Three sra topological lanthanide-organic frameworks built from 2,2'-dimethoxy-4,4'-biphenyldicarboxylic acid.

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DOI: 10.1039/C5DT00602C

Table of Contents Three

sra

Topological

Lanthanide-Organic

Frameworks

Built

from

2,2'-Dimethoxy-4,4'-biphenyldicarboxylic Acid

The first neutral 3D sra-LOF built from an 1D inorganic rod-shaped chain [Ln(CO2)2(HCO2)]n (Ln = Eu, Gd, Dy) was synthesized.

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Published on 16 April 2015. Downloaded by East Carolina University on 20/04/2015 12:37:06.

Xin Wang, Jie Zhao, Yan Zhao, Heng Xu, Xuan Shen, Dun-Ru Zhu, Su Jing

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DOI: 10.1039/C5DT00602C

Three sra topological lanthanide-organic frameworks built from 2,2'-dimethoxy-4,4'-biphenyldicarboxylic acid


a

College of Chemistry and Chemical Engineering, State Key Laboratory of Materials-oriented Chemical Engineering, b College of Science, Nanjing Tech University, Nanjing 210009, P. R. China, c School of Environmental Science and Engineering, North China Electric Power University, Baoding, 071003, Hebei, P. R. China, d State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. China

ABSTRACT: Three 3D lanthanide-organic frameworks (LOFs), [LnL(HCO2)(DMF)]n (Ln = Eu

(1), Gd (2), Dy (3); H2L = 2,2'-dimethoxy-4,4'-biphenyldicarboxylic acid), have been prepared by the solvothermal reaction of Ln(NO3)3·6H2O and H2L in DMF–H2O mixed solvent. Crystallographic data show that LOFs 1–3 are isomorphous and crystallize in the orthorhombic space group Pna21. Each Ln(III) is eight-coordinated to four O atoms from four L2- ligands, one O atom from DMF molecule and three O atoms from HCO2-. The adjacent Ln(III) ions are linked by the carboxylate groups of the L2- ligands and HCO2- to form an 1D inorganic rod-shaped [Ln(CO2)2(HCO2)]n chain as a secondary building unit (SBU). The infinite 1D chains are interconnected by the biphenyl groups, giving rise to a 3D framework along the c axis. LOFs 1-3 are the first neutral Ln-carboxylate/HCO2- chain-based sra-nets. 1 exhibits characteristic luminescence of Eu3+ upon 343 nm excitation. The investigation of magnetic properties shows very weak ferromagnetic interactions (J = 0.0092(3) cm-1) between Gd(III) ions in 2 with a Gd–O–Gd bridging angle of 125.6(1)°, and θ = −1.9(2) K in 3 due to thermal depopulation of the Stark levels of Dy(III) ions and/or the possible antiferromagnetic interactions between Dy(III) ions in contrast to the single-ion behavior observed in 1. ———————————————————————————————————— *To whom correspondence should be addressed. Tel: 86 25 83587717. Fax: 86 25 83172261. E-mail: [email protected]

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Xin Wang,a Jie Zhao,a Yan Zhao,c Heng Xu,a Xuan Shen,a Dun-Ru Zhu*,a,d and Su Jing*,b

