Three multinuclear Co(II), Zn(II) and Cd(II) complexes based on a single-armed salamo-type bisoxime: syntheses, structural characterizations and fluorescent properties

Article abstract of DOI:10.1080/00958972.2017.1324152

Three multinuclear complexes, [Co(L)(OAc)Co(CH₃CH₂OH)₂]·H₂O, [Zn(L)(OAc)Zn(CH₃OH)], and [{Cd(L)(OAc)Cd(CH₃OH)}₂], containing a single-armed salamo-type bisoxime H₃L ha

Full text of DOI:10.1080/00958972.2017.1324152

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Three multinuclear Co(II), Zn(II) and Cd(II)
complexes based on a single-armed salamo-type
bisoxime: Syntheses, structural characterizations
and fluorescent properties
Jing Hao, Ling-Zhi Liu, Wen-Kui Dong, Jing Zhang & Yang Zhang
To cite this article: Jing Hao, Ling-Zhi Liu, Wen-Kui Dong, Jing Zhang & Yang Zhang (2017):
Three multinuclear Co(II), Zn(II) and Cd(II) complexes based on a single-armed salamo-
type bisoxime: Syntheses, structural characterizations and fluorescent properties, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2017.1324152
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1324152
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Date: 30 April 2017, At: 18:54

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2017.1324152
Three multinuclear Co(II), Zn(II) and Cd(II) complexes based on a
single-armed salamo-type bisoxime: Syntheses, structural characterizations
and fluorescent properties
JING HAO, LING-ZHI LIU, WEN-KUI DONG*, JING ZHANG and YANG ZHANG
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, PR China
Three multinuclear complexes, [Co(L)(OAc)Co(CH3CH2OH)2]·H2O, [Zn(L)(OAc)Zn(CH3OH)]
and [{Cd(L)(OAc)Cd(CH3OH)}2], containing a single-armed salamo-type bisoxime H3L have
been synthesized and characterized structurally. The Co(II) complex forms a dimeric unit by
intermolecular hydrogen bond interactions of neighboring dimeric molecules. The Zn(II)
complex also forms a dimeric unit by intermolecular hydrogen bond interactions. Interesting
features of the crystal structure include O···O short contacts. Meanwhile, self-assembling infinite
1D, 2D and 3D supramolecular structures are formed by intermolecular hydrogen bond and
C–H···π interactions. The Cd(II) complex forms an infinite 2D supramolecular structure by
intermolecular hydrogen bond interactions. The photophysical properties of the Co(II), Zn(II)
and Cd(II) complexes have also been discussed.
Keywords: Single-armed salamo-type bisoxime; Multinuclear complex; Synthesis; Crystal
structure; Fluorescent property
1. Introduction
Transition metal complexes with Salen-type ligands have been extensively studied for many
decades [1-7] and have attracted much interest due to their catalytic activities [8], especially in
the area of asymmetric catalysis [9], biological activity, such as anticancer [10], fluorescent
characteristics [11, 3c, 4b] and magnetic properties [3b, 3d]. Photoluminescence has been one of
the highlights in modern coordination chemistry owing to its potential applications in
*Corresponding author. Email: dongwk@126.com
1

luminescent devices, which also have been observed for Salen-type compounds and their
transition metal complexes [12]. Noticeably, several excellent works have been devoted to
synthesizing and characterizing mononuclear, homo- or heteropolynuclear transition metal
complexes bearing a salamo-type ligand or its derivatives [13].
Compared with symmetric salamo-type ligands, the asymmetric configuration would
afford opportunities for a greater structural variation and infinite coordination polymers, which
would be expected to lead to novel characteristics [1b]. Selective synthesis of asymmetrical
salamo-type ligands is important because the electronic and steric effect of the ligands on
Salen-metal-assisted catalysis may be controlled by introduction of different substituents into the
two benzene rings [7b]. In order to study the structural features and fluorescent characteristics of
transition metal complexes with asymmetric salamo-type ligands, herein we designed and
synthesized a single-armed salamo-type bisoxime, H3L
(6-[2-nitrilomethylidyne(4,6-dibromobenzene)]-6ʹ-methoxy-2,2ʹ-[1,1ʹ-(ethylenedioxy(nitrilometh
ylidyne)(nitriloethylidyne)]triphenol), which has the capability to coordinate with metal ions to
form multinuclear complexes. The syntheses, crystal structures and fluorescent properties of the
Co(II), Zn(II) and Cd(II) complexes have been fully investigated.
2. Experimental
2.1. Materials and instruments
3,5-Dibromosalicylaldehyde, 2-hydroxy-3-aminoacetophenone and
2-hydroxy-3-methoxybenzaldehyde were purchased from Alfa Aesar and used without further
purification. The other reagents and solvents are of analytical grade from Tianjin Chemical
Reagent Factory.
C, H, and N analyses were obtained using a GmbH VarioEL V3.00 automatic elemental
analysis instrument. Elemental analyses for Co(II), Zn(II) and Cd(II) ions were measured using
an IRIS ER/S·WP–1 ICP atomic emission spectrometer. FT-IR spectra were recorded on a
VERTEX70 FT-IR spectrophotometer, with samples prepared as KBr (400-4000 cm-1) and CsI
2

