Synthesis, structure and properties of Nickel(II) and Cobalt(II) compounds with 1,5-dinitronaphthalene-3,7-dicarboxylate

Article abstract of DOI:10.1016/j.molstruc.2009.05.054

Two metal-organic compounds, [Co₂(NNDC)₂(H₂O)₆]·2H₂O (1) and [Ni(NNDC)(H₂O)₄]_n (2) (where H₂NNDC = 1,5-dinitronaphthalene-3,7-dicarboxylic acid) have been s

Full text of DOI:10.1016/j.molstruc.2009.05.054

Journal of Molecular Structure 933 (2009) 8–14
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and properties of Nickel(II) and Cobalt(II) compounds
with 1,5-dinitronaphthalene-3,7-dicarboxylate
Hua Tian a,b, Qin-Xiang Jia a, Yan-Qin Wang a, Yu Ma a, En-Qing Gao a,
*
a Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, China
b School of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two metal–organic compounds, [Co2(NNDC)2(H2O)6]ꢀ2H2O (1) and [Ni(NNDC)(H2O)4]n (2) (where
H2NNDC = 1,5-dinitronaphthalene-3,7-dicarboxylic acid) have been synthesized under hydrothermal
reaction conditions, which are characterized by single crystal X-ray determination, IR and Thermogravi-
Received 3 March 2009
Received in revised form 22 May 2009
Accepted 28 May 2009
metric Analysis (TGA). Compound 1 consists of binuclear Co(II) molecules with di(l-aqua)di(l-carboxy-
Available online 6 June 2009
lato) bridges. In the compound, each dicarboxylate ligand bridges metal ions using only one carboxylate
group, with the other carboxylate group involved in extensive hydrogen bonding with coordinated and
uncoordinated water molecules. The 1,5-dinitronaphthalene groups serve as pillars between the hydro-
gen-bonded layers in which the dinuclear moieties are connected through the O–Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH–O hydrogen
bonds mediated by uncoordinated carboxylate groups and lattice water molecules. In 2, the ligands serve
as long bridges to link the metal ions into infinite chains. The uncoordinated oxygen atoms of carboxylate
are hydrogen bonded to coordinated water molecules from the same and different chains to link the
metal spheres into (4,4) layers, which are formally pillared by the 1,5-dinitronaphthalene spacers to gen-
Keywords:
Hydrothermal synthesis
Cobalt(II)
Nickel(II)
Magnetic properties
Hydrogen bonds
erate a 3D architecture with the a-Po topology. Based on a model taking into account both magnetic cou-
pling and single-ion magnetic effects, detailed magnetic analysis on the Co(II) compound revealed a
ferromagnetic intradimer interaction through the mixed aqua and carboxylate bridges.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
One of the most intriguing characteristics of metal–organic
structures is that the organic ligand can potentially be functional-
The construction of metal–organic architectures sustained by
coordination bonds and weak noncovalent forces such as hydrogen
bonds is of current interest, not only because of their useful proper-
ties relevant to applications such as gas adsorption, catalysis, lumi-
nescence and magnetism, but also because of their fascinating
supramolecular topologies [1–7]. In this context, the carboxylate li-
gands are among most extensively studied ligands. Taking advanta-
ges of the versatile coordination ability of the carboxylate group and
the rigidity and stability of aromatic groups, aromatic dicarboxyl-
ates such as benzenedicarboxylates, biphenyldicarboxylates, and
2,6-naphthalenedicarboxylate (NDC), have been widely employed
as bridging ligands to connect metal ions into metal–organic frame-
works with extended coordination networks [2,8–10]. Meanwhile,
the carboxylate group can form strong hydrogen bonds, which serve
as additional forces to reinforce the coordination networks or as the
main organizing forces to assemble low-dimensional or discrete
coordination motifs into extended supramolecular structures
[5,11,12].
ized by different organic groups, such as amine, sulfonate, and car-
boxaldehyde [13–16]. We are interested in aromatic dicarboxylate
ligands bearing nitro groups. The nitro group would not be in-
volved in coordination, but it could impart high polarity to the ex-
pected metal–organic networks and hence may influence the
properties. Here we report the synthesis and crystal structures of
the first two coordination compounds derived from 1,5-dinitro-
naphthalene-3,7-dicarboxylic acid (H2NNDC), namely [Co2-
(NNDC)2(H2O)6]ꢀ2H2O (1) and [Ni(NNDC)(H2O)4]n (2). The mag-
netic properties of 1 are also included.
