ARTICLE pubs.acs.org/crystal
Coordination Polymers of 1,3,5-Tris(triazol-1-ylmethyl)-2,4,6trimethylbenzene: Synthesis, Structure, Reversible Hydration, Encapsulation, and Catalysis Oxidation of Diphenylcarbonohydrazide Tianjun Ni,†,§ Feifei Xing,† Min Shao,‡ Yongmei Zhao,† Shourong Zhu,*,† and Mingxing Li*,† †
Department of Chemistry, College of Science, and ‡Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444, China § Department of Chemistry, Xinxiang Medical University, East of Jinsui Road, Xinxiang, Henan 453003, China
bS Supporting Information ABSTRACT: Eight coordination polymers {[Co3(L)2(H2O)6Cl6] 3 4H2O}n (1), {[Co(L)2Cl2] 3 13H2O}n (2), {[Cu3(L)2(H2O)6Cl6] 3 4H2O}n (3), {[Cu(L)2Cl2] 3 12H2O}n (4), {[Zn(L)2(H2O)2](NO3)2 3 4H2O}n (5), {[Zn(L)2(H2O)2](PF6)2 3 6H2O}n (6), {[ZnL(mal)] 3 3H2O}n (7), and {[Zn3(L)2(fum)3(H2O)6] 3 2H2O}n (8) were synthesized by reactions of the flexible tripodal ligand 1,3,5-tris(triazol-1ylmethyl)-2,4,6-trimethylbenzene (L) and/or fumaric acid (H2fum)/malonic acid (H2mal), with corresponding metal salts, respectively. The structures of these polymers were established by elemental analysis, IR, powder and single-crystal X-ray diffraction analysis. Complexes 1 and 3 had an infinite two-dimensional (2D) honeycomb network. L as a cis-tridentate ligand coordinated to metal ions up and down alternatively. Complexes 2 and 4 possessed a one-dimensional (1D) chain hinged structure. L was a cis-bidentate ligand. Complexes 5 and 6 had a 2D network structure with (4,4) topology. L was a trans-bidentate ligand in 5, while in 6, L adopted a cis-configuration coordinated to metal ion bidentately. Complex 7 had a wavy 2D structure. L adopted a transconfiguration coordinated ion in the c-direction, while the malonate anion coordinated to metal ions in the b-direction in left- and right-helix alternatively. Complex 8 had an unusual 2D to three-dimensional (3D) interpenetration network structure. L was in trans-configuration coordinated to metal ions tridentately in the bc plane to form a ladder structure, and fumarate anion bridged the ladder in the a-axis to form a porous 2D coordination polymer. Adjacent 2D coordination polymers penetrated each other in the c-direction to form a 3D coordination with void dimensions consisting of 11 Å rhombic channels. The structures of 1 and 2 (or 3 and 4) indicate ligand/metal ratios had a significant influence on the structures of coordination polymers. The distinct structures of all these complexes demonstrated that the counteranions played an important role in the construction of coordination polymers. The isostructure between complexes 1 and 3, 2 and 4, and 5 indicate that the metal centers did not affect the structure of the complexes. Complex 8 with the characteristic of hydrophilic carboxylate groups and hydrophobic L was capable of absorbing water reversibly under 50 °C and encapsulating guest molecules, such as curcumin, diphenylcarbonohydrazide, and phenylfluorone, to form {(guest molecule)x ⊂ 8}n. (where x = 0.20.4). The encapsulation behavior of 8 had been studied by elemental analysis, IR, thermogravimetric analysis (TG), and X-ray powder diffraction patterns (PXRD). Complex 8 could heterogeneously catalyze the oxidation of diphenylcarbonohydrazide in the presence of H2O2 in ethanol effectively. The oxidation process was facile, efficient, and environmental friendly.
’ INTRODUCTION Unlike traditional inorganic materials, coordination polymers, especially metalorganic frameworks (MOFs), are typically synthesized under mild conditions, allowing for the incorporation of constituent building blocks with desired functionalities, leading to numerous functional coordination polymers that have shown promise for a number of applications. In recent years, coordination polymers have been rapidly developed and received great attention not only due to fantastic structures such as cage, honeycomb, grid, ladder, multidimensional framework, polyrotaxane, polycatenane, etc.1 but also because of their potential applications as functional materials in magnetism, catalysis and r 2011 American Chemical Society
gas storage, ionic/molecular recognition, ionexchange, and selective guest inclusion.2 Previous studies showed that structures and properties of coordination polymers depend on factors such as the metal ions with definite coordination geometry, the nature of organic ligands, and the reaction conditions.3 The rational design and synthesis of multidentate functional organic ligands and the efficient utilization of reaction conditions to obtain perfect/ideal Received: March 4, 2011 Revised: April 14, 2011 Published: May 06, 2011 2999
dx.doi.org/10.1021/cg2002749 | Cryst. Growth Des. 2011, 11, 2999–3012
Crystal Growth & Design coordination polymers, or MOFs, have always been the objective for many chemists. Tripodal ligands with arene cores have been found to be one of the most useful organic building blocks for the construction of novel coordination frameworks.4 Complexes with specific structures and interesting properties have been obtained through reactions of suitable metal salts with rigid exotridentate ligands, such as 2,4,6-tris(4-pyridyl)-1,3,5-triazine,5 1,3,5-tricyanobenzene,6 and 1,3,5-benzenetribenzoate.7 Among them, the rigid ligands have few or even no conformational changes when they react with metal salts, while flexible ligands can adopt varied conformations and coordination modes according to the different geometric requirements of the metal ions and as a result may offer coordination polymers with unique structures and useful properties, such as 1,3,5-tris(pyrazol-1ylmethyl)-2,4,6-triethylbenzene8 and 1,3,5-tris(imidazole-1ylmethyl)-2,4,6-trimethylbenzene.9 Meanwhile, counteranions, metal-to-ligand ratio, and temperature play very important roles in the synthesis of coordination polymers. In particular, counteranions can influence the structure of coordination polymers by playing different roles within the structure, for example, bridging the metal ions,10 coordinating with the ions as terminal coligands,11 or without coordinating with the metal ions but still having template effects on the structures of coordination polymers.12 For example, when flexible bridging ligand 1,4bis(imidazol-1-ylmethyl)-benzene (bix) reacted with silver(I) nitrate or zinc(II) nitrate hexahydrate, a two-dimensional (2D) polyrotaxane network was obtained.13 Coordination polymers based on flexible ligands tended to collapse upon heating. Many studies indicate that rigid ligands are a good choice in the construction of thermally stable coordination polymers.14 However, coordination polymers constructed from flexible ligands may change their geometry during guest encapsulation and preserve their basic structures.15 Some of the coordination polymers assembled from flexible ligands can increase their porosity by up to 40170%.16 Recently, lotusroot-like one-dimensional polymetallocages with drastic void adaptability constructed from the flexible ligand 4,40 -bis(1,2,4triazol-1-ylmethyl)biphenyl were reported.17 The polymetallic cage can increase its cavity size 5 times its original size after encapsulating a fluorescein dianion simply by rotating the saturated carbon. Dehydration and rehydration of coordination frameworks represent one of the current investigated topics, in which even the coordinating water molecules can sometimes be reversibly removed and reabsorbed. Systematic research on this subject is crucial in understanding the control of coordination polymers. Coordination polymers are particularly well-suited for immobilizing well-defined molecular catalysts and can lead to a new generation of solid catalysts with uniform catalytic sites and open channel structures for shape-, size-, chemo-, and enantioselective reactions. The ability to easily recover and reuse such MOFbased heterogeneous catalysts is also highly desirable for reducing processing and waste disposal costs in large-scale reactions. Compared to other immobilized catalytic systems, MOFs can have well-defined, single-crystalline solid structures, unprecedentedly high catalyst loadings, more uniform and accessible catalytic centers, and enhanced catalytic activity by eliminating multimolecular catalyst deactivation pathways.18 Although a large number of MOFs have been examined as heterogeneous catalysts, most of these studies rely on the intrinsic catalytic activity (e.g., weak Lewis acidity) of the metal-connecting points.18 Direct incorporation of a well-defined homogeneous
