Salamo-type trinuclear and tetranuclear cobalt(II) complexes based on a new asymmetry Salamo-type ligand: Syntheses, crystal structures, and fluorescence properties

Article abstract of DOI:10.1080/00958972.2016.1168520

Two multinuclear Co(II) complexes, [{Co(L)(i-PrOH)}₂Co(H₂O)]·2CH₃CN (1) and [{Co(L)(μ-OAc)Co(MeOH)₂}₂]·2CH₃COCH₃ (2), have been synthesized with a new asymmetric Salamo-type liga

Full text of DOI:10.1080/00958972.2016.1168520

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Salamo-type trinuclear and tetranuclear cobalt(II)
complexes based on a new asymmetry Salamo-
type ligand: syntheses, crystal structures, and
fluorescence properties
Wen-Kui Dong, Peng-Fei Lan, Wei-Min Zhou & Yang Zhang
To cite this article: Wen-Kui Dong, Peng-Fei Lan, Wei-Min Zhou & Yang Zhang (2016): Salamo-
type trinuclear and tetranuclear cobalt(II) complexes based on a new asymmetry Salamo-type
ligand: syntheses, crystal structures, and fluorescence properties, Journal of Coordination
Chemistry, DOI: 10.1080/00958972.2016.1168520
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1168520
Accepted author version posted online: 21
Mar 2016.
Published online: 04 Apr 2016.
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Date: 06 April 2016, At: 18:14

Journal of Coordination Chemistry, 2016
http://dx.doi.org/10.1080/00958972.2016.1168520
Salamo-type trinuclear and tetranuclear cobalt(II) complexes
based on a new asymmetry Salamo-type ligand: syntheses,
crystal structures, and fluorescence properties
Wen-Kui Dong, Peng-Fei Lan, Wei-Min Zhou and Yang Zhang
school of Chemical and Biological engineering, lanzhou Jiaotong university, lanzhou, Pr China
ARTICLE HISTORY
ABSTRACT
received 20 september 2015
accepted 26 february 2016
Two multinuclear Co(II) complexes, [{Co(L)(i-PrOH)}2Co(H2O)]∙2CH3CN (1)
and [{Co(L)(μ-OAc)Co(MeOH)2}2]∙2CH3COCH3 (2), have been synthesized
with a new asymmetric Salamo-type ligand (H3L = 6-hydroxy-6′-ethoxy-2,2′-
[ethylenediyldioxybis(nitrilomethylidyne)]diphenol). The Co(II) complexes
were obtained by different solvents, and the structures are completely
different. In the Co(II) complex 1, the ratio of the ligand H3L to Co(II) atom
is 2 : 3 and the Co(II) ions are all five-coordinate with trigonal bipyramidal
geometries. In the Co(II) complex 2, the ratio of the ligand H3L to Co(II) atom
is 2 : 4. Two central Co(II) ions are six coordinate with distorted octahedral
geometries and two terminal Co(II) ions are five coordinate with distorted
trigonal bipyramidal geometries. Self-assembling of an infinite 1-D
supramolecular chain is formed by C–H⋯π interactions in 1. Interestingly,
an infinite 2-D-layer plane structure is formed by the self-assembling array
of 2 linked by C–H⋯π interactions. 1 and 2 exhibit blue emissions with the
maximum emission wavelengths λmax = 403 and 395 nm when excited at
330 nm.
KEYWORDS
salamo-type ligand; Co(ii)
complex; synthesis; structure;
fluorescence property
O
O
N
O
O
Co
O
O
O
H
O
N
N
O
Co
Co(OAc)2·2H2
O
Co
O
H2
O
(CH3
)
2CHOH/CH3CN
2:3
OH
O
N
O
N
N
O
O
O
OH
HO
O
O
O
HO
H
O
O
O
N
H
N
O
O
Co
O
O
Co
Co
N
O
Co(OAc)2·2H2
O
O
Co
CH3OH/CH3OCH3
1:2
O
O
O
OH
O
N
O
O
OH
O
CONTACT Wen-Kui dong
dongwk@126.com
© 2016 informa uK limited, trading as taylor & francis Group

