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Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties
Journal of Molecular Structure xxx (xxxx) xxx
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Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties Jia-Qiang Du a, Jun-Liang Dong a, Fei Xie a, Ru-Xia Yang a, Hai-Ming Lan a, Duo-Zhi Wang a, b, * a b
School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi, 830046, PR China Key Laboratory of Energy Materials Chemistry, Ministry of Education, Xinjiang University, Urumqi, 830046, Xinjiang, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 July 2019 Received in revised form 31 October 2019 Accepted 1 November 2019 Available online xxx
Six new complexes {[Gd(L1)2(H2O)3]$Cl}n (1), [Eu(HL2)2(H2O)6]$(H2O)4$3Cl (2), [Ln(HL2)2(H2O)6]$3Cl [Ln ¼ Ho (3) and Sm (4)], {[Ln(HL3)2(H2O)2]·2Cl}n [Ln ¼ Eu (5) and Yb (6)] (H2L1 ¼ 2-(hydroxymethyl)1H-benzo[d]imidazole-5-carboxylic acid, H2L2 ¼ 2-(4-hydroxyphenyl)-1H-benzo[d]imidazole-5carboxylic acid, H3L3 ¼ 2-(2-carboxyethyl)-1H-benzo[d]imidazole-5-carboxylic acid) have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). Complexes 1, 5 and 6 are an infinite one-dimensional (1D) chain by hydrogen bonding interactions to give a 3D supermolecular structure. Complexes 2e4 are mononuclear structure, which further formed 3D supermoleculear structure through hydrogen-bonding interactions. Furthermore, luminescent properties of these lanthanide complexes have been assessed in the solid state at ambient temperature. In addition, magnetic measurements reveal that complexes 3e6 have a weak antiferromagnetic interaction, while complex 1 has a ferromagnetic interaction. © 2019 Published by Elsevier B.V.
Keywords: Benzimidazole carboxylic acid Supermoleculear structure Hydrogen-bonding interactions Luminescence Magnetic properties
1. Introduction Nowadays, the design and synthesis of metal-organic coordination polymers by metal ions and organic aromatic carboxylic acid ligands have been studied widely [1]. In particular, lanthanide coordination polymers (Ln-CPs) have attracted increasing attention, because of their superior functional properties and actual or potential applications in luminescence [2], molecular magnetism [3], gas storage/separation [4], proton conductivity [5] and catalysis and so forth [6]. As luminescent materials, compared to transition metal CPs, Ln-CPs have promising luminescent properties such as high luminescent quantum yield [7], narrow and intense band emission [8], large Stokes shift [9], and long luminescent lifetimes [10], which originated from f-f transitions through an “antenna effect” [11]. In the meantime, lanthanide coordination polymers containing N-heterocyclic ligands displayed excellent luminescence by the antenna effect, in general, in which the N-heterocyclic ligand
* Corresponding author. School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi, 830046, PR China. E-mail address: [email protected] (D.-Z. Wang).
function was as a sensitizer [12]. Therefore, lanthanide ion functionalized CPs could create dual luminescent centers (organic linkers, Ln3þ). White light emission materials have been widely used in displays and lightings [13], which profited from their long persistence, energy-efficient and environmental friendly advantages [14]. Apart from the excellent luminescent properties, the magnetic properties of Ln-CPs were unusual because of the diverse local magnetic anisotropy and the large-spin multiplicity of the spin ground-state of Ln3þ cations, which could be used to construct either single-molecule magnets (SMMs) and singlechain magnets (SCMs) [15]. Nowadays, SMMs were gaining increasing importance, owing to their impressive magnetic memory and quantum effect which lead them to be a prospective candidate in high-density information storage and quantum computing [16]. Although many Ln3þ based SMMs have been reported, it was still very challenging to obtain materials with real application value [17]. We selected these benzimidazole carboxylic acid ligand of 2(hydroxymethyl)-1H-benzo[d]imidazole-5-carboxylic acid (H2L1), 2-(4-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylic acid (H2L2), and 2-(2-carboxyethyl)-1H-benzo[d]imidazole-5carboxylic acid (H3L3) for the following reason: 1) These ligands have characteristics of the multiple sites to help to construct
https://doi.org/10.1016/j.molstruc.2019.127345 0022-2860/© 2019 Published by Elsevier B.V.
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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multidimensional structures. 2) They possess p-Electron-rich aromatic backbones, which facilitated the construction of complexes with excellent luminescence properties and magnetic properties [18]. Motivated by the aspects discussed above, six complexes based on these three ligands and lanthanide ions were constructed, namely, {[Gd(L1)2(H2O)3]$Cl}n (1), [Eu(HL2)2(H2O)6]$(H2O)4$3Cl (2), [Ln(HL2)2(H2O)6]$3Cl [Ln ¼ Ho (3) and Sm (4)], {[Ln(HL3)2(H2O)2]·2Cl}n [Ln ¼ Eu (5) and Yb (6)]. The six complexes were characterized by single-crystal X-ray diffraction analysis, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In addition, luminescence properties of complexes 1e6 were studied in detail. Complexes 3e6 showed antiferromagnetic interaction at low temperature, however, complex 1 has a ferromagnetic interaction. 2. Experimental section 2.1. Materials and measurements Synthesis of H2L1 ligand was reported in our previous work [19]. All other reagents and solvents for syntheses were purchased from Adamas Reagent Co., Ltd and employed without further purification. Elemental analysis of C, H and N was carried out with a Thermo Flash EA 1112-NCHS-O analyzer. Thermogravimetric analysis (TGA) was carried out with a PerkinElmer TG-7 analyzer heated from 25 to 1000 C at a heating rate of 10 C/min in an argon atmosphere. Powder X-ray diffraction (PXRD) was recorded on a Rigaku D/Max-2500 diffractometer at 40 kV, 100 mA for a Cu-target tube and a graphite monochromator. FT-IR spectra were measured on a Brucker Equinox 55 FT-IR spectrometer with KBr pellets at the range of 4000e400 cm1. Magnetic measurements were recorded on a Quantum Design MPMSXL-7 SQUID magnetometer on polycrystalline samples. Solid state luminescent spectra of ligands H2L, H2L1 and H3L2 and complexes 1e6 were measured by Hitachi F4500 Fluorescence Spectrophotometer with a Xe arc lamp as the light source and bandwidths of 2.5 nm at room temperature. 2.2. Synthesis of ligand H2L2 and H3L3 2.2.1. Synthesis of H2L2 A mixture of 3,4-diaminobenzoic acid (1.52 g, 10 mmol), 4hydroxybenzaldehyde (1.38 g, 11 mmol) and glacial acetic acid (30 mL) were stirred for about 15 min, the reaction mixture was refluxed for 7.5 h. The mixed solution was cooled to room temperature and the solid products were precipitated. The solid crude product was washed with a large amount of water, and then dried in the air. The product was transferred to a round bottom flask, adding a certain amount of methanol and steaming to remove the residual glacial acetic acid. Light green solid powder ligand H2L2 was obtained (about yield, 52%). 1H NMR (400 MHz, DMSO‑d6). d: 13.00 (s, 2H, carboxylic and NH), 10.29 (s, 1H, hydroxyl), 8.2e7.1 (m, 7H, benzene). Anal. Calcd (%) for C11H10N2O4: C, 56.41; H, 10.08; N, 11.96; O, 27.33. Found: C, 56.63; H,10.34; N, 11.75; O, 27.10. IR (KBr pellets, cm1): 3152(m), 3053(m), 2630(w), 2511(w), 1689(s), 1625(m), 1609(s), 1453(w), 1476(m), 1433(s), 1382(m), 1317(m), 1277(s), 1255(m), 1232(m), 1179(m), 1124(w), 1084(w), 1012(w), 974(w), 947(w), 885(w), 844(m), 768(w), 748(w), 727(w), 689(w), 647(w), 632(w). 2.2.2. Synthesis of H3L3 3,4-diaminobenzoic acid (10 mmol) of 1.52 g, amber acid (15 mmol) of 1.77 g was added to hydrochloric acid (4 M) of 30 mL in a 100 mL round-bottom flask equipped with magnetic stirrer. The reaction mixture was refluxed for 7 h. After completion of the reaction, residual was filtered off and the filtrate was concentrated.
