Discrete Octamer Water Cluster and 1D T5(2) - American Chemical

ARTICLE pubs.acs.org/crystal

Discrete Octamer Water Cluster and 1D T5(2) Water Tape Trapped in Two Luminescent Zn(II)/1,2-Bis(imidazol-10-yl)ethane/Dicarboxylate Hosts: From 2D (4,4) Net to 3D 5-Fold Interpenetrated Diamond Network Hong-Jun Hao,†,§ Di Sun,*,‡,§ Fu-Jing Liu,† Rong-Bin Huang,*,† and Lan-Sun Zheng† †

State Key Laboratory of Physical Chemistry of Solid Surface, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China ‡ School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China

bS Supporting Information ABSTRACT: Two new mixed-ligand Zn(II) coordination polymers, namely, [Zn(bime)(glu) 3 4H2O]n (1) and [Zn(bime)(sub) 3 3H 2 O]n (2) (bime = 1,2-bis(imidazol-1 0 -yl)ethane, H2glu = glutaric acid, H2sub = suberic acid), have been synthesized and structurally characterized. Complex 1 exhibits a wavy two-dimensional (2D) sheet with (4,4) topology. Complex 2 is a three-dimensional (3D) framework with 5-fold interpenetrated diamond topology. Of particular interest, a discrete octamer water cluster comprised of a chairlike hexamer water cluster with two extra water molecules dangling on two diagonally vertices of the chair was observed in the grid of the 2D sheet of 1. In 2, a 1D infinite T5(2) water tape constructed from edge-sharing pentamer water clusters accommodates in the channels of the 3D network. The results suggest that the dicarboxylates play crucial roles in the formation of the different host structures as well as different guest water aggregations. Additionally, the thermal stabilities and photoluminescence spectra of them were discussed.

’ INTRODUCTION The current upsurge in studying hydrogen-bonded water aggregations is aimed not only at understanding the anomalous properties (high boiling and melting points, high dielectric constant) of bulk water but also in probing its possible roles in the stabilization of biomolecules and in designing new materials.1 As we know, understanding the properties of water on the molecular level intensively depends on the precise structural data of various hydrogen-bonded water aggregations. This consciousness has led to the exploration of many interesting discrete water clusters (H2O)n,2 as well as one-dimensional (1D) chains,3 1D tapes,4 two-dimensional (2D) layers,5 and three-dimensional (3D) water structures.6 However, owing to the complexities of intermolecular interactions between the water and the host, it is still a huge stumbling block for completely understanding the water. Therefore, much more structural demonstrations of various water aggregations in diverse microenvironments are urgent for better understanding of the mysterious water. Recently, metalorganic frameworks (MOFs) with different kinds of channels or cavities have emerged as attractive hosts for the encapsulation and modulation of various water aggregations.7 Our group has reported the synthesis and modulation of a 1D rare T7(2) water tape and a 1D C4 water chain in a 3D network and a 2D sheet, respectively,8 which indicated that the dicarboxylates r 2011 American Chemical Society

with different lengths can modulate different hydrophilic environments to selectively trap the various water aggregations. In fact, hitherto, the modulation of water aggregations is still a huge challenge,5b despite hydrogen-bonding interactions, and their fluctuations are well-recognized to determine the arrangement of water. As an extension of previous work,8,9 we introduced the long chain aliphatic-dicarboxylates into the Zn(II)/1,2-bis(imidazol10 -yl)ethane (bime) system and studied the dicarboxylateinduced variation of structures as well as different water aggregations. To the best of our knowledge, the bime, an analogue to well-studied 1,2-bis(4-pyridyl)ethane,10 possesses gauche and anti conformations as a consequence of the free rotation of the ethyl group, which favor the possibility of generating fascinating MOFs11 and supramolecular isomers.12 On the other hand, aliphatic-dicarboxylate plays important roles in trapping and modulating various water aggregations in mixed-ligand MOFs due to (i) hydrophilic carboxyl groups to form abundant hydrogen-bonding interactions and to (ii) various orientations of carboxyl groups depending on the flexible carbon chain affording Received: August 16, 2011 Revised: September 19, 2011 Published: September 28, 2011 5475

