English

• 1. INTRODUCTION

  The coordination compounds containing lantha-nide cations have attracted extensive attention owing totheir interesting structures and potential applica-tions in luminescence,magnetism,catalysis and so on^[1-5]. Up to now,a great number of coordination compounds containing lanthanide cations and multifunctional ligands have been reported^[6-8]. The N,O-containing ligand of pyridine-2,6-dicarboxylic acid always exhibits some interesting characteristics and was used to design such compounds^{[9, 10]}. Its flexible and multidentate coordination sites provide manyadvantages in the formation of lanthanide coordination compounds. Furthermore,the coordina-tion compoundscontaining lanthanide cations always enhance their luminescent property.

  Coordination compounds assembled with trivalent lanthanide ions and H2pydc have a great trend to formwater clusters with differentshapes and sizes. The crystal water molecules can present as isolated ones by hydrogen bond with the coordination compounds or as aggregates filling in the empty space or channels generated in the crystal packing^[11]. Ifthe water clusters are released,the porous anhy-drous compounds will be constructed with several potential applications in areas such as catalysis,chemical separation,and sorption^{[12, 13]}. So far,stu-dies on coordination compounds self-assembled by lanthanide ions and H2pydc,which contain multi-core water clusters,are rarely reported^{[10a, 14]}. There-fore,further studies on these coordination com-pounds will enrich and develop this field.

  Based on this,we devoted to synthesizing novel lanthanide coordination compounds which contain multi-core water clusters by linking lanthanide ions withH2pydc and auxiliary N-containing ligands. Herein,a novel Dy³⁺ coordination compound,(H₂pipz)(H₃O)[Dy(pydc)₃]·11H₂O (1,pipz = piperazine and H2pydc = pyridine-2,6-dicarboxylic acid) was synthesized and structurally characterized. Moreover,the photoluminescent propertyof compound 1 was also investigated.

  2. EXPERIMENTAL

  2.1. Materials and equipments

  All starting materialsused in this work were commercially purchased and used without further purification. Elemental analyses of C,H and N were performed on an EA1110 CHNS-0 CE elemental analyzer. The IR spectrum was recordedon a Nicolet Magna 750FT-IR spectrometer in the range of 400～4000 cm^-1. Photoluminescent property of compound 1 was recorded with a VARIANCary Eclipase fluorescence spectrometer. The single-crystal data were measured on a Bruker APEX-II CCD with MoKαmonochromated radiation (λ = 0.71073 Å) at 296(2) K.

  2.2. Synthesis of 1

  A mixture of Dy(NO₃) 3·6H₂O (0.2739 g,0.60 mmol),H2pydc (2 mmol,0.3342 g),pipz·6H₂O (1 mmol,0.1942 g) and H₂O (20 mL) was placed in a 50 mL Teflon-lined stainless-steel autoclave. The resulting mixture was stirredfor 30 min at room temperature,and then the mixture was kept at 160℃ for three days. After being slowly cooled toroom temperature,light yellow columnar crystals of compound 1 were isolated. Elementalanalysis (%) forcompound 1: calcd: C,31.91; N,7.44; H,2.57. Found: C,31.82; N,7.48; H,2.60. IR (KBr pellet,cm^-1) for compound1: 2489～3464(br,m),1632～1653(s),1571(s),1559(s),1441(w),1425(s),1371(s), 1281(w),1186(m),1089(m),1042(w),1009(w),944(w),958(w),919(s),781(s),737(s),625(s),600(w),424(s),341(w),320(w).

