English

• Aluminium is a chemical element that occurs naturally in compounds^[1-4]. It is utilised in the field of architecture for the fabrication of window frames, curtain wall frames, and similar structures due to its low density and rigidity^[5]. In the field of transportation, aluminium alloys are extensively utilised in the manufacture of automobiles and aircraft, a practice that has been proven to result in a substantial weight reduction, enhancement of fuel efficiency, and optimisation of flight performance^[6-7]. The packaging industry also stands to benefit from aluminium's presence, as its remarkable barrier and plasticity properties ensure its frequent employment in the production of cans and aluminium foil, with the primary purpose of safeguarding food items and maximising shelf life^[8-9]. However, the production and utilization of aluminium concomitantly engender certain environmental issues. Bauxite mining has been linked to land degradation and ecological damage, while the aluminium production process has been observed to involve high energy consumption, thus giving rise to concerns regarding energy sustainability^[10-11]. While aluminium ions have minimal impact on human health under typical conditions, prolonged excessive intake of aluminium-containing compounds may accumulate in the human body, potentially causing harm to the nervous system, including interference with normal nervous system function and cognitive decline^[12-13]. Therefore, there is a necessity to develop an efficient and rapid method for the detection of trace Al³⁺.

  A plethora of methodologies for the detection of aluminium ions have been developed to date, principally encompassing spectrophotometry, atomic absorption spectrometry (AAS), and inductively coupled plasma mass spectrometry (ICP-MS), amongst others^[14-16]. However, in practical applications, these detection methods need to comprehensively select the appropriate detection methods based on factors such as detection requirements, sample properties, and cost-effectiveness, and require complex instruments, trained operators^[17-18]. Compared with these detection methods, fluorescence-based technology has attracted wide attention due to its advantages of simple operation, high selectivity, low cost, easy visualization, rapid response, and strong biological imaging ability^[19-24]. Although some fluorescent probes for the detection of aluminum ions have been reported in recent years, it is still a challenge to further improve the sensitivity of their detection.

  Herein, we present the design and synthesis of two new Zn(Ⅱ) complexes [Zn₂(L1)(HL1)(NO₃)]·CH₃OH (1) and [Zn₃(L2)(L3)₃Cl]·CH₃OH (2) through the self-assembly of cinnolin-3-yl-hydrazine and 2-hydroxy-4-methoxybenzaldehyde/2-hydroxy-3-methoxybenzaldehyde and Zn(Ⅱ), where H₂L1=5-methoxy-2-(phthalazin-1-yl-hydrazonomethyl)-phenol, H₂L2=2-methoxy-6-(phthalazin-1-yl-hydrazonomethyl)-phenol, HL3=2-(1, 8-dihydro-[1, 2, 4]triazolo[3,4-α]phthalazin-3-yl)-6-methoxy-phenol (Scheme 1). Complexes 1 and 2 were characterized by single-crystal X-ray diffraction, elemental analysis (EA), FTIR, and powder X-ray diffraction (PXRD). Interestingly, complex 1 can quickly and efficiently detect aluminum ions in aqueous solution, and the detection limit was 6.37 μmol·L^-1.

  Scheme 1

  

  Scheme 1.  Synthetic routes of complexes 1 and 2

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  1.   Experimental

  1.1   Materials and physical measurement

  All materials and solvents are provided by commercial suppliers and can be used without any further purification. EA was conducted using a Vario EL elemental analyzer. FTIR spectra were recorded on an Avatar 360 FT-IR spectrometer using KBr pellets in a range of 4 000-400 cm^-1. PXRD patterns were collected using a SHIMADZU XRD-7000 diffractometer with Cu Kα radiation (λ=0.154 184 nm) at 25 ℃ and recorded on crushed single crystals in a range of 5°-50°. The operating voltage and current were 40 kV and 25 mA, respectively. The fluorescence spectra were recorded on an FS5 fluorescence spectrophotometer with a quartz cuvette (path length of 1 cm). UV-Vis absorption spectra were determined on a spectrophotometer UV-2450.

