Three-Dimensional Cd (II) Coordination Polymers Based on Semirigid

Aug 29, 2011 - Polymer 1 shows a 3-fold interpenetrating dia array with a 4-connected 66 topology. Polymer 2 features a (3,4)-connected pillar-layered...
10 downloads 0 Views 4MB Size
Download PDF
ARTICLE pubs.acs.org/crystal

Three-Dimensional Cd(II) Coordination Polymers Based on Semirigid Bis(Methylbenzimidazole) and Aromatic Polycarboxylates: Syntheses, Topological Structures and Photoluminescent Properties Chunying Xu, Linke Li, Yinping Wang, Qianqian Guo, Xianjuan Wang, Hongwei Hou,* and Yaoting Fan Department of Chemistry, Zhengzhou University, Zhengzhou, Henan, 450052, People's Republic of China

bS Supporting Information ABSTRACT: To systematically explore the influence of aromatic polycarboxylate coligands on building high-dimensional Cd(II)bmb (1,4-bis(2-methylbenzimidazol-1-ylmethyl) benzene) coordination polymers, we synthesized six coordination polymers, namely {[Cd(bmb)(o-phda)] 3 H2O}n (1), [Cd(bmb)0.5(m-phda)]n (2), [Cd(bmb)(p-phda)]n (3), [Cd(bmb)0.5(oba)]n (4), [Cd(bmb)(bpdc)]n (5), [Cd2(bmb)(bta)(mta)0.5]n (6), (H2phda = phenylenediacetic acid, H2oba =4,40 -oxybis(benzoic acid), H2bpdc = biphenyl-4,40 -dicarboxylic acid, H3bta =1,2,4-benzenetricarboxylic acid, and H2mta = 2-(methoxycabonyl)terephthalic acid) by varying aromatic polycarboxylate coligands. Structural analyses reveal that polymers 16 display diverse 3D frameworks and topologies, in which all of the N-donor ligands bmb exhibit transconformation but with different Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angles. Polymer 1 shows a 3-fold interpenetrating dia array with a 4-connected 66 topology. Polymer 2 features a (3,4)-connected pillar-layered structure with (63)(65 3 8)-ins topology. Polymer 3 is a 4-connected framework with 66-dia topology and two types of meso-helical chains. Polymer 4 possesses a 2-fold interpenetrating 6-connected framework with (412 3 63)-pcu topology. The structure of polymer 5 is a 4-connected 5-fold interpenetrating architecture with 66-dia topology. Interestingly, in 6, part of bta3- anions are converted into a new ligand mta2- via in situ esterification reaction under solvothermal conditions. As a result, polymer 6 exhibits a scarce mixed-ligands framework with two O-donor and one N-donor ligands based on tetranuclear Cd(II) clusters. It is an 8-connected (36 3 418 3 53 3 6)-hex topology. A systematically structural comparison of these polymers indicates that the coordination modes of aromatic polycarboxylates along with the structural characteristics of the semirigid N-donor ligand bmb simultaneously play an important role in constructing the high-dimensional frameworks. Moreover, polymers 16 indicate high thermal stabilities and different photoluminescence behaviors in the solid state.

’ INTRODUCTION The flourishing scopes of crystal engineering have furnished a sound junction between aesthetics of crystalline architectures and their potential functions, of which the ultimate termini is to successfully achieve target materials with tailored structures and physicochemical properties.1 In particular, the design and synthesis of 3-dimensional (3D) coordination polymers represent a quite active area, not only for their potential applications as functional materials, but also for their undisputed beauty, often with more complicated architectures and intriguing topologies than the 2D, 1D, and 0D ones.2 Until now, although a large number of 3D frameworks have been reported, the construction of novel architectures and a systematic research still remain a long-term challenge.3 In order to build these high-dimensional frameworks, the crucial step is to choose multifunctional organic ligands and suitable synthetic strategy. According to our recent research,4 we anticipate that the semirigid N-donor ligand 1,4-bis(2-methylbenzimidazol-1-ylmethyl) benzene (bmb) would be a powerful precursor for the construction of diverse high-dimensional r 2011 American Chemical Society

structures and topologies: (1) the 2-position substituent methyl effectively enhances the donated electrons ability of benzimidazole ring, and makes bmb exhibit strong collaborative coordination ability with organic carboxylate ligands; (2) bmb often shows trans-conformation in the structure, which often plays a role of pillar and/or extension and tends to generate high-dimensional structures; (3) bmb favors the formation of meso-helices, and the character can greatly enrich and beautify multidimensional frameworks. As an important family of multidentate O-donor ligands, organic aromatic polycarboxylate ligands have been proven to be excellent structural constructors due to their various coordination modes to metal ions, which often generate multidimensional networks and interesting topologies.5 In view of a developmental synthesis strategy, the employment of mixed-ligands6 of aromatic polycarboxylates and bmb, would be a feasible method to Received: July 25, 2011 Revised: August 24, 2011 Published: August 29, 2011 4667

dx.doi.org/10.1021/cg200961a | Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design construct 3D coordination frameworks. That is because the combination of different ligands can better satisfy the coordination needs of metal ions and result in greater tenability7 of the resultant 3D features. Moreover, a systematic investigation about the impact of different aromatic polycarboxylates on the multidimensional networks is valuable. Taking all of the above discussion into account, by introducing a series of aromatic polycarboxylate coligands into the Cd(II)bmb synthesis system, six 3D coordination polymers with different structures and topologies, namely {[Cd(bmb)(o-phda)] 3 H2O}n (1), [Cd(bmb)0.5(m-phda)]n (2), [Cd(bmb)(p-phda)]n (3), [Cd(bmb)0.5 (oba)]n (4), [Cd(bmb)(bpdc)]n (5), and [Cd2(bmb)(bta)(mta)0.5]n (6) have been obtained. The crystal structures and topological analyses of these polymers, along with a systematic investigation of the effect of different aromatic polycarboxylates on the ultimate frameworks, will be represented and discussed. In addition, the thermal stabilities and photoluminescence properties of 16 in the solid state have also been investigated below in detail.

