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Solid State Sciences 13 (2011) 1542e1547

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Solid State Sciences

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Two new nickel(II) complexes constructed by biphenyl-2,20,6,60-tetracarboxylicacid: A case study with 2,20-bipyridine and 1H,1’H-2,20-biimidazole

Lin Cheng, Fei Liu, Shaohua Gou*

Pharmaceutical Research Center, School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China

a r t i c l e i n f o

Article history:Received 18 November 2010Received in revised form5 May 2011Accepted 24 May 2011Available online 30 May 2011

Keywords:Biphenyl-2,20 ,6,60-tetracarboxylic acidNickel(II) complexTerminal ligand2,20-bipyridine1H,10H-2,20-biimidazole

* Corresponding author.E-mail address: sgou@seu.edu.cn (S. Gou).

1293-2558/$ e see front matter Crown Copyright � 2doi:10.1016/j.solidstatesciences.2011.05.018

a b s t r a c t

Interactions of H4bta, Ni(II) ions with different terminal ligands (2,20-bipy and H2biim) in H2O led to theformation of two complexes, [Ni(bta)0.5(2,20-bipy)(H2O)]n (1) and Ni2(bta)(H2biim)4.2H2O (2)(H4bta ¼ biphenyl-2,20 ,6,60-tetracarboxylic acid, 2,20-bipy ¼ 2,20-bipyridine and H2biim ¼ 1H,1’H-2,20-biimidazole), in which 1 is a one-dimensional chain, while 2 is a binuclear compound. The bta ligands in1 and 2 adopt hexadentate (1kO: 2k2O3,O4: 10kO: 20k2O3’,O4’) and tetradentate (1k2O3,O4: 10k2O3’,O4’)coordination modes, respectively, and the corresponding angles of two benzene rings of bta ligands are65.15 and 82.87�. This study indicates that the nature of terminal ligands is a crucial factor for the self-assemble of complexes.

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1. Introduction

In recent years, coordination polymers with well-regulatednetworks have received remarkable attention owing to theirpotential applications as functional materials, in addition to theirintriguing variety of architectures and molecular topologies [1e4].Until now, a large number of coordination polymers have beenreported in the literature, but directed synthesis of novel archi-tectures still remains a long-term challenge. Generally, the struc-ture of the resultant framework is mainly influenced by variousfactors such as the metal/ligand nature, solvents, templates,counterions, terminal ligands, and so on [5]. Among them, terminalligands play an important role in the construction of these poly-mers with distinctive structures because they can occupy thecoordination sites of metal ions, resulting in intermitting and/ordisturbing the extension of high dimensional networks of thesecomplexes. 2,20-bipy (2,20-bipyridine) and H2biim (1H,1’H-2,20-bii-midazole) have been always used to construct new coordinationpolymers as terminal ligands in the chelating mode due to theireffective p/p stacking and/or hydrogen-bonding effect.

Furthermore, multidentate O-donor organic polycarboxylateligands have been proven to be good candidates as ligands in thepreparation of coordination polymers with interesting networksand attractive properties, not only because of their diverse

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coordination modes and high structural stability, but also becauseof their potential functions as hydrogen-bonding acceptors anddonors, depending upon the number of deprotonated carboxylicgroups [6,7], in which the aromatic multicarboxylates, such as 1,4-benzenedicarboxylate, 1,3,5-benzenetricarboxylate, 1,2,4,5-benzen-etetracarboxylate, have been extensively studied. However, asa series of multidentate O-donor ligands, biphenyl tetracarboxylicacids, such as biphenyl-2,20,3,30-tetracarboxylic acid [8], biphenyl-2,20,4,40-tetracarboxylic acid [9], biphenyl-2,20,5,50-tetracarboxylicacid and biphenyl-2,20,6,60-tetracarboxylic acid [10], have beenrarely used in the construction of coordination polymers, thoughthey have two attractive characteristics as follows: firstly, they havea rich variety of coordination modes and deprotonated forms withfour carboxylic groups, which cancontribute to construct novel andvarious coordination polymers; secondly, they have a flexible axissince two phenyl rings can be easily rotated around the CeC singlebond, which may be helpful to the synthesis of chiral coordinationpolymers because of the non-coplanarity of two phenyl rings.

