Journal of Molecular Structure 1004 (2011) 313–318

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Journal of Molecular Structure

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Different water clusters dependent on long-chain dicarboxylates in two Ag(I)coordination polymers: Synthesis, structure and thermal stability

Di Sun a,⇑, Fu-Jing Liu b, Hong-Jun Hao b, Rong-Bin Huang b,⇑, Lan-Sun Zheng b

a School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, Chinab State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen,Fujian 361005, China

a r t i c l e i n f o

Article history:Received 26 July 2011Accepted 17 August 2011Available online 25 August 2011

Keywords:Silver(I)4,40-BipyridineWater clusterSuberic acidAzelaic acid

0022-2860/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.molstruc.2011.08.028

⇑ Corresponding authors. Fax: +86 531 88364218.E-mail addresses: dsun@sdu.edu.cn (D. Sun),

Huang).

a b s t r a c t

Two mixed-ligand Ag(I) coordination polymers (CPs), [Ag2(bipy)2(sub)�5H2O]n (1), [Ag2(bipy)2(a-ze)�3H2O]n (2), (bipy = 4,40-bipyridine, H2sub = suberic acid, H2aze = azelaic acid) have been synthesizedand structurally characterized by elemental analysis, infrared (IR) spectroscopy, powder X-ray diffraction(PXRD), thermogravimetric (TG) analysis, and single crystal X-ray diffraction. Both 1 and 2 are two-dimensional (2D) sheets based on infinite [Ag(bipy)]n double chain incorporating Ag� � �Ag interactions.Interestingly, two different water clusters are encapsulated in the voids between the sheets of 1 and 2.For 1, one water decamer (H2O)10 based on a cyclic water tetramer was hydrogen-bonded with the host2D sheet. While, one water hexamer (H2O)6 also based on a cyclic water tetramer was observed in 2.Comparing the experimental results, it is comprehensible that the dicarboxylates play a crucial role inthe formation of the different water clusters. Moreover, the thermal stabilities of them were alsodiscussed.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction which are suitable to the various water aggregates being optimally

Water is of fundamental importance in life [1]. Exploration ofthe possible structures and stabilities of water clusters capturedin diverse environments is a key to obtain in-depth insight intothe nature of bulk water or ice, as well as in biological and chem-ical processes [2–4]. To understand the behavior of water mole-cules at the atom level, the structural analysis of diversehydrogen-bonded water clusters is requisite [5]. Metal–organiccoordination networks with carboxylate ligands can provide voidspaces incorporating hydrophilic environment where water clus-ters can be encapsulated with the help of hydrogen bonds. Up tonow, a variety of finite water clusters (H2O)n (n = 2–12, 14–18,20) and infinite water aggregations including one-dimensional(1D) water chains or tapes, two-dimensional (2D) water layers,and three-dimensional (3D) water structures have been trappedin the crystal hosts in the solid state and structurally characterized[6–8]. Although the structures of water clusters have been widelyinvestigated in both theoretical and experimental aspects [9–13],the modulation of water cluster is still a long-standing challengeand rarely reported [14,15]. Previously, we realized the modulationof 1D water tape and 1D water chain in a 3D network and 2D sheet,respectively [16], which suggested that the dicarboxylates withdifferent lengths can modulate different hydrophilic environments

ll rights reserved.

rbhuang@xmu.edu.cn (R.-B.

occupied both in terms of packing efficiency and the maximizationof intermolecular interactions. As extension of the work in Ag(I)/bipy/dicarboxylate system, in this contribution, we used two longdicarboxylates to obtained two 2D networks, namely [Ag2(bipy)2(-sub)�5H2O]n (1) and [Ag2(bipy)2(aze)�3H2O]n (2) (bipy = 4,40-bipyr-idine, H2sub = suberic acid, H2aze = azelaic acid), where a waterdecamer (H2O)10 and a water hexamer (H2O)6 based on a cyclicwater tetramer were observed (see Scheme 1).

2. Experimental

2.1. Materials and physical measurements

All chemicals and solvents used in the syntheses were of analyt-ical grade and used without further purification. IR spectra weremeasured on a Nicolet 330 FTIR Spectrometer at the range of4000–400 cm�1. Elemental analysis was carried out on a CE instru-ments EA 1110 elemental analyzer. TGA was measured from 25 to800 �C on a SDT Q600 instrument with a heating rate of 5 �C/minunder the N2 atmosphere (100 mL/min). X-ray powder diffractionswere measured on a Panalytical X-Pert pro diffractometer withCuKa radiation.