  1.2   Synthesis of complex 1

  A mixture containing Zn(NO₃)₂·6H₂O (27.4 mg, 0.1 mmol), cinnolin-3-yl-hydrazine (16.0 mg, 0.10 mmol), 2-hydroxy-4-methoxybenzaldehyde (15.2 mg, 0.10 mmol) and in 6 mL methanol was stirred for 30 min and then sealed in a 25 mL Teflon-lined stainless steel container and heated at 80 ℃ for 72 h, then allowed to cool to room temperature naturally. Yellow block crystals of complex 1 were washed with methanol and air-dried with a yield of 72.3%. Elemental analysis Calcd. (Found) for C₃₄H₃₃N₉O₉Zn₂(%): C 48.47 (48.37); H 3.95 (4.03); N 14.96 (14.99). IR (KBr, cm^-1): 3 508 w, 2 996 m, 2 718 m, 1 602 s, 1 560 s, 1 510 m, 1 471 m, 1 438 m, 1 362 m, 1 260 s, 1 206 m, 1 101 m, 1 018 m, 956 m, 903 m, 856 m, 750 m, 700 m, 647 m, 589 w, 480 w (Fig.S1, Supporting information).

  1.3   Synthesis of complex 2

  ZnCl₂ (13.6 mg, 0.10 mmol), cinnolin-3-yl-hydrazine (24.0 mg, 0.15 mmol), 2-hydroxy-3-methoxybenzaldehyde (22.8 mg, 0.15 mmol), and CH₃OH (6 mL) were mixed in a 25 mL Teflon-lined autoclave. Then the Teflon-lined autoclave was heated at 80 ℃ for 72 h and cooled to room temperature. Yellow block crystals were collected by filtration and dried in air and air-dried in a yield of 62.5%. Elemental analysis Calcd. (Found) for C₆₅H₄₉ClN₁₆O₉Zn₃(%): C 54.60 (54.48); H 3.46 (3.54); N 15.67 (15.69). IR (KBr, cm^-1): 3 519 w, 3 019 w, 2 998 w, 2 678 w, 2 537 w, 1 679 s, 1 585 s, 1 538 w, 1 509 s, 1 420 s, 1 373 m, 1 295 s, 1 238 s, 1 187 w, 1 114 w, 1 022 w, 935 w, 889 w, 781 s, 733 m, 643 w, 529 w (Fig.S2).

  1.4   Crystal structure determination

  Crystallographic data of complexes 1 and 2 were collected on an XtaLAB Synergy-DW diffractometer with Cu Kα radiation (λ=0.154 184 nm, powered at 4 kW). The crystal structures were solved and refined using the Olex2 program. All hydrogen atoms were added automatically, and all non-hydrogen atoms were refined anisotropically. H atoms attached to C atoms were placed geometrically and refined using a riding-model approximation, with C—H length of 0.095 nm and U_iso(H)=1.2U_eq(C). Crystal data and structure refinement parameters are summarized in Table 1. Selected bond distances and angles are displayed in Table 2.

  Table 1

  

  Table 1.  Crystal data and structure refinement details for complexes 1 and 2

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  Parameter	1	2
  Formula	C34H33N9O9Zn2	C65H49ClN16O9Zn3
  Formula weight	842.43	1 429.76
  Crystal system	Monoclinic	Triclinic
  Space group	P21/c	P1
  Temperature/K	293	100
  a/nm	1.303 539(17)	1.350 14(3)
  b/nm	1.705 37(2)	1.434 07(4)
  c/nm	1.549 07(2)	1.638 56(2)
  α/(°)		95.567 7(17)
  β/(°)	98.670 6(13)	106.433 1(17)
  γ/(°)		96.581 0(19)
  V/nm3	3.404 24(8)	2.994 90(11)
  Z	4	2
  Dc/(Mg·m-3)	1.646	1.588
  μ/mm-1	2.34	2.44
  Rint	0.047	0.059
  GOF	1.05	1.12
  F(000)	1 732	1 464
  R1[I > 2σ(I)]	0.040	0.074
  wR2[I > 2σ(I)]	0.117	0.212