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Introduction Lanthanide(III) ions with high and variable coordination numbers and flexible coordination from the electronic transitions within their partially filled 4f shell of the ions.1 Over the past decade, much work has focused on the design and construction of lanthanide-organic frameworks (LOFs) due to their potential applications in luminescence, magnetism, gas storage, ion exchange, and so on.2-4 However, the rational design and control over high-dimensional LOFs is also a formidable task owing to their variable coordination numbers and flexible coordination environments. To date, some ligands such as Schiff-bases, amino acids, imidazole and pyridine carboxylic acids have been utilized to build LOFs with interesting topologies.5-8 Another class of the widely used ligands for the construction of LOFs are rigid multicarboxylic acids, owing to their rich coordination modes and the high affinity of lanthanide ions for the oxygen atom.9 Among them, aromatic multicarboxylic acids such as 1,4-benzenedicarboxylic acid (H2BDC),10 1,3,5-benzenetricarboxylic acid (H3BTC)11 and 4,4'-biphenyldicarboxylic acid (H2BPDC)12 have been extensively studied. However, the synthesis of multidimensional LOFs by using the substituted aromatic multicarboxylic acids is less developed.13,14c,g Our interest for preparing MOFs (or LOFs) is to use the symmetrically substituted BPDC ligands.14 It is revealed that these ligands can not only create more robust MOFs with high thermal stabilities due to the substituted groups’ coordination or space-filling effects, but can also endow the MOFs (or LOFs) with more rich topology structures. For example, the MOFs built from Cd2+ ion and 2,2'-dimethoxy-BPDC ligand (H2L, Scheme 1a)15 show an unprecedented two-fold 3D/3D hetero-interpenetrated framework,14d,f while the LOFs built from Ln3+ (Eu, Gd, Dy) ions and 3,3'-dimethoxy-BPDC ligand exhibit a novel 3D framework with an unusual infinite nanosized ribbon.14c It is also noteworthy that the LOFs constructed directly from H2L ligand have not been reported so far. On the basis of these considerations, we report here the preparation of three 3D LOFs with the H2L ligand, [LnL(HCO2)(DMF)]n (Ln = Eu (1), Gd (2), Dy (3)). Their single-crystal structures, spectral properties, and thermal stabilities are systematically investigated. In addition, the luminescence of 1, the magnetic properties of 1-3 are also reported, together with the synthesis of H2L ligand.

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environments are of great interest because of their unique physicochemical properties arising

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Experimental section Materials and methods. All chemicals purchased were of analytical grade and used as received unless noted otherwise. Ln(NO3)3·6H2O (Ln = Eu, Gd, Dy), N,N'-dimethylformamide


point was determined using an X4 digital microscopic melting point apparatus and is uncorrected. Elemental analyses (C, H, N) were carried out with a Thermo Finnigan Flash 1112A elemental analyzer. IR spectra were recorded in the range 4000-400 cm-1 using KBr pellets on a Bruker Vector 22 FT-IR spectrophotometer. 1H NMR spectra in solution were recorded on a Bruker AM 500 Hz spectrometer. Chemical shifts are given in ppm. Electrospray ionization mass spectra (ESI−MS) were recorded with a Thermo Finnigan Fleet mass spectrometer. Thermogravimetric analyses (TGA) were performed on a NETZSCH STA 449C thermal analyzer under nitrogen atmosphere at a heating rate of 10 °C min-1. Powder X-ray diffraction (XRD) data were collected on a Bruker D8 Advance diffractometer with Cu Kα radiation (λ = 1.5406 Å). Fluorescence spectroscopy data for 1 were recorded on a Perkin-Elmer LS-55 spectrophotometer. Temperature-dependent magnetic measurements for 1-3 were carried out on a Quantum Design MPMS-7 SQUID magnetometer. Diamagnetic correction was made with Pascal’s constants.1c Synthesis of 2,2′-dimethoxy-BPDC (H2L). H2L ligand was obtained via a modified method provided by our group (Scheme S1 in ESI).15a Compared with the method reported by Arnold and Chen in a U.S. patent,15b our modified method can give a higher yield for the H2L ligand. A solution of the dimethyl 2,2'-dimethoxy-4,4'-biphenyldicarboxylate IV (5.02 g, 15.2 mmol) in 50 mL methanol was refluxed with potassium hydroxide (6.73 g, 120 mmol) under stirring for 1 h. Then 30 mL distilled water was added and the resulting light yellow solution was washed with diethyl ether (3 × 30 mL). The aqueous layers was acidified using 6 N HCl to pH = 2. A white precipitate was filtered, washed with water and dried in vacuo to give the target ligand H2L (4.37 g, 95.1%). m.p. 269-270 C. 1H NMR (d6-DMSO, 500 MHz): δ 3.78(s, 3H, CH3), 7.28-7.30(d, 1H, Ph-H6), 7.58(s, 1H, Ph-H3), 7.60-7.61(d, 1H Ph-H6); 13.02 (s, 1H, CO2H). IR (KBr, cm-1): ~3415(br, s), 2946(s), 1685(s), 1615(m), 1569(m), 1457(m), 1417(m), 1289(s), 1038(w). ESI−MS: m/z 300.85 (M−), 257.17. Anal. calcd for C16H14O6 (%): C 63.57, H 4.67. Found: C 63.45, H 4.48. Synthesis of [EuL(HCO2)(DMF)]n (1). The mixture of Eu(NO3)3·6H2O (0.0446 g, 0.1 mmol), H2L (0.0302 g, 0.1 mmol), DMF (2 mL), and H2O (2 mL) was heated in a 25 mL

