趙素琴 顧金忠

基于2，4，4′-聯(lián)苯三羧酸及菲咯啉的錳(Ⅱ)和鎳(Ⅱ)雙核配合物的合成、晶體結(jié)構(gòu)及磁性質(zhì)

趙素琴＊,1顧金忠＊,2

(1青海民族大學(xué)物理與電子信息工程學(xué)院，西寧810007) (2蘭州大學(xué)化學(xué)化工學(xué)院，蘭州730000)

通過水熱方法，用2，4，4′-聯(lián)苯三羧酸(H3btc)和菲咯啉(phen)分別與MnCl2·4H2O和NiCl2·6H2O反應(yīng)，合成了2個(gè)具有雙核結(jié)構(gòu)的配合物[Mn2(Hbtc)2(phen)4]·5H2O(1)和[Ni2(Hbtc)2(phen)4]·2H3btc·4H2O(2)，并對(duì)其結(jié)構(gòu)和磁性質(zhì)進(jìn)行了研究。結(jié)構(gòu)分析結(jié)果表明2個(gè)配合物的晶體都屬于三斜晶系，P1空間群。配合物1和2均為雙核結(jié)構(gòu)，通過分子間的O-H…O氫鍵作用，雙核的分子被進(jìn)一步連接成了三維超分子框架。研究表明，雙核分子中相鄰金屬離子間存在反鐵磁相互作用。

配位化合物；錳配合物；鎳配合物；磁性

0 Introduction

In the past decades,a considerable attention was focused on the crystal engineering of metal-organic and supramolecular architectures based on different carboxylic acid building blocks and assembled by covalent bonds and various non-covalent forces(strong and weak hydrogen bonds,π-πinteractions,andhalogen bonding)[1-6].This research was primarily justified by a diversity of applications of the obtained compounds that span from gas sorption,magnetism, sensing and molecular recognition to photochemistry, catalysis,and medicinalchemistry[7-15].

As is well known,many factors may seriously influence the structures of the resulting compounds, such as the ligands,kinds of metal salt,the solvent system,pH value,the metal-to-ligand ratio,reaction temperature and time,and so on[16-20].Multicarboxylate ligands are often employed as bridging blocks to construct coordination compounds due to their versatile coordination modes and the ability to act as H-bond acceptors and donors to assemble supramolecular structures[21-26].In order to extend our research in this field,we have selected biphenyl-2,4,4′-tricarboxylic acid(H3btc)as a functional building block on account of the following considerations:(a) H3btc possesses three carboxyl groups that may be completely or partially deprotonated,depending on pH value;(b)it is a flexible ligand allowing the rotation of two phenyl rings around the C-C single bond;(c)to ourknowledge,H3btc has notbeen adequately explored in the construction of coordination polymers[21-22].

Taking into account these factors,we herein report the syntheses,crystal structures,magnetic properties of Mn(Ⅱ)and Ni(Ⅱ)coordination compounds constructed from Hbtc2-and phen ligand.

1 Experimental

1.1 Reagents and physical measurements

All chemicals and solvents were of AR grade and used without further purification.Carbon,hydrogen and nitrogen were determined using an Elementar Vario EL elementalanalyzer.IR spectra were recorded using KBr pellets and a Bruker EQUINOX 55 spectrometer.Thermogravimetric analysis(TGA)data were collected on a LINSEIS STA PT1600 thermal analyzer 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[Mn2(Hbtc)2(phen)4]·5H2O(1)

A mixture of MnCl2·4H2O(0.060 g,0.3 mmol), H3btc(0.086 g,0.3 mmol),phen(0.120 g,0.6 mmol), NaOH(0.024 g,0.6 mmol),and H2O(10 mL)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.Yellow block-shaped crystals of 1 were isolated manually, and washed with distilled water.Yield:63%(based on Mn salt).Anal.Calcd.for C78H58Mn2N8O17(%):C 62.91, H 3.92,N 7.52;Found(%):C 62.78,H 3.95,N 7.61. IR(KBr,cm-1):3 394m,3 060m,1 700m,1 572s,1 516m, 1 424s,1 372s,1 344m,1 262m,1 170w,1 142w,1 102 m,1 050w,1 004w,912w,850m,774s,734s,682m, 660w,630w,550w.