’ EXPERIMENTAL SECTION Materials and Physical Measurements. All reagents and solvents were commercially available except for bmb, which was synthesized according to the literature.8 The FT-IR spectra were recorded from KBr pellets in the range of 4004000 cm1 on a Bruker Tensor 27 spectrophotometer. Elemental analyses (C, H, and N) were carried out on a FLASH EA 1112 elemental analyzer. PXRD Patterns were recorded using Cu Kα1 radiation on a PANalytical X’Pert PRO diffractometer. Thermal analyses were performed on a Netzsch STA 449C thermal analyzer from room temperature at a heating rate of 10 °C min1 in air. The luminescence spectra for the powdered solid samples were measured at room temperature on a Hitachi F-4500 Fluorescence Spectrophotometer. The excitation slit, as well as the emission slit were 2.5 nm. Synthesis of {[Cd(bmb)(o-phda)] 3 H2O}n (1). A mixture of Cd(NO3)2 3 4H2O (61.7 mg, 0.2 mmol), bmb (36.6 mg, 0.1 mmol), o-H2phda (38.8 mg, 0.2 mmol), and NaOH (8.0 mg, 0.2 mmol) in 10 mL distilled H2O was sealed in a 25 mL Teflon-lined stainless steel container and heated at 140 °C for 4 days. After the mixture cooled to room temperature at a rate of 5 °C/h, colorless block crystals of 1 were obtained with a yield of 48% (based on Cd). Anal. Calcd for C34H32N4O5Cd (%): C, 59.26; H, 4.68; N, 8.13. Found: C, 59.43; H, 4.66; N, 8.01. IR (KBr, cm1): 3426(m), 3054(w), 1942(w), 1703(m), 1586(s), 1483(m), 1455(w), 1415(m), 1383(s), 1316(w), 1286(w), 1246(m), 1154(w), 1120(m), 1072(w), 1017(m), 988(w), 914(w), 832(s), 742(s), 665(m), 602(m), 505(m), 425(m). Synthesis of [Cd(bmb)0.5(m-phda)]n (2). The same synthetic method as that for 1 was used except that o-H2phda was replaced by m-H2phda (38.8 mg, 0.2 mmol). Yield: 54% (based on Cd). Anal. Calcd for C22H19N2O4Cd (%): C, 54.17; H, 3.93; N, 5.74. Found: C, 53.98; H, 3.79; N, 5.89. IR (KBr, cm1): 3095(w), 3024(m), 2914(m), 1905(w), 1554(s), 1461(m), 1388(s), 1277(m), 1230(w), 1154(w), 1113(w), 1016(m), 984(w), 937(m), 871(m), 802(m), 728(s), 687(w), 608(m), 545(w), 478(w). Synthesis of [Cd(bmb)(p-phda)]n (3). The same synthetic method as that for 1 was used except that o-H2phda was replaced by p-H2phda (38.8 mg, 0.2 mmol). Yield: 62% (based on Cd). Anal. Calcd for C34H30N4O4Cd (%): C, 60.86; H, 4.51; N, 8.35. Found: C, 60.91; H, 4.62; N, 8.39. IR (KBr, cm1): 3056(w), 3020(m), 2968(w), 2929(w), 1917(w), 1577(s), 1553(s), 1510(m), 1453(m), 1382(s), 1286(s), 1227(m), 1159(m), 1088(w), 1013(w), 990(m), 928(m), 859(m), 746(s), 720(m), 665(w), 635(m), 580(m), 469(m), 433(m).

ARTICLE

Synthesis of [Cd(bmb)0.5(oba)]n (4). The same synthetic method as that for 1 was used except that o-H2phda was replaced by H2oba (51.65 mg, 0.2 mmol). Yield: 43% (based on Cd). Anal. Calcd for C26H19N2O5Cd (%): C, 56.59; H, 3.47; N, 5.08. Found: C, 56.32; H, 3.71; N, 5.19. IR (KBr, cm1): 3062(m), 1917(m), 1628(s), 1599(s), 1502(m), 1389(s), 1296(w), 1242(s), 1159(s), 1096(m), 1033(w), 1009(m), 874(m), 858(m), 778(s), 747(s), 691(m), 655(m), 619(m), 566(w), 505(m), 474(w), 435(m). Synthesis of [Cd(bmb)(bpdc)]n (5). The same synthetic method as that for 1 was used except that o-H2phda was replaced by H2bpdc (48.4 mg, 0.2 mmol) and the reaction temperature was 160 °C. Yield: 55% (based on Cd). Anal. Calcd for C38H30N4O4Cd (%): C, 63.47; H, 4.21; N, 7.79. Found: C, 63.32; H, 4.48; N, 7.64. IR (KBr, cm1): 3034(m), 1926(w), 1657(w), 1580(s), 1533(m), 1504(m), 1391(s), 1290(w), 1225(w), 1173(m), 1121(w), 1010(m), 988(m), 918(w), 849(s), 802(w), 762(s), 678(m), 615(w), 516(w), 472(w), 422(m). Synthesis of [Cd2(bmb)(bta)(mta)0.5]n (6). A mixture of Cd(NO3)2 3 4H2O (61.7 mg, 0.2 mmol), bmb (36.6 mg, 0.1 mmol), H3bta (48.8 mg, 0.2 mmol), and NaOH (1.2 mg, 0.3 mmol) in 10 mL mixture of methanol-H2O [1:4 (v/v)] was sealed in a 25 mL Teflon-lined stainless steel container and heated at 160 °C for 4 days. After the mixture cooled to room temperature at a rate of 5 °C/h, colorless block crystals of 6 were obtained with a yield of 47% (based on Cd). Anal. Calcd for C38H28N4O9Cd2 (%): C, 50.18; H, 3.10; N, 6.16. Found: C, 49.97; H, 3.02; N, 6.24. IR (KBr, cm-1): 3056(w), 2931(m), 1901(w), 1615(w), 1560(s), 1511(m), 1475(m), 1453(s), 1386(s), 1288(m), 1221(w), 1158(m), 1138(w), 1014(m), 983(m), 936(m), 864(m), 745(s), 719(m), 666(w), 634(m), 549(w), 435(w). Crystal Data Collection and Refinement. The data of the six polymers were collected on a Rigaku Saturn 724 CCD diffractomer (Mo-Kα, λ = 0.71073 Å) at temperature of 20 ( 1 °C. Absorption corrections were applied by using multiscan program. The data were corrected for Lorentz and polarization effects. The structures were solved by direct methods and refined with a full-matrix least-squares technique based on F2 with the SHELXL-97 crystallographic software package.9 The hydrogen atoms were placed at calculated positions and refined as riding atoms with isotropic displacement parameters. Crystallographic crystal data and structure processing parameters for 16 are summarized in Table 1. Selected bond lengths and bond angles of 16 are listed in Table S1 of the Supporting Information, SI.

