Synthesis and structure of a penta- and hexa-coordinated tri-nuclear cobalt(II) complex

Article abstract of DOI:10.3184/174751912X13366711594575

The tri-nuclear cobalt(II) complex, [(CoL)₂(μ-OAc) ₂Co]·2CHCl₃ (H₂L = 5,5'-dimethoxy-2,2'- [(ethylene)dioxybis(nitrilome thylidyne)]diphenol), has been synthesised. Its X-ray structure shows it to contain two ac

Full text of DOI:10.3184/174751912X13366711594575

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 387
JULY, 387–390
Synthesis and structure of a penta- and hexa-coordinated tri-nuclear
cobalt(II) complex
Xiu-Yan Dong*, Yin-Xia Sun, Li Wang and Li Li
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu, 730070, P. R. China
The tri-nuclear cobalt(II) complex, [(CoL)2(µ-OAc)2Co]·2CHCl3 (H2L = 5,5’-dimethoxy-2,2’-[(ethylene)dioxybis(nitrilome
thylidyne)]diphenol), has been synthesised. Its X-ray structure shows it to contain two acetate ions coordinating to
the three cobalt(II) atoms through Co−O−C−O−Co bridges, and four µ-phenoxo-oxygen atoms from two [CoL] chel-
ates also coordinating to the central cobalt(II) atom. The complex possesses two penta- and one hexa-coordinated
cobalt atoms. The crystal packing of the CoII complex shows that a 2D-layer supramolecular network parallel to the
ab-plane is formed through intermolecular C–H···O and C–H···Cl hydrogen bonding interactions.
Keywords: salen-type bisoxime ligand, CoII complex, synthesis, crystal structure
to a solution of H2L (11.9 mg, 0.033 mmol) in chloroform (6 mL) at
room temperature. The colour of the mixing solution turned to brown
immediately and the solution was stirred for 2 h at room temperature.
The resulting mixture was filtered and the filtrate was allowed to stand
at room temperature for about one week, after which the solvent
was partially evaporated to give rhombohedral reddish-brown single
crystals suitable for X-ray crystallographic analysis. Anal. Calcd for
C42H44Cl6Co3N4O16 {[(CoL)2(OAc)2Co]·2CHCl3}: C, 40.35; H, 3.55;
N, 4.48; Co, 14.14. Found: C, 40.43; H, 3.56; N, 4.45; Co, 14.02%.
The synthesis and reactivity of transition metal complexes
with tetradentate salen ligands have been playing an important
role in the development of coordination chemistry.1 The
cobalt(II) complexes of these ligands have been extensively
used to mimic cobalamin (B12) coenzymes,2 dioxygen carriers
and oxygen activators,3,4 reversible oxygen transport5 and
catalysts for the oxygenation reactions of organic molecules.6
The influence of versatile cobalt complexes stimulated us to
study their structures, chemical, spectroscopic and thermal
behaviour. We report here a new tri-nuclear cobalt(II) complex
[(CoL)2(µ-OAc)2Co]·2CHCl3 (1) with a salen-type bisoxime
ligand (H2L = 5,5′-dimethoxy-2,2′-[(ethylene)dioxybis(nitrilo-
methylidyne)]diphenol). In contrast to the complexation of
H2L with cobalt(II) acetate, the reaction of its parent, H2salen,
with cobalt(II) acetate is strikingly different from that of H2L,
giving a mononuclear complex [Co(salen)]7 upon complex-
ation.
Crystal structure determination
A single crystal of 1 with approximate dimensions of 0.54 × 0.43 ×
0.24 mm was selected and mounted on a Bruker Smart 1000 Apex
CCD area detector. The diffraction data were collected using a graph-
ite monochromated MoKα radiation (λ = 0.071073 nm) at 298(2) K.
The structure was solved by direct methods and difference Fourier
techniques (SHELXS-97),12 refined by full matrix least squares on F2
using the program (SHELXL-97).13 The final refinements converged at
R1 = 0.0562, wR2 = 0.1357 with w = 1/[σ2(F02) + (0.0791P)2 + 0.0000P],
