Hydrothermal Syntheses and Crystal Structures of Two Complexes with Cyclic Dimer and 2D Network Structures of 3-Nitrophthalate and N-Donor Ligand①

JIANG Xiu-Rong TANG Zhi-Wei XIE Gui-Xiang DONG Yan WEN De-Cai

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Hydrothermal Syntheses and Crystal Structures of Two Complexes with Cyclic Dimer and 2D Network Structures of 3-Nitrophthalate and-Donor Ligand①

JIANG Xiu-Rong TANG Zhi-Wei XIE Gui-Xiang DONG Yan WEN De-Cai②

(364000)

Two complexes, [Cd(nphth)(2,2?-bipy)(H2O)]2·2H2O(1) and [Cd(nphth)(4,4?- bipy)(H2O)]n(2) (nphth = 3-nitrophthalate, 2,2?-bipy = 2,2?-bipyridine, 4,4?-bipy = 4,4?-bipyridine), were synthesized by hydrothermal reactions and structurally characterized. Complex 1 crystallizes in triclinic with space group,= 0.7599(4),= 1.0551(6),= 1.2448(6) nm,= 88.96(2),= 75.40(2),= 76.76(2)°,= 0.9393(9) nm3,= 1,D= 1.816 Mg/m3,(000) = 512,= 1.217 mm-1,= 0.946, the final= 0.0238 and= 0.0631. Complex 2 crystallizes in monoclinic, space group21/,= 0.737(5),= 2.338(1),= 1.0030(6)nm,= 96.359(9)°,= 1.803(2) nm3,= 4,D= 1.826 Mg/m3,(000) = 984,= 1.260 mm-1,= 1.016, the final= 0.0455 and= 0.1007. Complex 1exhibits a discrete cyclic binuclear structure and complex 2 possesses a 2D layer structure with cyclic binuclear unit. The fluorescent spectrum study shows that complex 1 exhibits fluorescent emission in the solid state at room temperature.

cadmium complex, 3-nitrophthalic acid, hydrothermal synthesis, crystal structure;

1 INTRODUCTION

Much interest has been focused on the design and synthesis of geometrically shaped coordination com- pounds.The large variety of aesthetically pleasing structures has been reported in recent literature,fromdiscrete cyclic polynuclear complexes(e.g., triangles, rectangles, squares, etc.)[1, 2]to infinite 1D chains (e.g. zigzag chain, helix etc.),2D networks (e.g., honeycomb,herringbone,brick wall, square grid etc.) and 3D frameworks[3, 4]. This kind of complexes displays interesting functions and has potential applications in many areas such as magnetism,catalysis,chirality, luminescence, non-linear optics, molecular recognition and sorption[5, 6]. Many carboxylate ligandshave been shown to be good building blocks in preparing coordination polymers with desired topologies owing to their rich coor- dination modes[7-11].-Phthalic acid is a versatile ligand for designing new supramolecular construc- tions. Many coordination polymers with-phthalic acid and N-donor ligands, such as 2,2?-bipy and 4,4?-bipy, were found to display diverse structure types[12, 13], but only a few 3-series transition metal complexes with 3-nitrophthalateligand are repor- ted[14-17]. Herein, we report the syntheses and struc- ture characterizations of [Cd(nphth)(2,2?- bipy)(H2O)]2·bipy)(H2O)]2·2H2Oand [Cd(nphth)(4,4?-bipy)-(H2O)]n.

2 EXPERIMENTAL

2. 1 General

All of the chemicals were obtained from com- mercial sources and used without further purification. Elemental analyses were conducted on a Perkin- Elmer 2400 CHN elemental analyzer. IR spectra were recorded on a Nicolet 360 FT-IR spectrometer with KBr pellets. Thermogravimetric analysis was obtained on NETZSCH STA 449C thermogra- vimetric analyzer, carried out under N2with a heating rate of at 10℃·min-1. Fluorescence spectra were performed on a Hitachi F-4500 fluorescence spectrophotometer at room temperature.

2. 2 Synthesis of [Cd(nphth)(2,2?-bipy)(H2O)]2·2H2O(1)

A mixture ofCd(NO3)2·6H2O (0.2 mmol), 2,2?- bipy (0.1 mmol), 3-nitrophthalic acid (0.2 mmol) and distilled water (10 mL) was put into a Teflon- lined autoclave (20 mL) and then heated at 403 K for 72 h. Brown block-like crystals of the title com- plex in 50% yield based on Cd. Anal. Calcd. (%) for C36H30N6O16Cd2: C, 42.08; H, 2.94; N, 8.18. Found (%): C, 42.02; H, 2.91; N, 9.22.

