English

• Mechanical chromic luminescence (MCL) materials represent a significant category of intelligent luminescent substances^[1-2]. These materials undergo specific structural changes when subjected to external mechanical force, resulting in alterations to their luminescent properties, including shifts in emission wavelength and variations in emission intensity. Notably, under conditions such as solvent fumigation and soaking, the original structure and luminescent characteristics can be restored, thereby enabling a reversible luminescence response in these materials. Such properties confer considerable potential for applications in fields such as anti-counterfeiting measures, intelligent sensors, and switching systems; consequently, research related to MCL materials has garnered substantial attention^[3-5]. Although some MCL materials have been reported thus far, several challenges remain within this area of study^[2-6]. For instance, what factors determine whether a compound exhibits MCL or resistance MCL (RMCL) properties? Furthermore, weak interactions (such as aromatic stacking and hydrogen bonding) are generally acknowledged to significantly influence MCL characteristics; however, the precise mechanisms by which they affect these properties warrant further investigation.

  In recent years, luminescent metal-organic framework materials (LMOFs) have emerged as prominent candidates among various MCL materials due to their highly tunable luminescence properties and porous structures^[7-8]. LMOFs utilize coordination bonds to link inorganic metal ions or clusters with organic ligands, resulting in a multidimensional porous architecture. The structural characteristics and MCL properties of these compounds can be effectively regulated by varying the selection of metal ions, organic ligands, and synthesis conditions. However, synthesizing a series of structural isomers to investigate the relationship between the MCL/RMCL properties of LMOF-type materials remains a significant challenge.

  Herein, two new LMOFs, [Mg(L)(DMF)₂(H₂O)₂]₂·5DMF·2H₂O (1) with a 1D structure and [Mg₂(L)₂(DMSO)₃(H₂O)] (2) with a 2D (4, 4)-net structure were synthesized from the reaction of Mg²⁺ and 5-{1, 3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl}terephthalic acid (H₂L). 1 and 2 can be considered framework quasi-isomers. Photoluminescence (PL) studies indicate that 1 had excellent RMCL ability, while 2 showed reversible MCL property. Detailed analysis reveals that the RMCL of 1 is due to its predominant hydrogen bonds and the presence of high-boiling-point solvent molecules in its structure. In contrast, the MCL behavior of 2 arises from dominant offset face-to-face π-π interactions along with reversible destruction and restoration of its crystalline structure. Detailed structures and properties are reported.

  1.   Experimental

  1.1   Materials and methods

  All chemicals used in this study were commercially available reagents of analytical grade and were utilized as received. Luminescence spectra were obtained using a Hitachi F-7000 FL spectrophotometer. Powder X-ray diffraction (PXRD) patterns were collected on a D/MAX-2400 X-ray diffractometer employing Cu Kα radiation (λ=0.154 060 nm) at a scan rate of 10 (°)·min^-1 (voltage: 40 kV, current: 25 mA, scan range: 5°-50°). Infrared spectra were recorded in a range of 650-4 000 cm^-1 using a Nicolet-20DXB spectrometer via the KBr pellet pressing method. Thermogravimetric analyses (TGA) were conducted on a TA-Q50 thermogravimetric analyzer with a heating rate of 10 ℃·min^-1 under N₂ protection. Elemental analyses for C/H/N were performed using a Vario EL Ⅲ elemental analyzer. The synthesis of H₂L was carried out according to the established literature method^[9].

  1.2   Synthesis of compound 1

  Ligand H₂L (7.23 mg, 0.02 mmol), Mg(Ac)₂·4H₂O (6.43 mg, 0.03 mmol), and 0.1 mL (0.1 mol·L^-1) HCl were dissolved in DMF/H₂O (4 mL/0.3 mL). Then the solution was stirred at room temperature, filtered, and left undisturbed for 48 h. The colorless needle crystals can be obtained, washed with DMF several times, and then air dried at room temperature. Element analysis Calcd. for C₆₇H₉₃Mg₂N₁₁O₂₇(%): C, 52.49; H, 6.11; N, 10.05. Found(%): C, 52.51; H, 6.08; N, 10.09. IR (cm^-1): 1 703 (s), 1 657 (vs), 1 585 (s), 1 437 (m), 1 358 (m), 1 296 (w), 1 242 (s), 1 194 (w), 1 105 (s), 1 066 (m), 1 028 (w), 890 (s), 851 (w), 777 (w), 712 (m).

