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V-shaped dicarboxylate ligands induced structural variation of Zn(II) complexes based on N-heterocyclic ligand from 1D to 3D: Synthesis, structures and luminescence properties
Journal of Molecular Structure 1205 (2020) 127621
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
V-shaped dicarboxylate ligands induced structural variation of Zn(II) complexes based on N-heterocyclic ligand from 1D to 3D: Synthesis, structures and luminescence properties Yungen Ran a, Nan Hao b, Xinlong Wu b, Jinyu Li b, Yajuan Mu b, * a b
Hebei University, Baoding, 071000, PR China College of Traditional Chinese Medicine, Hebei University, Baoding, 071000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 September 2019 Received in revised form 16 December 2019 Accepted 18 December 2019 Available online 23 December 2019
In this work, three V-shaped dicarboxylate ligands, 5-tert-butyl isophthalic acid (H2tbip), 5hydroxyisophthalic acid (H2hip) and 4,40 -carbonyldibenzoic acid (H2cba) were employed as coligands to make a comparison on the structures of Zn(II)-mbbt coordination polymers (mbbt ¼ 1-(2methylbenzimidazol-1-ylmethyl)benzotriazole). Three new complexes, [Zn2(mbbt)(tbip)2]n (1), {[Zn(mbbt)(hip)(H2O)]$2H2O$mbbt}n (2) and [Zn(mbbt)(cba)]n (3) have been synthesized and characterized. Structural analyses indicate that complex 1 displays a 3D 66 topology based on triangular Zn2(COO)3 SBUs; complex 2 shows an infinite 1D chain; complex 3 presents a 2D 44-sql network based on paddle-wheel-like Zn2(COO)4 SBUs. The structural differences of the three complexes suggest that the Vshaped dicarboxylate ligands can tune the structural dimensionality of Zn(II)-mbbt complexes. Furthermore, the photoluminescence properties of 1e3 were studied in the solid state at room temperature. © 2019 Published by Elsevier B.V.
Keywords: V-shaped dicarboxylate ligand N-heterocyclic ligand Structural variation Zn(II) complexes
1. Introduction The rational design and well-controlled synthesis of coordination polymers with definite structures attract great interest in crystal engineering, not only for fascinating variety of architectures and topologies, but also for their extraordinary applications in adsorption and separation, optics, magnetism, catalysis and ion exchange [1e12]. It is well established that the final structures of desired crystalline products are frequently influenced by many factors in the structural assembly process including central metal ions, metal-ligand ratio, organic ligand, solvents, pH values, temperature and so on [13e22]. Among the reported studies, the organic carboxylate anions play a crucial role in directing the resulting architectures [23e26]. Especially, in the reported twoligand assembly systems, aromatic carboxylate anions are often used as the structure directing co-ligands on N-donor-metal complexes. The variation in substituent group, flexibility, length, angle and symmetry of aromatic carboxylate anions can result in a remarkable class of two-ligand complexes with diverse
* Corresponding author. E-mail address: [email protected] (Y. Mu). https://doi.org/10.1016/j.molstruc.2019.127621 0022-2860/© 2019 Published by Elsevier B.V.
architectures. For example, some groups obtained different dimensional networks ranged from one-to three-dimension (1D to 3D) through manipulating the carboxylate ligands in two-ligand complexes [27e29], and others introduced different carboxylate ligands into N-donor-metal system to construct various degrees of interpenetrating networks [30e32]. Obviously, great progress in two-ligand complexes has been made in many investigations on controlling the structural diversity by tuning the carboxylate ligands, and it was vigorously pursued to adjust the complex architectures through the modification of carboxylate ligands. The flexible N-donor ligand 1-(2-methylbenzimidazol-1ylmethyl)benzotriazole (mbbt) would be a powerful building unit for the synthesis of coordination polymers with diverse structures: (1) benzimidazole group and benzotriazole group exhibit strong coordination capacity and can provide more potential coordination sites; (2) benzimidazole group and benzotriazole group can freely twist around the eCH2e group with different angles to form distinct conformations. However, the combination of mbbt and carboxylate ligands to construct coordination polymers has not been investigated. Thus, the development of a comprehensive study in this topic is very necessary. Taking all the above into consideration, we have reacted mbbt
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and Zn(II) salts in the regulation of V-shaped dicarboxylate ligands, and as expected, three different structural complexes, namely, [Zn2(mbbt)(tbip)2]n (1), {[Zn(mbbt)(hip)(H2O)]$2H2O$mbbt}n (2) and [Zn(mbbt)(cba)]n (3) (H2tbip ¼ 5-tert-butyl isophthalic acid, H2hip ¼ 5-hydroxyisophthalic acid, H2cba ¼ 4,40 -carbonyldibenzoic acid) were successfully obtained by hydrothermal reaction. Structural analyses reveal that the V-shaped dicarboxylate ligands can adjust the dimensionality of complexes.
2. Experimental section 2.1. General information and materials All chemicals were commercially available and used as purchased. Ligand 1-(2-methylbenzimidazol-1-ylmethyl)benzotriazole (mbbt) was prepared according to the literatures [33]. IR data were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in the region of 400e4000 cm1. Elemental analyses (C, H and N) were carried out on a Flash EA 1112 elemental analyzer. Powder X-ray diffraction (PXRD) measurements were finished with a Bruker AXS D8 Advance using Cu Ka radiation. Thermal analyses were performed on a Netzsch TG 209 thermal analyzer at a heating rate of 10 C$ min1 in air. The luminescence spectra for the powdered solid samples were measured at room temperature on a Hitachi F-7000 Fluorescence Spectrophotometer. The excitation slit and the emission slit were both 5 nm.
2.2. Synthesis of complexes 2.2.1. Synthesis of [Zn2(mbbt)(tbip)2]n (1) A mixture of Zn(CH3COO)2$2H2O (40.05 mg, 0.15 mmol), mbbt (26.3 mg, 0.1 mmol), H2tbip (22.2 mg, 0.1 mmol) and NaOH (8.0 mg, 0.2 mmol) in 10 mL distilled H2O was kept in a 25 mL Teflon-lined stainless steel vessel at 120 C for three days. After the mixture was cooled to room temperature at a rate of 5 C/h, colorless crystals suitable for X-ray diffraction were obtained with a yield of 65% (based on Zn). Anal. Calcd for C39H37N5O8Zn2 (%): C, 56.13; H, 4.47; N, 8.39. Found: C, 56.19; H, 4.43; N, 8.30. IR (cm1, KBr): 3069(w), 2963(s), 2904(w), 2867(w), 1640(s), 1590(m), 1558(w), 1454(s), 1374(s), 1343(w), 1309(w), 1272(m), 1237(w), 1175(w), 1156(w), 1136(w), 1117(w), 989(w), 928(w), 911(w), 869(w), 778(s), 741(s), 712(s), 693(w), 569(w).
