Ligand-directed construction of Zn(II) complexes from zero-dimensional metallomacrocycle to one-, two-, and three-dimensional coordination polymers based on N-donor and β-diketone bifunctional ligands

Article abstract of DOI:10.1021/cg200850r

Six new complexes [Zn₂(L₁)₄]?2H ₂O?DMF (1), [Zn₂(L₂)₄] ₃?13H₂O (2), [Zn_1.5(L₃) ₃]₂ (3), Zn(L₄)₂?2H ₂O (4), Zn(L₅)₂?2CHCl₃ (5), and [Zn(L₆)₂]₂ (6) (where HL₁ = 1-(4-(1H-imidazol-1-yl)phenyl)butane-1,3-dione, HL₂ = 1-(4-(1H-benzimidazol-1-yl)phenyl)butane-1,3-dione, HL₃ = 1-(4-(1H-pyrazol-1-yl)phenyl)butane-1,3-dione, HL₄ = 1-(3-(1H-imidazol-1-yl)phenyl)butane-1,3-dione, HL₅ = 1-(3-(1H-benzimidazol-1-yl)phenyl)butane-1,3-dione and HL₆ = 1-(3-(1H-pyrazol-1-yl)phenyl)butane-1,3-dione) have been synthesized by the reaction of the bifunctional ligands and Zn(II) salts under similar experimental conditions. Structural analyses show that the ligands act as a tridentate and bind to two Zn(II) ions as a two-connected linker, generating a variety of geometries from discrete binuclear [2 + 2] metallomacrocycles (3 and 6) to a one-dimensional looped-chain coordination polymer (4) and two-dimensional (4,4) network (5) as well as three-dimensional frameworks with lvt (1) and NbO (2) topologies. The results demonstrate that the diverse structures are strongly dependent on the ligand geometries, due to the free rotation via the C-N/C-C bonds as well as the various coordinated sites of N-donor allowing the semirigidity ligands to take on appropriate conformations.

Full text of DOI:10.1021/cg200850r

Article
pubs.acs.org/crystal
Ligand-Directed Construction of Zn(II) Complexes from Zero-
Dimensional Metallomacrocycle to One-, Two-, and Three-
Dimensional Coordination Polymers Based on N-Donor and β-
Diketone Bifunctional Ligands
Ping Yang,† Jin-Ji Wu,† Hai-Yun Zhou,‡ and Bao-Hui Ye*,†
†MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen
University, Guangzhou, 510275, China
‡Instrumental Analysis and Research Center, Sun Yat-Sen University, Guangzhou 510275, China
S
* Supporting Information
ABSTRACT: Six new complexes [Zn2(L1)4]·2H2O·DMF (1),
[Zn2(L2)4]3·13H2O (2), [Zn1.5(L3)3]2 (3), Zn(L4)2·2H2O (4),
Zn(L5)2·2CHCl3 (5), and [Zn(L6)2]2 (6) (where HL1 = 1-(4-
(1H-imidazol-1-yl)phenyl)butane-1,3-dione, HL2 = 1-(4-(1H-
benzimidazol-1-yl)phenyl)butane-1,3-dione, HL3 = 1-(4-(1H-
pyrazol-1-yl)phenyl)butane-1,3-dione, HL4 = 1-(3-(1H-imida-
zol-1-yl)phenyl)butane-1,3-dione, HL5 = 1-(3-(1H-benzimida-
zol-1-yl)phenyl)butane-1,3-dione and HL6 = 1-(3-(1H-pyr-
azol-1-yl)phenyl)butane-1,3-dione) have been synthesized by
the reaction of the bifunctional ligands and Zn(II) salts under
similar experimental conditions. Structural analyses show that
the ligands act as a tridentate and bind to two Zn(II) ions as a two-connected linker, generating a variety of geometries from
discrete binuclear [2 + 2] metallomacrocycles (3 and 6) to a one-dimensional looped-chain coordination polymer (4) and two-
dimensional (4,4) network (5) as well as three-dimensional frameworks with lvt (1) and NbO (2) topologies. The results
demonstrate that the diverse structures are strongly dependent on the ligand geometries, due to the free rotation via the C−N/
C−C bonds as well as the various coordinated sites of N-donor allowing the semirigidity ligands to take on appropriate
conformations.
(1) the rotatable single C−N/C−C bond can be readily
modulated in a suitable angle and geometry for the
construction of diverse structures, (2) the rigid rod-like nature
is potentially attractive for having porous structures, (3) the
chelating nature of β-diketone ensures relatively high stability,
and (4) the negative charge on the ligand allows access to
neutral frameworks without anions in the pores.10 It needs to
be noted that the relative linear or symmetric bifunctional
ligands with N-donor and β-diketone chelate have been well
documented,11−14 in which the octahedral coordinate geo-
metries can be reduced as square-planar 4-connecting nodes
and assemble into the two-dimensional (2D) (4,4) or the three-
dimensional (3D) NbO net. However, the observation of
asymmetric bifunctional ligands containing a N-donor and β-
diketone is still rare.10,15 With these considerations in mind, we
have designed and synthesized six bifunctional ligands on the
basis of N-donor and β-diketone, namely, 1-(4-(1H-imidazol-1-
yl)phenyl)butane-1,3-dione (HL1), 1-(4-(1H-benzimidazol-1-
yl)phenyl)butane-1,3-dione (HL2), 1-(4-(1H-pyrazol-1-yl)-
INTRODUCTION
■
Design and assembly of metal−organic materials with definite
structures such as discrete metallomacrocycles and multidimen-
sional coordination polymers have grown rapidly in recent
decades due to their potential applications in magnetism,1
catalysis,2 adsorption,3 and luminescence,4 as well as their
intriguing architectures and topologies.5 However, how to
rationally control desired structures with specific properties still
remains a great challenge.6 In order to achieve the desirable
structures and properties, many efforts have been made using
different strategies. With respect to synthesis, the coordination
preference of metal ion as well as the shape and bonding mode
of the ligand are generally the primary considerations in self-
assembly reactions.7 Among them, most of the attention has
been paid to the multifunctional ligands, in which each ligand
possesses two or more coordination sites with different donor
ability and can be assembled around metal ions in various
arrangements with novel structural features.8,9 This also
provides a strategy for the design and synthesis of multifunc-
tional materials.
