Four new coordination polymers constructed using 2,2′-oxybis(benzoic acid) and auxiliary N-donor ligands: Syntheses, structures, magnetic behavior and DFT studies

Article abstract of DOI:10.1016/j.poly.2014.12.023

Four new coordination polymers [Cu(oba)(phen)] (1), [Co(oba)(phen)] (2), [Ni₂(oba)₂(bpe)] (3) and [Ni(oba)(bpe)_1.5]·2.5H₂O (4) [H₂oba = 2,2′-oxybis(benzoic acid), phen = 1,10-Phenanthroline, bpe = 1,2

Full text of DOI:10.1016/j.poly.2014.12.023

Polyhedron 88 (2015) 116–124
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Four new coordination polymers constructed using 2,20-oxybis(benzoic
acid) and auxiliary N-donor ligands: Syntheses, structures, magnetic
behavior and DFT studies
⇑
Long Tang, Feng Fu , JiJiang Wang, Loujun Gao, DanDan Chao, Zao Wang
Department of Chemistry and Chemical Engineering, Shaanxi Key Laboratory of Chemical Reaction Engineering, Yan0an University, Yan0an, Shaanxi 716000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new coordination polymers [Cu(oba)(phen)] (1), [Co(oba)(phen)] (2), [Ni2(oba)2(bpe)] (3) and
[Ni(oba)(bpe)1.5]ꢀ2.5H2O (4) [H2oba = 2,20-oxybis(benzoic acid), phen = 1,10-Phenanthroline, bpe = 1,2-
bis(4-pyridyl)ethylene] were synthesized by hydrothermal reactions and characterized by single-crystal
X-ray diffraction, thermogravimetric analyses, IR spectroscopy and elemental analysis. Compound 1
Received 11 October 2014
Accepted 19 December 2014
Available online 30 December 2014
shows a discrete binuclear structure. Compound 2 is a right-handed 1D helical chain, though p–p stack-
Keywords:
ing interactions to form a 2D wavelike network. Compound 3 displays a 2D wavy layer with the paddle-
wheel SBUs. Compound 4 features a 2-fold interpenetrating 3D structure with 2D brick-wall networks.
The magnetic properties of compounds 1, 2 and 4 have also been investigated. According to the crystal
structures, the full geometry optimizations of compounds 1–4 were carried out by using hybrid DFT
methods at B3LYP/6-31G(d) level. Meantime, the DFT-BS approach was applied to study the magnetic
coupling behavior for compounds 1, 2 and 4, the result reveals that the calculated exchange coupling con-
stants J were in good agreement with the experimental data.
Coordination polymers
Crystal structure
Magnetic behavior
DFT studies
2,20-oxybis(benzoic acid)
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
[19–22]. Because of its two oxo carboxylate groups, H2oba can
coordinate to metal ions in didentate, tridentate, tetradentate,
The rational design and synthesis of metal–organic coordina-
tion polymers is currently of significant interest not merely due
to the diverse network topology but mainly due to these extended
systems playing a significant role in catalysis [1,2], luminescence
[3,4], magnetism [5,6], nonlinear optics [7,8], adsorption and sepa-
ration [9,10]. In this context, the predesigned and assembly of
novel crystalline material by structure-directing factors, such as
central metal ions [11], organic ligands [12], metal–ligand ratio
[13], solvents [14], temperature [15], pH value [16], counterions
[17], and templates [18], have been validated and summarized.
Among them, the critical factor for the construction of coordination
polymers is the rational choice of organic building block and metal
center.
pentadentate and hexadentate modes. To investigate the effects
of rigid and flexible exo-bidentate pyridyl-containing ligands on
conformations of H2oba as well as the assembly process of H2oba
and metal ions, the hydrothermal reactions of H2oba with M(II)
and multidentate N-donor ligands were carried out, and a series
of coordination polymers were obtained. In this contribution, we
report the syntheses and structures of CuII, CoII and NiII coordina-
tion complexes with 2,20-oxybis(benzoic acid) (H2oba) as well as
organonitrogen co-ligands: [Cu(oba)(phen)] (1), [Co(oba)(phen)]
(2), [Ni2(oba)2(bpe)] (3) and [Ni(oba)(bpe)1.5]ꢀ2.5H2O (4). In addi-
tion, the magnetic properties of compounds 1, 2 and 4 have also
been investigated.
