Inorganic Chemistry Communications 13 (2010) 699–702

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Inorganic Chemistry Communications

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Assembly of two ferrous coordination polymers with triazole derivative:Syntheses, structures and magnetic properties

Yao Chen a, Shi-Yuan Zhang a, Xiao-Qing Zhao a, Jing-Jing Zhang a, Wei Shi a,b,⁎, Peng Cheng a

a Department of Chemistry, Nankai University, Tianjin 300071, PR Chinab State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China

⁎ Corresponding author. Department of Chemistry300071, PR China. Fax: +86 22 23502458.

E-mail address: shiwei@nankai.edu.cn (W. Shi).

1387-7003/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.inoche.2010.03.022

a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 February 2010Accepted 11 March 2010Available online 21 March 2010

Keywords:Crystal structureFe(II) complexCoordination polymerMagnetic property

The reactions of Fe(II) salts with 1,4-bis(1,2,4-triazole-1-ylmethyl-benzene) (btx) give two new Fe(II)coordination polymers {[Fe(btx)3](ClO4)2}n (1) and {[Fe(btx)(SO4)(H2O)2]}n (2), which have beencharacterized by element analysis, PXRD, single-crystal X-ray diffraction and magnetic susceptibility. 1 showsinfinite plait-like chain structure, while 2 exhibits as 2D grid. Magnetic studies indicate that the Fe(II) ions inthe two coordination polymers retain in high-spin ground state upon cooling from 300 to 2 K, showingantiferromagnetic interactions.

, Nankai University, Tianjin

l rights reserved.

© 2010 Elsevier B.V. All rights reserved.

In the past decade, there is great interest for chemists in the designand synthesis of new coordination polymers for their uniqueelectronic, optical, magnetic and catalytic properties [1–4]. 1,2,4-triazole and its derivatives as ligands have attractedmuch attention inthis field because: (1) different coordination modes of the triazolegroup are helpful to construct new products with various structures;(2) the active 1-position hydrogen atoms of the triazole group giverise to various derivatives by substitution reaction; (3) the N donors ofthe triazole group always afford moderate magnitude ligand fieldwhich can influence the spin state of the central metal ions, especiallyto obtain spin-crossover materials which has potential application ininformation storage [5–10]. Among the numerous 1,2,4-triazole deri-vatives, 1,4-bis(1,2,4-triazole-1-ylmethyl-benzene) (btx) was givenconsiderable interest for the various coordination modes includingthe cis- or trans-isomers [11–14]. However, the combination of btxwith Fe(II) ions in coordination polymers have been given lessattention, which may result from the instability of Fe(II) ions duringthe reaction. In this communication, two new Fe(II) coordinationpolymers {[Fe(btx)3](ClO4)2}n (1) and {[Fe(btx)(SO4)(H2O)2]}n (2)wereobtained and characterized by element analysis, PXRD, single-crystalX-ray diffraction and magnetic susceptibility.

Reagents were purchased commercially and used without furtherpurification. The ligand btx was prepared according to the literature

[14]. 1 and 2 were prepared in 45% and 62% yields [15,16],respectively, and the crystal structures were determined by single-crystal X-ray diffraction [17–19].

Single-crystal X-ray diffraction analysis reveals that 1 crystallizesin the trigonal space group P-3c1. There are one crystallographicallyindependent Fe(II) ion and one btx ligand in the asymmetric unit(Fig. 1). Fe1 is coordinated with six N atoms from six btx ligands, withFe–N distance of 2.188(7) Å. The coordination geometry around Fe1can be exactly described as a regular octahedron. Each btx ligand actsas bidentate linker, using two 4-position N atoms of the triazole ringswith cis-configuration to bridge two Fe(II) ions, with the Fe∙∙∙Fedistance of 11.029(2) Å. Every two Fe(II) ion is bridged by three btxligands, and an interesting plait-like 1D chain structure is formedalong a direction, as shown in Fig. 2. These chains are further linkedvia π ··· π stacking to form 3D supermolecular structure, in which thefree ClO4