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(DMF) were obtained from Sinopharm Chemical Reagent Co., Ltd. Shanghai, China. Melting

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capacity stainless-steel reactor lined with Teflon (Jinan Henghua Sci. & Tech. Co., Ltd. Shandong, China) at 120 °C for 2 days and then cooled to room temperature. Colorless prism crystals of 1 were obtained. Yield, 77.3% (44.1 mg) based on Eu(III). FT-IR (KBr, cm-1): 3429(b,


Anal. calcd for C20H20NEuO9 (%): C, 42.12; H, 3.53; N, 2.46. Found: C, 42.26; H, 3.38; N, 2.22. Synthesis of [GdL(HCO2)(DMF)]n (2). The procedure was the same as that for 1 except that Eu(NO3)3·6H2O was replaced by Gd(NO3)3·6H2O (0.0451 g, 0.1 mmol). Colorless prism crystals of 2 were obtained. Yield, 82.3% (47.4 mg) based on Gd(III). IR (cm-1): 3434(b, m), 3073(w), 2933(w), 1677(s), 1627(s), 1581(vs), 1540(s), 1411(vs), 1259(s), 1030(m), 786(s). Anal. calcd for C20H20NGdO9 (%): C, 41.73; H, 3.50; N, 2.43. Found: C, 41.59; H, 3.33; N, 2.27. Synthesis of [DyL(HCO2)(DMF)]n (3). The procedure was the same as that for 1 except that Eu(NO3)3·6H2O was replaced by Dy(NO3)3·6H2O (0.0457 g, 0.1 mmol). Colorless prism crystals of 3 were obtained in 85.7% (49.8 mg) yield based on Dy(III). IR (cm-1): 3410(b, m), 3073(w), 2932(w), 1679(s), 1629(s), 1582(vs), 1543(s), 1413(vs), 1259(s), 1030(m), 787(s). Anal. calcd for C20H20NDyO9 (%): C, 41.35; H, 3.47; N, 2.41. Found: C, 41.20; H, 3.25; N, 2.19. X-ray crystallography. Diffraction data for 1-3 were collected on a Bruker Smart APEX II CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature. Empirical absorption corrections were applied by using the SADABS program. The structures were solved by direct methods and refined by the full-matrix least-squares based on F2 using SHELXTL-97 program.16 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms, were placed on calculated positions (C-H 0.96 Å) and assigned isotropic thermal parameters riding on their parent atoms. The crystal data and structure refinement of 1–3 are summarized in Table 1. Selected bond lengths and bond angles of 1–3 are listed in Table S1 and Table S2, respectively in ESI.

Results and discussion Syntheses of LOFs 1-3. The solvothermal reactions of Ln(NO3)3·6H2O (Ln = Eu, Gd, Dy) and H2L with a metal-ligand ratio 1:1 in DMF-H2O at 120 °C gave LOFs 1-3, respectively. The yields for LOFs 1–3 are 77.3, 82.3, and 85.7%, respectively. LOFs 1-3 have been characterized by IR, elemental analyses, TGA, powder and single crystal XRD analyses. In LOF 1–3 each complex contains one Ln(III) ion, one L2- ligand, one HCO2- and one DMF molecule. The HCO2–

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m), 3072(m), 2933(w), 1675(s), 1627(s), 1581(vs), 1539(s), 1409(vs), 1259(s), 1030(m), 786(s).

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anions were generated from the hydrolysis of DMF during the solvothermal synthesis.12b,14c,17 Crystals of 1–3 are all air-stable and insoluble in common solvents, such as water, (CH3)2CO, CH3OH, C2H5OH, CH3CN, and DMF. Single-crystal X-ray diffraction analyses reveal that LOFs


