Ligands effect on the structures of A series of coordination polymers: Syntheses, structures, luminescence and magnetism

Inorganica Chimica Acta 427 (2015) 285–292

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Ligands effect on the structures of A series of coordination polymers: Syntheses, structures, luminescence and magnetism Xinyu Cao, Dandan Yang, Na Li, Rudan Huang ⇑ Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081, PR China

a r t i c l e

i n f o

Article history: Received 18 November 2014 Received in revised form 9 January 2015 Accepted 11 January 2015 Available online 17 January 2015 Keywords: Metal–organic coordination polymer UV–Vis absorption Luminescence Magnetism Hydrothermal reaction

a b s t r a c t Six coordination polymers, namely, Mn(dpd)(bpy)(H2O) (1), Co(dpd)(bpy) (2), Cu(dpd)(H2dpd)(bpy) (3), Mn(dpd)(phen)2(H2O) (4), Co(dpd)(phen)(H2O) (5), Co(dpd)(phen)(H2O) (6) (H2dpd = 2,4-diphenyl ether dicarboxylic acid, bpy = 2,20 -bipyridine, phen = 1,10-phenanthroline) have been synthesized under similar hydrothermal conditions by H2dpd, auxiliary ligands and different transition metal salts. Complex 1 is a 3D (3,3)-connected framework which is connected by dpd2 ligand. Complex 2 shows 1D zigzag chain, which is further connected by hydrogen bonds to form a 3D supramolecular net. Complex 3 is constructed from infinite 1D chains which are linked by dpd2 ligand exhibiting a 2D supramolecular layer. Complex 4 is a mononuclear structure which is further self-assembled through hydrogen bonding and pp stacking interactions to generate a 3D supramolecular structure. Complexes 5 and 6 are 1D chains and further connected by hydrogen bonding and p  p stacking interactions to form a 3D supramolecular structure. These complexes have been characterized by elemental analysis, infrared (IR), thermal gravimetric analysis (TGA), powder X-ray diffraction (PXRD) and single crystal X-ray diffraction. Furthermore, UV–Vis spectra and fluorescence properties of 1–6 have been investigated. Magnetic susceptibility measurements indicate that complexes 2–6 all show weak ferromagnetic behaviors. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction Metal–organic coordination polymers have attracted much attention in the field of crystal engineering, material, solid and coordination chemistry [1–6], which is owing to their intriguing architectures and promising applications in magnetism [7–9], catalysis [10–12] and optics [13–15]. The self-assembly of different metal centers and organic linkers is one of the most efficient strategies for the construction of diverse structures and desired functionalities of coordination polymers [16]. In this case, multidentate organic ligands containing O-donor or N-donor have been confirmed to play important roles in the construction of coordination polymers [17–19]. The dicarboxyl groups can possess four potential coordination sites to adopt different coordination modes (Scheme 1) and the – C@O groups can act as O-donors. It is well known that dicarboxylate ligand is a perfect candidate to form versatile coordination conformations from terminal monodentate to various modes to result in 0D cages, 1D chains, 2D grids and 3D porous frameworks [20,21]. Furthermore, bpy and phen ligands containing N-donor are

⇑ Corresponding author. Tel./fax: +86 010 68912667. E-mail address: [email protected] (R. Huang). http://dx.doi.org/10.1016/j.ica.2015.01.018 0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

often used for constructing coordination polymers because of their chelating ability with the metal centers [22]. They can also interact with the metal centers through p  p stacking interactions and act as hydrogen bond donors and acceptors to adjust to different structures of complexes [23,24]. Hence the 2,4-diphenyl ether dicarboxylic acid and N-containing auxiliary ligands were used to synthesize six novel metal–organic coordination polymers, Mn(dpd)(bpy)(H2O) (1), Co(dpd)(bpy) (2), Cu(dpd)(H2dpd)(bpy) (3), Mn(dpd)(phen)2(H2O) (4), Co(dpd)(phen)(H2O) (5), Co(dpd)(phen)(H2O) (6). These complexes are characterized by elemental analysis, IR, TG, and single crystal X-ray diffraction. UV–Vis spectra, fluorescent and magnetic properties of these complexes are also discussed.

