李歡　陳云舟　王艷君　陳云峰　王炳武　賈麗慧＊,

(1武漢工程大學(xué)化學(xué)與環(huán)境工程學(xué)院，綠色化工過程省部共建教育部重點實驗室，武漢430073)

(2北京大學(xué)化學(xué)與分子工程學(xué)院，北京分子科學(xué)國家實驗室，稀土材料化學(xué)及應(yīng)用國家重點實驗室，北京100871)

三個雙肼橋連金屬配合物的合成，結(jié)構(gòu)和磁性

李歡1陳云舟1王艷君1陳云峰1王炳武＊,2賈麗慧＊,1

(1武漢工程大學(xué)化學(xué)與環(huán)境工程學(xué)院，綠色化工過程省部共建教育部重點實驗室，武漢430073)

(2北京大學(xué)化學(xué)與分子工程學(xué)院，北京分子科學(xué)國家實驗室，稀土材料化學(xué)及應(yīng)用國家重點實驗室，北京100871)

采用水熱合成方法得到3個新的雙肼橋連過渡金屬化合物：[M(N2H4)2Cl2]n(M=Mn(1),Ni(2))，{[Co1.5(N2H4)3PO4(H2O)]·H2O}n(3)，用單晶X射線衍射方法對其晶體結(jié)構(gòu)進行表征?；衔?是以2個肼分子橋聯(lián)金屬Mn和Ni形成1D鏈狀結(jié)構(gòu)，而粉末XRD顯示1與2是同構(gòu)的?；衔?是以2個肼分子橋聯(lián)金屬Co形成1D鏈，不同的1D鏈再通過磷酸根PO43-進一步堆積形成3D結(jié)構(gòu)。磁性測試表明肼橋在磁性中心之間傳遞反鐵磁耦合作用。

肼；肼橋連配體；反鐵磁交換作用

0　Introduction

In molecule-based magnetic materials,transitionmetal compounds with short bridge ligand of one-to three-atom,such as O2-,CN-,N3-,HCOO-,and C2O42-are under intense investigation[1-2].As a short two-atom bridge ligand,the ability of unsubstituted hydrazine (N2H4)to mediate magnetic coupling was scarcelyinvestigated.In our previous work[3-5],we have already learned that hydrazine mediate AF coupling when it act as co-ligand.We also found thatsulfate can bridge Co2+and Ni2+ions and construct weak ferromagnets with hydrazine as its co-ligand.The mixed sulfate and hydrazine bridges of the weak ferromagnets prevent any detailed investigation of the ability of hydrazine to mediate magnetic coupling.More effort was here placed into synthesizing transition metal compounds containing solo hydrazine bridges.Here we have obtained three transition metal compounds containing hydrazine,two of them are 1D chain compounds containing double hydrazine bridges[M(N2H4)2Cl2]n(M= Mn(1),Ni(2)),the other is 3D framework compound containing double hydrazine bridges{[Co1.5(N2H4)3PO4(H2O)]·H2O}n.We studied the ability of hydrazine to mediate magnetic coupling and how it was affected by the structure of compounds and the anisotropy of the magnetic centers.

1　Experimental

Allstarting materials were commercially available at analytical grade and used as purchased without further purification.MnCl2·H2O(≥99%,AR),NiCl2(≥99%,AR),Co(NO3)2·6H2O(≥99%,AR),N2H4(85%),HCl(36.5%),HPF6(≥60%,AR).

1.1Preparations of compounds 1～3

Preparations of 1:MnCl2·H2O 1 mL(1 mol·L-1water solution),HCl 1 mL(1 mol·L-1),H2O 8 mL, N2H42 mL and 2 drops of C2H5OH were added to glass bottle,then the mixture was heated at 90℃for 2 days in a furnace and naturally cooled to obtain the colorless needle-like crystals.The crystals were washed by water and dried in the air.Yield based on MnCl2:65%.Elemental analysis Calcd.for MnN4H8Cl2(%):N 29.49,H 4.21;Found(%):N 29.46,H 4.24.

Preparations of 2:5 mL N2H4was added to 10 mL NiCl2water solution of 0.02 mol·L-1,at the speed of 1 mL·h-1,stirring while adding.Then we got light blue powder.Yield based on NiCl2:85%.Elemental analysis Calcd.for NiN4H8Cl2(%):N 28.91,H 4.13; Found(%):N 28.88,H 4.15.

