Syntheses, Crystal Structures, and Magnetic Properties of Novel

CRYSTAL GROWTH & DESIGN

Syntheses, Crystal Structures, and Magnetic Properties of Novel Copper(II) Complexes with the Flexible Bidentate Ligand 1-Bromo-3,5-bis(imidazol-1-ylmethyl)benzene

2006 VOL. 6, NO. 9 2092-2102

Wen-Li Meng,† Guang-Xiang Liu,† Taka-aki Okamura,‡ Hiroyuki Kawaguchi,§ Zheng-Hua Zhang,† Wei-Yin Sun,*,† and Norikazu Ueyama‡ Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, China, Department of Macromolecular Science, Graduate School of Science, Osaka UniVersity, Toyonaka, Osaka 560-0043, Japan, and Coordination Chemistry Laboratories, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan ReceiVed May 25, 2006; ReVised Manuscript ReceiVed July 19, 2006

ABSTRACT: Seven new metal-organic frameworks (MOFs) [Cu(bib)2(H2O)2](Cl3CCOO)2‚2MeOH‚2H2O (1), [Cu(bib)2]Cl2‚H2O (2), [Cu(bib)2(SO4)(H2O)]‚4H2O (3), [Cu(bib)(SO4)(H2O)2] (4), [Cu(bib)(N3)(OAc)]‚DMF (5) (OAc ) acetate), [Cu(bib)(ox)]‚MeOH‚ 2H2O (6) (ox ) oxalate), and [Cu(bib)(mal)]‚MeOH (7) (mal ) malonate) were obtained by reactions of flexible bidentate ligand 1-bromo-3,5-bis(imidazol-1-ylmethyl)benzene (bib) with corresponding copper(II) salts. The structures of these MOFs were established by single-crystal X-ray diffraction analysis. Complexes 1 and 2 have similar one-dimensional (1D) hinged chain structure. Complex 3 has a 2D network structure with (4,4) topology. Complex 4 has M2L2 metallocyclic ring structure and the rings are further linked by the sulfate anions to form a 1D tube-like chain. Complex 5 is also a dinuclear M2L2 metallocyclic ring, which is further connected by Br‚‚‚Br interactions to form 1D chain. While in the cases of complexes 6 and 7, both have 2D network structure in which the oxalate and malonate anions act as bridging ligands. The results showed that the counteranions play important roles in the construction of MOFs. In addition, the magnetic properties of complexes 6 and 7 were investigated. The results show that weak ferromagnetic interactions occurred between the copper(II) ions linked by the oxalate anions in complex 6, and there is no obvious magnetic interaction between the copper(II) ions bridged by the malonate anions in complex 7. Introduction Construction of metal-organic frameworks (MOFs) from metal salts and bridging ligands has been a hot research field in recent years due to the interesting structures of MOFs, such as cage,1 honeycomb,2 herringbone,3 rotaxanes, catenanes,4 etc., as well as the potential applications of MOFs in many areas such as magnetism,5 catalysis,6 and molecular recognition and sorption.7 The results of previous studies showed that the structure and properties of MOFs depend on factors such as the metal ions with definite coordination geometry, the nature of organic ligands, the counteranions, the reaction conditions, and so on. For example, copper(II), cobalt(II), nickel(II), and manganese(II) ions with unpaired electrons are often employed for the syntheses of complexes with magnetic properties,8 while lanthanide ions with f-f electronic transitions are often used to prepare complexes with luminescent properties.9 With regard to counteranions, on one hand, they can influence the structure of MOFs by playing different roles in the structure: bridging the metal ions,10,11a coordinating with them as terminal coligands,11 or without coordinating with the metal ions but still having template effects on the structures of MOFs.12 On the other hand, some bridging anions are efficient magnetic couplers, for example, the azide,13 oxalate anions,13c,14 and so on; thus, they can play important roles in the MOFs with magnetic properties. In addition, the nature of organic ligands has significant impacts on the structures and properties of MOFs. In particular, the use of flexible donor components could produce intriguing structures. For example, when the flexible * To whom correspondence should be addressed. Phone: +86-2583593485. Fax: +86-25-83314502. E-mail: [email protected]. † Nanjing University. ‡ Osaka University. § Institute for Molecular Science.

bridging ligand 1,4-bis(imidazol-1-ylmethyl)-benzene (bix) reacted with silver(I) nitrate or zinc(II) nitrate hexahydrate, a twodimensional (2D) polyrotaxane network was obtained.15a,15b In addition, an infinite 1D chain was obtained by the reaction of bix with manganese(II) nitrite,15c and an infinite three-dimensional (3D) entanglement network was obtained by the reaction between bix and cobalt(II) sulfate.15d Therefore, it is an efficient way to construct MOFs with a discreet selection of metal ions and counteranions, and the rational design of organic ligands. In our previous studies, we focused our attention on the construction of MOFs with varied metal salts and flexible bidentate ligands, for example, 4,4′-bis(imidazol-1-ylmethyl)biphenyl (bimb),16 1,3-bis(imidazol-1-ylmethyl)-5-methylbenzene (dimb),17 and 1-bromo-3,5-bis(imidazol-1-ylmethyl)benzene (bib).18 Since oxalate and malonate anions are versatile multidentate bridging ligands as well as efficient magnetic couplers, while sulfate, azide anions, and others can act as bridging ligands or terminal co-ligands, such kinds of counteranions are expected to have significant impacts on the structure and properties of complexes. To further investigate the effect of anions on the structure of MOFs, reactions of bib with varied copper(II) salts were carried out. In this paper, we report the syntheses, crystal structures, and properties of seven new coordination complexes, namely, [Cu(bib)2(H2O)2](Cl3CCOO)2‚ 2MeOH‚2H2O (1), [Cu(bib)2]Cl2‚H2O (2), [Cu(bib)2(SO4)(H2O)]‚4H2O (3), [Cu(bib)(SO4)(H2O)2] (4), [Cu(bib)(N3)(OAc)]‚DMF (5) (OAc ) acetate), [Cu(bib)(ox)]‚MeOH‚2H2O (6) (ox ) oxalate), and [Cu(bib)(mal)]‚MeOH (7) (mal ) malonate). In addition, the magnetic properties of complexes 6 and 7 were measured and discussed. Experimental Section All commercially available chemicals are of reagent grade and used as received without further purification. The ligand bib was prepared

