Syntheses, crystal structures and magnetic properties of three novel cobalt(ii) complexes containing imidazole derivative groups

Article abstract of DOI:10.1039/b808385a

Three Co(ii) complexes with the formulas: {[Co₂(Bib) ₃Cl₂]Cl(CH₃COO)}·CH ₃OH·H₂O (1), [Co₂(Bib) ₃Cl₂]Cl₂·(CH₃OH) ₂·H_2<

Full text of DOI:10.1039/b808385a

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www.rsc.org/dalton | Dalton Transactions
Syntheses, crystal structures and magnetic properties of three novel cobalt(II)
complexes containing imidazole derivative groups†
Hong Yang,a Jia-Min Chen,a Jing-Jia Sun,a Shi-Ping Yang,*a Jie Yu,b Hong Tanb and Wei Li*b
Received 19th May 2008, Accepted 23rd January 2009
First published as an Advance Article on the web 23rd February 2009
DOI: 10.1039/b808385a
Three Co(II) complexes with the formulas: {[Co2(Bib)3Cl2]Cl(CH3COO)}·CH3OH·H2O (1),
[Co2(Bib)3Cl2]Cl2·(CH3OH)2·H2O, (2) and [Co3K1(Tib)2(CH3COO)6]PF6 (3), were obtained by
self-assembly of a cobalt(II) salt with Bib and Tib (Bib = 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)-
benzene; Tib = 1,3,5-tris(4,5-dihydro-1H-imidazol-2-yl)benzene) and were structurally and
magnetically characterized. X-Ray single-crystal diffraction showed that each Co(II) ion was in a highly
distorted tetrahedral coordination geometry with a cis–trans ratio of 1 : 2 from the Bib ligand, which
functioned in a bidentate fashion in the binuclear triple-helical [Co2(Bib)3Cl2]2+ cations in 1 and 2. In
the [Co3K1(Tib)2(CH3COO)6]- anions in 3, each Co(II) ion was also in a highly distorted tetrahedral
coordination geometry and the Tib ligands acted in an offset fashion in C, C, C and A, A, A
coordination to the Co(II) ions with p–p stacking interactions between two benzene rings from the Tib
ligand in the cluster cation. Each Tib ligand in a cluster unit acted as a tridentate entity to coordinate
three Co(II) ions resulting in a cylinder-like cluster structure. The intermolecular hydrogen bonds in the
solid-state resulted in the well-shaped 2D layer network which formed a honeycomb in 1, the 3D
supramolecular architecture which was connected to the 2D sheet into 3D in 2 and the 3D
supramolecular architecture, which was extended into a well-shaped 2D honeycomb layer network in 3.
The results from magnetic data, in the high-temperature region, showed that 1 and 2 obeyed the
Curie–Weiss law with a Weiss constants q = -12.3, and -9.8 K and a Curie constants C = 5.31 and
5.32 cm3 K mo1-1, respectively, indicating antiferromagnetic interactions between adjacent cobalt(II)
ions. Both complex 1 and 2 showed magnetic ordering at low temperature due to the canting effect. The
zero-field AC magnetic susceptibility measurements for 1 and 2 displayed a maximum which was
frequency dependent owing to a slow relaxation process, which could be caused by either domain wall
movements or spin-glass behaviours.
final architecture might exhibit additional levels of supramolecular
organization, by exploiting other weak interactions such as
hydrogen bonding or p–p interactions, among others. We have
been interested in the preparation of novel MOFs with relevance
Introduction
Since the mid-1990s, research in coordination chemistry has been
strongly influenced by the development of metallo-supramolecular
chemistry,1 which involves the design and preparation of intricate
to the area of molecular magnetism. One of our goals is to organize
polymetallic coordination aggregates with specific structures or
magnetic coordinated complexes with predetermined structures
functions.2 The creation of supramolecular networks can be ac-
in order to gain control of the magnetic properties of the final
complished by the judicious combinations of organic ligands and
material.
metals, thus exploiting the ability of metal–ligand coordination
For some time, we have been exploring the coordination
bonds to provide simple and controlled routes to 1D, 2D, or 3D
chemistry of imidazole-based ligands as the product of the
metal–organic frameworks (MOFs),3 which constitute an exotic
attempted synthesis of transition metal complexes as structural
models of some metalloenzymes and crystal engineering.10,11 We
have now turned our attention to the ligand-containing imidazole
derivative groups (Bib = 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)-
benzene; Tib = 1,3,5-tris(4,5-dihydro-1H-imidazol-2-yl)benzene,
Scheme 1) as a polydentate coordination mode. These ligands
have been previously employed in the preparation of very inter-
esting MOFs aimed at fulfilling various roles such as host–guest
functions.12–13 The reactivity of Bib and Tib with simple complexes
of cobalt(II), was explored here in order to construct extended
magnetic materials. Fortunately, three new novel coordinated com-
pounds {[Co2(Bib)3Cl2]Cl(CH3COO)}·CH3OH·H2O (1), [Co2-
(Bib)3Cl2]Cl2·(CH3OH)2·H2O, (2) and [Co3K1(Tib)2(CH3COO)6]-
PF6 (3), can be obtained by the vapour diffusion method.
class of coordination polymers and may exhibit unique properties,
including adsorption, magnetism, and others.4–9 The bottom-up
assembly of MOFs from metal ions and organic linkers is one
of the cornerstones of crystal engineering. In this context, the
aDepartment of Chemistry, College of Life and Environmental Science,
Shanghai Normal University, Shanghai, 200234, P. R. China. E-mail:
shipingy@shnu.edu.cn
bNational Engineering Research Center for Compounding and Modification
of Polymeric Materials, Guiyang, Guizhou 550014, P. R. China. E-mail:
dearweili@gmail.com
† Electronic supplementary information (ESI) available: Additional struc-
tural diagrams. CCDC reference numbers 667565, 667566 and 667567 for
1, 2 and 3, respectively. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b808385a
2540 | Dalton Trans., 2009, 2540–2551
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1
67.15, H 6.61, N 26.10%. H NMR (300 MHz, D2O):d 3.60 (b,
4H, NH–CH2), 4.70 (b, 4H, N–CH2), 7.40 (t, 1H, C6H4), 7.70
(d, 2H, C6H4), 7.90 (s, 1H, C6H4). Main IR bands (KBr, cm-1):
3158 m, 2936 m, 2862 m, 1620 s, 1568 s, 1495 s, 1306 m, 1270 s,
1191 w, 1085 w, 980 m, 907 w, 808 w, 699 m, 652 w, 531 w,
486 w.