2.2.2. Synthesis of {[Zn(mbbt)(hip)(H2O)]·2H2O·mbbt}n (2) The process was similar to 1 except that H2tbip was replaced by H2hip (18.2 mg, 0.1 mmol). Colorless crystals of 2 were obtained with yield 70% based on Zn. Anal. Calcd for C76H70N20O15Zn2 (%): C, 55.85; H, 4.32; N, 17.14. Found: C, 55.90; H, 4.45; N, 17.18. IR (cm1, KBr): 3284(s), 3008(w), 1620(s), 1583(s), 1532(w), 1448(m), 1412(m), 1340(s), 1291(w), 1269(s), 1242(w), 1204(w), 1174(w), 1139(w), 1103(w), 1015(w), 980(w), 902(w), 853(w), 784(s), 741(s), 670(m), 622(w), 570(w).
2.2.3. Synthesis of [Zn(mbbt)(cba)]n (3) The process was similar to 1 except that H2tbip was replaced by H2cba (27.0 mg, 0.1 mmol). Colorless crystals of 3 were obtained with yield 50% based on Zn. Anal. Calcd for C60H42N10O10Zn2 (%): C, 60.36; H, 3.55; N, 11.73. Found: C, 60.45; H, 3.35; N, 11.60. IR (cm1, KBr): 3066(w), 2987(w), 2963(w), 1650(s), 1612(m), 1565(w), 1520(m), 1454(s), 1397(s), 1341(m), 1305(m), 1274(s), 1233(m), 1154(m), 1099(w), 1012(m), 981(s), 930(s), 865(w), 836(m), 786(m), 745(s), 660(w), 629(w), 592(w).
2.3. Crystal structure determination X-ray data were collected on a Bruker SMART APEX-II CCD diffractometer with graphite-monochromated Mo-Ka radiation (l ¼ 0.71073 Å). The data were collected at a temperature of 296(2) K and corrected for Lorentz-polarization effects. The structures were solved by direct methods and refined with a full-matrix leastsquares technique based on F2 with the SHELXL-2014 crystallographic software package [34]. The hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by using geometrical restrains. The tert-butyl group (C10, C11, C12), carboxylate oxygen atoms (O5, O8) and the mbbt ligand is disordered and refined using C atoms, O atoms and N atoms split over two equivalent sites with a total occupancy of 1. Crystallographic crystal data and structure processing parameters for complexes 1e3 are summarized in detail in Table 1. Selected bond lengths and bond angles are listed in Table 2. 3. Results and discussion 3.1. Crystal structure of [Zn2(mbbt)(tbip)2]n (1) The results of crystallographic analysis revealed that 1 crystallizes in orthorhombic system with Pan21 space group. The asymmetric unit of complex 1 consists of two crystallographically independent Zn(II) ions, two tbip2 ligands and one mbbt ligand. As shown in Fig. 1a, Zn1 is in a five coordinated by five carboxylate oxygen atoms from four tbip2 ligands, taking a distorted trigonal bipyramidal geometry. The Zn2 adopts a distorted tetrahedral coordination environment, defined by one nitrogen atom of one mbbt ligand and three carboxylate oxygen atoms from three tbip2 ligands. The ZneO/N bonds distances and OeZneO, OeZneN bond angles are in the range of 1.910(11)e2.20(3) Å and 62.6(12)e 152.9(12) , respectively, all of which are similar to other Zn-based complexes [35,36]. The two kinds of tbip2 ligands take different coordination modes. One kind of tbip2 ligand adopts the m3-mode with one m2-h1:h1 carboxylate group and one m1-h1:h1 carboxylate group. The other kind of tbip2 ligand adopts the m4-mode with two m2-h1:h1 carboxylate groups. The mbbt ligand only adopts a monodentate coordination mode. Further, the Zn(II) ions are connected by tbip2 ligands to form a 3D framework (Fig. 1b), which is composed of the triangular Zn2(COO)3 SBUs (Zn/Zn ¼ 3.456 Å). Topological analysis by TOPOS software [37] was carried out to get insight into the structure of 1. The triangular Zn2(COO)3 SBUs are surrounded by four bridging tbip2 ligands to afford a fourconnected node. So the framework can be simplified as a fourconnected topology with a point symbol of 66 (Fig. 1c). Furthermore, the pp stacking interactions are observed between the phenyl rings (C14eC15eC16eC17eC18eC19) of tbip2 and the triazole rings (N3eN4eN5eC35eC34) of mbbt (the centroid-tocentroid separation of 3.745 Å), which presumably help to reinforce the 3D framework. 3.2. Crystal structure of {[Zn(mbbt)(hip)(H2O)]·2H2O·mbbt}n (2) The results of crystallographic analysis revealed that 2 crystallizes in monoclinic system with P21/c space group. The asymmetric unit of complex 2 is composed of one Zn(II) ion, one hip2 ligand, one coordinated mbbt ligand and one lattice mbbt molecule, one coordinated water molecule and two lattice water molecules (Fig. 2a). The Zn(II) ion displays a distorted octahedral geometry, coordinated by four carboxylate oxygen atoms from two hip2 ligands, one oxygen atom from one coordinated water molecule and one nitrogen atom from one mbbt ligand. The ZneO/N bond distances and OeZneO, OeZneN bond angles vary from 1.9609(17)e
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Table 1 Crystal data and structure refinement details for complexes 1e3a. compound
1
2
3
formula fw T/K l (Mo Ka), Å cryst syst space group a/Å b/Å c/Å a/deg b/deg g/deg V/Å3 Z Dc/g$cm3 Reflns collected/unique R(int) Abs coeff/mm1 F(000) GOF R1 [I > 2s(I)] a wR2 (all data) b P P a R1 ¼ ׀׀Fo׀׀Fc ׀/׀׀Fo׀. P P b 2 wR2 ¼ [ w(Fo F2c )2/ w(F2o)2]1/2.
