Zinc halide template effects on the construction of [1 + 1] flexible Schiff-base macrocyclic complexes having pendant-armed dialdehyde components

Article abstract of DOI:10.1039/c4dt00605d

Two novel pendant-armed dialdehydes (1a and 1b) were prepared by a one-step reaction between 5-chloro-3-(chloromethyl)-2-hydroxybenzaldehyde/5-methyl-3- (chloromethyl)-2-hydroxybenzaldehyde and cyclohexylamine involving two nucleophilic substitutions, and they were used to react with 1,3-propanediamine to prepare Schiff-base macrocyclic complexes in the presence of ZnX₂ salts (X = Cl, Br, and I). As a result, five dinuclear (2a, 2b, 3b, 4a, and 4b) and one mononuclear (3a) [1 + 1] flexible macrocyclic Zn(ii) complexes have been structurally and spectrally characterized. The zinc centers in three pairs of macrocyclic complexes have the common four-coordinate tetrahedral geometry with one or two coordinated halide ions, where the template Zn(ii) cations and the auxiliary halide anions with different sizes and coordination abilities are believed to play important roles in forming the resulting macrocyclic complexes. In addition, subtle alterations of electron-withdrawing and electron-donating substituted groups (Cl versus CH₃) in the macrocyclic backbone result in different ¹H NMR and UV-vis spectra. the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt00605d

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Zinc halide template effects on the construction of
[1 + 1] flexible Schiff-base macrocyclic complexes
having pendant-armed dialdehyde components†
Cite this: Dalton Trans., 2014, 43,
8486
Hui-Qing Chen, Kun Zhang, Chao Jin and Wei Huang*
Two novel pendant-armed dialdehydes (1a and 1b) were prepared by a one-step reaction between
5-chloro-3-(chloromethyl)-2-hydroxybenzaldehyde/5-methyl-3-(chloromethyl)-2-hydroxybenzaldehyde
and cyclohexylamine involving two nucleophilic substitutions, and they were used to react with 1,3-pro-
panediamine to prepare Schiff-base macrocyclic complexes in the presence of ZnX2 salts (X = Cl, Br, and
I). As a result, five dinuclear (2a, 2b, 3b, 4a, and 4b) and one mononuclear (3a) [1 + 1] flexible macrocyclic
Zn(II) complexes have been structurally and spectrally characterized. The zinc centers in three pairs
of macrocyclic complexes have the common four-coordinate tetrahedral geometry with one or two
coordinated halide ions, where the template Zn(II) cations and the auxiliary halide anions with different
sizes and coordination abilities are believed to play important roles in forming the resulting macrocyclic
complexes. In addition, subtle alterations of electron-withdrawing and electron-donating substituted
groups (Cl versus CH3) in the macrocyclic backbone result in different 1H NMR and UV-vis spectra.
Received 27th February 2014,
Accepted 27th March 2014
DOI: 10.1039/c4dt00605d
www.rsc.org/dalton
introduced into the amine components to construct corres-
ponding macrocyclic ligands.9 In contrast, the expansion of
Introduction
There has been growing interest in Robson-type Schiff bases dialdehyde components with functional pendant arms is
since they were first developed in the 1970s.1 Studies on the much more challenging and has been less studied up to
approaches for forming this type of Schiff-base macrocyclic now.10 Our motivation is to design and prepare novel flexible
complexes have been performed by many groups and large Schiff-base macrocyclic ligands bearing extended pendant-
numbers of such complexes have been synthesized and charac- armed dialdehyde components, and to use them to build up
terized during the last four decades and they were found to macrocyclic complexes in the presence of certain templates.
