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Structural diversity and luminescence properties of a series of complexes based on terpyridine-4-carboxylic acid

Ru-Yi ZHANG ,  Xin CHEN ,  Yuan-Yuan GUO ,  Chong LIU ,  Kun-Lin HUANG

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Citation:  Ru-Yi ZHANG, Xin CHEN, Yuan-Yuan GUO, Chong LIU, Kun-Lin HUANG. Structural diversity and luminescence properties of a series of complexes based on terpyridine-4-carboxylic acid[J]. Chinese Journal of Inorganic Chemistry, 2023, 39(5): 928-938. doi: 10.11862/CJIC.2023.047 shu

基于三联吡啶-4-羧酸的系列配合物的结构多样性和发光性质

摘要: 在溶剂热条件下制备了系列新配合物：[Cr2(tpc)2(HCOO)2(OH)2]·4H2O (1)、[Ba(tpc)2(H2O)2]n (2)、[Zn2(tpc)2(NO3)2]n (3)、[Pb(Htpc)(NO3)2]·2H2O (4)和[Rh(Htpc)Cl3]·CH3OH·H2O (5)(Htpc=2，2′∶6，2″-三联吡啶-4-羧酸)。X射线单晶衍射分析表明，有机配体呈4种不同的配位方式；配合物1~5通过C—H…O/N氢键和π…π相互作用形成了新颖的超分子网络。研究了这些配合物的发光性能。在365 nm紫外辐射下，晶体2~5分别呈现绿色、蓝色、蓝紫色和金色。

English

  • 0.   Introduction

    Design and synthesis of multicomponent metalorganic supramolecular systems exhibiting wide structural diversity are of great current interest for fundamental studies of energy and electron transfer in terms of potential applications in molecular wires and devices, energy conversion, information storage, and pharmaceutical chemistry[1-8]. To date, the investigation on metalterpyridine derivatives has been carried out widely[9-21], and some complexes of 2,2′∶6,2″-terpyridine-4-carboxylic acid (Htpc) have been documented, such as coordination polymers [Ln(tpc) (NO3)2]n and [Ag2(tpc)Cl]n, monomers M(tpc)2 (M=Zn/Fe/Co/Cu/Ni), Ru(tpc)2, and [PtCl(Htpc)]Cl[22-28]. Htpc is a rigid ligand with two distinct coordination sites (terpyridine and carboxylate) and containing a π-electron conjugated chromophore, which has potential applications in fluorescence chemosensors, photocytotoxicity, magnetism, and gas absorption[29-31]. The three pyridine rings adopt an ideal coplanar conformation, providing conjugation of π electrons of the aromatic rings and metal cations and the carboxylate group can act as the bridging group or chelating group, which may extend the structure into a high dimensional framework[32-34]. In this work, we deeply explored the coordination behavior of Htpc as assembled with rare-earth-free transition metal salts and main group metal salts under different solvothermal conditions, and five new complexes have been obtained, namely [Cr2(tpc)2(HCOO)2(OH)2]·4H2O (1), [Ba(tpc)2(H2O)2]n (2), [Zn2(tpc)2(NO3)2]n (3), [Pb(Htpc)(NO3)2]·2H2O (4), and [Rh(Htpc)Cl3]·CH3OH·H2O (5) (Scheme 1). These complexes exhibit various structural chemistries and physical properties. Complexes 2 and 3 are coordination polymers. The solid luminescence properties, phase purity, and thermal stability of 1-5 have been investigated.

    Scheme 1

    Scheme 1.  Synthesis routes for 1-5
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    1.   Experimental

    1.1   Materials and methods

    All chemicals used in these syntheses are of reagent grade and used as purchased without further purification. Powder X-ray diffraction (PXRD) data were collected using Shimadzu XRD-6100 powder X-ray diffractometer (Cu Kα radiation, λ=0.154 12 nm, working with a tube voltage of 40 kV and a tube current of 30 mA in a 2θ range of 2°-40° at a scanning rate of 2 (°)·min-1). IR spectra were recorded from KBr pellets in a range of 400-4 000 cm-1 on a Nicolet Impact 410 FTIR spectrometer. Elemental analyses were performed on a Perkin-Elmer 2400 element analyzer. The thermogravimetric (TG) analyses were performed with a Mettler Toledo TGA/SDTA 851e analyzer in an air atmosphere with a heating rate of 5 ℃·min–1 from 30 to 800 ℃. Fluorescence spectra were collected on the ground samples using a Perkin-Elmer LS55 spectrophotometer.