(100-500 cm-1) pellets. UV-vis absorption spectra in the 200-600 nm range were recorded on a
Hitachi UV-3010 spectrophotometer in chloroform solution. 1H NMR spectra were determined
using a Bruker AVANCE DRX-400 spectrometer. Melting points were obtained by use of an X4
microscopic melting point apparatus made by Beijing Taike Instrument Limited Company and
were not corrected. Fluorescent spectra were taken on a LS-55 fluorescence photometer. X-ray
single crystal structures were determined on a Bruker Smart Apex CCD diffractometer.
2.2. Synthesis of
6-[2-nitrilomethylidyne(4,6-dibromobenzene)]-6ʹ-methoxy-2,2ʹ-[1,1ʹ-(ethylenedioxy(nitrilomet
hylidyne)(nitriloethylidyne)]triphenol (H3L)
1,2-Bis(phthalimidoxy)ethane was synthesized according to the literature [1c, 13c].
1,2-Bis(aminooxy)ethane was prepared according to an analogous method reported earlier [1b,
13c].
The single-armed salamo-type bisoxime H3L was synthesized by a modified method
reported in the earlier literature (scheme 1) [4e, 4f].
3

O
O
N
O
N
O
N
O
CHO
NH2
OH
H2N
O
O NH2
NH2
OH
HO
OH
OH
OCH3
H2N
OCH3
OCH3
1
2
O
N
O
N
CHO
Br
OH
OH
HO
Br
OCH3 OH
Br
N
H3L
Br
Scheme 1. Synthetic route to H3L.
To an ethanol solution (30 ml) of 2-hydroxy-3-methoxybenzaldehyde (304.3 mg,
2 mmol) was added an ethanol solution (20 ml) of 1,2-bis(aminooxy)ethane (276.0 mg, 3 mmol).
The solution 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, 10:1) to afford
a colorless flocculent crystalline solid of 2-[O-(1-ethyloxyamide)]oxime-6-methoxyphenol (1).
Yield, 48% (163.6 mg). M.p. 91-92 °C. Anal. Calc. for C10H14N2O4 (%): C, 53.09; H, 6.24; N,
12.38. Found (%): C, 53.12; H, 6.22; N, 12.37.
A solution of 1 (452.4 mg, 2 mmol) in ethanol (10 mL) was added dropwise to a solution
of 2-hydroxy-3-aminoacetophenone (303.2 mg, 2 mmol) in ethanol (10 mL), and the solution
was heated at 55–60 °C for 24 h. After cooling to room temperature, the brownish intermediate
product 6-amino-6ʹ-methoxy-2,2ʹ-[1,1ʹ-(ethylenedioxy(nitrilomethylidyne)(nitriloethylidyne)]-
bisphenol (2) was collected via suction filtration. Yield, 25% (179.7 mg). M.p. 123-124 °C. Anal.
Calc. for C18H21N3O5 (%): C, 60.16; H, 5.89; N, 11.69. Found (%): C, 60.27; H, 5.78; N, 11.54.
4

A solution of 2 (719.8 mg, 2 mmol) in ethanol (10 mL) was added to a solution of
3,5-dibromosalicylaldehyde (560.0 mg, 2 mmol) in ethanol (10 mL), and the solution was heated
at 50–55 °C for 4 h. Taking advantage of a hot filtration, the orange precipitate of H3L was
collected via suction filtration. Yield, 43% (532.4 mg). M.p. 165-167 °C. 1H NMR (400 MHz,
CDCl3) δ 15.13 (s, 1H), 11.89 (s, 1H), 9.72 (s, 1H), 8.65 (s, 1H), 8.37 (s, 1H), 6.82 – 6.96 (m,
6H), 6.69 (d, J = 7.8 Hz, 1H), 6.17 (s, 1H), 4.52 (s, 4H), 3.90 (s, 3H), 2.37 (s, 3H). IR (KBr,
cm−1) 3065(w), 1625(s), 1446(s), 1255(s), 1014(m), 725(s). Anal. Calc. for C25H23Br2N3O6 (%):
C, 48.33; H, 3.73; N, 6.76. Found (%): C, 48.46; H, 3.65; N, 6.70.
2.3. Synthesis of
diethanol(μ-acetato){6-[2-Nitrilomethylidyne(4,6-dibromobenzene)]-6ʹ-methoxy-2,2ʹ-[1,1ʹ-(eth
ylenedioxy(nitrilomethylidyne)(nitriloethylidyne)]triphenolato)dicobalt(II)} (1)
A solution of cobalt(II) acetate tetrahydrate (2.49 mg, 0.01 mmol) in ethanol (2 ml) was added to
a solution of H3L (3.11 mg, 0.005 mmol) in acetone (4 ml) at room temperature. The color of the
mixing solution turned dark-red immediately. The mixture was filtered, and the filtrate was
allowed to stand at room temperature for about one week. The solvent was partially evaporated,
and dark-red block-shaped single crystals suitable for X-ray crystallographic analysis were
obtained. Yield, 46% (404.6 mg). IR (KBr, cm−1) 3053(w), 1598(s), 1440(s), 1242(m), 1076(m),
734(m), 534(w), 433(w). Anal. Calc. for C31H37Br2Co2N3O11 (%): C, 41.13; H, 4.12; N, 4.64; Co,
13.02. Found (%): C, 41.35; H, 4.07; N, 4.70; Co, 13.11.
2.4. Synthesis of
methanol(μ-acetato){6-[2-Nitrilomethylidyne(4,6-dibromobenzene)]-6ʹ-methoxy-2,2ʹ-[1,1ʹ-(eth
ylenedioxy(nitrilomethylidyne)(nitriloethylidyne)]triphenolato)dizinc(II)} (2)
A solution of zinc(II) acetate dihydrate (2.19mg, 0.01mmol) in methanol (4 ml) was added to a
solution of H3L (3.11 mg, 0.005 mmol) in acetone (2 ml) at room temperature. The color of the
5

