Naphthalenediol-based bis(Salamo)-type homo- and heterotrinuclear cobalt(II) complexes: Syntheses, structures and magnetic properties

Article abstract of DOI:10.1016/j.poly.2017.05.051

Homo- and heterotrinuclear Co(II) complexes with a new acyclic bis(Salamo)-type ligand H₄L, which bears a C-shaped O₆ site by the metallation of the N₂O₂ Salamo moieties, were synthesized. The homotrinuclear complex [Co₃(L)(OAc)₂(CH₃OH)₂]·2CHCl₃ (1) was obtained by the reaction of H₄L with 3 equivalents of Co(OAc)₂·4H₂O. The heterotrinuclear complexes [Co₂(L)Ca(OAc)₂] (2), [Co₂(L)Sr(OAc)₂] (3) and [Co₂(L)Ba(OAc)₂(H₂O)]·2CH₃CH₂OH (4) were acquired by the reaction of H₄L with 2 equivalents of Co(OAc)₂·4H₂O and 1 equivalent of M(OAc)₂ (M?=?Ca(II), Sr(II) and Ba(II)). In the crystal structures, the three metal(II) atoms occupy both the N₂O₂ and O₆ sites of the ligand (L)^4? moiety. Owing to the different nature of the N₂O₂ and O₆ sites of the ligand H₄L, the introduction of two different metal(II) atoms to the site-selective moiety, when compared with complex 1, leads to the replacement of the central Co(II) atom by different alkaline earth metal(II) atoms, namely the Ca(II), Sr(II) and Ba(II) atoms for complexes 2, 3 and 4, respectively. Magnetic measurements were performed on complexes 1–4, where an intramolecular ferromagnetic interaction was found in complex 3 and intramolecular antiferromagnetic interactions were found in complexes 1, 2 and 4. The magnetic susceptibilities above 50?K obey the Curie–Weiss law and their constant values were determined for all the complexes.

Full text of DOI:10.1016/j.poly.2017.05.051

Accepted Manuscript
Naphthalenediol-based bis(Salamo)-type homo- and heterotrinuclear cobalt(II)
complexes: Syntheses, structures and magnetic properties
Han Zhang, Wen-Kui Dong, Yang Zhang, Sunday Folaranmi Akogun
PII:
S0277-5387(17)30407-2
DOI:
http://dx.doi.org/10.1016/j.poly.2017.05.051
POLY 12670
Reference:
Polyhedron
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Revised Date:
Accepted Date:
2 April 2017
12 May 2017
12 May 2017
Please cite this article as: H. Zhang, W-K. Dong, Y. Zhang, S. Folaranmi Akogun, Naphthalenediol-based
bis(Salamo)-type homo- and heterotrinuclear cobalt(II) complexes: Syntheses, structures and magnetic properties,
Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.05.051
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Naphthalenediol-based bis(Salamo)-type homo- and heterotrinuclear
cobalt(II) complexes: Syntheses, structures and magnetic properties
Han Zhang, Wen-Kui Dong *, Yang Zhang, Sunday Folaranmi Akogun
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu, 730070, P. R.
China
ABSTRACT
Homo- and heterotrinuclear Co(II) complexes with a new acyclic bis(Salamo)-type ligand H4L,
which bears a C-shaped O6 site by the metallation of the N2O2 Salamo moieties, were synthesized.
The homotrinuclear complex [Co3(L)(OAc)2(CH3OH)2]·2CHCl3 (1) was obtained by the reaction of
H4L with 3 equivalents of Co(OAc)2·4H2O. The heterotrinuclear complexes [Co2(L)Ca(OAc)2] (2),
[Co2(L)Sr(OAc)2] (3) and [Co2(L)Ba(OAc)2(H2O)]·2CH3CH2OH (4) were acquired by the reaction
of H4L with 2 equivalents of Co(OAc)2·4H2O and 1 equivalent of M(OAc)2 (M = Ca(II), Sr(II) and
Ba(II)). In the crystal structures, the three metal(II) atoms occupy both the N2O2 and O6 sites of the
ligand (L)4- moiety. Owing to the different nature of the N2O2 and O6 sites of the ligand H4L, the
introduction of two different metal(II) atoms to the site-selective moiety, when compared with
complex 1, leads to the replacement of the central Co(II) atom by different alkaline earth metal(II)
atoms, namely the Ca(II), Sr(II) and Ba(II) atoms for complexes 2, 3 and 4, respectively. Magnetic
measurements were performed on complexes 1-4, where an intramolecular ferromagnetic interaction
was found in complex 3 and intramolecular antiferromagnetic interactions were found in complexes
1, 2 and 4. The magnetic susceptibilities above 50 K obey the Curie-Weiss law and their constant
values were determined for all the complexes.
Keywords:
Salamo-type ligand; Trinuclear complex; Synthesis; Crystal structure; Magnetism
* Corresponding authors. Tel: +86 931 4938703; e-mail addresses: dongwk@126.com (W.-K. Dong).

