Structural diversity of Ni(ii) coordination polymers containing dipyridyl amide and angular dicarboxylate ligands: Synthesis, structures and magnetism

Article abstract of DOI:10.1039/c3ce26928k

Four new Ni(ii) coordination polymers containing dipyridyl amide and angular dicarboxylate ligands, {[Ni(L¹)(MBA)]·2H ₂O}_∞ [L¹ = N,N′-di(4-pyridyl)- adipoamide; H₂MBA = diphenylmethane-4,4′-dicarboxylic acid], 1, {[Ni(L¹)(OBA)]·H₂O}_∞ [H ₂OBA = 4,4′-oxybis(benzoic acid)], 2, {[Ni(L ¹)(SDA)]·2H₂O}_∞ (H₂SDA = 4,4′-sulfonyldibenzoic acid), 3, and {[Ni₂(L ²)(SDA)₂]·6H₂O}_∞ [L² = N,N′-di(4-pyridyl)suberoamide], 4, have been synthesized by hydrothermal reactions and were structurally characterized by single crystal X-ray diffraction analyses. Complex 1 is a 1D → 2D polycatenane derived from the helical channels, and the 2D layers are further mutually interdigitated, whereas complex 2 forms 2D rhombic grids with the (6,4) topology, which are interwoven with each other to give a two fold 2D → 2D interpenetrating net. Complex 3 shows the 1D looped chain structure, and complex 4 shows 2D layers which catenate to each other to form a 2D → 3D inclined polycatenation framework with the new (4²·6 ⁸·8·10⁴)(4)₂ topology. The C-X-C (X = CH₂, 1; O, 2; and SO₂, 3 and 4) angles are important in determining the structural diversity. Complex 1 exhibits a different magnetic reaction in the ZFC and FC processes, revealing the existence of a meta-state of ferromagnetic ordering, whereas the activation energies of spin-orbit coupling and antiferromagnetic interaction of complexes 2-4 are directed by the N...N and Ni...Ni distances, respectively.

Full text of DOI:10.1039/c3ce26928k

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PAPER
Structural diversity of Ni(II) coordination polymers
containing dipyridyl amide and angular dicarboxylate
ligands: synthesis, structures and magnetism3
Cite this: CrystEngComm, 2013, 15,
3974
Yu-Hung Liao,a Wayne Hsu,a Chun-Chuen Yang,*b Can-Yu Wu,b Jhy-Der Chen*a
and Ju-Chun Wangc
Four new Ni(II) coordination polymers containing dipyridyl amide and angular dicarboxylate ligands,
{[Ni(L1)(MBA)]?2H2O}‘ [L1 = N,N9-di(4-pyridyl)-adipoamide; H2MBA = diphenylmethane-4,49-dicarboxylic
acid], 1, {[Ni(L1)(OBA)]?H2O}‘ [H2OBA = 4,49-oxybis(benzoic acid)], 2, {[Ni(L1)(SDA)]?2H2O}‘ (H2SDA =
4,49-sulfonyldibenzoic acid), 3, and {[Ni2(L2)(SDA)2]?6H2O}‘ [L2 = N,N9-di(4-pyridyl)suberoamide], 4, have
been synthesized by hydrothermal reactions and were structurally characterized by single crystal X-ray
diffraction analyses. Complex 1 is a 1D A 2D polycatenane derived from the helical channels, and the 2D
layers are further mutually interdigitated, whereas complex 2 forms 2D rhombic grids with the (6,4)
topology, which are interwoven with each other to give a two fold 2D A 2D interpenetrating net.
Complex 3 shows the 1D looped chain structure, and complex 4 shows 2D layers which catenate to each
other to form a 2D A 3D inclined polycatenation framework with the new (42?68?8?104)(4)2 topology. The
C–X–C (X = CH2, 1; O, 2; and SO2, 3 and 4) angles are important in determining the structural diversity.
Complex 1 exhibits a different magnetic reaction in the ZFC and FC processes, revealing the existence of a
meta-state of ferromagnetic ordering, whereas the activation energies of spin–orbit coupling and
Received 27th November 2012,
Accepted 8th March 2013
DOI: 10.1039/c3ce26928k
…
…
antiferromagnetic interaction of complexes 2–4 are directed by the N N and Ni Ni distances,
www.rsc.org/crystengcomm
respectively.
mixed ligand system.6,7 However, due to the difficult predic-
tion of the resulting structure, the influential principles for
such a system are less ascertained and not conclusive.
Moreover, the formation of the bridge by the carboxylate
groups can inspire spin communication between adjacent
paramagnetic metal ions.
By using the linear and angular dicarboxylic acids and the
dipyridyl amide ligands N,N9-di(3-pyridyl)adipoamide and
N,N9-di(4-pyridyl)adipoamide (L1), we have recently shown
that the structural types and degree of interpenetration of
these Cd(II) coordination networks can be tuned by changing
the shapes of the dicarboxylate ligands. For complexes with
the L1 ligands, those with the linear dicarboxylate ligands form
the 3D interpenetrated coordination networks, whereas those
with the angular dicarboxylate ligands form coordination
Introduction
The syntheses and characterization of coordination polymers
have been the subject of intense focus during recent years.