Our recent studies are mainly focused on selecting biphenyltetracarboxylic acids as ligands under similar hydrothermal condi-tions to construct novel coordination architectures in order toinvestigate the influencesof synthetic conditionson the frameworksof these corresponding complexes [10e,11]. As our continuing work,we herein report two nickel(II) complexes, namely, [Ni(bta)0.5(2,20-bipy)(H2O)]n (1) and Ni2(bta)(H2biim)4.2H2O (2) (H4bta¼ biphenyl-2,20,6,60-tetracarboxylic acid, 2,20-bipy ¼ 2,20-bipyridine andH2biim ¼ 1H,1’H-2,20-biimidazole) derived from the mixture of

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Table 1Crystal and structure refinement data for complexes 1 and 2.

Complex 1 2

Empirical formula C18H13N2NiO5 C40H34N16Ni2O10

Formula weight 396.00 1016.21Crystal system Monoclinic MonoclinicSpace group P21/c C2/ca (Å) 9.660(5) 21.2459(13)b (Å) 21.858(11) 12.3057(7)c (Å) 18.050(7) 17.0447(10)a[�] 90 90b[�] 121.60(2) 109.077(1)g [�] 90 90V, Å3 3246(3) 4211.5(4)Z 8 4Dcalcd, (Mg/m3) 1.621 1.603m, mm�1 1.229 0.974F(000) 1624 2008Ref. collected/unique 29559/6357 (Rint ¼ 0.085) 8895/4073, (Rint ¼ 0.031)parameters 469 307R1a 0.0527 0.0535wR2b 0.1499 0.1612GOF 1.014 1.040

a R1 ¼ PjjFojejFcjj/PjFoj.

b wR2 ¼ [P

w(Fo2eFc2)2/

Pw(Fo2)2]1/2.

Table 2Selected bond lengths (Å) and angles (�) for complexes 1 and 2.

1Ni1-O1 2.040(4) Ni1-N2 2.079(4)Ni1-O1W 2.049(4) Ni1-O3a 2.122(3)Ni1-N1 2.047(4) Ni1-O4a 2.175(4)Ni2-O2W 2.079(4) Ni2-N4 2.085(4)Ni2-O6 1.993(3) Ni2-O7a 2.058(4)Ni2-N3 2.061(4) Ni2-O8a 2.242(3)O1-Ni1-O1W 94.05(14) O1W-Ni1-N2 89.83(15)O1-Ni1-N1 95.29(16) O1W-Ni1-O3a 95.95(13)O1-Ni1-N2 105.80(15) O1W-Ni1-O4a 90.58(14)O1-Ni1-O3a 90.40(14) N1-Ni1-N2 78.44(16)O1-Ni1-O4a 151.81(13) O3a-Ni1-N1 93.52(13)O1W-Ni1-N1 166.64(17) O4a-Ni1-N1 85.68(14)O4a-Ni1-N2 102.01(15) O3a-Ni1-N2 162.40(14)O3a-Ni1-O4a 61.44(14) O6-Ni2-N4 94.02(15)O2W-Ni2-O6 92.35(15) O6-Ni2-O7a 94.93(14)O2W-Ni2-N3 95.92(15) O6-Ni2-O8a 155.68(14)O2W-Ni2-N4 172.37(13) N3-Ni2-N4 78.82(16)O2W-Ni2-O7a 95.21(14) O7a-Ni2-N3 160.73(15)O2W-Ni2-O8a 88.90(14) O8a-Ni2-N3 103.76(12)O6-Ni2-N3 100.27(14) O7a-Ni2-N4 88.43(16)O7a-Ni2-O8a 60.78(12) O8a-Ni2-N4 87.02(14)2Ni1-O1 2.130(2) Ni1-N2 2.084(3)Ni1-O2 2.135(3) Ni1-N5 2.087(3)Ni1-N1 2.096(3) Ni1-N6 2.093(3)O1-Ni1-O2 61.54(9) O2-Ni1-N5 160.01(10)O1-Ni1-N1 163.06(11) O2-Ni1-N6 93.76(11)O1-Ni1-N2 93.51(10) N1-Ni1-N2 79.77(12)O1-Ni1-N5 99.96(10) N1-Ni1-N5 96.08(12)O1-Ni1-N6 95.56(10) N1-Ni1-N6 92.56(12)O2-Ni1-N1 103.16(11) N2-Ni1-N5 94.52(13)O2-Ni1-N2 94.18(11) N2-Ni1-N6 170.03(11)N5-Ni1-N6 79.88(12)

Symmetry code for 1: a, x, �1/2-y, �1/2 þ z.