10.1021/cg060304i CCC: $33.50 © 2006 American Chemical Society Published on Web 08/22/2006

1-Bromo-3,5-bis(imidazol-1-ylmethyl)benzene Complexes

Crystal Growth & Design, Vol. 6, No. 9, 2006 2093

Table 1. Crystal Data and Refinement Results for Complexes 1-7

a

complex

1

2

3

empirical formula formula weight crystal system space group Flack parameter a/Å b/Å c/Å R/° β/° γ/° V (Å3) Z T/K µ (mm-1) Dcalcd (g cm-3) λ (Å) Rint Ra/wRb

C34H42Br2Cl6CuN8O10 1158.82 triclinic P1h

C28H28Br2Cl2CuN8O 786.84 triclinic P1h

C28H36Br2CuN8O9S 884.07 monoclinic P21/c

8.421(5) 11.493(6) 13.234(7) 78.107(14) 72.502(19) 78.524(18) 1182.3(11) 1 200 2.550 1.628 0.71075 0.0634 0.0523/0.0535

8.952(13) 9.096(10) 10.114(12) 81.39(3) 86.47(4) 88.22(4) 812.5(18) 1 200 3.331 1.608 0.71075 0.1387 0.0615/0.0713

8.535(5) 9.280(4) 21.923(9) 90.00 94.810(17) 90.00 1730.3(14) 2 200 3.064 1.697 0.71075 0.1017 0.0644/0.1253

complex

4

5

6

7

empirical formula formula weight crystal system space group Flack parameter a/Å b/Å c/Å R/° β/° γ/° V (Å3) Z T/K µ (mm-1) Dcalcd (g cm-3) λ (Å) Rint Ra/wRb

C14H17BrCuN4O6S 512.82 triclinic P1h

C19H23BrCuN8O3 554.89 triclinic P1h

C17H21BrCuN4O7 536.83 monoclinic P21/c

7.141(3) 10.934(4) 11.979(5) 102.289(7) 97.310(4) 93.600(5) 902.5(6) 2 173.1 3.587 1.887 0.7107 0.022 0.0310/0.0910

9.2445(7) 11.1244 12.2060(13) 72.91(2) 88.68(2) 74.172(13) 1152.1(2) 2 173.1 2.725 1.599 0.7107 0.027 0.0390/0.1040

9.785(4) 8.912(3) 23.822(9) 90 91.540(6) 90 2076.6(14) 4 173.1 3.029 1.717 0.7107 0.030 0.0480/0.1520

C18H19BrCuN4O5 514.82 monoclinic P21 0.35(4) 9.240(5) 9.061(5) 11.600(6) 90 91.023(6) 90 971.1(9) 2 173.1 3.227 1.761 0.7107 0.025 0.0440/0.1420

R )∑||Fo| - |Fc||/∑|Fo|. b Rw ) |∑w(|Fo|2 - |Fc|2)|/∑|w(Fo)2|1/2, where w ) 1/[σ2(Fo2) + (aP)2 + bP]. P ) (Fo2 + 2Fc2)/3.

as reported previously.18 Solvents were purified according to the standard methods. C, H, and N analyses were made on a Perkin-Elmer 240C elemental analyzer at the analysis center of Nanjing University. Infrared (IR) spectra were recorded on a Bruker model Vector22 FTIR spectrophotometer, using KBr disks. Thermogravimetric analyses were performed on a simultaneous SDT 2960 thermal analyzer. Powder samples were loaded into alumina pans and heated under N2 at a heating rate of 20 °C/min. Powder X-ray diffraction patterns were taken on a Rigaku D/max-RA rotating anode X-ray diffractometer with graphitemonochromatic Cu KR (λ ) 1.542 Å) radiation at room temperature. Magnetic measurements in the range of 1.8-300 K were performed on a MPMS-SQUID magnetometer at a field of 2000 G on crystalline samples in the temperature settle mode. The diamagnetic contributions of the samples were corrected by using Pascal’s constants. Synthesis of [Cu(bib)2(H2O)2](Cl3CCOO)2‚2MeOH‚2H2O (1). The compound was prepared by a layering method. A buffer layer of a solution (5 mL) of methanol and water (1:1) was carefully layered over an aqueous solution (3 mL) of Cu(Cl3CCOO)2 (38.8 mg, 0.1 mmol). Then a solution of bib (31.7 mg, 0.1 mmol) in methanol (5 mL) was layered over the buffer layer. Blue platelet crystals were obtained after two weeks. Yield 62%. The crystal easily loses solvent molecules at room temperature. Anal. Calcd for C32H26Br2Cl6CuN8O4 (uncoordinated methanol and water molecules were lost upon drying): C 37.58; H 2.56; N 10.96. Found: C 37.37; H 2.49; N 10.95. IR (KBr, cm-1): 3441 br, 1674 vs, 1522 m, 1441 w, 1320 m, 1246 w, 1109 m, 1093 m, 1031 w, 830 m, 743 m, 675 m. Synthesis of [Cu(bib)2]Cl2‚H2O (2). An aqueous solution (5 mL) of CuCl2‚2H2O (8.5 mg, 0.05 mmol) was added slowly with constant stirring to a solution of bib (31.7 mg, 0.1 mmol) in acetonitrile (10 mL) to give a clear solution. The reaction mixture was left to stand at room temperature. Blue crystals were obtained after two weeks. Yield

