基于自由基配体的Dy配合物的设计、合成、结构及磁性

胡鹏 肖凤屏 植中强 杜凤翔 邓肖娟 黄国洪 张淼苏芬 王莉娜

(1肇庆学院化学化工学院，肇庆526061)(2北京联合大学北京市生物质废弃物资源化利用重点实验室，北京联合大学生物工程学院，北京100101)

胡鹏＊,1肖凤屏1植中强1杜凤翔＊,2邓肖娟1黄国洪1张淼1苏芬1王莉娜1

(1肇庆学院化学化工学院，肇庆526061)
(2北京联合大学北京市生物质废弃物资源化利用重点实验室，北京联合大学生物工程学院，北京100101)

以氮氧自由基为配体，合成了2例未见文献报道的氮氧自由基-稀土配合物[Dy(hfac)3(NIT-C3H5)(H2O)]与[Dy(hfac)3(NITC3H5)]n(hfac=六氟乙酰丙酮，NIT-C3H5=2-环丙烷基-4，4，5，5-四甲基-2-咪唑啉-3-氧化-1-氧基自由基)。单晶结构分析表明配合物1为单核结构，单斜晶系P21/c空间群；配合物2为一维结构，单斜晶系P21/c空间群。交流磁化率测试结果表明配合物2虚部表现出频率依赖，这表明配合物2是单链磁体。

氮氧自由基；镝；晶体结构；磁性

0 Introduction

Combination of different spin carriers within the same molecular entity is a widely employed strategy becausethe orthogonality of the magnetic orbitals of two different spin carriers,which lead to a ferromagnetic interaction,can be reached much more easily than the accidental orthogonality within the homospin systems;andeven if the magnetic coupling is antiferromagnetic,the resulting spin can be big enough when a large spin(5/2,7/2)interacts with a small one,such as a spin 1/2[4].Numbers SCMs and SMMswere prepared by this strategy[17-18].Among them metal-radical strategy that combining paramagnetic organic molecules with metal ions give rise to complexes with different structures and magnetic properties have been received more and more attention since the discovery of the first radical-4f SMM by Gatteschis group[19].Stable radical ligand can generate typically stronger intramolecular magnetic exchange coupling.The strong exchange coupling between lanthanides and radicals generally leads to superior SMMs.In 2011,a binuclear Tbcomplex bridged by a N2·3-radical has been reported with a record blocking temperature of 13.9 K[20-21].For the past few years,various organic radicals such as nitronyl nitroxide,verdazyl and semiquinone radicals have been reported[22-28].Nitronyl nitroxide(NIT)family of radicals are the most important type of radical ligand due to their relatively stable and easy to obtain derivativeswith substituents containing donor atoms.

In an effort to further study the magnetic properties of metal-radical complexes,we decided to choose the nitronyl nitroxide radical NIT-C3H5as ligand(NIT-C3H5=2-cyclopropyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide)(Scheme 1)to construct radical-4f complex.Finally we have successfully prepared one zero-dimensionalstructure lanthanide-nitronyl nitroxide complex[Dy(hfac)3(NIT-C3H5)(H2O)]and one one-dimensional structure lanthanide-nitronyl nitroxide complex[Dy(hfac)3(NIT-C3H5)]n(hfac=hexavfluoroacetylacetonate,NIT-C3H5=2-cyclopropyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide).Magnetic studiesshow that complex 2 shows the presence of frequencydependent signals at low temperature suggesting that it behaves as SCMs.

Scheme 1 NIT-C3H5

1 Experimental

1.1 M aterials and measurements

All the starting chemicals were obtained from Aldrich and used without further purification.The radical ligand NIT-C3H5was prepared according to literaturemethod[29].Elemental analyses(C,H,N)were determined by Perkin-Elmer 240 elemental analyzer. The infrared spectra were recorded from KBr pellets in the range of 4 000～400 cm-1with a Bruker Tensor 27 IR spectrometer.Themagneticmeasurementswere carried out with MPMSXL-7 SQUID magnetometer. Diamagnetic corrections were made with Pascal′s constants for all the constituent atoms.