2. Experimental 2.1. Materials and methods All reagents and solvents were purchased commercially and used as-purchased without further purification. Elemental analysis for C, H and N were carried out with a Perkin-Elmer 2400 CHN elemental analyzer. The IR spectra were recorded (as KBr pressed pellets) in the range of 400–4000 cm1 on a Nicolet 170SXFT-IR

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spectrometer. Thermal gravimetric analysis (TGA) data were collected on a Perkin-Elmer TGA 7 instrument in nitrogen at a heating rate of 10 °C/min. The PXRD diagrams were collected by a Shimadzu XRD-6000 diffractometer. Fluorescence spectra were measured by a Hitachi Model RF-5301 PC fluorescence spectrophotometer with a Xenon lamp light source. The magnetic measurements were performed on the Quantum Design SQUID MPMSXL-7 instruments in a magnetic field of 1000 Oe in the temperature range of 2–300 K. 2.2. Synthesis of complex 1 A mixture of Mn(OAc)24H2O (0.2 mmol, 0.0490 g), H2dpd (0.2 mmol, 0.0512 g), bpy (0.2 mmol, 0.0312 g), 25% (C2H5)4NOH (mass fraction) aqueous solution (0.1 ml) and H2O (5 mL) was sealed in a 23 mL Teflon-lined autoclave and heated to 160 °C for 3 days. After cooling to room temperature at a speed of 10 °C/h, yellow crystals of complex 1 were obtained, washed with H2O and dried in air (Yield: 42% based on Mn). Anal. Calc. for C24H18MnN2O6: C, 59.39; H, 3.74, N, 5.77. Found: C, 59.29; H, 3.88; N, 5.72%. IR (KBr, cm1): 3381 (s), 1590 (s), 1545 (s), 1479 (m), 1422(s), 1365 (m), 1243 (s), 1165 (m), 1102 (w), 1057 (w), 1032 (m), 1006 (w), 893 (m), 847 (m), 802 (w), 759 (s), 720 (w), 645 (w), 612 (w), 497(w). 2.3. Synthesis of complex 2 The synthetic procedure was similar to that of 1, except Co(OAc)24H2O (0.2 mmol, 0.0498 g) replaced Mn(OAc)24H2O. The dark red crystals were obtained, washed with H2O and dried in air (Yield: 65% based on Co). Anal. Calc. for C24H16CoN2O5: C, 61.16; H, 3.42; N, 5.94. Found: C, 61.06; H, 3.37; N, 5.85%. IR (KBr, cm1): 3381 (s), 1596 (s), 1551 (s), 1476 (m), 1440 (m), 1395(s), 1372 (s), 1221 (s), 1161 (m), 1092 (m), 1049 (s), 877 (m), 759 (s), 709 (w), 697 (w), 669 (w), 646 (m), 559 (w), 535 (w), 465 (w). 2.4. Synthesis of complex 3 The synthetic procedure was similar to that of 1, except Cu(OAc)2H2O (0.2 mmol, 0.0398 g) replaced Mn(OAc)24H2O. The blue crystals were obtained, washed with H2O and dried in air

