Polyhedron 139 (2018) 89–97

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Polyhedron

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Three coordination compounds based on tris(1-imidazolyl)benzene:Hydrothermal synthesis, crystal structure and adsorption performancestoward organic dyes

https://doi.org/10.1016/j.poly.2017.10.0110277-5387/� 2017 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Fax: +86 10 61209186.E-mail address: chongchenwang@126.com (C.-C. Wang).

Jun-Jiao Li, Chong-Chen Wang ⇑, Jie Guo, Jing-Rui Cui, Peng Wang, Chen ZhaoBeijing Key Laboratory of Functional Materials for Building Structure and Environment Remediation/Sino-Dutch R&D Centre for Future Wastewater Treatment Technologies,Beijing University of Civil Engineering and Architecture, Beijing 100044, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 31 July 2017Accepted 4 October 2017Available online 12 October 2017

Keywords:Coordination compound1,3,5-Tris(1-imidazolyl)benzeneAdsorptionOrganic dyesSeparation

Three coordination compounds, zero-dimensional Co(tib)(ADC)2 (BUC-60), one-dimensional Zn3(tib)2Cl6(BUC-61) and three-dimensional [Cu2(tib)2(MoO4)Cl]Cl (BUC-62), were obtained from the reaction of1,3,5-tris(1-imidazolyl)benzene (tib), 1,3-adamantanedicarboxylic acid (H2adc), phosphomolybdic acidhydrate (H3PO4�12MoO3) and the corresponding metal salts under hydrothermal conditions. The as-pre-pared samples were characterized by single-crystal X-ray diffraction, Fourier transform infrared spec-troscopy, CHN elemental analyses, thermal gravity analyses and photoluminescence spectroscopy.BUC-60 and BUC-61 exhibit good adsorption performances toward congo red (CR) and mordant blue13 (MB13). The maximum adsorption capacities of BUC-60 and BUC-61 toward CR are 1949 and 1992mg g�1, respectively, along with those toward MB13 being 564 and 209 mg g�1, respectively. In addition,BUC-60 can selectively capture anionic dyes molecules from a dye matrix.

� 2017 Elsevier Ltd. All rights reserved.

1. Introduction

Coordination polymers (CPs) or metal–organic frameworks(MOFs), as a new type of porous materials, have attracted increas-ing attention worldwide [1,2], due to their versatile applications,like catalysis [3], adsorption [4], electrical applications [5], lumi-nescence [6] and magnetism [7], resulting from their large func-tional surface area, high porosity, tunable pore size andgeometries [8–12]. In particular, CPs and MOFs have exhibitedgreat potential in applications with liquid phase adsorption, whichhas attracted more and more interest from scientists [13–15]. Forexample, Matzger and coworkers studied a stable MOF (MIL-100)which is completely water stable and possesses large adsorptioncapacities toward the pharmaceuticals furosemide and sul-fasalazine from water. Wang and coworkers reported a novelorganic–inorganic hybrid compound, (4-Hap)4[Mo8O26] (4-ap =4-aminopyridine), that shows ultra-high uptake of organic dyesand exhibits different dye adsorption capacities toward methyleneblue (MB) and methyl orange (MO), along with rapid andhighly selective adsorption of MB from a MB/MO matrix [16].Subsequently, Wang and coworkers prepared a silver coordination

polymer, which could quickly and efficiently separate the MO andMB from their mixture [17].

In addition, CPs and MOFs are also promising in samplepretreatment, especially in solid-phase extraction (SPE) or solid-phase microextraction (SPME), by virtue of their tunable pore size,permanent nanoscale porosity, high surface area and good thermaland water stabilities [18]. Wang and coworkers prepared a zinc(II)coordination polymer which could act as a novel sorbent for SPE totrace benzo[a]pyrene in edible oils [19]. Zhang and coworkerssynthesized a stable Zn(II) pyrazolate-carboxylate framework withexcellent sensitivity and selectivity for non-polar benzene homo-logs [20]. Ouyang and coworkers found that a MIL-101(Cr)-coatedSPME fiber could be applied for the determination of volatilecompounds [21].

