Synthesis and Magnetic Properties of a Fe-Mn-Cr Multinuclear Complex with
4-Amino-1,2,4-triazole and Oxalate Ligands
Iis Siti Jahro1), Djulia Onggo1), Ismunandar1), Susanto Imam Rahayu1),
Esther Jacoba Martha Vertelman2), Petra van Koningsbruggen2)
1)
Inorganic and Physical Chemistry Group, Faculty of Mathematics and Natural Sciences,
Bandung Institute of Technology, Bandung
2)
Stratingh Institute of Chemistry and Chemical Engineering,University of Groningen,
Groningen, The Netherlands
e-mail: jahrostiis@yahoo.com
Received May 2006, accepted for publication September 2006
Abstract
A multinuclear Fe-Mn-Cr complex with 4-amino-1,2,4-triazole (NH2trz) and oxalate (ox) ligands has been synthesized
successfully. The formula of the [Fe(NH2trz)3][ClO4][MnCr(ox)3].4H2O complex has been obtained based on the metal
and C, H, N contents. The presence of water molecules, metal-ligand bonding and bridge ligand in the multinuclear
complex has been confirmed by its infrared spectrum. The compound crystallizes in the hexagonal system with cell
parameters of a = b = 18.695 Å and c = 57.351 Å. The compound shows a gradual spin crossover for iron(II) in the
[Fe(NH2trz)3]2+ with transition temperature (T1/2) of 205 K. The antiferromagnetic interaction between Cr(III) and
Mn(II) ions in the [MnCr(ox)3]nn- network is observed from the Weiss constant (θ) of –2.3 K.
Keywords: [Fe(NH2trz)3]2+, [MnCr(ox)3]nn-, Magnetic properties, Spin crossover, Antiferromagnetic
Abstrak
Senyawa kompleks multi-inti Fe-Mn-Cr dengan ligan 4-amino-1,2,4-triazol (NH2trz) dan oksalat (ox) telah berhasil
disintesis. Rumus kimia senyawa kompleks [Fe(NH2trz)3][ClO4][MnCr(ox)3].4H2O diperoleh atas dasar kandungan ion
logam dan unsur C, H, dan N. Keberadaan molekul air, ikatan logam-ligan dan gugus ligan jembatan dibuktikan dari
spektrum inframerah. Senyawa ini termasuk pada sistim kristal heksagonal dengan parameter sel a = b = 18.695 Å dan
c = 57.351 Å. Senyawa ini menunjukkan transisi spin pada ion besi(II) dalam kromofor [Fe(NH2trz)3]2+ dengan
temperatur transisi (T1/2) 205 K. Adanya interaksi antiferomagnetik antara ion Cr(III) dan Mn(II) dalam jaringan
[MnCr(ox)3]nn- teramati dari nilai konstanta Weiss (θ) sebesar –2,3 K.
Kata kunci: [Fe(NH2trz)3]2+, [MnCr(ox)3]nn-, Sifat magnet, Spin crossover, Antiferomagnetik
The synthesis, structure, and magnetic
properties of the series of molecular magnets
formulated as [Z(bpy)3][ClO4][MCr(ox)3]; Z = Ru, Fe,
Co and Ni; M = Mn, Fe, Co, Ni, Cu, and Zn; bpy =
2,2’-bipyridine; ox = oxalate dianion, have also been
reported (Coronado et al., 2001). The magnetic
susceptibility behaviors of the series [Fe(bpy)3][ClO4]
[MCr(ox)3] in the temperature range 5–300K were
essentially similar. In all compounds, the Weiss
constants (θ) were positive, indicating ferromagnetic
interactions between neighboring Cr(III) and M(II)
ions, whereas the [Fe(bpy)3]2+ entity is a diamagnetic
cation containing divalent iron in the low spin state.