Synthesis of Tib. 1,3,5-Benzenedicarboxylic acid (1.51 g,
7.18 mmol), ethylenediamine (1.58 cm3, 23.7 mmol), ethylenedi-
amine dihydrochloride (3.15 g, 23.7 mmol) and toluene-p-sulfonic
acid (0.216 g, 1.12 mmol) were added to the solvent ethylene
glycol (10 cm3), and the mixture solution was refluxed for 5 h.
About half of the ethylene glycol solvent was then slowly removed
by distillation. The residue was dissolved in a mixture of water
(40 cm3) and concentrated HCl (11 M, 3 cm3). The addition of
50% aqueous NaOH gave a yellow precipitate that was purified by
recrystallization. The ligand Tib was obtained in ca. 30% ba◦sed
on 1,3,5-benzenedicarboxylic acid (ca. 620 mg). M.p. > 250 C.
Anal. calcd for C15H18N6: C 63.81, H 6.43, N 29.77. Found: C
Scheme 1 Synthesis of Bib and Tib.
Therefore in this paper, we reported the preparation and char-
acterization of these compounds by elemental analyses (EA),
infrared spectra (IR), thermogravimetry (TG) and X-ray single-
crystal diffraction. The magnetic properties of the complexes were
also investigated.
Experimental
1
63.78, H 6.49, N 29.80%. H NMR (300 MHz, CD3OD): d 8.24
All reagents are commercially available and used as received.
Solvents are dried by conventional procedures prior to use. All
samples are thoroughly dried prior to elemental analyses.
(s, 3H, C6H3), 3.31 (t, 12H, CH2). Main IR bands (KBr, cm-1):
3743 w, 3423 (s, b), 3268 (m, b), 3135 s, 2934 m, 2869 m, 1624 s,
1572 s, 1500 s, 1329 w, 1280 s, 1185 w, 1039 w, 985 w, 698 m,
526 (m, b).
Physical measurements
Synthesis of {[Co2(Bib)3Cl2]Cl(CH3COO)}·CH3OH·H2O, 1.
A solution of Co(CH3COO)2·4H2O (0.249 g, 1.0 mmol) in
methanol (15 mL) was slowly added to a methanolic solution
(10 mL) of¢ Bib (0.214 g, 1.0 mmol), and the pH value was adjusted
to ca. 7.5. by hydrochloric acid. The mixture was stirred for 30 min.
After three days, the blue-purple crystalline solid of 1 was obtained
by vapour diffusion of diethyl ether (ca. 75% yield based on Bib.
Calcd for C39H51Cl3Co2N12O4: C 47.99, H 5.27, N 12.77. Found:
C 47.88, H 5.26, N 12.75%). Main IR bands (KBr, v, cm-1): 3235
m, 2879 w, 1729 s, 1602 m, 1569 m, 1514 s, 1466 m, 1342 w, 1278 s,
1020 m, 787 s, 798 m, 560 w, 435 w.
The C, H and N elemental analyses were performed on a Perkin-
Elmer 204 elemental analyser. The IR spectra were recorded on a
Nicolet Avatar 370 DTGS spectrophotometer with KBr discs in
the 4000–400 cm-1 regions. The 1H NMR spectra were performed
on a Varian 300 MHz spectrometer with TMS as reference,
using D2O or CD3OD as matrix. The UV–vis spectrophotometric
investigations in the solvent and solid-state were performed on a
UV-2450 spectrophotometer (Shimadzu instruments) in a range
from 180–800 nm. Melting points were determined on a XT4A
microscope and were uncorrected. The TGA were performed
under N2 atmosphere on a Shi◦madzu DTG-60H instrument at
a temperature ramp rate of 10 C min-1. Magnetic susceptibility
was measured with a Quantum Design SQUID MPMS XL-7
magnetometer for 1 and 2. The measurements are taken from
2–300 K. Selected samples are contained in a gel capsule sample
holder. The magnetic susceptibility is corrected for the gel capsule
and core diamagnetism with Pascal’s constants.14 Magnetic sus-
ceptibility is measured with a Quantum Design SQUID PPMS-9
magnetometer for 3.
Synthesis of [Co2(Bib)3Cl2]Cl2·(CH3OH)2·H2O, 2. A solution
of CoCl2·6H2O (0.238 g, 1.0 mmol) in methanol (10 mL) was
slowly added to a methanolic solution (10 mL) of¢ Bib (0.214 g,
1.0 mmol). The mixture was stirred for 30 min. After seven days,
the blue-purple block crystalline solid of 2 was obtained by vapour
diffusion of diethyl ether (ca. 65% yield based on Bib. Calcd for
Co2C38H52N12O3Cl4: C 46.36, H 5.32, N 17.07. Found: C 46.30,
H 5.18, N 17.01%). Main IR bands (KBr, v, cm-1): 3341 m, 3238
m, 2881 w, 1617 m, 1572 m, 1510 s, 1460 m, 1339 w, 1282 s, 1016
m, 791 s, 700 m, 567 w, 436 w.
Preparation of ligands and metal complexes
Synthesis of Bib13. 1,3-Benzenedicarboxylic acid (2.31 g,
13.9 mmol), ethylenediamine (3.70 cm3, 50 mmol), ethylenedi-
amine dihydrochloride (6.64 g, 50 mmol) and toluene-p-sulfonic
acid (0.208 g, 1.09 mmol) were added to the solvent of ethylene
glycol (20 cm3), and the mixture solution was refluxed for 3 h.
About half of the ethylene glycol solvent was then slowly removed
by distillation. The residue was dissolved in a mixture of water
(40 cm3) and concentrated HCl (11 M, 3 cm3). The addition of
50% aqueous NaOH gave a yellow precipitate that was purified
by recrystallization. The ligand Bib was obtained in ca. 80% yield
based on 1,3-benzenedicarboxylic acid (ca. 2.38 g). M.p. > 250 ◦C.