After that, the resulting yellow solid was collected (about yield, 80%). 1H NMR (400 MHz, DMSO‑d6). d: 13.00 (s, 3H, carboxylic and iminazole), 7.83e8.26 (m, 3H, benzene), 2.99e3.35 (d, J ¼ 8.0 Hz, 4H, methylene). Anal. Calcd (%) for C11H10N2O4: C, 56.41; H, 10.08; N, 11.96; O, 27.33. Found: C, 56.63; H, 10.34; N, 11.75; O, 27.10. IR (KBr pellets, cm1): 2927(s), 2831(s), 2746(s), 2634(s), 1698(vs), 1634(w), 1615(m), 1568(m), 1508(w), 1453(w), 1422(s), 1353(w), 1313(s), 1258(m), 1201(s), 1127(w), 1087(w), 1044(w), 1019(w), 968(w), 925(m), 909(m), 840(m), 803(w), 791(w), 769(w), 743(w), 676(w), 639(w). 2.3. Preparation of complexes 1e6 2.3.1. Synthesis of {[Gd(L1)2(H2O)3]·Cl}n (1) A mixture of Gd(NO3)3$6H2O (35 mg, 0.1 mmol), H2L1 (20.5 mg, 0.1 mmol) and CH3CN/H2O (7:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 140 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 45% (based on H2L1). Anal. Calcd for C18H20ClN4O9Gd (%): C, 34.36; H, 3.20; N, 8.91. Found: C, 34.29; H, 3.16; N, 9.02. IR (KBr pellet, cm1): 3232 (m), 2846 (w), 2717 (w), 1787 (w), 1628 (w), 1593 (w), 1514 (s), 1409 (s), 1325 (m), 1286 (m), 1224 (m), 1128 (w), 1074 (w), 1025 (w), 950 (w), 892 (w), 838 (m), 781 (m), 751 (w), 699 (w), 630 (w). 2.3.2. Synthesis of {[Eu(HL2)2(H2O)6]·(H2O)4·3Cl}n (2) A mixture of EuCl3$6H2O (54.9 mg, 0.15 mmol), H2L2 (20.5 mg, 0.1 mmol) and CH3CN/H2O (7:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 130 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 39% (based on H2L2). Anal. Calcd for C28H40Cl3EuN4O16 (%): C, 35.51; H, 4.26; N, 5.92. Found: C, 35.45; H, 4.21; N, 6.19. IR (KBr pellet, cm1): 3364(s), 3030(m), 1900(w), 1610(s), 1553(s), 1488(s), 1399(s), 1287(s), 1260(s), 1183(s), 1127(w), 953(w), 899(w), 841(w), 812(w), 772(m), 736(w), 686(w), 642(w), 571(m), 517(w). 2.3.3. Synthesis of {[Ho(HL2)2(H2O)6]·3Cl}n (3) A mixture of HoCl3$6H2O (56.9 mg, 0.15 mmol), H2L2 (38.1 mg, 0.15 mmol) and CH3CN/H2O (5:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 140 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 39% (based on H2L2). Anal. Calcd for C28H30Cl3HoN4O12 (%): C, 37.96; H, 3.41; N, 6.32. Found: C, 37.61; H, 3.32; N, 6.56. IR (KBr pellet, cm1): 3364(s), 3030 (m), 1900(w), 1610(s), 1553(s), 1488(s), 1399(s), 1287(s), 1260(s), 1183(s), 1127(w), 953(w), 899(w), 841(w), 812(w), 772(m), 736(w), 686(w), 642(w), 571(m), 517(w). 2.3.4. Synthesis of {[Sm(HL2)2(H2O)6]·3Cl}n (4) A mixture of SmCl3$6H2O (72.9 mg, 0.2 mmol), H2L2 (38.1 mg, 0.15 mmol) and CH3CN/H2O (5:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 140 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 39% (based on H2L2). Anal. Calcd for C28H30Cl3SmN4O12 (%): C, 38.60; H, 3.47; N, 6.43. Found: C, 38.51; H, 3.39; N, 6.56. IR (KBr pellet, cm1): 3390(s), 2889(m), 1905(w), 1631(m), 1595(m), 1516(s), 1409(s), 1324(m), 1285(m), 1223(w), 1076(w), 1025(w), 950(w), 839(m), 782(m), 752(w), 698(w),
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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606(w), 549(w). 2.3.5. Synthesis of {[Eu(HL3)2(H2O)2]·2Cl}n (5) A mixture of EuCl3$6H2O (36.6 mg, 0.1 mmol), H3L3 (23.4 mg, 0.1 mmol) and CH3CN/H2O (4:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 130 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Yellow crystals were obtained by filtering and dried in air. Yield: 40% (based on H3L3). Anal. Calcd for C11H21Cl2EuN2O10 (%): C, 23.42; H, 3.75; N, 4.96. Found: C, 23.22; H, 3.68; N, 5.32. IR (KBr pellet, cm1): 3129(s), 2862(s), 1822(w), 1629(m), 1603(m), 1560(s), 1483(s), 1428(s), 1399(s), 1326(m), 1229(w), 1145(s), 1088(s), 1064(s), 1029(m), 969(w), 818(w), 779(m), 757(w), 714(w), 685(w), 593(w). 2.3.6. Synthesis of {[Yb(HL3)2(H2O)2]·2Cl}n (6) This complex 6 was synthesized by following a procedure similar to that for 5 but using YbCl3$6H2O (38.7 mg, 0.1 mmol) instead of EuCl3$6H2O. Yellow crystals were obtained by filtering, washed with ethanol absolute and dried in air. Yield: 42% (based on H2L3). Anal. Calcd for C11H19Cl2YbN2O9 (%):C, 23.29; H, 3.38; N, 4.94. Found: C, 23.22; H, 3.29; N, 5.29. IR (KBr pellet, cm1): 3345(s), 3098(m), 2165(w), 1919(w), 1629(m), 1601(m), 1545(s), 1513(s), 1488(s), 1440(s), 1415(s), 1375(s), 1302(s), 1271(s), 1059(m), 1030(m), 970(m), 818(m), 778(s), 757(s), 732(s), 653(s), 618(m). 2.4. X-ray crystallography The crystallographic data collections for complexes 1e6 were carried out on a Bruker Smart Apex CCD area-detector diffractometer with graphitemonochromated Mo Ka radiation (l ¼ 0.71073 Å) using u-scan technique. Semi-empirical absorption correction was applied by using the SADABS program [20]. The diffraction data were integrated by using the SAINT program [21], which was also used for the intensity corrections for the Lorentz and polarization effects. The structures were solved by direct methods and all the non-hydrogen atoms were refined with anisotropic displacement parameters using the SHELXL crystallographic software package [22]. All non-hydrogen atoms were refined with anisotropic displacement parameters during the final cycles, and the hydrogen atoms attached to the ligands were located in calculated positions and refined using a riding model. The hydrogen atoms attached to oxygen atoms were located from difference Fourier maps. The final chemical formula of complexes was calculated on the crystallographic data combined with TGA and elemental analysis. A summary of their crystallographic data and structure refinement were provided in Table 1. Selected bond distances and angles of the title complexes were listed in Table S1 of Supplementary 1. Hydrogen bonds distances and angles for complexes 1e6 are listed in Table S2 of Supplementary 1. 3. Results and discussion 3.1. Syntheses and general characterization Complex 1 was synthesized via solvothermal conditions with mixed Gd(NO3)3$6H2O and H2L1. Under the solvothermal conditions, H2L2 ligand reacted with EuCl3$6H2O, HoCl3$6H2O and SmCl3$6H2O to generate isostructural complexes 2e4, while EuCl3$6H2O, YbCl3$6H2O and H3L3 mixture reacted to form isomorphous complexes 5 and 6. Complexes 1, 5 and 6 have a 1D chain structure and further assembled to form 2D sheet and 3D supramolecular structure by hydrogen-bonding interactions or p … p stacking interactions. However, complexes 2e4 was mononuclear
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Table 1 Crystal data and structure refinement summary for complexes 1e6. 1
2
3
Formula Formular wt Crystal system Space group T/K a/Å b/Å c/Å a/deg b/deg g/deg V/Å3 Z D/g cm3 m/mm1 F(000) Messured reflns Obsd reflns Ra/wRb
C18H20ClN4O9Gd 629.08 monoclinic P21/n 100.00(10) 11.2050(7) 11.2268(5) 19.9289(10) 90 98.847(5) 90 2477.2(2) 4 1.687 2.837 1236 18133 4366 0.0490/0.1258 4
C28H40Cl3N4O16Eu 946.95 triclinic P-1 100.01(10) 8.8761(4) 10.2368(4) 20.5599(9) 99.951(3) 97.705(4) 90.130(3) 1822.79(14) 2 1.725 2.017 956 14361 6400 0.0585/0.1122 5
C28H30Cl3N4O12Ho 885.84 triclinic P-1 100.00(10) 8.8310(2) 10.2409(4) 20.4655(8) 100.135(3) 97.272(3) 90.195(2) 1806.68(11) 2 1.628 2.473 880 16744 6356 0.0384/0.0727 6
Formula Formular wt Crystal system Space group T/K a/Å b/Å c/Å a/deg b/deg g/deg V/Å3 Z D/g cm3 m/mm1 F(000) Messured reflns Obsd reflns Rc/wRd
C28H30Cl3N4O12Sm 871.26 triclinic P-1 100.00(10) 8.8299(5) 10.2519(6) 20.4593(12) 99.830(5) 97.228(5) 90.186(4) 1809.77(18) 2 1.599 1.906 870 13521 6370 0.0805/0.1746
C11H21Cl2N2O10Eu 564.16 triclinic P-1 100.01(10) 8.8876(2) 10.1955(3) 11.2150(3) 77.328(2) 87.281(2) 71.068(3) 937.53(5) 2 1.998 3.682 556 16292 3301 0.0216/0.0553
C11H19Cl2N2O9Yb 567.22 triclinic P-1 100.00(10) 8.1336(3) 11.2403(5) 11.2886(4) 113.229(4) 92.266(3) 109.827(4) 874.05(7) 2 2.155 5.704 550 9903 3081 0.0214/0.0507
a b c d
R ¼ S(jjF0jjFCjj)/SjF0j wR ¼ [Sw(jF0j2jFCj2)2/Sw(F20)]1/2 R ¼ S(jjF0jjFCjj)/SjF0j. wR ¼ [Sw(jF0j2jFCj2)2/Sw(F20)]1/2.
