Assembly of Iron(II)-Triazole Polymers from 1D Chains to 3D

Mar 4, 2008 - Zhi-Guo Gu, Yi-Fan Xu, Xin-Hui Zhou, Jing-Lin Zuo* and Xiao-Zeng You. Coordination Chemistry Institute and the State Key Laboratory of ...
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CRYSTAL GROWTH & DESIGN

Assembly of Iron(II)-Triazole Polymers from 1D Chains to 3D Interpenetrated Frameworks: Syntheses, Structures, and Magnetic Properties

2008 VOL. 8, NO. 4 1306–1312

Zhi-Guo Gu, Yi-Fan Xu, Xin-Hui Zhou, Jing-Lin Zuo,* and Xiao-Zeng You Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, People’s Republic of China ReceiVed October 30, 2007; ReVised Manuscript ReceiVed December 17, 2007

ABSTRACT: By the reactions of FeX2 with R,ω-bis(1,2,4-triazol-1-yl)alkane ligands (X ) ClO4-, BF4-, NCS-, and NCSe-), a series of novel iron(II) coordination polymers have been synthesized and characterized. Complexes [Fe(btp)3](ClO4)2 (1a), [Fe(btp)3](BF4)2 (1b), and [Fe(btp)2(NCS)2] (2) (btp ) 1,3-bis(1,2,4-triazol-1-yl)propane) are infinite 1D-linear chains. [Fe(btb)3](ClO4)2 (3a) and [Fe(btb)3](BF4)2 (3b) (btb ) 1,4-bis(1,2,4-triazol-1-yl)butane) are 3-fold interpenetrated R-polonium cubic frameworks. The two sorts of btb ligands with different conformations alternately link to the Fe(II) centers in [Fe(btb)2(NCS)2] · H2O (4) to form a 3D interpenetrating architecture of CdSO4-like topology. When NCSe- instead of NCS- was used as the framework-regulator, a 2D grid layer [Fe(btb)2(NCSe)2] · 2H2O (5) was obtained. The counteranions, spacer length, and conformation of the R,ω-bis(1,2,4triazol-1-yl)alkane ligands are responsible for the assembled topological architectures. Magnetic studies indicate that all of these iron(II) polymers retain a high-spin ground state upon cooling from 300 to 4 K. Introduction Octahedral iron(II) complexes that undergo a spin crossover (SCO) between the low-spin 1A1 (S ) 0) state and the highspin 5T2 (S ) 2) state after external perturbation such as light irradiation or change of temperature or pressure have potential applications as molecular switches, data displays, memory devices, and intelligent contrast agents.1,2 Polyazole-based ligands exert a strong influence on the architecture and properties of the resulting metal complexes; interestingly, some iron(II) coordination polymers exhibit cooperative spin-crossover properties.3 Therefore, it is of great interest to investigate new iron(II) complexes with polyazole-based ligands. Recently, new flexible bispolyazole-type ligands containing 1-substituted tetrazole, 2-substituted tetrazole, and 1-substituted 1,2,3-triazole rings tethered by analkyl spacer, have been found to be very effective in the formation of extended iron(II) networks with interesting spin-crossover behaviors.4 The iron(II) complexes with 4-substituted 1,2,4-triazole family ligands show an abrupt spin transition above or near room temperature accompanied by a pronounced change of color.5 This prompted us to use 1-substituted 1,2,4-triazoles as donor groups for the preparation of new iron(II) coordination polymers. Whereas a variety of Mn(II), Co(II), Cu(II), Zn(II), and Cd(II) polymeric frameworks have been studied, iron(II) complexes with R,ωbis(1,2,4-triazol-1-yl)alkane ligands have never been documented.6 In order to investigate the influence of the flexibility of these ligands and coordination counteranions on the architecture of coordination polymers, we report in this paper the self-assembly reactions of the flexible ligands 1,3-bis(1,2,4triazol-1-yl)propane (btp) or 1,4-bis(1,2,4-triazol-1-yl)butane (btb) and iron(II) salts with different anions ClO4-, BF4-, NCS-, and NCSe- (Scheme 1). The structural and magnetic characterizations of seven diverse structural iron(II) coordination polymers, [Fe(btp)3](ClO4)2 (1a), [Fe(btp)3](BF4)2 (1b), [Fe(btp)2(NCS)2] (2), [Fe(btb)3](ClO4)2 (3a) [Fe(btb)3](BF4)2 * To whom correspondence should be addressed. E-mail: [email protected]. Fax: +86-25-83314502.