2.2. Synthesis of CP [Ag2(bipy)2(sub)�5H2O]n (1)

A mixture of Ag2O (116 mg, 0.5 mmol), bipy�2H2O (194 mg,1 mmol) and H2sub (174 mg, 1 mmol) was treated in CH3OH–

Scheme 1. Water decamer (H2O)10 and water hexamer (H2O)6 dependent on the different dicarboxylates.

314 D. Sun et al. / Journal of Molecular Structure 1004 (2011) 313–318

H2O mixed solvent (10 mL, v/v: 1/1) under ultrasonic irradiation atambient temperature. Then aqueous NH3 solution (25%) wasdropped into the mixture to give a clear solution. The resultantsolution was allowed to evaporate slowly in darkness at ambienttemperature for several days to give colorless crystals of 1 (yield:73%, based on Ag2O). They were washed with a small volume ofcold methanol and diethyl ether. Anal. Calc. for C28H38Ag2N4O9: C42.55, H 4.85, N 7.09%. Found: C 42.52, H. 4.21, N 7.69%. SelectedIR peaks (cm�1): 3417 (s), 3038 (w), 2914 (w), 2815 (w), 1588(s), 1408 (m), 1383 (s), 1302 (s), 1227 (m), 1072 (w), 991 (w),815 (m), 627 (w).

2.3. Synthesis of CP [Ag2(bipy)2(aze)�3H2O]n (2)

Synthesis of 2 was similar to that of 1, but with H2aze (188 mg,1 mmol) instead of H2sub. Colorless crystals of 2 were obtained in81% yield (based on Ag2O). Elemental analysis: Anal. Calc. ForC29H36Ag2N4O7: C 45.33, H 4.72, N 7.29%. Found: C 45.71, H. 4.41,N 7.22%. Selected IR peaks (cm�1): 3461 (s), 3432 (s), 3353 (s),3131 (s), 2947 (m), 1645 (s), 1561 (s), 1478 (s), 1432 (s), 1288(m), 1190 (w), 1023 (w), 911 (w), 801 (w).

3. X-ray crystallography

Single crystals of the 1 and 2 with appropriate dimensions werechosen under an optical microscope and quickly coated with high

Table 1Crystallographic data for 1–2.

Complex 1 2

Empirical formula Ag2C28H38N4O9 Ag2C29H36N4O7

Formula weight 790.36 768.36Crystal system Monoclinic TriclinicSpace group P2(1)/n P-1a (Å) 11.796(2) 10.1035(3)b (Å) 14.455(3) 10.3932(4)c (Å) 18.283(4) 15.2929(4)a (�) 90.00 76.8780(10)b (�) 95.58(3) 72.2160(10)c (�) 90.00 86.8610(10)V(Å3) 3102.7(11) 1489.02(8)T(K) 173(2) 173(2)Z, Dcalcd (Mg/m3) 4, 1.692 2, 1.714F(000) 1600 776l(mm�1) 1.320 1.368Ref. collected/unique 5418/4660 5235/4801Rint 0.0313 0.0567Parameters 416 379Final R indices[I > 2r(I)] R1 = 0.0273 R1 = 0.0404

