Supramolecular networks of Mn(III)-Schiff base complexes assembled by nitrate counterions: X-ray crystal structures of 1D chains and 2D networks

Article abstract of DOI:10.1016/j.poly.2011.09.031

A series of Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by condensation of 3-methoxy-2- hydroxybenzaldehyde with different diamines. The complexes have been characterised by elemental analysis, ESI mass

Full text of DOI:10.1016/j.poly.2011.09.031

Polyhedron 31 (2012) 379–385
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Supramolecular networks of Mn(III)–Schiff base complexes assembled by nitrate
counterions: X-ray crystal structures of 1D chains and 2D networks
a
M. Ángeles Vázquez-Fernández a, M. Isabel Fernández-García a, , Ana M. González-Noya ,
⇑
Marcelino Maneiro a, , Manuel R. Bermejo b, M. Jesús Rodríguez-Doutón c
⇑
a Departamento de Química Inorgánica, Facultade de Ciencias, Universidade de Santiago de Compostela, Avda. Alfonso X, Lugo E-27002, Spain
b Departamento de Química Inorgánica, Facultade de Química, Universidade de Santiago de Compostela, Santiago de Compostela E-15782, Spain
c Department of Chemistry and INSTM Research Unit, University of Modena and Reggio Emilia, Via G. Campi 183, 41100 Modena, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 July 2011
Accepted 25 September 2011
Available online 1 October 2011
A series of Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases
obtained by condensation of 3-methoxy-2-hydroxybenzaldehyde with different diamines. The complexes
have been characterised by elemental analysis, ESI mass spectrometry, IR and 1H NMR spectroscopy.
Magnetic studies and molar conductivity measurements were also performed. Complexes [MnL1(H2O)2]2Á
2NO3Á2CH3OH (1), [MnL2(H2O)2]2Á2NO3Á2CH3OH (2) and [MnL5(H2O)2]2Á2NO3Á6H2O (5) were crystallo-
graphically characterised. The X-ray structures show an octahedral geometry around the metal with
the Schiff base in the equatorial plane acting as tetradentate and water or methanol molecules in the axial
Keywords:
Manganese complexes
Schiff bases
Supramolecular structure
Crystal structure
Hydrogen bonds
positions. The octahedron entities are linked in pairs by
l-aquo bridges between neighbouring axial
water molecules and also by stacking interactions, establishing dimeric and polymeric structures.
p–p
Nitrate anions are accommodated in the cavities of the framework and form hydrogen bonds with the
aqua ligands and the methanol or crystal water, leading to infinite supramolecular aggregates of the com-
plexes. Comparison of chloride, perchlorate and nitrate complexes indicate that the nature of the anions
is the key factor directing the structural topologies.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
For years, the coordination chemistry of manganese was fo-
cused on the active role of this metal ion in many redox enzymes
The design and synthesis of supramolecular architectures sus-
tained by noncovalent intermolecular forces (hydrogen bonding,
p–p stacking,. . .) represents a rapidly expanding field that offers
[14,15], but the supramolecular arrangements of manganese com-
plexes have been less studied. Most recently, with the skill and the
motivation acquired due to our successes in the construction of
well-appealing supramolecular architectures [7,16,17], we are
investigating the overlooked supramolecular arrangements of
manganese(III) complexes. Our scheme consists of obtaining the
aggregation of discrete manganese(III) complexes into multidi-
mensional arrays through metal-free self-assembly, using Schiff
base ligands with hydroxyl groups in adequate positions. Thus,
we have already reviewed the supramolecular arrangements with
carboxylate groups [18], chloride [19] and perchlorate [20] counte-
rions. The hydrogen bonding net led to supramolecular systems
with different dimensionality where the counterion plays a crucial
role. In this paper we describe the results of our research work
with the nitrate anion.