structure and further produced 3D supramolecular structure by hydrogen-bonding interactions. In the FT-IR spectra of the synthetic complexes 1e6 showed that the characteristic absorption peaks of OeH or NeH in free or coordinated water molecules and coordinated ligands were about 3300 cm1: 3232 cm1 (1); 3364 cm1 (2); 3364 cm1 (3); 3390 cm1 (4); 3129 cm1 (5); 3345 cm1 (6). The characteristic absorption peak of carbonyl group in the H2L1, H2L2 and H3L3 are 1680 cm1 and 1313 cm1, while the carbonyl groups were coordinated with the metal in complexes 1e6, the absorption bands of complexes 1e6 from 1600 cm1 to 1390 cm1 show the existence of the carboxylic groups: 1514 cm1, 1492 cm1 (1); 1610 cm1, 1399 cm1 (2); 1610 cm1, 1399 cm1 (3); 1595 cm1, 1409 cm1 (4); 1603 cm1, 1428 cm1 (5); 1601 cm1, 1415 cm1 (6). The H2L1, H2L2 and H3L3 ligands and complexes 1e6 exhibited the peaks in the 1420-1630 cm1 region clearly confirmed the formation of the benzimidazole groups.
3.2. Crystal structure description 3.2.1. Structural description of {[Gd(L1)2(H2O)3]·Cl}n (1) The X-ray results suggested that complex 1 crystallizes in the monoclinic crystal system with the P21/n space group and features a 1D linear chain structure. As shown in Fig. 1a, each asymmetric
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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unit consisted of one crystallographically independent Gd(III) ions, two incomplete deprotonated HL1- ligands, three coordinated H2O molecules, four lattice H2O molecules and one guest chloride ion. Nine coordination positions were occupied by a nitrogen atom (N2) from one H2L1 organic ligand, and the eight remaining coordination sites were occupied by the eight O atoms: four O atoms (O2, O3, O6, O7) from two carboxyl groups of two different H2L1 ligands another O atom (O1) from one hydroxyl group of one H2L1 ligand, and three oxygen atoms (O4, O5, O8) from three distinct coordinated H2O molecules, respectively. The central Gd (III) atoms were located in a distorted capped square antiprism configuration (Fig. 1b). Around the Gd(III) center, the (O1, O2, O3, O5, O6, O8, N2) atoms comprise the basal plane, and the (O4, O7) atoms occupy the axial positions. The GdeN bond length was 2.507(5) Å, while the GdeO bond distances fall in the region 2.423(5)-2.513(4) Å. In addition, the coordination angles of O-Gd-O and O-Gd-N were in the range of 53.04(14) to 143.22(15)o and 65.06(15) to 147.17(16)o, respectively. As illustrated in Fig. 1c, each pair neighboring Gd(III) ions were bridged by one carboxylate, one hydroxy groups and N atom from one H2L1 ligand to form an infinite 1D linear chain structure along a-axis, in which the Gd$$$Gd distance is 10.6561(8) Å. The chains were linked by hydrogen bonds of O(5)-H(5A)$$$O(2) and O(8)-H(8A)$$$O(3) (Table S2 of Supplementary 1) to formed a 2D layer structure (Fig. 1d). The neighboring 2D structures were further connected with each other by the O(1)-H(4B)/Cl(1) and O(1)-H(4A)$$$O(10) (Table S2 of Supplementary 1) hydrogen bonds to result in a 3D supermolecular network structure (Fig. 1e). 3.2.2. Structural description of [Ln(HL2)2(H2O)6]·3Cl [Ln ¼ Ho (3)] Because complexes 2e4 were isostructural, here only the structure of 3 was chosen for a detailed discussion. X-ray crystallographic analysis revealed that complex 3 crystallizes in the triclinic crystal system with the P-1 space group and features a mononuclear structure. As shown in Fig. 2a, each asymmetric unit consists of one crystallographically independent Ho ions, two incomplete deprotonated HL2- ligands, five coordinated H2O molecules, one lattice H2O molecule and three guest chloride ion. The Ho ions was eight-coordinated and displayed a distorted square antiprismatic {HoO8} geometry that was filled by two O atoms (O3, O10) from two distinct H2L2 ligands, five O atoms (O4, O5, O6, O8, O9) from five coordinated H2O molecules and another O atom (O7) from one lattice H2O molecule (Fig. 2b). Around the Ho center, the (O4, O5, O6, O7, O8, O9) atoms comprise the basal plane, and the (O3, O10) atoms occupy the axial positions. The HoeO bond distances varied from 2.259(3) to 2.410(3) Å and the O-Ho-O bond angles span from 71.02(10) to 147.35(10)o. As depicted in Fig. 2c, adjacent structural units form a 1D chain by hydrogen bond of O(1)eH(1) … O(2) (Table S2 of Supplementary 1). The chains were linked by abundant hydrogen bonding interactions O(1)eH(1) … O(2) and O(4)-H(4B)/O(1) (Table S2 of Supplementary 1) to formed a 2D layer structure (Fig. 2d). The neighboring 2D structures further link to each other by the O(8)-H(8A) … Cl(2), N(4)eH(4) … Cl(2), O(8)-H(8B)/O(11), O(12)eH(12) … O(11), N(1)-H(1A) … Cl(3) and O(6)-H(6B)/Cl(3) (Table S2 of Supplementary 1) hydrogen bonds to give a supramolecular 3D arrangement (Table S2 of Supplementary 1) (Fig. 2e).
Fig. 1. View of (a) The asymmetric unit of complex 1; (b) Distorted capped square antiprism configuration of Gd in complex 1; (c) The 1D chain of complex 1; (d) The 2D layer though the hydrogen bonds of O(5)-H(5A)$$$O(2) and O(8)-H(8A)$$$O(3); (e) The 3D supermolecular network structure though the hydrogen bonds of O(1)-H(4B)/ Cl(1) and O(1)-H(4A)$$$O(10).
3.2.3. Structural description of {[Ln(HL3)2(H2O)2]·2Cl}n [Ln ¼ Eu(5)] Single-crystal X-ray determination displayed that complexes 5e6 were isomorphous and all crystallized in the triclinic space group P-1, exhibiting 1D chain structure. As an example, the crystal structure of 5 will be described in detail. The asymmetric unit consists of one independent Eu(III) ions, two HL32 ligands, two coordinated water molecules, and two guest chloride ion (Fig. 3a).
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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5
Each Eu ions is nine-coordinated in a distored monocapped antiprismatic configuration by five oxygen atoms (O1B, O2C, O3A, O4A, O4) from five different H3L3 organic ligand and the four remaining coordination sites were occupied by four oxygen atoms (O5, O6, O7, O8) from four coordinated H2O moleculars (Fig. 3b). Around the Eu center, the (O1B, O2C, O3A, O4, O6, O7, O8) atoms comprise the basal plane, and the (O4A, O5) atoms occupy the axial positions. The EueO distances vary from 2.315(4) to 2.564(4) Å, and the angles of O-Eu-O range from 51.01(12) to 156.21(16) . The Eu ion is linked by the H3L3 ligands to generate a 1D chain structure (Fig. 3c). Then adjacent 1D chain were connected through p … p stacking interactions between the benzene and imidazole rings of H3L3 ligand to give a 2D supramolecular layers structure (Fig. 3d). The centroid to centroid distances fall in the range of 3.574(2)-3.848(2) Å, which were all in their normal ranges [23], thus complex 5 has p … p stacking interactions. The neighboring 2D structures were further produced a 3D supramolecular structure through O(8)H(8B)/O(9), O(6)-H(6A) … Cl(1) and N(1)eH(1) … O(6) (Table S2 of Supplementary 1) hydrogen bonding interactions (Fig. 3e).