2. Experimental
2.1. Materials and physical measurements
All the solvents and reagents for synthesis are commercially
available and used as received. H2NNDC was synthesized according
to the literature method [17]. Infrared spectra were recorded on a
NEXUS 670 FT-IR spectrometer using the KBr pellets. Elemental
analysis was carried out on an Elementar Vario El III elemental ana-
lyzer. Thermogravimetric Analysis (TGA) was performed using a
Mettler TGALSDTA851e/5FL1100 instrument. The bulk phase
* Corresponding author. Fax: +86 21 62233404.
E-mail address: eqgao@chem.ecnu.edu.cn (E.-Q. Gao).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.05.054

H. Tian et al. / Journal of Molecular Structure 933 (2009) 8–14
9
Table 1
purity of the samples has been confirmed by powder X-ray diffrac-
tion measurements, which were performed on a Bruker D8-Ad-
vance diffractometer equipped with Cu radiation.
Crystal data and structure refinements for compounds 1 and 2.
Ka
Compound
1
2
Temperature- and field-dependent magnetic measurements were
carried out on a Quantum Design SQUID MPMS-5 magnetometer.
Diamagnetic corrections were made with Pascal’s constants.
Formula
Mr
Temperature, K
Crystal system
Space group
a, Å
C24H24Co2N4O24
870.33
273
C12H12NiN2O12
434.95
296
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
2.2. Synthesis of [Co2(NNDC)2(H2O)6]ꢀ2H2O (1)
7.2588(16)
8.984(2)
12.369(3)
103.834(3)
101.434(3)
91.374(3)
765.5(3)
1
1.888
1.198
4460
3076/0.0347
0.0538
6.0335(2)
6.0515(2)
11.3412(4)
103.6910(10)
91.3570(10)
102.5920(10)
391.40(2)
1
1.845
1.314
5246
1716/0.0156
0.0219
b, Å
c, Å
Co(NO3)2ꢀ6H2O (0.012 g, 0.04 mmol) was added to an aqueous
solution of H2NNDC (0.006 g, 0.02 mmol), the pH value of which
had been adjusted to approximately 7 with 0.1 mol Lꢁ1 NaOH solu-
tion. The mixture was sealed in a 25 mL Teflon-lined stainless steel
autoclave, heated at 130 °C for 48 h, and then slowly cooled to
room temperature. The red rod-like products were collected after
washing with distilled water and ethanol, and dried in air at ambi-
ent temperature. Yield: 50% based on Co(NO3)2ꢀ6H2O. IR (KBr,
cmꢁ1): 3550 (br), 3360 (br), 3250 (w), 1625 (s), 1596 (s), 1407
(s), 1359 (s), 924 (w), 842 (w), 781 (s), 714 (s). Elemental analysis
calcd for C24H24Co2N4O24 (%): C 33.12, H 2.78, N 6.44. Found (%): C
33.25, H 3.14, N 6.71.
a
, °
b, °
c
, °
U, Å3
Z
Dc, g cmꢁ3
l
, mmꢁ1
Reflns collected
Unique reflns/ Rint
R1 [I > 2r(I)]
wR2(All data)
0.1284
0.988
0.0742
0.712
GOF
2.3. Synthesis of [Ni(NNDC)(H2O)4]n (2)
The compound was prepared as pale green sheet-like crystals
by the procedure described above for 1 except that cobalt nitrate
hexahydrate was replaced by nickel nitrate hexahydrate, and the
pH value of the solution was 8. Yield: 48% based on Ni(NO3)2ꢀ6H2O.
Elemental analysis calcd for C12H12NiN2O12 (%) (1): C 33.14, H 2.78,
N 6.44. Found (%): C 33.22, H 2.92, N 6.58. IR (KBr, cmꢁ1): 3540 (s),
3438 (w), 1618 (s), 1403 (s), 1360 (s), 924 (w), 893 (w), 846 (w),
784 (s), 722 (s).
2.4. Crystal data collection and refinement
Fig. 1. ORTEP drawing of compound 1 with atomic numbering scheme (thermal
ellipsoids at 50% probability). The hydrogen atoms attached to C atoms are omitted
for clarity. Symmetry codes: A, ꢁx, ꢁy, ꢁz.