(Yield: 33% based on Cu). Anal. Calc. for C38H25CuN2O10: C, 62.25; H, 3.44; N, 3.82. Found: C, 62.34; H, 3.57; N, 3.75%. IR (KBr, cm1): 3381 (s), 1598 (s), 1540 (s), 1473 (m), 1443 (s), 1416(s), 1315 (m), 1239 (s), 1159 (m), 1095 (m), 1056 (w), 1024 (w), 1013 (w), 887 (m), 855 (m), 806 (w), 774 (s), 765 (s), 735 (w), 714 (w), 666 (w), 649 (w), 606 (w), 510 (w). 2.5. Synthesis of complex 4 The synthetic procedure was similar to that of 1, except the temperature was adjusted to 110 °C and bpy was replaced by phen (0.2 mmol, 0.0360 g). The yellow crystals were obtained, washed with H2O and dried in air (Yield: 45% based on Mn). Anal. Calc. for C38H26MnN4O6: C, 66.19; H, 3.80; N, 8.12. Found: C, 66.25; H, 3.62; N, 8.15%. IR (KBr, cm1): 3381 (s), 1619 (s), 1593 (s), 1572 (m), 1562 (m), 1552 (m), 1514 (m), 1478 (w), 1444 (w), 1425 (m), 1370 (s), 1230 (s), 1153 (w), 1092 (w), 1040 (w), 881 (w), 863 (w), 847 (m), 809 (w), 757 (w), 728 (m), 669 (w), 544 (w), 506 (w), 493 (w), 455 (w), 440 (w). 2.6. Synthesis of complex 5 The synthetic procedure was similar to that of 4, except Co(OAc)24H2O (0.2 mmol, 0.0498 g) replaced Mn(OAc)24H2O. The orange block crystals were obtained, washed with H2O and dried in air (Yield: 58% based on Co). Anal. Calc. for C26H18CoN2O6: C, 60.83; H, 3.53; N, 5.46. Found: C, 60.72; H, 3.59; N, 5.56%. IR (KBr, cm1): 3381 (s), 1614 (s), 1589 (s), 1565 (s), 1540 (s), 1515 (m), 1485 (w), 1450 (w), 1423 (m), 1365 (s), 1235 (s), 1146 (m), 1081 (m), 1043 (w), 916 (w), 863 (w), 838 (m), 805 (w), 750 (m), 730 (m), 667 (m), 548 (w), 515 (w), 492 (w). 2.7. Synthesis of complex 6 The synthetic procedure was similar to that of 5 except the temperature was adjusted to 85 °C. The orange crystals were obtained, washed with H2O and dried in air (Yield: 63% based on Co). Anal. Calc. for C26H18CoN2O6: C, 60.83; H, 3.53; N, 5.47. Found: C, 60.91; H, 3.64; N, 5.62%. IR (KBr, cm1): 3381 (s), 1608 (s), 1601 (m), 1570 (s), 1558 (m), 1515 (m), 1487 (s), 1455 (m), 1422 (w), 1361 (s), 1240 (m), 1151 (m), 1143 (w), 1097 (s), 1043 (m), 873 (w), 845 (s), 804 (m), 764 (w), 662 (m), 621 (m), 540 (w), 497 (w).

Scheme 1. Coordination modes of H2dpd ligand in complexes 1–6 (Metal atoms: yellow balls). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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2.8. Single-crystal X-ray crystallography Diffraction data for 1–6 were collected on a Bruker Smart Apex CCD diffractometer by graphite-monochromated Mo Ka radiation (k = 0.71073 Å). Empirical absorption corrections were taken from SADABS [25]. The space group was determined by using XPREP [26]. The structures were solved by direct methods and refined on F2 with full-matrix least-squares method using the SHELXS-97 and SHELXL-97 [27]. Crystallographic data for complexes 1–6 were summarized in Table 1. Selected bond lengths and angles are given in Table S1, ESI. Hydrogen bonding interactions of 1–6 are given in Table S2, ESI.

3. Results and discussion 3.1. Synthesis Complexes 1–6 were obtained by hydrothermal reactions of H2dpd, N-donor ligands and different transition metal salts. The changes of temperature and reactants ratios remarkably influence the final structures of the products. Different complexes or none were obtained while the temperatures were changed. In addition, several other molar ratios of the reactants (0.1:0.1:0.2, 0.2:0.2:0.1) have been tried before, but only the ratio of Table 1 Crystallographic data for 1–6. Complex

1

2

3

Empirical formula M T (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Z D (Mg/m3) l (mm1) F(0 0 0) R1 (I > 2r(I)) R1 (all data) wR2 (I > 2r(I)) wR2 (all data) Goodness-of-fit (GOF) on F2

C24H18MnN2O6 485.34 293(2) monoclinic Cc 24.3807(17) 10.1541(6) 8.8260(5) 90 108.725(2) 90 4 1.558 0.685 996 0.0700 0.0787 0.1742 0.1838 1.065

C24H16CoN2O5 471.32 293(2) monoclinic P21/c 8.3064(4) 14.7299(7) 17.7972(8) 90.00 100.039(2) 90.00 4 1.460 0.839 964 0.0368 0.0813 0.0855 0.0973 1.004

C38H25CuN2O10 733.14 293(2) triclinic  P1 9.8065(8) 11.5724(13) 15.2320(11) 102.894(2) 91.0670(10) 106.558(2) 2 1.513 0.745 752 0.0405 0.0945 0.0527 0.1037 1.033

Complex

4

5

6

Empirical formula M T (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Z D (Mg/m3) l (mm1) F(0 0 0) R1 (I > 2r(I)) R1 (all data) wR2 (I > 2r(I)) wR2 (all data) Goodness-of-fit (GOF) on F2