There are few examples of Mn(III)–Schiff base (or porphyrin)
complexes with the nitrate anion. Of those found in the literature
some of them incorporate the ion to the first coordination sphere
[21]; the nitrate group may also be bridging manganese ions in
Mn–carboxylate complexes [22], but there a small number of cases
where the nitrate acts as counterion in this type of systems
[23,24]. Moreover, even these publications do not discuss the
potential for the development of new types of functional solids
[1–4]. The self-assembly of metal–organic frameworks is highly
influenced by factors such as the geometric requirements of metal
ions [5,6], the ligand design [7,8], the solvents used for crystallisa-
tion [9] or the selection of the counteranions [10,11]. The manage-
ment of all these factors makes it possible to know the synthetic
strategies that lead to the desired species with predictable struc-
tures and properties. However, establishing the general and precise
principles of constructing desirable framework topologies is still a
large challenge. In particular, the role of anions in self-assembly
processes has emerged as an increasingly active theme [12,13].
Our recent efforts on controlled coordination-driven self-assembly
of Mn–Schiff complexes also shed some lights on this point.
⇑
Corresponding authors. Tel.: +34 982824065; fax: +34 982285872 (M. Manei-
ro).
E-mail addresses: misabel.fernandez.garcia@usc.es (M. Isabel Fernández-García),
marcelino.maneiro@usc.es (M. Maneiro).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.09.031

380
M. Ángeles Vázquez-Fernández et al. / Polyhedron 31 (2012) 379–385
SQUID susceptometer. Sample was a 3 mm diameter pellet moul-
ded from ground crystalline sample. Electronic spectra were re-
corded on a Cary 230 spectrometer. Conductivities of 10À3
M
solutions in DMF were measured on a Crison microCM 2200
conductivimeter.
2.3. Preparation of the Schiff base ligands
All the Schiff bases used in this study were prepared by conden-
sation of the appropriate diamine with 3-methoxy-2-hydroxy-
benzaldehyde. H2L1–H2L5 have been already reported and
characterised by standard techniques [20,29,30]. H2L6 was pre-
pared by the method outlined below and satisfactorily character-
ised by elemental analysis, 1H- and 13C NMR and IR spectroscopy,
and ESI mass spectrometry.
2.3.1. H2L6
To a methanolic solution (100 mL) of 1.00 g (6.57 mmol) of 3-
methoxy-2-hydroxybenzaldehyde (1.00 g, 6.57 mmol) was added
1,4-diaminobutane (0.33 mL, 3.29 mmol). The mixture was re-
fluxed for 3 h in a round bottom flask fitted with a Dean-Stark trap
to remove the water produced during the reaction. After, the solu-
tion was concentrated to yield a yellow solid that was collected by
filtration, washed with diethyl ether and dried in vacuo. Yields
were almost quantitative. M.p. 143 °C. Anal. Calc. for C20H24N2O4
(356.4): C, 67.4; H, 6.8; N, 7.9. Found: C, 67.3; H, 6.8; N, 7.8%. MS
Scheme 1.
supramolecular arrangements of these complexes. We have also
previously added nitrate groups to Mn(III)–Gd(III)–Schiff base
complexes but this anion stabilised joining the Gd [25].
The ability of these anions for establishing hydrogen bonds
would lead to new supramolecular architectures and would also
lead to systems of interest for the selective recognition between
anions and receptors [26–28]. Now we report a series of Mn(III)–
Schiff-base complexes associated by nitrate counteranions, using
ligands with suitable OH groups. The key role of anions in tuning
the resultant structural topologies has been concluded. The se-
lected Schiff-base ligands, H2Ln (see Scheme 1) are the result of
the condensation of 3-methoxy-hydroxybenzaldehyde with di-
verse diamines (1,2-diaminoethane for H2L1; 1,2-diamino-2-meth-
ylethane for H2L2; 1,2-diamino-2,2-dimethylethane for H2L3; 1,3-
diaminopropane for H2L4; 1,3-diamino-2,2-dimethylopropane for
H2L5 and 1,4-diaminobuthane for H2L6). H2L1–H2L6 contain six po-
tential donor atoms, two imine nitrogen atoms and two phenol
oxygen atoms in an inner compartment and two outer methoxy
groups.
