English

• 0.   Introduction

  Metal coordination polymers are crystalline solids composed of metal ions and organic ligands. Their structures contain completely isolated metal sites, with advantages such as high catalytic activity, low crystal density, large surface area, adjustable structure, and ordered pore structure arrangement, making them promising new materials. Its application prospects in magnetism^[1-3], catalysis^[4-6], luminescence^[7-9], drug delivery^[10-12], as well as gas adsorption^[13-15] and chemical sensing^[16-24], have attracted widespread attention from chemical and material scientists. However, the rational design and assembly of complexes still face challenges, as factors such as organic ligands, metal ions, synthesis temperature, organic solvents, and pH value have a significant impact on their structure, making it difficult to predict the construction of their molecular structure^[25-27]. By combining metal ions with pre-designed organic ligands under appropriate reaction conditions, various structures of coordination polymers with ideal functions can be obtained. In coordination chemistry, Cu(Ⅱ) and Zn(Ⅱ) ions with variable coordination numbers and universal coordination geometries are widely used to construct 1D, 2D, or 3D coordination polymers. The mixed ligand has multiple functional groups, so a mixing strategy is adopted to obtain a more complex and versatile structure, with better performance coordination polymer^[28-30].

  In this work, 5-(dimethylamino)isophthalic acid (H₂dia) and 1H-imidazole (mdz) were used simultaneously to react with different transition metals under similar conditions, resulting in three new 1D complexes, [Zn(dia)(mdz)₂]·2H₂O (1), [Cu(dia)(mdz)₂(DMF)] (2), and [Cu(dia) (mdz)₂]·H₂O (3). The syntheses, crystal structures, and Hirshfeld surface analyses were investigated. By comparison, the effects of the metal centers and solvent conditions on the structures of complexes were surveyed. Thermal stability and fluorescence properties of complexes 1-3 were also studied.

  1.   Experimental

  1.1   Materials and physical measurements

  All reagents and solvents involved in this work were commercially available analytical pure reagents and were used directly without further purification. Powder X-ray diffraction (PXRD) data were collected on a Bruker D8 ADVANCE A25X diffractometer (Cu Kα, λ =0.154 056 nm) scanning at 40 kV and 40 mA with a speed of 8 (°)·min^-1 and a 2θ range of 5°-50° at room temperature. Elemental analyses (C, H, and N) were conducted using an Elementar Vario EL Ⅲ analyzer. The Fourier-transform infrared (FTIR) spectra were recorded using an FT-IR Nicolet Avatar 360 spectrophotometer within a range of 400-4 000 cm^-1 employing KBr pellets. Thermogravimetric analyses (TGA) were performed using a STA449F31 thermos analyzer from room temperature to 800 ℃ under an N₂ atmosphere at a heating rate of 15 ℃·min^-1. The solid fluorescence spectra were recorded on a Hitachi fluorescence spectrophotometer F-7000 spectrometer at room temperature. The fluorescence lifetime (τ) was recorded on an Edinburgh Molecular Fluorescence FLS 1000.

  1.2   Synthesis

  1.2.1   Synthesis of complex 1

  ZnCl₂·3H₂O (0.1 mmol, 13.63 mg), H₂dia (0.1 mmol, 25.09 mg), mdz (0.1mmol, 6.80 mg), 0.5 mL H₂O, and 3 mL N, N-dimethylformamide (DMF) were mixed and placed in a glass reactor with cover, heated at 80 ℃ for 48 h, cooled to ambient temperature and then filtered. The filtrate volatilized naturally at room temperature. After 5 d, colourless transparent crystals of complex 1 were obtained, with a yield of 34.7% (based on H₂dia). Elemental Anal. Cacld. for C₁₆H₂₁N ₅O₆Zn(%): C, 43.21; H, 4.76; N, 15.75. Found (%): C, 42.53; H, 4.87; N, 15.58. Main IR peaks (KBr, cm^-1): 3 134, 1 674, 1 566, 1 405, 1 144, 1 071, 1 014, 953, 840, 779, 658, 620.

