Synthesis, structure and properties of a fumarate bridged Ni(II) coordination polymer

Article abstract of DOI:10.1016/j.molstruc.2011.05.039

A 1-D coordination polymer catena[μ-fumaratobis(4-cyanopyridine) diaquanickel(II)],[Ni(μ-C₄H₂O₄)(4-CNpy) ₂(H₂O)₂]_n 1 has been synthesized and structurally characterized. Compound 1 is monoclinic, P2₁/c with unit cell parameters a = 8.8759(9) , b = 11.4112(11) , c = 8.8908(9) , β = 106.010(6)°, V = 865.6(1) ³, Z = 2 and D_{calc .} = 1.600 g cm^-3. The structure refined to R₁ = 0.0245, wR₂ = 0.0626 for all 2014 unique reflections and 152 parameters; GooF = 1.056. It consists of a polymeric chain of nearly octahedral Ni²⁺ centers bridged by bidentate fumarato ligands. Non-covalent interactions lead these chains to aggregate into an interesting metallosupramolecular assembly. Indexed PXRD pattern, solid state UV-vis-NIR spectral data, thermogravimetric behavior and variable temperature magnetic susceptibility data on 1 are presented.

Full text of DOI:10.1016/j.molstruc.2011.05.039

Journal of Molecular Structure 999 (2011) 83–88
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and properties of a fumarate bridged Ni(II)
coordination polymer
1
⇑
Sanchay J. Bora , Birinchi K. Das
Department of Chemistry, Gauhati University, Guwajhati 781 014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A 1-D coordination polymer catena[l-fumaratobis(4-cyanopyridine)diaquanickel(II)],[Ni(l-C4H2O4)(4-
CNpy)2(H2O)2]n 1 has been synthesized and structurally characterized. Compound 1 is monoclinic, P21/
Received 14 March 2011
Received in revised form 20 May 2011
Accepted 21 May 2011
c
with unit cell parameters a = 8.8759(9) Å, b = 11.4112(11) Å, c = 8.8908(9) Å, b = 106.010(6)°,
V = 865.6(1) Å3, Z = 2 and Dcalc. = 1.600 g cmꢀ3. The structure refined to R1 = 0.0245, wR2 = 0.0626 for all
2014 unique reflections and 152 parameters; GooF = 1.056. It consists of a polymeric chain of nearly octa-
hedral Ni2+ centers bridged by bidentate fumarato ligands. Non-covalent interactions lead these chains to
aggregate into an interesting metallosupramolecular assembly. Indexed PXRD pattern, solid state UV–
vis–NIR spectral data, thermogravimetric behavior and variable temperature magnetic susceptibility data
on 1 are presented.
Available online 13 June 2011
Keywords:
1-D coordination polymer
Nickel(II) fumarate
4-Cyanopyridine ligand
Graph-set analysis
Ó 2011 Elsevier B.V. All rights reserved.
Metallosupramolecular assembly
1. Introduction
described as promising materials for gas sorption as well as storage
[8,9]. These compounds have also been described as precursors for
Coordinated ligand systems containing electron donor and
acceptor sites lead to metallosupramolecular assemblies [1], and
in this context 4-cyanopyridine (4-CNpy) with the electron
-withdrawing nitrile group as the acceptor and the pyridyl nitro-
gen as the donor represents a suitable candidate [2]. Presence of
two regions of delocalized electron density also brings in the pos-
the synthesis of nanomaterials [10,11]. In this paper we describe
our results on the synthesis, crystal structure determination and
properties of a new 1-D coordination polymer of Ni(II), formulated
as [Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1.
2. Experimental
sibility of
p p interactions so as to direct preferences for thermo-
ꢀ
dynamically favoured solid state structures [3,4]. On the other
2.1. Materials
hand, presence of the dianion of fumaric acid (C4H2O2ꢀ) as a ligand
4
in metal organic compounds is known to give coordination poly-
mers of various dimensionalities [5,6]. Coordination polymer is a
family which is composed of 1-D chains, 2-D sheets, and 3-D
frameworks of building blocks connected via metal ligand coordi-
Reagents and solvents used in this work were used as obtained
from commercial sources. Disodium fumarate was prepared by
evaporating a NaOH-neutralized aqueous solution of fumaric acid.