mixing solution immediately turned to yellow. The mixture was filtered, and the filtrate was
allowed to stand at room temperature for about one week. After the solvent was partially
evaporated, several yellow block-shaped single crystals separated out which were suitable for
X-ray crystallographic analysis. Yield, 48% (399.1 mg). IR (KBr, cm−1) 3047(w), 1602(s),
1442(s), 1251(w), 1076(w), 740(m), 533(w), 445(w). Anal. Calc. for C28H27Br2Zn2N3O9 (%): C,
40.03; H, 3.24; N, 5.00; Zn, 15.57. Found (%): C, 40.08; H, 3.27; N, 5.04; Zn, 15.51.
2.5. Synthesis of
di{methanol(μ-acetato){6-[2-Nitrilomethylidyne(4,6-dibromobenzene)]-6ʹ-methoxy-2,2ʹ-[1,1ʹ-(
ethylenedioxy(nitrilomethylidyne)(nitriloethylidyne)]triphenolato)dicadmium(II)}} (3)
A solution of cadmium(II) acetate dihydrate (2.66 mg, 0.01 mmol) in methanol (4 ml) was added
dropwise to a solution of H3L (3.11 mg, 0.005 mmol) in acetone (2 ml) at room temperature. The
color of the mixing solution turned yellow immediately, then it was allowed to volatilize at room
temperature. After several weeks, the solvent had partially evaporated and several yellow
block-shaped single crystals were obtained, which were suitable for X-ray crystallographic
analysis. Yield, 51% (947.2 mg). IR (KBr, cm−1) 3059(w), 1608(s), 1438(s), 1240(m), 1043(w),
742(m), 521(w), 443(w). Anal. Calc. for C56H54Br4Cd4N6O18 (%): C, 36.00; H, 2.91; N, 4.50; Cd,
24.07. Found (%): C, 36.05; H, 2.93; N, 4.56; Cd, 24.02.
2.6. X-ray crystallography
X-ray diffraction data for the Co(II), Zn(II) and Cd(II) complexes were collected on a Bruker
Smart Apex CCD diffractometer at 293.42(10), 293.01(2) and 173.42(10) K, respectively, using
graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Data collection and reduction were
performed using SMART and SAINT software [14]. The structures were solved using the direct
2
method and refined by full-matrix least-squares on F using the SHELXL-97 program package
[15]. All non-hydrogen atoms were refined anistropically and hydrogens were added in
6

calculated positions and refined using a riding model. The X-ray crystallographic data collection,
solution and refinement parameters for the Co(II), Zn(II) and Cd(II) complexes are summarized
in table 1.
3. Results and discussion
3.1. X-ray crystal structures
3.1.1. The Co(ΙΙ) complex. The crystal structure and atom numbering of the Co(ΙΙ) complex are
given in figure 1. Selected bond distances and angles of the Co(ΙΙ) complex are listed in table 2.
The Co(II) complex crystallizes in the monoclinic system, space group C2/c, which
consists of two Co(II) ions, one (L)3- unit, one coordinated acetate ion, two coordinated ethanol
molecules and one crystallized water molecule. Moreover, the Co(II) complex forms a novel 1:2
((L)3- : Co(II)) dinuclear structure which is less common in the reported salamo-type complexes
[1, 13]. The Co1 ion is six-coordinate by one nitrogen (N1) and two oxygens (O1, O2) of the
(L)3- unit, one oxygen (O9) of the coordinated acetate ion and two oxygens (O7 and O8) of
coordinated ethanol molecules. Moreover the phenolic oxygens (O1 and O2), the oxime nitrogen
(N1) of the (L)3- unit and the oxygen (O9) of the coordinated acetate ion together constitute the
basal plane; two oxygens (O7 and O8) of coordinated ethanol molecules occupy the axial
positions. The Co2 ion is five-coordinate by two phenolic oxygens (O2 and O5), one oxygen
(O10) of the coordinated acetate ion and two oxime nitrogens (N2 and N3). Moreover the
oxygen (O10) of the coordinated acetate ion, the oxime nitrogen (N2) and the phenolic oxygen
(O5) together constitute the basal plane; the oxime nitrogen (N3) and the phenolic oxygen (O2)
occupy the axial positions. Here, we have synthesized a dinuclear Co(II) complex in which the
Co1 ion is six-coordinate with a slightly distorted octahedral geometry and the Co2 ion is
five-coordinate with a trigonal bipyramidal geometry which is deduced by calculating the value
of τ = 0.838 [16]. The non-coordinated water molecule in the structure of the Co(II) complex
is disordered unequally over three different positions. This was allowed for during refinement
7