33%. Anal. Calcd for C28H28Br2Cl2CuN8O: C 42.74; H 3.58; N 14.24. Found: C 42.77; H 3.65; N 14.24. IR (KBr, cm-1): 3416 br, 3125 m, 1636 w, 1606 m, 1523 s, 1441 m, 1405 w, 1357 w, 1236 m, 1107 s, 1092 s, 1029 m, 946 w, 868 w, 740 s, 661 s. Syntheses of [Cu(bib)2(SO4)(H2O)]‚4H2O (3) and [Cu(bib)(SO4)(H2O)2] (4). These two compounds were obtained simultaneously by the reaction of bib with CuSO4‚5H2O. A buffer layer of a solution (5 mL) of methanol and water (1:1) was carefully layered over an aqueous solution (3 mL) of CuSO4‚5H2O (25.0 mg, 0.1 mmol). Then a solution of bib (31.7 mg, 0.1 mmol) in methanol (5 mL) was layered over the buffer layer. Two clearly distinct crystals appeared in the test tube after two weeks. One was a dark-blue platelet crystal (3) in the middle of the test tube. Yield 42%. Anal. Calcd for C28H36Br2CuN8O9S: C 38.04; H 4.10; N 12.68. Found: C 38.11; H 4.15; N 12.59. IR (KBr, cm-1): 3422 br, 3126 m, 1636 m, 1577 m, 1523 s, 1440 m, 1403 w, 1245 m, 1115 vs, 950 w, 739 m, 661 m, 625 m. The other one was a light-blue platelet crystal (4) near the bottom of the test tube. Yield 18%. Anal. Calcd for C14H17BrCuN4O6S: C 32.79; H 3.34; N 10.93. Found: C 32.74; H 3.16; N 10.86. IR (KBr, cm-1): 3419 br, 3123 m, 1609 w, 1576 w, 1526 m, 1433 m, 1362 m, 1290 m, 1240 m, 1167 m, 1091 s, 1049 s, 947 m, 835 m, 764 m, 662 m, 619 m. Synthesis of [Cu(bib)(N3)(OAc)]‚DMF (5). A methanol solution (5 mL) of bib (31.7 mg, 0.1 mmol) was added dropwise to Cu(OAc)2‚ H2O (20.0 mg, 0.1 mmol) and NaN3 (6.5 mg, 0.1 mmol) in methanol (5 mL) to give a green precipitate. After the sample was stirred for 15 min at room temperature, the precipitate was isolated, dissolved in DMF (10 mL), and filtered. Blue prism crystals were obtained by slow diffusion of diethyl ether into the above filtrate over 3 days. Yield 70%. Anal. Calcd for C19H23BrCuN8O3: C 41.13; H 4.17; N 20.19. Found: C 41.10; H 4.13; N 20.23. IR (KBr, cm-1): 3441 br, 3129 m, 2958 vs,

2094 Crystal Growth & Design, Vol. 6, No. 9, 2006

Meng et al.

Table 2. Selected Bond Distances [Å] and Angles [deg] for Complexes 1-7a Cu1-N12 Cu1-O11 N12#1-Cu1-N12 N12-Cu1-N32

[Cu(bib)2(H2O)2](Cl3CCOO)2‚2MeOH‚2H2O (1) 2.017(3) Cu1-N32 2.477 180.0 N12#1-Cu1-N32 88.21(13) N32#1-Cu1-N32

2.023(4) 91.79(13) 180.0

[Cu(bib)2]Cl2‚H2O (2) Cu1-N32#2 N32#2-Cu1-N32#3 N32#3-Cu1-N12 Cu1-N12 Cu1-O11 N12-Cu1-N12#5 N12-Cu1-N32 O11-Cu1-O11#5

2.001(11) 180.0 86.7(4)

Cu1-N12 N32#2-Cu1-N12 N12-Cu1-N12#4

[Cu(bib)2 (SO4)(H2O)]‚4H2O (3) 1.995(4) Cu1-N32 2.563 180.0 N12#5-Cu1-N32 90.89(15) N32-Cu1-N32#5 180.0

2.036(8) 93.3(4) 180.0 2.013(4) 89.11(15) 180.0

[Cu(bib)(SO4)(H2O)2] (4) Cu1-O1 Cu1-N1 Cu1-O4 O1-Cu1-O2 O2-Cu1-N1 N4#3-Cu1-O1 O5#6-Cu1-O4 Cu1-O1 Cu1-N5 O1-Cu1-N1 N1-Cu1-N5 Cu1-O1 Cu1-O3 Cu1-N1 O1-Cu1-O3 O3-Cu1-N1 N1-Cu1-N3#10 O4#9-Cu1-N3#10 O2#8-Cu1-N1 O2#8-Cu1-O4#9 Cu1-O1 Cu1-O3 Cu1-N3#12 O1-Cu1-O3 O3-Cu1-N1 N1-Cu1-N3#12 O2#11-Cu1-O3

2.004(2) 2.012(2) 2.440(2) 90.52(7) 88.42(7) 88.7 173.79 1.976(3) 1.969(3) 89.5(1) 96.4(1)

Cu1-O2 Cu1-N4#3 Cu1-O5#6 O1-Cu1-N1 N4#3-Cu1-O2 N4#3-Cu1-N1

1.975(2) 1.973(2) 2.574(2) 169.36(7) 175.5 93.2

[Cu(bib)(N3)(OAc)]‚DMF (5) Cu1-N1 Cu1-N3#7 O1-Cu1-N5 N1-Cu1- N3#7

1.979(2) 1.982 160.7(2) 159.0

[Cu(bib)(ox)]‚MeOH‚2H2O (6) 2.007(2) Cu1-O2#8 2.006(2) Cu1-O4#9 1.995(3) Cu1-N3#10 86.62(9) O1-Cu1-N1 171.5(1) N3#10-Cu1-O3 92.7 O2#8-Cu1-N3#10 92.8 O4#9-Cu1-N1 97.6 O1-Cu1-N3#10 163.9° 1.919(7) 1.977(4) 1.994 91.2(2) 88.4(2) 90.3 94.0

[Cu(bib)(mal)]‚MeOH (7) Cu1-O2#11 Cu1-N1 O1-Cu1-N1 O1-Cu1-O2#11 O2#11-Cu1-N3#12 O2#11-Cu1-N1

2.333 2.308 2.005 91.1(1) 90.4 97.4 94.2 173.4°

2.261 1.998(5) 156.6(2) 112.8 89.8 90.6

a Symmetry transformations used to generate equivalent atoms: #1: 2 + x, 1 -y, -z. #2: x, y, -1 + z. #3: 1 - x, -y, 1 - z. #4: 1 - x, -y, -z. #5: -x, -y, 1 - z. #6: 1 + x, y, z. #7: -x, 1 - y, 1 - z. #8: 1 - x, -y, 2 - z. #9: 1 - x, 2 - y, 2 - z. #10: -x, 1/2 + y, 3/2 - z. #11: -1 - x, 1/2 + y, -1 - z. #12: -x, -1/2 + y, -2 - z.