Inspired by all the above and our previous works [16,17,22–24],our group is paying more attention to prepare suitable CPs or MOFsadsorbents to conduct high capacity adsorption and high-efficiencyseparation of organic pollutant matrices. By taking these aspectsinto account, the tridentate ligand 1,3,5-tris(1-imidazolyl)benzene(tib), 1,3-adamantanedicarboxylic acid (H2adc) and phospho-molybdic acid hydrate (H3PO4�12MoO3) (as illustrated inScheme 1) were utilized to prepare three coordination compounds,namely [Co(tib)(Hadc)2] (BUC-60), [Zn3(tib)2Cl6] (BUC-61) and[Cu2(tib)2(MoO4)Cl]Cl (BUC-62). The structure analyses based onsingle crystal X-ray diffraction data revealed that BUC-60,

Scheme 1. Structural formulae of tib, H2adc and H3PO4�12MoO3.

Table 1Details of the X-ray data collection and refinement for BUC-60, BUC-61 and BUC-62.

BUC-60 BUC-61 BUC-62

Formula C39H42N6O8Co C30H24N12Zn3Cl6 C30H24N12O4Cl2Cu2MoM 781.72 961.42 910.53Crystal system monoclinic monoclinic orthorhombicSpace group P2(1)/c P2(1)/c Pna2(1)a (Å) 10.8559(8) 9.0272(9) 16.9137(17)b (Å) 27.781(2) 14.9895(14) 15.7126(16)c (Å) 11.9622(9) 26.767(3) 12.9472(14)a (�) 90 90 90b (�) 105.590(2) 97.718(2) 90c (�) 90 90 90V (Å3) 3475.0(5) 3589.1(6) 3440.8(6)Z 4 4 4l (Mo Ka) (mm�1) 0.560 2.479 1.795Total reflections 17035 17485 13429Unique 6111 6311 5833F(000) 1636 1920 1816Goodness-of-fit (GOF) on F2 1.022 1.028 1.105Rint 0.0619 0.0721 0.0876R0 0.0497 0.0557 0.1156xR2 0.1046 0.1319 0.2720R1 (all data) 0.0967 0.0882 0.1300xR2 (all data) 0.1211 0.1459 0.2853Largest diff. peak and hole (e/Å3) 0456, �0.383 1.185, �0.635 7.540, �1.328Absolute structure parameter 0.06 (3)

90 J.-J. Li et al. / Polyhedron 139 (2018) 89–97

BUC-61 and BUC-62 possess 0D, 1D and 3D structures, respec-tively. In addition, their thermal stabilities, luminescence andadsorption properties have been investigated.

2. Experimental

2.1. Materials and measurements

All chemicals were commercially available reagent grade andused without further purification. CHN Elemental analyses wereperformed using an Elementar Vario EL-III instrument. FTIR spectrawere recorded on a Nicolet-6700 Fourier Transform infrared spec-trophotometer in the region ranging from 4000 to 400 cm�1. Ther-mogravimetric analyses were performed from 70 to 800 �C in anitrogen gas stream at a heating rate of 10 �C min�1 on a DTU-3cthermal analyzer using a-Al2O3 as a reference. Luminescence spec-tra of the solid powder samples were recorded on a Hitachi F-7000spectrophotometer at room temperature.

2.2. Synthesis of BUC-60

BUC-60 was hydrothermally synthesized by mixing H2adc (0.3mmol, 0.0673 g), CoSO4�7H2O (0.3 mmol, 0.0843 g), tib (0.3 mmol,0.0828 g) and deionized water (10 ml) with a molar ratio of1:1:1:1852 in a 25 mL Teflon-lined stainless steel Parr bomb underautogenous pressure, heating at 160 �C for 72 h. After thehydrothermal reaction, the Parr bomb was slowly cooled down

to room temperature. Purple rod crystals were produced (yield:72% based on CoSO4�7H2O). Anal. Calc. for BUC-60, C39H42N6O8Co:C, 42.1; N, 10.7; H, 5.4. Found: C, 42.3; N, 10.7; H, 5.5%. IR (KBr)/cm�1: 3335, 3181, 3149, 3120, 3095, 2927, 2914, 2859, 1731,1678, 1621, 1603, 1509, 1530, 1477, 1360, 1333, 1320, 1274,1257, 1213, 1157, 1105, 1013, 902, 876, 862, 737, 678, 650, 577,554, 532, 480, 420.