Anal. calcd for C12H14N4: C 67.27, H 6.59, N 26.15. Found: C
Synthesis of [Co3K1(Tib)2(CH3COO)6]PF6 3. A solution of
Co(CH3COO)2·4H2O (0.249 g, 1.0 mmol) in methanol (10 mL)
was slowly added to a methanolic solution (10 mL) of¢ Tib (0.262 g,
1.0 mmol). Then a solution of KPF6 (0.184 g, 1 mmol) in methanol
(5 mL) was poured in the mixture. Lastly, the mixture was stirred
for 30 min. After a month, the blue-purple block crystalline solid
of 3 was obtained by vapour diffusion of diethyl ether (ca. 45%
yield based on Tib. Calcd for Co3C42H54N12O12KPF6: C 39.42,
H 4.25, N 13.13. Found: C 39.15, H 4.29, N 13.59%). Main IR
bands (KBr, v, cm-1): 3436 (m, b), 3072 w, 2946 w, 2876 w, 1613 s,
1580 s, 1515 s, 1474 m, 1397 s, 1335 m, 1283 m, 1188 w, 846 s,
673 m.
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Table 1 The crystallographic data for complexes 1, 2 and 3
1
2
3
a
b
Empirical formula
Formula weight
T/K
C39H51Cl3Co2N12O4
976.13a
298(2)
0.71073
Monoclinic
C2/c
25.458(2)
13.8919(9)
27.979(2)
C38H52Cl4Co2N12O3
984.58b
298(2)
0.71073
Triclinic
¯
P1
10.976(1)
14.375(2)
14.749(2)
78.341(2)
88.920(2)
74.691(2)
2197.0(4)
2
C42H54Co3F6KN12O12P
1279.83
298(2)
0.71073
Hexagonal
P6322
14.575(3)
14.575(3)
13.889(4)
90
90
120
2555(1)
2
1.664
1.169
˚
l/A
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
90
110.223(1)
90
9285(1)
3
˚
V/A
Z
8
rc/g cm-3
1.397
0.939
3994.3
1.485
1.050
1016
m/mm-1
F(000)
1309.3
0.401 ¥ 0.067 ¥ 0.031
1.61–26.99
Crystal size/mm
0.518 ¥ 0.506 ¥ 0.325
1.70–27.00
-30 < h < 21, -15 < k < 16,
-33 < l < 33
8149/5676
0.0640
0.477 ¥ 0.176 ¥0.180
q range/◦
1.84–25.50
Limiting indices (h, k, l)
-13 < h < 10, -17 < k < 17,
-15 < l < 17
-13 < h < 18, -18 < k < 17,
-17 < l < 17
12 712/1515
0.1521
Reflections collected/unique
Rint
Refinement method
Data/restraints/parameters
Goodness of fit on F2
R1, wR2 (obs)
11 570/8185
0.0712
Full-matrix least-squares on F2
8149/123/589
1.001
Full-matrix least-squares on F2
8060/0/536
Full-matrix least-squares on F2
1515/6/133
1.000
0.997
0.0588, 0.1826
0.0767, 0.1895
1.099 and -0.367
0.0664, 0.1740
0.0974, 0.1964
1.753 and -0.924
0.1205, 0.1583
0.1205, 0.1748
0.362 and -0.434
R1, wR2 (all)
Largest and hole/e A )
-3
˚
a Containing the six hydrogen atoms of a methanol and a water molecules that were not found. b Containing the two hydrogen atoms of a water molecule
that were not found.
X-Ray crystallography
The crystallographic data for the three complexes are summarized
in Table 1. Selected bond distances and angles are given in
Table 2.
Diffraction intensities for 1, 2 and 3 are collected (hemisphere
technique) on a Bruker SMART Platform CCD diffractometer
˚
at 298 K with a molybdenum tube (lka = 0.71073 A), and the
absorption correction is applied with the SADABS program.15
The structure solution and full-matrix least-squares refinement
based on F2 are performed with the SHELXS-97 and SHELXL-
9716 program packages, respectively. All the non-hydrogen atoms
are refined anisotropically. Hydrogen atoms of the organic ligands
Results and discussion
Synthesis
The reaction of diamine and dicarboxylic acid and tricar-
boxylic acid depends very much on the reaction conditions,
such as the ratio of the reactants, solvent, concentration and
temperature.13 The reaction of 1,3-benzenedicarboxylic acid and
1,3,5-benzenetricarboxylic acid with 1,2-diaminoethane in the
presence of acid catalysis (toluene-p-sulfonic acid) offered Bib in
80% and Tib in 30% yield based on 1,3-benzenedicarboxylic acid
and 1,3,5-benzenetricarboxylic acid under reflux in ethylene glycol
solution for 3 h, respectively, as shown in Scheme 1. EA, NMR and
IR spectra confirmed the target product. The cobalt(II) complexes
with the formulas: {[Co2(Bib)3Cl2]Cl(CH3COO)}·CH3OH·H2O,
(1), [Co2(Bib)3Cl2]Cl2·(CH3OH)2·H2O, (2) and [Co3K1(Tib)2-
(CH3COO)6]PF6 (3), were obtained by the vapour diffusion
method due to the reaction of cobalt acetate tetrahydrate and
cobalt chloride hexhydrate with Bib and Tib ligands, respectively,
and were characterized by EA, NMR and IR methods. Although
there were four possible coordination configurations, A,C-cis,
C,A-cis, A,A-trans and C,C-trans for Bib, and four modes C,C,C;
C,C,A; A,A,A and A,A,C for Tib, as shown in Scheme 2, the
˚
are generated geometrically (C–H 0.95 or 0.99 A for 1, and
˚
˚
2, 0.98 or 0.99 for 3, O–H 0.84 A for 2 and N–H 0.88 A).
Analytical expressions of neutral-atom scattering factors are
employed, and anomalous dispersion correction incorporated.17
Both complex 1 and 3 are solved by restrained refinement and
constrained refinement because of disordered solvents or anions.
For the complex 1, the Cl3 atom is disorder over two sites (Cl3
and Cl3¢) and the site occupancy of the major components is
0.80. The oxygen atom from the solvent water molecule is also
disordered over two sites O1w and O2w with the occupancy
factor being 0.80 and 0.20. In addition, the methanol molecule
is disordered over two positions (0.75 : .25). The H positions
of the methanol and water molecules of compound 1 and of
the water molecule of compound 2 were not determined. The
-
PF6 anions from the complex 3, the P and F atoms are all in
special position and the occupancy factors for P, F1, F2 and F3
atoms were all 0.1667, 0.3333, 0.3333 and 0.3333, respectively.