    1.2   Syntheses of the complexes

    1.2.1   Synthesis of complex 1

    A mixture solution of DMF/CH3CN/H2O (1∶1∶9, V/ V, 11 mL; DMF=N,N-dimethylformamide) containing Htpc (27.7 mg, 0.1 mmol), CrCl3·6H2O (40 mg, 0.15 mmol), and HNO3 (20 µL, 7 mol·L-1) was sealed in a reactor of 25 mL and heated at 80 ℃ for 3 d, then cooled to room temperature. The crystals were washed with distilled water to give complex 1. Yield: 54.2% (23.1 mg) based on Htpc. Elemental analysis Calcd. for C34H32N6O14Cr2(%): C 47.89, H 3.78, N 9.86; Found (%): C 47.92, H 3.58, N 9.91. FT-IR (KBr, cm-1): 3 387 (w), 3 063(w), 2 865(w), 2 361(w), 2 208(w), 1 615(vs), 1 373(s), 1 297(s), 780(m), 736(m), 685(m), 551(m).

    1.2.2   Synthesis of complex 2

    Complex 2 was prepared as above starting from Htpc (27.7 mg, 0.1 mmol), BaCl2·2H2O (24.4 mg, 0.1 mmol), HNO3 (20 µL, 7 mol·L-1), and DMF/CH3CN/ H2O (2∶8∶2, V/V, 12 mL) at 80 ℃ for 3 d. Yield: 71% (25.8 mg) based on Htpc. Elemental analysis Calcd. for C32H24N6O6Ba(%): C 52.95, H 3.33, N 11.58; Found (%): C 52.89, H 3.29, N 11.61. FT-IR (KBr, cm-1): 3 337(m), 3 173(w), 3 068(w), 2 307(w), 1 639(w), 1 593 (vs), 1 540(vs), 1 396(vs), 1 324(m), 1 265(m), 1 258(m), 1 107(w), 1 062(m), 1 002(m), 779(s), 661(m), 596(m).

    1.2.3   Synthesis of complex 3

    Complex 3 was obtained similarly to that used of 1, using Htpc (27.7 mg, 0.1 mmol), Zn(NO3)2·6H2O (29.7 mg, 0.1 mmol), HNO3 (30 µL, 7 mol·L-1), and CH3CN/H2O (2∶8, V/V, 10 mL) as starting materials at 120 ℃ for 4 d. Yield: 89% (35.9 mg) based on Htpc. Elemental analysis Calcd. for C32H20N8O10Zn2(%): C 47.61, H 2.50, N 13.88; Found(%): C 47.65, H 2.53, N 13.94. FT-IR (KBr, cm-1): 3 436(w), 3 055(w), 1 645 (vs), 1 600(m), 1 554(m), 1 469(s), 1 377(vs), 1 291(vs), 1 245(m), 1 010(m), 767(s), 740(m), 675(m), 649(w).

    1.2.4   Synthesis of complex 4

    Complex 4 was prepared by a method analogous to that of 3, using Htpc(27.7 mg, 0.1 mmol), Pb(NO3)2 (66.2 mg, 0.2 mmol), HNO3 (10 µL, 7 mol·L-1), and CH3CN/H2O (8∶2, V/V, 10 mL) as starting materials at 70 ℃ for 4 d. Yield 51% (33.1 mg) based on Htpc. Elemental analysis Calcd. for C16H13N5O10Pb(%): C 29.91, H 2.04, N 10.90; Found(%): C 29.32, H 2.23, N, 10.76. FT-IR (KBr, cm-1): 3 416(w), 1 705(w), 1 587 (m), 1 527(m), 1 370(vs), 996(s), 780(s), 636(w).

