Chloride as supramolecular glue: Anion-directed assembly of a 2D network of MnIII complexes

Article abstract of DOI:10.1002/ejic.200400041

The Schiff base H₄L [where H₄L = N,N ^'-bis(3-hydroxysalicylidene)ethane-1,2-diamine], containing six potential donor atoms, is able to induce the formation of a novel [Mn ^III(H₂L)(CH₃OH)

Full text of DOI:10.1002/ejic.200400041

FULL PAPER
Chloride as Supramolecular Glue: Anion-Directed Assembly of a 2D Network
III
of Mn Complexes
[
a]
[b]
[b]
Manuel R. Bermejo,* M. Isabel Fern a´ ndez, Ana M. Gonz a´ lez-Noya,
[b]
[a]
[b]
[a]
Marcelino Maneiro, Rosa Pedrido, M. Jes u´ s Rodr ´ı guez, and Miguel V a´ zquez
Keywords: Supramolecular chemistry / Manganese / Schiff bases / Hydrogen bond / Self-assembly
The Schiff base H
idene)ethane-1,2-diamine], containing six potential donor
atoms, is able to induce the formation of novel
4 4
L [where H L = N,NЈ-bis(3-hydroxysalicyl- inner Schiff-base compartment. The neutral condition of the
complex is achieved with the presence of the chloride coun-
terion, which behaves as a multiple acceptor of hydrogen
a
III
[
Mn (H
2 3 2
L)(CH OH) ]Cl (1) complex, which was character- bonds. The chloride is involved in four O−H···Cl bonds, con-
1
ized by elemental analysis, FAB mass spectrometry, IR,
H
necting three neighbouring cationic complexes. To the best
of our knowledge, this constitutes the first example of self-
NMR and electronic spectroscopy, magnetic measurements,
X-ray diffraction techniques and conductivity measurements.
The study of its redox properties by cyclic and normal pulse
voltammetry is also reported. The crystal structure of 1 is
III
assembly of discrete units of Mn complexes in a 2D network
in the solid state through hydrogen bonding, where the anion
is acting as a supramolecular glue.
III
formed by monomeric cationic Mn complexes, where the
manganese ion is in an octahedral environment and is coord- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
inated in the equatorial plane to the N
2
O
2
donor set of the
Germany, 2004)
Introduction
interactions (hydrogen bonding, π-π stacking, and so forth)
are particularly rare.
[
10]
Of the first-row transition metals, manganese has a par-
ticularly appealing coordination chemistry due to its rich
redox behaviour, as demonstrated by the variety of struc-
tures and oxidation states in polynuclear manganese
In the last years, part of our research program has been
focused on reproducing the reactivity of some manganese
redox enzymes, and we have reported an important number
III
of active synthetic models of Mn systems derived from
[
1Ϫ3]
complexes.
In particular, manganese() derivatives
Schiff-base ligands. With the skill and the motivation ac-
quired due to our recent successes in the construction of
from tetradentate Schiff-base ligands have a clear tendency
to form infinite linear or helical chains, due to the predis-
position of these ligands to occupy a planar configuration
in an octahedral coordination geometry, leaving the axial
positions free to develop polymerization through bidentate
[11]
very appealing supramolecular architectures, we are now
interested in investigating the overlooked supramolecular
chemistry of manganese(). In particular, our new scheme
consists in obtaining the aggregation of discrete manga-
nese() complexes into multidimensional arrays through
metal-free self-assembly.
In this paper we describe the results of this research
work. We believed that the insertion of extra donor atoms
out of the classical tetradentate compartment of a salen-
type ligand would favour the aggregation of neighbouring
complexes through hydrogen bonding. This represents a
class of weaker, non-covalent interactions that not only in-
duce supramolecular arrays through self-organization of
[
4,5]
bridges.
Occasionally manganeseϪSchiff-base com-
[
4b,4f,5]
plexes can produce dimeric structures with µ-phenoxo
or µ-oxo bridges with the ligand in the equatorial plane
around each metal centre[ or, alternatively, µ-oxo bridges
6]
with the two ligands bridging both metal ions.[
4b,4e,8]
More-
over, some 2D polymerization processes via coordinative
bonding have been reported.[ In contrast, the aggregation
of manganese() discrete complexes or infinite chains in
multidimensional frameworks by metal-free supramolecular
9]
molecules, but also plays a crucial role in fundamental bio-
[
[
a]
b]
Departamento de Qu ´ı mica Inorg a´ nica, Facultade de Qu ´ı mica, logical processes, such as the expression and transfer of gen-
Universidade de Santiago de Compostela,
etic information, and is essential for molecular recognition
15782 Santiago de Compostela, Spain
[12]
Departamento de Qu ´ı mica Inorg a´ nica, Facultade de Ciencias, between receptors and substrates.