ARTICLE
Scheme 1. Conformations of the Flexible Tripodal Ligand L
catalyst (or precatalyst) into the framework of a MOF represents an attractive alternative that has been underexplored.18a Our recent work has focused on both the structures and properties of coordination polymers, especially porous coordination polymers.5c,19 Our studies indicate that {[Co(H2O)6] 3 [Co3L0 2(H2O)2] 3 10H2O}n,19c where L0 is a 4,40 -bipyridyl-2,20 ,6,60 tetracarboxylate anion, can absorb a considerable amount of methanol or ethanol. Porous {[Co5(2,4-bptc)2(μ3-OH)2(μ2H2O)2(μ1-H2O)2] 3 2H2O}n and {[Co5(2,4-bptc)2(μ3-OH)2(μ2-H2O)2(μ1-H2O)2] 3 6H2O}n, where 2,4-bptc is 2,20 ,4,40 -biphenyltetracarboxylate, can encapsulate methanol or ethanol molecules. Lotus-root metallocage {[Zn(btmb)3](PF6)2(H2O)2}n and {[Co(btmb)3](PF6)2(H2O)2}n, where btmb is 4,40 -bis(1,2,4-triazol-1-ylmethyl)-biphenyl, can encapsulate fluorescein dianion to replace the hexafluorophosphate anion. The cage in the former complex can increase its void size drastically to fit the size of fluorescein due to the flexibility of ligand. Compared to flexible bidentate ligands, such as the abovementioned btmb, tridentate tripodal ligands have more versatile coordination modes.20 To further investigate the nature of flexible ligands and their coordination polymers, a tripodal ligand containing triazolyl instead of the reported pyridyl and imidazol groups, namely, 1,3,5-tris(triazol-1-ylmethyl)-2,4,6- trimethylbenzene (L), which is quite similar to the well-studied 1,3,5tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene,21 was synthesized. Because of the presence of methylene groups between the triazole and benzene ring groups, 1,3,5-tris(triazol-1-ylmethyl)2,4,6- trimethylbenzene is a flexible divergent ligand. Unlike the well-studied 1,3,5-tris(imidazol-1 ylmethyl)-2,4,6-trimethylbenzene, only four papers concerning L have been published when we started to prepare this manuscript.20f,22 Two papers appeared during preparation of the manuscript. There are two different conformations (cis and trans) when L (or its imidazole count parts) reacts with metal ions (Scheme 1).20f,22a To further understand and elucidate the details of the assembly process of the flexible tripodal ligand with metal salts and the effect of anions on the structure of coordination polymers, reactions of L with varied metal salts were carried out. In this paper, we report the syntheses, crystal structures, and properties of eight coordination complexes, namely, {[Co3(L)2(H2O)6Cl6] 3 4H2O}n (1), {[Co(L)2Cl2] 3 13H2O}n (2), {[Cu3(L)2(H2O)6Cl6] 3 4H2O}n (3), {[Cu(L)2Cl2] 3 12H2O}n (4), {[Zn(L)2(H2O)2](NO3)2 3 4H2O}n (5), {[Zn(L)2(H2O)2](PF6)2 3 6H2O}n (6), {[ZnL(mal)] 3 3H2O}n (7), {[Zn3(L)2(fum)3(H2O)6] 3 2H2O}n (8). The results attest that the flexible ligand L can adopt different conformations and coordination modes to form complexes with various structures. Counteranions significantly influence the structures of the coordination polymers (Scheme 2). The 3000
dx.doi.org/10.1021/cg2002749 |Cryst. Growth Des. 2011, 11, 2999–3012
Crystal Growth & Design
ARTICLE
Scheme 2. Stoichiometric and Counterion Control in the Synthesis of Coordination Polymers
resulting porous coordination polymer 8 can encapsulate guest molecules with suitable size and also can effectively catalyze the oxidation of diphenylcarbonohydrazide heterogeneously.
’ EXPERIMENTAL SECTION Materials and Methods. Acetonitrile was dried and purified by distillation before use. All other chemicals were of reagent-grade quality, obtained from commercial sources, and were used as received without further purification. 1,3,5-Tris-(bromomethyl)-2,4,6-trimethylbenzene was synthesized according to the reported procedures.23 Elemental analyses were determined using a Vario EL III elemental analyzer. The IR spectra were recorded in the 4000400 cm;1 region using KBr pellets and a Nicolet AVATAR-370 spectrometer. Raman spectra were measured on a Renishaw inVia Raman spectrometer excited at 785 nm (300 mW). Excitation and emission spectra were recorded on a Shimadzu F-4500 fluorescence spectrophotometer using slit width of 3.0 nm for excitation and 3.0 nm emissions at room temperature for the solid samples. Thermogravimetric (TG) analysis data was collected on a Netzsch STA-409PC under air in the temperature range from room temperature to 800 °C with a heating rate of 10 °C/min. UVvis spectra were recorded on a Pgeneral TU-1900 spectrometer. Powder X-ray diffraction patterns were recorded on a Rigaku D/max-2550 X-ray diffractometer with graphite monochromatic CuKR (1.54056 Å) radiation at 40 kV/250 mA at room temperature. Preparation of 1,3,5-Tri(triazol-1-ylmethyl)-2,4,6-trimethylbenzene (L). Triazole (2.76 g, 40 mmol) was dissolved in dry acetonitrile (50 mL), and anhydrous potassium carbonate (10 g) was added to the above solution. After 2 h of stirring, 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene (4.0 g, 10 mmol) was added. The mixture was then vigorously stirred and refluxed for 12 h at 80 °C. A white residue was obtained after filtering and evaporating the filtrate in a vacuum. The crude product was recrystallized from water and then ethanol/hexane (1:1) to give white crystalline product. Yield: 82%. Mp:
146147 °C. 1H NMR (DMSO-d): δ 2.419 (s, 9H), 5.493 (s, 6H), 7.935 (s, 3H), 8.480 (s, 3H). IR (KBr pellet, cm1): 3387br, 3287br, 3085 m, 1506s, 1442 m, 1333 m, 1273s, 1214w, 1136s, 1031w, 1010s, 958w, 893 m, 871w, 778w, 679s, 646 m. Anal. Calcd. for C18H21N9(363.42): C, 59.49; H, 5.82; N, 34.69%. Found: C, 59.43; H, 5.89; N, 34.71%.
Preparation of the Complexes {[Co3(L)2(H2O)6Cl6] 3 4H2O}n (1) and {[Co(L)2Cl2] 3 13H2O}n (2). These two compounds
were obtained simultaneously through the reaction of L with CoCl2 3 2H2O in a 1:1 ratio in aqueous methanol solution. An aqueous solution (5 mL) of CoCl2 3 6H2O (23.8 mg, 0.1 mmol) was added slowly to a solution of L (36.3 mg, 0.1 mmol) in methanol (10 mL) and stirred 10 min at room temperature. After filtration, the filtrate was allowed to stand for two weeks upon slow evaporation of the solvent to give two clearly distinct crystals. After filtration and washing with water and methanol, the mixture of compounds was further separated and purified by depositing it in a separation funnel, followed by the addition of 3:2 (v:v) CH2Cl2:CH2BrCH2CH2Br. Resting at room temperature for a while, the pink crystals 1 sank to bottom, while brown-pink 2 floated on the liquid surface (Figure 1). (1): Yield 28% based on L. Anal. Calcd for C36H62N18O10Cl6Co3 (FW. 1296.51): C 33.35; H 4.82; N 19.45%. Found: C 33.54; H 4.51; N 19.72%. IR (KBr pellet, cm1): 3359br, 3126w, 2976w, 1647s, 1529s,1500 m, 1450w, 1364 m, 1288s, 1205 m, 1134s, 1029 m, 991s, 899 m, 713 m, 675s, 649 m. Floating red-brown block crystal (2): Yield: 32% based on L. Anal. Calcd for C36H68N18O13Cl2Co (FW 1090.91): C 39.64; H 6.28; N 23.11%. Found: C 39.86; H 6.05; N 23.32%. IR (KBr pellet, cm1): 3420br, 3114w, 3001w, 1635w, 1519s, 1449s, 1378 m, 1345 m, 1275s, 1203s, 1130s, 1032 m, 1009s, 987 m, 883 m, 702w, 676s, 641 m.