The off-white residue so obtained was dried at 110 °C. Ni(H2O)3
(SO4)(4-CNpy)2ꢁH2O has been prepared by following a published
method [12].
nation bonds. Hydrogen bonding and
pꢀp stacking interaction
may further be utilized to generate low-dimensional coordination
polymers into supramolecular networks of higher dimensionality.
Coordination polymers based on transition metals and multi-
functional organic ligands have received considerable recent atten-
tion in the design of supramolecular assemblies having potential
applications in diverse fields such as catalysis, cooperative magne-
tism, luminescence, NLO behavior, electrical conductivity, among
others [7]. It is also a notable fact that such compounds have been
2.2. Instrumentation
The C,H,N analysis was performed using a Perkin–Elmer 2400
Series II CHNS/O Analyzer. FT-IR spectra were recorded in a
Perkin–Elmer RX1 spectrophotometer in the mid-IR region
(4000–400 cmꢀ1) for KBr pellets. The solid state UV–vis–NIR
(240–2600 nm) spectra were obtained using a Hitachi U-4100
spectrophotometer equipped with an integrating sphere. BaSO4
powder was used as reference (100% reflectance). Absorption data
were calculated from the diffuse reflectance data using the Kub-
elka–Munk function (a/S = (1 ꢀ R)2/2R where a is the absorption
⇑
Corresponding author. Tel.: +91 361 2570535; fax: +91 361 2700311.
E-mail addresses: snachay.bora@gmail.com (S.J. Bora), das_bk@rediffmail.com
(B.K. Das).
1
Present address: Pandu College, Guwahati 781 012, India.
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.05.039

84
S.J. Bora, B.K. Das / Journal of Molecular Structure 999 (2011) 83–88
Table 2
Table 1
Selected geometric parameters for compound 1.
Crystal data and structure refinement for [Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1.
Bond distances (Å) and angles (°)
Empirical formula, FW
Crystal system, space group
Unit cell dimensions
C16H14N4O6Ni, 417.02
Monoclinic, P21/c
a = 8.8759(9) Å
b = 11.4112(11) Å
c = 8.8908(9) Å
M(1)AO(2)
M(1)AO(1)
M(1)AN(1)
O(2)AC(7)
O(3)AC(7)
N(1)AC(1)
2.031(1)
O(2)aAM(1)AO(1)
O(2)AM(1)AO(1)
O(2)AM(1)AN(1)
O(1)aAM(1)AN(1)
O(1)AM(1)AN(1)
O(2)AM(1)AN(1)a
89.95(4)
90.05(4)
92.00(4)
92.57(4)
87.43(4)
88.00(4)
2.098(1)
2.119(1)
1.260(2)
1.256(2)
1.342(2)
b = 106.010(6)°
Volume
865.57(15) Å3
Z, Calculated density
Absorption coefficient
Crystal size
Ratio of Tmin, Tmax
h range for data collection
hkl ranges
Reflections collected/unique
Data/restraints/parameters
R indicesa [all data]
Goodness-of-fitb on F2
(Shift/s.u.)max
2, 1.600 g/cm3
Hydrogen bonds
DꢀHꢁ ꢁ ꢁA
1.164 mmꢀ1
d(Hꢁ ꢁ ꢁA)
1.96(2)
1.95(2)
d(Dꢁ ꢁ ꢁA)
2.685(1)
2.773(1)
\ (DHA)
157(2)
177(2)
0.38 ꢂ 0.27 ꢂ 0.17 mm3
O(1)AH(7)...O(3)
O(1)AH(6)...O(3)b
0.86113
2.39–28.34°
Symmetry codes: a = ꢀx + 1, ꢀy, ꢀz; b = x, ꢀy ꢀ 1/2, z ꢀ 1/2.