With respect to the above, three exotopic bifunctional ligands
with N-donor (imidazole/benzimidazole/pyrazole) and β-
diketone chelating donors at the terminals are selected. Because
Received: July 6, 2011
Revised: November 29, 2011
Published: December 1, 2011
© 2011 American Chemical Society
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Article
Scheme 1. Molecular Conformations of the Asymmetric Bifunctional Ligands
General Procedure for the Syntheses of Ligands. To a stirred
solution of potassium tert-butoxide (2.24 g, 20 mmol) and the
substituted acetophenone (10 mmol) in 10 mL of anhydrous
tetrahydrofuran, 2 mL of ethyl acetate was slowly dropped under N2
at 0 °C. After that, the reaction mixture was stirred at room
temperature for 2 h. During this course, the appearance of white solid
was changed to yellow in a few minutes, indicating that the reaction
went smoothly. The yellow precipitates were collected by filtration and
washed with ethyl ether. The yellow precipitates were dissolved in
water and slowly neutralized by 1 M HCl (pH = 6−7). The resulting
solid was collected by filtration and purified on a silica gel column
chromatography using ethyl acetate/petroleum ether (1:1) as eluent.
1-(4-(1H-Imidazol-1-yl)phenyl)butane-1,3-dione (HL1). Yield
79%. MS m/z = 229 (M + 1). Anal. Calcd. for C13H12N2O2: C,
phenyl)butane-1,3-dione (HL3), 1-(3-(1H-imidazol-1-yl)-
phenyl)butane-1,3-dione (HL4), 1-(3-(1H-benzimidazol-1-yl)-
phenyl)butane-1,3-dione (HL5), and 1-(3-(1H-pyrazol-1-yl)-
phenyl)butane-1,3-dione (HL6) (see Scheme 1). Each ligand
may act as a tridentate ligand and bind two separate metal ions.
The vector angles between the N-donor lone pair and the β-
diketone chelate varies from 12° to 168° depending on syn and
anti conformations, and the dihedral angles between the N-ring
and the β-diketone chelating coordination plane, which tune
the final assembly into diverse structures. This is indeed the
case. Six Zn complexes with these ligands, namely,
[Zn2(L1)4]·2H2O·DMF (1), [Zn2(L2)4]3·13H2O (2),
[Zn1.5(L3)3]2 (3), Zn(L4)2·2H2O (4), Zn(L5)2·2CHCl3 (5),
and [Zn(L6)2]2 (6), have been synthesized to examine the
ligand-directed assembly for the structural diversity and to
understand the resulting coordination networks manipulation
via varying the conformation of the ligand. Structural analyses
exhibit that a variety of geometries from zero-dimensional (0D)
binuclear metallomacrocycle (3 and 6) to one-dimensional
(1D) looped-chain coordination polymer (4), 2D (4,4)
network (5), and interpenetrated 3D frameworks with lvt (1)
and NbO (2) topologies have been exploited.
1
68.41; H, 5.30; N, 12.27. Found: C, 68.02; H, 5.51; N, 11.97%. H
NMR (CDCl3, 300 MHz): δ 2.24 (s, 3H, −CH3), 6.20 (s, 1H, 
CH−), 7.25 (s, 1H, imidazole), 7.35 (s, 1H, imidazole), 7.50 (d, 2H,
benzene, J = 9.0 Hz), 7.96 (s, 1H, imidazole), 8.02 (d, 2H, benzene, J
= 9.0 Hz). IR (KBr cm−1): 3095 w, 1606 s, 1525 m, 1488 m, 1369 w,
1309 m, 1276 m, 1201 m, 1134 w, 1110 w, 1056 m, 960 m, 854 m, 783
m, 736 w, 653 w, 501w.
1-(4-(1H-Benzimidazol-1-yl)phenyl)butane-1,3-dione (HL2). Yield
88%. MS m/z = 279 (M + 1). Anal. Calcd. for C17H14N2O2: C, 73.37;
1
H, 5.07; N, 10.07. Found: C, 73.58; H, 5.21; N, 10.24%. H NMR
(CDCl3, 300 MHz): δ 2.26 (s, 3H, −CH3), 6.24 (s, 1H, CH−), 7.40
(m, 2H, benzene), 7.58 (m, 1H, benzene), 7.65 (d, 2H, benzene, J =
8.7 Hz), 7.91 (m, 1H, benzene), 8.11 (d, 2H, benzene, J = 8.7 Hz),
8.21 (s, 1H, imidazole). IR (KBr cm−1): 3091 w, 1606 s, 1515 m, 1488
m, 1452 m, 1361 w, 1284 m, 1236 m, 1207 m, 1082 w, 975 w, 933 w,
854 m, 777 m, 592 w, 524 w, 433 w.
1-(4-(1H-Pyrazol-1-yl)phenyl)butane-1,3-dione (HL3). Yield 78%.
MS m/z = 229 (M + 1). Anal. Calcd. for C13H12N2O2: C, 68.41; H,
5.30; N, 12.27. Found: C, 68.13; H, 5.52; N, 12.54%. 1H NMR
(CDCl3, 300 MHz): δ 2.22 (s, 3H, −CH3), 6.20 (s, 1H, CH−), 6.51
(t, 1H, pyrazole, J = 4.2 Hz, J′ = 1.8 Hz, J″ = 2.4 Hz), 7.76 (d, 1H,
pyrazole, J = 1.8 Hz), 7.81 (d, 2H, benzene, J = 8.7 Hz), 7.99 (d, 3H,
benzene and pyrazole, J = 8.4 Hz). IR (KBr cm−1): 3112 w, 1608 s,
1527 m, 1394 m, 1340 w, 1305 w, 1278 w, 1205 w, 1124 w, 1051 w,
937 m, 846 m, 783 m, 738 m, 651 w, 607 w.
