Synthesis, crystal structure, and magnetic properties of a very rare double μ-1,1-Azido- and a μ-1,1-(OMe)-bridged FeIII dimer containing a N,N,O-donor tridentate schiff base ligand

Article abstract of DOI:10.1002/ejic.201100552

Two new Fe^III complexes, [Fe₂L₂(μ-OMe) ₂(NCS)₂] (1) and [Fe₂L₂(μ-N ₃)₂(N₃)₂] (2), have been synthesized using a N,N,O-donor tridentate Schiff base ligand HL {2-[(2- dimethylaminoethylimino)methyl]phenol}, the condensation product of salicylaldehyde and N,N-dimethyl-1,2-diaminoethane. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both crystal structures are centrosymmetric dimers containing two Fe^III atoms, which are bridged in compound 1 by two methoxy anions and in compound 2 by two μ-1,1-azides. The chelating tridentate Schiff base and a terminal thiocyanato (for 1) or azido (for 2) group complete the hexacoordination of the distorted octahedral environment of each iron center. The magnetic properties of compound 1 show the presence of antiferromagnetic exchange interactions mediated by double methoxy bridges (J =-29.45 cm^-1). Compound 2 shows the presence of very weak ferromagnetic exchange interactions mediated by double μ-1,1-N₃ bridges (J = 1.08 cm^-1). A very rare μ-1,1-azido-bridged and a μ-OMe-bridged dinuclear Fe^III compound with a tridentate N,N,O-donor Schiff base have been synthesized and characterized structurally. The former is only the third example of μ-1,1-azido bridges in Fe ^III. The variable-temperature magnetic studies show that the former is ferromagnetically and the latter antiferromagneticallycoupled.

Full text of DOI:10.1002/ejic.201100552

FULL PAPER
DOI: 10.1002/ejic.201100552
Synthesis, Crystal Structure, and Magnetic Properties of a Very Rare Double
μ-1,1-Azido- and a μ-1,1-(OMe)-Bridged FeIII Dimer Containing a N,N,O-
Donor Tridentate Schiff Base Ligand
Subrata Naiya,[a,b] Michael G. B. Drew,[c] Carmen Diaz,*[d] Joan Ribas,[d] and
Ashutosh Ghosh*[a]
Keywords: Iron / Schiff bases / Magnetic properties / N,N,O ligand / Azido bridges
Two new FeIII complexes, [Fe2L2(μ-OMe)2(NCS)2] (1) and
[Fe2L2(μ-N3)2(N3)2] (2), have been synthesized using
μ-1,1-azides. The chelating tridentate Schiff base and a ter-
minal thiocyanato (for 1) or azido (for 2) group complete the
hexacoordination of the distorted octahedral environment of
each iron center. The magnetic properties of compound 1
show the presence of antiferromagnetic exchange interac-
tions mediated by double methoxy bridges (J = –29.45 cm–1).
Compound 2 shows the presence of very weak ferromagnetic
exchange interactions mediated by double μ-1,1-N3 bridges
(J = 1.08 cm–1).
a
N,N,O-donor tridentate Schiff base ligand HL {2-[(2-dimeth-
ylaminoethylimino)methyl]phenol}, the condensation prod-
uct of salicylaldehyde and N,N-dimethyl-1,2-diaminoethane.
The complexes were characterized by X-ray structural analy-
ses and variable-temperature magnetic susceptibility mea-
surements. Both crystal structures are centrosymmetric di-
mers containing two FeIII atoms, which are bridged in com-
pound 1 by two methoxy anions and in compound 2 by two
a ferromagnetic coupler with M–N–M angles as wide as
108°.[7] However, such ligands have seldom been used to
synthesize complexes with FeIII. They usually afforded
mononuclear bis(Schiff base) species,[8] except in a few cases
where oxido-, alkoxido- or hydroxido-bridged dinuclear
complexes resulted.[9] The mononegative tridentate Schiff
bases along with two pseudohalide ions balance the charge
of FeIII, but one of the pseudohalide ions should act as a
bridging ligand to complete the usual hexacoordination of
FeIII. Thus these groups of tridentate Schiff bases have the
potential to produce pseudohalide-bridged FeIII complexes
although no such example is found in the literature.