  1.2.2   Synthesis of complex 2

  The synthesis process of complex 2 was similar to that of 1, except that Cu(NO₃)₂·3H₂O (0.1 mmol, 24.16 mg) was used instead of ZnCl₂·3H₂O. Blue block crystals of complex 2 were obtained by evaporating at room temperature for 3 d. Yield: 29.3% based on H₂dia. Elemental Anal. Cacld. for C₁₉H₂₄N₆O₅Cu(%): C, 47.55; H, 5.04; N, 17.51. Found(%): C, 46.81; H, 5.13; N, 17.18. Main IR peaks (KBr, cm^-1): 3 072, 1 570, 1 380, 1 217, 1 062, 1 001, 832, 771, 683, 574.

  1.2.3   Synthesis of complex 3

  Complex 3 was synthesized in a similar way as 2, except that Cu(NO₃)₂·3H₂O was replaced with CuCl₂·3H₂O (0.1 mmol, 24.16 mg), and solvents were replaced with 0.25 mL H₂O, 2 mL N, N-dimethylacetamide (DMA) and 4 mL methanol. The filtrate volatilized naturally at room temperature, and the blue transparent crystals of complex 3 were obtained after 15 d in a yield of 26.5% (based on H₂dia). Elemental Anal. Cacld. for C₁₆H₁₉N₅O₅Cu(%): C, 45.23; H, 4.51; N, 16.48. Found(%): C, 44.40; H, 4.68; N, 16.17. Main IR peaks (KBr, cm^-1): 3 073, 1 585, 1 491, 1 404, 1 222, 1 072, 1 011, 781, 650.

  1.3   Crystallographic data collection and refinement

  Single-crystal X-ray diffraction data of complexes 1-3 were measured on Rigaku 003 single X-ray diffractometer equipped with Mo Kα radiation (λ =0.071 073 nm) at 293(2) K using Φ and ω scans. After absorption corrections, crystal structures were solved by direct methods and refined by the full-matrix least-squares method based on F² using the Olex2 program, and the SHELX-2018/3 package^[31-32]. All non-H atoms were refined anisotropically. All H atoms were generated theoretically and were refined isotropically. For 1 and 3, guest solvent molecules were highly disordered, which have been removed through the SQUEEZE routine in the PLATON package. Based on the single-crystal structure, TGA, elemental analysis, and SQUEEZE results, the final chemical formulas of 1-3 were determined. Details of the crystallographic data and refinements of 1-3 are summarized in Table 1, and selected bond lengths and angles are listed in Table 2. Hydrogen bonds are listed in Table 3.

  Table 1

  

  Table 1.  Crystallographic data and refinements of complexes 1-3

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  Parameter	1	2	3
  Empirical formula	C16H21N5O6Zn	C19H24N6O5Cu	C16H19N5O5Cu
  Formula weight	444.75	479.98	424.90
  Crystal system	Monoclinic	Monoclinic	Orthorhombic
  Space group	P21/c	P21/n	Pnma
  a/nm	0.788 12(5)	0.766 48(6)	0.907 27(6)
  b/nm	1.025 75(5)	1.010 58(6)	1.583 88(11)
  c/nm	2.629 28(15)	2.753 8(2)	1.254 19(9)
  β/(°)	92.120(5)	94.461(7)
  V/nm3	2.124 1(2)	2.126 6(3)	1.802 3(2)
  Z	4	4	4
  μ/mm-1	1.183	1.071	1.243
  F(000)	840	996	836
  Reflection collected	18 292	22 265	11 283
  Independent reflection	5 625	5 675	2 557
  Rint	0.031 9	0.040 1	0.025 0
  Goodness-of-fit on F2	1.055	1.023	1.069
  R1, wR2* [I > 2σ(I)]	0.038 8, 0.106 1	0.035 8, 0.083 9	0.038 7, 0.104 4
  R1, wR2 (all data)	0.050 1, 0.110 4	0.047 0, 0.087 8	0.049 6, 0.110 6
  * R1=∑(||Fo|-|Fc||)/∑|Fo|; wR2=[∑w(|Fo|2-|Fc|2)2/∑w(|Fo|2)2]1/2.

