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pH and Auxiliary Ligand Influence on the Structural Variations of 5(2′-Carboxylphenyl) Nicotate Coordination Polymers Jinzhong Gu,*,† Zhuqing Gao,‡ and Yu Tang† †

Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. China ‡ School of Chemistry and Biology Engineering, Taiyuan University of Science and Technology, Taiyuan 030021, P. R. China S Supporting Information *

ABSTRACT: A ligand 5-(2′-carboxylphenyl) nicotic acid (H2cpna) has been successfully applied to construct a series of coordination complexes {[Cd(Hcpna)2(H2O)2]·3H2O}n (1), [Cd(cpna)(H2O)]n (2), [M(cpna)(2,2′-bipy)(H2O)]n (M = Cd (3), Co (4), and Mn (5)), [Co(cpna)(phen)(H2O)]n (6), [Mn(cpna)(phen)(H2O)]n (7), {[Nd(Hcpna)(cpna)(H 2 O) 2 ]·3H 2 O} n (8), and {[Ln(Hcpna)(cpna)(phen)]·2H2O}n (Ln = Pr (9), Nd (10), Eu (11), and Gd (12), 2,2′-bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline) under hydrothermal conditions. By adjusting the reaction pH, H2cpna ligand is partially deprotonated to form Hcpna− in 1 and completely deprotonated to create cpna2− in 2−7, and both forms are observed in 8−12. Complexes 1−5 and 8 possess two-dimensional (2D) layered structures, which are further extended into 3D metal−organic supramolecular frameworks by C−H···O hydrogen bond and/or π−π stacking interactions. Complexes 6, 7, and 9−12 exhibit one-dimensional (1D) chain structures, which further build three-dimensional (3D) supramolecular architecture via C−H···O hydrogen-bonding and/or π−π stacking interactions. The results revealed that the pH value of the reaction system and auxiliary ligand play an important role in determining the structures of the complexes. Magnetic susceptibility measurements indicate that compounds 4−10 and 12 have dominating antiferromagnetic couplings between metal centers. Furthermore, thermal stabilities for 1−12 and luminescent properties for 1−3, and 11 are also discussed in detail.

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INTRODUCTION In recent years, the rational design and assembly of coordination polymers has been of considerable interest because of their intriguing architectures and potential applications, such as gas storage, sensor, separation, catalysis, ion exchange, magnetism, luminescence, and other applications in materials science.1 However, it is a great challenge to control structures with desired properties because many factors affect the result, such as the coordination geometry of the central metal ions, connection modes of organic ligands, reaction temperature, the ratio of reagents, solvents, pH value, anions, and so on.2 The most effective and facile approach to overcome this problem is the appropriate choice of the well-designed organic bridging ligands containing modifiable backbones and connectivity information, together with the metal centers with various coordination preferences. Many multicarboxylate or heterocylic carboxylic acids are used for this purpose.3 In addition, the pH value of the reaction system is also one of key factors in the assembly of coordination polymers. Adjusting the reaction pH value can influence the protonation degree of the organic ligand, resulting in different structures of coordination polymers.4,2d In order to extend our investigation in this field, we chose 5-(2′-carboxylphenyl) nicotic acid (H2cpna) as a © 2012 American Chemical Society

functional ligand, which was based on the following considerations: (1) H2cpna contains a pyridyl and a phenyl ring with structural flexibility and conformation freedom. Rotation of the C−C single bond between pyridyl and phenyl rings could form numbers of coordination geometries of metal ions. The potential coordination sites, one nitrogen atom from pyridyl ring and four oxygen atoms of two carboxylate groups, may supply anions of two different valences as compensating charge and various acidity-dependent coordination modes. The carboxylate groups can act not only as hydrogen-bond acceptors but also as hydrogen-bond donors, depending upon the degree of deprotonation, which is beneficial for the construction of coordination polymers. (2) To our knowledge, H2cpna has not been adequately explored in the construction of coordination polymers.6 In this work, by using ligand H2cpna, changing the reaction pH value and/or using auxiliary ligand, a series of coordination compounds {[Cd(Hcpna)2(H2O)2]·3H2O}n (1), [Cd(cpna)(H2O)]n (2), [M(cpna)(2,2′-bipy)(H2O)]n (M = Cd (3), Co Received: April 2, 2012 Revised: April 28, 2012 Published: May 1, 2012 3312