Diffraction intensity data were collected at 293 K on a Bruker
APEX II diffractometer equipped with a CCD area detector and
graphite-monochromated Mo Ka radiation (k = 0.71073 Å). Empir-
Table 2
ical absorption corrections were applied using the SADABS pro-
gram [18]. The structures were solved by the direct method and
refined by the full-matrix least-squares method on F2, with all
non-hydrogen atoms refined with anisotropic thermal parameters
[19,20]. The hydrogen atoms attached to carbon atoms were placed
in calculated positions and refined using the riding model. Perti-
nent crystallographic data and structure refinement parameters
are summarized in Table 1.
Bond lengths [Å] and angles [°] for compound 1.
Co(1)–O(2)A
Co(1)–O(1)
Co(1)–O(10)
2.026(3)
2.032(3)
2.047(4)
Co(1)–O(9)
Co(1)–O(11)A
Co(1)–O(11)
2.096(4)
2.179(3)
2.245(3)
O(2)A–Co(1)–O(1)
O(1)–Co(1)–O(10)
O(1)–Co(1)–O(9)
158.16(11)
95.15(13)
96.43(13)
83.55(11)
89.12(14)
81.57(11)
174.81(13)
94.22(10)
127.2(3)
104(4)
O(2)A–Co(1)–O(10)
O(2)A–Co(1)–O(9)
O(10)–Co(1)–O(9)
O(1)–Co(1)–O(11)A
O(9)–Co(1)–O(11)A
O(1)–Co(1)–O(11)
O(9)–Co(1)–O(11)
C(1)–O(2)–Co(1)A
Co(1)–O(9)–H(9W2)
Co(1)–O(9)–H(9W2)
Co(1)–O(10)–H(0W2)
Co(1)A–O(11)–Co(1)
Co(1)–O(11)–H(1W)
Co(1)–O(11)–H(1W2)
102.78(13)
95.84(13)
90.34(14)
84.37(12)
179.07(13)
81.26(11)
86.37(12)
127.9(3)
112(4)
112(4)
117(4)
85.78(10)
113(3)
112(3)
O(2)A–Co(1)–O(11)A
O(10)–Co(1)–O(11)A
O(2)A–Co(1)–O(11)
O(10)–Co(1)–O(11)
O(11)A–Co(1)–O(11)
C(1)–O(1)–Co(1)
Co(1)–O(9)–H(9W1)
Co(1)–O(9)–H(9W1)
Co(1)–O(10)–H(0W1)
Co(1)A–O(11)–H(1W)
Co(1)A–O(11)–H(1W2)
3. Results and discussion
3.1. Description of the structure of compound 1
104(4)
105(4)
121(3)
116(3)
According to X-ray crystallographic analyses, the structure of
compound 1 consists of binuclear Co(II) molecules with mixed car-
boxylate and water bridges. The molecular structure of 1 is shown
in Fig. 1, with selected bond distances and angles listed in Table 2.
The unique Co1 ion assumes the octahedral geometry completed
by two carboxylate oxygen atoms (O1, O2A) from two NNDC li-
gands at trans positions and four water molecules through O9
O10, and O11 O11A. Each NNDC ligates two metal ions through
two carboxylate oxygen atoms. Two equivalent Co(II) ions are qua-
druply bridged by two carboxylate groups in the syn–syn mode
and two water molecules (O9, O10/ O9A, O10A, respectively) to
Symmetry code: A, ꢁx, ꢁy, ꢁz.
metal ion. The two bridging water molecules generate a strictly
planar [Co2( 2-O)2] pseudo-rhombic ring, with Co–O–Co =
85.78(10)°. The two bridging carboxylate groups are disposed trans
to each other across the [Co2( 2-O)2] plane, and form an planar
eight-membered ring perpendicular to the [Co2( 2-O)2] plane.
l
l
l
give
a centrosymmetric binuclear di(l-aqua)di(l-carboxylato)
With the carboxylate groups being essentially coplanar with the
naphthalene ring, the whole dinuclear molecule except for the
water ligands and the nitro oxygen atoms are quasi-planar. It is
moiety. The Co–Obridging distances (2.179(3) Å and 2.245(3) Å) are
longer than other distances (2.026(3) Å ꢁ2.096(4) Å) around the

10
H. Tian et al. / Journal of Molecular Structure 933 (2009) 8–14
Table 3
O11 and O9 water molecules each form two hydrogen bonds with
Hydrogen bond lengths (Å) and angles (°) for compound 1.