3.3. Powder X-ray diffraction and thermogravimetric analysis The purity of bulk materials for complexes 1e6 was confirmed by comparison of their powder X-ray diffraction patterns (PXRD) with those calculated from single-crystal X-ray diffraction data. As shown in Supporting Information (Fig. S1 of Supplementary 2), the diffraction peaks of as-synthesized samples were almost in agreement with the simulated patterns calculated from the single-crystal diffraction data, demonstrating the good phase purity of the complexes 1e6. To examine the thermal stability of complexes 1e6, the thermal behaviors were carried out under an Argon atmosphere in the temperature range of 25e1000 C with a heating rate of 10 C$min1, and the TG curves were given in (Fig. S2 of Supplementary 2). In complex 1, there was no weight loss until about 95.5 C where there was a significant decrease of 10.8% from 100 to 154 C due to the loss of four lattice water molecules. With a further increase of temperature, the decomposition of coordination polymer occurred in the range of 155e980 C. For complex 2, a weight loss of nearly 14.6% was observed in the range of 35e135 C, corresponding to the release of two H2O molecules and three guest molecules (calc.14.63%). This plot was followed by the decomposition of the framework. For complex 3, a thermal effect in the 30e135 C range referred to the removal of five H2O molecules and one guest molecule (exptl.14.6%; calc.14.2%), followed by decomposition starting from 140 C. In complex 4, there was a significant decrease of 17.5% from 30 to 140 C due to the loss of three H2O molecules and three guest molecules (calc.18.3%). In the range of 140e945 C, it was the interval of framework decomposition of the complex. For complex 5, an initial weight loss of 17.2% was observed in the region 30e146 C, which could be attributed to loss of one H2O molecule and two guest molecules (calc.15.78%). With a further increase of temperature, the decomposition of coordination framework occurred in the range of 285e898 C. For complex 6, a weight loss of 15.18% was recorded in the region 28e136 C whereas the calculated weight loss of one H2O molecule and two guest molecules (calc. 15.69%), in the range of 340e921 C, the entire architecture began to collapse. Fig. 2. View of (a) The asymmetric unit of complex 3; (b) Distorted square antiprismatic coordination environment of Ho in complex 3; (c) The 1D chain by hydrogen bond of O(1)eH(1) … O(2); (d) The 2D layer though the hydrogen bonds of O(1)eH(1) … O(2) and O(4)-H(4B)/O(1); (e) The 3D supermolecular network structure though the hydrogen bonding interactions.
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3.4. Luminescence properties Lanthanide complexes have shown excellent luminescence properties in terms of their high color purity with high quantum efficiency [24], so the solid-state luminescence properties of the complexes 1e6 and free H2L1, H2L2 and H3L3 ligands were measured at room temperature (Fig. S3 of Supplementary 2). The emission peaks of free ligands H2L1 and H3L3 appeared at 372 nm and 375 nm upon excitation at 271 nm and 350 nm, respectively, which probably derived from p/p* or n/p* transitions [25,26]. The maximum excitation wavelengths of complex 1 was 288 nm, with the maximum emission wavelengths of 402 nm, 485 nm of complex 1 exhibited a slight red-shift compared with the H2L1 ligand, which may be attributed to the emission of ligand-to-metal charge transfer (LMCT) originated from the coordination of the L12 ligand to Gd(III) ions. Complexes 5 and 6 displayed fluorescence emission bands at 431 and 389 nm upon excitation at 349 and 423 nm, respectively, which were red-shifted around 56 and 14 nm as compared with the free H3L3 ligand. Such an emission was assigned to the intraligand pep* transition of H3L3. Interestingly, in comparison to the intensity of the emission spectrum of free H3L3 ligand, the intensity of the luminescence spectrum of complex 6 has been found to be enhanced, which might originated from the ligands coordination to the metal centers. The free H2L2 ligand displayed a fluorescence emission peaks at 578 nm (lex ¼ 318 nm), which probably derived from p/p* or n/p* transitions. Complexes 2e4 fluorescence maximum emission peak at 483 nm, 483 nm, 483 nm upon excitation at 295 nm exhibited a blue-shift compared with the H2L2 ligand. A blue shift of emission bands for 2e4 can be observed, which may be ascribed to the coordination action of the ligand to central lanthanide ions. 3.5. Magnetic properties
Fig. 3. View of (a) The asymmetric unit of complex 5; (b) Distorted monocapped antiprismatic configuration of Eu in complex 5; (c) The 1D chain of complex 5; (d) The 2D layer through p … p stacking interactions; (e) The 3D supermolecular network structure though hydrogen bonding interactions.
The variable-temperature magnetic susceptibility measurements of complexes 1 and 3e6 were carried out in the temperature range of 2e300 K under an applied magnetic field of 1 kOe. The data were plotted as cMT versus T (where, cMT is the molar magnetic susceptibility) in Fig. 4a. For complex 1, at 300 K, the parameter cMT has a value of 5.72 cm3 K mol1, which was coincident with a theoretical value of 7.88 cm3 K mol1 for one magnetically isolated Gd3þ ions (8S7/2, S ¼ 7/2, L ¼ 0, g ¼ 2) in the free-ion approximation. With decreasing temperature, the cMTvalue of complex 1 continuously increases to reach 7.33 cm3 K mol1 at 2 K, indicating that complex 1 may have ferromagnetic interaction. The data above 2 K followed the CurieWeiss law with Cm ¼ 5.87 cm3 K mol1 and q ¼ 5.67 K. The positive q value further supported the existence of ferromagnetic interactions. For complexes 3e6, at 300 K, the values of cMT are 1.20, 21.25, 0.17 and 2.45 cm3 K mol1, respectively. These results were in good agreement with the expected values of 14.07, 0.09, 1.33, and 5.14 cm3 K mol1 for one magnetically independent Ho3þ (5I8, g ¼ 5/4), Sm3þ (6H5/2, g ¼ 2/7), Eu3þ (7F0, g ¼ 1) and Yb3þ (2F7/2, g ¼ 8/7) atoms in complexes 3e6, respectively [27]. As the temperature was lowered, the cMT value of complexes 3e6 continued to reduce, finally reaching 0.01, 11.22, 0.02 and 2.02 cm3 K mol1 at 2 K, respectively. The decrease in value of the parameter cMT can be explained by three factors: (i) antiferromagnetic interactions between the lanthanide ions (ii) spin-orbital coupling of lanthanide complexes, which leads to the 4f configuration splitting into 2Sþ1LJ states, and finally into Stark components under the ligand field perturbation [28], and (iii) magnetic anisotropy. Due to the combined presence of all three effects in these complexes, it was difficult to separately quantify each contribution. For complex 3,
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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Fig. 4. View of (a) Magnetic property of complexes 1 and 3e6 in the form of cMT and c1 M versus T plot; (b) field-dependent magnetization from 0 to 70 kOe at 2 K for complex 1.
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the temperature dependence of the reciprocal susceptibilities (c1 M ) obeys the Curie-Weiss law (cM ¼ C/(T-q)), the best-fit parameters for the Curie-Weiss model in the temperature region of 50e300 K give C ¼ 14.23 cm3 K mol1 and q ¼ 3.49 K. For complex 4, the data above 2 K followed the Curie-Weiss law with C ¼ 0.21 cm3 K mol1 and q ¼ 114.4 K. In complex 5, the data above 2 K followed the Curie-Weiss law with C ¼ 4.14 cm3 K mol1 and q ¼ 687.69 K. In complex 6, the data above 2 K followed the Curie-Weiss law with C ¼ 632.91 cm3 K mol1 and q ¼ 1355.63 K. The negative q value further supported the existence of antiferromagnetic exchange interactions between the Ln3þ ions. The field dependence of the magnetization data of complex 1 was also investigated in the range of 0e70 kOe at 2 K (Fig. 4b). The magnetization of complex 1 increases linearly as the field is increased and the value is 0.09 Nb at 70 kOe, which is much lower than the expected value 6.87 Nb. The magnetization calculated with the Brillouin function (S ¼ 7/2) is above the experimental values of complex 1, which is consistent with the result obtained from the cMT-T curves. The result further supports the existence of ferromagnetic exchange interactions between the Gd3þ ions.
4. Conclusion We have successfully synthesized six new complexes constructed from 2-(hydroxymethyl)-1H-benzo[d]imidazole-5carboxylic acid (H2L1), 2-(4-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylic acid (H2L2), 2-(2-carboxyethyl)-1H-benzo[d] imidazole-5-carboxylic acid (H3L3) under solvothermal conditions. The distinct metal centers and reaction conditions are key factors to construct diverse structure. 1D chain structure of complex 1 has further assemble to form 2D sheet and 3D supramolecular network by hydrogen bonding interactions between the coordinated water molecules and the O atoms of the hydroxy group. Complexes 2e4 are isomorphic and display 3D supramolecular network constructed by hydrogen bonding interactions. Complexes 5 and 6 are an infinite one-dimensional (1D) chain by p … p stacking interactions to give a 3D supermolecular structure. Noteworthily, intense fluorescence emission of 6 exhibits better fluorescent materials as compared to others complexes. Magnetic studies shows that antiferromagnetic exchange couplings between neighboring Ln3þ ions that also exists in complexes 3e6, while complex 1 has ferromagnetic interactions. Acknowledgments This work was financially supported by the Natural Science Foundation of Xinjiang, China (No. 2019D01C042). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.127345.