  2.3. Structure determination

  A suitable single crystal was carefully selected andglued on a thin glass fiber for data collection which was performed at 296(2) K on a Bruker APEX-II CCD diffractometer equipped with a graphite-monochromatized MoKα radiation (λ = 0.71073 Å) by using a φ-ω scan mode at room temperature. The structure was determined by direct methods and refinedwith full-matrix least-squares techniques using the SHELXS 97 and SHELXL 97 programs^{[15, 16]}. In the range of 2.01<θ<25.00°,a total of 17736 reflections were collected,of which 6256 were unique with R_int = 0.0318. All non-hydrogen atoms were located by direct methods and subsequent differenceFourier syntheses.The hydro-gen atoms of water molecules were not located due to slight disorders. The hydrogen atoms bound to C atoms were located by geometrical calculations,and their positions and thermal parameters were fixed during the structure refinement. All non-hydrogen atoms were refined anisotropically and hydrogen atoms isotropically by full-matrix least-squares refinement with I > 2σ(I) to the final R = 0.0393,wR= 0.1104 (w= 1/[σ2(F_o²) + (0.0590P)² + 1.0042P], where P= (F ₀²+ 2F _c²) /3) ,S= 1.082 and (Δ/σ)_max =0.001. The highest and lowest residual peaks in the final difference Fourier map are 1.939 and0.737 e/ų,respectively. The selected bond lengths are given in Table 1.

  Table 1

  

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (°)

  DownLoad: CSV

  Bond	Dist.	Bond	Dist.	Bond	Dist.
  Dy(1)O(9)	2.384(4)	Dy(1)O(11)	2.396(4)	Dy(1)O(5)	2.402(4)
  Dy(1)O(2)	2.404(3)	Dy(1)O(3)	2.407(3)	Dy(1)O(8)	2.419(4)
  Dy(1)N(1)	2.468(4)	Dy(1)N(2)	2.469(4)	Dy(1)N(3)	2.474(4)
  Angle	(°)	Angle	(°)	Angle	(°)
  O(9)Dy(1)O(11)	129.00(13)	O(9)Dy(1)O(5)	145.07(13)	O(11)Dy(1)O(5)	77.92(13)
  O(9)Dy(1)O(2)	74.60(13)	O(11)Dy(1)O(2)	148.78(13)	O(5)Dy(1)O(2)	91.55(13)
  O(9)Dy(1)O(3)	90.00(13)	O(11)Dy(1)O(3)	77.01(13)	O(5)Dy(1)O(3)	73.55(13)
  O(9)Dy(1)O(8)	80.28(13)	O(11)Dy(1)O(8)	87.21(14)	O(2)Dy(1)O(3)	128.43(13)
  O(5)Dy(1)O(8)	128.14(13)	O(2)Dy(1)O(8)	76.28(12)	O(3)Dy(1)O(8)	150.05(13)
  O(9)Dy(1)N(1)	72.66(12)	O(11)Dy(1)N(1)	136.18(12)	O(5)Dy(1)N(1)	72.44(12)
  O(2)Dy(1)N(1)	64.25(11)	O(3)Dy(1)N(1)	64.18(11)	O(8)Dy(1)N(1)	136.57(12)
  O(9)Dy(1)N(2)	137.04(14)	O(11)Dy(1)N(2)	74.41(14)	O(5)Dy(1)N(2)	64.29(13)
  O(2)Dy(1)N(2)	74.54(12)	O(3)Dy(1)N(2)	132.80(12)	O(8)Dy(1)N(2)	63.86(13)
  N(1)Dy(1)N(2)	117.99(13)	O(11)Dy(1)N(3)	64.50(14)	O(5)Dy(1)N(3)	135.82(14)
  O(2)Dy(1)N(3)	132.60(13)	O(3)Dy(1)N(3)	76.01(13)	O(8)Dy(1)N(3)	74.23(13)
  N(1)Dy(1)N(3)	120.35(13)	N(2)Dy(1)N(3)	121.66(15)