’ RESULTS AND DISCUSSION Synthesis of the Polymers. The hydrothermal method can cause a reaction to shift from the kinetic to the thermodynamic domain and it has been extensively explored as an effective and powerful tool in the self-assembly of MOFs, especially for highdimensional frameworks.10 In addition, it is well-known that the Cd(II) ion is able to coordinate simultaneously in solution to both oxygen- and nitrogen-containing ligands. 11 So, Cd(NO3)2 3 4H2O was used in the synthesis of high-dimensional frameworks based on the mixed-ligands of bmb and various aromatic polycarboxylates by hydrothermal method. As a result, 3D polymers 15 were synthesized at hydrothermal temperature of 140 or 160 °C. We adopted a mixture of methanol-H2O [1:4 (v/v)] as solvent, and obtained the crystals of 6, because only precipitate was obtained when using the same synthetic method as that for 5. The presence of methanol results in the esterification of the carboxylate group at the 2-site position of partial bta3-, yielding a new ligand mta2- in situ. The reason is that strong steric hindrance of three carboxylate groups in bta3- leads to more remarkable chemical activity of the carboxylate group at the 2-site position. As evidenced in a review, solvothermal 4668

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design

ARTICLE

Table 1. Crystal Data and Structure Refinement for Complex 16a,b complex no. formula

2

3

4

5

6 C38H28N4O9Cd2

C34H32N4O5Cd

C22H19N2O4Cd

C34H30N4O4Cd

C26H19N2O5Cd

C38H30N4O4Cd

formula mass

689.05

487.81

671.04

551.86

719.08

909.47

temperature [K]

293(2)

293(2)

293(2)

293(2)

293(2)

293(2)

0.71073

0.71073

0.71073

0.71073

0.71073

0.71073

monoclinic

monoclinic

triclinic

monoclinic

monoclinic

monoclinic

wavelength [Å] crystal system

C2

P2(1)/c

P-1

P2(1)/c

C2/c

P2(1)/c

a (Å)

21.421(4)

10.938(2)

9.900(2)

11.941(2)

22.289(4)

13.967(3)

b (Å) c (Å)

11.107(2) 15.888(3)

20.601(4) 8.6455(17)

10.868(2) 15.037(3)

13.800(3) 14.351(3)

9.918(2) 17.866(4)

15.100(3) 17.078(3)

space group

α(°)

90.00

90.00

90.00(3)

90.00

90.00

90.00

β(°)

126.51(3)

99.75(3)

102.16(3)

97.81(3)

123.07(3)

105.38(3)

90.00

90.00

109.35(3)

90.00

90.00

90.00

3038.3(10)

1920.0(7)

1488.0(5)

2343.0(8)

3309.7(12)

3472.8(12)

γ(°) V (Å3) Z Dcalcd.(g 3 cm3)

μ (mm1) F(000)

a

1

4

4

2

4

4

2

1.502

1.688

1.498

1.564

1.443

1.739

0.768 1400

1.170 980

0.779 684

0.972 1108

0.706 1464

1.288 1806 2.0325.00

θ (°)

2.1825.00

2.1324.99

2.3425.00

2.2729.16

2.1825.00

GOF

1.062

1.074

1.050

1.076

1.078

1.064

R1 (I > 2sigma(I))

0.0648

0.0378

0.0390

0.0499

0.0393

0.0512

wR2 (I > 2sigma(I))

0.1620

0.0813

0.0901

0.0864

0.0947

0.1066

R1 = ∑||Fo|  |Fc||/∑|Fo|. b wR2 = [∑w(Fo2 Fc2)2/∑w(Fo2)2]1/2.

reactions, compared with routine synthetic methods, create more chances for in situ reaction owing to their relatively critical conditions.12 Therefore, the high temperature, pressure, and long time reactions facilitate the in situ synthesis of mta2- in 6. To our knowledge, the in situ generated mta2- is, for the first time, derived from 1,2,4-H3bta under solvothermal conditions, though it has been reported to synthesize H2mta directly.13 Crystal Structure of {[Cd(bmb)(o-phda)] 3 H2O}n (1). Single crystal X-ray diffraction analysis shows that the asymmetric unit of 1 consists of two half of Cd(II) ions lying on a mirror plane, one bmb ligand, one o-phda2- anion, and one guest water molecule. As depicted in Figure 1a, the Cd1 ion possesses a distorted octahedral geometry which is completed by two oxygen atoms (O1, O1A) from two symmetry-related carboxylate groups and two nitrogen atoms (N1, N1A) from two bmb composing the equatorial plane, and two oxygen atoms (O2, O2A) from two carboxylate groups at the apical positions. The coordination configuration of Cd2 ion is the same to that of Cd1, and completed by two oxygen atoms (O3, O3A) and two nitrogen atoms (N4A, N4B) composing the equatorial plane as well as two oxygen atoms (O4, O4A) at the axial sites. The CdN bond lengths vary from 2.273(6) to 2.31(6) Å, while the CdO bond lengths are from 2.242(6) to 2.576(10) Å, which are in the normal range.14Semirigid bmb adopts asymmetric trans-conformation with two different Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angles of 103.494° and 109.636°. Ligand o-pda2- also adopts asymmetric transconformation, and the angles of two CH2 are 111.431° and 118.065°. In 1, every two bmb and two o-phda2- with bidentate chelating carboxylate groups are linked by adjacent Cd(II) ions to form left- and right-handed helices (Figure 1b). Both the helical pitches are 21.421(4) Å corresponding to the length of a-axis. As shown in Figure 1c, the extension of the structure into a 3D framework is accomplished by the alternate arrangement of