  Table 2

  

  Table 2.  Selected bond lengths (nm) and bond angles (°) of complexes 1-3

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  1
  Zn1—N1	0.201 38(19)	Zn1—O3	0.202 95(15)	N1—C11	0.138 5(3)
  Zn1—O1	0.200 27(14)	C1—O1	0.127 9(2)	N1—C13	0.132 6(3)
  Zn1—N2	0.201 67(19)	C1—O2	0.124 6(3)	C1—C2	0.151 8(3)
  N1—Zn1—N2	116.05(8)	O1—Zn1—N2	109.58(7)	C11—N1—Zn1	127.42(15)
  N1—Zn1—O3	108.47(7)	O1—Zn1—O3	98.33(6)	C1—O1—Zn1	112.09(13)
  O1—Zn1—N1	110.56(7)	N2—Zn1—O3	112.42(7)	C13—N3—C12	107.9(2)
  2
  Cu1—N1	0.200 63(16)	Cu1—O3	0.204 70(12)	C6—N6	0.137 6(3)
  Cu1—N3	0.197 88(15)	Cu1—O4	0.241 42(17)	C1—C2	0.151 6(2)
  Cu1—O1	0.197 29(12)	C1—O1	0.127 4(2)
  N1—Cu1—O3	90.02(6)	N3—Cu1—O3	91.28(6)	O1—Cu1—N1	91.19(6)
  N1—Cu1—O4	83.62(6)	O1—Cu1—O3	147.92(6)	O1—Cu1—N3	92.07(6)
  N3—Cu1—N1	171.70(7)	O1—Cu1—O4	122.02(6)	O3—Cu1—O4	89.97(5)
  3
  Cu1—N1	0.198 3(2)	Cu1—N1A	0.198 3(2)	C7—N1	0.134 5(4)
  Cu1—O1	0.195 10(13)	Cu1—O1A	0.195 11(13)	C1—O1	0.128 1(2)
  O1—Cu1—N1	89.96(7)	O1A—Cu1—N1A	89.96(7)	C7—N1—Cu1	129.9(2)
  O1A—Cu1—N1	90.04(7)	O1—Cu1—O1A	180.0	C9—N1—C7	103.0(3)
  O1—Cu1—N1A	90.04(7)	N1—Cu1—N1A	180.00(11)	O1—C1—C2	115.00(16)
  Symmetry code: A: -x, 1-y, -z for 3.

  Table 3

  

  Table 3.  Hydrogen bond lengths and bond angles for complexes 1-3

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  D—H···A	d(D—H)/nm	d(H···A)/nm	d(D—A)/nm	∠DHA/(°)
  1
  N3—H3···O2E	0.086	0.194	0.279 5(3)	172
  N4—H4···O3C	0.086	0.209	0.294 4(3)	172
  2
  N2—H2···O2E	0.072	0.206	0.277 9(2)	174
  N4—H4···O5F	0.086	0.206	0.284 3(3)	151
  C15—H15···O5G	0.093	0.234	0.324 3(3)	164
  3
  N2—H2···O2K	0.086	0.205	0.285 7(3)	155
  Symmetry codes: C: -1+x, y, z; E: -x, -1/2+y, 1/2-z for 1; E: 3/2-x, -1/2+y, 1/2-z; F: 1+x, -1+y, z; G: 2-x, 1-y, -z for 2; K: -1/2+x, y, 1/2-z for 3.

