens from two L in the equatorial plane and two nitrogens from
two NCS(Se)– in the axial positions to form a distorted octahedron. Each L coordinates to
Fe(II) via N1 of pyridyl and N2 of the triazole, similar to those observed in related triazole-
based iron(II) complexes [5, 22, 23]. In 1, 1·2MeOH, and 2, the average Fe–N bond length
is 2.162, 2.139, and 2.161 Å, respectively, within the typical range for high-spin Fe(II)–N
(2.051–2.248 Å) [23]. The spin-state assignment based on the Fe(II)–N bond distance is
associated with octahedral distortion parameter (Σ), which is commonly used for quantifica-
tion of the angular deviation of an octahedron from ideal [24]. A smaller Σ value is
generally related with a stronger ligand field and, therefore, a low spin state of the metal
ion, while the opposite suggests a high-spin state [24, 25]. In the present case, Σ of 1 and
1·2MeOH are 85.2° and 87.5°, respectively, suggesting that the Fe(II) center is in a
high-spin state at 296 K (vide infra). The Fe–Npy distance in all the complexes is always
larger than Fe–Ntrz, consistent with those found in the analogous triazole-based Fe(II)

Iron(II) triazole complex
231
Figure 1. Projection of the structures of 1–2 with the atomic labeling system. Hydrogens are omitted for clarity.
complexes [4, 5, 22, 26–29]. The dihedral angle between pyridyl and triazole ring in 1,
1·2MeOH, and 2 are 7.0°, 16.2°, and 4.2°, respectively, smaller than (35.3°) in free L [20].
Compared to free L (25.2°), the p-bromophenyl-triazole twist angle in 1 and 2 is larger
(44.5° and 45.4°), while that (22.7°) in 1·2MeOH becomes smaller due to the influence of
CH3OH. In addition, the Fe1–N6–C14 angle in 1·2MeOH is slightly larger than those in 1
and 2 (table 2).
Table 3. Hydrogen-bond geometry, C–H···π and π···π interactions (Å, °) for 1–2.
Complex
D–H···A
d(D–H)
d(H···A)
d(D···A)
\D–H···A
1
C1‒H1A···N3ii
0.93
0.93
0.93
2.77
2.74
2.97
3.03
3.564
3.392
3.869
3.832
144
127
162
145
C10‒H10A···N5i
C19i‒H19Ai···Br1
C5‒H5A···π (C14‒C19)
π···π interaction
0.93
cent···cent (Å)
3.899
π···π (Å)
3.750
dihedral angle (°)
π (Ph‒Br)···π (Ph‒Br)iii
O1‒H1B ···S1vi
0
157
145
159
1·2MeOH
0.82
0.93
0.93
0.93
2.42
2.69
2.86
2.46
3.188
3.492
3.741
3.154
C1‒H1A···N3iv
C2‒H2A···S1v
C3‒H3A···O1
131
π···π interaction
cent···cent (Å)
3.921
0.93
0.93
cent···cent (Å)
3.774
π···π (Å)
dihedral angle (°)
π (Ph‒Br)···π (py)vii
C10ix‒H10Aix···Br1viii
C15‒H15A···Br1ix
π···π interaction
–
10.5
137
153
2
2.996
2.972
3.732
3.827
π···π (Å)
3.554
dihedral angle (°)
0
π (Ph‒Br)···π (Ph‒Br)viii
Symmetry codes: (i) 2 – x, –y, –z; (ii) 2 – x, –1 – y, –z; (iii) 1 – x, –y, –z; (iv) 2 – x, 1 – y, 1 – z; (v) 3 – x, 1 – y, 1 – z; (vi) x, 1/2 – y, 1/
2 + z; (vii) x – 1, y, z; (viii) 2 – x, 2 – y, 1 – z; (ix) –x, y – 1, z.

232
X. He et al.
Figure 2. Hydrogen bonding and C–H···π interactions in 1 and 1·2MeOH.
Figure 3. Hydrogen bonding and C–H···π interaction in 2.
There are three kinds of hydrogen bonds [C1–H1A···N3ii, C10–H10A···N5i, and
C19i–H19Ai···Br1], a kind of C–H···π [C5–H5A···π (C14–C19)] and one face-to-face
π···π interaction [π (Ph-Br)···π (Ph-Br)iii] in the structure of 1 (table 3). Due to the presence
of CH3OH in 1·2MeOH, there are four kinds of hydrogen bonds [O1–H1B···S1vi,
C1–H1A···N3iv, C2–H2A···S1v, C3–H3A···O1], and one weak face-to-face π···π
interaction [π (Ph-Br)···π (py)vii], linking the molecules of 1·2MeOH to form a 1-D chain
along the c axis (figure 2). In 2, there are only two kinds of hydrogen bonds
[C10ix–H10Aix···Br1vii, C15–H15A···Br1ix], and one strong face-to-face π···π interaction
[π (Ph-Br)···π (Ph-Br)ix], connecting the molecules of 2 to form a 2-D framework (figure 3).
3.3. IR spectra
In 1, 1·2MeOH, and 2, strong bands at 2061, 2060, and 2065 cm−1 are assigned to C≡N
stretches of two trans-coordinated NCS(Se)– groups, respectively [4, 22]. Bands at 1076,
1076, and 1075 cm−1 are attributed to stretch of C(Ph)–Br bond in 1, 1·2MeOH, and 2,
respectively [30]. In addition, a broad band at 3426 cm−1 in 1·2MeOH is due to the O‒H
stretch of MeOH. These features are in agreement with the results of X-ray crystallography
analyses.