Crystal structures of LOFs 1-3. The single-crystal X-ray structure analyses reveal that 1–3 are isomorphous and crystallize in the orthorhombic space group Pna21. Because 1–3 are isostructural LOFs, herein, only the structure of 2 is discussed in detail. There are one Gd(III) ion, one L2- ligand, one HCO2- ion and one DMF molecule in the asymmetric unit (see Fig. S2 in ESI). The Gd(III) center is coordinated by eight oxygen atoms from four carboxylate oxygen atoms (O1, O2i, O3iii and O4ii) of four L2- ligands, three oxygen atoms (O8, O8i and O9) of two HCO2ions and one DMF molecule (O7) (Fig. 1a). The bond distances of Gd-O (2.309(3)~2.568(3) Å) are comparable to the related Gd(III) LOFs.14c,18 The GdO8 unit displaying a dodecahedron geometry (Fig. 1b) is linked together by carboxylate groups and HCO2- to produce an 1D inorganic rod-shaped Gd(III) chain (SBU)12b along the c axis with a Gd···Gd distance of 4.445(3) Å and a Gd1-O8-Gd1iv angle of 125.6(1)° (Fig. 1c). These 1D chains are interconnected through the biphenyl groups of L2- to generate a 3D network which is further stabilized by weak C-H···O hydrogen bonding interactions (Fig. 3 and Table S3). Notably, 1D rhombus channels with the window sizes of 28.017 × 10.466 Å2 exist in 2 along the c axis (Fig. 2b). The channels are occupied by the coordinated DMF and the methoxy groups extruding into the channels, and the actual pores are too small to entrap any solvent molecules. If we connect all carboxylate C atoms in the same way as shown in Fig. 2a, the 1D chain consisting of Gd-O-C rods can be described as a ladder, and the biphenyl rings of L2- ligands acting as lines connect the ladders to give a typical sra net topology as shown in Fig. 2b. Although many sra-net MOFs (such as MIL-47, MOF-69A, MOF-70 and MOF-78)19a built on M-O-C rods (M = transition metal) have been reported,14a,f,19 the sra-net built on Ln-O-C rods (Ln = rare earth metal) is still very rare. To the best of our knowledge, 1-3 is the first neutral Ln-carboxylate/HCO2- chain-based 3D sra LOFs.14g,20 Coordination mode of the ligand. Organic polycarboxylates have been widely employed to prepare LOFs, partly due to their diverse coordination modes. In LOFs 1-3, all carboxyl groups of the ligand H2L are deprotonated and adopt only one type of coordination mode: a syn–syn bis(bridging bidentate) mode (Scheme 1b). The dihedral angles of the biphenyl rings in 1-3 are very similar (62.7°, 62.5°, 62.8°, respectively).

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1–3 are isomorphous and exhibit same structural topology (Table 1).

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IR spectra. IR spectra of LOFs 1-3 (Fig. S4-S6 in ESI) displayed the characteristic asymmetric and symmetric stretching vibrations of carboxylate groups at 1581, 1581, 1582 cm-1 and 1409, 1411, 1413 cm-1, respectively. In addition, the C=O stretching vibration of DMF in


absorption bands around 1710 cm-1 for 1-3 confirms complete deprotonation of the carboxyl groups of the H2L ligands during the reactions. These features are in accordance with the results of the X-ray diffraction analyses. PXRD and TG analyses. The simulated and experimental PXRD patterns of LOFs 1-3 are shown in Fig. S7-S9 in ESI. Their peak positions are in good agreement with each other, indicating the phase purity of the bulk products. The TGA study is performed under a N2 atmosphere, LOFs 1-3 show similar thermal decomposition behaviors (Fig. S10-S12 in ESI). The first weight loss of 13.4% for 1 from 40 to 303 °C, 13.3% for 2 from 40 to 300 °C and 13.4% for 3 from 40 to 302 °C is attributed to the loss of one coordinated DMF molecule (calcd. 12.8% for 1, 12.7% for 2 and 12.6% for 3). The frameworks of 1-3 began to collapse above 330 °C with the final residue of Ln2O3 (the observed loss of 30% at 588 °C and calcd. 30.8% for 1, the observed loss of 32.3% at 600 °C and calcd. 31.4% for 2 and the observed loss of 32.7% at 590 °C and calcd. 32.1% for 3). Luminescent properties. The solid-state excitation-emission spectra of the free H2L ligand and 1 were measured at room temperature (Fig. 4). The free H2L ligand shows an emission band at 407 nm (λex = 358 nm), which is attributed to the π*→n transitions.12b,14a 1 exhibits the typical emission bands of Eu(III) ions upon excitation at 343 nm, whereas the emission band from the free ligand is not observed, indicating there is an energy transfer from the ligand to the Eu(III) centre during photoluminescence.2,12b The emission bands in 1 arise from the 5D0/7FJ (J = 0–4) transitions of the Eu(III) ions.14c The most intense emission at 614 nm for 1 is attributed to the electric dipole induced