C38H26MnN4O6 689.57 293(2) triclinic  P1

C26H18CoN2O6 513.35 293(2) monoclinic P2(1)/n 10.0474(9) 22.0489(19) 10.5240(9) 90 107.6010(10) 90 4 1.534 0.820 1052 0.0504 0.1297 0.0894 0.1133 0.978

C26H18CoN2O6 513.35 293(2) monoclinic P2(1)/c 10.0668(5) 22.0695(8) 12.1783(7) 90 124.340(2) 90 4 1.526 0.815 1052 0.0421 0.0687 0.0803 0.0949 1.032

9.2653(7) 13.6899(18) 14.8025(11) 107.668(2) 92.9300(10) 109.157(2) 2 1.375 0.450 710 0.0727 0.1738 0.0821 0.1034 0.911

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0.2:0.2:0.2 succeeded to obtain the complexes. Auxiliary N-donor ligands and different coordination modes of dpd2 ligand may also play important roles in complexes 1–6, and may be a feasible method to adopt different ligands to construct coordination polymers with targeted structures. 3.2. Crystal structure of 1 Single crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the monoclinic crystal system Cc. The asymmetric unit contains one Mn(II) atom, one dpd2 ligand, one bpy ligand and one water molecule. As shown in Fig. 1a, each Mn(II) atom is placed in a distorted octahedron, which is completed by three oxygen atoms from three dpd2 ligands, two nitrogen atoms from one chelating bpy ligand and one water molecules. The Mn–O bond lengths are in the range of 2.121–2.227 Å, and the Mn–N bond lengths are 2.277 and 2.307 Å. Each dpd2 ligand adopts a bidentate and monodentate–bridging mode, linking three independent Mn(II) atoms (Scheme 1a). Adjacent Mn(II) atoms are connected by dpd2 ligands into a 3D metal–organic framework. The Mn(II) atom and dpd2 ligand can be simplified as 3-connected nodes. Thus, the whole framework can be considered as a (3,3)-connected net (Fig. 1d). 3.3. Crystal structure of 2 Complex 2 shows a zigzag 1D chain and crystallizes in the monoclinic space group of P21/c. In the asymmetric unit of complex 2, there are one Co(II) atom, one dpd2 ligand and one bpy ligand. The Co(II) atom is six-coordinated by four oxygen atoms from two dpd2 ligands and two nitrogen atoms from one chelating bpy ligand (Fig. 2a). The dpd2 ligand adopts a chelating coordination mode to connect two Co(II) atoms (Scheme 1b), linking the Co(II) atoms into a zigzag 1D chain (Fig. 2c). The p  p stacking interactions of the nearly bpy ligands with the distances between 3.7059 Å and 3.8962 Å connect the adjacent chains to a 3D supramolecular structures along a axis (Fig. 2b). 3.4. Crystal structure of 3 Single crystal structure analysis reveals that complex 3 crystallizes in the monoclinic crystal system with P2(1)/c space group. There are one Cu(II) atom, one dpd2 ligand, one H2dpd and one bpy ligand in the asymmetric unit (Fig. 3a). The coordination geometry of Cu(II) atom is completed by three oxygen atoms from two dpd2 ligand, one oxygen from one H2dpd ligand and two nitrogen atoms from one bpy ligand. The Cu–O bond lengths are in the range of 1.9095–1.9576 Å and Cu–N bond lengths are 1.984 and 2.001 Å. One type of dpd2 ligand is completely deprotonated, exhibiting both chelating and monodentate coordination modes (Scheme 1c). The other type of H2dpd ligand doesn’t deprotonated in order to reach the charge conservation, exhibiting a monodentate coordination mode (Scheme 1d). Adjacent Cu(II) atoms are connected by dpd2 ligands into an infinite 1D chain (Fig. 3b). These chains are further connected by the hydrogen bonding interactions between the uncoordinated carboxylate oxygen atoms (O  O distance of 2.6297 Å) and weak p  p stacking interactions existing between phenyl rings of dpd2 ligands (distances of 3.8010–3.9407 Å) into a 2D supromolecular layer (Fig. 3c). 3.5. Crystal structure of 4 Complex 4 shows a mononuclear structure, and crystallizes in  The asymmetric unit contains one the triclinic space group of P1. Mn(II) atom, one dpd2 ligand, two phen ligands and one

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Fig. 1. (a) The coordination environment of Mn(II) in 1. (b) 2D layer of 1, viewed along the b axis. (c) 1D layer of 1, viewed along the b axis. (d) 3D net of 1. Hydrogen atoms are omitted for clarity.