EXPERIMENTAL SECTION
■
Materials and Methods. The reagents and solvents employed
were commercially available and were used as received without further
purification. The C, H, and N microanalyses were carried out with a
1
Vario EL elemental analyzer. H NMR spectra were recorded on a
Varian 300 MHz spectrometer at 25 °C. Electron spray ionization
(ESI) mass spectra were obtained on a LCQ DECA XP quadrupole
ion trap mass spectrometer with methanol as the carrier solvent.
Thermogravimetric data were collected on a Netzsch TGS-2 analyzer
in nitrogen atmosphere at a heating rate of 10 °C min−1. Fourier
transform infrared (FT-IR) spectra were recorded from KBr pellets in
the range of 400−4000 cm−1 on a Bruker TENSOR 27 spectrometer.
Powder X-ray diffraction patterns were recorded on a D8 ADVANCE
diffractometer with Cu Kα radiation (λ = 1.5409 Å) at a scanning rate
of 4° min−1 with 2θ ranging from 5 to 35°. Fluorescence spectra were
collected on a FLSP920 at room temperature. The precursors 4-(1H-
imidazol-1-yl)-acetophenone, 4-(1H-benzimidazol-1-yl)-acetophe-
none, 4-(1H-pyrazol-1-yl)-acetophenone, 3-(1H-imidazol-1-yl)-aceto-
phenone, 3-(1H-benzimidazol-1-yl)-acetophenone, and 3-(1H-pyra-
zol-1-yl)-acetophenone were synthesized by literature procedures16
1-(3-(1H-Imidazol-1-yl)phenyl)butane-1,3-dione (HL4). Yield
50%. MS m/z = 229 (M + 1). Anal. Calcd. for C13H12N2O2: C,
1
68.41; H, 5.30; N, 12.27. Found: C, 68.54; H, 5.51; N, 12.53%. H
NMR (DMSO-d6, 300 MHz): δ 2.23 (s, 3H, −CH3), 4.38 and 6.732
(s, 1H, −CH2− and CH−), 7.12 (s, 1H, imidazole), 7.65 (t, 1H,
benzene, J = 15.6 Hz, J′ = 7.8 Hz, J″ = 7.8 Hz), 7.85 (m, 1H,
imidazole), 7.89 (d, 2H, benzene, J = 7.5 Hz), 8.12 (s, 1H, imidazole),
8.36 (s, 1H, benzene). IR (KBr cm−1): 3118 w, 1610 s, 1512 s, 1425 w,
1
and checked by H NMR spectra.
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Crystal Growth & Design
Article
Table 1. Crystal Data and Structure Refinement for 1−6
complex
empirical formula
1
2
3
4
5
6
C55H55N9O11Zn2
1148.82
tetragonal
I41/a
C204H182N24O37Zn6
3953.96
C78H66N12O12Zn3
1559.54
monoclinic
P21/c
C26H26N4O6Zn
555.88
C36H28Cl6N4O4Zn
858.69
C52H44N8O8Zn2
1039.69
Mr
crystal system
trigonal
triclinic
monoclinic
P21/c
triclinic
space group
R3
̅
P1
̅
P1
̅
a/Å
24.73040(10)
24.73040(10)
35.5900(3)
90
23.2562(6)
23.2562(6)
62.035(2)
90
20.500(3)
8.0727(10)
20.270(3)
90
8.6826(6)
8.9946(7)
17.6757(13)
89.330(1)
83.036(1)
68.522(1)
1274.28(16)
2
13.1420(11)
9.5179(8)
14.8006(12)
90
7.92(3)
10.90(4)
14.83(5)
71.19(9)
87.24(9)
74.45(6)
1166(7)
1
b/Å
c/Å
α/°
β/°
γ/°
V/Å3
90
90
90.534(2)
90
107.726(1)
90
90
120
21766.6(2)
16
29056.6(15)
6
3354.3(8)
2
1763.4(3)
2
Z
Dc/Mg m−3
1.402
1.356
1.544
1.449
1.617
1.481
μ/mm−1
1.651
0.811
1.141
1.012
1.199
1.095
data/restraints/parameters
GOF on F2
10269/1/709
1.060
12366/15/818
0.964
5663/0/481
1.080
4554/0/339
1.055
3458/0/233
1.021
4173/0/318
0.982
R indices [I > 2σ(I)], wR2 (all
0.0702, 0.2316
0.0673, 0.2287
0.0525, 0.1490
0.0321, 0.0855
0.0403, 0.1157
0.0663, 0.2817
data)
Δρmax/Δρmin (e Å−3
)
0.975/−0.708
1.336/−0.591
0.702/−0.721
0.446/−0.351
1.088/−0.390
0.702/−1.032
1369 m, 1307 m, 1271 m, 1110 w, 1066 m, 983 w, 906 w, 829 w, 786
m, 730 m, 676 w, 653 w, 536 w.
(KBr pellet, cm−1): 3109 w, 1596 s, 1568 s, 1498 s, 1448 m, 1388 m,
1336 m, 1303 m, 1280 m, 1199 m, 1126 w, 1045 w, 935 m, 852 m, 773
m, 696 w, 586 w, 509 w, 428 w.
Synthesis of Zn(L4)2·2H2O (4). The procedure is similar to that of
1, using ligand HL4 in place of HL1. Colorless crystals of 4 were
afforded in yield of 43% in a week. Anal. Calcd. for C26H26ZnN4O6: C,
56.13; H, 4.68; N, 10.07. Found: C, 56.40; H, 4.34; N, 10.30%. FT-IR
data (KBr pellet, cm−1): 3120 w, 1575 s, 1506 s, 1460 s, 1411 s, 1305
m, 1263 m, 1209 w, 1107 w, 1066 m, 1006 w, 983 w, 948 w, 910 w,
865 w, 757 m, 725 w, 686 w, 657 w, 559 w.