C78H74N10O16Zn4 1668.95 296(2) 0.71073 Orthorhombic Pan21 12.9318(6) 17.9248(9) 16.6091(9) 90 90 90 3850.0(3) 2 1.440 57376/8847 0.0887 1.304 1720 1.058 0.0928 0.2513
C76H70N20O15Zn2 1634.26 296(2) 0.71073 Monoclinic P21/c 9.4684(3) 27.6650(10) 14.5446(5) 90 101.938(2) 90 3534.0(2) 2 1.536 54742/8136 0.0797 0.765 1692 1.062 0.0476 0.1198
C60H42N10O10Zn2 1193.77 296(2) 0.71073 Monoclinic P2/n 14.222(3) 17.250(3) 23.230(5) 90 103.94(3) 90 5531(2) 4 1.434 71698/9750 0.0896 0.937 2448 1.062 0.0491 0.1076
Table 2 Selected bond lengths (Å) and bond angles (deg) for complexes 1e3a. Complex 1 Zn(1)eO(1) Zn(1)eO(5) Zn(1)eO(8) #2 Zn(2)eO(4) #1 Zn(2)eN(1) O(1)-Zn(1)-O(5) O(3)#1-Zn(1)-O(1) O(3) #1 -Zn(1)-O(7) #2 O(5) -Zn(1)-O(7) #2 O(7) #2-Zn(1)-O(8) #2 O(2)-Zn(2)-O(6) O(4)#1-Zn(2)-O(6) O(6) -Zn(2)-N(1) Complex 2 Zn(1)eO(1) Zn(1)eO(4)#1 O(1)-Zn(1)-O(6) O(4)#1-Zn(1)-O(6) O(1)-Zn(1)-N(1) Complex 3 Zn(1)eO(1) Zn(1)eO(6)#1 Zn(1)eN(6) Zn(2)eO(2) Zn(2)eO(8)#2 O(1)-Zn(1)-O(3) #1 O(3)#1-Zn(1)-N(6) O(3)#1-Zn(1)-O(9)#2 O(1)-Zn(1)-O(6) N(6) -Zn(1)-O(6) N(1) -Zn(2)-O(8)#2 O(8)#2-Zn(2)-O(2) O(8)#2-Zn(2)-O(7) N(1) -Zn(1)-O(4)#1 O(2) -Zn(1)-O(4)#1
1.962(12) 2.04(3) 2.20(3) 1.943(12) 1.96(4) 103.0(10) 108.4(6) 152.9(12) 73.5(14) 62.6(12) 117.9(7) 106.8(7) 95.8(12)
Zn(1)eO(3) #1 Zn(1)eO(7)#2 Zn(2)eO(2) Zn(2)eO(6) #2 O(1)-Zn(1)-O(7) #2 O(1)-Zn(1)-O(8)#2 O(3) #1-Zn(1)-O(5) O(3)#1-Zn(1)-O(8) #2 O(5) -Zn(1)-O(8) #2 O(2) -Zn(2)-O(4)#1 O(2)-Zn(2)-N(1) O(4) #1-Zn(2)-N(1)
1.950(12) 2.14 (3) 1.910(11) 1.949(13) 95.9(11) 82.1(8) 110.9(12) 108.1(9) 136.2(14) 116.4(6) 115.9(11) 101.0(11)
1.9701(17) 1.9609(17) 101.22(7) 111.11(8) 100.13(8)
Zn(1)eO(6) Zn(1)eN(1) O(4)#1-Zn(1)-O(1) O(4)#1-Zn(1)-N(1) O(6)-Zn(1)-N(1)
2.0111(18) 2.035(2) 112.63(8) 123.30(8) 105.82(8)
2.010(3) 2.072(3) 2.023(3) 2.039(3) 2.035(3) 90.72(13) 107.25(13) 84.65(13) 87.42(13) 100.39(12) 105.41(13) 155.79(13) 87.75(12) 97.05(13) 88.38(12)
Zn(1)eO(3)#1 Zn(1)eO(9)#2 Zn(2)eN(1) Zn(1)eO(7) Zn(1)eO(4)#1 O(1) -Zn(1)-N(6) O(1) -Zn(1)-O(9)#2 N(6)-Zn(1)-O(9) #2 O(3) #1-Zn(1)-O(6) O(9)#2 -Zn(1)-O(6) N(1)-Zn(2)-O(2) N(1) -Zn(2)-O(7) O(2) -Zn(2)-O(7) O(8)#2-Zn(2)-O(4) #1 O(7) -Zn(2)-O(4) #1
2.022(3) 2.067(3) 2.021(3) 2.042(3) 2.051(3) 102.39(13) 157.91(13) 99.61(13) 152.03(12) 86.68(13) 98.80(13) 101.56(13) 87.58(12) 88.50(12) 161.35(12)
a Symmetry transformations used to generate equivalent atoms in complex (1): #1 -x,-y, 0.5 þ z; #2 - 0.5 þ x,0.5-y, þz. (2): #1 1 þ x,þy,þz. (3): #1 þ x,2.5-y,0.5 þ z; #2 þ x,1.5-y,0.5 þ z.
2.035(2) Å and 100.13(8)e123.30(8) , respectively, which are within the reasonable range of observed values for other sixcoordinated Zn(II) complexes [38]. Each carboxylate group of hip2 ligand adopts a m1-h1:h1 mode. The Zn(II) ions are bridged by
hip2 ligand to form an infinite 1D chain (Fig. 2b). The mbbt ligands decorate on one side of the 1D chain with a monodentate coordination mode. Further, the adjacent chains are held together by pp stacking interactions between the phenyl ring
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Fig. 2. (a) Coordination environment around the Zn(II) center in 2. Hydrogen atoms and solvent molecules are omitted for clarity. Symmetry code: A ¼ 1 þ x, y, z. (b) The infinite 1D chain of complex 2.
structure. The structural stability is provided by the pp stacking interactions between midazole rings of coordinated and uncoordinated mbbt ligands (the centroid-to-centroid separation of 3.716 Å). The hydrogen bonding interactions (O6/N5 ¼ 2.939 Å, O5/O2 ¼ 2.727 Å and O7/O8 ¼ 2.537 Å) also stabilize the structure. 3.3. Crystal structure of [Zn(mbbt)(cba)]n (3)
Fig. 1. (a) Coordination environment around the Zn(II) center in 1. Hydrogen atoms are omitted for clarity. Symmetry codes: A ¼ -x, -y, 0.5 þ z; B ¼ 0.5 þ x, 0.5-y, z. (b) The 3D architecture constructed by tbip2 ligands. (c) Schematic representation of the topology.
(C2eC3eC4eC5eC6eC7) of hip2 and phenyl ring (C17eC18eC19eC20eC21eC22) of benzotriazole group with a centroid-to-centroid separation of 3.729 Å to afford a 2D layered
The results of crystallographic analysis revealed that 3 crystallizes in triclinic system with P21/c space group. The asymmetric unit of complex 3 possesses two inequivalent Zn(II) ions, two cba2 ligands and two mbbt ligands. As shown in Fig. 3a, the two crystallographically independent Zn(II) ions (Zn1 and Zn2) take the similar tetragonal-pyramidal geometry and have the same coordination environment, which are completed by four oxygen atoms from four cba2 ligands and one nitrogen atom of one mbbt ligand, respectively. The ZneO/N bonds distances and OeZneO, OeZneN bond angles range from 2.010(3)e2.072(3) Å and 84.65(13) 157.91(13) , respectively, all of which are within the reasonable range of those reported for other five-coordinated Zn(II) complexes [39]. The two kinds of cba2 ligands adopt the same coordination mode. Each kind of cba2 ligand connects four Zn(II) ions in which each carboxylate group possesses a m2-h1:h1 fashion. The Zn(II) ions are connected by cba2 ligand to give rise to a 2D layered structure, which is composed of the paddle-wheel-like Zn2(COO)4 SBUs (Zn/Zn ¼ 3.044 Å) (Fig. 3b). The two kinds of mbbt ligands also adopt the monodentate coordination mode. From the topological view, if the Zn2(COO)4 SBUs are simplified as nodes, complex 3 shows a 44-sql topology (Fig. 3c). In addition, the adjacent layers are interdigitated to each other and arranged into a 3D supramolecular architecture via the pp stacking interactions between the midazole rings and the triazole rings (the centroid-tocentroid distance of 3.615 Å).
