Hetero-trinuclear Zn(II)-M(II) (M = Sr, Ba) complexes based on a mononuclear Zn(II) complex metallohost: Syntheses, structures and fluorescence properties

Article abstract of DOI:10.1080/00958972.2016.1231302

A new mononuclear Zn(II) complex, [ZnL(HOAc)] (1) (H₂L = 6,6′-diethoxy-2,2′-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol), was synthesized by reaction of H₂L and Zn(II) acetate under solvothermal conditions. Complex 1 acts as a metallohost possessing a pentadentate O₅ donor. Complex 1 molecules bonded to one Sr(II) or Ba(II) form two new hetero-trinuclear complexes, [(ZnL)₂M(OAc)₂] (M = Sr (2), Ba (3)). In 2 and 3, Zn(II) ions are 5-coordinate, but the Sr(II) or Ba(II) ion is 10-coordinate by four μ-phenolic oxygens from two L^2-units, four oxygens from four ethoxy groups and two oxygens from two μ-acetato ligands. Furthermore, 1-3 exhibit blue emissions with the maximum emission wavelengths λ_max = 477, 500, and 471 nm when excited at 360 nm.

Full text of DOI:10.1080/00958972.2016.1231302

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Hetero-trinuclear Zn(II)-M(II) (M = Sr, Ba)
complexes based on a mononuclear Zn(II)
complex metallohost: Syntheses, structures
and fluorescence properties
Wen-Kui Dong, Jian-Chun Ma, Yin-Juan Dong, Li Zhao, Li-Chun Zhu, Yin-Xia
Sun & Yang Zhang
To cite this article: Wen-Kui Dong, Jian-Chun Ma, Yin-Juan Dong, Li Zhao, Li-Chun Zhu, Yin-
Xia Sun & Yang Zhang (2016): Hetero-trinuclear Zn(II)-M(II) (M = Sr, Ba) complexes based on a
mononuclear Zn(II) complex metallohost: Syntheses, structures and fluorescence properties,
Journal of Coordination Chemistry, DOI: 10.1080/00958972.2016.1231302
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Date: 17 September 2016, At: 20:01

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2016.1231302
Hetero-trinuclear Zn(II)-M(II) (M = Sr, Ba) complexes based on a mononuclear
Zn(II) complex metallohost: Syntheses, structures and fluorescence properties
WEN-KUI DONG*, JIAN-CHUN MA, YIN-JUAN DONG, LI ZHAO, LI-CHUN ZHU, YIN-XIA SUN
and YANG ZHANG
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, PR China
A new mononuclear Zn(II) complex, [ZnL(HOAc)] (1) (H2L =
6,6'-diethoxy-2,2'-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol), was synthesized by
reaction of H2L and Zn(II) acetate under solvothermal conditions. Complex 1 acts as a
metallohost possessing a pentadentate O5 donor. Complex 1 molecules bonded to one Sr(II) or
Ba(II) form two new hetero-trinuclear complexes, [(ZnL)2M(OAc)2] (M = Sr (2), Ba (3)). In 2
and 3, Zn(II) ions are five-coordinate, but the Sr(II) or Ba(II) ion is ten-coordinate by four
μ-phenolic oxygens from two L2- units, four oxygens from four ethoxy groups and two oxygens
from two μ-acetato ligands. Furthermore, 1, 2 and 3 exhibit blue emissions with the maximum
emission wavelengths λmax = 477, 500 and 471 nm when excited at 360 nm.
Keywords: Salamo-type ligand; Hetero-trinuclear complex; Metallohost; Synthesis; Crystal
structure
1. Introduction
The Salen-type N2O2 ligand is one of the most versatile ligands in inorganic chemistry [1-7]. In
host-guest chemistry, the use of 3-alkoxy N2O2 ligands as a building block often results in
multi-metal complexation systems [8-14]. The N2O2 tetradentate motif can coordinate with
d-block divalent transition metal ions and produce a neutral metal complex [15-18]. The two
phenolic O-H groups of N2O2 metal complexes are converted into more polarized O-M
*Corresponding author. Email: dongwk@126.com
1