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Crystal Growth & Design Table 1. Crystal Data for 1 and 2 complex

different hydrophilic environments. However, as indicated by a CSD (Cambridge Structure Database) survey with the help of ConQuest version 1.3,13 there are only 21 bime-containing complexes, and none of them contains aliphatic-dicarboxylate as an auxiliary ligand. In view of the above consideration, herein we wish to report the syntheses, crystal structures, characterizations, and photoluminescences of two Zn(II) mixed-ligand MOFs, namely, [Zn(bime)(glu) 3 4H2O]n (1) and [Zn(bime)(sub) 3 3H2O]n (2) (bime = 1,2-bis(imidazol-10 -yl)ethane, H2glu = glutaric acid, H2sub = suberic acid), as well as the interesting water aggregations in which they reside (Scheme 1).

Materials and General Methods. All chemicals and solvents used in the syntheses were of analytical grade and used without further purification. IR spectra were measured on a Nicolet 330 FTIR Spectrometer at the range of 4000400 cm1. Elemental analyses were carried out on a CE instruments EA 1110 elemental analyzer. Photoluminescence spectra were measured on a Hitachi F-7000 Fluorescence Spectrophotometer (slit width: 5 nm; sensitivity: high). X-ray powder diffractions were measured on a Panalytical X-Pert pro diffractometer with Cu Kα radiation. Thermogravimetic analyses were performed on a NETZSCH TG 209 F1 Iris Thermogravimetric Analyzer from 30 to 800 °C at a heating rate 10 °C/min under the N2 atmosphere (20 mL/min). Preparation of Complexes 1 and 2. [Zn(bime)(glu) 3 4H2O]n (1). A mixture of Zn(OOCCH3)2H2O (43.8 mg, 0.2 mmol), bime (32.4 mg, 0.2 mmol), and H2glu (26.4 mg, 0.2 mmol) was treated in DMFH2O mixed solvent (6 mL, v/v: 2/1) under ultrasonic irradiation at ambient temperature. Then aqueous NH3 solution (25%) was dropped into the mixture to give a clear solution. The resultant solution was allowed to evaporate slowly in darkness at ambient temperature for several days to give pale-yellow crystals of 1 (yield: 56%, based on Zn(OOCCH3)2H2O). They were washed with a small volume of cold CH3OH and diethyl ether. Anal. Calc for ZnC13H24N4O8: C 36.33, H 5.63, N 13.04%. Found: C 35.87, H. 5.11, N 13.79%. Selected IR peaks (cm1): 3429 (s), 3123 (w), 2964 (w), 1608 (m), 1571 (s), 1523 (m), 1388 (m), 1315 (w), 1217 (m), 1083 (m), 960 (w), 826 (m), 765 (w), 643 (w). [Zn(bime)(sub) 3 3H2O]n (2). The synthesis of 2 was similar to that of 1, but using H2sub (34.8 mg, 0.2 mmol) instead of H2glu. Pale-yellow crystals of 2 were obtained in 75% yield based on Zn(OOCCH3)2H2O. Elemental analysis: Anal. Calc for ZnC16H28N4O7: C 42.35, H 6.22, N 12.35%. Found: C 41.94, H. 5.71, N 12.23%. Selected IR peaks (cm1): 3429 (s), 3123 (w), 2928 (w), 2867 (w), 1571 (s), 1510 (w), 1425 (s), 1385 (s), 1302 (w), 1241 (w), 1095 (m), 997 (w), 936 (w), 667 (m). X-ray Crystallography. Single crystals of complexes 1 and 2 with appropriate dimensions were chosen under an optical microscope and quickly coated with high vacuum grease (Dow Corning Corporation)

2 ZnC16H28N4O7

formula

ZnC13H24N4O8 429.73

453.79

crystal system

monoclinic

orthorhombic

space group

P21/n

P212121

a (Å)

9.3287(3)

6.5568(11)

b (Å)

17.3921(6)

15.078(3)

c (Å)

12.0743(3)

20.543(3)

β (deg) V (Å3)

104.7950(9) 1894.05(10)

90 2031.0(6)

T (K)

173(2)

173(2)

Z, Dcalcd (g/cm3)

4, 1.507

4, 1.484

F(000)

896

952

μ (mm1)

