雜雙金屬Cuギ-Ndバ和Znギ-Ceバ的Salamo型配合物：合成、晶體結(jié)構(gòu)和熒光性質(zhì)

楊玉華 張 雨 于 盟 鄭姍姍 董文魁

(蘭州交通大學(xué)化學(xué)與生物工程學(xué)院，蘭州 730070)

0 Introduction

Much recent interests have been focused on 3d transition metal complexes with Salen-[1-7]or Salamotype[8-12]ligands,which have potential applications,such as luminescent[13-19]and magnetic[20-25]materials,supramolecular architectures[26-31],biological fields[32-39],molecular recognitions[40-43]and electrochemistries[44-45].Because of the high coordination ability of phenoxy groups,many central metals can be coordinated to form heteronuclear metal complexes[46-50].

Because the f-f transitions of lanthanide ions are parity forbidden,the absorption coefficients are very low and the emissive rates are slow[51],suitable organic ligands must be well-designed to strengthen luminescent intensity,which act as sensitizers to excite lanthanide ions(antenna effect)[52].

Herein,two kinds of hetero-bimetallic 3d-4f complexes containing a Salamo-type ligand O,O′-(ethane-1,2-diyl)bis(1-(3-ethoxy-2-hydroxyphenyl)-3-ethoxy-2-hydroxybenzaldehyde oxime)(H2L)were synthesized and structurally characterized.Furthermore,their fluorescence properties were investigated.

Scheme 1 Structure of the ligand H2L

1 Experimental

1.1 Materials and physical measurements

3-Ethoxybenzaldehyde(99%)was purchased from Alfa Aesar and used without further purification.Ethanol and methanol and other reagents and solvents were analytical grade reagents from Tianjin Chemical Reagent Factory.C,H and N analyses were obtained using a GmbH VarioEL V3.00 automatic elemental analysis instrument.Elemental analyses for metals were monitored with an IRIS ER/S-WP-1 ICP atomic emission spectrometer.Melting points were acquired by the use of a microscopic melting point apparatus made in Beijing Taike Instrument Limited Company and were uncorrected.IR spectra were recorded on a Vertex70 FT-IR spectrophotometer,with samples prepared as KBr(500～4 000 cm-1).UV-Vis absorption spectrawererecorded on aShimadzu UV-3900 spectrometer.Fluorescence spectra in solution were recorded on a Hitachi F-7000 spectrometer.1H NMR spectra were determined by a German Bruker AVANCE DRX-400 spectrometer.

1.2 Synthesis and characterization of H2L

The Salamo-type ligand H2L was synthesized according to an analogous method reported earlier[53].A solution of 1,2-bis(aminooxy)ethane(276.0 mg,3.0 mmol)in ethanol(10 mL)was added to a solution of 3-ethoxybenzaldehyde(996.0 mg,6.0 mmol)in ethanol(20 mL),and the mixture was heated at 55～60 ℃ for 5h.After cooling to room temperature,the precipitate was filtered off,and white crystalline H2L was obtained.Yield:784.0 mg,67.3%.m.p.462～463 K.Anal.Calcd.for C20H24N2O6(%):C,61.84;H,6.23;N,7.21.Found(%):C,61.80;H,6.30;N,7.19.1H NMR (400 MHz,CDCl3):δ 1.47(t,J=4 Hz,6H,CH3),4.11(dd,J=4,8 Hz,4H,CH2),4.46(s,4H,CH2),6.82(m,3H,ArH),6.88(m,3H,ArH),8.26(s,2H,CH=N),9.68(s,2H,OH).IR(KBr,cm-1):1 611(νC=N),1 248(νAr-O).UVVis(MeCN,10 μmol·L-1), λmax/nm:270,319.

1.3 Synthesis of complex 1

The ligand H2L(19.4 mg,0.05 mmol)was dissolved in 5 mL of ethanol and stirred with ethanol solution(5 mL)of Cu(OAc)2·2H2O(10.3 mg,0.05 mmol)and Nd(NO3)3·6H2O(22.6 mg,0.05 mmol),filtered to get a dark green solution.Through partial solvent evaporation,single crystals suitable for X-ray diffraction analysis were obtained after several days.Yield:60.3%.Anal.Calcd.for C22H28NdCuN5O16(%):C,31.98;H,3.42;N,8.48.Found(%):C,32.24;H,3.29;N,8.43.