These new complexes thus prepared have attracted great
attention not only due to their intriguing topological features
but also their potential applications in areas such as gas
storage, separation, catalysis, ion exchange and magnetism.1
The range and variety of the self-assembling structures that
can be constructed relies on the presence of suitable metal–
ligand interactions and supramolecular contacts, i.e., hydro-
gen bonding and other weak interactions,2 which are also
affected by factors such as counterion,3 metal-to-ligand ratio4
and solvent.5 The dicarboxylate ligands have been widely
adopted for the generation of new coordination networks in a
networks with less dimensionality, involving 1D
A 2D
aDepartment of Chemistry, Chung-Yuan Christian University, Chung-Li, Taiwan,
R.O.C.
bDepartment of Physics, Chung-Yuan Christian University, Chung-Li, Taiwan, R.O.C.
cDepartment of Chemistry, Soochow University, Taipei, Taiwan, R. O. C.
polycatenane and 2-fold 2D A 2D parallel interpenetration
network containing a rotaxane-like motif.7b To investigate the
influence of the bridging atom/group of the angular dicarbox-
ylate ligands on the structural diversity and to explore the
relationship between the magnetism and the structures of the
obtained coordination networks, we have reacted Ni(II) salts
and the flexible dipyridyl amide ligands, N,N9-di(4-pyridyl)-
adipoamide (L1) and N,N9-di(4-pyridyl)suberoamide (L2), with a
Electronic supplementary information (ESI) available: TGA curves for 1–4 (Fig.
3
S1). xT–T curves of complexes 1–4 (Fig. S2). Selected bond distances (Å) and
angles (u) for complexes 1–4 (Tables S1–S4). C–X–C angles of MBA22, OBA22 and
SDA22 ligands in known metal complexes (Table S5). CCDC 912093–912096. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3ce26928k
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crystal X-ray diffraction. Yield: 0.037 g (58%). Anal. calcd for
series of dicarboxylic acids, diphenylmethane-4,49-dicarboxylic
acid (H2MBA), 4,49-oxybis(benzoic acid) (H2OBA) and 4,49-sul-
C
31H32N4NiO8 (MW = 647.32): C, 57.52; H, 4.98; N, 8.66.
Found: C, 57.65; H, 4.68; N, 8.36%. IR (cm21): 3466 (w), 2991
(br), 1697 (m), 1602 (s), 1523 (s), 1427 (s), 1378 (m), 1327 (m),
1297 (m), 1214 (m), 1178 (m), 868 (m), 841 (m), 765 (m), 527
(m).
fonyldibenzoic
acid
(H2SDA),
which
afforded
2,
{[Ni(L1)(MBA)]?2H2O}‘,
1,
{[Ni(L1)(OBA)]?H2O}‘,
{[Ni(L1)(SDA)]?2H2O}‘, 3, and {[Ni2(L2)(SDA)2]?6H2O}‘, 4. The
syntheses, structures and thermal and magnetic properties of
these four complexes form the subject of this report.
{[Ni(L1)(OBA)]?H2O}‘, 2. Prepared as described for 1 except
that Ni(OAc)2?4H2O (0.025 g, 0.10 mmol) and H2OBA (0.026 g,
0.10 mmol) in 5 mL CH3OH solution were used. Yield: 0.049 g
(76%). Anal. calcd for C30H28N4NiO8 (MW = 631.27): C, 57.08;
H, 4.47; N, 8.87. Found: C, 56.90; H, 4.67; N, 8.81%. IR (cm21):
3535 (m), 3245 (br), 2490 (w), 1711 (w), 1598 (s), 1520 (s), 1418
(w), 1243 (br), 1169 (br), 876 (w), 839 (w), 784 (w), 670 (br).
{[Ni(L1)(SDA)]?2H2O}‘, 3. Prepared as described for 1, except
that Ni(NO3)2?6H2O (0.029 g, 0.10 mmol) and H2SDA (0.031 g,
0.10 mmol) in 5 mL CH3OH solution were used. Yield: 0.045 g
(64%). Anal. calcd for C30H30N4NiO10S (MW = 697.33): C,
51.67; H, 4.34; N, 8.03. Found: C, 52.17; H, 4.31; N, 8.14%. IR
(cm21): 3408 (m), 3279 (w), 3168 (w), 2332 (w), 1705 (m), 1596
(s), 1513 (s), 1424 (s), 1296 (m), 1162 (m), 1020 (w), 842 (w), 745
(s), 648 (w), 615 (w).
