Dinuclear and heptanuclear nickel(II) complexes: Anion coordination induced ligand arm hydrolysis and aggregation around a nickel(II) core

Article abstract of DOI:10.1016/j.poly.2013.01.009

The heptanuclear and tetracationic nickel(II) complex [Ni ₇(μ₃-OH)₆(μ₃-H ₂L)₄](NO₃)₄·2MeOH (3·2MeOH); (H₃L is 2,6-bis-[(3-hydroxy-propylimino)-methyl]-4- me

Full text of DOI:10.1016/j.poly.2013.01.009

Polyhedron 53 (2013) 32–39
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Dinuclear and heptanuclear nickel(II) complexes: Anion coordination induced
ligand arm hydrolysis and aggregation around a nickel(II) core
a
b
c
b
a,
⇑
Aloke Kumar Ghosh , Antonio Bauzá , Valerio Bertolasi , Antonio Frontera , Debashis Ray
a
Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India
Departament de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7,5, 07122 Palma (Baleares), Spain
Dipartimento di Chimica e Centro di Strutturistica Diffrattometrica, Universita’ di Ferrara, via L. Borsari, 4644100 Ferrara, Italy
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The heptanuclear and tetracationic nickel(II) complex [Ni7(l3-OH)6(l3-H L) ](NO ) ꢀ2MeOH (3ꢀ2MeOH);
2
4
3 4
Received 27 November 2012
Accepted 5 January 2013
Available online 26 January 2013
(H
3
L is 2,6-bis-[(3-hydroxy-propylimino)-methyl]-4-methyl-phenol), featuring four defective cubanes
around a pivotal nickel(II) ion, has been obtained via hydroxido-bridge-induced assemblage of two Ni
3
ꢁ
ꢁ
fragments. Presence of azido (N
imine arm hydrolysis and formations of [Ni
where H L1 is 2-hydroxy-3-[(3-hydroxy-propylimino)-methyl]-5-methyl-benzaldehyde. X-ray structural
3
) and bromido (Br ) ions in reactions on the contrary lead to one ligand
2
(N -HL1) (OH ] (1) and [Ni Br -HL1) (OH ] (2);
3
)
2
(
l
2
2
)
2
2
2
(
l
2
2 2
)
Keywords:
Schiff base
Hydroxido bridged
Nickel(II)
Crystals structure
DFT calculation
2
II
II
analyses of 3 show six symmetrically positioned Ni around a central Ni and bridged by six in situ gen-
erated hydroxido groups from solvent water molecules. Density functional theory (DFT) calculations have
also been performed to predict magnetic behavior of the complexes. The spin density surface of com-
pounds 1 and 2 has been also obtained.
Ó 2013 Elsevier Ltd. All rights reserved.
1
. Introduction
During conventional room temperature solvent based synthesis
observed in transition metal coordination chemistry [6–15]. In these
cubanes, the vertices are composed of either the metal ions or ligand
donor atoms (l- and l -O). The in situ generated or externally added
3
of high-nuclearity transition metal complexes, as opposed to high
temperature hydrothermal route, it is always very difficult to
understand the exact course of reaction [1a–d]. The supramolecu-
lar aggregate process is largely dependent upon the solvent sys-
tem, metal salts, temperature, concentrations of the reacting
ingredients and pH. Thus the contributing factors that control the
synthesis of high-nuclearity complexes are still not well recog-
nized. There is a continuing need for newer synthetic methodolo-
gies to obtain such species. Synthetic access to nickel(II) based
multinuclear aggregates showed renewed interests for their re-
cently identified single-molecule magnet behavior and expected
potential to serve as synthetic models for metallobiomolecules
hydroxido group is a very appropriate bridging ligand in the con-
struction of this motif, and its relevance in cluster coordination
chemistry has not studied much [16–18]. Polymetallic nickel com-
pounds involving hydroxido ligands as principal bridges are still
limited [2,17]. The existing hydroxido-based multinuclear nickel
compounds comprising fused cubanes feature the nuclearities
{Ni
tered binucleating Schiff base ligands for the construction of trinu-
clear compounds has recently been achieved by us for a Zn species
6 7 6 7
}, [27] {Ni }, [2] {Ni } [13] and {Ni } [17]. Use of phenoxide cen-
3
[28]. Assembly of two such species around a core metal ion can
give rise to a heptanuclear compound of new molecular structure
and symmetry. Such ligands bearing imine groups are prone to
hydrolysis in presence of different metal salts and other ancillary
groups. In this context, we have focused our attention to explore
[
2,3]. In the emerging area of cluster-based coordination systems,
significant progress has been made in recent years in sorting out
the formation and growth mechanism of 3d metal ion clusters.
Quite often this category of compounds is typically synthesized
via ‘serendipitous self-assembly’ processes by allowing ligand
bound metal ions to condense around the appropriate bridging
and/or nucleating ligands [4,5]. Several ‘fused defective cubanes’
within the giant structure is a common structural feature often
the reactivity of Schiff base ligand H
ferent nickel(II) salts and ancillary ligands. The aggregating ability
of nickel(II) bound-H L, together with the in situ generated hydrox-
ido groups, has now been exploited here with the preparation of a
novel heptanuclear complex [Ni -OH) -H L) ](NO
ꢀ2MeOH
(3ꢀ2MeOH). Unlike of our previous report of a azido-bridged {Ni
complex, the presence of azido anions in the present synthesis
gave only dinuclear compound [Ni (N -HL1) (OH ] (1). Bro-
mide anions also provided a similar one as [Ni Br -HL1) (OH
(2). In the latter two cases, one of the non-coordinating dangling
3
L (Chart 1, left) with two dif-
3
7
(l
3
6
(l
3
2
4
3 4
)
6
}
2
3
)
2
(l
2
2 2
)
⇑
Corresponding author. Tel.: +91 3222 283324; fax: +91 3222 82252.
E-mail address: dray@chem.iitkgp.ernet.in (D. Ray).
2
2
(l
2
2 2
) ]
0
277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.009

A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
33
Perkin–Elmer model 240C elemental analyzer. FT-IR spectra were
recorded on a Perkin–Elmer 883 spectrometer. The solution
electrical conductivity and electronic spectra were obtained using
a Unitech type U131C digital conductivity meter with a solute con-
ꢁ3
centration of about 10 M and a Shimadzu UV 3100 UV–Vis–NIR
spectrophotometer, respectively.