(phenoxo-metal) bonds, which leads to the negatively charged phenoxy groups. Because of the
negative charge, the phenoxy groups can further coordinate to d-block transition metals [19-24],
alkali metal [25-27], alkaline earth metal [28], and rare earth metal ions [29], which leads to the
formation of di- or polynuclear complexes. These second metal ions are regarded as guests and
the N2O2 metal complexes serve as metallohosts. In recent years, a number of 3d-4f complexes
have been synthesized with the H2(3-MeOsalamo) ligand [30-33], however, there are relatively
few studies on the complexes of transition metals with alkali metals [14].
We now report the syntheses, crystal structures and photophysical properties of Zn(II)
and Zn(II)-M(II) (M = Sr, Ba) complexes. The structures of 1, 2 and 3 were characterized by
elemental analyses, IR spectra, UV-Visible spectra, fluorescence spectra and X-ray single crystal
diffraction.
2. Experimental
2.1. Materials
3-Ethoxysalicylaldehyde was purchased from Aldrich and used without purification. The other
reagents and solvents were of analytical grade reagents from Tianjin Chemical Reagent Factory.
2.2. Synthesis
The synthetic route of H2L is shown in scheme 1.
2

O
C
O
C
O
C
.
NH2NH2 H2O
Br
Br
EtOH
N OH
N O
O
N
EtOH
C
O
C
O
C
O
O
O
N
O
N
OH
2
O
H2L
OH HO
H2N O
O NH2
EtOH
O
O
Scheme 1. The synthetic route of H2L.
2.2.1. Synthesis and characterization of 6,6'-diethoxy-2,2'-[1,2-ethylenedioxybis-
(nitrilomethylidyne)]diphenol (H2L). H2L was synthesized according to an analogous method
reported earlier [34, 35]. The synthetic route for the preparation of H2L is shown in scheme 1. A
solution of 1,2-bis(aminooxy)ethane (0.276 g, 3 mmol) in ethanol (10 mL) was added to a
solution of 3-ethoxybenzaldehyde (0.996 g, 6 mmol) in ethanol (20 mL) and the mixture was
heated at 60 °C for 5 h. After cooling to room temperature, the precipitate was filtered off, and a
white crystalline solid was obtained. Yield: 0.784 g, 67.3%. m.p. 189-190 °C. Anal. Calc. for
C20H24N2O6 (%): C, 61.84; H, 6.23; N, 7.21. Found: C, 61.80; H, 6.30; N, 7.19. 1H NMR
(400 MHz, CDCl3): δ 1.47 (t, J = 4 Hz, 6H, CH3), 4.11 (dd, J = 4, 8 Hz, 4H, CH2), 4.46 (s, 4H,
CH2), 6.82 (m, 3H, ArH), 6.88 (m, 3H, ArH), 8.26 (s, 2H, CH=N), 9.68 (s, 2H, OH). IR (KBr,
cm-1): 3134 (m), 2957 (m), 2897 (m), 1605 (s), 1578 (m), 1474 (s), 1423 (s), 1360 (m), 1315 (m),
1256 (s), 1170 (w), 1055 (s), 930 (s), 835 (m), 775 (m), 729 (s), 677 (m), 621 (s), 596 (m),
540 (w), 457 (w). UV-Visible (EtOH, λmax (nm)/εmax (L mol-1 cm-1)): 223/9.46 × 104 (π→π*),
271/6.38 × 104 (π→π*), 319/1.70 × 104 (π→π*). Fluorescence (EtOH, λex (λem) (nm)): 350 (409
(π*→π)).
3