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H2tbip was replaced by H2hip, complex 2 was obtained. The Zn(II) ions are bridged by hip2 ligands to form an infinite 1D chain. When the long V-shaped bridging ligand H2cba was used in the synthesis of 3, the 2D structure with paddle-wheel-like Zn2(COO)4 SBUs was generated. In complexes 1e3, ligand mbbt only takes monodentate coordination fashion, which has no effect on the formation of structural dimensionality of complexes. Therefore, the V-shaped dicarboxylate ligands play an important role in the regulation of the structural dimensionality of the complexes. 3.4. PXRD patterns, thermogravimetric analyses and IR spectra The PXRD patterns of complexes 1e3 are shown in Fig. S1. The peak positions of the simulated and experimental PXRD patterns are in line with each other, indicating the pure phase of these complexes. In order to further investigate the thermal stability of the compounds, the thermogravimetric analyses of these complexes were examined (Fig. S2). Complex 1 is thermally stable under 220 C and then experiences the first weight loss corresponding to the release of mbbt ligands (obsd: 30.47%, calcd: 31.51%). The second weight loss occurs from 431 to 516 C due to the decomposition of the coordination framework with ZnO as the residue (obsd: 17.57%, calcd: 19.15%). The TGA curve of 2 shows that it undergoes the initial weight loss from 119 to 166 C corresponding to the lattice water molecules (obsd: 5.03%, calcd: 4.41%). Then, complex 2 begins to lose the lattice mbbt ligand at 233 C (obsd: 32.01%, calcd: 32.18%). Subsequently, the structure occurs to decompose in the temperature range of 312e521 C and the ultimate residue corresponds to the formation of ZnO (obsd: 8.68%, calcd: 9.78%). For complex 3, there is no weight loss until the decomposition of the framework occurs at 215 C that ends at 530 C. The final residue can be assigned to ZnO (obsd: 11.52%, calcd: 13.38%). In the IR spectra of complexes 1e3, the absence of band in the region 1690e1730 cm1 (the OeH vibrations of eCOOH groups) indicates the complete deprotonation of the eCOOH in 1e3 [40]. The asymmetric and symmetric stretching vibration bands of eCOOH groups appear at 1640 and 1454 cm1 for 1, 1620 and 1448 cm1 for 2, 1650 and 1454 cm1 for 3, respectively, suggesting that the eCOOH groups adopt different coordination modes in 1e3. The analyses of IR spectra of 1e3 are consistent with X-ray diffraction analyses. 3.5. Photoluminescence properties of the complexes
Fig. 3. (a) Coordination environment around the Zn(II) center in 3. Hydrogen atoms are omitted for clarity. Symmetry codes: A ¼ x, 2.5-y, 0.5 þ z; B ¼ x, 1.5-y, 0.5 þ z. (b) The layered structure based on the paddle-wheel-like [Zn2(COO)4]. (c) The 2D network with 44-sql topology.
From the structural descriptions above, the V-shaped dicarboxylate ligands play an important role in directing the structures of the resulting Zn(II) complexes. In complex 1, H2tbip ligands were used as the V-shaped ligands. Zn(II) ions are linked by tbip2 ligands to form triangular Zn2(COO)3 SBUs. The SBUs are further connected by tbip2 ligands to obtain a 3D framework. When
Solid-state photoluminescent behavior of complexes 1e3 as well as ligand mbbt and V-shaped dicarboxylate ligands were investigated at room temperature and exhibited in Fig. S3. Ligand mbbt displays an emission band at 428 nm upon excitation at 352 nm, which may be attributed to p*/p transitions. The dicarboxylate ligands H2tbip and H2hip show strong emission bands at 321 nm (lex ¼ 273 nm) and 364 nm (lex ¼ 277 nm), respectively. The dicarboxylate ligand H2cba presents a weak emission band at 478 nm (lex ¼ 439 nm). The emission bands of the three dicarboxylate ligands can be assigned to the p*/n transition. Complexes 1e3 exhibited photoluminescence with emission maxima at 440 nm (lex ¼ 369 nm), 440 nm (lex ¼ 365 nm) and 453 nm (lex ¼ 403 nm), respectively. The resemblance between the emission spectra of complexes 1e3 and that of free ligand mbbt indicates that the luminescence of complexes 1e3 is mbbt-based emission. It is considered that the energy transfer may occur from the dicarboxylate ligands to the mbbt ligand, and therefore, these complexes exhibit the emission of mbbt ligand. For 1 and 3, the possibility of cluster-centered transitions cannot be excluded because of the metal$$$metal distance in the cluster is less than
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3.5 Å [41]. Moreover, complex 1 shows very strong luminescence compared with the ligand mbbt. The luminescence enhancement in complex 1 may result from increased the rigidity of the ligand upon metal coordination that reduces the loss of energy by radiationless decay [42e44]. In complex 2, the quenching of photoluminescent emission is pronounced due to the vibrational behavior of some coordinated or lattice water molecules [45,46]. 4. Conclusions In summary, we successfully synthesized three Zn(II) complexes with varying dimensionalities based on V-shaped dicarboxylate acids and N-heterocyclic ligand mbbt. Complex 1 shows a 3D framework based on triangular Zn2(COO)3 SBUs; complex 2 displays an infinite 1D chain; complex 3 exhibits 2D 44-sql network based on Zn2(COO)4 SBUs. Structural analyses show that the three complexes with the same metal components and mbbt ligands present dimensionality variation, which are derived from V-shaped dicarboxylate coligands. Therefore, this work demonstrates that Vshaped dicarboxylate coligands play a crucial role in the structural type and the dimensionality variation of the Zn(II) complexes. Author contributions section Yungen Ran: Writing- Reviewing and Editing, Resources, Software. Nan Hao: Investigation. Xinlong Wu: Investigation. Jinyu Li: Software. Yajuan Mu: Conceptualization, Methodology, Software, Data curation, Writing-Original Draft. Acknowledgment We gratefully acknowledge the financial support by the Natural Science Foundation of Hebei Province (No. B2018201226), the Education Department of Hebei Province (No. ZD2018027), the Youth Top Talent Project of Hebei Province and the National Natural Science Foundation of China (No. 21301045). Appendix A. Supplementary data Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center, CCDC reference numbers 1858334e1858336 for complexes 1e3, respectively. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336033). Details on XRD patterns, TGA curves, photoluminescence spectra and tables are list in supplementary content. Appendix B. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.127621. References [1] L.L. Yu, X.M. Wang, M.L. Cheng, H.R. Rong, Y.D. Song, Q. Liu, Cryst. Growth Des. 18 (2018) 280e285. [2] H. Furukawa, K.E. Cordova, M. O’Keeffe, O.M. Yaghi, Science 341 (2013) 1230444.
