Monohelical complexes of a novel asymmetric N4 Schiff base: Unfamiliar tetrahedral environments of manganese(II) and iron(II) helicates

Article abstract of DOI:10.1002/ejic.200390144

The electrochemical reaction of the bis-bidentate H₂ABATs Schiff base [H₂ABATs = N,N′-bis(2-tosylaminobenzylidene)-2-aminobenzylamine] with manganese, iron, cobalt, nickel, copper, zinc and cadmium was investigated. The reaction cell yields products of empirical formula M(ABATs). X-ray diffraction studies show that [Mn(ABATs)]·0.75H₂O (1), [Fe(ABATs)]·0.75H₂O (2), [Ni(ABATs)]·0.75H₂O (3), [Cu(ABATs)]·.0.5H₂O(4) and [Zn(ABATs)]·0.75H₂O (5) are mononuclear distorted tetrahedral helical complexes in the solid state. Complexes 1 and 2 confirm the ability of this type of ligand to dictate the geometry around the metal centre, as is shown by the unfamiliar tetrahedral environments of manganese(II) and iron(II) ions in complexation with the Schiff bases. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejic.200390144

FULL PAPER
Monohelical Complexes of a Novel Asymmetric N4 Schiff Base: Unfamiliar
Tetrahedral Environments of Manganese(II) and Iron(II) Helicates
[a]
[a]
[a]
[a]
´
´
Miguel Vazquez, Manuel R. Bermejo,* Matilde Fondo, Ana M. Garcıa-Deibe,
[a]
[a]
[b]
[b]
´
´
Jesus Sanmartın, Rosa Pedrido, Lorenzo Sorace, and Dante Gatteschi
Keywords: Electrochemistry / Helical structures / Schiff bases / Transition metals
The electrochemical reaction of the bis-bidentate H2ABATs
Schiff base [H2ABATs = N,NЈ-bis(2-tosylaminobenzylidene)-
2-aminobenzylamine] with manganese, iron, cobalt, nickel,
copper, zinc and cadmium was investigated. The reaction
cell yields products of empirical formula M(ABATs). X-ray
mononuclear distorted tetrahedral helical complexes in the
solid state. Complexes 1 and 2 confirm the ability of this type
of ligand to dictate the geometry around the metal centre,
as is shown by the unfamiliar tetrahedral environments of
manganese(II) and iron(II) ions in complexation with the
diffraction studies show that [Mn(ABATs)]·0.75H2O (1), Schiff bases.
[Fe(ABATs)]·0.75H2O
(2),
[Ni(ABATs)]·0.75H2O
(3),
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
[Cu(ABATs)]·0.5H2O (4) and [Zn(ABATs)]·0.75H2O (5) are
Germany, 2003)
Introduction
atom. In fact, a Schiff base with a flexible propylene spacer
separating the N-imine donors can give rise to complexes
Molecular architectures featuring helical arrangements of of different nuclearity, depending on the metal ion.
multidentate ligands around one or more metal centres are Regardless of the mono- or dinuclear nature of the helix,
one of the goals of supramolecular chemistry.[1Ϫ4] In this all complexes prepared with this kind of Schiff base show
search, many studies have been performed in order to de- coordination numbers of four for the metal centres. It there-
velop synthetic procedures for new multidentate ligands ex- fore seems that the stereochemical preferences of the metal
hibiting the potential to give bridged polynuclear do not play a fundamental role in the nuclearity of the com-
species.[5Ϫ11] Among the various ligand systems capable of plex in this case study. Until now, however, neither mangan-
promoting self-assembly of mononuclear and/or polynu- ese() nor iron() complexes of this type had been crystallo-
clear helical coordination complexes, careful design of im- graphically characterised, these metals having special pref-
ine-based ligands[12Ϫ20] demonstrates that this can be an in- erence for an octahedral coordination. To the best of our
expensive approach to supramolecular chemistry. These li- knowledge, in fact, no tetrahedral Schiff-base complexes
gands have the advantage of being easily modified, allowing with these metal atoms have been structurally characterised.
changes in the features (length, flexibility, donor ability) of
In an attempt to determine whether the presence of the
the spacer, the position of the donor atoms and the presence tosyl groups can always dictate the geometry around the
of different groups that can give rise to intermolecular inter- metal centre, and to examine the influence of the flexibility
actions and/or induce torsion of the ligand. A systematic of the spacer on the nuclearity of the helix, the new
study of the factors affecting the isolation of helical com- H2ABTs ligand (Scheme 1), with a semi-rigid benzylidene
plexes can therefore be done by changing just one of the group (three carbon atoms) between the two imine moieties,
variables.
was prepared. The interaction of H2ABATs with mangan-
We have recently prepared some bis-bidentate Schiff ba- ese, iron, cobalt, nickel, copper, zinc and cadmium in an
ses containing bulky tosyl groups and different electrochemical cell was investigated and the results
spacers.[21Ϫ22] These ligands yield mononuclear and/or di- achieved are described.
nuclear helicates, depending on the flexibility and/or the
length of the spacer, as well as on the nature of the metal
Results and Discussion
[a]
´
´
´
Departamento de Quımica Inorganica, Facultade de Quımica,
Universidade de Santiago de Compostela,
15706 Santiago de Compostela, Spain
E-mail: qimb45@usc.es
Synthesis of the Ligand
The Schiff base H2ABATs was prepared by conventional
condensation between 2-tosylaminobenzaldehyde and 2-
aminobenzylamine. The yellow solid showed a satisfactory
[b]
Dipartimento di Chimica, Universita degli Studi di Firenze,
Polo Scientifico Universitario,
50099 Sesto Fiorentino (Fi), Italy
1128  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0306Ϫ1128 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2003, 1128Ϫ1135

Monohelical Complexes of a Novel Asymmetric N4 Schiff Base
FULL PAPER
Elemental analyses show that all metals employed here
react with the ligand in a 1:1 molar ratio to afford com-
plexes of the bis-deprotonated [ABATs]2Ϫ with high purity.