In our strategy, multidentate O- or N-donor ligands have been
employed in the construction of coordination polymers. For
instance, the oxybis(benzoic acid) (H2oba) is a class example of
flexible ligands, it has proven to be able to establish bridges
between metal centers. Its coordination chemistry has been
studied and some coordination polymers have been obtained
2. Experimental
2.1. Materials and chemical analysis
The H2oba, bpe and phen ligands were purchased in the Alfa
Aesar Company; all other reagents and solvents employed were
commercially available and used without further purification.
Elemental analyses were performed with a Perkin–Elmer 2400
CHN Elemental analyzer. Infrared spectra on KBr pellets were
⇑
Corresponding author.
E-mail address: yadxgncl@126.com (F. Fu).
http://dx.doi.org/10.1016/j.poly.2014.12.023
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

L. Tang et al. / Polyhedron 88 (2015) 116–124
117
recorded on a Nicolet 170SX FT-IR spectrophotometer in the range
400–4000 cmꢁ1. TG analyses were conducted with a Netzsch STA
were obtained in 48% yield based on Cu. Elemental analysis. Calc.
for C32H28N3O7.5Ni: C, 60.69; H, 4.46; N, 6.64. Found: C, 60.85; H,
449C microanalyzer under atmosphere at
a
heating rate of
4.31; N, 6.47; IR data IR (KBr cmꢁ1 (KBr cmꢁ1): 3449(s),
)
5 °Cꢀminꢁ1. The magnetic susceptibilities were obtained on crystal-
line samples using a Quantum Design MPMS SQUID magnetome-
ter. Variable temperature magnetic susceptibility measurements
were carried out on an Oxford Maglab 2000 magnetometer with
an applied field of 10 kOe. Diamagnetic correction was estimated
from Pascal’s constants.
3065(w), 1642(vs), 1612(m), 1443(m), 1406(s), 1226(m),
1165(m), 1098(w), 1025(w), 876(m), 781(m), 662(w), 548(w).
2.7. X-ray crystallographic studies
Diffraction intensities for the three complexes were collected at
293 K on a Bruker SMART 1000 CCD diffractometer employing
2.2. Computational details
graphite-monochromated Mo
Ka radiation (k = 0.71073 Å). A
semi-empirical absorption correction was applied using the SADABS
program [26]. The structures were solved by direct methods and
refined by full-matrix least-squares on F2 using the SHELXS 97 and
SHELXL 97 programs, respectively [27,28]. Non-hydrogen atoms were
refined anisotropically and hydrogen atoms were placed in geomet-
rically calculated positions. The crystallographic data for com-
pounds 1–4 are listed in Table 1, and selected bond lengths and
angles are listed in Table S1.
All calculations have been processed in Gaussian 03 package
[23]. The geometries optimization was carried out with the hybrid
DFT method on the basis of B3LYP functional [24]. The magnetic
isotropic shielding tensors were also calculated using B3LYP/6-
31G(d) approach. The experimentally determined geometries for
the complete structures of compounds 1, 2 and 4 were used for
the calculation of the magnetic exchange coupling constants [25].
Neither variation of the geometrical parameters nor the geometry
optimization was attempted in this calculation because a small
variation in the geometry can have a big effect on the calculated
magnetic interaction parameters.