  Table 2

  

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

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  1
  Zn1—O1	0.199 02(17)	Zn1—N2	0.216 41(19)	Zn2—N6	0.207 70(19)
  Zn1—O6	0.199 13(18)	Zn2—O3	0.199 83(17)	Zn2—N1	0.210 16(18)
  Zn1—N5	0.207 23(19)	Zn2—O5	0.203 34(16)
  Zn1—N4	0.208 16(19)	Zn2—N8	0.205 77(19)
  O1—Zn1—O6	97.93(7)	O6—Zn1—N2	92.96(7)	O5—Zn2—N6	99.93(7)
  O1—Zn1—N5	96.77(7)	N5—Zn1—N2	91.97(7)	N8—Zn2—N6	76.18(8)
  O6—Zn1—N5	111.15(7)	N4—Zn1—N2	74.17(7)	O3—Zn2—N1	90.41(7)
  O1—Zn1—N4	88.34(7)	O3—Zn2—O5	91.12(7)	O5—Zn2—N1	114.35(7)
  O6—Zn1—N4	129.02(7)	O3—Zn2—N8	89.37(7)	N8—Zn2—N1	124.67(7)
  N5—Zn1—N4	118.26(8)	O5—Zn2—N8	120.97(7)	N6—Zn2—N1	94.28(7)
  O1—Zn1—N2	162.51(7)	O3—Zn2—N6	164.93(7)
  2
  Zn1—O3	0.201 0(4)	Zn2—O2	0.207 5(4)	Zn3—N9	0.207 0(5)
  Zn1—O2	0.201 3(4)	Zn2—O3	0.211 9(4)	Zn3—N12	0.222 1(5)
  Zn1—N2	0.202 1(5)	Zn2—N8	0.212 1(5)	Zn3—O6	0.194 1(4)
  Zn1—O1	0.222 6(4)	Zn2—N5	0.212 3(5)	Zn3—O5	0.200 7(4)
  Zn1—Cl1	0.222 71(16)	Zn2—N13	0.216 0(5)
  Zn2—O5	0.204 3(4)	Zn3—N11	0.206 9(5)
  O3—Zn1—O2	83.30(15)	O2—Zn2—Zn1	39.61(10)	O3—Zn2—N13	160.16(16)
  O3—Zn1—N2	87.90(18)	O3—Zn2—Zn1	39.71(11)	N8—Zn2—N13	88.33(19)
  2
  O2—Zn1—N2	114.36(17)	N8—Zn2—Zn1	99.28(13)	N5—Zn2—N13	92.96(18)
  O3—Zn1—O1	155.04(15)	N5—Zn2—Zn1	90.07(13)	N13—Zn2—Zn1	120.44(12)
  O2—Zn1—O1	74.21(14)	O5—Zn2—O2	167.14(16)	O5—Zn3—N9	88.49(19)
  N2—Zn1—O1	91.56(17)	O5—Zn2—O3	112.20(15)	N11—Zn3—N9	75.4(2)
  O3—Zn1—Cl1	106.45(13)	O2—Zn2—O3	79.21(14)	O6—Zn3—N12	98.38(19)
  O2—Zn1—Cl1	121.57(12)	O5—Zn2—N8	89.19(19)	O6—Zn3—O5	102.64(19)
  N2—Zn1—Cl1	123.28(14)	O2—Zn2—N8	95.92(17)	O6—Zn3—N11	90.8(2)
  O1—Zn1—Cl1	94.65(11)	O3—Zn2—N8	94.80(17)	O5—Zn3—N11	152.7(2)
  O3—Zn1—Zn2	42.34(10)	O5—Zn2—N5	79.29(18)	O6—Zn3—N9	165.7(2)
  O2—Zn1—Zn2	41.09(11)	O2—Zn2—N5	95.74(17)	O5—Zn3—N12	87.00(17)
  N2—Zn1—Zn2	102.45(13)	O3—Zn2—N5	87.92(17)	N11—Zn3—N12	114.72(19)
  O1—Zn1—Zn2	113.99(10)	N8—Zn2—N5	168.33(19)	N9—Zn3—N12	91.12(19)
  Cl1—Zn1—Zn2	125.24(5)	O5—Zn2—N13	87.40(17)
  O5—Zn2—Zn1	150.87(11)	O2—Zn2—N13	80.98(16)