All these neutral metal complexes are obtained in good
yields and appear to be stable both in the solid state and in
solution. It therefore seems that although an inert atmo-
sphere is necessary for the isolation of pure manganese()
and iron() complexes, these compounds are air-stable
once formed.
X-ray Studies
The crystal structures of [Mn(ABATs)]·0.75H2O (1),
[Fe(ABATs)]·0.75H2O (2), [Ni(ABATs)]·0.75H2O (3),
[Cu(ABATs)]·0.5H2O (4) and [Zn(ABATs)]·0.75H2O (5)
were solved as detailed below.
The five complexes are isomorphous and isostructural,
and so only the ORTEP diagram of 1 is shown in Figure 1.
Experimental details are recorded in Table 1 and the main
bond distances and angles in Table 2.
Metal-Ion Geometry
All the complexes consist of mononuclear compounds
with water as solvate. In each case the ligand uses its four
nitrogen atoms (two imine and two amide) to link to the
metal atom. In addition, one oxygen atom of each tosyl
group interacts weakly with the metal centre (Table 2).
These distances are too long to be regarded as true coordin-
ated bonds, and are better described as secondary intramo-
lecular interactions. The metal centre is therefore in a tetra-
coordinated environment, with the tosyl groups playing an
Scheme 1. H2ABATs
elemental analysis and was further characterised by IR and
1H NMR spectroscopy and FAB mass spectrometry.
Electrochemical Synthesis of the Complexes
All the complexes were prepared by a previously de- important role in the adopted coordination number. How-
scribed electrochemical method.[21]
ever, it is noteworthy that the higher preference for an octa-
Figure 1. An ORTEP view of complex 1, showing the P enantiomer (thermal ellipsoids are drawn at the 30% probability level; hydrogen
atoms and solvent molecules have been omitted for clarity)
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135
1129

M. R. Bermejo et al.
FULL PAPER
Table 1. Crystal data and structure refinement for 1؊5
1
2
3
4
5
Empirical formula
Molecular weight
Crystal system
Space group
C35H31.50MnN4O4.75S2 C35H31.50FeN4O4.75S2 C35H31.50NiN4O4.75S2 C35H31CuN4O4.5S2
C35H31.50ZnN4O4.75S2
713.63
703.20
704.11
706.97
707.30
Monoclinic
P2/c (No.13)
19.486(3)
10.696(2)
17.636(3)
90
Monoclinic
P2/c (No.13)
19.51830(10)
10.6748(2)
17.6367(10)
90
Monoclinic
P2/c (No.13)
19.3080(5)
10.7143(3)
17.7497(4)
90
Monoclinic
P2/c (No.13)
19.207(5)
10.636(4)
17.760(5)
90
Monoclinic
P2/c (No.13)
19.296(3)
10.736(2)
17.755(4)
90
114.823(13)
90
3338.3(11)
4
˚
a (A)
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
114.74(2)
90
114.8230(10)
90
115.1580(10)
90
114.98(2)
90
3
˚
V (A )
3338.4(10)
4
3335.2(2)
4
3323.59(15)
4
3288.7(18)
4
Z
Absorption coefficient (mmϪ1
Crystal size (mm3)
Reflections collected
Independent reflections
θ range (°)
)
0.568
0.25 ϫ 0.15 ϫ 0.10
20493
0.625
0.20 ϫ 0.10 ϫ 0.05
17037
0.757
0.40 ϫ 0.25 ϫ 0.15
16931
0.838
0.40 ϫ 0.25 ϫ 0.15
16721
0.908
0.40 ϫ 0.25 ϫ 0.10
16789
7647 [R(int) ϭ 0.0367] 7652 [R(int) ϭ 0.0638] 7625 [R(int) ϭ 0.0585] 7554 [R(int) ϭ 0.0888] 7607 [R(int) ϭ 0.0371]
1.90Ϫ27.54
7647/0/423
1.91Ϫ27.52
7652/0/429
1.17Ϫ27.58
7625/0/423
2.24Ϫ27.53
7554/0/419
1.16Ϫ27.55
7607/0/429
Data/restraints/parameters
Final R indices [I Ͼ 2σ(I)]
R1 ϭ 0.0538
wR2 ϭ 0.1153
R1 ϭ 0.0924
wR2 ϭ 0.1329
R1 ϭ 0.0698
wR2 ϭ 0.1456
R1 ϭ 0.1422
wR2 ϭ 0.1765
R1 ϭ 0.0590
wR2 ϭ 0.1570
R1 ϭ 0.1084
wR2 ϭ 0.1863
R1 ϭ 0.0774
wR2 ϭ 0.1539
R1 ϭ 0.1705
wR2 ϭ 0.1944
R1 ϭ 0.0488
wR2 ϭ 0.1100
R1 ϭ 0.0866
wR2 ϭ 0.1325
R indices (all data)
˚
Table 2. Selected bond lengths [A] and angles (°) for 1Ϫ5
1
2
3
4
5
M(1)ϪN(1)
M(1)ϪN(2)
M(1)ϪN(3)
M(1)ϪN(4)
M(1)···O(1)
M(1)···O(3)
N(1)ϪM(1)ϪN(2)
N(1)ϪM(1)ϪN(3)
N(1)ϪM(1)ϪN(4)
N(2)ϪM(1)ϪN(3)
N(2)ϪM(1)ϪN(4)
N(3)ϪM(1)ϪN(4)
2.047(3)
2.053(2)
2.091(3)
2.017(2)
2.680(2)
2.595(2)
87.07(11)
132.97(10)
123.65(10)
92.18(10)
135.32(11)
88.15(10)
2.029(4)
2.056(3)
2.096(3)
2.008(3)
2.634(3)
2.519(3)
86.23(14)
132.22(14)
126.44(14)
91.80(14)
135.16(15)
86.41(13)
1.989(3)
1.961(3)
2.000(3)
1.937(3)
2.828(3)
1.978(4)
1.940(4)
1.977(4)
1.956(4)
2.765(4)
1.990(3)
2.015(3)
2.045(2)
1.962(2)
2.763(2)
2.552(2)
2.647(4)
2.681(2)
89.55(13)
126.27(12)
117.93(13)
94.50(13)
140.19(13)
91.26(12)
90.79(19)
136.85(19)
108.20(18)
94.53(19)
143.2(2)
90.82(11)
130.14(11)
120.20(10)
92.36(10)
133.52(11)
91.83(10)
92.43(18)
hedral geometry is displayed in the shorter M···Otosyl dis- of a bidentate Schiff base (FeL2) has recently been charac-
tance.
