Metal- and Multicarboxylate-Dependent Structural Diversity in Metal–Organic Frameworks with Acylamide-Based Ligand
Abstract
Three new metal–organic frameworks, [Co2(L)2(ip)2·(H2O)4] (1), [Cu(L)(ip)·(H2O)2] (2), [Cd(µ-H2O)(L)(oip)·(H2O)3.5] (3) (ip = isophthalate, H2oip = 5-hydroxyl-isophthalate), built by acylamide-based ligand and multi-carboxylate ligand were synthesized and structurally characterized by X-ray crystallography. Complex 1 crystallizes in monoclinic space group P21, with a = 9.9171(3), b = 31.9531(10), c = 10.1780(3) Å, β = 118.8270(10)°. Complex 2 crystallizes in the monoclinic space group Cc, with a = 17.7490(3), b = 9.7363(2), c = 18.1202(3) Å, β = 115.0090(10)°. Complex 3 crystallizes in the monoclinic space group P21/c, with a = 9.7670(5), b = 30.3199(15), c = 10.3277(5) Å, β = 102.1680(10)°. All these compounds feature 2D 44 layers with two-fold interpenetration.
Graphical Abstract
Herein we describe the crystal structures of [Co2(L)2(ip)2(H2O)2]·(H2O)2 (1), [Cu(L)(ip)·(H2O)2] (2), [Cd(µ-H2O)(L)(oip)·(H2O)3.5] (3) (ip = isophthalate, H2oip = 5-hydroxyl-isophthalate). All these compounds feature 2D 44 layers with two-fold interpenetration.
Keywords
Metal–organic frameworks Multi-carboxylate ligand Crystal structure InterpenetrationIntroduction
The research of metal–organic frameworks (MOFs) remains a popular area of investigation, not only due to the impetus of elegant topology matrixes, but also their potential application in many fields such as gas storage, catalysis, optical materials, and magnetism [1, 2, 3, 4, 5, 6, 7].
To construct MOFs, the ligands of aromatic di- and tri-carboxylate such as isophthalate, terephthalate, or 1,3,5-benzenetricarboxylate are widely employed, e.g. in MOF-5, MIL-101, MIL-102, HKUST-1 [8, 9, 10]. Furthermore, another mixed ligand system with additional inclusion of neutral dipyridyl-type ligands has also proven very effective. Until now, several rigid dipyridyl-type ligands such as 4,4′-bipyridine, bis(4-pyridyl)ethane, 4,4′-azobis(4-pyridine), or flexible dipyridyl-type ligands such as 1,1′-(1,5-pentanediyl)bis(imidazole), 1,1′-(2,2′-oxybis(ethane-2,1-diyl)bis(1H-imidazole)), have been developed and extensively utilized to build MOFs [11, 12, 13]. In 2007 and 2009, Zheng and coworkers employed an acylamide-based dipyridyl-type ligand with the length of ca. 2.0 nm in the preparation of MOFs with mixed ligand systems [14, 15]. The resulting two MOFs display interpenetrating structures but considerable porosity. Further research indicates big progress in the field of acylamide-based MOFs involving three aspects: (i) synthesis, (ii) construction of multidimensional frameworks, and (iii) the thermal stability of the resulting frameworks.
Herein, we attempt the assembly of MOFs with elegant topology matrixes and utilized a flexible acylamide-based dipyridyl-type ligand L (Scheme 1, Refs. [14, 15]) that has not been used in coordination polymer chemistry to date. As a result, three new MOFs, [Co2(L)2(ip)2·(H2O)4] (1), [Cu(L)(ip)·(H2O)2] (2), [Cd(µ-H2O)(L)(oip)·(H2O)3.5] (3) (ip = isophthalate, H2oip = 5-hydroxyl-isophthalate), have been hydrothermally prepared and characterized by single crystal X-ray diffraction.
The mixed ligand system involved in this work
Experimental Section
Materials and Methods
Ligand L was synthesized according to literature procedures [14, 15]. All other starting materials were of analytical grade and obtained from commercial sources without further purification. Elemental analyses for C, H, and N were performed on a Perkin-Elmer 240 elemental analyzer.