For this purpose, we
Universidade de Santiago de Compostela,
designed the ligand H L that contains six potential donor
4
2
7002 Lugo, Spain
atoms: two imine nitrogen and four phenolic oxygen atoms.
Fax: (internat.) ϩ34-981-597525
E-mail: qimb45@usc.es
The reaction of H L with manganese() chloride, in fact,
4
Eur. J. Inorg. Chem. 2004, 2769Ϫ2774
DOI: 10.1002/ejic.200400041
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2769

M. R. Bermejo et al.
FULL PAPER
yields a supramolecular system, which we report herein and X-ray Diffraction Studies
where the main intermolecular interactions come from the
Single crystals of [Mn(H L)(CH OH) ]Cl (1), suitable for
2
3
2
special role of the halide counterion as a kind of supramol-
ecular glue. This type of networks, which have the ability to
bind negatively charged ions, also constitute a hot subject
of research in recent years due to their potential ability and
selectivity to recognize anion receptors in solution.[
X-ray diffraction studies were obtained as detailed in the
Exp. Sect. An ORTEP view of 1, together with the atomic
numbering scheme, is shown in Figure 1. Experimental de-
tails are given in Table 1. Main bond lengths and angles are
listed in Table 2. This structure reveals the existence of a
13,14]
ϩ
cationic octahedral [Mn(H L)(CH OH) ] complex; the
2
3
2
neutral condition is achieved by the presence of a chloride
anion, which acts as a counterion despite the known tend-
Results and Discussion
The hexadentate Schiff base, H L (see Scheme 1), reacts
4
with the manganese() chloride salt to yield a black crystal-
line complex with the formula [Mn(H L)(CH OH) ]Cl (1),
2
3
2
in accordance with the elemental analysis. The solid ap-
pears to be stable in the solid state and in solution; it melts
at over 300 °C and is insoluble or sparingly soluble in water
and also in common organic solvents, but quite soluble in
MeOH, DMF and DMSO.
Figure 1. ORTEP plot of 1; atoms showing the atomic numbering
scheme are represented by their 50 % probability ellipsoids; sym-
metry operation to generate equivalent atoms: A Ϫ x ϩ 2, y, Ϫz
ϩ 1/2
4
Scheme 1. Structure of the Schiff-base ligand H L
Table 1. Crystal data and structure refinement for 1
Spectroscopy techniques verified the coordination of the
ligand to the manganese ion. Thus, the IR spectrum of 1
Empirical formula
18 2 6
C H22ClMnN O
shows the shift of the ν(CNimine) band to lower frequency Molecular weight
452.77
298(2)
Ϫ13 cmϪ1) and a positive shift of the ν(COphenol) mode
Temperature (K)
(
(
˚
Ϫ1
Wavelength (A)
0.71073
Orthorhombic
Pbcn
7.6793(7)
14.8888(13)
17.7322(16)
2027.4(3)
4
1.483
0.819
936
0.40 ϫ 0.30 ϫ 0.30
2.30 to 28.30°
13540
2527 (Rint ϭ 0.0368)
99.9 %
Empirical
ϩ13 cm ) with respect to the free ligand. These data sug-
Crystal system
Space group
gest the coordination of the Schiff base in its dianionic form
through the inner phenol oxygen and the imine nitrogen a (A)
atoms.
spectrum indicates that the metal is not coordinated to the
chloride, as confirmed by the crystal structure of this com-
˚
˚
[
14]
The absence of ν(MnϪCl) bands in the far IR b (A)
˚
c (A)
˚
3
Volume (A )
Z
D
plex. The FAB mass spectrum shows a peak due to the frag-
calcd. (g cmϪ3
)
ment [Mn(H L)] , which thus further corroborates coordi- Absorption coefficient (mmϪ1)
ϩ
2
F(000)
nation of the ligand to the manganese ion.