{[Cu3(L)2(H2O)6Cl6] 3 4H2O}n (3) and {[Cu(L)2Cl2] 3 12H2O}n (4). These two compounds were obtained simultaneously through the reaction of L with CuCl2 3 2H2O in a manner similar to that in the synthesis of 1 and 2 except CuCl2 3 2H2O was used instead of CoCl2. The mixture of compounds was further separated and purified by depositing them in a separation funnel, followed by the addition of 3001
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ARTICLE
Figure 1. Crystal structure of 2. (a) Coordination environment of 2 with the hydrogen atoms and the water molecules omitted for clarity. (b) 1D coordination chain in 2. (c) Crystal packing diagram for complex 2 from the b-axis. Red balls are water oxygen atoms. (d) Water channel linked via Hbond viewed from the a-axis. Symmetry codes: #1: x þ 1, y þ 2, z þ 1; #2 x, y þ 1, z; #3 x þ 1, y þ 1, z þ 1.
Figure 2. Crystal structure of 5 (a) Coordination geometry with the atom numbering scheme; hydrogen atoms and uncoordinated water molecules were omitted for clarity. (b) 2D coordination polymer. (d) Crystal packing diagram from the b-axis. (c) H-bonds that link different layers. Blue dot lines represent H-bonds. Symmetry codes: #1: x þ 1, y þ 1, z; #2: x 1/2, y þ 1/2, z 1/2; #3: x þ 3/2, y þ 1/2, z þ 1/2. 2:1 (v:v) CH2Cl2:CH2BrCH2CH2Br. Deep-blue crystals of 5 floated on the liquid surface and the light-blue crystals of 3 sank to the bottom (Figure 2). Higher yields may be obtained through the reaction of a stoichimetric amount of ligand and metal salt for 3 or 5 in aqueous methanol solution (see Supporting Information). The yield of light-blue crystal of 3 was 21% based on L. Anal. Calcd for C36H62N18O10Cl6Cu3 (FW. 1310.35): C 33.00; H 4.77; N 19.24%. Found: C 33.28; H 4.43; N 19.58%. IR (KBr pellet, cm1): 3443br, 3126 m, 2983 m, 1639s, 1535s, 1502w, 1448w, 1341w, 1291s, 1207s,
1130s, 1023 m, 1000s, 898 m, 712 m, 672s, 640 m. Deep-blue block crystal (5): Yield: 27% based on L. Anal. Calcd for C36H66N18O12Cl2Cu (FW. 1077.51): C 40.13; H 6.17; N 23.40%. Found: C 40.23; H 6.07; N 23.58%. IR (KBr pellet, cm1): 3425br, 3110 m, 2997w, 1633w, 1524s, 1506s, 1451 m, 1275s, 1202 m, 1128s, 1031w, 1010 m, 995 m, 883w, 676s, 641 m. {[Zn(L)2(H2O)2](NO3)2 3 4H2O}n (5). An aqueous solution (5 mL) of Zn(NO3)2 3 6H2O (14.9 mg, 0.05 mmol) was added slowly to a solution of L (36.2 mg, 0.1 mmol) in methanol (10 mL) to give a 3002
dx.doi.org/10.1021/cg2002749 |Cryst. Growth Des. 2011, 11, 2999–3012
Crystal Growth & Design
ARTICLE
Table 1. Crystal Data and Refinement Results for Complexes 19 complex
a
1
2
3
4 C36H66O12N18Cl2Cu
empirical formula
C36H62O10N18Cl6Co3
C36H68O13N18Cl2Co
C36H62O10N18Cll6Cu3
formula weight
1296.53
1090.91
1310.36
1077.51
temperature (K)
296(2)
296(2)
296(2)
296(2)
wavelength (Å)
0.71073
0.71073
0.71073
0.71073
crystal system
trigonal
triclinic
trigonal
triclinic
space group
R3 hh 14.4038(16)
P1 h 10.318(4)
R3 hh 14.433(2)
P1
a/Å b/Å c/Å
14.4038(16) 21.667(5)
11.162(4) 12.354(4)
14.433(2) 21.418(7)
11.0830(18) 12.258(2)
R/deg
90
74.930(4)
90
75.341(2)
β/deg
90
72.332(4)
90
71.067(2)
γ/deg
120
80.816(5)
120
81.394(2)
V/Å3
3893.0(10)
1304.0(8)
3864.0(15)
1278.2(4)
Z
3
1
3
1
Dcalcd/g 3 cm3
10.3098(17)
1.659
1.389
1.689
1.4
μ/mm1 F(000)
1.328 2001
0.506 575
1.61 2019
0.605 567
R(int)
0.0313
0.0207
0.0371
0.0185
GOF on F2
1.027
1.051
1.081
1.05
R1 [I > 2σ(I)]a
0.0374
0.0906
0.0382
0.0931
wR2 [I > 2σ(I)]b
0.1033
0.2607
0.1009
0.2621
residuals/e 3 A3
0.292, 0.414
1.142, 1.284
0.405, 0.488
1.829, 1.269
complex
5
6
7
8
empirical formula formula weight
C36H54O12N20Zn 1024.36
C36H58O8N18P2F12Zn 1226.31
C21H29N9O7Zn 584.9
C48H64O20N18Zn3 1409.28
temperature (K)
296(2)
296(2)
296(2)
296(2)
wavelength (Å)
0.71073
0.71073
0.71073
0.71073
crystal system
monoclinic
monoclinic
monoclinic
triclinic
space group
P2(1)/n
P2(1)/n
C2/c
P1
a/Å
8.4837(9)
11.5300(15)
19.1020(14)
9.136(2)
b/Å
16.3767(18)
14.555(2)
11.5697(9)
14.991(4)
c/Å R/deg
17.5030(19) 90
16.181(2) 90
23.0912(17) 90
15.697(4) 62.185(3)
β/deg
101.2000(10)
101.440(2)
105.1320(10)
79.796(3)
γ/deg
90
90
90
89.508(3)
V/Å3
2385.5(4)
2661.6(6)
4926.3(6)
1864.6(8)
Z
2
2
8
1
Dcalcd/g 3 cm3
1.426
1.53
1.577
1.255
μ/mm1
0.594
0.628
1.059
1.028
F(000) R(int)
1072 0.0225
1264 0.0491
2432 0.0186
728 0.0137
GOF on F2
1.03
1.067
1.055
1.083
R1 [I > 2σ(I)]a
0.065
0.0779
0.0568
0.0492
wR2 [I > 2σ(I)]b
0.1967
0.217
0.1638
0.1802
residuals/e 3 A3
1.087, 1.035
0.943, 1.099
0.660, 0.544
1.225, 0.674
R1 = Σ||Fo| |Fc||/Σ|Fo|, b wR2 = [Σ(w(Fo2 Fc2)2)/Σ(wFo2)2]1/2.
clear solution. It was stirred for 10 min at room temperature. Colorless block crystals for X-ray diffraction were obtained upon slow evaporation of the solvent after two weeks. Yield: 68% based on Zn. Anal. Calcd for C36H54O12N20Zn (FW 1024.35): C 42.21; H 5.31; N 27.35%. Found: C 42.38; H 5.22; N 27.42%. IR (KBr pellet, cm1): 3454br, 3107 m, 1642w, 1531 m, 1510 m, 1383s, 1334s, 1278s, 1208 m, 1135s, 1034w, 1012 m, 990w, 895w, 696w, 676s, 642 m.