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◦
˚
molar ratio of 3 : 2 in 1 and 2. However, the data from 3 confirmed
that the molar ratio of Tib ligand and cobalt metal ions was 2 : 3.
These results were in agreement with the crystal structure results
of 1, 2 and 3 in the solid-state.
Table 2 Selected bond distances (A) and angles ( ) for complexes 1, 2
and 3
1
The IR spectra showed a few peaks at ca. 3158, 2936 and
1620 cm-1 for Bib and 3135, 2934 and 1624 cm-1 for Tib, which
were assigned to the stretching vibration of the C–H groups of
the benzene ring, C–H from CH2 groups of the hydrogenated
Co(1)–N(1)
Co(1)–N(5)
Co(2)–N(3)
Co(2)–N(11)
2.000(4)
2.007(3)
2.002(4)
2.012(4)
5.478 (4)
Co(1)–N(9)
Co(1)–Cl(1)
Co(2)–N(7)
Co(2)–Cl(2)
2.020(4)
2.261(1)
2.020(4)
2.256(1)
Co(1)–Co(2)
=
imidazole ring and C N groups of the hydrogen imidazole ring,
N(1)–Co(1)–N(5)
N(1)–Co(1)–N(9)
N(5)–Co(1)–N(9)
N(3)–Co(2)–N(11)
N(11)–Co(2)–N(7)
N(3)–Co(2)–N(7)
109.7(2)
N(9)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(1)
N(5)–Co(1)–Cl(1)
N(3)–Co(2)–Cl(2)
N(11)–Co(2)–Cl(2)
N(7)–Co(2)–Cl(2)
103.0(1)
120.4(2)
112.6(2)
117.0(2)
109.2(2)
115.8(1)
104.4(1)
105.0(1)
102.7(1)
106.5(1)
104.1(1)
respectively. It should be noted that there was a red-shift of the
=
C N groups stretching vibration from 1620, 1620 and 1624 to
1602, 1617 and 1613 cm-1 in comparison with those for 1, 2 and 3,
respectively, indicating direct coordination of the nitrogen atoms
=
in C N groups.
The data from the electronic spectra of the ligands Bib and Tib
and the complexes 1, 2 and 3 exhibited intense absorption bands at
ca. 260 and 310 nm in methanol, 210 and 280 nm in the solid-state,
respectively, which can be attributed to p → p* transition of the
conjugated benzene and hydrogenated imidazole chromospheres.
In the visible region, complexes 1, 2 and 3 exhibited a strong band
at ca. 620, 620 and 605 nm in the solid-state, respectively, which
2
Co(1)–N(11)
Co(1)–N(7)
Co(1)–N(1)
Co(1)–Cl(1)
1.998(4)
Co(2)–N(9)
Co(2)–N(3)
Co(2)–N(5)
Co(2)–Cl(2)
2.007(4)
2.018(4)
2.023(5)
2.264(2)
5.584 (2)
2.021(4)
2.022(4)
2.259(2)
Co(1)–Co(2)
N(11)–Co(1)–N(7)
N(11)–Co(1)–N(1)
N(7)–Co(1)–N(1)
N(11)–Co(1)–Cl(1)
N(7)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(1)
110.5(2)
N(9)–Co(2)–N(3)
N(9)–Co(2)–N(5)
N(3)–Co(2)–N(5)
N(9)–Co(2)–Cl(2)
N(3)–Co(2)–Cl(2)
N(5)–Co(2)–Cl(2)
118.9(2)
115.4(2)
113.2(2)
108.8(1)
103.9(1)
104.0(1)
106.3(2)
114.1(2)
103.9(1)
102.8(1)
110.1(1)
4
were assigned to the d–d (4A2→ T2) transition.
Thermogravimetric analyses
The thermogravimetric analysis curve of 1 confirms that the
process of decomposition of the complex has two stages. The
first stage decomposition was in the range of 70–160 ◦C and
the weight loss was about 5.6%, indicating the evaporation of
water and methanol molecules (calcd 5.1%). The DTA curve
also showed a weak endothermic peak. The second weight loss
occurs in the range of 324–698 ◦C and is characteristic of the
decomposition of the organic moiety. A weak endothermic peak
and a strong exothermic peak appeared on the DTA curves, which
were attributed to evaporation of the solvent and organic molecule
combustion, respectively.
3
Co–O(1)
O(1a)–Co–O(1)
O(1)–Co–N(1)
1.991(9)
79.8(6)
111.3(3)
Co–N(1)
O(1)–Co–N(1a)
N(1a)–Co–N(1)
2.026(5)
109.9(3)
125.5(3)
Symmetry code for 3: (a) x, x - y + 1, -z + 1/2.
The thermogravimetric analysis curve of 2 was slightly different
from that of 1. The first stage decomposition was in the range
of 70–120 ◦C and the weight loss was about 3.2%, indicating the
evaporation of crystal water (calcd 3.7%). The DTA curve also
showed a weak endothermic peak◦. The second stage decomposi-
tion was in the range of 120–303 C. The weight loss was about
6.7%, which corresponded to the loss of methanol molecules (calcd
6.5%). A weak endothermic peak also appeared on the DTA curve
and was attributed to evaporation of methanol molecules. The last
◦
stage decomposition was from 303–676 C. The weight loss was
about 64.1%, suggesting loss of the ligand (calcd 63.6%), and
indicated that the residue was CoCl2. A weak exothermic and a
strong endothermic peak around 560 and 630 ◦C, respectively,
on the DTA curve, which were attributed to organic molecule
combustion.
The thermogravimetric analysis curve of 3 was different from
those of 1 and 2. A two-step weight loss (24.8%) between 310
and 340 ◦C and a gradual loss of 45.0% among from 340–600 ◦C
could be observed. The observed total weight loss corresponds to
the removal of the organic (C, H and N) part which accounts for
66.2% of the mass of 3. These results indicated that the residue
was the mixture of Co2O3 and KPF6. A weak exothermic and
a strong endothermic peak appeared around 450 and 570 ◦C,
Scheme 2 Possible coordination configurations of Bib and Tib.
three coordination forms C,A-cis, A,A-trans and C,C-trans were
all found in 1 and 2 for Bib, and the two donated modes C,C,C
and A,A,A were also found in 3 for Tib. In our work, we tried
to complete more tests using different counter anions to examine
their effect. Unfortunately, we did not obtain the other counter
anion single-crystal compound.