    1.2.5   Synthesis of complex 5

    A mixture solution of CH3OH/H2O (8∶2, V/V, 10 mL) containing Htpc (14 mg, 0.05 mmol), RhCl3·3H2O (31.6 mg, 0.1 mmol), and HNO3 (20 µL, 7 mol·L-1) was sealed in a reactor of 25 mL and heated at 120 ℃ for 3 d, then cooled to room temperature. The crystals were washed with distilled water to give complex 5. Yield: 33% (8.6 mg) based on Htpc. Elemental analysis Calcd. for C17H15N3Cl3O4Rh(%): C 38.19, H 2.83, N 7.86; Found(%): C 38.21, H 2.82, N 7.91. FT-IR (KBr, cm-1): 3 450(m), 3 112(vs), 1 551(w), 1 476(w), 1 420 (w), 1 224(m), 1 072(w), 1 008(w), 801(s), 725(s), 561 (w), 485(w).

    1.3   Crystallographic studies

    Each of the suitable single crystals was glued to a thin glass fiber and mounted on a SMART APEX Ⅱ CCD diffractometer equipped with an X-ray source (graphite-monochromatic Mo Kα radiation, λ=0.071 073 nm). Intensity data were collected at room temperature. Data processing was performed using the SAINT processing program. The structure was solved by direct methods and refined on F2 by full-matrix least-squares methods using SHELXTL97[35-36] and Olex2[37]. All nonhydrogen atoms were easily found from the different Fourier maps and refined anisotropically. All hydrogen atoms were located in calculated positions and refined isotropically. The crystallographic data and details on refinements for complexes 1-5 are summarized in Table 1. Selected bond distances and angles are listed in Table S1 (Supporting information).

    Table 1

    Table 1.  Crystallographic data and structure refinement summary for complexes 1-5
    下载: 导出CSV
    Parameter 1 2 3 4 5
    Formula C34H32N6O14Cr2 C32H24N6O6Ba C32H20N8O10Zn2 C16H13N5O10Pb C17H15Cl3N3O4Rh
    Formula weight 852.65 725.91 807.30 642.50 534.58
    Crystal size / mm 0.25×0.21×0.18 0.21×0.20×0.20 0.21×0.21×0.20 0.25×0.22×0.20 0.30×0.25×0.19
    Crystal system Triclinic Monoclinic Triclinic Triclinic Monoclinic
    Space group P1 C2/c P1 P1 P21/c
    a / nm 0.815 8(5) 2.033 22(10) 0.731 63(6) 0.891 6(3) 1.142 2(5)
    b / nm 1.013 3(5) 1.746 43(9) 1.354 38(11) 1.024 4(4) 1.037 0(4)
    c / nm 1.115 6(5) 0.835 32(4) 1.627 54(12) 1.276 7(5) 1.706 6(8)
    α/(°) 87.338(19) 103.111 2(14) 83.917(2) 71.798(9) 97.603(13)
    β/(°) 78.236(18) 86.203(2) 85.843(13)
    γ/(°) 72.241(15) 74.925(3) 72.719(12)
    V / nm3 0.859 6(8) 2.888 8(2) 1.547 2(2) 1.057 4(7) 2.003 5(15)
    Z 1 4 2 2 4
    Dc / (g·cm-3) 1.647 1.669 1.733 2.018 1.772
    F(000) 438 1 448 816 612 1 064
    μ / mm-1 0.715 1.433 1.626 8.042 1.281
    Total reflection, unique 18 895, 3 022 24 211, 2 526 56 516, 5 430 36 904, 3 718 37 283, 3 509
    Rint 0.090 0 0.023 8 0.030 7 0.041 7 0.103 1
    GOF 1.039 1.139 1.032 1.059 1.083
    R1, wR2* 0.040 5, 0.095 0 0.017 3, 0.046 0 0.037 7, 0.097 1 0.018 3, 0.047 2 0.064 4, 0.181 0
    *R1=∑||Fo|-|Fc||/∑|Fo|, wR2={∑[w(Fo2-Fc2)2]/∑[w(Fo2)]2}1/2.

    2.   Results and discussion

    2.1   Synthesis and general characterization Although the organic ligand is the same, in this

    work, complexes 1-5 were successfully obtained under varied optimized conditions (Scheme 1), and the solvent and reaction temperature were found to play an important role in the metal/ligand assembly systems. Complexes 1 and 2 were prepared from Htpc and metal chloride salts (CrCl3 and BaCl2) in the mixture of DMF, CH3CN, and H2O with a volume ratio of 1∶1∶9 and 2∶8∶ 2, respectively. Complexes 3 and 4 were generated from Htpc and metal nitrate salts in the mixture of CH3CN and H2O with a volume ratio of 2∶8 and 8∶2 at 120 and 70 ℃, respectively, while for complex 5 the component solvent of CH3OH and H2O was used.

