High-spin tetranuclear iron(III) grids: Synthesis, crystal structure and magnetic properties

Article abstract of DOI:10.1016/j.poly.2012.07.014

Three new tetranuclear Fe^III complexs Fe₄L ¹₄Cl₄ (1), Fe₄L² ₄(ClO₄)₄ (2), Fe₄L³ ₄Cl₄5H₂O (3) and a binuclear complex Fe ₂L⁴(MeOH)₂Cl₄3MeOH (4) (the bis-Schiff base ligands H₂L^1-4 were obtained by the condensation of 2,4-dihydrazinopyrimidine and salicylicaldehyde or acetylacetone in a molar ratio of 1:2) have been synthesized and characterized by crystallography, spectroscopy and magnetic measurements. The tetranuclear 2 × 2 grid complex 1 crystallizes in a monoclinic space group C2/c with a = 29.040(3) A?, b = 10.9525(11) A?, c = 26.881(3) A?, β = 105.172(2)°, V = 8251.9(15) A?³. Complex 2 crystallizes in a monoclinic space group P2₁ with a = 12.536(3) A?, b = 23.148(5) A?, c = 17.506(4) A?, β = 102.96(3)°, V = 4950.6(17) A?³, and complex 3 in a triclinic space group P1? with a = 12.145(2) A?, b = 29.094(6) A?, c = 29.343(6) A?, α = 94.12(3)°, β = 93.17(3)°, γ = 97.62(3)°, V = 10228(4) A?³. All the Fe^III ions from 1, 2 and 3 are coordinated by an N₄O₂ sphere with two N atoms from pyrimidine, two N atoms from hydrazine, and two O atoms from phenoxo groups. Complex 4 has a binuclear structure crystallized in a triclinic space group P1? with a = 10.500(2) A?, b = 11.053(2) A?, c = 15.990(3) A?, α = 82.20(3)°, β = 89.64(3)°, γ = 70.77(3)°, V = 1734.4(6) A?³. Magnetic susceptibility measurements indicate that the Fe(III) ions are all high spin, and adjacent Fe(III) ions are weakly antiferromagnetically coupled via pyrimidine in complexes 1, 2, 3 and 4. Magneto-structural correlation studies show that a longer Fe-N_pym bond distance corresponds to a weaker antiferromagnetic coupling.

Full text of DOI:10.1016/j.poly.2012.07.014

Polyhedron 52 (2013) 970–975
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
High-spin tetranuclear iron(III) grids: Synthesis, crystal structure
and magnetic properties
⇑
Yi-Tong Wang, Ai-Li Cui, De-Zhong Shen, Hui-Zhong Kou
Department of Chemistry, Tsinghua University, Beijing 100084, PR China
a r t i c l e i n f o
a b s t r a c t
Three new tetranuclear FeIII complexs Fe4L14Cl4 (1), Fe4L24(ClO4)4 (2), Fe4L34Cl45H2O (3) and a binuclear
complex Fe2L4(MeOH)2Cl43MeOH (4) (the bis-Schiff base ligands H2L1–4 were obtained by the condensa-
tion of 2,4-dihydrazinopyrimidine and salicylicaldehyde or acetylacetone in a molar ratio of 1:2) have been
synthesized and characterized by crystallography, spectroscopy and magnetic measurements. The tetra-
nuclear 2 ꢀ 2 grid complex 1 crystallizes in a monoclinic space group C2/c with a = 29.040(3) Å,
b = 10.9525(11) Å, c = 26.881(3) Å, b = 105.172(2)°, V = 8251.9(15) Å3. Complex 2 crystallizes in a mono-
clinic space group P21 with a = 12.536(3) Å, b = 23.148(5) Å, c = 17.506(4) Å, b = 102.96(3)°,
Article history:
Available online 20 July 2012
Dedicated to Alfred Werner on the 100th
Anniversary of his Nobel prize in Chemistry
in 1913.