Scheme 1

(3b), [Fe(btb)2(NCS)2] · H2O (4), and [Fe(btb)2(NCSe)2] · 2H2O (5), are presented. Experimental Section General. All chemicals were reagent grade and used as received. The ligands btp and btb were prepared by modified literature methods.8 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 400–4000 cm-1 region. Thermogravimetric analyses (TGA) were carried out with a NETZSCH STA 449C unit at a heating rate of 10 °C/min under nitrogen. Magnetic susceptibility measurements of polycrystalline samples were measured over the temperature range of 4-300 K with a Quantum Design MPMSXL7 SQUID magnetometer and using an applied magnetic field of 2 kOe. Synthesis of [Fe(btp)3](ClO4)2 (1a) and [Fe(btp)3](BF4)2 (1b). An EtOH solution (5 mL) of btp (53 mg, 0.30 mmol) was diffused into an aqueous solution (5 mL) of Fe(ClO4)2 · 6H2O (36 mg, 0.10 mmol) and ascorbic acid (10 mg) in a straight glass tube. The presence of a small amount of ascorbic acid prevents air oxidation of FeII to FeIII. Blockshaped colorless single crystals of 1a were obtained after a few days and collected. They were washed with water and dried in air. Yield: 52%. Anal. Calcd for C21H30Cl2FeN18O8: C, 31.95; H, 3.83; N, 31.94. Found: C, 31.68; H, 3.92; N, 31.73. Selected IR (KBr, cm-1): 3128(s) (νC-H of the aromatic triazole rings); 2986(vw), 2965(w) (νC-H of the aliphatic C-H); 1521(s), 1460(s); 1287(s) (νC-C and νC-N of the triazole rings); 1130(w), 624(s) (ClO4-). Colorless crystals of 1b were also obtained by using Fe(BF4)2 · 6H2O as a starting material. Yield: 49%. Anal. Calcd for C21H30B2F8FeN18: C, 33.01; H, 3.96; N, 33.00. Found: C, 32.75; H, 3.99; N, 32.81. Selected IR (KBr, cm-1): 3132(s) (νC-H of the aromatic triazole rings); 2969(vw), 2865(w) (νC-H of the aliphatic C-H); 1521(s), 1460(s); 1523(s), 1462(s), 1288(s) (νC-C and νC-N of the triazole rings); 1130(w), 677(s) (BF4-). Synthesis of [Fe(btp)2(NCS)2] (2). A mixture of EtOH and water (1:1, 5 mL) was gently layered on the top of an aqueous solution (5

10.1021/cg7010666 CCC: $40.75  2008 American Chemical Society Published on Web 03/04/2008