1.4 Synthesis of complex 2

The synthesis of complex 2 is similar to that of complex 1,except that the solvent is replaced.The ligand was dissolved in acetone,while the metal salts Zn(OAc)2and Ce(NO3)3were dissolved in methanol.White crystals of complex 2 were collected.Yield:58.6%.Anal.Calcd.for C23H29CeZnN4O15(%):C,34.23;H,3.62;N,6,94.Found(%):C,34.39;H,3.47;N,6.82.

1.5 X-ray crystallography

The single crystals of complexes 1 and 2 were placed on a Super Nova Dual Eos four-circle diffractometer.The diffraction data were collected using a graphite monochromated Mo Kα radiation(λ=0.710 73 nm).Data collection and reduction were performed using CrysAlisPro and then processed with Olex2.The structures were solved with SHELXS-2008 and refined with SHELXL-2014[54].All non-hydrogen atoms were refined anistropically and hydrogen atoms were added in calculated positions and refined using a riding model.The crystallographic data and structural refinements for complexes 1 and 2 are listed in Table 1.

CCDC:1815944,1;1815943,2.

Table 1 Crystallographic data and refinement parameters for complexes 1 and 2

2 Results and discussion

2.1 IR spectra

IR spectra of H2L and its corresponding complexes 1 and 2 exhibited various bands in the region of 4 000～400 cm-1(Fig.1).The O-H stretching band of the free ligand H2L was observed at 2 981 cm-1that belongs to the phenolic hydroxyl group,whereas complexes 1 and 2 showed a vibration band at 3 413 and 3 402 cm-1that belong to coordinated ethanol or methanol molecules.

The free ligand H2L exhibited characteristic C=N stretching band at 1 611 cm-1,which is shied by 5～7 cm-1in complexes 1 and 2,respectively,indicating that the nitrogen atoms of C=N group are coordinated to the Cuギor Znギions,which is similar to previously reported metalギcomplexes[55].

Fig.1 IR spectra of H2L and its complexes 1 and 2

The Ar-O stretching frequency appeared at 1 248 cm-1for the ligand H2L,while the Ar-O stretching frequencies in complexes 1,and 2 are observed at 1 233 and 1 242 cm-1,respectively.The Ar-O stretching frequencies are shifted to lower frequencies,indicating that the Cu-O or Zn-O bonds are formed between the metalギ ions and oxygen atoms of phenolic groups.

2.2 UV-Vis absorption spectra

The absorption spectra of H2L and its complexes 1 and 2 in diluted acetonitrile solution are shown in Fig.2.The free ligand H2L showed three absorption bands at 222,270 and 319 nm.The peaks at 222 and 270 nm can be assigned to the π-π*transitions of the benzene rings and the latter peak at 319 nm can be assigned to intra-ligand π-π*transition of the oxime groups[56].Compared with the absorption peaks of H2L,with the emergence of the first absorption peaks at ca.276 and 277 nm were observed in complexes 1 and 2,respectively.These peaks are bathochromically shifted,indicating coordination of the ligand moieties with metalギions.The absorption peaks at ca.270 and 319 nm were absent in complexes 1 and 2.Meanwhile,new absorption peaks were observed at ca.344 and 350 nm in complexes 1 and 2,may be due to L→M charge-transfer transitions,which are characteristic of the transition metal complexes with Salen-type N2O2coordination spheres.

Fig.2 UV-Vis absorption spectra of H2L and its complexes 1 and 2 in acetonitrile(10 mol·L-1)

2.3 Description of the crystal structures

2.3.1 Crystal structure of complex 1

Selected bond lengths and angles for complex 1 are presented in Table 2.Complex 1 crystallizes in the monoclinic system,space group P21/n,An asymmetric unit of complex 1 includes one completely deprotonated L2-unit,one Cuバatom(Cu1),one Ndバion(Nd1),three NO3-ions and one coordinated ethanol molecule.The crystal structure of complex 1 and geometries of metal atoms are shown in Fig.3.