terised.[23] Nevertheless, it should be noted that this com-
The dihedral angle θ between the two MNN terminal plex was prepared in non-polar, non-coordinating solvents
planes (ca. 62.3° for 1, 62.6° for 2, 65.3° for 3, 55.9 for 4 and under an inert atmosphere. In our case the iron centre
64.9° for 5) shows that the metal ion displays a tetrahedral maintains its tetrahedral environment despite the presence
geometry with a square-planar distortion (θ ϭ 0° for of water in the solvent and trapped in the unit cell, which
square-planar geometry and θ ϭ 90° for tetrahedral geo- demonstrates the ability of this type of ligand to predeter-
metry). The value of θ for 4 indicates that the geometry mine the coordination polyhedron. It therefore seems that
around the copper atom could in fact be viewed as interme- the steric hindrance induced by the tosyl groups, in con-
diate between tetrahedral and square-planar. This geometry junction with the second order interactions of the metal
is quite unfamiliar for manganese() and iron() Schiff-base with the tosyl oxygen atoms, prevent any other donor from
complexes, which display clear stereochemical preferences coordinating to the metal ion.
for octahedral environments, and even for NiII, which also
In addition, it must be pointed out that Zn and Ni form
prefers octahedral or square-planar rather than tetrahedral dinuclear complexes with H2PTs [N,NЈ-bis(2-tosylamino-
geometries. To the best of our knowledge, no manganese benzylidene)-1,3-diaminopropane],[21] while they afford
Schiff-base complexes with this geometry have been de- mononuclear compounds with H2ABATs. The related
scribed previously, and just one iron() tetrahedral complex H2PTs ligand, like H2ABATs, contains three carbon atoms
1130
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135

Monohelical Complexes of a Novel Asymmetric N4 Schiff Base
FULL PAPER
between the imine moieties. However, the spacer in H2PTs It can clearly be observed (Figure 2) that, if only the donor
is an aliphatic chain and this emphasises the role of the atoms are taken into account, the wrapping angle is always
spacer flexibility in the nuclearity of the helix.
shorter than 360°. Nevertheless, if the tosyl groups are in-
The MϪN (M ϭ Ni, Cu, Zn) distances are typical of cluded, the ligand wraps slightly more than once. In that
tetracoordinate tetrahedral complexes,[21Ϫ22] but are shorter sense, the S···S distances could be taken as a close value for
˚
˚
˚
than those found for octahedral complexes with similar li- the pitch, being ca. 5.0 A for 1, 4.98 A for 2, 4.88 A for 3,
gands,[24] reflecting the lower coordination number. The 4.74 A for 4 and 4.99 A for 5. These distances show that
MϪNimine (MϪN2 and MϪN3) distances decrease mono- the shortest pitch corresponds to 4, which is in agreement
tonically from 1 to 4 and increase for 5, following the trend with its more distorted (tetrahedral towards square-
(1 ഠ 2 Ͼ 5 Ͼ 3 Ͼ 4) of the ionic radii. The MϪNamide planar) geometry.
˚
˚
(MϪN1 and MϪN4) distances show the same pattern.
Finally, the space group and the analysis of the crystal
The wide range of angles observed around the metal data indicate the formation of a racemic mixture, with both
centres, varying between ca. 87° and 143.2°, compares fairly P and M enantiomers present in the unit cell with 50% yield
well with those previously reported for this kind of complex for all the complexes.
and reflects the severe distortion from the ideal tetrahed-
ral geometry.
IR Spectra
The IR spectra of the free ligand and complexes show
two bands at ca. 1605 and 1630 cmϪ1, in agreement with
the presence of two inequivalent imine groups. Both ν(Cϭ
N) bands are shifted to higher wavenumber values
(1Ϫ15 cmϪ1) with respect to the free ligand for most of the
complexes. In addition, all complexes show a negative shift
of ν(CϪN) relative to free H2ABATs. This suggests the co-
ordination of the ligand to the metal centre through the
imine and amide nitrogen atoms. In addition, two bands
in the ranges 1250Ϫ1261 cmϪ1 and 1127Ϫ1138 cmϪ1 are
attributable to the asymmetric and symmetric vibration
modes of the SO2 group, respectively.[25Ϫ26] Finally, no
bands above 2500 cmϪ1 were detected for any of the com-
plexes, indicating the deprotonation of the NH groups and,
therefore, the dianionic character of the ligand.