ESI (m/z): 357. IR (KBr, cmÀ1):
m(O–H) 3099 (m), m(C@N) 1629
(vs),
m
(C–O) 1245 (s). 1H NMR (DMSO-d6, ppm): d 1.73 (q:quintu-
plet, 4H), 3.65 (t, 4H), 3.77 (s, 6H), 6.77 (t, 2H), 6.99 (d, 2H), 7.01
(d, 2H), 8.53 (s, 2H), 13.90 (br). 13C NMR (DMSO-d6, ppm): d 27.9
(–CH2–), 55.7 (@N–CH2–), 57.0 (–OCH3), 114.6–123.2 (Car), 148.1
(C–OH), 152.4 (C–OCH3), 165.9 (C@N).
2.4. Complex preparation
All the manganese(III) Schiff base complexes were prepared by
stirring a methanol solution (50 mL) of the corresponding ligand
and adding subsequently
a methanol solution (30 mL) of
Mn(NO3)2Á4H2O at room temperature. The initial light colour of
the solutions rapidly changed to brown. After 3 h of stirring at
room temperature slow evaporation of solvent lead to deposition
of brown compounds. The products were collected by filtration,
washed with diethyl ether (2 Â 20 mL) and then dried in vacuo.
Yields of the complexes vary, but are typically of the order of 70%.
2. Material and methods
2.4.1. [MnL1(H2O)2]ÁNO3ÁCH3OH, (1)
2.1. Materials
H2L1 (0.33 g, 1.00 mmol); Mn(NO3)2Á4H2O (0.26 g, 1.00 mmol);
yield: 0.36 g (70%). Anal. Calc. for C19H26MnN3O10 (511.4): C,
44.6; H, 5.1; N, 8.2. Found: C, 44.5; H, 4.9; N, 8.3%. MS ESI (m/z):
All the starting materials (Aldrich) and solvents (Probus) used
for the synthesis were of commercially available reagent grade
and were used without further purification.
381 [MnL1]+, 824 [Mn2L12(NO3)]+. IR (KBr, cmÀ1):
m(O–H) 3420
(m),
m(C@N) 1619 (vs), m(C–O) 1257 (s), m(NO3) 1384 (vs), 830
2.2. Physical measurements
(m), 738 (s). 1H NMR (DMSO-d6, ppm): d À30.52 (H4), À21.50
(H5).
l = 5.1 BM. KM = 81 lS.
Elemental analyses were performed on a Carlo Erba Model 1108
CHNS–O elemental analyzer. The IR spectra were recorded as KBr
pellets on a Bio-Rad FTS 135 spectrophotometer in the range
2.4.2. [MnL2(H2O)2]ÁNO3ÁCH3OH, (2)
H2L2 (0.20 g, 0.58 mmol); Mn(NO3)2Á4H2O (0.15 g, 0.58 mmol);
yield: 0.23 g (75%). Anal. Calc. for C20H28MnN3O10 (525.4): C,
45.7; H, 5.4; N, 8.0. Found: C, 45.4; H, 5.1; N, 8.0%. MS ESI (m/z):
4000–400 cmÀ1 1H and 13C NMR spectra were recorded on a Bru-
.
ker AC-300 spectrometer using DMSO-d6 (296 K) as solvent and
SiMe4 as an internal reference. The electro-spray mass spectra of
the compounds were obtained on a Hewlett–Packard model LC-
MSD 1100 instrument (positive ion mode, 98:2 CH3OH–HCOOH
as mobile phase, 30–100 V). Room-temperature magnetic suscepti-
bilities were measured using a digital measurement system MSB-
MKI, calibrated using mercury tetrakis(isothiocyanato)cobaltate(II)
Hg[Co(NCS)4] as a susceptibility standard. Variable-temperature
magnetic data were obtained with a Quantum Design MPMS
395 [MnL2]+, 852 [Mn2L22(NO3)]+. IR (KBr, cmÀ1):
m(O–H) 3415
(m),
m(C@N) 1619 (vs), m(C–O) 1254 (s), m(NO3) 1384 (vs), 859
(m), 735 (s). 1H NMR (DMSO-d6, ppm): d À27.77 (H4), À17.50,
À18.95 (H5).
l = 5.0 BM. KM = 72 lS.