coordinated water molecule. The Mn(II) atom is six-coordinated by two O donors from one dpd2 ligand with one coordinated water molecule and four N donors from two chelating phen ligands in a distorted octahedral coordination geometry (Fig. 4a). In 4, only one carboxyl group of the dpd2 ligand participates in bonding while the other one remains free satisfying the charge of the metal centers, exhibiting another coordination mode (Scheme 1e). There are two chelating phen ligands in each asymmetric unit, which occupy four coordination sites of Mn(II) atom. The chelating phen ligands terminate two possible dimensions, which may prevent the complex forming a higher dimensional network. The monomers self-assemble via hydrogen bonding interactions to form 1D linear chains (Fig. 4b). Theses chains are further connected by p  p

stacking interactions between the nearby phen ligands with the distances between 3.6042–3.8506 Å to lead a 3D supramolucular structure (Fig. 4c). 3.6. Crystal structure of 5 Single crystal structure analysis reveals that complex 5 crystallizes in the monoclinic crystal system with P2(1)/n space group. As shown in Fig. 5a, there are one Co(II) atoms, one dpd2 ligand, one phen ligand and one coordinated water molecule in the asymmetric unit. The Co(II) atom in 5 adopts a distorted octahedral coordination geometry formed by three oxygen atoms from two dpd2 ligands, one oxygen atom from coordinated water molecule and two nitrogen atoms from one phen ligand. The Co–O bond lengths range from 2.056–2.244 Å, and the Co–N bond lengths are 2.082 and 2.133 Å. The dpd2 ligand in complex 5 adopts the same coordination mode as it in complex 3 (Scheme 1c). Adjacent Co(II) atoms are connected by dpd2 ligands into an infinite 1D linear chain with a Co  Co distance of 11.718 Å (Fig. 5b). Then, these 1D chains are held together through the hydrogen bonding interactions to form a 2D supramolecular layer (Fig. 5c). Finally, p  p stacking interactions between the nearby phen ligands with the distances of 3.5299–3.8667 Å connect the adjacent 2D layer to a 3D supramolecular structure along c axis (Fig. 5d). 3.7. Crystal structure of 6

Fig. 2. (a) The coordination environment of Co(II) in 2. (b) 3D supramolecular structure of 2 constructed by p  p stacking interactions. (c) 1D zigzag chain of 2. Hydrogen atoms are omitted for clarity.

Single-crystal X-ray analysis reveals that complex 6 is a zigzag 1D chain which crystallizes in the monoclinic crystal system with P2(1)/c space group. In the asymmetric unit of complex 6, there are one Co(II) atom, one dpd2 ligand, one phen ligand and one coordinated water molecule (Fig. 6a). The Co(II) atom is six-coordinated in a distorted octahedral coordination geometry by three oxygen atoms from two dpd2 ligands, two nitrogen atoms from one phen ligands and one oxygen atom from one water molecule. In 6, dpd2 ligand shows the same coordination mode as it in complex 3

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Fig. 3. (a) The coordination environment of Cu(II) in 3. (b) 1D ladder chain of 3. (c) 2D supramolecular layer of 3. Hydrogen atoms are omitted for clarity.

Fig. 4. (a) The coordination environment of Mn(II) in 4. (b) 1D supramolecular chain of 4 (c) 2D supramolecular layer of 4. (d) 3D supramolecular structure of 4 constructed by hydrogen bonding and p  p stacking interactions. Hydrogen atoms are omitted for clarity.

(Scheme 1c), Co(II) atoms are linked by dpd2 ligands into a zigzag chain with a Co  Co distance of 11.7353 Å. The phen planes are coordinated with Co(II) atoms in a chelating fashion. The Co–O distances are in the range of 2.058–2.248 Å, and the Co–N distances are 2.084 and 2.144 Å. In addition, the 1D chains in 6 are linked together by hydrogen bonding interactions which are caused by the coordinated water molecule into a 2D layer supramolecular structure. Finally, the p  p stacking interactions between the nearby phen ligands with the distances of 3.5324–3.8742 Å connect the adjacent 2D layers to a 3D supramolecular structure along b axis (Fig. 6d). 3.8. The effects of the H2dpd ligand and co-ligands on the final structures of complexes 1–6 According to the descriptions above, we can see that factors such as H2dpd ligand and auxiliary ligands may influence the final