exhibit particular magnetic,2 catalytic,3 biological,4 and non- We report herein the syntheses and structural characterization
linear optical properties,5 and so on. Commonly, there are of a series of flexible [1 + 1] Schiff-base macrocyclic Zn(II) com-
two approaches to form this type of macrocyclic Schiff-base plexes bearing two extended dialdehyde components derived
metal complexes, namely, metal-free and metal-ion templated from 5-chloro-3-(chloromethyl)-2-hydroxybenzaldehyde and
methods of which the latter one has been proved to be more 5-methyl-3-(chloromethyl)-2-hydroxybenzaldehyde, where ZnX2
effective.6 In our previous work, quite a number of Robson- salts (X = Cl, Br, and I) were used to produce five dinuclear
type macrocyclic ligands and their metal complexes have been (2a, 2b, 3b, 4a, and 4b) and one mononuclear (3a) four-
prepared through template synthetic approaches.7
coordinate Zn(II) complexes countered by Cl−, Br−, and
The introduction of functional pendant arms into the I− anions (Scheme 1). Both the template Zn(II) cation and the
macrocyclic ligands is a useful method to extend the appli- auxiliary halide anion with different sizes and coordination
cations of macrocyclic complexes.8 Pendant arms are often abilities are believed to play important roles in forming the
resulting macrocyclic complexes.
State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of
Microstructures, School of Chemistry and Chemical Engineering, Nanjing University,
Nanjing 210093, P. R. China. E-mail: whuang@nju.edu.cn; Fax: +86-25-83314502;
Experimental
Materials and measurements
Tel: +86-25-83686526
†Electronic supplementary information (ESI) available: FT-IR spectra of all eight
compounds and powder X-ray diffraction patterns of six macrocyclic Zn(II) com-
The reagents of analytical grade were purchased from
commercial sources and used without any further purifi-
plexes. CCDC 988803–988809 for seven compounds. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c4dt00605d
8486 | Dalton Trans., 2014, 43, 8486–8492
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using ethylacetate–petroleum ether (v/v = 1 : 8) as the eluent,
and the final product 1a was obtained in a yield of 0.553 g
(51%). Mp: 149–150 °C. Main FT-IR absorptions (KBr pellets):
2968 (m), 2937 (w), 1674 (w), 1471 (m), 1386 (w), 837 (s), 557
1
(m). H NMR (500 MHz, CDCl3): δ = 10.01 (s, 2H), 7.45(d, 2H),
7.30 (d, 2H), 3.82 (s, 4H), 2.67 (t, 1H), 2.01–1.84 (d, 4H),
1.69–1.65 (d, 1H), 1.46–1.42 (d, 2H), 1.27–1.22 (m, 3H). Anal.
calc. for C22H23Cl2NO4: C, 60.56; H, 5.31; N, 3.21%. Found:
C, 60.60; H, 5.59; N, 3.09%. UV-vis in methanol: λmax = 220,
256, and 343 nm.
Dialdehyde 1b. Dialdehyde 1b was synthesized by using the
same method as that of 1a except that 5-methyl-3-(chloro-
methyl)-2-hydroxybenzaldehyde (1.030 g, 5.60 mmol) was
used. Compound 1b was obtained in a yield of 0.521 g (53%).
Mp: 118–120 °C. Main FT-IR absorptions (KBr pellets): 2931
(m), 2875 (w), 1645 (w), 1470 (m), 1384 (w), 838 (s), 559 (m).
1H NMR (500 MHz, CDCl3): δ = 10.06 (s, 2H), 7.28 (d, 2H), 7.16
(d, 2H), 3.81 (s, 4H), 2.69 (t, 1H), 2.26 (s, 6H), 2.02–1.87 (d,
4H), 1.68–1.66 (d, 1H), 1.48–1.46 (d, 2H), 1.27–1.22 (m, 3H).
Anal. calc. for C24H29NO4: C, 72.89; H, 7.39; N, 3.54%. Found:
C, 72.66; H, 7.54; N, 3.62%. UV-vis in methanol: λmax = 218,
261, and 343 nm.