{[Zn(L)2(H2O)2](PF6)2 3 6H2O}n (6). Zn(NO3)2 3 6H2O (14.9 mg, 0.05 mmol) and NH4PF6 (16.2 mg, 0.10 mmol) were dissolved in 3 mL of water. This solution was added to a 10 mL methanol solution containing L (36.3 mg, 0.10 mmol). The mixture was stirred for 10 min and then filtered. The filtrate was allowed to stand at room temperature for a week. Colorless block crystals suitable for X-ray analysis were obtained. Yield: 68% based on Zn. Anal. Calcd for 3003
dx.doi.org/10.1021/cg2002749 |Cryst. Growth Des. 2011, 11, 2999–3012
Crystal Growth & Design C36H58O8N18P2F12Zn (FW. 1226.30): C 35.26; H 4.77; N 20.56%. Found: C 35.52; H 4.65; N 20.87%. IR (KBr pellet, cm1): 3443br, 3151w, 1636w, 1530s, 1511 m, 1455w, 1384w, 1284 m, 1208 m, 1136s, 1015 m, 995w, 842vs, 675s, 640 m, 558s. {[ZnL(mal)] 3 3H2O}n (7). ZnO (16.4 mg, 0.20 mmol) and malonic acid (HO2CCH2CO2H) (20.8 mg, 0.20 mmol) were suspended in 10 mL aqueous solution, and the mixture was then refluxed and stirred for about 8 h. The aqueous solution was allowed to cool to room temperature and was then filtrated. A solution of L (72.8 mg, 0.20 mmol) in methanol (10 mL) was added to the aqueous solution at room temperature. After one week, colorless block crystals suitable for X-ray analysis were obtained. Yield: 68% based on L. Anal. Calcd for C21H29N9O7Zn (584.92): C 43.12; H 5.00; N 21.55%. Found: C 43.01; H 5.13; N 21.45%. IR (KBr pellet, cm1): 3426br, 3118w, 1611s, 1524s, 1248 m, 1369s, 1276 m, 1132s, 1010w, 996 m, 884w, 676s, 641w. {[Zn3(L)2(fum)3(H2O)6] (H2O)2}n (8). ZnO (16.4 mg, 0.20 mmol) and fumaric acid (HO2CCHCHCO2H) (23.2 mg, 0.20 mmol) were suspended in 10 mL aqueous solution, and the mixture was refluxed and stirred for about 8 h. The aqueous solution was filtrated and cooled to room temperature. A solution of L (18.2 mg, 0.05 mmol) in methanol (10 mL) was added to the aqueous solution at room temperature. Two weeks later, colorless rod-like crystals suitable for X-ray analysis were obtained. Yield: 72% based on L. Anal. Calcd for C48H64O20N18Zn3 (FW. 1409.28): C 40.91; H 4.58; N 17.89%. Found: C 41.02; H 4.42; N 17.93%. IR (KBr pellet, cm1): 3419br, 3134w, 1576s, 1452w, 1379s, 1281 m, 1207 m, 1134s, 1010 m, 988 m, 884w, 805 m, 674s, 641 m. Reversible H2O Breathe Properties. Reversible water breathe properties were investigated for samples after full vacuum dehydration at different temperatures overnight, respectively. A crystal of 8 (∼500 mg) went through full vacuum dehydration from 40 to 150 °C. The dried sample was immersed in water and refluxed for 12 h. The sample was filtrated off and washed with water and methanol. Guest Encapsulation. Guest encapsulations were investigated for samples after vacuum dehydration at 50 °C overnight. 500 mg of curcumin was dissolved in 10 mL of acetone. 8 (∼300 mg) was then added to the filtrate and the mixture was allowed to stand at room temperature for a week with occasional shaking or stirring. The sample was filtrated off and washed with acetone. The other encapsulation test was carried out in a similar procedure as the encapsulation of curcumin, except diphenylcarbonohydrazide (250 mg) in acetone or phenylfluorone (500 mg) in ethanol was used instead of curcumin acetone solution. From weight gains, the encapsulations were estimated. {(C21H20O6)0.2 ⊂ [Zn3(L)2(fum)3(H2O)6]}n: Anal. Calcd.: C, 43.33; H, 4.46; N, 17.42. Found: C, 43.12; H, 4.54; N, 17.21; {(C13H14N4O)0.4 ⊂[Zn3(L)2(fum)3(H2O)6]}n: Anal. Calcd.: C, 43.46; H, 4.50; N, 18.67. Found: C, 43.27; H, 4.82; N, 18.45. {(C19H11O5)0.36 ⊂ [Zn3(L)2(fum)3(H2O)6]}n: Anal. Calcd.: C, 44.32; H, 4.33; N, 16.90. Found: C, 44.07; H, 4.74; N, 16.72. Catalytic Oxidation. To 100 mL of 1.00 103 M diphenylcarbonohydrazide ethanol solution was added 30% H2O2 (1.0 mL, ∼100 equiv of diphenylcarbonohydrazide). To this solution was added 100 mg of 8 then stirred vigorously. Five milliliters of the reaction mixture was filtrated after some time. The filtrate was transferred to a 1 cm curvette to measure UVvis spectra from 200900 nm on a Pgeneral TU-1900 UVvis spectrometer (stray light < 0.01%, wavelength accuracy ( 0.3 nm). Reference solution was ethanol or solution without 8. X-ray Crystallographic Study. Well-shaped single crystals of 18 were selected for X-ray diffraction study. Data collections were performed with graphite-monochromatic Mo KR radiation (λ = 0.71073 Å) on a Bruker Smart Apex-II CCD diffractometer at T = 293(2) K. Determinations of the crystal system, orientation matrix, and cell dimensions were performed according to the established procedures. Lorentz polarization and absorption correction were applied. The structures were solved by direct method with SHELXS-97 program24
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Scheme 3. (A) Separation of Complexes 1 and 2 and PXRD Patterns of Pure 1 and 2 and Mixture of 1 and 2. Mixture of 1 and 2 (a), 1 simulated pattern (b), pure 1 (c), 2 simulated (d), and pure 2 (e). (B) Photo of the separation vial.
and refined by full-matrix least-squares on F2 with SHELXL-97 program.25 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located and included at their ideal position if possible. The crystal data and structure refinement results are summarized in Table 1. The selected bond distances and angles are presented in Table s1, Supporting Information. The hydrogen bond distances and angles are provided in Table s2, Supporting Information.
’ RESULTS AND DISCUSSION Syntheses of Complexes. Reaction of flexible triazole ligand L with CoCl2 in a 1:1 molar ratio in aqueousmethanol solvent afforded two complexes {[Co3(L)2(H2O)6Cl6] 3 4H2O}n (1) and {[Co(L)2Cl2] 3 13H2O}n (2), whose Co/L ratio totally differed from the reaction mixture. Complex 1 (the ratio of Co:L is 3:2) crystallized earlier than that of complex 2 (the ratio of Co:L is 1:2). It is reasonable to think that that crystallization of 1 will increase the M:L ratio in solution, inducing the crystallization of 2. The crystal densities of 1 and 2 are different, so they can be well separated by suitable density liquid that has no interaction with the complex (Scheme 3). Similarly, 3 and 4 can be obtained and separated (Scheme 4). Reaction of a stoichiometric amount of metal ion and L (as the formula) can synthesize a specific complex much more efficiently (Supporting Information). To compare anion effects, the corresponding nitrate salt was used to synthesize coordination polymers. Zn(II) or Cu(II) did not influence the composition of their complexes. Thus, 1 and 3, 2 and 4 have very similar or identical formulas except a metal ion difference. However, different anions significantly affect the coordination sphere of its coordination compound, such as 2, 4, 5, and 6. From the formulas, noncoordinating anions essentially do not influence the coordination sphere (framework). To avoid a noncoordinating anion that may block framework cavity, coordinating malonic acid and fumaric acid were used to react with ZnO, the product reacted with L giving 7 and 8, respectively. In the synthesis of 8, excess Zn(II) and fumaric acid were used to avoid a possible bidentate L complex. The reaction and formation of the complexes are schematically shown in Scheme 2. Description of Crystal Structures of {[Co3(L)2(H2O)6Cl6] 3 4H2O}n (1) and {[Cu3(L)2(H2O)6Cl6] 3 4H2O}n (3). Complexes 1 and 2, 3 and 4 were obtained simultaneously through the 3004
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Crystal Growth & Design Scheme 4. (A) Separation and PXRD patterns of 3 and 4. Mixtures of 3 and 4 (a), 3 simulated (b), 3 experimental (c), 4 simulated (d), and 4 experimental (e). (B) Photo of a separation via.l
reaction of L with CoCl2 or CuCl2 in aqueousmethanol solution. During preparation of this manuscript, similar complexes [Co3(L)2(H2O)6Cl6] 3 3H2O22c and {[Cu3(L)2(H2O)6Cl6] 3 3H2O}n,22a both one crystalline water less than in our complex 1 and 3, prepared from aqueousethanol were reported. The structures of 1 and 3 (Figures s1 and s2, Supporting Information) and [Co3(L)2(H2O)6Cl6] 3H2O 22c and {[Cu3(L)2(H2O)6Cl6] 3H2O}n 22a are quite similar and will not be discussed here. Description of Crystal Structures {[Co(L)2Cl2] 3 13H2O}n (2), {[Cu(L)2Cl2] 3 12H2O}n (4). Similar to that of complexes 1 and 3, complexes 2 and 4 are isomorphous with almost identical composition except for the different metal ions. Complex 2 had one more crystalline water molecule than that of 4. Their coordination environments are identical except for bond-lengths that differed slightly. The metal-to-ligand ratios were 2:1 and 1:2 in 1, 3 and 2, 4, respectively. Decreasing the metal-to-ligand ratio eliminated coordination water molecules in 2 and 4 because of sufficient donors from the ligand. The crystal structure of 2 is shown in Figure 1a with the atom numbering scheme. Complex 2 crystallized in the triclinic form with P1 space group with metal ion in the inversion center. Each asymmetric unit of 2 contained one Co(II) center, one L, and one chloride anion. Different from that in 1 and 3, L in 2 and 4 was bidentately bound to two Co(II) ions rather than tridentate L that bonded to three Co(II) in 1 and 3. The cobalt(II) atom lying on an inversion center is six coordinated by four N atoms from four individual L ligands with NCoN bond angles in the range of 87.27(16)180.0° and CoN bond distances of 2.147(4) and 2.151(4) Å. Two additional positions were occupied by two Cl atoms with a CoCl bond distance of 2.120(4) Å (Table s1, Supporting Information). CoN distances were comparable to that in 1, but the CoCl distance was obviously shorter than that in 1. CoCl was the longest distance around the coordination center in 1, while in 2, CoCl comprised the shortest distances in all coordination bonds. L in 2 and 4 adopted a cis-conformation (Figure 1b). The distances between the N1, N6, N9 atoms and the central benzene ring plane were 2.60, 3.43, and 3.27 Å, respectively. The noncoordinating N6 was further away from the central benzene ring compared to the coordinating triazole nitrogen atoms. The dihedral angles between each triazole group and the central