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Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties Jia-Qiang Du a, Jun-Liang Dong a, Fei Xie a, Ru-Xia Yang a, Hai-Ming Lan a, Duo-Zhi Wang a, b, * a b
School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi, 830046, PR China Key Laboratory of Energy Materials Chemistry, Ministry of Education, Xinjiang University, Urumqi, 830046, Xinjiang, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 July 2019 Received in revised form 31 October 2019 Accepted 1 November 2019 Available online xxx
Six new complexes {[Gd(L1)2(H2O)3]$Cl}n (1), [Eu(HL2)2(H2O)6]$(H2O)4$3Cl (2), [Ln(HL2)2(H2O)6]$3Cl [Ln ¼ Ho (3) and Sm (4)], {[Ln(HL3)2(H2O)2]·2Cl}n [Ln ¼ Eu (5) and Yb (6)] (H2L1 ¼ 2-(hydroxymethyl)1H-benzo[d]imidazole-5-carboxylic acid, H2L2 ¼ 2-(4-hydroxyphenyl)-1H-benzo[d]imidazole-5carboxylic acid, H3L3 ¼ 2-(2-carboxyethyl)-1H-benzo[d]imidazole-5-carboxylic acid) have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). Complexes 1, 5 and 6 are an infinite one-dimensional (1D) chain by hydrogen bonding interactions to give a 3D supermolecular structure. Complexes 2e4 are mononuclear structure, which further formed 3D supermoleculear structure through hydrogen-bonding interactions. Furthermore, luminescent properties of these lanthanide complexes have been assessed in the solid state at ambient temperature. In addition, magnetic measurements reveal that complexes 3e6 have a weak antiferromagnetic interaction, while complex 1 has a ferromagnetic interaction. © 2019 Published by Elsevier B.V.
Keywords: Benzimidazole carboxylic acid Supermoleculear structure Hydrogen-bonding interactions Luminescence Magnetic properties
1. Introduction Nowadays, the design and synthesis of metal-organic coordination polymers by metal ions and organic aromatic carboxylic acid ligands have been studied widely [1]. In particular, lanthanide coordination polymers (Ln-CPs) have attracted increasing attention, because of their superior functional properties and actual or potential applications in luminescence [2], molecular magnetism [3], gas storage/separation [4], proton conductivity [5] and catalysis and so forth [6]. As luminescent materials, compared to transition metal CPs, Ln-CPs have promising luminescent properties such as high luminescent quantum yield [7], narrow and intense band emission [8], large Stokes shift [9], and long luminescent lifetimes [10], which originated from f-f transitions through an “antenna effect” [11]. In the meantime, lanthanide coordination polymers containing N-heterocyclic ligands displayed excellent luminescence by the antenna effect, in general, in which the N-heterocyclic ligand
* Corresponding author. School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi, 830046, PR China. E-mail address: [email protected] (D.-Z. Wang).
function was as a sensitizer [12]. Therefore, lanthanide ion functionalized CPs could create dual luminescent centers (organic linkers, Ln3þ). White light emission materials have been widely used in displays and lightings [13], which profited from their long persistence, energy-efficient and environmental friendly advantages [14]. Apart from the excellent luminescent properties, the magnetic properties of Ln-CPs were unusual because of the diverse local magnetic anisotropy and the large-spin multiplicity of the spin ground-state of Ln3þ cations, which could be used to construct either single-molecule magnets (SMMs) and singlechain magnets (SCMs) [15]. Nowadays, SMMs were gaining increasing importance, owing to their impressive magnetic memory and quantum effect which lead them to be a prospective candidate in high-density information storage and quantum computing [16]. Although many Ln3þ based SMMs have been reported, it was still very challenging to obtain materials with real application value [17]. We selected these benzimidazole carboxylic acid ligand of 2(hydroxymethyl)-1H-benzo[d]imidazole-5-carboxylic acid (H2L1), 2-(4-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylic acid (H2L2), and 2-(2-carboxyethyl)-1H-benzo[d]imidazole-5carboxylic acid (H3L3) for the following reason: 1) These ligands have characteristics of the multiple sites to help to construct
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multidimensional structures. 2) They possess p-Electron-rich aromatic backbones, which facilitated the construction of complexes with excellent luminescence properties and magnetic properties [18]. Motivated by the aspects discussed above, six complexes based on these three ligands and lanthanide ions were constructed, namely, {[Gd(L1)2(H2O)3]$Cl}n (1), [Eu(HL2)2(H2O)6]$(H2O)4$3Cl (2), [Ln(HL2)2(H2O)6]$3Cl [Ln ¼ Ho (3) and Sm (4)], {[Ln(HL3)2(H2O)2]·2Cl}n [Ln ¼ Eu (5) and Yb (6)]. The six complexes were characterized by single-crystal X-ray diffraction analysis, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In addition, luminescence properties of complexes 1e6 were studied in detail. Complexes 3e6 showed antiferromagnetic interaction at low temperature, however, complex 1 has a ferromagnetic interaction. 2. Experimental section 2.1. Materials and measurements Synthesis of H2L1 ligand was reported in our previous work [19]. All other reagents and solvents for syntheses were purchased from Adamas Reagent Co., Ltd and employed without further purification. Elemental analysis of C, H and N was carried out with a Thermo Flash EA 1112-NCHS-O analyzer. Thermogravimetric analysis (TGA) was carried out with a PerkinElmer TG-7 analyzer heated from 25 to 1000 C at a heating rate of 10 C/min in an argon atmosphere. Powder X-ray diffraction (PXRD) was recorded on a Rigaku D/Max-2500 diffractometer at 40 kV, 100 mA for a Cu-target tube and a graphite monochromator. FT-IR spectra were measured on a Brucker Equinox 55 FT-IR spectrometer with KBr pellets at the range of 4000e400 cm1. Magnetic measurements were recorded on a Quantum Design MPMSXL-7 SQUID magnetometer on polycrystalline samples. Solid state luminescent spectra of ligands H2L, H2L1 and H3L2 and complexes 1e6 were measured by Hitachi F4500 Fluorescence Spectrophotometer with a Xe arc lamp as the light source and bandwidths of 2.5 nm at room temperature. 2.2. Synthesis of ligand H2L2 and H3L3 2.2.1. Synthesis of H2L2 A mixture of 3,4-diaminobenzoic acid (1.52 g, 10 mmol), 4hydroxybenzaldehyde (1.38 g, 11 mmol) and glacial acetic acid (30 mL) were stirred for about 15 min, the reaction mixture was refluxed for 7.5 h. The mixed solution was cooled to room temperature and the solid products were precipitated. The solid crude product was washed with a large amount of water, and then dried in the air. The product was transferred to a round bottom flask, adding a certain amount of methanol and steaming to remove the residual glacial acetic acid. Light green solid powder ligand H2L2 was obtained (about yield, 52%). 1H NMR (400 MHz, DMSO‑d6). d: 13.00 (s, 2H, carboxylic and NH), 10.29 (s, 1H, hydroxyl), 8.2e7.1 (m, 7H, benzene). Anal. Calcd (%) for C11H10N2O4: C, 56.41; H, 10.08; N, 11.96; O, 27.33. Found: C, 56.63; H,10.34; N, 11.75; O, 27.10. IR (KBr pellets, cm1): 3152(m), 3053(m), 2630(w), 2511(w), 1689(s), 1625(m), 1609(s), 1453(w), 1476(m), 1433(s), 1382(m), 1317(m), 1277(s), 1255(m), 1232(m), 1179(m), 1124(w), 1084(w), 1012(w), 974(w), 947(w), 885(w), 844(m), 768(w), 748(w), 727(w), 689(w), 647(w), 632(w). 2.2.2. Synthesis of H3L3 3,4-diaminobenzoic acid (10 mmol) of 1.52 g, amber acid (15 mmol) of 1.77 g was added to hydrochloric acid (4 M) of 30 mL in a 100 mL round-bottom flask equipped with magnetic stirrer. The reaction mixture was refluxed for 7 h. After completion of the reaction, residual was filtered off and the filtrate was concentrated.
