HOU Xiang-Yang WANG Xiao TANG Long WANG Ji-Jiang HOU Xiu-Fang KANG Wei-Wei LIU Xiao-Li

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Synthesis, Structure, and Properties of {[Mn(ADA)(Phen)]·(H2O)2}nConstructed from Azobenzene-4,4?-dicarboxylic Acid and 1,10-Phenanthroline①

HOU Xiang-Yang WANG Xiao②TANG Long WANG Ji-Jiang②HOU Xiu-Fang KANG Wei-Wei LIU Xiao-Li

(716000)

synthesis, structure, fluorescence, magnetic, electrochemical properties;

1 INTRODUCTION

C, N, O, S,) as building blocks have been used in the construction of CPs[7].Furthermore, the ligand of biphenylethene-4,4?-dicarboxylate containing “-C-C-” unit bridged Zn2+or Cd2+centers to produce 1D, 2D and 3D networks featuring in the previous researches[8]. There are rare researches about the flexibility ligand with “-N=N-” unit in the litera- ture[9]. Especially, the synthesis of complexes using the imidazole and pyridine flexible ligands con- taining “-X-X-” or“-X-X-X-” unit to bridge the metal ions has been reported[10-14].

Inspired by the above considerations, the flexibleH2ADA ligandscontaining two multi-dentate car- boxylates and rigidPhen ligand were prepared. The carboxylate group of H2ADA presents a variety of bridge modes, which can produce different magnetic exchange pathway and thus has been widely applied. The large conjugated system of H2ADA and Phen ligands possesses favorable possibility acting as an efficient super-exchange pathway to convey a variety of magnetic information and fluorescence property. The exact nature of the magneto-structural corre- lations, magnetic super exchange, and structural factors controlling the exchange coupling is vital issues requiring further investigation. Hence, the H2ADA and Phen are multipurpose ligands that could facilitate strong magnetic coupling and fluorescence property. The research about the fluorescence, magnetism and electrochemistry of the complexes can help probe the relation between structure and property. The synthesis, crystal struc- tures, fluorescence, magnetic and electrochemical properties, and natural bond orbital analysis of the title CP {[Mn(ADA)(Phen)](H2O)2}n(1) were discussed in detail.

2 EXPERIMENTAL

2. 1 Materials and methods

All starting materials of analytical grade were purchased and used without further purification. Elemental analysis (C, H, N) was determined on a Perkin-Elmer 2400 type elemental analyzer. The infrared spectra were measured between 4000～400 cm–1on a Bruker EQUINOX-55 spectrophotometer using KBr pellets. Thermal behaviors were per- formed under nitrogen with a heating rate of 20 °C·min-1using a NETZSCH STA 449C thermo- gravimetric analyzer. Magnetic experiments were accomplished using a Quantum Design MPMS-XL7 SQUID magnetometer on polycrystalline samples of the compound. The solid sample photo-luminescence analyses were performed on an Edinburgh Instru- ment FLS920 fluorescence spectrometer at ambient temperature. Cyclic voltammetry was performed on an Electrochemical Workstation CHI660E.

2. 2 Synthesis of {[Mn(ADA)(Phen)]·H2O}n (1)

A mixture containing H2ADA (0.15 mmol), KOH (0.3 mmol), Phen (0.15 mmol), and Mn(CH3COO)2·4H2O(0.2 mmol) was added into 15 mL deionized water, which was then sealed in a 25 mL Te?on-lined stainless-steel autoclave reactorunder autogenous pressure at 170 ℃ for about 96 h. The reaction system was cooled to room temperature at a rate of 5 °C·h-1. Colorless bulk crystals were collected in 57% yield based on H2ADA. C, H and N percentage analyses for C26H20N4O6Mn (%): Calcd.: H, 3.74; C, 57.89; N, 10.39. Found (%): H, 3.67; C, 57.61; N, 10.53.

2. 3 X-ray crystal structure determination

Crystallographic data for CP 1 were collected on a Bruker Smart 1000 CCD diffractometer using gra- phite-monochromated Moradiation with an X- scan mode. A semi-empirical absorption correction was applied using the SADABS program[15]. The structure was solved by direct methods and re?ned on2by full-matrix least-squares using SHELX- 97[16, 17]. All non-hydrogen atoms were re?ned aniso- tropically. Hydrogen atoms of coordinated and uncoordinated water molecules were located on a difference Fourier map, while other hydrogen atoms were included in the calculating positions and re?ned with anisotropic thermal parameters riding on the present atoms. Selected bond lengths and bond angles for CP 1 are listed in Table 1.

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

3 RESULTS AND DISCUSSION

3. 1 Crystal structure of CP{[Mn(ADA)(Phen)](H2O)2}n (1)

Fig. 1. Coordination environment of Mn(1)2+in 1

Fig. 2. One-dimensional structure of 1

Fig. 3. Three-dimensional supramolecular structure of 1

Table 2. Geometrical Parameters of All Hydrogen Bonds and π···π Interactions for 1

Symmetry codes: #1: 2+x, 1+y, 1+z; #2: 2–x, 3–y, 2–z. Cg(1): C(15)C(16)C(17)C(18)C(19)N(3), Cg(2): C(18)C(19)C(20)C(21)C(26)C(25); Cg(3): C(18)C(19) C(20)C(21)C(26)C(25); Cg(4): C(15)C(16)C(17)C(18)C(19)N(3)