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benzene ring plane were 87.99°, 86.37°, and 85.48°, respectively. Two triazole nitrogen atoms, N1 and N9 coordinated to Co(II). The third triazole group containing N6 did not participate in the coordination. Two ligands linked two metal atoms using their two flexible arms to generate an infinite 1D hinged neutral chain containing 24-membered M2L2 macrocycle (Figure 1b). The Co 3 3 3 Co distance within the M2L2 ring was 11.16 Å, which was significantly longer than the Co 3 3 3 Co distances of 7.20 Å in 1. The two benzene rings from two opposite ligands L within the M2L2 macrocyclic ring adopted a face-to-face orientation and are parallel to each other with a centroidcentroid distance of 10.52 Å as illustrated in Figure 1b. Figure 1c is the packing diagram viewed from the b-axis. Crystalline water molecules filled in the channel as shown in Figure 1c. Clearly, all water molecules were away from the hydrophobic ligand and located in the voids formed between two adjacent layers. It was the H-bond that held the water molecule in the void channel. The linkage of crystalline water molecules are shown in Figure 1d. All 13 water molecules link together via H-bond with O 3 3 3 O distances of 2.833.06 Å. O3, O4, and O6 form three H-bonds, and all others form two H-bonds. These hydrogen bonds as tabulated in Table s2, Supporting Information. From Figure 1d, all the H-bonds are very weak from their bond distances. Water molecules were easily lost and have large isotropic displacement parameters. This accounts for the comparative larger R value. The CuN and CuCl distances in 4 were obviously shorter than corresponding CoN and CoCl distances in 2. Accordingly, the Cu 3 3 3 Cu distances in the coordinate chain were 11.0829(5) Å. Description of Crystal Structures {[Zn(L)2(H2O)2](NO3)2 3 4H2O}n (5). In 1, 2, 3, and 4, the anion was a chloride which is coordinated to a central metal ion. To investigate the anion’s effect, a noncoordinating anion was used to synthesize coordination polymers. Using the reaction of L and Zn(NO3)2 3 6H2O, instead of CuCl2 3 2H2O and CoCl2 3 2H2O, under the same reaction conditions, new complex 5 was successfully prepared. Cobalt(II) complex with an identical composition was reported recently. X-ray crystallographic analysis revealed that 5 crystallized in the monoclinic form with space group P21/n. The coordination environment around the cobalt atom in complex 5 is exhibited in Figure 2a. The asymmetric unit of 5 contained one zinc(II) center sitting on an inversion center with one L and one nitrate anion. Each Zn(II) was coordinated by four N atoms from four different ligands L with a NZnN bond angle from 87.45(14)° to 180.0° and ZnN bond distances of 2.148(3) and 2.172(3) Å (Table s1, Supporting Information). Two additional positions were occupied by two O (water) atoms with a ZnO bond distance of 2.126(3) Å, which were comparable to those of reported Co(II) complexes. Therefore, the local coordination geometry around Zn(II) in 5 can be regarded as compressed octahedron with an N4O2 donor set, which was somewhat similar to coordination geometry in 2 but with a N4O2 rather than a N4Cl2 chromophore. The compositions in 5 were somewhat similar to that in 2 due to an identical metal to ligand ratio. There were coordinating water molecules in 5, which were different from the coordinating chloride in 2 and 4. Similar to that in 2 and 4, L in 5 served as a bidentate ligand connecting two Zn centers. However, the conformation of the ligand in 5 is different from that in 2 and 4. L in 5 was in trans configuration (Figure 2a). The two coordinating triazoles were trans relative to each other. N6 was free and cis to N3-containing triazole. The distances between benzene centroid and N3, N9, and N6 are 2.61, 2.64, and 2.78 Å, 3005
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Figure 3. (a) Coordination environment of zinc(II) in 6; hydrogen atoms were omitted for clarity. (b) The 2D layer formed by LZn with 48membered metallacycles in 6. (c) Crystal packing diagram viewed from the b-axis, different layers are presented with different colors. The green atom is fluoride. Symmetry codes: #1 x þ 1/2, y þ 3/2, z 1/2; #2 x þ 1/2, y 1/2, z þ 1/2; #3 x þ 1, y þ 1, z.
respectively. The noncoordinating N6 was further away from the central benzene ring compared with two coordinating N3 and N9 atoms. The dihedral angles between each of three triazole groups and the central benzene ring plane were 95.89°, 69.80°, and 110.2°, respectively. As shown in Figure 2b, each L coordinated to two Zn(II) atoms to give a 48-membered M4L4 macrocycle through the ZnN coordination interactions. In each Zn4 grid, the lengths of the edges were identical; namely, the distances between two adjacent Zn(II) atoms were all 12.13 Å, which was significantly longer than that in complexes 2 and 4. These can be explained by the trans conformation of the coordinating triazole groups rather than cis triazole in 2 and 4. The diagonals of the rhombus are 16.38 and 17.91 Å (the internal angles of the rhombus were 84.89 and 95.11°, Figure 2b). The layers were stacked along the b-axis (Figure 2c) with interlayer OH 3 3 3 O (2.642.85 Å) and CH 3 3 3 O(2.883.45 Å) hydrogen bonding interactions leading to the formation of a 3D network. The lattice water molecules and uncoordinated nitrate anions were located in the voids between two adjacent layers. (O1w 3 3 3 O2w 3 3 3 O3w 3 3 3 O2N10O3 3 3 3 )n infinite H-bond chains were linked by Zn1 via Zn1O1w coordination bond (Figure 2d). The hydrogen bonding data are summarized in Table s2, Supporting Information. Description of Crystal Structures {[Zn(L)2(H2O)2](PF6)2 3 6H2O}n (6). When NH4PF6 was added to the above reaction in the synthesis of 5, a 2D double layered 6 was obtained. Its composition was similar to that of 5 except for two more crystalline water molecules. The X-ray crystallographic analysis indicates that 6 crystallized in the monoclinic space group. Figure 3a illustrates the crystal structure of 6 with an atom numbering scheme. The coordination geometry around Zn in 6 was similar to that in 5. Each Zn(II) atom showed an octahedral geometry and was also coordinated by four triazole N atoms from
four different L and two O atoms from two water molecules. The bond lengths of ZnN1 and Zn;N6 bond lengths were almost identical (2.142(4) and 2.139(4) Å, respectively), while in 5, the two ZnN distances clearly differed (2.148(3) and 2.172(3) Å respectively). The two apical positions were occupied by two water molecules with a ZnO1W bond distance of 2.149(4) Å, which was obviously longer than that in 5 (2.126(3) Å). Although L acted as a bidentate ligand, which was the same as that in 5, its configuration in 6 was in cis-configuration, not the trans-configuration in 5. The distances between the N1, N6, and N9 atoms and the central benzene ring plane were 2.94, 2.58, and 2.62 Å, respectively. The dihedral angles between each of three triazole groups and the central benzene ring plane were 85.89, 73.61, and 77.72°, respectively. All these data are similar to that in 5. In the Zn4 rhombus, the lengths of the edges were all 13.04 Å and slightly longer than that in 5. The diagonals of the rhombus were 14.56 and 21.65 Å. The internal angles of the rhombus were 67.82 and 112.18° and are significantly different from that in 5 (almost square). The crystal packing diagram is present in Figure 3c. In complex 6, the uncoordinated PF6 anions were located in the voids between two adjacent layers and held there by OH 3 3 3 F hydrogen bonds to give a 3D network (Figure s3, Table s2, Supporting Information). Description of Crystal Structures {[ZnL(mal)] 3 3H2O}n (7). In all the above complexes, anions were noncoordinating NO3, PF6, or monodentate Cl. All complexes were 1D or 2D coordination polymers. To synthesize higher dimensional coordination polymer, bridging malonate was used and complex 7 was successfully obtained. X-ray crystallographic analysis revealed that 7 crystallized in the monoclinic form with space group C2/c. The coordination environment around the zinc(II) center is shown in Figure 4a. The zinc(II) atom was five 3006
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Figure 4. (a) Coordination environment of zinc(II) in 7; hydrogen atoms were omitted for clarity. (b) Structure of the 2D coordination polymer. Malonate links Zn in the b-direction in helix, and L links Zn in c-direction. (c) Crystal packing diagram viewed from the b-axis. Symmetry codes: #1 x, y, z þ 1/2; #2 x þ 1/2, y þ 1/2, z þ 1/2.