Assembly of Iron(II)-Triazole Polymers mL) of Fe(ClO4)2 · 6H2O (36 mg, 0.10 mmol) and ascorbic acid (10 mg) in a straight glass tube. A solution of btp (36 mg, 0.20 mmol) and KNCS (19 mg, 0.20 mmol) in EtOH/H2O (2:1, 6 mL) was added carefully as a third layer. Block-shaped colorless crystals were obtained after a few days and collected. They were washed with water and dried in air. Yield: 45%. Anal. Calcd for C16H20FeN14S2: C, 36.37; H, 3.81; N, 37.11. Found: C, 36.10; H, 3.92; N, 36.95. Selected IR (KBr, cm-1): 3107(s) (νC-H of the aromatic triazole rings); 2944(vw), 2867(w) (νC-H of the aliphatic C-H); 2072(s) (νNCS); 1518(s), 1452(s), 1280(s) (νC-C and νC-N of the triazole rings). Synthesis of [Fe(btb)3](ClO4)2 (3a) and [Fe(btb)3](BF4)2 (3b). Block-shaped colorless crystals of 3a and 3b were obtained by adopting the same synthetic procedure of 1a and 1b only with use of btb instead of btp. For 3a, yield: 48%. Anal. Calcd for C72H108Cl6Fe3N54O24: C, 34.67; H, 4.36; N, 30.32. Found: C, 34.38; H, 4.49; N, 30.24. Selected IR (KBr, cm-1): 3133(s) (νC-H of the aromatic triazole rings); 2972(vw), 2879(w) (νC-H of the aliphatic C-H); 1520(s), 1465(s), 1278(s) (νC-C and νC-N of the triazole rings); 1129(w), 623(s) (ClO4-). For 3b, yield: 46%. Anal. Calcd for C72H108B6F24Fe3N54: C, 35.76; H, 4.50; N, 31.28. Found: C, 35.53; H, 4.59; N, 31.03. Selected IR (KBr, cm-1): 3140(s), (νC-H of the aromatic triazole rings); 2974(vw), 2860(w) (νC-H of the aliphatic C-H); 1522(s), 1466(s), 1278(s) (νC-C and νC-N of the triazole rings); 1128(s), 682(s) (BF4-). Synthesis of [Fe(btb)2(NCS)2] · H2O (4) and [Fe(btb)2(NCSe)2] · 2H2O (5). Block-shaped colorless single crystals of 4 were obtained by adopting the same synthetic procedure as that for 2 only with use of btb instead of btp. Yield: 42%. Anal. Calcd for C18H26FeN14OS2: C, 37.63; H, 4.56; N, 34.14. Found: C, 37.43; H, 4.65; N, 33.86. Selected IR (KBr, cm-1): 3131(s) (νC-H of the aromatic triazole rings); 2941(vw), 2875(w) (νC-H of the aliphatic C-H); 2070(s) (νNCS); 1524(s), 1468(s), 1283(s) (νC-C and νC-N of the triazole rings). The colorless crystals of 5 were also obtained by using KNCSe as a starting material. Yield: 35%. Anal. Calcd for C18H28FeN14O2Se2: C, 31.50; H, 4.11; N, 28.57. Found: C, 31.32; H, 4.20; N, 28.38. Selected IR (KBr, cm-1): 3132(s) (νC-H of the aromatic triazole rings); 2939(vw), 2817(w) (νC-H of the aliphatic C-H); 2091(s) (νNCSe); 1523(s), 1459(s), 1288(s) (νC-C and νC-N of the triazole rings). X-ray Crystallography. The crystal structures were determined on a Siemens (Bruker) SMART CCD diffractometer using monochromated Mo KR radiation (λ ) 0.71073 Å) at 293 K. Cell parameters were retrieved using SMART software and refined using SAINT9 on all observed reflections. Data were collected using a narrow-frame method with scan width of 0.30° in ω and an exposure time of 10 s/frame. The highly redundant data sets were reduced using SAINT9 and corrected for Lorentz and polarization effects. Absorption corrections were applied using SADABS10 supplied by Bruker. Structures were solved by direct methods using the program SHELXL-97.11 The positions of metal atoms and their first coordination spheres were located from directmethods E-maps; other nonhydrogen atoms were found in alternating difference Fourier syntheses and least-squares refinement cycles and, during the final cycles, refined anisotropically. Hydrogen atoms were placed in calculated positions and refined as riding atoms with a uniform value of Uiso. Final crystallographic data and values of R1 and wR are listed in Tables 1 and 2. Selected bond lengths and angles are listed in Table 3.

Results and Discussions Structure of [Fe(btp)3](ClO4)2 (1a) and [Fe(btp)3](BF4)2 (1b). Complexes 1a and 1b adopt very similar solid-state organizations to the recently reported spin-crossover complex [Fe(btzp)3](ClO4)2 (btzp ) 1,2-bis(tetrazol-1-yl)propane).7 The basic frameworks of 1a and 1b consist of one-dimensional cationic triple-stranded chains and anions of ClO4- or BF4-. The Fe(II) ion is in an octahedral environment formed by six crystallographically related N1-coordinating 4-triazole moieties (Figure 1). The Fe-N1 distances of 2.202(3) Å for 1a and 2.196(2) Å for 1b at 293 K correspond to the value expected for an Fe(II) ion in a high-spin state, lying within the range of 2.068–2.271 Å.12 The Fe(II) ions are linked by three 1,3bis(1,2,4-triazol-1-yl)propane ligands, leading to a regular triplestranded chain running along the c axis with Fe · · · Fe separations