Octahedral complexes of Fe(II) ions may
exist in either the low spin (LS, S = 0) or high spin (HS,
S = 2) state, depending on the nature of the ligand field
of the metal ion. A transition or crossover between a
low spin and a high spin state may occur due to a
variation of temperature, pressure, or by light
irradiation (Decurtin et al., 1985; Grandjean et al.,
1989; Garcia et al., 1998; Gütlich et al., 2000; Floquet
1. Introduction
The synthesis and study of magnetic
properties in di- and multinuclear metal complexes
have been an active field of research in the past few
years (Decurtin et al., 1994; Min et al., 2005). The
multinuclear complexes could be synthesized using
bridging ligand such as the oxalate anion. The oxalate
(ox = C2O42-) ion can act as a mediator for magnetic
exchange interaction between the transition-metal
centers in multidimensional networks. Tremendous
progress in molecule-based magnets has been shown in
oxalate multinuclear complexes since the discovery of
new polymeric bimetallic phases of variable
dimensionality (Tamaki et al., 1992). Two-dimensional
bimetallic phases {[A][MM’(ox)3]}n, A = [N(n-C3H7)4],
[N(n-C4H9)4], [N(n-C5H9)4], [P(n-C4H9)4], [P(n-C6H5)4],
M = Mn, Fe, Cr, Ni, Cu; M’ = Cr, Fe have attracted a
lot of attentions due to their ferro- (Mathonière et al.,
1996), ferri- (Pellaux et al., 1997) or canted
antiferromagnets (Decurtins et al., 1996) with critical
temperature ranging from 5 up to 44 K.
95
Jahro et al., Synthesis and Magnetic Properties of a Fe-Mn-Cr Multinuclear 96
et al., 2003). The spin crossover from one spin state to
the other in Fe(II) (3d6) complexes is accompanied by
a modification of the magnetic behavior from the
diamagnetic (S = 0) to the paramagnetic (S = 2) state.
The series of Fe(II) complex compounds of general
formula [Fe(NH2trz)3]X2.XH2O show thermal spin
crossover. Variation of the non-coordinated anion (X)
in [Fe(NH2trz)3]X2.nH2O leads to compounds with
signifcantly different spin crossover characteristic (van
Koningsbruggen et al., 1997). It has been reported that
the pure [Fe(NH2trz)3][ClO4]2 material shows a smooth
transition around T1/2 = 130 K (Kröber et al., 1993).
Recently, Sieber et al. (2000) found a difference in magnetic properties for [Co(bpy)3]2+ entities embedded in various [MCr(ox)3]n2n- networks, where M(I)
is either sodium or lithium ions. In [Co(bpy)3][NaCr
(ox)3], the Co(II) complex is in a high spin ground
state, while in [Co(bpy)3][LiCr(ox)3], the Co(II) exhibits a thermal spin crossover, with a transition temperature of 161 K (Sieber et al., 2000).
Our group has explored the incorporation of
potential Fe(II) spin crossover chromophores in a
related bimetallic oxalate framework. In this paper, a
multinuclear Fe-Mn-Cr complex containing 4-amino1,2,4-triazole (NH2trz) and oxalate is reported. The
synthesis, characterization and magnetic properties of
[Fe(NH2trz)3][ClO4] [MnCr(ox)3].4H2O compound are
described.
2. Method
The research included preliminary work on the
solubility of the starting materials, synthesis, elemental
analysis, IR spectroscopic characterization and magnetic measurements of the complex compound.
2.1 Materials
Mn(NO3)2.4H2O, C2H4N4 (4-amino-1,2,4-triazole = NH2trz), methanol, and distilled water were used
as obtained without further purification. The K3[Cr
(ox)3].3H2O and [Fe(NH2trz)3](ClO4)2 have been prepared based on a published paper (Jahro, 2005).