2.4.3. [MnL3(H2O)2].NO3.H2O, (3)
H2L3 (0.20 g, 0.56 mmol); Mn(NO3)2Á4H2O (0.14 g, 0.56 mmol);
yield: 0.19 g (65%). Anal. Calc. for C20H28MnN3O10 (525.4): C,

M. Ángeles Vázquez-Fernández et al. / Polyhedron 31 (2012) 379–385
381
Table 1
45.7; H, 5.4; N, 8.0. Found: C, 45.8; H, 5.2; N, 8.2%. MS ESI (m/z):
409 [MnL3]+, 880 [Mn2L32(NO3)]+. IR (KBr, cmÀ1):
(O–H) 3415
Crystal data and structure refinement for 1, 2 and 5.
m
(m),
m(C@N) 1608 (vs), m(C–O) 1257 (s), m(NO3) 1384 (vs), 860
Complex
1
2
5
(m), 737 (s). 1H NMR (DMSO-d6, ppm): d À27.94 (H4), À17.40,
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
19H26MnN3O10 C20H28MnN3O10 C21H32MnN3O11
À18.80 (H5).
l = 5.0 BM. KM = 71 lS.
511.37
180(2)
0.71073
orthorhombic
Pbca
525.39
293(2)
0.71073
triclinic
557.44
100(2)
0.71073
monoclinic
I2/a
25.7414(14)
7.5727(4)
27.682(2)
90
115.236(2)
90
4881.0 (5)
8
1.517
0.606
2336
1.63/25.68
81746
4631
0.0984
11/371
2.4.4. [MnL4(H2O)2].NO3.2H2O, (4)
H2L4 (0.25 g, 0.73 mmol); Mn(NO3)2Á4H2O (0.18 g, 0.73 mmol);
yield: 0.29 g (75%). Anal. Calc. for C19H28MnN3O11 (529.4): C,
43.1; H, 5.3; N, 7.9. Found: C, 42.9; H, 5.0; N, 7.9%. MS ESI (m/z):
ꢀ
P1
12.9621(11)
14.2447(11)
23.9115(15)
90.00
90.00
90.00
4415.0(6)
8
1.539
0.659
2128
2.32/26.03
33158
4312
0.0456
6/311
9.089(2)
12.048(3)
12.761(3)
114.036(4)
108.147(4)
91.751(4)
1192.6(5)
2
1.463
0.612
548
1.87/26.44
13613
b (Å)
c (Å)
395 [MnL4]+, 852 [Mn2L42(NO3)]+. IR (KBr, cmÀ1):
m(O–H) 3425
a
(°)
(m),
m(C@N) 1613 (vs), m(C–O) 1253 (s), m(NO3) 1384 (vs), 860
b (°)
(m), 735 (s). 1H NMR (DMSO-d6, ppm): d À20.97 (H4), À16.28
c
(°)
V (Å3)
(H5).
l = 4.8 BM. KM = 72 lS.
Z
Dcalc. (g cmÀ3
)
2.4.5. [MnL5(H2O)2].NO3.3H2O, (5)
l
(mmÀ1
)
H2L5 (0.25 g, 0.68 mmol); Mn(NO3)2Á4H2O (0.18 g, 0.68 mmol);
yield: 0.29 g (79%). Anal. Calc. for C21H32MnN3O11 (557.4): C,
45.2; H, 5.8; N, 7.5. Found: C, 45.3; H, 5.7; N, 7.5%. MS ESI (m/z):
F(000)
hmin/max (°)
Total data
Unique data
Rint
4866
0.0238
6/330
423 [MnL5]+, 908 [Mn2L52(NO3)]+. IR (KBr, cmÀ1):
m(O–H) 3427
(m),
m(C@N) 1609 (vs), m(C–O) 1254 (s), m(NO3) 1384 (vs), 850
Restraints/
(m), 739 (s). 1H NMR (DMSO-d6, ppm): d À21.97 (H4), À18.00
parameters
Goodness-of-fit
(GOF)
1.025
1.099
1.071
(H5).
l = 5.3 BM. KM = 68 lS.