  3. RESULTS AND DISCUSSION

  3.1. Description of the structure

  X-ray crystal structure analysis reveals that com-pound 1 crystallizes in monoclinic,space group P2₁/c and its unique asymmetrical unit consists of one Dy(III) cation,three pydc2-ligands,one isolated H₂pipz²⁺ and 12 uncoordinated water molecules. Fig. 1a shows the molecular structural unit of compound 1. The Dy(III)center is nine-coordinatedby three nitrogen atoms (N(1) ,N(2) and N(3) atoms) and six carboxylic oxygen atoms (O(2) ,O(3) ,O(5) ,O(8) ,O(9) and O(11) atoms) from three differentpydc^2- ligands,forming a slightly distorted tricapped trigonal prismatic geometry in which six carboxylic oxygen atoms located on the vertices of trigonal prismand three nitrogen atoms occupy the equa-torial plane (Fig. 1b). Dy-O distancesrange from 2.383 to 2.417 Å with an average value of 2.401 Å. The bond lengths of Dy-N are 2.470,2.469 and 2.470 Å with an average value of 2.470 Å. The O-Dy-O and O-Dy-N angles are varying from 73.46～150.09 and 63.90～137.05. These Dy-O and Dy-N bond lengths and O-Dy-O and O-Dy-N angles are in agreement with those reported in other Dy(III) coordination polymers^[17].

  Figure 1

  

  Figure 1.  (a) Molecular structural unit of 1. (b) View of a slightly distorted tricapped trigonal prismatic geometry of Dy³⁺

  DownLoad: Full-Size Img PowerPoint

  Compound 1 could be viewed as a zero-dimen-sional structure. Four neighboring [Dy(pydc)₃]^3- entities form a ringlikepattern. Meanwhile,22 water molecules (three O(1W),two O(2W),one O(3W),two O(4W),two O(5W),one O(6W),one O(7W),twoO(8W),one O(9W),three O(10W),two O(11W) and two O(12W)) are located in the middle of the four [Dy (pydc)₃]^3- entities,which form a rare 22-core water cluster by means of hydrogen bonding interactions (Fig. 2) . The 22 water molecules con-stitute a similar 22-membered-ring in the novel (H₂O)₂₂ cluster of compound 1,which is different fromthe (H₂O)₂0 cluster in the reported com-plex composed of one (H₂O)₁₄ unit and six dangling O(4W) water molecules,the cages constituted by 22-core water clusters of 1 are larger than that of the reported complex^[10a]. Oxygen atoms of the 22-core water clusters exhibit one-,three-and four-coor-dination,which is completely different from the four-coordination at the surface of liquid water or ice^[18]. These water clusters are connected with each other,forming a two-dimensional layered structure,as given in Fig. 2.

  Figure 2

  

  Figure 2.  (a) View of the packing structure along the caxis. (b) Structure of22-core water cluster.(c) View of the net-structure constructed by water clusters

  DownLoad: Full-Size Img PowerPoint

  In addition,there are O-H···O hydrogen bonding interactions between the uncoordination water mole-cules and carboxylate groups belonging to the pydc2-ligands (Fig. 3) . By means of these hydrogen bon-ding interactions,a three-dimensional supramolecu-lar structure comes into being (Fig. 4) . These hydro-gen bonds further stabilize the three-dimen-sional supramolecular structure. Compound 1 representsa new example of Dy-containing coordination com-pound containing rare (H₂O)₂₂ clusters,whichen-riched the family of the Dy-containing coordina-tion compounds.

  Figure 3

  

  Figure 3.  O-H···O hydrogen bonding interactions between the uncoordination water molecules and carboxylate groups

  DownLoad: Full-Size Img PowerPoint

  Figure 4

  

  Figure 4.  View of the packing structure along the a axis

  DownLoad: Full-Size Img PowerPoint

  3.2. Photoluminescent property

  The luminescent property of compound 1 was investigated in the solid state at room temperature (Fig. 5) . Under excitation at 346 nm,it exhibits three main peaks located at 474,570 and 613 nm,cor-responding to the ⁴F_9/2 → 6H15/2,⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → 6H11/2 transition emissions of the Dy³⁺ ion,respectively.The strongest emissionis centered on 570 nm (⁴F_9/2 → ⁶H_13/2) ,which is responsible for the yellow emission. The emission intensity of com-pound 1 is much higher than that of Dy(NO₃) ₃·6H₂O and similar coordination compounds^[19-21]. The result reveals that H2pydc and pipz are good agents,and the behavior of Dy³⁺ ion coordinated to H2pydc and pipz is regardedas that of emissive species caused by a CHEF effect^[21]. The organic ligands can absorb the energy of UV lightand transfer to the center Dy³⁺ ion by the exchange interaction of intra-molecular resonance coupling.