3. Results and discussion
3.1. Crystal structures of [Cu(oba)(phen)] (1)
2.3. Synthesis of [Cu(oba)(phen)] (1)
Single-crystal X-ray analysis reveals that the asymmetric unit of
1 consists of one independent CuII ion, one oba ligand and one phen
ligand. Each CuII ion coordinates to two nitrogen atoms from one
phen ligand, four carboxylate oxygen atoms from two oba ligands,
A mixture of Cu(NO3)2ꢀ3H2O (0.1 mmol), H2oba (0.1 mmol),
phen (0.1 mmol) and water (10 mL) was stirred for 20 min in air.
The mixture was then transferred to a 23 mL Teflon reactor and
kept at 160 °C for 5 days under autogenous pressure, and then
cooled to room temperature at a rate of 5 °C hꢁ1. Blue crystals of
1 were obtained (yield: 56% based on Cu). Elemental analysis. Calc.
for C26H16N2O5Cu: C, 62.46; H, 3.23; N, 5.60. Found: C, 62.35; H,
3.16; N, 5.77%. IR data (KBr cmꢁ1): 3052(m), 1601(s), 1558(s),
1456(s), 1424(s), 1302(w), 1235(m), 1148(m), 1089(m), 1012(w),
874(m), 779(m), 721(w), 668(m).
forming
a CuN2O4 distorted octahedral geometry. The Cu–O
[1.953(2)–2.664(3) Å] and Cu–N [2.009(3)–2.037(3) Å] bond dis-
tances are all within the normal range found in other reported
experiments. The oba ligand adopts a bis(chelating bidentate)
coordination mode (Mode A in Scheme S1 in the supporting infor-
mation) to link two CuII ions, and phen ligands prevent the com-
pound to polymerize, forming a discrete binuclear structure (see
Fig. 1a). So, these CuII binuclear units interact via
p–p stacking
interactions (centroid-to-centroid distance: 3.672 Å) between
two different phen molecules, generating a 1D supermolecular lin-
ear chain viewing along a-axis (see Fig. 1b).
2.4. Synthesis of [Co(oba)(phen)] (2)
Complex 2 was prepared as for 1 by using Co(NO3)2ꢀ6H2O
instead of Cu(NO3)2ꢀ3H2O. Red crystals of 2 were obtained (yield:
62% based on Cu). Elemental analysis. Calc. for C26H16N2O5Co: C,
63.04; H, 3.26; N, 5.66%. Found: C, 63.15; H, 3.17; N, 5.76%. IR data
(KBr cmꢁ1): 3107 (m), 1606(vs), 1564(s), 1504(s), 1428(s), 1315(s),
1252(w), 1153(m), 1087(m), 1008(w), 870(m), 775(m), 665(m).
3.2. Crystal structures of [Co(oba)(phen)] (2)
Compound 2 shows a right-handed helical chain, and its struc-
tural features are depicted in Fig. 2. Each CoII ion is located in a dis-
torted octahedral geometry and is coordinated to four oxygen
atoms of two oba ligands and two nitrogen atoms of one phen
ligand, as shown in Fig. 2a. The bond lengths of Co–N are
2.099(2) and 2.117(2) Å, the Co–O bond lengths are in the range
of 2.1134(16)–2.158(2) Å, which are in good agreement with those
found in other Co-containing coordination complexes [29]. As
compared to compound 1, the coordination mode of oba ligand
in 2 is identical, which also adopts the bis(chelating bidentate)
coordination mode (Mode A). The adjacent CoII centers are linked
by oba ligands bridges to generate a right-handed 1D helical chain
along the c axis, with a Coꢀ ꢀ ꢀCo separation being 6.323 Å (Fig. 2b).
