Zn(II) metal-organic frameworks (MOFs) assembled from semirigid multicarboxylate ligands: Synthesis, crystal structures, and luminescent properties

Solid State Sciences 12 (2010) 1791e1796

Contents lists available at ScienceDirect

Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie

Zn(II) metal-organic frameworks (MOFs) assembled from semirigid multicarboxylate ligands: Synthesis, crystal structures, and luminescent properties Kang Wang, Hailong Wang, Yongzhong Bian*, Wenjun Li* Department of Chemistry, University of Science and Technology Beijing, Beijing 100083, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 May 2010 Received in revised form 25 July 2010 Accepted 31 July 2010 Available online 10 August 2010

Two new coordination polymers [Zn2L(2,20 -bpy)]n∙(H2O)2n (1) and [Zn2L(phen)]n∙(H2O)2n (2) have been assembled from a semirigid multicarboxylate ligand 3,30 -(1,3-phenylenebis(oxy))diphthalic acid (H4L) with the help of 2,20 -bipyridine (2,20 -bpy) or 1,10-phenanthroline (phen) as secondary ligand. Single crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the space group C2/c and displays a one-dimensional (1D) chain structure constructed from 2,20 -bpy and L ligand, which further forms a two-dimensional (2D) plane via intermolecular pep interactions. Compound 2 belongs to the space group P1 and features a 1D D- and L-typed chiral chain configuration despite the racemic nature for the whole complex. The neighboring chains with the same chirality are further stacked into a 2D DDD- or LLL-typed supramolecular structure via intermolecular pep interactions because of the chiral recognition mechanism. Photophysical properties over complexes 1 and 2 have been comparatively investigated, revealing the effect of secondary ligand on the luminescent properties of these two complexes. Ó 2010 Elsevier Masson SAS. All rights reserved.

Keywords: Semirigid multicarboxylate ligand One-dimensional chain Luminescent property

1. Introduction In the field of supramolecular chemistry and crystal engineering, the design and assembly of metal-organic coordination frameworks (MOFs) with appealing structures and properties have stimulated interests of chemists in recent years [1e8]. Thus far, a great number of metal-organic coordination polymers have been prepared [1e10]. The molecular structures of MOFs have been revealed to mainly depend on geometry and number of coordination sites provided by organic ligands [11e13]. However, there still remains a great challenge for rational design and synthesis of functional coordination architectures because of many subtle factors related with the crystallization process. In the past few years, multidentate O-donor ligands including 1,4-benzenedicarboxylate and 1,3,5-benzenetribenzoate with a rigid benzene central molecular framework were extensively employed for the preparation of functional MOFs, since their coordination geometry renders it possible to relatively easy predict the molecular structures of MOFs with the help of the reported literature [14e20]. Quite recently, a new family of multidentate Odonor ligands with a semirigid V-shaped molecular framework,

* Corresponding authors. E-mail address: [email protected] (Y. Bian). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.07.032

actually two benzene rings bridged by a nonmetallic atom (C, O, S, and N atoms) including 2,20 ,3,30 -oxidiphthalic acid, 4,40 -oxidiphthalic acid, 3,30 ,4,40 -oxidiphthalic acid, and 4,40 -(hexafluoroisopropyl idene)-bis(benzoic acid), have been employed to assemble MOFs with potential applications in the field of separation, absorption, catalysts, and sensors [21e27]. As can be seen, semirigid V-shaped multidentate carboxylate ligand provides the diverse coordination conformations as well as abundant acceptor and donor atoms to form hydrogen bond, leading to interesting molecular structures such as helices and interpenetrating networks. However, these semirigid V-shaped multidentate Odonor ligands possess semirigid backbone rotating around only one bridged nonmetallic atom at freedom, probably leading to the limitation in generation of the molecular structure and functionality of MOFs. To the best of our knowledge, the semirigid multidentate O-donor ligands with more than one bridged nonmetallic atom have been scarcely explored. It therefore seems interesting to prepare new semirigid multidentate O-donor species with more than one bridged nonmetallic atom for the purpose of assembling new MOFs with novel structural motifs and properties. In the present work, a new multidentate O-donor ligand 3,30 -(1,3phenylenebis(oxy))diphthalic acid (H4L) was synthesized with four coordinating carboxylic groups attached at the semirigid central molecular framework with three benzene rings connected by two etheric oxygen atoms. Fortunately, two coordination complexes