  2.   Results and discussion

  2.1   Crystal structure of complexes 1-3

  The X-ray diffraction analysis displays that complex 1 crystallizes in the monoclinic system with the space group P2₁/c. The asymmetric unit consists of one Zn(Ⅱ) ion, one deprotonated dia^2- anion, and two mdz ligands (Fig. 1a). The four-coordinated Zn(Ⅱ) center is connected by two μ₁-η¹ monodentate carboxylate O atoms from two dia^2- ions (O1 and O3), and two N atoms from two mdz molecules (N1 and N2) to form a [ZnN₂O₂] distorted tetrahedral geometries. The bond lengths of Zn—O and Zn—N are in a range of 0.200 27(14)-0.202 95(15) nm and 0.201 38(19)-0.201 67(19) nm, respectively. Adjacent Zn(Ⅱ) centers are orderly linked by dia^2- ligands facing the same direction, and form infinite 1D linear chains extending along the b-axis, with the intra-chain Zn···Zn distances of 1.025 75(6) nm (Fig. 1b). Hydrogen bonding between the N—H in mdz and coordination O atoms in dia^2- extend identical 1D chains to 2D layer (Fig. 1c), which are further oppositely linked and stabilized through the N —H···O hydrogen bonding between the mdz N—H and the dia^2- O atoms not involved in coordination to form the 2D bilayer network with rectangle-shaped porous channels of dimension 0.965 nm×0.725 nm along the b-axis direction (Fig. 1d). The N4— H4···O3 and N3—H3···O2 hydrogen bond distance is 0.209 and 0.194 nm (H···A), respectively. Finally, the 2D networks stack parallel to each other to obtain the 3D supramolecular structure of 1 (Fig. 1e).

  Figure 1

  

  Figure 1.  Crystal structure of complex 1: (a) coordination environment of Zn center with thermal ellipsoids at 50% level; (b)linear chain structure; (c) 2D layer constructed by N4—H4···O3 intermolecular hydrogen bonds; (d)2D network built by N3—H3···O2 hydrogen bonds; (e) 3D supramolecular structure

  Symmetry codes: A: x, 1+y, z; B: x, -1+y, z; C: -1+x, y, z; D: 1+x, y, z.

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  Complex 2 crystallizes in the monoclinic space group P2₁/n and also exhibits linear chain structures. While the asymmetric unit of 2 contains one Cu(Ⅱ) ion, one deprotonated dia^2- anion, two mdz ligands, and one coordinated DMF molecule (Fig. 2a). Each five-coordinated Cu(Ⅱ) center was attached to two monodentate carboxylate O atoms from two dia^2- ions(O1 and O3), one carbonyl O atom from DMF (O4), and two N atoms from two mdz ligands (N1 and N3) to form a [CuN₂O₃] triangular bipyramidal geometry with the Cu—O bond lengths ranging from 0.197 29(12) to 0.241 42(17) nm, and the two Cu—N bond lengths are 0.197 88(15) and 0.200 63(16) nm. As shown in Fig. 2b, the dia^2- ligands link the Cu(Ⅱ) centres into a 1D linear chain along the b-axis with the Cu···Cu separated by dia^2- is 1.010 58(7) nm. Neighbouring chains connect through the N4—H4···O5 intermolecular hydrogen bonding between the mdz N—H and the dia^2- uncoordinated O atoms to form a 2D layer (Fig. 2c). Two facing layers join with each other through N2—H2··· O2 hydrogen bonding between residual mdz N atoms and dia^2- uncoordinated O atoms, forming a bilayer structure (Fig. 2d). However, due to the presence of coordinated DMF molecules, there were no significant pores in this bilayer structure. Finally, C—H···O inter-molecular hydrogen bonding between mdz C—H and dia^2- uncoordinated O atoms expand bilayers into the 3D supramolecular structure of 2 (Fig. 2e).

  Figure 2

  

  Figure 2.  Crystal structure of complex 2: (a) coordination environment of Cu(Ⅱ) center with thermal ellipsoids at 50% level; (b)linear chain structure; (c) 2D layer constructed by N4—H4···O5 intermolecular hydrogen bonds; (d)2D bilayer structure built by N2—H2···O2 hydrogen bonds; (e) 3D supramolecular structure

  Symmetry codes: A: x, 1+y, z; B: x, -1+y, z; C: 1+x, y, z; D: -1+x, y, z.