Crystal size (mm)
The room temperature magnetic moment of 1 is 4.8
Theta range for data collection
B.M., close to the spin-only value of 4.9 B.M., as expected
Reflections collected
for a high-spin magnetically diluted d manganese() ion. Independent reflections
4
The magnetic behaviour obeys the CurieϪWeiss law in the Completeness to θ ϭ 28.30°
Absorption correction
range 40Ϫ300 K, showing little or no antiferromagnetic in-
Max. and min transmission
teraction between neighbouring metal centres. The elec-
Refinement method
0.7911 and 0.7352
Full-matrix least-squares on F
2527/0/160
2
tronic spectrum in methanol solution is also typical of a
Data/restraints/parameters
2
manganese() ion in an octahedral environment. On other Goodness-of-fit on F
1.012
Final Rint [IϾ2σ(I)]
Rint (all data)
Largest diff. peak and hole
R1 ϭ 0.0366, wR2 ϭ 0.0888
R1 ϭ 0.0729, wR2 ϭ 0.1017
0.213 and Ϫ0.190 e·A
hand, the conductivity measurements in DMF give a ΛM
Ϫ1
value of 90 µS cm for 1, indicating behaviour that is at-
˚
Ϫ3
tributable to 1:1 electrolytes.[
16]
2770
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 2769Ϫ2774

Chloride as Supramolecular Glue
FULL PAPER
˚
Table 2. Selected bond lengths (A) and angles (°) for 1
Mn(1)ϪO(1)
Mn(1)ϪO(1A)
Mn(1)ϪN(1)
Mn(1)ϪN(1A)
Mn(1)ϪO(1S)
Mn(1)ϪO(1SA)
Mn···Mn
1.8755(14)
1.8755(14)
1.9809(17)
1.9809(17)
2.2675(19)
2.2675(19)
7.67(9)
O(1)ϪMn(1)ϪO1(A)
O(1)ϪMn(1)ϪN(1A)
O(1)ϪMn(1)ϪN(1)
O(1A)ϪMn(1)ϪN(1)
O(1A)ϪMn(1)ϪN(1A)
N(1)ϪMn(1)ϪN(1A)
O(1)ϪMn(1)ϪO(1S)
O(1A)ϪMn(1)ϪO(1S)
N(1)ϪMn(1)ϪO(1S)
N(1A)ϪMn(1)ϪO(1S)
94.06(9)
173.90(7)
92.00(7)
173.90(7)
92.00(7)
81.96(11)
91.18(7)
91.21(7)
89.37(7)
87.97(7)
O(1S)ϪMn(1)ϪO(1SA)
176.48(9)
H bonds
DϪH···A
d(DϪH)
d(H···A)
d(D···A)
Ͻ(DHA)
O(1S)ϪH(1S)···Cl(1)#1[a]
O(2)ϪH(2A)···Cl(1)#2
O(2)ϪH(2A)···O(1)
0.73(3)
0.77(3)
0.77(3)
0.86(2)
2.35(3)
2.55(3)
2.31(3)
2.51(7)
3.081(2)
3.218(2)
2.668(2)
3.143(3)
178(3)
146(2)
103.6(10)
130.6(2)
C(7)ϪH(7)···O(2)#3
[
a]
Symmetry transformations used to generate equivalent atoms: #1x ϩ 1/2, ϩy ϩ 1/2, Ϫz ϩ 1/2; #2x ϩ 1, ϩy, ϩz; #3x ϩ 1/2, Ϫy ϩ
1/2 ϩ 1, Ϫz.
ency to appear coordinated to the metal ion in similar
III
[4b,17]
Mn compounds.
The structure of discrete mononuclear [Mn(H L)-
2
ϩ
(
CH OH) ] cations comprises the planar Schiff-base li-
3
2
gand tightly bound to manganese() through the inner
N O compartment through the N
and Ophenol atoms
2
2
imine
˚
(
MnϪNimine bond lengths of 1.9809(17) A and MnϪO
phenol
˚
[4,18]
1.8755(14) A, typical of such complexes).