2
W.-K. DONg eT AL.
1. Introduction
Transition metal complexes with Salen-type ligands have been frequently studied [1, 2] for their
catalytic activity [3, 4], especially in the area of asymmetric catalysis [5, 6], biological activity, such
as anticancer [7] and fluorescence characteristics [8, 9]. Photoluminescence in Salen-type com-
pounds may have application in luminescent devices [10–14]. Hence, structural characteristics of
transition metal complexes bearing Salen-type ligands may be a valuable source of information.
Co(ΙΙ) and Cu(ΙΙ) complexes with Salen-type ligands receive attention for their photoluminescent
characteristics [15–17]. Work has been devoted to synthesize and characterize mononuclear, homo-,
or heterodinuclear transition metal complexes bearing symmetric Salen-type bisoxime or its deriv-
atives [18].
This work stems from our interest in syntheses of asymmetric Salamo-type bisoximes. Compared with
symmetric Salamo-type bisoxime ligands, the composition (R1–CH=N–O–(CH)n–O–N=CH–R2) is rather
unusual. Selective synthesis of asymmetrical Salamo-type ligands is important because electronic and
steric effect of the ligand on Salen-metal-assisted catalysis may be controlled by the introduction of
different substituents on the ring [19]. The asymmetric configuration with Salamo-type ligands would
afford opportunities for greater structural variation and infinite coordination polymers [20], and would
be expected to have interesting characteristics [21].
In order to study, the structures and fluorescence characteristics of the transition metal complexes
with asymmetric Salamo-type ligands; herein, we report the syntheses, characterizations, and crystal
structures of [{Co(L)(i-PrOH)}2Co(H2O)]∙2CH3CN (1) and [{Co(L)(μ-OAc)Co(MeOH)2}2]∙2CH3COCH3 (2) with
H3L (6-ethoxy-6′-hydroxy-2,2′[ethylenediyldioxybis(nitrilomethylidyne)]diphenol) in different solvent
systems.
2. Experimental
2.1. Materials and methods
3-ethoxy-2-hydroxybenzaldehyde and 2,3-dihydroxybenzaldehyde from Aldrich were used without
purification. The other reagents and solvents were analytical grade reagents from Tianjin Chemical
Reagent Factory.
elemental analysis for Co was carried out by an IRIS eR/S·WP-1 ICP atomic emission spectrome-
ter, C, H, and N analyses with a gmbH VariuoeL V3.00 automatic elemental analyzer. 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. UV–vis absorption and fluorescence spectra were recorded on a Shimadzu
UV-2550 spectrometer and on a Perkin-elmer LS-55 spectrometer, respectively. DSC-Tg analyses were
carried out at a heating rate of 10 °C min−1 on a NeTZSCH STA 449 F3 thermoanalyzer. X-ray single-crystal
structures were determined on a Bruker Smart APeX CCD area detector. Melting points were measured
using a microscopic melting point apparatus made in Beijing Taike Instrument Limited Company, and
the thermometer was uncorrected.
2.2. Synthesis
The synthetic route of the ligand is shown in scheme 1.
2.2.1. Synthesis and characterization of H3L
1,2-Bis(aminooxy)ethane was synthesized by a similar method [17, 20]. Yield, 56.8%. Anal. Calcd for
C2H8N2O2 (%): C, 26.08; H, 8.76; N, 30.42. Found (%): C, 25.98; H, 8.69; N, 30.50.
3-ethoxysalicylaldehyde-O-(1-ethyloxyamide)oxime: A solution of 3-ethoxy-2hydroxybenzalde-
hyde (2.5 mmol) in ethanol (50 mL) was added to a solution of 1,2-bis(aminooxy)ethane (5 mmol)
in ethanol (100 mL) and the mixture was heated at 50–55 °C for 6 h. The solution was concentrated
in vacuo and the residue was purified by column chromatography (SiO2, chloroform/ethyl acetate,