1670 vs, 1575 s, 1520 m, 1399 m, 1340 w, 1239 m, 1093 m, 951 w, 864 w, 754 w, 655 w. Caution. Azide salt of metal complexes with organic ligands is potentially explosiVe and should be handled with care. Synthesis of [Cu(bib)(ox)]‚MeOH‚2H2O (6). An aqueous solution (10 mL) of Cu(NO3)2‚3H2O (24.1 mg, 0.1 mmol) and K2(ox)‚H2O (18.4 mg, 0.1 mmol) was refluxed and stirred for about 8 h. The aqueous solution was cooled to room temperature and filtrated, and a solution of bib (31.7 mg, 0.1 mmol) in methanol (10 mL) was carefully layered over the aqueous solution at room temperature. Blue platelet crystals were obtained two weeks later. Yield 30%. Anal. Calcd for C17H22BrCuN4O8 (uncoordinated water molecules were lost upon drying at room temperature): C: 40.86; H 3.23; N 11.21. Found: C 40.39; H 3.36; N 11.07. IR (KBr, cm-1): 3424 br, 3128 m, 1672 vs, 1524 m, 1437 m, 1406 m, 1358 w, 1287 w, 1236 w, 1109 m, 1094 m, 1004 m, 791 w, 740 w, 656 w. Synthesis of [Cu(bib)(mal)]‚MeOH (7). An aqueous solution (5 mL) of disodium malonate (14.8 mg, 0.1 mmol) was added dropwise to a methanol solution (10 mL) of CuCl2‚2H2O (17.0 mg, 0.10 mmol) to give a sky blue solution that was allowed to stir for 30 min; to this a methanolic solution (10 mL) of ligand bib (31.7 mg, 0.1 mmol) was

added slowly. The reaction mixture was left to stand at room temperature. Blue platelet crystals were obtained after 3 days. Yield 62%. Anal. Calcd for C18H19BrCuN4O5: C: 42.00; H 3.72; N10.88. Found: C 41.97; H 3.68; N 10.92. IR (KBr, cm-1): 3385 br, 3121 m, 1648 vs, 1591 vs, 1522 m, 1422 s, 1401 s, 1355 m, 1288 m, 1246 m, 1112 m, 1089 m, 952 w, 821 w, 767 w, 736 m, 656 w. Crystallography. The data collections were carried out on a Rigaku RAXIS-RAPID Imaging Plate diffractometer at 200 K for complexes 1-3 and on a Rigaku Saturn CCD area detector at 173 K for complexes 4-7, respectively, using graphite-monochromated Mo KR radiation (λ ) 0.7107 Å). The structures were solved by direct method with SIR9219 and expanded using Fourier techniques.20 All non-hydrogen atoms were refined anisotropically by the full-matrix least-squares method on F2. The hydrogen atoms were generated geometrically. All calculations were carried out on SGI workstation using the teXsan crystallographic software package of Molecular Structure Corporation.21 The chloride in 2 are disordered into two positions with the site occupancy factors of 0.618(3) and 0.382(3). The sulfate anion and water molecules in 3 are disordered into two positions, and each position has a site occupancy factor of 0.5. In complex 6, a solvent water molecule is disordered, and atom O7 is located at two positions with site occupancy factors of


Figure 1. (a) Coordination environment of copper(II) in complex 1 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity. (b) 1D polymeric chain representation for complex 1.

Scheme 1.

Conformations of Flexible Ligand bib

0.60 and 0.40. Details of the crystal parameters, data collection, and refinements for complexes 1-7 are summarized in Table 1, and selected bond lengths and angles with their estimated standard deviations are given in Table 2. Further details are provided in Supporting Information.

Results and Discussion Description of Structures. [Cu(bib)2(H2O)2](Cl3CCOO)2‚ 2MeOH‚2H2O (1). Complex 1 crystallizes in the triclinic form with P1h space group, and the coordination environment around the copper(II) center is shown in Figure 1a. The copper(II) atom lying on an inversion center is six coordinated by four N atoms from four different bib ligands with N-Cu-N bond angles in the range of 88.21(13)-180.0° and Cu-N bond distances of 2.017(3) and 2.023(4) Å, and two additional positions are occupied by two O atoms from two water molecules with a O-Cu-O bond angle of 180.0° and a Cu-O bond distance of 2.477 Å (Table 2). Therefore, the local coordination geometry of the copper(II) center is a distorted octahedron with a N4O2 donor set. On the other hand, two bib ligands link two metal atoms using their flexible arms to generate an infinite 1D hinged chain containing 24-membered M2L2 macrocyclic rings (Figure 1b), and the Cu‚‚‚Cu distance within the M2L2 ring is 11.49 Å. It can be seen that the ligand bib in complex 1 has an “L-shape” (Scheme 1) with the dihedral angles of 100.3° and 104.0° between the phenyl and each imidazolyl group, respectively.


Figure 2. (a) Coordination environment of copper(II) in complex 2 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity. (b) 1D polymeric chain structure of complex 2.

Similar 1D chain structure has been observed in the previously reported Pb(II) and Mn(II) complexes with the dimb ligand.17 The trichloroacetate anions, methanol, and uncoordinated water molecules are located in the voids among the 1D chains. There are C-H‚‚‚O hydrogen bonds between the O atoms of trichloroacetate anion and the imidazole ring C-H as well as the methylene C-H; the O atoms of the uncoordinated water molecule and the methylene C-H. In addition, O-H‚‚‚O hydrogen bonds were found between the O atom of coordinated water molecule and the O atoms of trichloroacetate anion, as well as between the O atom of uncoordinated water molecule and the O atom of the methanol molecule with O‚‚‚O distances in the range of 2.675(5)-3.549(5), although the hydrogen atoms of water molecules could not be found. The hydrogen bonding data are summarized in Table S1, Supporting Information. Such hydrogen bonds link the 1D chains into the 2D network structure (Figure S1, Supporting Information). [Cu(bib)2]Cl2‚H2O (2). When CuCl2‚2H2O, instead of Cu(Cl3CCOO)2, was used to react with bib, complex 2 was isolated. 2 also crystallizes in the triclinic space group P1h. Each copper(II) atom is four coordinated by four N atoms from four different bib ligands with N-Cu-N bond angles in the range of 86.7(4)180.0° and Cu-N bond distances of 2.001(11) and 2.036(8) Å (Figure 2a and Table 2). The Cu1 atom locates on an inversion center. Therefore, the local coordination geometry around Cu1 can be regarded as a square-planar with N4 donor set. Complex 2 is also a hinged 1D chain similar to that of complex 1, and the Cu‚‚‚Cu intraring distance is 10.11 Å, which is slightly shorter than that in complex 1 (Figure 2b), and the ligand bib also has a “L-shape”. In complex 2, there are imidazole ring C-H‚‚‚O (water molecule) and imidazole ring C-H‚‚‚Cl hydrogen bonds. In addition, the water molecule O1 also forms O-H‚‚‚Cl hydrogen bonds with Cl1 since the O1-Cl1 distance is 2.85(2) Å (Table 2), although the hydrogen atoms of water molecule could not be found. Furthermore, the chloride anion (Cl1) locates in the axial direction of the CuN4 square-plane, and the distance between Cl1 and Cu1 is 2.90 Å. The typical Cu-Cl bond distance of the six-coordinated copper(II) atom is about 2.30 Å,22 and a reported Cu-Cl bond distance of sixcoordinated copper(II) atom is as long as 2.835 Å.23 Therefore,