{[Ni2(L2)(SDA)2]?6H2O}‘, 4. Prepared as described for 1
except that Ni(NO3)2?6H2O (0.058 g, 0.20 mmol), L2 (0.033 g,
0.10 mmol) and H2SDA (0.062 g, 0.20 mmol) and 7.5 mL
CH3OH were used. Yield: 0.075 g (66%). Anal. calcd for
C46H50N4Ni2O20S2 (MW = 1160.44): C, 47.69; H, 4.18; N, 4.84.
Found: C, 47.72; H, 3.91; N, 4.52%. IR (cm21): 3445 (s), 2922
(w), 2359 (w), 1690 (m), 1602 (s), 1566 (s), 1525 (s), 1430 (s),
1401 (s), 1304 (s), 1216 (s), 1168 (s), 1101 (s), 835 (s), 778 (s),
740 (s), 694 (m), 618 (s).
Experimental section
Thermal gravimetric analysis. The samples were heated up
in nitrogen gas at a pressure of 1 atm with a heating rate of 10
uC min21 and finished at 700 uC. The thermal gravimetric
analysis (TGA) curve of 1 shows the gradual weight loss of
water molecules (calculated 5.56%, observed 5.30%) in 56–193
uC. The host framework starts to decompose at ca. 251 uC and
the weight loss of 84.78% between 251 and 418 uC corresponds
to the decomposition of L1 ligand and MBA ligand (calculated
85.31%). For complex 2, the TGA curve shows the gradual
weight loss of the water molecule (calculated 2.85%, observed
2.35%) in 84–208 uC. The host framework starts to decompose
at ca. 244 uC and the weight loss of 87.84% between 244 and
426 uC corresponds to the decomposition of L1 ligand and OBA
ligand (calculated 87.44%). The TGA curve of complex 3 shows
the gradual weight loss of water molecules (calculated 5.17%,
observed 3.05%) at 29–108 uC. The weight loss of 87.41%
between 233 and 451 uC corresponds to the decomposition of
L1 ligand and SDA ligand (calculated 86.41%). The TGA curve
of complex 4 shows the gradual weight loss of water molecules
(calculated 9.31%, observed 7.07%) at 31–93 uC, followed by
the decomposition of the host framework at ca. 314 uC. The
weight loss of 76.22% between 314 and 510 uC is due to the
decomposition of L2 ligand and SDA ligand (calculated
82.56%).
General procedures
Elemental analyses were performed on a PE 2400 series II
CHNS/O analyzer or a Vario EL-III analyzer. IR spectra (KBr
disk) were recorded on a JASCO FT/IR-460 plus spectro-
photometer. Thermal gravimetric analyses (TGA) measure-
ments were carried out on a TG/DTA 6200 analyzer over the
temperature range of 30 to 900 uC at a heating rate of 10 uC
min21
.
Materials
The reagents Ni(OAc)2?4H2O and 4,49-oxybis(benzoic acid)
were purchased from Alfa Aesar Co., Ni(NO3)2?6H2O from
Acros Organics Co., NiBr2 from Merck Schuchardt, diphenyl-
methane-4,49-dicarboxylic acid from Matrix Scientific Co. and
4,49-sulfonyldibenzoic from Aldrich Chemistry Co. The ligands
N,N9-di(4-pyridyl)adipoamide (L1) and N,N9-di(4-pyridyl)suber-
oamide (L2) were prepared according to published proce-
dures.8
Preparation
{[Ni(L1)(MBA)]?2H2O}‘, 1. A mixture of NiBr2 (0.022 g, 0.10
mmol), L1 (0.030 g, 0.10 mmol), H2MBA (0.026 g, 0.10 mmol)
and 5 mL NaOH (0.04 M) solution was sealed in a 23 mL
Teflon-lined stainless steel autoclave, which was heated under
autogenous pressure to 120 uC for two days. Slow cooling of
the reaction system afforded green crystals suitable for single
X-ray crystallography. The diffraction data for complexes 1–4
were collected on a Bruker AXS SMART APEX II CCD
diffractometer at 22 uC, which was equipped with a graphite-
monochromated Mo Ka (la = 0.71073 Å) radiation. Data
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reduction was carried by standard methods with use of well-
established computational procedures.9 The structure factors
were obtained after Lorentz and polarization. An empirical
absorption correction based on ‘‘multi-scan’’ was applied to
the data for all complexes. The position of some of the heavier
atoms, including the nickel atom, was located by the direct
method.10 The remaining atoms were found in a series of
alternating difference Fourier maps and least-square refine-
ments, while the hydrogen atoms, except those of the water
molecules, were added by using the HADD command in
SHELXTL 5.10. The hydrogen atoms of the water molecules of
1 were located from alternating difference Fourier maps and
refined isotropically, whereas those of 2 and 4 were first
located from the alternating difference Fourier maps and then
fixed as riding atoms by using the HADD command. The
structure of 3 has a disorder problem and the hydrogen atoms
of the water molecules were not located. Basic information
pertaining to crystal parameters and structure refinement is
summarized in Table 1. Selected bond distances and angles
Results and discussions
Structure of 1
Fig. 1a shows the coordination environment about the Ni(II)
metal center, which is six-coordinated by two nitrogen atoms
from two L1 ligands [Ni–N = 2.045(3) and 2.050(3) Å] and four
oxygen atoms from two m2-k2,k2-MBA22 ligands [Ni–O =
2.052(1)–2.191(2) Å], resulting in
a distorted octahedral
geometry. The Ni(II) ions are interlinked by two L1 and two
MBA22 ligands to give 1D infinite helical channels, Fig. 1b,
and the Ni(II) ions are separated by distances that are 16.30
(through L1) and 14.31 (through MBA22) Å. Each helical
channel is polycatenated by two others, giving a 1D A 2D
polycatenated network, with density of catenation (Doc) = 2
and index of separation (Is) = 1,11 Fig. 1c. In addition, these
polycatenated helical channels interdigitate to each other by
directing the back-carbon atoms of the L1 ligands into the
…
windows of the adjacent nets, Fig. 1d. The shortest Ni Ni
distance between the adjacent nets is found to be 7.66 Å.