After that, the resulting yellow solid was collected (about yield, 80%). 1H NMR (400 MHz, DMSO‑d6). d: 13.00 (s, 3H, carboxylic and iminazole), 7.83e8.26 (m, 3H, benzene), 2.99e3.35 (d, J ¼ 8.0 Hz, 4H, methylene). Anal. Calcd (%) for C11H10N2O4: C, 56.41; H, 10.08; N, 11.96; O, 27.33. Found: C, 56.63; H, 10.34; N, 11.75; O, 27.10. IR (KBr pellets, cm1): 2927(s), 2831(s), 2746(s), 2634(s), 1698(vs), 1634(w), 1615(m), 1568(m), 1508(w), 1453(w), 1422(s), 1353(w), 1313(s), 1258(m), 1201(s), 1127(w), 1087(w), 1044(w), 1019(w), 968(w), 925(m), 909(m), 840(m), 803(w), 791(w), 769(w), 743(w), 676(w), 639(w). 2.3. Preparation of complexes 1e6 2.3.1. Synthesis of {[Gd(L1)2(H2O)3]·Cl}n (1) A mixture of Gd(NO3)3$6H2O (35 mg, 0.1 mmol), H2L1 (20.5 mg, 0.1 mmol) and CH3CN/H2O (7:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 140 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 45% (based on H2L1). Anal. Calcd for C18H20ClN4O9Gd (%): C, 34.36; H, 3.20; N, 8.91. Found: C, 34.29; H, 3.16; N, 9.02. IR (KBr pellet, cm1): 3232 (m), 2846 (w), 2717 (w), 1787 (w), 1628 (w), 1593 (w), 1514 (s), 1409 (s), 1325 (m), 1286 (m), 1224 (m), 1128 (w), 1074 (w), 1025 (w), 950 (w), 892 (w), 838 (m), 781 (m), 751 (w), 699 (w), 630 (w). 2.3.2. Synthesis of {[Eu(HL2)2(H2O)6]·(H2O)4·3Cl}n (2) A mixture of EuCl3$6H2O (54.9 mg, 0.15 mmol), H2L2 (20.5 mg, 0.1 mmol) and CH3CN/H2O (7:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 130 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 39% (based on H2L2). Anal. Calcd for C28H40Cl3EuN4O16 (%): C, 35.51; H, 4.26; N, 5.92. Found: C, 35.45; H, 4.21; N, 6.19. IR (KBr pellet, cm1): 3364(s), 3030(m), 1900(w), 1610(s), 1553(s), 1488(s), 1399(s), 1287(s), 1260(s), 1183(s), 1127(w), 953(w), 899(w), 841(w), 812(w), 772(m), 736(w), 686(w), 642(w), 571(m), 517(w). 2.3.3. Synthesis of {[Ho(HL2)2(H2O)6]·3Cl}n (3) A mixture of HoCl3$6H2O (56.9 mg, 0.15 mmol), H2L2 (38.1 mg, 0.15 mmol) and CH3CN/H2O (5:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 140 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 39% (based on H2L2). Anal. Calcd for C28H30Cl3HoN4O12 (%): C, 37.96; H, 3.41; N, 6.32. Found: C, 37.61; H, 3.32; N, 6.56. IR (KBr pellet, cm1): 3364(s), 3030 (m), 1900(w), 1610(s), 1553(s), 1488(s), 1399(s), 1287(s), 1260(s), 1183(s), 1127(w), 953(w), 899(w), 841(w), 812(w), 772(m), 736(w), 686(w), 642(w), 571(m), 517(w). 2.3.4. Synthesis of {[Sm(HL2)2(H2O)6]·3Cl}n (4) A mixture of SmCl3$6H2O (72.9 mg, 0.2 mmol), H2L2 (38.1 mg, 0.15 mmol) and CH3CN/H2O (5:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 140 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Light yellow crystals were obtained by filtering and dried in air. Yield: 39% (based on H2L2). Anal. Calcd for C28H30Cl3SmN4O12 (%): C, 38.60; H, 3.47; N, 6.43. Found: C, 38.51; H, 3.39; N, 6.56. IR (KBr pellet, cm1): 3390(s), 2889(m), 1905(w), 1631(m), 1595(m), 1516(s), 1409(s), 1324(m), 1285(m), 1223(w), 1076(w), 1025(w), 950(w), 839(m), 782(m), 752(w), 698(w),
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606(w), 549(w). 2.3.5. Synthesis of {[Eu(HL3)2(H2O)2]·2Cl}n (5) A mixture of EuCl3$6H2O (36.6 mg, 0.1 mmol), H3L3 (23.4 mg, 0.1 mmol) and CH3CN/H2O (4:1, v/v, 4 mL) were sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 130 C for 12 h. Then the reaction system was cooled to room temperature at a rate of 5 C h1. Yellow crystals were obtained by filtering and dried in air. Yield: 40% (based on H3L3). Anal. Calcd for C11H21Cl2EuN2O10 (%): C, 23.42; H, 3.75; N, 4.96. Found: C, 23.22; H, 3.68; N, 5.32. IR (KBr pellet, cm1): 3129(s), 2862(s), 1822(w), 1629(m), 1603(m), 1560(s), 1483(s), 1428(s), 1399(s), 1326(m), 1229(w), 1145(s), 1088(s), 1064(s), 1029(m), 969(w), 818(w), 779(m), 757(w), 714(w), 685(w), 593(w). 2.3.6. Synthesis of {[Yb(HL3)2(H2O)2]·2Cl}n (6) This complex 6 was synthesized by following a procedure similar to that for 5 but using YbCl3$6H2O (38.7 mg, 0.1 mmol) instead of EuCl3$6H2O. Yellow crystals were obtained by filtering, washed with ethanol absolute and dried in air. Yield: 42% (based on H2L3). Anal. Calcd for C11H19Cl2YbN2O9 (%):C, 23.29; H, 3.38; N, 4.94. Found: C, 23.22; H, 3.29; N, 5.29. IR (KBr pellet, cm1): 3345(s), 3098(m), 2165(w), 1919(w), 1629(m), 1601(m), 1545(s), 1513(s), 1488(s), 1440(s), 1415(s), 1375(s), 1302(s), 1271(s), 1059(m), 1030(m), 970(m), 818(m), 778(s), 757(s), 732(s), 653(s), 618(m). 2.4. X-ray crystallography The crystallographic data collections for complexes 1e6 were carried out on a Bruker Smart Apex CCD area-detector diffractometer with graphitemonochromated Mo Ka radiation (l ¼ 0.71073 Å) using u-scan technique. Semi-empirical absorption correction was applied by using the SADABS program [20]. The diffraction data were integrated by using the SAINT program [21], which was also used for the intensity corrections for the Lorentz and polarization effects. The structures were solved by direct methods and all the non-hydrogen atoms were refined with anisotropic displacement parameters using the SHELXL crystallographic software package [22]. All non-hydrogen atoms were refined with anisotropic displacement parameters during the final cycles, and the hydrogen atoms attached to the ligands were located in calculated positions and refined using a riding model. The hydrogen atoms attached to oxygen atoms were located from difference Fourier maps. The final chemical formula of complexes was calculated on the crystallographic data combined with TGA and elemental analysis. A summary of their crystallographic data and structure refinement were provided in Table 1. Selected bond distances and angles of the title complexes were listed in Table S1 of Supplementary 1. Hydrogen bonds distances and angles for complexes 1e6 are listed in Table S2 of Supplementary 1. 3. Results and discussion 3.1. Syntheses and general characterization Complex 1 was synthesized via solvothermal conditions with mixed Gd(NO3)3$6H2O and H2L1. Under the solvothermal conditions, H2L2 ligand reacted with EuCl3$6H2O, HoCl3$6H2O and SmCl3$6H2O to generate isostructural complexes 2e4, while EuCl3$6H2O, YbCl3$6H2O and H3L3 mixture reacted to form isomorphous complexes 5 and 6. Complexes 1, 5 and 6 have a 1D chain structure and further assembled to form 2D sheet and 3D supramolecular structure by hydrogen-bonding interactions or p … p stacking interactions. However, complexes 2e4 was mononuclear
3
Table 1 Crystal data and structure refinement summary for complexes 1e6. 1
2
3
Formula Formular wt Crystal system Space group T/K a/Å b/Å c/Å a/deg b/deg g/deg V/Å3 Z D/g cm3 m/mm1 F(000) Messured reflns Obsd reflns Ra/wRb
C18H20ClN4O9Gd 629.08 monoclinic P21/n 100.00(10) 11.2050(7) 11.2268(5) 19.9289(10) 90 98.847(5) 90 2477.2(2) 4 1.687 2.837 1236 18133 4366 0.0490/0.1258 4
C28H40Cl3N4O16Eu 946.95 triclinic P-1 100.01(10) 8.8761(4) 10.2368(4) 20.5599(9) 99.951(3) 97.705(4) 90.130(3) 1822.79(14) 2 1.725 2.017 956 14361 6400 0.0585/0.1122 5
C28H30Cl3N4O12Ho 885.84 triclinic P-1 100.00(10) 8.8310(2) 10.2409(4) 20.4655(8) 100.135(3) 97.272(3) 90.195(2) 1806.68(11) 2 1.628 2.473 880 16744 6356 0.0384/0.0727 6
Formula Formular wt Crystal system Space group T/K a/Å b/Å c/Å a/deg b/deg g/deg V/Å3 Z D/g cm3 m/mm1 F(000) Messured reflns Obsd reflns Rc/wRd
C28H30Cl3N4O12Sm 871.26 triclinic P-1 100.00(10) 8.8299(5) 10.2519(6) 20.4593(12) 99.830(5) 97.228(5) 90.186(4) 1809.77(18) 2 1.599 1.906 870 13521 6370 0.0805/0.1746
C11H21Cl2N2O10Eu 564.16 triclinic P-1 100.01(10) 8.8876(2) 10.1955(3) 11.2150(3) 77.328(2) 87.281(2) 71.068(3) 937.53(5) 2 1.998 3.682 556 16292 3301 0.0216/0.0553
C11H19Cl2N2O9Yb 567.22 triclinic P-1 100.00(10) 8.1336(3) 11.2403(5) 11.2886(4) 113.229(4) 92.266(3) 109.827(4) 874.05(7) 2 2.155 5.704 550 9903 3081 0.0214/0.0507
a b c d
R ¼ S(jjF0jjFCjj)/SjF0j wR ¼ [Sw(jF0j2jFCj2)2/Sw(F20)]1/2 R ¼ S(jjF0jjFCjj)/SjF0j. wR ¼ [Sw(jF0j2jFCj2)2/Sw(F20)]1/2.
