Inorganica Chimica Acta 358 (2005) 2101–2106
www.elsevier.com/locate/ica
Note
Two cyano-bridged heterotrinuclear complexes built
from [(Tp)Fe(CN)3] (Tp = hydrotris(pyrazolyl)borate):
synthesis, crystal structures and magnetic properties
Shi Wang a, Jing-Lin Zuo
a
a,*
, Hong-Cai Zhou b, You Song a, Xiao-Zeng You
a,*
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
b
Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056-1465, USA
Received 29 June 2004; accepted 28 December 2004
Available online 11 February 2005
Abstract
Using an anionic precursor [(Tp)FeIII(CN)3] (1) as a building block, two cyano-bridged centrosymmetric heterotrinuclear comII
III
plexes, ½ðTpÞ2 FeIII
2 ðCNÞ6 Mn ðC2 H5 OHÞ4 2C2 H5 OH (2) and ½ðTpÞ2 Fe2 ðCNÞ6 NiðenÞ2 (3) (en = ethylenediamine), have been synthesized and structurally characterized. In each complex, [TpFe(CN)3] acts as a monodentate ligand toward a central
[Mn(C2H5OH)4]2+ or [Ni(en)2]2+ core through one of its three cyanide groups, the other two cyanides remaining terminal. The intramolecular Fe–Mn and Fe–Ni distances are 5.2354(4) and 5.0669(11) Å, respectively. The magnetic properties of complexes 2 and 3
have been investigated in the temperature range of 2.0–300 K. A weak antiferromagnetic interaction between the Mn(II) and Fe(III)
^ ¼
ions has been found in complex 2. The magnetic data of 2 can be fitted with the isotropic Hamiltonian:H
2J ðS^1 S^2 þ S^2 S^3 Þ 2J 0 S^1 S^ 3 where J and J 0 are the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively. This leads to values of J = 1.37 cm1 and g = 2.05. The same fitting method is applied to complex 3
to give values of J = 1.2 cm1 and g = 2.25, showing that there is a ferromagnetic interaction between the Fe(III) and Ni(II) ions.
2004 Elsevier B.V. All rights reserved.
Keywords: Cyanides; Heterometallic complexes; Magnetic properties; Iron complexes
1. Introduction
Cyano-bridged infinite systems (or Prussian blue analogues) and high-spin clusters have attracted great research interest due to their unique magnetic properties,
including high-Tc magnet, photoinduced magnetization,
etc. [1–4]. Among these interesting researches, lowdimensional complexes as well as polynuclear clusters
have attracted special attention. Because such system
can be used to investigate the intermetallic magnetic
coupling quantitatively, whereas lack of an appropriate
*
Corresponding
authors.
Tel.:
+862583593893;
+862583317761.
E-mail address: zuojl@nju.edu.cn (J.-L. Zuo).
fax:
0020-1693/$ - see front matter 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.12.034
model for high-dimensional systems is the problem for
quantitative magnetic analysis. Recently, synthetic strategies to prepare cyano-bridged bimetallic systems by
using modified cyanometalates as multidentate ligands
and linkers were developed. The following are representative examples: [(tacn)M(CN)3] (M = Co3+, Cr3+;
tacn = 1,4,7-triazacyclononane) [5], [(Me3tacn)M(CN)3]
(M = Cr3+, Mo3+; Me3tacn = N,N 0 ,N00 -trimethyl-1,4,7triazacyclononane) [6], [(tach)M(CN)3] (M = Cr3+,
Fe3+, Co3+; tach = 1,3,5-triaminocyclohexane) [7], [Fe(bipy)(CN)4], [Fe(bipy)(CN)4]2 and [Fe(phen)(CN)4]
(bipy = 2,2 0 -bipyridine;
phen = 1,10-phenanthroline)
[8,9]. In an effort to explore the potential of these
remarkable synthetic methodologies, we choose a tailored cyanometalate precursor, (Bu4N)[(Tp)Fe(CN)3] 1
2102
S. Wang et al. / Inorganica Chimica Acta 358 (2005) 2101–2106
(Bu4N+ = tetrabutylammonium cation), as our main
building block. It consists of an FeIII coordinated by
three CN groups and capped by the ligand of hydrotris(pyrazolyl)borate (Tp). 1 was also reported by Julves
group as a tetraphenylphosphonium salt [10]. Tp is a
classical scorpionate ligand bearing a C3 axis. Compared
to those precursors reported before, Tp is sterically similar but bearing a negative charge. Thus, it may direct
the formation of new complexes with interesting structures and magnetic properties. For example, a new single-chain magnet with blocking temperature at ca. 6 K,
½ðTpÞ2 FeIII
2 ðCNÞ6 CuðCH3 OHÞ 2CH3 OHn and a facecentered cubic cluster showing single-molecule-magnet
4þ
behavior, ½ðTpÞ8 ðH2 OÞ6 Cu6 FeIII
8 ðCNÞ24 , have been
prepared by us recently [11]. Herein, we report the preparation of the precursor complex (Bu4N)[(Tp)FeIII(CN)3] (1), the crystal structures and magnetic
properties of two derivatives based on the versatile
building block, ½ðTpÞ2 FeIII
2 ðCNÞ6 MnðC2 H5 OHÞ4 2C2
H5 OH (2) and ½ðTpÞ2 FeIII
2 ðCNÞ6 NiðenÞ2 (3).