2.3. Synthesis of BUC-61

A mixture of H2adc (0.3 mmol, 0.0673 g), ZnCl2 (0.3 mmol,0.0409 g) and tib (0.3 mmol, 0. 0828 g) was sealed in a 25 mLTeflon-lined stainless steel Parr bomb containing deionized H2O(10 mL), heated at 140 �C for 72 h and then cooled down to roomtemperature. Small white block-like crystals of BUC-61 (yield90% based on ZnCl2) were isolated and washed with deionizedwater and ethanol. Anal. Calc. for BUC-61, C30H24N12Zn3Cl6: C,37.4; N, 17.5; H, 2.5. Found: C, 37.6; N, 17.4; H, 2.6%. IR (KBr)/cm�1: 3371, 3130, 1671, 1622, 1546, 1514, 1385, 1359, 1317,1272, 1258, 1181, 1125, 1078, 1048, 1012, 973, 934, 848, 817,758, 664, 611.

2.4. Synthesis of BUC-62

Blue rod-like crystals of BUC-62 (yield: 81% based on CuCl2)were synthesized from a mixture of H3PO4�12MoO3 (0.25 mmol,0.4563 g), CuCl2�2H2O (0.2 mmol, 0.0341 g) and tib (0.4 mmol, 0.

J.-J. Li et al. / Polyhedron 139 (2018) 89–97 91

1104 g) with a molar ratio of 5:4:8 under the same condition asBUC-61. Anal. Calc. for BUC-62, C30H24N12O4Cu2MoCl2: C, 39.5; N,18.5; H, 2.6. Found: C, 39.6; N, 18.5; H, 2.8%. IR (KBr)/cm�1:3433, 3135, 3120, 3045, 1619, 1505, 1306, 1280, 1257, 1131,1109, 1082, 1074, 1016, 950, 941, 926, 906, 889, 874, 850, 813,801, 760, 691, 677, 652.

2.5. X-ray crystallography

X-ray single-crystal data collection for BUC-60, BUC-61 andBUC-62 was performed with a Bruker Smart 1000 CCD area detec-tor diffractometer with graphite-monochromatized MoKa radia-tion (k = 0.71073 Å) using the u–x mode at 298(2) K. SMARTsoftware [25] was used for data collection and SAINT software[26] for data extraction. Empirical absorption corrections were per-formed with the SADABS program [27]. The structures were solvedby direct methods (SHELXS-97) [28] and refined by full-matrix-least

Table 2Selected bonds and angles for BUC-60, BUC-61 and BUC-62 [Å and �].

BUC-60Bond lengths (Å)Co(1)–O(5) 1.941(3)Co(1)–N(4) 2.026(3)

Bond angles (�)O(5)–Co(1)–O(1) 110.47(11)O(1)–Co(1)–N(4) 110.06(11)O(1)–Co(1)–N(2) 116.09(10)

BUC-61Bond lengths (Å)Zn(1)–N(8) 2.000(5)Zn(1)–Cl(2) 2.2263(18)Zn(2)–N(10) 2.015(5)Zn(2)–Cl(3) 2.2296(17)Zn(3)–N(6) 2.017(5)Zn(3)–Cl(6) 2.2184(19)

Bond angles (�)N(8)–Zn(1)–N(2) 109.3(2)N(2)–Zn(1)–Cl(2) 106.40(16)N(2)–Zn(1)–Cl(1) 109.48(17)N(10)–Zn(2)–N(4) 113.8(2)N(4)–Zn(2)–Cl(3) 116.07(17)N(4)–Zn(2)–Cl(4) 101.15(17)N(6)–Zn(3)–N(11) 113.7(2)N(11)–Zn(3)–Cl(6) 108.87(16)N(11)–Zn(3)–Cl(5) 108.95(16)

BUC-62Bond lengths (Å)Mo(1)–O(2) 1.744(10)Mo(1)–O(3) 1.784(12)Cu(1)–N(7) 1.899(11)Cu(1)–O(1) 1.933(10)Cu(1)–Cl(2) 2.731(5)Cu(2)–N(4) 1.992(11)Cu(2)–N(12)#2 2.096(14)

Bond angles (�)O(2)–Mo(1)–O(4) 109.6(5)O(4)–Mo(1)–O(3) 111.5(5)O(3)–Mo(1)–O(1) 106.2(5)N(7)–Cu(1)–O(1) 85.4(4)N(7)–Cu(1)–O(3)#1 94.9(5)O(1)–Cu(1)–O(3)#1 162.9(5)N(2)–Cu(1)–Cl(2) 89.3(4)O(3)#1–Cu(1)–Cl(2) 101.5(4)N(10)–Cu(2)–N(6) 89.9(5)N(10)–Cu(2)–N(12)#2 90.2(6)N(6)–Cu(2)–N(12)#2 176.3(6)N(4)–Cu(2)–O(4)#3 93.2(4)N(12)#2–Cu(2)–O(4)#3 90.7(5)