Preparation of3:Co(NO3)2·6H2O 1mL(1 mol·L-1), N2H4·H2O 4 mL,HPF60.25μL and H2O 5 mL were added to a 25 mL Teflon-lined stainless-steel autoclave in sequence,then the mixture was heated at 90℃for 2 days in a furnace and naturally cooled to obtain the orange needle crystals and yellow microlite. The orange needle crystals were picked out,and washed by water and dried in the air.Yield based on Co(NO3)2:6.3%.Elemental analysis Calcd.for Co1.5N6H16O6P(%):N 26.63,H 5.11;Found(%):N 26.01,H 5.02.

1.2X-ray crystallography and physical measurements

The crystallographic data for the single crystal of compounds 1 or 3 was collected at293 K on an Agilent Technology SuperNova Atlas Dual System with a Cu microfocus source and focusing multilayer optics using radiation Cu Kα(λ=0.071 073 nm)Empiricalabsorption corrections were applied using the CrysAlisPro program[6-7].The structure was solved by the direct method and refined by full matrix least-squares on F2using SHELXL-97[8-9].All the non-hydrogen atoms were refined using anisotropic thermalparameters.Hydrogen atoms were located geometrically and refined in riding mode.The detailed crystallographic parametersof1 and 3 are listed in Table 1,and selected bond lengths and angles are listed in Table 2.

CCDC:1503462,1;1503463,3.

Table 1 Crystallographic data for compounds 1 and 3

Continued Table 1

Table 2 Selected bond lengths(nm)and bond angles(°)for compounds 1 and 3

Continued Table 2

PXRD data for compounds 1～3 were collected in the range of 5°～50°for 2θon crystalline samples using a Rigaku Dmax 2000 diffractometer with Cu Kα radiation(λ=0.154 18 nm,40 kV,40 mA)in flatplate geometry,at room temperature.The experimental powder X-ray diffraction pattern was compared to the calculated one from the single-crystal structure to identify the phase of the sample in the Fig.S1～S2 (Supporting information).

Elemental analysis of nitrogen and hydrogen was performed using an Elementar Vario EL analyzer.The FTIR spectra were recorded against pure crystal samples in the range of 4 000～600 cm-1using a Nicolet iN10 MX Microinfrared Spectrometer.(Fig.S3 in Supporting Information)

Magnetic measurements were performed on a MPMS XL-5 SQUID(Superconductivity Quantum Interference Device)magnetometer with crystalline samples fixed in a white capsule by parafilm or eicosane.Diamagnetic corrections were estimated by using Pascal constants[10]and background corrections by experimentalmeasurements on sample holders.

2　Results and discussion

2.1Synthesis

Hydrothermal reaction is a convenient and effective route to obtain high-quality single crystals[11-12]. For compound 1,its really hard to obtain good crystal for measurementbecause the 1D chain compounds are always needle-like crystals which is easy to be twin crystal.So we managed to do many experiments to look for the optimal reaction conditions through adjusting the hydrothermal temperature,pH value and solvent.For compound 3,it is got by accident.We were trying to get another compound,which is 1D chain compound containing hydrazine bridge and counter ion PF6-,but compound 3 was got by accident due to the oxidation of phosphorus and the PF6-were changed to the PO43-under the hydrothermal condition.

Fig.1 Geometry structure of compound 1(a)Coordination environment of Mn2+in 1;(b)1D chain of 1;(c)3D framework of 1

2.2Crystalstructures

Powder X-ray diffraction analysis reveals that compounds 1 and 2 are isomorphous(Fig.S1). Compound 1 crystallizes in monoclinic crystal system, I2/m space group.Single-crystal X-ray diffraction reveals that 1 has a chain structure,and the repeating unit is[M(N2H4)2Cl2],while no lattice water in the crystal.Mn2+ions locate in an octahedron coordination environment(Fig.1a),the octahedral Mn2+ions are surrounded by four equatorial N atoms from four differenthydrazine molecules and two Cl-atoms in the axial direction,which also act as counter ions.The angles of cis O-M-O ranges from 86.18°to 93.81°, while all the trans angles are 180°.Comparing with the reported compounds containing a monodentate hydrazine and the uncoordinated hydrazine(N-N 0.146 0 nm)[13-14],the distance between the two nitrogen atoms(0.150 62 nm)for 1 is slightly longer but the angle of M-N-N(113.34°)for 1 is a bit smaller than those ofreported compounds.This longerdistance and smaller angel in hydrazine molecule can be probably attributed to its coordination mode as bidentate ligand.

The hydrazine molecules connect the neighboring Mn2+centers through a syn-syn coordination mode and form a 1D chain structure along a-axis(Fig.1b),the intra-chain distance between the adjacent Mn2+ions is 0.429 nm.The 3D packing structure is shown in Fig. 1c,the distance between the chains is 0.641 6 nm.