Physical and spectroscopic study
EA satisfactorily indicated that the complex contained a unit
which was composed of Bib ligands, and cobalt metal ions with a
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Fig. 1 (a) Perspective view of the binuclear cation in 1. (b) Space-filling representation of the triple helical structure (c) 1D the chain (d) 2D structure.
respectively, on the DTA curve and were attributed to organic
molecule decomposition.
in a highly distorted tetrahedral coordination geometry. The
coordination angles around the Co(1) and Co(2) ions were in the
range of 103.0(1)–120.4(2)◦ and 102.7(1)–117.0(2)◦, respectively.
In the binuclear cation, the Co–N and Co–Cl bond lengths were
Crystal structures
˚
˚
in the range of 2.000(4)–2.020(4) A and 2.256(1)–2.261(1) A,
respectively, in which the Co–Cl bond length was longer than
that of the Co–N bond. The Co ◊ ◊ ◊ Co separation in the cation
{[Co2(Bib)3Cl2]Cl(CH3COO)}·CH3OH·H2O, 1. The complex
of 1 crystallized in the space group C2/c, and the asymmetric unit
contained 8 complex molecules. X-Ray single-crystal diffraction
showed that the crystal structure of 1 consisted of discrete
binuclear [Co2(Bib)3Cl2]2+ cations, an acetate anion, a methanol
and a water molecule. The binuclear [Co2(Bib)3Cl2]2+ cation is
shown in Fig. 1, and shows that the cation is a triple-helical
fashion. Each Co(II) ion was coordinated to nitrogen atoms
from three different ligands and a chloride anion, resulting
˚
was 5.478(4) A. It is worth noting that the Bib ligands acted in
two ways in cis (C,A), and trans (A,A and C,C) coordination
to the Co(II) ions with a cis–trans ratio of 1 : 2, as shown in
Fig. 1a and Scheme 2. These results are different from that of
silver(I) complexes12, in which the Bib ligand is only found in
the cis coordination configuration. Three benzene rings from the
Bib ligand in the binuclear cation were interlaced with each other
2544 | Dalton Trans., 2009, 2540–2551
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Table 3 Hydrogen bond parameters for 1, 2 and 3
∠C(N)HCl(O)/◦
˚
˚
˚
C(N)–H ◊ ◊ ◊ Cl
d(C(N)–H)/A
d(H ◊ ◊ ◊ Cl(O))/A
d(C(N) ◊ ◊ ◊ Cl(O))/A
1
N4–H(4) ◊ ◊ ◊ O(1 W)
N6–H(6A) ◊ ◊ ◊ O2ii
0.88
0.88
0.86
0.88
0.88
0.95
1.98(2)
2.05(2)
2.06(2)
2.40(1)
2.55(1)
2.77(1)
2.813(6)
2.841(6)
2.879(6)
3.258(5)
3.279(5)
3.554(5)
158
150
156
164
141
140
N12–H(12C) ◊ ◊ ◊ O1ii
N(8)–H(8A) ◊ ◊ ◊ Cl(3)
N(10)–H(10A) ◊ ◊ ◊ Cl(3)iii
C(6)–H(6) ◊ ◊ ◊ Cl(2)i
2
N2–H2 ◊ ◊ ◊ O2i
N4–H4 ◊ ◊ ◊ O3ii
N6–H6 ◊ ◊ ◊ O1i
O2–H2D ◊ ◊ ◊ Cl4
O3–H3 ◊ ◊ ◊ Cl3
N8–H8A ◊ ◊ ◊ Cl3
N10–H10 ◊ ◊ ◊ Cl3
N12–H12 ◊ ◊ ◊ Cl4
0.88
0.88
0.86
0.84
0.84
0.88
0.88
0.88
2.31(1)
1.97(2)
2.02(2)
2.56(1)
2.70(2)
2.48(1)
2.67(1)
2.35(2)
2.942(9)
2.842(8)
2.756(9)
3.304(8)
3.077(6)
3.1995(5)
3.226(5)
3.220(6)
129
172
141
148
109
140
123
169
3
N2–H2C ◊ ◊ ◊ O2i
C5–H5A ◊ ◊ ◊ O2ii
C2–H2B ◊ ◊ ◊ F3iii
0.88
0.95
0.99
2.38(1)
2.25(1)
2.21(2)
3.02(2)
3.17(2)
3.08(2)
130
166
146
Symmetry codes for 1: (i) 1/2 - x, -1/2 + y, 3/2 - z; (ii) -1/2 + x, 1/2 + y, z, (iii) -1/2 + x, -1/2 + y, z; 2: (i) x, y + 1, z; (ii) x, y, z - 1; 3: (i) 1 + x - y, x,
1/2 + z; (ii) 1 - x + y, y, 1/2 - z; (iii) 1 - x + y, 1 - x, z.
with a dihedral angle of 56.1(1), 66.7(1) and 78.8(1)◦, respectively.
The two hydrogenated imidazole five-member rings from each Bib
ligand were not co-planar with the matrix benzene ring. Each Bib
ligand in the binuclear cluster unit acted as a bidentate entity,
two ligands acted in the trans configuration and the other ligand
functioned in the cis mode, to ligate a pair of Co(II) ions by nitrogen
atom from the five-member hydrogenated imidazole ring, which
resulted in a triple-helical cluster structure (Fig. 1a and b and
Scheme 2). Until now, there are a lot of triple helical metal–
organic helicates have been reported. However, most of them
are constructed by flexible ligands, such as bipyridine derivatives,
terpyridine derivatives, 8-hydroxyquinoline derivatives etc., and
few examples are constructed by rigid ligands like Bib.18
The crystal packing of 1 exhibited an interesting feature in
which the 1D chain, the 2D sheet and the well-shaped 3D layer
network (Fig. 1c and d and ESI, Fig. S1),† which is quite common
in organic supramolecular architectures19 was stacked. The 1D
chain (Fig. 1c) and the 2D supramolecular sheet (Fig 1d) are
formed by N–H ◊ ◊ ◊ Cl weak hydrogen bonds (Table 3) between the
hydrogenated imidazole ring NH donors and Cl- anion acceptors.