JOURNAL OF COORDINATION CHeMISTRY
3
O
C
O
C
O
C
.
NH2NH2 H2O
Br
Br
H2N
O
O
NH2
N
O
O N
2
N OH
C
O
C
O
C
O
CHO
O
N
O
N
O
O
N
CHO
OH
NH2
OH
OCH2CH3
OH
OH
OH
HO
OCH2CH3
Scheme 1. the synthetic route of the salamo-type ligand.
OCH2CH3
HO
25 : 1) to afford crystals of 3-ethoxysalicylaldehyde-O-(1-ethyloxyamide)oxime. Yield, 80.5%. m.p.
67–68 °C. Anal. Calcd for C9H11ClN2O3 (%): C, 54.99; H, 6.71; N, 11.66. Found (%): C, 55.06; H, 6.65;
N, 11.73.
6-Hydroxy-6′-ethoxy-2,2′-[ethylenediyldioxybis(nitrilomethylidyne)]diphenol (H3L): A solution of
3-ethoxysalicylaldehyde-O-(1-ethyloxyamide)oxime (1.32 mmol) in ethanol (10 mL) was added to a
solution of 2,3-dihydroxybenzaldehyde (1.35 mmol) in ethanol (20 mL) and the mixture was heated at
50–55 °C for 6 h. After cooling to room temperature, white precipitates were collected. Yield, 80.7%.
m.p. 132–133 °C. Anal. Calcd for C18H20N2O6 (%): C, 59.99; H, 5.59; N, 7.77. Found: C, 59.87; H, 5.66; N, 7.85.
2.2.2. Synthesis of 1
A solution of cobalt(II) acetate dihydrate (3.08 mg, 0.01 mmol) in isopropanol (3 mL) was added drop-
wise to a solution of H3L (3.57 mg, 0.01 mmol) in acetonitrile (2 mL) at room temperature. The color of
the solution turned to bright brown immediately, the mixture was filtered and the filtrate was allowed
to stand at room temperature for about two weeks. The solvent was partially evaporated and sev-
eral brown needle-like single crystals suitable for X-ray crystallographic analysis were obtained. Yield,
28.07%. Anal. Calcd for C46H58Co3N6O15 (%): C, 49.69; H, 5.26; N, 7.56; Co, 15.90. Found: C, 49.66; H, 5.21;
N, 7.57; Co, 15.81.
2.2.3. Synthesis of 2
A solution of cobalt(II) acetate hydrate (3.82 mg, 0.015 mmol) in methanol (3 mL) was added dropwise
to a solution of H3L (5.29 mg, 0.1 mmol) in acetone/ethanol (1:2) (15 mL) at room temperature. The
color of the mixing solution turned to brown immediately, the mixture was filtered and the filtrate was
allowed to stand at room temperature for about two weeks. The solvent was partially evaporated and
several brown needle-like single crystals suitable for X-ray crystallographic analysis were obtained.
Yield, 34.52%. Anal. Calcd for C25H34Co2N2O11 (%): C, 45.74; H, 5.22; N, 4.27; Co, 17.96. Found: C, 45.77;
H, 5.19; N, 4.31; Co, 17.89.
2.3. X-ray crystallography of the Co(II) complexes
Single crystals of the Co(II) complexes with approximate dimensions of 0.12 × 0.05 × 0.03 mm and
0.32 × 0.26 × 0.25 mm were placed on a Bruker Smart Apex CCD area detector, respectively. The diffrac-
tion data were collected using graphite monochromated MoKα radiation (λ = 0.71073 Å) at 294.68(10)
K and 294.58(10) K. The structures were solved by using SHeLXL-97 and Fourier difference techniques,
and refined by full-matrix least-squares method on F2. All hydrogens were added theoretically. The
crystal and experimental data are shown in table 1.

