Nickel(II) complexes with N,N,O-donor Schiff bases. Self-assembly to two-dimensional network via hydrogen bonding

Article abstract of DOI:10.1007/s10870-005-6272-8

The syntheses, characterization and crystal structures of two mononuclear nickel(II) complexes are described. Reactions of Ni(O₂CCH ₃)₂·4H₂O with the Schiff bases derived from 2-pyridinecarbaldehyde and ortho-am

Full text of DOI:10.1007/s10870-005-6272-8

ꢀC
Journal of Chemical Crystallography, Vol. 35, No. 9, September 2005 ( 2005)
DOI: 10.1007/s10870-005-6272-8
Nickel(II) complexes with N,N,O-donor Schiff bases.
Self-assembly to two-dimensional network via
hydrogen bonding
Abhik Mukhopadhyay(1) and Samudranil Pal(1)∗
Received and accepted August 20, 2003
The syntheses, characterization and crystal structures of two mononuclear nickel(II) com-
plexes are described. Reactions of Ni(O2CCH3)2·4H2O with the Schiff bases derived from
2-pyridinecarbaldehyde and ortho-aminophenol (Hpaap) and 2-pyridinecarbaldehyde and
ortho-aminobenzoic acid (Hpaab) in methanolic media afford the complexes in good yields.
The elemental analysis, magnetic moments, and spectral features of the complexes are con-
sistent with the formulae [Ni(paap)2]·CH3COOH·H2O and [Ni(paab)2]·2H2O. Crystal data
˚
˚
for [Ni(paap)2]·CH3COOH·H2O: monoclinic, P21/c, a = 9.675(2) A, b = 17.109(5) A, c =
◦
3
˚
˚
14.403(4) A, β = 92.903(11) , V = 2381.1(11) A , and Z = 4 and for [Ni(paab)2]·2H2O:
˚
˚
˚
triclinic, P 1, a = 9.834(3) A, b = 11.319(3) A, c = 13.130(4) A, α = 84.68(3), β =
◦
3
˚
67.54(3), γ = 85.49(2) , V = 1343.4(6) A , and Z = 2. In each complex, two tridentate
monoanionic meridionally spanning ligands form a distorted octahedral N4O2 coordina-
tion sphere around the metal ion. In [Ni(paap)2]·CH3COOH·H2O, two metal coordinated
phenolate-O atoms are hydrogen bonded to CH3COOH and H2O, respectively. Intramolec-
---
---
ular C H···O interactions involving the water molecule and the C H from azomethine and
aromatic fragments lead to a two-dimensional network of [Ni(paap)2]·CH3COOH·H2O in
the crystal lattice. An uncoordinated carboxylate O-atom in [Ni(paab)2]·2H2O is hydrogen
bonded to both water molecules. One of the water molecules is again hydrogen bonded
to the corresponding symmetry related water molecule forming a dimer. The azomethine
groups and the metal coordinated carboxylate-O atoms in [Ni(paab)2] are involved in
---
intermolecular C H···O interactions forming a chain-like arrangement of the molecules.
The water dimers act as bridges between these chains and a two-dimensional network of
[Ni(paab)2]·2H2O is formed.
KEY WORDS: Nickel(II) complexes; Schiff bases; crystal structures; hydrogen bonding; self-assembly.
Introduction
networks are of considerable current interest
due to their photophysical, magnetic and
conducting properties.1 These metallo-organic
based materials are also attractive with respect
to mimicking the structural and functional
features of zeolites.2 Self-assembly of transition
metal ion complexes into a desired structural
network has been realized by utilizing the metal
Extended assemblies of complexed metal
ions having one-, two-, and three-dimensional
(1) School of Chemistry, University of Hyderabad, Hyderabad
500 046, India.
∗To whom correspondence should be addressed; e-mail: spsc@
uohyd.ernet.in.
737
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C
1074-1542/05/0900-0737/0 2005 Springer Science+Business Media, Inc.