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  Complex 3 crystallizes in orthorhombic space group Pnma, which was mainly composed of one Cu(Ⅱ) ion, one dia^2- anion, and two mdz molecules (Fig. 3a). Each Cu center is highly symmetric four-coordinated with two carboxylate O atoms from two dia^2- (O1 and O1A), and two N atoms from two mdz ligands (N1 and N1A) to form a [CuN₂O ₂] square-planar geometry. The lengths of the Cu—O bond are 0.195 10(13) and 0.195 11(13) nm, and both the Cu—N spatial distance is 0.198 3(2) nm. Neighbouring Cu(Ⅱ) ions are alternately bridged by centrosymmetric dia^2- into a 1D zigzag chain along the b-axis, with the Cu···Cu distance via the dia^2- ligand being 0.791 94(5) nm (Fig. 3b). Abundant intermolecular N—H···O hydrogen bonding interactions between the mdz N— H and the dia^2- O atoms not involved in coordination expand the zigzag chains into the 3D supramolecular structure of 3 (Fig. 3c).

  Figure 3

  

  Figure 3.  Crystal structure of complex 3: (a) coordination environment of Cu(Ⅱ) center with thermal ellipsoids at 50% level; (b) zigzag chain structure; (c) 3D supramolecular structure

  Symmetry codes: A: -x, 1-y, -z; B: x, 1/2-y, z; C: -x, 1/2+y, -z; D: -x, -1/2+y, -z; E: 1+x, y, z; F: -1+x, y, z; G: -1/2-x, 1-y, -1/2+z; H: 1/2-x, 1-y, -1/2+z; I: -1/2-x, 1-y, 1/2+z; J: 1/2-x, 1-y, 1/2+z.

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  In complexes 1-3, both H₂dia and mdz were used as ligands, aiming to explore the role of center metal ions and the effect of synthetic conditions on the structure of coordination complexes. The synthesis process, coordination geometries of the metal center, and structure representation of complexes are displayed in Scheme 1. Complexes 1 and 2 have identical synthesis conditions, and both of them show similar 1D linear chain structures. However, when we chose Zn(Ⅱ) as the center metal ion, the solvent molecule did not participate in the coordination, and Zn(Ⅱ) center adopted four coordination modes, displaying a distorted tetrahedral geometry. When the metal center is changed to Cu, DMF participates in the coordination in complex 2, and the five-coordinated Cu(Ⅱ) ion shows a distorted triangular bipyramidal geometry. In addition, due to the presence of DMF, there are no obvious porous in the 3D supramolecular structure of 2. In the meantime, when Cu(Ⅱ) was still used, but solvents were replaced with H₂O, DMA and methanol, a zigzag chain structure was constructed. Although the metal center of 3 adopts a four-coordination mode, it presents a square-planar geometry. The above results reveal that the coordination geometries of metal centers and the solvents used in the synthesis process play significant roles in the structures of coordination complexes.

  Scheme1

  

  Scheme1.  Synthesis process, coordination geometries of the metal center, and structure representation of complexes 1-3

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  2.2   Hirshfeld surface analyses of complexes 1-3

  Due to the rich intermolecular interactions existing in the three complexes, the CrystalExplorer software was used to analyze the CIF files and generate the Hirshfeld surfaces and 2D fingerprint plots of complexes 1-3, to deeply assess the inter-related molecular interactions in structures. The Hirshfeld surfaces for all complexes mapped with d_norm are given in Fig. 4. The bright red spots represent the closest contacts, the gray areas stand for the moderate interactions and the blue areas denote the weakest interactions. The results show that the strong interactions in 1-3 are all mainly derived from the hydrogen bonding between the carboxylate O atoms and the hydrogen atoms on the N atoms of mdz, and the coordination interactions between metal centers and carboxylate groups. To better quantitatively explore the interactions in 1-3, 2D fingerprint plots analyses with all characteristic features were carried out and are shown in Fig. 5. The results indicate that the contacts with important contributions to the crystal packing in complex 1 are H···H/H···H, O···H/H···O, C···H/H···C, and N···H/H···N interactions, accounted for 41.2%, 23.9%, 21.6% and 5.7%, respectively (Fig. 5a). Similarly, in complex 2, the primary interactions are from H···H/H···H, C···H/H···C, O··· H/H···O, and N···H/H···N, which covered 43.3%, 21.2%, 20.9% and 6.6%, respectively. While, in complex 3, the major contributions to the crystal packing are from H···H/H···H (41.8%), O···H/H···O (21.8%), C···H/H···C (18.6%), N···H/H···N (5.6%) and C···C/C···C (2.0%) interactions.