Figure 3. (a) Coordination environment of copper(II) in complex 3 with the ellipsoids drawn at the 30% probability level; hydrogen atoms and uncoordinated water molecules were omitted for clarity. (b) 2D network of 3 in which uncoordinated water molecules and hydrogen atoms were omitted for clarity.

weak interaction should exist between the copper(II) atom and the chloride atom. The hydrogen bonds and Cu-Cl weak

Meng et al.

coordination interactions link the 1D chains to form an infinite 3D framework (Table S1 and Figure S2, Supporting Information). [Cu(bib)2(SO4)(H2O)]‚4H2O (3). It is interesting that complexes 3 and 4 were obtained simultaneously by the reaction of bib with CuSO4‚5H2O (see Experimental Section and below). Complex 3 crystallizes in the monoclinic space group P21/c. The coordination environment around the metal atom in complex 3 is exhibited in Figure 3a. The copper(II) center sits on an inversion center and O11 atom belongs to the disordered sulfate anion and coordinated water molecule (each with site occupancy factor of 0.5), respectively. Each Cu(II) is coordinated by four N atoms from four different bib ligands with a N-Cu-N bond angle from 89.11(15)° to 180.0°, and Cu-N bond distances of 1.995(4) and 2.013(4) Å, respectively (Table 2). Two additional positions are occupied by two O atoms, one from water molecule and the other from the sulfate anion with a Cu-O bond distance of 2.563 Å, which is slightly longer than the previously reported Cu-O bond distance of about 2.30 Å of six-coordinated copper(II) atom.24 It has been reported that the Cu-O distance could be as long as 2.673 Å,25a and the weak coordination bond might exist even if the Cu-O distance is 2.80 Å.25b Therefore, the local coordination geometry around copper(II) in 3 can be regarded as octahedron with an N4O2 donor set. In contrast to the 1D chain structure of complexes 1 and 2, the polymeric structure of 3 is a 2D network with (4,4) topology (Figure 3b). The copper(II) atoms serve as nodes, while each bib ligand connects two copper(II) atoms and serves as rods (bridging ligand). Four copper(II) atoms and four bib ligands form a 48-membered rhombus ring, and such rhombus ring repeats to give an infinite 2D network. In the Cu4 rhombus, the distances between two adjacent copper(II) atoms linked by bib ligand are all 11.90 Å, and the diagonals of the Cu4 rhombus are 21.92 and 9.28 Å (the internal angles of the rhombus are 45.9° and 134.1°), respectively. Compared to 1 and 2, the ligand bib in 3 has a “Z-shape” (Scheme 1), while the ligands in 1 and 2 have a “L-shape”. Such a (4,4) network is similar to the previously reported structures of complexes [Zn(bib)2(H2O)2](NO3)2‚2H2O and [Mn(bib)2(H2O)2](NO3)2‚2H2O.18 In complex 3, O atoms of sulfate anions form C-H‚‚‚O hydrogen bonds with imidazole ring C-H and benzene ring

Figure 4. (a) The M2L2 metallocyclic ring formed in complex 4 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity. Top view (b) and side view (c) of 1D polymeric tube representation for complex 4.



Figure 5. (a) Coordination environment of copper(II) in complex 5 with the ellipsoids drawn at the 30% probability level; hydrogen atoms and DMF molecules were omitted for clarity. (b) 1D chain of complex 5 formed by Br‚‚‚Br interactions indicated by dashed lines.

C-H (Table S1, Supporting Information). The C‚‚‚O distances range from 3.126(9) to 3.455(9) Å, and the C-H-O angles range from 139° to 164°. In addition, there are O-H‚‚‚O hydrogen bonds between the O atoms of the uncoordinated water molecules, and between the O atom of the uncoordinated water molecule and the O atom of the sulfate anion with O‚‚‚O distances in the range of 2.800(9)-3.025(10) Å. Besides the C-H‚‚‚O hydrogen bonds and the O-H‚‚‚O hydrogen bonds, there are O-H‚‚‚Br hydrogen bonds between the O atom from the uncoordinated water molecules and Br atom from the ligand with the O‚‚‚Br distance of 3.555(9) Å. These hydrogen bonds give rise to a 3D framework of complex 3 (Figure S3, Supporting Information). [Cu(bib)(SO4)(H2O)2] (4). Crystallographic analysis revealed that complex 4 has a different structure from that of complex 3. Complex 4 crystallizes in triclinic space group P1h. As shown in Figure 4a, two bib ligands connect two copper(II) atoms to form a M2L2 metallocyclic ring with the intermetallic distance of 13.16 Å. Each copper(II) atom is coordinated by two N atoms with Cu-N bond distances of 2.012(2) and 1.973(2) Å, and by two O atoms from two water molecules with Cu-O bond distances of 2.004(2) and 1.975(2) Å (Table 2). The O1-Cu1N1 angle is 169.36(7)°, and the N4A-Cu1-O2 one is 175.5°. As shown in Figure 4b,c, two sulfate anions link two adjacent M2L2 rings to form an infinite 1D tube-like chain with CuOsulfate bond distances of 2.440(2) and 2.574(2) Å and an Osulfate-Cu-Osulfate bond angle of 173.79°. Therefore, the local coordination geometry of the copper(II) center is a distorted octahedron with a N2O4 donor set. There are C-H‚‚‚O hydrogen bonds between the O atom of the sulfate anion and the imidazole ring C-H as well as the methylene C-H; the O atom of the coordinated water molecule and the benzene ring C-H. The C‚‚‚O distances range from 2.879(4) to 3.420(4) Å. In addition, there are O-H‚‚‚O hydrogen bonds between the O atom of the sulfate anion and the O atom of the coordinated water molecule with the O‚‚‚O distances in the range of 2.646(3)-2.702(2) Å. Also, in complex 4, the C-H‚‚‚Br hydrogen bond is formed between the Br atom and the imidazole ring C-H with a C‚‚‚Br distance of 3.804(3) Å. The 1D tubes are held together through C-H‚‚‚Br, O-H‚‚‚O, and C-H‚‚‚O hydrogen bonds (Table S1,

Figure 6. (a) Coordination environment of copper(II) in complex 6 with the ellipsoids drawn at the 30% probability level; hydrogen atoms, methanol molecules and uncoordinated water molecules were omitted for clarity. (b) Infinite 2D network structure of complex 6.