1.344

1.254

ref collected/unique

14440/3300

10140/3567

Rint

0.0436

0.0261

parameters final R indices [I > 2σ(I)]

235 a R1 = 0.0764

a

b

b

a

a

b

b

0.943

1.049

wR2 = 0.2355

R indices (all data)

R1 = 0.0881 wR2 = 0.2355

goodness-of-fit on F2

307 R1 = 0.0322 wR2 = 0.0820 R1 = 0.0331 wR2 = 0.0826

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

a

’ EXPERIMENTAL SECTION

1

Mr

)

Scheme 1. Octamer Water Cluster and 1D T5(2) Water Tape Depending on the Different Dicarboxylates

ARTICLE

before being mounted on a glass fiber for data collection. Data were collected on a Rigaku R-AXIS RAPID Image Plate single-crystal diffractometer (Mo Kα radiation, λ = 0.71073 Å) equipped with an Oxford Cryostream low-temperature apparatus operating at 50 kV and 90 mA in ω scan mode for 1 and 2. A total of 44  5.00° oscillation images was collected, each being exposed for 5.0 min. Absorption correction was applied by correction of symmetry-equivalent reflections using the ABSCOR program.14 In all cases, the highest possible space group was chosen. All structures were solved by direct methods using SHELXS-9715 and refined on F2 by full-matrix least-squares procedures with SHELXL-97.16 Atoms were located from iterative examination of difference F-maps following least-squares refinements of the earlier models. Hydrogen atoms were placed in calculated positions and included as riding atoms with isotropic displacement parameters 1.21.5 times Ueq of the attached C atoms. The hydrogen atoms attached to oxygen were refined with OH = 0.85 Å and Uiso(H) = 1.2Ueq(O). All structures were examined using the Addsym subroutine of PLATON17 to ensure that no additional symmetry could be applied to the models. Pertinent crystallographic data collection and refinement parameters are collated in Table 1. Selected bond lengths and angles for 1 and 2 are collated in Table 2. The hydrogen bond geometries for 1 and 2 are shown in Table 3.

’ RESULTS AND DISCUSSION Synthesis and General Characterization. Compared to the widely used solvothermal synthesis method in Zn(II) MOFs, the ultrasound synthesis technique received less attention and the resulting high local temperatures and pressures, combined with extraordinarily rapid cooling, provide a unique means for driving chemical reactions under extreme conditions.18 In this system, the ultrasound method can achieve the rapid (10 min) and efficient (max. 30 different experiments in one batch) preparation of coordination complexes as we previously reported.19 5476

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Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and 2 Complex 1a Zn1O2

1.973(5)

Zn1N4

2.023(5)

Zn1O3i

1.976(5)

Zn1N1

2.023(5)

O2Zn1O3i

130.9(2)

O2Zn1N1

102.1(2)

O2Zn1N4

109.8(2)

O3iZn1N1

107.4(2)

O3iZn1N4

98.0(2)

N4Zn1N1

107.0(2)

1.969(2)

Zn1O3ii

2.011(2)

Zn1N1 O1Zn1N1i

2.004(2) 113.44(10)

Zn1N4 O1Zn1N4

2.040(2) 112.41(10)

O1Zn1O3ii

102.04(9)

N1iZn1N4

105.15(10)

N1 Zn1O3

125.35(10)

O3iiZn1N4

97.44(10)

Complex 2b Zn1O1 i

i

ii

Symmetry code: (i) x + 1/2, y + 1/2, z  1/2. b Symmetry codes: (i) x  1, y + 1/2, z + 1/2; (ii) x + 3/2, y + 1, z  1/2. a

Table 3. Hydrogen Bond Geometries for 1 and 2 DH 3 3 3 A

DH

H3 3 3A

D3 3 3A

DH 3 3 3 A

i

0.85 0.85

1.79 2.00

2.642(8) 2.852(8)

178 178

ii 3 O4W

0.85

1.87

2.718(9)

179

3 O3 3 O1

0.85

1.94

2.792(8)

179

0.85

1.99

2.832(8)

172

0.85

2.07

2.910(9)

172

iii 3 O1W

0.85

1.88

2.723(8)

173

3 O4

0.85

1.90

2.745(8)