Synthesis of [Co2(L)2(ip)2·(H2O)4] (1)
A mixture of Co(NO3)2·6H2O (0.0087 g, 0.03 mmol), H2ip (0.0050 g, 0.03 mmol), and L (0.0100 g, 0.03 mmol) in a ratio of 1:1:1 in distilled water (10 mL) was placed in a 25 mL Teflon-lined stainless steel container, heated to 160 °C for 3 days, and then cooled to room temperature. Subsequently, purple block-shaped crystals were obtained in 80% yield based on Co. Anal. Calcd for C28H24CoN4O8 (605.46): C, 55.54; H, 4.33; N, 9.25%; found: C, 55.56; H, 4.37; N, 9.31%.
Synthesis of [Cu(L)(ip)·(H2O)2] (2)
The procedure is similar to the synthesis of 1 except that Cu(NO3)2·5H2O (0.0075 g, 0.03 mmol) was used instead of Co(NO3)2·6H2O (0.0087 g, 0.03 mmol). Blue block-shaped crystals were obtained in 77% yield based on Cu. Anal. Calcd for C28H26CuN4O8 (610.07): C, 55.12; H, 4.30; N, 9.18%; found: C, 55.16; H, 4.37; N, 9.23%.
Synthesis of [Cd(µ-H2O)(L)(oip)·(H2O)3.5] (3)
A mixture of Cd(NO3)2 (0.0071 g, 0.03 mmol), H2oip (0.0055 g, 0.03 mmol), and L (0.0100 g, 0.03 mmol) in the ratio of 1:1:1 was added to 10 mL of deionized water. After the mixture was stirred for 30 min, it was placed in a 25 mL Teflon-lined reactor and heated at 160 °C in an oven for 3 days and then slowly cooled to room temperature. Colorless block-shaped crystals of 3 were obtained (yield 78% based on Cd). Anal. Calcd for C56H56Cd2N8O23 (1433.91): C, 46.91; H, 3.94; N, 7.81%; found: C, 46.96; H, 3.98; N, 7.88%.
Crystallographic Data Collection and Structure Determination
Crystals of compounds 1–3 were selected for data collection on a Bruker SMART APEX CCD diffractometer equipped with graphite-monochromatized MoKα radiation (λ = 0.71073 Å) at room temperature using an ω-scan technique. Intensity data of complexes 1–3 were corrected for absorption with semi-empirical methods using the SADABS program [16]. The structures were solved by direct method with SHELXS-97 [17] and refined by full-matrix least-squares on F2 using the SHELXL-97 program package [18]. All non-hydrogen atoms were anisotropically refined. The hydrogen atoms of organic ligands were included in the structure factor calculation at idealized positions using a riding model and refined isotropically. The hydrogen atoms of coordinated water molecules were located from difference Fourier maps, and then restrained at the fixed positions and refined isotropically. The crystal data and details of refinement are summarized in Table 1.
Crystallographic data for complexes 1–3
| 1 | 2 | 3 | |
|---|---|---|---|
| Formula | C28H24CoN4O8 | C28H26CuN4O8 | C56H56Cd2N8O23 |
| Mr | 605.46 | 610.07 | 1433.91 |
| Cryst. syst. | Monoclinic | Monoclinic | Monoclinic |
| Space group | P21 | Cc | P21/c |
| a (Å) | 9.9171(3) | 17.7490(3) | 9.7670(5) |
| b (Å) | 31.9531(10) | 9.7363(2) | 30.3199(15) |
| c (Å) | 10.1780(3) | 18.1202(3) | 10.3277(5) |
| α (°) | 90 | 90 | 90 |
| β (°) | 118.8270(10) | 115.0090(10) | 102.1680(10) |
| γ (°) | 90 | 90 | 90 |
| V/Å3 | 2825.55(15) | 2837.75(9) | 2989.7(3) |
| Z | 4 | 4 | 2 |
| Dc/g cm−3 | 1.423 | 1.428 | 1.593 |
| F(000) | 1252 | 1260 | 1456 |
| Reflns collected | 21,946 | 10,676 | 23,017 |
| Independent reflns | 8573 | 4863 | 5253 |
| Rint | 0.0290 | 0.0318 | 0.0359 |
| GOF on F2 | 1.037 | 1.029 | 1.075 |
| R1, wR2 (all data) | 0.0307, 0.0624 | 0.0453, 0.0908 | 0.0359, 0.0736 |
Results and Discussion
Syntheses
The change of metal sources or multi-carboxylate ligand usually results in the structural diversity [19, 20, 21] as we expected to see in our study. In our syntheses, above 170 °C, only black deposits were found in the Teflon-lined stainless steel autoclave. Variation of temperatures from 120 to 160 °C for the reaction and various reaction times under hydro(solvo)thermal conditions yielded however crystalline material.
