周馨慧

(南京郵電大學信息材料與納米技術(shù)研究院，南京 210046)

一個雙核鎳配合物[Ni2(Htda)2(H2O)6]·4H2O的合成、晶體結(jié)構(gòu)和性質(zhì)

周馨慧

(南京郵電大學信息材料與納米技術(shù)研究院，南京 210046)

雙核金屬配合物對于生物化學和磁化學都是非常重要的。在本文中，1，2，3-三氮唑-4，5-二羧酸(H3tda)配體和硝酸鎳在常溫常壓下反應(yīng)得到了1個三氮唑橋聯(lián)的雙核鎳配合物[Ni2(Htda)2(H2O)6]·4H2O(1)，并通過元素分析、紅外光譜、X-射線單晶衍射、熱重分析以及超導(dǎo)量子干涉儀(SQUID)對其晶體結(jié)構(gòu)和磁、熱性質(zhì)進行了表征。晶體數(shù)據(jù)表明該配合物屬三斜晶系，空間群為P1。在配合物1中，2個1，2，3-三氮唑-4，5-二羧酸配體利用2個相鄰的氮原子橋聯(lián)2個金屬鎳離子形成一個雙橋的雙核鎳配合物。這些雙核鎳單元又通過體系中存在的大量的氫鍵相互作用形成了三維超分子骨架。磁性分析顯示雙核鎳單元內(nèi)鎳鎳之間存在反鐵磁相互作用。

雙核鎳配合物；1，2，3-三氮唑-4，5-二羧酸；晶體結(jié)構(gòu)；氫鍵；磁性質(zhì)

Since a lot of metalloenzymes,such as leucine aminopeptidase,urease,methionineaminopeptidase,arginase,P1 nuclease,DNA polymerase I,phospholi-pase C,and alkaline phosphatase,contain a dinuclear metal active site featuring Zn,Ni,Co,Co,Cuand Mn,etc.bridged by carboxylate or hydroxide ion,artificial models for these dinuclear metalloenzymes are of particular interest because of their ability to increase the understanding of the catalytic mechanism of the enzymes and the possible applications in biotechnology[1-7].Consequently,the dinuclear metal complexes with two metal ions bound by the bridging ligands have attracted a great deal of attentions[8].Similarly,these dinuclear metal compounds are also useful for development of magnetic models and investigation of the magnetic properties of multimetal compounds.

1,2,3-triazole-4,5-dicarboxylic acid (H3tda)is a multifunctionalligand with abundantcoordination modes and multiple coordination sites involving three triazole nitrogen atoms and four carboxylate oxygen atoms and can react with various metals to produce intriguing poly-dimensional structures with complicated topologies and/or useful properties[9-11].Furthermore,it has three abstractable hydrogens,which is beneficial to meet the charge-balance requirement of the system.In this paper,we used H3tda as ligands reacting with Ni(NO3)2·6H2O and obtained a triazolato-bridged dinuclear Nicomplex[Ni2(Htda)2(H2O)6]·4H2O(1),and its synthesis,crystal structure,magnetic and thermal properties are reported herein.

1 Experimental

1.1 General

All chemicals are reagent grade and used as received.H3tda was synthesized according to the literature methods[12].Elemental analyses for C,H and N were performed on a Perkin-Elmer 240C analyzer.Infrared spectra were recorded on a Vector22 Bruker Spectrophotometer with KBr pellets in the 400～4 000 cm-1regions.Magnetic susceptibility measurements of polycrystalline samples were measured overthe temperature range 1.8～300 K with a Quantum Design MPMS-XL7 SQUID magnetometer.Thermogravimetric analyses were collected on a Perkin-Elmer Pyris 1 TGA analyzer from room temperature to 750℃with a heating rate of 20℃·min-1under nitrogen.

1.2 Synthesis of[Ni2(Htda)2(H2O)6]·4H2O(1)

H3tda(0.1 mmol,15.7 mg)dissolved in 10 mL of deionized water was slowly droped into Ni(NO3)2·6H2O(0.1 mmol,29.1 mg)dissolved in 5 mL of deionized water,with continuous stirring at room temperature for 1 h.The resulting green solutions were filtered and left to stand.Green block crystals of 1 suitable for X-ray diffraction were obtained by slow evaporation of the solvents for about 10 days.Yield:62%.Anal.Calcd for C8H22N6Ni2O18:C,15.81;H,3.65;N,13.83.Found:C,15.94;H,3.58;N,13.74%.IR (KBr)/cm-1:3 376 vs,1720vs,1554s,1376s,1228 m,781 m,622 w.