− ions fill the void, as shown in Fig. 3.Compound 2 crystallizes in the triclinic space group P-1. The

molecule structure of 2 is shown in Fig. 4. There are four crys-tallographically independent Fe(II) ions in the molecule structurewith similar coordination environments. All Fe(II) ions (Fe1, Fe2, Fe3and Fe4) are six-coordinated by two 4-position N atoms of triazolerings from two btx ligands, two O atoms from two SO4

2− anions andtwo water molecules. The differences among the four Fe(II) ions arethe bond lengths associated with them. For Fe1, Fe2, Fe3 and Fe4, theFe–OSO4 distances are 2.115(2), 2.143(6), 2.115(4) and 2.100(2) Å andthe Fe–Owater distances are 2.180(5), 2.112(4), 2.148(5) and 2.180(5) Å,while the Fe–Ndistances are 2.167(3), 2.208(3), 2.185(3) and 2.186(4) Å,respectively. The coordination geometries of the four Fe(II) ions canbe described as elongated octahedral with four O atoms lying in the

Fig. 1. The coordination environment of Fe(II) ion in 1 with atom-labeling scheme. The H atoms are omitted for clarity.

Fig. 2. The plait-like 1D chain of 1 viewed along a direction. Purple: Fe, blue: N, yellow: C (left) and space-filling diagram (right).

700 Y. Chen et al. / Inorganic Chemistry Communications 13 (2010) 699–702

equatorial plane while two N atoms occupying the axial position. SO42−

anions as bidentate ligands link Fe(II) ions to form two different 1Dchains: one consists of Fe1 and Fe2 ions, and the other contains Fe3and Fe4 ions. The distances of Fe1∙∙∙Fe2 and Fe3∙∙∙Fe4 are both 5.463(1) Å.

Fig. 3. The 3D structure viewed along c direction.

The 1D chains are further connected by bidentate btx ligands oftrans-configuration to form 2D grid structure, as shown in Fig. 5. Thenearest intrachain Fe1∙∙∙btx∙∙∙Fe4 and Fe2∙∙∙btx∙∙∙Fe3 distances areboth 15.095(28) Å.

The temperature-dependent magnetic susceptibilities of 1 and 2were measured in the temperature range of 2–300 K at 1000 Oe, asshown in Fig. 6. For 1, at 300 K, the χMT value is 3.95 cm3 K mol−1,which agrees well to the value expected for one Fe(II) ion (3.25–4.06 cm3 K mol−1) in the HS state. When the temperature is lowered,χMT values gradually decreases to 2.99 cm3 K mol−1 until 20 K andthen drops rapidly, reaching theminimumvalue of 1.50 cm3 K mol−1

at 2 K. For 2, at 300 K, theχMT value is to 3.52 cm3 K mol−1, also in therange expected for one Fe(II) ion in the HS state. Upon cooling, χMTvalue is almost constant down to 50 K and then decreases rapidlybelow 50 K reaching the minimum value of 0.92 cm3 K mol−1 at 2 K.For both 1 and 2, the decrease of the χMT values upon cooling can beattributed to theweak antiferromagnetic interactions between Fe(II)ions and no spin-crossover behavior was observed under thiscondition. The temperature dependence of the magnetic suscept-ibilities of 1 and 2 both obey the Curie–Weiss law in the temperaturerange of 2–300 K with C=3.98 cm3 mol−1 K, θ=−6.76 K for 1 andC=3.63 cm3 mol−1 K, θ =−2.27 K for 2. The small negative θ valuescould be possible due to the existence of both weak antiferromag-netic interactions and zero field splitting. Considering that the Fe(II)ions are bridged by long-shape σ-bonding ligands, the magneticsusceptibility data were fitted by a mononuclear Fe(II) model withzero field splitting parameter D, and the magnetic interactions

Fig. 4. The coordination environment of Fe(II) ion in 2 with atom-labeling scheme. The H atoms are omitted for clarity.