Iron(II) triazole complex
233
Figure 4. ESI-MS spectra of 1–2 in methanol solution.
3.4. Electrospray ionization mass spectra
The structures of 1, 1·2MeOH, and 2 in solution were also studied by ESI-MS [31, 32].
Figure 4 displays the positive ESI mass spectra of the three complexes in methanol. The
ESI-MS of 1 and 1·2MeOH are similar, the base peak at m/z 868.2 is [FeL2(NCS)]+ and the
−1
Figure 5. Plots of χM (ꢀ) vs. T and χM (ꢀ) vs. T for 1 and 1·2MeOH. Solid red line represents the best linear fit
(see http://dx.doi.org/10.1080/00958972.2013.877585 for color version).

234
X. He et al.
peaks at 777.4 and 379.2 are [NaL2]+ and [L + H]+, respectively. In 2, four main peaks were
observed; the base peak at 777.2 is [NaL2]+, and the peaks at m/z 915.2, 401.3, and 379.4
are [FeL2(NCSe)]+, [L + Na]+, and [L + H]+ ion, respectively.
3.5. Magnetic properties of 1 and 1·2MeOH
The temperature dependences of the magnetic susceptibilities of 1 and 1·2MeOH were
−1
measured on the crystalline sample at an applied field of 2000 Oe. The χM and χM versus
T plots are shown in figure 5. The results show that both 1 and 1·2MeOH remained in a
high-spin state from 2 to 300 K, which indicates that the crystal-field splitting energy
(Δ = 10 Dq) is lower than the electron pairing energy (P). The results are also consistent
with the octahedral distortion parameter (Σ). In accord with the Curie–Weiss law,
−1
χM = C/(T‒θ), the data for 1 and 1·2MeOH exhibit a good linear relationship between χM
and T with a Curie value of 3.45(1) cm3 mol−1 K for 1 and 3.59(1) cm3 mol−1 K for
1·2MeOH, and Weiss constant of –1.9(5) K for 1 and –1.8(3) K for 1·2MeOH. The results
are in agreement with those found in trans-[FeL′2(NCS)2] (L′ = 4-amino-3-(p-bromophe-
nyl)-5-(2-pyridyl)-1,2,4-triazole) [23]. Recently, we reported that the transition modes
and temperature of a family of mononuclear iron(II) SCO complexes, trans-[Fe(L1‒
L4)2(NCS)2] (L1‒L4 = triaryltriazole), can be tuned by remote substituent effects [5].
Compared to trans-[Fe(L4)2(NCS)2] (L4 = 3-(p-fluorophenyl)-4-(p-methylphenyl)-5-(2-
pyridyl)-1,2,4-triazole) displaying an incomplete (70%) spin transition with T1/2 = 97 K, 1
and 1·2MeOH are still high-spin species, revealing that after both p-fluorophenyl at the
3-position and p-methylphenyl at the 4-position of L4 are replaced simultaneously by
p-bromophenyl and phenyl group, the ligand field strength resulting from L cannot be
shifted to the region of SCO for Fe(II) complexes with NCS– as co-ligands.
4. Conclusion
Three mononuclear iron(II) complexes, trans-[FeL2(NCS)2] (1), trans-[FeL2(NCS)2]·2-
MeOH (1·2MeOH), and trans-[FeL2(NCSe)2] (2), with 3-(p-bromophenyl)-4-phenyl-5
(2-pyridyl)-1,2,4-triazole (L), have been synthesized and characterized by elemental analy-
sis, FT-IR, ESI-MS, and single crystal X-ray diffraction. Crystallographic studies reveal that
1, 1·2MeOH, and 2 possess a similar distorted octahedral [FeN6] core with two trans NCS
(Se)– anions. Each L coordinates to iron(II) via N1 of the pyridyl ring and N2 of the
triazole. Both 1 and 1·2MeOH are high-spin species from 2 to 300 K. Their paramagnetism
is similar to that observed in a related triazole-based iron(II) complex, [Cd2.98Fe2.02
(atrz)6(SCN)10]·2H2O (atrz = 4-amino-1,2,4-triazole) [33].
Supplementary material
Crystallographic data for the structures reported in this article have been deposited with the
Cambridge Crystallographic Data Center as supplementary publication Nos. CCDC 961234
(1), 961235 (1·2MeOH), and 961236 (2). Copies of the data can be obtained free of charge
via www.ccdc.cam.ac.uk (or from the Cambridge Crystallographic Center, 12 Union Road,
Cambridge CB21EZ, UK; Fax:+44 1223 336033; E-mail: deposit@ccdc.cam.ac.uk).

Iron(II) triazole complex
235
Funding
This work was funded by the National Nature Science Foundation of China [grant numbers
20771059 and 21171093].
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