LI Wei LI Chng-Hong ZHOU Shui-Qi LI Yu-Lin KUANG Yun-Fei

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

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

c (Zhejiang Center Good-testing Service Co. Ltd. Zhejiang 321025, China)

ABSTRACT A new manganese(II) complex [Mn(C14H9O3)2(C12H8N2)2]·4H2O (1) was synthesized with o-benzoylbenzoic acid, manganese sulfate and 1,10-phenanthroline (phen) in the mixture of acetonitrile and water solvent. It crystallizes (C52H42MnN4O10, Mr = 937.83) in monoclinic, space group P21/n with a = 13.3528(5), b =17.6963(6), c = 19.7889(7) ?, β = 109.647(4)o, V = 4403.8(3) ?3, Dc = 1.415 g/cm3, Z = 4, F(000) = 1948, μ(MoKα)= 0.368 mm-1, R = 0.0404 and wR = 0.0956. The crystal structure shows that the manganese ion is coordinated with two oxygen atoms from two o-benzoylbenzoic acid molecules and four nitrogen atoms from two phen molecules,forming a distorted octahedral coordination geometry. The TG, spectrum analysis and magnetic properties of 1 were studied.

Keywords: manganese(II) complex, spectrum analysis, thermal stability, magnetic property;

1 INTRODUCTION

The design and synthesis of metal directed supramolecular frameworks have received much attention in coordination chemistry because of their interesting molecular topologies and tremendous potential applications in host-guest chemistry,catalysis, molecular selection, nonlinear optics, ion exchange and microelectronics[1]. Manganese plays an important role in the enzymatic catalysis of biochemistry, and the study of manganese complexes has aroused great interest. In addition,in order to synthesize molecular magnets, multi-nuclear magnetic exchange between manganese has also attracted people's attention[2]. Aromatic carboxylic acid complexes exhibit rich topology structure and high stability, which have captured the extensive interest of researchers due to their potential applications in many fields such as magnetism,catalyst and biology[3]. 2-Benzoylbenzoic acid is an important benzoic acid, which acts as a crucial role in medicine and dyestuff[4]. For instance, it is an major principal material of the anthraquinone dyestuff intermediate, which can be used to produce anthraquinone benzanthrone amino anthraquinone, etc[5]. As a rigid aromatic carboxylic acid ligand, 2-benzoylbenzoic acid can also be used in the design and construction of coordination compounds. However, it is rarely reported[6]. A new manganese(II) complex[Mn(C14H9O3)2(C12H8N2)2]·4H2O witho-benzoylbenzoic acid and 1,10-phenanthroline (phen) as a ligand has been synthesized, and its structure was characterized by X-diffractometer. We also investigated its luminescent, magnetic and thermal stability properties. The result shows that 1 has one fluorescent emission band at around 424 nm. In addition,the magnetic behaviors of 1 are antiferromagnetism and it is stable under 383 K.

2 EXPERIMENTAL

2. 1 Reagents and instruments

All reagents from commercial sources were of analytical grade and used without further purification. Crystal structure was determined on a Bruker SMART CCD 6000 single-crystal diffractometer. IR spectra were recorded on a Bruker Vector22 FT-IR spectrophotometer using KBr discs.Thermogravimetric analyses were performed on a simultaneous SPRT-2 pyris1 thermal analyzer at a heating rate of 10 K/min. Magnetic measurements in the range of 300～2 K were performed on a MPMS-SQUID magnetometer at a field of 2 kOe on a crystalline sample in the temperature settle mode. The fluorescence for the powdered samples was measured on an RF-5301PC spectrofluorometer with a xenon arc lamp as the light source.

2. 2 Synthesis of the complex

2 mmol of manganese sulfate (about 0.302 g), 3 mmol ofo-benzoylbenzoic acid (about 0.720 g) and 3 mmol of phen(about 0.595 g) were added to 30 mL of acetonitrile-water solvent mixture (volume ratio: 5:3) by stirring at 343～353 K for about 4.0～5.0 h, and then mixed with pH being adjusted to 6.5～7.0 with dilute potassium hydroxide solution under stirring for about 23 h at 353 K. Afterwards, the resultant solution was filtrated, and the filtrate was kept untouched and evaporated slowly at room temperature. Yellow block-shaped single crystals suitable for X-ray diffraction analysis were obtained after one month in 46.5% yield based on phen. m.p.: 609 ～610 K. Anal. Calcd. (%) for C52H42MnN4O10: C, 66.60; H, 4.51; N, 5.97. Found (%): C,66.40; H, 4.53; N, 5.60. Main IR (KBr, cm–1): IR (v/cm-1):3410(w), 3055(w), 1662(vs), 1584(vs), 1560(vs), 1427(vs),1381(vs), 1313(m), 1273(m), 1146(m), 1101(m), 95(vs),851(vs), 767(m), 731(vs), 700(m), 671(w), 451(w).