2. 3 Synthesis of [Cd(nphth)(4,4?-bipy)(H2O)]n(2)

A mixture of Cd(NO3)2·6H2O (0.2 mmol), 4,4?- bipy (0.1 mmol), 3-nitrophthalic acid (0.2 mmol) and distilled water (10 mL) was put into a Teflon- lined autoclave (20 mL) and then heated at 403 K for 48 h. Brown block-like crystals of the title com- plex were obtained in 35% yield based on Cd. Anal. Calcd. (%) for C18H13N3O7Cd: C, 43.61; H, 2.64; N, 8.48. Found (%): C, 43.55; H, 2.60; N, 8.53.

2. 4 X-ray crystallography

Suitable single crystals with approximate dimen- sions of 0.30mm × 0.28mm × 0.27mm for 1 and 0.25mm × 0.23mm × 0.22mm for 2 were used for X-ray diffraction analyses. Data collection was carried out at 293 K on a Rigaku RAXIS-RAPID Weissengberg IP diffractometer with graphite- monochromated Moradiation (= 0.71073 ?) in anscan mode. The structures were solved by direct methods and difference Fourier syntheses. The non-hydrogen atoms were refined by full-matrix least-squares techniques on2with anisotropic thermal parameters. Most of the H atoms in the two title complexes were positioned geometrically, except that the H atoms of coordination water mole- cules were found in difference Fourier maps and refined as riding, with(H) = 1.5(parent atom). All calculations were carried out with SHELX 97 program[18].

Complex 1 crystallizes in triclinic with space group,= 0.7599(4),= 1.0551(6),= 1.2448(6) nm,= 88.96(2),= 75.40(2),= 76.76(2)°,= 0.9393(9) nm3,= 1,D= 1.816 Mg/m3,(000) = 512 and= 1.217 mm-1. A total of 9319 reflections were obtained and 4256 unique (int= 0.0254) were collected in the range of 3.07 <<27.48° by anscan mode, of which 3901 re- flections with> 2() were used in the succeeding refinement. The final= 0.0238,= 0.0631 (= 1/[2(F2) + (0.0452)2+ 0.1493], where= (F2+ 2F2)/3), (Δ)max= 0.754, (Δ)min= –0.620 e/?3, (Δ/)max= 0.003 and= 0.946.

Complex 2 crystallizes in monoclinic, space group21/,= 0.737(5),= 2.338(1),= 1.0030(6)nm,= 96.359(9)°,= 1.803(2) nm3,= 4,= 1.826 Mg/m3,(000) = 984 and= 1.260 mm-1. A total of 13999 reflections were obtained and 4115 unique (int= 0.0579) were collected in the range of 2.69<<27.49° by anscan mode, of which 3108 reflections with> 2() were used in the succee- ding refinement. The final= 0.0455,= 0.1007 (= 1/[2(2) + (0.0578)2+ 0.0000], where= (2+ 22)/3), (Δ)max= 1.119, (Δ)min= –1.109 e/?3, (Δ/)max= 0.001 and= 1.016. Selected bond lengths and bond angles of the two title complexes are listed in Table 1. The details of molecular hy- drogen bonding interactions in the two complexes are given in Table 2.

Table 1. Selected Bond Lengths (?) and Bond Angles (°) for 1 and 2

Table 2. Hydrogen Bond Lengths (?) and Bond Angles (°) for 1 and 2

3 RESULTS AND DISCUSSION

3. 1 Structural description

Themolecularstructure of complex 1isshowninFig.1.The Cd(1) is coordinated by two nitrogen atoms from 2,2?-bipy, three oxygen atoms from two3-nitrophthalateligands, and an oxygen atom of coordinated H2O molecule in a distorted octahedral geometry. The coordination modes of the two depro- tonated carboxylate groups in the 3-nitrophathalate ligand are different. One carboxylate group acts as a chelating ligand to coordinate to a Cd atom, while the other one as a monodentate ligand to a Cd atom. Two Cd atoms are linked bycarboxylategroups fromtwo3-nitrophathalate ligands.Thus, a discrete cyclic binuclear structureisconstructedby twoCdatoms, two 2,2?-bipyandtwo3-nitrophathalate ligands, the core of the binuclear structure being an 14-membered ring with the Cd···Cd distance of 5.68(8) ?.

Fig. 1 . Cyclic binuclear structure of complex 1 with 30% probability ellipsoid.Hydrogen atoms except those of coordinated water molecules andthe crystal water molecules are omitted for clarity.Symmetry code: A, 1–x, 1–y, 1–z

There are two kinds of O–H···Oand C–H···Ohy- drogen bonds in complex 1. TheO–H···Ohy- drogen bond is between the crystal and coordinated water molecules and oxygenatomsofcarboxylategroups. The C–H···O hydrogen bonds are between the C–H group of 2,2?-bipy ligands and the oxygen atoms of carboxylategroups.Detailed data are given in Table 2. Thereareinteractionsbetweenthearomatic ringsof2,2?-bipyoftheneighboringbi- nuclear structure unitwith a centroid-centroid dis- tance of 3.59(3) ?. Then adjacent binuclear structure units are connected together by the O–H···Oand C–H···Ohydrogen bonds andinteractions, resulting in an extended 2D network structure (Fig. 2)