Crystal Growth & Design, Vol. 8, No. 4, 2008 1307 Table 1. Crystallographic Data for Complexes 1a, 1b, and 2

formula fw crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Dcalcd, g cm-3 T, K µ, mm-1 θ, deg F(000) index ranges data/restraints/ params GOF (F2) R1,a wR2b (I > 2σ(I)) R1,a wR2b (all data) Rint a

1a

1b

2

C21H30Cl2FeN18O8 789.38 trigonal P3jc1 11.014(2) 11.014(2) 15.438(3) 90 90 120 1621.9(5) 2 1.616 293(2) 0.705 2.14–25.49 812 -10 e h e 13 -13 e k e 12 -18 e l e 17 1014/6/94

C21H30B2F8FeN18 764.10 trigonal P3jc1 10.971(6) 10.971(6) 15.291(3) 90 90 120 1594.1(4) 2 1.592 293(2) 0.568 2.14–28.07 780 -10 e h e 14 -14 e k e 13 -14 e l e 20 1285/4/94

C16H20FeN14S2 528.43 triclinic P1j 7.869(1) 8.604(2) 9.641(2) 77.951(4) 72.345(4) 66.951(4) 569.3(2) 1 1.541 293(2) 0.883 2.23–26.07 272 -6 e h e 9 -10 e k e 10 -7 e l e 11 2191/0/151

1.144 0.0663, 0.1549

1.005 0.0482, 0.1199

1.038 0.0417, 0.1136

0.0813, 0.1648

0.0665, 0.1266

0.0455, 0.1160

0.0649

0.0690

0.0439

R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑w(Fo - Fc ) /∑w(Fo2)]1/2. b

2

2 2

of 7.719 Å for 1a and 7.646 Å for 1b, as depicted in Figure 2. All the btp ligands adopt a gauche-gauche conformation with the shortest N · · · N distances of 5.311 Å in 1a and 5.234 Å in 1b between the two donor atoms and a dihedral angle of the two triazole rings of 36.6° and 35.3° in 1a and 1b, respectively. The Fe(II) triple-stranded chains perpendicular to the a axis and the linear chains are packed to form hexagonal cavities in the ab plane. The volumes of the effective void calculated using PLATON are 17.4% and 16.5% of the unit-cell volumes in 1a and 1b, respectively. The noncoordinated ClO4- or BF4- anions reside in the voids of this molecular architecture (Figure 3). There are no intermolecular contacts between the linear chains. Structure of [Fe(btp)2(NCS)2] (2). The structure of 2 exhibits a double-stranded chain. The iron(II) ion is in a distorted octahedral arrangement, in which the equatorial plane is formed by four triazole nitrogen atoms and the axial positions are occupied by two trans-isothiocyanate ligands (Figure 4). The Fe-NNCS distances [2.115(2) Å] are slightly shorter than the Fe-Nbtp distances [2.205(2) and 2.213(2) Å]. The connections between iron ions and NCS- groups are bent with a C-N-Fe angle of 153.0(2)°. Different from the ligand conformation found in 1a and 1b, the btp ligands exhibit the trans-gauche conformation in 2 with the shortest N · · · N distance of 7.533 Å and a dihedral angle of the two triazole rings of 106.1°. The Fe · · · Fe separation across the bridging btp ligand is 10.433 Å, ca. 2.7 Å longer than those in 1a and 1b. Two strands of btp ligands are wrapped around each other and are held together by Fe(II) ions, forming a double-stranded chain with 18membered rings (Figure 5). Structure of [Fe(btb)3](ClO4)2 (3a) and [Fe(btb)3](BF4)2 (3b). X-ray structural analysis revealed that 3a and 3b are composed of 3D R-polonium cubic networks with triple interpenetrating [Fe(btb)3]2+ macrocations and noncoordinated ClO4- or BF4- anions. The structures of 3a and 3b are very similar, and no detailed structural descriptions are presented here for 3b. In complex 3a, the asymmetric unit contains two parts and one anion of ClO4-, as shown in Figure 6. Part 1 contains

1308 Crystal Growth & Design, Vol. 8, No. 4, 2008

Gu et al.

