Cobalt(II) complex with a tridentate N donor ligand: Synthesis, crystal structure, antioxidation, and DNA binding studies

Article abstract of DOI:10.1002/zaac.201100325

A heptacoordinated mononuclear cobalt(II) complex of tridentate bis(N-ethylbenzimidazol-2-ylmethyl)aniline (Etbba) formulated as [Co(Etbba)(pic)₂]·(MeCN) (pic = picrate), was synthesized and characterized by elemental analysis, electric conduct

Full text of DOI:10.1002/zaac.201100325

ARTICLE
DOI: 10.1002/zaac.201100325
Cobalt(II) Complex with a Tridentate N Donor Ligand: Synthesis, Crystal
Structure, Antioxidation, and DNA Binding Studies
Huilu Wu,*[a] Bin Liu,[a] Fan Kou,[a] Fei Jia,[a] Jingkun Yuan,[a] and Ying Bai[a]
Keywords: Cobalt; Crystal structure; Antioxidants; DNA intercalation; Hydroxyl scavenging
Abstract. A heptacoordinated mononuclear cobalt(II) complex of tri- octahedral arrangement that comprises two picrate molecules and one
dentate bis(N-ethylbenzimidazol-2-ylmethyl)aniline (Etbba) formu-
Etbba ligand molecule. The DNA-binding properties of the cobalt(II)
lated as [Co(Etbba)(pic)2]·(MeCN) (pic = picrate), was synthesized and complex were investigated by electronic absorption and fluorescence
characterized by elemental analysis, electric conductivity measure-
ments, as well as IR and UV/Vis spectroscopy. The crystal structure
of the cobalt(II) complex was determined by single-crystal X-ray dif-
spectroscopy, as well as viscosity measurements. The experimental re-
sults suggest that the cobalt(II) complex binds to DNA in an intercalat-
ing mode. In addition, the complex shows strong scavenging effects
fraction. The study shows the metal atom in a distorted monocapped for hydroxyl radicals.
Description of the Structure
Introduction
The molecular structure of [Co(Etbba)(pic)2]·(MeCN) is
shown in Figure 1, selected key bond lengths and angles are
shown in Table 1. The cobalt atom adopts a distorted mono-
capped octahedral arrangement with a N3O4 donor set by coor-
dinating to three nitrogen donor atoms from the Etbba ligand
and four oxygen atoms from picrate, to give a coordination
number of seven. The equatorial plane of the complex is de-
fined by the atoms O4, O5, O9, and N8. The maximum devia-
tion (O4) from the plane containing the four nitrogen atoms is
0.346 Å and the deviation of the cobalt atom from the mean
plane is 0.131 Å. In case of the complex, the axial positions
are occupied by the atoms N11 and O32. The distance between
the axial N11 atom and the equatorial plane is 2.257 Å, but the
distance between the axial O32 atom and the equatorial plane
is 1.804 Å. The bond angle of the two atoms in axial positions
and the metal atom (N11–Co–O32) is 109.46(7)°. The capping
atom, N1, lies 1.006 Å out of the N8/O9/N11 trigonal plane.[21]
The crystal packing of [Co(Etbba)(pic)2]·(MeCN) is shown
in Figure 2. The crystal structure is stabilized because of weak
π–π stacking between the benzimidazole rings with centroid
distances of 3.859(7) Å.
Multidentate ligands designed to govern the coordination ar-
rangements of metal atoms have found several applications in
chemistry.[1–6] In bioinorganic chemistry, bis-benzimidazoles
were extensively used to model the active sites of metalloprot-
eins.[7] The benzimidazole ring is present in clinically ap-
proved anthelmintics, antiulcers, antivirals, and antihista-
mines.[8,9] Recently, benzimidazole derivatives exhibiting anti-
tumor and antimicrobial properties, which act as thrombopoie-
tin receptor agonists have been reported.[10–12] A large number
of benzimidazole derivatives were modeled in combinatorial
approaches with the aim to create structures with improved
pharmacological activity and lesser side effects.[13–20]
In this work, we prepared a heptacoordinate cobalt(II) com-
plex, [Co(Etbba)(pic)2]·(MeCN) (pic = picrate), with the ligand
bis(N-ethylbenzimidazol-2-ylmethyl)aniline (Etbba) and inves-
tigated its properties and crystal structure.