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D0/7F2 transition, which is hypersensitive to the coordination

environment of the Eu(III) ion.14c The medium-strong emission at 592 nm corresponds to the magnetic dipole induced 5D0/7F1 transition, which is fairly insensitive to the environment of the Eu(III) ion. The intensity ratio of (5D0/7F2)/(5D0/7F1) is ca. 3.8 for 1, indicating that the Eu(III) ion is not located at the inversion centre and the symmetry of the Eu(III) ion site is low, which are in agreement with the single-crystal structure of 1. Because of its good thermal stability, 1 could find application as the potential red-light-emitting materials.

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LOFs 1-3 can be observed at 1675, 1677, 1679 cm-1, respectively. The absence of any strong

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Magnetic properties. Temperature dependence of magnetic susceptibilities for 1-3 were measured on the polycrystalline samples in the range of 1.8-300 K under 100 Oe of external field (Fig. 5-7 and Fig. S13 and 14 in ESI).


lower than the theoretical high-temperature limit ((χMT)HT = 4.50 cm3 K mol-1). The χMT value decreases continuously to the value close to zero (0.0172 cm3 K mol-1) at 2 K, which is in agreement with the nonmagnetic 7F0 ground state the Eu(III) ion. So the magnetic behavior of 1 is mainly caused by single-ion properties, which is also similar to the results reported in literatures previously.12b,13f As shown in Fig. 6b, χMT of 2 is almost a constant from 8.38 cm3 K mol-1 at 300 K to 7.99 cm3 K mol-1 at 12 K, which is slightly larger than the spin-only value of 7.875 cm3 K mol-1 based on one Gd(III) ion. Upon further cooling, χMT vs. T curve exhibits a slightly increase from 8.08 cm3 K mol-1 at 10 K to 8.95 cm3 K mol-1 at 2 K. In accordance with the Curie−Weiss law, χM = C/(T − θ), the data in the range of 1.8−300 K show a good linear relationship between χM-1 and T with a Curie value of C = 7.77(3) cm3 mol−1 K and Weiss constant of θ = 0.26(1) K (Fig. 6a). The small θ value indicates the presence of very weak ferromagnetic coupling between Gd(III) ions. According to the structure of 2, the Gd(III) ions are bridged by carboxylate groups to form an 1D chain, and then the L2- ligands connect the chains in a long distance leading to a 3D sra network. So, other magnetic interactions are negligible except the coupling between Gd(III) ions within the chain in 2, which can be estimated by a uniform chain. By use of the well-known expression (equation 1) proposed by Fisher for 1D uniform chains of classical spins:14b,21

 chain 

Ng 2  2 S ( S  1) 1  u  JS ( S  1)   kT   and u  coth   3kT 1 u  kT   JS ( S  1) 

(1)

J is based on the spin Hamiltonian H = –J∑SiSi+1 with S = 7/2, N, k, T and β have the common meanings. The best fitting results from 1.8-300 K gave: g = 1.984(4), J = 0.0092(3) cm-1 with R = Σ[(χMT)calc – (χMT)obs]2/Σ(χMT)obs2 = 9 × 10−5. The small J value indicates the very weak ferromagnetic coupling between Gd(III) ions in 2. It is well known that the interaction between Gd(III) ions in the Gd(μ2-O)Gd complexes is either antiferromagnetic or ferromagnetic.22a An empirical formula proposed by Wu reveals that the coupling (J) interaction of Gd···Gd depends on the mean Gd–O–Gd bridging angle (φ) for the Gd(μ2-O)Gd complexes.22b It suggested that φ > 110.9° is a prerequisite for a Gd(μ2-O)Gd complex being ferromagnetic. LOF 2 with a Gd–O–Gd

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As shown in Fig. 5, the observed χMT value of 1 at 300 K is 1.92 cm3 K mol-1, obviously