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
V-shaped dicarboxylate ligands induced structural variation of Zn(II) complexes based on N-heterocyclic ligand from 1D to 3D: Synthesis, structures and luminescence properties Yungen Ran a, Nan Hao b, Xinlong Wu b, Jinyu Li b, Yajuan Mu b, * a b
Hebei University, Baoding, 071000, PR China College of Traditional Chinese Medicine, Hebei University, Baoding, 071000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 September 2019 Received in revised form 16 December 2019 Accepted 18 December 2019 Available online 23 December 2019
In this work, three V-shaped dicarboxylate ligands, 5-tert-butyl isophthalic acid (H2tbip), 5hydroxyisophthalic acid (H2hip) and 4,40 -carbonyldibenzoic acid (H2cba) were employed as coligands to make a comparison on the structures of Zn(II)-mbbt coordination polymers (mbbt ¼ 1-(2methylbenzimidazol-1-ylmethyl)benzotriazole). Three new complexes, [Zn2(mbbt)(tbip)2]n (1), {[Zn(mbbt)(hip)(H2O)]$2H2O$mbbt}n (2) and [Zn(mbbt)(cba)]n (3) have been synthesized and characterized. Structural analyses indicate that complex 1 displays a 3D 66 topology based on triangular Zn2(COO)3 SBUs; complex 2 shows an infinite 1D chain; complex 3 presents a 2D 44-sql network based on paddle-wheel-like Zn2(COO)4 SBUs. The structural differences of the three complexes suggest that the Vshaped dicarboxylate ligands can tune the structural dimensionality of Zn(II)-mbbt complexes. Furthermore, the photoluminescence properties of 1e3 were studied in the solid state at room temperature. © 2019 Published by Elsevier B.V.
Keywords: V-shaped dicarboxylate ligand N-heterocyclic ligand Structural variation Zn(II) complexes
1. Introduction The rational design and well-controlled synthesis of coordination polymers with definite structures attract great interest in crystal engineering, not only for fascinating variety of architectures and topologies, but also for their extraordinary applications in adsorption and separation, optics, magnetism, catalysis and ion exchange [1e12]. It is well established that the final structures of desired crystalline products are frequently influenced by many factors in the structural assembly process including central metal ions, metal-ligand ratio, organic ligand, solvents, pH values, temperature and so on [13e22]. Among the reported studies, the organic carboxylate anions play a crucial role in directing the resulting architectures [23e26]. Especially, in the reported twoligand assembly systems, aromatic carboxylate anions are often used as the structure directing co-ligands on N-donor-metal complexes. The variation in substituent group, flexibility, length, angle and symmetry of aromatic carboxylate anions can result in a remarkable class of two-ligand complexes with diverse
* Corresponding author. E-mail address: [email protected] (Y. Mu). https://doi.org/10.1016/j.molstruc.2019.127621 0022-2860/© 2019 Published by Elsevier B.V.
architectures. For example, some groups obtained different dimensional networks ranged from one-to three-dimension (1D to 3D) through manipulating the carboxylate ligands in two-ligand complexes [27e29], and others introduced different carboxylate ligands into N-donor-metal system to construct various degrees of interpenetrating networks [30e32]. Obviously, great progress in two-ligand complexes has been made in many investigations on controlling the structural diversity by tuning the carboxylate ligands, and it was vigorously pursued to adjust the complex architectures through the modification of carboxylate ligands. The flexible N-donor ligand 1-(2-methylbenzimidazol-1ylmethyl)benzotriazole (mbbt) would be a powerful building unit for the synthesis of coordination polymers with diverse structures: (1) benzimidazole group and benzotriazole group exhibit strong coordination capacity and can provide more potential coordination sites; (2) benzimidazole group and benzotriazole group can freely twist around the eCH2e group with different angles to form distinct conformations. However, the combination of mbbt and carboxylate ligands to construct coordination polymers has not been investigated. Thus, the development of a comprehensive study in this topic is very necessary. Taking all the above into consideration, we have reacted mbbt
2
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and Zn(II) salts in the regulation of V-shaped dicarboxylate ligands, and as expected, three different structural complexes, namely, [Zn2(mbbt)(tbip)2]n (1), {[Zn(mbbt)(hip)(H2O)]$2H2O$mbbt}n (2) and [Zn(mbbt)(cba)]n (3) (H2tbip ¼ 5-tert-butyl isophthalic acid, H2hip ¼ 5-hydroxyisophthalic acid, H2cba ¼ 4,40 -carbonyldibenzoic acid) were successfully obtained by hydrothermal reaction. Structural analyses reveal that the V-shaped dicarboxylate ligands can adjust the dimensionality of complexes.
2. Experimental section 2.1. General information and materials All chemicals were commercially available and used as purchased. Ligand 1-(2-methylbenzimidazol-1-ylmethyl)benzotriazole (mbbt) was prepared according to the literatures [33]. IR data were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in the region of 400e4000 cm1. Elemental analyses (C, H and N) were carried out on a Flash EA 1112 elemental analyzer. Powder X-ray diffraction (PXRD) measurements were finished with a Bruker AXS D8 Advance using Cu Ka radiation. Thermal analyses were performed on a Netzsch TG 209 thermal analyzer at a heating rate of 10 C$ min1 in air. The luminescence spectra for the powdered solid samples were measured at room temperature on a Hitachi F-7000 Fluorescence Spectrophotometer. The excitation slit and the emission slit were both 5 nm.
2.2. Synthesis of complexes 2.2.1. Synthesis of [Zn2(mbbt)(tbip)2]n (1) A mixture of Zn(CH3COO)2$2H2O (40.05 mg, 0.15 mmol), mbbt (26.3 mg, 0.1 mmol), H2tbip (22.2 mg, 0.1 mmol) and NaOH (8.0 mg, 0.2 mmol) in 10 mL distilled H2O was kept in a 25 mL Teflon-lined stainless steel vessel at 120 C for three days. After the mixture was cooled to room temperature at a rate of 5 C/h, colorless crystals suitable for X-ray diffraction were obtained with a yield of 65% (based on Zn). Anal. Calcd for C39H37N5O8Zn2 (%): C, 56.13; H, 4.47; N, 8.39. Found: C, 56.19; H, 4.43; N, 8.30. IR (cm1, KBr): 3069(w), 2963(s), 2904(w), 2867(w), 1640(s), 1590(m), 1558(w), 1454(s), 1374(s), 1343(w), 1309(w), 1272(m), 1237(w), 1175(w), 1156(w), 1136(w), 1117(w), 989(w), 928(w), 911(w), 869(w), 778(s), 741(s), 712(s), 693(w), 569(w).