right- and left-handed helical microchannels. A further analysis indicates that it is a typical diamondoid framework containing large cages, which are elongated significantly in one direction, and exhibit maximum dimensions of 33.321  25.664  21.421 Å (corresponding to the longest intracage Cd 3 3 3 Cd distances). The potential voids are filled via mutual interpenetration of the other two independent equivalent diamondoid frameworks in a normal mode, giving rise to a 3-fold interpenetrating dia array (Figure 1d). If Cd1 and Cd2 are simplified as 4-connected nodes, and the ligands are defined as linkers, then the 3D framework of 1 can be described as a 4-connected 66 topology. Crystal Structure of [Cd(bmb)0.5(m-phda)]n (2). Singlecrystal X-ray structural analysis reveals that 2 is a 3D pillarlayered framework. As shown in Figure 2a, the Cd(II) ion adopts a distorted octahedral geometry via coordinating with four oxygen atoms (O1, O2, O1A, O4A) from three m-phda2- anions in the equatorial plane and one oxygen atom (O3A) from m-phda2- anion as well as one nitrogen atom (N1) from bmb at the axial sites. The bond lengths of CdO and CdN are similar to those in other cadmium coordinated complexes.14 In 2, two carboxylate groups of m-phda2- adopt different coordination modes: one carboxylate group adopts bidentate chelating mode and the other adopts μ2-η1: η2-bridging mode. The m-phda2anion acts as μ3-bridge linking Cd(II) ions to produce a 2D puckered sheet (Figure 2b). Ligand bmb adopts a symmetrical trans-conformation with the Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angle of 68.315°, which supports the 2D Cd(II)/m-phda2- sheets to generate a 3D pillar-layered framework. The Cd 3 3 3 Cd distance across bmb is 14.212 Å. Furthermore, topological analysis is carried out to get insight of the structure of 2. If Cd(II) ion is simplified as a 4-connected node, and the m-phda2- ligand is defined as a 3-connected node, respectively, the 3D framework of 2 can be described as a binodal (3,4)-connected ins topology with point symbol of (63)(65 3 8) (Figure 2c). 4669

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design

ARTICLE

Figure 1. (a) Coordination environment of Cd(II) ion in 1 with hydrogen atoms and free water molecule omitted for clarity. (b) The Cd(II)/bmb/ o-phda2- left- and right-handed helical chains along the a-axis. (c) View of the 3D puckered grid accomplished by connecting four linear ligands (two bmb and two o-phda2-) to two kinds of Cd(II) ions (teal: Cd1; violet: Cd2). (d) The 3-fold interpenetrating 4-connected 66-dia topology.

Crystal Structure of [Cd(bmb)(p-phda)]n (3). In 3, the coordination environment around the Cd(II) center is best portrayed as a distorted [CdN2O4] octahedral geometry, ligated by two oxygen atoms (O1, O4) from two different p-phda2anions at the axial sites and two nitrogen atoms (N1, N3) from two distinct bmb as well as two oxygen atoms (O2, O3) from two different p-phda2- in the equatorial plane (Figure 3a). The bond lengths are Cd(1)O(1) = 2.265(3), Cd(1)O(4) = 2.391(3), Cd(1)O(2) = 2.499(3), Cd(1)O(3) = 2.306(3), Cd(1) N(1) = 2.292(3) and Cd(1)N(3) = 2.319(3) Å. There are two kinds of independent bmb, both of which exhibit symmetrical trans-conformation with Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angles of 94.556° and 113.718°, respectively. The two types of bmb act as bidentate mode to bridge two adjacent Cd(II) ions alternately resulting in a “lemniscate” shape pseudo meso-helix along the c-axis (Figure 3b). The Cd 3 3 3 Cd separations across the bmb bridges are 14.577 (bmb-I) and 15.208 (bmb-II) Å, respectively. There are also two kinds of crystallographically independent p-phda2- with symmetric trans-conformation, in which both the carboxylate groups adopt bidentate chelating mode and the angles of CH2 are 108.091° (p-phda2--I) and 112.758° (p-phda2--II), respectively. Two kinds of p-phda2- anions are connected by Cd(II) ions alternately to form a 1D zigzag chain. Every three p-phda2- anions (two p-phda2--I and one p-phda2--II) and three bmb (two bmb-I and one bmb-II) are connected by Cd(II) ions alternately to give rise to a meso-helical chain with the helical pitch of 9.900 Å along the a-axis (Figure 3c). The interlaced connection of Cd(II)-bmb and Cd(II)/p-phda2chains constructs the 3D framework of 3 by sharing Cd(II) ions.

Figure 2. (a) Coordination environment of Cd(II) ion in 2 with hydrogen atoms omitted for clarity. (b) The m-phda2- anions act as μ3-bridge linking Cd(II) ions to produce a 2D puckered sheet. (c) 3D pillar-layered framework of 2 with binodal (3,4)-connected (63)(65 3 8)ins topology (green: Cd(II); yellow: m-phda2-).

As depicted in Figure 3d, topological analysis is performed on 3. As for each Cd(II) ion, it links two bmb and two p-phda2ligands; hence the Cd(II) ion can be treated as a 4-connector. By sharing Cd(II) ions, simplified Cd(II)-bmb (blue) and Cd(II)/ p-phda2- (red) chains together form a 4-connected 3D framework with 66-dia topology, in which the dia units are distorted. Crystal Structure of [Cd(bmb)0.5(oba)]n (4). Single crystal X-ray diffraction analysis shows that 4 is a 3D 2-fold interpenetration structure. Each Cd(II) ion is coordinated by four oxygen atoms [CdO (average) 2.229 Å] from four oba2- anions at the basal positions and one axial nitrogen atom [CdN = 2.225(3) Å] from bmb to furnish a square pyramidal geometry (Figure 4a). Two carboxylate groups of the “V” shape ligand oba2- both adopt μ2-η1:η1 coordination mode and the dihedral angle between two benzene rings is 62.070°. Each pair of Cd(II) ions is bridged by such four oba2- anions to generate a well-known paddle-wheel binuclear clusters with a Cd 3 3 3 Cd separation of 3.137 Å. The binuclear clusters are further extended by oba2- anions into a 2D net with alternately arranged left- and right-handed helical chains (Figure 4b). Both of the helical pitches are 13.800(3) Å corresponding to the length of b-axis. Ligand bmb adopts symmetric trans-conformation with a Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angle of 58.919°. As shown in Figure 4c, the Cd(II)/oba24670

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design

ARTICLE

Figure 4. (a) Coordination environment of Cd(II) ion in 4 with hydrogen atoms omitted for clarity. (b) View of the 2D Cd(II)/oba2net constructed by alternately left- and right-handed helical chains. (c) Individual 3D architecture constructed by 2D Cd(II)/oba2- layers and bmb pillars (H atoms omitted for clarity). (d) Schematic illustrating the 2-fold interpenetrated 6-connected (412 3 63)-pcu network.

