一个手性四核铜配合物的合成、结构和CD光谱

向 华李焕勇郑晓丹姜 隆＊,黎 彧

(1广东轻工职业技术学院传播工程系，广州 510300)

(2中山大学化学与化学工程学院，广州 510275)

(3广东轻工职业技术学院精细化工研发中心，广州 510300)

一个手性四核铜配合物的合成、结构和CD光谱

向 华＊,1李焕勇2郑晓丹2姜 隆＊,2黎 彧3

(1广东轻工职业技术学院传播工程系，广州 510300)

(2中山大学化学与化学工程学院，广州 510275)

(3广东轻工职业技术学院精细化工研发中心，广州 510300)

香草醛和L-2-氨基-3-苯基-1-丙醇缩合得到的手性希夫碱配体(L-H2vap)与Cu(ClO4)2·6H2O，Gd(NO3)3·6H2O和三乙胺在4-羟基苯甲酸的存在下反应得到L-[Cu4(Hvap)2(vap)2(MeOH)2](ClO4)2·2MeOH·H2O(1)。通过元素分析、红外、热重分析和固体CD光谱对1结构进行了表征，并通过X-射线单晶衍射确定其单晶结构，结果表明1属于单斜晶系，P21手性空间群，Z=2，包含船型{Cu4O4}结构。1的Cu4簇通过配体、溶剂分子和高氯酸根离子的氧原子间的氢键沿b轴形成超分子链。固体CD光谱证实了1的手性。

手性多核配合物；四核铜（Ⅱ）配合物；晶体结构；CD光谱

0 Introduction

During the pastdecade,chiralpolynuclear complexes have become rather charmful because of their useful properties,such as ferroelectric and nonlinear optical properties[1-4].Generally,the use of chiral ligands is the most effective way to prepare such complexes to ensure the chirality of the finalproducts[5-7].Schiff-based ligands are good candidates for they are easy to possess chirality by the condensation of aldehyde molecules with chiral amine molecules or chiral aldehyde molecules with amine molecules[8-11].We are interested in chiral polynuclear chemistry,especially 3d-4f polynuclear clusters.Very recently,we have found that chiral Schiff-based ligand L-H2vap is a good ligand to constrcut chiral polynuclears[12],but failed to introduce lanthanide ions into the final clusters.As a following work,we tried to introduce lanthanide ions by the addition of 4-hydroxybenzoid acid and the replacement of Cu(Ac)2·H2O by Cu(ClO4)2·6H2O through the similar procedure.Finally,a similar complex L-[Cu4(Hvap)2(vap)2(MeOH)2](ClO4)2·2MeOH·H2O (1)was obtained.It seems such copper（Ⅱ） tetranuclear is the stablest structure in the system.Herein,we reported the synthesis,EA,IR,TGA and solidstate CD spectra of complex 1.

1 Experimental

1.1 General procedures

All of the chemicals are commercially available and used without further purification.All the reactions were carried out under aerobic conditions.Elemental analyses were determined using Elementar Vario EL elemental analyzer.The IR spectra were recorded in the 4 000～400 cm-1region using KBr pellets and a BrukerEQUINOX55spectrometer.Thermalgravimetric analysis(TGA)data were collected on a Netzsch TG-209 instrument under nitrogen atmosphere in the temperature range of 20～800 ℃ with a heating rate of 10 ℃·min-1.The solid-state circular dichroism(CD)spectra were recorded with KCl pellets on the same spectropolarimeter.

1.2 Syntheses of L-[Cu4(Hvap)2(vap)2(MeOH)2](ClO4)2·2MeOH·H2O(1)

Caution! Perchlorate salts of metal complexes with organic ligands are potentially explosive.They should be handled with care and prepared only in small quantities.