2. Experimental
2.1. Syntheses
All reagents used in the synthesis were of analytical
grade. The perchlorate complex of manganese ion is prepared by general methods. [FeII(Tp)2] [12] and
[Ni(en)3]Cl2 [13] were synthesized as described
previously.
Caution. Although we have experienced no problem
with the compounds reported in this work, manganese
perchlorate complex is potentially explosive. Cyanides
are toxic and should be handled with great care!
2.1.1. (Bu4N)[(Tp)Fe(CN)3] (1)
A mixture of [FeII(Tp)2] (0.97 g, 2 mmol) and KCN
(0.39 g, 6 mmol) in 25 ml of isopropanol was heated at
80 C for 12 h under continuous stirring. The resulting
mixture was cooled to room temperature and concentrated under reduced pressure. The residue was dissolved in 100 ml of hot water, the small fraction of
insoluble material (unreacted [FeII(Tp)2]) being removed
by filtration. (Bu4N)Cl (0.56 g, 2 mmol) and 30% H2O2
(20 ml) were added successively to the solution causing
the precipitation of 1 as an orange crystalline solid,
which was filtered, washed with water, and dried under
vacuum at room temperature. Yield: 78%. Anal. Calc.
for C44H82BFeN11: C, 63.53; H, 9.94; N, 18.52. Found:
C, 63.72; H, 9.87; N, 18.40%.
2.1.2. [(Tp)2 FeIII
2 (CN )6 Mn(C 2 H 5 OH )4 ]2C 2 H 5 OH (2)
Mn(ClO4)2 Æ 6H2O (36 mg, 0.1 mmol) was added to a
5 ml ethanol solution of (Bu4N)[(Tp)Fe(CN)3] (59 mg,
0.1 mmol) and the mixture was stirred at room temper-
ature for 2 min. After filtering, slow evaporation of the
filtrate in air afforded red plate-like crystals of 2. Yield:
74%. Anal. Calc. for C32H44MnFe2O4N18B2: C, 41.19;
H, 4.75; N, 27.02. Found: C, 41.74; H, 4.65; N, 26.88%.
2.1.3. [(Tp)2 FeIII
2 (CN )6 Ni(en)2 ] (3)
A mixture of ethanol and water (1:1, 10 ml) was
gently layered on the top of a solution of [Ni(en)3]Cl2
(91 mg, 0.2 mmol) in water (3 ml). A solution of
(Bu4N)[(Tp)Fe(CN)3] (118 mg, 0.2 mmol) in ethanol
(2 ml) was added carefully as a third layer. Orange crystals were obtained after 2 weeks, washed with ethanol
and ether, dried in air. Yield: 85%. Anal. Calc. for
C28H36N22B2NiFe2: C, 38.53; H, 4.16; N, 35.31. Found:
C, 38.17; H, 4.63; N, 35.41%.
2.2. Physical measurements
The IR spectra were taken on a Nicolet-170SX FTIR spectrophotometer with KBr pellets in the range
4000–400 cm1. Elemental analysis for C, H, N was performed on a Perkin–Elmer 240C analyzer. Variable-temperature magnetic susceptibility data were collected
using a Quantum Design MPMS SQUID magnetometer. The experimental susceptibilities were corrected for
the diamagnetism of the constituent atoms (Pascal
Tables).
2.3. Crystal data collection and refinement
The well-shaped single crystals of 2 and 3 were selected for X-ray diffraction study. Data collections were
performed on a Bruker Apex D8 diffractometer
equipped with a 4K CCD area detector for 2 at 213 K
and on a Siemens Smart CCD diffractometer for 3 at
273 K, respectively. Measurements were made by using
x scan mode in the range 1.84–26.00 for 2 and 1.19–
26.00 for 3, respectively. Structures were solved by direct methods using the program SHELXL -97 and refined
on F2 by full-matrix least-squares procedures using
SHELXTL software. All non-hydrogen atoms were aniostropically refined. All H atoms were located theoretically and not refined. Table 1 shows the crystal and
refinement data for complexes 2 and 3.