dx.doi.org/10.1021/cg300442b | Cryst. Growth Des. 2012, 12, 3312−3323

Crystal Growth & Design

Article

for 15 min, then sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 160 °C for 3 days, followed by cooling to room temperature at a rate of 10 °C/h. Crystals of 3−5 were isolated manually and washed with distilled water. Yield: 70% for 3, 50% for 4, and 45% for 5 (based on M). Calcd for C23H17N3CdO5 (3): C 52.34, H 3.25, N 7.96%. Found: C 52.61, H 3.47, N 7.67%. IR (KBr, cm−1): 3430 w, 3068 w, 1612 s, 1595 s, 1440 m, 1378 s, 1271 w, 1160 w, 1126 w, 1032 w, 1016 w, 900 w, 820 m, 789 m, 771 s, 738 m, 722 m, 670 w, 649 w, 628 w. Calcd for C23H17N3CoO5 (4): C 58.24, H 3.61, N 8.86%. Found: C 58.63, H 3.41, N 8.65%. IR (KBr, cm−1): 3430 w, 3068 w, 1612 s, 1595 s, 1440 m, 1378 s, 1271 w, 1160 w, 1126 w, 1032 w, 1016 w, 900 w, 820 m, 789 m, 771 s, 738 m, 722 m, 670 w, 649 w, 628 w. Calcd for C23H17N3MnO5 (5): C 58.73, H 3.64, N 8.93%. Found: C 58.51, H 3.38, N 8.59%. IR (KBr, cm−1): 3427 w, 3068 w, 1612 s, 1565 s, 1439 m, 1381 s, 1269 w, 1158 w, 1125 w, 1032 w, 1013 w, 918 w, 815 m, 790 m, 770 s, 739 m, 722 m, 689 w, 652 w, 626 w. Preparation of [Co(cpna)(phen)(H2O)]n (6). The preparation of 6 was similar to that of 4 except using phen instead of 2,2′-bipy. After being cooled to room temperature, pink needle-shaped crystals of 6 were isolated manually and washed with distilled water. Yield: 40% (based on Co). Calcd for C25H17N3CoO5: C 60.25, H 3.44, N 8.43%. Found: C 59.86, H 3.21, N 8.74%. IR (KBr, cm−1): 3430 w, 3060 m, 1612 s, 1573 w, 1426 m, 1381 s, 1283 w, 1146 w, 1127 w, 1037 w, 957 w, 850 m, 811 m, 790 m, 762 m, 727 m, 663 w, 638 w. Preparation of [Mn(cpna)(phen)(H2O)]n (7). The preparation of 7 was similar to that of 6 except using MnCl2·4H2O instead of CoCl2·6H2O. After being cooled to room temperature, yellow needleshaped crystals of 7 were isolated manually and washed with distilled water. Yield: 38% (based on Co). Calcd for C25H17N3MnO5: C 60.74, H 3.47, N 8.50%. Found: C 60.51, H 3.26, N 8.15%. IR (KBr, cm−1): 3438 m, 3059 w, 1611 s, 1573 w, 1425 w, 1383 s, 1343 w, 1284 w, 1147 w, 1126 w, 1025 w, 1034 w, 851 m, 810 m, 792 m, 760 m, 728 m, 687 w, 639 w. Preparation of {[Nd(Hcpna)(cpna)(H2O)2]·3H2O}n (8). A mixture of NdCl3·6H2O (74.6 mg, 0.2 mmol), H2cpna (72.9 mg, 0.3 mmol), and H2O (10 mL) was adjusted to pH = 4.0−5.0 with 0.5 M NaOH solution. The mixture was stirred at room temperature for 15 min, then sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 160 °C for 3 days, followed by cooling to room temperature at a rate of 10 °C/h. Purple block-shaped crystals of 8 were isolated manually, and washed with distilled water. Yield: 35% (based on H2cpna). Calcd for C26H25N2NdO13: C 43.51, H 3.51, N 3.90%. Found: C 43.73, H 3.24, N 4.27%. IR (KBr, cm−1): 3410 m, 3060 w, 1725 m, 1614 s, 1535 s, 1494 w, 1400 s, 1295 w, 1170 w, 1133 w, 1031 w, 955 w, 916 w, 895 w, 851 m, 791 m, 762 s, 706 m, 673 w, 598 w. Preparation of {[Ln(Hcpna)(cpna)(phen)]·2H2O}n (Ln = Pr (9), Nd (10), Eu (11), and Gd (12)). A mixture of LnCl3·6H2O (0.2 mmol), H2cpna (72.9 mg, 0.3 mmol), phen (39.6 mg, 0.2 mmol), and H2O (10 mL) was adjusted to pH = 4.0−5.0 with 0.5 M NaOH solution. The mixture was stirred at room temperature for 15 min, and then sealed in a 25 mL Teflon-lined stainless steel vessel, and heated at 160 °C for 3 days, followed by cooling to room temperature at a rate of 10 °C/h. Block-shaped crystals were isolated manually and washed with distilled water. Yield: 60% for 9, 10; 35% for 11 and 12 (based on H2cpna). Calcd for C38H27N4PrO10 (9): C 54.30, H 3.24, N 6.66%. Found: C 54.63, H 3.29, N 6.23%. IR (KBr, cm−1): 3491 w, 3059 w, 1695 m, 1630 s, 1582 s, 1536 w, 1493 w, 1429 m, 1389 s, 1285 m, 1165 w, 1135 m, 1100 w, 1051 w, 1024 w, 846 m, 791 w, 764 s, 724 m, 525 w, 424 m. Calcd for C38H27N4NdO10 (10): C 54.08, H 3.22, N 6.64%. Found: C 53.83, H 3.45, N 6.34%. IR (KBr, cm−1): 3490 w, 3059 w, 1694 m, 1610 s, 1580 s, 1542 w, 1492 w, 1432 m, 1387 s, 1291 m, 1165 w, 1133 m, 1098 w, 1032 w, 1028 w, 847 m, 791 w, 765 s, 725 m, 526 w, 425 m. Calcd for C38H27N4EuO10 (11): C 53.59, H 3.20, N 6.58%. Found: C 54.23, H 3.01, N 6.29%. IR (KBr, cm−1): 3491 w, 3060 w, 1695 m, 1614 s, 1581 s, 1543 w, 1493 w, 1428 m, 1386 s, 1292 m, 1166 w, 1133 m, 1099 w, 1050 w, 1028 w, 848 m, 791 w, 765 s, 725 m, 526 w, 427 m. Calcd for C38H27N4GdO10 (12): C 53.26, H 3.18, N 6.54%. Found: C 53.52, H 2.97, N 6.73%. IR (KBr, cm−1): 3488 w, 3060 w, 1695 m, 1614 s, 1584 s, 1546 w, 1492 w, 1427 m, 1386 s, 1298

(4), and Mn (5)), [Co(cpna)(phen)(H2O)]n (6), [Mn(cpna)(phen)(H2O)]n (7), {[Nd(Hcpna)(cpna)(H2O)2]·3H2O}n (8), and {[Ln(Hcpna)(cpna)(phen)]·2H2O}n (Ln = Pr (9), Nd (10), Eu (11), and Gd (12), 2,2′-bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline) were prepared by the hydrothermal method (Scheme 1). Their structural diversities show Scheme 1. Molecular Structures of Ligands in This Work

that the pH value of the reaction system and auxiliary ligand played a significant role in the structural self-assembled process. All the complexes were characterized by X-ray crystallography, IR, elemental, thermal stability, and powder X-ray diffraction analyses. Magnetic properties of 4−10 and 12 and luminescent properties of 1−3 and 11 were investigated.