Symmetry transformations used to generate equivalent atoms:#1 �x + 1, �y + 3, z + 1/2; #2 �x + 1/2, y + 1/2, z � 1/2; #3 x, y � 1, z; #4�x + 1/2, y � 1/2,2, y � 3/2, z � 1/2.

squares techniques on F2 with anisotropic thermal parameters forall of the non-hydrogen atoms (SHELXL-97) [28]. All hydrogen atomswere located by Fourier difference synthesis and geometrical anal-ysis. These hydrogen atoms were allowed to ride on their respec-tive parent atoms. All structural calculations were carried outusing the SHELX-97 program package [28]. Crystallographic dataand structural refinements for BUC-60, BUC-61 and BUC-62 aresummarized in Table 1. Selected bond lengths and angles for allthe coordination compounds are listed in Table 2.

2.6. Batch adsorption

In order to investigate the adsorption abilities of BUC-60, BUC-61 and BUC-62, three typical organic dyes, anionic congo red (CR),anionic mordant blue 13 (MB13) and cationic methylene blue(MB), were selected as models to conduct the adsorption experi-ments. Fifty milligrams of the CPs and MOFs adsorbent powders,

Co(1)–O(1) 1.980(2)Co(1)–N(2) 2.042(3)

O(5)–Co(1)–N(4) 111.12(11)O(5)–Co(1)–N(2) 93.31(11)N(4)–Co(1)–N(2) 114.68(11)

Zn(1)–N(2) 2.002(5)Zn(1)–Cl(1) 2.2661(19)Zn(2)–N(4) 2.031(5)Zn(2)–Cl(4) 2.232(2)Zn(3)–N(11) 2.021(5)Zn(3)–Cl(5) 2.2580(18)

N(8)–Zn(1)–Cl(2) 113.39(17)N(8)–Zn(1)–Cl(1) 106.40(16)Cl(2)–Zn(1)–Cl(1) 111.83(8)N(10)–Zn(2)–Cl(3) 106.47(15)N(10)–Zn(2)–Cl(4) 105.65(17)Cl(3)–Zn(2)–Cl(4) 113.35(7)N(6)–Zn(3)–Cl(6) 107.22(16)N(6)–Zn(3)–Cl(5) 102.68(16)Cl(6)–Zn(3)–Cl(5) 115.43(8)

Mo(1)–O(4) 1.780(11)Mo(1)–O(1) 1.814(11)Cu(1)–N(2) 1.913(13)Cu(1)–O(3)#1 1.950(11)Cu(2)–N(10) 1.987(11)Cu(2)–N(6) 2.069(14)Cu(2)–O(4)#3 2.377(11)

O(2)–Mo(1)–O(3) 110.7(5)O(2)–Mo(1)–O(1) 108.8(5)N(7)–Cu(1)–N(2) 178.2(5)N(2)–Cu(1)–O(1) 93.6(5)N(2)–Cu(1)–O(3)#1 85.7(5)N(7)–Cu(1)–Cl(2) 92.2(3)O(1)–Cu(1)–Cl(2) 95.6(4)N(10)–Cu(2)–N(4) 174.8(5)N(4)–Cu(2)–N(6) 90.6(5)N(4)–Cu(2)–N(12)#2 88.9(5)N(10)–Cu(2)–O(4)#3 91.9(4)N(6)–Cu(2)–O(4)#3

z + 1/2; #5 �x + 1/2, y + 3/2, z + 1/2 #6 �x + 1, �y + 3, z � 1/2 #7 x, y + 1, z #8 �x + 1/

Fig. 1. (a) Packing view of the framework for BUC-60. (b) Highlight of the coordination polyhedron for the Co(II) atom.

Fig. 2. (a) The asymmetric unit of BUC-61 and the coordination environments around the Zn(II) atoms. H atoms are omitted for clarity. (b) The 1D helix chain in BUC-61.