2.2. Synthesis
2
.2.1. 2,6-Bis-[(3-hydroxy-propylimino)-methyl]-4-methyl-phenol
3 2
Chart 1. H L and H L1.
(
3
H L)
To a MeOH solution (20 mL) of 2,6-diformyl-4-methylphenol
1.0 g, 6.1 mmol), 3-amino-1-propanol (0.91 g, 12.2 mmol) was
(
added in air at room temperature (28 °C) and stirred for 2 h to give
an orange colored semi-solid product after complete evaporation
of solvent in air for 12 h. The semi-solid product 2,6-bis-[(3-hydro-
xy-propylimino)-methyl]-4-methylphenol thus obtained was
washed with water and used directly without further purification
for complexation reactions. Yield: 1.32 g (78%).
2
.2.1.1. [Ni
of H L (0.278 g, 1.00 mmol) a MeOH solution (10 mL) of Ni(NO
O (0.290 g, 1.0 mmol) was added slowly and stirred under aer-
obic conditions at room temperature. After half an hour, NaN
0.65 g, 1.0 mmol) and then NEt (0.139 mL, 0.101 g, 1.00 mmol)
2 3 2 2 2 2
(N ) (l-HL1) (OH ) ] (1). To the MeOH solution (20 mL)
3
3
)
2
ꢀ
3
Scheme 1. Ni(II) coordination induced one-arm-hydrolysis of H L.
6H
2
3
(
3
in methanol was added while stirring and the mixture was stirred
for 2.5 h. The solvent was evaporated in air to give a green solid,
which was isolated, washed with cold methanol and dried under
vacuum over P O10. Green crystals suitable for X-ray analysis were
4
obtained from recrystallization of a MeOH solution of the above
green solid after three weeks. Yield: .494 g, 73%. Anal. Calc. for
ꢁ1
24 2 8 8
C H32Ni N O (677.99 g mol ): C, 42.51; H, 4.75; N, 16.52. Found: C,
ꢁ
1
4
2.42; H, 4.63; N, 16.42%. Selected FT-IR bands: (KBr, cm
s = strong, vs = very strong, m = medium, br = broad) 3401(b),
926(m), 2345(m), 2099(vs), 1642(s), 1456(s), 1346(s), 1236(s),
1146(s), 1121(s), 1076(s), 1032(m), 771(s), 637(s), 504(m). Molar
;
2
ꢁ
ꢁ
Scheme 2. Crystallographically established binding modes of H
complexes 1–3.
1
L1 and H
2
L
in
ꢁ1
2
ꢁ1
conductance,
spectra [kmax, nm (
68 (8519), 260 (67094).
M
K : (MeOH solution) 96.5 O cm mol . UV–Vis
ꢁ1
ꢁ1
e
, L mol cm )]: (MeOH solution) 674 (401),
3
ligand arm on each ligands undergoes hydrolysis in the presence of
Ni(NO O and NiBr ꢀ3H O (Scheme 1). The hydrolyzed and
ꢀ6H
unhydrolyzed H L have shown two types of binding behavior
Scheme 2).
The study reported in this paper on anion-bridge induced
3
)
2
2
2
2
2
of H
.2.1.2. [Ni
(Br)
L (0.278 g, 1.00 mmol) a MeOH solution (10 mL) of NiBr
(0.139 mL,
.101 g, 1.00 mmol) and stirred for 3 h at room temperature.
2 2 2 2
(l-HL1) (OH )
] (2). To the MeOH solution (20 mL)
2
3
2 2
ꢀ3H O
3
(
(
0.272 g, 1.0 mmol) was added slowly followed by NEt
3
0
self-assembly provides new examples of ligand for the exclusive
formation of dinuclear and heptanuclear complexes of nickel(II)
depending on the reaction condition and in situ generation of
bridging hydroxido groups.
The solvent was evaporated in air to give a light green solid,
which was isolated, washed with cold methanol and dried under
vacuum over P O10. Green crystals suitable for X-ray analysis were
4
obtained from recrystallization of a MeOH solution of the above
obtained light green solid after two weeks. Yield: .572 g, 76%. Anal.
ꢁ
1
2
. Experimental section
Calc. for C24
2 2 8 2
H32Ni N O Br (753.75 g mol ): C, 38.24; H, 4.27; N,
3
.71. Found: C, 38.12; H, 4.23; N, 3.62%. Selected FT-IR bands:
ꢁ1
2.1. Materials and physical methods
(KBr, cm ; s = strong, vs = very strong, m = medium, br = broad)
424(br), 1639(vs), 1458(vs), 1243(s), 1089(s), 972(s), 846(m),
764(s), 740(s), 698(s), 530 (s). Molar conductance, : (MeOH
nm
3
The chemicals used were obtained from the following sources:
K
M
ꢁ1
2
ꢁ1
nickel nitrate from S.D. Fine Chem (India), 3-amino-1-propanol
from Aldrich Chemical Co. Inc. and triethylamine, sodium azide
from Merck (India). 2,6-Diformyl-4-methylphenol (2-hydroxy-5-
methyl-benzene-1,3-dicarbaldehyde) was prepared following a lit-
solution) 102 O cm mol
.
UV–Vis spectra [kmax
,
(e,
ꢁ1
ꢁ1
L mol cm )]: (MeOH solution) 663 (119), 372 (1199), 259
(96903).
erature procedure [29]. Nickel(II) bromide trihydrate (NiBr
was prepared by the treatment of basic nickel(II) carbonate,
NiCO O (AR grade, E. Merck, India), with hydrobro-
mic acid (AR grade, E. Merck, India), followed by slow evaporation
on a steam bath. It was then filtered through a G4 glass frit and
2
ꢀ3H
2
O)
2.2.1.3. [Ni
MeOH solution (20 mL) of H
tion (10 mL) of Ni(NO
ꢀ6H
slowly followed by NEt (0.139 mL, 0.101 g, 1.00 mmol) and stirred
for 2.3 h at room temperature. The solvent was evaporated in air to
give a green solid, which was isolated, washed with cold methanol
7
(
l
3
-OH)
6
(
l
-H
2
L)
4
](NO
L (0.278 g, 1.00 mmol) a MeOH solu-
O (0.580 g, 2.0 mmol) was added
3
)
4
ꢀ2MeOH (3ꢀ2MeOH). To the
3
3
ꢀ2Ni(OH)
2
ꢀ4H
2
3
)
2
2
3
2
stored in a CaCl desiccator. All other chemicals and solvents were
reagent grade materials and were used as received without further
purification. Elemental analyses (C H N) were performed with a
and dried under vacuum over P
able for X-ray analysis were obtained from recrystallization of a
4
O10. Green plate-like crystals suit-

3
4
A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
MeOH solution of the above isolated green solid after 18 days.