1. Introduction
Salen-type ligands and their corresponding analogues are versatile and important compounds
[1-5]. Various kinds of functionalized Salen-type ligands have been synthesized by chemical
modification of aldehyde or diamine structures, which can be used for the synthesis of functional
metal complexes [6-8]. Salen-type N2O2 metal complexes are used as precursors to synthesize
oligometallic complexes owing to the high coordination ability of the phenoxo groups which can
bridge two metal centers in a µ2-M–O–M fashion [9-12]. Such µ2-phenoxo bridging is also
particularly important for d-block homo- and heterometallic complexes of Salen-type ligands,
some of which exhibit interesting electrochemical [4e,13], fluorescent [2c-2e,4f-4k,7a,7b] and
magnetic properties [14a,14b]. According to the recently reported acyclic bis(Salamo)-type
ligand H4L, in which two Salamo chelate moieties share one benzenediol group [15a,15b], when
alkoxy groups are introduced at the 3 position of the salicylidene moieties, an O6 coordination
site consisting of the alkoxy groups and phenoxo oxygen atoms is produced in addition to the
N2O2 site. Thus, the O6 sites of this type of ligand are particularly suitable for the larger radius of
alkaline earth and rare earth metals to afford 3d-2s and 3d-4f heterotrinuclear complexes, which
exhibit better magnetic and photochemical properties.
Recently, a part of our research project concentrated on the syntheses of a new acyclic
bis(Salamo)-type ligand H4L, in which two N2O2 Salamo chelate moieties share one naphthalenediol
group. Due to the presence of O6 sites in the bis(Salamo)-type ligand H4L, it was easy to synthesize
homo/heterotrinuclear metal complexes [15c-15e]. Here, the central Co(II) atom could be replaced
because the six oxygen atoms of the cavity could coordinate to other metal(II) atoms strongly. As a
result, taking advantage of the fact that H4L has both N2O2 and O6 sites with coordinating ability, we
have obtained 3d, 3d-2s trinuclear metal complexes and have explored their interesting crystal
structures and magnetic properties.
2. Experimental
2.1 Material and general methods
2-Hydroxy-3-methoxybenzaldehyde (99%), methyl trioctyl ammonium chloride (90%),
pyridiniumchlorochromate (98%) and borontribromide (99.9%) were purchased from Alfa Aesar.

Hydrobromic acid 33wt% solution in acetic acid was purchased from J&K Scientific Ltd. The other
reagents and solvents were purchased from Shanghai Darui Chemical Fine Chemicals Company.
Elemental analyses were performed using a GmbH VarioEL V3.00 automatic elemental analysis
instrument. FT-IR spectra were recorded on a VERTEX70 FT-IR spectrophotometer, with samples
prepared as KBr pellets (400-4000 cm-1). UV-vis absorption spectra were recorded on a Hitachi
1
U-3900H spectrometer. H and 13C NMR spectra were determined on a German Bruker AVANCE
DRX-400 spectrometer. FTICR-MS spectra were obtained on a Bruker Daltonics APEX-II 47e
spectrometer.
2.2 Synthesis of the ligand H4L
The reaction steps involved in the synthesis of the bis(Salamo)-type tetraoxime ligand (H4L) are
shown in Scheme 1. 2,3-Dihydroxynaphthalene-1,4-dicarbaldehyde was prepared according to a
literature
procedure
[16];
1,2-bis(aminooxy)ethane
and
2-[O-(1-ethyloxyamide)]oxime-6-methoxyphenol were synthesized according to an analogous
method [14c,14d]. A solution of 2,3-dihydroxynaphthalene-1,4-dicarbaldehyde (432.08 mg, 2 mmol)
in
ethanol
(20
mL)
was
added
dropwise
to
a
solution
of
2-[O-(1-ethyloxyamide)]oxime-6-methoxyphenol (904.4 mg, 4 mmol) in ethanol (20 mL) at room
temperature, the mixture was heated to reflux and kept refluxing for 6 h. After cooling down to room
temperature, the obtained yellow precipitates were filtered and washed successively with ethanol and
n-hexane. A light yellow powdery solid (H4L) was obtained and collected by filtration, washed with
absolute ethanol and dried under vacuum. Yield: 56.36%; m.p.: 172 ºC; 1H NMR (CDCl3, 400 MHz)
δ, ppm: 11.03 (s, 2H), 9.82 (s, 2H), 9.14 (s, 2H), 8.29 (s, 2H), 7.97 (q, J = 3.2 Hz, 2H), 7.41 (q, J =
6.0, 2.9 Hz, 2H), 7.06-6.68 (m, 6H), 4.58 (t, 8H), 3.89 (s, 6H) (Fig. 1). 13C NMR (DMSO, 151 MHz)
δ, ppm: 148.43 (s), 148.20 (s), 147.36 (s), 147.22 (s), 146.10 (s), 126.26 (s), 125.40 (s), 123.95 (s),
119.69 (s), 119.04 (s), 118.39 (s), 113.75 (s), 111.42 (s), 73.03 (s), 72.80 (s), 56.31 (s) (Fig. 2).
HRMS m/z, Calc. for C32H32N4O10Na: [H4L+Na]+ 655.20, found: 655.2011 (Fig. 3). Elemental
analysis: Anal. Calc. for C32H32N4O10: C, 60.75; H, 5.10; N, 8.86, found (%): C, 60.38; H, 5.38; N,
8.65. IR (KBr; cm–1): 1613 [ν(C=N)], 1254 [ν(Ar-O)], 3167 [ν(O-H)]. UV–vis [in
methanol/chloroform (1:1)], λmax (nm) [2.5 × 10-5 M]: 267, 356, 376.

Scheme 1. Synthetic route to the bis(Salamo)-type tetraoxime ligand H4L.
Fig. 1. 1H NMR spectrum of the ligand H4L (CDCl3, 400 MHz).
Fig. 2. 13C NMR spectrum of the ligand H4L (DMSO, 151 MHz).
Fig. 3. The HRMS of the ligand H4L.
2.3 Synthesis of complexes 1-4
Homo- and heterotrinuclear complexes were synthesized by the reaction of H4L with M(OAc)2
(M(II) = Co(II), Ca(II), Sr(II) and Ba(II)) (Scheme 2). A solution of the ligand H4L (12.64 mg, 0.020
mmol) in chloroform (4 mL) was added to a solution of Co(OAc)2·4H2O (14.94 mg, 0.060 mmol) in
methanol (4 mL) at room temperature. The color of the solution immediately turned brown. The
mixture was filtered and the filtrate was allowed to stand at room temperature for approximately
three weeks [14e,15f]. The solvent was partially evaporated and several clear dark brown prismatic
single crystals were obtained. Complex 1, yield: 45.68%. Elemental analysis, Anal. Calc. for
C40H44Cl6N4O16Co3 (%): C 39.18; H 3.62; N 4.57; Co 14.42. Found (%): C 38.86; H 3.40; N 4.86;
Co 14.88. IR (KBr; cm-1): 1606 [ν(C=N)], 1257 [ν(Ar-O)], 3407 [ν(O-H)]. UV-vis [in
methanol/chloroform (1:1)], λmax(nm) [2.5 × 10-5 M]: 280, 380, 410.
Scheme 2. Synthesis of the homo- and heterotrinuclear Co(II) complexes.
A solution of Co(OAc)2·4H2O (9.96 mg, 0.040 mmol) in methanol (2 mL) and Ca(OAc)2 (3.16
mg, 0.020 mmol) in water/methanol (1:3, 2 mL) were added to a solution of H4L (12.64 mg, 0.020
mmol) in chloroform (4 mL), and the resulting solution was evaporated to dryness, after which the
solid was redissolved in chloroform/methanol (1:1, 8 mL). The mixture was filtered and the filtrate
was allowed to stand at room temperature for several weeks to obtain complex 2. Complexes 3 and 4
were prepared by a similar procedure as for complex 2, however, complex 4 was prepared using
ethanol as the solvent instead of methanol that was used for complex 2.
Complex 2, dark yellow crystals, yield: 44.65%. Elemental analysis, Anal. Calc. for