Figure 3. (a) Coordination environment of Cd(II) ion in 3 with hydrogen atoms omitted for clarity. (b) Two types of bmb bridge two adjacent Cd(II) ions alternately to generate a “lemniscate” shape pseudo meso-helix along the c-axis (c) Perspective view (left) and simplified block diagram (right) of Cd(II)/bmb/p-phda2- meso-helices along the a-axis. (d) The 4-connected 66-dia topology (green line: bmb; red line: p-phda2-).

nets with elongate helical microchannels are pillared by bmb into a 3D framework. From a topological perspective, if the [Cd2(CO2)2] dimeric unit is taken as a 6-connected node, and the ligands are considered as linkers, the 3D structure can be classified as a pcu topology with point symbol of 412 3 63. The void space in the single framework is so large that two identical 3D frameworks interpenetrate each other to form a 2-fold interpenetrating architecture (Figure 4d). Crystal Structure of [Cd(bmb)(bpdc)]n (5). The Cd(II) center displays a distorted octahedral geometry (Figure 5a), which is provided by three oxygen atoms (O1, O2, O2A) from two bpdc2- anions and one nitrogen atom (N1) from bmb in the equatorial plane, and one oxygen atom (O1A) fom bpdc2- anions and one nitrogen atom (N1A) from bmb at the axial sites. The CdO bond distances vary from 2.225(3) to 2.436(3) Å, while the CdN bond lengths are 2.393(3) Å. In 5, bmb adopts symmetric trans-conformation with a Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angle of 118.685°. Both carboxylate groups of rigid bpdc2- anions adopt bidentate chelating coordination fashion. Every two bmb and two bpdc2- are in turn connected by Cd(II) ions to form left- and right-handed helical chains. It is notable

Figure 5. (a) Coordination environment of Cd(II) ion in 5 with hydrogen atoms omitted for clarity. (b) Space-filling representation of the 5-folded left- and right-handed helical chains. (c) Single 3D dia net with large rectangle channels. (d) The overall 5-fold interpenetrated construction and 66 topological representation.

that every left- or right-handed helical chain is entangled with other four same helices (Figure 5b). In addition, the overall framework of 5 extends into a 3D diamondoid network with large rectangle channels by connecting four linear ligands to the Cd(II) ions (Figure 5c). The Cd 3 3 3 Cd contact distances through bmb and bpdc2- are 16.131 and 14.926 Å, respectively. The typical diamondoid cage exhibits unusual maximum dimensions 4671

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design

Figure 6. (a) Coordination environment of Cd(II) ions in 6 with hydrogen atoms omitted for clarity. (b) Intricate coordination modes of bta3- and mta2- anions. (c) The tetranuclear Cd(II) building unit (left) and the linkages of the tetranuclear Cd(II) cluster with eight adjacent cores (right). (d) Schematic representation of the eight-connected net framework (green line: bta3-; yellow line: mta2-; plum line: bmb) with (36 3 418 3 53 3 6)-hex topology.

of 49.590  30.074  22.289 Å corresponding to the longest intracage Cd 3 3 3 Cd distances. The large vacancy within the diamondoid cage and relatively slim ligand facilitate the highfold interpenetration.15 In order to minimize the big hollow cavities in 5 and stabilize the overall network, the large cavities within the structure allow interpenetration of four other identical nets to form a 5-fold interpenetrated 3D architecture (Figure 5d). Better insight into such elegant framework can be accessed by the topological method. In 5, the Cd(II) ion acts as a 4-connected node, and the ligands serve as linkers, therefore, the combination of nodes and linkers suggests the 4-connected framework with a point symbol of 66. Crystal Structure of [Cd2(bmb)(bta)(mta)0.5]n (6). The single-crystal X-ray diffraction analysis reveals that polymer 6 crystallizes in the monoclinic system, space group P21/c. The asymmetric unit contains two crystallographically independent Cd(II) ions, one bmb, one completely deprotonated bta3- and half esterified mta2-. As illustrated in Figure 6a, Cd1 adopts a distorted octahedron coordination environment, which is completed by four oxygen atoms from three different bta3- (O2A, O4A, O6A) and one mta2- (O7) located at the equatorial plane, and one oxygen atom (O1A) from bta3- as well as one nitrogen atom (N1) from bmb at the axial positions. Cd2 also takes a distorted octahedron geometry, but completed by four oxygen atoms from two bta3- (O1A, O5, O6) and one mta2- (O8) locked at the equatorial plane, and one oxygen atom(O3A) from bta3- as well as one nitrogen atom (N4) from bmb at the axial positions. The CdO/N bonds lengths vary from 2.184 to 2.600 Å comparable with other Cd(II)-containing complexes.14 The bta3- anion acts as a μ6-bridge linking three Cd1 and three Cd2 ions, in which three carboxylate groups adopt μ2-η1: η1, μ2-η2: η1, μ2-η2: η1 coordination fashions, respectively (Figure 6b). Unusually, except completely deprotonated bta3- anions, part of