The different nets are linked by the water molecules through
are listed in Tables S1–S4, ESI.
3
…
Magnetic susceptibility measurement. Magnetic susceptibil-
ity measurements were performed using MPMS-XL (SQUID)
from Quantum Design with the standard setup. The samples
were cooled to 1.8 K in the absence of an applied magnetic
field at the center of signal pickup coils. x–T experiments were
carried out using both the zero field cooling (ZFC) and the
field cooling (FC) methods to determine the ordering
temperature of samples. Magnetic hysteresis loops were
measured to study the magnetization responses to various
applied magnetic fields (M–H curve), and to determine the
thermal average of the z component of the saturated magnetic
moment ,mz.s per chemical formula unit.
O–H O hydrogen bonds to the amide carbonyl oxygen atoms
1
…
…
of the L ligands [O O = 2.827(4) Å, /O–H O = 165(4)u and
…
…
O
O = 2.790(4) Å, /O–H O = 173(4)u] and to the carboxylate
oxygen atoms [O O = 2.769(4), /O–H O = 173(5)u and
…
…
…
…
…
2.753(4) Å, /O–H O = 172(5)u]. N–H O [N O = 2.818(4) Å,
…
…
…
/N–H O = 176.6(2)u and N O = 2.848(4) Å, /N–H O =
173.2(2)u] hydrogen bonds from the amine hydrogen atoms of
the L1 ligands to the oxygen atoms of the water molecules are
also observed. The solvent-accessible volume calculated by
PLATON program12 is 315.5 Å3, which is 10.0% of the unit cell
volume.
Table 1 Crystal data for complexes 1–4
Complex
1
2
3
4
Formula
Formula weight
C31H32N4NiO8
647.32
C30H28N4NiO8
631.27
C30H30N4NiO10
697.35
S
C46H50N4Ni2O20S2
1160.44
Crystal system
Space group
Monoclinic
P21/c
Orthorhombic
Pnna
Orthorhombic
Ima2
Monoclinic
C2/C
a, Å
b, Å
c, Å
11.9158(3)
14.3094(4)
18.5432(5)
94.685(1)
3151.20(15)
4
1.364
1352
0.671
12.4702(7)
22.7872(4)
11.0779(2)
90
3147.91(9)
4
1.332
1312
0.670
24.5212(18)
11.1701(8)
12.2369(8)
90
3351.7(4)
4
1.382
1448
0.700
21.5324(3)
12.8686(2)
20.5775(3)
93.497(1)
5691.24 (14)
4
1.354
2408
0.808
b, u
V, Å3
Z
Dcalc, mg mm23
F(000)
m (Mo Ka), mm21
Range (2h) for data collection, u 3.42 ¡ 2h ¡ 56.62
3.58 ¡ 2h ¡ 56.58
3.32 ¡ 2h ¡ 66.00
3.68 ¡ 2h ¡ 56.58
Independent reflections
7822
3921
5574
7030
[Rint = 0.0859]
7822/0/413
1.005
[Rint = 0.0329]
3921/0/214
1.072
[Rint = 0.0297]
5574/37/342
1.091
[Rint = 0.0396]
7030/0/323
1.057
Data/restraints/parameters
Quality-of-fit indicatora
Final R indices [I . 2s(I)]b
R indices (all data)
R1 = 0.0555, wR2 = 0.0900 R1 = 0.0420, wR2 = 0.1109 R1 = 0.0622, wR2 = 0.1706 R1 = 0.0567, wR2 = 0.1515
R1 = 0.1526, wR2 = 0.1125 R1 = 0.0736, wR2 = 0.1285 R1 = 0.0683, wR2 = 0.1760 R1 = 0.0990, wR2 = 0.1736
Quality-of-fit = [gw(|Fo22| 2 |Fc2|)2/(Nobserved 2 Nparameters)]1/2
.