Synthesis of Zn(L5)2·2CHCl3 (5). The procedure is similar to that of
2, using ligand HL5 in place of HL2. Colorless crystals of 5 were
afforded in yield of 23% in a week. Anal. Calcd. for C36H28ZnN4O4Cl6:
C, 50.31; H, 3.26; N, 6.52. Found: C, 50.67; H, 3.46; N, 6.72%. FT-IR
data (KBr pellet, cm−1): 3084 w, 1600 m, 1577 m, 1506 s, 1461 m,
1411 m, 1296 w, 1232 m, 1145 w, 1097 w, 1002 w, 757 m, 690 w, 551
w, 426 w.
Synthesis of [Zn(L6)2]2 (6). A solution of 0.01 mmol of
Zn(NO3)2·2H2O in 1 mL of MeOH/H2O was layered over a solution
of 0.02 mmol of HL6 and 3 μL of N(Et)3 in 1 mL of MeOH. Colorless
crystals of 6 were afforded in yield of 25% in a week. Anal. Calcd. for
C52H44Zn2N8O8: C, 60.02; H, 4.23; N, 10.77. Found: C, 60.21; H,
4.43; N, 10.58%. FT-IR data (KBr pellet, cm−1): 3111 w, 1569 s, 1519
s, 1481 m, 1450 m, 1415 s, 1388 m, 1338 w, 1294 w, 1199 w, 1076 w,
1041 w, 999 w, 946 w, 896 w, 765 w, 561 w, 420 w.
X-ray Crystallography. Diffraction intensities for the complexes
were collected on a Bruker Smart Apex CCD diffractometer (1 and 3−
5) or a Rigaku R-AXIS SPIDER IP diffractometer (2 and 6) with
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
Absorption corrections were applied using SADABS.17 The structures
were solved by direct methods and refined with full-matrix least-
squares technique using SHELXS-97 and SHELXL-97 programs,
respectively.18,19 Anisotropic thermal parameters were applied to all
non-hydrogen atoms. The organic hydrogen atoms were generated
geometrically (C−H 0.96 Å and N−H 0.86 Å). The hydrogen atoms
of the coordinated water molecules were located from difference maps
and refined with isotropic temperature factors. Crystal data, as well as
details of data collection and refinement for the complexes, are
summarized in Table 1. Selected bond distances and angles are listed
in Table S1, Supporting Information.
1-(3-(1H-Benzimidazol-1-yl)phenyl)butane-1,3-dione (HL5). Yield
59%. MS m/z = 279 (M + 1). Anal. Calcd. for C17H14N2O2: C, 73.37;
1
H, 5.07; N, 10.07. Found: C, 73.60; H, 5.27; N, 10.34%. H NMR
(DMSO-d6, 300 MHz): δ 2.21 and 2.25 (s, 3H, −CH3), 4.39 and 6.73
(s, 1H, −CH2− and CH−), 7.33 (m, 2H, benzene), 7.62 (d, 1H,
benzene, J = 6.6 Hz), 7.77 (m, 2H, benzene), 7.94 (d, 1H, benzene, J =
7.8 Hz), 8.06 (d, 1H, benzene, J = 7.8 Hz), 8.19 (s, 1H, imidazole),
8.63 (s, 1H, benzene). IR (KBr cm−1): 3091 w, 1685 m, 1614 m, 1500
s, 1458 m, 1361 w, 1296 m, 1263 w, 1234 m, 1141 w, 900 w, 802 w,
783 w, 763 w, 734 m, 688 w, 424 w.
1-(3-(1H-Pyrazol-1-yl)phenyl)butane-1,3-dione (HL6). Yield 46%.
MS m/z = 229 (M + 1). Anal. Calcd. for C13H12N2O2: C, 68.41; H,
5.30; N, 12.27. Found: C, 68.65; H, 5.47; N, 12.58%. 1H NMR
(CDCl3, 300 MHz): δ 2.24 (s, 3H, −CH3), 6.26 (s, 1H, CH−), 6.51
(t, 1H, pyrazole, J = 4.2 Hz, J′ = 2.4 Hz, J″ = 1.8 Hz), 7.54 (t, 1H,
benzene, J = 15.9 Hz, J′ = 7.8 Hz, J″ = 8.1 Hz), 7.76 (d, 1H, pyrazole, J
= 1.8 Hz), 7.80 (d, 1H, benzene, J = 7.8 Hz), 7.88 (d, 1H, benzene, J =
8.1 Hz), 8.01 (d, 1H, pyrazole, J = 2.4 Hz), 8.20 (s, 1H, benzene). IR
(KBr cm−1): 3141 w, 1591 s, 1523 m, 1390 m, 1344 m, 1278 w, 1244
w, 1205 w, 1062 w, 1043 m, 995 w, 950 m, 906 w, 773 m, 715 w, 673
w, 655 w, 615 w, 555 w.
Synthesis of [Zn2(L1)4]·2H2O·DMF (1). One milliliter of DMF is
carefully placed on top of the solution of 0.01 mmol of
Zn(OAc)2·2H2O in 1 mL of H2O. A solution of 0.02 mmol of HL1
and 3 μL of N(Et)3 in 1 mL of MeOH was then added to the top of
the buffer. Colorless crystals of 1 were afforded in a yield of 35% in a
week. Anal. Calcd. for C55H55Zn2N9O11: C, 57.45; H, 4.78; N, 10.97.
Found: C, 57.65; H, 4.46; N, 10.72%. FT-IR data (KBr pellet, cm−1):
3139 w, 1674 m, 1602 s, 1571 m, 1502 s, 1456 m, 1406 m, 1303 m,
1267 w, 1213 w, 1124 w, 1058 m, 964 w, 848 w, 773 w, 698 w, 657 w,
580 w, 518 w.