L. Cheng et al. / Solid State Sciences 13 (2011) 1542e1547 1543

Ni(NO3)2, H4bta, 2,20-bipy/H2biim and H2O for the purpose of look-ing into the influences of terminal ligands (2,20-bipy and H2biim) onthe structures of obtained complexes. X-ray single crystal diffractionstudy indicated that 1 is a one-dimensional chain, while 2 isa binuclear compound.

2. Experimental section

2.1. Materials and measurements

All solvents and reagents were of analytical grade and usedwithout further purification. H4bta was prepared in the samemanner as reported previously [12].

C, H and N microanalyses were performed on a PerkineElmer1400 C analyzer. Infrared spectra (4000e400 cm�1) weremeasuredwith a Nicolet FT-IR 200 spectrophotometer on KBr disks. Thermalanalysis (TG) was performed on a TGA Q500 thermal analyzerunder nitrogen atmosphere at a scan rate of 10 �C min�1.

2.2. Preparation of complexes

[Ni(bta)0.5(2,20-bipy)(H2O)]n (1): A mixture of H4bta (0.066 g,0.2 mmol), Ni(NO3)2,6H2O (0.116 g, 0.4 mmol), NaOH (0.032 g,0.8 mmol), 2,20-bipy (0.063 g, 0.4 mmol) and H2O (10 mL) wereheated in a 25 mL Teflon-lined vessel at 180 �C for 3 days, followedby slow cooling (5 �C h�1) to room temperature. After filtration andwashing with H2O, green block crystals were collected and dried inair (0.388 g, yield ca. 49% based on H4bta). Anal. Calcd. forC18H13N2NiO5: C, 54.59; H, 3.31; N, 7.07. Found: C, 56.15; H, 3.26; N,6.88%. Main IR (KBr, cm�1): 3209(b), 3069(w), 1601(vs), 1542(s),1490(w), 1472 (m), 1447(m), 1376(s), 1276(w), 1250(w), 1164(w),1025(w), 912(w), 810(w), 770(s), 735(w), 714(vs), 653(w), 634(w).

Ni2(bta)(H2biim)4.2H2O (2): An analogous way to 1was used byreplacing 2,20-bipy with H2biim (0.017 g，0.8 mmol). Yield: 23%(0.236 g). Anal. Calcd. for C40H34N16Ni2O10: C, 47.28; H, 3.37; N,22.05. Found: C, 46.29; H, 3.12; N, 20.67%. Main IR (KBr, cm�1):3146(b), 2360(w), 1636(w), 1597(w), 1573(vs), 1558(vs), 1526(s),1490(w), 1452(m), 1428(m), 1398(vs), 1372(s), 1320(w), 1277(w),1182(w), 1124(w), 1082(w), 995(w), 918(w), 867(w), 771(m),752(vs), 709(m), 691(m).

2.3. X-ray crystallography

Diffraction intensities for all the compounds were collected ona Bruker SMART CCD diffractometer (MoKa, l 0.71073 Å). Absorp-tion corrections were applied by using multiscan propram SADABS[13]. The structures were solved by directmethods and refinedwithfull-matrix least-squares technique with the SHELXTL programpackage [14]. Anisotropic thermal parameters were applied to allthe non-hydrogen atoms. The organic hydrogen atoms weregenerated geometrically (CeH 0.96 Å); the hydrogen atoms of aquaand secondary amines were located from difference maps andrefined with isotropic temperature factors. The crystallographicdata and selected bonds length and angles are listed in Tables 1 and2. Selected hydrogen bond distances and bond angles are listed inTable 3.

3. Results and discussion

3.1. Synthesis and spectral characterization

The reaction conditions employed for the preparations of 1 and2 were similar under hydrothermal conditions. Compound 1 wasobtained from the mixture of the Ni(NO3)2, H4bta, 2,20-bipy andH2O at 180 �C for 3 days; while just using H2biim instead of 2,20-

bipy and keeping all the other conditions unchanged, 2 wassynthesized.