h: ꢀ11 ? 11; k: ꢀ15 ? 12; l: ꢀ11 ? 11
6594/2014 [R(int) = 0.0193]
2014/0/152
R1 = 0.0245, wR2 = 0.0626
1.056
46.84%; H, 3.46%; N, 13.87%. IR spectral data (KBr disc, cmꢀ1):
3108(s), 2242(s), 1968(m), 1870(w), 1718(sh), 1608(sh), 1542(s),
1416(sh), 1384(s), 1220(s), 1126(w), 1098(m), 1070(s), 1020(m),
988(s), 864(sh), 838(m), 808(m), 770(m), 684(s), 596(m), 566(s)
[s, strong; m, medium; w, weak; br, broad; sh, shoulder].
BM.
0.000
Largest diff. peak and hole
0.286 and ꢀ0.325 e Åꢀ3
a
leff = 3.08
wR2 = {
GooF = S = {
R
[ w(F2o –F2c )2 ]/
R
R
[w(F2o )2]}1/2; R1
=
R
||Fo| ꢀ |Fc||/R|Fo|.
[w(Fo2 ꢀ Fc2)2]/(n ꢀ p)2}1/2
.
b
2.4. X-ray crystallography
coefficient, R the reflectance and S the scattering coefficient). Ther-
mogravimetric studies were carried out under a flow of N2 gas
using a Mettler Toledo TGA/DSC1 STARe system at a heating rate
of 10 °C minꢀ1. Room temperature magnetic susceptibilities were
measured at 300 K on a Sherwood Mark 1 Magnetic Susceptibility
Balance by Evans Method. Variable temperature magnetic suscep-
tibility data on compound 1 were measured using an MPMS Quan-
tum Design SQUID magnetometer at a constant magnetic field of
1000G. The initial ‘moment’ data given by the computer controlled
instrument were analyzed according to standard formulae of
magnetochemistry using Origin 8.0 [13].
Molecular and crystal structure of 1 was determined by single
crystal X-ray diffraction technique. Suitable crystals of 1 were
obtained upon slow evaporation of the preparative reaction mix-
tures obtained as above. The chosen crystals of suitable size were
mounted on a glass fiber for intensity data collection at room
temperature using graphite monochromatized Mo K
a radiation
(0.7107 Å) on a Bruker SMART CCD Diffractometer [14]. Crystal
structures were solved by direct methods (SHELXS) and refined
by full-matrix least squares techniques (SHELXL) with SHELX-97
[15] using the WinGX [16] platform available for personal comput-
ers. The hydrogen atoms in compound 1 were located in difference
Fourier maps and refined with isotropic atomic displacement
parameters. Crystallographic data for 1 are presented in Table 1.
The structural diagrams were drawn using ORTEP-3 for Windows
[17] and Diamond [18].
Powder X-ray diffraction patterns in the 3–60° 2h-range were
recorded on a Philips X’Pert PRO instrument using Cu Ka radiation
(1.5418 Å) at a scan rate of 0.5 s (0.5° 2h) per step at 40 kV/30 mA.
The calculated diffraction patterns assuming Bragg–Brentano
geometry were obtained from results of single crystal structure
analyses using the computer program PowderCell [19].
2.3. Synthesis of [Ni(l-C4H2O4)(4-CNpy)2(H2O)2] 1
About 0.9 g (2 mmol) of Ni(H2O)3(SO4)(4-CNpy)2.H2O [11] was
dissolved in 20 mL of water to obtain a light green solution. To that
resulting solution 0.32 g (2 mmol) of disodium fumarate was
added and the mixture was stirred mechanically for 2 h. The sky
blue precipitate formed was filtered, washed with small volumes
of water under suction and then with methanol and dried in a vac-
uum desiccator over fused CaCl2. Yield: 0.58 g (70%). Anal. calcd.
for C16H14N4O6Ni: C, 46.04%; H, 3.36%; N, 13.43%. Found: C,
Fig. 1. ORTEP diagram of a section of the polymeric chain of 1 with non-hydrogen atoms drawn as 50% probability ellipsoids.