  2.   Results and discussion

  2.1   Structural descriptions of complexes 1 and 2

  Single-crystal X-ray diffraction analyses reveal that complex 1 crystallizes in the monoclinic system with the space group P2₁/c. In complex 1, the Schiff base H₂L1 was synthesized by the condensation reaction of cinnolin-3-yl-hydrazine and 2-hydroxy-4-methoxybenzaldehyde. As shown in Fig. 1a, the unit cell of complex 1 contains two Zn²⁺ ions, one HL1^- ligand, one L1^2- ligand, one coordinated NO₃^-, and two free CH₃OH molecules. The Zn1 and Zn2 ions are five-coordinated and form a pentagonal pyramidal [ZnO₂N₃] geometry, which is completed by one O atom from the phenolic —OH group, three N atom donors coming from two imine groups of the Schiff base, and one O atom from nitrate. The Zn1—N distances are in a range of 0.205 77(19)-0.216 41(19) nm (Table 2). In addition, there are a large number of π⋯π weak interactions between adjacent molecules, as well as between 4-methoxysalicylaldehyde and phthalazine, phthalazine and phthalazine, with respective centroid⋯centroid distances of 0.350 2 nm (Cg2^ⅰ⋯Cg3), 0.353 7 nm (Cg1^ⅰ⋯Cg4), 0.363 3 nm (Cg4^ⅱ⋯Cg5), 0.376 2 nm (Cg1⋯Cg5^ⅲ) and 0.382 5 nm (Cg5⋯Cg5^ⅲ), respectively, and the dihedral angles between them are 4.44° (Cg2^ⅰ⋯Cg3), 2.34° (Cg1^ⅰ⋯Cg4), 3.28° (Cg4^ⅱ⋯Cg5), 4.91° (Cg1⋯Cg5^ⅲ) and 0° (Cg5⋯Cg5^ⅲ), respectively (Fig. 1b).

  Figure 1

  

  Figure 1.  Crystal structure of complex 1: (a) coordination mode of Zn²⁺ at 30% thermal ellipsoids; (b) intermolecular π···π interaction in 1

  Cg1 for the centroid of ring N1, N2, C1, C2, C7 and C8, Cg2 for the centroid of ring C10-C15, Cg3 for the centroid of ring C18-C23, Cg4 for the centroid of ring C26-C31, Cg5 for the centroid of ring C2-C7; Symmetry codes: ^ⅰ x, 0.5-y, 0.5+z; ^ⅱ x, 0.5-y, -0.5+z; ^ⅲ 1-x, -y, 1-z.