1792

K. Wang et al. / Solid State Sciences 12 (2010) 1791e1796

[Zn2L(2,20 -bpy)]n∙(H2O)2n (1) and [Zn2L(phen)]n∙(H2O)2n (2) were obtained under hydrothermal condition by utilizing the semirigid multicarboxylate ligand with the help of 2,20 -bpy or phen as secondary ligand. Their single crystal structures and optical properties have also been investigated. It is worth noting that the coordination polymers constructed on the basis of the semirigid multidentate O-donor ligand have not been reported thus far. 2. Experimental section All reagents and solvents employed in the present work were obtained from the commercial source and used directly without further purification. The ligand was synthesized according to the reported procedure [28,29]. 2.1. Synthesis of semirigid ligand H4L The ligand of 3,30 -(1,3-phenylenebis(oxy))diphthalic acid (H4L) was synthesized according to the following procedure. Resorcinol (0.53 g, 5 mmol) and anhydrous K2CO3 (3.91 g, 25 mmol) was added into DMF (25 mL) and stirred for 30 min at room temperature. Then 3-nitropthalonitrile (1.73 g, 10 mmol) was added to the resulting suspension and the reaction mixture was stirred at room temperature for a further 48 h. Then the mixture was poured into water (200 mL), and a slightly red solid was yielded and isolated by filtration. The crude product was dried in air, yielding 3,30 -(1,3phenylenebis(oxy))diphthalonitrile (1.65 g, 91%). 1H NMR (400 MHz, DMSO-d6): d 7.730e7.789 (m, 4H), d 7.514 (t, J ¼ 16.4 Hz, 1H), d 7.354 (d, J ¼ 8.0 Hz, 2H), d 7.155 (s, 1H), d 7.096 (d, J ¼ 8.0 Hz, 2H). The mixture of 3,30 -(1,3-phenylenebis(oxy))diphthalonitrile (0.9 g, 2.5 mmol) and NaOH (1.20 g, 30 mmol) in distilled water (15 mL) was refluxed until the solution turned clear. The solution was then cooled to room temperature and filtered. After the pH value of the filtrate was adjusted to about 5e6 with HCl (6.0 mol dm3), the filtrate was kept undisturbed at room temperature. After about one day, a large amount of yellow solid of H4L was collected by filtration with a yield of 0.8 g, 73%. IR/cm1 (KBr): 3072(m), 1710(s), 1599(m), 1479(s), 1454(s), 1247(s), 1124(s), 993(m), 761(m). 1H NMR (400 MHz, DMSO-d6): d 7.598 (d, J ¼ 7.6 Hz, 2H), d 7.347 (t, J ¼ 16.0 Hz, 2H), d 7.224 (d, J ¼ 8.0 Hz, 2H), d 7.084 (d, J ¼ 8.4 Hz, 2H), d 6.537e6.590 (m, 2H). 2.1.1. General synthesis procedure for complexes 1 and 2 The target complexes were obtained by utilizing the hydrothermal method with the same stoichiometric ratio for the starting materials. A Teflon-lined stainless steel container (25 mL) was employed as a reaction vessel containing all starting materials, which was heated to an appropriate temperature and held for 72 h, then cooled to 50  C at a descent rate of 10  C/h. Finally, the oven was turned off and kept for another 10 h, and perfect crystals were isolated with a high yield based on the ligand.