  Figure 5

  

  Figure 5.  Luminescent property of compound 1 in thesolid state at room temperature

  DownLoad: Full-Size Img PowerPoint

  4. CONCLUSION

  In summary,a novel Dy³⁺ coordination compound,(H2pipz)(H3O)[Dy(pydc)₃]·11H₂O,is featured with rare 22-core water clusters. The (H₂O)₂₂ clusters are newmodes which have never been found before. Compound 1 extended the family of Dy³⁺ coordina-tion compound containing rare 22-core water clusters. The emission intensity of compound 1 is much higher than that of Dy(NO₃) ₃·6H₂O and simi-lar coordination compounds because of the chelation enhancement of the fluorescence emission.

• 1. [1]

     Gu J. Z, Wu J, Lv D. Y, Tang Y, Zhu K, Wu J. Lanthanide coordination polymers based on 5-(2?-carboxylphenyl) nicotinate: syntheses, structure diversity, dehydration/hydration, luminescence and magnetic properties[J]. Dalton Trans., 2013, 42:  4822-4830. doi: 10.1039/c2dt32674d

  2. [2]

     Zhang F. M, Yan P. F, Zou X. Y, Zhang J. W, Hou G. F, Li G. M. Novel 3D alkali-lanthanide heterometal-organic frameworks with pyrazine-2,3,5,6-tetracarboxylic acid: synthesis, structure, and magnetism[J]. Cryst. Growth Des., 2014, 14:  2014-2021. doi: 10.1021/cg5001254

  3. [3]

     Wei X. H, Yang L. Y, Liao S. Y, Zhang M, Tian J. L, Du P. Y, Gu W, Liu X. A series of rare earth complexes with novel non-interpenetrating 3D networks: synthesis, structures, magnetic and optical properties[J]. Dalton Trans., 2014, 43:  5793-5800. doi: 10.1039/c3dt53112k

  4. [4]

     Feng X, Ling X. L, Liu L, Song H. L, Wang L. Y, Ng S. W, Su B. Y. A series of 3D lanthanide frameworks constructed from aromatic multi-carboxylate ligand: structural diversity, luminescence and magnetic properties[J]. Dalton Trans., 2013, 42:  10292-10303. doi: 10.1039/c3dt50810b

  5. [5]

     Vilela S. M. F, Firmino A. D. G, Mendes R. F, Fernandes J. A, Ananias D, Valente A. A, Ott H, Carlos L. D, Rocha J, Tome J. P. C, Paz F. A. A. Lanthanide-polyphosphonate coordination polymers combining catalytic and photoluminescence properties[J]. Chem. Commun., 2013, 49:  6400-6402. doi: 10.1039/c3cc42632g

  6. [6]

     Feng, W.; Zhang, Y.; Lü, X.; Hui, Y.; Shi, G.; Zou, D.; Song, J.; Fan, D.; Wong, W. K.; Richard, A. J. Near-infrared (NIR) luminescent homoleptic lanthanide salen complexes Ln4(Salen)4 (Ln = Nd, Yb or Er). CrystEngComm. 2012, 14, 3456-3463.

  7. [7]

     Xu J, Su W. P, Hong M. C. A series of lanthanide secondary building units based metal-organic frameworks constructed by organic pyridine-2,6-dicarboxylate and inorganic sulfate[J]. Cryst. Growth Des., 2011, 11:  337-346. doi: 10.1021/cg101343k

  8. [8]

     Ye Y. Z, Wu X. J, Wang A. L. Synthesis, structure and property of a novel coordination polymer[J]. J. Struct. Chem., 2014, 33:  1860-1864.