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EXPERIMENTAL SECTION

Materials and Instrumentation. All chemicals and solvents were of A.R. grade and used without further purification. Carbon, hydrogen, and nitrogen were determined using an Elementar Vario EL elemental analyzer. IR spectra were recorded using KBr pellets and a Bruker EQUINOX 55 spectrometer. UV/vis absorption spectra were determined on a Varian UV-Cary100 spectrophotometer. Thermogravimetric analysis (TGA) was performed under N2 atmosphere with a heating rate of 10 °C/min on a LINSEIS STA PT1600 thermal analyzer. Powder X-ray diffraction patterns (PXRD) were determined with a Rigaku-Dmax 2400 diffractometer using Cu-Kα radiation (λ = 1.54060 Å) in which the X-ray tube was operated at 40 kV and 40 mV. 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. Excitation and emission spectra were recorded on an Edinburgh FLS920 fluorescence spectrometer at room temperature for the solid samples. Preparation of {[Cd(Hcpna)2(H2O)2]·3H2O}n (1). A mixture of CdCl2·H2O (68.4 mg, 0.3 mmol), H2cpna (72.9 mg, 0.3 mmol), and H2O (10 mL) was adjusted to pH = 4.0 with 0.5 M NaOH solution. The mixture was stirred at room temperature for 15 min, and then sealed in a 25 mL Teflon-lined stainless steel vessel, and heated at 160 °C for 3 days, followed by cooling to room temperature at a rate of 10 °C/h. Colorless block-shaped crystals of 1 were isolated manually and washed with distilled water. Yield: 70% (based on H2cpna). Calcd for C26H26N2CdO13: C 45.46, H 3.82, N 4.08%. Found: C 45.28, H 3.74, N 4.34%. IR (KBr, cm−1): 3471 m, 3062 m, 1710 m, 1607 s, 1559 s, 1434 w, 1392 s, 1248 w, 1135 w, 1088 w, 804 m, 763 m, 710 m, 654 w. Preparation of [Cd(cpna)(H2O)]n (2). The preparation of 2 was similar to that of 1 except that the pH value was adjusted to 6.0 by addition of 0.5 M NaOH solution. After being cooled to room temperature, colorless block-shaped crystals of 2 were isolated manually and washed with distilled water. Yield: 45% (based on Cd). Calcd for C13H9NCdO5: C 42.02, H 2.44, N 3.77%. Found: C 42.29, H 2.76, N 4.06%. IR (KBr, cm−1): 3395 w, 3062 w, 1603 s, 1534 s, 1437 w, 1397 s, 1239 w, 1131 w, 1026 w, 903 w, 859 m, 782 m, 704 m, 680 w. Preparation of [M(cpna)(2,2′-bipy)(H2O)]n (M = Cd (3), Co (4), and Mn (5)). A mixture of MCl2·xH2O (x = 1 for 3, x = 6 for 4, and x = 4 for 5; 0.3 mmol), H2cpna (72.9 mg, 0.3 mmol), 2,2′-bipy (46.9 mg, 0.3 mmol), and H2O (10 mL) was adjusted to pH = 6.0 with 0.5 M NaOH solution. The mixture was stirred at room temperature 3313



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m, 1166 w, 1133 m, 1101 w, 1029 w, 847 m, 791 w, 766 s, 727 m, 528 w, 430 m. X-ray Crystallography. The X-ray single-crystal data collection for complexes was performed on a Bruker Smart CCD diffractometer, using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Semiempirical absorption corrections were applied using the SADABS program. The structures were solved by direct methods and refined by full-matrix least-squares on F2 using the SHELXS-97 and SHELXL-97 programs.5 All non-hydrogen atoms were refined anisotropically by full-matrix least-squares methods on F2. All the hydrogen atoms (except those bound to water molecules) were placed in calculated positions with fixed isotropic thermal parameters and included in structure factor calculations in the final stage of full-matrix leastsquares refinement. The hydrogen atoms of water molecules were located by difference maps and constrained to ride on their parent O atoms. CCDC-874031 for 1, 873971 for 2, 873972 for 3, 873963 for 4, 873967 for 5, 873964 for 6, 873968 for 7, 874030 for 8, 873970 for 9, 873969 for 10, 873965 for 11, and 873966 for 12 contain the supplementary crystallographic data for this paper, which can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Scheme 2. Synthetic Strategy of Compounds 1−12

Crystal Structures Descriptions. {[Cd(Hcpna)2(H2O)2]·3H2O}n (1). Single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the orthogonal space group Pca21. The asymmetrical unit of compound 1 contains one crystallographically unique Cd(II) ion, two Hcpna− ligands, two coordinated water molecules, and two solvent water molecules. The partial deprotonation of H2cpna to give Hcpna− in 1 is also confirmed by the IR spectral data of 1 since a middle band at 1710 cm−1 from −COOH was observed (see experimental section). As shown in Figure 1a, Cd(II) ion is six-coordinated with four O atoms and two N atoms, constructing a distorted octahedral coordination geometry with two carboxylate O atoms from two individual Hcpna− ligands, and two O atoms of two coordinated water molecules occupy the equatorial positions; two N atoms from two individual Hcpna− ligands take the axial positions. The lengths of Cd−O bonds range from 2.307(3) to 2.405(3) Å, the Cd−N bonds vary from 2.309(3) to 2.342(3) Å. The Hcpna− ligands in 1 have two different conformations, one is deformed trans type (Scheme 3, mode I) and the other is deformed cis type (Scheme 3, mode II) in which deprotonated carboxylate groups take different coordination modes, that is, μ1−η1:η0 monodentate mode and μ1−η1:η1 didentate mode, respectively. Hcpna− ligands connect Cd(II) atoms through N atoms of the pyridyl rings and O atoms of deprotonated carboxylate groups to generate a (4,4) 2D net (Figure 1b). The Cd···Cd distances bridged by Hcpna− ligands with deformed cis and trans conformation are 7.878(2) and 7.673(2) Å, respectively. The dihedral angles of the pyridyl and the phenyl rings in one Hcpna− ligand with deformed cis and trans conformation are 64.23° and 62.73°, respectively. The 2D layers are further extended into a 3D metal−organic supramolecular framework by weak C−H···O hydrogen bond interactions (C23i−H23i···O5, C23i···O = 3.636(6) Å, i = 1 + x, y, 1 + z; Figure S1, Supporting Information). [Cd(cpna)(H2O)]n (2). When the pH value of the same reaction system was changed from 4 to 6, complex 2 with complete deprotonated cpna2− ligand was isolated. The asymmetric unit of 2 contains one Cd(II) atom, one cpna2− ligand, and one coordinated water molecule. As depicted in Figure 2a, each Cd(II) atom adopts seven-coordinated pentagonal bipyramid geometry formed by one N atom of the pyridyl ring from one cpna2− ligand, five O atoms from three distinct cpna2− ligands, and one coordinated water molecule. The lengths of Cd−O bonds are in the range of 2.285(3)−2.499(3) Å, and those of the Cd−N bonds are 2.344(3) Å. In 2, the cpna2− ligand adopts coordination mode III (Scheme 3) in which two carboxylate groups show μ1−η1:η1 didentate mode and μ2−η1:η2 tridentate mode, respectively.