1.2 Synthesis of[Dy(hfac)3(NIT-C3H5)(H2O)](1)

Dy(hfac)3·2H2O(0.081 9 g 0.1 mmol)was added to 25 mL n-heptane and heated to reflux for 0.5 h. The solution was cooled to 50℃,then a solution of NIT-C3H5(0.019 7 g 0.1 mmol)in CH2Cl2(3 mL)was added and stirred for 1 min.The resulting mixture was cooled to room temperature filtrated then keep the solution in the fridge.The temperature was keptbetween 2 to 5℃for several days to give crystals suitable for X-ray analysis with a 52%yield.Anal. Calcd.for C25H22F18DyN2O9(%):C 30.05,H 2.22,N 2.80;Found(%):C 30.07,H 2.16,N 2.89.IR(KBr, cm-1):1 652(s),1 499(s),1 364(m),1 262(s),1 203(s), 1 149(s),803(m),663(m).

1.3 Synthesis of[Dy(hfac)3(NIT-C3H5)]n(2)

Dy(hfac)3·2H2O(0.081 9 g 0.1 mmol)was added to 25mL n-heptane and heated heated to reflux for 3 h. The solution was subsequently cooled to 70℃,then a solution of NIT-C3H5(0.019 7 g 0.1mmol)in CH2Cl2(3 mL)was added and stirred for 5 min.The solution was then cooled to room temperature,filtrated and the filtrate was evaporated at room temperature for several days to give crystals suitable for X-ray analysis,with a 47%yield.Anal.Calcd.for C25H20F18DyN2O8(%):C 30.06,H 2.05,N 2.85;Found(%):C 30.09,H 2.03, N 2.81.IR(KBr,cm-1):1 653(s),1 502(s),1 258(s), 1 201(s),1 145(s),802(m),661(m).

应用在线设计软件（http://www.oligoengine.com）设计获得针对HSP27基因的siRNA（HSP27-siRNA）。HSP27-siRNA正 义 链 序 列为 5’-AAGACCAAGGAUGGCGUGGUGdT-dT-3’，反义链序列为 5’-CACCACGCCAUCCUUGGUCUUdTdT-3’；同时设计了一条与HSP27基因无同源性的阴性对照（negative control，NC）-siRNA，NC-siRNA正义链序列为 5’-TTCTCCGAACGTGTCACGTdTdT-3’，反义链序列为5’-ACGUGACACGUUCGGAGAAdTdT-3’。

1.4 X-ray crystallographic study

X-ray single-crystal diffraction data for complexes 1 and 2 were collected using a Rigaku Saturn CCD diffractometer at 293 K and 113 K,respectively, equipped with graphite-monochromated Mo Kαradiation(λ=0.071 073 nm).Crystalsize of complexes 1 and 2 are 0.20 mm×0.20 mm×0.18 mm and 0.24 mm×0.2 mm×0.16mm,respectively.The structureswere solved by directmethods by using the program SHELXS-97[30]and refined by full-matrix least-squaresmethods on F2with the use of the SHELXL-97[31]program package. Anisotropic thermal parameters were assigned to all non-hydrogen atoms.The hydrogen atoms were set in calculated positions and refined as riding atomswith a common fixed isotropic thermal parameter.Disordered C and F atoms were observed for both complexes.The restraints of SPLIT,DELU and ISOR were applied for the three complexes to keep the disordered molecules reasonable.Pertinent crystallographic data and structure refinement parameters for complexes 1 and 2 were listed in Table 1 and 2.

CCDC:1533515,1;1533514,2.