Crystal Structure Description of Complex 1
Compound 1 crystallizes in the chiral P21 space group. The asymmetrical unit contains two crystallography-independent Co(II) ions, however their coordination surroundings are similar. Both Co1 and Co2 sites have CoO4N2 octahedral geometry, completed by three ip oxygen atoms, two nitrogen atoms, as well as one terminal coordinated water molecule (Fig. 1). The Co–O/N bond lengths range from 2.0414(17) Å to 2.1751(17) Å, comparable with those observed in other Co(II)-containing compounds [22]. As shown in Figs. 2 and 3, the Co(II) ions are linked by both L and ip spacers to build a 2D 44 net that allows two-fold interpenetration in a [2D + 2D] parallel pattern. This interpenetration is stabilized by N–H⋯O hydrogen bonds: N5–H5(L)⋯O5(ip) 3.16(12)Å/166.8°, N6–H6(L)⋯O5(ip) 2.97(11)Å/151.7°.
The coordination of Co(II) ion in 1
View of the two-fold interpenetration in the [2D + 2D] parallel pattern viewed down the b axis
View of the two-fold interpenetration in the [2D + 2D] parallel pattern viewed down the c axis
Crystal Structure Description of Complex 2
The basic composition of 2 is similar to 1, except for the metal. 2 crystallizes in the non-centrosymmetric space group Cc. The Cu(II) site has a five-coordinated square pyramidal geometry comprised of two ip oxygen atoms, two L nitrogen atoms, and one terminal water molecule (Fig. 4). The Cu–O/N bond lengths of 1.969(3) to 2.280(3) Å are in the normal range. Furthermore, similar structural features such as two-fold interpenetration in the [2D + 2D] parallel pattern and stabilization by hydrogen bonding as observed in 1 are also present in 2.
The coordination surrounding of Cu(II) ion in 2
Crystal Structure Description of Complex 3
Compound 3 crystallizes in the monoclinic space group P21/c. The asymmetrical unit contains one crystallographically independent Cd(II) ion that is six-coordinated by three oip oxygen atoms, two L nitrogen atoms, as well as one terminal water molecule. The Cd–O/N bond lengths range from 2.2533(19) to 2.533(2) Å (Fig. 5). As shown in Fig. 6, the Cd(II) ions are linked by L ligands to yield a meso-helical structure with the coexistence of left- and right-handed helical loops. Further, oip ligands connect these meso-helical chains together to form a corrugated 44 net (Figs. 7, 8) allowing for two-fold interpenetration in a [2D + 2D] parallel pattern (Figs. 9, 10).
The coordination surrounding of Cd(II) ion in 3
View of the meso-helical structure
View of the corrugated 44 net viewed down the b axis
View of the corrugated 44 net viewed down the c axis
View of the two-fold interpenetrating net
View of the two-fold interpenetrating net
Conclusion
In this work, we present the synthesis and structural studies of three new metal–organic coordination compounds with a double ligand system involving an acylamide-based ligand. Through the variation of metal sources and multi-carboxylate ligands, structural diversity was obtained. Additionally, the flexibility of the L ligand contributes to structural diversity.
Supplementary Materials
This data CCDC: 832139-832141 can be obtained free of charge at https://www.ccdc.cam.ac.uk/deposit or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 IEZ, UK; fax: + 44(0) 1223-336033; e-mail: deposit@ccdc.cam.ac.uk.
Notes
Acknowledgements
We gratefully acknowledge financial support by the National Natural Science Foundation of China (No. 21401112).
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