Fig. 2 . Extended 2D structure in complex 1 (at 30% probability ellipsoid). Hydrogen bonds and π-πinteractions are shown as dashed lines

As illustrated in Figs. 3 and 4, complex 2pos- sesses a 2D network structure.The Cd(1) is coor- dinated by two nitrogen atoms from two 4,4?-bipy molecules, four oxygen atoms from two 3-nitro- phthalate ligands, and an oxygen atom of coor- dinated H2O molecule in a distorted geometry. The two deprotonated carboxylate groups in the 3-nitro- phathalate ligand act as a chelating ligand to coor- dinate with a Cd atom. Two adjacent Cd atoms are linked by two 3-nitrophathalate ligands to form a 14-membered cyclic binuclear structure with Cd···Cd distance of 5.26(1) ?. Each Cd atom is attached to two 4,4?-bipy ligands. The binuclear clusters may be viewed as the nodes which were connected to the four 4,4?-bipy ligands, giving rise to a 2D network structure. There are two kinds of O–H···Oand C–H···Ohydrogen bonds in complex 2. TheO– H···Ohydrogen bonds are between the coordinated water molecules and oxygenatomsofcarboxylategroups. The C–H···O hydrogen bonds are between the C–H group of 4,4?-bipy ligands and the oxygen atoms of carboxylategroups and the coordinated water.Detailed data are given in Table 2. Thereareweakinteractions present among the interlayer aromatic groups of 3-nitrophthalateligands, with a centroid-centroid distance between neighbouring aromatic rings of 3.954(6) ?. All hydrogen bonds andstacking interactions lead to the formation of a 3D supramolecular framework structure.

3. 2 IR spectrum

IR spectrum of complex 1 reveals two strong bonds of the carboxylic groups at 1580 and 1390 cm-1for the asymmetric and symmetric vibrations, respectively. The characteristic absorption peak of 2,2?-bipy is 1595, 1551, 1441 cm-1. In addition, there also display characteristic bands of aromatic NO2at 1519 cm-1for asymmetric vibrations and 1340 cm-1for the symmetric vibrations.

3. 3 Thermogravimetric analysis

The thermogravimetric analysis of complex 1 was performed under N2atomsphere. The weight loss of 19.80% (calcd. 22.20%) between 110 and 200 ℃ corresponds to the release of the crystal and coor-dinated water and 2,2?-bipy molecules. The main framework began to collapse above 200 ℃.

Fig. 3 . View of the coordination environment of the Cd(II) atom and the binuclear cadmium unit in complex 2 (at 30% probability ellipsoid) with atomic numbering. Hydrogen atoms are omitted for clarity.Symmetry codes: A, 1–x, 1–y, –z; B, 1+x, 1.5–y, –0.5+z

Fig. 4 . 2D layer structure of complex 2 (at 30% probability ellipsoid).Hydrogen atoms are omitted for clarity

Fig. 5 . Fluorescence spectra for compounds 1 and H2nphth ligand in the solid state at room temperature

3. 4 Luminescent properties

It is well-known that metal coordination frame- works with a10configuration possess excellent luminescence property[19]. Herein, the solid-state luminescence properties of free H2nphth ligand and complex 1 were carried out at room temperature (Fig. 5). The emission spectrum of the free ligand, excited at 293 nm, displays an emission band with maximum wavelength at 402 nm, while the emission peaks centered at 423 nm for complex 1 (ex= 295 nm). Compared with the maximum emission wavelength of free ligand, a slight red-shift of 21 nm for com- plex 1 has been observed, which can probably be assigned to ligand-to-metal charge transfer (LMCT) transition, as indicated by the previous publi- cations[20].

4 CONCLUSION

Two complexes, [Cd(nphth)(2,2?- bipy)(H2O)]2·2H2O(1) and [Cd(nphth)(4,4?-bipy)(H2O)]n(2), have been synthesized under hydrothermal con- ditions. Complex 1exhibits a discrete cyclic binuc- lear structure and complex 2 possesses a 2D layer structure with cyclic binuclear unit. The versatile hydrogen bonds andstacking interactions in 1 and 2have an influence on the formation of supra- molecular framework.The fluorescent spectrum study shows that complex 1 exhibits fluorescent emission in the solid state at room temperature.

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25 September 2014; accepted 31 December 2014 (CCDC 1017152 for 1 and 1017153 for 2)

①This work was supported by the National Natural Science Foundation of China (21371088) and the Education Department of Fujian Province (No. JK2012048, JA12310,JB12207)

. Born in 1965, professor, majoring in coordination polymer. E-mail: wendecai1227@163.com

10.14102/j.cnki.0254-5861.2011-0465