structure and further produced 3D supramolecular structure by hydrogen-bonding interactions. In the FT-IR spectra of the synthetic complexes 1e6 showed that the characteristic absorption peaks of OeH or NeH in free or coordinated water molecules and coordinated ligands were about 3300 cm1: 3232 cm1 (1); 3364 cm1 (2); 3364 cm1 (3); 3390 cm1 (4); 3129 cm1 (5); 3345 cm1 (6). The characteristic absorption peak of carbonyl group in the H2L1, H2L2 and H3L3 are 1680 cm1 and 1313 cm1, while the carbonyl groups were coordinated with the metal in complexes 1e6, the absorption bands of complexes 1e6 from 1600 cm1 to 1390 cm1 show the existence of the carboxylic groups: 1514 cm1, 1492 cm1 (1); 1610 cm1, 1399 cm1 (2); 1610 cm1, 1399 cm1 (3); 1595 cm1, 1409 cm1 (4); 1603 cm1, 1428 cm1 (5); 1601 cm1, 1415 cm1 (6). The H2L1, H2L2 and H3L3 ligands and complexes 1e6 exhibited the peaks in the 1420-1630 cm1 region clearly confirmed the formation of the benzimidazole groups.
3.2. Crystal structure description 3.2.1. Structural description of {[Gd(L1)2(H2O)3]·Cl}n (1) The X-ray results suggested that complex 1 crystallizes in the monoclinic crystal system with the P21/n space group and features a 1D linear chain structure. As shown in Fig. 1a, each asymmetric
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unit consisted of one crystallographically independent Gd(III) ions, two incomplete deprotonated HL1- ligands, three coordinated H2O molecules, four lattice H2O molecules and one guest chloride ion. Nine coordination positions were occupied by a nitrogen atom (N2) from one H2L1 organic ligand, and the eight remaining coordination sites were occupied by the eight O atoms: four O atoms (O2, O3, O6, O7) from two carboxyl groups of two different H2L1 ligands another O atom (O1) from one hydroxyl group of one H2L1 ligand, and three oxygen atoms (O4, O5, O8) from three distinct coordinated H2O molecules, respectively. The central Gd (III) atoms were located in a distorted capped square antiprism configuration (Fig. 1b). Around the Gd(III) center, the (O1, O2, O3, O5, O6, O8, N2) atoms comprise the basal plane, and the (O4, O7) atoms occupy the axial positions. The GdeN bond length was 2.507(5) Å, while the GdeO bond distances fall in the region 2.423(5)-2.513(4) Å. In addition, the coordination angles of O-Gd-O and O-Gd-N were in the range of 53.04(14) to 143.22(15)o and 65.06(15) to 147.17(16)o, respectively. As illustrated in Fig. 1c, each pair neighboring Gd(III) ions were bridged by one carboxylate, one hydroxy groups and N atom from one H2L1 ligand to form an infinite 1D linear chain structure along a-axis, in which the Gd$$$Gd distance is 10.6561(8) Å. The chains were linked by hydrogen bonds of O(5)-H(5A)$$$O(2) and O(8)-H(8A)$$$O(3) (Table S2 of Supplementary 1) to formed a 2D layer structure (Fig. 1d). The neighboring 2D structures were further connected with each other by the O(1)-H(4B)/Cl(1) and O(1)-H(4A)$$$O(10) (Table S2 of Supplementary 1) hydrogen bonds to result in a 3D supermolecular network structure (Fig. 1e). 3.2.2. Structural description of [Ln(HL2)2(H2O)6]·3Cl [Ln ¼ Ho (3)] Because complexes 2e4 were isostructural, here only the structure of 3 was chosen for a detailed discussion. X-ray crystallographic analysis revealed that complex 3 crystallizes in the triclinic crystal system with the P-1 space group and features a mononuclear structure. As shown in Fig. 2a, each asymmetric unit consists of one crystallographically independent Ho ions, two incomplete deprotonated HL2- ligands, five coordinated H2O molecules, one lattice H2O molecule and three guest chloride ion. The Ho ions was eight-coordinated and displayed a distorted square antiprismatic {HoO8} geometry that was filled by two O atoms (O3, O10) from two distinct H2L2 ligands, five O atoms (O4, O5, O6, O8, O9) from five coordinated H2O molecules and another O atom (O7) from one lattice H2O molecule (Fig. 2b). Around the Ho center, the (O4, O5, O6, O7, O8, O9) atoms comprise the basal plane, and the (O3, O10) atoms occupy the axial positions. The HoeO bond distances varied from 2.259(3) to 2.410(3) Å and the O-Ho-O bond angles span from 71.02(10) to 147.35(10)o. As depicted in Fig. 2c, adjacent structural units form a 1D chain by hydrogen bond of O(1)eH(1) … O(2) (Table S2 of Supplementary 1). The chains were linked by abundant hydrogen bonding interactions O(1)eH(1) … O(2) and O(4)-H(4B)/O(1) (Table S2 of Supplementary 1) to formed a 2D layer structure (Fig. 2d). The neighboring 2D structures further link to each other by the O(8)-H(8A) … Cl(2), N(4)eH(4) … Cl(2), O(8)-H(8B)/O(11), O(12)eH(12) … O(11), N(1)-H(1A) … Cl(3) and O(6)-H(6B)/Cl(3) (Table S2 of Supplementary 1) hydrogen bonds to give a supramolecular 3D arrangement (Table S2 of Supplementary 1) (Fig. 2e).
Fig. 1. View of (a) The asymmetric unit of complex 1; (b) Distorted capped square antiprism configuration of Gd in complex 1; (c) The 1D chain of complex 1; (d) The 2D layer though the hydrogen bonds of O(5)-H(5A)$$$O(2) and O(8)-H(8A)$$$O(3); (e) The 3D supermolecular network structure though the hydrogen bonds of O(1)-H(4B)/ Cl(1) and O(1)-H(4A)$$$O(10).
3.2.3. Structural description of {[Ln(HL3)2(H2O)2]·2Cl}n [Ln ¼ Eu(5)] Single-crystal X-ray determination displayed that complexes 5e6 were isomorphous and all crystallized in the triclinic space group P-1, exhibiting 1D chain structure. As an example, the crystal structure of 5 will be described in detail. The asymmetric unit consists of one independent Eu(III) ions, two HL32 ligands, two coordinated water molecules, and two guest chloride ion (Fig. 3a).
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5
Each Eu ions is nine-coordinated in a distored monocapped antiprismatic configuration by five oxygen atoms (O1B, O2C, O3A, O4A, O4) from five different H3L3 organic ligand and the four remaining coordination sites were occupied by four oxygen atoms (O5, O6, O7, O8) from four coordinated H2O moleculars (Fig. 3b). Around the Eu center, the (O1B, O2C, O3A, O4, O6, O7, O8) atoms comprise the basal plane, and the (O4A, O5) atoms occupy the axial positions. The EueO distances vary from 2.315(4) to 2.564(4) Å, and the angles of O-Eu-O range from 51.01(12) to 156.21(16) . The Eu ion is linked by the H3L3 ligands to generate a 1D chain structure (Fig. 3c). Then adjacent 1D chain were connected through p … p stacking interactions between the benzene and imidazole rings of H3L3 ligand to give a 2D supramolecular layers structure (Fig. 3d). The centroid to centroid distances fall in the range of 3.574(2)-3.848(2) Å, which were all in their normal ranges [23], thus complex 5 has p … p stacking interactions. The neighboring 2D structures were further produced a 3D supramolecular structure through O(8)H(8B)/O(9), O(6)-H(6A) … Cl(1) and N(1)eH(1) … O(6) (Table S2 of Supplementary 1) hydrogen bonding interactions (Fig. 3e).