Keywords:
Fe(III) ions
Magnetic properties
Crystal structure
Grid
3
ꢀ
V = 4950.6(17) Å , and complex 3 in a triclinic space group P1 with a = 12.145(2) Å, b = 29.094(6) Å,
c = 29.343(6) Å,
a = 94.12(3)°, b = 93.17(3)°, c
= 97.62(3)°, V = 10228(4) Å3. All the FeIII ions from 1, 2 and
3 are coordinated by an N4O2 sphere with two N atoms from pyrimidine, two N atoms from hydrazine,
and two O atoms from phenoxo groups. Complex 4 has a binuclear structure crystallized in a triclinic space
Tetranuclear complexes
ꢀ
group P1 with a = 10.500(2) Å, b = 11.053(2) Å, c = 15.990(3) Å,
a = 82.20(3)°, b = 89.64(3)°, c = 70.77(3)°,
V = 1734.4(6) Å3. Magnetic susceptibility measurements indicate that the Fe(III) ions are all high spin,
and adjacent Fe(III) ions are weakly antiferromagnetically coupled via pyrimidine in complexes 1, 2, 3
and 4. Magneto-structural correlation studies show that a longer Fe–Npym bond distance corresponds to
a weaker antiferromagnetic coupling.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
from tridentate Schiff base ligands HL with N2O donors exhibit
SCO behavior [16–22]. We are interested in the assembly of mono-
To design well-defined molecular architectures and arrange the
ligands and metal ions in a predictable position is a challenging goal
in inorganic supramolecular chemistry [1]. Grid-type complexes
are one of those important structure models which stand on the
intersectional field of supramolecular chemistry and coordination
chemistry [2]. The regular arrangement of metal ions has been con-
sidered applicable to high-density information storage [3]. The
well-defined architectures are constructed from the assembly of
appropriate ligands induced by metal ions, scaled from 2 ꢀ 2 to
4 ꢀ 4 and even n ꢀ n (n = 6, 8, 10) [4], and some heterometallic tet-
ranuclear grids show interesting spin crossover (SCO) and single-
molecule magnet (SMM) behavior [5–10]. Several grid-like Fe(II)
complexes showed novel bistable or multi-stable spin-crossover
phenomenon [11], which provides an interesting way in attaining
molecular switching [12]. Among the large number of grid-like
complexes, complexes with SCO phenomenon were all centered
by FeII ions and with N6 coordination sphere [13–15]. Meanwhile,
it has been found that many mononuclear FeIII complexes derived
nuclear Fe(III) species to multinuclear, especially grid-like tetranu-
clear complexes, and wish to learn how the Fe(III) ions magnetically
couple and whether the SCO property retains in the multinuclear
complexes. The ligands H2Lx (x = 1–4) used for the synthesis of grid
FeIII complexes are shown in Scheme 1. We herein report three
2 ꢀ42 grid-like complexes with N4O2 coordination sphere for FeIII
ion. The complexes were characterized by X-ray crystallography,
spectroscopy, and magnetic measurements.
2. Results and discussion
2.1. Spectroscopy
The ESI-MS data for 1, 2 and 3 dissolved in CH3OH/H2O were stud-
ied (Supporting Information, Fig. S1–S3).L For complex 1, the ESI-MS
shows peaks (m/z) at 653.2 that corresponds to [Fe2L1Cl5H2O]ꢁ,
781.30 corresponding to [Fe(HL1)2(CH3OH)]+, and 437.31 for
[Fe4L14Cl4]4+ (tetranuclear grid). The ESI-MS data for complex 2 in
CH3OH/H2O display m/z peaks at 386.40 corresponding to
⇑
[Fe4L2 4+, 718.44 to [Fe(HL2)2]+, and 871.51 to [Fe4L2 (ClO4)2]2+
]
Corresponding author.
E-mail address: kouhz@mail.tsinghua.edu.cn (H.-Z. Kou).