2.2.2. Synthesis of (acetic acid-κO) {6,6'-diethoxy-2,2'-[1,2-ethylenedioxybis-
(nitrilomethylidyne)]diphenolato-κ4O,N,N',O'}zinc(II) (1). 1 was synthesized under
solvothermal conditions. A mixture of Zn(II) acetate dihydrate (21.95 mg, 0.1 mmol), H2L
(38.84 mg, 0.1 mmol), methanol (3 ml) and chloroform (1 ml) was kept in a Teflon-lined
stainless-steel container at 100 °C for 24 h. After slowly cooling the mixture to room temperature,
several yellow block-like single crystals suitable for X-ray crystallographic analysis were
obtained. Yield: 44.84 mg, 87.6%. Anal. Calc. for C22H26N2O8Zn (%): C, 51.62; H, 5.12; N, 5.47;
Zn, 12.78. Found: C, 51.59; H, 5.15; N, 5.45; Zn, 12.83. 1H NMR (400 MHz, DMSO-d6): δ 1.25
(t, J = 4 Hz, 6H, CH3), 1.98 (s, 3H, CH3), 3.97 (d, J = 4 Hz, 4H, CH2), 4.31 (s, 4H, CH2), 6.30 (t,
J = 6 Hz, 2H, ArH), 6.74 (m, 2H, ArH), 7.19 (s, 2H, ArH), 8.41 (s, 2H, CH=N), 9.30 (s, 1H, OH).
IR (KBr, cm-1): 3313 (m), 3169 (m), 2978 (m), 2887 (w), 1670 (m), 1597 (s), 1543 (m), 1456 (s),
1313 (s), 1242 (s),1209 (s), 1078 (s), 901 (s), 737 (s), 615 (m), 509 (m), 459 (w). UV-Visible
(EtOH, λmax (nm)/εmax (L mol-1 cm-1)): 232/9.02 × 104 (π→π*), 280/4.86 × 104 (π→π*),
363/1.79 × 104 (π→π*). Fluorescence (EtOH, λex (λem) (nm)): 360 (477 (π*→π)).
2.2.3. Synthesis of bis{μ-6,6'-diethoxy-2,2'-[1,2-ethylenedioxybis-
(nitrilomethylidyne)]diphenolato}bis[µ-acetatozinc(II)]strontium(II) (2). A solution of Sr(II)
acetate (1.03 mg, 0.005 mmol) in H2O (0.2 ml) was added dropwise to a solution of 1 (5.12 mg,
0.01 mmol) in methanol (3 ml) at room temperature and the color of the solution turned
yellow-green immediately. After stirring for 10 min at room temperature, the mixture was
filtered and the filtrate was allowed to stand at room temperature for two weeks. The solvent
partially evaporated and yellow block-like single crystals suitable for X-ray crystallographic
analysis were obtained. Yield: 3.77 mg, 68.0%. Anal. Calc. for C44H50SrN4O16Zn2 (%): C, 47.64;
H, 4.54; N, 5.05; Zn, 11.79; Sr, 7.90. Found: C, 47.61; H, 4.39; N, 4.96; Zn, 11.62; Sr, 7.78. IR
(KBr, cm-1): 3053 (w), 2976 (m), 2895 (m), 1603 (s), 1543 (m), 1463 (s), 1394 (m), 1309 (s),
1232 (s), 1207 (s), 1085 (s), 1045 (s), 895 (m), 732 (s), 669 (m), 615 (m), 516 (m), 459 (w).
4

UV-Visible (EtOH, λmax (nm)/εmax (L mol-1 cm-1)): 232/5.24 × 104 (π→π*), 280/2.92 × 104
(π→π*), 364/1.09 × 104 (π→π*). Fluorescence (EtOH, λex (λem) (nm)): 360 (500 (π*→π)).
2.2.4. Synthesis of bis{μ-6,6'-diethoxy-2,2'-[1,2-ethylenedioxybis(nitrilomethylidyne)]-
diphenolato}bis[µ-acetatozinc(II)]barium(II) (3). A solution of Ba(II) acetate (1.28 mg,
0.005 mmol) in H2O (0.2 ml) was added dropwise to a solution of 1 (5.12 mg, 0.01 mmol) in
methanol (3 ml) at room temperature and the color of the solution turned yellow-green
immediately. After stirring for 10 min at room temperature, the mixture was filtered and the
filtrate was allowed to stand at room temperature for two weeks. The solvent partially evaporated
and yellow block-like single crystals suitable for X-ray crystallographic analysis were obtained.
Yield: 3.80 mg, 65.7%. Anal. Calc. for C44H50BaN4O16Zn2 (%): C, 45.68; H, 4.18; N, 4.84; Zn,
11.30; Ba, 11.87. Found: C, 45.61; H, 4.21; N, 4.86; Zn, 11.26; Ba, 11.92. IR (KBr, cm-1):
3051 (w), 2980 (m), 2899 (m), 1604 (s), 1543 (m), 1463 (s), 1404 (m), 1229 (m), 1090 (s),
897 (m), 732 (s), 655 (w), 617 (m), 509 (m), 459 (w). UV-Visible (EtOH, λmax (nm)/εmax (L mol-1
cm-1)): 236/1.151 × 105 (π→π*), 280/6.09 × 104 (π→π*), 364/2.54 × 104 (π→π*). Fluorescence
(EtOH, λex (λem) (nm)): 360 (471 (π*→π)).
2.3. Methods
C, H and N analyses were obtained using a GmbH VarioEL V3.00 automatic elemental analysis
instrument. Elemental analyses for Zn, Sr and Ba were determined with an IRIS ER/SWP-1 ICP
atomic emission spectrometer. 1H NMR spectra were determined by a German Bruker AVANCE
DRX-400 spectrometer. IR spectra were recorded on a Vertex70 FT-IR spectrophotometer, with
samples prepared as KBr pellets (4000-400 cm-1). UV-Visible absorption and spectroscopic
titration spectra were recorded on a Shimadzu UV-2550 spectrometer. Fluorescence spectra were
recorded on a Perkin-Elmer LS-55 spectrometer. X-ray single crystal structures were determined
on a Bruker Smart 1000 CCD area detector. Melting points were measured by the use of a
microscopic melting point apparatus made in Beijing Taike Instrument Limited Company, and
the thermometer was uncorrected.
5