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  Structure analyses reveal that complex 2 crystallizes in a triclinic system with space group P1. Interestingly, the Schiff bases formed by cinnolin-3-yl-hydrazine and 2-hydroxy-3-methoxybenzaldehyde in complex 2 have two forms. One of the Schiff base ligands (H₂L2) is coordinated with the zinc ion in the form of an amide (O=C—N), and the other Schiff base ligand is coordinated with the zinc ion in the form of a five-membered ring formed (HL3) by cinnolin-3-yl-hydrazine and 2-hydroxy-3-methoxybenzaldehyde (Scheme 2). As shown in Fig. 2a, the asymmetric unit in complex 2 contains three Zn²⁺ ions, one L2^2- ligand, three L3^- ligands, one coordinated Cl^-, and one free CH₃OH molecule. In complex 2, the three Zn²⁺ ions adopt three different coordination modes. The Zn1 ion is five-coordinated and forms a triangular double pyramid [ZnO₃NCl] geometry completed by three O atoms from the two HL3 ligands, the N atom from the HL3 ligand, and one terminal Cl atom. Zn2 ion is a slightly distorted octahedral [ZnN₃O₃] geometry completed by three O atoms from three different HL3 ligands and three N atoms of two different HL3 ligands, and one H₂L2 ligand. The bond lengths of Zn2—O are in a range of 0.204 3(4)-0.211 9(4) nm. The angles of O—Zn2—O are 79.21(14)°-167.14(16)°. The Zn2—N bond length is 0.212 1(5)-0.216 0(5) nm and the angle of N—Zn2—N are 88.33(19)°-168.33(19)° (Table 2). The Zn3 ion is five-coordinated with a pentagonal cone, which is surrounded by one O atom and two N atoms from the same H₂L2 ligand, one O atom from the HL3 ligand, and one N atom from another HL3 ligand. Interestingly, the HL3 in complex 2 also adopts two forms of zinc coordination. One form is that the O atom in the methoxy group of HL3 also participates in the coordination and HL3 connects three zinc ions (Fig. 2b), while the other form of HL3 connects two zinc ions (Fig. 2c). In addition, there are also many weak π⋯π interactions in complex 2 (Fig. 2d). The centroid distance between rings are 0.352 1 nm (Cg1⋯Cg6^ⅰ), 0.354 4 nm (Cg2⋯Cg3^ⅱ), 0.382 6 nm (Cg5⋯Cg7), 0.382 6 nm (Cg1⋯Cg1^ⅰ), 0.361 2 nm (Cg4⋯Cg6), 0.366 8 nm (Cg4 ^ⅲ⋯Cg5), respectively, and the dihedral angles between them are 1.93° (Cg1⋯Cg6^ⅰ), 4.90° (Cg2⋯Cg3^ⅱ), 8.0° (Cg5⋯Cg7), 0° (Cg1⋯Cg1^ⅰ), 6.90° (Cg4⋯Cg6), and 8.8° (Cg4 ^ⅲ⋯Cg5), respectively (Fig. 1b).

  Scheme 2

  

  Scheme 2.  Schiff base in complex 2

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  Figure 2

  

  Figure 2.  Crystal structure of complex 2: (a) coordination environment of Zn²⁺ at 30% thermal ellipsoids; (b, c) coordination modes of HL3; (d) intermolecular π⋯π interaction in 2

  Cg1 for the centroid of ring N7, N16, C7, C36, C37 and C39, Cg2 for the centroid of ring N14, N15, C9-C12, Cg3 for the centroid of ring C1-C6, Cg4 for the centroid of ring C18-C23, Cg5 for the centroid of ring C26-C31, Cg6 for the centroid of ring C33-C38, Cg7 for the centroid of ring C44-C50; Symmetry codes: ^ⅰ 1-x, 1-y, 1-z, ^ⅱ 1-x, -y, 1-z; ^ⅲ 2-x, 1-y, 1-z.

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  To ascertain the purity of the samples of complexes 1 and 2, the PXRD patterns of these complexes were determined. As demonstrated in Fig. 3, the experimental PXRD patterns were in close agreement with the simulated data of single-crystal diffraction results, indicating that all complexes exhibit high phase purity.

  Figure 3

  

  Figure 3.  PXRD patterns of complexes 1 (a) and 2 (b)

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  2.2   Detection of Al³⁺

  The photoluminescence properties of complexes 1 and 2 in aqueous suspension were investigated. It was established that both complexes 1 and 2 exhibited photoluminescence properties. Specifically, complex 1 exhibited an emission peak at 540 nm when excited at 415 nm (Fig. 4a), while complex 2 demonstrated an emission peak at 402 nm when excited at 320 nm (Fig. 4b).

  Figure 4

  

  Figure 4.  Photoluminescence properties of the suspensions of complexes 1 (a) and 2 (b) at room temperature

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  The selective sensing ability of various cations (Zn²⁺, Pd²⁺, Na⁺, K⁺, Mn²⁺, Mg²⁺, Cd²⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, and Al³⁺) to the aqueous suspension of complexes 1 or 2 was studied by gradually adding 1 μmol·L^-1 (200 μL) chloride salt in aqueous solution. Interestingly, after the addition of Al³⁺ to the suspension of complex 1, the fluorescence intensity was significantly enhanced, and its intensity was 11 times that of the original fluorescence intensity, while the fluorescence intensity did not change significantly after the addition of other cations (Fig. 5a and 5b). However, the addition of different cations to the suspension of complex 2 did not result in a significant change in fluorescence (Fig.S3).