All phen ligands bristle out from the two sides of the helix, this ori-
entation plays a major role in packing into a higher network. So,
2.5. Synthesis of [Ni2(oba)2(bpe)] (3)
A mixture of Ni(NO3)2ꢀ6H2O (0.1 mmol), H2oba (0.1 mmol), bpe
(0.1 mmol), and water (10 mL) was placed in a Teflon reac-
tor(23 mL). The pH was adjusted to 7.0 by addition of triethyl-
amine, the mixture was heated at 160 °C for three days, and then
it was cooled to room temperature at 5 °C hꢁ1. Blue crystals of 3
were obtained in 54% yield based on Cu. Elemental analysis. Calc.
for C40H26N2O10Ni2: C, 59.16; H, 3.23; N, 3.45. Found: C, 59.25; H,
3.21; N, 3.38%. IR data IR (KBr cmꢁ1) (KBr cmꢁ1): 3063(w),
2924(w), 1646(vs), 1616(m), 1445(m), 1417(s), 1227(w),
1159(m), 1094(w), 1049(w), 875(m), 781(m), 665(w), 546(w).
through aromatic p–p stacking interactions between phen ligands
(centroid-to-centroid distance: 3.733 Å), the adjacent helical
chains generate a 2D wavelike network, as shown in Fig. 2c.
2.6. Synthesis of [Ni(oba)(bpe)1.5]ꢀ2.5H2O (4)
A mixture of Ni(NO3)2ꢀ6H2O (0.1 mmol), H2oba (0.1 mmol), bpe
(0.2 mmol), and water (10 mL) was placed in a Teflon reac-
tor(23 mL). The pH was adjusted to 7.0 by addition of triethyl-
amine, the mixture was heated at 160 °C for three days, and then
it was cooled to room temperature at 5 °C hꢁ1. Blue crystals of 3
3.3. Crystal structures of [Ni2(oba)2(bpe)] (3)
The asymmetric unit of 3 comprises one Ni atom, one oba dian-
ion, and half a bpe molecule which is disposed about a centre of

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L. Tang et al. / Polyhedron 88 (2015) 116–124
Table 1
Crystal data and structural refinement summary of the compounds 1–4.
Identification code
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
26H16N2O5Cu
C26H16N2O5Co
495.34
monoclinic
C2
20.7753(17)
10.2481(8)
9.9514(8)
90
104.1010(10)
90
2054.9(3)
1.601
C40H26N2O10Ni2
812.05
C32H28N3O7.5Ni
633.27
monoclinic
C2/c
36.400(7)
10.400(2)
16.800(3)
90
102.00(3)
90
6221(2)
1.342
499.96
triclinic
P1
triclinic
ꢀ
ꢀ
P1
10.027(3)
10.721(4)
12.044(4)
67.201(6)
65.580(5)
63.977(5)
1025.2(6)
1.620
8.2104(11)
11.026(2)
11.2571(14)
116.098(6)
93.817(15)
109.619(9)
833.9(2)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Dcalc (Mg mꢁ3
)
1.617
Z
2
2
1
8
l
(mmꢁ1
)
1.110
1.031
0.880
1.012
1.197
1.005
0.676
1.008
Goodness-of-fit (GOF) on F2
Final R indices [I > 2 (I)]
Largest difference in peak and hole (e Åꢁ3
r
R1 = 0.0446, wR2 = 0.0907
0.313 and ꢁ0.358
R1 = 0.0219, wR2 = 0.0671
0.286 and ꢁ0.441
R1 = 0.0580, wR2 = 0.1330
0.451 and ꢁ0.699
R1 = 0.0732, wR2 = 0.1576
0.440 and ꢁ0.285
)
Fig. 1. (a) The Cu(II) binuclear unit of compound 1. All hydrogen atoms are omitted for clarity. (b) The 1D supermolecular chain of 1.
inversion (Fig. 3a). Each end of the oba ligand bridges a pair of Ni
atoms to result in a paddle-wheel of the type [Ni2(OOCR)4], which
comprises two nickel metals and four di(monodentate) bridging
carboxylates. The bond length of Cd–N is 2.169(4) Å and the
Ni–O bond lengths lie in the range of 1.960(3)–1.977(4) Å. In addi-
tion, the distances of Ni1–Ni1A is 2.6494 (12) Å, indicating a Ni–Ni
single bond. Each NiII center has a pseudo-octahedral geometry,
whose equatorial plane consists of four oxygen atoms from four
oba carboxylates, the axial positions are occupied by one Ni atom
and one N atom from the bpe ligand. In 3 the oba ligands show a
bis(bridging-bidentate) mode (Mode B in Scheme S1 in the sup-
porting information), two nickel metals (Ni1 and Ni1A) and four
oba ligands form the paddle-wheel SBUs, which are linked by
oba ligands to give a 1D loop shaped chain in the [100] direction
(Fig. 3b). The 1D loop shaped chains are further bridged by the
bpe ligands to produce 2D wavy layer lying the ac plane (Fig. 3c).