In the present contribution, the tridentate N,N,O-donor
Schiff base (HL), which results from the monocondensation
of salicylaldehyde and 1,2-bis(dimethylamino)ethane
(Scheme 1), has been used to synthesize the two new ferric
compounds [Fe2L2(μ-OMe)2(NCS)2] (1) and [Fe2L2(μ-N3)2-
(N3)2] (2). Herein, we present the syntheses, crystal struc-
tures, and variable-temperature magnetic properties of these
two compounds. Complex 1, a double methoxy-bridged di-
mer is antiferromagnetically coupled whereas complex 2 a
double μ-1,1-azido-bridged dimer is ferromagnetically cou-
Introduction
The chemistry of iron(III) complexes is dominated by
oxygen-bridged species because of the high oxygen affinity
of the iron(III) ion.[1] This type of oxygen-bridged dinuclear
iron(III) unit is also valuable to synthetic chemists because
of its relevance in biological systems.[2] Such units are pres-
ent at the active site of numerous non-heme metalloen-
zymes such as hemerythrin, a dioxygen carrier protein.[3]
Synthetic efforts to prepare model complexes of iron pro-
teins have yielded several unexpected and interesting oxy-
gen-bridged polyiron compounds, the magnetic properties
of which have motivated interesting studies concerning their
unusual electronic structure.[4]
The tridentate Schiff base ligands, derived from the
monocondensation of a diamine and salicylaldehyde deriva-
tive have been used extensively along with pseudohalides to
construct various polynuclear complexes of CuII and NiII
that show interesting structural and magnetic properties.[5–6]
Among them the μ-1,1 (end-on) azido-bridged compounds
are of special interest in designing new polynuclear species
exhibiting ferromagnetic coupling as this bridging mode is
[a] Department of Chemistry, University College of Science,
University of Calcutta,
92, A. P. C. Road, Kolkata 700009, India
[b] Susil Kar College, Ghoshpur, Champahati,
Baruipur, 24 Parganas (S), West Bengal 743330, India
[c] School of Chemistry, The University of Reading,
P. O. Box 224, Whiteknights, Reading RG6 6AD, UK
[d] Departament de Química Inorgànica, Universitat de Barcelona,
Marti i Franques 1-11, 08028 Barcelona, Spain
Scheme 1. The ligand HL.
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pled. To the best of our knowledge, complex 2 is only the base. In the spectrum of complex 1 a strong band at
third example of a μ-1,1-azido-bridged FeIII species and the 2108 cm–1 is indicative of the presence of the N-coordinated
first one with a tridentate Schiff base as coligand.
thiocyanate.[10] While two overlapping but distinct peaks at
2051 to 2063 cm–1 for complex 2 corroborate the presence
of two types of azido (terminal and μ-1,1 bridging, respec-
tively) in the complex.[5b]
The electronic spectra of compounds 1 and 2 are re-
corded in methanol and acetonitrile solution, respectively.
The spectrum of complex 1 shows one band in the visible
Results and Discussion
Synthesis of the Complexes
The hydroxido- and oxido-bridged dinuclear FeIII com-
plexes with the monocondensed tridentate Schiff base li-
gand 2-[(2-dimethylaminoethylimino)methyl]phenol (HL)
(Scheme 1) have been reported by us recently.[9d] In the
present investigation we have used this ligand for the syn-
thesis of two new FeIII dinuclear complexes. The two metals
are bridged by two methoxy anions in 1 and by two azides
in 2. Complex 1 has been synthesized by the reaction of
FeCl3, the Schiff base ligand (HL), and a coligand thiocyan-
ate ion in a 1:1:2 molar ratio in a methanol medium
(Scheme 2). When we tried to obtain complex 2 by the same
procedure using azide instead of thiocyanate as coligand,
we obtained a mixture of products: a good crystalline com-
pound that turned out to be 2 along with a microcrystalline
product. The elemental analysis and spectral study of the
latter suggested that its formula was [Fe2L2(OMe)2(N3)2].
As we could not synthesize it in pure form, we do not re-
port details here. However compound 2 could be obtained
as the sole product when FeCl3, the Schiff base (HL), and
sodium azide were allowed to react in an acetonitrile me-
dium.