  Figure 4

  

  Figure 4.  Hirshfeld surface of complexes 1-3 mapped with d_norm

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  Figure 5

  

  Figure 5.  Hirshfeld surface of complexes 1 (a), 2 (b), and 3 (c) with 2D fingerprint plots

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  2.3   PXRD analyses of complexes 1-3

  To meet the property tests, extensive powder crystals of complexes 1-3 were synthesized using the same methods as single crystal cultures, and PXRD experiments were conducted to determine the purity of the powder crystals and whether the crystal structures truly represent the test materials. Fig. 6 presents the experimental and simulated PXRD patterns of 1-3. The synthesized PXRD patterns were consistent with the simulated ones, which suggests that the crystal structure of samples 1-3 are truly representative of the bulk crystal products, respectively.

  Figure 6

  

  Figure 6.  Simulated and experimental PXRD patterns of complexes 1-3

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  2.4   TGA of complexes 1-3

  To estimate the thermal stabilities of complexes, the TGA of complexes 1-3 were investigated by heating the powder crystal samples from room temperature to 800 ℃ at a heating rate of 10 ℃·min^-1 under a nitrogen atmosphere. The TG curves in Fig. 7 revealed that 1-3 all have good thermal stability. Complex 1 displayed a gradual weight loss between 70 and 172 ℃, which can be attributed to the loss of two free water molecules (Obsd. 8.69%, Calcd. 8.10%). Subsequently, a flat region was observed from 172 to 306 ℃. When the temperature exceeded 307 ℃, a sharp weight loss occurred corresponding to the losses of organic ligands and the decomposition of the framework, leaving about 19. 1% ZnO. For complex 2, the structure remained stable within a range of room temperature to 132 ℃. In a temperature range of 132-352 ℃, slow weight loss was observed, which may be caused by the detachment of coordinated DMF molecules. Until 371 ℃ complex 2 began to decompose, leaving CuO residue. For complex 3, the gradual weight loss in a range of 73 to 144 ℃ is due to the release of a free water molecule (Obsd. 4.24%, Calcd. 4.96%). The decomposition of frameworks was observed at 278 ℃ with CuO residue.

  Figure 7

  

  Figure 7.  TGA curves of complexes 1-3

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  2.5   Fluorescence analyses of complexes 1-3

  It is considered that many transition metal complexes, especially those with d¹⁰ metal centers, have excellent fluorescence properties. The fluorescence emission spectra of the H₂ dia ligand and complex 1 were measured in the solid state at room temperature. As shown in Fig. 8, the free H₂dia ligand exhibited a broad band with a maximum peak at 446 nm under excitation of 360 nm ultraviolet light. Under the same test conditions, 1 displayed a similar but stronger fluo-rescence emission peak at 434 nm with a slight blue shift of 12 nm. Due to the d¹⁰ configuration, Zn(Ⅱ) ions are hard to oxidize or reduce, the emission of 1 can be attributed to the π* → π transitions of ligands. The blue shift is probably because of the intraligand (ILCT) or ligand-to-ligand charge transfer (LLCT)^[33]. Moreover, the fluorescence lifetime (τ) and fluorescence quantum yield (Φ) of complex 1 are 3.82 ns and 2.6%, respectively.