    The synthetic reproducibility was high. The phase purity of the bulk materials for each complex was confirmed by comparison of the corresponding PXRD patterns (Fig.S1), where the major peak positions matched well with the results simulated from the single crystal data. Due to the preferred crystal orientation of the samples, there were differences in intensity at the same peaks. As shown in Fig. S2, TG curves were recorded for 1-5 (the dried samples were directly used for testing without any other treatment). The TG curve of 1 exhibited the first weight loss of 8.8% in a range of 70-100 ℃, which is presumably due to the loss of lattice water molecules (Calcd. 8.45%). Complex 2 showed a weight loss of 1.6% in a range of room temperature to 200 ℃, which might be ascribed to the release of the ca. 30% coordinated water molecules (Calcd. 4.95% for all H2O). In the case of 3, the curve did not display an obvious decrease from 30 to 250 ℃. The curve of 4 displayed a decrease of 5.7% from 30 to 210 ℃, which might be ascribed to the release of the lattice H2O molecules (Calcd. 5.6%). Dissimilar to the curves of 1-4, the curve of 5 displayed an uninterrupted decrease. Complexes 1-5 were stable below 300 ℃. On further heating, the complexes began to decompose rapidly until 500 ℃. The remaining residue of 18.30% for 1, 22.05% for 2, 20.70% for 3, 35.13% for 4, and 25.40% for 5 may be Cr2O3 (Calcd. 17.83%), BaO (Calcd. 21.12%), ZnO (Calcd. 20.16%), PbO (Calcd. 34.83 %), and Rh2O3 (Calcd. 23.81 %), respectively. The results of bulk elemental analyses of them are consistent with their chemical formulas.

    2.2   Description of crystal structures

    2.2.1   Structure of complex 1

    X-ray crystallographic analysis reveals that complex 1 crystallizes in the P1 space group of the triclinic system. As shown in Fig. 1a, the Cr(Ⅲ) center is six-coordinated by three nitrogen atoms from the tpc- ion with the Cr—N distances of 0.199 1(2)-0.207 4(3) nm and three oxygen atoms from two OH- ions and one HCO2- group with the Cr—O distances of 0.192 1(2)-0.196 7(2) nm. The HCO2- is from the DMF decomposition. Each tpc- ion in 1 acts as a chelate mode to link one Cr(Ⅲ) ion (Scheme 2, mode-Ⅰ). Two μ2-OH- groups bridge two Cr(Ⅲ) ions to organize a [Cr2O2] four-membered (4M) ring with distances of Cr…Cr 0.301 8 nm and O…O 0.242 3 nm, which indicates there exist strong O—H…O hydrogen bonds (H-bonds) inside the 4M ring.

    Figure 1

    Figure 1.  Crystal structure of complex 1: (a) binuclear monomer [Cr2(tpc)2(HCOO)2(OH)2] and coordination modes of tpc- and Cr(Ⅲ) ions (thermal ellipsoids probability level: 30%); (b) ringed {H2O}4 water cluster; (c) 2D supramolecular layer (Cg1: N1-C12-C13-C14-C15-C16, Cg2: N2-C10-C9-C8-C7-C6); (d) sandwich-type 3D supramolecular architecture

    Symmetry codes: #1:-x+1, -y, -z+1, #2: -x+1, -y+1, -z+2, #3: x+1, y, z, #4: x+1, y-1, z

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    Scheme 2

    Scheme 2.  Coordination modes of the organic ligand in 1-5
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    Interestingly, four lattice water molecules in complex 1 build a ringed {H2O}4 water cluster through O—H…O H-bonds (O7…O8 0.275 3(5) nm, O7…O8#2 0.282 7(5) nm, Table S2, Fig. 1b). The hydrogen-bonded {H2O}4 cluster is stabilized by surrounding O—H…O H-bonds (O3#3…O8 0.272 4(4) nm, O5…O7 0.280 1(4) nm) between H2O molecules and deprotonated carboxyl terminals. A 2D supramolecular polymeric layer is assembled from the monomer [Cr2(tpc)2(HCOO)2(OH)2] unit through inter-unit H-bonds (O1…O2#4 0.256 4(3) nm) and strong face-to-face π-π interactions (Cg1… Cg2 (center of gravity) with the dihedral angle of 2.695°, the Cg…Cg and the average vertical plane-plane distances of 0.360 3 and 0.328 24 nm, respectively, Fig. 1c). Further, with the {H2O}4 cluster as a supramolecular second building unit (W4-SBU), a sandwich-type 3D supramolecular architecture is constituted from the W4-SBU and above 2D supramolecular layer (Fig. 1d).