two carboxylate groups from different ligands. Thus, each uncoor-
dinated carboxylate group is linked to two binuclear units, forming
two cyclic hydrogen bonding motifs (graph set R22(8) [25], each
motif consisting of a Co(II) ion, two coordinated water molecules
D–H. . .A
d(D–H)
d(H. . .A)
d(D. . .A)
(DHA)
O(9)–H(9W2). . .O(4)#1
O(9)–H(9W1). . .O(3)#2
O(10)–H(0W2). . .O(12)#3
O(10)–H(0W1). . .O(12)#4
O(11)–H(1W1). . .O(3)#1
O(11)–H(1W2). . .O(4)#2
O(12)–H(2W1). . .O(3)
0.839(19)
0.846(19)
0.849(19)
0.832(19)
0.837(18)
0.854(18)
0.83(2)
2.12(3)
2.05(2)
1.92(2)
2.23(3)
1.863(19)
1.82(2)
2.12(6)
2.147(17)
2.879(4)
2.882(5)
2.759(5)
3.035(7)
2.699(4)
2.666(4)
2.742(5)
2.969(5)
151(4)
168(6)
169(6)
164(6)
178(4)
171(4)
131(7)
162(6)
and a carboxylate group). The adjacent binuclear [Co2(l2-O)2(l2-
COO)2] moieties are linked by two uncoordinated carboxylate
groups via a total of eight O–Hꢀ ꢀ ꢀO hydrogen bonds to give a hydro-
gen-bonded tape along the a direction. The eight hydrogen bonds
arrange the eight oxygen atoms (four from uncoordinated carbox-
ylates and four from coordinated waters) into a distorted cube (or
tetragonal prism), for which each of the two basal faces is defined
by a quadruple hydrogen-bonded R42(8) cyclic motif consisting of
two uncoordinated oxygen atoms from different carboxylates and
two water molecules from different binuclear units.
O(12)–H(2W2). . .O(9)#5
0.852(17)
Symmetry codes: #1, x, y ꢁ 1, z ꢁ 1; #2, ꢁx + 1, ꢁy + 1, ꢁz + 1; #3, ꢁx, ꢁy + 1,
ꢁz + 1; #4, x, y, z ꢁ 1; #5, x, y, z + 1.
noteworthy that the di(l-aqua)di(l-carboxylato)dicobalt(II) moi-
In addition, the coordinated O10 water molecule donates its
hydrogen atoms to two equivalent lattice water molecules (O12),
and consequently, two O10 waters from different binuclear units
and two O12 waters form another R42(8) cyclic motif (marked in
Fig. 2b), which serves as the linker between the neighboring binu-
clear units along the b direction. Finally, the hydrogen atoms of the
lattice water molecule form hydrogen bonds with the uncoordi-
nated carboxylate O3 atom and the coordinated O9 water mole-
cule. With all the above O–Hꢀ ꢀ ꢀO hydrogen bonds involving
ety is very rare in the literature [21]. The Coꢀ ꢀ ꢀCo distance
(3.011(1) Å) in 1 is comparable to those (3.05–3.07 Å) for the few
previous compounds with this bridging system [21], and signifi-
cantly shorter than those (3.45–3.70 Å) for some Co(II) compounds
with mono(l-aqua)di(l-carboxylato) bridges [22–24].
It is noted that the NNDC ligand uses only one carboxylate
group for coordination, although the other carboxylate group is
also deprotonated. The latter group, together with the coordinated
water molecules (either bridging or terminal), provides a rich store
of hydrogen bonding sites for intermolecular interactions. Actually,
all the water hydrogen atoms and all the uncoordinated carboxyl-
ate oxygen atoms are involved in hydrogen bonding. The relevant
hydrogen-bonding parameters are listed in Table 3. As shown in
Fig. 2a, each uncoordinated carboxylate oxygen atom (O3 or O4)
accepts two hydrogen atoms from a bridging (O11) and a terminal
(O9) water molecule from different binuclear units, and in turn, the
carboxylate groups and water molecules, the [Co2(l2-O)2(l2-
COO)2] moieties are organized into an elegant 2D supramolecular
network along the ab plane. The whole 3D structure of 1 may be
regarded as a pillared multilayer architecture, where the naphtha-
lene groups serve as pillars between the hydrogen-bonded layers
(Fig. 2c). The 3D structure is simultaneously reinforced by
p–p
interactions between the naphthalene rings stacked along a direc-
Fig. 2. (a) A hydrogen-bonded tape along the a direction. (b) The 2D hydrogen bonding layer structure of compound 1. (c) The 3D hydrogen bonding network.