1.3 Structure determination

A single crystal of 1 with dimensions of 0.12mm ×0.15mm × 0.17mm was mounted on a Bruker Smart Apex CCD diffractometer equipped with a graphitemonochromatic Mo Kα radiation(λ =0.071 073 nm)radiation using the φ-ω scan mode in the range 2.31°≤θ≤24.99°at 291(2)K.A total of 2502 reflections were collected and 1742 were independent with Rint=0.043 3,of which 1576 were observed with I＞2σ(I).Raw frame data were integrated with the SAINT program[13].The structure was solved by direct methods and refined by full-matrix least-squares on F2using SHELX-97[14].An empirical absorption correction was applied with the program SADABS[15].All non-hydrogen atoms were refined anisotropically.Hydrogen atom H(3)was located in the difference Fourier maps and all other hydrogen atoms were set in calculated positions and refined by a riding mode,with a common thermal parameter.Crystallographic details have been summarized in Table 1.Selected bond lengths and angles and hydrogen-bonding geometry parameters for 1 are listed in Tables 2 and 3.

CCDC:747631.

Table 1 Crystallographic data for complex 1

Continued Table 1

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

Table 3 Hydrogen-bonding geometry parameters for complex 1

2 Results and discussion

Strong absorption peak at 1 720 cm-1for-COOH are observed,indicating that the carboxyl groups of H3tda ligands are not all deprotonated[16].According to the difference Fourier maps,charge balance and the C-O bond lengths,we think that the O(3)atom is protonated.

2.1 Structure description

The X-ray crystallographic analysis reveals that 1 is a dinuclear Nicomplex.An ORTEP view of complex 1 is shown in Fig.1.The asymmetric unit of 1 contains one nickel ion(Ni(1)),one Htda2-ligand,three coordinated water molecules(O(5),O(6)and O(7))and two lattice aqua molecules(O(8)and O(9)).The Htda2-ligand acts in μ3-η2N,O,η1N′fashion,chelating a Ni(1)center through a carboxylate oxygen atom(O(1))and a triazole nitrogen atom(N(1)),and bridging another one crystallographically equivalent Ni(1)center through the N(2)atom neighboring to the N(1)atom,respectively.Each Ni2+ion is six-coordinated by a carboxylate oxygen atom and a triazole nitrogen atom from an Htda2-ligand,a triazole nitrogen atom from another one Htda2-ligand and three water molecules.The coordination geometry around Ni2+ion is a slightly distorted octahedron.The two Ni2+ions coordinated to one Htda2-ligand are simultaneously bound to another one crystallographically equivalent Htda2-ligand to form a dinuclear Niunit[Ni2(Htda)2].The[Ni2(Htda)2]unit is almost planar with the largest deviation of 0.00548 nm for O(4)atom from the mean plane defined by the triazole ring.The Ni(1)…Ni(1)idistance is 0.4050(1)nm.The shortest Ni…Ni distance between the dinuclear Niunits is 0.624 1(1)nm.The Ni-N bond lengths range from 0.203 7(3)to 0.204 9(3)nm and the Ni-O bond lengths range from 0.205 2(3)to 0.210 7(3)nm,which are all similar to those values found in other Nicomplexes[17-23].with the dinuclear Niunits.Each lattice aqua molecule is connected with three dinuclear Niunits through the O(6)-H(6A)…O(8)iii,O(7)-H(7B)…O(8)iv,O(8)-H(8A)…O(5)vand O(8)-H(8B)…O(7)hydrogenbonds for O(8),the O(5)-H(5B)…O(9)i,O(6)-H(6B)…O(9)iii,O(9)-H(9B)… O(4)viand O(9)-H(9B)… O(3)vihydrogen-bonds for O(9),respectively,which ulteriorly stabilize the 3D supramolecular structure of 1.

Fig.2 3D Supramolecular network formed by hydrogenbonding interactions in 1

Fig.1 View of the crystal structure of complex 1

There exist lots of hydrogen-bond interactions in crystal structure of complex 1 (Fig.2,Table 3).The intermolecular hydrogen-bond interactions O(7)-H(7A)…O(4)iv,O(6)-H(6B)…O(6)iiiand O(5)-H(5A)…O(2)iimake the dinuclear Niunits extend along three different directions,i.e. [110],the a and c axes,respectively,leadingto athree-dimensional(3D)supramolecular architecture.Furthermore,the lattice aqua molecules play dual roles as both donor and acceptor to construct hydrogen-bonding interactions

2.2 Magnetic property

The temperature-dependent magnetic susceptibility data of complex 1 have been measured for polycrystalline samples in the temperature range of 1.8～300 K under a 2 000 Oe applied magnetic field,as shown in Fig.3.