2.2 Instruments
The instruments used were atomic absorption spectrophotometer (AAS) Shimadzu AA8801S,
infrared spectrophotometer Shimadzu FTIR-8400 and
X-ray Diffractometer Philips PW 1835. The C, H, N,
elemental analyses by CHNSO Mikrounsure Analyzer
model Fison EA 1108 have been done in Universiti
Kebangsaan Malaysia (UKM). Variable-temperature
magnetic susceptibility measurements were performed
on a Quantum Design magnetometer with a superconducting quantum interference device. The field was
kept constant at 0.1 T, while the temperature was varied
from 5–340 K.
2.3 Synthesis of the Fe-Mn-Cr Multinuclear Complex
A solution of [Fe(NH2trz)3](ClO4)2 (0.015
mmol) in aqueous methanol 70% (15 mL) was added to
a mixed solution containing K3[Cr(C2O4)3]3H2O (0.015
mmol) and Mn(NO3)2.4H2O (0.015 mmol) in aqueous
methanol 30% (9 mL). The mixture was stirred at room
temperature for 12 hours. The purple-grayish precipitate was filtered off and dried over P4O10.
3. Results and Discussion
3.1 Synthesis
The [Fe(NH2trz)3][ClO4] [MnCr(ox)3].4H2O
compound was isolated from aqueous methanol with
48% yield. The synthesis method had been chosen
based on the solubility of [Fe(NH2trz)3]2+ which was
mainly soluble in methanol, while the [MnCr(ox)3]complex was soluble in water. The Fe-Mn-Cr complex
was obtained as powder material with purple-grayish
colour. It was hardly soluble in water and organic
solvents like acetone, diethyl ether, methanol, ethanol,
acetonitrile,
dimethylformamide
(DMF)
and
dimethylsulfoxide (DMSO). The formula of this
compound has been obtained based on the metal ions
and the C, H, N analyses. The elemental contents are
listed in Table 1.
Table 1. The metal ion and C, H, N contents of
[Fe(NH2trz)3][ClO4][MnCr(ox)3].4H2O
The elemental contents (%)
Fe
Mn
6.26
(6.57)
5.98
(6.46)
Cr
C
H
N
7.04
17.72
2.86
19.30
(6.11) (16.95) (2.37) (19.76)
(Calculated values)
Attempts to obtain single crystals suitable for
single-crystal X-ray diffraction analysis so far had been
unsuccessful. The compound was obtained as a powder
form material. The material was characterized by X-ray
powder diffraction profile and indexed in P6/MMM to
derive unit cell parameters by Le Bail refinement in
Rietica program.
This compound crystallized in the hexagonal
system with the cell parameters a = b = 18.695 Å and c
= 57.351 Å. The structure of this compound resembled
that found by X-ray single-crystal diffraction for
[A][MnCr(ox)3] with A = [P(C6H5)4]+ (Decurtin et al.,
1994). The structure consisted of two-dimensional
bimetallic network. This network was formed by bisbidentate oxalate ligands connecting Mn(II) and Cr(III)
ions in such a way that each Mn(II) ion was surrounded
by three Cr(III) ions and vice versa, leading to
polymeric nets with all metal ions maintaining the
different chirality. The anionic network sublattices left
97 JURNAL MATEMATIKA DAN SAINS, SEPTEMBER 2006, VOL. 11 NO. 3
some holes where the cationic Fe(II) complex and
perchlorate counterion were located.
The presence of the various molecular constituents could be confirmed by its infrared (IR) spectrum.
The spectrum of this complex was confined to the most
important vibrations in the 350–4000 cm-1 region as
shown in Figure 1.
3.2 Magnetic property
The spin crossover behaviour of [Fe(NH2trz)3]
(ClO4)2 is normally observed at lower than room
temperature. However, when this compound was
combined with the [MnCr(ox)3]n- complex, the spin
transition behaviour shifted to higher temperature. The
magnetic properties of the [Fe(NH2trz)3][ClO4]
[MnCr(ox)3].4H2O compound had been measured
between 5–340K, and the plot of the product of the
magnetic susceptibility and the temperature, as well as
the magnetic moments vs the temperatures are shown in
Figure 2.