Final R indices
R1 = 0.0319
wR2 = 0.0791
R1 = 0.0418
wR2 = 0.0840
R1 = 0.0499
wR2 = 0.1503
R1 = 0.0600
wR2 = 0.1595
R1 = 0.0433
wR2 = 0.0804
R1 = 0.0730
wR2 = 0.0884
2.4.6. [MnL6(H2O)2]ÁNO3Á3H2O, (6)
[I > 2r(I)]
H2L6 (0.20 g, 0.56 mmol); Mn(NO3)2Á4H2O (0.14 g, 0.56 mmol);
yield: 0.28 g (90%). Anal. Calc. for C20H32MnN3O12 (561.4): C,
42.8; H, 5.7; N, 7.5. Found: C, 42.4; H, 5.3; N, 7.4%. MS ESI (m/z):
R indices (all data)
409 [MnL6]+, 880 [Mn2L62(NO3)]+. IR (KBr, cmÀ1):
m(O–H) 3438
(m),
m(C@N) 1612 (vs), m(C–O) 1254 (s), m(NO3) 1384 (vs), 868
All the complexes show similar IR spectra, exhibiting a strong
(m), 742 (s). 1H NMR (DMSO-d6, ppm): d À26.23 (H4), À20.56
band between 1619–1608 cmÀ1 characteristic of the
m(C@N)
stretching mode, which is shifted 8–21 cmÀ1 lower with respect
to the free Schiff base ligand, indicating the coordination to the
manganese through the nitrogen atoms of the imine group. The
(H5).
l = 5.3 BM. KM = 69 lS.
2.5. Crystallographic data collection and refinement of the structures
band attributed to the m
(C–O) mode is shifted 4–10 cmÀ1 to higher
frequencies with respect to the free ligand. These data suggest the
coordination of the Schiff bases through the inner phenol oxygens
and the imine nitrogen atoms. Strong bands centred at ca.
Single crystals of the complexes 1, 2 and 5, suitable for X-ray
diffraction studies, were obtained by slow evaporation of the
methanolic solution at room temperature.
Detailed crystal data collection and refinement for the com-
plexes are summarised in Table 1. Intensity data were collected
on a Bruker-Smart CCD-1000 diffractometer employing graphite-
3400 cmÀ1 can be assigned to a combination of the
m(O–H) modes
of coordinated and lattice water/methanol, now present in the
complexes. The appearance of a new strong and sharp band at
1384 cmÀ1, together with bands at ca. 740 and 850 cmÀ1 are char-
acteristic of the presence of the non-coordinated nitrate counterion
(see Supplementary data, Fig. S1) [34].
monochromated MoK
a radiation (k = 0.71073 Å) for 2 at room
temperature, and for 5 at 180 K. Data for 1 were collected at
180 K on a Stoe Imaging Plate Diffractometer System (IPDS) using
ESI mass spectra registered in methanol show peaks corre-
sponding to the fragment [MnL]+ for all the complexes, indicating
the coordination of the Schiff base ligand to the metal centre. Other
minor signals could be assigned to [Mn2L2(NO3)]+ units, which
could be attributed to the presence of dimeric species (see Section
2 and also Supplementary data, Fig. S2).
a graphite monochromated MoK
a radiation (k = 0.71073 Å) and
equipped with an Oxford Cryosystems cooler device. The struc-
tures were solved by direct methods [31] and finally refined by
full-matrix least-squares base on F2. An empirical absorption cor-
rection was applied using SADABS [32]. All non-hydrogen atoms were
included in the model at geometrically calculated positions.
3. Results and discussion
3.1. 1H NMR studies of the complexes
The manganese(III) complexes 1–6 were prepared as detailed in
the Section 2. They appear to be stable in the solid state and in
solution, and they are moderately soluble in common organic sol-
vents and soluble in polar aprotic coordinating solvents such as
DMF and DMSO. Elemental analysis establishes their general
formulae as [MnL(H2O)2]ÁNO3ÁxSolv (Solv = H2O or CH3OH). These
formulations are in agreement with molar conductivity measure-
ments in 10À3 M DMF solutions, which are in the range 68–
Paramagnetic 1H NMR studies of the complexes were registered
using DMSO-d6 as solvent, and the data serve to substantiate the
formation of the manganese(III) complexes. The data interpreta-
tion was based on previous findings for manganese(III) complexes
with related Schiff base ligands made by Pecoraro and co-workers
[35] and on our own results [18,19]. The data are collected in the
Section 2 and Fig. S3 of Supplementary data shows one of these
spectra. The spectra contain between two and three upfield proton
resonances, outside the diamagnetic region (d = 0–14 ppm), due to
the isotropically shifting of the ligand protons for high-spin man-
ganese(III) complexes in an octahedral field. The signals must arise
from the H4 and H5 protons of the aromatic phenoxy rings. The
81 l
S cmÀ1, indicating behaviour attributable to 1:1 electrolytes
[33]. Furthermore, other spectroscopic techniques support such
formula and give insights into both solid and solution structure
of the complexes.