738
Mukhopadhyay and Pal
ion’s preference for a particular coordination
geometry, design and use of suitable ligands and
weak noncovalent intermolecular interactions
such as van der Waals interactions, hydrogen
bonding and π–π interactions.1−3 The proton
Experimental
Materials and physical measurements
The chemicals and solvents used in this work
were of analytical grade available commercially
and were used without further purification.
Microanalytical (C, H, N) data were ob-
tained with a Perkin-Elmer Model 240C elemen-
tal analyzer. Room temperature solid state mag-
netic susceptibilities were measured by using a
Sherwood Scientific magnetic susceptibility bal-
ance. Diamagnetic corrections calculated from
Pascal’s constants5 were used to obtain the mo-
lar paramagnetic susceptibilities. Solution electri-
cal conductivities were measured with a Digisun
DI-909 conductivity meter. Infrared spectra were
collected by using KBr pellets on a Jasco-5300
FT-IR spectrophotometer. Electronic spectra were
recorded on a Shimadzu 3101-PC UV/vis/NIR
spectrophotometer.
---
---
---
of polarized azomethine ( CH N ) group
---
in metal coordinated Schiff bases may help in
self-assembly of the complex molecules by par-
ticipating in intermolecular hydrogen bonding.4
The acceptor atom in this type of hydrogen
bonding can be a part of the complex molecule
or of the solvent molecule trapped in the crystal
lattice. Thus the resulting network pattern can
be influenced by the orientation of the acceptor
atom with respect to the azomethine moiety.
Herein, we report the syntheses, characterization
and crystal structures of two hexacoordinated
nickel(II) complexes with Schiff bases obtained
by condensation reactions of 2-pyridine-
carbaldehyde with ortho-aminophenol (Hpaap)
and with ortho-aminobenzoic acid (Hpaab). In the
Synthesis of [Ni(paap)2]·CH3COOH·H2O
To
a
methanol solution (20 mL) of
2-aminophenol (230 mg, 2.1 mmol), 0.2 mL
(225 mg, 2.1 mmol) of 2-pyridinecarbaldehyde
was added and the mixture was refluxed for
1.5 h. Powdered Ni(O2CCH3)2·4H2O (260 mg,
1.05 mmol) was added to the clear light yellow
solution. The resulting red mixture was refluxed
for another 1.5 h and then cooled to room tem-
perature. The red–brown crystalline solid sep-
arated was collected by filtration, washed with
ice-cold methanol and finally dried in air. Yield
obtained was 470 mg (84%). A single crystal
suitable for X-ray structure determination was
selected from this material. Anal. Calcd for
C26H24N4O5Ni: C, 58.77; H, 4.55; N, 10.54%.
Found: C, 58.43; H, 4.39; N, 10.29%. Selected
infrared bands (cm−1): 3046 br, 1703 s, 1586 s,
1559 m, 1537 m, 1479 s, 1456 s, 1362 m, 1317 m,
1300 w, 1281 s, 1250 m, 1184 m, 1144 s, 1044 m,
864 m, 806 m, 756 s, 637 w, 586 w, 515 s, 447 w,
417 w. Electronic spectral data in CH3OH solution
deprotonated state, these Schiff bases can co-
ordinate a metal ion via the pyridine-N, the
imine-N and the phenolate-O (paap−) or the
carboxylate-O (paab−). The paap− will form
two five-membered chelate rings, whereas the
paab− will form one six- and one five-
membered chelate ring. The complexes have
been isolated as [Ni(paap)2]·CH3COOH·H2O and
[Ni(paab)2]·2H2O. In the crystal lattice, both
species form two-dimensional network via hydro-
gen bonding interactions involving the polarized
azomethine moieties and the water molecules.