172

0.85 0.85

1.95 1.97

2.796(3) 2.798(3)

174 165

Complex 1a O1WH1WA 3 3 O1WH1WB 3 3 O2WH2WA 3 3 O2WH2WB 3 3 O3WH3WB 3 3 O3WH3WA 3 3 O4WH4WA 3 3 O4WH4WB 3 3

3 O2W 3 O2

iii 3 O1W

b

Complex 2

O1W H1WB 3 3 3 O3 O1W H1WA 3 3 3 O2Wiii O2W H2WA 3 3 3 O1W

0.85

1.91

2.713(3)

157

O2W H2WB 3 3 3 O3Wiv O3W H3WA 3 3 3 O2iv

0.85

1.92

2.720(3)

157

0.85

1.96

2.813(3)

179

O3W H3WB 3 3 3 O1W

0.85

1.95

2.800(3)

178

Symmetry codes: (i) x + 1, y, z + 1; (ii) x  1/2, y + 1/2, z  1/2; (iii) x + 1/2, y + 1/2, z + 1/2. b Symmetry codes: (iii) x  1/2, y + 3/2, z + 1; (iv) x + 1, y, z. a

Powder X-ray diffraction (PXRD) has been used to check the phase purity of the bulk samples in the solid state. For complexes 1 and 2, the measured PXRD patterns closely match the simulated patterns generated from the results of single-crystal diffraction data (Figure S1, Supporting Information), indicative of pure products. The dissimilarities in intensity may be due to the preferred orientation of the crystalline powder samples. In the IR spectra (Figure S2, Supporting Information) of complexes 1 and 2, the broad peaks at ca. 3400 cm1 indicate the presence of water molecules. The IR spectra also show characteristic absorption bands mainly attributed to the asymmetric (νas: ca. 1600 cm1) and symmetric (νs: ca. 1385 cm1) stretching vibrations of the carboxylic groups. No band in the region 16901730 cm1 indicates complete deprotonation of the carboxylic groups,20 which is consistent with the result of the X-ray diffraction analysis.

Figure 1. (a) Coordination environment of Zn(II) ion in 1 with the thermal ellipsoids at the 50% probability level. Hydrogen atoms and water molecules were omitted for clarity. (b) Presentation of a 2D (4,4) net. (c) Packing of 2D sheets in the crystal. (Symmetry codes: (i) x + 1/2, y + 1/2, z  1/2; (iv) x + 1, y, z; (v) x + 1, y + 1, z).

Structure Descriptions. [Zn(bime)(glu) 3 4H2O]n (1). Singlecrystal X-ray diffraction analysis reveals that complex 1 crystallizes in the space group P21/n and is a 2D wavy (4,4) net of rectangular grids with lattice water molecules. There are one Zn(II) ion, one bime, one glu, and four lattice water molecules in an asymmetric unit of 1. Every bime ligand locates on the inversion center. As depicted in Figure 1a, the Zn1 is located in a tetrahedral geometry and coordinated by two N atoms from two bime ligands and two O atoms from two glu ligands (Zn1O2 = 1.973(5) Å, Zn1O3i = 1.976(5) Å, Zn1N1 = Zn1N4 = 2.023(5) Å). The maximum and minimum bond angles for Zn1 are 130.9(2) and 98.0(2)°, respectively. The distortion of the tetrahedron can be indicated by the calculated value of the τ4 parameter introduced by Houser21 to describe the geometry of a four-coordinate metal system, which is 0.85 (for ideal tetrahedron τ4 = 1). Both ZnN and ZnO bond lengths are well-matched to those observed in similar complexes.22 According to the stereochemistry terminology,23 the conformation of the bime in 1 belongs to gauche with a torsion angle of 180° defined by N2C9C9ivN2iv atoms. The flexible glu shows a gaucheanti conformation due to the two torsion angles of the carbon chain being 73.3(8) and 177.4(6)°. (Symmetry codes: (i) x + 1/2, y + 1/2, z  1/2; (iv) x + 1, y, z.) The Zn(II) ions are bridged by μ2-bime and μ2-η1,η1-glu ligands to form a 2D infinite undulated sheet (Figure 1b) incorporating a [Zn4(bime)2(glu)2] window of 8.52  11.52 Å2 based on the Zn 3 3 3 Zn distances. This sheet exhibits an undulated character with a thickness of about 7.44 Å. To better understand the structure of 1, the topological analysis approach is employed. If all nodes in one net have the identical connectivity, then according to Wells it is a platonic uniform net and can be represented by the symbol (n,p), where n is the size of the shortest circuit and p is the connectivity of the nodes.24 In the sheet of 1, all Zn(II) ions are 4-connecting and the shortest circuit is a four-membered ring. So this 2D sheet can be simplified to a (4,4) net. The adjacent sheets further interdigitate with each 5477