where P = (F02+2Fc2)/3. All atoms were refined with anisotropic dis-
placement parameters. The crystal data and experimental parameters
relevant to the structure determination are listed in Table 1. The non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were added theoretically. The full crystallographic data were depos-
ited in the form of CIF files at the Cambridge Structural Database
(CCDC No. 647076) and are available freely upon request citing the
deposition number from the web site: www.ccdc.cam.ac.uk/data_
request/cif.
Experimental
4-Methoxy-2-hydroxybenzaldehyde (≥98%) was purchased fromAlfa
Aesar and used without further purification. The other reagents and
solvents were analytical grade reagents from Tianjin Chemical
Reagent Factory. Elemental analysis for Co was determined by
an IRIS ER/S·WP-1 ICP atomic emission spectrometer. C, H and N
analyses were carried out with a GmbH Vario EL V3.00 automatic
elemental analyser. IR spectra were recorded on a VERTEX70 FT-IR
spectrophotometer, with samples prepared as KBr (500–4000 cm−1)
and CsI (100–500 cm−1) pellets. The X-ray single crystal structure
was determined on a Bruker Smart 1000 APEX CCD area detector.
Melting points were measured by the use of a microscopic melting
point apparatus, (Beijing Taike Instrument Company Limited), and
are uncorrected.
Table 1 Crystal data and structure refinement for complex 1
Empirical formula
Formula weight
T /K
C42H44Cl6Co3N4O16
1250.30
298(2)
Synthesis of H2L: 1,2-Bis(phthalimidoxy)ethane was prepared accord-
ing to the literature.8 Yield: 95.6%, m.p. 250 °C. 1,2-Bis(aminooxy)-
ethane was synthesised according to an analogous method reported
earlier.9 1H NMR (400 MHz, CDCl3) 3.97 (s, 4H), 5.52 (s, 4H). H2L
was prepared by modification of the reported method.10,11 To an
ethanol solution (5 mL) of 4-methoxysalicylaldehyde (393.7 mg,
2.59mmol)wasaddedanethanolsolution(3mL)of1,2-bis(aminooxy)-
ethane (118.0 mg, 1.28 mmol). The mixing solution was stirred at
55 °C for 5 h. After cooling to room temperature, the resulted solid
was filtered on a G3 glass frit, and washed successively with ethanol
and ethanol/hexane (1:4), respectively. The product was dried in a
vacuum, to give a colourless flocculent crystalline solid (352.2 mg
Wavelength /nm
0.071073
Crystal system, Space group Triclinic, P-1
a, b, c, Å
10.881(2), 11.095(2), 13.008(2)
67.574(2), 65.887(2), 71.093(3)
α, b, γ, deg
Volume, Å3
1298.4 (4)
1, 1.599
1.325
Z, Calculated density/g cm−3
Absorption correction/mm−1
F (000)
635
Crystal size, mm
0.54×0.43×0.24
θ range for data collection/deg 1.97–25.01
Limiting indices
−12 ≤ h ≤ 12, −10 ≤ k ≤ 13,
−15 ≤ l ≤ 15
Reflections collected/unique
Completeness to θ/deg
Absorption correction
6643/4479 [Rint = 0.0327]
98.1% (θ = 25.01)
Semi-empirical from
equivalents
1
76.3% yield). M.p. 97–98 °C. H NMR (400 MHz, CDCl3) 3.79
(s, 6H), 4.41 (s, 4H), 6.46 (d, J = 2.8 Hz, 2H), 6.47 (s, 2H), 7.04 (d,
J = 2.8 Hz 2H), 8.17 (s, 2H), 9.94 (s, 2H). Anal. Calcd for C18H20N2O6
(H2L): C, 59.99; H, 5.59; N, 7.77. Found: C, 59.95; H, 5.86; N,
7.63%.
Max./min. transmission
Refinement method
Data/restraints/parameters
GOOF F2
0.7415/0.5347
Full-matrix least-squares on F2
4479/0/322
Synthesis of CoII complex (1): A solution of cobalt(II) acetate tetra-
hydrate (8.3 mg, 0.033 mmol) in ethanol (2 mL) was added dropwise
0.993
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0562, wR2 = 0.1357
R1 = 0.0983, wR2 = 0.1527
Largest diff. peak/hole/ e Å–3) 0.827/−0.812
* Correspondent. E-mail: dxy568@163.com