Chelate Rings and Helical Coiling
The ligand forms three chelate rings around the central
metal atom. The two terminal six-membered rings are reas-
onably planar while the central six-membered ring is less
so, as would be expected, due to the presence of one sp3
carbon atom. The loss of planarity between the Nimine
atoms is also shown by the N(2)C(15)C(16)C(21) torsion
angles, which range from Ϫ58.7(5)° for 3 to 63.0(4)° for 2,
showing the strain of the ligand. The central
N(2)C(15)C(16)C(21)N(3) chelate ring forms angles of ca.
46° and 27° for 1Ϫ3 and 5 and of ca. 41° and 23° for 4 with
N(1)C(8)C(13)C(14)N(2) and N(3)C(22)C(23)C(28)N(4),
respectively. These angles show the screwing of this thread,
which affords monohelical single-stranded molecules. The
twisting of the ligand can be attributed to an attempt by
the additional peripheral tosyl groups to minimise the steric
hindrance, being orientated in different directions, as shown
in Figure 2.
Magnetic Studies
The magnetic moments of all the paramagnetic com-
plexes were recorded in the solid state between 2 and 280 K.
In agreement with the observed long distances between
The extent of helical coiling in these chiral complexes can
be described in terms of the ligand wrapping angle. How-
ever, the value of this angle, and of the helical pitch of the
thread, can change significantly depending on different con-
siderations, such as the actual helix top-ends or the helical
axis declination, so only qualitative aspects are considered.
˚
magnetic centres (ca. 9.5 A), and with the absence of any
efficient exchange pathway, the temperature dependence of
the magnetic susceptibilities between 2 and 280 K for all
the complexes shows deviation from Curie behaviour only
at low temperature, with the exception of the NiII complex
for which, due to the expected partially unquenched orbital
contribution, a deviation is observed below 50 K (Figure 3).
The values of the magnetic moment, obtained by the
CurieϪWeiss fit of 1/χ vs. T plots (Table 3), are very close
to those expected for magnetically diluted tetrahedral MII
ions, with g values that, except for MnII, differ greatly from
that of the free electron.[27] This provides confirmation of
the oxidation state ϩII for the metal centre, indicating the
deprotonation of the Schiff-base ligand, and the achieved
high-spin configuration for [Mn(ABATs)] and [Fe(ABATs)],
as would be expected. The EPR spectra essentially confirm
this picture; indeed, a typical tetrahedral CuII spectrum is
observed for the complex [Cu(ABATs)], which yielded g
values g|| ϭ 2.185 gЌ ϭ 2.095 with an average g value of
2.125, in good agreement with the magnetic moment ob-
served at room temperature. On the other hand, the EPR
Figure 2. Stick view of 1, showing the wrapping of the ligand
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135
1131

M. R. Bermejo et al.
FULL PAPER
spectrum of the MnII derivative, recorded at low temper- vation of an EPR spectrum for the CoII derivative, a Kra-
ature, clearly shows a fine structure deriving from a non- mers ion, could be attributable to fast relaxation.[29]
negligible zero field splitting (ZFS) of the S ϭ 5/2 multiplet
Thus, in view of the formulations of the complexes and
(Figure 4). Finally, no EPR spectra are observed for the FeII their magnetic moments, it seems quite reasonable to pro-
and CoII derivatives: the absence of a spectrum for the for- pose a tetrahedral environment around the metal atoms for
mer is in agreement with the expected large ZFS and integer all the paramagnetic complexes, as the crystal structures of
spin state that usually make tetrahedral high-spin FeII com- 1 to 5 confirm.
plexes silent at EPR X-band frequencies.[28] The non-obser-
FAB Mass Spectra
FAB mass spectra of all the complexes show peaks due
to [M(ABATs)]ϩ fragments (M ϭ Mn, Fe, Co, Ni, Cu, Zn
or Cd), corroborating the coordination of the ligand to the
metal. However, no peaks attributable to [ML]2ϩ fragments
could be detected for any of the complexes, suggesting
mononuclear natures in solution for all of them.
NMR Studies
The 1H NMR spectra of H2ABATs, [Zn(ABATs)] and
[Cd(ABATs)] were recorded in [D6]DMSO as solvent. The
spectra show two sets of aromatic signals in a 1:1 ratio,
indicating that the two arms are not magnetically equiva-
Figure 3. CurieϪWeiss plots for paramagnetic complexes; ∆ Cu
lent. The assignments of the signals were based on COSY
and NOESY experiments, as well as on previous
results.[21Ϫ22]
derivative, ᮀ Ni derivative, ᭺ Co derivative, ᭿ Fe derivative and ᭞
Mn derivative
The comparison of the free ligand spectrum with those
of the complexes allows some conclusions to be drawn:
1. The NH protons present in the free ligand disappear in
the spectra of the complexes, in agreement with bis-depro-
tonation of the Schiff base.
Table 3. Value of the Curie constant for the complexes
Complex
C (cm3·K·molϪ1
)
2. The imine hydrogen atoms (3-H and 3Ј-H) show a shift
to lower field for the zinc complex, while 3-H is shifted to
higher field in the cadmium complex, indicating that the
coordination of the imine groups to the metal centre in-
duces opposite shielding effects on these hydrogen atoms.
This situation was also found for zinc and cadmium com-
plexes with ligands containing an aliphatic spacer.[21b]
The imine protons of the cadmium complex are flanked
by satellites arising from spin-spin coupling to 111/113Cd,
suggesting that the complex is kinetically inert on the
NMR timescale.
Mn(ABATs)
Fe(ABATs)
Co(ABATs)
Ni(ABATs)
Cu(ABATs)
3.88
3.17
2.5
1.28
0.44
3. The methylene protons (11-H) are magnetically equiva-
lent in the free ligand and appear as a singlet at δ ϭ
5.08 ppm. However, the room-temperature spectrum of the
zinc complex contains a well resolved AB doublet of doub-
lets for the 11-H protons. The AB pattern for the methylene
hydrogen atoms implies that the strong coordination of the
hard imine nitrogen to the zinc atom abolishes the erstwhile
enantiotopic nature of these protons to make them diastere-
otopic. This observation can be interpreted in terms of a
helical conformation of the new complex, making it chiral.