  1.3   Synthesis of compound 2

  Liand H₂L (7.23 mg, 0.02 mmol) and Mg(Ac)₂·4H₂O (6.43 mg, 0.03 mmol) were dissolved in DMSO/H₂O (2 mL/0.3 mL) in a 20 mL glass vial. Then the vial was sealed and placed in an oven at 115 ℃ for 3 h, and cooled naturally to room temperature. The colorless flake crystals can be obtained, washed with DMSO several times, and then air dried at room temperature. Element analysis Calcd. for C₄₆H₃₈Mg₂N₂O₁₆S₃(%): C, 54.19; H, 3.76; N, 2.75. Found(%): C, 54.27; H, 3.88; N, 2.81. IR (cm^-1): 1 701 (s), 1 655 (s), 1 608 (m), 1 576 (vs), 1 537 (w), 1 435 (m), 1 366 (m), 1 294 (w), 1 243 (s), 1 202 (w), 1 151 (m), 1 107 (s), 1 028 (m), 895 (m), 828 (s), 774 (m), 705 (m).

  1.4   Structure determination

  Intensity data from single crystals were collected at 120 K for compound 1 and 193 K for compound 2 on a Bruker SMART APEX Ⅱ CCD area detector system with graphite-monochromated Mo Kα (λ=0.071 073 nm) radiation. Data reduction and unit cell refinement were performed with Smart-CCD software. The structure was solved by the direct method using SHELXS-2014 and refined by full-matrix least squares method using SHELXS-2014^[10]. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms related to the C and N atoms were generated geometrically. Hydrogen atoms attached to oxygen atoms were located from the difference Fourier map and refined with restrained O—H and H⋯H distances for 1. A summary of crystal structure refinement data is given in Table 1.

  Table 1

  

  Table 1.  Crystal data collection and structure refinement parameters for compounds 1 and 2

  下载: 导出CSV

  Parameter	1	2
  Empirical formula	C67H93Mg2N11O27	C46H38Mg2N2O16S3
  Formula weight	1 533.14	1 019.58
  Crystal system	Triclinic	Monoclinic
  Space group	P1	P21/n
  a/nm	0.869 0(2)	0.916 05(7)
  b/nm	1.132 8(2)	0.158 087(14)
  c/nm	2.019 6(2)	0.164 179(14)
  α/(°)	97.658(7)
  β/(°)	98.835(9)	96.505(5)
  γ/(°)	96.415(8)
  V/nm3	1.929 2(8)	2.362 3(3)
  Z	1	2
  Dc/(g·cm-3)	1.320	1.433
  μ/mm-1	0.117	0.257
  F(000)	812	1 056
  θ range/(°)	2.394-24.999	2.436-25.000
  Reflection collected, unique, observed	12 279, 10 020, 4 904	15 532, 4 145, 2 845
  Rint	0.119 5	0.056 3
  GOF on F2	0.946	1.171
  R1a[I > 2σ(I)] (all)	0.084 8 (0.192 2)	0.099 2 (0.131 8)
  wR2b[I > 2σ(I)] (all)	0.183 9 (0.224 5)	0.270 6 (0.287 8)
  Max/mean shift in final cycle	0.000/0.000	0.000/0.000
  a R=∑(||Fo|-|Fc||)/∑|Fo|; b wR=[∑w(Fo2-Fc2)2/∑w(Fo2)2]1/2, w=1/[σ2Fo2+(aP)2+bP], P=(Fo2+2Fc2)/3, a=0.092 4, b=0.000 0 for 1, a=0.126 3, b=4.777 2 for 2.

  2.   Results and discussion

  2.1   Crystal structure of compound 1

  Single-crystal X-ray diffraction studies reveal that compound 1 crystallizes in the triclinic P1 space group and exhibits a 1D neutral chain structure. The asymmetric unit comprises two independent L^2- ligands and two independent Mg²⁺ ions. As illustrated in Fig. 1a, the two Mg²⁺ ions possess identical coordination environments, except differing configurations of the coordinating DMF molecules. Each Mg²⁺ ion is coordinated by six oxygen atoms, resulting in a distorted octahedral coordination polyhedron; four oxygen atoms are derived from solvent molecules while two originate from the carboxylate groups of the ligands. The Mg—O bond lengths range from 0.201 7(9) to 0.216 0(11) nm. Each L^2- ligand coordinates with two Mg²⁺ ions through a μ₂-κ_O¹∶κ_O¹ coordination mode. The primary differences between them are reflected in the dihedral angles between their naphthalene and benzene rings, which measure approximately 73.9(7)° and 87.1(7)°, respectively.