C36H34CaN4O14Co2 (%): C 47.80; H 3.79; N 6.19; Co 13.03; Ca 4.43. Found (%): C 47.49; H 3.23; N
6.42; Co 12.89; Ca 4.20. IR (KBr; cm-1): 1596 [ν(C=N)], 1250 [ν(Ar-O)], 3417 [ν(O-H)]. UV-vis [in
methanol/chloroform (1:1)], λmax (nm) [2.5 × 10-5 M]: 290, 373, 415.
Complex 3, dark orange crystals, yield: 38.69%. Elemental analysis, Anal. Calc. for
C36H34SrN4O14Co2 (%): C 45.41; H 3.60; N 5.88; Co 12.38; Sr 9.20. Found (%): C 45.23; H 3.62; N
5.75; Co 12.26; Sr 8.98. IR (KBr; cm-1): 1596 [ν(C=N)], 1250 [ν(Ar-O)], 3417 [ν(O-H)]. UV-vis [in
methanol/chloroform (1:1)], λmax (nm) [2.5 × 10-5 M]: 288, 370, 412.
Complex 4, dark yellow crystals, yield: 39.65%. Elemental analysis, Anal. Calc. for
C39.5H44BaN4O16.5Co2 (%): C 43.37; H 4.05; N 5.12; Co 10.77; Ba 12.55. Found (%): C 42.98; H
3.72; N 5.52; Co 10.54; Ba 12.31. IR (KBr; cm-1): 1596 [ν(C=N)], 1250 [ν(Ar-O)], 3406 [ν(O-H)].
UV-vis [in methanol/chloroform (1:1)], λmax (nm) [2.5 × 10-5 M]: 282, 389, 420.
2.4 X-ray crystallographic analysis
Single crystals of complexes 1-4 were placed on a Bruker Smart 1000 CCD area detector. The
diffraction data were collected using graphite monochromated Mo Kα radiation (λ = 0.71073 Å) (for
1, 2 and 4) and Cu Kα radiation (λ = 1.54184 Å) (for 3). Reflection data were corrected for Lorentz
and polarization factors and for absorption using the multi-scan method [17,18]. The structures were
solved using the program SHELXL-97 and Fourier difference techniques, and refined by the
full-matrix least-squares method on F2. Anisotropic thermal parameters were used for the
non-hydrogen atoms and isotropic parameters for the hydrogen atoms. Hydrogen atoms were added
geometrically and refined using a riding model. The crystallographic data are summarized in Table 1.
Table 1 Crystallographic data and refinement parameters for complexes 1-4.
2.5 Cyclic voltammetry
Cyclic voltammetry experiments for complexes 1–4 were implemented by an Auto Lab
electrochemical workstation (PGSTAT128N, EcoChemie, Netherlands).
A
conventional
three-electrode system was used with a modified glassy carbon (working electrode), Ag/AgCl
(reference electrode) and a platinum wire (counter electrode). The sample was made of a 1.0×10-3 M
DMF solution with the addition of 0.1 M tetrabutylammonium perchlorate (TBAP) as the supporting

electrolyte [19]. The potentials were recorded in the range -1.8 to +1.8 V at a 300 mV/s scan rate.
2.6 Magnetic measurements
Magnetic susceptibility data of the complexes 1-4 were collected on powdered samples using a
Quantum Design model MPMS XL7 SQUID magnetometer. Magnetic susceptibility measurements
were performed at 1000 Oe in the temperature range 2-300 K [2f,20].
3. Results and discussion
The ligand H4L and its corresponding metal complexes 1-4 are stable in air. The ligand H4L is
remarkably soluble in DMF and DMSO, but only slightly soluble in ethyl acetate, acetone,
acetonitrile, methanol and ethanol. Complexes 1-4 are completely soluble in DMF and DMSO, but
only slightly soluble in chloroform, methanol and ethanol at room temperature.
3.1 IR spectra analyses
The IR spectra of H4L and its corresponding Co(II) complexes 1-4 exhibit various bands in the
region of 4000-400 cm-1 (Fig. 4). The spectrum of the ligand shows an O−H stretching band at 3167
cm−1 that belongs to the phenolic hydroxyl group, whereas complex 1 shows a band at 3407 cm−1
that belongs to coordinated methanol molecules. The free ligand H4L exhibits characteristic C=N and
Ar−O stretching bands at 1613 and 1254 cm−1, respectively, which are shifted by ca. 8 and 5 cm−1 in
complex 1. This lowering of energy results from the Co−N and Co−O interactions upon
complexation, which is similar to previously reported Co(II) complexes [10b]. Compared with
complex 1, the C=N and Ar−O stretching bands belonging to the heterotrinuclear complexes are
shifted by ca. 4~7 and 6~8 cm−1, respectively. This results from replacing the central Co(II) atom by
the M(II) atom and forming new M−O and M−N coordination bonds. Meanwhile, the O−H
stretching band disappeared for complexes 2 and 3. The O−H stretching band at 3417 cm−1 belonging
to a water molecule of complex 4 is shifted by ca. 10 cm−1. The above facts are consistent with the
results determined by X-ray diffraction.
Fig. 4. IR spectra of the ligand H4L and its corresponding complexes 1-4.

