2,5-bis(p-ethoxycarbonylphenyl)-1-aminobenzene (C) was synthesized by previously reported procedures. To a 1,000 ml round-bottom flask was added with 2, 5-dibromoaniline (1.2 g, 5 mmol), p-ethoxycarbonylphenylboronoc acid (2.9 g, 15 mmol), Pd(PPh₃)₄ (0.58 g, 0.5 mmol), CsF (3.6 g, 24 mmol) and tetrahydrofuran (75 ml). The mixture solution was bubbled with N₂ for more than 10 min and refluxed for 3 days. TLC (hexane : ethyl acetate = 6:1) showed that the reaction has finished. After cooling to room temperature, water was added onto the reaction mixture and then extracted with ethyl acetate (30 ml × 3). The combined organic solution was dried with anhydrous MgSO₄ and concentrated in vacuum. The crude residues were purified by column flash chromatography with the eluant (hexane:ethyl acetate = 30:1) to give a light yellow solid as target product (1.35 g, yield: 67.3%).

Compound C (1.35 g, 3.4 mmol), KOH (6.24 g, 111 mmol), tetrahydrofuran (THF, 40 ml) and water (100 ml) were added to a 1 L round-bottom flask. The mixture solution was bubbled with N₂ for more than 10 min and stirred at 50 C for 12 h. After removing THF in vacuum, the residue was added with water and then acidified with diluted HCl (1 M) until no precipitate formed. The atrovirens powder was collected by filtration as target product (0.88 g, yield: 72%). LC-MS (M + H)⁺ _found = 334.12.

2,1,3-Benzothiadiazole (D) (0.5 g, 3.68 mmol), N-bromosuccinimide (NBS, 1.35 g, 7.61 mmol) and H₂SO₄ (98%, 5 ml) were added to a 25 ml round round-bottom flask. The reaction mixture was stirred at 60°C for 3 h. After cooling to room temperature, the solution was added with distilled water (25 ml) dropwise in an ice bath. The white desired solid was collected by filtration (1.06 g, yield: 97%).

Compound F (2.49 g, 10 mmol), p-ethoxycarbonylphenylboronoc acid (5.82 g, 30 mmol), Pd(PPh₃)₄ (1.16 g , 1 mmol), Cs₂CO₃ (8.15 g , 25 mmol), N,N-dimethylformamide (DMF, 100 ml), and toluene (100 ml) were added to a 500 ml round-bottom flask. The reaction solution was bubbled with N₂ for more than 10 min and refluxed at 110°C for 24 h. TLC (hexane:ethyl acetate = 8:1) showed that the reaction has finished. The reaction solution was added with water and extracted with ethyl acetate (20 ml × 3). The combined organic solution was dried with anhydrous MgSO₄ and concentrated in vacuum. The crude product was purified by column flash chromatography with the eluant (hexane:ethyl acetate = 40:1) to give an orange solid as the target product (2.25 g, yield: 49%).

To a solution of H (1,296 mg, 3 mmol) in EtOH/THF (3:1, EtOH = ethyl alcohol) was added sodium borohydride (0.46 g, 12 mmol) and CoCl₂·6H₂O (29 mg, 0.12 mmol). The reaction solution was bubbled with N₂ for more than 10 min and refluxed for 3 h. After removal of EtOH and THF, the residues were added with water and extracted with ethyl acetate (20 ml × 3). The combined organic phase was dried with anhydrous MgSO₄ and concentrated in vacuum. The obtained solid was purified by column flash chromatography with the eluant (hexane:ethyl acetate = 20:1) to give a grey solid as the target product (0.92 mg, yield: 74.3%) . LC-MS (M + H)⁺ _found = 405.30.

Compound I (0.90 g, 2.22 mmol), KOH (4.09 g, 73 mmol), THF (20 ml), and water (60 ml) were added to a 500 ml round-bottom flask. The reaction solution was bubbled with N₂ for more than 10 min and stirred at 60 C for 24 h. After removing THF in vacuum, the mixture was added with water and then acidified with diluted HCl (1 M) until no precipitate formed. The yellow powder was collected by filtration as target product (0.63 mg, 82% yield). LC-MS (M + H)⁺ _found = 349.23.