(λmax = 433 nm) and another in the near-UV (λmax
=
330 nm) region. The former (lower energy) band can be at-
tributed to thiocyanato–FeIII charge transfer and the latter
(higher energy) band at 330 nm is a superposition of the
azomethine π–π* transition band and the charge-transfer
bands from oxygen to FeIII [9a,9e]
The spectrum of 2 presents
.
similar features to that of complex 1. The higher energy
band (near UV region) lies at λmax = 325 nm, which is at-
tributed to the π–π* transition of the azomethine linkage
and the lower energy band (near the Vis region) λmax
=
425 nm corresponds to an azide-to-FeIII charge-transfer
band.
Description of Structures of the Complexes
Complex 1
Both the structures are centrosymmetric dimers in which
the iron atoms have distorted six-coordinate octahedral en-
vironments. Bond lengths and bond angles are given in
Table 1. The structure of 1 is shown in Figure 1 together
with the atom numbering scheme in the metal coordination
sphere.
Table 1. Dimensions in the metal coordination sphere, distances
[Å], angles [°].
Bond lengths
1, X = O
2, X = N
Fe(1)–N(19)
Fe(1)–N(22)
Fe(1)–O(11)
Fe(1)–N(1)
Fe(1)–X(4)a
Fe(1)–X(4)
2.134(2)
2.252(1)
1.913(1)
2.061(2)
1.983(1)
2.003(1)
2.109(2)
2.240(2)
1.911(2)
2.002(2)
2.088(2)
2.137(2)
Bond angles
O(11)–Fe(1)–X(4)a
O(11)–Fe(1)–X(4)
X(4)–Fe(1)–X(4)a
O(11)–Fe(1)–N(1)
X(4)a–Fe(1)–N(1)
X(4)–Fe(1)–N(1)
O(11)–Fe(1)–N(19)
X(4)a–Fe(1)–N(19)
X(4)–Fe(1)–N(19)
N(1)–Fe(1)–N(19)
O(11)–Fe(1)–N(22)
X(4)a–Fe(1)–N(22)
X(4)–Fe(1)–N(22)
N(1)–Fe(1)–N(22)
N(19)–Fe(1)–N(22)
100.27(5)
92.64(5)
74.24(6)
92.12(6)
93.42(6)
167.40(6)
86.06(6)
171.34(5)
99.74(5)
92.23(6)
162.72(5)
97.00(5)
92.52(5)
86.32(6)
76.81(5)
101.21(7)
91.40(7)
72.21(9)
93.82(8)
92.12(8)
164.19(8)
86.47(7)
164.15(7)
93.94(7)
101.26(8)
163.03(7)
95.60(7)
91.52(7)
87.83(8)
76.65(7)
Scheme 2. Synthetic route to 1 and 2.
IR and UV/Vis Spectra of the Complexes
The spectroscopic data and their assignments are given
in the Experimental Section. The IR spectra of the two
complexes are very similar to each other with regard to the
tridentate L– ligand. Both of them show a strong and sharp
peak for ν(C=N) at 1616 and 1619 cm–1 for complexes 1
Symmetry elements for 1, a: 2 – x, 2 – y, 1 – z; for 2, a: 1 – x, –y,
and 2, respectively, indicating the presence of the Schiff 2 – z.
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Rare Bridged FeIII Dimers
anato ligand, and the shortest Fe-μ-OMe bond [1.983(1) Å]
is trans to the imino nitrogen atom.
In compound 1, there are two weak intramolecular H-
bonding interactions: one between the H22E and O11 atom
(1 – x, –y, 2 – z) with dimensions C221···O11 3.251(2) Å,
H22E···O11 2.33 Å, and C221···H22A···O11 161° and the
other between the H5A and N1 atom (1 – x, –y, 2 – z)
with dimensions C5···N1 3.184(3) Å, H5A···N1 2.57 Å, and
C5···H5A···N1 122° (Figure S1). No significant intermo-
lecular interactions have been found.
Complex 2
The structure of 2 is shown in Figure 2 together with the
atomic numbering scheme. Bond lengths and bond angles
are given in Table 1. Complex 2 differs from 1 only in that
the bridging groups and one of the coligands are azido
rather than methoxy. The geometry of the ligand is similar,
with Fe(1)–O(11) 1.911(2) Å, Fe(1)–N(19) 2.109(2) Å, and
Fe(1)–N(22) 2.240(2) Å, but the bonds to the bridging ni-
trogen atoms are significantly longer at 2.088(2) and
2.137(2) Å than those to the bridging methoxy oxygen
atoms in 1. The equatorial plane is far more distorted than
Figure 1. Structure of complex 1. (a) The centrosymmetric struc-
ture with ellipsoids drawn at 50% probability. (b) Edge-sharing di-
meric structure of 1.