Supporting Information) to generate a 3D architecture (Figure S4, Supporting Information). [Cu(bib)(N3)(OAc)]‚DMF (5). When the bib ligand reacts with Cu(OAc)2 and NaN3, complex 5 was isolated. It is interesting that both N3- and OAc- exist in the complex and coordinated with the copper(II) atom. Crystallographic analysis provides direct evidence of the M2L2 metallocyclic ring-like structure of complex 5. The complex crystallizes in triclinic space group P1h. As shown in Figure 5a, two bib ligands with “L-shape” (Scheme 1) are held together by two copper(II) atoms. Each copper(II) atom is coordinated by two N atoms from two different bib ligands, one N atom from an azide anion and one O atom from an acetate anion. The Cu-N bond distances range from 1.969(3) to 1.982 Å, and the Cu-O bond distance is 1.976(3) Å. The O1-Cu1-N5 angle is 160.7°, and the N1Cu1-N3A angle is 159.0° (Table 2); thus, the copper(II) has a slightly distorted square-planar coordination environment. The intermetallic distance between the two copper(II) atoms (i.e., Cu1‚‚‚Cu1A) is 7.83 Å, and the two benzene ring planes are strictly parallel to each other with a separation of 12.34 Å. A remarkable structure feature of complex 5 is that there are Br‚‚‚Br interactions involved in the stabilization of the crystal lattice. The Br-Br distance within the range of 3.3-3.9 Å is considered to have Br‚‚‚Br interactions.26 As shown in Figure 5b, in complex 5 the distance between two adjacent Br atoms from two adjacent M2L2 metallocycles is 3.35 Å, and the M2L2 metallocyclic rings are joined together by such Br‚‚‚Br interactions to lead to the formation of an infinite 1D chain. In our previous studies, we have also obtained a complex [Zn2(bib)2(OAc)4]‚2H2O with M2L2 structure, in which Br‚‚‚Br interactions also exist.18 However, in complex [Zn2(bib)2(OAc)4]‚2H2O,


the Br‚‚‚Br interactions joined the M2L2 ring to form a 1D pseudopolyrotaxane structure, which is different from that in complex 5. In complex 5, O atoms of the acetate anions form intermolecular hydrogen bonds with the benzene C-H from the adjacent M2L2 ring with C‚‚‚O distances in the range of 2.865(4)-3.434(7) Å. In addition, there are also C-H‚‚‚N hydrogen bonds between the N atom of the azide anion and the imidazole ring C-H as well as the benzene ring C-H with C‚‚‚N distances in the range of 3.140(5)-3.336(6) Å. Such intermolecular hydrogen bonds, together with the Br‚‚‚Br interactions, link the M2L2 metallocycles to produce a 3D structure (Figure S5, Supporting Information). The DMF molecules locate in the voids of the M2L2 metallocycles and are held there by C-H‚‚‚O hydrogen bonds as listed in Table S1, Supporting Information. [Cu(bib)(ox)]‚MeOH‚2H2O (6). When the reaction of the bib ligand with Cu(NO3)2‚3H2O and K2(ox) was performed, complex 6 was successfully obtained. The complex crystallizes in the monoclinic space group P21/c, and Figure 6a illustrates the coordination environments of copper(II) atom. Each copper(II) atom is six coordinated by two N atoms from two bib ligands and four O atoms from two oxalate anions. The copper(II) atom locates on the equatorial plane composed of N1, N3, O1, and O3, while O2 and O4 occupy the axial positions. The Cu-N bond distances are 1.995(3) and 2.005 Å. Cu-O bond distances in the equatorial plane are 2.007(2) and 2.006(2) Å, while the Cu-O bond distances in the axial directions are 2.333 and 2.308 Å, which are longer than these in the equatorial plane due to the Jahn-Teller effect. Such a difference of Cu-O bond distances indicates that the oxalate groups are involved in an asymmetric bridge between copper(II) atoms in complex 6. The O3-Cu1-N1, O1-Cu1-N3A, and O2A-Cu1-O4A angles are 171.5(1)°, 173.4°, and 163.9° (Table 2), respectively. These values represent that the environment around the copper(II) atom is an elongated rhombic octahedron with a N2O4 donor set. The copper(II) atoms are bridged sequentially by oxalate anions to form a 1D zigzag polymeric chain (Figure 6a). The Cu‚‚‚Cu distance between Cu1, Cu1A is 5.60 Å, and the distance between Cu1, Cu1B is 5.55 Å. Such 1D zigzag chain structure is similar to those reported copper complexes [Cu(ox)(H2O)(pur)] (pur ) purine)14c and [Cu(bpy)(ox)]‚2H2O (bpy ) 2,2′-bipyridine).14a Furthermore, in complex 6, the zigzag chains are further connected by bib, which adopts a “V-shape” conformation to form a 2D infinite network, as shown in Figure 6b. The 2D layers are further linked by C-H‚‚‚O (between O atoms of oxalate anions and benzene C-H as well as the methylene C-H) and C-H‚‚‚Br (between Br atoms and the imidazole ring C-H) hydrogen bonds to produce a 3D framework (Figure S6, Supporting Information). The uncoordinated water molecules and methanol molecules locate in the voids formed between two adjacent layers, and they are held by forming C-H‚‚‚O hydrogen bonds with the layers. [Cu(bib)(mal)]‚MeOH (7). Similar to the oxalate anion, the malonate anion is also a versatile multidentate bridging ligand due to its different coordination modes of the carboxylate groups. Therefore, we synthesized complex 7 in which the malonate anion also acts as a bridging ligand. Complex 7 crystallizes in monoclinic space group P21. As illustrated in Figure 7a, the copper(II) atom sits on the equatorial plane composed of two N atoms from two different bib ligands and two O atoms from one malonate anion. The Cu-N bond distances range from 1.994 to 1.998(5) Å, and the Cu-O bond distance ranges from 1.960(5) to 1.977(4) Å. The O1-Cu1O3 angle is 91.2(2)°, and the O3-Cu1-N1 angle is 88.4(2)°.