  Figure 5

  

  Figure 5.  (a, b) Fluorescence spectra of the suspension of complex 1 after adding different metal ions (1 μmol·L^-1, 200 μL); (c) Effect of the concentration of Al³⁺ on the fluorescence intensity of 1; (d) Stern-Volmer plots for 1 sensing Al³⁺

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  To study the effect of pH on the sensing of complex 1 to Al³⁺, the fluorescence response of probe 1 to Al³⁺ ions at 475 nm was investigated in a pH range of 2.0-13.0. As shown in Fig.S4, the probe shows the best fluorescence response near neutral pH, which is consistent with the range of biological and environmental applications (Fig.S4).

  To understand the sensitivity of complex 1 to Al³⁺, the luminescence of complex 1 was studied when the concentration of Al³⁺ increased. As shown in Fig. 5c, with the increase of Al³⁺ concentration, the fluorescence intensity of complex 1 suspension increased gradually. The quantitative explanation of the luminescence enhancement effect was realized by fitting the experimental data using a Stern-Volmer plot. The formula I/I₀=1+K_SVc_M was used, where I₀ and I are the emission intensities at 475 nm in the absence or presence of analytes, respectively, K_SV represents the quenching constant, and c_M is the concentration of the analytes. There was a significant linear correlation between I/I₀ and c_{Al^{3 +}} (Fig. 5d), and the K_SV was calculated to be 4.89×10⁶ L·mol^-1. According to the K and standard deviation (σ) of five repeated blank measurements, the detection limit (LOD=3σ/K) for complex 1 sensing Al³⁺ was 6.37 μmol·L^-1.

  Examining the influence of mixed cations is crucial for a comprehensive understanding of the behavior of the system. As shown in Fig. 6, the addition of Al³⁺ to the suspension of complex 1, which contains a variety of metal ions, has been shown to enhance the fluorescence emission. This observation indicates that the presence of other cations does not exert a significant influence on the detection of Al³⁺.

  Figure 6

  

  Figure 6.  Interference of different metal cations on the sensing of Al³⁺ by complex 1 in solution

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  The sensing mechanism of complex 1 was discussed. In our previous work, the ligand H₂L1 can form an aluminum complex with Al^{3+ [17]}. In this work, the addition of Al³⁺ to the suspension of complex 1 is also likely to produce HL-Al complex. Therefore, we tested the UV-Vis absorption spectra of the Al³⁺ complex and the addition of Al³⁺ to complex 1. As shown in Fig. 7, the absorption peaks of HL-Al complex and complex 1 were almost the same after dropping Al³⁺, indicating that complex 1 is gradually dissociated to form complex HL-Al after dropping Al³⁺. Meantime, the PXRD pattern of complex 1 after adding Al³⁺ was consistent with the position of the main peak of the PXRD pattern of the HL-Al crystal, which also indicates the formation of Al³⁺ complexes (Fig.S5). The combination of Al³⁺ with the acceptor eliminates the enol emission and leads to enhanced fluorescence emission by chelating the fluorescence enhancement effect.

  Figure 7

  

  Figure 7.  Liquid UV-Vis spectra of HL‐Al and complex 1+Al³⁺ in the solution

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  3.   Conclusions

  In summary, based on the cinnolin-3-yl-hydrazine ligand and metal zinc, two novel coordination polymers were designed and synthesized by adjusting the position of the methoxy group in R-CHO. It is noteworthy that within complex 2, the Schiff bases formed by cinnolin-3-yl-hydrazine and 2-hydroxy-3-methoxybenzaldehyde ligands manifest in two distinct forms (H₂L2 and HL3), exhibiting a diversification of coordination modes. Furthermore, the suspension of complex 1 has been shown to possess the ability to detect Al³⁺ in solution, with a detection limit of 6.37 μmol·L^-1. This phenomenon can be attributed to the formation of a complex between the ligand H₂L1 and Al³⁺ ions, resulting in a significant enhancement of fluorescence. This work provides a new perspective and idea for the detection of Al³⁺ ions by complexes.