Table 1 Crystal data and structure refinements of complexes 1 and 2. Compound

1

2

Formula fw Crystal system Space group a b c

C46H48N4O16Zn2 1043.6 monoclinic C2/c 16.5460(12) 16.5940(12) 15.3220(11) 90 97.639(5) 90 4169.5(5) 4 1.663 1.235 2160 0.0451 0.1556 0.1596 1.127

C46H32N4O13Zn2 979.5 triclinic P1 11.3151(19) 13.296(2) 15.131(3) 97.730(3) 105.271(3) 103.569(3) 2087.4(6) 2 1.558 1.224 1000 0.0653 0.1744 0.1964 0.972

a b g V Z Fcalcd (g/cm3) m mm1 F(000) R1 (I > 2q) Rw2 (I > 2q) Rw2 for all GOF on F2

2.1.2. [Zn2L(2,20 -bpy)2]n∙(H2O)6n∙(CH3CH2OH)2n (1) A mixture containing Zn(OAc)2$2H2O (11.0 mg, 0.05 mmol), 2,20 bpy (7.8 mg, 0.05 mmol), H4L (11.0 mg, 0.025 mmol), KOH (4.2 mg, 0.075 mmol), and H2O (15 mL), and CH3CH2OH (1 mL) was sealed in a teflon-lined stainless steel reactor and heated to 120  C (pH ¼ 10.0).Colorless block-shaped crystals were separated by filtration and dried in air. Yield 12.2 mg, 46.9% (based on ligand). Anal. Calcd. For C46H48N4O16Zn2: C 53.02, H 4.37, N 5.38. Found: C 53.40, H 4.50, N 5.27. IR/cm1 (KBr): 3413 (m), 1598 (s), 1564 (s), 1475 (s), 1444 (s), 1389 (s), 1238(m), 1122(m), 992 (m), 769 (s), 735 (s). 2.1.3. [Zn2L(phen)2(H2O)]n∙(H2O)2n (2) A mixture containing Zn(OAc)2$2H2O (11.0 mg, 0.05 mmol), phen (8.6 mg, 0.05 mmol), H4L (11.0 mg, 0.025 mmol), KOH (4.2 mg, 0.075 mmol), and H2O (15 mL), and CH3CH2OH (1 mL) was sealed in a teflon-lined stainless steel reactor and heated to 160  C (pH ¼ 10.0). Colorless block-shaped crystals were separated by filtration and dried in air. Yield 10.6 mg, 40.0% (based on ligand). Anal. Calcd. For C46H32N4O13Zn2: C 56.36, H 3.27, N 5.72. Found: C 56.22, H 3.41, N 5.66. IR/cm1 (KBr): 3398 (m), 1565 (s), 1516 (s), 1468 (s), 1429 (s), 1391 (s), 1259 (m), 1233 (m), 1233 (m), 1125 (m), 855 (m), 767 (m), 727 (m), 694 (m). 2.1.4. Physical measurements 1 H NMR spectra were recorded on a Bruker ultrashield AvanceZ 400 spectrometer (400 MHz) in DMSO-d6 using the residual solvent resonance of DMSO-d6 at 2.40 ppm relative to SiMe4 as internal reference. Elemental analyses were carried out with an Elementary Vario El. The infrared spectroscopy on KBr pellets were performed on a Bruker Tensor 37 spectrophotometer in the region of 4000e400 cm1. Luminescence spectra for the solid samples were

Scheme 1. Synthetic route to the quadridentate ligand H4L.

K. Wang et al. / Solid State Sciences 12 (2010) 1791e1796

1793

Scheme 2. The synthesis of Zn(II) complexes 1 and 2.

recorded with a Hitaichi F-4500 fluorescence spectrophotometer. Thermogravimetric analysis (TGA) were performed on a PerkineElmer TG-7 analyzer heated from 30 to 600  C with a heating rate of 10  C/min under nitrogen. Power X-ray diffraction (PXRD) measurements were carried out on a Rigaku D/max-cB X-ray diffractometer.