Fig.3 (a)Molecule structure and atom numberings of complex 1 with 30%probability displacement ellipsoids;(b)Coordination polyhedron for Cuギa(chǎn)nd Ndバions of complex 1

Table 2 Selected bond lengths(nm)and angles(o)for complexes 1 and 2

Continued Table 2

Cu1 atom was penta-coordinated by inner N2O2(N1,N2,O1 and O5)cavity from the deprotonated L2-unit and one oxygen atom (O16)of the coordinated ethanol molecule.According to the calculation of structural index parameter τ1=0.196,Cu1 atom adopts a slightly distorted square pyramidal configuration,which N2O2site occupies the basal plane and O16 is in the axial position.The bond lengths of Cu-N bonds are in the range of 0.194 3(3)～0.199 2(3)nm,and those of Cu-O bonds are in 0.194 1(2)～0.227 8(3)nm with longer bond exists in the axial position.In addition,the angles of N1-Cu1-O16 and O5-Cu1-O16 are 92.04(13)°and 88.39(11)°,respectively,nearly equal to the upright angle.Compared with crystal structures of other analogous,acetate ions no longer bridge two metal ions in a common μ2-fashion[57]or as a terminalmonodentate ligand,which doesnot participate in the coordination of complex 1.Nd1 atom is deca-coordinated with outer O4site (O1,O2,O5 and O6)and six oxygen atoms provided by three bidentate NO3-ions(O7,O8,O10,O11,O13 and O14),showing a distorted bicapped twelve surface geometry.The Nd-O bond lengths are in the range of 0.240 1(2)～0.259 7(3)nm,as can be seen from Fig.3b the distances are close to each other.

2.3.2 Crystal structure of complex 2

Selected bond lengths and angles for complex 2 are presented in Table 2.Complex 2 crystallizes in the triclinic system,space group P1.The crystal structure of complex 2 and geometries of metal atoms are shown in Fig.4.

For complex 2,an asymmetric unit includes a fully deprotonated L2-unit,one Znギ ion(Zn1),Ceバion (Ce1),one μ2-acetate ion,two NO3-ions and one coordinated methanol molecule.Five donor atoms(N1,N2,O2,O5 and O8)of Zn1 atom come from N2O2cavity and the μ2-acetate ion,respectively.The structural index parameter τ1is equal to 0.412 by calculated.It is well known that the geometry of pentacoor-dinated complex is decided by geometric parameter τ,when τ=0,metal ions adopt square pyramidal configuration,when τ=1,will adopt the trigonal bipyramidal geometry.Herein,the τ value is closed to 0.5,indicating that the geometry ofZn1 atom is distorted square pyramidal configuration,where N2O2are basal plane and O8 occupies the axial position.The bond lengths of Zn-N bonds are 0.206 1(3)and 0.210 5(3)nm,and those of Zn-O bonds is in the range of 0.197 4(3)～0.205 0(2)nm,which are obvious shorter than Zn-N.It is worth noting that the angle of O5-Zn1-N1 is 160.94(12)°,which is relatively close to 180o,also implying that the geometry of Zn1 atom possesses square pyramidal.

Fig.4 (a)Molecule structure and atom numberings of complex 2 with 30%probability displacement ellipsoids;(b)Coordination polyhedron for Znギ and Ceバ ions of complex 2

The coordination number and geometry of Ce1 atom are same with Nd1 of complex 1,and both of them adopt a deca-coordinated bicapped twelve surface geometry.The differences are one methanol molecule and one μ2-acetate ion coordinated with Ce1.The bond lengths of Ce-O bonds are in the range of 0.243 0(3)～0.274 4(3)nm,while Ce1-O2 and Ce1-O5 have a shortest bond lengths and Ce1-O6 are the longest.