µ eff (BM)
From the IR spectrum, the characteristic
absorptions of the oxalato-bridged group, NH2trz
ligands and O–M–O bonding (M = Cr, Mn) had been
observed. For the oxalate-bridged group, the wide νas
O–C band at 1624 cm-1, a sharp νs O–C located at 1384
cm-1 and a doublet δ O–C band at 800 cm-1 had been
obtained. The peak at 414 cm-1 clearly supports O–M–
O (M = Cr, Mn) bonds. For the NH2trz ligand, the
wide band in the 3433 cm-1 was characteristic of – N–H
aromatic ring, the characteristic of – C = N – aromatic
absorbed in the range 1650–1550 cm-1, the wide band
at 1624 cm-1 was due to this. The wide band at 3413
cm-1 also suggested that water molecules were present
in this complex.
χMT (cm3ml-1K)
Figure 1. The infrared spectrum of [Fe(NH2trz)3][ClO4] [MnCr(ox)3].4H2O.
T (K)
Figure 2. Plot of the temperature dependence of the
product of the magnetic susceptibility and the
temperature (ƒ = χMT vs T) and the magnetic moment
(● = µeff vs T).
There were three potentially paramagnetic
transition metal ions present in the [Fe(NH2trz)3]
[ClO4][MnCr(ox)3].4H2O complex i.e. the Cr(III),
Mn(II) and Fe(II) ions. The spin value (S) of Cr(III)
was 3/2, Mn(II) was 5/2 in high spin state and Fe(II)
was 0 in low-spin (LS) and 2 in high-spin (HS) state.
The magnetic data were expected to be a superposition
of those for the paramagnetic Mn-Cr oxalate network
and the Fe(II) fragment. The antiferromagnetic
interaction between Cr(III) and Mn(II) in the
Jahro et al., Synthesis and Magnetic Properties of a Fe-Mn-Cr Multinuclear 98
1/χM (cm3
mol)
χM (cm3ml-1)
[MnCr(C2O4)3]-n network yielded S = 1, resulting in a
χMT value equal to 1 cm3mol-1 K, and µeff = 2.83
BM. From the data at 5 K, the χMT value was
observed to be 2.96 cm3 mol-1K. As the temperature
increased the value of χMT reached 3.25 cm3mol-1K at
25 K and formed a plateau up to 226 K. The χMT value
suggested a superposition of the magnetic contribution
of the Mn-Cr oxalate framework together with a
fraction of almost 50 % of the Fe(II) ions being in the
high-spin state. From 226 K the value of χMT was
markedly increased, which was the sign for the
occurence of an Fe(II) spin crossover. The maximum
value of 4.51 cm3 mol-1 K observed at 337 K was lower
than the χMT value of 6.01 cm3mol-1K which would be
expected for a system in which all Fe(II) ions in the
high-spin state. From the data, it was evident that the
spin crossover of Fe(II) was not complete.
The unpaired spins on neighboring Cr(III) and
Mn(II) ions in [MnCr(C2O4)3]n- networks to be coupled
with each other was mediated by the oxalate ion as a
bridging ligand, a phenomenon referred as magnetic
exchange. The magnetic exchange tended to an
antiparallel arrangement of the coupled spins which
was called antiferromagnetism.
The indication of an antiferromagnetic
interaction between Cr(III) and Mn(II) in [Fe(NH2trz)3]
[ClO4][MnCr(ox)3].4H2O was clearly shown by the plot
of magnetic susceptibilittes (χM) and its reciprocal
equivalent (1/χM) versus temperature (T) as given in
Figure 3. The 1/χM curve was fitted with a straight line
and from this the Curie constant (C) and the CurieWeiss constant (θ) were obtained using the equation χM
= C/(T – θ). Fitting the curve in the temperature range
5–245 K resulted in a Weiss constant (θ) of –2.3 K.