Results and Discussion
The ligand Etbba and the complex [Co(Etbba)(pic)2]·
(MeCN) are stable in air and remarkably soluble in polar
aprotic solvents such as DMF, DMSO, and MeCN, slightly
soluble in ethanol, methanol, ethyl acetate, and chloroform,
and insoluble in water, Et2O, and petroleum ether. The molar
conductivities in DMF solution indicate that Etbba and
[Co(Etbba)(pic)2]·(MeCN) are non-electrolytes.
IR and UV/Vis Spectroscopy
The IR spectroscopic data of the free ligand and
[Co(Etbba)(pic)2]·(MeCN) were measured to identify their
structures. The IR spectrum of the free ligand Etbba shows
characteristic absorption bands of the benzimidazole group at
1613, 1499, and 1269 cm–1, which are assigned to ν(C=C)
,
ν(C=N), and ν(C–N), respectively.[22–24] The bands are shifted by
around 10 cm–1 in the spectrum of the complex, which implies
direct coordination of the metal ion to three nitrogen atoms
(two benzimidazole nitrogen atoms and one aniline nitrogen
* Prof. Dr. H. Wu
E-Mail: wuhuilu@163.com
[a] School of Chemical and Biological Engineering
Lanzhou Jiaotong University
Lanzhou 730070, P. R. China
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Cobalt(II) Complex with a Tridentate N Donor Ligand
DMF solutions of the ligand Etbba and [Co(Etbba)(pic)2]·
(MeCN) show, as expected, similar UV/Vis spectra. The UV
bands of Etbba (280 nm) are only marginally blue-shifted
(5 nm) in the complex, which is a clear evidence of C=N coor-
dination to cobalt(II). The absorption band is assigned to
πǞπ* (benzimidazole) transitions.
DNA Binding Properties
Electronic Absorption Titration
The UV absorbance at 260 and 280 nm of the CT-DNA
solution in 5 mM tris-HCl/NaCl (pH = 7.2) gave a ratio of
1.8–1.9, which indicated that the DNA was sufficiently free of
protein.[26] The stock solution of the complex was dissolved in
DMF to give a concentration of 3ϫ10–3 m. The stock solution
of DNA (2.5ϫ10–3 m) was prepared in 5 mM tris-HCl /
50 mM NaCl buffer (pH = 7.2, stored at 4 °C and used within
4 days). The concentration of CT-DNA was determined from
its absorption intensity at 260 nm using the molar absorption
coefficient as 6600 M–1·cm–1.[27] The binding constant was de-
termined using Equation (1):[28]
[DNA]/(εa–εf) = [DNA]/(εb–εf) +1/Kb(εb–εf)
(1)
Herein, [DNA] is the concentration of DNA in base pairs
and, the apparent absorption coefficients εa, εf, and εb corre-
spond to Aobsd/[M], the extinction coefficient of the free com-
pound and the extinction coefficient of the compound when
fully bound to DNA, respectively.
The application of electronic absorption spectra in DNA
binding studies is one of the most useful techniques. The ab-
Figure 1. (a) Molecular structure of [Co(Etbba)(pic)2]·(MeCN). Hy-
drogen atoms and one acetonitrile molecule are omitted for clarity. sorption spectra of the ligand Etbba and [Co(Etbba)(pic)2]·
(b) Edge-sharing distorted monocapped octahedral arrangement of the
(MeCN) in the absence and presence of CT-DNA (at a constant
N3O4 donor set coordinated to each cobalt(II) ion. Hydrogen atoms
concentration of complexes) are given in Figure 3. As can be
and noncoordinating acetonitrile molecules are omitted for clarity.
seen from Figure 3c, [Co(Etbba)(pic)2]·(MeCN) exhibits an
absorption band at 283 nm, which is assigned to πǞπ* transi-
atom). Further information on the possible binding modes of tions of the benzimidazole and picrate groups, and addition of
the picrate and benzimidazole rings may also be obtained from increasing amounts of CT-DNA results in hypochromism in
the bands at 712, 1166, 1327, and 1613 cm–1.[25] The results the UV/Vis spectra of the CoII complex. With increasing DNA
are in agreement with those determined by X-ray diffraction.
concentrations, the hypochromism values are 28.06% at
Table 1. Selected bond lengths /Å and bond angles /°.