A mixture of H₂BCPAB (6.7 mg, 0.02 mmol), Cd(NO₃)₂∙4H₂O (31 mg, 0.1 mmol), DMA (3.5 ml), H₂O (3 ml) was placed in a 25 ml glass vial and heated at 95°C for 4 days. The resultant plate crystals were washed with fresh DMA and collected. Yield: 72% (based on H₂BCPAB).

A mixture of H₂BDAB (7 mg, 0.02 mmol), Cd(NO₃)₂∙4H₂O (31 mg, 0.1 mmol), DMF (2 ml), H₂O (4 ml) was placed in a 25 ml glass vial and heated at 95°C for 4 days. The resultant plate crystals were washed with fresh DMA and collected. Yield: 93% (based on H₂BDAB).

A mixture of H₂BDAB (7 mg, 0.02 mmol), BPD (1.5 mg, 0.01 mmol), Zn(NO₃)₂∙6H₂O (30 mg, 0.1 mmol), DMF (3.5 ml), H₂O (2.5 ml) was placed in a 25 ml glass vial and heated at 100°C for 3 days. The resultant red featheriness crystals were washed with fresh DMF and collected. Yield: 36% (based on H₂BDAB).

A mixture of H₂BDAB (7 mg, 0.02 mmol), DBPB (3.5 mg, 0.01 mmol), Zn(NO₃)₂∙6H₂O (30 mg, 0.1 mmol), DMF (3.5 ml), and H₂O (1.5 ml) was placed in a 25 ml glass vial and heated at 105°C for 3 days. The resultant red featheriness crystals were washed with fresh DMF and collected. Yield: 59% (based on H₂BDAB).

SC-XRD analysis revealed that complex 1 was crystallized in the orthorhombic system with a space group of Pbca and each asymmetric unit consisted of one Cd(II) metal center, one BCPAB²⁻ ligand and one water molecule. As shown in Figure 1, atom Cd1 adopted a distorted pentagonal bipyramid coordination geometry to coordinate with four carboxylate oxygen atoms (O1, O2, O3#2, O4#2) from two neighboring BCPAB²⁻ ligands, two coordinated water molecules (O5, O5#3) and one nitrogen atom (N1#1) from the amino group of BCPAB²⁻ ligand. The Cd-O bond lengths were in the range of 2.281–2.448 Å and the Cd-N bond length was 2.425 Å, which are comparable to the previous Cd-based coordination complexes. (Spek, 1998) Further structural analysis revealed that each carboxylate group of BCPAB²⁻ was bound to one Cd²⁺ ion and each Cd²⁺ ion coordinated with two carboxylate groups from two adjacent BCPAB²⁻ ligands, which thus resulted in the formation of one-dimensional (1D) coordination chains (Figure 2A). Furthermore, the coordination bonds between amino groups of the BCPAB²⁻ ligands and Cd²⁺ ions joined the 1D Cd²⁺-BCPAB²⁻ chains together to afford two-dimensional (2D) coordination layers (Figure 2B). On the other hand, each water molecule linked two Cd²⁺ ions to give 1D Cd-O coordination and thus the 2D Cd²⁺-BCPAB^2- layers were connected by the μ ₂-H₂O molecules into the final 3D frameworks (Figure 2C; Supplementary Figure S1A). From the viewpoint of topology, the seven coordination secondary building unit and the BCPAB²⁻ ligand can be regarded as a 5-connected and 3-connected node, respectively, and the structure of 1 could be represented as seh-3, 5-Pbca nets with point symbol of {4.6²}{4.6⁷.8²} (Supplementary Figure. S1B).