  Figure 1

  

  Figure 1.  Crystal structure of compound 1: (a) coordination environment of Mg²⁺ ions; (b) interaction between two neighboring chains; (c) packing of the 1D belts viewed along the c-axis

  π⋯π interaction is represented as the green dotted line; C/N atoms from the DMF molecules, and H atoms are omitted for clarity; Symmetry code: ⁱ x, y-1, z.

  下载: 全尺寸图片 幻灯片

  One Mg²⁺ ion, along with two carboxylate groups, forms a {Mg(COO)₂} secondary building unit (SBU). These SBUs are subsequently linked by ligands to create a 1D chain extending along the b-axis. Notably, all naphthylimide groups are positioned on one side of the chain. The neighboring chains are packed in such a close mode that strong offset face-to-face π-π interaction is formed between contiguous naphthalene rings with ring (center)-ring (center) separation of ca. 0.393 4(1) nm. The resulting belts are further connected by hydrogen bonds between coordinated and free H₂O molecules, sulfoxide oxygen atoms from free DMF solvent molecules, and carboxylate oxygen atoms into a 3D supramolecular structure (Table 2). The corresponding O⋯O separations are in a range of 0.264 4(13)-0.277 8(15) nm.

  Table 2

  

  Table 2.  Hydrogen bond parameters for compound 1

  下载: 导出CSV

  D—H⋯A	d(D—H)/nm	d(H⋯A)/nm	d(D⋯A)/nm	∠DHA/(°)
  O13—H13C⋯O2	0.089(5)	0.190(7)	0.266 0(12)	142(5)
  O13—H13B⋯O22A	0.084(5)	0.189(6)	0.272 4(14)	172(9)
  O14—H14B⋯O26	0.086(5)	0.191(6)	0.268 1(12)	149(12)
  O14—H14A⋯O3B	0.088(5)	0.195(8)	0.269 4(12)	142(5)
  O18—H18B⋯O8	0.084(6)	0.195(8)	0.268 8(12)	146(12)
  O18—H18C⋯O27	0.087(6)	0.178(7)	0.264 4(13)	172(14)
  O20—H20A⋯O9B	0.102(5)	0.179(7)	0.272 0(12)	150(4)
  O20—H20B⋯O25C	0.089(5)	0.197(7)	0.272 6(13)	142(10)
  O26—H26A⋯O21	0.087(6)	0.190(7)	0.275 3(15)	168(13)
  O26—H26B⋯O8	0.086(6)	0.203(12)	0.267 3(14)	131(14)
  O27—H27A⋯O3B	0.083(6)	0.194(7)	0.274 5(13)	164(13)
  O27—H27B⋯O24	0.089(6)	0.200(10)	0.277 8(15)	146(14)
  Symmetry codes: A: x-1, y, z; B: x, y-1, z; C: x+1, y+1, z.

  2.2   Crystal structure of compound 2

  Compound 2 features a 2D neutral layer structure, comprising one independent Mg⁺ ion within its asymmetric unit (Fig. 2). Each Mg²⁺ ion exhibits a distorted octahedral {O₆} donor set, formed by coordination with two O atoms from the coordinated solvent molecules, and four carboxylate O atoms contributed by four L^2- ligands. Two adjacent Mg²⁺ ions are interconnected through two carboxylate groups and further chelated by an additional pair of carboxylate groups, resulting in the formation of a binuclear {Mg₂(COO)₄} SBU, with a corresponding Mg⋯Mg separation of approximately 0.443 4(2) nm. The ligand adopts a μ₃-κ_O¹∶κ_O¹∶κ_O² coordination mode, coordinating to three metal ions.