It therefore seems that the zinc complex in solution main-
tains the structure found in solid state.
Figure 4. EPR band spectrum (at 9.225 GHz) of Mn(ABATs)
recorded at 4.2 K
1132
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135

Monohelical Complexes of a Novel Asymmetric N4 Schiff Base
FULL PAPER
ture was then allowed to cool. The resultant yellow solution was
concentrated to ca. 10 mL. The solid that precipitated was collected
by filtration, washed with diethyl ether (4 mL) and dried in vacuo.
Yield: 5.20 g (90%); m.p. 187 °C. C35H32N4O4S2 (636): calcd. C
66.0, H 5.1, N 8.8, S 10.1; found C 66.1, H 5.1, N 8.7, S 10.2. IR
(KBr): ν˜ ϭ 1628, 1605 [s, ν(CϭN)], 1339 [s, ν(CϪN)], 1285, 1165 [s,
ν(SO2)] cmϪ1. FAB-MS: m/z ϭ 637.3 [H3Lϩ]. 1H NMR (500 MHz,
[D6]DMSO): δ ϭ 2.09 (s, 3 H, 10Ј-H), 2.22 (s, 3 H, 10-H), 5.09 (s,
2 H, 11-H), 6.95Ϫ7.0 (m, 4 Harom.), 7.10Ϫ7.13 (m, 4 Harom.),
7.38Ϫ7.53 (m, 9 Harom.), 7.67 (d, 2 H, 8-H), 7.76 (d, 1 H, 4-H),
8.65 (s, 1 H, 3Ј-H), 8.88 (s, 1 H, 3-H), 12.82 (s, 1 H, NH), 12.94 (s,
1 H, NH) ppm.
The spectrum of the cadmium complex at room temper-
ature shows just one broad signal at δ ϭ 4.97 ppm for the
11-H protons. This could indicate that the complex is not
chiral or that a fast interconversion of enantiomers of the
chiral single helicate takes place in solution.
Finally, it should be noted that just one diastereoisomer
exists in solution for both complexes, as no additional
peaks indicative of a second species could be detected.
Conclusions
Synthesis of the Complexes: All the complexes were obtained by an
electrochemical procedure. The cell can be summarised as:
Pt(Ϫ)|H2ABATs ϩ MeCN|M(ϩ), where M stands for the metal.
The synthesis can be typified by the preparation of Cu(ABATs). A
suspension of the ligand (0.2 g, 0.32 mmol) in acetonitrile (80 mL),
containing tetramethylammonium perchlorate (10 mg), was electro-
The electrochemical interaction of manganese, iron, co-
balt, nickel, copper, zinc and cadmium with the bis-bident-
ate H2ABATs Schiff base yields mononuclear [MII(ABATs)]
complexes. The bulky tosyl groups induce torsion in the
ligand, giving rise to monohelical, single-stranded, tetra-
hedral compounds. This geometry is quite unusual for man- lysed with a current of 10 mA for 3.4 h. Concentration of the res-
ultant solution to a third of its initial volume yielded a yellow-
brown solid that was washed with diethyl ether and dried under
vacuum. Recrystallisation of the bulk sample by diffusion of diethyl
ether into an acetonitrile solution, produced dark-green crystals of
[Cu(ABATs)]·0.5H2O (4).
ganese() and iron() with Schiff bases. In fact, to the best
of our knowledge, there are no previous crystallographically
characterised examples of this type of complex obtained
from non-anhydrous solvents. This demonstrates the ability
of this type of ligand to dictate the coordination number in
spite of the geometrical preferences of the metal.
CAUTION: Perchlorate salts are potentially explosive and should
Finally, this work further contributes to make the role of
the flexibility of the spacer in the nuclearity of the helix
evident: nickel and zinc double-helical compounds have
previously been reported for a related ligand (H2PTs) with
a flexible propylene spacer (three aliphatic carbon atoms
between imine-N atoms), while the semi-rigid benzylidene
spacer in H2ABATs (three carbon atoms, two aromatic and
one aliphatic, between imine-N atoms) only allows the
isolation of monohelical complexes.
therefore be handled with the appropriate care.
The synthetic procedure is the same for all the metals except for
manganese and iron. These two compounds were prepared in a
closed cell under an argon atmosphere. Prismatic crystals of
[Mn(ABATs)]·0.75H2O (1, orange brown), [Fe(ABATs)]·0.75H2O
(2,
brown),
[Ni(ABATs)]·0.75H2O
(3,
brown),
[Cu(ABATs)]·0.5H2O (4, dark green) and [Zn(ABATs)]·0.75H2O
(5, yellow) were obtained by slow evaporation of a saturated ace-
tonitrile solution in air. No crystals suitable for X-ray studies could
be obtained for [Co(ABATs)] or [Cd(ABATs)].
[Mn(ABATs)]:
Dark
red
solid.
Yield
0.17 g
(78%).
Experimental Section
C35H30MnN4O4S2 (688.9): calcd. C 60.9, H 4.3, N 8.1, S 9.3; found
C 60.9, H 4.4, N 8.2, S 9.3. IR (KBr): ν˜ ϭ 1632, 1605 [s, ν(CϭN)],
1281 [s, ν(CϪN)], 1250, 1127 [s, ν(SO2)] cmϪ1. FAB-MS: m/z ϭ
690.2 [MnL]ϩ. µ (280 K) ϭ 5.6 BM.
