配位聚合物[Ni(cpna)(bpy)(H2O)]n的合成、晶體結構及磁性質

呂東煜 高竹青 顧金忠＊, 竇 偉

(1甘肅省有色金屬化學與資源利用重點實驗室，蘭州大學化學化工學院，蘭州 730000)

(2太原科技大學化學與生物工程學院，太原 030021)

配位聚合物[Ni(cpna)(bpy)(H2O)]n的合成、晶體結構及磁性質

呂東煜1高竹青2顧金忠＊,1竇 偉1

(1甘肅省有色金屬化學與資源利用重點實驗室，蘭州大學化學化工學院，蘭州 730000)

(2太原科技大學化學與生物工程學院，太原 030021)

通過水熱方法，采用 H2cpna(H2cpna=5-(2′-carboxylphenyl))和 bpy(bpy=2，2′-bipyridine)與 Ni(OAc)2·4H2O 反應，合成了一個具有二維結構的配位聚合物[Ni(cpna)(bpy)(H2O)]n(1)，并對其結構和磁性質進行了研究。結構分析結果表明該聚合物的晶體屬于單斜晶系，P21/c空間群。3個鎳(Ⅱ)離子、3個cpna配體、3個2，2′-bpy配體和3個配位水分子形成了一個[Ni3(cpna)3(bpy)3(H2O)3]環(huán)，這些環(huán)通過鎳(Ⅱ)離子與cpna配體的配位作用形成了一個二維層狀結構。層與層之間又通過π-π堆積作用形成了一個三維的配位框架。研究表明，該聚合物中相鄰鎳(Ⅱ)離子之間存在很弱的反鐵磁相互作用。

配位聚合物；鎳(Ⅱ)配合物；磁性

Recently,the design and synthesis of transition metal coordination polymers with interesting magnetic properties have received enormous attention[1-6].The most useful strategy to construct such supramolecular structures is to employ appropriate bridging ligands.Many multi-carboxylate or heterocyclic carboxylic acids have been used for this purpose[7-12].In order to extend our investigations in this field,we chose 5-(2′-carboxylphenyl)nicotic acid (H2cpna)as a functional ligand,based on the following considerations.First,H2cpnashould be an excellentbridging ligand forthe construction of coordination polymers,since it has diversified coordination modes and flexible conformation,in which pyridyl and phenyl rings can rotate around the C-C bond.Second,to the best of our knowledge,no complexes bearing cpna ligands have been reported until now.Herein,we report the synthesis,crystal structure,magnetic properties of Ni(Ⅱ)compound with cpna ligands.

1 Experimental

1.1 Reagents and physical measurements

All chemicals and solvents were of A.R.grade and used without further purification.Carbon,hydrogen and nitrogen were determined using an Elementar Vario EL elemental analyzer.IR spectra were recorded using KBr pellets and a Bruker EQUINOX 55 spectrometer.Thermogravimetric analysis(TG)data were collected on a Netzsch TG-209 instrument with a heating rate of 10℃·min-1.Magnetic susceptibility data were collected in the 2～300 K temperature range with a Quantum Design SQUID Magnetometer MPMS XL-7 with a field of 0.1 T.A correction was made for the diamagnetic contribution prior to data analysis.

1.2 Synthesis of[Ni(cpna)(bpy)(H2O)]n(1)

A mixture of Ni(OAc)2·4H2O(0.025 g,0.1 mmol),H2cpna (0.024 g,0.1 mmol),2,2′-bpy (0.016 g,0.1 mmol),NaOH (0.004 g,0.1 mmol)and H2O-EtOH(10 mL,5:1,V:V)was stirred at room temperature for 15 min,and then sealed in a 25 mL Teflon-lined stainless steel vessel,and heated at 160℃for 3 days,followed by cooling to room temperature at a rate of 10 ℃·h-1.Green block-shaped crystalsof1 were isolated manually,and washed with distilled water.Yield:78%(based on Ni).Anal.Calcd for C23H17N3NiO5(%):C 58.27,H 3.61,N 8.86;found:C 58.71,H 3.26,N 8.43.IR (KBr,cm-1):3063w,1606s,1562s,1440m,1383s,1157w,929m,820m,771s,738m,697m.The compound is insoluble in water and common organic solvents,such as methanol,ethanol,acetone,and DMF.

1.3 Structure determinations

Single-crystal data of 1 were collected at 296(2)K on a Bruker Smart Apex 1000 CCD diffractometer with Mo Kα radiation(λ=0.071073 nm).A summary of the crystallography data and structure refinement is given in Table 1,and selected bond lengths and angles of the complex 1 are listed in Table 2.The structure was solved using directmethods,which yielded the positions of all non-hydrogen atoms.These were refined first isotropically and then anisotropically.All the hydrogen atoms (except for those bound to water molecules)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.The hydrogen atoms of the water molecules were located by difference maps and constrained to ride on their parent O atoms.All calculations were performed using the SHELXTL-97 system[13].

CCDC:816351.