and their total occupancy is 1.0 with the O1W, O2W and O3W atoms occupancies refined to 0.4,
0.3 and 0.3, respectively.
The Co(II) complex molecules form a dimeric structure via intramolecular and
intermolecular hydrogen bond interactions. As illustrated in figure 2, three pairs of
intramolecular hydrogen bonds, O7-H7A···O5, C15-H15A···O3 and C17 –H17···O10, are
formed. The adjacent Co(II) complex molecules are interlinked into a dimer via intermolecular
hydrogen bond interactions O8-H8···O9 between the O8–H8 units of the coordinated ethanol
molecules and the O9 atom of the μ2-acetate ion from the adjacent Co(II) complex molecule
[1, 5-7]. The hydrogen bond data for the Co(II) complex are summarized in table 3.
3.1.2. The Zn(ΙΙ) complex. The structural features of the Zn(II) complex are very similar to
those of the Co(II) complex. The crystal structure and atom numbering of the Zn(II) complex are
presented in figure 3 and selected bond distances and angles of the Zn(II) complex are shown in
table 2.
The Zn(II) complex crystallizes in the triclinic system, space group P-1, and the unit cell
contains two crystallographically independent, but chemically identical, dinuclear complexes
(figure 3) consisting of two Zn(II) atoms, one (L)3- unit, one coordinated acetate ion and and one
coordinated methanol molecule as expected from the analytical data. Moreover, the Zn(II)
complex forms a novel 1:2 ((L)3- : Zn(II)) dinuclear structure which is different from the
structures of 1:1 [1d, 1h], 2:3 [13g], 2:4 [1c], 4:8 [13d] (L: Zn(II)) salamo-type Zn(II) complexes
reported earlier. The Zn1 ion is five-coordinate by two nitrogens (N1 and N2) and two oxygens
(O1 and O5) of the (L)3- unit and one oxygen (O7) of the coordinated acetate ion in a μ2-fashion.
Moreover the phenolic oxygen (O1), the oxime nitrogen (N2) of the (L)3- unit and the oxygen
(O7) of the coordinated acetate ion together constitute the basal plane, while one phenolic
oxygen (O5) and one oxime nitrogen (N1) occupy the axial positions. The Zn2 ion is
five-coordinate by two phenolic oxygens (O5 and O6), one oxygen (O8) of the coordinated
8

acetate ion also in a μ2-fashion, one oxime nitrogen (N3) and one oxygen (O9) of the coordinated
methanol molecule. Moreover the oxygen (O8) of the coordinated acetate ion, the oxime
nitrogen (N3) and the oxygen (O9) of the coordinated methanol molecule together constitute the
basal plane; the two phenolic oxygens (O5 and O6) occupy the axial positions. As we know, the
coordination number of Zn(II) is generally four or six and the coordination geometry around
Zn(II) atom is tetrahedral or octahedral [1d]. However, there are only a few reports of
five-coordinate salamo-type Zn(II) complexes having distorted square–pyramidal or
trigonal–bipyramidal configurations [1e]. Here, we have designed and synthesized a dinuclear
Zn(II) complex in which the Zn1 and Zn2 ions are both five-coordinate with distorted trigonal
bipyramidal geometries which are deduced by calculating the values of τ1 = 0.875, τ2 = 0.600,
respectively [16].
In the crystal structure, the Zn(II) complex molecules form a dimeric structure via two
pairs of intermolecular C24−H24···O2 and C18−H18···O9 hydrogen bond interactions [17].
Meanwhile, an interesting feature of the crystal structure are two pairs of short O1···O9 contacts
[18] (figure 4). The hydrogen bond data are summarized in table 3.
As shown in figure 4, the dimers are interlinked by C7–H7···Cg3 (C41-C46) interactions
into a 1D chain structure along the b axis [1f]. In addition, the adjacent chains along the b axis
are held together to form an infinite 2D network structure on the ab crystallographic plane by
C37–H37A···Cg2 (C19-C24) interactions (figure 5) [1g, 13h]. The planes are interlinked further
by C40–H40B···Cg1 (C1-C6) interactions to form an infinite 3D structure [19]. Thus, a
self-assembled infinite 3D supramolecular structure is formed by abundant intermolecular
hydrogen bonds, three pairs of C–H···π interactions of neighboring dimers (table 3).
3.1.3. The Cd(ΙΙ) complex. The crystal structure and atom numberings of the Cd(II) complex
are drawn in figure 6. The selected bond distances and angles are summed in table 2.
Previously, the mononuclear salamo-type Cd(II) complex, [Cd(Br4salamo)(H2O)2], was
9