R1 = g||Fo| 2 |Fc||/g|Fo|. wR2 = [gw(Fo 2 Fc2)2/gw(Fo2)2]1/2. w = 1/[s2(Fo2) +
a
b
2
(ap)2 + (bp)], p = [max(Fo or 0) + 2(Fc2)]/3. a = 0.0493, b = 0.0000, 1; a = 0.0606, b = 1.1538, 2; a = 0.0681, b = 2.7125, 3; a = 0.0877, b = 7.5828,
4.
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Fig. 1 (a) Coordination environment of Ni(II) ion in 1. Symmetry transformations
used to generate equivalent atoms: (A) 2x, y + 1/2, 2z + 3/2; (B) x, y + 1, z. (b) A
drawing showing the 1D helical channel chain. (c) A schematic view of 1D A 2D
…
polycatenated framework. (d) The different nets are linked through O–H
hydrogen bonds, which also interdigitate to each other.
O
Fig. 2 (a) Coordination environment of Ni(II) ion in 2. Symmetry transformations
used to generate equivalent atoms: (A) x, 2y + 1/2, 2z + 1/2. (b) A drawing
showing the 2D pleated net. (c) A drawing showing the 2-fold interpenetrated
…
Structure of 2
nets. (d) The two-fold interpenetrated sheets are interlinked through N–H
hydrogen bonds to form a 3D supramolecular structure.
O
The coordination sphere of the Ni(II) ion is shown in Fig. 2a.
The Ni(II) ion has a slightly distorted octahedral coordination
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geometry by two pyridyl nitrogen atoms from two L1 ligands
and four oxygen atoms from two OBA22 ligands, with Ni–O
distances of 2.104(3) and 2.126(3) Å and Ni–N distances of
2.022(3) Å. The adjacent Ni(II) atoms are linked to each other
by the L1 ligands and the OBA22 ligands through the pyridyl
nitrogen atoms and the oxygen atoms, respectively, to form a
two-dimensional rhombic grid structure, Fig. 2b, and the Ni(II)
ions are separated by distances that are 19.36 (through L1) and
14.70 (through OBA22) Å. The grid structure is not planar but
undulated, resulting from the inherent bent conformation of
the L1 molecules and OBA ligands. If the O atoms of the OBA22
ligands are defined as 2-connected nodes and the Ni(II) ions as
4-connected nodes, the structure of complex 2 can be regarded
as a 2,4-connected two-fold 2D A 2D parallel interpenetration
framework with the (64?82)(6) topology for the 2D layer,13
…
Fig. 2c. The shortest Ni Ni distance between the adjacent nets
is found to be 8.34 Å.
The adjacent two-fold interpenetrated sheets are interlinked
…
…
through the N–H O hydrogen bonds [N O = 2.916(6) Å, /N–
H
…
O = 159.7(3)u] between the carboxylate oxygen atoms and
amine hydrogen atoms of the L1 ligands, resulting in a 3D
supramolecular structure, Fig. 2d. The solvent-accessible
volume calculated by PLATON program is 400.2 Å3, which is
12.7% of the unit cell volume.
Structure of 3
The coordination sphere of the Ni(II) ion is shown in Fig. 3a.
Each Ni(II) ion is six-coordinated by two pyridyl nitrogen atoms
from two L1 ligands and four oxygen atoms from two
tetradentate SDA22 ligands, resulting in a slightly distorted
octahedral coordination geometry, with Ni–O distances of
2.075(2) and 2.156(2) Å and Ni–N distances of 2.110(1) and
1.957(9) Å. The adjacent Ni(II) ions are linked to each other by
the L1 and SDA22 ligands through the pyridyl nitrogen atoms
and the oxygen atoms, respectively, to form a one-dimensional
looped chain structure, and the adjacent Ni(II) ions are
…
separated by distances that are 12.26 Å. The shortest Ni Ni
distance between the adjacent chains is found to be 8.28 Å.
The L1 and SDA22 ligands are disordered such that four
disordered chains can be resolved. Fig. 3b shows one of the 1D
chains and Fig. 3c depicts the overlapped drawing of the four
disordered chains. Each chain is symmetry-related by the C2
axis passing through S atom of SDA22 ligand and the middle
of C(16)–C(17) bond of the L1 ligand. Noticeably, the rings of
the looped chains are mutually perpendicular but not parallel.
The 1D chains lie parallel to each other, forming 2D sheets
…
…
…
in the ab plane through N–H O [N O = 3.043(5) Å, /N–H O
= 159.1(3)u] hydrogen bonds between the carboxylate oxygen
atoms and amine hydrogen atoms of the L1 ligands, Fig. S2,
ESI, which are further stacked along the c direction by the
3
Fig. 3 (a) Coordination environment of Ni(II) ion in 3. Symmetry transformations
used to generate equivalent atoms: (A) 2x + 1, 2y + 1, z; (B) x 2 1/2, 2y + 1, z.