General: Elemental analyses were performed on a Carlo Erba EA
1108 analyser. Infrared spectra were recorded as KBr pellets on a
Bio-Rad FTS 175 spectrophotometer in the 4000Ϫ600 cmϪ1 range.
NMR spectra were recorded on a Bruker AMX 500 spectrometer
in [D6]DMSO as solvent. Fast atom bombardment (FAB) mass
spectra were performed on a Kratos MS-50 mass spectrometer, em-
ploying Xe atoms at 70 keV in m-nitrobenzyl alcohol as matrix.
EPR spectra were recorded on a Varian ESR9 spectrometer
working at the X-band frequency (9.225 GHz) equipped with a 4He
continuous flow cryostat for low temperature measurements. Mag-
netic measurements were performed between 2 and 280 K with a
Cryogenics Squid S600 magnetometer with applied field of 1 T. The
data were corrected for sample holder contribution and diamagnet-
ism of the sample by the use of Pascal constants.
[Fe(ABATs)]: Red solid. Yield 0.15 g (70%). C35H30FeN4O4S2
(689.5): calcd. C 60.9, H 4.3, N 8.1, S 9.3; found C 60.8, H 4.5, N
8.1, S 9.2. IR (KBr): ν˜ ϭ 1636, 1606 [s, ν(CϭN)], 1290 [s, ν(CϪN)],
1255, 1136 [s, ν(SO2)] cmϪ1. FAB-MS: m/z ϭ 691.1 [FeL]ϩ.
µ (280 K) ϭ 5.0 BM.
[Co(ABATs)]: Dark red solid. Yield 0.17 g (81%). C35H30CoN4O4S2
(692.9): calcd. C 60.6, H 4.3, N 8.1, S 9.2; found C 60.7, H 4.4, N
8.0, S 9.2. IR (KBr): ν˜ ϭ 1632, 1605 [s, ν(CϭN)], 1285 [s, ν(CϪN)],
1258, 1134 [s, ν(SO2)], cmϪ1. FAB-MS: m/z ϭ 694.1 [CoL]ϩ.
µ (280 K) ϭ 4.3 BM.
[Ni(ABATs)]: Dark green solid. Yield 0.15 g (72%).
C35H30N4NiO4S2 (692.7): calcd. C 60.6, H 4.3, N 8.1, S 9.2; found
C 60.6, H 4.4, N 8.2, S 9.0. IR (KBr): ν˜ ϭ 1640, 1605 [s, ν(CϭN)],
1285 [s, ν(CϪN)], 1254, 1138 [s, ν(SO2)] cmϪ1. FAB-MS: m/z ϭ
693.1 [NiL]ϩ. µ (280 K) ϭ 2.7 BM.
Synthesis: All the starting materials were purchased from Aldrich
and used without further purification. 2-Tosylaminobenzaldehyde
was prepared and characterised according to the literature.[30Ϫ31]
Ligand Preparation: 2-Aminobenzylamine (1.13 g, 9.1 mmol) was
added to
a
solution of 2-tosylaminobenzaldehyde (5.0 g,
18.2 mmol) in chloroform (150 mL), and the mixture was heated [Cu(ABATs)]: Dark green solid. Yield 0.15 g (69%).
to reflux. The volume of the solution was reduced to ca. 50 mL
C35H30CuN4O4S2 (697.5): calcd. C 60.2, H 4.3, N 8.0, S 9.2; found
over a 4 h period with the aid of a DeanϪStark trap, and the mix-
C 60.1, H 4.3, N 8.0, S 9.0. IR (KBr): ν˜ ϭ 1636, 1605 [s, ν(CϭN)],
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135
1133

M. R. Bermejo et al.
FULL PAPER
[6] [6a]
1285 [s, ν(CϪN)], 1258, 1138 [s, ν(SO2)], cmϪ1. FAB-MS: m/z ϭ
P. N. W. Baxter, J. M. Lehn, K. Rissanen, Chem. Commun.
[6b]
698.2 [CuL]ϩ. µ (280 K) ϭ 2.1 BM.
1997, 1323Ϫ1324.
K. M. Gardinier, R. G. Khoury, J. M.
Lehn, Chem. Eur. J. 2000, 6, 4124Ϫ4131.
[7a] J. S. Fleming, K. L. V. Mann, S. M. Couchman, J. C. Jeffery,
J. A. McCleverty, M. D. Ward, J. Chem. Soc., Dalton Trans.
[7]
[8]
[Zn(ABATs)]: Yellow solid. Yield 0.17 g (80%). C35H30N4O4S2Zn
(699.4): calcd. C 60.0, H 4.3, N 8.0, S 9.1; found C 60.1, H 4.3, N
8.1, S 9.2. IR (KBr): ν˜ ϭ 1643, 1615 [s, ν(CϭN)], 1296 [s, ν(CϪN)],
1261, 1138 [s, ν(SO2)], cmϪ1. FAB-MS: m/z ϭ 699.1 [ZnL]ϩ. 1H
NMR (500 MHz, [D6]DMSO): δ ϭ 2.22 (s, 3 H, 10Ј-H), 2.35 (s, 3
H, 10-H), 4.72 (d, 1 H, 11-H), 5.44 (d, 1 H, 11-H), 6.95Ϫ7.03 (m,
3 H, 2 ϫ 9Ј-H ϩ 6Ј-H), 7.26Ϫ7.38 (m, 7 H, 2 ϫ 9-H ϩ 7-H ϩ 7Ј-
H ϩ 6-H ϩ 5-H ϩ 4Ј-H ϩ 2Ј-H), 7.44Ϫ7.73 (m, 6 H, 2 ϫ 8Ј-H ϩ
7-H ϩ 2-H ϩ 1-H ϩ 1Ј-H), 7.81(d, 1 H, 4-H), 7.90 (d, 2 H, 8-H),
8.75 (s, 1 H, 3Ј-H), 8.92 (s, 1 H, 3-H) ppm.