382
M. Ángeles Vázquez-Fernández et al. / Polyhedron 31 (2012) 379–385
signals between À20.97 and À30.52 ppm arise from the H4 pro-
tons, while the resonances from À16.28 to À21.50 ppm arise from
H5 protons. The signal corresponding to the H5 protons appears
splitted in two in complexes including H2L2 and H2L3 Schiff bases;
this fact can be attributed to the asymmetric nature of the Schiff
base ligand of these complexes.
3.2. Electronic spectroscopic
The electronic spectroscopic data recorded are very similar for
all compounds 1–6, indicating that the MnIII complexes are
behaving as high-spin octahedral d4 systems, suffering a Jahn–Tell-
er distortion which affects the spectra and complicates its interpre-
Fig. 1. An ORTEP view of the environment around the manganese centre for 5,
including the atomic numbering scheme. Thermal ellipsoids are drawn at the 50%
probability level. Hydrogen atoms and aqua uncoordinated are omitted for clarity.
This structure shows a boat-shaped conformation.
tation.
MÀ1 cmÀ1) is attributable to a d–d transition, while it is reasonable
to assign the broad band obtained at 480–490 nm ( = 2600–
3300 MÀ1 cm–1) to the phenolate ? Mn(III) charge-transfer.
The peak, appearing around 300 nm = 21000–23000
MÀ1 cm–1), can be assigned to intraligand p⁄. The energy and
A broad shoulder at about 520–600 nm (e = 120–500
e
(
e
around the metal centre (from 81.92° to 94.38°), as well as by
the interaxial angle OW–Mn–OW of 170.10–178.70°.
The differences between 1, 2 and 5 arise from the superstruc-
ture of the complexes. All of them show associations via a combi-
p–
intensity of the LMCT and d–d transitions are in agreement with
those reported for related MnIII complexes [36–38].
nation of
p-aryl offset interactions (3.71–3.89 Å) [39–40] and
3.3. Crystallographic studies
hydrogen bonds between capping water molecules and both phen-
oxy and methoxy oxygen atoms of the neighbouring Schiff base li-
gand. These hydrogen bonds are charge-assisted, that is, the
hydrogen bond donor and/or acceptor carry positive and negative
ionic charges, respectively, and hence they are rather strong and
short [41]. As result of these supramolecular interactions, the
MnÁ Á ÁMn distances of about 4.7–5.1 Å are short for monomeric
The structures of the complexes 1, 2 and 5 have been crystallo-
graphically solved. Main crystallographic data for these complexes
are summarised in Table 1, and bond lengths and angles are listed
in Table 2.
In all cases the geometry around the manganese ion can be de-
scribed as distorted octahedral. An ORTEP view of 5 with the atom-
ic numbering scheme is shown in Fig. 1.
The coordination sphere around each manganese centre for 1, 2
and 5 comprises the planar Schiff base ligand, tightly bound to the
metal ion through the inner N2O2 compartment by the Nimine and
Ophenol atoms (Mn–Nimine bond lengths of 1.97–2.03 Å and Mn–
Ophenol of 1.87–1.90 Å, which are typical of such complexes and
corroborate the bisdeprotonation of the ligands [19,20]), occupying
the equatorial positions and giving rise to two six-membered che-
late rings (which are nearly planar) and an additional five- or six-
membered chelate ring (depending of the diamine R). The axial
positions of the octahedron are occupied by capping water mole-
cules in all cases. The Jahn–Teller elongation expected for d4
high-spin manganese(III) appears outstanding in the axis orthogo-
nal to the plane of the Schiff base ligand, with distances ranging
from 2.20 to 2.32 Å, considerably longer than the equatorial Mn–
O bond lengths quoted earlier. The deviation from an ideal octahe-
dral geometry is also revealed by the range of angles observed
2+
compounds, yielding [MnL(Solv)2]2 dimers for 1 and 2 (being
L
Schiff base and Solv the water/solvent molecules), and
[MnL(Solv)2]nn+ polymers in 5. The positions of the nitrate counte-
rions and the uncoordinated methanol and water molecules are
the determining factors to induce the resulting different crystal
packing of these complexes:
2+
(i) The [MnL(Solv)2]2
l-aquo dimers in 1 and 2 are electro-
statically stabilised by nitrate counterions (Fig. 2). These
anions are acting as hydrogen-bonding acceptors with coor-
dinated water or methanol, interconnecting the
dimers and enriching the final supramolecular structure.