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Table 4. Bond Angles (deg) for the Octamer Water Cluster in 1 and the 1D T5(2) Water Tape in 2 Complex 1a iii

O3W 3 3 3 O1W 3 3 O3W 3 3 3 O1Wiii 3 3 O1Wiii 3 3 3 O2Wiv 3

iv

3 O2W 3 O4W

104.3(3) 81.2(3)

v 3 3 O4W iv v iv O2W 3 3 3 O4W 3 3 3 O1W O4Wv 3 3 3 O1Wiv 3 3 3 O2Wiii

Complex 2 O1W 3 3 3 O2W 3 3 3 O1Wv O2W 3 3 3 O1Wv 3 3 3 O3Wv O1Wv 3 3 3 O3Wv 3 3 3 O2Wiii O3Wv 3 3 3 O2Wiii 3 3 3 O1W

113.1(3) 108.8(3) 112.8(3) b

113.0(1) 97.2(1) 105.4(1) 100.5(1)

Symmetry codes: (iii) x + 1/2, y + 1/2, z + 1/2; (iv) x + 3/2, y + 1/2, z + 3/2; (v) x + 2, y + 1, z + 2. b Symmetry codes: (iii) x  1/2, y + 3/2, z + 1; (v) 0.5 + x, 1.5  y, 1  z. a

Figure 2. Side view (a) and top view (b) of octamer water. (c) The octamer water clusters interact with the 2D sheet. (Symmetry codes: (iii) x + 1/2, y + 1/2, z + 1/2; (iv) x + 3/2, y + 1/2, z + 3/2; (v) x + 2, y + 1, z + 2).

other to form the resulting 3D supramolecular framework (Figure 1c) through classic OH 3 3 3 O hydrogen bonds (2.852(8) Å), nonclassic CbimeH 3 3 3 Oglu hydrogen bonds (3.244(9) and 3.210(8) Å), and CgluH 3 3 3 πbime interactions (3.594(9) Å). We previously obtained two 2D f 2D and 2D f 3D interpenetrated networks based on two kinds of 2D undulated (4,4) nets with the window dimensions of 12.36  9.17 and 11.70  11.51 Å2, respectively.25 However, no interpenetration was observed in 1, which may be caused by the relatively smaller window dimensions in 1, precluding the insertion of a rod of adjacent windows. The most striking feature of 1 is the existence of a discrete octamer water cluster. As shown in Figure 2a and b, the centrosymmetric octamer water cluster consists of four water molecules (O1WO4W) and their centrosymmetric equivalents. The short contacts and the reasonable angles between them indicate the existence of hydrogen bonds, which drive the formation of a hydrophilic octamer water cluster. The water octamer can be seen as a chairlike hexamer in the core which links two extra water molecules dangling at two diagonally vertices of the chair with a distance of 9.416(9) Å, which is structurally analogous to the simple hydrocarbon (1r,4r)-1,4-dimethylcyclohexane. In the cyclic hexamer, each water molecule acts as a single hydrogen bond donor and a single hydrogen bond acceptor; as a result, the hydrogen bonding motif is R66(12), according to the graph-set analysis nomenclature.26 The O1Wiii derivates 1.13 Å from the plane determined by O2Wiv, O4Wv, O2Wiii, and O4W. As listed in Table 3, the O 3 3 3 O distances in the octamer water cluster fall in the range of 2.642(8)2.910(9) Å with an average value of 2.748(8) Å, compared to 2.76 Å (90 °C) in hexagonal (Ih) ice,27 2.74 Å in cubic (Ic) ice,28 or 2.85 Å in liquid water.29 The O 3 3 3 O 3 3 3 O angles (Table 4) vary from