3.4. Crystal structures of [Ni(oba)(bpe)1.5]ꢀ2.5H2O (4)
Single-crystal X-ray analysis reveals that compound 4 shows a 2-
fold interpenetrating 3D structure with 2D brick-wall networks.
Each six-coordinated NiII center is surrounded by three nitrogen
atoms coming from three different bpe ligands, and three oxygen
atoms from one oba ligands, taking a distorted octahedral geometry
(Fig. 4a). The bond lengths of Ni-N and Ni-O are in the range of
2.041(4)–2.107(3) Å and 2.006(3)–2.107(3) Å, respectively. Nota-
bly, the oba ligands in 3 show one another coordination mode differ-
ent from compounds 1–3, a tridentate chelating coordination mode
(Mode C in Scheme S1 in the supporting information) to link every
NiII ion, and that each NiII ion is linked by three bpe ligands bridges
to generate a 2D brick-wall layer along the ac plane (Fig. 4b). Fur-
ther, two such 2D brick-wall networks interpenetrate to each other,
resulting in a 2-fold interpenetrating 3D framework (Fig. 4c).

L. Tang et al. / Polyhedron 88 (2015) 116–124
119
Fig. 2. (a) The coordination environments of Co(II) ions in compound 2. All hydrogen atoms are omitted for clarity. (b) The 1D right-handed helical chain of 2. (c) The 2D
wavelike network of 2.
3.5. Structural diversity of 1–4
different dimensional frameworks (compound 1 for 0D, compound
2 for 1D, compound 3 and 4 for 2D). The different N-containing co-
ligands and metal ions were employed to investigate their influence
on the structure of compounds, which will influence the final coor-
dination architectures. Compare 1 and 2: when a chelate ligand
(phen) and CuII ions are employed to generate 0D structure for 1,
changing metal center from CuII to CoII ion and forming a 1D
It is noteworthy that a variety of framework structures can be
achieved on the basis of the choice of 2,20-oxybis(benzoic acid)
and N-containing auxiliary ligands. From oba containing com-
pounds 1–4, oba ligand shows three types of coordination modes:
mode A for 1 and 2, mode B for 3 and mode C for 4, resulting in three

120
L. Tang et al. / Polyhedron 88 (2015) 116–124
Fig. 3. (a) The coordination environments of Ni(II) ions in compound 3. All hydrogen atoms are omitted for clarity. (b) The 1D loop shaped chain of 3. (c) The 2D wave-like
layer of 3.
right-handed helical chain for 2. In 3 and 4, when a linear ligand
(bpe) and NiII ions are attended, two 2D layer structures are
obtained. By comparing of the structures of compounds 1–4, the
N-donor ligand and metal ions can also slightly tune the final struc-
tural features.
This framework remains begin to decompose at 225 °C and decom-
position finishes at 500 °C. Compounds 1 and 2 indicate the final
residue to be CuO and CoO, respectively. The final decomposition
products of 3 and 4 were confirmed to be NiO, which have also
been further confirmed by PXRD patterns of compounds.