[7b]
1998, 2047Ϫ2052.
C. R. Rice, S. Wörl, J. C. Jeffery, R. L.
Paul, M. D. Ward, J. Chem. Soc., Dalton Trans. 2001, 550Ϫ559.
G. Baum, E. C. Constable, D. Fenske, C. E. Housecroft, T.
Kulke, M. Neuburger, M. Zehnder, Chem. Eur. J. 2000, 6,
4510Ϫ4517.
[9] [9a]
C. Piguet, J. Incl. Phenom. Macrocycl. Chem. 1999, 34,
361Ϫ391. [9b] G. Muller, J. C. G Bunzli, K. J. Schenk, C. Piguet,
G. Hopfgartner, Inorg. Chem. 2001, 40, 2642Ϫ2651.
[10] [10a]
[10b]
M. Albrecht, Chem. Soc. Rev. 1998, 27, 281Ϫ288.
M.
Albrecht, O. Blau, H. Röttele, New J. Chem. 2000, 24,
[Cd(ABATs)]: Pale yellow solid. Yield 0.19 g (83%).
C35H30CdN4O4S2 (746.4): calcd. C 56.2, H 4.0, N 7.5, S 8.6; found
C 56.2, H 3.9, N 7.5, S 8.7. IR (KBr): ν˜ ϭ 1636, 1613 [s, ν(CϭN)],
1289 [s, ν(CϭN)], 1258, 1127 [s, ν(SO2)] cmϪ1. FAB-MS: m/z ϭ
749.1 [CdL]ϩ. 1H NMR (500 MHz, [D6]DMSO): δ ϭ 2.26 (s, 3 H,
10Ј-H), 2.28 (s, 3 H, 10-H), 4.97 (br., 2 H, 2 ϫ 11-H), 6.75 (t, 1 H,
5Ј-H), 6.97 (t, 1 H, 5-H), 7.08Ϫ7.16 (m, 6 H, 2 ϫ 9-H ϩ 2 ϫ 9Ј-
H ϩ 6Ј-H ϩ 7Ј-H), 7.25 (t, 1 H, 6-H), 7.33Ϫ7.36 (m, 2 H, 4Ј-H ϩ
2Ј-H), 7.41Ϫ7.50 (m, 4 H, 7-H ϩ 2-H ϩ 1-H ϩ 1ЈH), 7.67 (d, 1
H, 4-H), 7.74 (d, 2 H, 8ЈH), 7.82 (d, 2 H, 8-H), 8.68 (s, 1 H, 3Ј-H),
8.70 (s, 1 H, 3-H) ppm.
619Ϫ622.
[11]
O. Mamula, A. von Zelewsky, T. Bark, G. Bernardinelli, An-
gew. Chem. Int. Ed. Eng. 1999, 38, 2945Ϫ2948.
[12] [12a]
L. Zhu, Y-X. Tong, X-M. Cheng, J. Chem. Soc., Dalton
[12b]
Trans. 2000, 4182Ϫ4186.
G. Yang, S. L. Zheng, X-M.
Chen, H. K. Lee, Z-Y. Zhou, T. C. W. Mak, Inorg. Chim. Acta
2000, 303, 86Ϫ93.
G. C. van Stein, G. van Koten, K. Vrieze, C. Brevard, A. L.
Spek, J. Am. Chem. Soc. 1984, 106, 4486Ϫ4492.
P. K. Boyer, K. A. Porter, A. D. Rae, A. C. Willis, B. Wild,
Chem. Commun. 1998, 1153Ϫ1154.
[13]
[14]
[15] [15a]
M. J. Hannon, C. L. Painting, A. Jackson, J. Hamblin,
[15b]
W. Errington, Chem. Commun. 1997, 1807Ϫ1808.
M. J.
Crystallographic Measurements: Crystals of 1 to 5 suitable for X-
ray diffraction studies were obtained as described previously. Data
were collected on a Siemens SMART CCD diffractometer for 1, 2,
4 and 5 and on a Siemens P4 diffractometer for 3, with graphite
Hannon, S. Bunce, A. J. Clarke, N. W. Alcock, Angew. Chem.
[15c]
Int. Ed. 1999, 38, 1277Ϫ1278.
L. J. Chields, N. W. Alcock,
M. J. Hannon, Angew. Chem. Int. Ed. 2001, 40, 1079Ϫ1081.
V. Amendola, L. Fabbrizzi, L. Linati, C. Mangano, P. Pallavic-
ini, V. Pedrazzini, M. Zema, Chem. Eur. J. 1999, 5, 3679Ϫ3688.
H. Cheng, D. Chun-Ying, F. Chen-Jie, M. Qing-Jin, J. Chem.
Soc., Dalton Trans. 2000, 2419Ϫ2424.
[16]
[17]
˚
monochromatised Mo-Kα radiation (λ ϭ 0.71073 A), at room tem-
perature. The structures were solved by direct methods and refined
by full-matrix, least-squares based on F2 with the SHELX-97 pro-
gram package.[32] Absorption corrections were carried out semiem-
pirically from equivalents by use of the Sadabs program.[33] All
non-hydrogen atoms were refined anisotropically, except for some
of those corresponding to solvated water molecules (2؊4), which
are disordered over two different positions (0.5 and 0.25 occupan-
cies sites) for 1؊3 and 5. Hydrogens bonded to carbon atoms were
included in the model at geometrically calculated positions and re-
fined with a riding model. Only some H atoms corresponding to
solvated water molecules could be located, fixed and given isotropic
[18] [18a]
N. Yoshida, K. Ichikawa, Chem. Commun. 1997,
1091Ϫ1092. [18b] N. Yoshida, H. Oshio, T. Ito, Chem. Commun.