2.4. X-ray crystal structure determination
Single crystals of 1, 2 and 3 were placed on a Bruker Smart 1000 CCD area detector. The
diffraction data were collected using graphite monochromated MoKα radiation (λ = 0.71073 Å).
Data collection and reduction were performed using SMART and SAINT software [36]. The
2
structures were solved using the direct method and refined by full-matrix least-squares on F
using the SHELXL-97 program package [37]. All non-hydrogen atoms were refined
anistropically and hydrogens were added in calculated positions and refined using a riding model.
For 2 and 3, the SQUEEZE program was used to estimate the solvent accessible voids in the
structure [38]. Crystal data, as well as details of data collection and refinements for 1, 2 and 3,
are summarized in table 1.
3. Results and discussion
3.1. Spectroscopic behaviors and 1H NMR spectra
3.1.1. IR spectra. IR spectra of H2L, 1, 2 and 3 exhibit various bands from 4000-400 cm-1
(figure S2). The free H2L exhibits a characteristic C=N stretch at 1605 cm-1, while the νC=N of 1,
2 and 3 are at 1597, 1603 and 1604 cm-1. The C=N band shifts to lower wavenumber in the IR
spectra of complexes compared to the free ligand, but some Salen-type complexes are opposite
in behavior and the C=N band shifts to higher wavenumber or no obvious shift in the IR spectra
of complexes is observed compared to the free ligand [39, 40]. The Ar–O stretching frequency
occurs at 1256 cm-1 for H2L and at 1242, 1232 and 1229 cm-1 for 1, 2 and 3. These results
confirm the involvements of the oxime nitrogen and phenolic oxygen in the metal–ligand
bonding [41], consistent with the X-ray diffraction results obtained for 1, 2 and 3. The
metal-nitrogen and metal-oxygen coordination bonds are also confirmed by new bands in spectra
of 1, 2 and 3 at ca. 509–516 cm−1 and 459 cm−1, assigned to νM–N and νM–O, respectively [41-43].
In addition, the infrared spectrum of 1 shows absorption bands at ca. 3313 and 3169 cm−1,
assigned to νO–H of the coordinated acetic acid [44].
Since acetate can coordinate to a metal ion bidentate or monodentate, the ‘“Δcriterion”,
which is based on the difference in the νas(COO-) and νs(COO-) values compared to the
6