(a) In 2 the external apical water molecules of the dimers
form two hydrogen bonds with two oxygen atoms of
the nitrate group; one of them is also bound to a meth-
anol molecule. Thus, there are two nitrate groups and
l-aquo
two methanol molecules between
ating a 1D chain (Fig. 3).
l-aquo dimers, gener-
(b) In the case of 1 an apical water molecule establishes two
hydrogen bonds: to O8 of the nitrate group and to O10 of
the methanol; the nitrate ion also establishes a hydrogen
bond through the O9 to a different methanol molecule,
which is bound to another apical water molecule of a
neighbouring dimer. This supramolecular interaction
originates a 2D net (Fig. 4).
Table 2
Selected bond lengths (Å) and angles (°) for the complexes 1, 2 and 5.
Complex
Mn–Op
1
2
5
1.8718(12)
1.8725(12)
1.9780(14)
1.9783(14)
2.2405(12)
2.3257(13)
93.14(5)
91.63(5)
92.06(6)
174.38(6)
175.18
83.16(6)
1.8774(18)
1.8820(18)
1.978(2)
1.972(2)
2.257(2)
2.263(2)
94.38(8)
91.98(9)
81.92(11)
173.77(9)
173.64(9)
88.88(9)
178.70(10)
4.876
1.9026(16)
1.9051(16)
2.032(2)
2.029(2)
2.2040(18)
2.2063(19)
87.34(7)
89.63(7)
89.29(7)
176.63(8)
176.96(8)
93.74(8)
169.63(7)
5.082
Mn–Ni
(ii) The polymeric structure of 5 grows in one dimension,
through hydrogen bonding between capping water mole-
cules and both phenoxy and methoxy oxygen atoms of the
neighbouring Schiff base ligand. In this case, nitrate groups
and solvent water molecules are connecting through hydro-
gen bonds but they do not establish any of these interactions
to the Mn–Schiff base moiety. This result in a 1D Mn–Schiff
base chain, parallel to a channel made up of the nitrate coun-
terions and the water molecules (Fig. 5). The disposition of
the Schiff base ligand is not planar, and the two phenyl rings
are located on the same side of the N2O2 coordination site
Mn–Oax
Op–Mn–Op
Op–Mn–Ni
N–Mn–N
Oa–Mn–Oa
MnÁ Á ÁMn
170.10(5)
4.736
Op = Ophenolic; Ni = Niminic; Oa = Oaxial
.

M. Ángeles Vázquez-Fernández et al. / Polyhedron 31 (2012) 379–385
383
Fig. 4. Stick diagram for
1
showing the hydrogen bonding between adjacent
[MnL1(H2O)2]2
molecules.
dimeric units through nitrate anions and methanol solvent
2+
Magnetic studies at variable temperature have been done for 1
(between 150 and 2 K) in a 0.8 T applied magnetic field. The data
obtained for complex 1 are collected in Table S1 of Supplementary
Fig. 2. Molecular structure of 1.
data. Fig. 6 shows the thermal dependence of the
Mn2 unit. The Curie–Weiss law is obeyed in the 15–150 K temper-
ature range. At 150 K the
MT product is equal to 5.91 cm3 molÀ1 K,
which is close to the room temperature value. As the temperature
is lowered, the MT is almost constant from 150 to 45 K, it de-
vMT product per
v
v
creases smoothly down to 14 K (2.54) and then more steeply,
reaching a value of 0.55 cm3 molÀ1 K at 2 K. This behaviour is con-
sistent with weak antiferromagnetic interactions and/or zero field
splitting effects originating from the Mn(III) ion.