Syntheses of [1 + 1] macrocyclic Zn(II) complexes 2–4
Complex 2a. ZnCl2 (0.028 g, 0.20 mmol) dissolved in aceto-
nitrile (10 cm3) and 1,3-propanediamine (0.008 g, 0.11 mmol)
dissolved in ethanol (10 cm3) were added to a solution of 1a
(0.046 g, 0.10 mmol) in ethanol (20 cm3) at reflux. After 2 h,
the solution was cooled and filtered and the solvent evapor-
ated gradually under room temperature to give product 2a as
yellow crystals in a yield of 0.024 g (70%). Main FT-IR absorp-
tions (KBr pellets): 3442 (m), 2937 (w), 2857 (w), 1637 (s), 1433
Scheme 1 Synthetic route for a pair of extended dialdehydes and six
[1 + 1] flexible macrocyclic Zn(II) complexes.
cation. 5-Chloro-3-(chloromethyl)-2-hydroxybenzaldehyde and
5-methyl-3-(chloromethyl)-2-hydroxybenzaldehyde were pre-
pared via our previously reported method.11 Elemental ana-
lyses (EA) for carbon, hydrogen and nitrogen were performed
using a Perkin-Elmer 1400C analyzer. Infrared (IR) spectra
(4000–400 cm−1) were recorded using a Nicolet FT-IR 170X
spectrophotometer on KBr disks. UV-vis spectra were recorded
with a Shimadzu UV-3150 double-beam spectrophotometer
using a quartz glass cell with a path length of 10 mm.
Powder X-ray diffraction (PXRD) measurements were per-
formed on a Philips X’pert MPD Pro X-ray diffractometer using
Cu Kα radiation (λ = 0.15418 nm), in which the X-ray tube
was operated at 40 kV and 40 mA at room temperature.
1H NMR spectra were obtained using a Bruker 500 MHz NMR
spectrometer.
1
(m), 1031 (w), 776 (w). H NMR (500 MHz, DMSO-d6): δ = 8.05
(s, 2H), 7.02 (d, 4H), 4.54 (t, 2H), 4.10 (t, 2H), 3.95 (d, 2H),
3.61 (d, 2H), 2.74 (m, 1H), 2.23 (m, 2H), 2.07 (m, 2H), 1.88
(m, 2H), 1.77–1.64 (m, 2H), 1.39–1.24 (m, 6H). Anal. calc.
for C25H29Cl4N3O3Zn2: C, 43.38; H, 4.22; N, 6.07%; found:
C, 43.12; H, 4.45; N, 5.99%. UV-vis in methanol: λmax = 225
and 358 nm.
Complexes 3a and 4a were prepared by a similar method to
that of 2a by using ZnBr2 (0.046 g, 0.21 mmol) and ZnI2
(0.066 g, 0.21 mmol), respectively. 3a: Yield, 0.025 g (68%).
Main FT-IR absorptions (KBr pellets): 3526 (m), 2939 (w), 2859
(w), 1634 (s), 1551 (s), 1460 (s), 1220 (w), 1128 (w), 784 (w).
1H NMR (500 MHz, DMSO-d6): δ = 8.37 (s, 1H), 8.07 (s, 1H),
7.07 (s, 2H), 7.02 (s, 2H), 4.62 (t, 2H), 4.16 (t, 2H), 3.97 (d, 2H),
Synthesis of pendant-armed dialdehydes 1a and 1b
Dialdehyde 1a. An acetone solution (20 cm3) of 5-chloro- 3.65 (d, 2H), 2.74 (m, 1H), 2.24 (m, 2H), 1.88–1.24 (m, 10H).