S.J. Bora, B.K. Das / Journal of Molecular Structure 999 (2011) 83–88
85
Fig. 2. Inter-chain and intra-chain hydrogen bonding interactions observed in the crystal structure of 1. Graph-set notations are indicated. For clarity, the 4-CNpy ligands
have been shown only by their pyridyl N atoms.
The chain polymers run along the c-axis in the crystal structure
of 1. The observed Ni(1)ꢀN(1) distance of 2.119(1) Å for 1 is com-
parable to the corresponding distance of 2.165(1) Å in [Ni(H2O)4(4-
CNpy)2]ꢁ(BPh4)2ꢁ2(4-CNpy)ꢁ4H2O [2]. The distances Ni(1)ꢀO(3) =
3.316(1) Å for the uncoordinated O-atoms of the carboxyl groups
confirm the presence of fumarate ions in monodenate coordination
mode in the polymeric chains of the compound. Ni2+ ion is present
in a distorted octahedral environment where the angles subtended
at the metal center vary from 87.65(4)° to 92.35(4)°. A cobalt(II)
compound ‘[Co(
ported by Zhang et al. [20] is structurally similar with 1. However,
l
-fumarato)(
c
-methylpyridine)]2ðH2OÞ ꢃ0
re-
2
1
Mn(l-C4H2O4)(phen)(H2O)2 was found to be a zig-zag 1-D polymer
[21] due to the presence of the bidentate ligand. The Niꢁ ꢁ ꢁNi dis-
tance of 1 is 8.891(1) Å which is significantly low compared to
the corresponding values of 9.728 Å and 9.730 Å reported for the
fumarate bridged dimers [Ni(C4H2O4)(bpp)(H2O)] (bpp = 1,3-bis
(4-pyridyl)propane) [6] and [Ni2(C4H2O4)(phen)4(H2O)2]ꢁC4H2O4
ꢁ16H2O [22] (phen = 1,10-phenanthroline) respectively.
Extensive hydrogen bonding interactions between the uncoor-
dinated OAatoms (fumarate) and the coordinated water molecules
are observed in the crystal structure of 1. The hydrogen bonding
network is extended via intra-chain as well as inter-chain links
which give rise to a 2-D supramolecular architecture (Fig. 2). The
hydrogen bond parameters are given in Table 2. The hydrogen
bonding interactions in 1 can be analyzed by making use of Graph
Set Theory [23]. The coordinated water molecules and the uncoor-
dinated carboxyl oxygen atoms are self-assembled to form supra-
molecular chains that run approximately along the direction of
the polymers in the crystal lattice. In graph set notation such a
chain is describable as C22 (4) where the subscripts and superscripts
are the number of hydrogen bond donors and acceptors respec-
tively. A 11-membered hydrogen-bonded R22 (11) ring identified
as ‘(OH)aquaAOfumA(H)aquaAOfumAC4OANi0 is also an important
pattern exhibited by the crystal structure of 1. These rings are
linked to each other by another type of intra-molecular hydrogen
bonded rings of description S(6).
Fig. 3.
CAHꢁ ꢁ ꢁ
p
p
ꢀ
p
interaction observed for ꢀC„N fragments with pyridyl rings and
interaction between pyridyl ring hydrogen and aromatic -systems.
p
3. Results and discussion
3.1. Synthesis
Compound 1 of composition [Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1
can be prepared in good yield by adding one equivalent of the diso-
dium salt of fumaric acid, Na(C4H2O4), to an aqueous solution of
[Ni(H2O)3(4-CNpy)2(SO4)]ꢁH2O [12] and stirring the mixture at
room temperature. Sky blue crystals of 1 can be obtained on slow
evaporation of the said reaction mixture. The non-hygroscopic
solid is sparingly soluble in water as well as common organic sol-
vents. Crystals of 1 remain indefinitely stable against dehydration
under ambient conditions.