wR2 = 0.0677 wR2 = 0.1049R indices (all data) R1 = 0.0336 R1 = 0.0436

wR2 = 0.0706 wR2 = 0.1074R1 = R||Fo| � |Fc||/R|Fo|,

wR2 ¼ ½RwðF2o � F2

c Þ2�=RwðF2

oÞ2�1=2

vacuum grease (Dow Corning Corporation) before being mountedon a glass fiber for data collection. Data were collected on a RigakuR-AXIS RAPID Image Plate single-crystal diffractometer (MoKaradiation, k = 0.71073 Å) equipped with an Oxford Cryostreamlow-temperature apparatus operating at 50 kV and 90 mA in xscan mode for 1 and 2. A total of 44 � 5.00� oscillation imageswas collected, each being exposed for 5.0 min. Absorption correc-tion was applied by correction of symmetry-equivalent reflectionsusing the ABSCOR program [17]. In all cases, the highest possiblespace group was chosen. All structures were solved by direct meth-ods using SHELXS-97 [18] and refined on F2 by full-matrix least-squares procedures with SHELXL-97 [19]. Atoms were located fromiterative examination of difference F-maps following least squaresrefinements of the earlier models. Hydrogen atoms were placed incalculated positions and included as riding atoms with isotropicdisplacement parameters 1.2–1.5 times Ueq of the attached Catoms. The hydrogen atoms attached to oxygen were refined withO–H = 0.85 Å, and Uiso(H) = 1.2Ueq(O). All structures were exam-ined using the Addsym subroutine of PLATON [20] to assure thatno additional symmetry could be applied to the models. Pertinentcrystallographic data collection and refinement parameters arecollated in Table 1. Selected bond lengths and angles for 1 and 2are collated in Table 2. The hydrogen bond geometries for 1 and2 are shown in Table 3.

4. Results and discussion

4.1. Synthesis

The syntheses of 1 and 2 were carried out in the darkness toavoid photodecomposition. As is well known, the reactions of

Table 2Selected bond lengths and angles for 1–2.

Complex 1Ag1–N1 2.176(2) Ag2–N3 2.173(2)Ag1–N4i 2.183(2) Ag2–N2i 2.178(2)Ag1–O4ii 2.496(2) Ag2–O1 2.5894(18)N1–Ag1–N4i 161.96(8) N3–Ag2–N2i 159.85(8)N1–Ag1–O4ii 96.44(7) N3–Ag2–O1 100.77(7)N4i–Ag1–O4ii 95.28(7) N2i–Ag2–O1 99.34(7)Symmetry codes: (i) x + 1/2, �y + 1/2, z � 1/2; (ii) x + 1, y, z

Complex 2Ag1–N1 2.186(2) Ag2–N2ii 2.194(2)Ag1–N4 2.197(3) Ag2–N3 2.207(3)Ag1–O3 2.495(3) Ag2–O1iii 2.475(2)Ag2–O3iii 2.675(3)Ag1–Ag1i 3.2556(5) Ag2–Ag2iv 3.1652(6)N1–Ag1–N4 157.77(11) N2i–Ag2–N3 153.24(10)N1–Ag1–O3 102.21(9) N2i–Ag2–O1ii 102.16(9)N4–Ag1–O3 96.05(9) N3–Ag2–O1ii 104.30(9)Symmetry codes: (i) �x + 1, �y + 2, �z + 2; (ii) x � 2, y � 1, z + 1; (iii) x � 2, y,

z + 1; (iv) �x � 1, �y + 1, �z + 3

Table 3The hydrogen bond geometries for 1–2.

D–H� � �A D–H H� � �A D� � �A D–H� � �A

Complex 1O1W–H1WB� � �O2 0.85 1.93 2.770(3) 170O1W–H1WA� � �O2iii 0.85 2.03 2.867(3) 170O2W–H2WB� � �O1Wiv 0.85 1.98 2.820(3) 171O2W–H2WA� � �O4 0.85 1.86 2.693(3) 165O3W–H3WA� � �O5Wv 0.85 2.07 2.841(3) 151O3W–H3WB� � �O4Wii 0.85 1.99 2.826(3) 168O4W–H4WB� � �O2Wvi 0.85 1.99 2.813(3) 164O4W–H4WA� � �O3 0.85 1.93 2.778(3) 174O5W–H5WB� � �O1 0.85 1.96 2.808(3) 174O5W–H5WA� � �O3Wvii 0.85 1.97 2.799(3) 165Symmetry codes: (ii) x + 1, y, z; (iii) �x, �y + 1, �z; (iv) x � 1/2, �y + 1/2, z + 1/

2; (v) x + 1/2, �y + 1/2, z + 1/2; (vi) �x � 1/2, y + 1/2, �z + 1/2; (vii) �x + 1/2, y � 1/2, �z + 1/2.