Nickel(II) complexes with N,N,O-donor Schiff bases
739
(λmax, nm (ε, M−1 cm−1)): 855 (23), 480 (18,800),
323 (21,000), 241 (21,100). Solid state magnetic
moment at 300 K (µeff, µB): 3.17.
sition of the unique nickel atom was deter-
mined from a Patterson map. The remaining non-
hydrogen atoms were determined from successive
Fourier difference syntheses. The model was then
refined by full-matrix least-squares procedures on
F2. For both structures all the non-hydrogen atoms
were refined anisotropically. The hydrogen atoms
Synthesis of [Ni(paab)2]·2H2O
---
of the water molecule and the COOH goup
[Ni(paab)2]·2H2O was prepared in methano-
lic medium from 2-aminobenzoic acid, 2-
pyridinecarbaldehyde and Ni(O2CCH3)2·4H2O
(2:2:1 mole ratio) as brown microcrystalline solid
in 75% yield by following the same procedure
as described above. Single crystal suitable for X-
ray structure determination was obtained directly
from the synthetic reaction mixture. Anal. calcd.
for C26H22N4O6Ni: C, 57.26; H, 4.07; N, 10.27%.
Found: C, 57.05; H, 3.96; N, 10.14%. Selected
infrared bands (cm−1): 3397 br, 1589 s, 1560 s,
1483 m, 1441 m, 1358 s, 1236 w, 1153 w, 1101 w,
1049 m, 1017 m, 918 s, 864 s, 824 s, 777 s, 745 m,
692 s, 640 m, 579 w, 546 w, 488 w, 417 m. Elec-
tronic spectral data in CH3OH solution (λmax, nm
(ε, M−1 cm−1)): 900 (15), 350sh (15,300), 328
(19, 800), 243sh (16,700). Solid state magnetic
moment at 300 K (µeff, µB): 3.19.
in [Ni(paap)2]·CH3COOH·H2O were located in
a difference map. For [Ni(paab)2]·2H2O hydro-
gen atoms of only one water molecule could
be located in a difference map. For each struc-
ture all the hydrogen atoms were included in the
model at idealized positions for structure factor
calculation, but not refined. Calculations were
done using the programs of WinGX6 for data
reduction, and SHELX-97 programs7 for struc-
ture solution and refinement. The Ortex6a8 and
Platon9 packages were used for molecular graph-
ics. Significant crystal data are summarized in
Table 1.
Results and discussion
Synthesis and some properties
Two new hexacoordinated nickel(II) com-
plexes have been synthesized in good yields by
reacting one mole equivalent of Ni(O2CCH3)2·
4H2O with the Schiff bases Hpaap and Hpaab
preformed in methanolic media by refluxing 2
mole equivalents each of 2-pyridinecarbaldehyde
and the corresponding ortho substituted anilines.
The elemental analysis data for the isolated
crystalline solids are consistent with the formu-
lae [Ni(paap)2]·CH3COOH·H2O and [Ni(paab)2]·
2H2O. The solid state room temperature (300 K)
magnetic moments of [Ni(paap)2]·CH3COOH·
H2O and [Ni(paab)2]·2H2O are 3.17 and 3.19 µB,
respectively. These values are consistent with an
S = 1 spin state of the metal ion in each com-
plex. Both species are electrically nonconduct-
ing in methanol solutions. Thus the ligands are
monoanionic and the oxidation state of the metal
ion is +2 in each complex.
X-ray crystallography
For each of the two complexes, the crystal
was mounted at the end of a glass fibre and covered
with a thin layer of epoxy. The data were collected
on an Enraf-Nonius Mach-3 single crystal diffrac-
tometer using graphite monochromated MoKα ra-
˚
diation (λ = 0.71073 A) by ω-scan method. Unit
cell parameters of [Ni(paap)2]·CH3COOH·H2O
and [Ni(paab)2]·2H2O were determined by the
least-squares fit of 25 reflections having 2θ
values in the range 19–21◦ and 18–22◦, re-
spectively. Stability of the crystal was mon-
itored by measuring the intensities of three
check reflections after every 1.5 h during the
data collection. No decay was observed in
either case. [Ni(paap)2]·CH3COOH·H2O and
[Ni(paab)2]·2H2O crystallize in P21/c and P 1
space group, respectively. In each case, the po-