Synthesis of [Zn2(L2)4]3·13H2O (2). A solution of 0.01 mmol of
Zn(OAc)2·2H2O in 1 mL of MeOH/CHCl3 was layered over a
solution of 0.02 mmol of HL2 and 3 μL of N(Et)3 in 1 mL of CHCl3.
Colorless crystals of 2 were afforded in yield of 15% in a week. Anal.
Calcd. for C204H182Zn6N24O37: C, 61.91; H, 4.60; N, 8.50. Found: C,
61.52; H, 4.34; N, 8.38%. FT-IR data (KBr pellet, cm−1): 3057 w, 1595
m, 1566 m, 1502 s, 1450 m, 1402 m, 1290 m, 1234 m, 1207 w, 991 w,
783 w, 767 w, 742 m, 703 w, 590 w, 526 w.
Synthesis of [Zn1.5(L3)3]2 (3). The procedure is similar to that of 1,
using ligand HL3 in place of HL1. Colorless crystals of 3 were afforded
in yield of 26% in a week. Anal. Calcd. for C78H66Zn3N12O12: C, 60.02;
H, 4.23; N, 10.77. Found: C, 60.43; H, 4.06; N, 10.54%. FT-IR data
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The asymmetric bifunc-
tional ligands containing a terminal N-donor (imidazole/
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Article
benzimidazole/pyrazole) and a β-diketone chelate linking via a
phenyl spacer were successfully synthesized by Claisen
condensation of N-donor substituted acetophenone and ethyl
acetate using potassium tert-butoxide as a catalyst.20 These
ligands can be seen as three potential exotopic donors with
monodentate and bidentate chelate fashions. Their constitu-
tions were confirmed by MS and NMR spectra. The
coordination behaviors of these ligands with Zn(II) ion were
observed in different solvents. A variety of geometries from 0D
binuclear metallomacrocycle (3 and 6) to 1D (4), 2D (5), and
3D (1 and 2) coordination polymers have been assembled,
depending on the ligand. Although these solvents have different
coordination abilities to metal ions, they do not bind to Zn(II)
ion in the synthetic conditions. We also found that the solvent
molecule has no impact on the coordination geometry under
the experimental conditions. Moreover, the influence of anion
on Zn(II) coordination geometry was also examined by using
different Zn(II) salts as starting materials; the identical complex
was obtained by checking the unit cell parameters. That is to
say, the anion has no impact on the structure in our cases.
The phase purity of these complexes was convincingly
established by comparison of the powder X-ray diffraction
patterns of the as-synthesized products with the simulated ones
from the single-crystal data (see Figures S1−S6 in the
Supporting Information). The solvent molecules were also
confirmed by thermogravimetric analysis experiments. Total
weight loss of 9.4%, 6.0%, and 5.7% (see Figures S7−S9 in the
Supporting Information) were observed for complexes 1, 2, and
4, respectively, in the temperature range of 25−200 °C, which
were ascribed to the loss of four water molecules and two DMF
molecule in 1 (calcd 9.5%), 13 water molecules in 2 (calculated
5.9%), and two water molecules in 4 (calcd 6.4%).
Figure 1. ORTEP drawing of 3 (a) and 6 (b) with thermal ellipsoids
at 30% probability. Symmetry codes for 3, A: x − 1, −y, −z + 1; B: −x,
−y + 1, −z. For 6, A: −x + 1, −y + 1, −z + 1.
2.085(9) Å) and two chelating β-diketone with trans
configuration at the basal plane (Zn−O = 2.001(7)−2.073(7)
Å). Two coordination conformations syn and anti for ligand L6
are observed, in which the dihedral angles between the pyrazol
ring and the chelating β-diketone coordination plane within a
ligand are 61.73° and 85.41°, respectively. The almost
perpendicularity of the pyrazol ring to the chelating β-diketone
coordination plane allows construction into a [2 + 2]
metallomacrocycle with a Zn···Zn distance of 8.68 Å, as
shown in Figure 1b. The ligand with syn conformation provides
a pair of chelating oxygen atoms to bind to the Zn(II) ion and
the N atom in there is free.
Crystal Structures for 0D Binuclear Macrocyclic
Complexes 3 and 6. Complex 3 crystallizes in the
monoclinic space group P21/c. There are two crystallo-
graphically independent Zn(II) ions and three L3 anions in
an asymmetric unit, in which Zn2 lies on a 2-fold axis and was
refined in 0.5 occupancy positions due to the positional
disorder.21 The coordination geometry of the Zn(II) ion is
better described as a distorted square-pyramid (τ = 0.15 and
0.02)22 with the N atom occupying at the apical position (Zn−
N = 2.093(3) and 2.274(3) Å) and two chelating β-diketone
with trans configuration at the basal plane (Zn−O = 1.977(2)−
2.047(3) Å), as shown in Figure 1. It should be pointed out that
three kinds of coordination geometries for ligand L3 are
observed in 3, in which N2 and N6 atoms from the ligands that
act as anti conformation bind to Zn2 and Zn1, respectively, and
the N4 atom from the ligand in syn conformation is free. The
dihedral angles between the pyrazol ring and the chelating β-
diketone coordination plane within a ligand are 73.17°, 28.91°,
and 22.24°, respectively. The ligand with a larger dihedral angle
favors assembly into a [2 + 2] metallomacrocycle with a
Zn···Zn distance of 9.06 Å. The oxygen atoms and partial N
atom from the other two ligands further bind to the Zn(II) ion
to satisfy the coordination number. However, the free N-donor
is too close to the phenyl ring, which prohibits the N atom
further to connect the Zn(II) ion, resulting in a 0D binuclear
metallomacrocycle.