Meng et al.

Figure 7. (a) Coordination environment of copper(II) in complex 7 with the ellipsoids drawn at the 30% probability level; hydrogen atoms and uncoordinated water molecules were omitted for clarity. (b) Infinite 2D network structure of complex 7.

The axial position of the copper(II) atom is occupied by an O atom from another malonate anion with a Cu-O bond distance of 2.261 Å, and a O3-Cu1-O2A bond angle of 94.0°. Therefore, the copper(II) atom is five-coordinated, and it exhibits a distorted CuN2O3 tetragonal pyramid surrounding. Each malonate group adopts simultaneously bidentate (O1 and O3) and monodentate (O2) coordination modes, and O4 atom does not coordinate with the metal atom. This is quite different from the previous reported copper-malonate complexes in which malonate group adopts bidentate and bismonodentate coordination modes.27 The copper(II) atoms are bridged sequentially by malonate anion to form 1D polymeric chains. The distance between two adjacent copper(II) atoms in the chain is 5.89 Å. The carboxylate bridge O1-C15-O2 (bridge with Cu1 and Cu1B) exhibits the anti-syn conformation within the chain. Such bridging mode of the malonate group makes the - - -Cu-mal-Cu-mal- - - 1D polymeric chain a helix with inherent chirality, while in 6 the - - -Cu-ox-Cu-ox- - - is a simple zigzag 1D chain as described above. Therefore, complex 7 crystallizes in a chiral space group P21 (Table 1), which should be particularly noticed since this is caused by achiral ligands. The copper-malonato 1D chains are further bridged by bib to form an infinite 2D network (Figure 7b), which is similar to complex 6. Ligand bib in complex 7 adopts a “V-shape” conformation (Scheme 1). The methanol molecules are located in the voids between the 2D networks. There are C-H‚‚‚O hydrogen bonds between the O atoms of malonate anion and the imidazole ring C-H as well as the methylene C-H. And


Figure 8. Schematic drawing for reactions between the bib ligand and copper(II) salts.

C-H‚‚‚O hydrogen bonds also exist between the O atoms of methanol molecules and the imidazole ring C-H as well as the benzene ring C-H. In addition, there are C-H‚‚‚Br hydrogen bonds between the Br atom and the imidazole ring C-H. Because of the existence of these hydrogen bonds, the 2D layers are further linked to produce a 3D framework (Table S1 and Figure S7, Supporting Information). Comparison of Structures. Seven new MOFs of Cu(II) with ligand bib were successfully synthesized. The X-ray crystallographic analysis indicates that these complexes have different structures as schematically shown in Figure 8. (1) Because of the flexibility of the bib, there are several modes for bib to bind the copper(II) atoms. In complexes 1, 2, 4, and 5, 24-membered M2L2 macrocyclic moieties are formed with two copper(II) atoms and two bib ligands, while in complex 3, four copper(II) atoms and four bib ligands form 48-membered rhombus moieties. In complexes 6 and 7, if the existence of bridging counteranions of ox and mal is ignored, it can be found that two copper(II) atoms are linked by one bib ligand to form a zigzag chain. In addition, because the bib ligand has a different conformation, and it can distort to different extents, and the intermetallic distances between two adjacent copper(II) atoms linked by bib are also different. For example, complexes 1, 2, 4, and 5 all have a 24-membered M2L2 macrocyclic moiety; however, the intermetallic distances between two copper(II) atoms bridged by bib ligands in complex 1 and 2 (the bib ligand adopts an “L-shape” conformation) are 11.49 and 10.11 Å, which are obviously shorter than that distance of 13.16 Å in complex 4 (bib ligand adopts a Z-shape conformation). In complex 5, although the bib ligand also adopts an L-shape, the intermetallic distance is only 7.83 Å because bib in complex 5 distorts more seriously than that in complexes 1 and 2. (2) The counteranions play important roles in the architectures of MOFs. For complexes 1, 2, 3, and 5, the anions do not act as bridging ligands, so the main frameworks of these four complexes are just constructed by ligand bib and copper(II) atoms. For


example, the M2L2 moieties of complexes 1 and 2 repeat themselves to form 1D infinite chains, and the M4L4 rhombus moiety of complex 3 repeats itself to form a 2D network with (4,4) topology. The azide anion and acetate anion in complex 5 both adopt terminal coordination modes, so complex 5 retains its M2L2 ring structure formed by two copper(II) atoms and two bib ligands. In contrast to the above four complexes, the counteranions in complexes 4, 6, and 7 all act as bridging ligands. Therefore, the adjacent M2L2 rings are connected by the sulfate anions that adopt a bridging mode to form a 1D tube structure in complex 4, and the 1D zigzag Cu-bib chains are further linked by the bridging oxalate or malonate anions to form 2D networks in complexes 6 and 7. (3) Complexes 3 and 4 were obtained by the same method and even in the same test tube, but they have distinct structures. This may result from the different ratios between the metal salt and the ligand during the formation of the complexes, since the complexes were obtained by slowly diffusing the methanol solution of bib (top) and the copper(II) sulfate solution (bottom). Complex 3 (the ratio between Cu and bib is 1:2) appears in the middle of the test tube where the bib ligand is relatively more concentrated, while complex 4 (the ratio between Cu and bib is 1:1) appears in the bottom of the test tube where the copper(II) sulfate is relatively more concentrated. Thermal Stability Property of the Complexes. Complexes 1-7 were readily prepared in reasonable yields by reactions of the bib ligand with the corresponding Cu(II) salts. The pure phase of the products was confirmed by X-ray powder diffraction (XRPD) patterns (typical examples are given in Figure S8, Supporting Information). The thermal stability property of the complexes was investigated by thermogravimetric analysis (TGA) except for complex 5, which contains azide and might be explosive upon heating. Complexes 1 and 6 lose solvent and water molecules from room temperature when they were isolated from the reaction solution (see Experimental Section), and the TGA results of 1 and 6 showed that the residue decomposed below 200 °C, which means that these two complexes have low thermal stability. Complexes 2, 3, 4, and 7 lose methanol and noncoordinated and coordinated water molecules below 150 °C. For example, a weight loss of 10.3% (calculated 10.2%) below 113 °C indicates the loss of five water molecules for 3, and the TGA data of 4 showed that a weight loss of 7.3% (calculated 7.0%) corresponding to the loss of two water molecules was observed between 118 and 147 °C. The decomposition of the residue starts around 250 °C for 2 and 3, 310 °C for 4, and 190 °C for 7, respectively. Magnetic Properties of Complexes 6 and 7. Variabletemperature magnetic susceptibility measurements of complexes 6 and 7 were carried out on a crystalline sample in the range of 1.8-300 K. Figure 9a gives a plot of χMT vs T for complex 6. The χMT value for 6 is 0.45 emu mol-1 K at room temperature. It increases continuously by cooling the sample, and it reaches 0.76 emu mol-1 K at 1.8 K. In the plot of M-H (inset of Figure 9a), a saturated magnetization of 1.05 Nβ mol-1 was observed at 7 T due to a nonzero spin ground state in complex 6. No hysteresis loop was observed, suggesting the magnetic phase critical temperature is probably lower than 1.8 K. In addition, from the AC magnetic measurements (Figure 9b), it could be found that the in-phase magnetization increases with decreasing temperature, but no peak was observed, and the magnetization of out-phase keeps constant within the whole temperature range. The result further supports that the magnetic phase critical temperature of 6 is probably lower than 1.8 K.