4
W.-K. DONg eT AL.
Table 1. Crystal data and structure refinements for 1 and 2.
Compound code
1
2
empirical formula
formula weight
temperature (K)
Wavelength (Å)
Crystal system
space group
Unit cell dimensions
a (Å)
C46h58Co3n6o15
1111.77
294.68(10)
0.71073
monoclinic
c2/c
C25h34Co2n2o11
656.40
294.58(10)
0.71073
triclinic
P-1
21.966(4)
10.1801(8)
23.081(3)
90.00
97.023(10)
90.00
5122.6(11)
4
1.442
9.8007(9)
12.2530(7)
12.5487(9)
73.575(6)
87.115(6)
85.465(6)
1440.30(18)
2
b (Å)
c (Å)
α (°)
β (°)
γ (°)
Volume (Å3)
Z
dc (mg m−3
)
1.514
1.212
680.0
μ (mm−1
F(0 0 0)
)
1.031
2308.0
Crystal size (mm)
θ range (°)
0.12 × 0.05 × 0.03
3.37 to 26.02
−26 ≤ h ≤ 27
−7 ≤ k ≤ 12
−28 ≤ l ≤ 22
10,229
5036
0.0871
99.71%
5025/4/325
0.989
0.32 × 0.26 × 0.25
3.36 to 26.02
−12 ≤ h ≤ 12
−15 ≤ k ≤ 15
−15 ≤ l ≤ 15
10,648
5679
0.0459
99.76%
5666/6/373
1.035
index ranges
reflections collected
independent reflections
R(int)
Completeness to θ = 26.32
data/restraints/parameters
Gof
final R indices [I>2σ(I)]
R1 = 0.0679,
wR2 = 0.0747
R1 = 0.1651,
wR2 = 0.1026
0.344 and −0.244
R1 = 0.0586,
wR2 = 0.1084
R1 = 0.1005,
wR2 = 0.1350
0.357 and −0.387
R indices (all data)
Δρmax, min (e Å−3
)
3. Results and discussion
3.1. X-ray crystal structures
The crystal structures of 1 and 2 are shown in figure 1(a) and (b), respectively. The crystal data and exper-
imental details are given in table 1. The selected bond lengths and angles of 1 and 2 are listed in table 2.
Complex 1 crystallizes in the monoclinic system, space group c2/c, the assembly of three Co(II)
ions, two (L)3− units and two isopropanol molecules result in a trinuclear Co(II) complex. The coordina-
tion sphere of the terminal Co1 or Co1# is completed by four N2O2 donors and O1 from isopropanol.
Meanwhile, the sphere of central Co2 is completed by four oxygens of two (L)3− units and O1 of coor-
dinated H2O. The terminal Co1 adopts a trigonal bipyramidal geometry, the apical positions occupied
by O1 and N2 from one (L)3− unit (τ = 0.827) [22]. One axial bond length of Co1–N2 is 2.114(5) Å, which
is longer than the bond length of Co1–N1 (2.041(4) Å). Another axial bond length Co1–O1 (2.028(3)
Å) is also longer by 0.105(3) Å than the Co1–O5 bond length (1.923(3) Å) and by 0.006(3) Å than the
Co1–O7 bond length (2.022(3) Å). The central Co2 also has trigonal bipyramidal geometry with axial
donors of O1 and O1# (τ = 0.711). The bond length of Co2–O1 is 2.089(3) Å, which is longer than the
bond length of Co2–O8 (2.005(4) Å). Thus, the same coordination geometries (trigonal bipyramid) are
formed in 1 (figure 2(a)).
The special interest of 1 is self-assembling array linked by intermolecular hydrogen bonds. In 1,
the hydrogen bond data are summarized in table 3 [23]. Monomers of 1 are linked by intermolecular
C17–H17A⋯Cg(C1–C6) hydrogen bond interactions into an infinite 1-D supramolecular chain along the
b-axis (figure 2(b)).

JOURNAL OF COORDINATION CHeMISTRY
5
Figure 1. molecular structures of 1 and 2 with the atom numbering. thermal ellipsoids are plotted at the 30% probability level.
hydrogens and solvent Ch3Cn or Ch3CoCh3 molecules are omitted for clarity. (a) molecular structure of 1; (b) molecular structure 2.
Complex 2 crystallizes in the triclinic system, space group P-1, the assembly of four Co(II) ions, two
(L)3− units, two acetates and four coordinated methanol molecules result in a tetranuclear Co(II) com-
plex. The structure can be described as two [Co(L)(μ-OAc)Co(MeOH)2] units connected with diphenoxy
bridges. The coordination sphere of terminal Co1 or Co1# is completed by N2O2 donors and O7 of the
acetate ion. Meanwhile, the sphere of Co2 or Co2# is completed by three μ-phenolic oxygens, O8 of the
acetate and two oxygens (O9 and O4AA) of the two methanol molecules. The acetate coordinates to
two Co(II) ions via a Co1–O–C–O–Co2 bridge. The terminal Co1 adopts trigonal bipyramidal geometry
with axial donors of O2 and N2 (τ = 0.882) [22]. The bond length of Co1–N2 between Co1 and the apical
nitrogen (N2) is 2.109(4) Å, which is about 0.055(3) Å longer than the Co1–N1 bond length (2.054(4) Å)
between Co1 and the basal nitrogen (N1). The axial bond length Co1–O2 (2.026(3) Å) is also longer by