81.2(3) to 113.1(3)° with an average value of 104.0(3)°, which slightly deviates from the angle of 109.3° in hexagonal ice. The octamer water cluster interacts with the 2D (4,4) net through the O2WH2WB 3 3 3 O3 and O1WH1WB 3 3 3 O2 hydrogen bonds with the O 3 3 3 O distances of 2.792(8) and 2.852(8) Å, respectively (Figure 2c). This octamer water cluster is similar to that found in [Ce(dipic)2(H2O)3 3 4H2O] (dipicH2 = dipicolinic acid) with slightly different O 3 3 3 O distances,30 but it is different from a cubelike (H2O)8 in a Co complex31 and an icelike, cyclic (H2O)8 in an organic supramolecular complex.32 (Symmetry codes: (iii) x + 1/2, y + 1/2, z + 1/2; (iv) x + 3/2, y + 1/2, z + 3/2; (v) x + 2, y + 1, z + 2.) [Zn(bime)(sub) 3 3H2O]n (2). When using a longer dicarboxylate (sub), we obtained complex 2 as a 5-fold interpenetrated 3D framework with a diamond topology. Single crystal X-ray analysis reveals that 2 crystallized in an orthorhombic chiral space group of P212121 with a Flack parameter of 0.047(12). As shown in Figure 3a, the asymmetric unit of 2 consists of one crystallographically independent Zn(II) ion, one bime, one sub, and three guest water molecules. The Zn1 also adopts a tetrahedral geometry completed by two N atoms from two bime ligands and two O atoms from two sub ligands (Zn1O1 = 1.969(2) Å, Zn1O3ii = 2.011(2) Å, Zn1N1i = 2.004(2) Å, and Zn1N4 = 2.040(2) Å). The bond angles for Zn1 are in the range of 97.44(10)125.35(10)°, with an average value of 109.31(10)°, which slightly deviates from an angle of 109.47° in a perfect tetrahedron. The τ4 parameter is 0.86. The conformation of the bime in 2 is the same as that in 1 with a torsion angle of 173.1(5)°. The sub has a longer carbon chain than glu, so it has five torsion angles of 178.1(3)°, 69.6(5)°, 176.7(3)°, 63.2(4)°, and 171.0(3)°, giving an antigaucheantigaucheanti conformation. A conformational analysis of crystal structures containing the sub fragment with or without metals was carried out on the basis of the CSD13 survey (Table S1 of the Supporting Information) and revealed that, out of 89 nonequivalent sub ligands, 53 exhibit the antiantiantiantianti conformation (59.55%), 21 exhibit the gaucheantiantiantigauche conformation (23.60%), 8 exhibit the antiantiantiantigauche conformation (8.99%), and the antigauche-antigauche-anti conformation in 2 has not appeared yet. The extension of the structure of 2 into a 3D network is accomplished by binding two μ2-bime and two μ2-η1,η1-subligands 5478

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Figure 4. Side view (a) and top view (b) of 1D T5(2) water tape. Symmetry codes: (iii) x  1/2, y + 3/2, z + 1; (iv) x + 1, y, z; (v) 0.5 + x, 1.5  y, 1  z.

Figure 3. (a) Coordination environment of Zn(II) ion in 2 with the thermal ellipsoids at the 50% probability level. Hydrogen atoms and water molecules were omitted for clarity. (Symmetry codes: (i) x  1, y + 1/2, z + 1/2; (ii) x + 3/2, y + 1, z  1/2.) (b) Perspective (left) and simplified (right) view of the single superadamantane. (c) Five interpenetrated adamantanoid cages. (d) Schematic representation of the 5-fold interpenetrated 3D diamond network.