The infrared spectra of 1 and 2 were consistent with theirformulations. Features corresponding to the skeletal vibrations ofaromatic rings and heterocyclic rings for these complexes wereobserved in the rangeof 1315e1490 cm�1 for 1 and1319e1452 cm�1

for 2. Asymmetric and symmetric carboxylate stretching modes

Table 3Selected hydrogen bond lengths (Å) and bond angles (�) of 1 and 2 (D, donor atom; A,acceptor atom).

D-H/A D-H [Å] H/A [Å] D/A [Å] D-H/A [�]

1O1w-H1WA/O2 0.85 1.78 2.613(5) 166O1w-H1WB/O7a 0.85 1.81 2.664(5) 180O2w-H1WA/O5 0.85 1.86 2.642(5) 153O2w-H1WB/O3a 0.85 2.07 2.885(4) 1612O1w-H1WA/O4 0.85 2.20 2.829(7) 131O1w-H1WB/O3a 0.85 2.25 3.104(8) 179N3eH3A/O3b 0.86 2.06 2.827(6) 149N4-H4A/O3b 0.86 2.11 2.862(5) 146N7-H7B/O4c 0.86 2.04 2.708(5) 133N8-H8B/O1d 0.86 2.05 2.801(4) 145

Symmetry code for 1: a, x,�1/2�y,�1/2þ z. for 2: a, 1�x, y, 3/2�z; b, 1�x, 1 þ y, 3/2�z; c, 1/2 þ x, 7/2�y, 1/2 þ z; d, 3/2�x, 7/2�y, 2�z.

L. Cheng et al. / Solid State Sciences 13 (2011) 1542e15471544

were observed at 1601 and 1541 cm�1, respectively, for 1; while for2, characteristic bands of carboxylate groups at 1597 cm�1 for theasymmetric stretching and at 1558 and 1526 cm�1 for symmetricstretching.

3.2. X-ray crystallographic studies of complexes

3.2.1. [Ni(bta)0.5(2,20-bipy)(H2O)]n (1)Single-crystal XRD study has revealed that [Ni(bta)0.5(2,20-

bipy)(H2O)]n (1) crystallizes in a monoclinic system with spacegroup P21/c. The asymmetric unit of 1 contains one bta ligand, twocrystallographically independent Ni(II) ions, two chelating 2,20-bipy and two coordinated water molecules.

The two crystallographically independent Ni1 and Ni2 ions,owning the same coordinationmodewith similar bond lengths andbond angles, both display a slightly distorted octahedral geometry,being surrounded by one chelating carboxylate and one carbox-ylate oxygen atom from two bta ligands, respectively, one chelating2,2-bipy and one coordinated water molecule, as shown in Fig. 1a.On the other hand, each bta ligand is coordinated to two Ni1 andtwo Ni2 atoms in a hexadentate (1kO: 2k2O3,O4: 1’kO: 20k2O3’,O4’,two chelating and two monodentate) mode (Fig. 2a). In a bta anion,the angle of two benzene rings is 65.15�.

As shown in Fig. 1a, Ni1 and Ni2 are coordinated by 2,2-bipyand H2O, respectively, resulting in the nodes of [Ni(2,20-bipy)( H2O)].Two bta ligands link two [Ni(2,20-bipy)(H2O)] nodes, constructedby one Ni1 and one Ni2, respectively, to build a binuclear [Ni2(b-ta)2(2,20-bipy)2(H2O)2] unit with the Ni1/Ni2 distance of 5.207 Å.Thesebinuclearunits are linked to eachother by sharingbta ligands to

Fig. 1. Structures of one-dimensional chain (a) and tw

build a one-dimensional chain running along the crystallographic caxis with the shortest intrachain Ni1/Ni1 and Ni2/Ni2 distances of10.264and10.465Å, respectively, across thebta ligands.Moreover, theone-dimensional chain is reinforced by intrachain O-H/Ohydrogen-bonds (O1w/O2 2.613(5), O1w/O7a 2.664(5), O2w/O5 2.642(5)and O2w/O3a 2.885(4) Å, symmetry code: a, x, �1/2-y, �1/2 þ z)between coordinated water molecules and bta anions.