Bond length
Co–O(32)
Co–N(11)
Co–O(4)
Co–N(1)
2.022(3)
2.163(3)
2.459(2)
2.778(3)
Co–O(5)
Co–N(8)
Co–O(9)
2.140(2)
2.188(3)
2.719(4)
Bond angle
O(32)–Co–O(5)
O(5)–Co–N(11)
O(5)–Co–N(8)
O(32)–Co–O(4)
N(11)–Co–O(4)
O(32)–Co–O(9)
N(8)–Co–O(9)
O(32)–Co–N(1)
N(11)–Co–N(1)
O(4)–Co–N(1)
89.90(11)
105.99(10)
95.17(10)
87.54(10)
77.70(9)
130.09(9)
131.15(10)
102.64(10)
67.99(9)
O(32)–Co–N(11)
O(32)–Co–N(8)
N(11)–Co–N(8)
O(5)–Co–O(4)
N(8)–Co–O(4)
N(11)–Co–O(9)
O(4)–Co–O(9)
O(5)–Co–N(1)
N(8)–Co–N(1)
O(9)–Co–N(1)
109.46(7)
102.42(12)
97.78(10)
70.85(8)
163.02(10)
87.40(10)
65.45(9)
161.88(8)
69.59(9)
67.72(9)
122.08(8)
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H. Wu, B. Liu, F. Kou, F. Jia, J. Yuan, Y. Bai
ARTICLE
Figure 2. Structure of [Co(Etbba)(pic)2]·(MeCN) linked by π–π stacking interactions.
Figure 3. Electronic spectra of Etbba (a) and [Co(Etbba)(pic)2]·(MeCN) (c) in tris-HCl buffer upon addition of calf-thymus DNA. [compound]
= 3ϫ10–5 M, [DNA] = (0–10)ϫ10–5 M. The arrows show the emission intensity changes upon increasing the DNA concentration. Plots of
[DNA] / (εa–εf) versus [DNA] for the titration of Etbba (b) and [Co(Etbba)(pic)2]·(MeCN) (d) with CT-DNA.
288 nm for the ligand Etbba and 25.63% at 283 nm for the CoII complex interacts with DNA, most likely through a mode
CoII complex. These spectral characteristics suggest that the that involves a stacking interaction between the aromatic chro-
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Cobalt(II) Complex with a Tridentate N Donor Ligand
mophore and the base pairs.[29,30] The binding constant Kb was
estimated to be 1.22ϫ105 M–1 (R2 = 0.9995 for ten points) for
[Co(Etbba)(pic)2]·(MeCN) and 5.56ϫ104 M–1 (R2 = 0.99754
for ten points) for the ligand Etbba, respectively. Compared
with those of a so-called DNA intercalative ruthenium
complex,[31] the binding constants (Kb) of Etbba and
[Co(Etbba)(pic)2]·(MeCN) suggest that the two compounds
most probably bind to DNA in an intercalating mode. With the
above intrinsic binding constant values, the binding affinity of
[Co(Etbba)(pic)2]·(MeCN) is stronger than that of Etbba.
In order to further study the binding properties of the com-
plex with DNA, competitive binding experiments were carried
out. Relative binding of [Co(Etbba)(pic)2]·(MeCN) to CT-
DNA was studied by fluorescence spectroscopy using an EB-
bound CT-DNA solution in tris-HCl / NaCl buffer (pH = 7.2).
Ethidium bromide (EB) is a weakly fluorescing compound, but
in the presence of DNA its emission intensity is greatly en-
hanced because of its strong intercalation between the adjacent
DNA base pairs. It was previously reported that the enhanced
luminescence can be quenched by adding a second mole-
cule.[32,33]
A competitive binding of [Co(Etbba)(pic)2]·
(MeCN) to CT-DNA resulted in the displacement of bound EB
or in quenching of the bound EB, and as a consequence the
emission intensity of ethidium bromide decreased. In the com-
petitive binding experiment, 10 μL of a CT-DNA solution was
added to 10 μL of an EB buffer solution (pH = 7.2), and the
fluorescence intensity was measured using an excitation wave-
length of 520 nm resulting in an emission at about 600 nm.
Upon addition of the CoII complex, the emission intensity
of the EB-bound calf thymus (CT-DNA) solution decreases,
which indicates that [Co(Etbba)(pic)2]·(MeCN) competes with
Competitive Binding with Ethidium Bromide
Fluorescence quenching experiments were studied by add-
ing a solution of [Co(Etbba)(pic)2]·(MeCN) (30 μM) into a
EB-bound calf thymus DNA (CT-DNA) solution in 5 mM tris-
HCl / 50 mM NaCl buffer (pH = 7.2) at different concentra-
tions. The fluorescence spectra of ethidium bromide (EB) were
measured using an excitation wavelength of 520 nm, the emis-
sion range being set between 550 and 750 nm.