Crystal Structure for 1D Looped-Chain Coordination
Polymer 4. Complex 4 crystallizes in a triclinic space group
P1 and consists of a Zn(II) ion, two L ligands, and two lattice
̅
4
water molecules. As shown in Figure 2a, two crystallo-
graphically independent Zn(II) ions lie on the a-axis. Each
Zn(II) ion is 0.5 occupancy and is coordinated by four β-
diketone O atoms (Zn−O = 2.058(1)−2.111(1) Å) and two
imidazolyl N atoms (Zn−N = 2.174(2) and 2.160(2) Å) to
furnish an octahedral geometry. Similar to the ligands L3 in 1
and L6 in 6, ligand L4 acts as a three exotopic donor bridging
two separate metal ions into a [2 + 2] metallomacrocycle with a
metal−metal distance of 8.838 Å. However, only syn
conformation was observed in ligand L4 with the dihedral
angles between the imidazolyl ring and the β-diketone plane of
40.85° and 51.61°. These are different from those observed in
complexes 3 and 6, in which the ligands L3 and L6 within the
macrocycle all adopt anti conformation with larger dihedral
angles (73.17° for 3 and 85.41° for 6). Moreover, two water
molecules are located in each metallomacrocycle via formation
of hydrogen bonding each other (O1W···O2W = 2.894(2) Å)
and with the oxygen atoms of diketone (O1W···O1A =
2.814(2) Å, O1W···O2 = 2.809(2) Å and O2W···O3B =
2.840(2) Å). The macrocycles fuse into 1D looped-chain
coordination polymers via sharing the metal ions along the a
axis (see Figure 2b).
Crystal Structure for 2D (4,4) Network 5. Complex 5
crystallizes in the monoclinic space group P21/c and consists of
a Zn(II) ion, two L5 anions, and two CHCl3 molecules. The
Zn(II) ion lies on a symmetric inversion center and is
coordinated by four oxygen atoms from two β-diketones with
Complex 6 crystallizes in the triclinic space group P1. There
̅
are one crystallographically independent Zn(II) ion and two L6
anion in the asymmetric unit. Similar to 3, the coordination
geometry of Zn(II) ion is a distorted square-pyramid (τ =
0.33)22 with the N atom sitting at the apical position (Zn−N =
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Figure 3. (a) ORTEP drawing of 5 with thermal ellipsoids at 30%
probability. (b) View of a 2D network in 5. Symmetry codes, A: −x, −
y, −z; B: x, −y + 1/2, −z + 1/2.
Figure 2. (a) ORTEP drawing of 4 with thermal ellipsoids at 30%
probability. (b) View of 1D looped-chain along the a-axis in 4 and
schematic drawing. Symmetry codes, A: −x, −y + 1, −z + 1; B: −x, −y
+ 1, −z.
instance of [Zn(nicotinate)2] with a square-planar node self-
assembled into 2D (4,4) and 3D lvt (42.84) topologies under
different solvent systems.23a In complex 1, each four-connected
planar node generates two types of rhombic cavities; one is
planar eight-membered circuit with edges of 24.95 Å, and the
other is nonplanar four-membered circuit with edges of 12.46
Å. The planar square-grids (blue and red) are fused together by
sharing the metal atoms at the midpoints of the rhombic edges,
generating the four-membered rings. The sizes of the circuit are
so large that they allow 4-fold interpenetration to occur (see
Figure 4d).
Moreover, the asymmetry of the ligand produces two types
of nanoporous channels along the crystallographic c-axis (see
Figure 5). Both are square section (ca. 8.5 × 8.5 Å) with a
chessboard disposition. The channels surrounded by methyl
groups are simple formed by the stacking of the nonplanar four-
membered circuit in the lvt net and filled by solvated water
molecules, whereas the others decorated by imidazolyl groups
are enclosed by 4-fold entangled 41 and 43 helices with a pitch
length of 35.59 Å. These channels are filled by solvated DMF
molecules. Although the networks are 4-fold interpenetration,
there is still approximately 17.7% potential solvent-accessible
volume calculated by using the PLATON program24 after the
guest water molecules are removed.
trans configuration (Zn−O = 2.065(2) and 2.038(2) Å) and
two benzimidazolyl nitrogen atoms (Zn−N = 2.247(2) Å) to
furnish an octahedral geometry, as shown in Figure 3a. The
ligand L5 acts as syn conformation and the dihedral angle
between the benzimidazole and the β-diketone coordination
plane within a ligand is 63.44°. Each ligand bridges two Zn(II)
ions, and each Zn(II) ion links to four ligands, resulting in a 2D
(4,4) network with rhombic cavities, as shown in Figure 3b.
The M···M distances across the L5 ligands and through the
diagonals are 8.80, 9.52, and 14.80 Å. Two benzimidazol rings
fill in a rhombic cavity with a distance of 3.7 Å, indicating π−π
interactions between them.