If taking a bpt ligand as a combination of two isophthalates, eachisophthalate section links two Ni1 or two Ni2 atoms in a tridentate(one chelating and one monodentate) mode to build a one-dimensional zig-zag chain, respectively. These two zig-zag chainsare linked together with the CeC single bonds of bta to builda double chain (Fig. 1a).

The one-dimensional chains are further constructed intoa three-dimensional supramolecular structure by effective p/p

stacking between the interlayer adjacent 2,20-bipy rings with thecentroid-centriod separation of 4.118 Ǻ, as shown in Fig. 1b.

3.2.2. Ni2(bta)(H2biim)4.2H2O (2)Compound 2 crystallizes in a monoclinic system of space group

C2/c. The asymmetric unit of 2 contains one Ni(II) atom, half of a btaligand, twoH2biim ligands and one freewatermolecule. As shown inFig. 3a, each Ni atom displays a slightly distorted octahedral geom-etry, being coordinated by two chelating H2biim and one chelatingcarboxylate from a bta ligand. Each bta acts as a bis-chelating ligandto ligate two Ni(II) ions into a binuclear compound with the Ni/Nidistance of 6.690 Å (Fig. 3a). Interestingly, different from thosecompounds we reported [10cee], only two carboxylates in twobenzene rings of each bta ligand, respectively, are coordinated toNi(II) ions, while the other two carboxylates are free (Fig. 2b). Thebinuclear structure is further stabilized by effective p/p stackingbetween the two adjacent imidazole rings from twoH2biimwith thecentroid-centriod separation of 3.555 Å (Fig. 3a). It is noted that theangle of two benzene rings in a bta ligand is 82.87�, being muchlarger than that in 1 (65.15�), which may be attributed that theintramolecular p/p stacking interaction in the binuclear structureof 2 makes the two benzene rings far away from a plane.

Meanwhile, each binuclear unit is connected to four adjacentunits via N-H/O hydrogen-bonds (N3/O3b 2.827(6), N4/O3b2.862(5), N7/O4c 2.708(5), N8/O1d 2.801(4) Å, symmetry code:b,1�x,1þ y, 3/2�z; c, 1/2þ x, 7/2�y,1/2þ z; d, 3/2�x, 7/2�y, 2�z)between bta anions and H2biim ligands to form a two-dimensionalhydrogen bonding network along the ab plane (Fig. 3b). From thetopological view, each dimer can be considered as a four-connecting node, which is connected by N-H/O hydrogen-bonds.Consequently, the two-dimensional network can be regarded asa (4, 4) topology, as shown in Fig. 3c.

o-dimensional supramolecular structure (b) in 1.

Fig. 2. Coordination modes of bta ligands observed in 1 (a) and 2 (b).

L. Cheng et al. / Solid State Sciences 13 (2011) 1542e1547 1545

It is noted that there are “empty” spaces in the two-dimensionalnetwork, which are filled with free water molecules. These crystalwater molecules are stabilized in the apertures of this two-dimensional construction by the hydrogen bonds, which involvesthe water molecules and the carboxylate oxygen atoms [O2w/O42.829(7) Å, O2w/O4a 3.104(8) Å, symmetry code: a, 1�x, y, 3/2�z]from bta anions (Fig. 3b).

3.3. Thermogravimetric properties

The thermogravimetric analyses of powder samples 1 and2werecarried out from 19 to 737 �C under nitrogen atmosphere at theheating rate of 10 �Cmin�1, as shown in Fig. 4. For compound1, thereare two distinct weight losses of the coordinated water moleculesbetween 19 and 222 �C (expt. 5.3%, calcd. 4.5%): (1) a slow weightloss of 1.4% from 19 to 180 �C shows some of the coordinated watermolecules begin to escape from the whole framework; (2)

subsequently, a quick weight loss of 3.9% from 180 to 222 �C corre-sponds to the release of the residual coordinated water molecules.Then, the structure without the coordinated water molecules aremaintained until 308 �C. The weight loss of 35.9% in a range of308e398 �C indicates the removal of 2,20-bipy ligands and thedecomposition of the whole structure. The TG curve of 2 showsaweight loss of 2.3% in the temperature range of 19e96 �C, which isin agreement with the removal of the lattice water molecules (3.5%calculated). The compoundwithout the freewatermolecules is thenstable until 363 �C, which indicates the binuclear construction israther thermally stable. The second weight loss of 34.8% between363 and 467 �C corresponds to the removal of tba ligands (32.1%calculated) and the decomposition of the binuclear structure.