H. Tian et al. / Journal of Molecular Structure 933 (2009) 8–14
11
Fig. 3. ORTEP drawing of compound 2 with atomic numbering scheme (thermal ellipsoids at 50% probability). The hydrogen atoms attached to C atoms are omitted for
clarity. Symmetry codes: A, ꢁx + 1, ꢁy + 1, ꢁz + 1; B, ꢁx + 2, ꢁy, ꢁz; C, x ꢁ 1, y + 1, z + 1.
Table 5
tion (Fig. 2c), with each ring overlapping with two neighboring
rings. The interplane distances are 3.45 and 3.42 Å for the two
independent interactions, respectively, with the center-to-center
distances being 3.62 and 3.64 Å, respectively.
Hydrogen bond lengths (Å) and angles (°) for compound 2.
D–H. . .A
d(D–H)
d(H. . .A)
d(D. . .A)
(DHA)
O(6)–H(6W1). . .O(2)
0.852(15)
0.801(15)
0.829(14)
0.821(15)
1.888(16)
2.005(19)
1.923(16)
2.131(17)
2.6825(15)
2.7507(14)
2.7363(15)
2.9341(15)
155(2)
155(2)
166.9(19)
166(2)
O(5)–H(5W2). . .O(2)#1
O(5)–H(5W1). . .O(2)#3
O(6)–H(6W2). . .O(4)#2
3.2. Description of the structure of compound 2
The structure of compound 2 consists of one-dimensional coor-
dination chains. The chain structure is shown in Fig. 3, with se-
lected bond distances and angles listed in Table 4. The unique
Ni1 ion resides at a crystallographic inversion center, and assumes
the trans-octahedral geometry completed by two carboxylate oxy-
gen atoms (O1, O1B) from two NNDC ligands at axial positions and
four water molecules (O5, O5B, O6, O6B) at equatorial positions.
The equatorial Ni–Owater distances (2.0548(10) and 2.0615(10) Å)
are a little longer than Ni–Ocarboxylate (2.0426(10) Å). The NNDC li-
gand is centrosymmetric and links two metal ions through two
monodentate carboxylate groups, with Ni. . .Ni = 13.72 Å. Conse-
quently, a linear neutral chain in which [Ni(H2O)4] cations are
linked by NNDC anions is formed along the (ꢁ1 1 1) direction. With
the carboxylate groups being essentially coplanar with the naph-
thalene ring, the whole chain except for the water ligands and
the nitro oxygen atoms is quasi-planar. The uncoordinated carbox-
ylate oxygen atoms and the coordinated water molecules provide a
rich store of interaction sites for intra- and intermolecular hydro-
gen bonding. As in 1, all the water hydrogen atoms and all the
uncoordinated carboxylate oxygen atoms are involved in hydrogen
bonding. The relevant hydrogen-bonding parameters are listed in
Table 5. As shown in Fig. 3, each uncoordinated carboxylate oxygen
atom (O2) forms an intrachain hydrogen bond with a coordinated
water molecule (O6), resulting in two cyclic hydrogen bonding mo-
tifs [graph set S(6)] around Ni(II). The O2 atom is also involved in
two independent hydrogen bonds with the O5 water molecules
from different chains. With these interchain hydrogen bonds, two
independent hydrogen bonding motifs, each consisting of two
Symmetry codes: #1, x, y ꢁ 1, z; #2, x, y, z ꢁ 1; #3, ꢁx + 1, ꢁy, ꢁz.
complementary and equivalent O–Hꢀ ꢀ ꢀO interactions, are formed
between the adjacent metal spheres along the a and b directions,
respectively. Consequently, the metal spheres are interlinked into
a 2D network along the ab plane. The network features a quadruple
hydrogen-bonded R42(8) cyclic motif consisting of two carboxylate
oxygen atoms and two water molecules from four metal spheres
(Fig. 4a). Similar to that of 1, the whole 3D structure of 2
(Fig. 4b) may be regarded as a pillared multilayer architecture,
where the naphthalene groups serve as pillars between the hydro-
gen-bonded layers. Topologically, the metal coordination spheres
can be reduced into nodes, and then the hydrogen-bonded layer
can be regarded as a 44 net and the 3D architecture as
(Fig. 4c). Finally, the O6 water molecule uses the remaining hydro-
gen atom to form a hydrogen bond with a nitro oxygen atom (O4),
providing additional stabilization energy for the 3D structure
a-Po net
(Fig. 4b). No p–p interactions are observed in 2.