701Y. Chen et al. / Inorganic Chemistry Communications 13 (2010) 699–702

between the Fe(II) ions are further considered as a molecular fieldparameter zJ′. The total expression is [20]:

χll =2Ng2β2

kT ⋅exp −xð Þ + 4exp −4xð Þ

1 + 2exp −xð Þ + 2exp −4xð Þ

χ⊥ =Ng2β2

kT ⋅6 = xð Þ 1− exp −xð Þð Þ + 4= 3xð Þ exp −xð Þ− exp −4xð Þð Þ

1 + 2exp −xð Þ + 2exp −4xð Þ x = D = kTð Þ

χFe = χll + 2χ⊥ð Þ = 3

χM = χFe = 1−χFe 2zJ0 =Ng2β2� �h i

:

Fig. 5. The 2D grid structure of 2. Green:

The best fits using least-squares method gave D=−3.55 cm−1,g=2.31, zJ′=−1.50 cm−1 and R=8.6×10−5 for 1 and D=−3.12 cm−1, g=2.22, zJ′=−0.53 cm−1 and R=2.7×10−5 for 2.The fitting results show the existence of weak antiferromagneticinteractions between Fe(II) ions. The similar magnetic behavior hasalso been found in other Fe(II) complexes with bis-1,2,4-triazoleligands [21], which indicate that the magnitudes of the ligand field inthese coordination modes are weak, and against to show detectablethermal spin-crossover behaviors. For the aim to obtain spin-crossover complexes in this system, the ligands with stronger ligandfield such as cyanogen should be introduced, and this work isunderway in our lab.

Fe, yellow: S, red: O, blue: N, gray: C.

Fig. 6. Plots of χM (O) and χMT (△) vs. T for 1 (left) and 2 (right). The solid line denotes the theoretical fit of the experimental data.

702 Y. Chen et al. / Inorganic Chemistry Communications 13 (2010) 699–702

In summary, by using different Fe(II) salts in H2O/MeOH solution,two new coordination polymers 1 and 2 have been synthesized andcharacterized. By using Fe(ClO4)2·6H2O, a 1D plait-like chainstructure of 1 is resulted, while by using FeSO4·7H2O instead of Fe(ClO4)2·6H2O, a 2D grid structure of 2 is obtained. The btx ligandsadopt cis-configuration in 1 and trans-configuration in 2. Variablemagnetic susceptibilities studies show antiferromagnetic interactionsamong the HS Fe(II) ions in both 1 and 2.

Acknowledgements

This work was supported by the National Natural ScienceFoundation of China (nos. 20971073 and 20801028), the NSF ofTianjin (no. 09JCYBJC04000) and MOE (no. 20070055046) of China.

Appendix A. Supplementary data

CCDC 761939 (1) and 761938 (2) contain the supplementarycrystallographic data for this paper. These data can be obtained free ofcharge from the Cambridge Crystallographic Data Centre, 12 UnionRoad, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:deposit@ccdc.cam.ac.uk. Supplementary data associatedwith this articlecan be found, in the online version, at doi: 10.1016/j.inoche.2010.03.022.

References

[1] B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 111 (1989) 5962.[2] N.W. Ockwig, O. Delgado-Friedrichs, M. O'Keeffe, O.M. Yaghi, Acc. Chem. Res. 38

(2005) 176.[3] V.A. Friese, D.G. Kurth, Coord. Chem. Rev. 252 (2008) 199.[4] J.R. Long, O.M. Yaghi, Chem. Soc. Rev. 38 (2009) 1213 and reviews in the issue.[5] O. Kahn, C.J. Martinez, Science 279 (1998) 44.[6] A.B. Gaspar, V. Ksenofontov, M. Seredyuk, P. Gutlich, Coord. Chem. Rev. 249

(2005) 2661.[7] J.P. Zhang, X.M. Chen, J. Am. Chem. Soc. 130 (2008) 6010.[8] Y.Q. Huang, B. Ding, H.B. Song, B. Zhao, P. Ren, P. Cheng, H.G. Wang, D.Z. Liao, S.P.