3.6. Thermogravimetric analysis
3.7. Magnetic property
To study the thermal stability of 1–4, thermogravimetric (TG)
analyses were performed on polycrystalline samples under a nitro-
gen atmosphere with a heating rate of 10 °C/min (see Figs. S1–S4 in
the supporting information). The TG curves of 1 and 2 are very sim-
ilar, no weight loss were observed until 240 °C for 1 and 210 °C for
2, above which, significant weight loss occurred and ended at
about 460 °C for 1 and 440 °C for 2, indicating complete decompo-
sition of the oba and phen ligands. The whole weight losses of 1
and 2 were in accordance with the expected value (obsd 87.4%
and 88.3%, calcd 87.29% and 88.10%). The TG curve of 3 shows
two step weight losses, the first weight loss in the range 220–
300 °C (obsd 22.6%, calcd. 22.44%) was assignable to the loss of
bpe ligand. The two weight loss (obsd 63.2%) should correspond
to the decomposition of the oba ligand (calcd. 63.10%) in the range
of 310–450 °C. The TG curve of 4 reveals that the first weight loss of
7.3% from 80 to 120 °C corresponds to the loss of the lattice water
molecules (calcd. 7.11%), leaving a framework of [Ni(oba)(bpe)1.5].
The magnetic susceptibility data measured for 1 from 3 to 300 K
is shown in Fig. 5a. As observed, the experimental
vMT value at
300 K is 0.728 cm3ꢀKꢀmolꢁ1, which is littler than the expected value
(0.750 cm3ꢀKꢀmolꢁ1) of the two isolated spin-only Cu(II) ions
(S = 1). The
vMT value of 1 remains almost constant from 300 to
30 K, and then decreases on further cooling, decreasing speedily
a value of 0.255 cm3ꢀKꢀmolꢁ1 at 3 K. The temperature dependence
of the reciprocal susceptibilities (1/vM) obeys the Curie–Weiss
law (v
= C/(T ꢁ h)) above 3 K with h = ꢁ4.862 K, C = 0.378 cm3ꢀ
Kꢀmolꢁ1 and R = 3.842 ꢂ 10ꢁ5. The negative values of h for 1 indi-
cate weak antiferromagnetic interactions between the adjacent
Cu(II) ions.
The susceptibility data of 2 were measured from 5 to 300 K
(Fig. 5b). It can be observed as the experimental vMT value remains
practically constant from 300 to 75 K, and then decreases when
cooling down to a value of 1.458 cm3ꢀKꢀmolꢁ1 at 5 K. The
vMT value
at 300 K is 1.905 cm3ꢀKꢀmolꢁ1, which is somewhat larger than the

L. Tang et al. / Polyhedron 88 (2015) 116–124
121
Fig. 4. (a) The coordination environments of Ni(II) ions in compound 4. All hydrogen atoms and the free H2O molecules are omitted for clarity. (b) The 2D brick-wall layer of 4.
(c) The 2-fold interpenetrating 3D framework of 4.

122
L. Tang et al. / Polyhedron 88 (2015) 116–124
Fig. 5. Thermal variation of vM and
v
MT for 1 (a), 2 (b) and 4 (c). Open points are the experimental data, and the solid line represents the best fit obtained from the
Hamiltonian given in the text.
expected value (1.875 cm3ꢀKꢀmolꢁ1) of the spin-only Co(II) ions
(S = 3/2). Reciprocal susceptibility obeys the Curie–Weiss law from
300 K down to 5 K with values of h = ꢁ1.762 K, C = 0.894 cm3ꢀ
Kꢀmolꢁ1 and R = 4.082 ꢂ 10ꢁ4. The values of h for 2 indicate weak
antiferromagnetic interactions between the adjacent Co(II) ions.
The susceptibility data of 4 were measured from 4.4 to 300 K
In these compounds, this behavior indicates a dominant antifer-
romagnetic interaction between the M(II) ions in the structures.
Compound 1 is 0D structure and compound 2 is a 1D helical chain
structure. The Cuꢀ ꢀ ꢀCu distance across the carboxylate groups of
oba ligands is 6.435 Å in 1, and the Coꢀ ꢀ ꢀCo separation through
the oba ligand is 6.323 Å in 2. In comparison to compound 1 and
2, the magnetic exchange coupling through the oba ligands is rel-
atively strong in 1 than in 2, the magnetic exchange coupling
may be due to the different metal ions. However, compound 4 fea-
tures a 2-fold interpenetrating 3D structure with 2D brick-wall
networks, the Niꢀ ꢀ ꢀNi separation through the bpe ligand is
13.412 Å in 4, compound 4 indicate weak antiferromagnetic inter-
actions, which is owed to the greater distances between the metal
ions.