…
…
…
other N–H O [N O = 2.923(5) Å; /N–H O = 158.1(3)u]
hydrogen bonds, forming a 3D supramolecular structure,
Fig. 3d. The solvent-accessible volume calculated by PLATON
program is 243.7 Å3, which is 7.3% of the unit cell volume.
(b) A drawing showing the 1D looped chain. (c) A drawing showing the
…
disordered structure. (d) The 1D chains are interlinked through N–H
hydrogen bonds to form a 3D supramolecular structure.
O
Structure of 4
L2 ligand [Ni–N = 2.063(7) Å] and four oxygen atoms of the
SDA22 ligands [Ni–O = 2.248(7), 2.090(7), 2.066(7) and 2.016(7)
Å] to give a distorted square planar coordination geometry [/
Fig. 4a depicts a drawing showing the coordination environ-
ment about the Ni(II) ions, in which both of the Ni(1) and Ni(2)
ions are five-coordinated by one pyridyl nitrogen atom of the
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(42?68?8?104)(4)2 topology, determined using TOPOS.13
Moreover, the 2D layers are interlocked in a inclined fashion,
resulting in a 2D A 3D inclined polycatenation framework,
Fig. 4c.
The H2O molecules of 4 interact with each other to form
…
…
…
O
(H2O)3 trimers through O–H O [O O = 2.456(21) Å, /O–H
= 128.6(3)u] hydrogen bonds, which link the 2D nets through
…
…
…
…
O
…
N–H O [N O = 2.871(3) Å, /N–H O = 151.6(2)u] and O–H
hydrogen bonds to the oxygen atoms of the SO2 groups [O O =
…
2.948(11) Å, /O–H O = 112.6(7)u] and to the oxygen atoms of
…
…
the carboxylate groups [O O = 3.299(11) Å, /O–H O =
150.4(7)u], Fig. 4d. The solvent-accessible volume calculated
by PLATON program is 1648.0 Å3, which is 29.0% of the unit
cell volume.
Conformations of the ligands
It has been shown that L1 can be arranged in anti–anti–anti
(AAA), anti–anti–gauche (AAG), anti–gauche–anti (AGA), anti–
gauche–gauche (AGG), gauche–anti–gauche (GAG) and gauche–
gauche–gauche (GGG) conformations, and based on the relative
orientation of the CLO (or N–H) groups, each conformation
can adopt a cis or trans arrangement.8 The A and G
conformations are given when the C–C–C–C torsion angle (h)
is 0 ¡ h ¡ 90u and 90 ¡ h , 180u, respectively. Accordingly,
thirty-eight ligand conformations can be shown for the L2
ligand. Based on these descriptors, the L1 and L2 ligands in 1–
4 show four different conformations of AAG trans, AAG cis,
GAG cis and AGAGA trans, respectively, which also differ in the
dihedral angles between the two pyridyl rings, Table 2. The L1
and L2 ligands are thus sufficiently flexible and adopt the
conformations that maximize the intra- and intermolecular
forces.
Structural comparisons
Table 3 lists the C–X–C (X = CH2, 1; O, 2; SO2, 3 and 4) and
dihedral angles of the dicarboxylate ligands in complexes 1–4.
The coordination of the dicarboxylate and dipyridyl amide
ligands to the Ni(II) ions leads to different dihedral angles
between the phenyl rings of the dicarboxylate ligands and
different ligand conformations for the dipyridyl amide
ligands, respectively, resulting in different structural types.
However, the C–X–C angles of 115.3, 121.9, 101.8 and 102.8u in
these complexes are similar to those of the corresponding
MBA22, OBA22 and SDA22 ligands found for the known metal
complexes, which are 114.1u, 117.3–122.5u and 101.4–104.9u,
Fig. 4 (a) Coordination environment of Ni(II) ion in 4. Symmetry transformations
used to generate equivalent atoms: (A) 2x + 1, 2y + 1, 2z + 1; (B) x 2 1/2, y 2
1/2, z; (C) 2x + 3/2, 2y + 3/2, 2z + 1. (b) A drawing showing the 2D layer. (c) A
schematic drawing showing the inclined interpenetration. (d) The different nets
respectively, Table S5, ESI, indicating that the C–X–C angles
3
…
…
are interlinked through N–H O and O–H O hydrogen bonds.
are not subjected significantly to the changes of metal ions
and co-ligands. The structural diversity in 1–3 can thus be
ascribed to the different C–X–C angles due to the different
bridging atom/group of the angular dicarboxylate ligands. The
structural difference between 3 and 4 is most probably due to
the different donor atom positions between L1 and L2.
O(5A)–Ni(1)–O(4)
96.26(24)u, /O(5A)–Ni(1)–O(3)
Ni(1)–O(2) = 84.80(22)u]. Each Ni(II) ion is also interacting
with one carboxylate oxygen atom [Ni O(2) = Ni O(2A) =
2.345(2) Å]. The two symmetry-related Ni(II) ions are bridged by
four carboxylate groups of the SDA22 ligands, resulting in
paddlewheel type core structure with a metal separation of
2.71 Å, and forming infinite looped chain structures that are
connected by L2 ligands to give a 2D network, Fig. 4b.