2.2.2. Synthesis of {[Zn(mbbt)(hip)(H2O)]·2H2O·mbbt}n (2) The process was similar to 1 except that H2tbip was replaced by H2hip (18.2 mg, 0.1 mmol). Colorless crystals of 2 were obtained with yield 70% based on Zn. Anal. Calcd for C76H70N20O15Zn2 (%): C, 55.85; H, 4.32; N, 17.14. Found: C, 55.90; H, 4.45; N, 17.18. IR (cm1, KBr): 3284(s), 3008(w), 1620(s), 1583(s), 1532(w), 1448(m), 1412(m), 1340(s), 1291(w), 1269(s), 1242(w), 1204(w), 1174(w), 1139(w), 1103(w), 1015(w), 980(w), 902(w), 853(w), 784(s), 741(s), 670(m), 622(w), 570(w).
2.2.3. Synthesis of [Zn(mbbt)(cba)]n (3) The process was similar to 1 except that H2tbip was replaced by H2cba (27.0 mg, 0.1 mmol). Colorless crystals of 3 were obtained with yield 50% based on Zn. Anal. Calcd for C60H42N10O10Zn2 (%): C, 60.36; H, 3.55; N, 11.73. Found: C, 60.45; H, 3.35; N, 11.60. IR (cm1, KBr): 3066(w), 2987(w), 2963(w), 1650(s), 1612(m), 1565(w), 1520(m), 1454(s), 1397(s), 1341(m), 1305(m), 1274(s), 1233(m), 1154(m), 1099(w), 1012(m), 981(s), 930(s), 865(w), 836(m), 786(m), 745(s), 660(w), 629(w), 592(w).
2.3. Crystal structure determination X-ray data were collected on a Bruker SMART APEX-II CCD diffractometer with graphite-monochromated Mo-Ka radiation (l ¼ 0.71073 Å). The data were collected at a temperature of 296(2) K and corrected for Lorentz-polarization effects. The structures were solved by direct methods and refined with a full-matrix leastsquares technique based on F2 with the SHELXL-2014 crystallographic software package [34]. The hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by using geometrical restrains. The tert-butyl group (C10, C11, C12), carboxylate oxygen atoms (O5, O8) and the mbbt ligand is disordered and refined using C atoms, O atoms and N atoms split over two equivalent sites with a total occupancy of 1. Crystallographic crystal data and structure processing parameters for complexes 1e3 are summarized in detail in Table 1. Selected bond lengths and bond angles are listed in Table 2. 3. Results and discussion 3.1. Crystal structure of [Zn2(mbbt)(tbip)2]n (1) The results of crystallographic analysis revealed that 1 crystallizes in orthorhombic system with Pan21 space group. The asymmetric unit of complex 1 consists of two crystallographically independent Zn(II) ions, two tbip2 ligands and one mbbt ligand. As shown in Fig. 1a, Zn1 is in a five coordinated by five carboxylate oxygen atoms from four tbip2 ligands, taking a distorted trigonal bipyramidal geometry. The Zn2 adopts a distorted tetrahedral coordination environment, defined by one nitrogen atom of one mbbt ligand and three carboxylate oxygen atoms from three tbip2 ligands. The ZneO/N bonds distances and OeZneO, OeZneN bond angles are in the range of 1.910(11)e2.20(3) Å and 62.6(12)e 152.9(12) , respectively, all of which are similar to other Zn-based complexes [35,36]. The two kinds of tbip2 ligands take different coordination modes. One kind of tbip2 ligand adopts the m3-mode with one m2-h1:h1 carboxylate group and one m1-h1:h1 carboxylate group. The other kind of tbip2 ligand adopts the m4-mode with two m2-h1:h1 carboxylate groups. The mbbt ligand only adopts a monodentate coordination mode. Further, the Zn(II) ions are connected by tbip2 ligands to form a 3D framework (Fig. 1b), which is composed of the triangular Zn2(COO)3 SBUs (Zn/Zn ¼ 3.456 Å). Topological analysis by TOPOS software [37] was carried out to get insight into the structure of 1. The triangular Zn2(COO)3 SBUs are surrounded by four bridging tbip2 ligands to afford a fourconnected node. So the framework can be simplified as a fourconnected topology with a point symbol of 66 (Fig. 1c). Furthermore, the pp stacking interactions are observed between the phenyl rings (C14eC15eC16eC17eC18eC19) of tbip2 and the triazole rings (N3eN4eN5eC35eC34) of mbbt (the centroid-tocentroid separation of 3.745 Å), which presumably help to reinforce the 3D framework. 3.2. Crystal structure of {[Zn(mbbt)(hip)(H2O)]·2H2O·mbbt}n (2) The results of crystallographic analysis revealed that 2 crystallizes in monoclinic system with P21/c space group. The asymmetric unit of complex 2 is composed of one Zn(II) ion, one hip2 ligand, one coordinated mbbt ligand and one lattice mbbt molecule, one coordinated water molecule and two lattice water molecules (Fig. 2a). The Zn(II) ion displays a distorted octahedral geometry, coordinated by four carboxylate oxygen atoms from two hip2 ligands, one oxygen atom from one coordinated water molecule and one nitrogen atom from one mbbt ligand. The ZneO/N bond distances and OeZneO, OeZneN bond angles vary from 1.9609(17)e
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3
Table 1 Crystal data and structure refinement details for complexes 1e3a. compound
1
2
3
formula fw T/K l (Mo Ka), Å cryst syst space group a/Å b/Å c/Å a/deg b/deg g/deg V/Å3 Z Dc/g$cm3 Reflns collected/unique R(int) Abs coeff/mm1 F(000) GOF R1 [I > 2s(I)] a wR2 (all data) b P P a R1 ¼ ׀׀Fo׀׀Fc ׀/׀׀Fo׀. P P b 2 wR2 ¼ [ w(Fo F2c )2/ w(F2o)2]1/2.