Complex 2D–H� � �A D–H H� � �A D� � �A D–H� � �AO1W–H1WA� � �O2Wv 0.85 2.19 2.765(3) 124.4O1W–H1WB� � �O3W 0.85 2.15 2.859(3) 141.4O2W–H2WA� � �O3 0.85 1.88 2.732(3) 178.6O2W–H2WB� � �O1Wvi 0.85 2.00 2.853(4) 178.4O3W–H3WA� � �O2vii 0.85 1.94 2.790(4) 177.5O3W–H3WB� � �O4 0.85 2.00 2.848(3) 177.5Symmetry codes: (v) �x + 1, �y + 1, �z + 2; (vi) x + 1, y, z; (vii) x � 1, y, z

D. Sun et al. / Journal of Molecular Structure 1004 (2011) 313–318 315

Ag(I) with dicarboxylates in aqueous solution often result in theformation of insoluble silver salts, presumably due to the fast coor-dination of the carboxylates to Ag(I) ions to form polymers. Hence,properly lowering the reaction speed, such as using ammoniacalconditions or layer-separation diffusion method, may favor to theformation of crystalline products. Ultrasonic method has foundan important niche in the preparation of inorganic materials [21].The high local temperatures and pressures, combined withextraordinarily rapid cooling, provide a unique means for drivingchemical reactions under extreme conditions. In this system, ultra-sound technique also realizes the rapid (10 min) and efficient(max. 30 different experiments in one batch) preparation of CPs[22].

4.2. Crystal structures

4.2.1. Crystal structure of [Ag2(bipy)2(sub)�5H2O]n (1)X-ray single-crystal diffraction analysis reveals that 1 crystal-

lizes in the monoclinic P2(1)/n space group with an asymmetricunit containing two crystallographically independent Ag(I) ions,two bipy ligands, one sub ligand, and five lattice water molecules.As shown in Fig. 1a, both Ag1 and Ag2 ions adopt a T-shaped geom-etry. The maximum angles around Ag1 and Ag2 are 161.96(8) and159.85(8)�, respectively. The Ag–N and Ag–O bond lengths fall inthe ranges of 2.173(2)–2.183(2) and 2.496(2)–2.5894(18) Å,respectively. In 1, both Ag1 and Ag2 are coordinated by two Natoms from two different bipy ligands and one O atom from sub li-gand. The bond lengths of Ag–N and Ag–O are comparable to thosereported CPs [23–28]. The shortest Ag1� � �Ag2 distance of3.2246(7) Å is longer than the Ag� � �Ag separation of 2.88 Å in themetallic state but shorter than the van der Waals contact distancefor Ag� � �Ag of 3.44 Å, showing the existence of argentophilic inter-actions between them [29–32]. The pyridyl rings of bipy ligand arenoncoplanar with dihedral angles of 34.9 and 28.0�, respectively.

In 1, the bipy as a bidentate bridging ligand links the Ag(I) toform a 1D chain. The adjacent chains are extended to 1D doublechain by the Ag� � �Ag interaction and intra-chain p� � �p interactions(Cg1� � �Cg3 = 3.8200(17) and Cg2� � �Cg4 = 3.7322(16) Å, Cg1–Cg4are the centroids of aromatic ring N1/C1–C5, N2/C6–C10, N3/C11–C15, N4/C16–C20, respectively, Fig. 1b). The l2–g1:g0:g1:g0 sub adopts a gauche–anti–anti–anti–gauche confor-

mation (torsion angles: 46.9, 147.5, 123.9, 177.4 and 50.9�) andlinks the 1D double chain into the 2D sheet (Fig. 1c).

The most striking feature of 1 is the existence of a centrosym-metric decamer water cluster comprised of five water moleculesand their equivalents. As shown in Fig. 1d, each water molecule isa double hydrogen bond donor and single hydrogen bond acceptor.The decamer water cluster can be seen as a planar udud tetramer[33] with three additional water molecules (O1W, O2W andO4W) dangling at two diagonally opposite positions. The hydro-gen-bonded O� � �O separations in the decamer span the range2.799(3)–2.841(3) Å with an average value of 2.820(3) Å, which iscomparable to the 2.74 Å in ice Ic [34], 2.76 Å in ice Ih [35] or2.85 Å in liquid water [36]. The O� � �O� � �O angles are in the range88.77(8)–142.47(11)�. PLATON [20] calculation indicated that theresulting effective free volume, after removal of encapsulated deca-meric water cluster, was 18.0% of the crystal volume (558.0 Å3 outof the 3102.7 Å3 unit cell volume). The structural landscape associ-ated with the water decamer is extensive, and theoretical calcula-tion at the HF/6-31G(d,p) level indicates that fused pentamericstructure to be energetically the most stable, with 15 hydrogenbonds [37]. Hence, in spite of the decameric water cluster in 1 with10 hydrogen bonds may be a high-energy configuration with re-spect to other conformers of the cluster as shown by theoretical cal-culations, the specific chemical environment may offer additionalstabilization energy for it. This water decamer interacts with the2D sheet through Owater� � �Osub hydrogen bonds ranging from2.693(3) to 2.867(3) Å (Fig. S1, Supporting information).