740
Mukhopadhyay and Pal
Table 1. Crystallographic Data
Compound
[Ni(paap)2]·CH3COOH·H2O [Ni(paab)2]·2H2O
CCDC deposition no.
Empirical formula
Crystal system
216554
216555
NiC26H24N4O5
Monoclinic
P21/c
NiC26H22N4O6
Triclinic
P 1
Space group
Unit cell dimensions
˚
a (A)
9.675(2)
17.109(5)
14.403(4)
90
92.903(11)
90
2381.1(11)
4
1.482
9.834(3)
11.319(3)
13.130(4)
84.68(3)
67.54(3)
85.49(2)
1343.4(6)
2
˚
b (A)
˚
c (A)
α (◦)
β (◦)
γ (◦)
3
˚
V (A )
Z
ρcalcd. (g cm−3
µ (mm−1
)
1.348
0.768
)
0.861
Reflections collected
Unique reflections
Rint
4287
4033
0.214
4487
4487
0.00
Reflections (I > 2σ(I))
Parameters
2594
326
2797
334
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
Goodness-of-fit on F2
0.0747, 0.1899
0.1206, 0.2249
1.060
0.747, −0.748
0.0790, 0.1908
0.1292, 0.2275
1.009
0.694, −0.392
−3
˚
Largest peak, hole (e A
)
Infrared and electronic spectral characteristics
der at the higher energy band is possibly due
---
---
---
to the HC N group of the ligand. Like
---
The infrared spectrum of [Ni(paap)2]·
CH3COOH·H2O displays a broad band centered
at 3046 cm−1 and a strong band at 1703 cm−1.
These two bands are ascribable to the carboxyl
group10 of the acetic acid molecule that is hydro-
gen bonded to the metal coordinated phenolate-O
of one of the two ligands (vide infra). The strong
[Ni(paap)2]·CH3COOH·H2O, [Ni(paab)2]·2H2O
also displays medium to strong bands in the range
1560–1441 cm−1 attributable to the aromatic parts
of the ligands.
In methanol solutions, [Ni(paap)2]·
CH3COOH·H2O and [Ni(paab)2]·2H2O display a
weak absorption at 855 and 900 nm, respectively.
This absorption is assigned to the ν1 transition
for an octahedral nickel(II) complex.14 The
difference in this band position suggests that
paap− is a stronger ligand than paab−. The
other two coordinating atoms being same in
both ligands the better σ-bonding ability of the
phenolate-O compared to that of the carboxylate-
O is likely to be one of the major reasons
for this observation. In addition to this weak
absorption, both complexes display three intense
absorptions in the range 480–240 nm. These
higher energy absorptions are most likely due to
ligand-to-metal charge transfer and intraligand
transitions.
and sharp band observed at 1586 cm−1 is most
11
---
likely due to the azomethine C N stretching.
---
The medium to strong bands in the range 1559–
1456 cm−1 are possibly due to the vibrations as-
---
sociated with the aromatic C C fragments of the
---
ligands.11 The broad band observed at 3397 cm−1
in the infrared spectrum of [Ni(paab)2]·2H2O is
most likely due to the lattice water molecules.12
The origin of the strong band with a shoulder at
1589 cm−1 and another strong band at 1358 cm−1
might involve the metal coordinated carboxylate
functionalities present in the ligands. The for-
mer is assigned to the νas stretch and the lat-
ter is assigned to the νs stretch.13 The shoul-