  Figure 8

  

  Figure 8.  Fluorescence emission spectra of ligand H₂dia and complex 1

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  3.   Conclusions

  In summary, three transition metal complexes were synthesized from a dicarboxylic acid ligand (H₂dia) and an N-donor ligand (mdz). Crystal structure analyses show that complexes 1 and 2 have similar synthesis conditions and similar 1D linear chains, but the Zn(Ⅱ) center of 1 is four-coordinated and adopts distorted tetrahedral coordination geometry, while Cu(Ⅱ) ion of 2 features a five-coordinated and holds a triangular bipyramidal geometry. Changing the solvent conditions, a zigzag 1D chain of complex 3 was obtained, and each four-coordinated Cu center displays squareplanar geometry in 3. The results illustrate that the coordination modes of the metal center and the synthetic solvent have powerful influences on the structures of complexes. Hirshfeld surface analyses indicated that the existence of abundant intermolecular hydrogen bonding interactions plays an important role in the formation and stability of the 3D supramolecular structures of complexes. TGA results showed that three complexes have good thermal stabilities, and the decomposition of structures happens when the temperature exceeds 307, 371 and 278 ℃, respectively. Fluorescence analyses showed that complex 1 has excellent fluorescence.

  
  
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  Figure 1  Crystal structure of complex 1: (a) coordination environment of Zn center with thermal ellipsoids at 50% level; (b)linear chain structure; (c) 2D layer constructed by N4—H4···O3 intermolecular hydrogen bonds; (d)2D network built by N3—H3···O2 hydrogen bonds; (e) 3D supramolecular structure

  Symmetry codes: A: x, 1+y, z; B: x, -1+y, z; C: -1+x, y, z; D: 1+x, y, z.

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  Figure 2  Crystal structure of complex 2: (a) coordination environment of Cu(Ⅱ) center with thermal ellipsoids at 50% level; (b)linear chain structure; (c) 2D layer constructed by N4—H4···O5 intermolecular hydrogen bonds; (d)2D bilayer structure built by N2—H2···O2 hydrogen bonds; (e) 3D supramolecular structure

  Symmetry codes: A: x, 1+y, z; B: x, -1+y, z; C: 1+x, y, z; D: -1+x, y, z.

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  Figure 3  Crystal structure of complex 3: (a) coordination environment of Cu(Ⅱ) center with thermal ellipsoids at 50% level; (b) zigzag chain structure; (c) 3D supramolecular structure

  Symmetry codes: A: -x, 1-y, -z; B: x, 1/2-y, z; C: -x, 1/2+y, -z; D: -x, -1/2+y, -z; E: 1+x, y, z; F: -1+x, y, z; G: -1/2-x, 1-y, -1/2+z; H: 1/2-x, 1-y, -1/2+z; I: -1/2-x, 1-y, 1/2+z; J: 1/2-x, 1-y, 1/2+z.

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  Scheme1  Synthesis process, coordination geometries of the metal center, and structure representation of complexes 1-3

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  Figure 4  Hirshfeld surface of complexes 1-3 mapped with d_norm

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  Figure 5  Hirshfeld surface of complexes 1 (a), 2 (b), and 3 (c) with 2D fingerprint plots

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  Figure 6  Simulated and experimental PXRD patterns of complexes 1-3

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  Figure 7  TGA curves of complexes 1-3

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  Figure 8  Fluorescence emission spectra of ligand H₂dia and complex 1

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  Table 1.  Crystallographic data and refinements of complexes 1-3

  Parameter	1	2	3
  Empirical formula	C16H21N5O6Zn	C19H24N6O5Cu	C16H19N5O5Cu
  Formula weight	444.75	479.98	424.90
  Crystal system	Monoclinic	Monoclinic	Orthorhombic
  Space group	P21/c	P21/n	Pnma
  a/nm	0.788 12(5)	0.766 48(6)	0.907 27(6)
  b/nm	1.025 75(5)	1.010 58(6)	1.583 88(11)
  c/nm	2.629 28(15)	2.753 8(2)	1.254 19(9)
  β/(°)	92.120(5)	94.461(7)
  V/nm3	2.124 1(2)	2.126 6(3)	1.802 3(2)
  Z	4	4	4
  μ/mm-1	1.183	1.071	1.243
  F(000)	840	996	836
  Reflection collected	18 292	22 265	11 283
  Independent reflection	5 625	5 675	2 557
  Rint	0.031 9	0.040 1	0.025 0
  Goodness-of-fit on F2	1.055	1.023	1.069
  R1, wR2* [I > 2σ(I)]	0.038 8, 0.106 1	0.035 8, 0.083 9	0.038 7, 0.104 4
  R1, wR2 (all data)	0.050 1, 0.110 4	0.047 0, 0.087 8	0.049 6, 0.110 6
  * R1=∑(||Fo|-|Fc||)/∑|Fo|; wR2=[∑w(|Fo|2-|Fc|2)2/∑w(|Fo|2)2]1/2.

