Hydrothermal Synthesis, Crystal Structure and Properties of a New Binuclear Cage-like Yttrium(III) Complex Y2(TMBA)6(phen)2①

LI Chang-Hong KUANG Yun-Fei LI Wei LI Yu-Lin

a (School of Materials and Chemical Engineering, Hunan Institute of Technology, Hengyang 421002, China)

b (School of Chemistry and Materials Science, Hengyang Normal University, Hengyang 421008, China)

ABSTRACT A new binuclear cage-like yttrium(III) complex Y2(TMBA)6(phen)2 (1) with yttrium nitrate, 2,4,6- trimethylbenzoic acid (TMBA) and 1,10-phenanthroline (phen) was synthesized. It crystallizes in the triclinic space group with a = 11.9086(15), b = 12.4843(17), c = 14.2101(18) Å, α = 104.977(4), β = 111.750(4), γ = 95.874(5)º, V = 1848.8(4) Å3, Dc = 1.363 g/cm3, Z = 1, μ(MoKa) = 1.627, F(000) = 788, the final GOOF = 1.039, R = 0.0353 and wR = 0.0826. The whole molecule consists of two yttrium ions bridged by four 2,4,6-trimethylbenzoic acid anions. The Y(III) ion is coordinated by eight atoms to give a distorted square antiprism coordination geometry. The TG analysis and fluorescent properties of 1 were studied.

Keywords: binuclear yttrium(III) complex, thermal stability, fluorescent property;

1 INTRODUCTION

Lanthanide coordination complexes have gained much interest due to their broad applications in light emitting diodes, fluorescent probes, sensors, bioimaging utilities, time- resolved luminescent immunoassays, and anion sensing[1-3]. In particular, the photoluminescent properties of lanthanide complexes are notable due to their unique properties such as sharp emission bands, long emission lifetime and large stokes shift[4-7]. Therefore, researches on crystal and molecular structures of Y(III) complexes are needed. Yttrium element is an optical inert element with weak fluorescence performance, and the study on its complex properties mainly focuses on biological activity[8-10], while the study on rare earth ion perturbation ligand luminescence is seldom reported[11-13]. In order to obtain luminescent lanthanide complexes, the selection and design of organic ligand are very important, and it should be able to efficiently absorb and transfer energy to the central metal ion and encapsulate and protect the lanthanide ion from the coordination of solvent molecules[14,15]. As an important organic and inorganic intermediate, 2,4,6-trimethylbenzoic acid is widely used in dye synthesis, pesticide, medicine, photo sensitized initiation reagent, flavor synthesis, photomechanical process and analytic reagent. With the aim of proceeding previous jobs[16-18], we report herein a new yttrium(III) complex Y2(TMBA)6(phen)2with 2,4,6- trimethylbenzoic acid(TMBA) and 1,10-phenanthroline(phen). The TG analysis and fluorescent properties of 1 were also reported.

2 EXPERIMENTAL

2. 1 Materials and instruments

All reagents were of analytical grade and used as obtained from commercial sources without further purification. Crystal structure determination was carried out on a Bruker SMART CCD 6000 single-crystal diffractometer. Elemental analyses were performed on a Perkin-Elmer 2400 elemental analyzer. XT4 binocular microscope melting point apparatus was used to measure the melting point with thermometer unadjusted. IR spectra were recorded on a Bruker Vector22 FT-IR spectrophotometer using KBr discs. The fluorescent spectra for the powdered samples were measured on a RF-5301PC spectrofluorometer with a xenon arc lamp as the light source. In the measurement of emission and excitation spectra, the pass width is 5 nm, and all the measurements were carried out in the solid state at room temperature. Thermogravimetric analyses were performed on a simultaneous SPRT-2 pyris1 thermal analyzer at a heating rate of 10 K/min.

2. 2 Synthesis of 1

A mixture of TMBA (98.52 mg, 0.6 mmol), phen (54.0 mg, 0.3 mmol) and Y(NO3)3·4H2O (70.50 mg, 0.2 mmol) was dissolved in 25 mL of mixed solvent (The volume ratio of ethanol and water is 1:1). The pH value of the resultant mixture was adjusted to 6.8 by adding sodium hydroxide solution. The reaction was kept at 140 for ℃68 h, and it was cooled to room temperature at the speed of 10 /h℃ . Colorless crystals of 1 suitable for X-ray diffraction analysis were obtained in 60.26% yield. m.p.: 257～259 ℃. Anal. Calcd. (%) for C84H82N4O12Y2: C, 66.49; H, 5.45; N, 3.69. Found (%): C, 66.35; H, 5.43; N, 3.71. Main IR (KBr, cm–1): IR (v/cm–1): 2920(s), 1626(vs), 1528(m), 1443(m), 1429(vs), 1185(w), 1109(w), 1240(w), 1063(m), 847(m), 729(m), 604(w), 478(w).