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bridging angle of 125.6(1)° (Fig. 1c) shows a weak ferromagnetic behavior. This feature is also in agreement with those Gd(μ2-O)Gd complexes with similar Gd–O–Gd bridging angles (φ = 115.48°, J = 0.06 cm-1; φ = 112.44°, J = 0.006 cm-1; φ = 114.07°, J = 0.046 cm-1; and φ = 112.62°,


As shown in Fig. 7b, the χMT value of 3 is 14.20 cm3 K mol−1 at 300 K, which is consistent with the value of 14.17 cm3 K mol−1 expected for one independent Dy(III) ion including the significant contribution of the 4f orbital (4f9, J = 15/2, S = 5/2, L = 5, g = 4/3, 6H15/2). As the temperature decreases, χMT gradually decreases reaching 13.52 cm3 K mol−1 at 60 K and then abruptly decreases to a minimum value of 11.84 cm3 K mol−1 at 5 K, which is mainly ascribed to the progressive depopulation of excited Stark sublevels.24 Then the χMT value increases sharply to a maximum of 14.0 cm3 K cm−1 at 1.8 K, which probably suggests the presence of ferromagnetic interactions between the metal centers, as observed in other Dy(III) compounds.25 Fitting the data in the range of 1.8−300 K with the Curie−Weiss law [χM = C/(T − θ)] gives the result of C = 14.29(2) cm3 mol−1 K and θ = −1.9(2) K (Fig. 7a). Variable-field magnetization at 1.8 K (Fig. S13 in ESI) shows the quick increase in low fields and slow increase in high fields, and reaches 6.08 NμB in 7 T but cannot be saturated (M = gJ = 15/2 × 4/3 = 10 NμB), which may result from large magnetic anisotropy and/or the lack of a well-defined ground state, as also confirmed by nonsuperposition on M/Nβ versus HT−1 data (Inset in Fig. 7b). The large amount of magnetic anisotropy for the Dy(III) ion render the fitting of the susceptibility curve difficult, especially for such a 3D sra system. Therefore, there is no available expression to determine the nature and the strength of the interactions between the present Dy(III) centres. To examine the spin dynamics, the temperature dependencies of the alternating-current (ac) magnetic susceptibility for 3 were collected at zero direct-current (dc) field with an ac field of 5 Oe and an oscillating frequency of 1000 Hz, given in Fig. S14 in ESI as plots of χM′ and χM′′ versus T. However, no imaginary component of the ac susceptibility χM′′ was observed, which clearly exclude an SMM behavior for 3 above 1.8 K.

Conclusions In summary, three novel LOFs with 2,2'-dimethoxy-4,4'-biphenyldicarboxylic acid (H2L), [LnL(HCO2)(DMF)]n (Ln = Eu (1), Gd (2), Dy (3)), have been successfully prepared in solvothermal conditions. The LOFs 1-3 contain an infinite 1D rod-shaped [Ln(CO2)2(HCO2)]n

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J = 0.0201 cm-1, respectively).23

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chain, and these chains are interconnected by the biphenyl groups give a typical sra net topology. The solid-state luminescent spectrum of 1 exhibits strong red luminescence upon 343 nm excitation. 1 displays single-ion behavior of Eu(III) and 2 shows a very weak ferromagnetic


Acknowledgement Financial supports from the National Natural Science Foundation of China (Nos. 21171092, 21171093, 21476115) are gratefully acknowledged. Electronic Supplementary Information (ESI) Available: CCDC Nos. 976991 (1), 976992 (2), 976993 (3). Synthetic route of the H2L ligand, selected bond lengths and bond angles, molecule structures, IR, the simulated and experimental P-XRD patterns, TGA curves, and magnetic properties of 1-3. For ESI and crystallographic data in CIF see DOI: 10.1039/b000000x/