This negative value indicated an antiferromagnetic
interaction between the Cr(III) and Mn(II) ions.
Temperature (K)
Figure 3. Plot of the temperature (T) dependence of the
reciprocal magnetic susceptibilities and magnetic
susceptibilities (• = χM Vs T, ƒ = χM Vs T).
4. Conclusion
The multinuclear complex of formula [Fe(NH2
rz)3]ClO4][MnCr(ox)3].4H2O had been synthesized.
The molecular composition had been supported by
metal ion contents, the elemental C, H, N data and the
IR spectra in 350–4000 cm-1 range.
The temperature dependence of the magnetic
(χMT) data recorded in the temperature range 5–340K
indicated a characteristic of thermal spin crossover of
[Fe(NH2trz)3]2+ and an antiferromagnetic interaction
between neighboring Cr(III) and Mn(II) ions in
[MnCr(C2O4)3]n- networks.
Acknowledgement
This research was funded by Direktorat
Jendral Pendidikan Tinggi, Departemen Pendidikan
Nasional Indonesia, Research Grant No. 322/SP3/PP/
DP2M/II/2006. The authors are thankful to Prof.
Ibrahim Baba (UKM) for C, H, N elemental analysis.
References
Coronado, E., J. R. Galán-Mascarós, C. J. GómezGarcia, and J. M. Martinez-Agudo, 2001,
Molecule-based Magnets Formed by Bimetallic Three-dimensional Oxalate Networks
and Chiral Tris(bipyridyl) Complex Cations.
The Series [ZII(bpy)3][ClO4][MIICrIII(ox)3] (ZII
= Ru, Fe, Co, and Ni; MII = Mn, Fe, Co, Ni,
Cu, and Zn; ox = Oxalate Dianion), Inorg.
Chem., 40, 113-120.
Decurtin, S., P. Gütlich, K. M. Hasselbach, A. Hauser,
and H. Spiering, 1985, Light-induced Excitedspin-state Trapping in Iron(II) Spin-crossover
Systems. Optical Spectroscopic and Magnetic
Susceptibility Study, Inorg. Chem., 24, 21742178.
Decurtin, S., H. W. Schemalle, and H. R. Oswald,
1994, A Polymeric Two-dimensional Mixedmetal Network. Crystal Structure and Magnetic Properties of {[P(Ph)4][MnCr (ox)3]}n,
Inorg. Chem. Acta, 216, 65-73.
Decurtin, S., W. H. Schmalle, R. Pellaux, P.
Schneuwly, and A. Hauser, 1996, Chiral,
Three-dimensional Supramolecular Compounds: Homo-and Bimetallic Oxalate and 1,2Dithiooxalate-bridged Networks. A Struc-tural
and Photophysical Study, Inorg. Chem., 35,
1451-1460.
Decurtin, S., H. W. Schemalle, P. Schneuwly, J.
Ensling, and P. Gütlich, 1994, A Concept for
the Synthesis of 3-Dimensional Homo- and
Bimetallic Oxalate-bridged Networks [M2(ox)
3]n. Structural, Mössbauer, and Mag-netic Studies in the Field of Molecular-based Magnets,
J. Am. Chem. Soc., 116, 9521-9528.
99 JURNAL MATEMATIKA DAN SAINS, SEPTEMBER 2006, VOL. 11 NO. 3
Floquet, S., B. Marie-Laure, E. Rivière, F. Varret, K.
Boukheddaden, D. Morineau, and P. Nègrier,
2003, Spin Transition with a Large Thermal
Hysteresis Near Room Temperature in a
Water Solvate of an Iron(III) Thiosemi
carbazone Complex, New J. Chem., 27, 341348.
Garcia, Y., P. J. van Koningsbruggen, R. Lapouyade, L.