4.2.2. Crystal structure of [Ag2(bipy)2(aze)�3H2O]n (2)When using the longer H2aze, we obtained 2 as a similar 2D

sheet based on 1D [Ag(bipy)]n double chain. As shown in Fig. 2a,there are two crystallographically independent Ag(I) ions, two bipyligands, one aze ligand as well as three solvent water molecules.The Ag1 is coordinated to two N atoms of bipy ligands (Ag1–N1 = 2.186(2) and Ag1–N4 = 2.197(3) Å) and one O atom fromaze. The Ag2 is located in a four-coordinated seesaw geometrywith two N atoms and two O atoms as donors (Ag2–O1iii = 2.475(2), Ag2–O2iii = 2.675(3), Ag2–N2ii = 2.194(2) andAg2–N3 = 2.207(3) Å). For Ag1 and Ag2, two weak interactions(Ag1� � �O4i = 3.120(2) and Ag2� � �O1v = 3.059(2) Å) were observedwhich were not included into their coordination geometries. Dif-ferent from 1, the pyridyl rings of bipy ligand in 2 are approxi-mately coplanar with two small dihedral angles of 16.2� and 4.1�,respectively. The shortest Ag1� � �Ag1i and Ag2� � �Ag2iv distancesare 3.2556(5) and 3.1652(6) Å, respectively. (Symmetry codes: (i)�x + 1, �y + 2, �z + 2; (ii) x � 2, y � 1, z + 1; (iii) x � 2, y, z + 1;(iv) �x � 1, �y + 1, �z + 3.)

In 2, the bipy also acts as a bidentate bridging ligand linking theAg(I) to form a 1D chain. The adjacent chains are extended to 1Ddouble chain by the Ag� � �Ag interactions and intra-chain p� � �pinteractions (Cg1� � �Cg4i = 3.6186(19) and Cg2� � �Cg3i = 3.651(2) Å,Cg1–Cg4 are the centroids of aromatic ring N1/C1–C5, N2/C6–C10, N3/C16–C20, N4/C11–C15, respectively, Fig. 2b). The l3–g1:g0:g1:g1 aze adopts a gauche–anti–anti–anti–anti–gauche con-formation (torsion angles: 69.5, 177.8, 179.4, 179.2, 175.6 and63.3�) and links the 1D double chain into the 2D sheet (Fig. 2c).(Symmetry code: (i) �x + 1, �y + 2, �z + 2.)

Different from 1, a water hexamer was observed in the void of2D sheet of 2. As shown in Fig. 2d, each water molecule is also adouble hydrogen bond donor and single hydrogen bond acceptor.The hexamer water cluster has a similar centrosymmetric ududplanar water tetramer, but with two short suspenders which werehydrogen bonded to the water tetramer at two diagonally oppositepositions. The hydrogen-bonded O� � �O separations in the hexamerfall in the range 2.765(3)–2.859(3) Å with an average value of2.826(3) Å, which is slightly longer than those in 1. The O� � �O� � �O

Fig. 1. (a) The coordination geometries of Ag(I) ions in 1 with the thermal ellipsoids at 50% probability level. (b) Scheme of 1D double chain incorporating Ag� � �Ag and p� � �pinteractions. (c) The view of 2D sheet. (d) Water decamer in 1. (Symmetry codes: (i) x + 1/2, �y + 1/2, z � 1/2; (ii) x + 1, y, z.)

316 D. Sun et al. / Journal of Molecular Structure 1004 (2011) 313–318

angles are in the range 78.8(1)–115.0(1)�. According to PLATON[20], the hexameric water cluster occupies 10.1% of the unit cellvolume (161.3 Å3 out of the 1489.0 Å3 unit cell volume). The waterhexamer was anchored by the 2D sheet through Owater� � �Osub

hydrogen bonds ranging from 2.732(3) to 2.848(3) Å (Fig. S2, Sup-porting information).