Topological analysis reveals that the 2D layer adopts a new
=
164.98(27)u, /O(5A)–Ni(1)–N(1)
=
=
92.25(24)u and /O(5A)–
…
…
…
Noticeably, the N N distances between the two pyridyl
nitrogen atoms of the dipyridyl amide ligands are 13.46 Å for
1, 15.70 Å for 2, 9.97 Å for 3 and 16.64 Å for 4. Therefore,
…
flexible spacer ligands that show longer N N distances in the
solid state are better candidates for the formation of entangled
coordination networks due to their propensity to form large
voids.
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Table 2 Ligand conformations and corresponding angles for complexes 1–4
Diagram
Torsion angle (u)
Conformation
Dihedral angle (u)
1
2171.5, 2178.4, 77.2
AAG trans
75.6
2
3
4
174.1, 2165.3, 267.7
AAG cis
41.7
55.9
0
279.6, 173.4, 270.7
GAG cis
2173.7, 264.7, 2180.0, 64.7, 173.7
AGAGA trans
2 mB (spin 1, g = 2, ,mz.s = gJmB = 2 mB) of the [Ar]3d8 electronic
configuration. The fractional magnetic moments may originate
from the asymmetric distribution of charges in the bonding
environments, due to the different bonding strengths and crystal
fields from the two surrounding N and four O atoms. This
environmental factor may have weakened the effect of quenching
the orbital angular momentum orbital, further increasing
,mz.s.14 For complex 4, a relatively smaller ,mz.s of 0.32 mB
per f.u. was obtained, and an extra x0H term must be taken into
account in the Langevin equation. This result implies that the
Pauli exclusion principle plays an important role at 1.8 K, and
tends to arrange the spins of the bonding valence electrons of
nearest-neighbor Ni(II) ions in an anti-parallel manner and leads
to a reduction of the net magnetic moment.
Thermal properties
In order to estimate the stability of the frameworks, thermal
gravimetric analyses (TGA) of complexes 1–4 were carried out
in nitrogen atmosphere from 30 to 700 uC. The TGA results,
Fig. S1, ESI, show that the host frameworks of complexes 1–4
3
starts to decompose at ca. 251, 244, 233 and 314 uC,
respectively, indicating that the 2D A 3D inclined polycatena-
tion framework of 4 has the better thermal stability.
Magnetism
Magnetic hysteresis loop (M–H curve) and susceptibility (x–T
curve) were measured to identify the magnetic properties of
complexes 1–4. The hysteresis behaviors of all samples were
measured at both 1.8 K and 300 K to verify the formation of the
loop, Fig. 5. All the magnetizations of these complexes
increased linearly with the applied magnetic field below 1 T
at both 1.8 K and 300 K and gradually approached saturation
at 1.8 K in a field of 7 T. Since no hysteresis loop can be found,
the Langevin function
Fig. 6 shows the experimentally determined curves of
magnetic susceptibility against temperature. Both ZFC and
FC processes were performed for the four complexes. The
modified Curie–Weiss law in the form
ꢀ
ꢁ
C
x(T)~x0z
TzTh
1
mH
vmz(H)w~vmzws cothðxÞ{
,
x:
x
kBT
was first employed to fit the curves in the weakest applied fields.14
Here, C is the Curie constant, T is the temperature at which the
measurements were made, and Th is the fitted Weiss temperature.
was applied to these four curves to yield ,mz.s (saturation ,mz.),
which are listed in Table 4. The obtained ,mz.s of complexes 1–3
are 2.63, 2.55, and 2.17 mB per f.u., respectively, which are close to
Table 3 C–X–C angle (u) and dihedral angle (u) of the dicarboxylate ligands in complexes 1–4
Complex
Dicarboxylate/Xa
C–X–C angle
Dihedral angle
Structure
1
2
3
4
MBA22/CH2
OBA22/O
115.3
121.9
101.8
102.8
89.9
61.3
80.9, 86.0
84.3
1D A 2D polycatenane
2-fold 2D A 2D interpenetrating net
SDA22/SO2
SDA22/SO2
1D looped chain
2D A 3D inclined polycatenation
a
X is the bridging atom/group of the dicarboxylate ligand.
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ferromagnetic-like shape. For complex 4, the x–T curve exhibited
Curie–Weiss behavior only above 50 K and the relatively large Th
(14 K) indicates the strong antiferromagnetic coupling between
Ni(II) ions. To study further the magnetic behavior of these
complexes, the Rueff’s equation,15
E
E
2
kT
1
kT
xT~Ae{ zBe
{
is used. Here, the sum of A and B equals the Curie constant C, and
E1 and E2 are the ‘‘activation energies’’ of spin–orbit coupling and
the antiferromagnetic exchange interaction. This equation
describes the xT curve of complexes 2–4, but not complex 1,
owing to the antiferromagnetic phase transition. Table 4 and Fig.