388 JOURNAL OF CHEMICAL RESEARCH 2012
Analysis of FT-IR spectra
IR spectra of H2L and 1 are shown in Fig. 1. The free ligand H2L
exhibits Ar–O and C=N stretching bands at 1211 and 1633 cm−1,
which are shifted to lower frequencies by ca 49 and 23 cm−1 upon
complexation. This lowering of energy results from the Co–O and
Co–N interaction upon complexation and is similar to that reported
for copper(II),8,10 zinc(II), cobalt(II)9 and nickel(II)14 complexes.
Moreover, a bending vibration of phenolic alcohols in H2L at 1282
cm−1, which disappears in 1, indicates that the oxygen atoms in the
phenolic groups of 1 have been completely deprotonated and coordi-
nate to the cobalt(II) atoms. In addition, 1 shows the expected strong
absorption band due to ν(C–Cl) at ca 742 cm−1, which is evidence for
the existence of a chloroform molecule.
The spectrum of 1 was also obtained in the region 500–100 cm−1 in
order to identify frequencies due to the Co–O and Co–N bonds. 1
shows ν(Co–O) and ν(Co–N) vibrational absorption frequencies at
403 cm−1 and 472 cm−1, respectively. These assignments are consistent
with the literature frequency values.15
Fig. 2 Molecular structure of complex 1 with the atomic num-
bering. Displacement ellipsoids for non-hydrogen atoms are
drawn at the 30% probability level.
Determination of molar conductance
Complex 1 is soluble in DMSO, DMF, but not soluble in methanol,
ethanol, THF, acetonitrile, acetone, ethyl acetate and hexane.
The molar conductance value of 1 at 25 °C of 10−3 mol·dm−3 DMF
solutions is 8.6 Ω−1·cm2·mol−1, indicating that the complex is a non-
electrolyte. These data imply that all the acetate groups in 1 are always
held in the coordination sphere in solution or the solid state.
The coordination number of cobalt(II) atoms in salen-cobalt(II)
complexes is generally four or six and the coordination
geometry around Co(II) atom is tetrahedral or octahedral.2,16
However, there are a few reports of penta-coordinated cobalt(II)
complexes,8 which have distorted square-pyramidal or trigo-
nal-bipyramidal geometry. We have synthesised and structur-
ally characterised a trinuclear cobalt(II) complex in which the
terminal cobalt atoms (Co2 and Co2#1) show the coordination
number of five and the central cobalt atom shows the coordina-
tion number of six, whereas the salen-cobalt(II) complex is
penta-coordinated in the dimer of {Co(salen)}.7
Results and discussion
X-ray crystallographic analysis reveals the crystal structure of
1. Selected bond lengths and angles are summarised in Table 2
and the ORTEP representation of 1 is shown in Fig. 2.
X-ray crystallographic analysis of 1 reveals formation of a
trinuclear structure [(CoL)2(µ-OAc)2Co]·2CHCl3 consisting of
three cobalt(II) atoms, two L2− units, two coordinated acetate
atoms and two chloroform molecules of crystallisation as
expected from the analytical data. The cobalt(II) atom (Co2) is
penta-coordinated by N2O2 donors (N1, N2, O3, O5) of L2−
unit and one oxygen atom (O8) of the acetate ion, which
constitute a distorted square-pyramidal geometry around the
Co2 atom. The dihedral angle between the coordination plane
of O3–Co2–N1 and that of O5–Co2–N2 is 35.95(3)º, indicat-
ing significant distortion toward tetrahedral geometry from the
square planar structure. The equatorial plane of Co2 atom is
defined by N1, N2, O3, O5 atoms with the largest deviation
of Co2 at 0.416(3) Å. The ethylenedioxime carbons C1 and
C2 are buckled asymmetrically from the Co2–N1–N2 plane,
with the displacement for C1 being 1.906(2) Å toward the
plane and for C2 being only 1.350(3) Å in the same direction.
Fig. 1 IR absorption spectra of H2L and 1.
Table 2 Selected bond lengths (Å) and bond angles (deg) for complex 1
Bond lengths
Co(1)–O(5)
Co(1)–O(5)#1
Co(1)–O(7)#1
Co(1)–O(7)
2.064(3)
2.064(3)
2.067(3)
2.067(3)
Co(1)–O(3)
Co(1)–O(3)#1
Co(2)–O(3)
Co(2)–O(8)
2.163(3)
2.163(3)
1.954(3)
1.972(4)
Co(2)–N(2)
Co(2)–N(1)
Co(2)–O(5)
2.013(4)
2.049(4)
2.080(3)
Bond angles
O(5)–Co(1)–O(5)#1
O(5)–Co(1)–O(7)#1
O(5)#1–Co(1)–O(7)#1
O(5)–Co(1)–O(7)
O(5)#1–Co(1)–O(7)
O(7)#1–Co(1)–O(7)
O(5)–Co(1)–O(3)
O(5)#1–Co(1)–O(3)
O(7)#1–Co(1)–O(3)
180.0
O(7)–Co(1)–O(3)
O(5)–Co(1)–O(3)#1
O(5)#1–Co(1)–O(3)#1
O(7)#1–Co(1)–O(3)#1
O(7)–Co(1)–O(3)#1
O(3)–Co(1)–O(3)#1
O(3)–Co(2)–O(8)
O(3)–Co(2)–N(2)
O(8)–Co(2)–N(2)
91.46(12)
103.98(12)
76.02(12)
91.46(12)
88.54(12)
180.0
102.44(14)
145.40(17)
110.41(16)
O(3)–Co(2)–N(1)
O(8)–Co(2)–N(1)
N(2)–Co(2)–N(1)
O(3)–Co(2)–O(5)
O(8)–Co(2)–O(5)
N(2)–Co(2)–O(5)
N(1)–Co(2)–O(5)
89.35(14)
99.27(16)
95.68(16)
80.36(12)
94.99(14)
86.16(15)
163.94(15)
91.35(13)
88.65(13)
88.65(13)
91.35(13)
180.00(7)
76.02(12)
103.98(12)
88.54(12)
Symmetry transformations used to generate equivalent atoms: # –x,–y+1,–z+1