Additionally, the C–H ◊ ◊ ◊ Cl weak interactions and the N–H ◊ ◊ ◊ H
hydrogen bonds (Table 3) between the 2D sheets also found, which
resulted in 3D supramolecular networks.
the cation was also a triple-helical fashion. Each Co(II) ion was
well coordinated to nitrogen atoms from three different ligands
and a chloride anion, resulting in a highly distorted tetrahedral
coordination geometry. The coordination angles around the Co(1)
and Co(2) ions were in the range of 103.91(1)–115.4(2)◦ and
102.8(1)–118.9(2)◦, respectively. In the binuclear cation, the Co–N
˚
and Co–Cl bond lengths were in the range of 1.998(4)–2.023(5) A
˚
and 2.259(2)–2.264(2) A, respectively, in which the Co–Cl bond
length was also longer than that of the Co–N bond. These data
are almost the same as those of 1. The Co ◊ ◊ ◊ Co separation in the
˚
cation was 5.584(2) A, which was longer than that of 1. It is worth
noting that the Bib ligands acted in two ways in cis (C,A) and trans
(A,A and C,C) coordination to the Co(II) ions with a cis–trans ratio
of 1 : 2, as shown in Fig. 2a and Scheme 2. Three benzene rings
from the Bib ligand in the [Co2(Bib)3Cl2]2+ cation were interlocked
with each other at a dihedral angle of 51.6(1), 69.3(1), and 78.6(1)◦,
respectively. The two hydrogenated imidazole five-member rings
from each Bib ligand were also not co-planar with the matrix
benzene ring. Each Bib ligand in the binuclear cluster unit acted as
a bidentate entity, two ligands acted in trans configuration and the
other ligand functioned in cis mode, to ligate a pair of Co(II) ions
by nitrogen atoms from the five-member hydrogenated imidazole
ring, which resulted in a triple-helical cluster structure (Fig. 2a
and b and Scheme 1). These results are similar to those of 1 apart
from tiny differences. Nevertheless, it is interesting to note that
there was a surprising structural feature of 1 and 2 in the solid
structure. Although they had the same coordinated configurations,
all Bib ligands adopted a different helical direction for 1 and 2,
respectively. (Fig. 1a and b and Fig. 2a and b).
[Co2(Bib)3Cl2]Cl2·(CH3OH)2·H2O, 2. The complex of 2 crys-
¯
tallized in the space group P1, and the asymmetric unit contained
two complex molecules. X-Ray single-crystal diffraction showed
that the crystal structure of 2 consisted of discrete binuclear
[Co2(Bib)3Cl2]2+ cations, one water molecule, two methanol
molecules and two chloride anions. The binuclear [Co2(Bib)3Cl2]2+
cation, which was similar to 1, is shown in Fig. 2a, and shows that
The crystal packing of 2 exhibited a different feature (Fig. 2c and
ESI, Fig. S2†) in which the 2D sheet and 3D structure, which were
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Fig. 2 (a) Perspective view of the binuclear cation in 2. (b) Space-filling representation of the triple helical structure (c) 2D structure.
composed of binuclear [Co2(Bib)3Cl2]2+ cations was formed. The
2D sheet was caused by formation of O–H ◊ ◊ ◊ Cl and N–H ◊ ◊ ◊ Cl
weak hydrogen bonds between the hydrogenated imidazole ring
NH groups and the solvent water molecule OH groups donors
and Cl- anion acceptors (Table 3). It is worth noting that there
were significant structural differences between 1 and 2 in the solid
state. In 2, there were more classic hydrogen bonds among chloride
atoms from counter anions, oxygen atoms of methanol and water
molecules and between nitrogen atoms from N–H groups of the
hydrogenated imidazole ring (Table 3), which connected the 2D
sheet into 3D supramolecular architecture. These findings may
result in different magnetic and thermal properties between 1 and
2 in the solid state.
[Co3K1(Tib)2(CH3COO)6]PF6, 3. The complex 3 crystallizes
in the hexagonal crystal system space group P6322. The crystal
structure of 3 featured [Co3K1(Tib)2(CH3COO)6] cluster cations
and PF6- anions. As illustrated in Fig. 3a and c, the cluster cation
possessed more fold axis passing through the center of ligand Tib.
The K+ cations and the P atom are localized on special positions:
a three-fold axis passing through K+ cations and P atom, which
result in the occupancies of P, F1, F2 and F3 atoms with 0.16667,
0.5000, 0.16667 and 0.3333, respectively when the structure is re-
fined. In addition, a 63 screw axis passes through the centroid of the
phenyl ring in ligand Tib. In the [Co3K1(Tib)2(CH3COO)6] unit,
each Co(II) ion was well coordinated to nitrogen atoms from two
different ligands and two oxygen atoms from two acetate groups,
2546 | Dalton Trans., 2009, 2540–2551
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Fig. 3 (a) Perspective view of the trinuclear cation, (b) Co2+ coordination geometry, (c) K+ coordination geometry, (d) packing of the 2D layers (no
containing K+).
resulting in a highly distorted tetrahedral coordination geometry
member rings from each Tib ligand were not co-planar with the
matrix benzene ring. Each Tib ligand in the cluster unit acted as a
tridentate entity to ligate three Co(II) ions by nitrogen atom from
the five-member hydrogenated imidazole ring, which resulted in a
cylinder-like cluster structure.
˚
(The distance of Co–O2 = 2.616(6) A, it was obvious that there was
no bond formation, due to weak contacts between Co ions and the
O2 atom with two oxygen atoms. Further analysis demonstrated
that O1, O1A, O2, O2A, Co and K1 atoms were all co-planar
and the angles of ∠O2CoO2A and ∠O1CoO2 were 179.3(3) and
50.2(3)◦, respectively, (Fig. 3b) which were not in agreement with
the angle value of the octahedron. These data proved that the
Co(II) ion was not in octahedral geometry). The bond angles
around all the Co ions were in the range of 79.8 (6)–125.5(3)◦,
which deviated from the ideal value of 109.5◦. In the cluster cation,
The crystal packing of 3 exhibited the well-shaped 2D honey-
comb layer network (Fig. 3d), which is quite common in organic
supramolecular architectures.19 Such stacking of the 2D layers is
caused by formation of C–H ◊ ◊ ◊ F weak hydrogen bonds between
the hydrogenated imidazole ring CH donors and the F atom of
-
PF6 group acceptors (Fig. 3d and Fig. 3b). The basic unit of the
˚
˚
the Co–N (2.026(5) A) and Co–O (1.991(9) A) bond lengths were
almost equal. The three Co ions were at the apex of a triangle with
honeycomb network was composed of three cluster [Co3(Tib)2]
cations three PF6- groups, a K+ cations and three CH3COO groups
due to six non-classic weak hydrogen bonds (C–H ◊ ◊ ◊ F) (Fig. 3d
and ESI, Fig. S3b).† It was noted in the packing of 3 (ESI, Fig.