1.3 Synthesis of[Ni2(Hbtc)2(phen)4]·2H3btc·4H2O (2)

A mixture of NiCl2·6H2O(0.071 g,0.3 mmol), H3btc(0.172 g,0.6 mmol),phen(0.120 g,0.6 mmol), NaOH(0.024 g,0.6 mmol),and H2O(10 mL)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.Purple needle-shaped crystals of 2 were isolated manually, and washed with distilled water.Yield:65%(based on Ni salt).Anal.Calcd.for C108H76Ni2N8O28(%):C 62.24, H 3.73,N 5.46;Found(%):C 62.41,H 3.71,N 5.49. IR(KBr,cm-1):3 573w,3 428w,1 683s,1 585s,1 517m, 1 423s,1 382w,1 367w,1 304w,1 278w,1 231m,1 180 w,1 154w,1 086w,1 003w,925w,910w,868w,848w, 811w,769w,728w,676w,655w,645w,531w.

1.4 Structure determination

Single-crystal data of 1 and 2 were collected at 293(2)K on a Bruker APE-ⅡCCD diffractometer with Mo Kαradiation(λ=0.071 073 nm).The crystallographic data are summarized in Table 1.The selected bond lengths and angles are listed in Table 2. Hydrogen bond parameters of the compounds 1 and 2 are given in Tables 3 and 4.The structure was solved using direct methods,which yielded the positions ofall non-hydrogen atoms.These were refined first isotropically and then anisotropically.Allthe 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 at the final stage of full-matrix leastsquares 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 SHELXL program[27].

CCDC:1456513,1;1456514,2.

Table 1 Crystal data for compounds 1 and 2

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

Continued Table 2

Table 3 Hydrogen bond lengths(nm)and angles(°)of compound 1

Table 4 Hydrogen bond lengths(nm)and angles(°)of compound 2

2 Results and discussion

2.1 Description of the structures

2.1.1 [Mn2(Hbtc)2(phen)4]·5H2O(1)

The X-ray crystallography analysis reveals that the compound 1 crystallizes in the triclinic system space group P1.The asymmetric unit of compound 1 contains two crystallographically unique Mn(Ⅱ)atoms, two Hbtc2-ligands,four phen moieties,and five lattice water molecules.The partial deprotonation of H3btc to give Hbtc2-is also confirmed by the IR spectral data of 1,since a band-COOH band at 1 700 cm-1wasobserved(Experimental Section).As depicted in Fig.1, both Mn1 and Mn2 atoms are six-coordinated by two carboxylate O atoms of two independent Hbtc2-ligands and four N atoms of two phen moieties, forming a distorted octahedral geometry.The Mn-O (0.210 0(4)～0.215 4(3)nm)and Mn-N(0.225 5(5)～0.239 7(4)nm)bond lengths are in good agreement with those distances observed in some other Mn(Ⅱ)compounds[17,21,23-24].As shown in Fig.2,two crystallographically equal Mn1 centers are bridged by 2-and 4-carboxylate groups of two different Hbtc2-blocks, giving rise to a dinuclear unitⅠwith a Mn…Mn separation of 0.810 0(4)nm.Simultaneously,2-carboxylate groups of two different Hbtc2-blocks bridge two crystallographically equal Mn2 centers to form another dinuclear unitⅡwith a Mn…Mn separation of 0.427 9(4)nm.Obviously,dinuclear Mn2unitsⅠandⅡare isomers.The dihedral angles of two benzene rings in the Hbtc2-blocks are 45.04°and 63.97°, respectively.These dinuclear Mn2units are further extended into the 3D supramolecular frameworks through O-H…Ohydrogen bonding(Fig.3 and Table 3).