Figure 4. Emission spectra of Etbba (a) and [Co(Etbba)(pic)2]·(MeCN) (c) in tris-HCl buffer upon addition of calf-thymus DNA. [compound]
= (0–6)ϫ10–5 M; λex = 520 nm. The arrows show the emission intensity changes upon increasing the DNA concentration. Plots of I0/I versus
[compound] for the titration of Etbba (b) and [Co(Etbba)(pic)2]·(MeCN) (d) with CT-DNA.
Z. Anorg. Allg. Chem. 2012, 122–128
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H. Wu, B. Liu, F. Kou, F. Jia, J. Yuan, Y. Bai
ARTICLE
EB for DNA-binding (Figure 4c). The extent of the reduction
of the emission intensity gives a measure of the binding pro-
pensity of the complex to CT-DNA. According to the classical
Stern–Volmer equation:[32,34]
I0/I = 1 + KSV[Q],
where I0 is the emission intensity in absence of the quencher,
I is the emission intensity in presence of the quencher, KSV is
the quenching constant and [Q] is the CoII complex. As shown
in Figure 4, the fluorescence intensity decrease obviously with
the increasing concentration of the ligand Etbba and the CoII
complex. The KSV value is 7.21ϫ102 M–1 (R2 = 0.99322 for
eight points) for the ligand and 4.37ϫ103 M–1(R2 = 0.98804
for eight points) for the CoII complex, respectively. The
quenching plots illustrate that the amounts of quenching of EB
bound to DNA by the compounds are in good agreement with
the linear Stern–Volmer equation and the binding ability of
the two compounds follows the order: CoII complex Ͼ Etbba.
Furthermore, the quenching constants of the ligand and the
CoII complex suggest that the interaction of the compounds
with DNA should be intercalating.
Figure 5. Effect of increasing amounts of Etbba and
[Co(Etbba)(pic)2]·(MeCN) on the relative viscosity of CT-DNA at
25.0Ϯ0.1 °C.
Hydroxyl Radical Scavenging Activity
The hydroxyl radicals in aqueous media were generated
through the Fenton-type reaction.[40,41] The 3 cm3 reaction
mixtures contained 1.0 cm3 of 0.10 mmol aqueous safranin,
1 cm3 of 1.0 mmol aqueous EDTA–FeII, 1 cm3 of 3% aqueous
H2O2, and a series of quantitatively microadded solutions of
the tested compound. An item without the tested compound
was used as control sample. The reaction mixtures were incu-
bated at 37 °C for 60 min in a water-bath. Absorbance at
520 nm was measured and the solvent effect was corrected
throughout. The hydroxyl radicals bleached the safranine, so a
decreased absorbance of the reaction mixture indicated de-
creased hydroxyl radical scavenging ability.[42] The scavenging
effect for OH· was calculated from the following expression:
Viscosity Studies
Viscosity experiments were conducted with an Ubbelodhe
viscosimeter, immersed in a thermostated water-bath main-
tained at 25 °C. Titrations were performed for the compounds
(3–30 μM), and the complex was introduced into the CT-DNA
solution (50 μM) present in the viscometer. Data were pre-
sented as (η/η0)1/3 versus the ratio of the concentration of the
compound to CT-DNA, where η is the viscosity of CT-DNA
in the presence of the complex, and η0 is the viscosity of CT-
DNA alone. Viscosity values were calculated from the ob-
served flow time of CT-DNA containing solutions corrected
for the flow time of the buffer alone (t0) with the equation:[35]
η = (t–t0)/t0
Optical photophysical probes generally provide necessary,
but not sufficient clues to support a binding model. Measure-
ments of DNA viscosity that is sensitive to DNA length are
regarded as the least ambiguous and the most critical tests of
binding in solution in the absence of crystallographic structural
data.[36,37] Intercalating agents are expected to elongate the
double helix to accommodate the ligands in between the bases
leading to an increase in the viscosity of DNA. In contrast,
complexes that bind exclusively in the DNA grooves by partial
and/or non-classical intercalation under the same conditions
typically cause less pronounced (positive or negative) or no
change in DNA solution viscosity.[38] The values of (η/η0)1/3
were plotted against [compound]/[DNA] (Figure 5). Upon ad-
dition of the ligand or [Co(Etbba)(pic)2]·(MeCN), the viscosity
of rod-like CT-DNA increased significantly, which suggests
that Etbba and [Co(Etbba)(pic)2]·(MeCN) are able to bind to
DNA in an intercalating mode.[39]
Scavenging effect (%) = (Asample – Ablank) / (Acontrol
Ablank)ϫ100,
–
where Asample is the absorbance of the sample in the pres-
ence of the tested compound, Ablank is the absorbance of the
blank in the absence of the tested compound and Acontrol is the
absorbance in the absence of the tested compound and EDTA–
FeII.[43,44] The IC50 values for the complexes were determined
by plotting the graph of percentage inhibition of hydroxyl radi-
cal reduction against the increase in the concentration of the
complex. The concentration of the complex, which causes
50% inhibition of the hydroxyl radical reduction is reported as
IC50.