Table 1 Crystal data for complex 1

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

2 Results and discussion

2.1 Description of the structure

As shown in Fig.1,the asymmetrical unit of the cell of compound 1 contains one crystallographically unique Ni(Ⅱ) atom,one cpna ligand,one 2,2′-bpy ligand and one water ligand.The Ni(Ⅱ) center is sixcoordinated by two N atoms of the 2,2′-bpy ligand,one N and two O atoms of cpna ligands,and one O atom from the coordinated water molecule,resulting in a distorted octahedral coordination geometry.The distances of Ni-O and Ni-N bonds span the range of 0.203 0(3)～0.211 1(3)and 0.209 1(3)～0.209 5(3)nm,which are in good with the bond lengths observed in other Ni(Ⅱ)complexes[4,14].

Three Ni(Ⅱ) atoms,three cpna ligands,three 2,2′-bpy ligands,and three water ligands form a[Ni3(cpna)3(bpy)3(H2O)3]ring(Fig.2).The rings are connected by the coordination interactions of cpna ligands and Ni(Ⅱ)ions to generate a 2D sheet,which are further extended into a 3D metal-organic supramolecular framework by π-π stacking interactions between 2,2′-bpy ligands with the centroid-centroid distance of 0.407 2(3)nm(Fig.3).

The cpna ligand adopts a μ3-bridging mode with two carboxylate groups in a μ1-η1∶η0monodentate mode(Fig.2).In the cpna ligand,the phenyl and pyridine rings are not coplanar,with the dihedral angle ofca.73.62°.

2.2 TG analysis

To study the stability of compound 1,thermal gravimertric analyses(TG)were performed.As shown in Fig.4,complex 1 undergoes a mass loss of 4.10%between 180 and 216℃,which corresponding to the loss of one coordinated water molecule(Calcd 3.80%).Above 355℃ the framework is destroyed gradually.

2.2 Magnetic properties

The magnetic susceptibility per Ni unit measured on a polycrystalline sample of 1 under an applied field of 1000 Oe is shown in Fig.5.The χMTvalue at 300 K is 1.29 cm3·mol-1·K,which is higher than the spin only value of 1.00 cm3·mol-1·K for one magnetically isolated Ni(Ⅱ) center(SNi=1,g=2.0).Upon cooling,χMTvalue drops down very slowly from 1.29 cm3·mol-1·K at 300 K to 1.21 at 24 K and then decreased steeply to 0.62 cm3·mol-1·K at 2 K.The plot of χM-1vsTfor compound 1 2～300 K obeys the Curie-Weiss law with a Weiss constant θ of-2.42 K and a Curie constantCof 1.29 cm3·mol-1·K,suggesting a weak antiferromagnetic interaction between the Ni(Ⅱ) ions.

An empirical(Wang′s)formula has been reported in the literature to analyze 1D systems withS=1,using numerical procedures[15-16];

Using this method,the best-fit parameters for 1 wereg=2.10,J=-0.87 cm-1andR=6.3×10-5,whereR=∑[(χMT)obs-(χMT)calcd]2/∑[(χMT)obs]2.TheJvalue of-0.87 cm-1for complex 1 indicates that the coupling between the Ni(Ⅱ)centers is weakly antiferromagnetic,which can be attributed to the large Ni…Ni separations(0.7583(6)and 0.8387(6)nm)in complex 1.

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Synthesis,Crystal Structure and Magnetic Properties of a Coordination Polymer[Ni(cpna)(bpy)(H2O)]n

(1Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province,College of Chemistry and Chemical Engineering,Lanzhou University,Lanzhou 730000,China)
(2School of Chemistry and Biology Engineering,Taiyuan University of Science and Technology,Taiyuan 030021,China)

A coordination polymer,namely[Ni(cpna)(bpy)(H2O)]n(1)has been constructed hydrothermally using H2cpna(H2cpna=5-(2′-carboxylphenyl)nicotic acid),bpy(bpy=2,2′-bipyridine)and Ni(OAc)2·4H2O.The complex crystallizes in the monoclinic system,space group P21/c with a=1.666(2)nm,b=0.962 2(12)nm,c=1.2702(16)nm,β=105.978(12)°,V=1.957(4)nm3,Dc=1.608g·cm-3,Z=4,R=0.038 7 and wR=0.089 3(I＞2σ(I)).Three Ni(Ⅱ)atoms,three cpnaligands,three 2,2′-bpy ligands,and three water ligands form a[Ni3(cpna)3(bpy)3(H2O)3]ring.The rings are connected by the coordination interactions of cpna ligands and Ni(Ⅱ)ions to generate a 2D sheet,which are further extended into a 3D metal-organic supramolecular framework by π-π stacking interactions.Magnetic studies for complex 1 show a weak antiferromagnetic coupling between the nearest Ni(Ⅱ) centers,with g=2.10 and J=-0.87 cm-1.CCDC:816351.

coordination polymer;nickel(Ⅱ)complex;magnetic properties

O614.81+3

A

1001-4861(2011)11-2318-05

2011-03-21。收修改稿日期：2011-07-05。

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