3.3. Infrared spectra and thermogravimetric analysis
The FT-IR spectra of compounds 1 and 2 exhibit broad adsorp-
tion bands in the range of 3550–3250 cmꢁ1 due to
m
(OH) vibrations
of water molecules. The bands in the ranges of 1625–1596 cmꢁ1
and 1407–1403 cmꢁ1 may be attributed to the
as(COO) and
s(COO) absorptions of the NNDC ligand. The as(NO2) and s(NO2)
vibrations appear at about 1520 and 1360 cmꢁ1 [26].
m
m
m
m
Thermogravimetric analysis (TGA) was carried out in nitrogen
atmosphere from room temperature to 800 °C with heating and
cooling rates of 5.0 °C/min. The removal of water molecules in com-
pound 1 is characterized by a rapid weight loss between 70 and
112 °C (15.7%, calcd: 16.6% for eight water molecules per formula).
Upon heating up to 235 °C, a small weight loss (0.3%), which may
correspond to the release of residue water, was observed. The com-
pound shows rapid decomposition above 360 °C, and the residue
mass is consistent with CoO (17.5%, calcd: 17.2%). Compound 2 loses
the coordinated water molecules from 85 to 140 °C (calcd: 16.6%,
obsd: 17.5%), and evident decomposition begins above 380 °C, the
residue mass corresponding to NiO (17.1%, calcd: 17.2%).
Table 4
Selected bond lengths (Å) and angles (°) for compound 2.
Ni(1)–O(1)B
Ni(1)–O(6)
Ni(1)–O(1)
2.0426(10)
2.0615(10)
2.0426(10)
Ni(1)–O(5)B
Ni(1)–O(6)B
Ni(1)–O(5)
2.0548(10)
2.0615(10)
2.0548(10)
O(1)B–Ni(1)–O(1)
O(1)–Ni(1)–O(5)
O(1)–Ni(1)–O(5)B
O(1)B–Ni(1)–O(6)
O(5)–Ni(1)–O(6)
O(1)B–Ni(1)–O(6)B
O(5)–Ni(1)–O(6)B
O(6)–Ni(1)–O(6)B
Ni(1)–O(5)–H(5W2)
Ni(1)–O(6)–H(6W2)
180.00(6)
90.38(4)
89.62(4)
87.11(4)
87.86(4)
92.89(4)
92.14(4)
180.00(6)
118.0(18)
118.5(17)
O(1)B–Ni(1)–O(5)
O(1)B–Ni(1)–O(5)B
O(5)–Ni(1)–O(5)B
O(1)–Ni(1)–O(6)
O(5)B–Ni(1)–O(6)
O(1)–Ni(1)–O(6)B
O(5)B–Ni(1)–O(6)B
C(1)–O(1)–Ni(1)
89.62(4)
90.38(4)
180.00(4)
92.89(4)
92.14(4)
87.11(4)
87.86(4)
127.20(9)
109.4(14)
104.4(15)
3.4. Magnetic properties of 1
Ni(1)–O(5)–H(5W1)
Ni(1)–O(6)–H(6W1)
The magnetic susceptibility of compound 1 was measured in the
v
T and vꢁ1 versus T
Symmetry codes: B, ꢁx + 2, ꢁy, ꢁz.