(Fig. 5c). As observed, the experimental
vMT value decreases from
1.043 cm3ꢀKꢀmolꢁ1 at room temperature to 0.001 cm3ꢀKꢀmolꢁ1 at
10 K. The reciprocal susceptibility obeys the Curie–Weiss law from
300 K down to 100 K with values of h = ꢁ9.89 K, C = 1.12 cm3ꢀ
Kꢀmolꢁ1 and R = 4.146 ꢂ 10ꢁ4. The values of h for 4 indicate weak
antiferromagnetic interactions between the adjacent Ni(II) ions.
To simulate the experimental magnetic behavior, we analyzed
the experimental
vMT data of 1 by the dinuclear models as
expressed by Eq. (1) [30]. However, we used the analytical expres-
sion by a one-dimensional Heisenberg chain of classical spins for 2
and 4, the magnetic susceptibility was given in Eq. (2) [31].
3.8. Optimized geometry structure of 1–4
2Ng2b2
kT
expðꢁJ=kTÞ
The theoretical calculations of 1–4 would be a difficult task for
such a large periodical system. Here, the molecule structures of 2–
4 were intercepted except compound 1, and then the geometries of
the intercepting units of 2–4 and dinuclear unit of 1 were opti-
mized by the DFT method with the B3LYP functional. The data of
the main bond lengths and bond angles for 1–4 in the optimization
structure are showed in Table S1. The bond length calculated are
slightly less than those experimental values, and the Dcal.-exp.(the
difference between calculated and experimental values) of bond
lengths is range from 0.001 to 0.016 Å. The highest deviation is
about 0.41° for the bond angles in compounds 1–4. There is a little
deviation between the calculation and the experimental values.
The reason of the deviation is maybe as follows: the approximation
vM
vM
¼
ꢀ
ð1Þ
ð2Þ
1 þ 3expðꢁJ=kTÞ
ꢀ
ꢁ
ꢀ
ꢁ
Ng2b2SðSþ1Þ 1þu
JSðSþ1Þ
kT
JSðSþ1Þ
¼
ꢀ
; where u ¼ coth
ꢁ
3kT
1ꢁu
kT
Regarding the dinuclear copper of compound 1, this expression
fits very well with the experimental susceptibilities, giving
J = ꢁ15.9cmꢁ1, g = 1.99 and R = 2.18 ꢂ 10ꢁ5. Concerning the com-
pounds 2 and 4, the best fit of Eq. (2) to the experimental data were
achieved with J = ꢁ1.87 cmꢁ1, g = 2.19, R = 3.46 ꢂ 10ꢁ4 for 2 and
J = ꢁ2.62 cmꢁ1, g = 2.23, R = 4.28 ꢂ 10ꢁ4 for 4, where the J value
is in agreement with the value of h deduced above.

L. Tang et al. / Polyhedron 88 (2015) 116–124
123
Table 2
Calculated energy(au.) and magnetic exchange constant J (cmꢁ1) for 1, 2 and 4.
Compound
EBS/(au.)
EHS/(au.)