References 1 (a) S. Roy, A. Chakraborty and T. K. Maji, Coord. Chem. Rev., 2014, 273, 139; (b) J. C. G. Bünzli and C. Piguet, Chem. Soc. Rev., 2005, 34, 1048; (c) O. Kahn, Molecular Magnetism; VCH, Weinheim, Germany, 1993; (d) S. Fordham, X. Wang, M. Bosch and H.-C. Zhou, Struct. Bond., 2015, 163, 1; (e) L. Chen, F. Jiang, K. Zhou, M. Wu and M. Hong, Struct. Bond., 2015, 163, 145. 2 (a) Z. H. Zhang, Y. Song, T. Okamura, Y. Hasegawa, W. Y. Sun and N. Ueyama, Inorg. Chem., 2006, 45, 2896; (b) J. Xia, B. Zhao, H. S. Wang, W. Shi, Y. Ma, H. B. Song, P. Cheng, D. Z. Liao and S. P. Yan, Inorg. Chem., 2007, 46, 3450. 3 (a) Q. Zhu, T. Sheng, R. Fu, S. Hu, J. Chen, S. Xiang, C. Shen and X. Wu, Cryst. Growth Des., 2009, 9, 5128; (b) M. D. Allendorf, C. A. Bauer, R. K. Bhakta and R. J. T. Houk, Chem. Soc. Rev., 2009, 38, 1330. 4 (a) J. Xu, W. Su and M. Hong, Cryst. Growth Des., 2011, 11, 337; (b) X. Feng, B. Liu, L. Y. Wang, J. S. Zhao, J. G. Wang, N. S. Weng and X. G. Shi, Dalton Trans., 2010, 39, 8038; (c) B. Zhao, X. Y. Chen, Z. Chen, W. Shi, P. Cheng, S. P. Yan and D. Z. Liao, Chem. Commun., 2009, 3113; (d) J. Rocha, L. D. Carlos, F. A. A. Paz and D. Ananias, Chem. Soc. Rev., 2011, 40, 926; (e) D. Liu, K. Lu, C. Poon and W. Lin, Inorg. Chem., 2014, 53, 1916. 5 Y. Qiu, H. Liu, Y. Ling, H. Deng, R. Zeng, G. Zhou and M. Zeller, Inorg. Chem. Commun., 2007, 10, 1399.

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coupling between Gd(III) ions, while 3 does not exhibit any single-molecule magnet behavior.

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L. Hou, L. Wei, X. J. Jing, B. Liu, Y. Y. Wang and Q. Z. Shi, Cryst. Growth Des., 2013, 13,

Dalton Transactions



Scheme 1 (a) 2,2'-Dimethoxy-4,4'-biphenyldicarboxylic acid (H2L) and (b) the coordination mode of L2- anion in LOFs 1-3.

Table 1 Crystal data and structure refinements for LOFs 1-3 LOFs Empirical formula Formula weight T (K) Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z F (000)  (g cm-3)  (mm-1) Crystal size (mm3) Reflections collected Independent reflections Data/restraints/parameters GOF on F2 R1/wR2 [I > 2σ(I)] R1/wR2 (all data) Largest diff. peak & hole (eÅ-3)

1 C20H20EuNO9 570.33 296(2) Orthorhombic Pna21 28.044(2) 9.6262(7) 8.2546(6) 2228.4(3) 4 1128 1.700 2.864 0.24×0.14×0.08 15199 3691 [Rint = 0.0409] 3691/26/281 1.037 0.0255/0.0496 0.0328/0.0519 0.345, -0.332

13

2 C20H20GdNO9 575.62 296(2) Orthorhombic Pna21 28.017(3) 9.6175(9) 8.2586(7) 2225.3(3) 4 1132 1.718 3.030 0.20×0.10×0.08 15156 3770 [Rint = 0.0285] 3770/44/281 1.045 0.0207/0.0418 0.0244/0.0431 0.482, -0.549

3 C20H20DyNO9 580.87 296(2) Orthorhombic Pna21 27.951(4) 9.6124(13) 8.1937(11) 2201.4(5) 4 1140 1.753 3.444 0.22×0.12×0.08 15014 3746 [Rint = 0.0420] 3746/37/281 1.006 0.0251/0.0494 0.0339/0.0521 0.451, -0.577


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Captions for the illustrations:


with the GdO8 dodecahedron. (c) View of 1D inorganic rod-shaped chain [Gd(CO2)2(HCO2)]n along the c axis. All hydrogen atoms are omitted for clarity.

Fig. 2 (a) SBUs in LOF 2 shown as polyhedra, in which the carboxylate carbon atoms can be connected to form a zigzag ladder. (b) View of the sra net with inorganic SBUs linked together via biphenyl rings of L2- ligand. All hydrogen atoms and DMF are omitted for clarity.