    2.2.2   Structure of complex 2

    Complex 2 crystallizes in the C2/c space group of the monoclinic system. As shown in Fig. 2a, the Ba(Ⅱ) center is eight-coordinated by six oxygen atoms from four tpc- ions with the Ba—O distances of 0.268 22(13)-0.288 97(13) nm and two oxygen atoms from two H2O with the Ba—O distances of 0.271 28(15) nm. Each tpc- ligand bridges two Ba(Ⅱ) ions only by its CO2- group while the active terpyridyl group is free (Scheme 2, mode-Ⅱ). Drove by the metal-oxygen (M-O) coordination, a 1D Ba-organic coordination polymer is built up from the tpc-, Ba2+ ions and coordinated H2O molecules, which contains a zigzag polynuclear [Ba(CO2)2(H2O)]n chain with the Ba…Ba distance of 0.435 2 nm (Fig. 2b).

    Figure 2

    Figure 2.  Crystal structure of complex 2: (a) ellipsoidal coordination modes of tpc- and Ba2+ ions (thermal ellipsoids probability level: 30%); (b) view of 1D Ba-organic coordination polymer containing zigzag polynuclear [Ba(CO2)2(H2O)]n chain with Ba…Ba distance of 0.435 2 nm; (c) inter-chain C(sp2)—H…N (C9…N1 0.3714 nm) and face-to-face π…π interactions (Cg1…Cg2 0.374 74 nm, Cg1: N1-C7-C8-C11-C10-C9, Cg2: N2-C4-C3-C2-C6-C5) between adjacent aromatic rings; (d) 3D supramolecular aggregate

    Symmetry codes: #1:-x+1, y, -z+1/2; #2: x, -y+1, z-1/2; #3: -x+1, -y+1, -z+1, #4: -x+1, -y+1, -z

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    In most reported metallosupramolecular derivatives of Htpc, the N atoms of three pyridyl groups are coordinated with the same metal ion. But in this work, the terminal pyridyl groups of complex 2 could rotate around the C—C single bonds (C4—C7 or C5—C12, Fig. 2a). The crystal data analysis reveals that there exist the inter-chain C(sp2)—H…N H-bonds(Fig. 2c, C9…N1 0.371 4 nm) and face-to-face π … π interactions between adjacent aromatic rings (Fig. 2c, Cg1… Cg2 with the dihedral angle of 1.012°, the Cg…Cg and the average vertical plane-plane distances of 0.374 74 and 0.347 30 nm, respectively). With plenty of interchain interactions, a 3D supramolecular aggregate is successfully organized in which each Ba-organic poly-mer chain is surrounded by other six chains (Fig. 2d).

    2.2.3   Structure of complex 3

    Complex 3 crystallizes in the P1 space group of the triclinic system. As shown in Fig. 3a, the asymmetric unit contains two crystallographic independent Zn centers (Zn1, Zn2) and two tpc- (N1, N4) ions. Each Zn(Ⅱ) center adopts a five-coordinated mode by two oxygen atoms from the tpc- and NO3- with the Zn—O lengths of 0.193 9(2)-0.204 8(3) nm, and three nitrogen atoms from the other tpc- ion with the Zn—N lengths of 0.206 7(2)-0.218 4(3) nm. The Zn1…O9(NO3-) and Zn2…O6(NO3-) distances are 0.289 9 and 0.269 1 nm, respectively, which indicate there have weak static interactions. Data analysis display there exists many C(sp2)—H…O H-bonds with C(sp2) …O distances of 0.305 2-0.343 2 nm (Fig.S2). The tpc- ligand bridges Zn1 and Zn2 ions (Scheme 2, mode-Ⅲ) to organize an infinite 1D zigzag Zn-organic coordination polymeric chain (Fig. 3b). Further, by interchain C(sp2)—H…O H-bonds and π…π contacts (Cg1…Cg2 with the dihedral angle of 10.409°, the Cg…Cg (center of gravity) and the average vertical plane-plane distances of 0.398 32 and 0.346 73 nm, respectively), the 1D chains build up a supramolecular double-chain unit adopting a head-to-tail arrangement (Fig. 3c). Through other C(sp2)—H…O H-bonds, the double-chain unit assemble a 2D supramolecular network.