Table 2. Crystallographic Data for Complexes 3a, 3b, 4, and 5

formula fw crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Dcalcd, g cm-3 T, K µ, mm-1 θ, deg F(000) index ranges data/restraints/params GOF (F2) R1,a wR2b (I > 2σ(I)) R1,a wR2b(all data) Rint a

3a

3b

4

5

C72H108Cl6Fe3N54O24 2494.37 trigonal R3j 19.061(7) 19.061(7) 25.329(7) 90 90 120 7970.5(8) 3 1.559 293(2) 0.650 2.03–25.00 3870 -22 e h e 22 -22 e k e 17 -30 e l e 26 3124/34/258 0.974 0.0608, 0.1282 0.1130, 0.1451 0.0816

C72H108B6F24Fe3N54 2418.53 trigonal R3j 19.030(8) 19.030(8) 25.288(3) 90 90 120 7931.7(1) 3 1.519 293(2) 0.518 2.03–28.02 3726 -15 e h e 25 -25 e k e 25 -25 e l e 33 4171/7/268 1.041 0.1082, 0.1489 0.2237, 0.1879 0.1171

C18H26FeN14OS2 574.50 monoclinic P2/c 8.998(2) 9.709(2) 15.555(4) 90 91.066(4) 90 1358.7(6) 2 1.404 293(2) 0.748 2.26–26.09 596 -10 e h e 10 -9 e k e 11 -19 e l e 18 2666/2/189 1.039 0.0434, 0.1220 0.0509, 0.1269 0.0719

C18H28FeN14O2Se2 686.31 triclinic P1j 7.699(8) 9.434(2) 10.527(2) 114.725(3) 90.979(3) 96.368(4) 688.5(3) 1 1.655 293(2) 3.235 2.14–25.99 344 -8 e h e 9 -11 e k e 11 -12 e l e 12 2621 /0/ 169 0.959 0.0371, 0.0957 0.0448, 0.0992 0.0724

R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo2)]1/2.

Table 3. Selected Bond Lengths (Å) and Angles (deg) for Complexes 1–5 Complex 1a Fe(1)-N(1) N(1)-Fe(1)-N(1)

2.202(3) 180.00(2)

Fe(1)-N(1) N(1)-Fe(1)-N(1)

2.196(2) 180.00(1)

N(1)-Fe(1)-N(1) N(1)-Fe(1)-N(1)

90.01(1) 89.99(1)

Complex 1b N(1)-Fe(1)-N(1) N(1)-Fe(1)-N(1)

90.17(7) 89.83(7)

Complex 2 Fe(1)-N(1) Fe(1)-N(5) N(1)-Fe(1)-N(2) N(2)-Fe(1)-N(5)

2.115(2) 2.213(2) 90.62(8) 92.66(7)

Fe(1)-N(1) Fe(2)-N(7) N(4)-Fe(1)-N(4) N(7)-Fe(2)-N(7) N(7)-Fe(2)-N(7) N(4)-Fe(1)-N(1)

2.211(3) 2.175(4) 90.91(4) 91.72(2) 180.00(2) 177.43(1)

Fe(1)-N(2) C(1)-N(1)-Fe(1) N(1)-Fe(1)-N(5) N(1)-C(1)-S(1)

2.205(2) 153.0(2) 90.05(8) 177.4(2)

Complex 3a Fe(1)-N(4)

2.188(4)

N(1)-Fe(1)-N(1) N(7)-Fe(2)-N(7) N(4)-Fe(1)-N(1) N(4)-Fe(1)-N(1)

88.86(1) 88.28(2) 88.62(1) 91.62(1)

Figure 1. View of the coordination environment of iron(II) ions in 1a with thermal ellipsoids drawn at the 30% probability level. Noncoordinated ClO4- anion is omitted for clarity.