In 1 the iron atom is bonded to three atoms of the merid-
ionally coordinated tridentate ligand with the following
bond lengths: Fe–O(11) 1.913(1) Å, Fe–N(19) 2.134(2) Å,
and Fe–N(22) 2.252(1) Å. The equatorial plane is com-
pleted by a bridging methoxy group with an Fe–O(4)a bond
length of 1.983(1) Å. In the axial positions a second meth-
oxy group, O(4) with a bond length of 2.003(1) Å, and a
terminal thiocyanato group, N(1) with a bond length of
2.032(3) Å, are present. Thus the two FeIII octahedra are
joined together by two bridging methoxy groups sharing an
edge as shown in Figure 1 (b). The four donor atoms in the
equatorial plane are nearly coplanar with an r.m.s. devia-
tion of 0.066 Å. The iron atom is 0.041(1) Å from this plane
in the direction of N(1). Within the dimer the Fe–Fe separa-
tion is 3.178(1) Å and the distance between the two bridg-
ing oxygen atoms is 2.405(4) Å, both of which are compar-
able with those reported previously in di-μ-methoxy-
bridged diferric complexes.[9a,9b] The μ-OMe bridge in this
complex leads to a perfectly planar Fe2(μ-OMe)2 ring as the
dimer sits on a crystallographic inversion center. The Fe–
O–Fe angle [105.75(6)°] and O–Fe–O angle [74.25(6)°] also
lie within the ranges of similar compounds.[9a,9b,11] The two
Fe-μ-OMe bond lengths are slightly different making the
Fe2O2 core asymmetric, which is a common feature for such
dimers. The phenyl rings are almost perpendicular to the
Fe2(μ-OMe)2 core with a dihedral angle of 85.90(8)°. The
Figure 2. Structure of complex 2. (a) The centrosymmetric struc-
ture with ellipsoids drawn at 50% probability. (b) Edge-sharing di-
longest Fe-μ-OMe [2.003(1) Å] bond is trans to the thiocy- meric structure of 2.
Eur. J. Inorg. Chem. 2011, 4993–4999
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S. Naiya, M. G. B. Drew, C. Diaz, J. Ribas, A. Ghosh
FULL PAPER
in 1 with an r.m.s. deviation for the four donor atoms of Magnetic Properties
0.123 Å. The iron atom is 0.130(1) Å from the mean plane
The variable-temperature magnetic susceptibility of com-
in the direction of the terminal N(1) azido group. Two azido
ions bridge the FeIII ions in a μ-1,1 (end-on) fashion. Like
complex 1 two FeIII octahedrals are joined together by two
bridging azido groups sharing an edge as shown in Figure 2
(b). The bond length involving the axial bridging azido is
2.137(2) Å, much longer than that of the equatorial bridg-
ing azido [2.088(2) Å]. The Fe2N2 ring is perfectly planar as
the dimer sits on a crystallographic inversion center. The
intradimer metal···metal separation is 3.413(1) Å, and the
plexes 1 and 2 has been recorded in the region 2–300 K,
under an applied field of 5000 G in all ranges of tempera-
ture and 300 G only at low temperatures. A plot of χMT vs.
T for complex 1 is shown in Figure 3. The χMT value at
300 K (5.62 cm3 mol–1 K) is well below the expected value
for two high-spin Fe3+ ions (8.75 cm3 mol–1 K assuming g =
2). Upon cooling, the χMT product decreases continuously
to 0 cm3 mol–1 K at 2 K, indicating the occurrence of an
antiferromagnetic intramolecular interaction between the
two Fe3+ ions. The χMT vs. T data were fitted to the theo-
retical equation[14] derived for a Heisenberg exchange
model, (H = –JS1S2) with S1 = S2 = 5/2. The best fit gave
J = –29.45 cm–1, g = 2.03 and R = 4.8ϫ10–5. The agree-
ment factor R is defined as R = Σi[(χMT)obsd – (χMT)calcd]2/
Σi[(χMT)obsd]. It is to be emphasized that the magniude of
the J value must be taken with a certain amount of caution
because we have not considered the possible D value or the
zЈJЈ value (antiferromagnetic) resulting from the molecular
packing. This consideration is made for antiferromagnetic
systems because their effect on the curve, at low tempera-
tures, is the same as JAF and, thus, their inclusion only over-
parametrizes the fit. However, the D and/or zЈJЈ values
must be considered when the coupling is ferromagnetic (see
below for complex 2). Indeed, the value of the exchange
coupling constant of complex 1 is perfectly in line with the
values reported for other dimethoxido-bridged iron(III)
complexes with similar structural features: Fe···Fe distances,
Fe–O–Fe angles, and Fe···O distances.[9a,11,15–20] In Table 2
we list the examples of dimethoxido-bridged iron(III) com-
plexes upon which both structures and magnetic studies
have been performed, including J values and the three
structural parameters. Although it is clear that the above
geometrical parameters play a role in their contribution to
the coupling constant J, the trend of the J parameter in
systems with analogous geometrical parameters and similar
J values is still largely unexplained.