Calculation J/(cmꢁ1
)
Experiment J/(cmꢁ1
)
1
2
4
ꢁ6252.209103
ꢁ5662.903639
ꢁ6379.937968
ꢁ6252.209057
ꢁ5662.903513
ꢁ6379.937892
ꢁ10.10
ꢁ4.61
ꢁ5.56
ꢁ15.9
ꢁ1.87
ꢁ2.62
of calculation methods and basis set, the neglect of anionic effect in
the course of calculation and the chemical environmental differ-
ence of the complex. The deviation can be accepted in theoretical
calculation for a big system.
and 2, compound 1 is 0D structure, and compound 2 is a 1D helical
chain structure. When chelate ligand was substituted with linear
ligand, we gain compounds 3 and 4, which compound 3 displays
a 2D wavy layer with the paddle-wheel SBUs and compound 4 fea-
tures a 2-fold interpenetrating 3D structure with 2D brick-wall
networks. By comparing of the structures of compounds 1–4, the
N-donor ligand and metal ions can also slightly tune the final
structural features. Moreover, magnetic properties of compounds
1, 2 and 4 have also been investigated. According to the crystal
structures, the DFT-BS approach was applied to study the magnetic
coupling behavior for compounds 1, 2 and 4, the result reveals that
the calculated exchange coupling constants J were in good agree-
ment with the experimental data.
3.9. Magnetic properties of DFT calculations
The DFT calculations have been widely proved to be one of the
most efficient tools to investigate magnetic structure of transition
metal complexes [32–34]. We used a phenomenological Heisen-
^
^
^
berg Hamiltonian H ¼ ꢁJ S1 ꢀ S2 to describe the exchange coupling
in a dinuclear compound, the coupling constant J can be related
to the energy difference between the lowest and highest spin
states. For the case in which S1 = S2, the coupling constant may
be obtained by using the following Eq. (3) [35].
Acknowledgments
EHS ꢁ ELS ¼ ꢁ2JSiðSi þ 1=2Þ
Where EHS is the energy that corresponds to the state with the
highest total spin, ELS corresponds to the state with the lowest total
spin (S = 0), and Si is the total spin on each metal atom.
When using DFT-based wave functions, a reasonable estimate
of the energy corresponding to the low spin state, ELS can be
obtained directly from the energy of a broken-symmetry solution
EBS. In this case, introducing the copper (Si = 1/2), cobalt (Si = 3/2)
and nickel (Si = 1) dinuclear compounds for 1, 2 and 4, respectively,
we arrive to the following expressions for J:
ð3Þ
This work was supported by the National Natural Science
Foundation of China (No. 21373178), the Nature Scientific
Research Foundation of Shaanxi Provincial Education Department
(No. 2013Jk0668), the Nature Scientific Research and Overall inno-
vation plan major project of Shaanxi Provincial Education Office of
China (No. 2012KTCL03-16), the National College Students’ innova-
tion and entrepreneurship training program (201310719002).
Thanks to Professor Wang Wen-liang of Shaanxi Normal University
provided Gauss calculation Software.
Appendix A. Supplementary data
EHS ꢁ EBS ¼ ꢁJCuACu
EHS ꢁ EBS ¼ ꢁ6JCoACo
EHS ꢁ EBS ¼ ꢁ3JNiANi
ð4Þ
ð5Þ
ð6Þ
CCDC 1025824–1025827 contains the supplementary
crystallographic data for 1–4. 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 http://dx.doi.org/10.
1016/j.poly.2014.12.023.
The calculated coupling constant J and related quantities are
listed in Table 2. We have used via Eqs. (4)–(6) to estimate the
magnetic coupling constants (J) of compounds 1, 2 and 4. The com-
puted J values (J = ꢁ10.10 cmꢁ1 for 1, J = ꢁ4.61 cmꢁ1 for 2 and
J = ꢁ5.56 cmꢁ1 for 3) predict antiferromagnetic, the results were
agreed with the experimental data. We have used the non-spin
projected, giving a better agreement for compounds 1, 2 and 4. This
is due to the strong localization of the wavefunction at the metal
centers both computational technics produce results that are in
remarkable agreement with the experimental value. Full molecule
calculation using hybrid B3LYP functional to reproduce BS–HS
energy gap of compounds is not only found to be successful in
describing the magnetic behavior of the compounds correctly in
this study but also yielded J that are in excellent agreement with
the experimental value. So the full molecule DFT based calculation
based on X-ray structural data could be successfully used to ratio-
nalize the magnetic behavior of this class of compounds.
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