C78H74N10O16Zn4 1668.95 296(2) 0.71073 Orthorhombic Pan21 12.9318(6) 17.9248(9) 16.6091(9) 90 90 90 3850.0(3) 2 1.440 57376/8847 0.0887 1.304 1720 1.058 0.0928 0.2513
C76H70N20O15Zn2 1634.26 296(2) 0.71073 Monoclinic P21/c 9.4684(3) 27.6650(10) 14.5446(5) 90 101.938(2) 90 3534.0(2) 2 1.536 54742/8136 0.0797 0.765 1692 1.062 0.0476 0.1198
C60H42N10O10Zn2 1193.77 296(2) 0.71073 Monoclinic P2/n 14.222(3) 17.250(3) 23.230(5) 90 103.94(3) 90 5531(2) 4 1.434 71698/9750 0.0896 0.937 2448 1.062 0.0491 0.1076
Table 2 Selected bond lengths (Å) and bond angles (deg) for complexes 1e3a. Complex 1 Zn(1)eO(1) Zn(1)eO(5) Zn(1)eO(8) #2 Zn(2)eO(4) #1 Zn(2)eN(1) O(1)-Zn(1)-O(5) O(3)#1-Zn(1)-O(1) O(3) #1 -Zn(1)-O(7) #2 O(5) -Zn(1)-O(7) #2 O(7) #2-Zn(1)-O(8) #2 O(2)-Zn(2)-O(6) O(4)#1-Zn(2)-O(6) O(6) -Zn(2)-N(1) Complex 2 Zn(1)eO(1) Zn(1)eO(4)#1 O(1)-Zn(1)-O(6) O(4)#1-Zn(1)-O(6) O(1)-Zn(1)-N(1) Complex 3 Zn(1)eO(1) Zn(1)eO(6)#1 Zn(1)eN(6) Zn(2)eO(2) Zn(2)eO(8)#2 O(1)-Zn(1)-O(3) #1 O(3)#1-Zn(1)-N(6) O(3)#1-Zn(1)-O(9)#2 O(1)-Zn(1)-O(6) N(6) -Zn(1)-O(6) N(1) -Zn(2)-O(8)#2 O(8)#2-Zn(2)-O(2) O(8)#2-Zn(2)-O(7) N(1) -Zn(1)-O(4)#1 O(2) -Zn(1)-O(4)#1
1.962(12) 2.04(3) 2.20(3) 1.943(12) 1.96(4) 103.0(10) 108.4(6) 152.9(12) 73.5(14) 62.6(12) 117.9(7) 106.8(7) 95.8(12)
Zn(1)eO(3) #1 Zn(1)eO(7)#2 Zn(2)eO(2) Zn(2)eO(6) #2 O(1)-Zn(1)-O(7) #2 O(1)-Zn(1)-O(8)#2 O(3) #1-Zn(1)-O(5) O(3)#1-Zn(1)-O(8) #2 O(5) -Zn(1)-O(8) #2 O(2) -Zn(2)-O(4)#1 O(2)-Zn(2)-N(1) O(4) #1-Zn(2)-N(1)
1.950(12) 2.14 (3) 1.910(11) 1.949(13) 95.9(11) 82.1(8) 110.9(12) 108.1(9) 136.2(14) 116.4(6) 115.9(11) 101.0(11)
1.9701(17) 1.9609(17) 101.22(7) 111.11(8) 100.13(8)
Zn(1)eO(6) Zn(1)eN(1) O(4)#1-Zn(1)-O(1) O(4)#1-Zn(1)-N(1) O(6)-Zn(1)-N(1)
2.0111(18) 2.035(2) 112.63(8) 123.30(8) 105.82(8)
2.010(3) 2.072(3) 2.023(3) 2.039(3) 2.035(3) 90.72(13) 107.25(13) 84.65(13) 87.42(13) 100.39(12) 105.41(13) 155.79(13) 87.75(12) 97.05(13) 88.38(12)
Zn(1)eO(3)#1 Zn(1)eO(9)#2 Zn(2)eN(1) Zn(1)eO(7) Zn(1)eO(4)#1 O(1) -Zn(1)-N(6) O(1) -Zn(1)-O(9)#2 N(6)-Zn(1)-O(9) #2 O(3) #1-Zn(1)-O(6) O(9)#2 -Zn(1)-O(6) N(1)-Zn(2)-O(2) N(1) -Zn(2)-O(7) O(2) -Zn(2)-O(7) O(8)#2-Zn(2)-O(4) #1 O(7) -Zn(2)-O(4) #1
2.022(3) 2.067(3) 2.021(3) 2.042(3) 2.051(3) 102.39(13) 157.91(13) 99.61(13) 152.03(12) 86.68(13) 98.80(13) 101.56(13) 87.58(12) 88.50(12) 161.35(12)
a Symmetry transformations used to generate equivalent atoms in complex (1): #1 -x,-y, 0.5 þ z; #2 - 0.5 þ x,0.5-y, þz. (2): #1 1 þ x,þy,þz. (3): #1 þ x,2.5-y,0.5 þ z; #2 þ x,1.5-y,0.5 þ z.
2.035(2) Å and 100.13(8)e123.30(8) , respectively, which are within the reasonable range of observed values for other sixcoordinated Zn(II) complexes [38]. Each carboxylate group of hip2 ligand adopts a m1-h1:h1 mode. The Zn(II) ions are bridged by
hip2 ligand to form an infinite 1D chain (Fig. 2b). The mbbt ligands decorate on one side of the 1D chain with a monodentate coordination mode. Further, the adjacent chains are held together by pp stacking interactions between the phenyl ring
4
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Fig. 2. (a) Coordination environment around the Zn(II) center in 2. Hydrogen atoms and solvent molecules are omitted for clarity. Symmetry code: A ¼ 1 þ x, y, z. (b) The infinite 1D chain of complex 2.
structure. The structural stability is provided by the pp stacking interactions between midazole rings of coordinated and uncoordinated mbbt ligands (the centroid-to-centroid separation of 3.716 Å). The hydrogen bonding interactions (O6/N5 ¼ 2.939 Å, O5/O2 ¼ 2.727 Å and O7/O8 ¼ 2.537 Å) also stabilize the structure. 3.3. Crystal structure of [Zn(mbbt)(cba)]n (3)
Fig. 1. (a) Coordination environment around the Zn(II) center in 1. Hydrogen atoms are omitted for clarity. Symmetry codes: A ¼ -x, -y, 0.5 þ z; B ¼ 0.5 þ x, 0.5-y, z. (b) The 3D architecture constructed by tbip2 ligands. (c) Schematic representation of the topology.
(C2eC3eC4eC5eC6eC7) of hip2 and phenyl ring (C17eC18eC19eC20eC21eC22) of benzotriazole group with a centroid-to-centroid separation of 3.729 Å to afford a 2D layered
The results of crystallographic analysis revealed that 3 crystallizes in triclinic system with P21/c space group. The asymmetric unit of complex 3 possesses two inequivalent Zn(II) ions, two cba2 ligands and two mbbt ligands. As shown in Fig. 3a, the two crystallographically independent Zn(II) ions (Zn1 and Zn2) take the similar tetragonal-pyramidal geometry and have the same coordination environment, which are completed by four oxygen atoms from four cba2 ligands and one nitrogen atom of one mbbt ligand, respectively. The ZneO/N bonds distances and OeZneO, OeZneN bond angles range from 2.010(3)e2.072(3) Å and 84.65(13) 157.91(13) , respectively, all of which are within the reasonable range of those reported for other five-coordinated Zn(II) complexes [39]. The two kinds of cba2 ligands adopt the same coordination mode. Each kind of cba2 ligand connects four Zn(II) ions in which each carboxylate group possesses a m2-h1:h1 fashion. The Zn(II) ions are connected by cba2 ligand to give rise to a 2D layered structure, which is composed of the paddle-wheel-like Zn2(COO)4 SBUs (Zn/Zn ¼ 3.044 Å) (Fig. 3b). The two kinds of mbbt ligands also adopt the monodentate coordination mode. From the topological view, if the Zn2(COO)4 SBUs are simplified as nodes, complex 3 shows a 44-sql topology (Fig. 3c). In addition, the adjacent layers are interdigitated to each other and arranged into a 3D supramolecular architecture via the pp stacking interactions between the midazole rings and the triazole rings (the centroid-tocentroid distance of 3.615 Å).