3. Results and discussion
3.1. IR Spectra
In general, the bridging and terminal cyanide groups
are usually differentiated by the positions of the corresponding C„N stretching absorption bands. The bridging cyanide ligands lead to a shift to higher
wavenumbers. At room temperature, in the solid infra-
S. Wang et al. / Inorganica Chimica Acta 358 (2005) 2101–2106
Table 1
Crystal and refinement data for complexes 2 and 3
Formula
Formular weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a ()
b ()
c ()
Z
V (Å3)
Dcalc (g cm3)
T (K)
k (Å)
l (mm1)
F(0 0 0)
h Range ()
h k l Range
Collected
Unique
Parameters
Goodness of fit
R1 (I > 2r(I))
wR2 (I > 2r(I))
(D map) maximum/
minimum (e Å3)
2
3
C36H56B2Fe2MnN18O6
1025.25
monoclinic
P21/c
9.4767(6)
16.8097(10)
14.7522(8)
90
93.3340(10)
90
2
2346.1(2)
1.451
213(2)
0.71073
0.939
1066
1.84–26.00
6 6 h 6 11,
20 6 k 6 20,
17 6 l 6 18
14 616
4615
295
1.071
0.0397
0.1034
0.629/0.956
C28H36B2Fe2N22Ni
872.82
monoclinic
P21/c
17.290(5)
8.017(2)
13.584(4)
90
97.053(6)
90
2
1868.7(9)
1.551
273(2)
0.71073
1.321
896
1.19–26.00
21 6 h 6 21,
8 6 k 6 9,
16 6 l 6 15
10 969
3663
270
1.017
0.0500
0.1114
1.003/0.960
2103
Table 2
Selected bond lengths and angles in complex 2
Bond lengths (Å)
Fe(1)–N(1)
Fe(1)–N(5)
Fe(1)–C(12)
C(13)–N(13)
Mn(1)–O(2)
Bond angles ()
Fe(1)–C(11)–N(11)
Fe(1)–C(13)–N(13)
C(11)–Fe(1)–C(13)
C(11)–Fe(1)–C(12)
N(13)–Mn(1)–O(3)
1.966(2)
1.973(2)
1.934(2)
1.148(3)
2.1647(17)
176.8(2)
176.8(2)
87.03(10)
89.99(10)
88.37(7)
Fe(1)–N(3)
Fe(1)–C(11)
Fe(1)–C(13)
Mn(1)–N(13)
Mn(1)–O(3)
1.985(2)
1.926(2)
1.916(2)
2.199(2)
2.2075(18)
Fe(1)–C(12)–N(12)
Mn(1)–N(13)–C(13)
C(12)–Fe(1)–C(13)
N(13)–Mn(1)–O(2)
O(2)–Mn(1)–O(3)
176.5(2)
170.0(2)
88.60(10)
91.87(7)
88.71(7)
Table 3
Selected bond lengths and angles in complex 3
Bond lengths (Å)
Fe(1)–C(10)
Fe(1)–C(12)
C(13)–C(14)
C(10)–N(7)
Ni(1)–N(10)
Bond angles ()
Fe(1)–C(10)–N(7)
Fe(1)–C(12)–N(9)
N(10)–C(13)–C(14)
N(7)–Ni(1)–N(10)
1.914(4)
1.927(4)
1.55(8)
1.161(5)
2.077(3)
174.6(3)
175.4(4)
114(3)
92.08(14)
Fe(1)–C(11)
C(13)–N(10)
C(14)–N(11)
Ni(1)–N(7)
Ni(1)–N(11)
1.932(4)
1.444(17)
1.44(8)
2.156(3)
2.159(4)
Fe(1)–C(11)–N(8)
Ni(1)–N(7)–C(10)
N(10)–Ni(1)–N(11)
N(7)–Ni(1)–N(11)
174.2(4)
153.8(3)
83.25(14)
90.40(13)
red spectrum of the precursor complex (Bu4N)[(Tp)Fe(CN)3] (1), only one C„N stretching (2117 cm1)
has been observed. However, in its derivatives, the
C„N stretching frequencies are located at 2154 and
2130 cm1 for 2, and at 2143 and 2125 cm1 for 3, which
are consistent with the presence of bridging and terminal
cyanide ligands.
3.2. Crystal structures
Selected bond lengths and angles are compiled in
Tables 2 and 3.