2–300 K temperature range and is shown as

12
H. Tian et al. / Journal of Molecular Structure 933 (2009) 8–14
Fig. 4. (a) The 2D hydrogen bonding layer structure of compound 2. (b) The hydrogen-bonded three-dimensional structure of 2. (c) The a
-Po net derived from the 44 net.
plots in Fig. 5. The
v
T value per dimer at 300 K is 6.03 emu molꢁ1 K,
occur between the ground doublets of the relevant Co(II) ions, the
effective spin Hamiltonian for a dinuclear Co(II) system being de-
scribed by Eq. (2).
much larger than the spin-only value (3.75 cm3 K molꢁ1) for S = 3/2,
but typical of octahedral Co(II) systems with a significant contribu-
tion from unquenched orbital momentum. The vꢁ1 versus T plot
above 60 K follows the Curie–Weiss law with C = 7.99 emu molꢁ1 K
and h = 5.86 K. The positive h value suggests that a ferromagnetic
interaction between adjacent metal ions is mediated through the
^
^
S ¼ ð5=3ÞSeff
ð1Þ
ð2Þ
ꢀ
ꢁ
A
B
A
^
B
^
^
^
^
H ¼ ꢁð25=9ÞSeff ꢀ Seff ꢁ GðT; JÞbH Seff þ Seff
2
quadruple bridge. Upon cooling, the
vT value increases smoothly
2Nb2½GðT; JÞꢂ
1
vdim
¼
ð3Þ
to an approximate plateau in the range from 50 to 20 K, then in-
creases rapidly below 20 K to a maximum of 7.69 emu molꢁ1 K at
6 K, and finally drops rapidly to 6.45 emu molꢁ1 K at 2 K. Such a
kT
3 þ exp½ð25=9ÞJ=ðkTÞꢂ
The expression of the magnetic susceptibility (Eq. (3)) is derived
in the form similar to the Lines model for systems with ideal octa-
hedral Co(II) environments [32]. In Eqs. (2) and (3), the fictitious
Landé factor G(T, J) is a temperature and exchange dependent func-
tion accounting for the magnetic contributions from the excited
states through spin–orbital coupling, ligand-field distortion, and
exchange coupling. An empirical expression of G(T, J) has been de-
rived, and the variable parameters include k (spin–orbital coupling
complex temperature-dependent behavior of vT is the consequence
of the interplay and competition of several concurrent effects,
including first-order spin–orbital coupling, ligand-filed distortion
of Co(II) sites, and intra- and intermolecular magnetic interactions
between Co(II) ions. The overall increase of
6 K suggests that ferromagnetic interactions dominate in 1. The
dominating ferromagnetic interactions are also reflected in the
value (6.45 emu molꢁ1 K) of 1 at 2 K, which is significantly larger
vT from 300 K down to
vT
parameter),
a (orbital reduction factor) and D (ligand-field distor-
tion factor. An axial distortion is assumed), besides the magnetic
exchange parameter (J). The fit of the experimental data using
Eq. (3) failed to simulate the increase of vT below 20 K. Therefore,
the molecular field approximation accounting for the possible
than expected for two isolated Co(II) centers. The typical
vT value
for an isolated Co(II) ion with Seff = 1/2 at 2 K is 1.6–2.0 emu molꢁ1
K
[27–30].
To quantitatively interpret the behavior, we employed the
empirical approach proposed recently by Lloret et al. [31]. In the
framework of this approach, each Co(II) ion in the ground Kramer’s
doublet arising from spin–orbital coupling is considered to have an
effective spin Seff = 1/2, which is related to the real spin (S = 3/2) by
a factor of 5/3 (Eq. (1)), and the magnetic exchange is assumed to
intermolecular interaction was applied (Eq. (4)).
vdim
v
¼
ð4Þ
1 ꢁ zJ0ðNb2Þꢁ1½GðT; JÞꢂꢁ2vdim
According to the structural data, the dimer is associated with
four neighbors through OCoordinated–Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH–OCoordinated hydro-
gen bonding bridges, the central O atom arising from either unco-
ordinated carboxylate or lattice water (see Fig. 2c). It follows that
z = 4, assuming that the intermolecular magnetic interactions
through the similar pathways have the same value (J0). The least-
squares fit using Eqs. (3) and (4) can satisfactorily simulates the
experimental
vT(T) plot above 10 K, including the approximate
plateau region from 50 to 20 K and the rapidly increasing region
below 20 K. The best-fit parameter set is J = 15.4 cmꢁ1
,
J0 = 0.74 cmꢁ1, k = ꢁ120 cmꢁ1
,
a
= 1.42 and
= 881 cmꢁ1. The val-
and D fall within the most
D
ues of the single-ion parameters k,
a
common ranges expected for six-coordinated Co(II) complexes.