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H2tbip was replaced by H2hip, complex 2 was obtained. The Zn(II) ions are bridged by hip2 ligands to form an infinite 1D chain. When the long V-shaped bridging ligand H2cba was used in the synthesis of 3, the 2D structure with paddle-wheel-like Zn2(COO)4 SBUs was generated. In complexes 1e3, ligand mbbt only takes monodentate coordination fashion, which has no effect on the formation of structural dimensionality of complexes. Therefore, the V-shaped dicarboxylate ligands play an important role in the regulation of the structural dimensionality of the complexes. 3.4. PXRD patterns, thermogravimetric analyses and IR spectra The PXRD patterns of complexes 1e3 are shown in Fig. S1. The peak positions of the simulated and experimental PXRD patterns are in line with each other, indicating the pure phase of these complexes. In order to further investigate the thermal stability of the compounds, the thermogravimetric analyses of these complexes were examined (Fig. S2). Complex 1 is thermally stable under 220 C and then experiences the first weight loss corresponding to the release of mbbt ligands (obsd: 30.47%, calcd: 31.51%). The second weight loss occurs from 431 to 516 C due to the decomposition of the coordination framework with ZnO as the residue (obsd: 17.57%, calcd: 19.15%). The TGA curve of 2 shows that it undergoes the initial weight loss from 119 to 166 C corresponding to the lattice water molecules (obsd: 5.03%, calcd: 4.41%). Then, complex 2 begins to lose the lattice mbbt ligand at 233 C (obsd: 32.01%, calcd: 32.18%). Subsequently, the structure occurs to decompose in the temperature range of 312e521 C and the ultimate residue corresponds to the formation of ZnO (obsd: 8.68%, calcd: 9.78%). For complex 3, there is no weight loss until the decomposition of the framework occurs at 215 C that ends at 530 C. The final residue can be assigned to ZnO (obsd: 11.52%, calcd: 13.38%). In the IR spectra of complexes 1e3, the absence of band in the region 1690e1730 cm1 (the OeH vibrations of eCOOH groups) indicates the complete deprotonation of the eCOOH in 1e3 [40]. The asymmetric and symmetric stretching vibration bands of eCOOH groups appear at 1640 and 1454 cm1 for 1, 1620 and 1448 cm1 for 2, 1650 and 1454 cm1 for 3, respectively, suggesting that the eCOOH groups adopt different coordination modes in 1e3. The analyses of IR spectra of 1e3 are consistent with X-ray diffraction analyses. 3.5. Photoluminescence properties of the complexes
Fig. 3. (a) Coordination environment around the Zn(II) center in 3. Hydrogen atoms are omitted for clarity. Symmetry codes: A ¼ x, 2.5-y, 0.5 þ z; B ¼ x, 1.5-y, 0.5 þ z. (b) The layered structure based on the paddle-wheel-like [Zn2(COO)4]. (c) The 2D network with 44-sql topology.
From the structural descriptions above, the V-shaped dicarboxylate ligands play an important role in directing the structures of the resulting Zn(II) complexes. In complex 1, H2tbip ligands were used as the V-shaped ligands. Zn(II) ions are linked by tbip2 ligands to form triangular Zn2(COO)3 SBUs. The SBUs are further connected by tbip2 ligands to obtain a 3D framework. When
Solid-state photoluminescent behavior of complexes 1e3 as well as ligand mbbt and V-shaped dicarboxylate ligands were investigated at room temperature and exhibited in Fig. S3. Ligand mbbt displays an emission band at 428 nm upon excitation at 352 nm, which may be attributed to p*/p transitions. The dicarboxylate ligands H2tbip and H2hip show strong emission bands at 321 nm (lex ¼ 273 nm) and 364 nm (lex ¼ 277 nm), respectively. The dicarboxylate ligand H2cba presents a weak emission band at 478 nm (lex ¼ 439 nm). The emission bands of the three dicarboxylate ligands can be assigned to the p*/n transition. Complexes 1e3 exhibited photoluminescence with emission maxima at 440 nm (lex ¼ 369 nm), 440 nm (lex ¼ 365 nm) and 453 nm (lex ¼ 403 nm), respectively. The resemblance between the emission spectra of complexes 1e3 and that of free ligand mbbt indicates that the luminescence of complexes 1e3 is mbbt-based emission. It is considered that the energy transfer may occur from the dicarboxylate ligands to the mbbt ligand, and therefore, these complexes exhibit the emission of mbbt ligand. For 1 and 3, the possibility of cluster-centered transitions cannot be excluded because of the metal$$$metal distance in the cluster is less than
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3.5 Å [41]. Moreover, complex 1 shows very strong luminescence compared with the ligand mbbt. The luminescence enhancement in complex 1 may result from increased the rigidity of the ligand upon metal coordination that reduces the loss of energy by radiationless decay [42e44]. In complex 2, the quenching of photoluminescent emission is pronounced due to the vibrational behavior of some coordinated or lattice water molecules [45,46]. 4. Conclusions In summary, we successfully synthesized three Zn(II) complexes with varying dimensionalities based on V-shaped dicarboxylate acids and N-heterocyclic ligand mbbt. Complex 1 shows a 3D framework based on triangular Zn2(COO)3 SBUs; complex 2 displays an infinite 1D chain; complex 3 exhibits 2D 44-sql network based on Zn2(COO)4 SBUs. Structural analyses show that the three complexes with the same metal components and mbbt ligands present dimensionality variation, which are derived from V-shaped dicarboxylate coligands. Therefore, this work demonstrates that Vshaped dicarboxylate coligands play a crucial role in the structural type and the dimensionality variation of the Zn(II) complexes. Author contributions section Yungen Ran: Writing- Reviewing and Editing, Resources, Software. Nan Hao: Investigation. Xinlong Wu: Investigation. Jinyu Li: Software. Yajuan Mu: Conceptualization, Methodology, Software, Data curation, Writing-Original Draft. Acknowledgment We gratefully acknowledge the financial support by the Natural Science Foundation of Hebei Province (No. B2018201226), the Education Department of Hebei Province (No. ZD2018027), the Youth Top Talent Project of Hebei Province and the National Natural Science Foundation of China (No. 21301045). Appendix A. Supplementary data Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center, CCDC reference numbers 1858334e1858336 for complexes 1e3, respectively. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336033). Details on XRD patterns, TGA curves, photoluminescence spectra and tables are list in supplementary content. Appendix B. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.127621. References [1] L.L. Yu, X.M. Wang, M.L. Cheng, H.R. Rong, Y.D. Song, Q. Liu, Cryst. Growth Des. 18 (2018) 280e285. [2] H. Furukawa, K.E. Cordova, M. O’Keeffe, O.M. Yaghi, Science 341 (2013) 1230444.
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