To observe the thermal stability of 1 and 2 upon the removal ofthe water molecules, XRD data of both the complexes before andafter removing the water molecules were measured (see Figs. S1-S2), indicating that the framework of 1 collapses after the

Fig. 3. Structures of the binuclear Ni(II) compound (a), two-dimensional hydrogen bonding layer (b) and the (4, 4) topology (c) in 2.

Fig. 4. TG plots for 1 and 2.

L. Cheng et al. / Solid State Sciences 13 (2011) 1542e15471546

coordinated water molecules are lost, while 2 remains intact afterthe removal of the free water molecules.

3.4. Influences of terminal ligands on the crystal structures

1 and 2 were synthesized by the interaction of H4bta, Ni(NO3)2and H2O at 180 �C under solvothermal conditions, in which 1 and 2were obtained with 2,20-bipy and H2biim, respectively. 1 is a one-dimensional chain, while 2 is a binuclear complex. In 1 and 2, thecoordination modes of Ni(II) and bta ligands are different, and theweak interactions are also different, in which there are hydrogenbonding and p/p stacking interactions in 1 and only hydrogenbonding interactions in 2.

In a bta ion, the two benzene rings are not coplanar (Scheme 1)[10]. The angle between two benzene rings of bta ligands in 1 is65.15�, being much smaller than that in 2 (82.87�), due to theintramolecular p/p stacking interaction in the binuclear structureof 2making the two benzene rings nearer to mutual perpendicular,which is a crucial factor that has caused the generation of twodistinct compounds [11].

-OOC

COO-

COO-

-OOC

Scheme 1. Structure of bta ion.

L. Cheng et al. / Solid State Sciences 13 (2011) 1542e1547 1547

4. Conclusions

In this study, two new complexes with different architectures,[Ni(bta)0.5(2,20-bipy)(H2O)]n (1) and Ni2(bta)(H2biim)4.2H2O (2)were constructed from H4bta and Ni(II) ions with different terminalligands, inwhich 1 is a one-dimensional chain, while 2 is a binuclearcomplex. The present studydemonstrates that the nature of terminalligands is an important factor for the self-assemble of the structures.

Acknowledgements

The authors are grateful to the financial support from NationalNatural Science of Foundation of China (project No. 20801011 andNo. 21001024) and the Funding from Southeast University (No.4007041121 and No. 9207040016).

Appendix. Supplementary data

Supplementary data related to this article can be found online atdoi:10.1016/j.solidstatesciences.2011.05.018.

References

[1] (a) O.M. Yaghi, H. Li, C. Davis, D. Richardson, T.L. Groy, Acc. Chem. Res. 31(1998) 474;(b) D. Braga, F. Grepioni, G.R. Desiraju, Chem. Rev. 98 (1998) 1375;(c) A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem. Int. Ed. 38 (1999) 3268.

[2] (a) G.S. Papaefstathiou, L.R. MacGillivray, Coord. Chem. Rev. 246 (2003) 169;(b) D. Bradshaw, J.B. Claridge, E.J. Cussen, T.J. Prior, M.J. Rosseinsky, Acc. Chem.Res. 38 (2005) 273;(c) D. Fiedler, D.H. Leung, R.G. Bergman, K.N. Raymond, Acc. Chem. Res. 38(2005) 351.

[3] (a) W. Lin, O.R. Evans, R.G. Xiong, Z. Wang, J. Am. Chem. Soc. 120 (1998) 13272;(b) K. Biradha, Y. Hongo, M. Fujita, Angew. Chem. Int. Ed. 41 (2002) 3395;(c) N. Zheng, X. Bu, P. Feng, Angew. Chem. Int. Ed. 43 (2004) 4753;(d) M.B. Zhang, J. Zhang, S.T. Zheng, G.Y. Yang, Angew. Chem. Int. Ed. 44 (2005)1385.