coordinated by two N atoms (N1, N4) from two different ligands with ZnN bond lengths of 2.020(3) and 2.026(4) Å, and two O atoms (O3, O4) from a malonate with ZnO bond lengths of 2.429(7), 2.059(6) Å. The fifth positions were occupied by one O atom (O1) from another malonate with ZnO bond distance of 1.961(3) Å. The monodentate carboxylate oxygen had the shortest OZn distances, while the chelate carboxylate had longest bond distances. The bond angles around Zn were in the range of 53.6(2)131.3(2)° (Table s1, Supporting Information). The τ for the five-coordinate Zn(II) is 0.025, indicating that Zn(II) is squarepyramidal environment with a N2O3 donor set. L adopted trans-conformation in 7 as shown in Figure 4a. Of the three triazole groups, only two triazoles, cis to each other, coordinated to the Zn(II) ion. The N9 atom was not coordinated to Zn(II). The distances between the center of the benzene ring and N1, N4, and N9 were 3.27, 2.93, and 3.01 Å, respectively. The dihedral angles between each of three triazole groups and the central benzene ring plane were 82.10°, 77.82°, and 80.16°, respectively. Each L acted as a bidentate ligand bridges Zn(II) from the c-direction. Malonate anion linked Zn(II) from the bdirection. It is worthy to mention that the malonate bridged Zn(II) in a left-hand and right-hand helix alternatively as shown in Figure 4b. The 2D polymer packs into 3D as shown in Figure 4c. Description of Crystal Structures {[Zn3(L)2(fum)3(H2O)6] 3 2H2O} (8). Although we attempted to obtain 3D porous coordination polymer by employing coordinating malonate anion, 7 remained a 2D coordination polymer. We tried excess Zn(II) and fumaric acid to avoid a possible bidentate L complex (2D coordination polymer). The X-ray crystallographic analysis provided unambiguous evidence for the porous structure of 8.
Complex 8 crystallized in the triclinic space group P1. Figure 5a shows the structure of 8 in the atom numbering scheme. There were one and a half Zn(II), one and a half fumarate anion, and one L in the asymmetric unit. As illustrated in Figure 5a, both Zn(II) ions were coordinated to two triazole nitrogen, two carboxylate oxygen, and two water oxygen atoms to form octahedron coordination environment with a N2O4 donor set. Zn(1) was located in the inversion center. The Zn1N bond length was 2.123(4) Å. Two O atoms (O5, O5#1) from two distinct fumarates had Zn1O bond lengths of 2.077(3) Å, which were obviously shorter than the Zn1N distance. Additional positions are occupied by two O atoms from two water molecules with a ZnO bond distance of 2.149(3) Å. The bond angles around Zn1 were in the range of 86.42(12)180.0° (Table s1, Supporting Information). The coordination geometry of Zn2 was quite similar to that of Zn1 except for differences in bond lengths. The two triazole nitrogen atoms coordinated to Zn2 at 2.127(3) and 2.151(3) Å, respectively. All other bond lengths were comparable to that around Zn1. Carboxylate oxygen coordinated to Zn much more strongly than that of a water molecule (Table s1, Supporting Information). L in 8 adopted a trans-conformation as shown in Figure 5a. The distances between the N1, N4, and N7 atoms of triazole and the central benzene ring plane were 2.67, 2.96, and 2.63 Å, respectively, and obviously shorter than a cis-tridentate L in 1 (3.27 Å). The dihedral angles between each of three triazole groups and the central benzene ring plane were 87.63°, 69.73°, and 72.98°, respectively. The Zn1 and Zn2 atoms were linked together by L to give an infinite 1D ladder on the bc plane as illustrated in Figure 5b. Zn2 ion was in the ladder edges while Zn1 was in ladder steps. Four L and four Zn(II) formed a 3007
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Figure 5. (a) Coordination environment of zinc(II) atoms in 8; hydrogen atoms are omitted for clarity. (b) 2D coordination polymer viewed from the a-axis. (c) A simplified structure of the 2D coordination polymer. Small triangle represents benzene ring. L links Zn in the bc plane, fumarate links Zn in the a-axis. (d) Packing diagram viewed from the a-axis, each color represents one 2D coordination polymer. Adjacent 2D polymers penetrate each other. The inset is a space-filling diagram. The void channel has a diameter of ∼1.0 nm. Symmetry codes: #1 x þ 1, y þ 1, z þ 1; #2 x þ 1, y, z; #3 x, y 1, z; #4 x þ 2, y þ 1, z þ 1; #5 x, y þ 1, z; #6 x 1, y, z.
46-membered ring with a cavity dimension of 15 19 Å. The nearest Zn 3 3 3 Zn distance was 10.17 Å. Adjacent ZnL ladders were further linked together via furmarate anion in the a-axis as shown in Figure 5c. The asymmetric fumarate (gray stick in Figure 5c) bridged Zn2 via O1 and O3 atoms, while the central symmetric fumarate (red stick in Figure 5c) bridged Zn1 via O5. All the carboxylate groups in both symmetric and asymmetric fumarates adopted monodentate coordination mode. Thus, the complex was a 2D porous structure with void channels of 14.99 19.25 Å as illustrated in Figure 5c. These 2D porous structures penetrated each other from the c-axis (the longer edge of the rhombic cavity) to give a 3D porous structure as shown in Figure 5d. The void of the 3D structure, although much smaller than the 2D structure due to penetration, was still large enough (∼11 Å diameter) to hold small molecules. The solvent accessible volume was 27% estimated by PLATON software. This could also be proved by the calculated density of the crystal. The composition of 7 and 8 was quite similar, but their densities are 1.577 and 1.255 g/cm3, respectively; this is also an indication of large pores existing in 8. In 1, 2, 3, 4, and 6, L adopted cis-conformation. In the case of 5, 7, and 8, L had a trans-conformation. Noncoordinating anion will also influence the geometry of L. 5 had noncoordinating NO3, 6 had noncoordinating PF6, and L adopted trans and cis-configuration in 5 and 6, respectively. The results attest that the flexible tripodal ligand L can adopt different conformations and lead to the formation of a great variety of supramolecular frameworks. Thermal Analysis and Photoluminescence Properties. Thermogravimetric analyses (TGA) were carried out for the synthesized complexes, and the results are shown in Figures s5s12, Supporting Information. For 1, a weight loss of 13.76%
was observed in the temperature range of 90150 °C, which corresponded to the loss of the 10 water molecules (calcd 13.88%). Complex 2 showed a weight loss of 21.22% below 125 °C corresponding to the loss of free water molecules (calcd 21.45%), and the residue was stable up to about 285 °C. Complex 3 showed a weight loss of 13.65% below 135 °C which corresponded to the loss of both the coordinated and uncoordinated water molecules (calcd 13.74%), and the residue is stable up to about 235 °C. A total weight loss of 19.87% was observed for 4 below 150 °C, which was attributed to the release of free water molecules (calcd 20.05%). Decomposition of the residue occurred at 230 °C. Weight loss (10.44%) was found for complexes 5 before the decomposition of the framework at ∼200 °C, which is in good agreement with the release of six water molecules in the crystal structure (calcd 10.54%). A weight loss of 11.72% (calculated 11.74%) below 241 °C indicates the loss of eight water molecules for 6. As a whole, water molecules were lost completely at ∼130 °C. The framework of 1 and 2 remained stable at ∼300 °C, while frameworks of 3 and 4 were only stable up to ∼240 °C. Cu(II) complexes were less thermally stable than that of Co(II) and Zn(II) complexes due to Cu(II) acting as the oxidizing ion. Although 5 and 6 were both Zn(II) complexes, 6 was much more stable than that of 5 because the framework of 6 decomposed at ∼300 °C, whereas 5 decomposed at ∼250 °C with NO3 as the oxidizing anion instead of PF6 . Complex 7 showed a weight loss of 9.18% below 150 °C, which corresponded to the loss of three crystalline water molecules (calcd 9.23%). These three crystalline water molecules were divided into two categories. The first two water molecules were lost under 112 °C, and the remaining one was lost from 112 to 150 °C. The framework remained stable up to 190 °C. The 3008
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Figure 6. IR spectra of different forms of 8: (a) as-synthesized; (b) dried at 40 °C for 12 h; (c) dried at 50 °C for 12 h; (d) dried at 80 °C for 12 h; (e) immersion in reflux water of 50 °C dried sample for 12 h; (f) immersion in reflux water of 80 °C dried sample for 12 h.