The coordi-
nation spheres of the slightly distorted octahedral manga-
nese centres are then completed by capping trans methanol
˚
molecules [MnϪOmethanol 2.2675(19) A]. The elongation in
the trans MnϪOmethanol bonds is usually attributed to a
4
III
JahnϪTeller distortion for a d high-spin Mn system but
in this case the poor donor strength of the methanol mol-
ecules may also contribute to this elongation. The MnN O2
2
core forms two six-membered chelate rings, which are
nearly planar [maximum deviation of any atom from its le-
˚
ast-squares calculated plane is Ϫ0.1170(11) A, with the
˚
manganese atom 0.1027(09) A above this plane]. This indi-
cates a slight distortion from the ideal geometry. The slight
distortion of the octahedron is also shown by the angles
between the manganese and adjacent donor atoms, which
range from 81.96(11)° to 94.06(9)°. The angle between the
Figure 2. Part of the unit cell of 1, exhibiting the net of interactions
metal atom and the trans donor atoms is 176.48(9)°. All between three neighbouring cationic complexes; the chloride anion
is tetra-coordinated to four hydroxy groups through hydrogen
distances and angles lie in the range expected for this type
bonding
III
[4,17,18]
of Mn complexes;
1
the N(1)ϪC(7) bond length of
˚
.277(3) A suggests a double bond, which is confirmed by
the IR spectrum with a strong vibration band at 1620 cm
The [Mn(H L)(CH OH) ] cations are interconnected involve the hydroxy groups from the axial methanol ligands
Ϫ1
.
ϩ
2
3
2
through the chloride anions by hydrogen bonds yielding a of two different complexes [H(1S)···Cl(1) 2.35(3),
˚
supramolecular structure. Each chloride anion is involved O(1S)···Cl(1) 3.081(2) A and O(1S)ϪH(1S)···Cl(1) 178(3)°]
in four OϪH···Cl hydrogen bonds with four different (see Table 2).
hydroxy groups from three neighbouring cationic complexes
The other two intermolecular contacts imply the outer
(
see Figure 2).
hydroxy groups of the third complex [H(2A)···Cl(1) 2.55(3),
˚
Two of these interactions are in the range of strong hy- O(2)···Cl(1) 3.218(2) A and O(2)ϪH(2A)···Cl(1) 146(2)°],
drogen bonds with an almost linear angle OϪH···Cl, and and can be categorized as intermediate in strength,[ prob-
19]
Eur. J. Inorg. Chem. 2004, 2769Ϫ2774
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M. R. Bermejo et al.
FULL PAPER
ably because of the additional interaction of these outer ure 4). The oxidation state ϩIII for the manganese ion in
hydroxy groups with the inner hydroxy groups through in- DMF solutions of 1 is determined by NPV, as it exhibited
tramolecular hydrogen bonding [H(2A)···O(1) 2.31(3), anodic and cathodic currents when an anodic potential scan
˚
O(2)···O(1) 2.668(2) A and O(2)ϪH(2A)···O(1) 103.6(10)°]. was performed (Figure 4b), but when a cathodic potential
This rich supramolecular structure is completed and scan was used, only cathodic current was observed (Fig-
further stabilized with intermolecular hydrogen bonds be- ure 4c). This behaviour suggests that only the oxidized form
II
III
tween carbon atoms from imine groups and oxygen atoms of the implied redox system Mn ϪMn is present in solu-
[
4b]
from the free phenolic sets of adjacent molecules. In this tion, as we have previously reported.
˚
case the H(7)···O(2) distance is of 2.51(7) A, the C(7)···O(2)
˚
distance is of 3.143(3) A, and the C(7)ϪH(7)···O(2) angle
is 130.6(2)°.
The packing of 1 determines the existence of a supramol-
ecular structure in which the chloride counterions are act-
ing as multiple acceptors, connecting three neighbouring
complexes through very different hydrogen bonding. How-
˚
ever, the Mn···Mn distances of 7.67(9) A are too long to
establish intermetallic interactions between neighbouring
manganese ions, which is in accordance with the non-anti-
ferromagnetic behaviour showed by the magnetic studies.
These multiple intermolecular interactions are extended
into the solid to form an infinite array (see Figure 3) consti-
tuting, to the best of our knowledge, the first example of
an anion-directed assembly of a 2D network of manga-
nese() complexes.