to the four-connected Zn(II) nodes, and the free water molecule occupies the remaining void space. The 3D network consists of elongated [Zn10(bime)6(sub)6] adamantane-liked subunits (Figure 3b) and has a top-to-bottom length of 32.784(5) Å, equivalent to five times the crystallographic a-axis length. This large superadamantane gives the single diamond network a huge chamber, which is filled via mutual interpenetration of four independent equivalent networks, generating a 5-fold interpenetrated 3D architecture (Figure 3c and d). An analysis of the topology of interpenetration according to a recent classification33d reveals that 2 belongs to Class Ia (all the interpenetrated nets are generated only by translation and the translating vector is the crystallographic a axis (6.5568(11) Å)). In spite of the fact that

many 3D nets with diamond topology of various interpenetration degrees ranging from 2- to 11-fold have been reported,33 5-fold interpenetrating MOFs in the presence of mixed ligands with different lengths are relatively scarce.34 As a consequence of Mother Nature’s horror vacui, complex 2 adopts 5-fold interpenetration to avoid extremely large voids. However, in spite of interpenetration, 2 still possesses free void space along the a direction estimated to be about 315.5 Å3, that is, 15.5% of the unit cell. Interestingly, the single-directional open channels were alternately occupied by well-resolved infinite T5(2) water tape (Figure S3, Supporting Information).35 Five lattice water molecules, O1W, O2W, O1Wv, O3Wv, and O2Wiii, are arranged in a nonplanar cyclic pentagon. The adjacent pentagons are fused together to form a 1D T5(2) water tape (Figure 4) through a O1W 3 3 3 O2W hydrogen bond (2.798(3) Å) along the a axis. One water molecule O1W locates above the plane formed by the other four water molecules of 0.86 Å. Within the pentamer water cluster, each water molecule acts as a single hydrogen bond donor and acceptor; as a consequence, the hydrogen bonding motif is R55(10). The distances of hydrogen-bonded water molecules fall in the range of 2.713(3)2.800(3) Å with an average value of 2.758(3) Å, which is compared to that in the octamer water cluster in 1. The O 3 3 3 O 3 3 3 O angles (Table 4) vary from 81.2(3) to 113.1(3)°. Previously, some similar T5(2) water tapes were discovered in hydrophilic crystal hosts such as purines,36 diamines,37 tetraamide macrocycle,38 and porous frameworks consisting of metal carboxylates.39 This 1D water tape interacts with the 1D channels through O1WH1WB 3 3 3 O3 (2.796(3) Å) and O3WH3WA 3 3 3 O2iv (2.813(3) Å) hydrogen bonds. (Symmetry codes: (iii) x  0.5, y + 1.5, z + 1; (iv) x + 1, y, z; (v) 0.5 + x, 1.5  y, 1  z.) Influence of Dicarboxylates on Structures of Both MOFs and Water Aggregates. It has been illustrated that the structural variations of both host MOFs and guest water aggregates in complexes 1 and 2 are undoubtedly associated with the lengths and configurations of auxiliary dicarboxylates. For 1 and 2, the main ligand bime adopts the identical μ2 bridging coordination mode and anti conformation, so the influence of it on the MOFs can be neglected. However, the auxiliary dicarboxylates (glu and sub) with the same μ2-η1,η1 coordination mode possess different lengths and conformations, which play important roles in the formation of diverse MOFs as well as water aggregations. 5479

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Photoluminescence Properties. The photoluminescence spectra of complexes 1 and 2 are shown in Figure 5. The free ligand bime displays photoluminescence with an emission maximum at 356 nm (λex = 300 nm, Figure S6, Supporting Information). It can be presumed that this peak originated from the π* f π transition. To the best of our knowledge, the emission of dicarboxylate belongs to π* f n transitions and is very weak compared to that of the π* f π transition of the bime, so the dicarboxylates almost have no contribution to the fluorescent emission of as-synthesized MOFs.40 Upon complexation of these ligands with Zn(II) ions, intense emissions are observed at 443 nm for 1 and 446 nm for 2, under 300 nm excitation, respectively. The resemblance between the emissions of 1 and 2 and that of the free bime indicates that the emissions of 1 and 2 originate from the π* f π electronic transition of bime ligand.

Figure 5. Photoluminescences of complexes 1 and 2.