  9. [9]

     Yang L. R, Song S, Shao C. Y, Zhang W, Zhang H. M, Bu Z. W, Ren T. G. Synthesis, structure and luminescent properties of 3D lanthanide (La(III), Ce(III)) coordination polymers possessing 1D nanosized cavities based on pyridine-2,6-dicarboxylic acid[J]. Synth. Met., 2011, 161:  1500-1508. doi: 10.1016/j.synthmet.2011.04.016

  10. [10]

      (a) Li, M.; Feng, R.; Huang, Q. Z.; Feng, Y. Q.; Shi, H. Z. Synthesis, crystal structure and luminescent property of a novel lanthanide coordination polymer containing (H₂O)20 clusters. Inorg. Chem. Commun. 2014, 50, 8-12. (b) Aghabozorg, H.; Motieiyan, E.; Salimi, A. R.; Mirzaei, M.; Manteghi, F.; Shokrollahi, A.; Derki, S.; Ghadermazi, M.; Sheshmani, S.; Eshtiagh-Hosseini, H. Piperazinediium, Zr(IV) and Ce(IV) pyridine-2,6-dicarboxylates: syntheses, characterizations, crystal structures, ab initio HF, DFT calculations and solution studies. Polyhedron 2010, 29, 1453-1464. (c) Dalai, S.; Rana, A.; Chowdhuri, D. S.; Bera, M.; Zangrando, E. Cubane-like water clusters in a 3D supramolecular network of zinc with pyridine-2,6-dicarboxylic acid and 5-aminotetrazole. Inorg. Chim. Acta 2010, 363, 1052-1055. (d) Deng, D. S.; Liu, P.; Fu, W. J.; Li, L.; Yang, F. X.; Ji, B. M. Metal-organic open frameworks with one-dimension channels assembled with pyridine 2,6-dicarboxylic acid and N-containing auxiliary ligands: syntheses, crystal structures, and physical characterization. Inorg. Chim. Acta 2010, 363, 891-898.

  11. [11]

      Zhu T. Y, Ikarashi K, Ishigaki T, Uematsu K, Toda K, Okawa H, Sato M. Structure and luminescence of sodium and lanthanide(III) coordination polymers with pyridine-2,6-dicarboxylic acid[J]. Inorg. Chim. Acta, 2009, 362:  3407-3414. doi: 10.1016/j.ica.2009.01.036

  12. [12]

      Deng D. S, Liu P, Fu W. J, Li L, Yang F. X, Ji B. M. Metal-organic open frameworks with one-dimension channels assembled with pyridine 2,6-dicarboxylic acid and N-containing auxiliary ligands: syntheses, crystal structures, and physical characterization[J]. Inorg. Chim. Acta, 2010, 363:  891-898. doi: 10.1016/j.ica.2009.12.044

  13. [13]

      Dalai S, Rana A, Chowdhuri D. S, Bera M, Zangrando E. Cubane-like water clusters in a 3D supramolecular network of zinc with pyridine-2,6-dicarboxylic acid and 5-aminotetrazole[J]. Inorg. Chim. Acta, 2010, 363:  1052-1055. doi: 10.1016/j.ica.2009.12.018

  14. [14]

      Zeng X. Z, Zhang A. Y, He C, Li Y. W. Synthesis, structure and thermal properties of two cerium(Ⅳ) complexes with 2,6-pyridinedicarboxylic acid[J]. Chin. J. Inorg. Chem., 2013, 29:  1557-1562.

  15. [15]

      Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution. University of G?ttingen, G?ttingen (Germany) 1997.

  16. [16]

      Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures. University of G?ttingen, G?ttingen (Germany) 1997.

  17. [17]

      Biswas S, Jena H. S, Goswami S, Sanda S, Konar S. Synthesis and characterization of two lanthanide (Gd3+and Dy3+)-based three-dimensional metal organic frameworks with squashed metallomacrocycle type building blocks and their magnetic, sorption, and fluorescence properties study[J]. Cryst. Growth Des., 2014, 14:  1287-1295. doi: 10.1021/cg401804e

  18. [18]

      Ghosh S. K. Structure of a discrete hexadecameric water cluster in a metal-organic framework structure[J]. Inorg. Chem., 2004, 43:  6687-6889.

  19. [19]

      Mao P. D, Yan L. L, Wu W. N, Liu M. Q, Zhou L. H, Fu S. L. Lanthanide (La, Tb, Dy) complexes with quinolinyloxy acetamide ligand: crystal structures and fluorescence properties[J]. Chin. J. Inorg. Chem., 2016, 32:  1095-1100.