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RESULTS AND DISCUSSION Synthesis and Characterization. The reactions of metal chloride and H2cpna ligands resulted in formation of precipitates by common methods. Therefore, the hydrothermal method was employed in this work for the syntheses of the title complexes. In the process of hydrothermal synthesis, several elements can influence the formation of crystal phases, such as initial reactants, molar ratio, pH value, reaction time, temperature, etc. In this work, parallel experiments show that the pH values of the reaction system and the auxiliary ligands are crucial for formation of the compounds. We first carried out the reaction at a pH value of 4.0, and compound 1 with (4,4) 2D layered structure was obtained in which H2cpna ligand is partially deprotonated to give Hcpna− form. When pH value in the same reaction mixture was adjusted to 6.0, compound 2 with 2D layered structure based on a binuclear unit was isolated in which H2cpna ligand is completely deprotonated to afford cpna2− form. Meanwhile, if pH value of the reaction system was adjusted to 4−5, a series of lanthanide(III) coordination polymers (complexes 8−12) were synthesized in which both forms of H2cpna ligand were observed. In order to explore auxiliary ligand effects on modulating the structures of coordination polymers, we introduced the chelating N-donor ligand 2,2′-bipy in the reaction system. Then, complexes 3−5 with 2D layered structures were obtained. When another chelating N-donor ligand phen with a large steric hindrance was selected to replace 2,2′-bipy ligand, compounds 5 and 6 exhibiting 1D step-like chain structures were isolated (Scheme 2). The large steric hindrance of phen ligand is responsible for the difference in the structures of 3−5 as well as 6 and 7. The structure of 8 is different from that of 9, which can be attributed to the same reason. In the IR spectra of H2cpna, the absorption band at 1694− 1710 cm−1 is attributed to the asymmetric stretching vibration of uncoordinated carboxylic groups in 1 and 8−12. The absence of the band 1694−1710 cm−1 indicates that H2cpna ligands are completely deprotonated in 2−7. Crystallographic data as well as details of data collection and refinement for these complexes are summarized in Table 1, and important bond lengths and bond angles are listed in Table S1, Supporting Information. Hydrogen bonds in crystal packing for the compounds 1−7 and 9−12 are listed in Table S2, Supporting Information. 3314



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Table 1. Crystal Data and Structure Refinements for the Compounds 1−12 complex

1

2

3

4

5

6

empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) volume (Å3) Z Dcalcd (g cm−3) M (Mo Kα) (mm−1) F (000) data/restraints/parameters goodness-of-fit on F2 final R indices, [I > 2σ(I)] R indices (all data)

C26H26CdN2O13 686.89 orthorhombic Pca21 8.0615(16) 25.852(5) 13.293(3) 90 90 90 2770.2(9) 4 1.647 0.86 1392 5142/11/403 1.009 R1 = 0.0334 wR2 = 0.0723 R1 = 0.0408 wR2 = 0.0756 7

C13H9CdNO5 371.61 monoclinic P21/c 12.103(8) 10.228(7) 11.123(7) 90 114.342(5) 90 1254.6(14) 4 1.967 1.759 728 2330/4/189 1.075 R1 = 0.0185 wR2 = 0.0446 R1 = 0.0221 wR2 = 0.0472 8

C23H17CdN3O5 527.8 monoclinic P21/c 16.639(6) 9.887(4) 13.205(5) 90 106.768(3) 90 2079.9(13) 4 1.685 1.092 1056 3835/0/297 0.998 R1 = 0.0229 wR2 = 0.0550 R1 = 0.0286 wR2 = 0.0585 9

C23H17CoN3O5 474.33 monoclinic P21/c 16.603(12) 9.712(7) 12.777(9) 90 105.503(6) 90 1985(2) 4 1.587 0.908 972 3681/0/294 1.026 R1 = 0.0437 wR2 = 0.1042 R1 = 0.0602 wR2 = 0.1134 10

C23H17MnN3O5 470.34 monoclinic P21/c 16.567(4) 9.838(2) 13.030(3) 90 105.955(2) 90 2041.9(8) 4 1.53 0.689 964 3761/0/290 1.038 R1 = 0.0542 wR2 = 0.1178 R1 = 0.0910 wR2 = 0.1363 11

C25H17CoN3O5 498.35 triclinic P1̅ 9.4178(6) 10.2005(7) 12.0937(9) 76.185(6) 89.248(6) 67.319(6) 1036.89(12) 2 1.596 0.874 510 3876/2/315 1.026 R1 = 0.0357 wR2 = 0.0702 R1 = 0.0500 wR2 = 0.0757 12

C26H25NdN2O13 717.72 orthorhombic Pca21 8.080(11) 25.88(3) 13.345(18) 90 90 90 2791(6) 4 1.708 1.932 1436 5136/4/378 1.198 R1 = 0.0693 wR2 = 0.1811 R1 = 0.0829 wR2 = 0.1936

C38H27PrN4O10 840.55 triclinic P1̅ 9.173(5) 13.657(7) 14.292(7) 97.179(4) 96.766(5) 104.724(4) 1697.1(15) 2 1.645 1.503 844 6221/2/480 1.022 R1 = 0.0426 wR2 = 0.0774 R1 = 0.0543 wR2 = 0.0812

C38H27NdN4O10 843.88 triclinic P1̅ 9.073(16) 13.54(2) 14.06(2) 97.219(16) 96.430(18) 104.87(2) 1637(4) 2 1.712 1.656 846 5950/2/480 0.991 R1 = 0.0497 wR2 = 0.0735 R1 = 0.0796 wR2 = 0.0795

C38H27EuN4O10 851.6 triclinic P1̅ 9.172(10) 13.688(15) 14.179(15) 97.073(11) 96.666(10) 105.301(10) 1683(3) 2 1.68 1.932 852 6134/1/475 1.037 R1 = 0.0478 wR2 = 0.0785 R1 = 0.0776 wR2 = 0.0873

C38H27GdN4O10 856.89 triclinic P1̅ 9.141(3) 13.712(4) 14.123(5) 97.311(3) 96.607(3) 105.351(3) 1672.6(9) 2 1.701 2.052 854 6130/1/483 1.03 R1 = 0.0355 wR2 = 0.0882 R1 = 0.0445 wR2 = 0.0942

complex empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) volume (Å3) Z Dcalcd (g cm−3) M (Mo Kα) (mm−1) F(000) data/restraints/parameters goodness-of-fit on F2 final R indices, [I > 2σ(I)] R indices (all data)

C25H17MnN3O5 494.36 triclinic P1̅ 9.397(4) 10.234(4) 12.236(5) 76.491(4) 89.120(4) 67.549(4) 1053.8(8) 2 1.558 0.672 506 3859/0/308 1.032 R1 = 0.0665 wR2 = 0.1234 R1 = 0.1198 wR2 = 0.1477

crystallographically unique Cd(II) atom, one cpna2− ligand, one 2,2′-bipy ligand, and one coordinated water molecule. As shown in Figure 3a, the Cd(II) center is six-coordinated by two N atoms of the 2,2′-bipy ligand, one N and two O atoms of three individual cpna2− ligands, and one O atom from the coordinated water molecule, resulting in a distorted octahedral coordination geometry. The distances of Cd−O and Cd−N bonds span the range of 2.221(2)−2.380(2) Å and 2.330(2)− 2.379(2) Å. All the Cd−O and Cd−N distances in 1−3 are in good with the bond lengths observed in other Cd(II) complexes.1a,2a,3d,e,6 In 4, the Co−O bond lengths range from 2.045(3) to 2.171(3) Å, and the Co−N bond distances are 2.155(3)−2.163(3) Å. In 5, the Mn−O bond lengths range from 2.103(3) to 2.245(3) Å, and the Mn−N bond distances are 2.252(3)−2.302(3) Å. The cpna2− ligand takes coordination mode IV in which both carboxylate groups adopt μ1−η1:η0