Complex 3b Fe(1)-N(1) Fe(2)-N(7) N(4)-Fe(1)-N(4) N(7)-Fe(2)-N(7) N(7)-Fe(2)-N(7) N(4)-Fe(1)-N(1)

2.205(4) 2.182(6) 90.57(17) 91.6(3) 179.99(7) 89.29(16)

Fe(1)-N(4)

2.189(4)

N(1)-Fe(1)-N(1) N(7)-Fe(2)-N(7) N(4)-Fe(1)-N(1) N(4)-Fe(1)-N(1)

89.03(2) 88.4(3) 91.12(16) 178.30(17)

Complex 4 Fe(1)-N(1) Fe(1)-N(5) N(1)-Fe(1)-N(2) N(2)-Fe(1)-N(5)

2.112(2) 2.194(2) 89.41(8) 86.88(7)

Fe(1)-N(2) C(1)-N(1)-Fe(1) N(1)-Fe(1)-N(5) N(1)-C(1)-S(1)

2.201(2) 177.8(3) 89.51(8) 163.4(4)

Complex 5 Fe(1)-N(1) Fe(1)-N(5) N(1)-Fe(1)-N(2) N(2)-Fe(1)-N(5)

2.142(2) 2.183(2) 90.34(9) 88.01(9)

Fe(1)-N(2) C(1)-N(1)-Fe(1) N(1)-Fe(1)-N(5) N(1)-C(1)-Se(1)

2.189(2) 154.0(2) 91.73(1) 176.4(3)

one Fe(II) ion and one btb molecule, while part 2 contains one Fe(II) ion and half of one btb ligand. The site occupation factors of iron(II) ions in part 1 and part 2 are 1/3 and 1/6, respectively.

Figure 2. View of the 1D chain in 1a along the a axis. Hydrogen atoms and perchlorate are omitted for clarity.

The iron(II) ions in both part 1 and part 2 are coordinated by six 4-triazole nitrogen atoms in the form of an almost regular FeN6 octahedron. The Fe-N bond lengths (2.175(4)-2.211(3) Å) show clearly that they are divalent iron ions in a high-spin state. The N-Fe-N bond angles are close to 90°. All the btb ligands bridge two adjacent iron(II) atoms, and simultaneously, the six btb molecules are coordinated to one central iron(II) atom, leading to an open 3D network with R-polonium topology (Figure 7). Interestingly, there are two independent but quite similar such 3D cubic networks in 3a, A and B. While the A networks are single, those of type B are 2-fold interpenetrated (Figure 8a). This is possible because of the flexibility of the btb ligands with different conformations in the networks of type A and B. The btb ligands adopt the trans-trans conformation

Assembly of Iron(II)-Triazole Polymers

Figure 3. View of stacking of the chains in 1a along the c axis.

Figure 4. View of the coordination environment of iron(II) ions in 2 with thermal ellipsoids drawn at the 30% probability level.

Crystal Growth & Design, Vol. 8, No. 4, 2008 1309

Figure 7. View of the 3D R-polonium cubic network in 3a. Hydrogen atoms and perchlorate are omitted for clarity.

Figure 8. (a) View of two types of 3D nets in 3a and (b) schematic drawing of the 3-fold interpenetrated 3D structure of 3a.

Figure 5. View of the 1D chain in 2 along the c axis.

Figure 9. View of the 3D R-polonium cubic network in 3a along the c axis. Figure 6. View of the coordination environment of iron(II) ions in 3a with the thermal ellipsoids drawn at the 30% probability level. Noncoordinated ClO4- anion is omitted for clarity.

in the networks of type A and trans-gauche conformation in the networks of type B, with the shortest N · · · N distances of 10.155 and 9.570 Å and dihedral angles of the two triazole rings of 180° and 169.0° for types A and B, respectively. Surprisingly,

although the btb ligands adopt different conformations, the Fe-Fe separations (13.871 Å) are the same in the two types of networks. The two different structural motifs interlock with each other to form 3-fold interpenetrating cubic networks (Figure 8b). Furthermore, channels with dimensions of approximately 9 × 9 Å2 are formed, which are filled by ClO4- anions (Figure 9). The volume of the effective void calculated using PLATON is 20.0% of the unit-cell volume. The structure of 3a is very

1310 Crystal Growth & Design, Vol. 8, No. 4, 2008

Figure 10. View of the coordination environment of iron(II) ions in 4 with thermal ellipsoids drawn at the 30% probability level. Noncoordinated water molecule is omitted for clarity.