weight loss of 7.50% from 190 to 247 °C corresponded to release CO2 from the coordinated malonate (7.52%). Complex 8 exhibited a total weight loss of 10.17% from room temperature to 150 °C, which agreed with the departure of water molecules (calcd 10.22%). The framework was stable in temperature ranges from 150 to 280 °C. The framework started to decompose L from ∼290 °C. The 72.46% weight was lost up to 690 °C, which corresponded to the loss of all ligand L (calcd. 68.17%). The percentage of the remnant was 17.37% corresponding to ZnO (calcd 17.36%). The mixed inorganicorganic hybrid coordination polymers were investigated for fluorescence properties and for potential applications.26 The photoluminescence properties of complexes 58 were studied in the solid state at room temperature. The measurements were carried out under the same experimental conditions and excited at a wavelength of 375 nm. As shown in Figure s20, Supporting Information, the maximum emission wavelength of complexes 58 was at 446 nm, 423 and 443 nm, respectively, which was close to that of the free L (emission maximum at 424 nm upon excitation at 375 nm). The emissions observed in complexes 58 were tentatively assigned to the ππ intra ligand fluorescence due to their close resemblance of the emission bands.27 Reversible De-/Rehydration Behaviors in Complex 8. The IR spectra of complex 8, after drying and rehydration at different temperatures, are shown in Figure 6. The 3406 cm;1 of hydrogen bond in complex 8 then became narrow and shifted to 3421, 3425, and 3432 cm;1 after drying at 40, 50, to 80 °C respectively. The 3133 cm1 CH vibration of the benzene shifted to a lower wavenumber (3124, 3115, 3119 cm;1) up on vacuum drying. The CdO asymmetric stretching vibration (1573 cm1) absorption band in 8 shifted to higher wavenumber (1583, 1590, 1597 cm1) after desiccation. The CdO symmetric stretching vibration (1374 cm1) remained unchanged below 50 °C but shifted to 1367 cm1 in 80 °C. Immersion of vacuumdried sample in refluxed water for 12 h will fully recovery its IR spectra if the dryness temperature is below 50 °C. IR spectra cannot fully recover if the drying temperature is higher than 80 °C (Figure 6). PXRD patterns are consistent with IR data
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Figure 7. PXRD patterns of 8, dehydrated 8, and rehydrated samples. (a) 8 simulated; (b) 8 experimental; (c) dried at 40 °C; (d) dried at 50 °C; (e) immersion in reflux water of 50 °C dried sample; (f) dried at 80 °C; (g) immersion in reflux water of 80 °C dried sample; (h) dried at 120 °C; (i) immersion in reflux water of 120 °C dried sample.
(Figure 6). The crystal is alive and breathable at 50 °C or below. High temperature will permanently damage the crystallinity of 8. PXRD of complex 8, dehydrated 8, and rehydrated samples indicate the crystallinity may have changed after drying and rehydration (Figure 7). By vacuum-drying 8 at different temperatures for 12 h, the water molecules could be removed in a stepwise fashion, resulting in a series of dehydrated products. The X-ray powder pattern of 8 after removal of the water molecules will gradually lose crystallinity as the temperature increases to 50 °C or higher. To investigate whether the drying and rehydration were reversible, the vacuum-dried samples were immersed in a refluxing aqueous solution for 24 h. The resulting rehydrated complex showed the identical PXRD pattern if the drying temperature is 50 °C or lower. Higher temperature dried sample could also recovery crystallinity, but their PXRD patterns are samewhat different from that of as-synthesized 8 (Figure 7). The most significant change was the presence of a new peak at 9.48°. These data indicate that 8 is a breathable porous coordination polymer. At 50 °C or below, 8 breathes reversibly.
’ GUEST ENCAPSULATION Complex 8 is a porous coordination polymer with lower crystal density and ∼11 Å diameter void channel in the bc plane.28 We hypothesized that 8 was capable of encapsulation of guest molecules with suitable sizes. The guest molecules we chose were curcumin, diphenylcarbonohydrazide, and phenylfluorone (scheme 5) due to their neutral nature. Thus, we could easily identify whether the encapsulation takes place simply by observing sample color changes. As shown in Figure 8, colorless 8 became colored after a week-long soak in diphenylcarbonohydrazide, curcumin, or phenylfluorone solution. Of the three guest molecules, curcumin is the longest with a length of 17.2 Å, while phenylfluorone is the shortest but widest with a dimension of 9.79 7.05, and diphenylcarbonohydrazide is in the middle. All these molecules can fit in 11 15 Å void channel in 8. From weight gains and elemental analysis, {(curcumin)0.2 ⊂ [Zn3(L)2(fum)3(H2O)6]}n {(diphenylcarbonohydrazide)0.4⊂ [Zn3(L)2(fum)3(H2O)6]}n and {(phenylfluorone)0.36⊂ [Zn3(L)2(fum)3(H2O)6]}n were formed. 3009
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Scheme 5. Structure of the Guest Molecules
Figure 10. Fluorescence spectra of L, 8 before and 8 after guest encapsulation in solid state at room temperature. (a) L: EX = 375 nm; (b) 8: EX = 375 nm; (c) curcumin: EX = 375 nm. (d) curcumin encapsulated 8: EX = 375 nm; (e) diphenylcarbonohydrazide encapsulated 8: EX= 361 nm; (f) diphenylcarbonohydrazide: EX = 360 nm; (g) phenylfluorone: EX = 361 nm; (h) phenylfluorone encapsulated 8: EX = 360 nm.
Figure 8. Guest encapsulation of 8.
Figure 9. IR spectra of 8 before and after guest encapsulation. (a) Before encapsulation; (b) curcumin soaked; (c) diphenylcarbonohydrazide soaked; (d) phenylfluorone soaked.