2.1.5. Single crystal X-ray diffraction determination Crystal data for these two complexes were collected on a Bruker SMART APEXII CCD diffractometer with graphite monoA) using the SMART and chromatic Mo Ka radiation (l ¼ 0.71073  SAINT programs at 298 K, and the structures were solved by the direct method (SHELXS-97) and refined by full-matrix leastsquares (SHELXL-97) on F2. Anisotropic thermal parameters were used for the nonhydrogen atoms and isotropic parameters for the hydrogen atoms. Hydrogen atoms were added geometrically and refined using a riding model. Crystallographic data and other pertinent information for the complexes are summarized in Table 1. CCDC 763871 and 763872 for complexes 1 and 2, respectively, contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.

3. Results and discussion 3.1. Synthesis of the multicarboxylate ligand and complexes 1 and 2

Fig. 1. The powder X-ray diffraction pattern of complex 1 and 2 (blue line: simulated from single crystal X-ray diffraction data; black line: experimental X-ray diffraction patterns). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

As shown in Scheme 1, the precursor of the multicarboxylate ligand 30 -(1,3-phenylenebis(oxy))diphthalonitrile is prepared easily by a nucleophilic replacing reaction of 3-nitropthalonitrile and resorcinol in the presence of anhydrous K2CO3 in DMF solution. The resulting precursor is transformed into the target multicarboxylate ligand through a hydrolyzation reaction of cyanide groups. The semirigid multicarboxylate ligand H4L is separated by filtration and employed in a hydrothermal reaction without further purification. In the present study, complexes 1 and 2 were prepared from the hydrothermal reaction between ligand H4L and Zn(OAc)2 salt together with 2,20 -bpy or phen as secondary ligand in a molar ratio of 1:2:2 (Scheme 2). A series of reactions were performed to investigate the effect of pH value (from 7.0, 8.0, 9.0, 10.0, 11.0, to 12.0) and reaction temperature (including 120, 140, 160, and 180  C) on the formation of coordination polymers from the ligand. The reactions between the multidentate ligand and Zn(OAc)2 salt without a secondary ligand were carried out at different temperature, giving only some white precipitates. However, when the second suitable auxiliary chelating N-donor ligand such as 2,20 -bpy or phen was introduced, perfect single crystals of both complexes were obtained under suitable pH and reaction temperature. The pH value was revealed to play an important role in the formation of MOFs. Hydrothermal reactions gave compounds with good crystal quality and high yields for both 1 and 2 only when KOH with a molar ratio 3:1 to the tricarboxylate ligand was added to deprotonate the ligand

1794

K. Wang et al. / Solid State Sciences 12 (2010) 1791e1796

Fig. 2. (A) The molecular structure of 1. The solvented water molecule and hydrogen atoms were omitted for clarity. (B) a 1D chain in 1. (C) a 2D network packed by 1D chain via pep interactions.

(pH ¼ 10.0) again under suitable temperature. This is also true for the reaction temperature. Under all the above mentioned reaction conditions, good crystals for complexes 1 and 2 can be obtained only at 120 and 160  C, respectively. 3.2. IR spectra In the IR spectra of semirigid multidentate ligands, the absorption band at 1710 cm1 for the H4L ligand is attributed to the asymmetric stretching vibration of uncoordinated carboxylic groups, which red-shifts to 1598 and 1565 cm1 in the spectra of complexes 1 and 2, respectively, due to the formation of the Zn(II)eO coordination bond of carboxylic oxygen atom in these two ligands. 3.3. Thermal analyses and PXRD patterns The thermal behaviors for compounds 1 and 2 were studied to reveal their thermal stability. TGA experiments were performed on pure single crystal sample of complexes 1 and 2 under N2 atmosphere with a heating rate of 10  C/min in the range of 30e600  C. Complex 1 loses all its solvent at 363  C, obsd. 35.66%, calcd. 38.42%, and the framework begins to collapse at 408  C. For 2, the TGA curve shows that the water molecules are lost from room temperature to