3.2 UV-vis spectral analyses
Methanol/chloroform (1:1) solutions of the ligand H4L and its homo/heterotrinuclear Co(II)
complexes show, as expected, almost identical UV-vis spectra (Fig. 5). The free ligand H4L shows
three strong absorption bands at 267, 356 and 376 nm. The absorption peak at 267 nm can be
assigned to the π–π* transition of the benzene rings and the other two bands at 356 and 376 nm can
be attributed to the intra-ligand π-π* transition of the C=N bonds [4i]. Compared to the absorption
peaks of the free ligand H4L, corresponding absorption peaks at ca. 380 and 410 nm are observed in
complexes 1-4, which are bathochromically shifted, indicating the coordination of the metal(II)
atoms with the free ligand H4L. The auxochromes (–OH) attached to the benzene and naphthalene
rings could be responsible for the bathochromic shift observed in the absorption peaks [14f,6b,14g].
In summary, it is evident that complexes 1-4 containing benzene and naphthalene rings were
synthesized.
Fig. 5. UV-vis spectra of the ligand H4L and its corresponding complexes 1-4 in
methanol/chloroform (1:1) (c = 2.5 × 10-5 M).
3.3 HRMS analyses
The synthesized Co(II) complexes 1-4 were further characterized by high resolution mass
spectrometry (HRMS). The HRMS of complex 1 was consistent with the proposed empirical formula
(Fig. 6), with m/z = 804.9855 [M-2CH3COO-2CH3OH]2+, calcd = 804.98. The HRMS of complexes
2 and 3 were also consistent with the proposed empirical formulae (Fig. 7, Fig. 8), with m/z =
786.0127 [M-2CH3COO]2+, calcd = 786.01 and m/z = 833.9557 [M-2CH3COO]2+, calcd = 833.95.
The HRMS of complex 4 was consistent with the proposed empirical formula (Fig. 9), with m/z =
901.0833 [M-2CH3COO-2CH3CH2OH]2+, calcd = 901.96. Therefore, the discrete trinuclear
structures of the complexes in solution were confirmed by HRMS.
Fig. 6. The HRMS of complex 1.
Fig. 7. The HRMS of complex 2.

Fig. 8. The HRMS of complex 3.
Fig. 9. The HRMS of complex 4.
3.4 Description of the crystal structures
The structures of the homo- and heterotrinuclear complexes were determined by single-crystal
X-ray diffraction. Selected bond lengths and angles of complexes 1-4 are listed in Table 2.
Table 2 Selected bond lengths (Å) and angles (°) of complexes 1-4.
3.4.1 Crystal structure of complex 1
The crystal structure and atom numbering of complex 1 is shown in Fig. 10. Complex 1
crystallizes in the monoclinic crystal system, space group P21/n. X-ray crystallography clearly shows
the formation of complex 1, which was isolated as dark brown crystals. Interestingly, the formation
process of complex 1 was highly cooperative. In the crystal structure of complex 1, two terminal
Co(II) atoms (Co1 and Co2) are located in the N2O2 cavities of the Salamo moieties, while the third
one (Co3) is located in the central O6 cavity. Two chelating acetate ions bridge the trinuclear Co(II)
atoms in a familiar µ2-fashion, which probably contributes to the cooperative formation of complex 1.
The terminal Co(II) atoms (Co1 and Co2) are both penta-coordinated with distorted trigonal
bipyramidal geometries, which were deduced by calculating the value of τ1 = 0.7268 and τ2 = 0.8743,
respectively [21]. The distances between the Co3 atom and the coordinated oxygen atoms range from
2.027(3) to 2.150(4) Å. The central Co3 atom is hexa-coordinated in the central O6 cavity and has a
distorted octahedral geometry with six oxygen-donor atoms, including two µ2-acetato ligands,
phenoxy oxygen groups and methanol molecules.
Fig. 10. (a) View of the molecular structure of complex 1 (hydrogen atoms and solvent molecules are
omitted for clarity and thermal ellipsoids are drawn at the 30% probability level). (b) Coordination
polyhedra for the Co(II) atoms of complex 1.
As a result, when the two N2O2 Salamo moieties are metallated with d-block transition metals,

the conformation of the molecules is restricted so that the phenoxo oxygen atoms are directed inward
to form an O6 cavity. The complexation of the (L)4- unit with the Co(II) atom takes place in a
cooperative fashion and produces the homotrinuclear complex [Co3(L)]2+, in which the third Co(II)
atom is in the O6 cavity. However, the size of the O6 cavity seems to be too large to fit the central
Co(II) atom because only two oxygen donor atoms coordinate to the central Co(II) atom in the
crystal structure. Thus, this structure suggests that the central Co(II) atom could be replaced by
another metal(II) atomswith a suitable size for the O6 cavity, such as Ca(II), Sr(II) or Ba(II), to form a
C-shaped complex.
3.4.2 Crystal structure of complex 2
The crystal structure and atom numbering of complex 2 is shown in Fig. 11. Complex 2
crystallizes in the triclinic crystal system, space groupP1. In complex 2, two terminal Co(II) atoms
(Co1 and Co2) are located in the N2O2 sites of the Salamo moieties, two chelating acetate ions bridge
the Co(II) atoms and the Ca(II) atom in a µ2-fashion. The Co1 and Co2 atoms are both
penta-coordinated with distorted tetragonal pyramidal geometries, which were deduced by
calculating the value of τ3 = 0.3828 and τ4 = 0.0453, respectively [21]. The central Ca1 atom is
octa-coordinated with a distorted square antiprism geometry, replacing the central Co(II) atom of
complex 1. Here, all the six oxygen atoms of the [Co2(L)] moiety coordinate nicely to the Ca(II)
atom. Complex 2 has strong coordination with methoxy groups, determined by analyzing the
distances between the Ca1 atom and the oxygen atoms of the methoxy groups. The distances
between the Ca1 atom and the four phenoxy oxygen atoms of the Salamo moieties range from
2.384(3) to 2.435(3) Å, which are obviously shorter than the methoxy groups (Ca1–O1 2.604(3) Å
and Ca1–O10 2.612(3) Å). This fact clearly shows this C-shaped O6 cavity is suitable for more
metal(II) atoms of different sizes and it is easy to form heterotrinuclear complexes.
Fig. 11. (a) View of the molecular structure of complex 2 (hydrogen atoms are omitted for clarity,
and thermal ellipsoids are drawn at the 30% probability level). (b) Coordination polyhedra for the
Co(II) and Ca(II) atoms of complex 2.
As a result, the stable complex 2 was synthesized by the reaction of H4L with 2 equivalents of