corresponding value in sodium acetate, is employed to determine the coordination mode of the
acetate [45]. The absorption bands νas(COO-), νs(COO-) of 1, 2 and 3 are 1670, 1456 cm−1, 1543,
1463 cm−1 and 1543, 1463 cm−1, respectively. The data of Δν suggest that the acetic acid in 1 is
monodentate and the acetate groups in 2 and 3 are bidentate [46].
3.1.2. UV-Visible absorption spectra. The UV-Visible absorption spectra of H2L and its
corresponding complexes were determined in 1.0 × 10-5 mol L-1 ethanol solution (figure 1). The
absorption peaks of 1, 2 and 3 are obviously different from that of the ligand upon complexation.
The electronic absorption spectrum of H2L consists of three relatively intense bands centered at
223, 271 and 319 nm, assigned to the π–π* transitions of the benzene ring and the C=N bonds,
respectively [47]. The intraligand π–π* transition of the benzene ring of salicylaldehyde is
slightly shifted by 9 nm to longer wavelength in 1, 2 and 3. The peak of H2L at 319 nm is absent
for 1, 2 and 3. However, new absorptions are observed at 363, 364 and 364 nm, respectively,
assigned to the n-π* charge transfer transition from the lone pair electron of N atom of C=N
group to the benzene rings [48, 49].
3.1.3. UV-Visible spectroscopic titration. Addition of a 1.0 × 10−4 mol L−3 solution of Zn(II)
acetate to a 1.0 × 10−4 mol L−3 solution of H2L shows the appearance of a new band (363 nm) in
the UV-Visible spectrum (figure 2). The UV-Visible spectroscopic titration of H2L and Zn(II)
acetate clearly indicates the exclusive formation of a 1:1 mononuclear complex. The structure of
1 is different from previously reported analogous Salamo-type complexes [30], which are
analogous with the parent H2salen ligand that gives a monomeric five-coordinate Zn(II) complex
[Zn(salen)X] (X = H2O [48], py [50]).
3.1.4. Fluorescence properties. The fluorescent properties of H2L and its corresponding
complexes were investigated at room temperature (figure 3). The ligand exhibits an intense
emission peak at 409 nm upon excitation at 350 nm, which should be assigned to the intraligand
π–π* transition [51]. 1, 2 and 3 show intense broad photoluminescence with maximum emission
at ca. 477, 500 and 471 nm upon excitation at 360 nm, respectively, red-shifted to that of H2L.
2 is red-shifted compared to 1 and 3, displaying enhanced emission intensities compared to 1,
7

although it is slightly blue-shifted to that of 1. The emission peaks in the spectra of 1, 2 and 3
may arise from the intraligand transition. No emission originating from metal-centered or
metal-to-ligand/ligand-to-metal charge-transfer excited states are expected for the Zn(II)
complex, since Zn(II) is d10 [52, 53]. Thus, the emissions observed in 1, 2 and 3 are tentatively
assigned to the (π–π*) intraligand fluorescence.
3.1.5. 1H NMR spectra. 1H NMR spectra of H2L in CDCl3, 1 and CH3COOH in CD3SOCD3
were determined (figure S1). 1H NMR spectrum of H2L contains a signal for ArOH protons at δ
9.68 ppm. 1H NMR data of 1 contains a new signal for OH at δ 9.30 ppm and a signal for CH3
protons at δ 1.98 ppm compared with free H2L, indicating the structure of 1 exists with one
acetic acid molecule. The OH proton of the coordinated acetic acid molecule for 1 shifts to
9.30 ppm compared with free acetic acid molecule (11.95 ppm) because it forms an
intramolecular hydrogen bond. This fact agrees with the result determined by IR and X-ray
diffraction.
3.2. X-ray crystal structures
The crystal data and experimental details are given in table 1. Selected bond lengths and angles
(table 2, S1 and S2) of 1, 2 and 3 are summarized.
X-ray crystallographic analysis reveals that 1 crystallizes in the monoclinic system, space
group P21/n; the assembly of one Zn(II) ion, one deprotonated L2- unit and one acetic acid
molecule results in 1. The structure of 1 is shown in figure 4. Zn(II) is five-coordinate and the
value of τ = 0.495, indicating that the coordination environment of the Zn(II) is neither limiting
geometry, but truly between square pyramidal and trigonal bipyramidal [54]. The L2- is
N2O2-tetradentate forming two six- and one seven-membered chelate ring around Zn(II) ion. N1,
N2 and O5 of L2- and O8 of acetic acid lie in an equatorial plane in which the axial site is
occupied by O2. The acetic acid molecule forms one intramolecular hydrogen bond O7-H7···O6
(table 3) to stabilize the crystal structure. The distances between Zn(II) and oxime nitrogens
(N1 and N2) are 2.163(6) and 2.230(6) Å, and phenolic O2 and O5 are 1.958(4) and 1.982(4) Å,
respectively. The Zn1-O8 distance is 2.020(5) Å, longer than the lengths between Zn(II) and
8