3.3. Powder X-ray diffraction and thermogravimetric analysis The purity of bulk materials for complexes 1e6 was confirmed by comparison of their powder X-ray diffraction patterns (PXRD) with those calculated from single-crystal X-ray diffraction data. As shown in Supporting Information (Fig. S1 of Supplementary 2), the diffraction peaks of as-synthesized samples were almost in agreement with the simulated patterns calculated from the single-crystal diffraction data, demonstrating the good phase purity of the complexes 1e6. To examine the thermal stability of complexes 1e6, the thermal behaviors were carried out under an Argon atmosphere in the temperature range of 25e1000 C with a heating rate of 10 C$min1, and the TG curves were given in (Fig. S2 of Supplementary 2). In complex 1, there was no weight loss until about 95.5 C where there was a significant decrease of 10.8% from 100 to 154 C due to the loss of four lattice water molecules. With a further increase of temperature, the decomposition of coordination polymer occurred in the range of 155e980 C. For complex 2, a weight loss of nearly 14.6% was observed in the range of 35e135 C, corresponding to the release of two H2O molecules and three guest molecules (calc.14.63%). This plot was followed by the decomposition of the framework. For complex 3, a thermal effect in the 30e135 C range referred to the removal of five H2O molecules and one guest molecule (exptl.14.6%; calc.14.2%), followed by decomposition starting from 140 C. In complex 4, there was a significant decrease of 17.5% from 30 to 140 C due to the loss of three H2O molecules and three guest molecules (calc.18.3%). In the range of 140e945 C, it was the interval of framework decomposition of the complex. For complex 5, an initial weight loss of 17.2% was observed in the region 30e146 C, which could be attributed to loss of one H2O molecule and two guest molecules (calc.15.78%). With a further increase of temperature, the decomposition of coordination framework occurred in the range of 285e898 C. For complex 6, a weight loss of 15.18% was recorded in the region 28e136 C whereas the calculated weight loss of one H2O molecule and two guest molecules (calc. 15.69%), in the range of 340e921 C, the entire architecture began to collapse. Fig. 2. View of (a) The asymmetric unit of complex 3; (b) Distorted square antiprismatic coordination environment of Ho in complex 3; (c) The 1D chain by hydrogen bond of O(1)eH(1) … O(2); (d) The 2D layer though the hydrogen bonds of O(1)eH(1) … O(2) and O(4)-H(4B)/O(1); (e) The 3D supermolecular network structure though the hydrogen bonding interactions.
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3.4. Luminescence properties Lanthanide complexes have shown excellent luminescence properties in terms of their high color purity with high quantum efficiency [24], so the solid-state luminescence properties of the complexes 1e6 and free H2L1, H2L2 and H3L3 ligands were measured at room temperature (Fig. S3 of Supplementary 2). The emission peaks of free ligands H2L1 and H3L3 appeared at 372 nm and 375 nm upon excitation at 271 nm and 350 nm, respectively, which probably derived from p/p* or n/p* transitions [25,26]. The maximum excitation wavelengths of complex 1 was 288 nm, with the maximum emission wavelengths of 402 nm, 485 nm of complex 1 exhibited a slight red-shift compared with the H2L1 ligand, which may be attributed to the emission of ligand-to-metal charge transfer (LMCT) originated from the coordination of the L12 ligand to Gd(III) ions. Complexes 5 and 6 displayed fluorescence emission bands at 431 and 389 nm upon excitation at 349 and 423 nm, respectively, which were red-shifted around 56 and 14 nm as compared with the free H3L3 ligand. Such an emission was assigned to the intraligand pep* transition of H3L3. Interestingly, in comparison to the intensity of the emission spectrum of free H3L3 ligand, the intensity of the luminescence spectrum of complex 6 has been found to be enhanced, which might originated from the ligands coordination to the metal centers. The free H2L2 ligand displayed a fluorescence emission peaks at 578 nm (lex ¼ 318 nm), which probably derived from p/p* or n/p* transitions. Complexes 2e4 fluorescence maximum emission peak at 483 nm, 483 nm, 483 nm upon excitation at 295 nm exhibited a blue-shift compared with the H2L2 ligand. A blue shift of emission bands for 2e4 can be observed, which may be ascribed to the coordination action of the ligand to central lanthanide ions. 3.5. Magnetic properties
Fig. 3. View of (a) The asymmetric unit of complex 5; (b) Distorted monocapped antiprismatic configuration of Eu in complex 5; (c) The 1D chain of complex 5; (d) The 2D layer through p … p stacking interactions; (e) The 3D supermolecular network structure though hydrogen bonding interactions.
The variable-temperature magnetic susceptibility measurements of complexes 1 and 3e6 were carried out in the temperature range of 2e300 K under an applied magnetic field of 1 kOe. The data were plotted as cMT versus T (where, cMT is the molar magnetic susceptibility) in Fig. 4a. For complex 1, at 300 K, the parameter cMT has a value of 5.72 cm3 K mol1, which was coincident with a theoretical value of 7.88 cm3 K mol1 for one magnetically isolated Gd3þ ions (8S7/2, S ¼ 7/2, L ¼ 0, g ¼ 2) in the free-ion approximation. With decreasing temperature, the cMTvalue of complex 1 continuously increases to reach 7.33 cm3 K mol1 at 2 K, indicating that complex 1 may have ferromagnetic interaction. The data above 2 K followed the CurieWeiss law with Cm ¼ 5.87 cm3 K mol1 and q ¼ 5.67 K. The positive q value further supported the existence of ferromagnetic interactions. For complexes 3e6, at 300 K, the values of cMT are 1.20, 21.25, 0.17 and 2.45 cm3 K mol1, respectively. These results were in good agreement with the expected values of 14.07, 0.09, 1.33, and 5.14 cm3 K mol1 for one magnetically independent Ho3þ (5I8, g ¼ 5/4), Sm3þ (6H5/2, g ¼ 2/7), Eu3þ (7F0, g ¼ 1) and Yb3þ (2F7/2, g ¼ 8/7) atoms in complexes 3e6, respectively [27]. As the temperature was lowered, the cMT value of complexes 3e6 continued to reduce, finally reaching 0.01, 11.22, 0.02 and 2.02 cm3 K mol1 at 2 K, respectively. The decrease in value of the parameter cMT can be explained by three factors: (i) antiferromagnetic interactions between the lanthanide ions (ii) spin-orbital coupling of lanthanide complexes, which leads to the 4f configuration splitting into 2Sþ1LJ states, and finally into Stark components under the ligand field perturbation [28], and (iii) magnetic anisotropy. Due to the combined presence of all three effects in these complexes, it was difficult to separately quantify each contribution. For complex 3,
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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Fig. 4. View of (a) Magnetic property of complexes 1 and 3e6 in the form of cMT and c1 M versus T plot; (b) field-dependent magnetization from 0 to 70 kOe at 2 K for complex 1.
Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345
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the temperature dependence of the reciprocal susceptibilities (c1 M ) obeys the Curie-Weiss law (cM ¼ C/(T-q)), the best-fit parameters for the Curie-Weiss model in the temperature region of 50e300 K give C ¼ 14.23 cm3 K mol1 and q ¼ 3.49 K. For complex 4, the data above 2 K followed the Curie-Weiss law with C ¼ 0.21 cm3 K mol1 and q ¼ 114.4 K. In complex 5, the data above 2 K followed the Curie-Weiss law with C ¼ 4.14 cm3 K mol1 and q ¼ 687.69 K. In complex 6, the data above 2 K followed the Curie-Weiss law with C ¼ 632.91 cm3 K mol1 and q ¼ 1355.63 K. The negative q value further supported the existence of antiferromagnetic exchange interactions between the Ln3þ ions. The field dependence of the magnetization data of complex 1 was also investigated in the range of 0e70 kOe at 2 K (Fig. 4b). The magnetization of complex 1 increases linearly as the field is increased and the value is 0.09 Nb at 70 kOe, which is much lower than the expected value 6.87 Nb. The magnetization calculated with the Brillouin function (S ¼ 7/2) is above the experimental values of complex 1, which is consistent with the result obtained from the cMT-T curves. The result further supports the existence of ferromagnetic exchange interactions between the Gd3þ ions.
4. Conclusion We have successfully synthesized six new complexes constructed from 2-(hydroxymethyl)-1H-benzo[d]imidazole-5carboxylic acid (H2L1), 2-(4-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylic acid (H2L2), 2-(2-carboxyethyl)-1H-benzo[d] imidazole-5-carboxylic acid (H3L3) under solvothermal conditions. The distinct metal centers and reaction conditions are key factors to construct diverse structure. 1D chain structure of complex 1 has further assemble to form 2D sheet and 3D supramolecular network by hydrogen bonding interactions between the coordinated water molecules and the O atoms of the hydroxy group. Complexes 2e4 are isomorphic and display 3D supramolecular network constructed by hydrogen bonding interactions. Complexes 5 and 6 are an infinite one-dimensional (1D) chain by p … p stacking interactions to give a 3D supermolecular structure. Noteworthily, intense fluorescence emission of 6 exhibits better fluorescent materials as compared to others complexes. Magnetic studies shows that antiferromagnetic exchange couplings between neighboring Ln3þ ions that also exists in complexes 3e6, while complex 1 has ferromagnetic interactions. Acknowledgments This work was financially supported by the Natural Science Foundation of Xinjiang, China (No. 2019D01C042). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.127345.
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Please cite this article as: J.-Q. Du et al., Lanthanide complexes supported via benzimidazole carboxylic acid ligand: Synthesis, luminescence and magnetic properties, Journal of Molecular Structure, https://doi.org/10.1016/j.molstruc.2019.127345