reported [1d]. Here, the Cd(II) complex is composed of four Cd(II) ions, two (L)3- units, two
coordinated acetate ions and methanol molecules. The Cd(II) complex crystallizes in the
orthorhombic system, space group Pbca, is a symmetric tetranuclear structure, and is a dimer of
the {Cd(L)(OAc)Cd(CH3OH)} unit. The Cd(II) complex has a “stepped” conformation as
observed in the dimers of [Cu(salamo)] [13a]. Two Cd(II) ions (Cd1 and Cd2) have two different
coordination geometries. The Cd1 ion is six-coordinate by two nitrogens (N2 and N3) and two
oxygens (O2 and O5) of the (L)3- unit and two oxygens (O7 and O8) of one chelating acetate ion.
Meanwhile, the phenolic oxygen (O2), the phenolic oxygen (O5) and one oxygen (O8) of the
chelate acetate ion together constitute one triangular plane, while the oxime nitrogens (N2 and
N3) and one oxygen (O7) of the chelating acetate ion together constitute another triangular plane.
The coordination geometry around the Cd1 center can be regarded as a distorted triangular prism.
The Cd2 atom is uncommon as it is seven-coordinate, bonded by four phenolic oxygens (O1, O2,
O5 and O1#), one oxygen (O6) of a methoxy group of an (L)3- unit, one oxime nitrogen (N1) and
one oxygen (O9) of a coordinated methanol molecule. Moreover, the oxygen (O6) of a methoxy
group of the (L)3- unit, the oxime nitrogen (N1) and the phenolic oxygens (O1, O2 and O5)
together constitute the basal plane, while the phenolic oxygens (O1#) and the oxygen (O9) of
coordinated methanol molecule occupy the axial positions. The coordination geometry around
the Cd2 center can be described as slightly distorted pentagonal bipyramidal geometry [20]. As
far as we know, this is the first time a seven-coordinate salamo-type Cd(II) complex has been
reported. Thus, this novel 2:4 ((L)3-: Cd) tetranuclear structure is different from that of 1:1
(L : Cd(II)) reported earlier in a salamo-type Cd(II) complex [1d]. In addition, the dihedral angle
between the coordination plane of N2-Cd1-O2 and that of N3-Cd1-O5 is 52.51(3)°; the two
planes are bent asymmetrically making angles of 23.09(3)° and 21.88(3)°, respectively, with
respect to the plane of O1-Cd2-N1, indicating the salamo moiety and the single-armed
salicylaldehyde unit have good coplanarity. The dimer is bridged through O1 across the
crystallographic center of symmetry (Cd2···O1# = 2.344(3) Å, Cd2···Cd2# = 3.593(4) Å,
10

∠Cd2···O1···Cd2# = 100.79(10)° and ∠O1···Cd2···O1# = 79.21(10)).
As shown in figure 7, the Cd(II) complex molecules are interlinked by intermolecular
hydrogen bonds C15−H15C···O3, O9−H9X···O8, C16−H16···O7 and C17−H17A···N2 to form
an infinite 2D network structure on the ab crystallographic plane (table 3) [21]. Synchronously,
this linkage is further stabilized by short intermolecular Br1···Br1 contacts between the bromine
atoms coming from the bromo-substituted salicylaldehyde of one Cd complex unit and that of
another Cd complex unit, to form a 1D supramolecular chain-like structure [22].
3.2. IR spectra
The FT-IR spectra of H3L and its corresponding Co(II), Zn(II) and Cd(ΙΙ) complexes exhibit
various bands from 400–4000 cm-1 (figure S1). The Co(II), Zn(II) and Cd(ΙΙ) complexes have
similar FT-IR spectra which indicate that they have similar structures. The free ligand H3L
shows a broad characteristic band of the OH group at 3065 cm-1. This band disappeared in the
FT-IR spectra of the Co(II), Zn(II) and Cd(ΙΙ) complexes, which is indicative of the fact that the
phenolic OH groups of H3L have been deprotonated and coordinated to the Co(II), Zn(II) and
Cd(ΙΙ) atoms [23].
The free ligand H3L exhibits a characteristic C=N stretching band at 1625 cm-1, while the
C=N stretching bands of the Co(II), Zn(II) and Cd(ΙΙ) complexes are observed at 1598, 1602 and
1608 cm-1, respectively. The C=N stretching frequencies are shifted to lower frequencies by
ca. 27, 23 and 17 cm-1 upon complexation, indicating that the Co(II), Zn(II) and Cd(ΙΙ) atoms are
coordinated by N2O2 donor atoms of (L)3- units. Thus, it provides evidence for the coordination
of H3L with Co(II), Zn(II) and Cd(ΙΙ) atoms. In the 1438-1446 cm-1 region, the observed bands
are attributed to aromatic C=C vibration. Upon coordination these bands shift to lower
frequencies for the Co(II), Zn(II) and Cd(ΙΙ) complexes.
The Ar–O stretching frequency appears at 1255 cm-1 for H3L, while the Ar–O stretching
frequencies of the Co(II), Zn(II) and Cd(ΙΙ) complexes are observed at 1242, 1251 and 1240 cm-1,
respectively. The Ar–O stretching frequencies are shifted to lower frequencies, indicating that
11

the Co–O, Zn–O and Cd–O bonds are formed between the Co(II), Zn(II) and Cd(ΙΙ) atoms and
oxygen atoms of phenolic groups [1h]. In addition, there is a broad absorption centered on 3053,
3047 and 3059 cm-1 in the Co(II), Zn(II) and Cd(ΙΙ) complexes, respectively, which may be
assigned to the O-H stretching vibration of CH3OH or CH3CH2OH molecules.
The far-infrared spectra of the Co(II), Zn(II) and Cd(ΙΙ) complexes were also obtained in
the region 550-100 cm-1 in order to identify frequencies due to the M-O and M-N bonds. The
bands at 433, 445 and 443 cm-1 in the Co(II), Zn(II) and Cd(ΙΙ) complexes are assigned to νCo–O
Zn–O and νCd–O, while the bands at 534, 533 and 521 cm-1 are assigned to νCo–N, νZn–N and νCd–N
,
ν
,
respectively.
3.3. UV–vis absorption spectra
The UV-vis absorption spectra of the free ligand H3L and its Co(II), Zn(II) and Cd(II) complexes
were determined in chloroform solution (c = 1×10-5 mol⋅L-1) and are shown in figure S2. The
absorption peaks of the Co(II), Zn(II) and Cd(II) complexes are obviously different from those of
H3L.
The UV-vis spectrum of H3Lexhibits three absorption bands at 263, 270 and 447 nm.
The former absorption band at 263 nm can be assigned to the π–π* transition of the benzene
rings, the second can be attributed to the π–π* transition of the oxime groups [24], and the latter
one at 447 nm which is ascribed to the quinoid form of H2Salen. It is of note that this band
cannot be seen sometimes in the corresponding salen derivatives [25]. Upon coordination of the
ligand, the absorption band at 263 nm for the Co(II), Zn(II) and Cd(ΙΙ) complexes is
hypochromically shifted to ca. 240, 239 and 241 nm, respectively, and the band at 270 nm is
bathochromically shifted to 282, 282 and 280 nm, respectively, which indicate that the phenolic
oxygen and oxime nitrogens are involved in coordination to the Co(II), Zn(II) or Cd(ΙΙ) atoms. In
addition, new bands are observed at 457, 443 and 432(372) [au: is this correct?] nm in the
Co(ΙΙ), Zn(ΙΙ) and Cd(ΙΙ) complexes, respectively, which are assigned to the n–π* charge transfer
12