The ORTEP drawing for 2 is depicted in Fig. 1. Complex 2 consists of centrosymmetric neutral trinuclear
entities of the formula [{(Tp)Fe(CN)3}2Mn(C2H5OH)4]
and ethanol molecules. In this trinuclear cluster,
[(Tp)Fe(CN)3] acts as a monodentate ligand through
one of its three cyanide groups toward a central
[Mn(C2H5OH)4]2+ core. Each iron (III) ion is coordinated by three Tp nitrogen atoms and three cyanide carbon atoms, taking a similar C3v symmetry. The Fe(1)–
C(cyano) bond length (1.916(2)–1.934(2)Å) is in good
agreement with those observed in the low-spin iron
(III) cases [8,9]. The Fe–C„N angles for both terminal
(176.5(2) and 176.8(2)) and bridging (176.8(2)) cyanide
groups depart somewhat from strict linearity. The man-
Fig. 1. Molecular structure of complex 2. The solvated ethanol
molecules and hydrogen atoms have been omitted for clarity (ORTEP,
50% ellipsoids).
ganese atom is six-coordinated in a distorted N2O4 environment. Four oxygen atoms from the ethanol
molecules form the equatorial plane. The Mn(1)–O distances (2.1647(17) and 2.2075(18) Å) are almost equivalent. Two cyanide nitrogen atoms occupy the axial
positions. The Mn(1)–N(13) bond distance is 2.199(2)
Å. The Mn(1)–N(13)„C(13) bond angle is 170.0(2),
which departs clearly from 180. The O(2)–Mn(1)–
N(13) and O(3)–Mn(1)–N(13) bond angles are
91.87(7) and 88.37(7), respectively. Noncoordinated
C2H5OH molecules are inserted into crystal spacing.
The intramolecular Fe Mn and Fe Fe separations through bridging cyanides are 5.2354(4) and
2104
S. Wang et al. / Inorganica Chimica Acta 358 (2005) 2101–2106
5.4
-1
χmT/ cm mol K
4.8
3
4.2
3.6
3.0
Fig. 2. Molecular structure of complex 3. The hydrogen atoms have
been omitted for clarity (ORTEP, 50% ellipsoids).
2.4
1.8
10.4707(8) Å, respectively. The shortest intermolecular
Fe Fe, Fe Mn and Mn Mn separations through
bridging cyanides are 7.7572(7), 7.2781(5) and
9.4767(6) Å, respectively.
The crystal structure of complex 3 is similar to complex 2 except the central [Ni(en)2]2+ core (Fig. 2). The
Fe–C„N angles for both terminal (174.2(4)–175.4(4))
and bridging (174.6(3)) cyanide groups also depart
from strict linearity. The nickel atom is octahedrally
coordinated through four nitrogens from the ethylenediamines and two nitrogens from the bridging cyanide
groups. The carbon atoms of the ethylenediamine molecules are disordered as shown in Fig. 2, which is often
seen in the ethylenediamine complexes. The Ni(1)–N(cyano) bond distance is 2.156(3) Å, which is similar to the
Ni(1)–N(en) bond lengths (2.077(3)–2.159(4) Å). The
bridging cyanide ligands coordinate to the nickel (II)
in a bent fashion with Ni–N„C bond angle of
153.8(3), which is comparable with 153.4(7) and
169.2(7) in other Ni–N„C complexes [14]. The intramolecular Fe Ni and Fe Fe separations through
bridging cyanides are 5.0669(11) and 10.134(2) Å,
respectively. The shortest intermolecular Fe Fe,
Fe Ni and Ni Ni separations through bridging cyanides are 6.7934(19), 6.3858(13) and 7.8866(17) Å,
respectively.
3.3. Magnetic properties
The temperature dependence of vmT for complex 2
(vm being the magnetic susceptibility per Fe2Mn unit)
is shown in Fig. 3. The value of vmT at room temperature is 5.30 cm3 mol1 K (6.51lB). This value is consistent with the presence of a high spin Mn(II) atom and
two low-spin Fe(III) atoms magnetically isolated. It is
almost independent of temperature in the range of 80–
300 K but decreases with further lowering temperature
up to the minimum value of 2.20 cm3 mol1 K at 2 K,
indicating a weak antiferromagnetic interaction between
the Mn(II) and Fe(III) ions.
The magnetic data were fitted into the isotropic
Hamiltonian:
0
50
100
150
200
250
300
T/K
Fig. 3. Plot of temperature dependence of vmT measured at 2 kOe field
for 2; the solid line represents the best-fit curve from 10 to 300 K.