Fig.1 Drawing of the asymmetric unit of compound 1 with 30%probability thermal ellipsoids

Fig.2 Dinuclear Mn2unitsⅠandⅡin compound 1

Fig.3 Perspective view of 3D supramolecular structure in the bc plane

Fig.4 Drawing of the asymmetric unit of compound 2 with 30%probability thermal ellipsoids

2.1.2 [Ni2(Hbtc)2(phen)4]·2H3btc·4H2O(2)

In complex 2,the asymmetric unit consists of one Ni(Ⅱ)atom,one Hbtc2-block,two lattice water molecules,and a molecule of co-crystallized H3btc (Fig.4).The six-coordinate Ni1 center is bound by four N atoms from two phen ligands and two carboxylate O atoms from two different Hbtc2-blocks,thus formingan octahedral{NiN4O2}geometry.The Ni-O bonds are in the range of 0.205 9(2)～0.208 3(2)nm,while the Ni-N distances vary from 0.206 8(2)～0.210 4(2)nm; all these distances are comparable to those found in the reported Ni(Ⅱ)compounds[21-22,26,28].In 2,two crystallographically equal Ni1 centers are bridged by 2-carboxylate groups of two different Hbtc2-blocks, giving rise to a dinuclear Ni2unit with a Ni…Ni separation of0.479 8(4)nm(Fig.5).Obviously,the Ni2dinuclear unit and the Mn2dinuclear unitⅡin 1 are isostructural.The dihedral angle of two benzene rings in the Hbtc2-and H3btc are 45.80°and 35.07°,respectively.The discrete Ni2units and free H3btc molecules are interlinked by the strong O-H…O hydrogen bonds to form a 3D supramolecularframework(Fig.6,Table4).

Fig.5 Dinuclear Ni2unit in compound 2

Fig.6 Perspective view of 3D supramolecular structure in the ac plane

2.2 TGA analysis

The thermal stability of 1 and 2 was investigated under nitrogen atmosphere by thermogravimetric analysis(TGA);the obtained plots are shown in Fig.7. Compound 1 loses its five lattice water molecules (Found 5.85%;Calcd.6.04%)in the 28～116℃range, followed by the decomposition starting at 205℃.For 2,there are two distinct thermal effects in the 98～238℃range that correspond to the removal of four free H2O molecules(Found 3.45%;Calcd.3.51%)and two co-crystallization H3btc molecules(Found 32.1%;Calcd. 31.5%),followed by the concomitant decomposition.

Fig.7 TGA curves of compounds 1 and 2

2.3 Magnetic properties

Variable-temperature magnetic susceptibility studies were carried out on powder samples of 1 and 2 in the 2～300 K temperature range.For 1,theχMT value at 300 K is 8.81 cm3·mol-1·K,which is close to the value of 8.76 cm3·mol-1·K expected for two magnetically isolated high-spin Mn(Ⅱ)centers(SMn=5/2, g=2.0).Upon cooling,theχMT value drops down very slowly from 8.81 cm3·mol-1·K at 300 K to 8.38 cm3· mol-1·K at 98 K and then decreases steeply to 1.50 cm3·mol-1·K at2 K(Fig.8).TheχM-1vs T plot for 1 in the 2～300 K interval obeys the Curie-Weiss law with a Weiss constantθof-10.40 K and a Curie constant C of 9.10 cm3·mol-1·K.The negative value ofθand the decrease of theχMT should be attributed to the overall antiferromagnetic coupling between the Mn(Ⅱ)centers within the Mn2unit.We tried to fit the magnetic data of 1 using the following expression[29-30]for the dinuclear Mn(Ⅱ)unit:

Fig.8 Temperature dependence ofχMT(○)and 1/χM(□) vs T for compound 1

Least-squares analysis of magnetic susceptibility data led to J=-3.82 cm-1,g=2.00 and R=3.46×10-5. These values confirm the presence ofantiferromagnetic interaction between the Mn(Ⅱ)ions within the dinuclear units.Because of the long separation within the dinuclear Mn2unitⅠ(0.810 0(4)nm),the negative value of J should be attributed to the antiferromagnetic coupling between the Mn(Ⅱ)atoms within the Mn2unitⅡ.