  Figure 2

  

  Figure 2.  Crystal structure of complex 2: (a) coordination environment of Mg²⁺; (b) coordination mode of the L^2- ligand; (c) 2D layer structure; (d) framework topology; (e) packing of the layers viewed along the b-axis; (f) π⋯π interaction chain inside the structure

  The intra-layer and inter-layer face-to-face π⋯π interactions are represented as green and blue dotted lines, respectively; All H atoms are omitted for clarity; C/S atoms from the DMSO molecules in some pictures are omitted for clarity; Symmetry codes: ^ⅰ-x, 2-y, 2-z; ^ⅱ 0.5+x, 1.5-y, z-0.5; ^ⅲ-x-0.5, 0.5+y, 2.5-z.

  下载: 全尺寸图片 幻灯片

  The {Mg₂(COO)₄} SBU can be treated as a 4-connected node, while the ligand functions as a 2-connected linker. Their combination yields a (4, 4) layer network. Notably, within each grid of the layer structure, pairs of adjacent naphthalimide groups are closely stacked together, facilitating strong offset face-to-face π-π interactions between naphthalene rings with a ring (center)-ring (center) separation of ca. 0.351 4(1) nm (Fig. 2f). Furthermore, robust offset face-to-face π-π interactions between neighboring naphthalimide groups across different layers enhance the stability of layer stacking, ultimately leading to the formation of the final 3D supramolecular architecture. The corresponding ring (center)-ring (center) is about 0.394 4(1) nm.

  2.3   Characterization of the compounds

  Bulk samples of the compounds were analyzed using PXRD. The results indicate that the experimental patterns closely align with the calculated patterns (Fig. 3a), suggesting that the products exhibit excellent crystallinity and phase purity.

  Figure 3

  

  Figure 3.  Characterization of compounds 1 and 2: (a) experimental (Exp.) and calculated (Cal.) PXRD patterns and (b) TG curves

  下载: 全尺寸图片 幻灯片

  The thermal stability of the two compounds was investigated using TGA. As illustrated in Fig. 3b, compound 1 exhibited stability up to 60 ℃, after which it rapidly lost 30.92% of its weight within a temperature range of 61-115 ℃. Subsequently, it experienced a gradual weight loss of 19.22% between 116 and 438 ℃. Overall, all solvent molecules are eliminated before reaching 438 ℃ (Obsd. 50.14%, Calcd. 49.96%). Beyond this temperature, the sample underwent rapid weight loss, indicating framework decomposition. Compound 2 completely lost all H₂O molecules before reaching 105 ℃ (Obsd. 2.29%, Calcd. 1.76%). Following this, all DMSO molecules were expelled between temperatures of approximately 106 and 370 ℃ (Obsd. 22.06%, Calcd. 22.99%). After surpassing the temperature of 371 ℃, the sample continued to lose weight, signifying skeleton decomposition.

  2.4   Luminescence properties of the compounds

  Solid-state emission spectra of compounds 1, 2, and H₂L were measured at room temperature. At 345 nm excitation, the emission peak of the H₂L ligand was located near 470 nm (Fig. 4), which can be attributed to the π→π* transition. Interestingly, under the same excitation, the emission peak of 1 with a 1D chain structure was redshifted to 480 nm concerning that of the ligand. In contrast, the emission peak of 2 with a 2D layered structure was blueshifted (ca. 446 nm). The luminescence color of the compounds under a 365 nm UV lamp was consistent with their spectra (Fig. 4c).

  Figure 4

  

  Figure 4.  Luminescence properties of the compounds: (a) normalized emission spectra of H₂L, 1, and 1 after being ground for 10 min (1-G); (b) normalized emission spectra of 2, 2 after being ground for 10 min (2-G); (c) photographs of the samples under a 365 nm UV lamp

  下载: 全尺寸图片 幻灯片

  Subsequently, compounds 1 and 2 were subjected to MCL experiments. Remarkably, the sample of 1 showed no significant luminescence color change after being ground for 20 min, indicating its excellent RMCL properties (Fig. 4a). The emission spectrum test showed that the emission peak of the sample (1-G) after being ground for 20 min was located at 475 nm, which was almost unchanged from the peak position of the initial sample. In contrast, the sample of 2 showed excellent MCL properties. After being ground for 3 min, the luminescence color of 2 gradually changed from purple to blue, and the luminescence intensity was significantly enhanced, indicating that it has obvious stimulus-response ability. After about 20 min of grinding, the luminescence intensity reached its maximum and did not change with time. The resulting sample (2-G) was also subjected to PL measurements (Fig. 4b). Compared with that of the initial sample, the emission peak of 2-G was significantly redshifted (ca. 477 nm). Interestingly, after soaking 2-G in DMSO, the initial luminescence of the sample can be recovered, as confirmed by luminescence photos (Fig. 4c).