2. 3 Structure determination

3 RESULTS AND DISCUSSION

3. 1 Crystal structure of the complex

The crystal structure of the title complex is revealed in Fig. 1.Hydrogen bonding between adjacent molecules of the title complex is given in Fig. 2. Selected bond lengths and bond angles are shown in Table 1, and the hydrogen bond lengths and bond angles in Table 2.

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

Table 2. Hydrogen Bond Lengths (?) and Bond Angles

Table 2. Hydrogen Bond Lengths (?) and Bond Angles

Symmetry codes: (a): 3/2–x, –1/2+y, 1/2–z; (b): –1/2+x, 1/2–y, –1/2+z

?

Fig. 1. Molecular structure of the title complex

Fig. 2. Hydrogen bonding between adjacent molecules of the title complex

3. 2 Spectral analysis of 1

The wide adsorption peak at about 3410 cm-1is the characteristic peak of OH group of H2O[11]. Two strong peaks at 1662 and 1381 cm-1could be assigned to thevas(coo-)andvs(coo-)stretching vibration ofo-benzoylbenzoic acid ligand,with Δvcoo-= 281 cm-1(Δvcoo-=vas(coo-)–vs(coo-)) greater than 200 cm-1, which indicates that carboxylic radicals in theo-benzoylbenzoic acid ligand coordinated with the manganese ions in a monodentate manner. The characteristic absorption peak of the phen ligand in complex has obvious shift from 1421, 853 and 739 cm-1to 1427, 851 and 731 cm-1,respectively, thus revealing the coordination of nitrogen atoms in phen with the manganese(II). There are Mn–O and Mn–N characteristic absorption peaks at 671 and 451 cm-1[12]. The above analysis conforms to the crystal test results.

Fig. 3 shows the emission spectra, recorded in the range of 360～520 nm, of the title complex and free ligands in solid state at ambient temperature. As seen in Fig. 3, phen,o-benzoylbenzoic acid and the title complex display the characteristic emission peaks at 436, 422 and 424 nm,respectively. Compared with the free ligand ando-benzoylbenzoic acid, the title complex has the same characteristic emission peak and similar figure, but its luminescence is relatively stronger, suggesting that this may be mainly ascribed to electronic transition of the intraligando-benzoylbenzoic acid[13].

Fig. 3. Luminescence property curves of the title complex and ligands a: phen; b: o-benzoylbenzoic acid; c: the title complex

3. 3 Magnetic properties of 1

The temperature dependence of the magnetic susceptibility of 1 was investigated from 300 to 2 K with an applied magnetic field of 2 kOe. TheXmT vs.TandXmvs.Tcurves are in Fig. 4. The maximum experimental value ofXm Tis 3.03362 at 300 K, then theXm Tof 1 decreases with reducing the temperature, which indicates antiferromagnetic interaction in the complex[14]. When the temperature reaches 2 K, theXmTvalue is 2.098. The linear regression equation is 1/Xm=0.3411T+ 3.3263 with a correlation coefficient of 0.9961.According to the Curie-Weiss law, fromXm=C/(T?θ), the Weiss constantθcan be obtained,C= 3.914 andθ=?87.088 K. These magnetic behaviors show that the title complex exhibits antiferromagnetism. In this work, the magnetic behavior is attributed to the interaction between manganese ions and free ligands[15].

Fig. 4. Temperature dependence of the magnetic susceptibility of the title complex in the form of (a) XmT vs. T, Xm vs. T; (b) 1/Xm vs. T, Xm vs. T

3. 4 TG and DTG analyses of 1

The thermogravimetric analysis (Fig. 5) of 1 demonstrates that the weight loss in air from room temperature to 973 K occurs mainly in 3 stages. The first one takes place from 373 to 383 K with the weight loss of 7.70%, corresponding to the release of free and coordinated water molecules (calcd.:7.69%). At the same time, one thermal absorption peak of DTG appears at about 375 K, indicating the decomposition of free water molecules[16]. The second stage is found from 383 to 673 K with the weight loss of 38.50%, resulting from the departure of two phen molecules (calcd.: 38.43%). The second DTG thermal absorption peak is observed at about 609 K which is the melting point of the complex. During stage 3,the weight loss of 46.30% (theoretical value: 46.32%)presents at 673～833 K due to the loss of 28 carbon, 18 hydrogen and 5 oxygen atoms from twoo-benzoylbenzoic acid molecule anions. The final product is manganese oxide,with the final residual rate to be 7.50% (calcd.: 7.56%).

Fig. 5. TG and DTG curves of the title complex