S2, ESI, present the obtained fitting parameters and curves,
3
respectively. Clearly, the sums of A and B for complexes 2–4 are
equal or close to Curie constant C, obtained from the Curie–Weiss
law, indicating consistency between both models. The activation
energies of spin–orbit coupling, E1, which are 5.92, 61, and 0.32 K
for complexes 2, 3, and 4, respectively, are correlated with the
Fig. 5 Magnetic hysteresis loop of complexes (a) 1 (b) 2 (c) 3 and (d) 4. Solid
curves at 1.8 K are consistent with Langevin function.
…
N N distances between the two pyridyl nitrogen atoms of the
Positive and negative signs of Th represent antiferromagnetic
(AFM) and ferromagnetic (FM) interaction of magnetic ions,
respectively. The proper temperature range of Curie–Weiss fitting
is determined by the linear part of the 1/x9–T curve. The insets in
Fig. 6b and 6c reveal that complexes 2 and 3 yield almost linear 1/
x9–T curves over the entire temperature range of interest, and no
difference between the FC and ZFC processes can be found. The Th
values obtained from these two curves were both positive and
close to zero, implying very weak AFM interactions between Ni(II)
ions. The FC and ZFC curves of complex 1 separated at 25 K,
indicating the formation of magnetic ordering. The negative Th
reflects FM interactions at high temperatures, which become AFM
interactions when an antiferromagnetic cusp appears in the x–T
profile of the 50 Oe ZFC process at 25 K. Notably, only the
application of a 50 Oe magnetic field in the FC process alters the
shape of the x–T curve to make it ferromagnetic-like, indicating
the existence of a meta-state of FM ordering below 25 K. This may
arise from the helical structure with the octahedrally coordinated
Ni(II) ions, as shown in Fig. 1b, such that the frustrated AFM
interactions occur between ions in the absence of an external
magnetic field. Alternatively, in an applied external magnetic field,
the Ni(II) moments tend to arrange parallel to each other, forming
dipyridyl amide ligands (15.70 Å for 2, 9.97 Å for 3 and 16.64 Å for
4). The higher spin–orbit coupling energy of 3 is associated with
complicated bonding status of the four disordered chains of L1
and SDA22 ligands. The order of magnitude of this energy is
similar to that reported for complexes that contain magnetic
ions.15–17 The fact that the activation energies of the antiferro-
magnetic exchange interaction, E2, of 2 and 3 are smaller than that
of 4 reflects the larger separation between Ni(II) ions in 2 and 3.
The shortest distances between the Ni(II) ions are 8.34 and 8.28 Å
in 2 and 3, respectively, whereas the shortest separation is 2.71 Å
in 4. The obtained energies E2 of 2, 3, and 4 are highly consistent
with the fitted Th values from the Curie–Weiss Law, indicating that
Rueff’s equation is also applies to these complexes and provides
deeper insight into the magnetic properties and surrounding
environments of Ni(II) ions.
Conclusions
By using the flexible dipyridyl amide ligands, L1 and L2, and
the angular dicarboxylic acids, H2MBA, H2OBA and H2SDA,
four new Ni(II) coordination polymers were successfully
Table 4 Fitted magnetic parameters of complexes 1–4
Complex
1a
1
2
3
4
Ms (emu g21
)
11.67(1)
2.63(1)
22.41(53)
2.84(5)
2.35(1)
22.33(21)
14.23(1)
2.55(1)
249(5)
2.39(1)
3.41(1)
1.55(5)
26(2)
2.68(15)
5.92(81)
1.47(9)
12.11(1)
2.17(1)
21.92(93)
1.62(4)
3.01(4)
0.72(2)
1.8(2)
1.44 (2)
61(7)
0.53(19)
14.68(1)
0.32(1)
1.18(27)
2.42(2)
2.37(1)
14.0(2)
3.5(1)
2.07(1)
0.32(1)
16.03(10)
,mz.s (mB per f.u. at 1.8 K)
x0 (1027 emu g21 Oe21
)
20.05(10)
1.03(1)
3.24(1)
C (1023 emu K g21 Oe21
meff (mB per Ni)
Th (K)
)
20.67(3)
A (1024 emu K g21 Oe21
B (1023 emu K g21 Oe21
E1 (K)
)
)
E2 (K)
a
The fitting parameters were obtained from the x–T curve of 50 Oe FC process.
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Fig. 6 ZFC and FC magnetic susceptibility curves of complex (a) 1 (b) 2 (c) 3 and (d) 4. Inset shows Curie–Weiss fitting result and 1/x–T plots.
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complexes 2 to 4 are directed by the N N distances between
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…
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Acknowledgements
We are grateful to the National Science Council of the Republic
of China for support, under Grants NSC 101-2112-M-033-004
and NSC 99-2113-M-033-004-MY3. We also thank Miss C.-W.
Lu of the Instrumentation Center, National Taiwan University,
for CHNS (EA) analysis experiments.
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