Co(OAc)2·4H2O and 1 equivalent of Ca(OAc)2, in which the Ca(II) atom is in the O6 cavity.
Compared with complex 1, the Ca(II) atom has stronger coordination with the oxygen atoms of the
methoxy groups, which probably results from its larger radius compared to the Co(II) atom.
3.4.3 Crystal structure of complex 3
The crystal structure and atom numbering of complex 3 is depicted in Fig. 12. Complex 3
crystallizes in the triclinic crystal system, space groupP1. The Co(II) atoms of complex 3 have
similar coordination environments and geometries, with τ values of τ5 = 0.4508 (Co1) and τ6 =
0.1733 (Co2) [21]. They are both penta-coordinated with distorted tetragonal pyramidal geometries.
The central Sr1 atom is octa-coordinated with a distorted hexagonal bipyramidal geometry, which is
different from the Ca1 atom of 2. The distances between the Sr1 atom and the four phenoxy oxygen
atoms of the Salamo moieties range from 2.521(4) to 2.565(5) Å, which are clearly shorter than those
to the methoxy groups (Sr1–O1 2.650(4) Å and Sr1–O10 2.672(4) Å). Obviously, the Sr–O bond
lengths in complex 3 are larger than the corresponding Ca–O bond lengths found in complex 2.
Fig. 12. (a) View of the molecular structure of complex 3 (hydrogen atoms are omitted for clarity,
and thermal ellipsoids are drawn at the 30% probability level). (b) Coordination polyhedra for the
Co(II) and Sr(II) atoms of complex 3.
3.4.4 Crystal structure of complex 4
The crystal structure and atom numbering of complex 4 is shown in Fig. 13. Complex 4
crystallizes in the triclinic crystal system, space groupP1, which is similar to complexes 2 and 3.
The Co(II) atoms of complex 4 are both penta-coordinated with tetragonal pyramidal and trigonal
bipyramidal geometries for the Co1 and Co2 atoms, respectively, which were obtained by calculating
the τ values, τ7 = 0.38 and τ8 = 0.7383 for Co1 and Co2, respectively [21]. Owing to the coordination
of one water molecule, the central Ba1 atom is nona-coordinated with a distorted tricapped trigonal
prismatic geometry, which is different from the Ca1 and Sr1 atoms of complexes 2 and 3. The
distances between the Ba1 atom and the four phenoxy oxygen atoms of the Salamo moieties range
from 2.733(5) to 2.851(5) Å, which are evidently shorter than the distances to the methoxy groups
(Ba1–O1 2.975(5) Å and Ba1–O10 3.109(5) Å). The same situation was observed in complexes 2

and 3.
Fig. 13. (a) View of the molecular structure of complex 4 (hydrogen atoms and solvent molecules are
omitted for clarity, and thermal ellipsoids are drawn at the 30% probability level). (b) Coordination
polyhedra for the Co(II) and Ba(II) atoms of complex 4.
Therefore, the resulting geometries of the Co1 and Co2 atoms are both penta-coordinated square
pyramidal and the Ca1 and Sr1 are both octa-coordinated with square antiprismatic and distorted
hexagonal bipyramidal geometries, respectively. However, the Ba1 atom is larger than the size of the
cavity, so coordination of the Ba1 atom with a water molecule makes the structure more stable. The
resulting geometry of the Ba1 atom is the rare single square tricapped trigonal prism. As the cation
radius increases, the coordination bond lengths of the central cation are distinctly becoming larger
and larger. This fact suggests that the radius size of central cation is a significant factor which affects
the binding ability of the central O6 site. As a result, the coordinating capability in the central O6 site
is in the order Ca(II) > Sr(II) > Ba(II).
3.5 Cyclic voltammetry
The electrochemistry of the four complexes 1-4 was studied by cyclic voltammetry using DMF
as the solvent. Fig. 14 shows the cyclic voltammograms for complexes 1-4 in the potential range -1.8
to 1.8 V. The plot for complex 1 exhibits two different redox pairs. The first anodic/cathodic couple
potential (Epa = -0.758, Epc = -0.670) is attributed to the Co(II)(Salamo)/Co(I)(Salamo) process
(Co(II)(Salamo) + e ↔ Co(I)(Salamo)). The ratio of the anodic to cathodic peak currents Ipa/Ipc
=
2.201 (Ipa = -22.09, Ipc = 10.04) and ∆E = |Epa - Epc| = 0.088 V are in agreement with a
quasi-reversible electron-transfer process [4e,22]. The second couple potential is attributed to the
Co(II/I)(Salamo) process, but an anodic peak is not observed, indicating an irreversible redox
process. The cathodic peak potential is observed at Epc = 1.042 V which corresponds to the
Co(III)(Salamo) + e ↔ Co(II)(Salamo) process. In this system, the Co(II)(Salamo) complex is more
stable than the Co(III)(Salamo) complex. A similar argument is applicable to the remaining Co(II)
complexes (2-4).