Meng et al.

Figure 9. (a) Temperature dependence of magnetic susceptibilities in the form of χMT at an applied field of 2000 Oe from 1.8 to 300 K for complex 6 (0). The solid line is the fitting result. Inset is the plot of M-H at 1.8 K. (b) AC magnetic measurements with Hdc ) 0, Hac ) 5 G, and f ) 10 Hz for complex 6.

Although complex 6 exhibits a 2D network structure, the exchange coupling through the bib ligand is expected to be very weak; therefore, the magnetic coupling of complex 6 mainly depends on the bridging oxalate anions. Crystal structure of complex 6 indicates that it contains two oxalate groups with very slight structural differences, so the intrachain-exchange coupling constants of the two oxalate groups could be considered as the same. The magnetic susceptibility data of complex 6 were analyzed by the Heisenberg linear chain model. The Hamiltonian is H ) -2J∑SiSi+1, Where J is the intrachain-exchange coupling constant, and the summation is over all members of the chain. Over the entire temperature range, the data are best fit by the Bonner-Fisher model for a uniformly spaced chain of S ) 1/2 metal centers; the numerical expression is

χM )

[

]

Ng2β2 1.0 + 5.7979916y + 16.902653y2 + 29.376885y3 + 29.832959y4 + 14.036918y5 4kT 1.0 + 2.7979916y + 7.0086780y2 + 8.65344y3 + 4.5743114y4

2/3

+ TIP

where y ) J/2kT, and TIP is the temperature independent paramagnetism; the best fit to the data for 6 yielded g ) 2.16, J/k ) 1.58(2) cm-1 and R ) 2.0 × 10-5 (R ) ∑[(χMT)calcd - (χMT)obs]2/∑(χMT)2obs). This value is similar to that obtained for [Cu(bpy)(ox)]3‚2H2O chain structured material in which J/k ) 1.22 cm-1.14a Thus, magnetically, 6 behaves as a 1D chain with appreciable ferromagnetic coupling between the local spin doublets. Previous studies of oxalato-copper(II) complexes indicate that the type and value of magnetic coupling of copper-oxalate complexes mainly depend on the orientations of copper(II) magnetic orbitals (usually dx2-y2) and the oxalate groups when the oxalate bridges the copper(II) ions.14 When the oxalate anions symmetrically coordinate to copper(II) ions with short equatorial bonds, the complexes usually exhibit antiferromagnetic coupling.14c While in the case of the oxalate anion asymmetrically coordinated to copper(II) ions (i.e., two O atoms of oxalate anion coordinate to the copper(II) in the axial direction, and the other two O atoms coordinate to copper(II) in the equatorial plane, such as complex 6), the complexes might exhibit weak anti- or ferromagnetic coupling.14a,14b,28 And the type of the coupling is governed by the value of the bond angle C-O-Cu involving the axial oxalate O atom (e.g., R1 and R2 in Scheme 2). When R e 109.5°, complexes usually exhibit ferromagnetic interactions, and when R > 109.5°, complexes usually show antiferromagnetic interactions. In complex 6, the central copper(II) atom is coordinated by two different oxalate anions, and

1-Bromo-3,5-bis(imidazol-1-ylmethyl)benzene Complexes Scheme 2.

Schematic Representation of the Orbital Topology in Complex 6

the R value is R1 ) 108.4°, R2 ) 107.9° (Scheme 2), which are both less than 109.5°. From the prediction described above, complex 6 should show weak ferromagnetic property, and it well coincides with the experimental result. Figure S9, Supporting Information gives the plots of χM and χMT vs T for complex 7. In the temperature range of 1.8-300 K, the χMT value of complex 7 nearly remains constant between 0.39 and 0.42 emu mol-1 K, which is in accordance with the theoretical value 0.41 emu mol-1 K based on the mononuclear copper(II) unit (S ) 1/2 and assuming g ) 2.1) without interactions between the Cu(II). Such result indicates that although the copper(II) ions are bridged by malonate anions, there is no obvious magnetic interaction between the copper(II) ions. Conclusions Seven new metal-organic frameworks (MOFs) constructed from 1-bromo-3,5-bis(imidazol-1-ylmethyl)benzene (bib) with corresponding copper(II) have been prepared and structurally characterized, and the magnetic properties of complexes 6 and 7 were studied. From the above results, it was found that due to the flexibility of bib and with the aid of counteranions, the MOFs could exhibit various structures. Variable-temperature magnetic susceptibility measurements on complex 6 indicate ferromagnetic interactions between copper(II) ions. Acknowledgment. This work was supported by the National Natural Science Foundation of China (Grant No. 20231020) and the National Science Fund for Distinguished Young Scholars (Grant No. 20425101). Supporting Information Available: X-ray crystallographic file in CIF format, crystal packing diagrams for complexes 1-7 (Figures S1S7), hydrogen bonding data for 1-7 (Table S1), XRPD patterns of the complexes (Figure S8), and χMT vs T and χM vs T plots of complex 7 (Figure S9). This material is available free of charge via the Internet at http://pubs.acs.org.

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