ARTICLE

bta3- form a new ligand 2-(methoxycabonyl)terephthalate (mta2-) in the CH3OHH2O medium by the in situ esterification reaction. Both carboxylate groups of the mta2- anion adopt bidentate mode (μ2-η1: η1) coordinating with two Cd1 and two Cd2 ions. Such complicated coordination modes of the two aromatic polycarboxylate ligands lead to the formation of Cd(II) clusters in 6. Eight carboxylate groups from four bta3- and two mta2- associate Cd1, symmetry-related Cd1A (2-x, 1-y, 1-z), Cd2 and symmetry-related Cd2A (2-x, 1-y, 1-z) to give rise to a Cd4(CO2)8 unit (Figure 6a). The four Cd(II) ions in the Cd(II) clusters produce a planar rhombus with the Cd 3 3 3 Cd distances of 3.813 and 4.281 Å. Ligand bmb adopts asymmetric trans-conformation with the dihedral angle between two methylbenzimidazole rings being 10.275° and the Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angles being 97.335° and 51.691°. Every two bmb associate adjacent Cd4(CO2)8 unit together. The Cd4(CO2)8 units are further bridged by four bta3-, two mta2- and four bmb (Figure 6c) to generate a 3D framework. To the best of our konwledge, the mixed-ligands complex of transition metal with two kinds of organic carboxylate ligands is scarcely reported up to now. A better insight into the complicated framework can be achieved by topological approach (Figure 6d). In 6, by means of topological analysis, the fragment of Cd4(CO2)8 unit can be viewed to be node, and bta3-, mta2-, and bmb are all considered as linkers. According to the analysis of above, Cd4(CO2)8 node connects four bta3-, two mta2-, and four bmb to display a eight connectivity, thus resulting in the overall 8-connected hex net. The topological symbol is 36 3 418 3 53 3 6. Among the reported nets based on polynuclear metal clusters, the one with such high connections is rare so far. Effect of Semirigid Bis(Methylbenzimidazole) Ligand. Due to the semirigid character, bmb can show stable cis/transconformation4 and symmetric (with the same Ndonor 3 3 3 N Csp3 3 3 3 Csp3 torsion angles of two methylbenzimidazol arms)/ asymmetric (with different Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angles of two methylbenzimidazol arms) conformations. From the structural descriptions above, it shows asymmetric transconformation in 1 and 6, and symmetric trans-conformation in 25. All of the Ndonor 3 3 3 NCsp3 3 3 3 Csp3 torsion angles are different in 16, which result in different Cd 3 3 3 Cd distances from 12.218 to 16.131 Å. Such variety of trans-conformations make bmb exhibit special coordination ability with metal centers and favor the generation of high dimensional motifs. In addition, freely conformational bmb greatly enriches and beautifies multidimensional frameworks 16. In 1 and 5, bmb and aromatic polycarboxylates together form left- and right-handed helices. In 3, bmb bridges adjacent Cd(II) ions leading to a “lemniscate” shape pseudo meso-helix. At the same time, bmb and p-phda2together generate another kind of meso-helix. bmb acts as pillars in 2 and 4, which makes them show 3D pillar-layered frameworks. In 6, every two bmb associate adjacent Cd4(CO2)8 units together and assist polycarboxylate ligands to form a rare highconnected topology. Apparently, these analyses above forcefully demonstrate that the freely conformational bmb with distinct torsion angles plays an essential role in determining the final 3D frameworks. Effect of Aromatic Polycarboxylate Coligands. Many researchers have demonstrated that the structural diversities of complexes are undoubtedly related to the secondary liganddirected inclusion.16 So, the effect of aromatic polycarboxylate coligands with different constructions, flexibility and multifarious coordination modes on the resultant 3D structures and 4672

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design topologies cannot be neglected. In this work, we first selected three phenylenediacetate (phda2-) isomers with conformationally flexible pendant arms as coligands. Different coordination fashions and angles of two acetate moieties of phda2- generate various structures and topologies in polymers 1-3. In 1, o-pda2adopts asymmetric trans-conformation with two bidentate-chelating carboxylate groups, which act as linkers in 3-fold interpenetrating 4-connected 66-dia topology. In 2, trans-conformational m-pda2- with μ3-bridge fashion acts as a 3-connected node, which leads to the formation of binodal (3,4)-connected (63)(65 3 8)-ins topology. In 3, two carboxylate groups of p-phda2with bidentate-chelating mode locate at the para-position. The character of p-phda2- makes it act as linker and the final framework exhibits a 4-connected 66-dia topology. By introducing long “V” shape ligand H2oba, a 3D 2-fold interpenetrating 6-connected (412 3 63)-pcu network 4 is obtained. oba2- bridges Cd(II) ions to generate well-known paddle-wheel binuclear clusters and the binuclear clusters are further extended by oba2- anions into a 2D net with alternately arranged left- and right-handed helical chains. When H2bpdc with a rigid biphenyl spacer is introduced into the synthetic procedure, a 5-fold interpenetrating 4-connected 66-dia network 5 is obtained, in which long bpdc2- anions with bidentatechelating carboxylate groups act as linkers. Compared the interpenetrating frameworks 1, 4 and 5, the long rigid ligand is easier to form multi-interpenetration network than the flexible ligand. Increasing the number of carboxylate group, asymmetric H3bta is used in 6. Unusually, part of bta3- form a new ligand mta2- by the in situ esterification reaction. Both bta3- (μ6-bridge) and mta2- (μ4bridge) adopt intricate multibridges fashions, which result in the formation of Cd4(CO2)8 unit. Considering the Cd4(CO2)8 clusters to be a 8-connected node, the 3D structure of 6 can be classified as a (36 3 418 3 53 3 6)-hex topology. The formation of 8-connected topology 6 discloses that the aromatic polycarboxylate coligands with intricate multibridges fashions favor the generation of metal clusters and high-connected products. It can be observed that the aromatic polycarboxylate coligands have an important effect on the features and overall structures of Cdbmb polymers, with respect to their constructions, flexibility, coordination modes, etc. The results further confirm that the subtle difference in secondary ligand has a great influence on the architecture of 3D frameworks. XRD Patterns and Thermal Analyses. In order to confirm the phase purity of these polymers, the PXRD patterns were recorded for polymers 16, and they were comparable to the corresponding simulated ones calculated from the single-crystal diffraction data (Figure S1 of the SI), indicating a pure phase of each bulky sample. The thermal analyses indicate that all the six 3D polymers possess high thermal stabilities (Figure S2 of the SI). For polymer 1, there is no weight loss until the decomposition of the framework occurs at 336 °C. The guest water molecule (calculated 2.61%) is lost during the storage, which is verified with an elemental analysis on the sample held for a week. A white residue of CdO (observed 20.10%, calculated 19.14%) is obtained at 560 °C. The TGA curve of 2 shows a one step weight loss process from 350 to 567 °C, corresponding to the decomposition of organic components. A CdO residue of 25.7% (calculated 26.32%) is observed. No obvious weight loss is observed for anhydrous polymer 3 until the decomposition of the framework occurs at 357 °C. At 564 °C, a CdO residue of 18.34% (calculated 19.14%) is obtained. The overall framework of 4 begins to collapse at a high temperature of 412 °C, and the CdO residue