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  Table 2.  Selected bond lengths (nm) and bond angles (°) of complexes 1-3

  1
  Zn1—N1	0.201 38(19)	Zn1—O3	0.202 95(15)	N1—C11	0.138 5(3)
  Zn1—O1	0.200 27(14)	C1—O1	0.127 9(2)	N1—C13	0.132 6(3)
  Zn1—N2	0.201 67(19)	C1—O2	0.124 6(3)	C1—C2	0.151 8(3)
  N1—Zn1—N2	116.05(8)	O1—Zn1—N2	109.58(7)	C11—N1—Zn1	127.42(15)
  N1—Zn1—O3	108.47(7)	O1—Zn1—O3	98.33(6)	C1—O1—Zn1	112.09(13)
  O1—Zn1—N1	110.56(7)	N2—Zn1—O3	112.42(7)	C13—N3—C12	107.9(2)
  2
  Cu1—N1	0.200 63(16)	Cu1—O3	0.204 70(12)	C6—N6	0.137 6(3)
  Cu1—N3	0.197 88(15)	Cu1—O4	0.241 42(17)	C1—C2	0.151 6(2)
  Cu1—O1	0.197 29(12)	C1—O1	0.127 4(2)
  N1—Cu1—O3	90.02(6)	N3—Cu1—O3	91.28(6)	O1—Cu1—N1	91.19(6)
  N1—Cu1—O4	83.62(6)	O1—Cu1—O3	147.92(6)	O1—Cu1—N3	92.07(6)
  N3—Cu1—N1	171.70(7)	O1—Cu1—O4	122.02(6)	O3—Cu1—O4	89.97(5)
  3
  Cu1—N1	0.198 3(2)	Cu1—N1A	0.198 3(2)	C7—N1	0.134 5(4)
  Cu1—O1	0.195 10(13)	Cu1—O1A	0.195 11(13)	C1—O1	0.128 1(2)
  O1—Cu1—N1	89.96(7)	O1A—Cu1—N1A	89.96(7)	C7—N1—Cu1	129.9(2)
  O1A—Cu1—N1	90.04(7)	O1—Cu1—O1A	180.0	C9—N1—C7	103.0(3)
  O1—Cu1—N1A	90.04(7)	N1—Cu1—N1A	180.00(11)	O1—C1—C2	115.00(16)
  Symmetry code: A: -x, 1-y, -z for 3.

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  Table 3.  Hydrogen bond lengths and bond angles for complexes 1-3

  D—H···A	d(D—H)/nm	d(H···A)/nm	d(D—A)/nm	∠DHA/(°)
  1
  N3—H3···O2E	0.086	0.194	0.279 5(3)	172
  N4—H4···O3C	0.086	0.209	0.294 4(3)	172
  2
  N2—H2···O2E	0.072	0.206	0.277 9(2)	174
  N4—H4···O5F	0.086	0.206	0.284 3(3)	151
  C15—H15···O5G	0.093	0.234	0.324 3(3)	164
  3
  N2—H2···O2K	0.086	0.205	0.285 7(3)	155
  Symmetry codes: C: -1+x, y, z; E: -x, -1/2+y, 1/2-z for 1; E: 3/2-x, -1/2+y, 1/2-z; F: 1+x, -1+y, z; G: 2-x, 1-y, -z for 2; K: -1/2+x, y, 1/2-z for 3.

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