The large value suggests significant magnetic anisotropy arising
from ligand-field distortion. Notably, the J value suggests an intra-
molecular ferromagnetic interaction through the quadruple di(
aqua)di( -carboxylato) bridge. It is noted that no information on
D
l-
l
the magnetic exchange through such quadruple bridges is avail-
able in the literature, but antiferromagnetic interactions have been
Fig. 5. Plot of temperature dependence of
vmT and 1/vm for compound 1.
reported for the triple (l-aqua)di(l-carboxylato) bridges [23,24].

H. Tian et al. / Journal of Molecular Structure 933 (2009) 8–14
13
The J0 value suggests that weak ferromagnetic intermolecular inter-
actions are operative through the O–Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH–O hydrogen bond-
ing pathways. Magnetic interactions through hydrogen bonds have
been reported for many systems, but the nature and magnitude
differs with the diverse hydrogen bonding patterns [33–35]. The
molecules with di(
l
-aqua)di(
l
-carboxylato) quadruple bridges.
In the compound, each dicarboxylate ligand bridges metal ions
using only one carboxylate group, with the other carboxylate
group involved in extensive hydrogen bonding with coordinated
and uncoordinated water molecules. The 1,5-dinitronaphthalene
groups serve as pillars between the hydrogen-bonded layers in
which the dinuclear moieties are connected through the O–
Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH–O hydrogen bonds mediated by uncoordinated carbox-
ylate groups and lattice water molecules. In the Ni(II) compound,
the ligands serve as long bridges to link the metal ions into infinite
chains. The uncoordinated oxygen atom of carboxylate is hydrogen
bonded to coordinated water molecules from the same and differ-
magnetic analyses failed to reproduce the rapid decrease of vT be-
low 6 K. Qualitatively, this very-low-temperature behavior may be
due to the presence of weak antiferromagnetic intermolecular
interactions, which can operate between the hydrogen-bonded
layers separated by the long organic ligands and should be dipolar
in nature, and/or the occurrence of zero-field splitting, which can
be anticipated for a ferromagnetic ground state with S > 1/2.
The ferromagnetic interactions in 1 are also supported by the
isothermal magnetization behavior measured at 2 K. The experi-
mental curve is compared with two theoretical ones predicted
according to the Brillouin function, one for two isolated Co(II) ions
in the ground Kramer’s doublet with Seff = 1/2, and the other for the
Seff = 1 system arising from two ferromagnetically coupled Co(II)
ent chains to generate a 3D architecture with the
a-Po topology.
Based on a model taking into account both magnetic coupling
and single-ion magnetic effects, detailed magnetic analysis on
the Co(II) compound revealed a ferromagnetic intradimer interac-
tion through the mixed aqua and carboxylate bridges.
ions. Using the J, k,
a and D values obtained by modeling the
5. Supplementary material
vT(T) data (see above), the G(T, J) factor in Eqs. (2) and (3) is calcu-
lated to be 4.4 at 2 K. Notably, this value is in good agreement with
the typical geff factor (4.3) expected for Co(II). Therefore, geff = 4.4
was used in calculating the Brillouin function. As can be seen from
Fig. 6, the experimental magnetization increases significantly more
rapidly than that predicted for isolated Co(II) ions, evidently sup-
porting the overall ferromagnetic interactions between Co(II) ions
in 1. Furthermore, the increase of the experimental magnetization
is more rapid than that predicted for the Seff = 1 state, indicating
that ferromagnetic interactions not only occur within the dinuclear
molecule but also dominate among the molecules. This supports
the intermolecular ferromagnetic interactions through hydrogen
bonds. Finally, it is noted that the magnetization does not reach
saturation at 50 kOe but tends to increase slowly upon further
increasing the field. This is different from the behaviors expected
for isotropic systems (see the theoretical curves in Fig. 6), and is
typical of Co(II) systems with large magnetic anisotropy. Further
magnetic measurements revealed no indications of long-range
ordering (no hysteresis and no out-of-phase ac susceptibility
signals).
Crystallographic data as .cif files for the structures reported in
this paper have been deposited with the Cambridge Crystallo-
graphic Data Center. CCDC Nos. are 722341 for 1 and 722342 for
2. Copies of the data can be obtained free of charge from CCDC,
12 Union Road, Cambridge CB2 1EZ, UK.
Acknowledgements
We are thankful for the financial support from NSFC (20571026
and 20771038), MOE (NCET-05-0425), Shanghai Leading Academic
Discipline Project (B409).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.05.054.
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