transition from a nonbonding electron pair of the bridging phenolic oxygen to the vacant
d-orbital of the metal(II) ions [1].
3.4. Fluorescence properties
The fluorescent properties of H3L and its corresponding Co(II), Zn(II) and Cd(II) complexes
were measured at room temperature (figure S3). The Zn(II) and Cd(II) complexes display
enhanced emission intensities compared to the corresponding ligand (H3L) when excited at
452 nm. Enhancement of fluorescence through complexation is of much interest as it creates the
opportunity for photochemical applications of these complexes [26, 27]. The fluorescence of the
free ligand is quenched by the occurrence of a photoinduced electron transfer process, probably
due to the presence of lone pairs on the nitrogen atoms, and as such, the process is prevented by
the complexation of the free ligand with metal atoms. Thus the fluorescence intensity may be
effectively enhanced by the coordination of Zn(II) and Cd(II) atoms [28].
The free ligand exhibits a weak emission peak at 548 nm upon excitation at 452 nm. The
Co(II) complex shows a lower photoluminescence upon excitation at 452 nm (figure S3). Since
the emission peak position of the Co(II) complex is similar to that of the free ligand, the emission
peak of the Co(II) complex may also arise from the intraligand transition. Compared with the
free ligand, the Co(II) complex’s emission intensity is reduced significantly which indicates that
the Co(II) ions have the property of fluorescent quenching. The emission spectrum shows that
the emission spectral shape of the Zn(II) complex closely resembles that of the Cd(II) complex.
In comparison with the corresponding H3L with the maximum emission wavelength at 548 nm
when excited at 452 nm, the Zn(ΙΙ) and Cd(ΙΙ) complexes exhibit blue-shifts with the maximum
emission at 510 and 502 nm when excited at 452 nm, which could be assigned to ligand-to-metal
charge transfer (LMCT) [29].
4. Conclusion
Three new complexes with the chemical formulas [Co(L)(OAc)Co(CH3CH2OH)2]·H2O,
13

[Zn(L)(OAc)Zn(CH3OH)] and [{Cd(L)(OAc)Cd(CH3OH)}2] have been synthesized and
structurally characterized. There is good coplanarity between the salamo moiety and the
single-armed salicylaldehyde unit in the Cd(II) complex, while that of the Co(II) or Zn(II)
complex is poor. The Co(II) complex forms a dimeric unit by intermolecular hydrogen bond
interactions of neighboring dimeric molecules. The Zn(II) complex also forms a dimeric unit by
intermolecular hydrogen bond interactions. Self-assembling infinite 1D, 2D and 3D
supramolecular structures are formed by intermolecular hydrogen bond and C–H···π interactions.
Also, the Cd(II) complex forms an infinite 2D supramolecular structure via intermolecular
hydrogen bond interactions. In the FT-IR spectra of the Co(II), Zn(II) and Cd(II) complexes, the
ν(M-O) and ν(M-N) vibrational absorption frequencies have been observed. Meanwhile, the
Zn(II) and Cd(II) complexes exhibit blue emission with the maximum emission wavelength at
510 and 502 nm when excited at 452 nm.
Supplementary material
Further details of the crystal structure investigation(s) may be obtained from the Cambridge
Crystallographic Data Centre, 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 depository number CCDC Nos. 1534113, 1484600 and
1534112 for the Co(II), Zn(II) and Cd(II) complexes, respectively.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (21361015),
which is gratefully acknowledged.
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18

Figure 1. (a) Molecular structure of the Co(II) complex with the atom numbering (hydrogens
omitted for clarity); (b) Coordination polyhedra for Co(II) atoms of the Co(II) complex.
19

Figure 2. A dimeric unit of the Co(II) complex formed by intramolecular and intermolecular
hydrogen bonds.
20

Figure 3. (a) Molecular structure of the Zn(II) complex with the atom numbering (hydrogens
omitted for clarity); (b) Coordination polyhedra for Zn(II) atoms of the Zn(II) complex.
21

Figure 4. View of an infinite 1D chain motif of the Zn(II) complex along the b axis.
22

Figure 5. View of an infinite 2D network of the Zn(II) complex on the ab plane.
23

Figure 6. (a) Molecular structure of the Cd(II) complex with the atom numbering (hydrogens
omitted for clarity); (b) Coordination polyhedra for Cd(II) atoms of the Cd(II) complex.
24