6
W.-K. DONg eT AL.
Table 2. selected bond distances (Å) and angles (°) for 1 and 2.
Complex 1
Co1–o1
2.028(3)
1.923(3)
2.022(3)
Co1–n1
Co1–n2
Co2–o1
2.040(4)
2.114(5)
2.089(3)
93.03(16)
89.8(2)
82.23(14)
115.43(10)
94.10(8)
120.16(15)
94.23(14)
131.2(4)
Co2–o1
Co2–o8
Co2–o2
2.089(3)
2.005(4)
1.948(3)
113.0(3)
109.6(3)
128.3(3)
120.3(4)
127.0(4)
123.9(3)
126.2(5)
127.6(3)
Co1–o5
Co1–o7
o1–Co1–n1
o1–Co1–n2
o5–Co1–o1
o5–Co1–o7
o5–Co1–n1
o5–Co1–n2
o7–Co1–o1
o7–Co1–n1
Complex 2
86.42(18)
175.60(17)
95.46(14)
112.89(15)
121.15(16)
88.39(17)
87.44(14)
125.94(16)
o7–Co1–n2
n1–Co1–n2
o2–Co2–o1
o2–Co2–o8
o8–Co2–o1
Co1–o1–Co2
o2–Co2–o1
C16–o5–Co1
C2–o2–Co2
C1–o1–Co2
C19–o7–Co1
o3–n1–Co1
C7–n1–Co1
o4–n2–Co1
C10–n2–Co1
C1–o1–Co1
Co1–o2
2.026(3)
1.945(3)
Co1–n1
Co1–n2
2.054(4)
2.109(4)
2.072(3)
Co2–o2
Co2–o8
Co2–o9
2.049(3)
2.035(4)
2.204(3)
Co1–o5
Co1–o7
2.001(3)
Co2–o1
Co2–o4aa
o2–Co2–o1
o2–Co2–o4aa
o2–Co2–o9
o8–Co2–o2
o2–Co1–n1
o2–Co1–n2
o8–Co2–o1
o9–Co2–o4aa
2.217(3)
Co2–o1
2.040(3)
79.14(12)
99.30(13)
86.97(11)
97.21(13)
86.38(15)
175.67(14)
171.38(13)
172.90(13)
C2–Co2–o1
o1–Co2–o1
o1–Co2–o2
o1–Co2–o4aa
o1–Co2–o9
o8–Co2–o1
o8–Co2–o4aa
79.14(12)
79.43(13)
157.43(13)
85.01(13)
95.06(13)
104.96(13)
90.01(14)
o5–Co1–o2
o5–Co1–o7
o5–Co1–n1
o5–Co1–n2
o7–Co1–o2
o7–Co1–n1
n1–Co1–n2
94.95(13)
117.66(14)
119.49(14)
88.35(15)
92.21(13)
122.74(15)
89.55(17)
Figure 2. (a) Coordination geometries of [{Co(l)(i-Proh)}2Co(h2o)]∙2Ch3Cn (1); (b) View of the 1-d chain motif within 1 along the b axis.