92 J.-J. Li et al. / Polyhedron 139 (2018) 89–97

with a particle size less than 0.08 mm, were added to 200 mL CR(100 mg L�1), MB13 (20 mg L�1) or MB (10 mg L�1) aqueous solu-tions in a 300 mL breaker and were vibrated for the desired contacttime in a water bath shaker with a speed of 150 r min�1 at roomtemperature. Five milliliter aliquots were extracted, in which theadsorbent particles were separated by centrifugation (ZONKIASC-3610) at 5000 rpm for 10 min. A Laspec Alpha-1860 spectrom-eter was used to determine the CR, MB13 and MB concentrationchanges from their maximum absorbance at 493, 551 and 672nm, respectively. The maximum adsorption capacity experimentswere also conducted under different experiment conditions; 20mg (0.020 g) of BUC-60 and BUC-61 were mixed with CR andMB13 solutions (200 ml of 200 mg L�1). The other experimentsconditions were the same as above.

2.7. Selective adsorption toward different dyes

To test the selective adsorption abilities of the above-stated CPsand MOFs as adsorbents, 50 mg powder adsorbents were added to

200 mL of a CR (100 mg L�1)/MB (20 mg L�1) matrix. The mixtureswere vibrated at 150 r min�1 at room temperature, controlled by awater bath shaker. At a certain time intervals, UV–vis absorptionspectroscopy was used to record the maximum absorbance to cal-culate the residual dye concentration of the aqueous solutions.

3. Result and discussion

All three coordination compounds are stable and insoluble inwater and common organic solvents, including but not limited tomethanol, ethanol, ether and N,N-dimethylformamide (DMF). It isworth to noting that we failed to synthesize BUC-61 without theaddition of H2adc, implying H2adc might play a role of a catalystand pH regulator [22].

3.1. Structural description of BUC-60

In the 0D discrete structure of BUC-60 (Fig. 1a), the Co(II) atoms,in a tetrahedral geometry (Fig. 1b), are four-coordinated by two

Fig. 3. (a) The asymmetric unit of BUC-62 and the coordination environments around the Cu(II) atoms. H atoms are omitted for clarity. (b) CuCl-MoO4 chains bridged by tibligands (Cl atoms are not shown). (c) Highlight of the coordination polyhedrons for the Cu1 and Cu2 atoms.

Fig. 4. (a) The [Cu2(tib)2]n4n+ layer of BUC-62. (b) 3D framework of the MOF BUC-62 along the b-axis.

J.-J. Li et al. / Polyhedron 139 (2018) 89–97 93

oxygen atoms from two partly deprotonated Hadc� ligands andtwo nitrogen atoms from two tib ligands. The Co-O and Co-N bonddistances are comparable to those in the counterparts reportedpreviously [29,30]. Each tib ligand, acting as a bidentate bridgingligand, links two Co(II) atoms, which makes the third imidazolegroup in the tib ligand to be terminal (Fig. 1a), similar to the pre-viously reported [Cu(tib)2(N3)2]�2H2O [31]. The partly deproto-nated Hadc� ligands act as both monodentate ligands tocomplete the tetrahedral geometry and counterions to balancethe charge of the cationic [Co(tib)]2+ moiety. The terminal groupsof both the tib and Hadc� ligands result in the zero-dimensionaldiscrete unit of [Co(tib)(Hadc)2].

3.2. Structural description of BUC-61

The coordination polymer BUC-61 is built up of 1D neutral[Zn3(tib)2Cl6] chains, as illustrated in Fig. 2a, in which the Zn(II)ion is tetrahedrally coordinated by two Cl� ligands and two nitro-gen atoms from two tib ligands. The Zn–N and Zn–Cl bond dis-tances are similar to the normal values in the reportedcounterparts [32,33]. It can be clearly seen that the Zn1, Zn2 andZn3 centers in BUC-61 are almost identical. Each tib ligand, as a tri-dentate ligand, joins Zn(II) centers via the tridentate mode into a1D helix chain running parallel to the a-axis (Fig. 2b), which is verydifferent from the coordination mode of the tib ligand in BUC-60.

Fig. 5. The TGA curves of BUC-60, BUC-61 and BUC-62.Fig. 6. Luminescent spectra of BUC-61 at room temperature.