The dihedral angle of the pyridyl and the phenyl rings in one cpna2− ligand is 58.64°. Two crystallographically equal Cd(II) centers are bridged by two O atoms of carboxylate groups from two different cpna2− ligands into a binuclear unit with Cd−Cd distance of 3.779(2) Å and Cd−Ocarboxylate−Cd angle of 103.41(7)° (Figure 2b), which is further connected by cpna2− ligands to form a 2D sheet structure (Figure 2c). The 2D layers are further extended into a 3D metal−organic supramolecular framework by weak C−H···O hydrogen bond interactions (C5i−H5i···O5, C5i···O5 = 3.494(4) Å, i = 1 − x, 1.5 + y, 1.5 − z; Figures S2 and S3, Supporting Information). [Cd(cpna)(2,2′-bipy)(H2O)]n (3), [Co(cpna)(2,2′-bipy)(H2O)]n (4), and [Mn(cpna)(2,2′-bipy)(H2O)]n (5). Singlecrystal X-ray analyses revealed that compounds 3−5 are isostructrural, and the structure of 3 is selected and described in detail. The asymmetrical unit of compound 3 contains one 3315



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Figure 1. (a) Coordination environment of the Cd(II) ions in 1. The hydrogen atoms are omitted for clarity except those bond to carboxylate oxygen atoms. Symmetry codes: i = −x − 1/2, y, z + 1/2; ii = −x + 1/2, y, z + 1/2. (b) Views of the 2D layer along the ac plane. (c) A perspective of 3D framework along the c-axis.

Scheme 3. Various Coordination Modes for Hcpna−/cpna2− in Compounds 1−12

Figure 2. (a) Coordination environment of the Cd(II) ions in 2. The hydrogen atoms are omitted for clarity except those bonded to oxygen atoms of the coordinated water molecules. Symmetry codes: i = −x + 2, −y + 1, −z + 2; ii = x, −y + 1/2, z + 1/2, iii = x, y −1, z. (b) Dinuclear unit. The hydrogen atoms are omitted for clarity. (c) A perspective of 2D framework along the bc plane.

monodentate modes with trans conformation (Scheme 3). Each cpna2− ligand connects three Cd(II) atoms through one

N atom of the pyridyl ring and two O atoms of two monodentate carboxylate group to generate a 2D net (Figure 3316



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Figure 3. (a) Coordination environment of the Cd(II) ions in 3. The hydrogen atoms are omitted for clarity except ones bonded to oxygen atoms of the coordinated water molecules. Symmetry codes: i = x, −y + 1/2, z − 2; ii = x, −y + 3/2, z −1/2. (b) A perspective of the 2D layer along the bc plane. The hydrogen atoms are omitted for clarity. (c) A perspective of 3D framework along the bc plane.

Figure 4. (a) Coordination environment of the Co(II) ions in 4. The hydrogen atoms are omitted for clarity except those bonded to oxygen atoms of the coordinated water molecules. Symmetry codes: i = −x, −y + 1, −z + 1; ii = −x + 1, −y + 1, −z + 1. (b) Views of the 1D ladder chain along ac plane. The hydrogen atoms are omitted for clarity. (c) A perspective of 3D framework along the b-axis.

complexes.1b,g,2b,d,3e,7 In 7, the Mn−O bond lengths are 2.127(3)−2.229(3) Å, the Mn−N bond lengths vary from 2.287(4) to 2.308(4) Å. In 5 and 7, all the Mn−O and Mn−N bond lengths are also comparable to those observed in other Mn(II) complexes.2b,d,e,7 Two Co(II) ions, two cpna2− ligands, two phen ligands, and two coordinated water molecules form a [Co2(cpna)2(phen)2(H2O)2] ring. The rings are further linked by the coordination interaction of cpna2− ligands and Co(II) ions to generate a 1D edge-sharing step-like chain (Figure 4b). The chains are further extended into a 2D sheet by C−H···O hydrogen bond (C10−H10···O5i, C10···O5i = 3.412(4) Å, i = 1 − x, 2 − y, 1 − z) and π−π stacking interactions (N2/C8−C12 and N2/C8i−C12i, Cg···Cg = 3.661(3) Å, i = 1 + x, 1 + y, z; Figure S5, Supporting Information) between neighboring phen planes. The sheets are linked by π−π stacking interactions between adjacent benzene planes of cpna2− ligands (C19−C24 and C19i−C24i, Cg···Cg = 3.548(3) Å, i = 1 + x, 1 + y, z; Figure S6, Supporting Information) to generate a 3D metal− organic supramolecular framework (Figure 4c). In 6, the cpna2− ligand adopts the coordination mode V (Scheme 3) in which both carboxylate groups adopt μ1−η1:η0 monodentate modes with cis conformation. In the cpna2− ligand, the dihedral angles of the phenyl and pyridine rings are 71.11° for 6 and 68.64° for 7, respectively.

3b). The Cd···Cd distance bridged by cpna2− ligand is 8.718(3) Å. The dihedral angles of the pyridyl and the phenyl rings in one cpna2− ligand are 76.55° for 3, 73.09° for 4, and 74.18° for 5, respectively. The 2D layers are linked by C−H···O hydrogen bond (C2i−H2i···O5, C2i···O5 = 3.222(4) Å, I = x, 1 + y, −1 + z) and π−π stacking interactions between adjacent pyridyl planes of cpna2− ligand (N1/C1−C5 and N1ii/C1ii−C5ii, Cg···Cg = 3.706(2) Å, ii =1 − x, 1.5 + y, 0.5 − z; Figure S4, Supporting Information) to generate a 3D metal−organic supramolecular framework (Figure 3c). [Co(cpna)(phen)(H2O)]n (6) and [Mn(cpna)(phen)(H2O)]n (7). Complexes 6 and 7 are also isostructural, hence, only the structure of 6 is described in detail here. The asymmetrical unit of 6 contains one crystallographically unique Co(II) ion, one cpna2− ligand, one phen ligand, and one coordinated water molecule. Co(II) ion is six-coordinated with three O atoms and three N atoms, forming a distorted octahedral geometry in which two carboxylate O atoms from two individual cpna2− ligands and two N atoms of one phen ligand occupy the equatorial positions; one O atom from one coordinated water molecule and one N atom from one cpna2− ligand take the axial positions (Figure 4a). The Co−O distances range from 2.070(2) to 2.171(2) Å, the Co−N distances vary from 2.164(2) to 2.207(2) Å. All the Co−O and Co−O distances in 4 and 6 are comparable with those observed in other Co(II) 3317



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Figure 5. (a) Coordination environment of the Nd(III) ion in 8. The hydrogen atoms are omitted for clarity except those bonded to oxygen atoms of the coordinated water molecules and the carboxylate groups. Symmetry codes: i = −x + 2/5, y, z + 1/2; ii = −x + 3/2, y, z + 1/2. (b) Views of the [Nd4(Hcpna)4(cpna)4] ring. The hydrogen atoms are omitted for clarity. (c) A perspective of the 2D sheet along the b-axis.

