Synthesis and Luminescence Properties of the Binary/Ternary Complex of Samarium Ion with Phenacylmethyl P-Tolyl Sulfoxide and Benzoic Acid

. A new ligand phenacylmethyl p-tolyl sulfoxide (denoted as L 1 ) has been synthesized by an asymmetric synthesis method. Its novel binary complex Sm(L 1 ) 7  (ClO 4 ) 3  6H 2 O, and ternary complex Sm(L 1 ) 6 ·(L 2 )·(ClO 4 ) 2 ·6H 2 O (benzoic acid denoted as L 2 ) have been synthesized. The structure and composition of the samarium complexes characterized by elemental analysis, molar conductivity, IR, UV, and 1 HNMR. Additionally, fluorescence spectra measurements shows that the complexes display stronger fluorescence intensity in solid state, indicating the ligands could efficiently transfer the energy to Sm 3+ ions in the complexes. The ternary complex has stronger fluorescence intensity than the


Introduction
Rare earth complexes have attracted much attention for a wide variety of applications in the fields of lighting devices, and biomedical analysis [1,2]. There are numerous examples of luminescent rare earth complexes reported in the literature [3,4]. As is known, the intra-configuration 4f→4f transitions in rare earth ions are forbidden, so the luminescence intensity of the RE 3+ ions are weakening [5]. The organic ligands with great conjugated action the as sensitizers coordinated with the RE 3+ which can transfer the energy to it effectively and further to increase its luminescence intensity. The organic ligands that exhibited this property were called as "antennas" [6]. In the past several decades, many sulfoxide complexes had been synthesized and intensively studied due to the superb coordination ability of the sulfoxide ligand [7,8]. Europium and terbium complexes are studied a lot. There are few researches about samarium complexes. So it is extremely vital significant for the comprehensive utilization of Sm 3+ to research the luminescence properties of the samarium complexes.
Thus, we have synthesized a phenacylmethyl p-tolyl sulfoxide (L1). Furthermore, the L1 as the first ligand and benzoic acid (L2) as the second ligand coordinated with samarium ions in the paper. The luminescence properties of as-synthesized binary and ternary samarium complexes were studied. The luminescence study indicates that ternary samarium complex has higher fluorescence intensity than binary samarium complex.

Materials and physical measurements.
Sm2O3 (purity > 99.99 %) was supplied by Beijing Chemical Reagent Company. The Sm(III) perchlorate was prepared from dissolving in 2 mol•L -1 HClO4, and then evaporated and dried in vacuum. All other chemicals were analytical grade and were used as received without further purification. Elemental analysis was carried out on a HANAU analyzer. Conductivity measurement was made on a DJS-1 conductivity meter. The infrared spectra were determined on a Nicolet NEXUS-670 FT-IR spectrophotometer. The ultraviolent spectral were recorded on a TU-1901 double beam spectrophotometer. 1 HNMR spectra were measured on Bruker AC-500 spectrometer in DMSO-d6. Fluorescence spectra and fluorescent lifetime were determined on a FLS920 with the slit width of 1nm.

Preparation of the europium ternary complex.
The L1 was prepared by oxidation of C6H5COCH2SC6H4CH3 according to the literature [9]. The appropriate concentration of L1 anhydrous ethanol solution was added into samarium perchlorate anhydrous ethanol solution under magnetic stirring for 1.0 h. A white precipitate appeared, the white precipitate was separated by suction filtration, purified by washing with anhydrous ether for several times. Finally, white powder was obtained. The preparation of binary samarium complex was similar to the ternary samarium complex.

Composition analysis.
The elemental analysis and molar conductivity data of samarium complexes showed in Table 1. The λ m value of the binary complex in DMF is in good accordance with the formula as 1:3 electrolyte and the λ m value of the ternary complex in DMF is in good accordance with the formula as 1:2 electrolyte [10]. According to the elemental analysis, the compositions of the binary and the ternary complexes are suggested as Sm(L1)7(ClO4)36H2O and Sm(L1)6(L2)(ClO4)26H2O, respectively.