[4] (a) D.F. Sun, S. Ma, Y. Ke, T.M. Petersen, H.C. Zhou, Chem. Commun. (2005) 2663;(b) S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki, Y. Kinoshita,S. Kitagawa, J. Am. Chem. Soc. 129 (2007) 2607;(c) L. Chen, J. Kim, T. Ishizuka, Y. Honsho, A. Saeki, S. Seki, H. Ihee, D. Jiang, J. Am.Chem. Soc. 131 (2009) 7287;(d) Q.T. He, X.P. Li, Y. Liu, Z.Q. Yu, W. Wang, C.Y. Su, Angew. Chem. Int. Ed. 48(2009) 6156.

[5] (a) L. Cheng, J.B. Lin, J.Z. Gong, A.P. Sun, B.H. Ye, X.M. Chen, Cryst. Growth Des 6(2006) 2739;(b) M.L. Tong, X.M. Chen, B.H. Ye, S.W. Ng, Inorg. Chem. 37 (1998) 2645;(c) C.Y. Su, Y.P. Cai, C.L. Chen, F. Lissner, B.S. Kang, W. Kaim, Angew. Chem. Int.Ed. 41 (2002) 3371.

[6] (a) Z.H. Zhou, J.M. Yang, H.L. Wan, Cryst. Growth Des 5 (2005) 1825;(b) S.L. Childs, L.J. Chyall, J.T. Dunlap, V.N. Smolenskaya, B.C. Stahly, G.P. Stahly,J. Am. Chem. Soc. 126 (2004) 13335;(c) P. Vishweshwar, A. Nangia, V.M. Lynch, Cryst. Growth Des 3 (2003) 783.

[7] (a) D.T. de Lill, N.S. Gunning, C.L. Cahill, Inorg. Chem. 44 (2005) 258;(b) L.A. Borkowski, C.L. Cahill, Inorg. Chem. 42 (2003) 7041;(c) Y.Y. Liu, J.F. Ma, J. Yang, J.C. Ma, Z.M. Su, Cryst. Eng. Comm. 10 (2008) 894;(d) H.F. Zhu, J. Fan, T. Okamura, Z.H. Zhang, G.X. Liu, K.B. Yu, W.Y. Sun,N. Ueyama, Inorg. Chem. 45 (2006) 3941.

[8] (a) S.Q. Zang, Y. Su, C.Y. Duan, Y.Z. Li, H.Z. Zhu, Q.J. Meng, Chem. Commun.(2006) 4997;(b) S.Q. Zang, Y. Su, Y.Z. Li, J.G. Lin, C.Y. Duan, Q.J. Meng, S. Gao, Cryst. Eng.Comm. 11 (2009) 122.

[9] (a) T.T. Jia, S.Y. Zhu, M. Shao, Y.M. Zhao, M.X. Li, Inorg. Chem. Commun. 11(2008) 1221;(b) L.L. Wen, F. Wang, X.K. Leng, C.G. Wang, L.Y. Wang, J.M. Gong, D.F. Li, Cryst.Growth Des 10 (2010) 2835.

[10] (a) M.P. Suh, H.R. Moon, E.Y. Lee, S.Y. Jang, J. Am. Chem. Soc. 128 (2006) 4710;(b) Y.G. Huang, Y.Q. Gong, F.L. Jiang, Y.G. Huang, Y.Q. Gong, F.L. Jiang, D.Q. Yuan,M.Y. Wu, Q. Gao, W. Wei, M.C. Hong, Cryst. Growth Des. 7 (2007) 1385;(c) L. Cheng, J.Q. Wang, L.M. Zhang, Acta Cryst. E66 (2010) m1329;(d) L. Cheng, J.Q. Wang, S.H. Gou, Inorg. Chem. Common 14 (2011) 261e264;(e) L. Cheng, S.H. Gou, L.M. Zhang, Solid State Sci. 12 (2010) 2163e2169.

[11] L. Cheng, S. H Gou, J.Q. Wang, J. Mol. Struct. 991 (2011) 149e157.[12] K.E. Pryor, G.W. Shipps Jr., D.A. Skyler, J. Rebek Jr., Tetrahedron 54 (1998)

4107.[13] G.M. Sheldrick, SADABS 2.05. University of Göttingen, 2002.[14] SHELXTL 6.10, Bruker Analytical Instrumentation Madison, Wisconsin, USA

(2000).