According to the X-ray structure of 1, which consists of l-aquo
dimers (Fig. 2), the magnetic data were analysed by using a Ham-
iltonian that takes into account an isotropic coupling between
Mn(1)–Mn(2) centres through the hydrogen bonds [42]. The esti-
mation of the coupling constant was performed using the Hamilto-
nian H = ÀJSMn1SMn2 + DMn(S2Mnz1 + S2Mnz1), which includes the
axial single-ion local anisotropy of the Mn(III) ions, according to
the solved crystal structure. This model does not take into account
any intermolecular interactions, since they are expected to be
weaker than J because of significantly greater distances involved.
The best fit of the experimental susceptibility data with the
above Hamiltonian led to the following parameters: J =
À0.46 cmÀ1, D = 2.48, and the mean Landé factor g = 2.016. The J
value, taking into account the magnetic exchange interaction
through the pair of complementary hydrogen bonds, as well as
the D value, are similar to those observed in other Mn(III)–Schiff
base l-aquo dimers with different counterions [29,42].
The solved crystal structures of 2 and 5 show a bridging scheme
between the manganese(III) ions similar to 1, through hydrogen
bonding between capping water molecules and both phenoxy
and methoxy oxygen atoms of the neighbouring Schiff base ligand.
Previous magnetic studies on related compounds between 300 and
5 K also indicated little or no antiferromagnetic interaction be-
tween the metal centres [29,43,44]. The room temperature mag-
netic moments observed in this study do not give cause to
suppose that any different magnetic behaviour should occur.
Fig. 3. View along the c axis of 2, showing two nitrate groups and two methanol
molecules between l-aquo dimers, generating a 1D chain.
plane. The deviation from the Mn–N2O2 mean plane in such
a way gives rise to a boat-shaped conformation, already
observed in literature for similar cases [25].
3.4. Magnetic studies
Values for the
3.5. Anion control of the self-assembly
v
MT product of compound 1–6 at room temper-
We have early published the behaviour of the chloride and per-
chlorate counterions as multiple hydrogen-bond acceptors for sim-
ilar manganese(III)–Schiff base complexes. Thus, each chloride ion
ature are very close to the spin-only value of 3 cm3 molÀ1 K ex-
pected for high-spin magnetically diluted d4 manganese(III) ion.

384
M. Ángeles Vázquez-Fernández et al. / Polyhedron 31 (2012) 379–385
Fig. 5. (a) View along the c axis of the 1D chain of Mn(III) complexes for 5; hydrogen atoms and uncoordinated nitrates and solvent water molecules are omitted for clarity;
(b) packing view of 5 showing the 1D chains placing nitrates and solvent water molecules in channels.
4. Conclusions
This work again further emphasises the suitability of Schiff
bases with inner and outer O–X (X = CH3 in the present work)
groups for establishing rich hydrogen-bonding networks. The re-
sults show that the nature of the counterion can control the archi-
tecture of final products in the self-assembly process by choosing
more favourable noncovalent interactions in a cooperative manner.
The dimensionality of the supramolecular array is affected by the
nature of the anion which induces the assembly.
Acknowledgments
We thank Xunta de Galicia (09DPI004291PR and
10PXIB262132PR) for financial support.
Appendix A. Supplementary data
Fig. 6. Plot of
vMT vs. temperature for 1 per Mn2 unit.
CCDC 785922, 785923 and 786041 contain the supplementary
crystallographic data for 1, 2 and 5. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/j.
poly.2011.09.031.
could be involved in four O–HÁ Á ÁCl bonds, connecting three neigh-
bouring cationic complexes and assembling them to constitute a
2D network [19]. The dimensionality of the supramolecular
arrangement is reduced by the assembly through perchlorate
counterions because each anion is able to form only two hydrogen
bonds, directing preference to one direction and forming 1D chain
[20].
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planar nitrate anion also preferably induces 1D arrangement. This
is the case of all the structures reported in this work but 1, where
the 2D network arises from the sum of the contacts due to the ni-
trate, methanol and water molecules.
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