3-(chloromethyl)-2-hydroxybenzaldehyde (1.154 g, 5.62 mmol) Anal. calc. for C25H35Br2Cl2N3O4Zn: C, 40.70; H, 4.78; N,
was added dropwise to
a mixture of K2CO3 (7.067 g, 5.70%. Found: C, 40.55; H, 4.80; N, 5.68%. UV-vis in methanol:
51.13 mmol) and 1-cyclohexanamine (0.248 g, 2.50 mmol) dis- λmax = 224 and 360 nm. 4a: Yield, 0.032 g, 72%. Main FT-IR
solved in acetone (40 cm3), and the mixture was stirred for 1 h absorptions (KBr pellets): 3452 (m), 2935 (w), 2370 (w), 1633
at room temperature. The solid was filtered off, washed with (m), 1548 (w), 1452 (w), 1083 (s), 789 (w), 466(m). 1H NMR
acetone, and the solvent of the filtrate was removed using a (500 MHz, DMSO-d6): δ = 8.38 (s, 1H), 8.17 (s, 1H), 7.11 (s, 2H),
rotatory evaporator under reduced pressure. The yellow-green 7.07 (s, 2H), 4.65 (t, 2H), 4.28 (t, 2H), 3.94 (d, 2H), 3.66
solid 1a was purified by silica gel column chromatography (m, 2H), 2.74 (m, 1H), 2.25 (m, 2H), 1.91–1.07 (m, 16H). Anal.
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calc. for C27H33Cl2I2N3O3Zn2: C, 35.91; H, 3.68; N, 4.65%. program package. Details of the data collection and refinement
Found: C, 35.62; H, 3.39; N, 4.56%. UV-vis in methanol: λmax
=
for 1a and complexes 2–4 are given in Table 1, and the selec-
221 and 357 nm.
tive bond lengths and angles of seven compounds are listed in
Complex 2b. ZnCl2 (0.028 g, 0.21 mmol) dissolved in Table 2.
ethanol (10 cm3) was added to a solution of 1b (0.039g,
0.10 mmol) in ethanol (20 cm3). The mixture was refluxed for
10 min, and then 1,3-propanediamine (0.008 g, 0.11 mmol)
dissolved in ethanol (10 cm3) was added. After an additional
Results and discussion
Syntheses and spectral characterizations
2 h of refluxing, the solution was cooled to room temperature
and filtered. The solvent was removed to give the product 2b as
light orange crystals in a yield of 0.024 g (69%). Main FT-IR The two N-modified dialdehydes (1a and 1b) can be prepared
absorptions (KBr pellets): 3452 (m), 2936 (w), 2861 (w), 1631 (s), by a one-step reaction in medium yields between cyclohexyl-
1557 (m), 1467 (m), 1127 (w), 789 (w). 1H NMR (500 MHz, amine and 5-chloro-3-(chloromethyl)-2-hydroxybenzaldehyde
DMSO-d6): δ = 8.00 (s, 2H), 6.80 (s, 2H), 6.77 (s, 2H) , 4.40 (t, 2H), and 5-methyl-3-(chloromethyl)-2-hydroxybenzaldehyde invol-
4.12 (t, 2H), 3.78 (d, 2H), 3.61 (d, 2H), 2.71 (m, 1H), 2.52 (s, 4H), ving two nucleophilic substitutions (Scheme 1). The [1 + 1]
2.24 (m, 5H), 2.04 (s, 6H), 1.87–1.07 (m, 16H). Anal. calc. for Zn(II) Schiff-base complexes 2–4 have been produced by metal-
C30H46Cl2N3O3Zn2: C, 51.59; H, 6.64; N, 6.02%. Found: C, 51.30; ion templated condensation. In the synthesis of metal macro-
H, 6.91; N, 6.41%. UV-vis in methanol: λmax = 221, 239, 266, and cyclic Schiff bases, the Zn(II) ion is found to show good
363 nm.
template effects in comparison with other metal ions and the
Complexes 3b and 4b were prepared in a way similar to that macrocyclic products can be isolated successfully. A pre-orga-
of 2a by using ZnBr2 (0.046 g, 0.21 mmol) and ZnI2 (0.065 g, nized synthetic strategy is used in our reactions, where dialde-
0.21 mmol), respectively. 3b: Yield, 0.028 g (71%). Main FT-IR hydes and metal ions are mixed together at first for 10 min,
absorptions (KBr pellets): 3501 (m), 2933 (w), 2858 (w), 1631 and then 1,3-propanediamine is added for another 2 h of
(s), 1556 (s), 1467 (s), 1220 (w), 1128 (w), 813 (w). 1H NMR refluxing.