Yield: 0.663 g, 68%. Anal. Calc. for
1934.49 g mol ): C, 38.50; H, 5.11; N, 8.69. Found: C, 38.42; H,
ing X-ray data collection and structure refinement of the com-
pound is summarized in Table 1. For complex 1 a total of 4445
reflections were recorded with Miller indices hmin = ꢁ12, hmax = 12,
62 7 12 32
C H98Ni N O
ꢁ1
(
ꢁ1
5
.03; N, 8.52%. Selected FT-IR bands: (KBr, cm ; s = strong,
k
min = ꢁ22, kmax = 19, lmin = ꢁ17, lmax = 15. For complex 2 a total of
vs = very strong, m = medium, br = broad) 3398(br), 2926(s),
4220 reflections were recorded with Miller indices hmin = ꢁ12,
max = 12, kmin = ꢁ21, kmax = 21, lmin = ꢁ15, lmax = 16. For 3 2MeOH,
a total of 6680 reflections were recorded with Miller indices
1
6
638(s), 1549(s), 1383(vs), 1235(s), 1239, 1058(vs), 970(m),
h
ꢁ
1
2
18(m). Molar conductance,
M
K : (MeOH solution) 391.5 O cm
ꢁ1
ꢁ1
ꢁ1
mol . UV–Vis spectra [kmax, nm (
e, L mol cm )]: (MeOH solu-
h
min = ꢁ28, hmax = 28, kmin = ꢁ22, kmax = 22, lmin = ꢁ17, lmax = 16.
2
tion) 673 (417), 371 (1813), 260 (89459).
In the final cycles of full-matrix least squares on F , all non-hydro-
gen atoms were assigned anisotropically. The structures were
solved using the SHELX-97 [30] program system. For the structure
2.3. Theoretical methods
3
ꢀ2MeOH the probable presence of other solvent molecules was
treated, during the refinement, by means of the routine SQUEEZE in-
cluded in the PLATON system of programs [31].
Calculations have been carried out using density functional the-
ory (DFT) combined with the broken symmetry approach [19,20]
by means of GAUSSIAN 09 package [21]. The level of theory used in
⁄
this study is B3LYP/6-31+G which is a good compromise between
3
. Results and discussion
the size of the system and the computational demands. For these
calculations we have used the crystallographic coordinates. It
should be mentioned that the widely and successfully used [22–
3.1. Synthetic considerations
2
4] broken symmetry DFT approach is not the unique methodology
The Schiff base ligand 2,6-bis-[(3-hydroxy-propylimino)-
to compute and interpret magnetic properties in quantum chemis-
try. For instance ab initio methods based on Difference Dedicated
Configuration Interaction [25] (e.g. CASSCF/DDCI) give excellent re-
sults and offers the possibility to finely analyze the mechanisms
and origin of magnetic properties taking advantage of the access
to the wavefunction of all spin states of interest. This approach
has been recently used in the study of cis/trans isomeric effects
on magnetic properties of copper complexes [26].
methyl]-4-methyl-phenol (H
Supporting Information) following a modified literature procedure
28]. The first two complexes of this series to be identified were the
3
L) was prepared (Scheme S1 in the
[
green binuclear ones [Ni
-HL1) (OH ] (2), obtained from the reactions of Ni(NO
plus NaN and NiBr O in NEt added methanolic H
ꢀ3H
and 76% yields. Room temperature stirring was done for 2.5 and
h using a 1:1 ligand to metal salt stoichiometry for 1 and 2,
2
(N
3
) (l
2
2 2
-HL1) (OH )
2
] (1) and [Ni
2
Br
2
(l
2
2
)
2
3
)
2
ꢀ6H
2
O
3
2
2
3
3
L in 73%
3
respectively. The synthesis of 1 and 2 are summarized by Eqs. (1)
2.4. X-ray crystallography
and (2), considering the coordination induced hydrolytic transfor-
ꢁ
ꢁ
mation of H L to HL1 (Scheme 3). Interestingly, such a coordina-
2
The diffraction data of the complex 1, 2 and 3ꢀ2MeOH was col-
tion induced hydrolysis reaction in the presence of metal ions is
not a routinely observable pathway and is not observed as part
lected on a Bruker APEX-II CCD X-ray diffractometer using single
crystals that uses graphite-monochromated Mo K
a
radiation
of previously reported compounds with H
gand HL1 (Scheme 1, right) originates from the hydrolysis of one
3
L. The in situ formed li-
ꢁ
(
k = 0.71073 Å) by -scan method at 293 K. Information concern-
x
Table 1
Crystallographic data for 1, 2 and 3ꢀ2MeOH.
Compound
1
2
3ꢀ2MeOH
90Ni
1934.49
C2/c
Formula
m
Space group
Crystal system
a (Å)
C
24
H
2
32Ni N
8
O
8
C
24
H
2
32Ni N
2
O
8
Br
2
C
60
H
7
N
8
O
18ꢀ4(NO )ꢀ2(MeOH)
3
677.99
P2 /n
753.75
P2 /c
1
1
monoclinic
8.807(2)
15.001(3)
11.577(3)
90.00
109.301(5)
90.00
1443.6(6)
293
monoclinic
8.986(2)
15.349(4)
11.009(3)
90.00
113.874(7)
90.00
1388.5(6)
293
monoclinic
26.1425(15)
21.0145(12)
16.1156(9)
90.0
104.2888(16)
90.0
8579.6(8)
293
4
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
U (Å )
T (K)
Z
2
2
ꢁ
D
c
(g cm 3
)
1.560
1.803
1.498
F(000)
Crystal size (mm)
704
760
4024
0.39 ꢂ 0.26 ꢂ 0.13
0.43 ꢂ 0.36 ꢂ 0.18
0.40 ꢂ 0.32 ꢂ 0.19
ꢁ
1
l(Mo K
a) (cm
)
13.65
42.83
15.87
Measured refl.ns
Unique ref.ns
17380
4445
20115
4220
33392
5571
R
int
0.0365
0.0474
0.0413
Obs. refl.ns I P 2
min ꢁ hmax (°)
hkl Ranges
r
(I)]
2291
2.31–31.91
2667
2.42–31.50
4236
1.61–22.50
h
ꢁ12, 12; ꢁ22, 19; ꢁ17, 15
ꢁ12, 12; ꢁ21, 21; ꢁ15, 16
ꢁ28, 28; ꢁ22, 22; ꢁ17, 16
2
R(F ) (Obs.Refl.ns)
0.0601
0.0416
0.1158
184
0.0976
0.2930
524
2
wR(F ) (All refl.ns)
0.2469
206
No. variables
Goodness of fit
1.136
1.013
1.094
min (e Å 3
ꢁ
)
0.784; ꢁ1.265
1.014; ꢁ0.576
0.829; ꢁ1.667
D
q
max
;
D
q
CCDC No.