Nickel(II) complexes with N,N,O-donor Schiff bases
741
Fig. 1. Structure of [Ni(paap)2]·CH3COOH·H2O with the
atom-labeling scheme. All non-hydrogen atoms are repre-
sented by their 15% probability thermal ellipsoids. Hydro-
gen bonding interactions are shown by dashed lines.
Fig. 2. Structure of [Ni(paab)2]·2H2O with the atom-
labeling scheme. All non-hydrogen atoms are represented
by their 15% probability thermal ellipsoids. Hydrogen bond-
ing interactions are shown by dashed lines.
Description of structures
The structures of [Ni(paap)2]·CH3COOH·
H2O and [Ni(paab)2]·2H2O are depicted in
Figs. 1 and 2, respectively. In each complex, the
tridentate ligands bind the metal ion meridionally
and form a N4O2 coordination sphere. The bond
parameters associated with the metal ion (Tables 2
and 3) indicate a distorted octahedral coordination
geometry. The average chelate bite angle (78.23◦)
in the five-membered ring formed by the
pyridine-N and the imine-N in [Ni(paap)2] is
slightly smaller than that (80.57◦) in [Ni(paab)2].
The same for the other five-membered ring
constituted by the imine-N and the phenolate-O
in [Ni(paap)2] is 81.32◦. On the other hand,
for [Ni(paab)2] the average chelate bite angle
(89.36◦) in the six-membered ring formed by
the imine-N and the carboxylate-O is very close
to the ideal value of 90◦. As a consequenc◦e,
--- ---
N(imine) Ni N(imine) angles are very similar
in both complexes. The values are 176.13(19)
and 176.6(2)◦ for [Ni(paap)2] and [Ni(paab)2], re-
---
---
spectively. The Ni N(pyridine), Ni N(imine),
---
---
Ni O(phenolate), and Ni O(carboxylate) bond
distances observed in these complexes are
within the range reported for nickel(II) com-
plexes having the same coordinating atoms.14a,15
In [Ni(paap)2]·CH3COOH·H2O, the acetic acid
molecule is hydrogen bonded to one of the
phenolate-O atoms (Fig. 1). The O1···O3 distance
˚
---
and the O1···H O3 angle are 2.605(8) Aand
148.54◦, respectively. The water molecule is hy-
drogen bonded with the other phenolate-O atom.
---
The O2···O5 distance and the O2···H O5 angle
◦
˚
--- ---
the average trans N Ni O angle (169.62 )
are 2.721(8) Aand 112.23 , respectively. On the
other hand, both water molecules are hydrogen
bonded to the same uncoordinated carboxylate-O
in [Ni(paab)2] is significantly larger than that
(159.41◦) in [Ni(paap)2]. However, the trans

742
Mukhopadhyay and Pal
Table 2. Selected Bond Parameters for [Ni(paap)2]·CH3COOH·H2O
˚
Bond distances (A)
----
----
Ni N(4)
Ni N(1)
----
2.114(5)
2.007(5)
2.122(5)
2.005(5)
2.053(4)
2.086(4)
----
Ni N(2)
Ni O(1)
----
----
Ni O(2)
Ni N(3)
Bond angles (◦)
---- ----
---- ----
N(1) Ni N(3)
---- ----
N(2) Ni O(2)
---- ----
N(3) Ni N(4)
N(1) Ni N(2)
78.17(19)
90.0(2)
98.65(19)
78.3(2)
---- ----
---- ----
N(1) Ni O(1)
---- ----
N(3) Ni O(1)
N(1) Ni N(4)
105.68(19)
159.01(18)
92.99(18)
101.5(2)
176.13(19)
81.01(18)
91.51(19)
159.82(18)
95.12(18)
81.64(19)
92.77(18)
---- ----
N(3) Ni O(2)
---- ----
---- ----
N(4) Ni O(1)
N(1) Ni O(2)
---- ----
N(2) Ni N(3)
---- ----
N(4) Ni O(2)
---- ----
---- ----
O(1) Ni O(2)
N(2) Ni N(4)
---- ----
N(2) Ni O(1)
water molecules are the basic units for linking
the [Ni(paap)2]·CH3COOH units into a two-
dimensional arrangement (Fig. 3). Each water
molecule acts as the bridge between three of
these units by participating in three hydrogen
in [Ni(paab)2]·2H2O (Fig. 2). The O2···O5 and
˚
O2···O6 distances are 2.728(13) and 3.25(2) A,
◦
---
respectively. The O2···H O5 angle is 143.28 .
There is no interaction between the two water
molecules.
---
bonding interactions. These are one O H···O
---
---
and two C H···O interactions. In the O H···O
interaction, the O-atom of the water molecule
acts as the donor atom and the phenolate-O of
one [Ni(paap)2] moiety acts as the acceptor atom
Hydrogen bonding and self-assembly
The
self-assembly
of
[Ni(paap)2]·
---
(vide supra). In the C H···O interactions, the
CH3COOH·H2O and [Ni(paab)2]·2H2O via
intermolecular hydrogen bonding interactions
leads to the two-dimensional network in each case
(Figs. 3 and 4). For [Ni(paap)2]·CH3COOH·H2O
acetic acid has no role in the formation of the
network. As mentioned before it is only connected
to one of the phenolate-O in [Ni(paap)2] through
a hydrogen bond. In the crystal lattice, the
water O-atom acts as the acceptor atom. The
aromatic C-atom (C20) meta to the phenolate-O
of the second [Ni(paap)2] unit and the C-atom
(C6) of the azomethine fragment of the third
[Ni(paap)2] unit act as the donor atoms in
these two hydrogen bonds. The C20···O5 and
˚
C6···O5 distances are 3.364(10) and 3.424(8) A,
Table 3. Selected Bond Parameters for [Ni(paab)2]·2H2O
˚
Bond distances (A)
----
----
Ni N(4)
Ni N(1)
----
2.085(5)
2.064(4)
2.079(5)
2.045(5)
2.011(5)
2.011(5)
----
Ni N(2)
Ni O(1)
----
----
Ni O(3)
Ni N(3)
Bond angles (◦)
---- ----
---- ----
N(1) Ni N(3)
---- ----
N(2) Ni O(3)
N(1) Ni N(2)
81.26(19)
96.09(18)
96.00(19)
169.87(18)
90.4(2)
92.20(18)
79.89(19)
87.6(2)
168.38(18)
93.94(18)
89.86(19)
87.7(2)
---- ----
N(3) Ni N(4)
---- ----
---- ----
N(3) Ni O(1)
N(1) Ni N(4)
---- ----
N(1) Ni O(1)
---- ----
N(3) Ni O(3)
---- ----
---- ----
N(4) Ni O(1)
N(1) Ni O(3)
---- ----
N(2) Ni N(3)
---- ----
N(2) Ni N(4)
---- ----
98.31(19)
176.6(2)
N(4) Ni O(3)
---- ----
O(1) Ni O(3)
---- ----
N(2) Ni O(1)
88.87(19)