  To further investigate the distinct luminescence responses of these compounds to mechanical stimuli, PXRD tests were conducted on the samples during the grinding process. The results indicate that as grinding time increased, the intensity of certain peaks in the PXRD pattern of compound 1 decreased, while others exhibited an increase (Fig. 5a). However, the positions of these peaks remained largely unchanged. Notably, 1 retained its crystallinity even after 20 min of grinding, with diffraction peak positions essentially mirroring those of the initial sample. These findings suggest that 1 possesses remarkable structural stability and is largely unaffected by external mechanical forces, which may account for its excellent RMCL properties. In contrast, under external grinding conditions, the crystallinity of compound 2 diminished rapidly, although its diffraction peak positions remained similar to those observed in the initial sample (Fig. 5b). After 20 min of grinding, compound 2 became completely amorphous and exhibited a blue-green emission characteristic of 2-G. Upon being soaked in DMSO, the initial structure can be restored. Consequently, this restoration also leads to a recovery of the original luminescence properties of the sample.

  Figure 5

  

  Figure 5.  (a) PXRD patterns of compound 1 being ground for different times; (b) PXRD patterns of compound 2 being ground for different times and then soaked in DMSO (2-G-R)

  下载: 全尺寸图片 幻灯片

  Many materials exhibiting MCL or RMCL have been reported to date^[1-7]; however, the factors that determine whether a compound possesses MCL or RMCL properties remain unclear. The characterization of the single crystal structures presented above indicates that the two compounds can be regarded as framework quasi-isomers, composed of identical metal ions and ligands. However, they exhibited diametrically opposed luminescence responses to grinding stimuli, thereby providing an excellent model for investigating the determining factors influencing the RMCL and MCL properties of MOFs. The weak interactions that predominantly govern the structures of compounds 1 and 2 are hydrogen bonds and π-π interactions, respectively. Consequently, it is proposed that the hydrogen bond plays a more significant role in stabilizing the crystallinity of 1, enabling it to effectively withstand external mechanical force stimuli. Notably, in 1, the high boiling point solvent DMF contributes to the formation of hydrogen bonds, further enhancing its ability to resist external mechanical perturbations. This assertion is corroborated by TGA, which reveals that all solvent content in 1 was lost at temperatures up to 438 ℃. In contrast, π-π interactions are more susceptible to disruption by external mechanical forces; this characteristic allows 2 to demonstrate remarkable MCL properties. As grinding time increased, a red shift in the position of the luminescent peak for 2 was observed. This phenomenon can be attributed to an intensification of π-π interactions within the system due to grinding and a consequent increase in conjugation degree, as also reported in the literature^{[6, 11]}. These findings suggest that strong hydrogen bonds may play a crucial role in governing RMCL properties for 1, while robust π-π interactions enhance MCL characteristics for 2.

  3.   Conclusions

  To summarize, two MOF quasi-isomers were synthesized, [Mg(L)(DMF)₂(H₂O)₂]₂·5DMF·2H₂O (1) which features a 1D structure and [Mg₂(L)₂(DMSO)₃(H₂O)] (2) characterized by a 2D (4, 4)-net structure. Notably, in response to external mechanical stimulation, compound 1 exhibited distinct RMCL properties, whereas compound 2 demonstrated reversible MCL characteristics. It is proposed that weak interactions play a crucial role in the differing luminescent responses; specifically, the hydrogen bond is advantageous for the RMCL behavior of the first compound, while π-π interaction contributes positively to the MCL properties observed in the second compound. This study investigates key factors influencing MCL and RMCL behaviors in materials and offers new opportunities for their development.