Single-crystal X-ray diffraction reveals that 3 crystallizes in the monoclinic system，P21/c space group and the repeating unitis[Co1.5(N2H4)3PO4(H2O)]· H2O.The main structure of 3 is a 3D neutral network involving Co2+centers connected by hydrazine molecules N2H4and phosphate anions PO43-bridges(Fig.2). As shown in Fig.2a,each Co2+ion resides at an inversion center and is six-coordinated in a distorted octahedral configuration,which includes four N atoms from four different hydrazine bridges in the equatorial plane and two O atoms from two PO43-anions or from two H2O molecules in the axis direction.The cisangles of O-Co-O range from 84.55°to 93.41°(Table 2) and the trans-angle is from 175.26°to 180°.Different from 1D compound 1,the N-N bond distance for 3 are 0.145 7(3)and 0.146 4(3)nm,and the angle of Co -N-N ranges from 114.79(15)°to 120.96(15)°.The N-N bond distance and the angle for 3 in the hydrazine bridging ligand are similar to the former ones[4,13,15].

Similar to our previous 3D compounds containing hydrazine[4],the structures of 3 can be regarded as the hydrazine bridged 1D chain Co-N2H4-Co which are connected into 3D framework by phosphate anions (Fig.2b,2c).The hydrazine molecules act as a transbridging bidentate ligands and link the adjacent Co2+metal ions into the 1D infinite chains,with the Co…Co distance 0.426 nm.All these 1D chains are parallel to the ab plane,and run along two directions alternately:the a,b direction and a,-b direction. Here phosphate anions act as bidentate mode to bridge the two Co2+metal ions from different two 1D chains and so every PO43-anion links two chains,one is with a,b direction and the other is with a,-b direction.The bridging PO43-anions are above and below the layer alternatively.The adjacent distance of Co…Co bridged by PO43-is 0.619 nm.Every 1D chain is connected further with other chains by PO43-anions to generate a 3D structure.

Fig.2(a)Coordination environments of the metal ion and ligands for 3;(b)Perspective view of the 3D framework structure of 3 viewed along the b axis;(c)Schematic view of the 3D network structure of 3 with phosphate (PO43-)represented by P atom and H atom omitted

2.3Magnetic property

Magnetic measurements were carried out on solid samples of compounds 1～3 According to the magnetic data,it was suggested dominant antiferromagnetic coupling interactions between the M2+ions in all three compounds.Although compounds 1,2 are 1D structure and compound 3 is 3D structure,the magnetic properties of the three compounds are similar due to their isomorphic structures with double hydrazine bridge.

TheχMT values increase sharply in the low temperature range and then smoothly in higher temperature and reach 4.47 cm3·mol-1·K(1),1.22 cm3·mol-1·K(2)and 4.28 cm3·mol-1·K(3)at room temperature(Fig.3a),theχMT values of 1～2 are as expected for the isolated divalent metal ions[16],but the χMT value of 3 is significantly larger than the spinonly value 1.875 cm3·mol-1·K for S=3/2,which is close to the experimental values reported for other Co2+compounds[15,17].The magnetic susceptibilitiesχMforcompounds 1～3 in a field of 1 kOe obey Curie-Weiss lawχM=C/(T-θ)(Fig.3b)with the Curie constant C= 4.54 cm3·mol-1·K(1),1.24 cm3·mol-1·K(2)and 4.71 cm3·mol-1·K(3),negative Weiss constantsθof-3.29 K(1),-6.04 K(2)and-22.8 K(3).The negative Weiss constant indicate the overall AF coupling in compounds 1～3.The field dependence of the magnetization of1～3 measured at 2 K increase linearly(Fig. 3c).At 2 K,the magnetization at 50 kOe reach 4.77Nβfor 1,0.74Nβfor 2 and 3.Nβfor 3, approaching to saturation magnetization values of ca. 5Nβ,2Nβand 3Nβexpected for one isolated spin S= 5/2,S=3/2 and S=1,which indicated that the AF coupling was weak.

Fig.3(a)Temperature dependence ofχMT of 1～3 with solid lines being fitted results;(b)Temperature dependence ofχMof 1～3;(c)Field dependence of M of 1～3

Considering the 1D equally spaced chain structures,theχMT value of 1 can be fitted by Fisher′s 1D Heisenberg chain model[18-20](S=5/2 and S=3/2, H=-2JSiSj)expressed by the following equation:

TheχMT value of 2 also can be fitted with the following analytical expression for an antiferromagnetic chain of S=1 with the Hamiltonian H=-2JSiSj[18,21]:

The best fitting parameters are J=0.37 cm-1,g= 2.03,and R=4.46×10-4for1(R isdefined asΣ[(χMT)obsd-(χMT)calc]2/Σ[(χMT)obsd]2).For 2,the corresponding fitting parameters are J=1.22 cm-1,g=2.22,and R=1.37× 10-4.