JOURNAL OF COORDINATION CHeMISTRY
7
0.081(3) Å than the bond length Co1–O5 (1.945(3) Å) and by 0.025(3) Å longer than the bond length
Co1–O7 (2.001(3) Å). This significant enlargement indicates the (L)3− unit has serious distortion, probably
as a result of the asymmetry. Interestingly, the geometry of the central Co2 is different from the Co1.
Co2 has octahedral geometry (τ = 0.02) in which the axial positions are occupied by O4AA and O9 from
two ethanol molecules and the four donors (O1, O1, O2 and O8) in a relative plane. The bond length
of Co2–O9 between the Co2 and the apical oxygen (O9) is 2.204(3) Å, shorter than the bond length of
Co2–O4AA between Co2 and the apical oxygen (O4AA) of 2.217(3) Å. The basal bond lengths Co2–O1
and Co2–O2 (2.072(3) Å and 2.049(3) Å) are longer than bond lengths Co2–O1 and Co2–O8 (2.040(3) Å
and 2.035(4) Å). Thus, two kinds of coordination geometries (trigonal bipyramid and slightly deformed
octahedral) are contained in 2.
The special interest of 2 is its self-assembling array linked by intermolecular hydrogen bonds.
The hydrogen bond data are summarized in table 3. Complex 2 monomers are linked by one
C9–H9B⋯Cg(C1–C6) hydrogen bond interaction into an infinite 2-D-layer structure along the bc plane
(figure 3) [24].
Table 3. hydrogen bonding distances (Å) and angles (°) for 1 and 2.
D–H⋯A
d(D–H)
d(H⋯A)
d(D⋯A)
∠D–H⋯A
Complex 1
C17–h17a⋯Cg
0.97(8)
0.97(2)
2.99(2)
2.95(4)
3.82(7)
3.845
144.2(4)
Complex 2
C9–h9B⋯Cg
154.35(5)
for 1 or 2, Cg is the centroids of atoms C1–C6.
Figure 3. (a) Coordination geometries of [{Co(l)(μ-oac)Co(meoh)2}2]∙2Ch3CoCh3; (b) View of the 2-d-layer structure within 2 along
the bc plane.

8
W.-K. DONg eT AL.
3.2. IR spectra
IR spectra of H3L, 1 and 2 exhibit various bands from 500–4000 cm−1 (figure 4). The free ligand exhibits
characteristic C=N stretches at 1612 cm−1, while νC=N of 1 and 2 are observed at 1587 and 1591 cm−1
,
respectively. In 1, the C=N stretching frequency shifts to higher frequency by ca. 38 cm−1, but in 2,
the C=N stretching frequency shifts to lower frequency by ca. 21 cm−1 upon complexation, indicating
coordination of the oxime nitrogen lone pair [25].
The Ar–O stretch is a strong band at 1263–1213 cm−1 as reported for similar Salen-type ligands
[26–28]. This band is at 1259 cm−1 for H3L, and at 1249 and 1267 cm−1 for 1 and 2, respectively. The Ar-O
stretching frequency shifts to different frequency, indicating that Co–O bonds are formed between Co(ΙΙ)
and oxygen of the phenolic groups [25]. Infrared spectrum of 1 shows the expected strong absorp-
tion band due to ν(O–H) at ca. 3442 cm−1, evidence for isopropanol molecules. The expected strong
absorption bands in 2 were observed at 3445, indicating the presence of coordinated methanol [29].
The characteristic absorption bands at 3442, 1656, and 561 cm−1 in 1 are assigned to coordinated water,
substantiated by the crystal structure.
The far-infrared spectra of 1 and 2 were obtained from 500–100 cm−1 to identify frequencies due
to the Co–O and Co–N bonds. The IR spectrum of 1 shows ν(Co–N) and ν(Co–O) frequencies at 522 and
461 cm−1, respectively [29], and 2 shows ν(Co–N) and ν(Co–O) at 511 and 453 cm−1, respectively [30]. As
pointed out by Percy and Thornton [31], the metal–oxygen and metal–nitrogen frequency assignments
are at times very difficult.
3.3. UV–vis absorption spectra
The UV–vis absorption spectra of H3L, 1 and 2 were determined in 5.0 × 10−5 mol L−1 ethanol solution
(figure 5). Absorption peaks of 1 and 2 are obviously different from those of the ligand upon compl-
exation. The electronic absorption spectrum of the Salen-type bisoxime H3L consists of two relatively
intense bands centered at 272 and 319 nm, assigned to the π–π* transitions of the benzene ring of
salicylaldehyde and the oxime group, respectively [32]. Upon coordination of the ligand, the absorp-
tion band at 319 nm disappears from the UV–vis spectra, which indicates that the oxime nitrogens are
involved in coordination [33]. The intraligand π–π* transition of the benzene ring of salicylaldehyde is
slightly shifted in the corresponding complexes to 278 and 281 nm for 1 and 2, respectively. Moreover,
Figure 4. infrared spectra of h3l, 1 and 2.