(500 MHz, DMSO-d6): δ = 8.04 (s, 1H), 8.02 (s, 1H), 6.84 (s, 1H),
Because of the strong coordination capability of the halide
6.80 (s, 1H), 6.71 (s, 1H), 6.61 (s, 1H), 4.52 (t, 2H), 4.12 (t, 2H), anion with the metal center, one or more coordination sites of
3.76 (d, 2H), 3.61 (d, 2H), 2.75 (m, 1H), 2.25 (m, 4H), 2.07 (s, the Zn(II) ion can be occupied by the halide anions, which will
6H), 1.88–1.24 (m, 10H). Anal. calc. for C27H35Br2N3O3Zn2: C, more or less influence the cationic template effects in the
43.81; H, 4.77; N, 5.68%; Found: C, 43.65; H, 4.98; N, 5.49%. process of constructing macrocyclic complexes. Furthermore,
UV-vis in methanol: λmax = 220, 241, 268, and 365 nm. 4b: large steric hindrance effects of coordinated halide anions
Yield, 0.034 g (78%). Main FT-IR absorptions (KBr pellets): favor to form lower coordination numbers for the metal
2968 (w), 2858 (w), 1631 (w), 1556 (w), 1471 (w), 1035 (w), 838 coordination centers. As a result, six dinuclear or mononuclear
(s), 557 (m). 1H NMR (500 MHz, DMSO-d6): δ = 8.12 (s, 1H), four-coordinate macrocyclic Zn(II) complexes have been
8.08 (s, 1H), 6.91 (s, 1H), 6.86 (s, 1H), 6.74 (s, 1H), 6.63 (s, 1H), obtained in this work. Moreover, [1 + 1] Schiff-base macrocyclic
4.57 (t, 2H), 4.16 (t, 2H), 3.77 (d, 2H), 3.61 (s, 2H), 2.76 (m, Zn(II) complexes are found to be the main products, which
1H), 2.25 (m, 2H), 2.07 (s, 6H), 1.88–1.07 (m, 16H). Anal. calc. may be attributed to the size-matching effect of the Zn(II) ion
for C29H39I2N3O3Zn2: C, 40.40; H, 4.56; N, 4.87%. Found: C, as well as the use of flexible dialdehyde and diamine com-
40.25; H, 4.78; N, 4.62%. UV-vis in methanol: λmax = 219, 267, pounds. Actually, the discrepancy of halide anions for forming
and 365 nm.
different macrocyclic Zn(II) complexes is not obvious in this
case, owing to the fact that similar [1 + 1] Schiff-base macro-
cyclic complexes are obtained. However, in the case of 3a, only
X-ray crystallographic analysis
Single-crystal X-ray diffraction data were measured on a Bruker a mononuclear macrocyclic complex was obtained as the main
SMART CCD diffractometer using graphite monochromatic product, which is different from all the other five dinuclear
Mo Kα radiation (λ = 0.71073). Data collection was performed macrocyclic complexes. We have tried to do exact control
by using the SMART program, and cell refinement and data experiments including the alterations of the molar ratios of
reduction were made using the SAINT program.12 The struc- the Zn(II) ion and the ligands and the reaction solvents,
tures were solved by direct methods and refined on F2 by using in order to produce corresponding [1 + 1] dinuclear Zn(II)
full-matrix least-squares methods with SHELXTL version complexes as the other five ones, but we were unsuccessful.