^ ¼ 2J ðS^1 S^2 þ S^2 S^3 Þ 2J 0 S^1 S^3 ;
H
ð1Þ
where S^1 , S^2 and S^3 are the spin operators of iron (III),
manganese (II) and iron (III), respectively; J and J 0 are
the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively.
Because the two iron (III) ions in the iron (III)–manganese (II)–iron (III) heterotrinuclear clusters are far
apart, the quality of fit does not depend on J 0 and hence
the fit with J 0 = 0 has been accepted to be more plausible. The theoretical expression of the magnetic susceptibility of the FeIII–MnII–FeIII(S1 = S3 = 1/2, S2 = 5/2) is:
vm ¼ Ng2 b2 =4kT ðA=BÞ;
ð2Þ
A ¼ 35 þ 10 expð7J =kT Þ þ 35 expð2J =kT Þ
þ 84 expð5J =kT Þ;
B ¼ 3 þ 2 expð7J =kT Þ þ 3 expð2J =kT Þ
þ 4 expð5J =kT Þ:
The best fit to the experimental data above 10 K gives
1
J
=
The agreement factor R ¼
P 1.37 cm , g = 2.05.
2 P
2
½ðvM T Þobsd ðvM T Þcald = ½ðvM T Þobsd is 6.9 · 105
(Fig. 3). The J-value can be compared with the value
of 1.8 cm1 observed in another centrosymmetric
Fe(III)–Mn(II)–Fe(III) trinuclear complex [9b].
The magnetic centers in complex 3 have similar linkages to complex 2, but they show the very different magnetic behaviors due to the replacement of the Mn(II) ion
in 2 by the Ni(II) ion in 3 (Fig. 4). For complex 3, the
value of vmT at room temperature is 2.88 cm3 mol1 K
(4.80lB), higher than the expected spin-only value of
1.75 cm3 mol1 K per Fe2Ni unit (gFe = gNi = 2,
SFe = 1/2 and SNi = 1), indicating a possible ferromagnetic coupling between the Fe(III) and Ni(II) centers.
When the temperature is lowered, it slowly increases
up to a maximum value of 3.11 cm3 mol1 K around
S. Wang et al. / Inorganica Chimica Acta 358 (2005) 2101–2106
Union Road, Cambridge, CB2 1EZ, UK. (Fax: +441223-336-033; email: http://deposit@ccdc.cam.ac.ukor
www: http://www.ccdc.cam.ac.uk).
3.2
2.8
χ mT / cm3 mol-1 K
2105
2.4
Acknowledgments
2.0
This work was supported by The Major State Basic
Research Development Program (G2000077500), the
National Natural Science Foundation of China
(NSF20201006 and 90101028). The X-ray diffractometer
is supported by NSF Grant EAR-0003201.
1.6
1.2
0
50
100
150
200
250
300
T/K
Fig. 4. Plot of temperature dependence of vmT measured at 2 kOe field
for 3; the solid line represents the best-fit curve from 20 to 300 K.
18 K and then abruptly decreases below this temperature. This indicates a weak ferromagnetic interaction between metal ions dominating the magnetic properties in
this system. The ferromagnetic interaction is due to the
orthogonality of the magnetic orbitals of the low-spin
Fe(III) and Ni(II) ions.
The same fitting method as complex 2 is available to
the magnetic properties of complex 3 except S2 = 1 (for
Ni(II) ion), the theoretical expression of the magnetic
susceptibility is:
vM ¼ 2Ng2 b2 =kT ðA=BÞ;
ð3Þ
A ¼ 1 þ 5 expð2J =kT Þ þ expð2J =kT Þ;
B ¼ 3 þ 5 expð2J =kT Þ þ 3 expð2J =kT Þ þ expð4J =kT Þ:
The best fit to the experimental data above 20 K gives
1
J
=
factor R ¼
P 1.2 cm , g = 2.25. 2 The
P agreement
2
½ðvM T Þobsd ðvM T Þcald = ½ðvM T Þobsd is 2.44 · 106,
which corresponds to a good agreement as shown in
Fig. 4. The small NiII–FeIII exchange coupling parameter might be attributed to the more bent Ni–N„C bond
angle (153.8(3)) and is comparable with the value of
1.9, 2.1 and 2.4 cm1 reported in the cyano-bridged
NiII–FeIII complexes with Ni–N„C bond angles ranging from 147.1(6) to 169.2(7) [14]. However, in the Ni4Fe4(CN)12 cluster containing more linear Ni–N„C
bond angles (177(3)), the value of J is 5.5 cm1 [7].
4. Supplementary material
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Center, CCDC Nos.
243065 and 243066. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
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