phenolic oxygens. The dihedral angle between the coordination plane of N1-Zn1-O2 and
N2-Zn1-O5 is 63.88(3)°, which is larger than that of the reported Zn(II) complex
[Zn3(3-MeOsalamo)2(OAc)2] [22].
X-ray crystallographic analysis of the Zn(II)-Sr(II) complex 2 reveals formation of a
hetero-trinuclear structure, which is composed of two Zn(II) ions, two deprotonated L2-, two
μ-acetato ions and one Sr(II) as expected (figure 5). The Zn(II) ions are located in the N2O2 sites
of each L2- to form a [ZnL(OAc)]- unit. The Zn(II) ions are five coordinate with a geometry
between square pyramidal and trigonal bipyramidal, in which the values of τ of Zn1 and Zn2 are
0.501 and 0.503, respectively [54]. The two [ZnL(OAc)]- units are semicircular pentadentate O5
chelating ligands and coordinate to Sr(II) forming a ten-coordinate Sr(II) which is bridged by
four phenolic oxygens and two μ-acetato ligands. A pair of μ-acetato ligands bridging Zn1···Sr1
and Zn2···Sr1 neutralize the charge of 2 and stabilize the trinuclear structure. The two μ-acetato
ions are in the same side. The Sr-O bond lengths are 2.590(3)-2.931(3) Å. The longest is the
Sr-O (ethoxy) and the shortest is the Sr-O (μ-acetato). The Zn-O(N) distances are
1.959(3)-2.150(3) Å (table 2).
The crystal structure of Zn(II)-Ba(II) complex 3 is similar with that of 2 and consists of
two Zn(II) ions, two deprotonated L2- units, two μ-acetato ligands and one Ba(II) (figure 6). The
Zn(II) ions are located in the N2O2 sites of each L2- group to form [ZnL(OAc)]- units. The Zn(II)
ions are five-coordinate with a geometry between square pyramidal and trigonal bipyramidal, in
which the values of τ of Zn1 and Zn2 are 0.574 and 0.518, respectively [54]. The two
[ZnL(OAc)]- units are semicircular pentadentate O5 chelating ligands coordinated to Ba(II)
forming a ten-coordinate Ba(II) center bridged by four phenolic oxygens and two μ-acetato
ligands. A pair of μ-acetato ligands bridging Zn1···Ba1 and Zn2···Ba1 neutralize the charge of 3
and stabilize the trinuclear structure. The Ba-O bond lengths are 2.705(4)-3.004(4) Å; the longest
is Ba-O (ethoxy) and the shortest is Ba-O (μ-acetato). The Zn-O(N) distances are
1.961(4)-2.216(5) Å (table 2). The dihedral angle between the coordination plane of N1-Zn1-O2
9

or N3-Zn2-O13 and that of N2-Zn1-O5 or N4-Zn2-O10 is 49.66(4)° or 50.78(4)°, respectively,
smaller than in 1.
4. Conclusion
Three new complexes (1, 2 and 3) have been synthesized and structurally characterized. The
X-ray crystallographic analysis and UV-Visible spectroscopic titration of 1 indicated a
mononuclear structure, assembled from one Zn(II) ion, one deprotonated L2- unit and one acetic
acid molecule. Two complex 1 molecules are bonded to one Sr(II) or Ba(II) ion, forming
hetero-trinuclear Zn(II)-M(II) (M = Sr (2), Ba (3)) complexes. Zn(II) of 2 and 3 are
five-coordinate and the Sr(II) or Ba(II) ion is ten-coordinate. The Zn(II) and M(II) (M = Sr (2),
Ba (3)) ions are bridged by four phenolic oxygens and two μ-acetato ligands. Furthermore, 1, 2
and 3 exhibit blue emission with the maximum emission wavelengths λmax = 477, 500 and 471
nm.
Further investigations on the syntheses and structures of 1 with other metal ions such as
rare earth ions are now in progress.
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 the depository number CCDC Nos. 1061492, 1463115 and
1061491 for 1, 2 and 3, respectively.
Funding
This work was supported by the National Natural Science Foundation of China (21361015),
which is gratefully acknowledged.
10