6.10.13 All non-hydrogen atoms were refined on F2 by the full-
FT-IR spectra are very useful to monitor this type of macro-
matrix least-squares procedure using anisotropic displacement cyclic Schiff-base condensation reactions. In our experiments,
parameters. Hydrogen atoms were inserted into the calculated a medium FT-IR absorption peak at 1676 and 1681 cm−1 in 1a
positions assigned fixed isotropic thermal parameters at 1.2 and 1b (Fig. SI1 and SI2†) can be assigned to the existence of
times the equivalent isotropic U of the atoms to which they aldehyde groups. However, it disappears and a new absorption
are attached (1.5 times for the methyl groups and oxygen peak is observed for six macrocyclic Zn(II) complexes 2–4 in the
atoms) and allowed to ride on their respective parent atoms. range of 1632–1637 cm−1 (Fig. SI3–SI8†), indicating the trans-
All calculations were carried out using the SHELXTL PC formation from the aldehyde groups to the Schiff-base CvN
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Table 2 Selected bond distances and bond angles of 1a and 2–4
Bond distances
Bond angles
1a
Cl1–C4
Cl2–C12
O1–C1
O2–C7
O3–C15
O4–C16
N1–C17
N1–C8
N1–C9
1.741(4)
1.746(4)
1.347(4)
1.205(5)
1.350(4)
1.195(5)
1.483(4)
1.483(4)
1.481(4)
C8–N1–C17
C8–N1–C9
C9–N1–C17
O1–C1–C6
O1–C1–C2
O2–C7–C6
N1–C8–C2
N1–C9–C10
N1–C17–C18
N1–C17–C22
111.8(3)
111.4(3)
113.5(3)
119.4(3)
119.9(3)
124.8(4)
111.7(3)
112.1(3)
114.7(3)
110.8(3)
2a
Zn1–Cl3
Zn1–O1
Zn1–O3
Zn1–N3
Zn2–Cl4
Zn2–O2
Zn2–O3
Zn2–N2
2.217(5)
1.953(6)
2.037(10)
2.007(9)
2.202(5)
1.922(9)
2.241(10)
2.099(14)
Cl3–Zn1–O1
Cl3–Zn1–O3
Cl3–Zn1–N3
O1–Zn1–O3
O1–Zn1–N3
O3–Zn1–N3
Cl4–Zn2–O2
Cl4–Zn2–O3
Cl4–Zn2–N2
O2–Zn2–O3
O2–Zn2–N2
O3–Zn2–N2
112.2(2)
114.7(3)
110.6(3)
109.5(3)
95.3(3)
112.9(4)
115.6(3)
110.9(3)
116.1(4)
108.7(4)
89.9(5)
114.0(4)
3a
Zn1–Br1
Zn1–Br2
Zn1–O2
Zn1–N2
2.358(1)
2.401(1)
1.936(3)
2.022(4)
Br1–Zn1–Br2
Br1–Zn1–O2
Br1–Zn1–N2
Br2–Zn1–O2
Br2–Zn1–N2
O2–Zn1–N2
110.7(0)
111.5(1)
119.1(1)
113.1(1)
107.4(1)
94.1(1)
4a
Zn1–I1
I2–Zn2
Zn1–O1
Zn1–O3
Zn1–N1
Zn2–O2
Zn2–O3
Zn2–N2
2.549(2)
2.533(2)
1.951(7)
1.928(10)
2.024(8)
1.919(8)
1.897(12)
2.037(9)
I1–Zn1–O1
I1–Zn1–O3
I1–Zn1–N1
O1–Zn1–O3
O1–Zn1–N1
O3–Zn1–N1
I2–Zn2–N2
O2–Zn2–O3
O2–Zn2–N2
O3–Zn2–N2
117.5(2)
116.7(3)
109.3(2)
102.8(4)
93.6(3)
114.8(4)
112.1(3)
105.8(4)
94.2(3)
105.9(4)
2b
Zn1–Cl1
Zn1–O1
Zn1–O2
Zn1–N1
2.214(4)
1.955(7)
1.963(7)
2.033(10)
Cl1–Zn1–O1
Cl1–Zn1–O2
Cl1–Zn1–N1
O1–Zn1–O2
O1–Zn1–N1
O2–Zn1–N1
117.8(2)
113.4(3)
112.3(3)
108.0(4)
94.1(3)
109.6(4)
3b·CH3CN
Zn1–Br1
Zn2–Br2
Zn1–O1
Zn1–O3
Zn1–N1
Zn2–O2
Zn2–O3
Zn2–N2
2.374(3)
2.365(3)
1.944(8)
2.030(9)
2.028(12)
1.938(8)
2.106(9)
2.047(11)
Br1–Zn1–O1
Br1–Zn1–O3
Br1–Zn1–N1
O1–Zn1–O3
O1–Zn1–N1
O3–Zn1–N1
Br2–Zn2–O2
Br2–Zn2–O3
Br2–Zn2–N2
O2–Zn2–O3
O2–Zn2–N2
O3–Zn2–N2
114.1(3)
114.9(3)
109.7(3)
108.0(3)
95.9(4)
112.7(4)
114.1(3)