    Figure 3

    Figure 3.  Crystal structure of complex 3: (a) coordination modes and C(sp2)—H…O hydrogen bonds of crystallographic independent Zn1 and Zn2 centers and two tpc- (N1, N4) ligands; (b) 1D Zn-organic coordination polymeric chain; (c) supramolecular double-chain unit from 1D chains by interchain C—H…O H-bonds and face-to-face π…π contacts (Cg1…Cg2, Cg1: N4-C25-C24-C23-C22-C21, Cg2: N5-C20-C19-C18-C26-C27) and its simplified motif

    Symmetry codes: #1: x, y, z-1, #2: x, y, z+1

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    2.2.4   Structures of complexes 4 and 5

    Monomers 4 and 5 crystallize in the P1 and P21/c space groups of the triclinic and monoclinic systems, respectively. Of the two complexes, the Htpc components adopt the same chelate coordination mode by terpyridine groups (Scheme 2, mode-Ⅳ).

    As shown in Fig. 4a, the Pb(Ⅱ) center of complex 4 adopts a six-coordinated mode with a distorted octahedral coordination environment (PbN3O3) by three oxygen atoms from two NO3- anions with the Pb—O lengths of 0.247 4(3)-0.286 1 nm, and three nitrogen atoms from the Htpc ligand with the Pb—N lengths of 0.253 1(3)-0.255 5(3) nm. Of particular interest is that the coordination geometry of Pb(Ⅱ) can be regarded as hemi-directed, in which the Pb—O/N bonds are directed throughout only part of an encompassing globe, implying the presence of a stereochemically active lone pair of electrons. Of complex 4, a double aggregate is constituted from the monomer [Pb(Htpc)(NO3)2] through O—H…O (O2#1…O3, Symmetry code: #1: -x+1, -y+ 1, - z+1) H-bonds and π…π contacts (Cg1…Cg2 with the dihedral angle of 10.866°, the Cg…Cg and the average vertical plane-plane distances of 0.394 77 and 0.342 29 nm, respectively), building up a 1D supramolecular chain (Fig. 4b and 4c).

    Figure 4

    Figure 4.  (a) Coordination modes of Pb(Ⅱ) center and Htpc ligand in 4; (b) Double aggregate [Pb(Htpc)(NO3)2]2 of 4 formed by O—H…O H-bonds and π…π contacts (Cg1…Cg2, Cg1: N1-C12-C13-C14-C15-C16, Cg2: N2-C5-C6-C2-C3-C4) (Symmetry code: #1: -x+1, -y+1, -z+1); (c) 1D supramolecular chain of 4 from the double aggregate by face-to-face π…π contacts; (d) Coordination modes of Rh(Ⅲ) center and Htpc ligand in 5; (e) 1D supramolecular chain of 5 from the monomer [Rh(Htpc)Cl3] by π…π contacts (Cg1…Cg2 and Cg1…Cg3, Cg1: N1-C5-C6-C2-C3-C4, Cg2: N2-C7-C8-C11-C9-C10, Cg3: N3-C12-C13-C14-C15-C16)
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    Of complex 5, the Rh(Ⅲ) center also adopts a sixcoordinated mode with a distorted octahedral coordination environment, namely [RhN3Cl3], by three nitrogen atoms from the Htpc ligand with the Rh—N lengths of 0.193 6(6)-0.202 6(6) nm, and three chlorine anions with the Rh—Cl lengths of 0.232 3(2)-0.235 2(2) nm (Fig. 4d). Further, the 1D supramolecular chain originated from the monomer [Rh(Htpc)Cl3] is formed by π … π interactions (Cg1…Cg3 with the dihedral angle of 0.892°, the Cg…Cg and the average vertical plane-plane distances of 0.387 53 and 0.341 42 nm, respectively, and Cg1…Cg2 with the dihedral angle of 3.347°, and the Cg…Cg distance of 0.428 21 and 0.380 84 nm, respectively) (Fig. 4e).