902757
869970
902758
2
)2]1/2. w = 0.75/(
2(F
) + 0.0010F 2
R
1
=
R
(||F
o
| ꢁ |F
c
||)/
R
|F
o
|. wR
2
= [
R
w(|F
o
| ꢁ |F
c
|) /
R
w(F
o
r
o
o
).

A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
35
4
H
3
L þ 7NiðNO
½Ni l3-OHÞ6ð
ꢂ ðNO Þ þ 6HNO
3
Þ2 ꢀ 6H
2
O þ 4NEt
3
þ 2MeOH
!
7
ð
l-H
2
LÞ ꢃðNO
3
Þ4 ꢀ 2MeOH þ 4ðHNEt Þ
3
4
3
3
þ 36H
2
O
ð3Þ
The elemental analysis and molar conductivity data are consis-
tent with the formula [Ni -OH) -H L) ](NO
ꢀ2MeOH for
ꢀ2MeOH and the existence of tetra-cationic complex species was
further confirmed from X-ray structure determination. The molar
7
(l
3
6
(l
2
4
3 4
)
3
ꢁ1
2
ꢁ1
M
conductivity value (K ) [32] for 3 in MeOH is 391.5 O cm mol
which is slightly lower than the prescribed value for 1:4 electrolyte
behavior. The nature of the final reaction product as 3 is greatly
ꢁ
influenced by the stabilization of the H
2
L , solvent system used,
generation of hydroxido groups and the sequence of addition of
the reactants.
3.2. Description of the crystal structures
Single crystals suitable for X-ray structure determination were
obtained by slow evaporation of saturated MeOH solutions of 1,
and 3 after three and two weeks, and 18 days, respectively. The
selected bond lengths and bond angles are collected in Table 2.
2
3.2.1. [Ni
2 3 2 2 2 2
(N ) (l-HL1) (OH ) ] (1)
Complex 1 forms green crystals belonging to the monoclinic
crystals system, space group P2 /n. View of 1 with the atom-num-
1
Table 2
Selected inter-atomic distances (Å) and angles (°) for complex 1, 2 and 3ꢀ2MeOH.
1
Distances
N(2)–Ni(1)
O(3)–Ni(1)
Ni(1)–O(1)
2.095(4)
2.037(3)
2.015(2)
Ni(1)–N(1)
Ni(1)–O(1)
Ni(1)–O(2)
2.018(3)
2.024(3)
2.135(3)
a
Scheme 3. Schematic representation of two different courses of reaction for {Ni
and {Ni } assemblies.
2
}
7
Angles
O(1)–Ni(1)–N(1)
a
90.20(12)
81.14(12)
170.75(12)
169.98(12)
99.62(13)
88.94(12)
88.53(16)
93.75(18)
O(1) –Ni(1)–N(2)
89.29(17)
92.79(18)
89.44(13)
92.42(16)
84.31(15)
88.16(14)
173.51(17)
a
O(1)–Ni(1)–O(1)
N(1)–Ni(1)–O(1)
O(1)–Ni(1)–O(3)
N(1)–Ni(1)–O(3)
O(1)–Ni(1)–O(3)
O(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(2)
O(3)–Ni(1)–N(2)
O(1)–Ni(1)–O(2)
N(1)–Ni(1)–O(2)
a
of the imine arms of H
dination of nickel(II) ions. Change of metal salt from Ni(NO
to NiBr O could not stop the ligand arm hydrolysis.
ꢀ3H
3
L, as assisted in all probability by the coor-
3 2 2
) ꢀ6H O
a
O(1) –Ni(1)–O(2)
2
2
O(3)–Ni(1)–O(2)
N(2)–Ni(1)–O(2)
2
H
3
L þ 2NiðNO
3
Þ2 ꢀ 6H
2
O þ 2NaN
Þ2ꢃ þ 2ðHNEt
Þ3OH þ 2NaNO þ 10H
3
þ 2NEt
3
!