interesting: it has similar 3D cubic networks A and B in the same crystal and has a new (3D + 3D) type of entanglement. To the best of our knowledge, there are rare examples of different interlocked motifs with the same dimension: (1D + 1D) type13 and (2D + 2D) type.14 Structure of [Fe(btb)2(NCS)2] · H2O (4). The structure of 4 is a three-dimensional network of four-connected nodes with the (658) CdSO4 topology. The network appears distorted in contrast to the ideal tetragonal net (Figure 11a). The coordination geometry of the iron atoms is very similar to that observed in the 1D polymer of 2 [Fe-NNCS: 2.112(2) Å, Fe-Nbtb: 2.201(2) Å, 2.194(2) Å)] (Figure 10). Each iron(II) center, linked by four btb ligands, acts as the square-planar node. The btb ligands exhibit two different conformations: a combination of trans-trans isomers (shortest N · · · N and Fe · · · Fe distances of 9.024 and 13.237 Å and dihedral angles of the two triazole rings of 180°) and iron(II) nodes form 1D undulating chains, which are further alternately connected along two perpendicular directions by the coordination of trans-gauche isomers (shortest N · · · N and Fe · · · Fe distances of 8.771 and 12.002 Å and dihedral angles of the two triazole rings of 146.4°) with iron(II) nodes. Consequently, a 3D network with a CdSO4-type topology is generated. The most striking feature of complex 4 is that a pair of identical CdSO4-like nets is interlocked with each other, thus directly leading to the formation of the 2-fold interpenetrated 3D f 3D architecture (Figure 11b). Although a number of CdSO4-like frameworks have been reported, there are only a few compounds that exhibit interpenetration.15 Furthermore, the CdSO4-like architecture of 4 produces channels that have an opening of about 18 × 7 Å2. The 2-fold interpenetration of CdSO4-like networks in the crystal effectively reduces the void space, and it still shows a porous structure. The volume of the

Gu et al.

effective void calculated using PLATON is 9.7% of the unitcell volume in the self-inclusion structure, which is occupied by the noncoordinated water molecules (Figure 12). Structure of [Fe(btb)2(NCSe)2] · 2H2O (5). The structure of complex 5 is comprised of 2D undulated layers of grid meshes. The iron(II) atom in 5 is in a distorted octahedral arrangement with two NCSe- groups in trans positions (Fe-NNCSe 2.142(2) Å) and four triazole nitrogen atoms in a basal plane (Fe-Nbtb 2.183(2) Å, 2.189(2) Å) (Figure 13). The connection between Fe atoms and NCSe- groups is bent with a C-N-Fe angle of 154.0(2)°. Each btb ligand connects two iron(II) ions to form a two-dimensional (4,4) network containing square Fe4(btb)4 units shown in Figure 14. The basic grid of the two-dimensional network is puckered due to the two kinds of trans-gauche conformations of the btb ligands in complex 5 with the shortest N · · · N distances of 8.819 Å and 9.069 Å, and dihedral angles of the two triazole rings of both 180°. The Fe · · · Fe separation across the bridging btb is 12.536 and 13.148 Å. The adjacent 2D layers repeat in an · · · ABCABC · · · stacking sequence, and significant intermolecular Se · · · Se (3.546 Å) interactions exist in both adjacent AA, BB, and CC layers, forming three independent three-dimensional supramolecular frameworks interlocked with each other with channels filled by solvated water molecules (Figure 15). Scheme 2 summarizes the assembly of different topological architectures by anion replacement, spacer length, and conformation of the R,ω-bis(1,2,4-triazol-1-yl)alkane ligands. ClO4and BF4- anions induce the formation of 1D triple-stranded chains with btp ligands for 1 and 3-fold interpenetrating R-polonium cubic networks with btb ligands for 3. NCS- anions tune 1D double-stranded chain with btp ligands for 2 and CdSO4-like architecture with btb ligands for 4, while NCSeanions tune 2D undulated grid layers with btb ligands for 5. The flexible btp ligands exhibit gauche-gauche and transgauche conformations in 1 and 2, respectively. The btb ligands in both 3 and 4 adopting two different conformations of trans-trans and trans-gauche afford two similar frameworks interlocking with each other in 3 and 2-fold interpenetrating 3D CdSO4-like architecture in 4. The basic grid of the 2D network is puckered due to the two kinds of trans-gauche conformations of the btb ligands in complex 5. These results demonstrated that for the iron(II) R,ω-bis(1,2,4-triazol-1-yl)alkane system, counteranions, spacer length, and conformations of the ligands show significant effects on the assembled topological architectures. Magnetic Properties. The temperature-dependent magnetic susceptibility data of complexes 1–5 have been measured for polycrystalline samples in the temperature range of 4–300 K. As shown in Figure 16, the µeff values at 300 K for complexes 1–5 correspond to the expected value for a HS iron(II) ion.