S3a and S3c†) that there were more no-classic hydrogen bonds
C–H ◊ ◊ ◊ O hydrogen bonds and N–H ◊ ◊ ◊ O classic hydrogen bonds
(Table 3) between the adjacent 2D layer, which connected the 2D
layers into a 3D supramolecular architecture (ESI, Fig. S3a and
S3c).†
◦
˚
a distance of 7.172 (1) A and an angle of 60 . It is worth noting
that the Tib ligands acted in an offset fashion in C,C,C and A,A,A
coordination to the Co(II) ions, as shown in Fig. 3a and Scheme 1.
Two benzene rings from the Tib ligand in the cluster cation were
parallel to each other with a face-to-face distance of 3.315(1) A,
indicating that there was a strong p–p stacking interaction between
˚
the pair of benzene rings. The three hydrogenated imidazole five-
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Magnetic properties
2Ng2 b2 e-2x + 5e-6x + 14e-12x
(1)
cmT =
k
1 + 3e-2x + 5e-6x + 7e-12x
{[Co2(Bib)3Cl2]Cl(CH3COO)}·CH3OH·H2O, 1. The tem-
perature-dependent magnetic susceptibilities of compound 1 were
investigated at a temperature range of 2–300 K, in the form of
cM and cMT vs. T, and are represented in Fig. 4, respectively,
where cM is the molar susceptibility for 1. The susceptibility data
between 100–300 K followed the Curie–Weiss law with a Weiss
constant q = -12.3 K and a Curie constant of C = 5.31 emu K
mo1-1, indicating that there was an antiferromagnetic interaction
between two adjacent cobalt(II) ions. The cMT value per Co2 unit
(5.15 emu K mol-1) at room-temperature is much higher than
the expected spin-only value for S = 3/2 (3.75 emu K mol-1) in
tetrahedral geometry. Upon cooling the sample, cMT basically
stays from 5.15 to 4.74 emu K mol-1 in the range of 300–60 K,
then show an abrupt increase to a maximum value of 27.94 emu
K mol-1 at 14 K. Below this temperature, the cMT drops rapidly
to a value of 6.64 emu K mol-1 at 2 K. Taking into account the
dimmer character in the structure of compound 1, the cMT data
x = -J/kT
(2)
The best fit for calculated and experimental data was achieves
above 60 K for J = -2.07 cm-1 and g = 2.35 with the agreement
factor R = R(cmTexp - cmTcal)2/R(cmTexp)2 of 3.4 ¥ 10-5.
Below 15 K the cmT product experiences an upturn, reaching
27.94 emu K mol-1 at 14 K with an applied field of 500 Oe. This low
temperature behaviour suggests the occurrence of ferromagnetic
ordering in 1, which may arise from the presence of canting
between the antiparallel alignment of the spins.21 The hysteresis
loop measured at 2 K shows values of the coercive field (HC)
and remnant magnetization (MR) of 881 Oe and 0.038 Nb mol-1,
respectively, being characteristic of a soft magnet. It is well
known that the occurrence of spin canting is usually caused by
either single-ion magnetic anisotropy or antisymmetric exchange
in magnetic entities. Because there is not an inversion center
in the Co2 entity and Co2+ ions has large magnetic anisotropy,
the observation of the spin canting in 1 should arise from the
antisymmetric exchange in the dinuclear entity together with the
anisotropy of the Co2+ ions.22
ˆ
ˆ ˆ
were fitted by using the isotropic Heisenberg model H = -2JSASB
for two interacting S = 3/2 centers to determine the exchanging
parameters via the Bib ligands.20
To obtain the critical temperature of the long-range magnetic
ordering precisely, the ac magnetic susceptibility measurements
were performed under Hac = 1000 Oe and a frequency range of
1–397 Hz. Surprisingly, both the in-phase and out-of-phase
signals, cM¢ and cM¢¢, display a maximum which is frequency
dependent (Fig. 5), implying a slow relaxation process. This
slow relaxation process could be caused by either domain wall
movements23 or spin-glass behaviours.24 The shift of the peak
temperature (Tp) of cM¢ is measured by a parameter f =
(DTp/Tp)/D (logf ) = 0.03 (f is the frequency of Hac), which
is in the range of a normal spin-glass. The frequency dependence
of Tp on cM¢¢ can be fitted well to the Arrhenius law: t(T) =
t0exp(D/kBT), where t0 is the pre-exponential factor and D is the
energy gap. The best fit results in parameters t0 = 1.2 ¥10-10 s and
D/kB = 46 K. The activation energy may be compared with those
typical for the domain wall movements.23
[Co2(Bib)3Cl2]Cl2(CH3OH)2H2O,
dependent magnetic susceptibilities of compound
2. The
temperature-
were
2
Fig. 4 Plot of cM (block) and cMT vs. T (blue) in the 340–2 K range
of temperatures for 1 measured under external magnetic field of 0.1 T,
respectively. Inset: (a) hysteresis loop, (b) M–H curve at 2 K.
investigated in the temperature range of 2–300 K, in the form
of cM and cMT vs. T, are represented in Fig. 6, respectively,
Fig. 5 Temperature dependence of zero-field ac magnetic susceptibility for 1.
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Fig. 7 Temperature dependence of zero-field ac magnetic susceptibility
for 1.