4
4
(tetranuclear grid). For complex 3 in CH3OH/H2O, ESI-MS shows
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.07.014

Y.-T. Wang et al. / Polyhedron 52 (2013) 970–975
971
Table 1
Crystallographic data for complexes 1, 2 and 4.
1
2
4
Formula
Fw
T (K)
C
72H64N24O8Cl4Fe4 C64H88N24O24Cl4Fe4 C25H38N6O7Cl4Fe2
1750.61
293
1942.78
293
788.11
143
Crystal
monoclinic
monoclinic
triclinic
system
Space group
ꢀ
C2/c
P2(1)
P1
a (Å)
b (Å)
c (Å)
29.040(3)
10.9525(11)
26.881(3)
90
105.172(2)
90
12.536(3)
23.148(5)
17.506(4)
90
102.96(3)
90
10.500(2)
11.053(2)
15.990(3)
82.20(3)
89.64(3)
70.77(3
1734.4(6)
2
Scheme 1. The chemical structure of ligands H2L1–4
.
a
(°)
b (°)
c
(°)
V (Å3)
Z
8251.9(15)
4
4950.6(17)
2
m/z peaks at 870.30 that should be assigned to [Fe(HL3)2]+, and
532.23 to [Fe4(L3)4Cl8]4ꢁ. The results indicate that the mononuclear
species [Fe(HLx)2]+ forms when the tetranuclear complexes are
dissolved in methanol–H2O solution.
qcalc
1.409
1.303
1.509
(g cmꢁ3
)
l
(mmꢁ1
)
0.711
2284
0.756
11249
1.193
4194
Observed
data
[I > 2
Goodness-
of-fit
r
(I)]
2.2. Structural descriptions
1.021
1.033
1.000
Crystal data and structure refinement details for complexes 1, 2
and 4 are listed in Table 1, and important structural parameters of
the three complexes are collected in Tables 2–4. The crystal struc-
ture analyses of complexes 1 and 2 (Fig. 1) reveal that in all the
cases, the ligands and metal ions form similar 2 ꢀ 2 tetranuclear
grids, which is constructed by four ligands and four FeIII ions.
Two of the ligands lie above the mean plane through four metal
ions while other two lie below. Adjacent FeIII ions were linked by
the pyrimidine bridge with the Feꢂ ꢂ ꢂFe distances in the range
6.113–6.340 Å via the –N–C„N– linkages. The distances of diago-
nal FeIII ions range from 8.466 Å to 9.073 Å. The FeIII ions have a
similar N4O2 coordination sphere with two N atoms from pyrimi-
dine, two N atoms from hydrazine groups and two phenol O atoms.
For complex 3, the ligand H2L3 has a similar structure but an ortho-
methoxy group other than H in H2L1.1
In complex 1, there are two ligands and two metal ions in the
asymmetric unit, which make up half of the grid. The other half
is generated by an inversion center. The iron ions along one side
of the grid are separated by 6.330(2) Å and 6.269(2) Å, and have
the diagonal separations of 8.790(3) Å and 8.985(3) Å. The average
Fe–Npym (pyrmidine) bond length is 2.166(8) Å, which is slightly
longer than the average Fe–Nimine (hydrazine) bond length of
2.113(8) Å. However, these bond lengths are not significantly
different. The average Fe–O bond length is 1.885(7) Å. It has been
concluded that for FeIIIN4O2 Schiff base complexes [21–24] the
Fe–Npym, Fe–Nimine, and Fe–O bonds in the range 2.168–2.224 Å,
2.051–2.155 Å and 1.895–1.938 Å, respectively correspond to
high-spin state of Fe(III), while 1.993–2.024 Å, 1.905–1.961 Å and
1.850–1.885 Å to low-spin Fe(III). The bond lengths in 1 suggest
that each of the FeIII ions should have a high-spin state. The ligand
H2L1 in 1 is stabilized in a plane which implies the strong conjuga-
(GOF)
R1[I > 2
r
I]
0.0941
0.2394
0.0941
0.3116
0.0764
0.2358
wR2 (all
data)
Table 2
Selected bond distances (Å) and bond angles (°) for Complex 1.