½Ni
2
ðN
3
Þ ð
ðCH
l
-HL1Þ ðOH
2
3
ÞðNO Þ
3
2
2
2
þ 2NH
2
2
3
2
O
ð1Þ
ð2Þ
Distances
O(3)–Ni(1)
O(2)–Ni(1)
Ni(1)–N(1)
2.041(2)
2.117(3)
1.999(3)
Ni(1)–O(1)
Ni(1)–Br(1)
2.025(2)
2.6454(7)
2.014(2)
2
H
3
L þ 2NiBr
2
ꢀ 3H O þ 2NEt ! ½Ni Br
2
3
2
2
ð
l
-HL1Þ ðOH
2
Þ ꢃ
b
2
2
O(1) –Ni(1)
þ 2ðHNEt
þ 2NH ðCH
3
ÞðBrÞ
Angles
N(1)–Ni(1)–O(1)b
N(1)–Ni(1)–O(1)
O(1)–Ni(1)–O(1)b
N(1)–Ni(1)–O(3)
170.41(10)
91.00(10)
79.71(10)
99.97(11)
89.23(10)
168.83(9)
90.49(13)
87.41(12)
O(1)–Ni(1)–O(2)
O(3)–Ni(1)–O(2)
91.70(11)
86.17(12)
90.66(9)
92.18(7)
92.78(7)
89.20(8)
175.35(9)
2
Þ3OH þ 4H
2 2
O
N(1)–Ni(1)–Br(1)
Formation of 1 and 2 as electro-neutral compounds was further
confirmed from the elemental analysis and molar conductivity
measurements and by the single crystal X-ray structure determi-
O(1) b–Ni(1)–Br(1)
b
O(1) –Ni(1)–O(3)
O(1)–Ni(1)–Br(1)
O(3)–Ni(1)–Br(1)
O(2)–Ni(1)–Br(1)
O(1)–Ni(1)–O(3)
N(1)–Ni(1)–O(2)
nations (vide infra). When the reaction of Ni(NO
ried out with H L in MeOH in presence of NEt
obtained. Keeping in mind the formation of 1 and 2, several other
L/Ni(NO O/NEt ratios were explored, and we report here
3
)
2
ꢀ6H
2
O was car-
b
O(1) –Ni(1)–O(2)
3
3
as base, 3 was
3
ꢀ2MeOH
Distances
H
3
3
)
2
ꢀ6H
2
3
Ni(1)–O(8)
Ni(1)–O(8)
Ni(1)–O(9)
Ni(1)–O(9)
Ni(1)–O(7)
Ni(1)–O(7)
2.047(7)
2.047(7)
2.062(6)
2.062(6)
2.076(7)
2.076(7)
1.997(10)
2.015(7)
2.043(6)
2.066(6)
2.079(8)
2.095(7)
Ni(3)–N(1)
Ni(3)–O(8)
2.044(9)
2.052(6)
2.059(7)
2.059(8)
2.066(7)
2.095(6)
2.006(6)
2.018(7)
2.018(9)
2.090(6)
2.092(7)
2.160(8)
the optimized one that gave a clean and characterizable product in
high yield. At room temperature, complex 3 is isolated by stirring a
methanolic solution of a mixture of the above stated components
in a 4:7:4 molar ratios for 2.5 h. The complex precipitates directly
from the reaction mixture as a green solid in ꢄ68% yield. The
c
c
c
c
Ni(3)–O(4)
c
Ni(3)–N(4)
Ni(3)–O(1)
Ni(3)–O(9)
c
Ni(2)–N(2)
Ni(2)–O(8)
Ni(2)–O(1)
Ni(2)–O(7)
Ni(4)–O(4)
Ni(4)–O(9)
Ni(4)–N(3)
Ni(4)–O(7)
Ni(4)–O(5)
3
synthesis of 3 from H L is summarized in Eq. (3), considering the
non-hydrolytic behavior of the ligand as opposed to the process
dominant in previous two cases and generation of hydroxido
bridges from the water molecule present in the solvent during
the complexation reaction.
c
Ni(2)–O(6)
Ni(2)–O(3)
c
Ni(4)–O(2)
(
continued on next page)

3
6
A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
Angles
O(8)–Ni(1)–O(8) c
O(8)–Ni(1)–O(9)
93.4(4)
166.3(3)
82.0(3)
82.0(3)
166.3(3)
105.2(4)
94.7(3)
84.7(3)
82.9(3)
97.7(3)
84.7(3)
84.7(3)
97.7(3)
82.9(3)
179.0(4)
171.1(3)
91.5(3)
79.6(3)
92.4(3)
85.7(3)
87.5(3)
87.4(4)
94.6(3)
93.5(3)
179.0(3)
95.4(3)
93.4(3)
173.1(3)
92.1(3)
86.9(3)
N(1)–Ni(3)–O(8)
N(1)–Ni(3)–O(4)
164.9(3)
101.1(3)
92.0(3)
89.7(3)
98.2(3)
88.6(3)
88.2(3)
78.2(3)
169.5(3)
96.5(3)
93.8(3)
81.1(3)
79.2(3)
167.8(3)
95.3(3)
82.3(3)
92.3(3)
174.4(4)
96.1(3)
83.6(3)
97.5(3)
175.5(3)
93.5(3)
91.9(3)
85.0(3)
89.6(3)
94.3(3)
85.2(3)
173.6(3)
89.0(3)
c
c
O(8)–Ni(3)-O(4)c
O(8)–Ni(1)–O(9)
c
c
O(8) –Ni(1)–O(9)
O(8) –Ni(1)–O(9)
N(1)–Ni(3)–N(4)
c
c
c
O(8)–Ni(3)–N(4)
c
c
c
O(9)–Ni(1)–O(9)
O(4) –Ni(3)–N(4)
c
c
O(8) –Ni(1)–O(7)
N(1)–Ni(3)–O(1)
O(8)–Ni(3)–O(1)
O(8)–Ni(1)–O(7)c
O(9)–Ni(1)–O(7)
c
O(4) –Ni(3)–O(1)
c
c
O(9) –Ni(1)–O(7)
N(4) –Ni(3)–O(1)
c
c
c
O(8) –Ni(1)–O(7)
N(1)–Ni(3)–O(9)
O(8)–Ni(1)–O(7)c
O(8)–Ni(3)–O(9)
c
c
c
c
c
O(9)–Ni(1)–O(7)
O(4) –Ni(3)–O(9)
c
c
c
O(9) –Ni(1)–O(7)
N(4) –Ni(3)–O(9)
O(1)–Ni(3)–O(9)c
O(4)–Ni(4)–O(9)
O(4)–Ni(4)–N(3)
O(9)–Ni(4)–N(3)
O(4)–Ni(4)–O(7)
O(9)–Ni(4)–O(7)
N(3)–Ni(4)–O(7)
O(4)–Ni(4)–O(5)
O(9)–Ni(4)–O(5)
N(3)–Ni(4)–O(5)
O(7)–Ni(4)–O(5)
O(4)–Ni(40–O(2)
O(9)–Ni(4)–O(2)c
O(7)–Ni(1)–O(7)
N(2)–Ni(2)–O(8)
N(2)–Ni(2)–O(1)
O(8)–Ni(2)–O(1)
N(2)–Ni(2)–O(7)
O(8)–Ni(2)–O(7)
O(1)–Ni(2)–O(7)
2 3 2 2 2 2
Fig. 1. View of [Ni (N ) (l-HL1) (OH ) ] unit in 1 with partial atom-numbering
scheme. H atoms are omitted for clarity. Color code: Ni green, N blue, O red, C black.