Fig. 6 Plot of cM (block) and cMT vs. T (blue) in the 300–2 K range
of temperatures for 2 measured under external magnetic field of 0.1 T,
respectively. Inset: (a) hysteresis loop, (b) M–H curve at 2 K.
is in the range of a normal spin-glass. The relaxation time t
may be calculated from the Arrhenius law, leading to parameters
frequency t0 = 2.1 ¥10-17 s and D/kB = 131 K. The activation
energy may be compared with those typical for the domain wall
movements,23 although the t0 value is too small.
where cM is the molar paramagnetic susceptibility for 2. The
susceptibility data between 70–300 K follows the Curie–Weiss law
with a Weiss constant q = -9.8 K and Curie constant of C =
5.32 emu K mo1-1, indicating that there is an antiferromagnetic
interaction between neighbouring cobalt(II) ions. cMT value
per Co2 unit (5.14 emu K mol-1) at room-temperature is much
higher than the expected spin-only value for S = 3/2 (3.75 emu
K mol-1) in tetrahedral geometry. Upon cooling the sample, cMT
decrease slowly from 5.14 to 4.74 emu K mol-1 in the range of
300–70 K, then shows an abrupt increase to a maximum value
of 11.0 emu K mol-1 at 6.7 K. Below this temperature, the cMT
drops rapidly to a value of 5.45 emu K mol-1 at 2 K. To determine
the exchange parameters via three bib ligands, cmT was fitted
The observation of canted antiferromagnetism in 1 and 2 is not
unexpected due to the unsymmetrical exchange couplings between
the neighbouring metal ions. However, the coexistence of the slow
relaxation process is unusual. This relaxation process could be due
to the spin-glass behaviours and/or domain wall movements. The
small f values obtained from the frequency dependence of Tp on
cM¢ support a spin-glass behaviour in 1 and 2, while the activation
energies obtained from the frequency dependence of Tp on cM¢¢
suggest the presence of domain wall movements. Apparently,
1 and 2 showed quite unusual magnetic behaviours and were
tentatively ascribed to the canted antiferromagnetism with spin-
glass-like relaxation. Since the randomness (defects, disorder, etc.)
and frustration (geometrical or competitive) are responsible for the
spin-glass system21, the spin-glass-like behaviour of 1 and 2 could
be related to possible crystal defects and/or the presence of some
degree of superparamagnetic relaxation of the magnetization of 1
and 2.
ˆ
ˆ ˆ
by using a dimmer isotropic Heisenberg model H = -2JS1S2
for two interacting S = 3/2 centers as well as compound 1. The
best fit for calculated and experimental data was achieved above
70 K for J = -1.83 cm-1 and g = 2.36 with the agreement factor
R = R(cmTexp - cmTcal)2/R(cmTexp)2 of 3.7 ¥ 10-5. The coupling
interactions in the two dimmers are of same magnitude, which is
consistent with the similar structures in compound 1 and 2.
Below 50 K an abrupt increase in cMT vs. T was observed,
suggesting a ferromagnetic phase transition.25 This low temper-
ature behaviour may arise from the presence of canting between
the antiparallel alignment of the spins26. Furthermore, a hysteresis
loop was observed at 2 K with a coercive field (HC) of 265 Oe and
remnant magnetization (MR) of 0.032 Nb mol-1 (Fig. 6, Inset a),
indicating a soft-magnet-type behaviour. The data from an M–
H curve at 2 K (Fig. 6, Inset b) showed that the magnetization
attained a highest value at 7 KOe. As well as 2, the observation of
the spin canting in 2 should arise from the antisymmetric exchange
in the dinuclear entity together with the anisotropy of the Co2+ ions
because they have similar molecular structures.22
Conclusion
In this work we have synthesized and characterized three
novel coordinated compounds {[Co2(Bib)3Cl2]Cl(CH3COO)}·
CH3OH·H2O, (1), [Co2(Bib)3Cl2]Cl2·(CH3OH)2·H2O, (2) and
[Co3K1(Tib)2(CH3COO)6]PF6 (3) (Bib = 1,3-bis(4,5-dihydro-1H-
imidazol-2-yl)benzene; Tib = 1,3,5-tris(4,5-dihydro-1H-imidazol-
2-yl)benzene). In the crystal structure of binuclear triple-helical
[Co2(Bib)3Cl2]2+ cations in 1 and 2, each Co(II) ion was in a highly
distorted tetrahedral coordination geometry with a cis–trans ratio
of 1 : 2 from the Bib ligand. In the [Co3K1(Tib)2(CH3COO)6] unit
in 3, each Co(II) ion was also in a highly distorted tetrahedral
coordination geometry and the Tib ligands acted in an offset
fashion in C,C,C and A,A,A coordination to the Co(II) ions
with p–p stacking interactions between two benzene rings from
the Tib ligand in the cluster cation. Each Tib ligand in the
cluster unit acted as a tridentate entity to ligate three Co(II) ions
resulting in a cylinder-like cluster structure. The intermolecular
hydrogen bonds in the solid-state resulted in the well-shaped 2D
The zero-field ac magnetic susceptibility measurements were
performed under 1–997 Hz. Surprisingly, both the in-phase and
out-of-phase signals, cM¢ and cM¢¢, display a maximum which is
strong frequency dependent (Fig. 7), implying a slow relaxation
process. This slow relaxation process could be caused by either
domain wall movements23 or spin-glass behaviours.24 The shift of
the peak temperature (Tp) of cM¢ is measured by a parameter
f = (DTp/Tp)/D(logf ) = 0.01 (f is the frequency of Hac), which
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layer network which was formed in a honeycomb hexagonal ring
and 3D supramolecular architecture in 1, the 3D supramolecular
architecture which was connected to the 2D sheet into 3D for
2 and the 3D supramolecular architecture which was extended
to a well-shaped 2D sheet layer network for 3. The results from
magnetic data, in the high-temperature region, showed that 1 and 2
obeyed the Curie–Weiss law with an antiferromagnetic interaction
property. In addition, 1 and 2 showed magnetic ordering at low
temperature due to the canting effect. The zero-field ac magnetic
susceptibility measurements for 1 and 2 displayed a maximum,
which was frequency dependent owing to a slow relaxation process,
which could be caused by either domain wall movements or spin-
glass behaviours.
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Acknowledgements
This work was financially supported by LADPSHNU (DZL806),
NSFC (50802059), FSHE (07ZZ68), KSTS (065212050), SLADP
(S30406), KLSH (07dz22303), SMEC (08YZ68) and SNU (PL619
and SK200718).
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