1 HNMR spectra analysis.
The 1 HNMR of L1 shows that there are multiple resonance peaks for two phenyl groups at δ7.375-7.980 ppm, and the integral intensity illustrates it contains nine protons. The proton resonances peaks of one methylene and one methyl group are at δ4.685-4.747 ppm and δ 2.370-2.504 ppm, which have two and three proton respectively (Fig. 1a). The result showed that we have synthesized the L1 successfully and the purity of the obtained ligand is supernal. The 1 HNMR spectra of the samarium complexes are similar as that of L1, which have shifted at different degree (Fig.1b,c). The reason may be concerned with coordinate effect.  Fig. 2a show the IR spectrum of L1, the stretching vibration absorption of sulflnyl group appeared at 1049 cm -1 (νS=O). It shifts to 982 cm -1 and 979 cm -1 in IR spectra of binary and ternary samarium complexes (Fig. 2c,d), respectively, which suggests that Sm 3+ ions are bonded with the oxygen atom of the sulflnyl group. Whereas the carbonyl group stretching vibration absorption in IR spectrum of L1 (Fig. 2a) appears at 1677 cm -1 (νC=O), no significant shift is found in IR spectra of binary and ternary systems (Fig. 2c,d), which is an evidence that the oxygen atom in carbonyl group is not coordinated with Sm 3+ ion. The νas(COO -) and νs(COO -) absorption of L2 occurred at 1550 cm −1 and 1416 cm −1 , and the Δν value is 134 cm −1 (Fig. 2b). The νas(COO -) and νs(COO -) absorption bands appear at 1641 cm −1 and 1335 cm -1 in the ternary samarium complex and the Δν value was 306 cm −1 larger than that of L2 (Fig. 2d), which can be deduced that carboxyl group is coordinated with Sm 3+ ion by monodentate type [11]. In terms of molar conductivities, it can be suggested that none of ClO4 − is coordinated with Sm 3+ ions.

UV spectra analysis.
The UV spectra of ligands displayed in Fig. 3a and b, the major absorption bands of π-π* electronic transition in phenyl group are observed at 284 nm and 272 nm, respectively. A strong absorption also observed at 284 nm and 285 nm for the binary and ternary samarium complexes, respectively (Fig. 3c,d), Which is no shift happening compared with the L1 (Fig.  3b). While the absorption band of binary samarium complex is red shift comparing to the absorption of L2 absorption band, from 272 nm to 285 nm. It is found that the major absorption bands of the ligands still appeared after the formation of the complexes.  Fig. 4 shows the excitation and emission spectra of binary samarium complex (a) and ternary samarium complex (b). The excitation spectra of the complexes were obtained by monitoring the emission of the complexes at the wavelength of 596 nm. The maximum peak of binary complex was at 317 nm and ternary complex was at 322 nm. The excitation peaks of the two complexes are similar. The emission peaks of the binary and ternary samarium complexes centered at 561, 596 and 643 nm, which are assigned to the transitions of 4 G5/2→ 6 H5/2, 4 G5/2→ 6 H5/2, 4 G5/2→ 6 H9/2, respectively. The binary and ternary samarium complexes display stronger emission intensity, indicating the ligands could efficiently transfer the energy to Sm 3+ ions in the complexes. The strongest emission intensity of the ternary complex (19680 a.u) is 1.37 times as great as that of the binary complex (14330 a.u.). The result illustrate that the second ligand L2 can play a synergistic effect for the energy transfer process between the first ligand and Sm 3+ ion.

Conclusions
In this paper, a new ligand phenacylmethyl p-tolyl sulfoxide has been synthesized by an asymmetric synthesis method. The binary and ternary samarium complexes with phenacylmethyl p-tolyl sulfoxide as first ligand and benzoic acid as second ligand have been synthesized. The samarium complexes display preferable luminescence properties. The emission intensity of the ternary complex is 1.37 times as great as that of the binary complex, and the ternary complex has longer lifetime.