(For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
c
N(2)–Ni(2)–O(6)
c
O(8)–Ni(2)–O(6)
O(1)–Ni(2)–O(6)c
O(7)–Ni(2)–O(6)c
N(2)–Ni(2)–O(3)
O(8)–Ni(2)–O(3)
O(1)–Ni(2)–O(3)
O(7)–Ni(2)–O(3)
c
c
N(3)–Ni(4)–O(2)
O(7)–Ni(4)–O(2)c
O(5)–Ni(4)–O(2)c
c
O(6) –Ni(2)–O(3)
a
1
1
1
ꢁ x, ꢁy, 2 ꢁ z.
ꢁ x, ꢁy, 1 ꢁ z.
ꢁ x, y, 1ꢀ5 ꢁ z.
b
c
bering scheme is given in Fig. 1. The structure consists of a hydro-
lyzed ligand bridged [Ni (N -HL1) (OH ] complex as a neu-
2
3
)
2
(
l
2
2 2
)
II
tral aggregate with the Ni cations linked together by the action
ꢁ
of two O
2
N donor binucleating ligands HL1 (Fig. S1). The asym-
metric unit consists of one-half of the dinuclear unit and the sec-
ond half of the dimer is generated by symmetry operations
2 2 2 2 2
Fig. 2. Structure of [Ni (Br) (l-HL1) (OH ) ] unit in 2 with partial atom-numbering
(
1 ꢁ x, ꢁy, 2 ꢁ z).
scheme. H atoms are omitted for clarity. Color code: Ni green, N blue, O red, Br dark
yellow, C black. (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)
The two bridging functions are accomplished by the central
ꢁ
phenoxido moiety of HL1 , while the imine N and carbonyl O
atoms at opposite sides contribute two other coordination sites.
Exogenous azido N and water O atoms fulfil the hexacoordination
around each Ni ion. Each Ni atom is in a N
2
O
4
environment with
scheme is given in Fig. 2. The asymmetric unit consists of one-half
of the dinuclear unit and no interstitial solvent molecule. The sec-
ond half of the dimer is generated by symmetry operations (1 ꢁ x,
ꢁy, 1 ꢁ z).
the two octahedrons sharing the edge defined by the bridging phe-
nolate oxygen atoms (Fig. 1). The equatorial planes intersecting at
this edge form an angle of 180°. The geometric restrictions result-
ꢁ
ing from the symmetrical dispositions of two HL1 provide a Ni–
The groups below and above the ligand planes register longer
O–Ni angle of 98.8° but the O–Ni–O angle is shorter at 81.12°.
The Ni–O (carbonyl) separations at 2.03 Å are similar to other re-
ported values [33]. The water molecules are loosely bound at
distances (Ni–Owater, 2.12 Å; Ni–Br, 2.64 Å) compared to those from
ꢁ
HL1 (Ni–Ocarbonyl, 2.04 Å; Ni–Ophenoxido, 2.01 and 2.02 Å; Ni–Nimine
,
1.99 Å) (Fig. S4). The dihedral angles between intersecting equato-
rial planes is 180°; the bridging Ni–O–Ni angle is 100.2°, and the
Niꢀ ꢀ ꢀNi separation is 3.101 Å. The trigonal planar orientation of
the bridging phenoxido oxygen atoms keep the phenyl rings copla-
nar with the basal O N planes around each nickel(II) ion. No special
3
hydrogen bonding network was observed within the crystal lattice
2
2
.13 Å (Fig. S1). The azido ligands, opposite to water ligands, at
.095 Å indicate a tetragonally elongated octahedron around nick-
el(II) ions (Figs. S1 and S2). The intramolecular Niꢀ ꢀ ꢀNi distance is
.068 Å. Intermolecular hydrogen bonds are absent within the
crystal lattice due to the absence of any lattice solvent molecules
Fig. S3).
3
(
of 2 (Fig. S5).
3
.2.2. [Ni
2
Br
2
(
l
-HL1)
2
(OH
2
)
2
] (2)
3.2.3. [Ni
7
(
l
3
-OH)
6
(
l
-H
2
L)
4
](NO
3
)
4
ꢀ2MeOH (3ꢀ2MeOH)
Complex 2 forms green crystals in monoclinic P21/c crystal sys-
The green plate-like crystals of 3 crystallize in the monoclinic
space group C2/c. The molecular structure of the compound
3ꢀ2MeOH is shown in Fig. 3. The structure consists of a heptametal-
II
tem. It is a dinuclear aggregate of Ni ions bridged and chelated by
the hydrolyzed ligands HL1 in a manner as in complex 1. The face-
to-face orientations of two hydrolyzed ligands bind two Ni(II) ions
leaving behind two other coordination sites for anion and water
coordination. Two such octahedral units share the phenoxido
bridged Oꢀ ꢀ ꢀO edge (Fig. S4). View of 2 with the atom-numbering
ꢁ
4
+
ꢁ
3
lic tetra-cationic [Ni
7
(l
3
-OH)
6
(
l
-H
2
4
bpmp) ]
part and four NO
anions. The asymmetric unit consists of one-half of the heptanucle-
ar unit and two MeOH solvent molecules. The second half of the
heptamer is generated by symmetry operations (1 ꢁ x, y, 1ꢀ5 ꢁ z).

A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
37
7
Fig. 4. The Ni skeleton of 3 2MeOH showing all the inter-metallic distances.
ꢁ
2
Interestingly, all the protonated alcohol arms of the ligand H L
II
remain coordinated to the Ni ions and show hydrogen-bonding
interactions with the methanol oxygen (O1A) atom is bonded to
(
H)O6 at a Oꢀ ꢀ ꢀO separation of 2.694 Å. The pendent ligand alcohol
arms (H)O2, (H)O3 and (H)O5 are hydrogen bonded to O11(NO ),
O15(NO ) and O13(NO
) at the Oꢀ ꢀ ꢀO separation of 2.612, 2.625
3
3
3
and 2.712 Å, respectively. The complex crystallizes with two sol-
vent methanol molecules which are hydrogen bonded to the oxy-
gen atoms of the ligand alcohol arm. One of the methanol
oxygen (O1A) atom is suitably hydrogen bonded to ligand (H)O6
at a Oꢀ ꢀ ꢀO separation of 2.694 Å. The same methanol oxygen
(
O1A) atom shows hydrogen bonding interactions with lattice
7
water oxygen (O1B) at 2.749 Å. Near the [Ni ] unit the lattice water
and methanol molecules establish hydrogen-bonding network
ꢁ
through interactions with NO
3
groups (Fig. S8).