N
(bridging)–Fe–N(bridging) and Fe–N–Fe bond angles are
72.21(9)° and 107.79(9)°, respectively. These values are close
to those reported for other high-spin dinuclear bis(μ-end-
on-azido)iron(III) complexes.[12–13] The dihedral angle be-
tween the phenyl rings and the Fe2N2 core (75.159°) is
slightly less than that in complex 1, where the distance be-
tween the two bridging nitrogen atoms [2.49(1) Å] is slightly
greater than that in 1. Both the bridging and terminal azido
ligands are quasi-linear, and the value of the N–N–N angle
varies between 178.2(3)° and 179.4(3)°.
In this compound, there is a weak intramolecular H-
bonding interaction between the H22A and O11 atoms (2 –
x, 2 – y, 1 – z) with dimensions C221···O11 3.411(3) Å,
H22A···O11 2.48 Å, and C221···H22A···O11 162°. There
are also two other very weak interdimer interactions: one
between the N6 atom of one molecule and the H20A atom
of a neighboring molecule (3/2 –x, –1/2 + y, 1/2 – z) and
the other between the N6 atom and H22D atom of another
neighboring molecule (1/2 + x, 3/2 – y, 1/2 + z) with dimen-
sions
C20···N6
3.273(4) Å,
H20A···N6
2.54 Å,
C20···H20A···N6 133°, C222···N6 3.206(4) Å, H22D···N6
2.59 Å, and C222···H22D···N6 122°. These noncovalent in-
teractions are likely to control the packing of the molecules
(Figure S2).
It is worth noting that most of the previously reported
FeIII complexes of tridentate N,N,O-donor Schiff base li-
gands are bis(Schiff base) complexes with non-coordinating
–
–
–
counter anions such as ClO4 , NO3 , PF6 , etc.[8] Only a
few mono(Schiff base) complexes are reported and among
them two are methoxido-,[9a,9b] one ethoxido-,[9b] one hy-
droxido-,[9d] and two are oxido-bridged diferric com-
pounds.[9c–9d] Therefore, the methoxy-bridged diferric com-
pound 1 is rather uncommon with tridentate Schiff bases
although commonplace with other types of ligands. On the
other hand, μ-1,1-azido bridged iron(III) complexes are
very rare with any type of coligands. To the best of our
knowledge, only two such examples are reported to date.
One is a double μ-1,1-azido-bridged diiron(III) complex de-
rived from a tetradentate N2O2 donor Schiff base, N,NЈ-
bis(salicylidene)-1,3-diaminopropane, while the other is a
III
dinuclear μ-1,1-azido-bridged anionic species, [Fe2
-
(N3)10]4–, isolated with the help of a cationic species, [FeII-
(bpym)]2+ (bpym = 2,2Ј-bipyrimidine). Thus compound 2
is the first example of a double 1,1-azido-bridged dimer of
FeIII with a tridentate N,N,O-donor Schiff base ligand,
Figure 3. Plot of χMT vs. T of compound 1. The solid line is the
best fit to the experimental data.
A plot of χMT vs. T, for complex 2, where χM is the mag-
whereas more than thirty similar CuII and at least five NiII netic susceptibility per formula unit, in the temperature
complexes are known with this type of ligands.
range 2–300 K is shown in Figure 4. The χMT value is
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Rare Bridged FeIII Dimers
Table 2. Relative bond angles and bond lengths of other reported dimethoxido-bridged iron(III) complexes.