Fig. 14. Cyclic voltammograms of 10-3 M solutions of 1-4 in DMF. Rate = 300 mv/s.
3.6 Magnetic properties
Powder X-ray diffraction (PXRD) data were recorded by a RIGAKU-DMAX2500 X-ray
diffractometer using Cu Kα radiation (λ = 0.154 nm) at a scanning rate of 5°/min for 2θ ranging from
5° to 50°. (Fig. 15) The PXRD data at room temperature on the samples of complexes 1-4 well
matched the calculated results from single crystal data. We determined the magnetic susceptibility of
crystal samples of the four complexes in the temperature range 2.0-300 K. The temperature
dependence of the magnetic susceptibilities complex 1 is shown in Fig. 16, as a plot of χMT versus T.
The χMT value for the homotrinuclear complex 1 is 9.42 cm3 K mol-1 at 300 K, which is higher than
the calculated value of 5.625 cm3 K mol-1 expected for three high spin Co(II) (3d7, S = 3/2)
non-interacting ions [23-26]. On lowering the temperature, the χMT value kept decreasing smoothly
and reached a value of 8.32 cm3 K mol-1 at ca. 50 K, followed by a rapid decrease. The χMT value
decreased with decreasing temperature, indicating an intramolecular antiferromagnetic interaction
between the three Co(II) atoms. At 2 K, the χMT value reached a minimum value of 5.36 cm3 K mol-1.
The reciprocal susceptibility (1/χM) of complex 1 obeys the Curie-Weiss law with θ = -5.5723 K and
C = 9.335 cm3 K mol-1 (Fig. 16, inset) [27-32]. A negative Weiss constant again confirms the
antiferromagnetic interaction exhibited by complex 1.
Fig. 15. PXRD patterns for the homo- and heterotrinuclear complexes 1-4.
Fig. 16. Plot of χM T vs. T for complex 1 between 2 and 300 K. Inset: Temperature dependence of
χM-1. The red solid line represents the best fitting results.
The temperature dependence of the magnetic susceptibilities of complex 2 is shown in Fig. 17,
as a plot of χMT against T. The χMT value of 4.97 cm3 K mol-1 at 300 K for the heterotrinuclear
complex 2 is slightly higher than the value of 4.73 cm3 K mol-1 expected for two Co(II) (3d7, S=3/2)
and one Ca(II) (S=0) magnetically isolated ions. Because the Ca(II) ions have no single unpaired
electrons, they exhibit weak paramagnetism and can be neglected [33,34]. Upon cooling, the χMT

value decreased gradually to reach a value of 4.68 cm3 K mol-1 at ca. 50 K and then rapidly
decreased to reach a value of 3.01 cm3 K mol-1 at 2 K. Therefore, the magnetic susceptibilities (1/χM)
obey the Curie–Weiss law in the temperature range 2-300 K for complex 2, giving a positive Weiss
constant θ = -3.7864 K and C = 4.921 cm3 K mol-1 (Fig. 17, inset), again confirming the
antiferromagnetic interaction exhibited by complex 2, which is consistent with complex 1.
Fig. 17. Plot of χM T vs. T for complex 2 between 2 and 300 K. Inset: Temperature dependence of
χM-1. The red solid line represents the best fitting results.
The temperature dependence of the magnetic susceptibilities of complex 3 is shown in Fig. 18,
depicting a plot of χMT against T. The plots for complex 3 display different magnetic characteristics
when compared with complexes 1 and 2. The χMT value of 5.54 cm3 K mol-1 at 300 K for complex 3
is slightly higher than the value of 4.73 cm3 K mol-1 expected for two Co(II) (3d7, S=3/2) and one
Sr(II) (S=0) magnetically isolated ions [35,36]. On lowering the temperature to 35 K, the χMT value
decreased slowly, and when the temperature was further decreased, the χMT value increased sharply
and reached a maximum value of 8.07 cm3 K mol-1 at 12 K. Finally, a further decrease in temperature,
resulted in a sharp decline in χMT, reaching a value of 4.32 cm3 K mol-1 at 2 K. The trend of the
change in χMT values with temperature in the region above 12 K could be an indicator that the two
Co(II) atoms in complex 3 are ferrimagnetically interacting. In addition, when the temperature
dropped below 12 K, the sharp decrease in the χMT value is mainly due to the interaction between
antiferromagnetic molecules, Zero-field splitting and Zeeman effects. The magnetic susceptibilities
(1/χM) obey the Curie-Weiss law in the temperature range 2-300 K for complex 3, giving a positive
Weiss constant θ = -0.3245 K and C = 5.294 cm3 K mol-1 (Fig. 18, inset), again confirming the
antiferromagnetic interaction exhibited by complex 3.
Fig. 18. Plot of χM T vs. T for complex 3 between 2 and 300 K. Inset: Temperature dependence of
χM-1. The red solid line represents the best fitting results.
The temperature dependence of the magnetic susceptibilities of complex 4 is given in Fig. 19, as
a plot of χMT versus T. The χMT value at 300 K for complex 4 is 9.45 cm3 K mol-1, which is higher