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13

1.2
236
H2L
Complex 1
Complex 2
Complex 3
1.0 223
232
0.8
0.6
0.4
0.2
0.0
271
280
280
232
280
363
364
364
319
250
300
350
400
450
500
Wavelength (nm)
Figure 1. UV-Visible absorption spectra of H2L, 1, 2 and 3 in ethanol (1×10−5 mol L-1).
14

Figure 2. UV-Visible spectral changes of H2L upon addition of Zn(II) acetate dihydrate (EtOH,
H2L = 1.0 × 10-4 mol L-3, 0 ≤ [Zn2+]/[H2L] ≤ 2.5). The inset shows the plot of absorbance at
364 nm against the molar ratio of [Zn2+]/[H2L].
15

471
477
H2L
800
600
400
200
0
Complex 1
Complex 2
Complex 3
409
500
400
500
600
Wavelength (nm)
Figure 3. Emission spectra of H2L (λex = 350 nm, λem = 409 nm), 1, 2 and 3 (λex = 360 nm, λem
=
477, 500 and 471 nm, respectively) in ethanol (1 × 10−5 mol L-1).
16

Figure 4. Molecular structure of 1. Thermal ellipsoids are plotted at 30% probability level
(hydrogens, except H7, are omitted for clarity).
17

Figure 5. Molecular structure of 2. Thermal ellipsoids are plotted at 30% probability level
(hydrogens are omitted for clarity).
18

Figure 6. Molecular structure of 3. Thermal ellipsoids are plotted at 30% probability level
(hydrogens are omitted for clarity).
19

Table 1. Crystal data and structure refinements for 1-3.
Compound code
1
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions (Å, °)
a
C22H26N2O8Zn
511.82
C44H50SrN4O16Zn2
1109.24
C44H50BaN4O16Zn2
1156.94
293(2)
293(2)
293(2)
0.71073
Monoclinic
P21/n
0.71073
0.71073
Monoclinic
I2/c
Monoclinic
I2/c
11.0915(15)
11.2381(12)
18.667(2)
103.745(14)
2260.2(5)
4
18.0614(6)
13.6892(4)
39.5607(17)
94.080(3)
9756.4(6)
8
18.1992(5)
13.6518(5)
40.1126(14)
95.789(3)
9915.2(6)
8
b
c
β
Volume (Å3)
Z
Dc (Mg/m3)
1.504
1.510
1.550
μ (mm-1)
1.138
2.136
1.816
F (000)
1064
4544
4672
Crystal size (mm)
θ Range (°)
Index ranges
0.04 × 0.05 × 0.09
3.5 to 26.0
-13 ≤ h ≤ 13,
-13 ≤ k ≤ 13,
-23 ≤ l ≤ 23
9291
0.25 × 0.27 × 0.31
3.7 to 26.0
-18 ≤ h ≤ 22,
-16 ≤ k ≤ 16,
-38 ≤ l ≤ 48
18762
0.14 × 0.24 × 0.29
3.5 to 25.0
-21 ≤ h ≤ 21,
-15 ≤ k ≤ 16,
-37 ≤ l ≤ 47
21961
Reflections collected
Independent reflections
Rint
9291
9542
8621
0.000
0.044
0.054
Completeness to θ
Data / restraints / parameters
GOF
99.5 % (θ = 26.015)
9291 / 1 / 306
0.944
99.2 % (θ = 26.021)
9542 / 0 / 610
0.963
98.1 % (θ = 25.049)
8621 / 0 / 610
1.038
R1, wR2[I>2σ(I)]
R1, wR2 (all data)
∆ρmin
0.0738, 0.0853
0.2325, 0.0983
-0.54 and 0.88
0.0471, 0.0882
0.0838, 0.0997
-0.46 and 0.58
0.0511, 0.1222
0.0750, 0.1414
-0.98 and 1.23
,
min (eÅ-3)
20