94 J.-J. Li et al. / Polyhedron 139 (2018) 89–97

3.3. Structural description of BUC-62

In the three-dimensional structure of the metal–organic frame-work BUC-62, as shown in Fig. 3a, the Cu1 atom is five-coordinatedin a distorted square-pyramidal geometry with the Addison tauparameter s = 0.26 (Fig. 3c), by two oxygen atoms (O1 and O3) fromtwo (MoO4)2� units in the axial direction, two pyridyl nitrogenatoms (N7 and N2) from two tib ligands and a Cl– ligand in theequatorial plane. The Cu2 atom is five-coordinated in a distortedsquare-pyramidal geometry with s = 0.03 (Fig. 3c) by one oxygenatom from a (MoO4)2� anion and four nitrogen atoms from four dif-ferent tib ligands. The Cu–O, Cu–N and Cu–Cl bond lengths are com-parable to related CPs and MOFs [34,35]. The Cu2-centeredcoodination square pyramid is slightly distorted, with the bondlengths 2.377(11) Å for the Cu–O bond and 1.987(11)–2.069(14) Åfor the Cu–N bonds, and the bond angles approximate to 90� or180�. The (MoO4)2� units, as a tridentate inorganic linker, join threeCu(II) centers via the atoms O1, O3 and O4 to form an infinite[Cu2(MoO4)]n chain along the c-axis, depicted in Fig. 3b. The tibligands act as tridentate ligands to join the Cu(II) ions into a 3Dstructure (Fig. 4). The 3D framework of BUC-62 is also describedas coordination polymeric layers, [Cu2(tib)2]n4n+ (Fig. 4), bridgedby (MoO4)2� ligands through the Cu1–N2 and Cu2–N4 coordinatedbonds.

The tib ligand plays very different roles in BUC-60, BUC-61 andBUC-62. In detail, the tib ligand acts as a bidentate linker in BUC-60, and as a tridentate linker in BUC-61 and 62. In addition, thepartly deprotonated ligand Hadc� in BUC-60 acts as a counter-ion to balance the cationic charge of [Co(tib)]2+; while in BUC-61and 62, Cl� and (MoO4)2� act as counter-ions, respectively. Fur-thermore, the tib ligand in the CP BUC-61 acts as a tridentatebridging linker to join two Zn(II) atoms to form an approximatelyrectangular metallamacrocycle and to join the third Zn(II) atominto a 1D infinite chain; however, in MOF BUC-62, the tib ligandsact as tridentate bridging ligands to join the Cu(II) atoms to forma three-dimension framework.

3.4. Thermal properties

The thermal stabilities of the three coordination compoundswere examined from 70 to 800 �C under a nitrogen gas stream ata heating rate of 10 �C min�1, as shown in Fig. 5 and Table 3. TakingBUC-60 as an example, the thermal decomposition process of BUC-60 can be divided into two stages. The first weight loss of 35.3%(calcd. 35.3%) in the temperature range 375–435 �C corresponds

well to the removal of the tib ligand. The second weight loss ofabout 53.8% (calcd. 55.1%) occurs in the temperature range 435–465 �C and can be assigned to the removal of the Hadc� ligand.The final residue of 10.9% (calcd: 9.6%) is presumably assigned toCoO, resulting from the rich nitrogen gas environment.

3.5. Photoluminescence properties

Zn(II)-based coordination polymers have been widely investi-gated for photoluminescent properties [36–38]. Hence, in the pre-sent study, the emission spectra of BUC-61 along with the free tibligand were examined in the solid state at room temperature. Themaximum emission at a wavelength of 405 nm with an excitationwavelength of 360 nm can be assigned to the p⁄–p transition of thefree tib ligand [33,39–43]. As shown in Fig. 6, an intense band wasfound at 412 nm (kex = 360 nm) for BUC-61, which is similar to thefree tib ligand. It is difficult to oxidize or reduce the Zn(G) ion, withthe d10 Configuration [41], which is the reason that the emission ofBUC-61 is neither metal-to-ligand charge transfer (MLCT) norligand-to-metal charge transfer (LMCT) in nature [44–46]. There-fore, it may be tentatively be ascribed to an intraligand transitionof tib or a ligand-to-ligand charge transition (LLCT) [33,41]. Thesmall red shift of the emission maximum between BUC-61 andthe tib ligand is mainly due to the influence of the coordinationof the ligand to the metal atom [47].