According to SC-XRD measurements, complex 2 was crystallized in the tetragonal P4/nnc space group and each asymmetric unit contained half one Cd²⁺ and half one BDAB²⁻ ligand. As depicted in Figure 3, atom Cd1 was six-coordinated in a disordered octahedral coordination geometry with four carboxylate oxygen atoms (O1, O2, O1#1, O2#1) form two neighboring BDAB²⁻ ligands and two amino groups (N1#2, N1#3) from another two adjacent BDAB²⁻ ligands. Each Cd²⁺ ion connected two carboxylate groups from different BDAB²⁻ ligands to form 1D helical coordination chains (Figure 4A). Further inspection into the structure found that every four helical chains could assemble into a coordination nanotubular structure with the help of the binding between Cd²⁺ atoms and amino groups of BDAB²⁻ ligands on the chains (Figure 4B). The Cd²⁺ ions in the structure of nanotube were only coordinated with carboxylate groups or amino groups and thus they could bind to the amino groups or carboxylate groups from neighboring nanotubes, which then resulted in the formation of the final 3D coordination frameworks with 1D channels running along c-axis. From the point of topological view, because one Cd²⁺ cation connects four BDAB²⁻ ligands and one BDAB²⁻ ligand links four Cd²⁺ cations, the central Cd²⁺ cation and BDAB²⁻ ligand can both be treated as 4-connected nodes. Thence, the network of 2 can be represented with the point symbol is {4².8⁴} calculated by TOPOS software (Supplementary Figure S2). The total solvent cavity volume of 2 is 35.0% per unit cell calculated by PLATON. (Zou et al., 2010)

According to the results of SC-XRD measurements, complexes 3 and 4 were both crystallized in the monoclinic C2/c space group and shared a similar framework structure. Each asymmetric unit of 3 consisted of one Zn²⁺ cation, one BDAB²⁻ ligand, half of one BPD molecule, and one coordinated water molecule. As illustrated in Figure 5, atom Zn1 in 3 adopted a slightly disordered tetrahedral coordination geometry surrounded by two carboxylate oxygen atoms (O2, O4#1) from two adjacent BDAB²⁻ ligands, one nitrogen atom (N3) from the BPD ligand and one coordinated water molecule (O5). The connection between Zn²⁺ cations and the carboxylate groups of BDAB²⁻ ligands afforded 1D coordination chains (Figure 6A), which were further assembled by the coordination between Zn²⁺ cations and the nitrogen atoms of BPD ligands to give 2D coordination networks (Figure 6B). On closer inspection, due to the existence of the large pores in the 2D networks, it could be found that six adjacent 2D networks could interlace with each other to give 6-fold interpenetrated 2D supramolecular layers via the π…π, C-H…π interactions (Figures 6C,D; Supplementary Figure S3A). Furthermore, the interpenetrated layers were joined together to generate the final 3D supramolecular architecture by the noncovalent interactions including hydrogen bonds, π…π and C-H…π interactions (Figure 6E; Supplementary Figure S3B).

Although a more complicated pyridine ligand DBPB was used instead of BPD to prepare complex 4, the structure of 4 was almost identical to that of 3 and shared the same topological structure with complex 3 (Supplementary Figure S4). Each asymmetric unit of 4 also consisted of one Zn²⁺ cation, one BDAB²⁻ ligand, half of one DBPB molecule, and one coordinated water molecule. Similar to that of 3, the central Zn²⁺ cations in 4 also adopted a distorted tetrahedral geometry (Figure 7A) and connected the organic ligands BDAB²⁻ and DBPB to generate 2D coordination networks (Figure 7B). But differently, due to the much larger size, the pyridine ligand DBPB could allow more 2D BDAB²⁻-Zn²⁺-DBPB coordination networks to interpenetrate with each other to give an 8-fold interpenetrated 2D supramolecular layers (Figures 7C,D; Supplementary Figure S4A). These supramolecular layers further interact with each other to give the final 3D supramolecular frameworks (Figure 7E; Supplementary Figure S4B) via various noncovalent interactions including C-H…π interactions and hydrogen bonds (Supplementary Figure S4C). Furthermore, one more difference between the structure of 3 and 4 was that 1D channels along b-axis could be observed in the framework of 4 (Figure 7E) and the total solvent cavity volume is 22.5% per unit cell calculated by PLATON. (Zou et al., 2010).