The addition of Cu(ClO4)2·6H2O(371 mg,1.0 mmol)and Gd(NO3)3·6H2O(451 mg,1.0 mmol)to a stirred solution of o-vanillin(3-methoxy-4-hydroxybenzaldehyde)(152 mg,1.0 mmol),L-2-amino-3-phenyl-1-propanol(152 mg,1.0 mmol)and triethylamine(101 mg,1.0 mmol)in methanol (40 mL)produce dark green solution.After stirring at about 50 ℃ for 40 min,4-hydroxybenzoid acid (138 mg,1.0 mmol)and then triethylamine (303 mg,3.0 mmol)were added to the solution,following a continuous heating about 5 h.The resulting solution was allowed to cool down to room temperature,then filtered and the filtrate was evaporated slowly at room temperature.After two weeks,green rhombus crystals of 1 (81 mg,18.5%)isolated from the solution.Anal.Calcd.for Cu4C72H90N4O26Cl2(%,taking in H2O,1H2O,FW=1 752.59):C,49.34;H,5.18;N,3.20.Found(%):C,49.17;H,5.09;N,3.53.IR(KBr,cm-1):3 538,3 331,3 063,3 028,2 930,2 836,1 629,1 604,15 46,1 496,1 470,1 458,1 411,1 377,1 326,1 296,1 251,1 221,1 085,1 052,975,926,856,780,736,702,654,624,587,509,472,447.

1.3 Crystal structure determination

Single-crystal data for 1 were collected at 173 K on a Bruker Smart 1000 CCD diffractometer with Mo Kα radiation (λ=0.071 073 nm).The empirical absorption corrections were applied using the SADABS program[13].The structures were solved using direct method,which yielded the positions of all nonhydrogen atoms.These were refined first isotropically and then anisotropically.All the hydrogen atoms of the ligands were placed in calculated positions with fixed isotropic thermal parameters and included in structure factor calculations in the final stage of fullmatrix least-squares refinement.All calculations were performed using the SHELXTL-97 system of computer programs[14].The detailed crystallographic data are listed in Table 1 and the selected bond lengths and angles are included in Table 2.

CCDC:883888.

2 Results and discussion

2.1 Preparation chemistry

Thereaction ofo-vanillin and L-2-amino-3-phenyl-1-propanol with Cu(ClO4)2·6H2O(371 mg,1.0 mmol),Gd(NO3)3·6H2O and triethylamine in thepresence of4-hydroxybenzoid acid produced 1 reproducibly.We have tried the same procedures without Gd(NO3)3·6H2O and 4-hydroxybenzoid acid and failed to get products.The reason why this happened has been not clarified yet.It is speculated that both gadolinlium nitrate and 4-hydroxybenzoid acid have played structure-directing-agent roles in the formation of 1.

Table 1 Crystal data and structure refinements for complex 1

Table 2 Selected bond lengths(nm)and angles(°)for complex 1

2.2 Crystal structure of 1

Single crystal X-ray structural analyses reveal complex 1 crystallizes in monoclinic,chiral space group P21with Z=2.As shown in Fig.1,the molecular structure of complex 1 is based on a {Cu4}8+core,similar to that of the copper（Ⅱ）tetranuclear recently reported[12].Four copper（Ⅱ）atoms are held together by two alkoxide μ3-O2-atoms from two individual bideprotonated η1∶η1∶η3∶μ3-vap2-ligands (O4,O7)and two phenoxide μ2-O2-atoms from two individual monodeprotonated η2∶η3∶μ2-Hvap-ligands(O2,O11)to form a boat-shaped {Cu4O4}unit (Fig.1a).The coordination modes of the Schiff-base ligands are shown in Fig.2.Peripheral ligation is provided by two methanol molecules.Cu2 and Cu3 ions are sixcoordinated with one nitrogen atom and five oxygen atoms from Schiff-base ligands,adopting a distorted octahedral coordination sphere.The five-coordinated Cu1/Cu4 is surrounded by one oxygen atom from a methanol molecule and one nitrogen atom and three oxygen atoms from Schiff-base ligands,adopting a distorted square-pyramid geometry in which the oxygen atom from methanol molecule locates at the vertex of the distorted square-pyramid.There are intramolecular hydrogen bonding interactions between coordinated methanol molecule and vap2-anions(Fig.1b and Table 3).Charge balance is afforded by two perchlorate anions in the lattice.Unlike discrete Cu4clusters in the complex recently reported[12],such boatshaped Cu4clusters are further connected through intermolecularhydrogen bonding between oxygen atoms of the ligands, solvent molecules and perchlorate anions to form supramolecular chains along b-axis(Fig.3,Table 3).