than the calculated value of 4.73 cm3 K mol-1 expected for two Co(II) (3d7, S=3/2) magnetically
isolated ions. However, the value of χMT, which is different from that of complex 2, gradually
increased with decreasing temperature, and reached a maximum value of 10.44 cm3 K mol-1 at 70 K;
finally, the χMT value reduced to 8.10 cm3 K·mol-1 when the temperature reached 2 K. The trend of
the change in χMT value with temperature in the region above 70 K could a proof that the two Co(II)
atoms in complex 4 are ferromagnetically interacting. The magnetic susceptibilities (1/χM) obey the
Curie–Weiss law in the temperature range 2-300 K for complex 4, giving a positive Weiss constant θ
= 1.4257 K and C = 9.653 cm3 K mol-1 (Fig. 19, inset), confirming the ferromagnetic interaction
exhibited by complex 4. The complexes have the same ligand but different coordination
environments, so their magnetic behaviors are different. The results show that the coordination
environment of the metal ions has some influence on the magnetic properties.
Fig. 19. Plot of χM T vs. T for complex 4 between 2 and 300 K. Inset: Temperature dependence of
χM-1. The red solid line represents the best fitting results.
4. Conclusion
The homo- and heterotrinuclear Co(II) complexes 1-4 have been designed and synthesized.
Their X-ray crystal structures reveal that the different nature of the N2O2 and O6 sites of the ligand
H4L leads to the site-selective introduction of two different kinds of metal(II) atoms for the
replacement of the central Co(II) atom by Ca(II), Sr(II) and Ba(II) atoms. The coordination number
of the Co(II), Ca(II), Sr(II) and Ba(II) atoms in the O6 environment are 6, 8, 8 and 9, respectively,
and have slightly distorted octahedral, square antiprismatic, hexagonal bipyramidal and square
tricapped trigonal prismatic geometries. As a result, the coordinating capability in the central O6 site
is in the order Ca(II) > Sr(II) > Ba(II). The magnetic properties of all these complexes were studied.
For complex 1, the χMT value was directly proportional to temperature change, thereby, showing an
antiferromagnetic interaction between the three Co(II) atoms. In contrast, the χMT values of
complexes 2-4 showed anomalous behavior to a change in temperature, with different magnetic
coupling effects. The measurement of cyclic voltammetry potentials and magnetic properties of the
complexes indicated the complexes could show a good application for molecular materials. Owing to

their electrostatic interaction and their size-fit principle, rare-earth(III) atoms should replace the
central Co(II) atom successfully, which could be used for the recognition of rare-earth(III) atoms and
for the study of the magnetic properties of 3d-4f complexes. Related research is underway.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (21361015),
which is gratefully acknowledged.
Appendix A. Supplementary data
CCDC 1519396, 1519397, 1519394 and 1519395 contain the supplementary crystallographic data
for 1, 2,
3
and 4. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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Table 1
Crystallographic data and refinement parameters for complexes 1-4.
Complex
1
2
3
4
Empirical formula
Formula weight
T(K)
C40H44Cl6N4O16Co3 C36H34CaN4O14Co2
C36H34SrN4O14Co2
952.15
C39.5H44BaN4O16.5Co2
1093.98
1226.28
293(10)
Mo Kα, 0.71073
monoclinic
P21/n
904.61
297(10)
293(2)
294(2)
Radiation (Å)
Crystal system
Space group
a (Å)
Mo Kα, 0.71073
triclinic
Cu Kα, 1.54184
triclinic
Mo Kα, 0.71073
triclinic
P1
P1
P1
14.1780(12)
16.6498(14)
23.873(2)
90
12.5293(11)
13.1610(19)
15.0421(17)
109.147(12)
103.296(9)
100.181(9)
2192.9(5)
2
12.5545(11)
13.2283(10)
15.0117(12)
109.370(7)
103.548(7)
99.312(7)
2207.2
10.2217(6)
13.551(8)
16.9476(10)
74.825(5)
79.515(5)
81.710(5）
2216.1(2)
2
b (Å)
c (Å)
α (°)
100.520(9)
90
β (°)
γ (°)
Volume (Å3)
5540.8(8)
4
2
Z
Dc (g cm-3)
Absorption coefficient
(mm-1)
1.470
1.370
1.433
1.639
1.241
0.937
7.929
1.694
θ range for data collection
(°)
3.570 to 23.882
2492.0
3.806 to 24.942
928.0
4.504 to 69.676
964.0
3.663 to 23.831
1102.0
F (000)
-17,17/-20,14/-28,29 -15,15/-16,16/-18,18 -14,15/-15,11/-18,18 -13,13/-18,17/-21,22
h/k/l (min, max)
Crystal size (mm)
0.24×0.27×0.33
22010/10873
[Rint=0.086]
10873
0.31×0.33×0.34
14193/8464
[Rint =0.054]
8464
0.24×0.25×0.32
15730/8176
[Rint=0.058]
8176
0.14×0.15×0.21
25177/12334
[Rint=0.052]
12334
Reflections collected
Independent reflection
Data/restraints/parameters 10873/6/634
8464/0/518
R1= 0.0555
wR2= 0.1150
R1= 0.0901
wR2= 0.1366
1519397
8176/0/518
R1= 0.0616
wR2= 0.1678
R1= 0.0791
wR2= 0.1869
1519394
12334/48/594
R1=0.0569
wR2= 0.1097
R1=0.1204
wR2=0.1212
1519395
Final R indices [I > 2σ
(I)]a
R1=0.0817
wR2= 0.1916
R1= 0.1357
wR2= 0.2436
1519396
R indices (all data)b
CCDC deposit number
− |
a R1 = ΣǁFo| Fcǁ/Σ|Fo|; b. wR2 = [Σw(Fo2 − Fc2)2/Σw(Fo ) ] , w = [σ2(Fo ) + (0.0784P)2 + 1.3233P]−1, where
2 2 1/2
2
P = (Fo2 + 2Fc2)/3;
Wen-Kui Dong et al.,