290  C (obsd. 3.33%, calcd. 3.67%), and the decomposition temperature of the residual composition spans the range of 290e500  C. Samples of 1 and 2 in the single crystal state were also analyzed by powder X-ray diffraction. The composition and phase purity of these two compounds were confirmed by the good correspondence between experimental X-ray diffraction patterns and simulated ones obtained on the basis of single crystal X-ray diffraction data, Fig. 1. 3.4. Crystal structure of complex 1 X-ray diffraction analysis reveals that complex 1 belongs to the space group C2/c and exhibits a one-dimensional (1D) chain structure assembled from 2,20 -bpy and L ligands. The asymmetric unit contains one Zn(II) ion, half L ligand, one coordinated 2,20 -bpy ligand, one ethanol molecule, and three solvented water molecules. As shown in Fig. 2A, the Zn(II) ion locates in a distorted pyramid coordination sphere completed by two nitrogen atoms of 2,20 -bpy ligand and three oxygen atoms of two different carboxylic groups from two L ligands. The ZneO bond length ranges between 1.952(3) and 2.170(3)  A, and the distance of ZneN bonds ranges between 2.069(3) and 2.092(4)  A, Table S1 (Supporting Information), which are comparable to those reported for compounds containing

K. Wang et al. / Solid State Sciences 12 (2010) 1791e1796

1795

Fig. 3. (A) The molecular structure of 2. The solvented water molecule and hydrogen atoms were omitted for clarity. (B) D- and L-typed 1D chains in 2. Coordinated phen ligands were omitted for clarity. (C) 2D DDD- and LLL-typed supramolecular structure united by 1D chain via intermolecular pep interactions.

OeZneN segments [30e32]. As to L ligand, the dihedral angles between the two terminal benzene rings and middle one are 79.68 , and the dihedral angle of the two terminal benzene rings is 20.25 . In complex 1, multidentate L ligand is completely deprotonated, and its four deprotonated carboxylate groups adopt two independent kinds of coordination modes. Two carboxylate groups attached nearby the bridged etheric oxygen atoms adopt a chelating coordination mode, and the remaining two carboxylate groups coordinate to the Zn centers in a monodentate coordination mode. Two phthalic acid segments from different L ligands coordinate to two Zn(II) ions to form a dinuclear unit, which expands a 1D chain bridged by the middle benzene rings, Fig. 2B. In the dinuclear Zn(II) unit, the adjacent zinc ions are separated by the distance of 5.074  A, and all Zn(II) ions bounded by the L ligand are coplanar. The individual chains are further packed into a 2D network via intermolecular pep interactions between coordinated 2,20 -bpy ligands, Fig. 2C. The centroid separation between the A, which is in the normal adjacent 2,20 -bpy groups amount to 3.68  range to form pep interaction [33,34]. 3.5. Crystal structure of complex 2 The molecular structure of compound 2 is shown in Fig. 3. This compound crystallizes in the space group P1 and also exhibits a 1D chain framework. The asymmetric unit contains two crystallographically independent Zn(II) ions, one L ligand, two coordinated phen ligands, one coordinated water molecule, and two solvented water molecules. As shown in Fig. 3A, Zn1 ion is coordinated by two nitrogen atoms of chelating phen ligand, two oxygen atoms from two L ligands, and one oxygen atom from water molecule. Zn2 ion possesses distorted tetrahedral coordination geometry constructed by two nitrogen atoms of phen ligand and two oxygen atoms from two L ligands. The distances of Zn1---Zn2 and Zn1---Zn1A are 5.203 and 15.304  A, respectively. The bond length of ZneO ranges