3.6. Adsorption experiments

The adsorption performances of BUC-60, BUC-61 and BUC-62toward some typical organic dyes, namely anionic CR, anionicMB13 and cationic MB, were carried out in a batch system. Theadsorption experiments results revealed that both BUC-60 andBUC-61 exhibit good adsorption performances toward CR andMB13. As illustrated in Fig. 7, 91.4% and 90.0% CR (the initial con-centration being 100 mg L�1) could be removed after 30 min con-tact with BUC-60 and BUC-61 as adsorbents, also, after 300 mincontact, 59.2% and 94.4% MB13 (initial concentration: 20 mg L�1)could be adsorbed by BUC-60 and BUC-61, respectively. BothBUC-60 and BUC-61 demonstrated poor adsorption activities tothe cationic MB dye. It is also worth noting that BUC-62 exhibitedweak uptake performances to both anionic dyes (CR and MB13)and the cationic dye (MB). As listed in Table 4, both BUC-60 andBUC-61 present high adsorption capacities toward CR and MB13,much higher than the uptake capacities of activated carbon. Thepossible mechanism involved in the adsorption process of BUC-

Table 3The TGA weight loss of BUC-60, BUC-60 and BUC-62.

First weight loss Second weight loss Residue

T/�C Found/% Calcd./% Comp. T/�C Found/% Calcd./% Comp. Found/% Calcd./% Comp.

BUC-60 375–435 35.3 35.3 tib 435–465 53.8 55.1 Hadc� 10.9 9.6 CoOBUC-61 330–410 21.2 22.2 Cl� 410–655 58.7 54.6 tib 21.2 25.3 ZnOBUC-62 220–365 7.9 7.8 Cl� 365–570 58.6 60.6 tib 33.4 33.4 CuO & MoO4

Fig. 7. UV–vis absorption spectra of CRwith BUC-60 (a), BUC-61 (d), BUC-62 (g);MB13with BUC-60 (b), BUC-61 (e), BUC-62 (h); MBwith BUC-60 (c), BUC-61 (f), BUC-62 (i)as adsorbents.

Table 4The adsorption capacities of BUC-60, BUC-61 and activated carbon toward CR andMB13.

Adsorption capacity (mg g�1) BUC-60 BUC-61 Activate carbon

CR 1949 1992 35MB13 564 209 34

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60 and BUC-61 toward to CR andMB13 is electrostatic interactionsbetween the anionic sulfonic groups of CR and MB13 and the pos-itively charged Co2+ and Zn2+ ions of BUC-60 and BUC-61, respec-tively [48]. Moreover, the p–p interactions between the aromaticrings of CR andMB13 and the aromatic imidazole rings of the coor-dination compounds also should be considered in the adsorptionprocesses of CR and MB13 on BUC-60 and BUC-61, respectively[22,23,49]. Also, BUC-60 can selectively capture anionic dyes mole-

cules from a dye matrix, namely CR andMB (200 mL, CCR = 100 mgL�1 and CMB = 20 mg L�1).

4. Conclusions

In summary, three new coordination compounds based on thetib ligand have been successfully synthesized and structurallycharacterized. The structure analyses indicate that BUC-60, BUC-61 and BUC-62 possessed 0D, 1D and 3D structures, respectively.All the coordination compounds are thermally stable. BUC-61 exhi-bits luminescent activity resulting from an intraligand transition ofthe tib ligand or a ligand-to-ligand charge transition (LLCT). BothBUC-60 and BUC-61 display good capability for adsorption towardthe anionic dyes CR and MB13, which may be contributed to elec-trostatic interactions and p–p stacking interactions. BUC-60 couldalso efficiently separate different organic dyes from their mixturein simulated wastewater.

96 J.-J. Li et al. / Polyhedron 139 (2018) 89–97

Acknowledgements

We give thanks for the financial support from the NationalNatural Science Foundation of China (51578034), Project of Con-struction of Innovative Teams and Teacher Career Developmentfor Universities and Colleges Under Beijing Municipality(IDHT20170508), the Beijing Natural Science Foundation &Scientific Research Key Program of Beijing Municipal Commissionof Education (KZ201410016018), Beijing Talent Project (2016023)and BUCEA Post Graduate Innovation Project (PG2017012).

Appendix A. Supplementary data

CCDC 1491060, 1482298 and 1539469 contains the supplemen-tary crystallographic data for BUC-60, BUC-61 and BUC-62, respec-tively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the CambridgeCrystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.

Supplementary data associated with this article can be found, inthe online version, at https://doi.org/10.1016/j.poly.2017.10.011.

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