Crystal Structure for 3D Frameworks with lvt Top-
ology 1. Complex 1 crystallizes in the I41/a space group. The
asymmetric unit has two independent Zn(II) ions, four L1
anions, one DMF, and two water molecules. Each Zn(II) is
coordinated by four equatorial oxygen atoms from two β-
diketones (Zn−O = 2.052(3)−2.122(3) Å) in trans config-
uration and two imidazolyl nitrogen atoms (Zn−N =
2.135(3)−2.147(3) Å) to furnish an octahedral geometry, as
shown in Figure 4a. Each ligand L1 adopts anti conformation
with the dihedral angles between imidazole and diketone
coordination plane of 7.88−27.01°. Each Zn(II) ion is
coordinated by four ligands as a planar four-connected node,
and each ligand links two Zn(II) ion, generating a 3D
Crystal Structure for 3D Frameworks with NbO
Topology 2. Complex 2 crystallizes with trigonal symmetry
in the R3 space group. The asymmetric unit has two
̅
independent metal ions, four L2 anions, and four and one-
third water molecules. Each metal ion adopts a distorted
octahedral geometry involving four oxygen atoms (Zn−O =
2.062(4)−2.097(5) Å) and two N atoms (Zn−N = 2.157(5)−
2.189(5) Å), as shown in Figure 6a. The four oxygen atoms are
provided by two β-diketone ligands, locating at the basal sites in
the chelate mode with trans configuration; the two nitrogen
framework with lvt topology (Schlafli symbol 4284),23 as
̈
shown in Figure 4b,c. This is much different from the self-
assembled [Cu(Pyac)2] framework with a square-planar node,
in which two structural topologies of 2D (4,4) square-grid and
3D NbO are obtained from different solvents.11a However, the
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Figure 4. (a) The coordination environment of the Zn(II) ions in 1. (b) Schematic representation of the connectivity of the Zn centers in 1. (c) The
lvt topology and (d) the four interpenetrated nets in 1. Symmetry codes, A: −y + 5/4, x − 1/4, z − 1/4; B: −y + 7/4, x − 3/4, z + 1/4; C: y + 1/4,
−x + 5/4, z + 1/4; D: y + 3/4, −x + 7/4, z − 1/4; E: −y + 5/4, x + 3/4, z − 1/4; F: −y + 3/4, x + 1/4, z + 1/4; G: y − 3/4, −x + 5/4, z + 1/4; H: y
− 1/4, −x + 3/4, z − 1/4.
Figure 5. A view of the two distinct types of helices (a) and channels (b) along the c axis in 1. All hydrogen atoms are deleted for clarity.
atoms are provided by the other two L2 ligands, occupying the
apical positions. Each L2 ligand in anti conformation binds two
separate metal ions, and each metal ion links four ligands,
acting as a four-connected node, generating a neutral NbO-type
(64,82 topology) structure (Figure 6b).25 The shortest circuit
can be defined as a chairlike, hexagonal [Zn6(L2)6] ring, which
has two different edge-lengths of 12.314(2) and 12.346(3) Å as
well as two different angles of 57.34(3) and 57.57(2)°. These
are significantly different from the reported complex [Cu-
(Pyac)2], where the metal−metal distances are 10.228(2) and
10.058(3) Å, and the angles are 111.64(3) and 68.36(4)°.11a
Furthermore, the NbO frameworks are interpenetrated with
each other generating a 2-fold interpenetration structure
(Figure 6c). Despite this interpenetration, complex 2 retains
one-dimensionally hexagonal channels. These channels are
decorated by the methyl group and benzimidazole, and filled
with solvent water molecules. Analysis of the crystal volume
available for the solvent-accessible calculated by using
PLATON program24 shows that there is approximately 13.8%
after removal of the lattice water molecules.
Ligand-Directed Assembly for Diverse Topologies.
Ligands HL1−HL6, combination of a terminal N-donor
(imidazole/benzimidazole/pyrazole) with a β-diketone chelate
via a phenyl linker, can be regarded as potential tridentate
ligands and reduced to a two-connected linker. Free rotation via
the C−N/C−C bonds as well as the various coordinated sites
of N-donor allow the semirigidity ligands to take on
appropriate conformations, which may play a crucial role in
the final supramolecular architecture when they react with the
Zn(II) ion. Indeed, two coordination geometries for Zn(II) are
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Figure 6. (a) ORTEP plot showing coordination sphere around a Zn(II) ion of 2. (b) Schematic representation of the NbO framework and (c) the
2-fold interpenetrating NbO topology in 2. Symmetry codes, A: x − 2/3, y − 1/3, z − 1/3; B: −x + y + 5/3, −x + 4/3, z + 1/3; C, −x + y + 2, −x +
1, z.
found in the complexes. One is a square-pyramid with a N atom
occupying the apical position and two chelating β-diketone
with trans configuration at the basal plane, which can be
reduced to a three-connected node with T shape. The other is
an octahedral geometry with four oxygen atoms from two
chelating β-diketones at the equatorial plane in trans
configuration and two N atoms occupying the apical position,
which can be abbreviated as a planar four-connected node, as
shown in Scheme 2. In complexes 3 and 6, the potential
coordination N-donors from the ligands HL3 and HL6 are close
to the hydrogen atoms of the phenyl ring. To relieve the
repulsion from hydrogen atoms, the pyrazole rings rotate to
approximately vertical to the phenyl plane, in which the N-
donor departs from the hydrogen atoms of the phenyl ring and
binds to Zn(II) ions. In these cases, each Zn(II) ion is five-
coordinate in a square-pyramidal geometry, acting as a T shape
node; each ligand within the macrocycle binds to two Zn(II)
ions as a tridentate ligand in anti conformation and can be
reduced as a V-shape connector with an approximate 90° angle,
generating a discrete [2 + 2] metallomacrocycle.
Scheme 2. Schematic Representation of the 3- and 4-
Connected Nodes
In complexes 4 and 5, the meta-substituted ligands HL4 and
HL5 were also employed to observe the structural diversity.
However, the imidazolyl and benzimidazolyl groups are used
instead of pyrazolyl (HL6), respectively, and the N-donor sites
depart from the phenyl rings. In complex 4, the Zn(II) ion is
six-coordinate in an octahedral geometry, acting as a planar
four-connected node; the ligand L4 binds to two Zn(II) ions as
a tridentate ligand in syn conformation and can be regarded as
a V-shape connector with a approximate 120° angle, generating
a discrete [2 + 2] metallomacrocycle. Furthermore, the
macrocycles fuse into 1D looped-chain coordination polymers
via sharing the metal ions along the a axis. This is markedly
different from complex 6 and reminiscent of the distinct
coordinate sites and capabilities between ligands L4 and L6. In
complex 5, the Zn(II) coordinate geometry and the behavior of
the ligand are very similar to those in complex 4; however, it is
a 2D (4,4) network and different from the 1D looped chain in
4. This may be attributed to the π−π interactions between the
benzimidazolyl groups via careful comparison of their
structures.9c In complex 5, such π−π interaction changes the
coordinate direction of the ligand and enlarges the dihedral
angle between the benzimidazolyl and the diketone coordina-
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Scheme 3. Schematic Representation of the Interconversion between Complexes 5 and 4
Scheme 4. Schematic Representation of the Difference between the lvt (a) and NbO (b) nets
Figure 7. Solid-state photoluminescent spectra of 1−6 and the free ligands at room temperature.