Figure 6. (a) Coordination environment of the Nd(III) ions in 10. The hydrogen atoms are omitted for clarity except those bonded to oxygen atoms of the carboxylate groups. Symmetry codes: i = −x + 1, −y + 1, −z + 1; ii = −x + 2, −y + 1, −z + 1; iii = x − 1, y, z. (b) Dinuclear unit. The hydrogen atoms are omitted for clarity except those bonded to oxygen atoms of the carboxylate groups. (c) Views of the 1D wheel chain along ab plane. The hydrogen atoms are omitted for clarity except those bonded to oxygen atoms of the carboxylate groups. (d) A perspective of 3D framework along the b-axis.

{[Nd(Hcpna)(cpna)(H2O)2]·3H2O}n (8). X-ray single crystal diffraction analyses reveal that complex 8 crystallizes in the space group of Pca21 and features a 2D (4,4) structure. The asymmetrical unit of 8 contains one crystallographically unique Nd(III) ion, one cpna2− ligand, one Hcpna− ligand, two coordinated water molecules, and three lattice water molecules.

As shown in Figure 5a, the Nd(III) ion has a seven-coordinate environment, five of which are occupied by three O atoms of carboxyl groups from two individual cpna2− ligands and two O atoms from two coordinated water molecules, and the remaining two sites are occupied by two N atoms of two different cpna2− ligands, forming a distorted pentagonal 3318



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by O−H···N hydrogen−bonding interactions (Figure 6c; Table S2 and Figure S9, Supporting Information). The dihedral angles of the pyridyl and the phenyl rings in one Hcpna− ligand are 70.95° for 9, 72.02° for 10, 73.81° for 11, and 74.27° for 12. Those in one cpna2− ligand are 68.54° for 9, 69.33° for 10, 69.83° for 11, and 70.22° for 12, respectively. Coordination Modes of H2cpna Ligand. Usually H2cpna ligand can show cis and trans conformations. Because of the existence of protonated and/or deprotonated carboxyl groups, the H2cpna ligand exists in partially and fully deprotonated forms, that is, Hcpna− and cpna2−, depending on the pH. Scheme 3 shows eight different coordination modes of H2cpna ligands observed in complexes 1−12 in which the carboxylate groups take four coordination modes, that is, μ 1−η 1:η0 monodentate mode, μ1−η1:η 1 didentate mode, μ2−η1:η1 didentate mode, and μ2−η1:η2 tridentate mode, respectively. The pyridyl N atoms of both Hcpna− and cpna2− ligands coordinated to metal ions in 1−8, but remain uncoordinated and involved in the interchain hydrogen bonding in 9−12. In order to fulfill the requirement of coordination geometries of metal ions in the assembly process, the C−C single bond between pyridyl and phenyl rings of the H2cpna ligand can relatively free rotate (Table S3, Supporting Information). The dihedral angle between the pyridyl and the phenyl rings in one Hcpna−/cpna2− ligand is in the range of 58.64−76.55°. The results indicate that the H2cpna ligands can have various coordination modes to meet the center metal ions in the compounds. Influence of the pH Value and Auxiliary Ligand on the Structures of Compounds 1−12. Complexes 1 and 2 were synthesized under the same reaction conditions, except for the pH values of the reactions (pH = 4.0 for 1 and 6.0 for 2). Their structural differences ambiguously indicate that the assembly process is pH-dependent. On the basis of the structures of 1− 12, it was found that the influence of the pH value on the structures is in fact based on the protonated extend of H2cpna ligand. For example, at pH = 4.0, H2cpna ligand is partially deprotonated to give Hcpna− form in 1. When pH value is adjusted to 6.0, the ligand is completely deprotonated to afford cpna2− form in 2−7. When pH value is adjusted to 4−5, both forms exist in 8−12. The different structure between 2 and 3 is caused by adding auxiliary ligand 2,2′-bipy in 3 under the same reaction conditions. Complexes 4 and 6 (5 and 7) were also isolated under the same reaction conditions except using different auxiliary ligands (2,2′-bipy for 4 and 5; phen for 6 and 7), which result in different structure, that is, 4 and 5 show 2D layer structure and 6 and 7 possess a 1D ladder-chain structure. The reduction of the dimensionality of the structures attribute to the large steric hindrance of phen ligand. The different structures between 8 and 9 can be attributed to the same reason. These results imply that the reaction pH value and auxiliary ligand are important in determining the final structures of the complexes. Thermal Analysis and PXRD Results. Powder X-ray diffraction experiments were carried out for compounds 1−12. The patterns for the as-synthesized bulk materials closely match the simulated ones from the single-crystal structure analysis, which are indicative of the pure solid-state phases (Figure S10, Supporting Information). To further determine the thermal stability of these compounds, their thermal behaviors were investigated under nitrogen atmosphere by TGA (Figure 7). For the discussion in detail, see Table S4, Supporting Information.