Fig.3 Temperature dependences of the χM(□)and χMT(▽)curves for complex 1

At 300 K,the χMT value of 1 is 2.36 cm3·K·mol-1,which is higher than the expected value of 2 cm3·K·mol-1for two isolated nickelS=1 species with a g factor of 2.This difference might be caused by the spinorbit coupling characteristic for nickelcomplexes with an3A2gground state resulting in an increasing g factor[24-25].While the temperature decreases,the χMT values remain roughly constant down to 60 K and then it decreases rapidly and reaches minimum of 0.29 cm3·K·mol-1at 1.8 K,indicating dominant antiferromagnetic interactions in the complex.Since the shortest Ni…Ni distance between the dinuclear Niunits is 0.6241(1)nm and is long for any significant magnetic interactions,the magnetic Ni…Niexchange interaction should primarily exist within the dinuclear Niunit coupled through the triazole nitrogen atoms.The experimental data for 1 were modeled in the range from 300 K to 1.8 K using Equation(1)deduced from the Hamiltonian H=-2JS1S2for a simple dinuclear cluster model,where J is the exchange interaction between nickelions in the dinuclear units,Sithe spin operate for each S=1 Ni[26].A satisfactory fit was obtained with the parameters g=2.15,J=-1.53 cm-1(with an agreementfactor R=[( χMT)calcd-( χMT)obsd]2/(χMT)obsd2=1 ×10-5),confirming the antiferromagnetic interactions.The g values are reasonable,falling near the range 2.0～2.4 for octahedral nickel[27].Antiferromagnetic exchange ranging from weak to moderate is quite frequently observed in dinuclear Niand Cusystems and trinuclear Cusystems[28-30].

2.3 Thermal property

TGA measurements were performed for crystalline samples of 1 in the temperature range of 25～750 ℃(Fig.4).A weight loss of 30.43%in 25 ～250 ℃corresponds to the release of six coordinated water molecules and four lattice water molecules and is in agreement with calculated value(29.64%)for complex 1.From 250～450 ℃,the further weight loss is ascribed to the combustion of the organic ligands Htda2-.The final product is NiO.At 750℃,the residual weight of 23.17% is slight lower than the calculated value(24.58%).

Fig.4 Thermogravimetric curve for 1

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ZHOU Xin-Hui
(Institute of Advanced Materials,Nanjing University of Posts and Telecommunications,Nanjing 210046)

The dinuclear metal complexes are important not only for biochemistry but also for magnetochemistry.In this paper,a dinuclear Nicomplex[Ni2(Htda)2(H2O)6]·4H2O(1)with 1,2,3-triazole-4,5-dicarboxylic acid(H3tda)as ligands has been synthesized and characterized by element analysis,IR spectra,single-crystal X-ray diffraction,thermo gravimetric analysis and superconducting quantum interference device (SQUID).The crystallographic data shows that complex 1 crystallizes in triclinic space group P1 with a=0.721 19(16)nm,b=0.812 81(18)nm,c=0.940 2(2)nm,α=109.526(4)°,β=91.868(4)°,γ=103.304(4)°,V=0.501 88(19)nm3,C8H22N6Ni2O18,Mr=607.74,Dc=2.011 g·cm-3,μ(Mo Kα)=1.982 mm-1,F(000)=312,GOF=1.037,Z=1,the final R1=0.045 1 and wR2=0.117 7 for I＞2σ(I).In 1,two 1,2,3-triazole-4,5-dicarboxylic acid ligands bridge two Niions by two neighboring nitrogen atoms in triazole ring to form a dinuclear Niunit,which is further connected with each others through plenty of hydrogen-bond interactions to construct a three-dimensional(3D)supramolecular architecture.The magnetic study shows that the antiferromagnetic interactions exist between Niions in dinuclear Niunits.CCDC:747631.

dinuclear Nicomplex;1,2,3-triazole-4,5-dicarboxylic acid;crystal structure;hydrogen bond;magnetic property

O614.24+1

A

1001-4861(2010)05-0801-06

2009-11-09。收修改稿日期：2010-01-15。

南京郵電大學引進人才科研啟動基金(No.NY209032)資助。

E-mail：iamxhzhou@njupt.edu.cn

作者：周馨慧，男，30歲，博士，講師；研究方向：功能配位化合物。