Figure 9 is the IR spectra of complex 8 before and after guest encapsulation. After soaking 8 in curcumin ethanol solution for a week, the 3406, 1573, 1374 cm1 peak in 8 shifted to a higher wave number slightly. A new peak appeared 1708 cm1, which could be assigned CdO vibration of curcumin. Similarly, the
1709 cm1 peak after diphenylcarbonohydrazide encapsulation was attributed to the CdO vibration of encapsulated diphenylcarbonohydrazide/diphenylcarbazone.29 A coniderable IR shift took place after the encapsulation of phenylfluorone. Phenylfluorone can form a Zn(II) complex in basic aqueous solution; the 1621, 1486, 1295, 1178, 834, 580 cm1 peaks indicate that phenylfluorone interacted with 8 strongly. Although phenylfluorone encapsulation significantly changed the IR and Raman spectra of 8 (Figure s18, Supporting Information), its crystallinity kept well as indicated by the PXRD pattern (Figure s19, Supporting Information). Guest encapsulations did not change the framework size. It worthy to mention that diphenylcarbonohydrazide was colorless. The encapsulation process gradually altered the color of the solution and solid complex. We noticed that the color change occurred much faster in the presence than in the absence of 8. L and 8 have luminescence at 424 and 443 nm, respectively, upon excitation at 375 nm. Curcumin and encapsulated 8 had 567 and 539 nm, respectively (Figure 10). Compared with free curcumin, encapsulated curcumin luminescent shifted to shorter a wavelength ∼28 nm. This indicates that guest curcumin had interacted with the framework of 8. Diphenylcarbonohydrazide and encapsulated diphenylcarbonohydrazide had luminescence at ∼421 nm after being excited at 360 nm. The luminescent of diphenylcarbonohydrazide or encapsulated sample was very weak if excited at 375 nm. Phenylfluorone and encapsulated phenylfluorone both had luminescence at ∼465 nm. Free phenylfluorone had 387 nm emissions but encapsulated phenylfluorone had 404 nm emissions when excited at 360 nm. These emission spectra indicate that guest molecules were encapsulated by the framework of 8. Catalytic Oxidation of Diphenylcarbonohydrazide in the Presence of Complex 8. As mentioned above, diphenylcarbonohydrazide was colorless. Its acetone solution gradually changed to red in the presence of 8 during the encapsulation process. It is well known that colorless diphenylcarbonohydrazide can be oxidized into red diphenylcarbazone.30 The encapsulated guest 3010
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frameworks. Malonate or fumarate can bridge LZn into 2D coordination polymer. The fumarate bridged complex 8 has cavities that can encapsulate curcumin, diphenylcarbonohydrazide, and phenylfluorone without changing its crystallinity but may change its IR and Raman significantly. 8 can reversibly dehydrate/hydrate depending on temperature. 8 can also catalyze the oxidation of colorless diphenylcarbonohydrazide into red diphenylcarbazone in ethanol solution in an effective and environmental friendly manner.
’ ASSOCIATED CONTENT Supporting Information. X-ray crystallographic file in CIF format, the TG and DSC curves of complexes 18 (Figures S1S9), XRPD patterns of the complexes 18 (Figure S10S17), crystal packing diagrams for complexes 18 (Figures S18S25), important bond distances (Å) and angles (°) (Table s1), hydrogen bonding data for 18 (Table s2). This material is available free of charge via the Internet at http://pubs. acs.org.
bS
Figure 11. UVvis spectra of 1.0 103 M diphenylcarbonohydrazide 0.10 M H2O2 ethanol solution in the presence of 0.1 g of complex 8 at 25 °C (identical solution without 8 as a reference).
molecule in diphenylcarbonohydrazide acetone solution was actually its oxidized form, that is, diphenylcarbazone. To study the catalytic effect of 8, we used ethanol to measure UVvis spectra in a wide range, although solvents may have a great influence on the oxidation process. The spectra change of 1.0 103 M diphenylcarbonohydrazide ethanol solution in the presence of 0.1 M H2O2 at 25 °C is shown in Figure s22, Supporting Information. Its 333 nm absorbance increased continuously (against diphenylcarbonohydrazide without H2O2), while 535 nm absorbance increased slightly in the first 10 min, then continually decreased to insignificant levels (absorbance change less than 0.1). As a whole, the 535 nm absorbance was insignificant within 3 h in the absence of 8. In the presence of 8, the 522 nm absorbance increased monotone (against diphenylcarbonohydrazideH2O2 without 8) (Figure 11). The absorbance increased to 2.5 or higher and were completed within 2 h. The 522 nm absorbance was attributed to diphenylcarbazone or its complexes.31 From the absorbance at 522 nm, the oxidation to diphenylcarbazone was in very high yield. Clearly, 8 catalyzed the oxidation of diphenylcarbonohydrazide to diphenylcarbazone effectively. 8 remained white after catalytic oxidation, which indicates that there was no observable encapsulation at this concentration level. Encapsulation takes place at high guest concentration. This method is much more convenient than any of the reported procedures for the synthesis of diphenylcarbazone.30a,32 The oxidation process is facile, efficient, and environmentally friendly. The catalytic effect was possibly due to the cavity’s ability to fix/ encapsulate diphenylcarbonohydrazide and provide a microenvironment suitable for H2O2 oxidation.
’ CONCLUSIONS Eight novel coordination polymers have been synthesized by reactions of the flexible tripodal ligand L and corresponding metal salts. Their structure was approved by elemental analysis, IR, TG, and crystal structures. The results showed that the ligand-to-metal ion ratio and counterions have an significant effect on the structure of the complexes. The flexible tripodal ligand can adopt different conformations and coordination mode (bidentate/tridentate) to achieve a great variety of supramolecular
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected] (S.Z.), mx_li@staff.shu.edu. cn (M.L.); fax: 86-21-60947570; tel: 86-21-66132403.
’ ACKNOWLEDGMENT The project was supported by the National Natural Science Foundation, China (Grant Nos. 20801035 and 20971084). We also thank Mr. Linhai Zhu (Worcester Polytechnic Institute) for his careful proofreading. ’ REFERENCES (1) (a) Moon, D.; Kang, S.; Park, J.; Lee, K.; John, R. P.; Won, H.; Seong, G. H.; Kim, Y. S.; Kim, G. H.; Rhee, H.; Lah, M. S. J. Am. Chem. Soc. 2006, 128, 3530. (b) Robin, A. Y.; Fromm, K. M. Coord. Chem. Rev. 2006, 250, 2127. (c) Hill, R. J.; Long, D. L.; Champness, N. R.; Hubberstey, P.; Schroder, M. Acc. Chem. Res. 2005, 38, 335. (d) Rosi Nathaniel, L.; Eckert, J.; Eddaoudi, M.; Vodak David, T.; Kim, J.; O’Keeffe, M.; Yaghi Omar, M. Science 2003, 300, 1127. (2) (a) Evans, O. R.; Lin, W. B. Acc. Chem. Res. 2002, 35, 511. (b) Zeng, M. H.; Yao, M. X.; Liang, H.; Zhang, W. X.; Chen, X. M. Angew Chem Int Edit 2007, 46, 1832. (c) Fan, J.; Yee, G. T.; Wang, G.; Hanson, B. E. Inorg. Chem. 2006, 45, 599. (d) Kitagawa, S.; Kitaura, R.; Noro, S.-i. Angew. Chem., Int. Ed. 2004, 43, 2334. (e) Wu, C.-D.; Hu, A.; Zhang, L.; Lin, W. J. Am. Chem. Soc. 2005, 127, 8940. (3) (a) Forster, P. M.; Burbank, A. R.; Livage, C.; Ferey, G.; Cheetham, A. K. Chem Commun 2004, 368. (b) Dong, Y.-B.; Jiang, Y.-Y.; Li, J.; Ma, J.-P.; Liu, F.-L.; Tang, B.; Huang, R.-Q.; Batten, S. R. J. Am. Chem. Soc. 2007, 129, 4520. (4) (a) Wang, S. N.; Xing, H.; Li, Y. Z.; Bai, J. F.; Scheer, M.; Pan, Y.; You, X. Z. Chem Commun 2007, 2293. (b) Park, J.; Hong, S.; Moon, D.; Park, M.; Lee, K.; Kang, S.; Zou, Y.; John, R. P.; Kim, G. H.; Lah, M. S. Inorg. Chem. 2007, 46, 10208. (c) Wang, S. N.; Bai, J. F.; Li, Y. Z.; Pan, Y.; Scheer, M.; You, X. Z. CrystEngComm 2007, 9, 1084. (5) (a) Ohmori, O.; Kawano, M.; Fujita, M. J. Am. Chem. Soc. 2004, 126, 16292. (b) Halder, G. J.; Neville, S. M.; Kepert, C. J. CrystEngComm 2005, 7, 266. (c) Li, M. X.; Miao, Z. X.; Shao, M.; Liang, S. W.; Zhu, S. R. Inorg. Chem. 2008, 47, 4481. (d) Takaoka, K.; Kawano, M.; Ozeki, T.; Fujita, M. Chem. Commun. 2006, 1625. 3011
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