Figure 7. View of an infinite 2D network of the Cd(II) complex on the ab plane.
25

Table 1. X-ray crystallographic data collection, solution and refinement parameters for the Co(II), Zn(II)
and Cd(II) complexes.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C31H37Br2Co2N3O11
905.31
C28H27Br2Zn2N3O9
840.09
293.01(2)
MoKα, 0.71073
Triclinic
C56H54Br4Cd4N6O18
1868.29
293.42(10)
MoKα, 0.71073
Monoclinic
C2/c
173.42(10)
MoKα, 0.71073
Orthorhombic
Pbca
P-1
10.0471(13)
31.7717(18)
24.9332(14)
90
14.2905(13)
15.1159(16)
15.6405(13)
93.113(8)
93.401(7)
93.276(8)
4
16.9945(6)
17.4212(5)
19.9811(5)
90
b (Å)
c (Å)
α (º)
β (º)
92.652(3)
90
8
7950.5(12)
1.513
2.900
90
90
4
5915.7(3)
2.098
4.199
γ (º)
Z
Volume (Å3)
Dc (Mg m–3)
μ (mm–1)
3361.4(5)
1.660
3.857
F (0 0 0)
3648
1672
3632
Crystal size (mm)
θ range (°)
Index ranges
0.26 × 0.24 × 0.22
2.05–25.12
−12 ≤ h ≤ 12,
0 ≤ k ≤ 39,
0 ≤ l ≤ 30
17831
7830
0.0202
100% (θ = 26.00)
7830 / 3 / 465
1.024
0.28 × 0.26 × 0.25
3.39–26.02
−17 ≤ h ≤ 16,
−18 ≤ k ≤ 18,
−19 ≤ l ≤ 19
24793
13167
0.102
99.4% (θ = 26.02)
13167 / 6 / 807
0.916
0.24 × 0.22 × 0.20
1.96–25.997
−20 ≤ h ≤ 10,
−12 ≤ k ≤ 21,
−22 ≤ l ≤ 24
15856
5813
0.0223
100% (θ = 25.997)
5813 / 0 / 401
1.082
Reflections collected
Independent reflections
Rint
Completeness to θ
Data / restraints / parameters
GOF
R , wR [I>2σ(I)]
R11, wR22 (all data)
Δρmax,min (e / Å3)
0.0349, 0.0808
0.0512, 0.0847
0.913 and -0.331
0.0739, 0.1402
0.1331, 0.1740
1.22 and -1.12
0.0299, 0.0935
0.0405, 0.0986
0.847 and -0.712
26

Table 2. Selected bond distances (Å) and angles (º) for the Co(II), Zn(II) and Cd(II) complexes.
Co(II) complex
Cd(II) complex
Zn(II) complex
Co1-O1
1.9765(17)
2.1802(19)
2.026(2)
2.039(3)
2.0820(19)
2.0764(19)
1.9339(18)
2.123(3)
2.1827(18)
2.071(2)
2.012(2)
166.24(8)
98.93(7)
94.10(7)
175.57(7)
95.79(7)
175.21(10)
119.09(10)
125.04(10)
89.23(11)
87.02(7)
89.70(8)
93.15(8)
94.56(7)
88.45(7)
95.91(8)
86.95(9)
88.72(9)
94.27(7)
85.46(7)
79.62(8)
81.07(7)
166.85(8)
93.49(8)
93.49(8)
86.02(9)
Zn1-O1
1.977(5)
2.131(6)
1.962(6)
2.026(6)
2.047(5)
2.062(7)
1.972(6)
1.992(6)
2.105(5)
2.066(5)
93.5(2)
Cd1-O2
2.194(3)
Co1-O8
Zn1-N1
Cd1-O5
2.227(3)
Co2-O2
Zn2-O6
Cd1-O7
2.332(3)
Co2-N2
Zn2-N3
Cd1-N3
2.371(4)
Co1-O2
Zn1-O5
Cd1-N2
2.392(4)
Co1-O9
Zn1-N2
Cd1-O8
2.424(3)
Co2-O5
Zn2-O8
Cd2-O5
2.274(3)
Co2-N3
Zn1-O7
Cd2-O1
2.318(3)
Co1-O7
Zn2-O5
Cd2-N1
Cd2-O1#
2.322(4)
Co1-N1
Zn2-O9
2.344(3)
Co2-O10
O1-Zn1-O5
O1-Zn1-N2
O7-Zn1-O5
N2-Zn1-N1
O6-Zn2-O9
O8-Zn2-O9
N3-Zn2-O5
O1-Zn1-O7
O5-Zn1-N1
O7-Zn1-N1
O6-Zn2-O5
O6-Zn2-N3
O8-Zn2-N3
N3-Zn2-O9
O1-Zn1-N1
O5-Zn1-N2
O7-Zn1-N2
O6-Zn2-O8
O8-Zn2-O5
O9-Zn2-O5
Cd2-O2
2.375(3)
O1-Co1-O2
O1-Co1- O9
O2-Co1- O8
O7-Co1- O8
N1-Co1- O7
O2-Co2-N3
O5-Co2-N2
O10-Co2-N2
N2-Co2-N3
O1-Co1- O7
O1-Co1-N1
O2-Co1- O9
O9-Co1- O7
N1-Co1-O8
O5-Co2-O2
O5-Co2-N3
O10-Co2-N3
O1-Co1-O8
O2-Co1- O7
O2-Co1-N1
O9-Co1- O8
N1-Co1- O9
O5-Co2-O10
O10-Co2-O2
N2-Co2-O2
120.8(3)
93.6(2)
Cd2-O9
2.398(4)
Cd2-O6
2.580(3)
91.5(3)
O2-Cd1-O5
O2-Cd1-O7
O5-Cd1-O7
O2-Cd1-N3
O5-Cd1-N3
O7-Cd1-N3
O2-Cd1-N2
O5-Cd1-N2
O7-Cd1-N2
N3-Cd1-N2
O2-Cd1-O8
O5-Cd1-O8
O7-Cd1-O8
N3-Cd1-O8
N2-Cd1-O8
O2-Cd1-C27
O5-Cd1-C27
O7-Cd1-C27
N3-Cd1-C27
N2-Cd1-C27
O8-Cd1-C27
O5-Cd2-O1
O5-Cd2-N1
76.64(10)
131.96(12)
120.26(12)
132.60(12)
76.37(11)
95.34(13)
77.07(11)
141.54(11)
98.20(11)
102.27(13)
82.67(11)
89.83(11)
55.25(11)
135.08(12)
113.99(12)
107.50(13)
106.81(14)
27.69(14)
117.27(14)
107.58(14)
27.57(14)
139.53(10)
140.68(11)
93.0(2)
105.4(2)
77.5(2)
116.1(2)
175.6(3)
90.2(3)
168.5(2)
91.5(2)
132.5(2)
121.3(2)
86.9(2)
84.5(2)
123.1(3)
94.6(3)
95.5(2)
89.7(2)
27