111.9(2)
114.1(3)
110.6(4)
93.7(4)
111.2(4)
4b
Zn1–I1
Zn1–O1
Zn1–O2
Zn1–N1
2.551(1)
1.928(4)
1.937(3)
2.016(6)
I1–Zn1–O1
I1–Zn1–O2
I1–Zn1–N1
O1–Zn1–O2
O1–Zn1–N1
O2–Zn1–N1
120.4(1)
113.0(2)
110.9(2)
106.3(2)
94.6(2)
109.9(2)
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Fig. 1 1H NMR spectra of 2a in DMSO-d6 and 1a in CDCl3.
units after the condensation and the following metal-ion
complexation.
Fig. 2 UV-vis spectra in CH3OH at 1.0 × 10−4 mol L−1 for 1–4.
With regard to the anti-magnetic Zn(II) complexes with a
d10 electronic structure, NMR spectroscopy has been proved to
be a feasible technique to indicate the formation of Schiff-
Description of single-crystal structures
1
base macrocyclic Zn(II) complexes. H NMR spectra have been
The molecular structures of seven compounds 1a and 2–4 with
the atom-numbering scheme are illustrated in Fig. 3 and 4. In
ligand 1a, the two phenolic rings are staggered with the separ-
ation between two phenolic oxygen atoms of 4.985(4) Å. In con-
trast, the distance between two phenolic oxygen atoms is
significantly shortened to 3.186(12) Å in 2a, 3.108(7) Å in 3a,
3.192(10) Å in 4a, 3.093(8) Å in 2b, 3.154(12) Å in 3b, and 3.088(5)
Å in 4b in the three pairs of macrocyclic complexes because
of the affixation of Zn–O coordinative bonds. Furthermore,
strong intramolecular π–π stacking interactions between two
offset phenolic rings are observed with the centroid-to-centroid
separation of 3.489(4) Å in 1a, and it is elongated to 3.503(6) Å
in 2a, 3.575(13) Å in 2b, 3.508(3) Å in 3a, 3.468(3) Å in 3b,
3.467(8) Å in 4a, and 3.597(6) Å in 4b. Additionally, the di-
hedral angle between the two phenol rings in the extended di-
aldehyde 1a is 18.7(3)°, while it changes to 15.4(3)° in 2a,
18.4(3)° in 2b, 14.8(1)° in 3a, 12.7(3)° in 3b, 13.6(4)° in 4a, and
20.2(2)° in 4b.
recorded for both pendant-armed dialdehydes 1a and 1b in
CDCl3 and corresponding [1 + 1] macrocyclic Zn(II) complexes
2–4 in DMSO-d6. In extended dialdehydes, the two ortho aro-
matic protons of the phenolic ring and the aldehyde protons
are found at 7.30, 7.45, 10.01 ppm in 1a and 7.16, 7.28,
10.06 ppm in 1b, respectively, indicative of the discrepancy
of the electron-withdrawing and electron-donating effects of
Cl and CH3 substituted groups. After the Schiff-base conden-
sation, the aldehyde protons disappear and the ortho
protons of the phenolic ring are shifted to around 7.02 ppm.
In addition, new peaks are observed in the range of
8.00–8.07 ppm in 2–4, corresponding to the formation of
Schiff-base units (Fig. 1). In conclusion, by means of the vari-
ations of chemical shifts for certain protons in the 1H NMR
spectra, one can easily distinguish the starting dialdehydes
and the formation of final Zn(II) macrocyclic products as well
as the substituent effects (Cl and CH3) in the macrocyclic
backbone.