between 1.948(7) and 2.147(8)  A, and the ZneN bond distance spans the range of 2.065(8) and 2.169(9)  A. The difference between the coordination environments of Zn1 and Zn2 probably is caused by the bigger conjugated systems of phen ligand than that of 2,20 bpy ligand. As a result, it diminishes the symmetry of the dinuclear Zn(II) moiety to C1, leading to intrinsic chirality for the dinuclear unit. The chirality of the dinuclear Zn(II) ions are further transferred to the whole 1D chain, generating a D- or L-typed molecular structure, Fig. 3B. The neighboring 1D chains with the same chirality are further connected into a 2D DDD- or LLL-typed supramolecular structure via intermolecular pep interactions possibly because of the chiral recognition mechanism, Fig. 3C. The centroid separation between the adjacent phen ligands are 3.408  A, shorter than that of 1, revealing an increase in pep interactions between the neighboring phen ligands than between 2,20 -bpy ligands in 1. In addition, the dihedral angles between the two terminal benzene rings and middle one are different with the value of 73.17 and 82.90 , respectively, and the dihedral angle of the two terminal benzene rings is 32.38 . These changes on the L ligand may be also a result of the bigger spacer effect for phen ligand than 2,20 -bpy ligand. 3.6. Luminescent properties The solid state emission spectra of complexes 1 and 2 together with the H4L have been recorded at room temperature and shown in Figure S2. The emission band for the metal free ligand H4L observed at 448 nm is assigned to the typical intraligand pep* electronic transition [35]. Formation of Zn(II) complexes with dinuclear subunits from metal free H4L ligands with the help of secondary ligand induces change in the luminescent emission of 1 and 2. The intraligand emission band of metal free ligand H4L takes blue shift to 416 and 388 nm in the luminescent emission spectra of 1 and 2, Figure S2, which is considered to be a result of the change

1796

K. Wang et al. / Solid State Sciences 12 (2010) 1791e1796

of conformation of ligand according to Perkovic’s hypothesis [36,37]. The difference in the peak position is due to the different secondary ligand, which may also participate in the process of energy transfer involved in the luminescence. 4. Conclusion In this paper, a new versatile multicarboxylate ligand has been employed for the first time to construct two new Zn(II) coordination polymers with the help of 2,20 -bpy or phen as secondary ligand. Structural investigation of these two complexes reveals the framework structure of coordination polymers could be tuned by changing size of the secondary chelating N-donor ligand. Unexpected blue-shifted emissions of 1 and 2 relative to the metal free ligand were observed. Further systematic work towards fabricating more MOFs with interesting structure and functionalities using semirigid multicarboxylate ligands is in progress. Acknowledgments Financial support from the Natural Science Foundation of China (Grant Nos. 20931001), Beijing Natural Science Foundation, Independent Innovation Foundation of USTB, and Beijing Municipal Commission of Education is gratefully acknowledged. Appendix. Supplementary data Supplementary data associated with this article can be found in the on-line version, at doi:10.1016/j.biomaterials.2010.11.091. References [1] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature 423 (2003) 705. [2] L. Carlucci, G. Ciani, D.M. Proserpio, Coord. Chem. Rev. 246 (2003) 247. [3] S. Leininger, B. Olenyuk, P.J. Stang, Chem. Rev. 100 (2000) 853. [4] D. Bradshaw, J.B. Claridge, E.J. Cussen, T.J. Prior, M.J. Rosseinsky, Acc. Chem. Res. 38 (2005) 273. [5] J.-H. Chou, M.E. Kosal, S. Nakagaki, D.W. Smithenry, S.R. Wilson, Acc. Chem. Res. 38 (2005) 283.