O1-Cd2-N1
O5-Cd2-O1#
O1#-Cd2-O1
N1-Cd2-O1#
O5-Cd2-O2
O1-Cd2-O2
N1-Cd2-O2
O2-Cd2-O1#
O5-Cd2-O9
O1-Cd2-O9
N1-Cd2-O9
O9-Cd2-O1#
O2-Cd2-O9
O5-Cd2-O6
O1-Cd2-O6
N1-Cd2-O6
O6-Cd2-O1#
O2-Cd2-O6
O9-Cd2-O6
79.47(10)
88.44(10)
79.21(10)
108.57(10)
72.23(10)
147.82(10)
68.50(10)
113.32(10)
88.58(13)
94.70(11)
81.74(14)
166.56(13)
78.13(12)
64.25(10)
76.23(10)
149.58(11)
84.62(10)
132.37(10)
82.28(13)
Symmetry transformations used to generate equivalent atoms: #, 1-x, 1-y, 1-z for the Cd(II) complex.
28

Table 3. Hydrogen-bonding interactions [Å, º] for the Co(II), Zn(II) and Cd(II) complexes.
d(H···A)
(DCC)
d(D···A)
∠D-H···A
D-H···A
d(D-H) (α)
Symmetry code
(CgI-perp)
(CgJ-perp)
Co(II) complex
O7-H7A···O5
O8-H8···O9
0.85
0.93
0.96
1.93
1.91
2.23
2.26
2.695(3)
2.798(3)
2.605(4)
3.153(4)
150
158
102
152
[x, y, z]
[-x, y, 1/2-z]
[x, y, z]
C15-H15A···O3
C17 –H17···O10
[x, y, z]
0.97
Zn(II) complex
O9-H9···O1
O9 -H9···O2
0.86
0.86
2.18
2.30
2.577(8)
3.110(9)
108
157
[x, y, z]
[x, y, z]
O18-H18A···O10
O18-H18A···O11
C8-H8B···O7
0.86
0.86
0.97
0.96
0.93
0.93
0.97
0.96
0.93
2.30
1.88
2.51
2.19
2.66
2.47
2.47
2.29
2.55
2.87
3.033(8)
2.567(7)
3.297(11)
2.599(12)
3.474(4)
3.321(11)
3.286(11)
2.651(12)
3.469(10)
3.754(10)
143
136
138
104
147
152
141
101
168
158
[x, y, z]
[x, y, z]
[x, y, z]
C10-H10C···O4
[x, y, z]
[x, y, z]
C18−H18···O9
C24-H24···O2
C37-H37B···O17
C40-H40C···O13
C53-H53···O10
C7-H7···Cg3
[1-x, 1-y, 1-z]
[x, y, z]
[x, y, z]
[2-x, 2-y, -z]
[x, -1+y, z]
C37-H37A···Cg2
C40-H40B···Cg1
2.89
2.95
3.803(11)
3.539(11)
157
121
[x, y, z]
[2-x, 1-y, 1-z]
Cd(II) complex
C16-H16B···Br2
O9-H9X···O8
0.99
0.85
0.98
0.99
0.99
2.92
2.12
2.03
2.35
2.56
3.873(6)
2.680(5)
2.535(6)
3.308(7)
2.955(6)
163
123
110
163
104
[-1/2+x,1/2-y,1-z]
[x, y, z]
C15-H15C···O3
C16-H16A···O7
C17-H17A···N2
[x, y, z]
[x, y, z]
[x, y, z]
DCC = distance between ring centroids; α = dihedral angle between planes I and J; CgI-perp = perpendicular
distance of Cg(I) from ring J; CgJ-perp = perpendicular distance of Cg(J) from ring I. Zn(II) complex Cg1 =
C1-C6; Cg2 = C19-C24; Cg3 = C41-C46.
29