In 1, the glu ligand adopts a gaucheanti conformation and combines with bime to link the Zn(II) ions to a 2D undulated (4,4) net. Although the Zn(II) adopts a tetrahedral geometry favoring the formation of a 3D network, the gaucheanti conformation of glu in 1 breaks the directionality kept by the tetrahedral Zn(II) ion, which precludes the formation of a 3D network. In 2, the longer sub ligand adopts a antigaucheantigaucheanti conformation and combines with bime to link the Zn(II) ions to form a 3D network with huge voids occupied by four other independent networks, resulting in a 5-fold interpenetrated 3D diamond network. Although the sub ligand has a more flexible carbon bone than glu, the antigaucheantigaucheanti conformation can keep the same linking direction to the tetrahedral Zn(II) ion, which favors the formation of the 3D network. These results show diverse dicarboxylates can fine-tune themselves to satisfy the coordination preference of metal centers and the lower energetic arrangement in the self-assembly process. Moreover, different dicarboxylates not only change the structures of the MOFs but also modulate different hydrophilic environments which match with the various water aggregations being optimally occupied in terms of both the packing efficiency and the maximization of hydrogen bond interactions. Consequently, the water aggregations are successfully tuned by a change in the shape or distribution of the hydrophilic groups on the host MOFs. Thermal Analysis. The thermogravimetric (TG) measurements were performed in N2 atmosphere on polycrystalline samples of complexes 1 and 2, and the TG curves are shown in Figure S4 of the Supporting Information. The TGA curve of 1 displays a weight loss of 15.9% (calcd: 16.8%) at 30100 °C, corresponding to complete loss of the lattice water molecules. Its framework is stable to 328 °C, and then the framework begins to collapse, accompanying the release of bime and glu ligands. Complex 2 shows a first weight loss of 12.5% at 30115 °C, corresponding to the loss of the lattice water molecules (calcd: 11.9%). The dehydrated framework is stable to 325 °C, and then the framework begins to collapse, accompanying the release of organic ligands. On the basis of the TG curve of 2, the stability of the porous 3D network after removal of water clusters in 2 was also investigated by PXRD (Figure S5, Supporting Information). The PXRD pattern of dehydrated 2 after calcinations at 200 °C for 2 h is similar to that of as-synthesized 2, indicating the host 3D network can retain its integrity after removal of water clusters.

’ CONCLUSIONS In summary, we succeeded in tuning not only the structures of the MOFs from a 2D noninterpenetrated (4,4) net to a 3D 5-fold interpenetrated diamond network but also the water aggregations including a discrete octamer water cluster and a 1D T5(2) water tape by employment of different aliphatic dicarboxylates. This work demonstrates that, by using various dicarboxylate ligands with different lengths and flexibilities, diverse MOFs can be assembled to trap lattice water molecules in different morphologies. ’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic data in CIF format, additional figures of the structures, powder X-ray diffraction (PXRD) patterns, and TGA and IR spectra for 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (D. Sun). Fax: +86-531-88364218. *E-mail: [email protected]. (R.-B. Huang). Fax: +86-5922183047. Author Contributions §

These authors contributed equally to this work.

’ ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (Nos. 21021061 and 21071118), 973 Project (Grant 2007CB815301) from MSTC, and the Independent Innovation Foundation of Shandong University. ’ REFERENCES (1) (a) Ludwig, R. Angew. Chem., Int. Ed. 2001, 40, 1808. (b) Ball, P. H2O: A Biography of Water; Weidenfeld & Nicolson: London, 1999. (c) Debenedetti, P. G. Metastable Liquids; Princeton University Press: Princeton, 1996. (d) Dorsey, E. Properties of Ordinary Water Substance; American Chemical Society Monograph; New York, 1968. (e) Liu, K.; Cruzan, J. D.; Saykally, R. J. Science 1996, 271, 929–933. (f) Liu, K.; Brown, M. G.; Cruzan, J. D.; Saykally, R. J. Science 1996, 271, 62. (g) Cruzan, J. D.; Braly, L. B.; Liu, K.; Brown, M. G.; Loeser, J. G.; Saykally, R. J. Science 1996, 271, 59. (h) Liu, K.; Brown, M. G.; Carter, C.; Saykally, R. J.; Gregory, J. K.; Clary, D. C. Nature 1996, 381, 501. (i) Pugliano, N.; Saykally, R. J. Science 1992, 257, 1937. (j) Smith, J. D.; Cappa, C. D.; Wilson, K. R.; Messer, B. M.; Cohen, R. C.; Saykally, R. J. 5480

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