  
  Acknowledgements: This research is supported by the National Natural Science Foundation of China (Grant No.21871038).
• 1. [1]

     ZHOU Q, ZHANG X M, NING L J, SONG Y H, WANG Y L, FENG J K, GONG Q Y, HUANG Y J. Stimuli-chromic multi-component smart organic materials[J]. J. Mater. Chem. C, 2024, 12(47):  18991-19016. doi: 10.1039/D4TC04185B

  2. [2]

     YIN Y, CHEN Z, LI R H, YI F, LIANG X C, CHENG S Q, WANG K, SUN Y, LIU Y. Highly emissive multipurpose organoplatinum(Ⅱ) metallacycles with contrasting mechanoresponsive features[J]. Inorg. Chem., 2022, 61(6):  2883-2891. doi: 10.1021/acs.inorgchem.1c03563

  3. [3]

     NI J, WANG Y G, WANG H H, XU L, ZHAO Y Q, PAN Y Z, ZHANG J J. Thermo- and mechanical-grinding-triggered color and luminescence switches of the diimine-platinum(Ⅱ)) complex with 4-bromo-2, 2'-bipyridine[J]. Dalton Trans., 2014, 43(1):  352-360. doi: 10.1039/C3DT51936H

  4. [4]

     HUANG J X, ZHAO H, ZHANG J J, ZHANG B L, NI J, SONG B, LI Y Q, LIU S Q, DUAN C Y. Diemissive dye@CP composites with full-spectrum tunable mechanoluminescence[J]. J. Mater. Chem. C, 2021, 9(42):  15165-15174. doi: 10.1039/D1TC02841C

  5. [5]

     LI M Y, FANG W J, LIU S Q, NI J, ZHANG J J. Two new Zn(Ⅱ)/Cd(Ⅱ) one-dimensional coordination polymers based on naphthalimide dicarboxylic ligand[J]. Chin. J. Struct. Chem., 2019, 38(10):  1807-1813.

  6. [6]

     王会玉, 刘淑芹, 冯珂新, 张建军. 一个苯并咪唑衍生物的基于晶态-晶态转变的余辉刺激响应行为[J]. 无机化学学报, 2023,39,(8): 1571-1578. WANG H Y, LIU S Q, FENG K X, ZHANG J J. Afterglow stimulation response behaviors of a benzimidazole derivative based on crystalline-to-crystalline transition[J]. Chinese J. Inorg. Chem., 2023, 39(8):  1571-1578.

  7. [7]

     LI R F, CHEN X Y, ZHANG H, WANG Y R, LV Y, JIANG H P, GUO B W, FENG X. Co-based metal-organic framework nanosheets for robust hydrogen evolution in alkaline media[J]. Inorg. Chem., 2024, 63(4):  2282-2288. doi: 10.1021/acs.inorgchem.3c04291

  8. [8]

     WU W W, CAI J J, LIANG X Y, LI Z Z, ANDRA S, GAO K, LUN H J, LI Y M. Anisotropic single-crystal proton conduction in a sodium chain-based coordination polymer[J]. ACS Appl. Mater. Interfaces, 2024, 16(49):  68358-68367. doi: 10.1021/acsami.4c15534

  9. [9]

     SINGH D, BHATTACHARYYA P K, BARUAH J B. Structural studies on solvates of cyclic imide tethered carboxylic acids with pyridine and quinoline[J]. Cryst. Growth Des., 2010, 10(1):  348-356. doi: 10.1021/cg900938x

  10. [10]

      SHELDRICK G M. SHELXT-integrated space-group and crystal-structure determination[J]. Acta Crystallogr. Sect. A, 2015, A71:  3-8.

  11. [11]

      FENG K X, WANG H Y, ZHANG P P, ZHANG J J, ZHANG W Q, WANG T, LIU S Q, NI J. Two calcium coordination polymers with multi-stimuli-responsive properties[J]. Eur J. Inorg. Chem., 2023, 26(9):  e202200686. doi: 10.1002/ejic.202200686

• 

  Figure 1  Crystal structure of compound 1: (a) coordination environment of Mg²⁺ ions; (b) interaction between two neighboring chains; (c) packing of the 1D belts viewed along the c-axis

  π⋯π interaction is represented as the green dotted line; C/N atoms from the DMF molecules, and H atoms are omitted for clarity; Symmetry code: ⁱ x, y-1, z.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  Crystal structure of complex 2: (a) coordination environment of Mg²⁺; (b) coordination mode of the L^2- ligand; (c) 2D layer structure; (d) framework topology; (e) packing of the layers viewed along the b-axis; (f) π⋯π interaction chain inside the structure