Figure 3. Perspective view of the 2D network formed, which shows
the chlorideЈs role as supramolecular glue in the assembly of the
manganese() complexes
1H NMR Studies
Paramagnetic 1H NMR studies of 1 were undertaken
using [D ]DMSO as a solvent, and the data serve to sub-
6
stantiate the formation of the manganese() complex. The
Ϫ1
spectrum of 1 is essentially as would be expected, in accord- Figure 4. Cyclic voltammogram for 1 at a scan rate of 0.02 V s
[
20]
(a); normal pulse voltammogram (NPV) with anodic scan of 1 (b);
NPV with cathodic scan of 1 (c)
ance with the assignments proposed by Pecoraro
and
also from our own results.[
4d,18]
The spectrum contains two
upfield proton resonances at Ϫ16.3 and Ϫ28.1 ppm that lie
outside the diamagnetic region (δ ca. 0Ϫ10) and must arise
from the H5 and H4 protons of the aromatic rings, respec-
CV of
1 exhibits a quasi-reversible one-electron
reductionϪoxidation wave (Figure 4a) centred at E1/2
ϭ
[
4d]
Ϫ0.159 V (versus saturated calomel electrode, SCE). Al-
though this negative potential belongs to the range which
would favour the potential catalytic activity, as we have pre-
tively.
Electrochemical Studies
The electrochemical behaviour of 1 in DMF solution was viously reported for other manganese()ϪSchiff base sys-
studied by cyclic and normal pulse voltammetry (see Fig- tems,[4g] the peak-to-peak separation of 0.318 V (Eox
ϭ
2772
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2769Ϫ2774

Chloride as Supramolecular Glue
FULL PAPER
0
.007 V; Ered ϭ Ϫ0.311 V) becomes a significant handicap was concentrated to yield a yellow solid. The product was collected
by filtration, washed with diethyl ether and dried in air. The yield
was almost quantitative; M.p. 240 °C. C16 (300.2): calcd.
C 63.9, H 5.4, N 9.3; found C 63.3, H 5.6, N 9.4. MS FAB (m/z):
01.1. IR (KBr): ν(OϪH) 3258, 3389 (m), ν(CϭN) 1633 (vs),
for the possible use of this complex in catalysis.
16 2 4
H N O
3
Conclusion
Ϫ1
1
ν(CϪO) 1246 (s) cm . H NMR ([D
6
]DMSO): δ ϭ 3.93 (s, 4 H),
6
2
.65 (t, 2 H), 6.82 (d, 2 H), 6.85 (d, 2 H), 8.54 (s, 2 H), 8.97 (br. s,
In the present work, we have shown how a ligand such
1
3
H), 13.46 (br. s, 2 H) ppm. C NMR ([D
), 116Ϫ122 (Car), 145.8 (C-OHinner), 151.0 (C-OHouter), 167.2
CϭN) ppm.
6
]DMSO): δ ϭ 58.0
as H L is able to induce, simultaneously, the formation of
4
(CH
2
a manganese() complex and its aggregation into an infi-
nite 2D array in the solid state through hydrogen bonding.
The chloride anions, contrary to their typical behaviour, are
not directly coordinated to the manganese atom at the first
coordination sphere, but they act as multiple hydrogen-
bonding-acceptor counterions as a kind of supramolecular
(
Synthesis of the Complex [Mn(H
1.0 mmol, 0.30 g) was dissolved in methanol (40 mL) and
MnCl ·4H O (1.0 mmol, 0.20 g), dissolved in methanol was added
2 3 2 4
L)(CH OH) ]Cl (1): H L
(
2
2
to the initial yellow solution, which changed to green. After stirring
for 10 min, NaOH (2 mmol, 0.08 g), dissolved in a small quantity
of water, was added and the mixture turned dark. The reaction
mixture was refluxed for 2 hours, and then concentrated in vacuo
III
glue, promoting the assembly of the Mn complexes. Fi-
nally, it must be noted that the development of molecular
and supramolecular systems, such as this one, with the to half its volume. The complex was obtained as black crystals,
ability to bind negatively charged ions could play an im- suitable for single X-ray-diffraction studies, after slow concen-
portant role in biology, medicine and the environment.
tration of the solution. These crystals were isolated by filtration,
washed with diethyl ether and dried in air, yield: 0.23 g, 50 %.