JOURNAL OF CHEMICAL RESEARCH 2012 389
Fig. 3 View of the 1D chain motif of complex 1 along the a axis (hydrogen atoms, except those forming hydrogen bonds, are
omitted for clarity).
Table 3 Hydrogen bonds (Å, °) in complex 1
These are not similar to our previously reported complexes
[L4Co8(H2O)2X] (X = H2O or EtOH).8
D–H···A
d(D–H) d(H···A) ∠DHA
d(D···A)
The cobalt atom (Co1) is hexa-coordinated by four oxygen
atoms (O3, O5, O3#1, O5#1) of phenolic alcohols which have
been completely deprotonated in two [CoL] chelates, and by
two oxygen atoms (O7 and O7#1) of the acetate ions. The L2−
units serve both as tetradentate N2O2 ligands for terminal cobalt
atoms (Co2 and Co2#1) and at the same time bidentate moieties
C17–H17···Cl3
C20–H20C···Cl3
C21–H21···O7
C2−H2A···O8
C2−H2B···O4
0.93
0.96
0.98
0.97
0.97
2.94
2.95
2.36
2.67
2.41
154
149
161
142
149
3.793(3)
3.802(2)
3.298(3)
3.480(5)
3.279(2)
Fig. 4 View of the 1D chain motif of complexes 1 along the b axis (hydrogen atoms, except those forming hydrogen bonds, are
omitted for clarity).
Fig. 5 View of a 2D-layer supramolecular network within complex 1 (hydrogen atoms, except those forming hydrogen bonds, are
omitted for clarity).

390 JOURNAL OF CHEMICAL RESEARCH 2012
for the central cobalt atom (Co1). The double µ-acetato-
bridges adopt the more familiar µ-O–C–O form and connect
the Co2–Co1 and Co1–Co2#1, respectively, so four µ-phenoxo
oxygen atoms from two L2− moieties and the two oxygen atoms
from the µ-acetato-groups constitute a distorted octahedral
geometry around the Co1 atom.
This work was supported by the Foundation of the Education
Department of Gansu Province (No. 0904-11) and the
“Jing Lan” Talent Engineering Funds of Lanzhou Jiaotong
University, which are gratefully acknowledged.
Received 11 March 2012; accepted 9 April 2012
Paper 1201205 doi: 10.3184/174751912X13366711594575
Published online: 26 June 2012
The distances of Co2–Co1 (3.056(3) Å) and Co1–Co2#1
(3.056(3) Å) are significantly longer than those of all the Co–O
and Co–N bonds [the range of Co–O and Co–N is 1.954(3)–
2.163(3) Å] in [(CoL)2(µ-OAc)2Co]·2CHCl3, indicating a weaker
inter-metal interaction. This is similar to that of complexes
reported previously.17,18
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