bipyramid geometry. The Nd−O distances range from 2.329(7) to 2.693(8) Å, the Nd−N distances vary from 2.308(7) to 2.350(7) Å. The Hcpna− ligand adopts the same coordination mode (Scheme 3 type II) as that in 1, in which the deprotonated carboxylate group shows μ1−η1:η1 didentate mode. The cpna2− ligand adopts coordination mode VI in which one carboxylate group shows μ1−η1:η0 monodentate mode, and another one is free of coordination, which can be confirmed by the observation of a vibration band at 1725 cm−1 in the IR spectrum (see experimental section). Four Nd(III) ions, four Hcpna− ligands, and four cpna2− ligands form a [Nd4(Hcpna)4(cpna)4] ring (Figure 5b). The rings are further connected by the coordination interaction of Hcpna− and cpna2− ligands and Nd(III) ions to generate a 2D (4,4) sheet structure (Figure 4b). The Nd···Nd distances bridged by Hcpna− and cpna2− ligands are 7.912(8) and 7.693 Å, respectively. The dihedral angles of the pyridyl and the phenyl rings in one Hcpna− and one cpna2− ligand are 64.41° and 62.30°, respectively. The sheets are further extended into a 3D metal−organic supramolecular framework by C−H···π hydrogen bond (C11−H11···π (C7i−C12i), i = −1 + x, y, 1 + z; H···π = 2.758(3) Å; Figures S6 and S7, Supporting Information). {[Ln(Hcpna)(cpna)(phen)]·2H2O}n (Ln = Pr (9), Nd (10), Eu (11), and Gd (12)). Compounds 9−12 are isostructural and feature a 1D wheel-chain structure based on a binuclear unit. The structure of complex 10 will be described as an example. The asymmetrical unit of compound 10 contains one crystallographically unique Nd(III) ion, one Hcpna− ligand, one cpna2− ligand, and two lattice water molecules. Unlike compound 8, Nd(III) ion is nine-coordinated by five carboxylate O atoms of four individual cpna2− ligands, two carboxylate O atoms from one Hcpna− ligand, and two N atoms of one phen ligand, which resembles a distorted tricapped trigonal geometry (Figure 6a). The Nd−O bond lengths range from 2.398(4) to 2.741(5) Å, the Nd−N distances vary from 2.597(6) to 2.608(6) Å. All the Ln−O and Ln−N distances in compounds 8−12 are comparable to those reported for other Ln−O and Ln−N donor complexes.1i,k,o,2b,8 The Ln−O and Ln−N distances and cell volumes decrease with the lanthanide contraction (Tables 1 and S1, Supporting Information). The Hcpna− ligand adopts coordination mode VII in which a deprotonated carboxylate group shows μ1−η1:η1 didentate mode. The cpna2− ligand takes coordination mode VIII in which two carboxylate groups take μ2−η1:η1 didentate mode and μ2−η1:η2 tridentate mode, respectively. It should be mentioned that in 9−12, the N atoms of both Hcpna− and cpna2− ligands remain uncoordinated and are involved in the interchain hydrogen bonding (O9−H1W···N1i, O3−H5···N2ii, i = −x + 1, −y + 1, −z + 1; ii = −x + 1, −y, −z + 1), which is different from that in the above-mentioned 1−8. Two crystallographically equal Nd(III) centers are bridged by two O atoms of carboxylate groups from two different cpna2− ligands and two carboxyl groups from two individual cpna2− ligands in bidentate mode into a binuclear unit (Figure 6b) with a Nd−Nd distance of 3.994(5) Å (4.049(2) Å for Pr−Pr in 9, 4.005(4) Å for Eu−Eu in 11, and 4.002(3) Å for Gd−Gd in 12) and Nd−O carboxylate −Nd angle of 103.41(7)° (101.41(11)° for Pr−Ocarboxylate−Pr in 9, 102.38(14)° for Eu− Ocarboxylate−Eu in 11, and 102.73(11)° for Gd−Ocarboxylate−Gd in 12), which is further joined by cpna2− ligands to form a 1D wheel-chain structure (Figure 6b). The 1D chains are further extended into a 3D metal−organic supramolecular framework 3319



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extremely sensitive to chemical bonds in the vicinity of Eu(III). Furthermore, the intensity of the 5D0 → 7F2 transition increases as the site symmetry of Eu(III) decreases. Therefore, the intensity ratio of the 5D0 → 7F2 transition compared with that of the 5D0 → 7F1 transition has been widely used as a measure of the coordination state and the site symmetry of the rare earth ions.10 For complex 11, the intensity of the 5D0 → 7F2 transition is much stronger than that of the 5D0 → 7F1 transition; the intensity ratio I(5D0 → 7F2)/I(5D0 → 7F1) is ca. 8.5, which suggests that the Eu(III) ions in 11 have a noncentrosymmetric coordination environment. This is also consistent with the result of the single-crystal X-ray analysis. Magnetic Properties. Variable-temperature magnetic susceptibility measurements were performed on powder samples of 4−10 and 12 in the temperature range of 2−300 K (Figure 9). For 4 and 6, as shown in Figure 9, the χMT values at room temperature are 3.14 cm3 mol−1 K for 4 and 3.18 cm3 mol−1 K for 6, which are larger than that (1.87 cm3 mol−1 K) expected for one magnetically isolated high-spin CoII ion with S = 3/2, revealing a significant orbital contribution as also found in other high spin Co complexes.11 The monotonic decrease in χMT with cooling temperature is indicative of dominant antiferromagnetic interaction. At the temperature range of 50−300 K, the magnetic susceptibility obeys the Curie−Weiss law, χM = CM/(T − θ), with θ = −11.2 K, CM = 3.26 cm3 K mol−1 for 4, and θ = −10.8 K, CM = 3.30 cm3 mol−1 K for 6, respectively. The negative θ values indicate the presence of dominant antiferromagnetic interactions adjacent to CoII centers. We tried to fit the magnetic data of 6 using the following expression12 for a 1D Co(II) chain:

Figure 7. Thermogravimetric analyses (TGA) curves of compounds 1−12.

Luminescent Properties. Coordination polymers, especially those with Eu, Tb, and d10 metal centers, have been investigated for their luminescent properties and potential applications. Therefore, the luminescent properties of complexes 1−3, 11, and free H2cpna ligand were measured in the solid state, as shown in Figure 8. The maxima of emission band is observed at 506 nm (λex = 445 nm) for free H2cpna ligand, which is assigned to the π* → π electronic transitions of the free ligand. For complexes 1−3, these peaks are shifted to 514, 520, and 524 nm (λex = 472 nm for 1, 465 for 2, and 482 for 3), respectively. Since the profiles and locations of the emission band in the spectra of the compounds are similar to those observed in the free ligand, they can be assigned mainly to intraligand transitions.9 The red-shift of emission spectra observed in complexes 1−3 in comparison with the corresponding to free ligand, may be attributed to the deprotonation of the ligand in complexes. Complex 11 emits intense red luminescence under UV light (Figure 8b). When excited at 393 nm, compound 11 yields intense red luminescence and exhibits characteristic peaks at 592 (5D0 → 7F1), 612 (5D0 → 7F2), 650 (5D0 → F3), and 701 nm (5D0 → 7F4) originating from the transition of 5D0 → 7FJ (J = 1−4) of the Eu(III) ion. It is to be noted that the 5D0 → 7F1 transition is a magnetic dipole transition, and its intensity varies with the crystal field strength acting on Eu(III). However, the 5 D0 → 7F2 transition is an electric dipole transition, and it is