Both CAHꢁ ꢁ ꢁ
crystal structure of 1. CAHꢁ ꢁ ꢁ
the pyridyl ring hydrogen of one 4-CNpy and the aromatic
tem of another 4-CNpy ligand (Fig. 3). The observed value of
Cꢁ ꢁ ꢁ (pyridyl ring centroid) distance for compound 1 is 3.793 Å
with a \CAHꢁ ꢁ ꢁ angle of 113.80°. These values are in good agree-
ment with similar interactions reported earlier by other workers
[24,25]. The so called interactions are observed between the
aromatic -system of the pyridyl rings and the nitrile -systems
p
and
p
–
p
interactions are found to occur in the
interaction is observed between
sys-
p
p
3.2. Crystal structure
p
The title compound [Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1 is a lin-
p
ear one-dimensional coordination polymer wherein the fumarate
dianion (C4H2O2ꢀ) bridges the nearly octahedral Ni2+ ions in a cen-
4
p–p
trosymmetric fashion (Fig. 1). Table 2 presents the geometrical
data on the crystal structure.
p
p

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S.J. Bora, B.K. Das / Journal of Molecular Structure 999 (2011) 83–88
Fig. 4. (a) Line drawing to show overall 3-D supramolecular structure of 1; (b) Illustration of
p(nitrile)ꢀp(nitrile) interactions between two adjacent polymeric chains.
Fig. 5. Observed (top) and simulated (bottom) X-ray powder diffraction patterns of
[Ni( -C4H2O4)(4-CNpy)2(H2O)2]n 1.
l
Fig. 7. TG and DTG curves for [Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1.
Hartree–Fock and DFT calculations were found to support the
occurrence of these interactions [12]. As can be seen from Fig. 4a
and b, these interlayer
p–p interactions between anti-parallel ni-
trile groups extend the supramolecular structure in the 3rd dimen-
sion. Indeed, these non-covalent interactions appear to be an
important factor for stabilizing the crystal structures of 1.
3.3. Powder X-ray diffraction
All the observed peaks in the experimental powder pattern are
seen in the powder pattern calculated on the basis of structural re-
sults obtained from single-crystal data. A comparison of experi-
mental and calculated PXRD patterns is shown in Fig. 5. The
close similarity between observed and calculated XRD patterns
suggests the purity of crystalline bulk sample and also the veracity
of the structure described by us. Powder XRD data with hkl indices
for the prominent lines have been determined by comparing the
two patterns.
Fig. 6. Solid state UV–vis–NIR spectrum of [Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1.
3.4. Spectral properties
with centroidꢁ ꢁ ꢁcentroid distances of 3.681 Å for compound 1. In
addition, the anti-parallel alignment of nitrile fragments, coming
A powdered sample obtained from light green crystals of
[Ni(l-C4H2O4)(4-CNpy)2(H2O)2]n 1 shows three d–d transitions at
from two different layers also leads to weak
The observed C„N(centroid)ꢁ ꢁ ꢁC„N(centroid) distances for com-
pound 1 is 3.953(3) Å. This kind of interactions were also ob-
served in some of our other structures containing 4-CNpy ligands.
p–p interactions.
342 nm, 622 nm and 1082 nm (Fig. 6). These are associated with
the spin allowed transitions from the 3A2g ground term to the three
p–p
3
3
3
excited triplet terms viz., T2g(F), T1g(F) and T1g(P) as applicable

S.J. Bora, B.K. Das / Journal of Molecular Structure 999 (2011) 83–88
87
Fig. 8. Temperature dependence magnetic susceptibilities and their inverses for [Ni(
l-C4H2O4)(4-CNpy)2(H2O)2]n 1. The inset in the figure shows the variations of
vMT and
leff with temperature.
for octahedral nickel(II) complexes. The first spin allowed transi-
tion, to the T2g(F) state occurs at a kmax value of 1082 nm. The
complexes. To determine the temperature dependence of magnetic
properties we measured the variable temperature susceptibilities
in the temperature range 2–300 K at a constant magnetic field of
3
bands at 622 nm and 342 nm are assigned to the transitions to
3
3T1g(F) and T1g(P) states respectively. In addition to this, a band
1000G. The
vV and 1/vV vs. T plots are shown in Fig. 8. Theoretical
due to
p
?