Mannitol is a well-known natural antioxidant, so we also
studied the scavenging activity of mannitol against hydroxyl
radicals using the same mode.[45] Figure 6 shows the plots of
hydroxyl radical scavenging effects (%) for Etbba and
[Co(Etbba)(pic)2]·(MeCN), respectively, which are concentra-
tion-dependent. Notably, the hydroxyl radical scavenging ef-
fect of [Co(Etbba)(pic)2]·(MeCN) is much higher than that of
Etbba, possibly because the larger conjugated metal complex
is able to react with OH· to form larger stable macromolecular
radicals than the ligand.[46] As shown in Figure 6, the
IC50 value of [Co(Etbba)(pic)2]·(MeCN) for OH· is 56 μM,
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Cobalt(II) Complex with a Tridentate N Donor Ligand
whereas the IC50 value of mannitol is 9.6 mM.[47] Notably,
[Co(Etbba)(pic)2]·(MeCN) has much stronger scavenging abil-
ity for OH·. It was believed that the information obtained from
present work would be useful to develop new potential antioxi-
dants and therapeutic agents for some diseases.
Synthesis of Bis(benzimidazol-2-ylmethyl)aniline(bba): A mixture
of phenylimiodiacetic acid (54.25 g, 0.25 mol)[48] and o-phenylenedia-
mine (54.00 g, 0.50 mol) in ethylene glycol (250 mL) was heated to
reflux for 24 h. The yellow precipitate was filtered and washed with
distilled water. M.p. 258–259 °C. Yield 82.05 g (75.8%). Calculated
for C22H19N5: C 74.77, H 5.42, N 19.82%; found: C 74.79, H 5.41,
N 19.83%. IR (KBr): ν˜ = 1600 (m), 1445 (m), 1272 (m), 743 (m)
cm–1. 1H NMR (400 MHz, [D6]DMSO): δ = 7.2–7.68 (m, 10 H, benz-
imidazole), 6.55–7.10 (m, 5 H, Ph), 5.14 (s, 4 H, CH2) ppm. ΛM (DMF,
297 K): 2.69 S·cm2·mol–1. UV/Vis (DMF): λ = 282 nm.
Synthesis of Bis(N-ethylbenzimidazol-2-ylmethyl)aniline (Etbba):
Bis(benzimidazol-2-ylmethylene)aniline (5.3 g, 0.015 mol) with potas-
sium (1.17 g, 0.03 mol) in evaporated tetrahydrofuran (150 mL) was
followed by adding iodoethane (4.6 g, 0.03 mol) . The resulting solu-
tion was concentrated and recrystallized from methanol, which gave
pale yellow block crystals of Etbba. Yield 6.6 g, 61.3%. Calculated
for C26H27N5: C 76.25, H 6.65, N 17.10%; found: C 76.35, H 6.50,
N, 17.15%. IR (KBr): ν˜ = 1599 (m), 1460 (m), 1268 (m), 745 (m)
cm–1. 1H NMR (400 MHz, [D6]DMSO): δ = 7.22–7.60 (m, 8 H, benz-
imidazole), 7.21–6.83 (m, 5 H, Ph), 4.87 (s, 4 H, CH2), 4.16–4.05 (s,
10 H, CH2CH3) ppm. ΛM (DMF, 297 K): 2.82 S·cm2·mol–1. UV/Vis
(DMF): λ = 280 nm.
Figure 6. Plots of hydroxyl radical scavenging effect (%) for Etbba
and [Co(Etbba)(pic)2]·(MeCN).