Fig. 3 The network of 2 stabilized by weak C-H···O hydrogen bonds (blue dotted lines).

Fig. 4 The photoluminescence emission spectra of the free H2L ligand (λex = 358 nm) and LOF 1 (λex = 343 nm) at room temperature.

Fig. 5 The molar magnetic susceptibilities of 1 in the plots of χM-1 and χMT vs. T.

Fig. 6 Temperature dependence of the molar magnetic susceptibilities of 2. (a) The plots of χM and χM-1 vs. T. Solid blue lines were derived from the fitting by the Curie-Weiss law. (b) The plots of χM and χMT vs. T. Solid red line represents the best fitting curve with the model as described in the text.

Fig. 7 Temperature dependence of the molar magnetic susceptibilities of 3. (a) The plots of χM and χM-1 vs. T. Solid red lines were derived from the fitting by the Curie-Weiss law. (b) The plot of χMT vs. T. Inset: Reduced magnetization data for 3 at low temperatures.

14


Fig. 1 (a) Ball-and-stick structure view of LOF 2. (b) View of the environment of Gd(III) ion

Dalton Transactions


Fig. 1 (a) Ball-and-stick structure view of LOF 2. (b) View of the environment of Gd(III) ion with the GdO8 dodecahedron. (c) View of 1D inorganic rod-shaped chain [Gd(CO2)2(HCO2)]n along the c axis. All hydrogen atoms are omitted for clarity.

Fig. 2 (a) SBUs in LOF 2 shown as polyhedra, in which the carboxylate carbon atoms can be connected to form a zigzag ladder. (b) View of the sra net with inorganic SBUs linked together via biphenyl rings of L2- ligand. All hydrogen atoms and DMF are omitted for clarity.

15



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Page 17 of 18


800 5

407 nm 700

2.0

H2L

7

D 0 F2 614 nm

LOF 1

600

Intensity

1.5

1.0

500 400 300

5

7

D0

5

F1 5

0.5

100

5

D0

7

D0

7

F4

700 nm

592 nm

200

D0

7

F3

652 nm

F0

0

0.0

400

450

(nm)

500

500

550

600

 (nm)

700

800

Fig. 4 The photoluminescence emission spectra of the free H2L ligand (λex = 358 nm) and LOF 1 (λex = 343 nm) at room temperature.

165 2.0

150

-3

M / cm mol

MT / cm K mol

1.5

135

1.0

-1

3

0.0 105 0

50

100

150

T/K

16

200

250

300

-1

0.5

120


Fig. 3 The network of 2 stabilized by weak C-H···O hydrogen bonds (blue dotted lines).

Intensity


DOI: 10.1039/C5DT00602C

Dalton Transactions


DOI: 10.1039/C5DT00602C

Fig. 5 The molar magnetic susceptibilities of 1 in the plots of χM-1 and χMT vs. T. 40

5

4

4 -1

M / cm mol

3

3

-3

10

7 2 6

-1

1

3

M / cm mol

20

2

8 3

MT / cm K mol

-1

3

M / cm mol

-1

30

1 5 0

0 0

50

100

150

200

250

0 4

300

0

50

100

T/K

150

200

250

300

T/K

Fig. 6 Temperature dependence of the molar magnetic susceptibilities of 2. (a) The plots of χM and χM-1 vs. T. Solid blue lines were derived from the fitting by the Curie-Weiss law. (b) The plots of χM and χMT vs. T. Solid red line represents the best fitting curve with the model as described in the text.

25

14.5

20

14.0

8

3 2

5

6.0

13.5 5.5

M / NB

3

10

-3

4

MT / cm K mol

-1

15

5

3

-1

6

-1

M / cm mol

(b )

(a)

7

M / cm mol


9

(b)

(a)

13.0

7T 6T 5T 4T 3T 2T 1T

5.0

4.5

12.5

4.0

1

12.0 3.5 0.0

0

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

H / T (T/K)

0

50

100

150

200

250

11.5

300

0

50

100

T/K

150

200

250

300

T/K

Fig. 7 Temperature dependence of the molar magnetic susceptibilities of 3. (a) The plots of χM and χM-1 vs. T. Solid red lines were derived from the fitting by the Curie-Weiss law. (b) The plot of χMT vs. T. Inset: Reduced magnetization data for 3 at low temperatures.

17


5

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