  20. [20]

      Li H. H, Li H, Niu Z, Wang Y. P. Structural diversity of two novel Dy(III) metal-organic frameworks based on binuclear nodes with furan-2,5-dicarboxylic acid: crystal structures and luminescent properties[J]. Inorg. Chem. Commun., 2015, 55:  103-107. doi: 10.1016/j.inoche.2015.03.013

  21. [21]

      Yang R, He S. Y, Wu W. T, Wen Z. Y, Shi Q. Z, Wang D. Q. Crystal structure, fluorescence characterization of dysprosium(III) multicomponent complex with acylhydrazone and 1,10-phenanthroline[J]. Acta Chimica Sinica, 2004, 62:  2040-2044.

• 

  Figure 1  (a) Molecular structural unit of 1. (b) View of a slightly distorted tricapped trigonal prismatic geometry of Dy³⁺

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) View of the packing structure along the caxis. (b) Structure of22-core water cluster.(c) View of the net-structure constructed by water clusters

  下载: 全尺寸图片 幻灯片
  

  Figure 3  O-H···O hydrogen bonding interactions between the uncoordination water molecules and carboxylate groups

  下载: 全尺寸图片 幻灯片
  

  Figure 4  View of the packing structure along the a axis

  下载: 全尺寸图片 幻灯片
  

  Figure 5  Luminescent property of compound 1 in thesolid state at room temperature

  下载: 全尺寸图片 幻灯片

  Table 1.  Selected Bond Lengths (Å) and Bond Angles (°)

  Bond	Dist.	Bond	Dist.	Bond	Dist.
  Dy(1)O(9)	2.384(4)	Dy(1)O(11)	2.396(4)	Dy(1)O(5)	2.402(4)
  Dy(1)O(2)	2.404(3)	Dy(1)O(3)	2.407(3)	Dy(1)O(8)	2.419(4)
  Dy(1)N(1)	2.468(4)	Dy(1)N(2)	2.469(4)	Dy(1)N(3)	2.474(4)
  Angle	(°)	Angle	(°)	Angle	(°)
  O(9)Dy(1)O(11)	129.00(13)	O(9)Dy(1)O(5)	145.07(13)	O(11)Dy(1)O(5)	77.92(13)
  O(9)Dy(1)O(2)	74.60(13)	O(11)Dy(1)O(2)	148.78(13)	O(5)Dy(1)O(2)	91.55(13)
  O(9)Dy(1)O(3)	90.00(13)	O(11)Dy(1)O(3)	77.01(13)	O(5)Dy(1)O(3)	73.55(13)
  O(9)Dy(1)O(8)	80.28(13)	O(11)Dy(1)O(8)	87.21(14)	O(2)Dy(1)O(3)	128.43(13)
  O(5)Dy(1)O(8)	128.14(13)	O(2)Dy(1)O(8)	76.28(12)	O(3)Dy(1)O(8)	150.05(13)
  O(9)Dy(1)N(1)	72.66(12)	O(11)Dy(1)N(1)	136.18(12)	O(5)Dy(1)N(1)	72.44(12)
  O(2)Dy(1)N(1)	64.25(11)	O(3)Dy(1)N(1)	64.18(11)	O(8)Dy(1)N(1)	136.57(12)
  O(9)Dy(1)N(2)	137.04(14)	O(11)Dy(1)N(2)	74.41(14)	O(5)Dy(1)N(2)	64.29(13)
  O(2)Dy(1)N(2)	74.54(12)	O(3)Dy(1)N(2)	132.80(12)	O(8)Dy(1)N(2)	63.86(13)
  N(1)Dy(1)N(2)	117.99(13)	O(11)Dy(1)N(3)	64.50(14)	O(5)Dy(1)N(3)	135.82(14)
  O(2)Dy(1)N(3)	132.60(13)	O(3)Dy(1)N(3)	76.01(13)	O(8)Dy(1)N(3)	74.23(13)
  N(1)Dy(1)N(3)	120.35(13)	N(2)Dy(1)N(3)	121.66(15)

  下载: 导出CSV
•