  
  Supporting information is available at http://www.wjhxxb.cn
  
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• 

  Scheme 1  Synthetic routes of complexes 1 and 2

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  Figure 1  Crystal structure of complex 1: (a) coordination mode of Zn²⁺ at 30% thermal ellipsoids; (b) intermolecular π···π interaction in 1

  Cg1 for the centroid of ring N1, N2, C1, C2, C7 and C8, Cg2 for the centroid of ring C10-C15, Cg3 for the centroid of ring C18-C23, Cg4 for the centroid of ring C26-C31, Cg5 for the centroid of ring C2-C7; Symmetry codes: ^ⅰ x, 0.5-y, 0.5+z; ^ⅱ x, 0.5-y, -0.5+z; ^ⅲ 1-x, -y, 1-z.

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  Scheme 2  Schiff base in complex 2

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  Figure 2  Crystal structure of complex 2: (a) coordination environment of Zn²⁺ at 30% thermal ellipsoids; (b, c) coordination modes of HL3; (d) intermolecular π⋯π interaction in 2

  Cg1 for the centroid of ring N7, N16, C7, C36, C37 and C39, Cg2 for the centroid of ring N14, N15, C9-C12, Cg3 for the centroid of ring C1-C6, Cg4 for the centroid of ring C18-C23, Cg5 for the centroid of ring C26-C31, Cg6 for the centroid of ring C33-C38, Cg7 for the centroid of ring C44-C50; Symmetry codes: ^ⅰ 1-x, 1-y, 1-z, ^ⅱ 1-x, -y, 1-z; ^ⅲ 2-x, 1-y, 1-z.

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  Figure 3  PXRD patterns of complexes 1 (a) and 2 (b)

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  Figure 4  Photoluminescence properties of the suspensions of complexes 1 (a) and 2 (b) at room temperature

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  Figure 5  (a, b) Fluorescence spectra of the suspension of complex 1 after adding different metal ions (1 μmol·L^-1, 200 μL); (c) Effect of the concentration of Al³⁺ on the fluorescence intensity of 1; (d) Stern-Volmer plots for 1 sensing Al³⁺

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  Figure 6  Interference of different metal cations on the sensing of Al³⁺ by complex 1 in solution

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  Figure 7  Liquid UV-Vis spectra of HL‐Al and complex 1+Al³⁺ in the solution

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  Table 1.  Crystal data and structure refinement details for complexes 1 and 2

  Parameter	1	2
  Formula	C34H33N9O9Zn2	C65H49ClN16O9Zn3
  Formula weight	842.43	1 429.76
  Crystal system	Monoclinic	Triclinic
  Space group	P21/c	P1
  Temperature/K	293	100
  a/nm	1.303 539(17)	1.350 14(3)
  b/nm	1.705 37(2)	1.434 07(4)
  c/nm	1.549 07(2)	1.638 56(2)
  α/(°)		95.567 7(17)
  β/(°)	98.670 6(13)	106.433 1(17)
  γ/(°)		96.581 0(19)
  V/nm3	3.404 24(8)	2.994 90(11)
  Z	4	2
  Dc/(Mg·m-3)	1.646	1.588
  μ/mm-1	2.34	2.44
  Rint	0.047	0.059
  GOF	1.05	1.12
  F(000)	1 732	1 464
  R1[I > 2σ(I)]	0.040	0.074
  wR2[I > 2σ(I)]	0.117	0.212