Nickel(II) complexes with N,N,O-donor Schiff bases
743
each [Ni(paab)2] molecule are involved in two
---
pairs of reciprocal C H···O interactions with
its two neighbours on both sides (Fig. 4). The
C6···O3 and C19···O1 distances are 3.172(7)
˚
and 3.256(7) A, respectively. The correspond-
◦
---
ing C H···O angles are 142.95 and 150.32 , re-
spectively. Due to these interactions [Ni(paab)2]
molecules exist in a chain-like arrangement. Both
water molecules are hydrogen bonded to one
of the uncoordinated carboxylate-O atoms (vide
supra). The O-atom (O6) of one of these two wa-
˚
ter molecules is at a distance of 3.10(3) A from
the O-atom of the corresponding symmetry re-
lated water molecule. This distance suggests that
they exist as a hydrogen bonded water dimer.
These water dimers provide the bridges between
the chains of [Ni(paab)2]·H2O moieties (Fig. 4)
and complete the two dimensional network of
[Ni(paab)2]·2H2O.
Fig. 3. A view of the two-dimensional network of
[Ni(paap)2]·CH3COOH·H2O along the a-axis. The acetic
acid molecules are not shown for clarity.
---
respectively. The corresponding C H···O angles
are 161.19 and 163.81◦, respectively.
In the self-assembly of [Ni(paab)2]·2H2O,
the azomethine groups of the ligands play the
crucial role. Two azomethine fragments and the
two metal coordinated carboxylate-O atoms in
Acknowledgments
X-ray crystallographic studies were per-
formed at the National Single Crystal Diffrac-
tometer Facility, School of Chemistry, Univer-
sity of Hyderabad (funded by the Department of
Science and Technology, New Delhi). We thank
the University Grants Commisssion, New Delhi
for the facilities provided under the Universities
with Potential for Excellence program. Mr. A.
Mukhopadhyay thanks the Council of Scientific
and Industrial Research, New Delhi for a research
fellowship.
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clarity the water molecule having no role in the formation
of the network is not shown.

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