JOURNAL OF COORDINATION CHeMISTRY
9
Figure 5. uV–vis absorption spectra ofh3l, 1 and 2. h3l (—), 1 (---) in ethanol (5 × 10−5 mol l−1), 2 (-·-·-) in ethanol (5 × 10−5 mol l−1).
Figure 6. emission spectra of 1 and 2. 1 (—) and 2 (- - -) (C = 5 × 10−5 mol l−1, λex = 330, λem = 395 and 403 nm).
the new bands observed at 381 and 368 nm for 1 and 2 are assigned to those of L→M charge-transfer
transitions which are characteristic of the transition metal complexes with N2O2 coordination spheres
[34].
3.4. Fluorescence properties
The fluorescent properties of H3L, 1 and 2 were investigated at room temperature (figure 6). The ligand
exhibits an intense emission at 403 nm upon excitation at 330 nm, which should be assigned to the
intraligand π–π* transition [35]. Complex 2 shows an intense broad photoluminescence with maximum
emission at ca. 395 nm upon excitation at 330 nm, which is slightly red-shifted to that of H3L. The emis-
sion peak in the spectra of 1 and 2 may also arise from the intraligand transition. The emission observed
in 1 is tentatively assigned to the (π–π*) intraligand fluorescence.

10
W.-K. DONg eT AL.
Figure 7. five mg monocrystalline 1 and 2 with heating rate of 10 °C min−1 in n2; 1 (a) and 2 (b) analyzed by tG and dsC curves.
3.5. Thermal properties
Thermal decomposition process of 1 can be divided into three phases. The first phase of DSC curves with
an endothermic peak between 30–170 °C involves 6.8% weight loss roughly equal to two CH3CN mole-
cules (theoretical value of 7.3%). The second phase is an endothermic peak between 170–240 °C, losing

JOURNAL OF COORDINATION CHeMISTRY
11
11.2%, for loss of two isopropanol molecules (theoretical of 10.8%). 1 is temperature more thermally
stable than H3L, because deprotonated (L)3− enhances the thermal stability of free H3L. Heating was
continued; the decomposition of 1 is 240–600 °C (figure 7(a)).
Single-crystal sample of 2 lost acetone with thermal drying at 100 °C. Thermal decomposition of 2
has two phases, an endothermic peak between 100–240 °C, losing 10.2%, from four methanol molecules
(theoretical value of 10.7%). The decomposition temperature of 2 is 240–600 °C (figure 7(b)).
4. Conclusion
[{Co(L)(i-PrOH)}2Co(H2O)]∙2CH3CN (1) and [{Co(L)(μ-OAc)Co(MeOH)2}2]∙2CH3COCH3 (2), with an
asymmetric Salamo-type ligand, have been synthesized and structurally characterized. In FTIR spectra
of 1 and 2, νCo–O and νCo–N are observed. 1 and 2 were obtained by different solvent and their struc-
tures are different. In 1, the ratio of the ligand H3L to Co(II) is 2 : 3, with five coordinate Co(II) with
trigonal bipyramidal geometries. In 2, the ratio of H3L to Co(II) is 2 : 4. Two central Co(II) ions are six
coordinate with distorted octahedral geometries, and two terminal Co(II) ions are five coordinate with
distorted trigonal bipyramidal geometries. 1 and 2 exhibit blue emissions with the maximum emission
wavelengths λmax = 403 and 395 nm when excited at 330 nm.
Supplementary material
Further details of the crystal structure investigation(s) may be obtained from the Cambridge Crystallographic Data Center,
Postal Address: CCDC, 12 Union Road, Cambridge CB2 1eZ, UK (Telephone: (44) 01223 762910; Facsimile: (44) 01223
336033; e-mail: deposit@ccdc.cam.ac.uk) on quoting the depository number CCDC Nos. 1424952 and 1424952 for 1 and
2, respectively.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Natural Science Foundation of China [grant number 21361015], which is gratefully
acknowledged.
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