Fe(1)–O(1)
1.872(7)
Fe(2)–O(4)
1.875(7)
Fe(1)–O(3)
Fe(1)–N(7)
Fe(1)–N(1)
Fe(1)–N(9)
Fe(1)–N(3)
1.890(6)
2.114(7)
2.116(7)
2.175(7)
2.177(8)
Fe(2)–O(2)
Fe(2)–N(12)
Fe(2)–N(6)
Fe(2)–N(4)
Fe(2)–N(10)
1.902(8)
2.104(7)
2.119(8)
2.125(8)
2.189(7)
O(1)–Fe(1)–N(3)
N(1)–Fe(1)–N(7)
O(3)–Fe(1)–N(9)
159.1(3)
164.3(3)
157.3(3)
O(4)–Fe(2)–N(10)
N(6)–Fe(2)–N(12)
O(2)–Fe(2)–N(4)
159.6(3)
159.1(3)
158.2(3)
of the magnitude of structural distortion is given by the octahedral
h
i
2
P
ðdnꢁ<d>Þ
<d>
1
6
distortion parameter (
D
) defined as
D
¼
where
n¼1;6
<d> and dn are the mean Fe–O/N bond length and the six Fe–O/N
Table 3
Selected Bond Lengths (Å) and Bond Angles (deg) for Complex 2.
Fe(1)–O(1)
1.952(8)
Fe(2)–O(3)
1.918(8)
Fe(1)–O(7)
Fe(1)–N(1)
Fe(1)–N(3)
Fe(1)–N(19)
Fe(1)–N(21)
Fe(3)–O(4)
Fe(3)–O(6)
Fe(3)–N(10)
Fe(3)–N(12)
Fe(3)–N(16)
Fe(3)–N(18)
O(1)–Fe(1)–N(3)
O(7)–Fe(1)–N(21)
N(1)–Fe(1)–N(19)
O(4)–Fe(3)–N(10)
O(6)–Fe(3)–N(16)
N(12)–Fe(3)–N(18)
1.920(8)
2.052(9)
2.175(8)
2.055(9)
2.169(8)
1.956(7)
1.949(7)
2.169(7)
2.058(9)
2.187(8)
2.051(9)
155.1(3)
151.6(3)
170.1(4)
154.9(3)
152.9(3)
170.1(3)
Fe(2)–O(8)
Fe(2)–N(7)
Fe(2)–N(9)
Fe(2)–N(22)
Fe(2)–N(24)
Fe(4)–O(2)
Fe(4)–O(5)
Fe(4)–N(4)
Fe(4)–N(6)
Fe(4)–N(13)
Fe(4)–N(15)
O(3)–Fe(2)–N(9)
O(8)–Fe(2)–N(22)
N(7)–Fe(2)–N(24)
O(2)–Fe(4)–N(4)
O(5)–Fe(4)–N(15)
N(6)–Fe(4)–N(13)
1.932(7)
2.062(9)
2.185(8)
2.182(8)
2.152(10)
1.921(7)
1.929(8)
2.191(7)
2.029(9)
2.047(9)
2.163(8)
155.3(3)
153.9(3)
171.9(4)
155.2(3)
158.6(3)
177.1(3)
tion of
p bond. Two crossing ligands are perpendicular to each
other, but the average bond angle of trans-Nimine–Fe–Nimine is
161.7(4)°, and the average bond angle of trans-O–Fe–Npym is
159.6(3)°. Thus, the FeN4O2 core of 1 consists of an irregular octa-
hedral configuration, similar to that of the spin-crossover complex
{[Fe(mph)2](ClO4)(MeOH)0.5(H2O)0.5
}
2
(mphꢁ = anion of 2-meth-
oxy-6-(pyridine-2-ylhydrazonomethyl)phenol) [22k] and the
high-spin complex [Fe(salpm)2]NO3 (salpmꢁ = anion of N-(pyri-
din-2-ylmethyl)-salicylideneamine) [21b]. A quantitative measure
1
The crystals of complex 3 diffract weakly because of the small size of the crystals
and the large crystal cell volume, and therefore the crystal data are not good enough
for publication. Nevertheless, the raw crystal data clearly show the tetranuclear
structure of complex 3 similar to that of complexes 1 and 2. The crystal data of
complex 3 have been deposited as Supporting Information for reference

972
Y.-T. Wang et al. / Polyhedron 52 (2013) 970–975
Table 4
a small range, 6.245–6.339 Å. The octahedral distortion parameter
values are 0.0037 for Fe(1), 0.0029 for Fe(2), 0.0020 for Fe(3) and
0.0026 for Fe(4), respectively [25].