tion plane to 63.44°, leading to generation of the 2D (4,4)
network. Scheme 3 presents the structural interconversion
between complexes 4 and 5 via changing the coordination
direction.
structural differences between 1 and 2 lies in the interleaving of
the planar square-grids, as shown in Scheme 4. In complex 1,
the planar eight-membered circuits are fused together by
sharing the metal atoms, generating the four-membered circuits
and further stacking into 1D channels with a square section
along the c axis. While in sharp contrast, the six-membered
circuits are formed in complex 2, which further stack into 1D
hexameric channels along the crystallographic c axis (see Figure
S10 in the Supporting Information). The various topologies
may be attributed to the bulk benzimidazolyl group in ligand
HL2. As shown in Figure 5b, four imidazolyl groups locate in a
1D channel with ca. 8.5 × 8.5 Å square section in complex 1;
however, this is too small to accommodate four benzimidazolyl
groups. Therefore, the larger hexameric 1D channels are
formed in complex 2.
In complexes 1 and 2, the ligands HL1 and HL2 are para-
substituted and in anti conformation with a basically linear
shape, which can be considered as a two-connected linker and
favors generation of high-dimensional structure. Each Zn(II)
ion is six-coordinate with an octahedral geometry, two chelating
β-diketones in trans arrangement at the equatorial plane and
two imidazolyl groups from the other two ligands occupying
the apical positions, which can be reduced to a planar four-
connected node, generating a 3D framework with lvt net for 1
and NbO net for 2, respectively. The factor that governs the
choice of topology is thus of great interest. More careful
examination indicates that the most salient feature of the
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especially those with d10 metal centers, have been investigated
for their fluorescent properties and potential applications.
Therefore, the photoluminescence properties of complexes 1−
6 and free ligands were measured in the solid state, as shown in
Figure 7. The maxima of emission band are observed at 481,
478, 496, 510, and 469 nm for free ligands HL1, HL2, HL3, HL4,
HL5, and HL6, respectively. These emission bands are assigned
to the π* → π electronic transitions of the free ligands. For
complexes, these peaks are shifted to 512, 493, 497, 509, 504,
and 485 nm, respectively. Since the profiles and locations of the
emission band in the spectra of the complexes are similar to
those observed in the free ligands, they can be assigned mainly
to intraligand transitions.26 The red-shift of emission spectra
observed in complexes 1, 2, 5, and 6, in comparison with the
corresponding free ligands, may be attributed to the
deprotonation of the ligands in complexes.
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CONCLUSION
■
(10) Vigato, P. A.; Peruzzo, V.; Tamburini, S. Coord. Chem. Rev.
2009, 253, 1099.
A variety of geometries from [2 + 2] metallomacrocycles to a
1D looped-chain coordination polymer and 2D (4,4) network
as well as 3D frameworks with lvt and NbO topologies have
been assembled on the basis of the bifunctional ligands
containing a N-donor and a β-diketone chelate and Zn(II) salts.
The studies clearly demonstrate that the ligand geometries play
vital roles in determination of the coordination geometries of
the metal centers and building blocks, leading to generation of
diverse supramolecular structures.
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Commun. 2003, 2166. (b) Chen, B. L.; Fronczek, F. R.; Maverick, A.
W. Inorg. Chem. 2004, 43, 8209. (c) Zhang, Y. X.; Chen, B. L.;
Fronczek, F. R.; Maverick, A. W. Inorg. Chem. 2008, 47, 4433.
(d) Zhang, Y. X.; Maverick, A. W. Inorg. Chem. 2009, 48, 10512.
(e) Pariya, C.; Fronczek, F. R.; Maverick, A. W. Inorg. Chem. 2011, 50,
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(12) (a) Vreshch, V. D.; Chernega, A. N.; Howard, J. A. K.; Sieler, J.;
Domasevitch, K. V. Dalton Trans. 2003, 1707. (b) Vreshch, V. D.;
Lysenko, A. B.; Chernega, A. N.; Howard, J. A. K.; Krautscheid, H.;
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V. D.; Lysenko, A. B.; Chernega, A. N.; Sieler, J.; Domasevitch, K. V.
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ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic files in CIF format, selected bond
distances and angles, TG curves, figure for 2, and experimental
and simulated X-ray powder diffraction patterns for complexes.
This material is available free of charge via the Internet at
http://pubs.acs.org
(13) (a) Turner, S. S.; Collison, D.; Mabbs, F. E.; Halliwell, M. J.
Chem. Soc., Dalton Trans. 1997, 1117. (b) Aromí, G.; Gamez, P.;
Krzystek, J.; Kooijman, H.; Spek, A. L.; MacLean, E. J.; Teat, S. J.;
Nowell, H. Inorg. Chem. 2007, 46, 2519. (c) Shiga, T.; Ito, N.; Hidaka,
A.; Ohkawa, H.; Kitagawa, S.; Ohba, M. Inorg. Chem. 2007, 46, 3492.
(d) Dohring, A.; Goddard, R.; Jolly, P. W.; Kruger, C.; Polyakov, V. R.
Inorg. Chem. 1997, 36, 177. (e) Won, T.-J.; Clegg, J. K.; Lindoy, L. F.;
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Iremonger, S. S.; Hayter, M. J.; Southon, P. D.; Macquart, R. B.;
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AUTHOR INFORMATION
Corresponding Author
*E-mail: cesybh@mail.sysu.edu.cn.
■
ACKNOWLEDGMENTS
This work was supported by the NSF of China (20771104 and
21071154) and Sun Yat-Sen University.
■
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