1998, 63Ϫ64. [18c] N. Yoshida, K. Ichikawa, M. Shiro, J. Chem.
Soc., Perkin Trans. 2000, 17Ϫ26.
[19]
L. Carbonaro, M. Isola, V. Liuzzo, F. Marchetti, F. Balzano,
C. S. Pomelli, A. Raffaelli, Eur. J. Inorg. Chem. 2001, 353Ϫ357.
[20] [20a]
´
´
J. Sanmartın, M. R. Bermejo, A. M. Garcıa-Deibe, O. Piro,
[20b]
E. E. Castellano, Chem. Commun. 1999, 1953Ϫ1954.
J.
´
´
Sanmartın, M. R. Bermejo, A. M. Garcıa-Deibe, A. L.
Llamas-Saiz, Chem. Commun. 2000, 795Ϫ796.
2
˚
[21] [21a]
displacement parameters of 0.1 A .
´
´
M. Vazquez, M. R. Bermejo, M. Fondo, A. M. Gonzalez,
´
J. Mahıa, L. Sorace, D. Gatteschi, Eur. J. Inorg. Chem. 2001,
CCDC-190797Ϫ190801 (1Ϫ5, respectively) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html [or from the Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/
336-033; E-mail: deposit@ccdc.cam.ac.uk].
[21b]
´
M. Vazquez, M. R. Bermejo, M. Fondo, A.
1863Ϫ1868.
´
´
Garcıa- Deibe, A. M. Gonzalez, R. Pedrido, Eur. J. Inorg.
Chem. 2002, 465Ϫ472.
[22] [22a]
´
´
M. Vazquez, M. R. Bermejo, M. Fondo, A. M. Garcıa-
´
´
Deibe, A. M. Gonzalez, R. Pedrido, J. Sanmartın, Z. Anorg.
[22b]
´
M. Vazquez, M. R.
Allg. Chem. 2002, 628, 1068Ϫ1074.
Bermejo, J. Sanmartin, A. M. Garcia-Deibe, C. Lodeiro, J.
Mahia, J. Chem. Soc., Dalton Trans. 2002, 870Ϫ877.
M. A. Torzilli, S. Colquhoun, J. Kim, R. H. Beer, Polyhedron
2002, 21, 705Ϫ713.
[23]
[1]
Transition Metals in Supramolecular Chemistry (Eds.: L. Fab-
rizzi and A. Poggi), Kluwer Academic, Dordecht, 1994.
J. M. Lehn, Supramolecular Chemistry-Concepts and Perspect-
[24] [24a]
M. R. Bermejo, A. Sousa, M. Fondo, M. Helliwell, New.
[24b]
[2]
J. Chem. 2000, 24, 33Ϫ41.
A. Sousa, M. R. Bermejo, M.
´
Fondo, A. Garcıa-Deibe, A. Sousa-Pedrares, O. Piro, New J.
Chem. 2001, 25, 647Ϫ654.
ives, VCH, Weinheim, 1995.
[3] [3a]
E. C. Constable, in Comprehensive Supramolecular Chem-
[25]
[26]
[27]
[28]
[29]
M. Morioka, M. Kato, H. Yoshida, T. Ogata, Heterocycles
1997, 45, 1173Ϫ1181.
K. Nakamoto, in Infrared and Raman Spectra of Inorganic and
Coordination Compounds, John Wiley & Sons, New York, 1997.
J. S. Griffith, ‘‘The Theory of Transition Metal Ions’’, Cam-
bridge University Press, Cambridge, 1961.
M. J. Knapp, J. Krzystek, L. C. Brunel, D. N Hendrickson,
Inorg. Chem. 2000, 39, 281Ϫ288.
A. Bencini, D. Gatteschi, in Transition Metal Chemistry (Eds.:
istry, Vol. 9 (Eds.: J. P. Sauvage, M. W. Hosseini), Pergamon,
Oxford, 1996, 213Ϫ252. [3b]E. C. Constable, C. E. Housecroft,
M. Neuburger, D. Phillips, P. R. Raithby, E. Schofield, E.
Sparr, D. A. Tocher, M. Zehnder, Y. Zimmermann, J. Chem.
Soc., Dalton Trans. 2000, 2219Ϫ2228.
C. Piguet, G. Bernarddinelli, G. Hopfgartner, Chem. Rev. 1997,
97, 2005Ϫ2062.
[4]
[5]
Y. Zhang, A. Thompson, S. J. Rettig, D. Dolphin, J. Am. Chem.
Soc. 1998, 120, 13537Ϫ13538.
1134
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135

Monohelical Complexes of a Novel Asymmetric N4 Schiff Base
FULL PAPER
[32]
[33]
B. N. Figgis, G. Melson) vol. 8, p. 1, Marcel Dekker, New
G. M. Sheldrick, SHELX-97 (SHELXS 97 and SHELXL 97),
Programs for Crystal Structure Analyses, University of
Göttingen, Germany, 1998.
SADABS, Area-Detector Absorption Correction. Siemens In-
dustrial Automation Inc., Madison, WI, 1996.
Received October 8, 2002
York, 1982.
[30]
N. I. Chernova, Y. S. Ryabokobylky, V. G. Brudz, B. M. Bolo-
tin, Zh. Neorg. Khim. 1971, 1680Ϫ1684.
[31]
´
J. Mahia, M. Maestro, M. Vazquez, M. R. Bermejo, A. M.
Gonzalez, M. Maneiro, Acta Crystallogr., Sect. C 1999, C55,
2158Ϫ2160.
[I02557]
Eur. J. Inorg. Chem. 2003, 1128Ϫ1135
1135