structures of complexes 1–6. There exist five different coordination modes of H2dpd in 1–6 (Scheme 1a–e), which have never been reported before. In complex 1, the carboxyl groups of dpd2 adopt bidentate and monodentate-bridging to the Mn(II) atoms, forming a 3D architecture. In complex 2, dpd2 shows a chelating mode and the auxiliary ligand also occupies two coordination sites of Co(II) atom, preventing the 1D structure further forming a higher dimension. In complexes 3, 5 and 6, dpd2 bridges two metal atoms with chelating and monodentate modes, obtaining 1D chain structures. Interestingly, one carboxyl group of H2dpd ligand in 3 coordinates with the Cu(II) atom in a monodentate coordination mode without deprotonation in order to reach the charge conservation. In complex 4, the bpy ligand terminates the Mn(II) atoms on each side preventing the coordination among dpd2 and Mn(II) atoms. Thus, the dpd2 ligand in complex 4 shows a monodentate coordination mode, forming a mononuclear structure. In addition, phen and bpy ligands both show chelating modes in 1–6, which influence the

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Fig. 5. (a) The coordination environment of Co(II). (b) 1D linear chain of 5 (c) 2D supramolecular layer of 5. (d) 3D supramolecular structure of 5. Hydrogen atoms are omitted for clarity.

final structures a lot. Supramolecular interactions between the terminal O atoms and auxiliary ligands such as hydrogen bonding and p  p stacking interactions benefit the assembly of supramolecular structures of 2–6 with higher dimensions. Thus, both the main and auxiliary ligands in 1–6 may have remarkable effects on the final structures.

of 30–126 °C and 30–112 °C, respectively, corresponding to the loss of one coordinated water molecule (calculated: 3.51% and 3.51%, respectively). The residual complexes begin to decompose at 282 and 270 °C leading to the Co2O3 (calculated: 16.15%, found: 15.05%) and Co2O3 (calculated: 16.15%, found:16.70%), respectively.

3.9. Thermogravimetric analysis

3.10. UV–Vis spectra

In order to confirm the phase purity of complexes 1–6, powder X-ray diffraction (PXRD) patterns were measured at room temperature. As seen in Figs. S1–S6, the peaks of the simulated and experimental PXRD patterns are in good agreement with each other, confirming the phase purities of 1–6. Then the thermal stabilities of complexes 1–6 have been studied, their thermogravimetric analyses (TGA) were performed in the temperature of 30–600 °C (Figs. S7–S12). For complex 1, the weight loss is from 30 to 123 °C which is corresponded to the removal of one coordinated water molecule (calculated: 3.71%, found: 3.45%). The residual framework begins to decompose at 227 °C and the retention weight is 14.73% (calculated: 14.62%), corresponding to MnO powder. Complex 2 and 3 remain stable up to 322 °C and 300 °C, respectively, then start to decompose. The remaining weight can be attributed to the formation of Co2O3 (calculated: 17.60%, found: 17.55%) and CuO (calculated: 10.85%, found: 11.06%). The TGA curve of 4 shows a weight loss of 2.91% occurring in the range of 30–120 °C corresponding to the removal of one water molecule (calculated: 2.61%). After the loss of the coordinated water molecule, the residue is stable up to 308 °C and begins to decompose upon further heating. The departure of the structure finally leads to the formation of MnO (calculated: 10.29%, found: 10.79%). In the cases of 5 and 6, weight losses of 4.02% and 3.92% were observed in the temperature ranges

The UV–Vis absorption spectra were carried out in the solid state at room temperature, as shown in Fig. 7. The free ligand H2dpd showed an intense peak ascribed to the p⁄–p or p⁄–n transition at ca. 257 nm [28]. And the broad absorption peaks of complexes 1–4 and 6 are centered at 250 and 296 nm (for 1); 250, 296 and 536 nm (for 2); 245, 303 and 660 nm (for 3); 239, 283 and 397 nm (for 4); 237, 270 and 512 nm (for 6), respectively, which might probably attributed to the intraligand charge–transfer [29]. 3.11. Fluorescence properties The solid-state emission spectra of complexes 1–6 with free H2dpd and auxiliary ligands have been investigated at room temperature. As shown in Fig. 8, the main emission peaks of the H2dpd, bpy and phen ligands are at 361, 390, 379 nm (kex = 250 nm), respectively, which may be attributed to the p⁄–p or p⁄–n transitions of the intraligands [30–31]. Upon excitation of solid samples of 1–6 at 300 nm, these complexes show emissions bands with maximum at 392 nm for 1, 386 nm for 2, 389 nm for 3, 369 nm for 4, 394 nm for 5 and 390 nm for 6, respectively. The emissions of 1–6 may be assigned to intraligand transition upon the combination of the mixed ligands with metal ions [32–34]. The different red shifts and intensities of the emission peaks of these complexes were observed compared with the emission of