All five Zn(II) complexes (2a, 2b, 3b, 4a, and 4b) are
18-membered [1 + 1] macrocyclic dinuclear complexes where
the coordination configuration for each four-coordinate Zn(II)
center is distorted tetrahedra. It is found that each Zn(II) ion is
coordinated by one halide atom, one oxygen atom from the
bridging water/ethanol molecule, one imine nitrogen atom
from the azomethine group, and one phenolic oxygen atom.
In five dinuclear Zn(II) complexes, one oxygen atom from
either a water or an ethanol molecule serves as the μ2 linker
connecting two neighboring Zn(II) ions with the Zn⋯Zn separ-
ations of 3.382(6) Å in 2a, 3.284(7) Å in 2b, 3.326(3) Å in 3b,
3.293(8) Å in 4a, and 3.281(6) Å in 4b. It was noted that the dis-
tance between the two ortho carbon atoms of each phenolic
hydroxyl group has been elongated from 2.451(3) Å in 1a
to 2.545(6) Å in 2a, 2.519(7) Å in 2b, 2.513(3) Å in 3a, 2.517(3) Å
in 3b, 2.517(8) Å in 4a, and 2.525(6) Å in 4b.
UV-vis spectra of 1–4 in CH3OH are shown in Fig. 2 for full
comparison. In comparison with the absorption bands at
343 nm for both extended dialdehydes 1a and 1b, all six
Schiff-base macrocyclic Zn(II) complexes 2–4 exhibit red shifts
to different extents, namely 358 nm in 2a, 360 nm in 3a,
357 nm in 4a, 363 nm in 2b, and 365 nm in 3b and 4b, which
can be attributed to the formation of the azomethine groups.
Besides, the bathochromic shifts of several nanometers from
2a–4a to 2b–4b in their UV-vis spectra indicate the discrepancy
of the electron-withdrawing and electron-donating effects of Cl
and CH3 substituted groups in the macrocyclic skeleton.
Furthermore, as illustrated in Fig. SI9–SI14,† the pure
phase of the three pairs of Zn(II) macrocyclic complexes 2–4
was also confirmed by PXRD patterns which are in good agree-
ment with their single-crystal diffraction simulative data that
will be discussed below.
8490 | Dalton Trans., 2014, 43, 8486–8492
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with 1,3-propanediamine to prepare Schiff-base macrocyclic
complexes in the presence of ZnX2 salts (X = Cl, Br, and I). As a
result, five dinuclear (2a, 2b, 3b, 4a, and 4b) and one mono-
nuclear (3a) [1 + 1] flexible Schiff-base macrocyclic Zn(II) com-
plexes have been obtained and characterized by elemental
analyses, FT-IR spectra, UV-vis and mass spectrometry,
1H NMR spectra, and single-crystal and powder X-ray diffrac-
tion analyses.
The zinc centers in three pairs of macrocyclic complexes
exhibit a low coordination number of 4 with one or two co-
ordinated halide ions adopting the common tetrahedral geo-
metry, where the template Zn(II) cations and the auxiliary
halide anions with different sizes and coordination abilities
are believed to play important roles in forming the resulting
Schiff-base macrocyclic complexes. In addition, subtle altera-
tions of the electron-withdrawing and electron-donating sub-
stituted groups (Cl versus CH3) in the macrocyclic backbone
result in different 1H NMR and UV-vis spectra.
Acknowledgements
This work was financially supported by the Major State Basic
Research Development Programs (no. 2013CB922101 and
2011CB933300), the National Natural Science Foundation of
China (no. 21171088), and the Natural Science Foundation of
Jiangsu Province (grant BK20130054).
Fig. 3 ORTEP diagrams (30% thermal probability ellipsoids, all H atoms
and uncoordinated solvent molecules are omitted for clarity) of the
molecular structures of 1a–4a.
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