Selected Bond Lengths (Å) and Angles (deg) for Complex 4.
Fe(1)–O(1)
1.868(4)
Fe(2)–O(4)
1.874(4)
The dinuclear complex (4) can be considered as one of the four
edges in the tetranuclear complexes 1, 2 and 3, and therefore it is a
prototype for the tetranuclear Fe4 grids. In complex 4, two octahe-
dral FeIII ions are coordinated by (L4)2ꢁ, and the coordination sphere
is completed by two Clꢁ ions and a methanol molecule (Fig. 2). The
Fe–Cl bond distances are apparently longer than the Fe–N/O bond
distances, owingto thelarger ionicradius of the Clꢁ anion. Therefore,
the coordination configuration of Fe(III) is distorted octahedral
(Table 4). The Fe–Npym bond lengths are in the range 2.133(4)–
2.182(4) Å, comparable to that for complexes 1–3. The Feꢂ ꢂ ꢂFe sepa-
ration through the pyrimidine groups is 6.094 Å.
Fe(1)–N(5)
Fe(1)–N(3)
Fe(1)–O(2)
Fe(1)–Cl(1)
Fe(1)–Cl(2)
2.148(4)
2.178(5)
2.178(5)
2.286(2)
2.326(2)
Fe(2)–N(4)
Fe(2)–N(6)
Fe(2)–O(3)
Fe(2)–Cl(3)
Fe(2)–Cl(4)
2.133(4)
2.182(4)
2.182(4)
2.281(2)
2.337(2)
O(1)–Fe(1)–N(5)
O(2)–Fe(1)–Cl(2)
N(3)–Fe(1)–Cl(1)
158.8(2)
169.69(15)
167.06(15)
O(4)–Fe(2)–N(4)
O(3)–Fe(2)–Cl(4)
N(6)–Fe(2)–Cl(3)
158.5(2)
169.19(14)
167.38(16)
bond lengths along six different directions, respectively [25]. The
calculated values are 0.0038 for Fe(1) and 0.0034 for Fe(2).
In complex 2, the diagonal length of Fe(1)ꢂ ꢂ ꢂFe(3) is 9.072 Å,
which is much longer than the other diagonal length of
Fe(2)ꢂ ꢂ ꢂFe(4), 8.681 Å, and the average value (8.888 Å) of 1. The
average Fe–Npym and Fe–Nimine bond lengths are 2.178(7) Å and
2.051(8) Å, which are comparable with that in complex 1. The
average Fe–O bond length is 1.935(7) Å, longer than that
(1.885(7) Å) in 1. The bond lengths also suggest the FeIII ions in
complex 2 are in the high spin state. The bond angles of trans-Ni-
mine–Fe–Nimine are in the range 170.1(4)–177.1(3)°, much larger
than that in 1, while the bond angles of trans-O–Fe–Npym are in
the range 151.6(3)–158.6(3)°, smaller than in 1. The Feꢂ ꢂ ꢂFe separa-
tions through the pyrimidine groups in the grid molecule are within
2.3. Magnetic properties
Variable-temperature magnetic data for complexes 1–4 were
obtained using a 1000 Oe field in the temperature range 2–300 K,
which were shown in Figs. 3 and 4 in the form of
The magnetic behavior of the complexes is similar and shows the
decrease of mT with the decrease of the temperature, suggesting
vmT versus T.