The geometrical configuration of Mn2+center in1 was investigated. All calculations were performed with the Gaussian 09 suite of programs[19]. The geometry of the molecular structure from the expe- rimental data was optimized without symmetry cons- traints on the B3LYP level of theory. The 6-31g basis set was performed for hydrogen, carbon, oxygen and nitrogen. At the same time, the LANL2DZ basis set was adopted to the metal Mn2+. Frequency analysis calculates at the same theoretical level. The natural population analysis has been made with the natural bond orbital (NBO) analysis[20]. The selected natural atomic charges, spin density and electron con- figuration of 1 are shown in Table 3. The electronic configurations of Mn,O and N atoms are 40.2335.7240.41, 21.725.0, and 21.324.1, respectively. Based on theabove results, one can conclude that the Mn2+ioncoordination with N and O atoms was mainly on the 4and 4orbitals. All O and N atoms supply electrons of 2and 2to the Mn2+ion and form coordinationbonds. Therefore, theMn2+ion obtained some electrons from O and N atoms of the ligands. From the natural charge, it shows covalent interactions between the coordinated atoms and Mn2+ion. The spin density was mainly in the Mn2+ion. The HOMO-1 and HOMO-2 were located largely in the Phen ligand from Fig. 5. The LUMO andLUMO+1 mainly consist of the Mn ion.The HOMO and LUMO+2 werelocated largely on twoADA2-, respectively. The calculation results show obvious covalent interaction between the Mn2+ion and coordinated atoms.

3. 2 IR spectra and thermogravimetric analyses

IR spectrum displays characteristic absorption bands for water molecules, carboxylate, phenyl units,. As shown in Fig. 6, theIR spectra of CP 1 show a broad absorption band and maximum absorption peak at 3407 cm?1, which indicates the presence ofO?Hstretching frequencies. The maximum absorp- tion peak at 1597 cm-1was the characteristic stre- tching vibration of COO-1in1. The characteristic IR band for the phenyl rings is 830 cm?1due to the=C?Hvibration in 1.

Table 3. Selected Natural Atomic Charges, Spin Density and Electron Configuration of 1

Fig. 4. Schematic diagram of···interactions in 1

Fig. 5. Frontier molecular orbitals of 1

Fig. 6. IR spectra of 1

Fig. 7. Thermal stability curve of 1

The thermal analysis curve of 1 was investigated (Fig. 7). The ?rst weight loss of 7.16% observed from 65 to 210 °C corresponds to the loss of water molecule (calculated 6.67%). It keeps losing weight from 230 to 560 °C, which can be attributed to the departure of ADA2-and Phen ligands. The final residue was MnO (Found: 12.73%, Calcd. 13.15%).

3. 3 Magnetic property

As shown in Fig. 8, the magnetic susceptibility data of 1 were measured in the temperature range of 2～300 K under an applied field of 1 kOe.The value ofmis 4.43 cm3·K·mol-1, which is very close to the expected value of 4.375 cm3·K·mol-1for an isolated Mn2+ion with g = 2.0. Themremains basic constant until about 100 K. As this temperature was lowered, themvalue decreases gradually to a minimum of 1.53 cm3·K·mol-1at 2 K, indicating the antiferromagnetic (AF) interaction between the Mn2+paramagnetic centers (ground state with S = 0)[21]. The AF interaction was further suggested by the negative Weiss Constant= ?4.90 K, obtained from the data of 1/mversusin the temperature range of 17～200 K.

Fig. 8. Temperature dependence of magnetic susceptibility in formM, and 1/M~(inset) of1

Fig. 9. Emission spectra of 1 and the H2ADA ligand

Fig. 10. Cyclic volatmmetry of 1

3. 4 Photoluminescent property

In this study, the luminescence properties of complex 1 andH2ADAligand were investigated in the solid state at room temperature. As shown in Fig. 9, the emission peak of H2ADAligand was located at 416 nm (ex= 365 nm), probably ascribed to theortransitions. Complex 1 exhibits the maximum emission peaks at 429 nm in broad bands upon excitation at 350 nm, which were red-shifted by 13 nm for the free H2ADA ligand.Comparing the luminescence of complex 1 and the free ligand, the emission mechanism may be attributed to the metal charge transfer (LMCT) transition[22].

3. 5 Electrochemical property

As shown inFig. 10, the cyclic voltammetry of 1was measured with a three electrode cell in aqueous solution to the complex of 5.0 × 10-5mol·L-1at the scanning rates of 30 and 50 mv·s-1. The cyclic voltammogram curve of 1has one pair of oxidation-reduction peaks, which correspond to the Mn2+/Mn3+redox process. At different scanning rates, the oxidation peaks of 1were 0.73 and 0.82 V. The results show that electron transfer of Mn2+between Mn3+in electrolysis was quasi-reversible process[23].

4 CONCLUSION

One new CP, {[Mn(ADA)(Phen)](H2O)2}n(1), has been synthesized. The structure of 1 has been deter- mined and characterized by single-crystal X-ray diffraction analysis, elemental analysis, IR spec- troscopy, and thermal behaviors. The crystal struc- ture of 1 contains one-dimensional zigzag chains which form a stable three-dimensional supramo- lecular compound by means of stronginterac- tion and hydrogen bonding. Interestingly, the fluore- scence, magnetic and electrochemical properties, andnatural bond orbital analysis of 1 have been inves- tigated.

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10 December 2017;

20 March 2018 (CCDC 847696)

① This work was supported by the National Natural Science Foundation of China (21503183, 21663031), and the Provincial Level Innovation Programs Fund of undergraduatefor 2017 (No. D2017010)

. Wang Xiao (1977-), functional materials. E-mail: wx2248@126.com

10.14102/j.cnki.0254-5861.2011-1918