[6] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319. [7] R.J. Hill, D.L. Long, N.R. Champness, P. Hubberstey, M. Schrooder, Acc. Chem. Res. 38 (2005) 337. [8] G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, Acc. Chem. Res. 38 (2005) 217. [9] S.R. Batten, R. Robson, Angew. Chem. Int. Ed. 37 (1998) 1460. [10] S.R. Batten, CrystEngComm. 3 (2001) 67. [11] O.R. Evans, R. Xiong, Z. Wang, G.K. Wong, W. Lin, Angew. Chem. Int. Ed. 38 (1999) 536. [12] S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int. Ed. 43 (2004) 2334. [13] M.D. Hollingsworth, Science 295 (2002) 2410. [14] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keefe, O.M. Yaghi, Science 295 (2002) 469. [15] C. Serre, F. Millange, J. Marrot, G. Férey, Chem. Mater. 14 (2002) 2409. [16] H. Chun, H. Jung, G. Koo, H. Jeong, D.-K. Kim, Inorg. Chem. 47 (2008) 5355. [17] L. Xu, E.-Y. Choi, Y.-U. Kwon, Inorg. Chem. 46 (2007) 10670. [18] J.-W. Ye, J. Wang, J.Y. Zhang, P. Zhang, Y. Wang, CrystEngComm 9 (2007) 515. [19] D. Bradshaw, T.J. Prior, E.J. Cussen, J.B. Claridge, M.J. Rosseinsky, J. Am. Chem. Soc. 126 (2004) 6106. [20] Z. Lin, D.S. Wragg, J.E. Warren, R.E.J. Morris, Am. Chem. Soc. 129 (2007) 10334. [21] X.-L. Wang, C. Qin, E.-B. Wang, Y.-G. Li, Z.-M. Su, L. Xu, L. Carlucci’, Angew. Chem. Int. Ed. 44 (2005) 5824. [22] P. Mahata, G. Madras, S.J. Natarajan, Phys. Chem. B 110 (2006) 13759. [23] S.-L. Li, Y.-Q. Lan, J.-F. Ma, J. Yang, G.-H. Wei, L.-P. Zhang, Z.-M. Su, Cryst. Growth Des. 8 (2008) 1610. [24] D.-R. Xiao, E.-B. Wang, H.-Y. An, Y.-G. Li, Z.-M. Su, C.-Y. Sun, Chem. Eur. J. 12 (2006) 6528. [25] Y.-Q. Lan, S.-L. Li, K.-Z. Shao, X.-L. Wang, D.-Y. Du, Z.-M. Su, D.-J. Wang, Cryst. Growth Des. 9 (2009) 737. [26] X.-L. Chen, B. Zhang, H.-M. Hu, F. Fu, X.-L. Wu, T. Qin, M.-L. Yang, G.-L. Xue, J.W. Wang, Cryst. Growth Des. 8 (2008) 3706. [27] Q. Chu, G.-X. Liu, Y.-Q. Huang, X.-F. Wang, W.-Y. Sun, Dalton Trans. (2007) 4302. [28] H.-L. Wang, D.-P. Zhang, D.-F. Sun, Y.-T. Chen, L.-F. Zhang, L.-J. Tian, J.-Z. Jiang, Z.-H. Ni, Cryst. Growth Des. 9 (2009) 5273. [29] Q.-R. Wu, X.-L. Chen, H.-M. Hu, T. Qin, F. Fu, B. Zhang, X.-L. Wu, M.-L. Yang, G.L. Xue, L.-F. Xu, Inorg. Chem.Commun. 11 (2008) 28. [30] S.-Q. Zang, Y. Su, Y. Li, Z. Ni, Q. Meng, Inorg. Chem. 45 (2006) 174. [31] Z. Pan, H. Zheng, T. Wang, Y. Song, Y. Li, Z. Guo, R.B. Stuart, Inorg. Chem. 47 (2008) 9528. [32] L.-Y. Zhang, G.-F. Liu, S.-L. Zheng, B.-H. Ye, X.-M. Zhang, X.-M. Chen, Eur. J. Inorg. Chem. 2003 (2003) 2965. [33] S. Tsuzuki, K. Honda, T. Uchimaru, M. Mikami, K.J. Tanabe, Am. Chem. Soc. 124 (2002) 104. [34] M. Kamishima, M. Kojima, Y.J. Yoshikawa, Comput. Chem. 22 (2001) 835. [35] S. Jin, W. Chen, H. Qiu, Cryst. Growth Des. 7 (2007) 2071. [36] Marc W. Perkovic, Inorg. Chem. 39 (2000) 4962. [37] B.-L. Wu, D.Q. Yuan, F.-L. Jiang, R.-H. Wang, L. Han, Y.-F. Zhou, M.-C. Hong, Eur. J. Inorg. Chem. 2004 (2004) 2695.