v
the presence of antiferromagnetic coupling between adjacent
Fe(III) ions via the pyrimidine pathways. The room temperature
v
mT value of the tetranuclear Fe4 complexes is 17.0 cm3 molꢁ1
K
(1), 16.1 emu molꢁ1 K (2), and 15.5 emu molꢁ1 K (3), respectively,
corresponding to four high-spin FeIII ions with the theoretic value
Fig. 1. Crystal structure of the tetranuclear cations for complexes 1 (a) and 2 (b) (Fe, yellow green; C, grey; N, blue; O, red). The hydrogen atoms and anions are omitted for
clarity. (Color online.)
Fig. 2. Dinuclear structure of Fe2L42(MeOH)2Cl43MeOH (4). Hydrogen atoms and the methanol solvents are omitted for clarity.

Y.-T. Wang et al. / Polyhedron 52 (2013) 970–975
973
of 17.5 emu molꢁ1 K.For the Fe4 complexes 1–3, the magnetic sus-
ceptibility data (20–300 K) were fitted to a theoretical expression
^ ^ ^ ^
^
(Eq. (1), SI) derived from the Hamiltonian H ¼ ꢁ2JðS1S2 þ S3S4þ
^ ^
^ ^
S2S3 þ S1S4Þ assuming that the magnetic coupling via the pyrimi-
dine pathways is identical. Least-squares fitting gave the parame-
ters of J = ꢁ1.13(4) cmꢁ1, g = 1.92(1) for complex 1, J = ꢁ1.35(1)
cmꢁ1, g = 1.97(1) for complex 2, and J = ꢁ1.42(1) cmꢁ1, g = 1.95(1)
Fig. 4. Temperature dependence of
vmT for complex 4. The solid line represents the
best-fit result with the parameters described in the text.
for complex 3. The J values obtained correspond to a weak antifer-
romagnetic coupling between adjacent high spin FeIII ions.
The magnetic property of the Fe2 complex (4) is shown in Fig. 4.
The
sponds to two high-spin FeIII ions with the theoretical value of
8.75 emu K molꢁ1 mT decrease to 0.592 emu K molꢁ1 at 2 K, indi-
v
mT value of 8.25 emu molꢁ1 K at room temperature corre-
.
v
cating the presence of antiferromagnetic coupling in complex 4.
We analyzed the data (20–300 K for consistency) by using the
^
^ ^
Hamiltonian H ¼ ꢁ2JS1S2 known as Heisenberg-van Vleck model
[26]. The optimized parameters are J = ꢁ1.62(2) cmꢁ1 and
g = 1.98(1). The dinuclear prototype showed weak antiferromag-
netic coupling between two HS FeIII ions bridged by the pyrimidine
N–C@N group, consistent with the antiferromagnetic coupling in
tetranuclear complexes 1–3.
All the four complexes present weak antiferromagnetic cou-
pling property between the adjacent FeIII centers through pyrimi-
dine bridges. The electron configuration of octahedral high-spin
iron(III) ion is 3d5 (t2g3eg2), which means it has both d
r and dp
spins simultaneously. According to Ishida [27] and Takano
[28], the magnetic coupling is very complicated due to the pres-
ence of different kinds of interaction pathways.