These hydrogen-bonding interactions provide an aesthetically
pleasing 3D network structure (Figs. S8 and S9). A space-filling dia-
gram of 3ꢀ2MeOH along the crystallographic b-axis identifies the
compactness of the seven metal atoms (Fig. S10). Inspection of
Fig. 3 suggests indeed that the formation of 3 occurs through trap-
Fig. 3. Molecular structure of [Ni
7
(
l
3
-OH)
6
(
l
-H
2
L)
4
]4+ unit viewed perpendicular
2+
ping of two such trinuclear fragments [Ni
much similar to our recently reported [Zn
3 2 2 2
(OH) (l-H L) ] , very
(
top) and parallel (bottom) to the best [Ni
7
] plane in 3ꢀ2MeOH with partial atom-
3
] complex [35a–c, 36],
numbering scheme. H atoms are omitted for clarity. Color code: Ni green, N blue, O
red, C gray. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
by in situ generated Ni(OH)
2
template (Scheme S2). While the four
ꢁ
3
l -trigonal pyramidal HO bridging modes present in this complex
are quite common, the planar T-shaped feature observed in 3
Fig. S11) is rather exceptional. The unique hexagonal Ni arrange-
ment (Fig. S6) of complex 3 results from the peculiar preferences of
(
7
The core in 3 is best described as a body centered hexagon where
by six Ni ions surround a central Ni centre to form an arrange-
ment featuring four fused defective cubanes (Fig. S6). Topologically
ꢁ
II
ꢁ
II
II
H
2
L
in front of the Ni /HO system, as opposed to other well-
II
established structures observed for Ni clusters with similar sets
of ligands, such as discs [17,35a] and others [36]. The O–Ni–O an-
gles on the other hand are different within 81.9–175.1° and not ob-
7
analogous [Ni ] complexes are known with different organic shell
II
ligands [17,34a–c]. In a strained cluster-like arrangement all Ni
ꢁ
3
served in other structures. The Ni–O bond lengths involving l -OH
centers enjoy octahedral geometries. The six
l
3
-bridging OH ions
linkers remain within 2.00–2.09 Å. The metallic skeleton and two
views of the core of complex 3 2MeOH are illustrated in Figs. S7
and S12, respectively.
(
O5, O8 and O9 and symmetry equivalents, s.e.) link the central
nickel (Ni1) to the six peripheral nickel ions (Ni2, Ni3 and Ni4
II
and s.e.). The central Ni ion is located at a site with imposed C
2
II
ꢁ
symmetry. Out of the six bridging HO ions around the central Ni
ion functioning as a trap in the cluster growth, four are squeezed
3.3. FT-IR spectroscopy
trigonal pyramidal (solid angle around O atom are 294.16° and
2
97.6°) and two are planar T-shaped (solid angle around O atom
The broad and sharp peaks in the FT-IR spectra of 1 and 2 at
ꢁ1
is 352.4°) connectors (Fig. 3). The four singly deprotonated (at
3401, 3424 and 1642 and 1639 cm are due to the stretching
modes characteristic of the uncoordinated ligand O–H and bound
ꢁ
II
the phenolate site) H
Thus six hydroxido and four phenoxido oxygen atoms complete
the [Ni 10] core (Fig. S7), where the bridging is ensured by six
) bridging hydroxido ( -mode) and four (O4) phenoxido
2
L ligands bridge the peripheral Ni centres.
ꢁ
C@N functionalities of HL1 . In addition, complex 1 shows a very
ꢁ1
7
O
strong and sharp band at 2099 cm for the
vibration of the nickel(II) bound terminal N
m
ꢀas(N–N–N) stretching
ꢁ
(
O
6
l
3
3
groups, while the
II
bridges. The remaining coordination sites of the octahedral Ni
ions are completed by peripheral imine groups and alcohol resi-
symmetric vibration
m
ꢀs(N–N–N) appears as
a
weak band at
ꢁ1
ꢁ1
1346 cm [37]. For complex 3 the sharp peak at 1638 cm is
ꢁ
ꢁ
dues (from H
Ni
2
L ) making the ligand
l
3
-bridging. Within the
due to the
m
C@N stretching frequency of H
2
L
and a broad medium
OH vibrations from
ꢁ1
[
3
1
7
O
10] nickel–oxygen core the Niꢀ ꢀ ꢀNi distances range from
.00 to 3.15 Å and the Ni–O–Ni angles span the range of 93.10–
02.07° (Fig. 4).
band centered at 3398 cm attributable to the
m
ꢁ
the nickel(II) bound
l
3
-HO bridges, ligand OH groups and crystal
lattice trapped water molecules. The very strong band at

3
8
A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
ꢁ1
1
383 cm in 3 is indicative of the presence of ionic nitrates out-
side the coordination sphere [38].
3.4. Electronic UV–Vis spectra
Moderate solubility in MeOH of all the three complexes allowed
us to record multiple optical absorption bands in the 200–900 nm
regions. Broad absorption bands (k), with maxima at 674 nm
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
(
6
e
= 401 L mol cm ), 663 nm
(
e
= 119 L mol cm
)
and
ꢁ1
ꢁ1
73 nm (
e = 417 L mol cm ) for 1, 2 and 3, respectively can be
assigned to the spin-allowed A2g(F) ? T1g(F) transition consistent
with their slightly distorted octahedral configurations. The
F) ? T2g(F) transitions usually appear above 700 nm region are
systematically missing for all the three complexes [39]. The
F) ? T1g(P) transitions appear at 368 nm (
= 1199 L mol cm ) and 371 nm (
cm ) for 1, 2 and 3, respectively [33]. The intense absorptions at
3
3
3
A
2g
3
(
3
A
2g
3
ꢁ1
ꢁ1
(
3
e
= 8519 L mol cm ),
ꢁ1
ꢁ1
ꢁ1
72 nm (
e
e
= 1813 L mol
⁄
Fig. 5. Spin density map computed for compounds 1 and 2 at the UB3LYP/6-31+G
level of theory.