Synthesis of the Complex Co(Etbba)(pic)2: To a stirred solution of
Etbba (0.129 g, 0.5 mmol) in hot MeOH (10 mL) was added Co(pic)2
(0.205 g, 0.25 mmol) in MeOH (5 mL). A pale-yellow crystalline
product formed rapidly. The precipitate was filtered off, washed with
MeOH and absolute Et2O, and dried in vacuo. The dried precipitate
was dissolved in DMF to form a yellow solution into which Et2O was
allowed to diffuse in at room temp. Pale yellow crystals of
Co(Etbba)(pic)2 suitable for X-ray diffraction were obtained after five
days. Calculated for C40H34N12O14Co: C 49.75, H 3.55, N 17.40, Co
6.10%; found: C 49.55, H 3.35, N 17.60, Co 6.20%. IR (KBr): ν˜ =
1613 (m), 1499 (m), 1327 (m), 746 (m) cm–1. ΛM (DMF, 297 K): 13.7
S·cm2·mol–1. UV/Vis (DMF): λ = 275, 380 nm.
Conclusions
The novel complex [Co(Etbba)(pic)2]·(MeCN) was synthe-
sized and characterized by elemental analysis, molar conduc-
1
tivity, H NMR, IR, and UV/Vis spectroscopy. DNA binding
properties of the free ligand Etbba and [Co(Etbba)(pic)2]·
(MeCN) were investigated by UV absorption spectroscopy,
fluorescence spectroscopy, and viscosity measurements. The
results support the fact that both compounds bind to DNA in
an intercalating mode. In addition, [Co(Etbba)(pic)2]·(MeCN)
has active scavenging effects on OH·. Our research should be
valuable for seeking and designing new antitumor drugs and
antioxidants, as well as for understanding the mechanism of
DNA-binding.
X-ray Structure Determination: A suitable single crystal was
mounted on a glass fiber and the intensity data were collected with a
Bruker APEX-II CCD diffractometer with graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å) at 153 K. Date reduction and cell
refinement were performed using SAINT programs.[49] The absorption
corrections were carried out by the empirical method. The structure
was solved by direct methods and refined by full-matrix least-squares
against F2 of data using SHELXTL software.[50] All hydrogen atoms
were found in difference electron maps and were subsequently refined
in a riding model approximation with C–H distances ranging from 0.95
to 0.98 Å and Uiso (H) = 1.2 Ueq (C). A summary of parameters for
the data collections and refinements is given in Table 2.
Experimental Section
Materials and Physical Measurements: Ethidium bromide (EB) and
calf thymus DNA (CT-DNA) were obtained from Sigma Chemicals
Co. (USA). Solvents used in this research were purified by standard
procedures. Tris-HCl buffer solution was prepared using bidistilled
water. Other reagents and solvents were reagent grade obtained from
commercial sources and used without further purification. Elemental
analyses were performed with a Carlo Erba 1106 elemental analyzer.
IR spectra were recorded with a Nicolet FT-Vertex 70 spectrometer in
the range 4000–400 cm–1 using KBr pellets. Electronic absorption
spectra were taken with a Lab Tech UV Bluestar plus UV/Vis Spectro-
photometer. Fluorescence spectroscopic data were obtained with a Ls-
45 Spectrofluorophotometer at room temperature. Viscosity experi-
ments were conducted with an Ubbelodhe viscosimeter, immersed in
Crystallographic data (excluding structure factors) for the structure in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the
depository number CCDC-828741 (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk)
Acknowledgement
1
a thermostated water-bath maintained at 25 °C. H NMR spectra were
The authors acknowledge the financial support and a grant from “Qing
Lan” Talent Engineering Funds. The grant from “Long Yuan Qing
Nian” of Gansu Province is also acknowledged.
obtained with a Mercury plus 400 MHz NMR Spectrometer with TMS
as internal standard and [D6]DMSO as solvent.
Z. Anorg. Allg. Chem. 2012, 122–128
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ARTICLE
Table 2. Crystal data and structure refinement for Co(Etbba)(pic)2.
Formula
Mw /g·mol
C40H34N12O14Co
965.72
C2/c
monoclinic
20.633(3)
19.698(3)
23.894(4)
113.05(3)
8
293(2)
1.436
0.452
3976
1.85 to 25.00
–24 Յ h Յ 24
23 Յ k Յ 23
–28 Յ l Յ 28
Full-matrix least-squares on F2
7839 / 402 / 607
1.094
–1
Crystal system
Space group
a /Å
b /Å
c /Å
β /°
Z
T /K
Dcalcd /g·cm–3
Absorption coefficient /mm–1
F(000)
θ Range for data collection /°
hkl Range
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
R1/wR2 [I Ն 2σ(I)]a)
0.0619/ 0.1720
0.0853/0.1859
Large diff. peak and hole /e·Å–3
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Published Online: September 29, 2011
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