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

  1
  Zn1—O1	0.199 02(17)	Zn1—N2	0.216 41(19)	Zn2—N6	0.207 70(19)
  Zn1—O6	0.199 13(18)	Zn2—O3	0.199 83(17)	Zn2—N1	0.210 16(18)
  Zn1—N5	0.207 23(19)	Zn2—O5	0.203 34(16)
  Zn1—N4	0.208 16(19)	Zn2—N8	0.205 77(19)
  O1—Zn1—O6	97.93(7)	O6—Zn1—N2	92.96(7)	O5—Zn2—N6	99.93(7)
  O1—Zn1—N5	96.77(7)	N5—Zn1—N2	91.97(7)	N8—Zn2—N6	76.18(8)
  O6—Zn1—N5	111.15(7)	N4—Zn1—N2	74.17(7)	O3—Zn2—N1	90.41(7)
  O1—Zn1—N4	88.34(7)	O3—Zn2—O5	91.12(7)	O5—Zn2—N1	114.35(7)
  O6—Zn1—N4	129.02(7)	O3—Zn2—N8	89.37(7)	N8—Zn2—N1	124.67(7)
  N5—Zn1—N4	118.26(8)	O5—Zn2—N8	120.97(7)	N6—Zn2—N1	94.28(7)
  O1—Zn1—N2	162.51(7)	O3—Zn2—N6	164.93(7)
  2
  Zn1—O3	0.201 0(4)	Zn2—O2	0.207 5(4)	Zn3—N9	0.207 0(5)
  Zn1—O2	0.201 3(4)	Zn2—O3	0.211 9(4)	Zn3—N12	0.222 1(5)
  Zn1—N2	0.202 1(5)	Zn2—N8	0.212 1(5)	Zn3—O6	0.194 1(4)
  Zn1—O1	0.222 6(4)	Zn2—N5	0.212 3(5)	Zn3—O5	0.200 7(4)
  Zn1—Cl1	0.222 71(16)	Zn2—N13	0.216 0(5)
  Zn2—O5	0.204 3(4)	Zn3—N11	0.206 9(5)
  O3—Zn1—O2	83.30(15)	O2—Zn2—Zn1	39.61(10)	O3—Zn2—N13	160.16(16)
  O3—Zn1—N2	87.90(18)	O3—Zn2—Zn1	39.71(11)	N8—Zn2—N13	88.33(19)
  2
  O2—Zn1—N2	114.36(17)	N8—Zn2—Zn1	99.28(13)	N5—Zn2—N13	92.96(18)
  O3—Zn1—O1	155.04(15)	N5—Zn2—Zn1	90.07(13)	N13—Zn2—Zn1	120.44(12)
  O2—Zn1—O1	74.21(14)	O5—Zn2—O2	167.14(16)	O5—Zn3—N9	88.49(19)
  N2—Zn1—O1	91.56(17)	O5—Zn2—O3	112.20(15)	N11—Zn3—N9	75.4(2)
  O3—Zn1—Cl1	106.45(13)	O2—Zn2—O3	79.21(14)	O6—Zn3—N12	98.38(19)
  O2—Zn1—Cl1	121.57(12)	O5—Zn2—N8	89.19(19)	O6—Zn3—O5	102.64(19)
  N2—Zn1—Cl1	123.28(14)	O2—Zn2—N8	95.92(17)	O6—Zn3—N11	90.8(2)
  O1—Zn1—Cl1	94.65(11)	O3—Zn2—N8	94.80(17)	O5—Zn3—N11	152.7(2)
  O3—Zn1—Zn2	42.34(10)	O5—Zn2—N5	79.29(18)	O6—Zn3—N9	165.7(2)
  O2—Zn1—Zn2	41.09(11)	O2—Zn2—N5	95.74(17)	O5—Zn3—N12	87.00(17)
  N2—Zn1—Zn2	102.45(13)	O3—Zn2—N5	87.92(17)	N11—Zn3—N12	114.72(19)
  O1—Zn1—Zn2	113.99(10)	N8—Zn2—N5	168.33(19)	N9—Zn3—N12	91.12(19)
  Cl1—Zn1—Zn2	125.24(5)	O5—Zn2—N13	87.40(17)
  O5—Zn2—Zn1	150.87(11)	O2—Zn2—N13	80.98(16)

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