Yan, Chem. Commun. (2006) 4906.

[9] E. Coronado, J.R. Galan-Mascaros, M. Monrabal-Capilla, J. Garcia-Martinez, P.Pardo-Ibanez, Adv. Mater. 19 (2007) 1359.

[10] Z.G. Gu, Y.F. Xu, X.H. Zhou, J.L. Zuo, X.Z. You, Cryst. Growth Des. 8 (2008) 1306.[11] B. Ding, Y.Y. Liu, Y.Q. Huang,W. Shi, P. Cheng, D.Z. Liao, S.P. Yan, Cryst. Growth Des.

9 (2009) 593.[12] B.X. Dong, Q. Xu, Inorg. Chem. 48 (2009) 5861.[13] C. Qin, X.L. Wang, L. Yuan, E.B. Wang, Cryst. Growth Des. 8 (2008) 2093.[14] X.R. Meng, Y.L. Song, H.W. Hou, H.Y. Han, B. Xiao, Y.T. Fan, Y. Zhu, Inorg. Chem. 43

(2004) 3528.[15] Synthesis of {[Fe(btx)3]·2ClO4}n (1): A mixture of MeOH and water (1:1, 5 mL)

was gently layered on the top of an aqueous solution (5 mL) of Fe(ClO4)2·6H2O(145.1 mg, 0.4 mmol) and ascorbic acid (10.0 mg, 0.057 mmol) in a straight glasstube. A solution of btx (48.1 mg, 0.2 mmol) in MeOH (5 mL) was added carefullyas a third layer. Block-shaped colorless crystals were obtained after a few days andcollected. Yield: 45% based on Fe. Elemental Anal. calcd (%) for C36H36Cl2FeN18O8:C 44.32, H 3.72, N 25.85; found: C 44.53, H 3.80, N 25.79.

[16] Synthesis of {[Fe(btx)(SO4)(H2O)2]}n (2): block-shaped colorless crystals of 2were obtained by similar synthetic procedure of 1 using FeSO4·7H2O instead of Fe(ClO4)2·6H2O. Yield: 62%, based on Fe. Elemental Anal. calcd (%) for C24H32Fe2N12O12S2: C 33.66, H 3.77, N 19.63; found: C 33.27, H 3.50, N 19.69.

[17] Single-crystal analyseswere performed on aRigaku Saturn 007 CCDdiffractometerwith Mo Ka radiation (λ=0.71073 Å) by the ω–φ scan technique. All data werecollected for absorption by semiempirical method. The structures were solvedprimarily by direct method with SHELXL-97 program. All non-hydrogen atomswere refined anisotropically. The hydrogen atoms were set in calculated positionsand refined as riding atoms with a common fixed isotropic thermal parameter.Crystal data for 1: Trigonal, space group P-3c1with a=11.116(2) Å, b=11.116(2)Å, c=22.058(4) Å, V=2360.4(7) Å3, Z=2, F(000)=1004, GOF=1.257,R1=0.1599, wR2=0.3995 [I N 2σ(I)]. Crystal data for 2: Triclinic, space groupP-1 with a=10.9258(3) Å, b=12.3827(7) Å, c=12.6162(6) Å, α=102.095(4)°,β=90.269(3) °, γ=102.022(4) °, V=1630.3(1) Å3, Z=2, F(000)=880, GOF=1.042, R1=0.0474, wR2=0.1309 [I N 2σ(I)]. The large R1 value of 1 comes fromboth the disorder of the benzene ring and low-quality of the crystal. However, it isthe best one can be obtained byus. The pure phase of 1 and2were verifiedby PXRD(Figure S1).

[18] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structures,University of Göttingen, Germany, 1997.

[19] G.M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structures,University of Göttingen, Germany, 1997.

[20] R.L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, 1986.[21] Y. Garcia, G. Bravic, C. Gieck, D. Chasseau, W. Tremel, P. Gultlich, Inorg. Chem. 44

(2005) 9723.