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Fig. 6. (a) The coordination environment of Co(II). (b) 1D linear chain of 6. (c) 2D supramolecular layer of 6. (d) 3D supramolecular structure of 6. Hydrogen atoms are omitted for clarity.

Fig. 8. Solid state emission spectra of complexes 1–6 at room temperature. Fig. 7. UV–Vis spectra of complexes 1–6 at room temperature.

the free ligands, which may be assigned to the differences of the coordination environment and the different structures because the photoluminescence behavior is closely associated with the coordinated ligands and metal ions [35,36]. Complexes 1–6 may be good candidates for optical materials. 3.12. Magnetic properties The magnetic behavior of complexes 2–6 have been measured at a temperature range of 2–300 K under an applied magnetic field of 1000 Oe, which is shown as plots of the product 1/vm versus T and versus T in Fig. 9 and 10 and Figs. S13–S15. The 1/vm versus T plot for 2 displays Curie–Weiss behavior from 300 to 50 K, the best linear fit of vm1(T) data above 50 K yields C = 3.04 cm3 K mol1 and h = 1.18 K. This positive Weiss constant indicates the presence of an ferromagnetic interaction between Co(II) centers

through the intermolecular interactions. The vmT value at 300 K is 2.78 cm3 K mol1. Upon cooling the vmT value exhibits a slight increase until 160 K; this may be indicative of the occurrence of ferromagnetic interactions between the Co(II) centers of onedimensional molecular chains. At low temperature starting from 160 K, the vmT value sharply decreases to a minimum value of 1.85 cm3 K mol1 at 2 K. The magnetic behaviors of complexes 5 and 6 are similar to that of complex 2. The 1/vm versus T plots for 5 and 6 display Curie–Weiss behaviors from 300 to 50 K, the best linear fit of vm1(T) data above 50 K yields C = 3.04 cm3 K mol1, h = 3.29 K for 5 and C = 3.04 cm3 K mol1, h = 1.18 K for 6. This positive Weiss constant indicates the presence of a ferromagnetic interaction between Co(II) centres. For complexes 3 and 4, however, upon cooling the vmT value exhibits a rapid increase until 10 K and 45 K; this may be indicative of the occurrence of weak ferromagnetic interactions between Cu(II) and Mn(II) centers through the intermolecular interactions.

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be potential applications as optical materials. In addition, complexes 2–6 all show ferromagnetic behaviors. Acknowledgments This work was financially supported by the National Nature Science Foundation of China (Nos. 21271024 and 20971014), supported by Beijing Natural Science (No 2112037), Foundation the 111 Project (B07012) in China. Appendix A. Supplementary material

Fig. 9. Temperature dependence of magnetic susceptibilities in the form of the vm and vmT vs. T for 2 at 1000 Oe. Inset: vm1 vs. T; the solid line is fit to the experimental data.

Fig. 10. Temperature dependence of magnetic susceptibilities in the form of the vm and vmT vs. T for 3 at 1000 Oe. Inset: vm1 vs. T; the solid line is fit to the experimental data.

As shown in Fig. 10 and Fig. S7, the inverse molar susceptibility above 50 K fits well with the Curie–Weiss law with a Curie constant C = 0.5874 cm3 K mol1 and a Weiss temperature h = 42.37 K for 3 and C = 4.03 cm3 K mol1, h = 6.93 K for 4. The positive Weiss constant indicated ferromagnetic coupling between the Cu(II) and Mn(II) ions. 4. Conclusions In conclusion, six metal–organic coordination polymers assembled by H2dpd and auxiliary ligands have been hydrothermally synthesized and structural characterized. According to the analyses of structures, it seems that the H2dpd and auxiliary ligands play important roles in the constructions of final structures in complexes 1–6. Fluorescent measurements show that the red shifts and intensities of the emission peaks may be assigned to the differences of the coordination environment, indicating that they may

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