Fe···Fe [Å]
Fe–O–Fe [°]
Fe···O [Å]
J [cm–1]
Complex 1[a]
3.178
3.145
3.164
3.085
3.18
3.11
3.087
3.105
3.194
105.8
104.2
104.97
102.73
104.44
104.35
102.0
103.7
104.7
104.3
103
1.993
1.992
1.994
1.967
1.955
2.00
1.987
1.974
1.987
1.948
1.920
–29.35
–24.2
–27
[Fe2(H3L3)2(OMe)2]·8MeOH[b]
[c]
[Fe2(mxba)2(OMe)2]·CH2Cl2
[Fe2(HL)4(OMe)2][d]
–27.4
–29.4
–27.3
–15.4
–19.0
–26.8
–28.6
–16.3
[Fe2Cl4(amp)4(OMe)2][e]
[Fe2(Cl)2(salEen)2(OMe)2][f]
[Fe2(dbm)4(OMe)2][g]
[Fe2(dpm)4(OMe)2][g]
[Fe2(chp)4(dmbipy)2(OMe)2]·2MeOH[h]
[Fe2(chp)4(phen)2(OMe)2]·2MeOH[h]
[Fe2Cl2L(OMe)2][i]
3.153
3.106 / average
[a] This work. [b] H5L3 = 2-hydroxy-N-{3-hydroxy-5-[(2-hydroxybenzoyl)amino]pentyl} benzamide, ref.[15] [c] mxba = m-xylylenebis(acet-
ylacetone), ref.[16] [d] H2L = 2-salicyloylhydrazono-1,3-dithiolate, ref.[17] [e] amp = 2-(aminomethyl)pyridine, ref.[18] [f] HsalEen = N-ethyl-
N-(2-aminoethyl)salicylaldimine, ref.[9a] [g] dbm = dibenzoylmethane, dpm = dipivaloylmethanate, ref.[19] [h] Hchp = 6-chloro-2-pyridone,
dmbipy = 4,4Ј-dimethyl-2,2Ј-bipyridine, phen = 1,10-phenanthroline, ref.[20] [i] L = 1,4-piperazinebis(N-ethylenesalicylaldimine), ref.[11]
8.36 cm3 mol–1 K at 300 K. This value agrees well with that butions from both are impossible to separate. As a conclu-
expected for the two spin-only FeIII ion (S = 5/2) values sion, it is important to underline that |D| is not necessarily
of 8.75 cm3 mol–1 K. Upon cooling the χMT value increases 6.8 cm–1; this value is simply the limit when zЈJЈ is (artifi-
smoothly to a maximum of 9.48 cm3 mol–1 K at 12 K, which cially) assumed to be 0.
suggests the presence of ferromagnetic coupling between
The magnetic susceptibility data treatment for complex
the FeIII ions. Below 12 K, χMT drops down, reaching 2 was made using the MAGPAK program[21] employed with
5.50 cm3 mol–1 K at 2 K. Considering the rhombicity of the a nonlinear least-squares curve-fitting program DSTE-
iron sides (see structural part), and the drastic decrease of PIT.[22]
the susceptibility data at low temperature, the experimental The above results are in accordance with the literature
data was fitted using the following Hamiltonian in which data since azido ligands are known to generally propagate
single-ion anisotropy is assumed:
ferromagnetic coupling interactions between nickel(II),
manganese(II), or copper(II) centers when bound in a μ-1,1
end-on mode. Correlations between structural parameters
that exert the largest influence, in particular the M–N–M
angle, and the energy gap between the magnetic orbitals has
been well-established experimentally for μ-1,1-N3-bridged
CuII dinuclear complexes.[7] In the case of iron(III) dinu-
clear complexes, this structure relationship has not been
tested to date since only two such compounds have been
reported.[12–13] The value of the exchange coupling constant
of complex 2 (Fe···Nav.dist. 2.112 Å, Fe–N–Feangle 107.78°,
and J = 1.08 cm–1) is perfectly in line with the previously
H = –J(S1S2) + Σi = 1–2 (gFeμBSi·Hi + Si·Di·Si)
reported
complexes:
[Fe(bpym)3]2[Fe2(N3)10]·2H2O
(Fe···Nav.dist. 2.179 Å, Fe–N–Fe 106.0°, and
J
=
4.80 cm–1),[13] and [Fe2(N3)2(salpn)2] (Fe···Nav.dist. 2.118 Å,
Fe–N–Fe 107.1°, and J = 1.05 cm–1).[12] The D value of the
FeIII ion is of the same order as that reported by Boca for
high-spin FeIII mononuclear complexes.[23]
Figure 4. Plot of χMT vs. T of compound 2. The solid line is the
best fit to the experimental data.