Figure 11. (a) View of a portion of the 3D net in 4 with CdSO4 topology, in which hydrogen atoms and NCS- are omitted for clarity, and (b) schematic representation of the 3D interpenetration mode of 4.

Assembly of Iron(II)-Triazole Polymers

Crystal Growth & Design, Vol. 8, No. 4, 2008 1311

Figure 15. View of the 3-fold interpenetration of the 3D supramolecular cubic network in 5. Se · · · Se interactions are shown as dash lines. Figure 12. View of the 2-fold interpenetrated CdSO4-like network in 4 along the c axis showing one cavity filled by noncoordinated water molecules.

Figure 13. View of the coordination environment of iron(II) ions in 5 with thermal ellipsoids drawn at the 30% probability level. Noncoordinated water molecule is omitted for clarity.

Scheme 2. Schematic Showing the Coordination Topologies in 1–5

K. The decrease below ca. 50 K can be attributed to very weak antiferromagnetic interactions as indicated by large metal-metal distances or the presence of zero-field splitting or both. The same magnetic behavior was observed in the warming mode. The inverse molar magnetic susceptibility, 1/χM, of 1–5 are linear between 50 and 300 K and the linear least-squares fits yield the Curie constant of ca. 3.26 cm3 K mol-1 for 1–5. Obviously, complexes 1–5 showed no detectable thermal spincrossover behaviors. Such lack of spin-crossover behavior has also been found in a few other polymeric iron(II) complexes with bis-1,2,4-triazole ligands.16 Thermogravimetric Analysis. The decomposition behaviors of 1–5 were examined via thermogravimetric analysis (TGA)

Figure 14. View of the undulating 2D (4,4) network in 5 along the b axis.

When the temperature is lowered, µeff values for 1–5 remain constants down to ca. 50 K and then smoothly decrease and drop rapidly below ca. 20 K reaching the minimum values at 4

Figure 16. µeff and 1/χM versus T product for 1–5 at 2 kOe.

1312 Crystal Growth & Design, Vol. 8, No. 4, 2008

Figure 17. Thermogravimetric curves for 1–5.

(Figure 17). TGA curves of 1–3 are similar and exhibit one main step of weight loss corresponding to the combustion of the organic groups. The TGA traces of 4 and 5 are similar, and each exhibits three main steps of weight losses. The first step started at 40 °C and completed at ca. 110 °C, which corresponds to the release of lattice water molecules. The observed weight loss of 2.9% (for 4) and 4.9% (for 5) are close to the calculated values (3.1% for 4 and 5.2% for 5). The second step covers from 200 to 350 °C for 4 and 200 to 280 °C for 5, during which the organic groups are partially burned. The third step, 490 to 610 °C for 4 and 320 to 420 °C for 5, corresponds to the further decomposition of the compound. Conclusion In summary, using various anions in the synthesized systems of R,ω-bis(1,2,4-triazol-1-yl)alkane and iron(II) ions in H2O/ EtOH solution, we successfully isolated seven novel coordination polymers with five kinds of coordination topologies: 1D triple-stranded chain, 1D double-stranded chain, 3-fold interpenetrating R-polonium cubic network, 2-fold interpenetrating 3D CdSO4-like architecture, and 2D undulated grid layer. Magnetic studies indicate that 1–5 show no detectable thermal spin-crossover behaviors. Further investigations on iron(II) polyazole compounds with both interesting structures and magnetic properties are currently underway in our laboratory. Acknowledgment. This work was supported by the Major StateBasicResearchDevelopmentProgram(Grants2006CB806104 and 2007CB925100), the National Science Fund for Distinguished Young Scholars (Grant 20725104), the National Natural Science Foundation of China (Grant 20721002), and National Fund for Fostering Talents of Basic Science (Grant J0630425). Supporting Information Available: X-ray crystallographic files in CIF format for 1–5. This material is available free of charge via the Internet at http://pubs.acs.org.

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