-pathway in pyrimidine bridge bring about either ferromagnetic
or antiferromagnetic coupling, respectively. Owing to a positive
spin density polarized at nitrogen atom (Fig. 5a), the -pathway
contributes to a ferromagnetic coupling between two iron(III) cen-
ters, and the -pathway Fe-NN-Fe transmits an antiferromagnetic
p-pathway and
r
p
r
coupling between two metal centers (Fig. 5b). At the same time,
many interactions are also possible in the system, including
dp-dr interactions through pyrimidine bridge that give rise to fer-
romagnetic coupling as well. The experimental results indicate
that the antiferromagnetic interaction is slightly stronger than fer-
romagnetic contribution, giving the global antiferromagnetic prop-
erty of complexes 1–4.
Comparing the structural difference and the magnetic coupling
of complexes 1–4, we found that the elongation of the FeIII–Npym
bond causes a weaker antiferromagnetic interaction (Table 5).
Fig. 6 displays the correlation between the magnetic coupling con-
stant (J) and the FeIII–Npym bond distances (d) based on the data
shown in Table 5. Antiferromagnetic interaction weakens more
rapidly than the ferromagnetic contribution when the Fe–Npym
bonds are elongated, eventually resulting in the decrease of abso-
lute value of magnetic coupling constant J. It is worth mentioning
that the pyrimidine-bridged MnII system [27] is also in line with
this assumption (Fig. 6). It suggest a linear relation between the
Fig. 3. Temperature dependence of
represent the best-fit results with the parameters described in the text.
vmT for complexes 1–3. The solid lines

974
Y.-T. Wang et al. / Polyhedron 52 (2013) 970–975
Fig. 5. Magnetic interactions of Fe(III) ions through the pyrimidine bridge. (a)
p
-pathway contributing to ferromagnetic coupling and (b) r-pathway giving rise to
antiferromagnetic coupling.
4. Experimental
Table 5
Relationship between M–Npym bond length and the magnetic coupling constants for
pyrimidine-bridged complexes with 3d5 electronic configuration.
4.1. Materials and synthesis
Complex 1 Complex 2 Complex 3 Complex 4 DPPM-Mn [27]
The reagents FeCl26H2O, Fe(ClO4)26H2O, FeCl36H2O, salicylical-
dehyde, 2,4-dichloropyrimidine, hydrazine, methylhydrazine are
all purchased from commercial sources. 2,4-dihydrazinopyrimidine
was synthesized according to the literature method [29]. All the
ligands H2L1–4 were synthesized by the similar procedure as H2L1,
whichis described herein in detail. A mixture of 2,4-dihydrazinopyr-
imidine (2.80 g, 20 mmol) and salicylicaldehyde (5.0 g, 41 mmol) in
ethanol (30 mL) was stirred for 30 min. The formed precipitate was
filtered off, washed with ethanol and diethyl ether and dried. The
yield of the product was nearly quantitative. IR (KBr): = 3069(m),
2948(m), 1630(s), 1482(m), 1200(m), 1152(w), 1111(w), 815(w),
759(w), 557(w) cmꢁ1. H2L2: IR: = 3167(m), 2963(m), 2924(m),
1622(s),1583(s), 1486(m), 1283(m), 1106(m), 975(m), 873(m), 742
M–Npym/Å 2.182
J/cmꢁ1
ꢁ1.121
2.178
ꢁ1.353
2.155
ꢁ1.427
2.139
ꢁ1.615
2.263
ꢁ0.542
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
-1.8
.
(m), 485(w) cmꢁ1 H2L3: IR: = 3167(m), 2963(m), 2924(m),
1622(s),1583(s), 1486(m), 1283(m), 1106(m), 975(m), 873(m), 742
(m), 485(w) cmꢁ1. H2L4: IR (cmꢁ1): = 3167(m), 2963(m), 2924(m),
1622(s),1583(s), 1486(m), 1283(m), 1106(m), 975(m), 873(m), 742
(m), 485(w).
Caution! Perchlorate salts of metal complexes with organic
ligands are potentially explosive. They should be handled in small
quantities with care.