4.3. Influence of dicarboxylates on the water cluster

In 1 and 2, the metal–organic coordination networks have sim-ilar 2D sheets, which indicates that the long dicarboxylates havelittle impact on the resulting networks. However, obviously differ-ent water clusters, (H2O)10 and (H2O)6, were characterized in twosimilar 2D sheets. Based on above analysis, we found that,although different dicarboxylates do not change the basic struc-tures of the metal–organic networks, they unambiguously modu-late different hydrophilic environments which are suitable to thevarious water aggregates being optimally occupied both in termsof packing efficiency and the maximization of intermolecular inter-actions. Consequently, different water clusters are successfullytuned by a change in the shape or distribution of the hydrophilicgroups on the host metal–organic networks.

4.4. IR spectra and thermal analyses

As shown in Fig. S3, the IR spectra of 1 and 2 show featuresattributable to the carboxyl groups stretching vibrations. No bandin the region 1690–1730 cm�1, indicates complete deprotonation

of the carboxylic groups. The characteristic bands of carboxylgroups of dicarboxylates are shown in the range 1541–1665 cm�1 for asymmetric stretching and 1382–1482 cm�1 forsymmetric stretching [38]. Moreover, the IR spectra show a veryintense broad band around 3400 cm�1 attributed to the water mol-ecules in both 1 and 2.

Powder X-ray diffraction (PXRD) has been used to check thephase purity of the bulky samples in the solid state (Fig. S4, Sup-porting information). For complexes 1 and 2, the peak positionsof simulated and experimental patterns are in good agreementwith each other, demonstrating the phase purity of the product.The dissimilarities in intensity may be due to the preferred orien-tation of the crystalline powder samples.

The thermogravimetric (TG) analysis was performed in N2

atmosphere on polycrystalline samples of 1 and 2 and the TGcurves are shown in Fig. 3. The TG curve of 1 shows the first weightloss of 11.09% in the temperature range of 30–115 �C, which indi-cates the loss of five lattice water molecules per formula unit(calcd: 11.40%), and then the metal–organic network starts todecompose accompanying loss of bipy (obsd: 40.12% and calcd:39.52%) and sub (obsd: 20.92% and calcd: 21.78%) in the rangesof 115–216 �C and 260–305 �C, respectively. For 2, the weight lossattributed to the gradual release of three water molecules per for-mula unit is observed in the range of 30–122 �C (obsd: 6.69% andcalcd: 7.03%), then the framework starts to collapse in the temper-ature range of 124–235 �C, accompanying loss of bipy (obsd:39.69% and calcd: 40.65%), then the release of aze starts at276 �C and ends at 318 �C (obsd: 25.10% and calcd: 24.23%).

Fig. 2. (a) The coordination geometries of Ag(I) ions in 2 with the thermal ellipsoids at 50% probability level. (b) Scheme of 1D double chain incorporating Ag� � �Ag and p� � �pinteractions. (c) The view of 2D sheet. (d) water hexamer in 2. (Symmetry codes: (ii) x � 2, y � 1, z + 1; (iii) x � 2, y, z + 1).

Fig. 3. TG curves for complexes 1 and 2.

D. Sun et al. / Journal of Molecular Structure 1004 (2011) 313–318 317

5. Conclusions

In summary, we succeed in modulating the water clustersincluding water decamer and hexamer by utilization of aliphaticdicarboxylates with different lengths. Both water clusters com-prised of centrosymmetric water tetramer incorporating differentsuspenders. These results illustrate the structural diversity ofwater clusters and the sensitive dependence of their structuresupon the details of their environment. The precise structural anal-ysis and the cooperative association of the water aggregates andcrystal hosts may provide insight into the hydrogen-bonding motifof the aqueous environment in living systems and a clear under-standing of the structure of ice and bulk water as well.

Acknowledgments

This work was financially supported by the National NaturalScience Foundation of China (Nos. 21021061 and 21071118), 973Project (Grant 2007CB815301) from MSTC and Independent Inno-vation Foundation of shandong university, IIFSDU.

318 D. Sun et al. / Journal of Molecular Structure 1004 (2011) 313–318

Appendix A. Supplementary material

CCDC 836626 and 836627 contain the supplementary crystallo-graphic data for 1 and 2. These data can be obtained free of chargefrom the Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-ated with this article can be found, in the online version, atdoi:10.1016/j.molstruc.2011.08.028.

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