Table 2. Selected bond distances (Å) and angles (°) for 1-3.
1
2
3
Zn1-N1
Zn1-N2
Zn1-O2
Zn1-O5
2.163(6)
2.230(6)
1.958(4)
1.982(4)
2.020(5)
106.59(19)
112.8(2)
94.97(19)
114.7(2)
79.1(2)
Sr1-O1
Sr1-O2
Sr1-O5
Sr1-O6
Sr1-O7
Sr1-O8
Sr1-O11
Sr1-O12
Sr1-O14
Sr1-O15
Zn1-N1
Zn1-N2
Zn2-N3
Zn2-N4
Zn1-O2
Zn1-O5
2.931(3)
2.660(2)
2.617(2)
2.852(3)
2.852(3)
2.636(2)
2.595(2)
2.799(2)
2.656(3)
2.590(3)
2.150(3)
2.080(3)
2.174(3)
2.059(3)
1.973(2)
2.047(3)
1.983(2)
2.039(2)
1.959(3)
1.969(3)
84.71(10)
87.53(11)
133.36(13)
163.41(12)
86.24(12)
84.15(10)
109.52(12)
115.33(11)
98.38(11)
98.19(12)
111.24(14)
88.49(14)
94.93(12)
91.69(13)
164.65(12)
86.27(11)
115.97(12)
100.10(11)
86.48(11)
99.66(9)
99.83(9)
99.60(10)
99.01(10)
Ba1-O1
Ba1-O2
Ba1-O5
Ba1-O6
Ba1-O8
Ba1-O9
Ba1-O10
Ba1-O13
Ba1-O14
Ba1-O16
Zn1-N1
Zn1-N2
Zn2-N3
Zn2-N4
Zn1-O5
Zn1-O7
2.908(4)
2.789(4)
2.742(4)
2.893(4)
2.771(4)
2.939(4)
2.787(4)
2.811(3)
3.004(4)
2.705(4)
2.216(5)
2.072(5)
2.164(4)
2.095(5)
2.052(3)
1.968(4)
Zn1-O8
O2-Zn1-O5
O2-Zn1-O8
O5-Zn1-O8
O2-Zn1-N2
O5-Zn1-N2
O2-Zn1-N1
O5-Zn1-N1
O8-Zn1-N2
O8-Zn1-N1
N1-Zn1-N2
85.4(2)
161.5(2)
131.8(2)
93.2(2)
83.0(2)
Zn2-O8
Zn2-O11
Zn2-O13
Zn1-O16
Zn2-O10
Zn2-O13
Zn2-O15
2.046(4)
1.986(4)
1.961(4)
O2-Zn1-N2
O2-Zn1-O5
O2-Zn1-N1
O5-Zn1-N2
O5-Zn1-N1
O7-Zn1-N1
O7-Zn1-O2
O7-Zn1-N2
O7-Zn1-O5
O13-Zn2-O10
O13-Zn2-N4
O10-Zn2-N4
O15-Zn2-O10
O15-Zn2-N3
O15-Zn2-O13
O15-Zn2-N4
O13-Zn2-N3
N2-Zn1-N1
N4-Zn2-N3
O10-Zn2-N3
Zn1-O2-Ba1
Zn2-O8-Ba1
Zn1-O5-Ba1
Zn2-O11-Ba1
131.38(16)
86.16(15)
85.62(17)
85.11(17)
165.81(16)
93.85(17)
117.92(17)
110.71(19)
100.22(16)
86.85(16)
131.47(19)
85.02(19)
98.66(17)
98.75(17)
116.15(17)
112.4(2)
86.64(16)
91.68(19)
87.20(19)
162.54(18)
99.58(15)
99.75(14)
99.34(15)
98.67(16)
O2-Zn1-O5
O2-Zn1-N1
O2-Zn1-N2
O5-Zn1-N1
O5-Zn1-N2
O8-Zn2-O11
O13-Zn2-N4
O16-Zn1-O2
O16-Zn1-O5
O16-Zn1-N1
O16-Zn1-N2
N2-Zn1-N1
O13-Zn2-N3
N4-Zn2-N3
O11-Zn2-N3
O11-Zn2-N4
O13-Zn2-O8
O13-Zn2-O11
O8-Zn2-N3
Zn2-O11-Sr1
Zn2-O8-Sr1
Zn1-O2-Sr1
Zn1-O5-Sr1
21

Table 3. Hydrogen bonding distances (Å) and angles (°) for 1.
D-H···A
d(D-H)
d(H···A)
2.51
d(D..A)
3.319(8)
∠D-H···A
O7-H7···O6 0.826
168
22

Graphical abstract
23