  The intra-layer and inter-layer face-to-face π⋯π interactions are represented as green and blue dotted lines, respectively; All H atoms are omitted for clarity; C/S atoms from the DMSO molecules in some pictures are omitted for clarity; Symmetry codes: ^ⅰ-x, 2-y, 2-z; ^ⅱ 0.5+x, 1.5-y, z-0.5; ^ⅲ-x-0.5, 0.5+y, 2.5-z.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  Characterization of compounds 1 and 2: (a) experimental (Exp.) and calculated (Cal.) PXRD patterns and (b) TG curves

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Luminescence properties of the compounds: (a) normalized emission spectra of H₂L, 1, and 1 after being ground for 10 min (1-G); (b) normalized emission spectra of 2, 2 after being ground for 10 min (2-G); (c) photographs of the samples under a 365 nm UV lamp

  下载: 全尺寸图片 幻灯片
  

  Figure 5  (a) PXRD patterns of compound 1 being ground for different times; (b) PXRD patterns of compound 2 being ground for different times and then soaked in DMSO (2-G-R)

  下载: 全尺寸图片 幻灯片

  Table 1.  Crystal data collection and structure refinement parameters for compounds 1 and 2

  Parameter	1	2
  Empirical formula	C67H93Mg2N11O27	C46H38Mg2N2O16S3
  Formula weight	1 533.14	1 019.58
  Crystal system	Triclinic	Monoclinic
  Space group	P1	P21/n
  a/nm	0.869 0(2)	0.916 05(7)
  b/nm	1.132 8(2)	0.158 087(14)
  c/nm	2.019 6(2)	0.164 179(14)
  α/(°)	97.658(7)
  β/(°)	98.835(9)	96.505(5)
  γ/(°)	96.415(8)
  V/nm3	1.929 2(8)	2.362 3(3)
  Z	1	2
  Dc/(g·cm-3)	1.320	1.433
  μ/mm-1	0.117	0.257
  F(000)	812	1 056
  θ range/(°)	2.394-24.999	2.436-25.000
  Reflection collected, unique, observed	12 279, 10 020, 4 904	15 532, 4 145, 2 845
  Rint	0.119 5	0.056 3
  GOF on F2	0.946	1.171
  R1a[I > 2σ(I)] (all)	0.084 8 (0.192 2)	0.099 2 (0.131 8)
  wR2b[I > 2σ(I)] (all)	0.183 9 (0.224 5)	0.270 6 (0.287 8)
  Max/mean shift in final cycle	0.000/0.000	0.000/0.000
  a R=∑(||Fo|-|Fc||)/∑|Fo|; b wR=[∑w(Fo2-Fc2)2/∑w(Fo2)2]1/2, w=1/[σ2Fo2+(aP)2+bP], P=(Fo2+2Fc2)/3, a=0.092 4, b=0.000 0 for 1, a=0.126 3, b=4.777 2 for 2.

  下载: 导出CSV

  Table 2.  Hydrogen bond parameters for compound 1

  D—H⋯A	d(D—H)/nm	d(H⋯A)/nm	d(D⋯A)/nm	∠DHA/(°)
  O13—H13C⋯O2	0.089(5)	0.190(7)	0.266 0(12)	142(5)
  O13—H13B⋯O22A	0.084(5)	0.189(6)	0.272 4(14)	172(9)
  O14—H14B⋯O26	0.086(5)	0.191(6)	0.268 1(12)	149(12)
  O14—H14A⋯O3B	0.088(5)	0.195(8)	0.269 4(12)	142(5)
  O18—H18B⋯O8	0.084(6)	0.195(8)	0.268 8(12)	146(12)
  O18—H18C⋯O27	0.087(6)	0.178(7)	0.264 4(13)	172(14)
  O20—H20A⋯O9B	0.102(5)	0.179(7)	0.272 0(12)	150(4)
  O20—H20B⋯O25C	0.089(5)	0.197(7)	0.272 6(13)	142(10)
  O26—H26A⋯O21	0.087(6)	0.190(7)	0.275 3(15)	168(13)
  O26—H26B⋯O8	0.086(6)	0.203(12)	0.267 3(14)	131(14)
  O27—H27A⋯O3B	0.083(6)	0.194(7)	0.274 5(13)	164(13)
  O27—H27B⋯O24	0.089(6)	0.200(10)	0.277 8(15)	146(14)
  Symmetry codes: A: x-1, y, z; B: x, y-1, z; C: x+1, y+1, z.

  下载: 导出CSV
•