Fournès, L. Rabardel, O. Kahn, V. Ksenofontov, G. Levchenko, and P. Gütlich, 1998,
Influences of Temperature, Pressure, and
Lattice Solvents on the Spin Transition
Regime of the Polymeric Compound [Fe
(hyetrz)3]A2.3H2O (hyetrz = 4-(2’-hydroxyethyl)-1,2,4-triazole and A- = 3-nitrophenylsulfonate), Chem. Mater., 10, 2426-2433.
Grandjean, F., G. J. Long, B. B. Hutchinson, L.
Ohlhausen, P. Neill, and J. D. Holcomb, 1989,
Study of the High Temperature Spin-state
Crossover in the Iron(II) Pyrazolylborate
Complex Fe[HB(pz)3]2, Inorg. Chem., 28,
4406-4414.
Gütlich, P., Y. Garcia, and H. A. Goodwin, 2000, Spin
Crossover Phenomena in Fe(II) Complexes,
Chem. Soc. Rev., 29, 419-427.
Jahro, I. S., D. Onggo, Ismunandar, dan S. I. Rahayu,
2005, Sintesis dan Karakterisasi Senyawa Spin
Crossover [Fe(NH2trz)3]Cl2.3H2O, Proceedings of Joint Seminar on Chemistry ITBUKM VI, 439-443.
Kröber, J., E. Codjovi, O. Kahn, F. Grolière, and C.
Jay, 1993, A Spin Transition System with a
Thermal Hysteresis at Room Temperature, J.
Am. Chem. Soc., 115, 9810-9811.
Mathonière, C., J. C. Nuttall, G. S. Carling, and P. Day,
1996, Ferrimagnetic Mixed-metal Tris (oxa-
lato)iron(III) Compounds: Synthesis, Structure, and Magnetism, Inorg. Chem., 35, 12011206.
Min, K. S., A. L. Rhinegold, and J. S. Miller, 2005,
Synthesis, Structure, and Magnetic Ordering
of Layered (2-D) V-Based Tris(oxalato) metalates, Inorg. Chem., 44, 8433-8441.
Pellaux, R., W. H. Schmalle, R. Huber, P. Fischer, T.
Hauss, B. Ouladdiaf, and S. Decurtin, 1997,
Molecular-based Magnetism in Bimetallic
Two-dimensional Oxalate-bridged Networks.
An X-ray and Neutron Diffraction Study,
Inorg. Chem., 36, 2301-2308.
Sieber, R., S. Decurtin, H. Stoeckli-Evans, C. Wilson,
D. Yufit, J. A. K. Howard, S. C. Capelli, and
A. Hauser, 2000, A Thermal Spin Transition
in [Co(bpy)3][LiCr(ox)3] (ox = C2O42-; bpy =
2,2’-bipyridine), Chem. Eur. J., 6, 361-368.
Tamaki, H., Z. J. Zhong, N. Matsumoto, S. Kida, M.
Koikawa, N. Achiwa, Y. Hashimoto, and H.
Okawa, 1992, Design of Metal-complex
Magnets. Syntheses and Magnetic Properties
of Mixed-metal Assemblies {NBu4[MCr
(ox)3]}x (NBu = Tetra(n-butylammonium Ion;
ox2- = Oxalate Ion; M = Mn2+, Fe2+, Co2+,
Ni2+, Cu2+, Zn2+), J. Am. Chem. Soc., 114,
6974-6979.
van Koningsbruggen, P. J., Y. Garcia, E. Codjovi,
Lapouyade, O. Kahn, L. Fournès, and L.
Rabardel, 1997, Non-classical Spin-crossover
Behaviour in Polymeric Iron(II) Compounds
of Formula [Fe(NH2trz)3].X2.xH2O (NH2trz =
4-amino-1,2,4-triazole; X = derivates of naphthalene sulfonate), J. Mater. Chem., 7, 2069–
2075.