The PXRD experiments were carried out to confirm whether the crystal structures are truly representative of the bulk materials. The PXRD experimental and computer-simulated patterns of the corresponding complexes are shown in the ESI (Supplementary Figures S5–S8). The experimental data shows that the bulk synthesized materials are the same as the measured single crystals, suggesting the bulk-phase purity of the obtained MOFs. Furthermore, TGA experiments were also carried out in the N₂ atmosphere from 30 to 500°C to examine the thermal stability of 1–4 and the results were depicted in Supplementary Figures S9–S12. Complex 1 showed a weight loss of 3.6 % from 30 to 260°C, suggesting the release of the coordinated water molecules (calcd 3.92 %) and their structure began to collapse at 400 °C. Complex 2 shows a weight loss of 19 % before 250°C, which corresponds to the release of free water and DMF molecules (calcd 19 %), and further weight loss was observed at about 380°C owing to the collapse of the framework of 2. The TGA curve of complex 3 showed that the framework structure began to decomposing at 350°C. Complex 4 displayed a weight loss of 5.4 % before 110°C corresponding to the release of free water molecules (calcd 5.6 %) and then a weight loss of 2.7 % between 110 and 180°C corresponding to the release of coordinated water molecules (calcd 2.8%). Further quick weight losses were observed at 360°C owing to the decomposition of the frameworks of 4.

Previous studies have demonstrated that MOFs containing d¹⁰-metal ions usually exhibit outstanding fluorescence properties and could function as sensing materials for various substances. On the other hand, in consideration of the existence of channels or uncoordinated amino groups in the structure of complexes 2–4, their fluorescence properties and sensing capability were checked. Thence, the solid-state fluorescence properties of 2–4 were firstly examined at room temperature. As illustrated in Figure 8, the free ligand H₂BDAB exhibited characteristic emission bands with maxima at 571 nm upon excitation at 356 nm, while the fluorescence emission maxima of 2–4 were observed at 401, 396, and 473 nm upon excitation at 330, 330, and 380 nm, respectively. Compared to the free ligand, apparent blue-shift emissions were observed for 2–4, which may be attributed to the coordination of multi-aromatic ligands to the metal centers. (Nagarkar et al., 2015) Then, the sensing capacities of 2–4 towards common metal ions were checked as well. Before the sensing experiments, the powder samples of 2–4 were fully ground and immersed in DMF to prepare stable suspension (1.0 mg ml⁻¹), respectively. Then, the DMF solutions (50 μl, 100 mM) containing different metal ions, including K⁺. Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, and Ag⁺, were added into the DMF suspension of 2–4. The changes in the fluorescence emission intensities were recorded (Supplementary Figures S13–S15) and the results were depicted in Figure 9. It could be found that the existence of Cu²⁺ could cause obvious reduction in the fluorescence intensity of 2 while there was no significant change for other metal ions. As for 3, the addition of Cu²⁺ and Ag⁺ both lead to the quenching of the fluorescence quenching and the addition of other metal ions only caused slight or moderate change in the emission intensities of 3. The fluorescence emissions of 4 were either almost unchanged or enhanced and no specific response was observed for metal ions. Therefore, complex 2 may function as a fluorescent sensor for Cu²⁺ and complex 3 could detect Cu²⁺ and Ag⁺ via fluorescence quenching effect.

Coordination polymers 3 and 4 can maintain the stability of the frameworks after 10 h heating and activation. We using CO₂ as the adsorptive gas to measure the sorption properties of these two complexes. The CO₂ sorption isotherms of these two complexes measured at 298 K are shown in Figure 7. The gas sorption isotherms indicated a CO₂ uptake of 2.4 cm³/g for 3, 15.9 cm³/g for 4. Complex 4 exhibits much more adsorption than complex 3 due to its high porosity: 1,455.9 ų and the accessible volumes 22.5% for 4. It is speculated that the reason for the low porosity of 3 is that the length of the co-ligand in 3 is relatively short, and the double interspersed would serve to occupy more of the free void space within the porous structure, so that the carbon dioxide molecules cannot enter the hole.