Further examples of FeIII complexes with this structural
type are needed to characterize the influence of the angle
at the azido bridge on the nature and magnitude of the
magnetic coupling.
The single-ion anisotropy parameters, D and E, are as-
sumed to be the same for the two iron ions. The best fit was
found with J = 1.1(1) cm–1, g = 2.02, |D| = 6.4(2) cm–1and
|E| = 0.31(2) cm–1. However, the χMT decrease at very low
temperatures could also be due to intermolecular interac-
tions (generally antiferromagnetic). For this reason we have
also fitted the experimental curve by means of the mean-
field approach, assuming (in an artificial manner) that D
Conclusions
The tridentate Schiff base ligand 2-[(2-dimethylamino-
= 0. With this approach the best fit parameters were J = ethylimino)methyl]phenol produces two new dinuclear com-
1.08(1) cm–1, g = 2.02, zЈJЈ = –0.19(3) cm–1. As a conse- plexes, [Fe2L2(μ-OMe)2(NCS)2] (1) and [Fe2L2(μ-N3)2-
quence, we can state that the decreasing χMT has a combi- (N3)2] (2), with pseudohalide coligands, thiocyanato and
nation of the two parameters, D and zЈJЈ, and the contri- azido, respectively. In 1, two FeIII centers are joined to-
Eur. J. Inorg. Chem. 2011, 4993–4999
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4997

S. Naiya, M. G. B. Drew, C. Diaz, J. Ribas, A. Ghosh
FULL PAPER
acetonitrile/water solution (9:1, v/v) of NaN3 (0.650 g, 10 mmol)
was added. By slow evaporation of the solution, needle-shaped,
black-colored X-ray-quality, single crystals were obtained over-
night; yield 1.29 g; (78%). C22H30Fe2N16O2 (2, 662.28): calcd. C
39.90, H 4.57, N 33.84; found C 39.95, H 4.54, N 33.81. IR (KBr
gether by methoxy bridges and the thiocyanato ions remain
terminally coordinated. This is to be expected because of
the high oxophilicity of FeIII. On the other hand, a double
μ-1,1-azido bridge, which has rarely been found in FeIII
complexes, holds the two iron centers in 2. It is therefore
apparent that under suitable conditions the azido-bridged
complexes of FeIII can also be formed with tridentate
N,N,O-donor Schiff base ligands as is the case for other
metal ions e.g. CuII, NiII, etc. The moderate intradimer cou-
pling in 1 with J = –29.45 cm–1 is in good agreement with
that found in similar methoxy-bridged complexes. The weak
pellet): ν = 2063 ν(N=N) (bridging), 2051 ν(N=N) (terminal), 1616
˜
ν(C=N) cm–1. λmax (acetonitrile) = 325 and 425 nm.
Crystal Data Collection and Refinement: Crystal data for the two
crystals are given in Table 3. 4080 and 4289 independent reflections
were collected for Compound 2 and 1, respectively, with Mo-Kα
radiation at 150 K using the Oxford Diffraction X-Calibur CCD
System. The crystals were positioned at 50 mm from the CCD. 321
frames were measured with a counting time of 10 s. Data analyses
were carried out with the CrysAlis program.[24] The structures were
ferromagnetic coupling in 2 corroborates with that in FeIII
also the μ-1,1-azido bridge mediates ferromagnetic coupling
,
with an Fe–N–Fe angle as high as 107.78°, like in the other solved by direct methods with the Shelxs97 program.[25] The non-
hydrogen atoms were refined with anisotropic thermal parameters.
The hydrogen atoms bonded to carbon were included in geometric
positions and given thermal parameters equivalent to 1.2 times (1.5
times for methyl groups) those of the atom to which they were
attached. Absorption corrections were carried out using the AB-
SPACK program.[26] The structures were refined on F2 using
Shelxl97[25] to R1 0.0333, 0.0414; wR2 0.0835, 0.0941 for 3102, 2478
reflections with IϾ2σ(I).
first transition metal ions.
Experimental Section
Materials: The reagents and solvents used were of commercially
available reagent quality.