Table 2
Selected bond lengths (Å) and angles (°) of complexes 1-4.
Complex 1
Co3-O5
2.071(4)
2.040(4)
79.44(14)
83.38(17)
96.09(17)
Co3-O6
2.030(3)
2.150(4)
97.60(14)
95.33(17)
87.94(18)
Co3-O12
2.027(3)
Co3-O14
Co3-O15
Co3-O(16)
O5-Co3-O14
O6-Co3-O12
O6-Co3-O16
2.141(4)
O5-Co3-O6
O5-Co3-O15
O6-Co3-O14
O5-Co3-O12
O5-Co3-O16
O6-Co3-O15
169.83(17)
172.22(16)
86.91(18)
O12-Co3-O14 87.95(18)
O14-Co3-O15 87.36(17)
Complex 2
O12-Co3-O15 98.91(18)
O14-Co3-O16 93.53(18)
O12-Co3-O16 86.20(18)
O15-Co3-O16 174.84(19)
Ca1-O1
2.604(3)
2.421(3)
2.405(4)
123.01(9)
68.43(10)
65.51(9)
105.94(9)
63.42(9)
76.08(10)
122.43(10)
61.68(9)
Ca1-O2
2.435(3)
Ca1-O5
2.384(3)
Ca1-O6
Ca1-O9
2.395(3)
Ca1-O10
2.612(3)
Ca1-O12
Ca1-O14
2.397(4)
O1-Ca1-O2
O1-Ca1-O9
O1-Ca1-O14
O2-Ca1-O9
O2-Ca1-O14
O5-Ca1-O10
O6-Ca1-O9
O6-Ca1-O14
O9-Ca1-O14
61.14(9)
O1-Ca1-O5
O1-Ca1-O10
O2-Ca1-O5
O2-Ca1-O10
O5-Ca1-O6
O5-Ca1-O12
O6-Ca1-O10
O9-Ca1-O10
O1-Ca1-O6
O1-Ca1-O12
O2-Ca1-O6
O2-Ca1-O12
O5-Ca1-O9
O5-Ca1-O14
O6-Ca1-O12
O9-Ca1-O12
151.78(10)
109.11(10)
128.03(10)
77.26(10)
127.22(10)
99.99(10)
99.11(11)
101.47(10)
107.81(10)
75.33(10)
166.84(10)
103.82(10)
148.21(11)
65.12(9)
76.47(11)
78.57(10)
O10-Ca1-O12 72.14(11)
O10-Ca1-O14 111.79(12)
O12-Ca1-O14 175.16(12)
Complex 3
Sr1-O1
2.650(4)
Sr1-O2
2.565(4)
Sr1-O5
2.521(4)
2.672(4)
Sr1-O6
2.514(4)
Sr1-O9
2.543(4)
Sr1-O10
Sr1-O12
2.562(5)
Sr1-O14
2.538(5)
O1-Sr1-O2
O1-Sr1-O9
O1-Sr1-O14
O2-Sr1-O9
O2-Sr1-O14
O5-Sr1-O10
O6-Sr1-O9
O6-Sr1-O14
O9-Sr1-O14
59.56(13)
114.92(13)
77.73(14)
173.82(13)
104.74(15)
146.97(15)
63.03(13)
74.62(15)
75.71(15)
O1-Sr1-O5
O1-Sr1-O10
O2-Sr1-O5
O2-Sr1-O10
O5-Sr1-O6
O5-Sr1-O12
O6-Sr1-O10
O9-Sr1-O10
121.34(13)
75.06(14)
63.97(13)
114.66(13)
61.22(13)
74.22(14)
119.14(13)
59.80(13)
O1-Sr1-O6
O1-Sr1-O12
O2-Sr1-O6
O2-Sr1-O12
O5-Sr1-O9
O5-Sr1-O14
O6-Sr1-O12
O9-Sr1-O12
151.82(13)
103.28(14)
123.12(13)
73.86(13)
122.09(13)
103.09(15)
104.11(14)
105.95(13)
O10-Sr1-O12 74.02(15)
O10-Sr1-O14 108.69(16)
O12-Sr1-O14 177.29(16)
Complex 4
Ba1-O1
2.935(5)
2.733(5)
2.789(7)
54.73(14)
134.40(15)
Ba1-O2
2.781(5)
Ba1-O5
2.751(5)
Ba1-O6
Ba1-O9
2.851(5)
Ba1-O10
3.109(5)
Ba1-O12
O1-Ba1-O2
O1 -Ba1-O9
Ba1-O14
O1-Ba1-O5
O1-Ba1-O10
2.747(7)
Ba1-O16
2.797(15)
124.63(14)
111.50(15)
103.83(13)
132.21(13)
O1-Ba1-O6
O1-Ba1-O12

O1-Ba1-O14
O2-Ba1-O6
O2-Ba1-O12
O5-Ba1-O6
O5-Ba1-O12
O6-Ba1-O9
O6-Ba1-O14
O9-Ba1-O12
71.56(16)
110.67(14)
68.15(15)
55.80(13)
70.46(14)
56.90(14)
69.33(15)
109.55(15)
O1-Ba1-O16
O2-Ba1-O9
O2-Ba1-O14
O5-Ba1-O9
O5-Ba1-O14
O6-Ba1-O10
O6-Ba1-O16
O9-Ba1-O14
67.8(4)
O2-Ba1-O5
O2-Ba1-O10
O2-Ba1-O16
O5-Ba1-O10
O5-Ba1-O16
O6-Ba1-O12
O9-Ba1-O10
O9-Ba1-O16
58.90(13)
133.29(15)
81.8(4)
166.77(14)
113.73(16)
107.88(13)
108.03(16)
97.89(13)
165.8(3)
119.02(13)
132.1(5)
107.64(14)
51.35(14)
110.0(4)
67.99(16)
O10-Ba1-O12 68.33(15)
O12-Ba1-O14 176.76(16)
O10-Ba1-O14 110.60(16)
O12-Ba1-O16 69.9(5)
O10-Ba1-O16 68.1(3)
O14-Ba1-O16 112.7(5)
Wen-Kui Dong et al.,

Scheme 1.
Wen-Kui Dong et al.,

Scheme 2.
Wen-Kui Dong et al.,

Fig. 1.
Wen-Kui Dong et al.,

Fig. 2.
Wen-Kui Dong et al.,

Fig. 3.
Wen-Kui Dong et al.,

Fig. 4.
Wen-Kui Dong et al.,

Fig. 5.
Wen-Kui Dong et al.,

Fig. 6.
Wen-Kui Dong et al.,