Fe4L14Cl4 (1)
2.12 2.14 2.16 2.18 2.20 2.22 2.24 2.26 2.28
H2L1 (34.8 mg, 0.1 mmol) and FeCl36H2O (27.5 mg, 0.1 mmol)
were dissolved in the mixture of DMF (5 mL) and MeCN (10 mL)
and stirred at room temperature for 30 min. The suspension was
filtered, and the dark-brown solution was diffused with deionized
water in a sealed tube. Dark brown block-like single crystals suit-
able for structural analysis were obtained after 2 weeks. The crys-
tals were then collected for further characterization. Yield: 30%. IR
d
/Angstrom
Fig. 6. M–Npym bond distance dependence of the magnetic coupling constant for
the pyrimidine-bridged 3d5 complexes listed in Table 5. The line is the least-squares
fitting result.
(cmꢁ1):
m = 3069(m), 2948(m), 1630(s), 1597(s), 1482(m),
bond length and the J value of the high spin 3d5 ions agrees the fol-
lowing equation J = 8.5265dꢁ19.816.
1200(m), 1111(m),1031(m), 870(m), 759 (m), 557(w).
Fe4L24(ClO4)4 (2
H2L2 (33.2 mg, 0.1 mmol) and Fe(ClO4)26H2O (36.3 mg,
0.1 mmol) were dissolved in MeOH (10 mL) and stirred at room tem-
perature for 30 min. The suspension was filtered, and dark green
block-like single crystals were obtained by slow evaporation of the
solution in a refrigerator after 2 days. The crystals were then col-
lected for further characterization. Yield: 60%. IR (cmꢁ1):
= 3167(m), 2963(m), 2924(m), 1622(s), 1583(s), 1486(m),
1283(m), 1106(m), 975(m), 873(m), 742 (m), 485(w).
3. Conclusion
A series of novel tetranuclear grid-like FeIII complexes have
been synthesized by using new multi-dentate Schiff base ligands.
The structure and magnetic properties have shown that four FeIII
centers are high-spin. Antiferromagnetic coupling was found
between adjacent FeIII ions through the pyrimidine bridge. The
studies on relationship between structure and magnetic property
show that the Fe–Npym bond distance is a principal factor for the
magnetic interaction. Spin-crossover FeIII4 complexes are expected
by modulating the ligands, and this work is in progress in our
laboratory.
Fe4L34Cl45H2O (3)
H2L3 (40.5 mg, 0.1 mmol) and FeCl36H2O (27.0 mg, 0.1 mmol)
were dissolved in the mixture of DMF (5 mL) and MeCN (10 mL)

Y.-T. Wang et al. / Polyhedron 52 (2013) 970–975
975
4503;
and stirred at room temperature for 30 min. After filtration of the
(h) L.N. Dawe, K.V. Shuvaev, L.K. Thompson, Inorg. Chem. 48 (2009) 3323.
suspension, the dark brown solution was diffused with deionized
water in a sealed tube. Dark brown block-like single crystals were
obtained after 1 week. The crystals were than collected for further
characterizations. Yield: 40%. IR (cmꢁ1): = 3127(m), 2934(m),
1625(s), 1598(s), 1481(m), 1286(m), 1106(m), 762 (m), 625(w).
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Fe2L4(MeOH)2Cl43MeOH (4)
H2L4 (37.8 mg, 0.1 mmol) and FeCl36H2O (54.1 mg, 0.2 mmol)
were dissolved in the mixture of MeOH (10 mL) and stirred at room
temperature for 30 min. The dark brown solution was then filtered,
evaporated slowly at room temperature, affording dark brown
plate single crystals after 1 week. Yield: 50%. IR (cmꢁ1):
= 3431(m), 2922(m), 1610(s), 1510(s), 1436(m), 1322(m),
1119(m), 758 (m), 623(w).
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dependent magnetic susceptibility measurements were carried
out on a Quantum Design MPMS SQUID magnetometer from 2 to
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The authors would like to acknowledge the financial support of
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graphic data for complexes 1–4. These data can be obtained free
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