p⁄ transition of pyridine origin appears at 278 nm.
fitting of the 1/vV vs. T
curve using the Curie–Weiss law,
The FT-IR spectrum of compound 1 shows the characteristic
v
¼ C=ðT ꢀ
H
Þ (where, C is the Curie constant and h the Weiss con-
m
(CAH) stretching vibration of the fumarate ligand at around
stant), gives a negative h value of ꢀ2.54 K which suggests antifer-
3108 cmꢀ1
.
The
1542 cmꢀ1 and 1384 cmꢀ1 respectively, which are significantly
lower than the uncoordinated [ as(OCO)] and [ as(OCO)] bands. It
[mas(OCO)] and [ms(OCO)] bands appear at
romagnetic behavior. The Curie constant, C for this compound is
found to be 1.19 emu-K molꢀ1. Both
vVT vs. T as well as leff vs. T
m
m
plots indicate the inherent weakness of the antiferromagnetic
exchange interaction. The reported Co(II) complex mentioned
above [20] was also found to be weakly antiferromagnetic
(J = ꢀ0.22 cmꢀ1).
also shows two medium intensity bands around ꢄ805 and
ꢄ760 cmꢀ1 assigned to the OCO bending frequencies. The
m(C@N)
vibration of the pyridine ring for 1 occurs at 1608 cmꢀ1. A sharp
band appearing at 2242 cmꢀ1 for the compound is assigned to
the C°N vibration of the 4-CNpy ligand.
4. Conclusion
3.5. Thermal properties
The ease of isolation of 1 confirms the tendency of the fumarate
dianion to act as a bridging spacer in coordination polymers. It is
also found that by making use of ancillary ligands like pyridine
and substituted pyridines it is possible to generate 1-D coordina-
tion polymers. It appears from our study that non-covalent inter-
In the TG curve for compound 1 (Fig. 7), the first step of decom-
position involves the release of two 4-CNpy molecules with a
weight loss of ca. 49.31% (calculated value is 48.88%) in the tem-
perature range 143–305° C (bp of 4-CNpy, 196 °C). The most strik-
ing aspect of the thermogram is the absence of steps assignable to
weight loss due to dehydration. Over the temperature range
310–392 °C, a weight loss of about 32.37% occurs due to the calcu-
lated value of 32.13% for the species C2H2, CO2, CO and 2H2O. On
heating above 400° C, the residue left behind is NiO (by PXRD). This
proposed pathway however remains tentative. It is possible that
before the temperature reaches 305 °C, the water molecules take
part in the formation of fumaric acid and also that the resulting hy-
droxyl groups remain attached to the metal ion as ligands. More
detailed studies will be required to establish the above mechanism.
molecular interactions like hydrogen bonding, CAHꢁ ꢁ ꢁ
p and p–p
interactions may give extra thermal stability to coordination poly-
mers. Magnetic exchange interaction in the coordination polymer
having paramagnetic Ni2+ ions bridged by the fumarate dianion
is weakly antiferromagnetic.
Acknowledgments
Financial support from University Grants Commission and
Department of Science & Technology, India (FIST) is gratefully
acknowledged. SJB thanks CSIR, India, for a Junior Research Fellow-
ship awarded to him. The authors also thank Yoshitaka Matsushita
of Hyogo, Japan for kindly providing us with the SQUID data and
the Department of Chemistry, Indian Institute of Technology,
Guwahati for the single crystal X-ray diffraction data. The powder
3.6. Magnetic properties
The leff (300 K) value of 3.08 BM for compound 1 falls within
the commonly observed values for six-coordinate high spin Ni(II)

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S.J. Bora, B.K. Das / Journal of Molecular Structure 999 (2011) 83–88
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Appendix A. Supplementary material
CCDC 777425 contains the supplementary crystallographic data
for 1. 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.molstruc.2011.05.039.
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