Caution: Azide salts of metal complexes with organic ligands are
potentially explosive. Only a small amount of material should be
prepared and it should be handled with care.
Table 3. Crystal data and structure refinement of complexes 1 and
2.
Physical Measurements: Elemental analyses (C, H, and N) were
performed using a Perkin–Elmer 2400 series II CHN analyzer. IR
spectra in KBr pellets (4500–500 cm–1) were recorded using a Per-
kin–Elmer RXI FT-IR spectrophotometer. Electronic spectra in
methanol (1000–200 nm for complexes 1) and acetonitritile (1000–
200 nm for complex 2) were recorded with a Hitachi U-3501 spec-
trophotometer. Magnetic measurements were carried out with the
“Unitat de Mesures Magnètiques (Universitat de Barcelona)” on
polycrystalline samples (20 mg) with a Quantum Design SQUID
MPMS-XL magnetometer working in the 2–300 K range. The dia-
magnetic corrections were evaluated from Pascal’s constants.
1
2
Empirical formula
Mr [gmol–1]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C26H36Fe2N6O4S2
672.42
monoclinic
P21/c
13.1267(2)
9.3627(8)
13.6752(2)
118.602(8)
1475.6(3)
2
1.513
1.167
700
0.0516
C22H30Fe2N16O2
662.32
monoclinic
P21/n
11.0863(9)
10.9650(14)
12.1782(17)
107.868(11)
1409.0(3)
2
1.561
1.083
684
0.0501
β [°]
V [Å3]
Z
Dc [gcm–3]
μ [mm–1]
F(000)
Synthesis of the Schiff Base Ligand 2-[(2-Dimethylaminoethylimino)-
methyl]phenol (HL): The ligand (HL) (Scheme 1) has been synthe-
sized in two different solvents: methanol and acetonitrile. For the
first set: A solution of salicylaldehyde (10 mmol, 1.05 mL) and 1,2-
bis(dimethylamino)ethane (10 mmol, 1.10 mL) in methanol
(40 mL) was refluxed for 1 h. For the second set: A solution of
salicylaldehyde (10 mmol, 1.05 mL) and 1,2-bis(dimethylamino)-
ethane (10 mmol, 1.10 mL) in acetonitrile (40 mL) was refluxed for
1 h. The resulting dark yellow solutions were then used directly for
complex formation.
R(int)
Total reflections
Unique reflections
IϾ2σ(I)
R1, wR2
T [K]
9960
4289
3102
0.0333, 0.0835
150(2)
9647
4080
2478
0.0414, 0.0941
150(2)
CCDC-819886 (for 1) and -819887 (for 2) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of [Fe2L2(OMe)2(SCN)2] (1): FeCl3 (0.810 g, 5 mmol),
dissolved in methanol (10 mL), was added to a methanolic solution
of the ligand (HL) (5 mmol) with constant stirring. After 5 min, a
methanol/water solution (9:1, v/v) of NaSCN (0.56 g, 10 mmol)
was added. The color of the solution turned to reddish-black. By
slow evaporation of the resulting solution at room temperature,
black-colored X-ray-quality, plate-shaped single crystals were ob-
tained in 2 d; yield 1.26 g; (75%). C26H36Fe2N6O4S2 (1, 672.42):
calcd. C 44.46, H 5.40, N 12.50; found C 44.47, H 5.35, N 12.54.
Acknowledgments
We thank Engineering and Physical Sciences Research Council
(EPSRC) and the University of Reading for funds for the X-Cali-
bur system and we also thank the Spanish Government (grant
number CTQ2009-07264) and Comissió Interdepartamental de Re-
cerca i Innovació Tecnològica de la Generalitat de Catalunya (grant
number 2009 SGR 1454) for their financial support.
IR (KBr pellet): ν = 3181 ν(NH), 2079 ν(SCN), 1616 ν(C=N) cm–1.
˜
λmax (methanol) = 433 and 330 nm.
Synthesis of [Fe2L2(N3)2(N3)2] (2): The procedure was the same as
that for complex 1, except that FeCl3 (0.810 g, 5 mmol), dissolved
in acetonitrile (10 mL), was added to an acetonitrilic solution of
the ligand (HL) (5 mmol) with constant stirring and after 5 min an
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Published Online: October 11, 2011
Eur. J. Inorg. Chem. 2011, 4993–4999
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4999