Table 1 Crystal data and structure refinement for 1 and 2

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

2 Results and discussio n

2.1 Crystal structure of comp lex 1

As shown in Fig.1,complex 1 crystallizes in the monoclinic space group P21/c.The central Dyions areeight-coordinated in square antiprism(D4d)geometry (Table S1).Six oxygen atoms from three hfacmolecules with the Dy-O bond lengths in the range of 0.226 0(6)～0.245 4(5)nm.The other two oxygen atoms are from one radical molecule and one water molecule respectively.The bond length of Dy(1)-O(8)radis0.230 7(3) nm and Dy(1)-O(7)wateris 0.228 6(5)nm.The nitronyl nitroxide radical act as monodentate ligand to Dyion through one N-O group,the N(1)-O(8)bond lengths are 0.129 8(9)nm while the uncoordinated N(2)-O(9) bond lengthsare0.129 9(12)nm,which are comparable to those of reported radical-Lncomplexes[32-35].

Fig.1 Molecular structure of complex 1

2.2 Crystal structure of com plex 2

Fig.2 Molecular structure of complex 2

As shown in Fig.2,complex 2 crystallizes in the monoclinic space group P21/c.The central Dyions are eight-coordinated in trigonal dodecahedron(D2d)geometry(Table S2).Six oxygen atoms from three hfac molecules with the Dy-O bond lengths in the range of 0.231 4(2)～0.235 5(2)nm.The other two oxygen atoms are from two radical molecules with the Dy(1)-O(8) and Dy(1)-O(7)bond length of 0.234 1(3)nm and 0.236 1(3)nm,respectively.The nitronyl nitroxide radicals act as bridging ligands to Dyion through N-O group,the N(1)-O(8)and N(2)-O(7)bond lengths are0.128 3(4)nm 0.128 6(4)nm,which are comparable to those of reported radical-Dycomplexes.Selected bond lengths and angles of complex 1 and 2 are listed in Table 2.

2.3 M agnetic properties of comp lex 1

The temperature dependence of the magnetic susceptibilities 1 and 2 were measured from 300 to 2.0 K in an applied field of 1 kOe and the magnetic behaviors of complex 1 are shown in Fig.3.At 300 K theχMT value of 1 is 12.32 cm3·K·mol-1.This value is close to the expected value 14.45 cm3·K·mol-1(uncoupled system of one Dyion(f9electron configuration,χMT=14.17 cm3·K·mol-1)plus one organic radical(S=1/2,χMT=0.375 cm3·K·mol-1)).Upon cooling, theχMT value gradually decreases and reaches to the value of 11.13 cm3·K·mol-1at 18 K.Below 18 K,the χMT rapidly increases to 11.82 cm3·K·mol-1at 6 K then decreases on further cooling and reaches to the value of 11.46 cm3·K·mol-1at 2.0 K.The decrease of χMT upon lowering of the temperature in the hightemperature range is most probably governed by depopulation of the DyStark sublevels.The increase ofχMT at low temperature suggests the presence of ferromagnetic interaction between the Dyions and the coordinated NO group of the organic radical.

The field dependences of magnetizations for complex 1 have been determined at 2 K in the range of 0～70 kOe(Fig.3).Upon increasing in the applied field M increases up to 7.02Nβat 70 kOe,which does not reach the saturation values,indicating the presence ofamagnetic anisotropy and/or low-lying excited states in the system,which corresponds to the reported results[35].The M value ofa single Dyin high applied field is usually around 5.23Nβ[36].The experimental results revealing ferromagnetic interactions between Dyand radical.

Fig.3 Temperature dependence ofχMT for complex 1(left)and field dependence ofmagnetization of 1 at2.0 K(right)

Alternating current(ac)susceptibility measurements for complex 1 were carried out in low temperature regime under a zero dc field to investigate the dynamics of the magnetization.As shown in Fig.4 there are no obvious frequency dependent out-ofphase signals.We do not think that complex 1 express SMM behavior at low temperature.Thismay due to the small energy barrier which could not prevent the inversion of spin.