2.4 Supramolecular interactions

2.4.1 Supramolecular interaction of complex 1

Fig.5 (a)View of the intramolecular hydrogen-bonding interactions of complex 1;(b)View of intermolecular interactions of complex 1

Table 3 Intra-and inter-molecular hydrogen geometries for complexes 1 and 2

As shown in Fig.5 and 6,the self-assembling array of complex 1 islinked byintramolecular hydrogen bonds and intermolecular interactions.The hydrogen bond data and intermolecular interaction data are given in Table 3.In the crystal structure,there are eight intramolecular hydrogen bond interactions:O16-H16…O13,O16-H16A…O13,C2-H2A…O14,C9-H9…O12#2,C10-H10B…O14#2,C12-H12…O7#1,C16-H16B…O8#3 and C22-H22F…O15#4[58-61](Table 3), which is shown in Fig.5 involving the coordinated ethanol molecule andions in each molecule.There is also one intermolecular C-H…π(C11-H11A…Cg6)interaction.The molecule is interlinked through intermolecular C-H…π interactions into an infinite 1D chain(Fig.6).

Fig.6 View of intermolecular C-H…π interactions of complex 1

2.4.2 Supramolecular interaction of complex 2

Fig.7 (a)View of the intramolecular hydrogen-bonding interactions of complex 2;(b)View of intermolecular interactions of complex 2

In the crystal structure of complex 2,there are seven intra-and inter-molecularhydrogen bond interactions:O32-H32…O7,O32#5-H32…O11#5,C2-H2B…O12,C10-H10A…O8,C10-H10B…O12#7,C12-H12…O14#6 and C19-H19B…O13#6,which are show in Table 3[62-66].Due to the presence of the methanol molecule,hydrogen bonds constructed via the hydroxyl(Fig.7).The hydrogen bonds make the crystal structure of complex 2 more stable.

2.5 Fluorescence properties

The fluorescence properties of H2L and its complexes 1 and 2 were investigated in acetonitrile(10 μmol·L-1)with excitation at 318 nm at room temperature(Fig.8).The ligand exhibited an intense emission peak at 384 nm,which should be assigned to the intraligand π-π*transition.The emission spectra of complex 2 showed one main peak at 389 nm(λex=318 nm).Meanwhile,it can be seen that complexes 1 and 2 exhibit a red-shift with respect to the ligand H2L,which is tentatively assigned to a ligand-to-metal charge transfer (LMCT).In addition,compared with the emission spectrum of H2L,the enhanced fluorescence intensity of complex 2 was observed,which is attributed to the following reasons: (1)the more rigidity of the ligand coordination to Znギion that effectively reduces the loss of energy and increase the emission efficiency;(2)the full d10electronic configuration of Znギion; (3)an increased rigidity in structure of complex 2 and a restriction in the photoinduced electron transfer(PET)[67].In addition,the differences of the peak positions may be considered to be a result of the dissimilar coordination of the metal centers because the emission behavior is closely associated to the metal ions and ligand L2-units around them.Compared with the free ligand H2L,an extremely weak fluorescence intensity ofcomplex 1 was observed,indicating that fluorescent characteristic has been influenced by the introduction of the Cuギion.

Fig.8 Emission spectra of H2L and its complexes 1 and 2 in acetonitrile solutions(10 μmol·L-1)at room temperature

3 Conclusions

Two new heterobinuclear 3d-4f complexes were prepared by the one-pot reaction of a Salamo-type ligand H2L with lanthanideバ nitrate and zincギa(chǎn)cetate or copperギa(chǎn)cetate,respectively.The crystal structures of complexes 1 and 2 were confirmed by X-ray single crystal diffraction,and in complexes 1 and 2,Cuギ and Znギ ions are both penta-coordinated with a distorted square pyramidal geometry and the Ndバ and Ceバ ions are both deca-coordinated adopting a distorted bicapped twelve surface geometry.

Acknowledgements:This work was supported by the National Natural Science Foundation of China (Grants No.21361015,21761018)and the Program for Excellent Team of Scientific Research in Lanzhou Jiaotong University (Grant No.201706),which is gratefully acknowledged.

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