C
4
{
18
H
22ClMnN
7.5, H 4.7, N 6.3. MS FAB (m/z): 353 {Mn(H
Mn (H L) }. IR (KBr): ν(OϪH) 3414 (br), ν(CϭN) 1620 (vs),
2
O
6
(452.77): calcd. C 47.7, H 4.9, N 6.2; found C
2
L)}, 705
Experimental Section
2
2
2
Ϫ1
1
ν(CϪO) 1259 (s) cm . Magnetic moment µeffϭ 4.8 B.M. H NMR
300 MHz, [D ]DMSO): δ ϭ Ϫ28.1, Ϫ16.3 ppm. Conductivity (in
DMF) Λ ϭ 90 µS cm . Eoxϭ 0.007 V, Eredϭ Ϫ0.311 V, E1/2
Ϫ0.159 V.
General: Elemental analyses were performed on a Carlo Erba EA
(
6
1108 analyser. NMR spectra were recorded on a Bruker AC-300
Ϫ1
M
ϭ
spectrometer using [D ]DMSO (296 K) as a solvent. Infrared spec-
6
tra were registered as KBr pellets on a Bio-Rad FTS 135 spectro-
photometer in the range 4000Ϫ200 cmϪ1. Fast atom bombardment
X-ray Crystallographic Studies: Crystals of 1, suitable for X-ray dif-
fraction studies, were obtained as described above. Data were col-
(FAB) mass spectra were obtained on a Kratos MS-50 mass spec-
trometer, employing Xe atoms at 70 KeV in m-nitrobenzyl alcohol
as a matrix. Room-temperature magnetic susceptibilities were
measured using a digital measurement system MSB-MKI, cali-
brated using tetrakis(isothiocyanato)cobaltate(). Magnetic suscep-
tibility measurements in the 40Ϫ300 K temperature range were ob-
tained using a SQUID-QUANTUM model MPMS magnetometer
operating at 5000 G. Electronic spectra were recorded on a Cary
lected with a Smart CCD-100 Bruker diffractometer employing
˚
graphite-monochromated Mo-K
structure was solved by direct methods and finally refined by
full-matrix least-squares base on F . An empirical absorption cor-
α
(λ ϭ 0.71073 A) radiation. The
[22]
2
[23]
rection was applied using SADABS.
All non-hydrogen atoms
were anisotropically refined, and all hydrogen atoms were included
in the model at geometrically calculated positions. Detailed data
collection and refinement of the compound are summarized in
Table 1.
2
30 spectrometer. Conductivities of 10Ϫ3  solutions in DMF were
measured on a Crison microCM 2200 conductivimeter.
CCDC-212667 contains the supplementary crystallographic data for
Electrochemical Measurements: Measurements were performed
using an EG&G PAR model, 273 potentiostat, controlled by an
EG&G PAR model, 270 software. A Metrohm model, 6.1204.000
graphite disc, coupled to a Metrohm model, 628Ϫ10 rotating elec-
trolyte device, was used as a working electrode. A saturated calomel
electrode was used as a reference and a platinum wire as an auxili-
ary electrode.
1. These data can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
(
internat.) ϩ 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
Ϫ3
Acknowledgments
Measurements were made with ca. 10  solution of 1 in dimethyl-
formamide using 0.1  tetraethylammonium perchlorate as a sup-
porting electrolyte. Cyclic voltammetry measurements were per-
formed with a static graphite electrode, whilst direct-current and
pulse voltammograms were recorded with the graphite disc rotating
at 2000 revolutions per minute.
We thank Ministerio de Ciencia y Tecnolog ´ı a of Spain (BQU2003-
00167) for financial support.
[
[
1]
2]
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ethylenediamine (Aldrich), manganese() chloride tetrahydrate (Al-
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purification.
[3]
3
707Ϫ3712.
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N. Aurangzeb, C. E. Hulme, C. A. McAuliffe, R. G. Pritch-
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28.96 mmol, 4 g).[ This mixture was refluxed in a round bot-
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J. Sanmart ´ı n, A. Sousa, Chem. Commun. 1994, 1153Ϫ1155.
tomed flask fitted with a DeanϪStark trap to remove the water
M. R. Bermejo, A. Casti n˜ eiras, J. C. Garc ´ı a-Monteagudo, M.
produced during the reaction. After refluxing for 3 h, the solution
Rey, A. Sousa, M. Watkinson, C. A. McAuliffe, R. G. Pritch-
Eur. J. Inorg. Chem. 2004, 2769Ϫ2774
www.eurjic.org
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