As for 3，the weak antiferromagnetic coupling is likely to mediate through the hydrazine chains(-Co-N2H4-)n.However,it is too weak to show up against spin-orbit coupling due to the small anisotropic pseudo-spins of cobalt（Ⅱ）ion(S=1/2 under 30 K)[10,18], which led to unsatisfactory accordance with Fisher′s 1D Heisenberg chain model.In order to get an estimate of the strength of the antiferromagnetic exchange interaction,a simple phenomenological equation can be used[22]:

where A+B equals Curie constant,and E1,E2represent the activation energies corresponding to the spin-orbit coupling and the antiferromagnetic exchange interaction.The value found for Curie constant(C=A+B)above 15 K is 4.62 cm3·mol-1·K, which agrees well with that obtained from the Curie-Weiss law in the high temperature range.Moreover, the value found for the antiferromagnetic exchange is rather weak(-E2/k=-2.16 K)，corresponding to interactions(J=-3.00 cm-1)within the Ising chain approximation(χT∝exp[J/(2kT)]).

From magnetic data of the above three compounds,it is clear that AF coupling mainly occurs between intrachain metal ions and obviously the antiferromagnetic coupling between intrachain metal ions is mediated by the hydrazine bridges.The magnetic coupling mechanism of hydrazine bridge is consistent with that of our previous work[4]which was examined using DFT+BS method.

3　Conclusions

To the best of our knowledge,it is the first time that compounds containing poly-hydrazine bridge have been synthesized and magnetically characterized.The X-ray crystallography analysis shows that two hydrazine molecules act as the bridge ligand forming the 1D chain compounds and 3D compound.The magnetic data revealthe overall AF magnetic coupling and the negative fitted values of J indicating intrachain interactions are AF coupling.This work is the complement of our previous work[4-5]and provides an unprecedented data for studying the coordination chemistry and magnetic properties of hydrazine compounds,and further enriches the field of molecule-based magnetic material.

Acknowledgments:We acknowledge the support of the National Natural Science Foundation of China(Grants No. 21101123,21441007)and Department of Hubei Province (Grant No.D20131506).We also thank the Wuhan Institute of Technology(Grant No.CX2015160),supported by Graduate Innovative Fund of Wuhan Institute of Technology.

Supporting information is available athttp://www.wjhxxb.cn

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Syntheses,Structures and Magnetic Studies of Three Double Hydrazine Bridging Transition Metal Compounds

LIHuan1CHEN Yun-Zhou1WANG Yan-Jun1CHEN Yun-Feng1WANG Bing-Wu＊,2JIA Li-Hui＊,1
(1Key Laboratory for Green Chemical Process of Ministry of Education,School of Chemistry and Environmental Engineering, Wuhan Institute of Technology,Wuhan,430074,China)
(2Beijing National Laboratory for Molecular Science,The State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering,Peking University,Beijing 100871,China)

By employing the hydrothermal method,we have synthesized three transition metal compounds with double hydrazine(N2H4)as bridge:[M(N2H4)2Cl2]n(M=Mn(1),Ni(2)),{[Co1.5(N2H4)3PO4(H2O)]·H2O}n(3).Single-crystal X-ray diffraction reveals that the compound 1 are one-dimensional(1D)chains with two hydrazine molecules as bridge ligands.And powder X-ray diffraction analysis reveals that compounds 1 and 2 are isomorphous.The compound 3 firstform 1D chains through two hydrazine molecules as bridge ligands and the PO43-connectthe chains into a 3D extended structure.The magnetic measurement reveals the hydrazine as bridge ligand can mediate the antiferromagnetic(AF)coupling interaction between magnetic centers.CCDC:1503462,1;1503463,3.

hydrazine;hydrazine bridge ligand;antiferromagnetic interaction

O614.7+11；O614.81+3；O614.81+2

A

1001-4861(2016)12-2198-07

10.11862/CJIC.2016.250

2016-07-02。收修改稿日期：2016-09-14。

國家自然科學(xué)基金(No.21101123,21441007)和武漢工程大學(xué)研究生創(chuàng)新基金(No.CX2015160)資助項目。

＊通信聯(lián)系人。E-mail：jialihui715@wit.edu.cn;bwwang@pku.edu.cn