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ1
2
60 nm (
and 260 nm (
tions centered on the ligand back bone.
e
= 67095 L mol cm ), 259 nm (
e
= 96905 L mol cm
)
ꢁ1
ꢁ1
⁄
e
= 89460 L mol cm ) are due to
p
?
p
transi-
the spin delocalization is strong enough that >18% of the spin for
the unpaired electrons on the Ni(II) centers are delocalized to the
ligand atoms. The spin densities on the Ni(II) centers in compound
1 (±1.688) are higher in absolute value than those of compound 2
(±1.620), which indicates that the differences between the antifer-
romagnetic singlet and the high spin state can be rationalized in
terms of the spin density on the metal centers.
3
.5. Spin density distribution analysis for possible magnetic
interactions in 1 and 2
In order to provide the magnetic coupling interactions theoret-
ically, the spin density distribution is analyzed in compounds 1 and
According to the active-electron approximation, it can be con-
sidered that in the bridged magnetic coupling systems, only the
overlaps between the singly occupied molecular orbitals (SOMO)
of the metal centers and the p orbitals of the ligands contribute
2. According to the molecular orbital theory, spin delocalization is
the result of electron transfer from the magnetic centers to the li-
gand atoms. The spin densities of compounds 1 and 2 in the bro-
ken-symmetry state are summarized in Table 3, where positive
II
to the magnetic coupling interaction. In octahedral Ni , the
and negative signs denote
should be mentioned that for both complexes the antiferromag-
netic singlet (two electrons on one Ni and two b electrons on
a
and b spin states, respectively. It
magnetic orbitals are formed by the dx
containing an unpaired electron. Therefore, for the diphenoxido-
bridged compounds 1 and 2, only the dx
2ꢁy2
and dz orbitals, each
2
a
2ꢁy2
orbitals of the metal
the other Ni) is energetically more stable than the high spin config-
uration (multiplicity 5). This difference is higher in compound 2
atoms and the local orbitals of the bridging ligand are involved
in the magnetic coupling pathway. A theoretical confirmation of
this explanation comes from the spin density map computed for
compounds 1 and 2 (Fig. 5), that clearly agrees with the aforemen-
tioned mechanism. Unfortunately, for compound 3 the theoretical
analysis of the spin density has been computationally unaffordable
at this level of theory due to convergence problems in the calcula-
tions likely due to the large number of unpaired electrons (14) in
the high spin state.
(
ꢁ0.51 mHa) than in 1 (ꢁ0.34 mHa), therefore it is expected a lar-
ger (in absolute value) coupling constant J for compound 2. In Ta-
ble 3 it is shown that the spin densities on the two Ni(II) ions in
compounds 1 and 2 have similar absolute values but opposite
signs. For instance in 1, the Ni1 atom is mainly populated by the
⁄
unpaired electrons with
a
spin (1.688) and Ni1 with b spin
(
ꢁ1.688). It is obvious that the unpaired electrons are mainly local-
ized on each Ni(II) ions, which indicates that the Ni(II) ions are in-
deed the magnetic centers. The spin densities on the ligand (O1,
O2W, O3, N1 and N2/Br1) atoms have the same signs as that of
the Ni(II) atoms to which they are bonded, which reveals that there
is spin delocalization from the Ni(II) ions to the ligands. In addition,
4
. Concluding remarks
As part of the generation of self-assembled super structures
based on ligated metal ion motifs, we have previously shown that
II
reaction of H
have shown that the reaction with Ni is responsible for trapping
of two such hitherto unknown trinuclear fragments [Ni (OH)
species for the generation
3 3
L with Zn leads to a novel Zn complex. Now we
II
Table 3
The spin densities on the selected atoms for compounds 1 and 2 at the UB3LYP/6-
3
2
(l-
2
+
3
1+G⁄ level of theory.
2
H L)
2
]
by in situ generated Ni(OH)
2
of [Ni
7
(
l
3
-OH)
6
(
l
3
-H
2
L)
4
](NO
3
)
4
ꢀ2MeOH. Similar reactions in pres-
Compound 1
Atoms
Compound 2
Atoms
ꢁ
ꢁ
ence of externally added N
3
and metal salt derived Br anions in-
Spin density
Spin density
hibit the growth of the heptametallic species and provided only
basic dinuclear compounds [Ni (N -HL1) (OH ] and [Ni Br
-HL1) (OH ] through hydrolysis of single imine arm of the li-
Ni1
Ni1
1.688
ꢁ1.688
0.038
Ni1
Ni1
1.620
ꢁ1.620
0.044
2
3
)
2
(l
2
2
)
2
2
2
*
*
(l
2
2 2
)
O1
O1
O1
O1
*
*
gand. These results clearly indicate the superiority of reaction
medium derived hydroxido groups, as against azido and bromido
groups, for cluster growth and hydrolysis of single ligand arm.
ꢁ0.038
ꢁ0.044
O2W
O2W
0.025
O2W
O2W
0.028
*
*
ꢁ0.025
0.080
ꢁ0.028
0.097
N1
N1
N1
N1
*
*
ꢁ0.080
ꢁ0.097
N2
N2
0.037
Br1
Br1
0.115
Acknowledgements
*
*
ꢁ0.037
ꢁ0.007
0.007
ꢁ0.115
ꢁ0.004
0.004
O3
O3
O3
O3
A.K.G. is thankful to the Council of Scientific and Industrial Re-
search, New Delhi for the financial support. The authors also give
thanks to DST, New Delhi, for providing the Single Crystal X-ray
*
*
*
Symmetry equivalents.

A.K. Ghosh et al. / Polyhedron 53 (2013) 32–39
39
Diffractometer facility in the Department of Chemistry, IIT Kharag-
pur under its FIST program. V.B. acknowledges Italian Ministry of
University and Scientific Research, MIUR, Rome, Italy. A.F. and
A.B. acknowledge financial support from the Ministerio de Ciencia
e Innovación (MICINN) of Spain (projects CTQ2011-27512/BQU and
CONSOLIDER INGENIO 2010, CSD2010-00065), FEDER funds and
Direcció General de Recerca i Innovació del Govern Balear (project
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Appendix A. Supplementary data
CCDC 902757, 869970 and 902758 contain the supplementary
crystallographic data for 1, 2 and 3ꢀ2MeOH. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.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 http://
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