ARTICLE

Figure 7. Solid-state photoluminescent spectra of (a) free ligands and (b) polymers 16.

of 22.34% (calculated 22.33%) is observed at 527 °C. The framework of 5 remains intact until it is heated to 402 °C, and the CdO residue of 19.12% (calculated 17.85%) is obtained at 566 °C. Polymer 6 also displays a high thermal stability, which is stable up to 382 °C and then keeps losing weight until to 542 °C corresponding to the losses of bmb and the decomposition of the bta3- and mta2-. Finally, the white CdO residue of 28.24% (calculated 29.86%) is observed. Photoluminescence Properties. Coordination polymers with d10 metal centers and conjugated organic linkers are promising candidates for photoactive materials with potential applications such as chemical sensors and photochemistry.17 Hence, the solid state photoluminescence properties of Cd(II) polymers 16, together with the free bmb ligand and all of the aromatic polycarboxylic acids were investigated at room temperature (Figure 7) under the same experimental conditions. The emission and excitation maxima wavelengths are listed in Table 2. Obviously, the fluorescent emission bands of 1 and 2 can be attributed to the intraligand π*fπ charge transitions of bmb due to their similar emission bands. Polymer 3 exhibits an intense emission band at 449 nm. Since it is similar to that of p-H2phda, the emission can probably be assigned to the intraligand charge transitions of p-H2phda. The significant blue-shift of 23 nm 4673

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design

ARTICLE

Table 2. Emission and Excitation Maxima Wavelengths (nm) ligand

bmb o-H2phdc m-H2phdc p-H2phdc H2oba H2bpdc H3bta

λem (nm) 309

374

371

472

318

399

349

λex (nm)

293

330

317

400

296

341

320

polymer

1

2

3

4

5

6

λem (nm) 305

306

449

316

411

442

λex (nm)

287

361

301

337

343

286

should be attributed to the metalligand coordination interactions. The emission band of 4 appears in 316 nm. Both the intensity and shape are similar to that of free H2oba, so it can be assigned to the intraligand charge transitions of H2oba. As to 5, the emission peak exhibits a small red-shift (about 12 nm) with respect to the free H2bpdc, which may be assigned to the intraligand charge transitions of H2bpdc. It is possible that the coordination of carboxylate groups to Cd(II) ion decrease the π*fn gap of the carboxylate ligand, resulting in the red-shift of emission peak. For polymer 6, the emission band is highly redshifted (93 nm) compared to the free H3bta. This result indicates that the fluorescence of 6 may be attributed to a mixture characteristic of intraligand and ligand-to-ligand charge transition (LLCT), as reported for other d10 metal complexes with N-donor ligands.18 In addition, further investigation indicates that the fluorescent intensities of polymers 13 and 56 dramatically decrease compared with the corresponding ligands. It may be attributed to the ligand coordination to the metal center, which lower the rigidity of the ligands and increase the loss of energy via vibration motions. From the above discussion, polymers 16 with the same metal center and N-donor ligand show different photoluminescence behavior, which are probably attributed to the differences in the aromatic polycarboxylate coligands and the coordination environments around the central metal ions. The results further highlight that photoluminescent behavior has a close relationship with the coordination environment around metal ions.19

’ CONCLUSIONS In summary, we have successfully synthesized six 3D Cd/ bmb/polycarboxylate polymers with diverse frameworks and topologies. Our research demonstrates that the employment of mixed-ligands of bmb and aromatic polycarboxylates is a feasible strategy to construct 3D coordination frameworks. The semirigid N-donor ligand bmb is an excellent high-dimensionality structural constructor. The structural differences of polymers 16 highlight that various aromatic polycarboxylate coligands can effectively tune the final structural features and build much more complicated and fascinating topologies. This work represents a rational synthesis strategy to modulate and control the formation of high-dimensionality architectures, and further enriches the crystal engineering. Moreover, all of the Cd(II) polymers exhibit intense emissions, which appear to be potential hybrid inorganicorganic photoactive materials. Subsequent studies will be focused on the structures and properties of a series of coordination polymers constructed by bmb with more aromatic polycarboxylate ligands and other metal ions. ’ ASSOCIATED CONTENT

bS

Supporting Information. X-ray crystallographic files in CIF format, selected bond lengths and bond angles, powder

X-ray patterns, thermal analyses for 16 and the structural formulas of the free ligands. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Fax: (86) 0371-67761744; E-mail: [email protected].

’ ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation (Nos. 20971110, 91022013, and 20801048), the Outstanding Talented Persons Foundation of Henan Province. ’ REFERENCES (1) (a) Montney, M. R.; Krishnan, S. M.; Supkowski, R. M.; LaDuca, R. L. Inorg. Chem. 2007, 46, 7362. (b) Lu, Z.-Z.; Zhang, R.; Li, Y.-Z.; Guo, Z.-J.; Zheng, H.-G. J. Am. Chem. Soc. 2011, 133, 4172. (c) Qiu, W.; Perman, J. A.; Wojtas, y.; Eddaoudi, M.; Zaworotko, M. J. Chem. Commun. 2010, 46, 8734. (d) Hou, L.; Shi, W.-J.; Wang, Y.-Y.; Guo, Y.; Jin, C.; Shi, Q.-Z. Chem. Commun. 2011, 47, 5464. (e) Wei, W.; Wang, G.; Zhang, Y.; Jiang, F.; Wu, M.; Hong, M. Chem.—Eur. J. 2011, 17, 2189. (f) Carlucci, L.; Ciani, G.; Proserpio, D. M. Coordin. Chem. Rev. 2003, 246, 247. (2) (a) Shyu, E.; Supkowski, R. M.; LaDuca, R. L. Cryst. Growth Des. 2009, 9, 2481. (b) Liu, J.-Q.; Liu, B.; Wang, Y.-Y.; Liu, P.; Yang, G.-P.; Liu, R.-T.; Shi, Q.-Z.; Batten, S. R. Inorg. Chem. 2010, 49, 10422. (c) Bu, X.-H.; Tong, M.-L.; Chang, H.-C.; Kitagawa, S.; Batten, S. R. Angew. Chem., Int. Ed. 2004, 43, 192. (d) Yang, Q.-Y.; Li, K.; Luo, J.; Pana, M.; Su, C.-Y. Chem. Commun. 2011, 47, 4234. (3) (a) Yuan, D.; Zhao, D.; Sun, D.; Zhou, H.-C. Angew. Chem., Int. Ed. 2010, 49, 1. (b) Lee, J. Y.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450. (c) Su, S.; Guo, Z.; Li, G.; Deng, R.; Song, S.; Qin, C.; Pan, C.; Guo, H.; Cao, F.; Wanga, S.; Zhang, H. Dalton Trans. 2010, 9123. (4) Xu, C.; Guo, Q.; Wang, X.; Hou, H.; Fan, Y. Cryst. Growth Des. 2011, 11, 1869. (5) (a) Ok, K. M.; O’Hare, D. Dalton Trans. 2008, 5560. (b) Perry, J. J., IV; Perman, J. A.; Zaworotko, M. J. Chem. Soc. Rev. 2009, 38, 1400. (c) Ma, S.; Simmons, J. M.; Yuan, D.; Li, J.-R.; Weng, W.; Liua, D.-J.; Zhou, H.-C. Chem. Commun. 2009, 4049. (d) Zheng, B.; Bai, J.; Duan, J.; Wojtas, L.; Zaworotko, M. J. J. Am. Chem. Soc. 2011, 133, 748. (6) (a) Du, M.; Jiang, X.-J.; Zhao, X.-J. Inorg. Chem. 2006, 45, 3998. (b) Jin, J.-C.; Zhang, Y.-N.; Wang, Y.-Y.; Liu, J.-Q.; Dong, Z.; Shi, Q.-Z. Chem. Asian J. 2010, 5, 1611. (c) Wang, X. L.; Bi, Y. F.; Lin, H. Y.; Liu, G. C. Cryst. Growth Des. 2007, 7, 1086. (d) Yang, E. C.; Liu, Z. Y.; Shi, X. J.; Liang, Q. Q.; Zhao, X. J. Inorg. Chem. 2010, 49, 7969. (e) Xu, J.; Pan, Z. R.; Wang, T. W.; Li, Y. Z.; Guo, Z. J.; Batten, S. R.; Zheng, H. G. CrystEngComm 2010, 12, 612. (7) (a) Li, J.-R.; Timmons, D. J.; Zhou, H.-C. J. Am. Chem. Soc. 2009, 131, 6368. (b) Yang, Jin.; Li, Bo.; Ma, J.-F.; Liu, Y.-Y.; Zhang, J.-P. Chem. Commun. 2010, 46, 8383. (c) Xu, Y.; Chen, P.-K.; Che, Y.-X.; Zheng, J.-M. Eur. J. Inorg. Chem. 2010, 5478. (8) Aakero€y, C. B.; Desper, J.; Leonard, B.; Urbina, J. F. Cryst. Growth Des. 2005, 5, 865. (9) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (10) Liu, G.-X.; Zhu, K.; Xu, H.-M.; Nishihara, S.; Huang, R.-Y.; Renac, X.-M. CrystEngComm 2010, 12, 1175. (11) Lin, J.-D.; Cheng, J.-W.; Du, S.-W. Cryst. Growth Des. 2008, 8, 3345. (12) (a) Zhang, X. M. Coord. Chem. Rev. 2005, 249, 1201. (b) Chen, X.-M.; Tong, M.-L. Acc. Chem. Res. 2007, 40, 162. (13) Fujita, K.; Ma, S.; Li, R.; Li, J.; Ikemi, T.; Nishiyama, N. Dent. Mate. J. 2007, 26, 792. (14) Shi, X.; Wang, X.; Li, L.; Hou, H.; Fan, Y. Cryst. Growth Des. 2010, 10, 2490. 4674

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675

Crystal Growth & Design

ARTICLE

(15) (a) Yang, J.; Ma, J. F.; Liu, Y. Y.; Batten, S. R. CrystEngComm 2009, 11, 151. (b) Ma, Y.; Cheng, A. L.; Zhang, J. Y.; Yue, Q.; Gao, E. Q. Cryst. Growth Des. 2009, 9, 867. (c) Qi, Y.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2008, 8, 3602. (d) Wei, Y. Q.; Yu, Y. F.; Wu, K. C. Cryst. Growth Des. 2007, 7, 2262. (16) (a) Wang, S. N.; Bai, J. F.; Li, Y. Z.; Pan, Y.; Scheer, M.; You, X. Z. CrystEngComm 2007, 9, 1084. (b) Sun, Q.; Zhang, J. Y.; Wang, L.; Li, X.; Gao, E. Q. Cryst. Growth Des. 2009, 9, 2310. (c) Yang, G.-P.; Wang, Y.-Y.; Liu, P.; Fu, A.-Y.; Zhang, Y.-N.; Jin, J.-C.; Shi, Q.-Z. Cryst. Growth Des. 2010, 10, 1443. (17) (a) Allendorf, M. D.; Bauer, C. A.; Bhaktaa, R. K.; Houka, R. J. T. Chem. Soc. Rev. 2009, 38, 1330. (b) Braverman, M. A.; LaDuca, R. L. Cryst. Growth Des. 2007, 7, 2343. (c) Yao, X.-Q.; Zhang, M.-D.; Hu, J.-S.; Li, Y.-Z.; Guo, Z.-J.; Zheng, H.-G. Cryst. Growth Des. 2011, 11, 3039. (d) Lan, A.; Li, K.; Wu, H.; Olson, D. H.; Emge, T. J.; Ki, W.; Hong, M.; Li, J. Angew. Chem., Int. Ed. 2009, 48, 2334. (18) Liu, H.-Y.; Wu, H.; Ma, J.-F.; Liu, Y;-Y; Liu, B.; Yang, J. Cryst. Growth Des. 2010, 10, 4795. (19) (a) Liu, Y. Y.; Wang, Z. H.; Yang, J.; Liu, B.; Liu, Y. Y.; Ma, J. F. CrystEngComm 2011, 13, 3811. (b) Hu, J. S.; Shang, Y. J.; Yao, X. Q.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G.; Xue, Z. L. Cryst. Growth Des. 2010, 10, 2676.

4675

dx.doi.org/10.1021/cg200961a |Cryst. Growth Des. 2011, 11, 4667–4675