Synthesis, Crystal Structure and Photoluminescence of a New Zn(II) Dimer Constructed by 1,10-Phenanthroline Derivative and Flexible Dicarboxylate①

WANG Xiu-Yn LIU Fu-Yi ZHANG Yn-N XU Zhn-Lin ② (Key Lortory of Preprtion nd Applictions of Environmentl Friendly Mterils, Jilin Norml University, Siping 136000, Chin)

b (Department of Chemistry, Jilin Normal University, Siping 136000, China)

1 INTRODUCTION

The crystal engineering of supramolecular architecture based on metals and organic ligands has been rapidly expanding in recent years because of their intriguing variety of architectures and potential applications in gas absorption, luminescence, catalysis, and magnetism[1-5]. During the syntheses of supramolecular molecules, the careful selection of ligands, such as shape, functionality and flexibility,is a key step for the rational design of structures and specific physical properties[6-9]. It is well-known that 1,10-phenanthroline (phen) as the typical chelating N,N΄-based secondary ligand has been extensively studied to build novel supramolecular architectures because of its excellent conjugated system and coordinating ability[10-11]. So far, a great many compounds with phen molecules have been designed and characterized[12]. Ongoing research in our laboratory has been directed toward the design and synthesis of novel supramolecular architectures with phen derivatives[13]. To further investigate the supramolecular architectures based on phen derivatives, we present herein a new compound, 1. The luminescent property for compound 1 has also been investigated.

2 EXPERIMENTAL

2. 1 Generals

All the materials were of analytical reagent grade and used as received without further purification.The photoluminescent properties were measured on a Renishaw inVia Raman Microscope at room temperature.

2. 2 Synthesis and crystal growth

A mixture of 1,4-H2chdc (0.086 g, 0.5 mmol), L(0.150 g, 0.5 mmol) and ZnCl2(0.068 g, 0.5 mmol)was suspended in 8 mL of deionized water. The pH value of the mixture was adjusted to about 5.3 by adding triethylamine. The resultant solution was heated at 463 K in a Teflon-lined stainless steel autoclave for 7 days. The reaction system was cooled to room temperature and crystals were obtained from the reaction system by filtration.Yield: 26% (based on Zn).

2. 3 X-ray structure determination

A single crystal with dimensions of 0.27mm ×0.21mm × 0.18mm was chosen and mounted on a Rigaku RAXIS-RAPID diffractometer equipped with a graphite-monochromatized Mo Kα (λ =0.71073 Å) radiation by using an ω scan mode at 293(2) K. Out of the 11023 total reflections collected in the 3.20≤θ≤27.48º range, 5052 were independent with Rint= 0.0281, of which 3895 were considered to be observed (I ＞ 2σ(I)) and used in the succeeding refinement. The structure was solved by direct methods with SHELXS-97 program[14]and refined with SHELXL-97[15]by full-matrix leastsquares techniques on F2. All H atoms were positioned geometrically (C–H = 0.93 Å) and refined as riding, with Uiso(H) = 1.2Ueq(carrier). The water H atoms were not included in the model. The final R =0.0426 and wR = 0.1171 (w = 1/[σ2(Fo2) +(0.0741P)2+ 0.1937P], where P = (Fo2+ 2Fc2)/3). S= 1.091, (Δρ)max= 0.516, (Δρ)min= –0.429 e/Å3and(Δ/σ)max= 0.001.

3 RESULTS AND DISCUSSION

3. 1 Description of the crystal structure

Selected bond lengths and bond angles for the compound are given in Table 1. X-ray crystallographic analysis reveals that the crystal of 1 is solved in triclinic space group P. The asymmetric unit of 1 contains one Zn(II) atom, one 1,4-chdc anion, one L ligand, and one free water molecule (Fig. 1). Each Zn(II) atom is coordinated by two carboxylate oxygen atoms from two 1,4-chdc anions (Zn(1)–O(2)= 1.964(2), Zn(1)–O(4)i= 1.952(2) Å) and two nitrogen atoms from one chelating L ligand(Zn(1)–N(1) = 2.106(3), Zn(1)–N(2) = 2.084(2) Å)in a tetrahedral geometry. The Zn–O and Zn–N distances are very close to the reported ones found in other related complexes [Zn(mpa)(phen)]nand[Zn2(mpa)2(2,2΄-bpy)2]n(mpa = m-phthalate and 2,2΄-bpy = 2,2΄-bipyridine)[16]. Strikingly, two 1,4-chdc ligands in bidentate modes bridge two adjacent Zn(II) atoms to yield a dimer with a long Zn··Zn distance of 7.863 Å. The secondary N-donor ligands L are located on both sides of the dimer. It is noteworthy that there exist two types of π-π stacking interactions among neighboring L ligands in adjacent dimers (centroid-to-centroid distance being ca. 3.64 Å, face-to-face distance of ca. 3.43 Å, and dihedral angle of 6.7ofor one type of π-π stacking interactions; centroid-centroid distance being ca.3.66 Å, face-to-face distance of ca. 3.48 Å, and dihedral angle of 1.0ofor another type of π-π stacking interactions), as shown in Fig. 2. These π-π stacking interactions extend the dimers into a 2D supramolecular layer (Fig. 2). It is clear that the π-π stacking interactions play an important role in stabilizing the 2D supramolecular architecture of 1.

3. 2 Luminescent property

It is well-known that coordination compounds with d10metals show luminescent properties[16]. In this work, the luminescent properties of free organic ligands and compound 1 have been studied in the solid state at room temperature (Fig. 3). The main emission peaks of 1,4-H2chdc and L are located at about 415 (λex= 325 nm) and 492 nm (λex= 325 nm),respectively, which may be attributed to π*-n or π*-π transition. Compound 1 shows an emission peak at about 550 nm (λex= 325 nm). Compared with the free L ligand, the emission peak of 1 is red-shifted by 58 nm. The emission of the compound is neither ligand-to-metal charge transfer (MLCT)nor metal-to-ligand charge transfer (LMCT). The emission of 1 can probably be attributed to the intraligand transitions[16].

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

Fig. 1. View of the coordination environment of the Zn(II) atom in 1. Symmetry code: i x–1, –y, 1–z

Fig. 2. View of the 2D supramolecular layer of 1 formed by π-π stacking interactions among L ligands of the neighboring dimers

Fig. 3. Solid-state photoluminescent spectra of 1,4-H2chdc, L and 1 at room temperature

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