χchain = (Ng 2β 2 /kT )[2.0 + 0.0194x + 0.777x 2] × [3.0 + 4.346x + 3.232x 2 + 5.834x 3]−1

x = |J | /kT

Using this rough model, the susceptibilities for 6 above 100 K were simulated, leading to J = −3.52 cm−1, g = 2.58, and the agreement factor R = 5.35 × 10−5. R = 3.21 × 10−4 (R = ∑(χobsT − χcalcT)2/∑(χobsT)2). The rather low J parameter indicates that an extremely weak antiferromagnetic exchange coupling exists between the adjacent Co(II) centers, which is agreement with a negative θ value. The χMT values at room temperature, 4.55 cm3 mol−1 K for 5 and 4.61 cm3 mol−1 K for 7, are close to the value of 4.38 cm3

Figure 8. Solid state emission spectra of 1−3 (a) and 11 (b) at room temperature. 3320



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Figure 9. Temperature dependence of χMT (○) and 1/χM (□) vs T for compounds 4−10 and 12. The blue lines represent the best fit to the fitted equation in the text. The red lines show the Curie−Weiss fitting.

mol−1 K expected for magnetically isolated high-spin Mn(II) (SMn = 5/2, g = 2.0). The χMT values steadily decrease with decreasing temperature to reach minimum values of 3.88 cm3 mol−1 K at 51.0 K for 5 and 3.94 cm3 mol−1 K at 43.0 K for 7. Between 50 and 300 K, the magnetic susceptibilities can be fitted to the Curie−Weiss law with CM = 4.77 cm3 mol−1 K, θ = −14.2 K for 5 and CM = 4.61 cm3 mol−1 K, θ = −12.0 K for 7, respectively. These results show a weak antiferromagnetic interaction between the Mn(II) centers. Upon further cooling,

the χMT values increase up to a maximum of 4.18 cm3 mol−1 K at TN = 35.0 K for 5 and 4.34 cm3 mol−1 K at TN = 38.5 K for 7 and then decrease with decreasing temperature. This effect might probably be related to a spin-canted antiferromagnetic behavior with a weak ferromagnetic ordering taking place below the Neel temperature.13 We tried to fit the magnetic data of 7 using the following expression14 for a 1D Mn(II) chain: χchain = (Ng 2β 2 /kT )[A + Bx 2][1 + Cx + Dx 3]−1 3321



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with A = 2.9167, B = 208.04, C = 15.543, D = 2707.2, and x = | J|/kT Using this rough model, the susceptibilities for 7 above 43 K were simulated, leading to J = −1.15 cm−1, g = 2.08, and the agreement factor R = 6.24 × 10−6 (R = ∑(χobsT − χcalcT)2/ ∑(χobsT)2). The rather low J parameter confirms that an extremely weak antiferromagnetic exchange coupling exists between the adjacent Mn(II) centers, which is in agreement with a negative θ value. For 8, at 300 K, the χMT value of 1.70 cm3 mol−1 K is close to the value expected (1.64 cm3 mol−1 K) for one insulated Nd(III) ion (S = 3/2, L = 6, 4I9/2, g = 8/11). χMT value gradually decreases to reach 0.52 cm3 mol−1 K at 2 K. Between 90 and 300 K, the magnetic susceptibilities can be fitted to the Curie−Weiss law, χM = CM/(T − θ), with CM = 1.76 cm3 K mol−1 and θ = −12.5 K. These results imply a weak antiferromagnetic interaction between the adjacent Nd(III) centers. The thermal variation of the χMT product for 9 is shown in Figure 9. At 300 K, χMT is equal to 1.57 cm3 mol−1 K, which is the value expected (1.60 cm3 mol−1 K) for one Pr(III) (S = 1, L = 5, 3H4, g = 4/5). Upon lowering the temperature, the χMT value decreases continuously to a value of 0.10 cm3 mol−1 K at 2 K. Between 20 and 300 K, the magnetic susceptibilities can be fitted to the Curie−Weiss law with CM = 1.74 cm3 K mol−1 and θ = −31.5 K. These results indicate a strong antiferromagnetic interaction between the neighboring Pr(III) ions. For 10, the χMT value at room temperature is 1.67 cm3 mol−1 K, which is close to the value expected (1.64 cm3 mol−1 K) for one insulated Nd(III) ion (S = 3/2, L = 6, 4I9/2, g = 8/11). χMT value decreases continuously to a value of 0.63 cm3 mol−1 K at 2 K. Between 20 and 300 K, the magnetic susceptibilities can be fitted to the Curie−Weiss law with CM = 1.85 cm3 K mol−1 and θ = −33.1 K. These results demonstrate a strong antiferromagnetic interaction between the adjacent Nd(III) centers. For 12, at 300 K, the χMT value of 7.97 cm3 mol−1 K is close to the value expected (7.87 cm3 mol−1 K) for one magnetically isolated Gd(III) ion (S = 7/2, L = 0, 8S7/2, g = 2.0). The χMT value gradually decreases to reach 0.28 cm3 mol−1 K at 2 K. Between 100 and 300 K, the magnetic susceptibilities can be fitted to the Curie−Weiss law with CM = 8.24 cm3 mol−1K and θ = −11.8 K. These results indicate a weak antiferromagnetic interaction between the adjacent Gd(III) centers. According to the chain topology of compounds 9−12, because of the long metal−metal distance between the metal centers of dinuclear units, only the coupling interactions between the metal centers within them are considered. There are two sets of magnetic exchange pathways within the dinuclear units, which consist of two carboxylate groups in syn−syn fashion and two η2−O bridges from the μ2-carboxylate groups, cooperatively contributed by the antiferromagnetic coupling transported by mixed bridges, with large La−O−La (101.41−103.41°) angles. The larger antiferromagnetic coupling observed in 10 than that in 8 can be attributed to the small Nd···Nd separation (3.994(5) Å) in the diametric Nd(III) ions.

pH value of the reaction system and auxiliary ligand play a crucial role in determination of the structures of the coordination polymers.

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ASSOCIATED CONTENT

* Supporting Information S

Tables of selected bond distances and angles, hydrogen bonds in crystal packing of the complexes, 2D and 3D renderings of Figures S1−S9, the TGA table, UV−vis absorption spectra, and room temperature PXRD patterns of the compounds 1−12; crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-931-8915196. Fax: +86-931-8915196. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (Projects 20931003 and 21071068).

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REFERENCES

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CONCLUSIONS In this work, by adjusting the reaction pH value and/or using auxiliary ligand, a series of coordination compounds based on H2cpna ligand were prepared by the hydrothermal method. These compounds possess different types of 1D and 2D frameworks. Their structural diversities demonstrate that the 3322



Article

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