2. 3 Determination of the crystal structure

A single crystal with dimensions of 0.20mm × 0.20mm × 0.20mm was put on a Bruker SMART CCD 6000 diffrac- tometer equipped with a graphite-monochromatic MoKα radiation (λ = 0.71076 Å) using an ω scan mode at 296(2) K. A total of 22328 reflections were collected in the range of 2.92≤θ≤27.24°, of which 6503 were independent (Rint= 0.0864) and 5394 were observed (I > 2σ(I)). All data were corrected by Lp factors and empirical absorption. The crystal structure was solved directly by program SHELXS-2008, and refined by program SHELXL-2013[19]. The hydrogen and non-hydrogen atoms were corrected by isotropic and anisotropic temperature factors respectively through full-matrix least-squares method. The final R = 0.0353, wR = 0.0826 (w = 1/[σ2(Fo2) + (0.0486P)2+ 0.0000P], where P = (Fo2+ 2Fc2)/3), (∆/σ)max= 0.001, S = 1.039, (∆ρ)max= 0.335 and (∆ρ)min= –0.253 e·Å–3.

3 RESULTS AND DISCUSSION

3. 1 Crystal structure of 1

The coordination structure of 1 is revealed in Fig.1, square antiprism coordination geometry of the central Y(III) ion of 1 is shown in Fig.2, and its packing diagram is given in Fig.3. Selected bond lengths and bond angles are shown in Table 1.

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

Fig.1. Coordination structure of complex 1 (Undo part carbon atoms)A: 1 – x, 1 – y, 1 – z

Fig.2. Square antiprism coordination geometry of the central Y(III) ion of 1

Fig.3. Packing diagram of the title complex in a cell

Fig.4. Fluorescence of complex 1 and ligands (a: excitation spectrum of 1; b: emission spectrum of 1; c: excitation spectrum of TMBA; d: emission spectrum of TMBA）

3. 2 Spectroscopic characterization of 1

Infrared spectrum of the complex demonstrates an absorp- tion peak at 2292 cm–1ascribed to the characteristic absorp- tion peak of CH3- in TMBA. The antisymmetrical and symmetrical stretching vibration absorption peaks of carboxy- lic group in the ligand appear at 1626, 1528 cm–1and 1626 and 1443, which are in contrast with the corresponding peaks of free ligands (at 1686 and 1436 cm–1, respectively) and shift remarkably. The Δvcoo–(vas(coo–)– vs(coo–)) of the complex is 98 and 183 cm–1, one of which is smaller than 100 cm–1, and the other falls between 100 and 200 cm–1, so the carboxyl in the complex is coordinated with bidentate chelate and bidentate bridge modes[23]. The strong peaks at 1429, 847 and 729 cm–1are ascribe to the characteristic absorption peaks of phen ligand.

The fluorescent properties of 1 and the free ligand TMBA have also been studied, as shown in Fig.4. The title complex displays characteristic emission peaks at λem= 398 nm (λex= 360 nm), while at λem= 394 nm (λex= 360 nm) for the TMBA. Compared with that of free ligand TMBA, the emission spectrum of the title complex has the same characteristic emission peak and similar figure, suggesting that fluorescence of the title complex may be mainly ascribed to electronic transition of the intra ligand TMBA because the Y(III) ion has the electron configuration of ns2np6and its electron transition requires high energy, thereby the fluorescence emission of the complex is the ligand fluorescence of the center ion perturbation type[24].

3. 3 Thermal stability of 1

The thermogravimetric analysis (Fig.5) of 1 demonstrated that the weight loss of the complex in the air from room temperature to 600 ℃ occurred mainly in 2 stages. The first stage occurs from 140～260 ℃ with the weight loss of 23.70%, resulting from the loss of two phen molecules (calcd.: 23.75%). The second stage takes place from 260 to 390 ℃ with the weight loss of 61.40% due to the departure of six TMBA anions (calcd.: 61.37%). In air, the final product is yttrium oxide with the final residual rate to be about 14.90% (calcd.: 14.88%).

Fig.5. TG of complex 1