2.4 M agnetic properties of com plex 2

For complex 2,at 300 K,theχMT value is 14.58 cm3·K·mol-1.This value is close to the expected value of 14.45 cm3·K·mol-1(uncoupled system of one Dyion(f9electron configuration,χMT=14.17 cm3· K·mol-1)plus one organic radical(S=1/2,χMT=0.375 cm3·K·mol-1)).Upon cooling,theχMT value remains almost unchanged down to 50 K.Below this temperature,theχMT value decreasesmarkedly and reaches avalue of 1.43 cm3·K·mol-1at 2.0 K.For the present 1D magnetic system,both nearest-neighbor(NN) metal-radical magnetic coupling and next-nearestneighbor(NNN)metal-metalor radical-radicalmagnetic interactions coexist.These NN exchange interactions are always ferromagnetic for heavy lanthanides,while the NNN interactions are always antiferromagnetic[18]. The magnetic behavior of complex 2 can be ascribed to the combination of possible magnetic interactions and the depopulation of the Dy ions Stark levels.A strictly theoretical treatment ofmagnetic properties for this system is still a difficult task due to the large anisotropy of Dyion.

Fig.4 Temperature dependence of the in-phase and outof-phase components of ac susceptibility for 1 in zero dc field with an oscillation of 3.5 Oe

The field dependences of magnetizations for complex 2 is typical of ametamagnetic system with a sigmoidal curve.As show in Fig.5,the magnetization curve reveals two-step field induced transition.The first step is probably corresponds to the weak antiferromagnetic next-nearest-neighbor(NNN)interactions between chains.The spin flip transition at around 6 kOe,then as themagnetic field increases,M increases steadily to reach 8.41Nβat 70 kOe.This step is probably nearest-neighbor(NN)ferromagnetic interactions between the Dyand the radical.

Alternating current(ac)susceptibility measurements for complex 2 were carried out in low temperature regime under a zero dc field to investigate the dynamics of the magnetization.As shown in Fig.6, complex 2 exhibits frequency dependent out-of-phase signals indicating that it behaves as SCM.

Fig.5 Temperature dependence ofχMT for complex 2(left)and field dependence ofmagnetization of 2 at 2.0 K(right)

Fig.6 Temperature dependence of the in-phase(left)and out-of-phase(right)components of ac susceptibility for 2 in zero dc field with an oscillation of 3.5 Oe

3 Conclusions

Supporting information isavailable athttp://www.wjhxxb.cn

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HU Peng＊,1XIAO Feng-Ping1ZHIZhong-Qiang1DU Feng-Xiang＊,2
DENG Xiao-Juan1HUANG Guo-Hong1ZHANGMiao1SU Feng1WANG Li-Na1
(1Chemical Engineering College,Zhaoqing University,Zhaoqing,Guangdong 526061,China)
(2Key Laboratory of BiomassWaste Resource Utilization,Biochemical Engineering College, Beijing Union University,Beijing 100101,China)

Two Dy-nitronylnitroxide radical complexes[Dy(hfac)3(NIT-C3H5)(H2O)]and[Dy(hfac)3(NIT-C3H5)]n(NIT-C3H5=2-cyclopropyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide,hfac=hexafluoroacetylacetonate),have been successfully prepared with different synthetic condition.Single crystal X-ray crystallographic analyses reveal that complex 1 is mononuclear complex which crystallize in the P21/c space group while complex 2 is onedimensional complex which crystallize in the P21/c space group as well.Magnetic studies reveal that complex 2 exhibits frequency-dependence of ac magnetic susceptibilities,indicating that it behaves as single-chain magnet. CCDC:1533515,1;1533514,2.

nitronyl nitroxide radical;dysprosium;crystal structure;magnetic properties

O614.342

A

1001-4861(2017)07-1273-07

10.11862/CJIC.2017.149

2017-02-24。收修改稿日期：2017-05-17。

北京市朝阳区协同创新项目(No.XC1608)、北京联合大学科研启动项目和广东省大创项目(No.201610580046))资助。＊

。E-mail：hp8286799@zqu.edu.cn;1656054217@qq.com