As listed in Table 2,the Cu-N distances are in the normal range.The axial Cu-O distances(0.238 7(8)～0.247 3(8)nm)of Cu2/Cu3 ion are much longer than the equatorial Cu-O distances(0.188 3(8)～0.199 1(7)nm)due to the Jahn-Teller effect of an octahedral Cu（Ⅱ） ion.As far as Cu1/Cu4 ion is concerned,the Cu-OMeOHbond length(0.201 8(7)and 0.230 8(9)nm)is longer than the squared Cu-O bond lengths(0.192 7(7)～0.197 6(8)nm).Each Cu … Cu distance is different from other Cu…Cu distances in the range from 0.314 52(16)to 0.383 08(20)nm,indicative of the unsymmetry nature in the Cu4core structure.

2.3 Thermogravimetric analyses

The TGA curve of complex 1 (Fig.4)shows an initial weight loss of 8.69%from room temperature to 120℃,corresponding to the removal of four methanol(two coordinated ones and two lattice ones)and one lattice water molecules (calcd.8.42%),following a plateau until 210℃.Then complex 1 began to decompose upon further heating.

Table 3 Intramolecular hydrogen-bond parameters in complex 1

2.4 CD spectra

Considering that complex 1 is chiral,the solidstate circular dichroism(CD)spectra were recorded to probe the whole chiral nature of the bulk samples.As shown in Fig.5,the results of solid-state circular dichroism (CD)measurements show the chiral nature of complex 1 in crystalline state,revealing that the bulk crystals of complex 1 show a negative Cotton effect at 368 and 582 nm,respectively,indicative of the homochiral nature of complex 1.

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Synthesis,Structure and CD Spectra of a Chiral Tetranuclear Copper（Ⅱ）Complex

XIANG Hua＊,1LI Huan-Yong2ZHENG Xiao-Dan2JIANG Long＊,2LI Yu3
(1Department of Media and Communication,Guangdong Industry Technical College,Guangzhou 510300,China)
(2School of Chemistry and Chemical Engineering,Sun Yat-Sen University,Guangzhou 510275,China)
(3Research Center of Fine Chemical Engineering,Guangdong Industry Technical College,Guangzhou 510300,China)

Chiral Schiff-based ligand L-H2vap,derived from the condensation of o-vanillin and L-2-amino-3-phenyl-1-propanol,reacts with Cu(ClO4)2·6H2O,Gd(NO3)3·6H2O and triethylamine in the presence of 4-hydroxybenzoid acid to give L-[Cu4(Hvap)2(vap)2(MeOH)2](ClO4)2·2MeOH·H2O(1).The structure of 1 was characterized by EA,IR,TGA,solid-state CD spectra and the single-crystal X-ray diffraction analyses.The X-ray diffraction analyses reveal that the complex crystallize in the monoclinic system,chiral space group P21with Z=2,containing a boat-shaped {Cu4O4}structure.Cu4clusters in 1 are connected through intermolecular hydrogen bonding to form supramolecular chains along b axis.The solid-state CD spectra comfirm the chiral nature of 1.CCDC:883888.

chiral polynuclear complex;copper（Ⅱ）complex;crystal structure;CD spectra

O614.121

A

1001-4861(2012)08-1763-06

2011-12-12。收修改稿日期：2012-05-10。

广东省高等学校高层次人才(2011QY01)和国家自然科学基金(No.21001119)资助项目。

＊通讯联系人。E-mail：joyce_xiang1211@hotmail.com(向华)，jianlonchem@yahoo.com.cn(姜隆)