For 2,theχMT value at 300 K is 2.18 cm3·mol-1· K,which is higher than the spin only value of 2.00 cm3·mol-1·K for two magnetically isolated Ni(Ⅱ)center (SNi=1,g=2.0).Upon cooling,theχMT value drops down very slowly from 2.18 cm3·mol-1·K at 300 K to 2.11 cm3·mol-1·K at 96 K,and then decreases steeply to 0.73 cm3·mol-1·K at 2 K(Fig.9).In the 2～300 K interval,theχM-1vs T plotfor 2 obeys the Curie-Weiss law with a Weiss constantθof-6.58 K and a Curie constant C of 2.11 cm3·mol-1·K,suggesting a weak antiferromagnetic interaction between the Ni(Ⅱ)ions.

We tried to fit the magnetic data of 2 using the following expression[31]for a dinuclear Ni(Ⅱ)unit:

Fig.9 Temperature dependence ofχMT(○)and 1/χM(□) vs T for compound 2

whereρis a paramagnetic impurity fraction and TIP is temperature independentparamagnetism.Using this model,the susceptibility for 2 above 2.0 K was simulated,leading to the values of J=-2.35 cm-1,g= 2.09,ρ=0.011,and TIP=4.56×10-6cm3·mol-1,with the agreementfactor R=7.57×10-4(R=∑(Tobs-Tcalc)2/∑Tobs2). The negative J parameter confirms that a weak antiferromagnetic exchange coupling exists between the adjacent Ni(Ⅱ)centers,which is in agreement with a negativeθvalue.In compounds 1 and 2,there is one type of the magnetic exchange pathway within the dinuclear Mn2and Ni2units,namely via doubleμ2-η1∶η1-carboxylate(syn-syn)bridges(Fig.1 and 5).

3 Conclusions

In summary,two new compounds,namely [Mn2(Hbtc)2(phen)4]·5H2O(1)and[Ni2(Hbtc)2(phen)4]· 2(H3btc)·4H2O(2)have been synthesized under hydrothermal conditions.Both compounds feature the dinuclear structures,which are further extended into the 3D supramolecular frameworks through O-H…O hydrogen bonding.Magnetic studies for two compounds show a weak antiferromagnetic couplingbetween the adjacentmetal centers.

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Syntheses,Crystal Structures and Magnetic Properties of Mn(Ⅱ)and Ni(Ⅱ)Dinuclear Coordination Compounds Constructed from Biphenyl-2,4,4′-Tricarboxylate and Phenanthroline

ZHAO Su-Qin＊,1GU Jin-Zhong＊,2
(1College of Physics and Electronic Information Engineering,Qinghai University for Nationalities,Xining 810007,China)
(2College of Chemistry and Chemical Engineering,Lanzhou University,Lanzhou 730000,China)

Two coordination compounds,namely[Mn2(Hbtc)2(phen)4]·5H2O(1)and[Ni2(Hbtc)2(phen)4]·2H3btc· 4H2O(2)have been constructed hydrothermally using H3btc(H3btc=biphenyl-2,4,4′-tricarboxylic acid),phen(phen =phenanthroline),MnCl2·4H2O and NiCl2·6H2O.Both compounds crystallize in the triclinic system,space group P1.The compounds possess the dinuclear structures,which are further extended into the 3D supramolecular frameworks through O-H…O hydrogen bonding.Magnetic studies for compounds 1 and 2 show a weak antiferromagnetic coupling between the neighbouring metal centers,with J=-3.82 cm-1(1)and-2.35 cm-1(2).CCDC: 1456513,1;1456514,2.

coordination compound;Mn(Ⅱ)compound;Ni(Ⅱ)compound;magnetic properties

O614.7+11；O614.81+3

A

1001-4861(2016)09-1611-08

10.11862/CJIC.2016.203

2016-04-16。收修改稿日期：2016-07-22。

青海省應(yīng)用基礎(chǔ)研究計(jì)劃(No.2015-ZJ-738)資助項(xiàng)目。

＊通信聯(lián)系人。E-mail：qhzhsq@sina.com，gujzh@lzu.edu.cn；會(huì)員登記號(hào)：S06N5892M1004。