    2.3   Luminescent properties

    In recent years, the luminescent properties of a variety of metallosupramolecular complexes have been reported. Htpc is a rigid aromatic ligand showing the large conjugated π-system. Hence, the luminescent properties of 2-5 as well as the free ligand Htpc in the solid state were investigated at room temperature (Fig. 5).

    Figure 5

    Figure 5.  Solid-state luminescence emission spectra of complexes 2-5 and the free ligand Htpc at room temperature

    Inset: the images of crystals 2-5 radiated at 365 nm ultraviolet light

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    Upon excitation at 340 nm, the ligand Htpc displayed the narrow blue or purple-blue emission band with the maximum intensity at 400 nm that could be ascribed to the π → π* and/or n→ π* transitions. Complex 2 showed narrow green emissions centered at 519 nm upon excitation at 374 nm. An obvious 119 nm red-shifted emission band has been observed by comparison with the emission of the ligand Htpc. Therefore, the photoluminescence behavior of complex 2 can be attributed to the ligand-to-metal charge transfer (LMCT), which is similar to the reported Ba(Ⅱ) -organic complexes with O-donor ligands[38-40]. Complex 3 showed broad blue emission centered at 446 nm with a shoulder peak at 408 nm excited at 374 nm, and its photoluminescence mechanism can be also attributed to the LMCT. The blue emission of complex 4 was similar to that of the free ligand Htpc excitation at 350 nm, and its photoluminescence behavior can be ascribed to the ligand-to-ligand charge transfer (LLCT). Upon excitation at 367 nm, complex 5 exhibited the blue emission band with the maximum intensity at 483 nm and the weak orange emission at 613 nm, and its photoluminescence behavior also belongs to the LMCT. Under 365 nm ultraviolet radiation, the photographs of crystals 2-5 displayed green, blue, purple-blue, and golden colors, respectively, which are coincident with their emission spectra. The photoluminescence emissions of these complexes were different, which may be caused by different coordination modes of metal centers and the ligand, further affecting the rigidity of the supramolecular structures and the energy transfer during the processes of luminescence excitation and emission.

    3.   Conclusions

    Five complexes, [Cr2(tpc)2(HCOO)2(OH)2]·4H2O (1), [Ba(tpc)2(H2O)2]n (2), [Zn2(tpc)2(NO3)2]n (3), [Pb(Htpc) (NO3)2]·2H2O (4), and [Rh(Htpc)Cl3]·CH3 OH·H2O (5), based on Htpc have been synthesized by adjusting the reaction solvent, temperature and selecting different metal centers. Single-crystal X-ray diffraction analysis reveals that the Htpc ligand took four different coordination fashions in 1-5. The luminescent properties of 2-5 varying according to the central metal ions and the coordination patterns of the Htpc ligand indicate that these complexes may be suitable candidates for optical materials.

    Supporting information is available at http://www.wjhxxb.cn


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  • Scheme 1  Synthesis routes for 1-5

    下载: 全尺寸图片 幻灯片

    Figure 1  Crystal structure of complex 1: (a) binuclear monomer [Cr2(tpc)2(HCOO)2(OH)2] and coordination modes of tpc- and Cr(Ⅲ) ions (thermal ellipsoids probability level: 30%); (b) ringed {H2O}4 water cluster; (c) 2D supramolecular layer (Cg1: N1-C12-C13-C14-C15-C16, Cg2: N2-C10-C9-C8-C7-C6); (d) sandwich-type 3D supramolecular architecture

    Symmetry codes: #1:-x+1, -y, -z+1, #2: -x+1, -y+1, -z+2, #3: x+1, y, z, #4: x+1, y-1, z

    下载: 全尺寸图片 幻灯片

    Scheme 2  Coordination modes of the organic ligand in 1-5

    下载: 全尺寸图片 幻灯片

    Figure 2  Crystal structure of complex 2: (a) ellipsoidal coordination modes of tpc- and Ba2+ ions (thermal ellipsoids probability level: 30%); (b) view of 1D Ba-organic coordination polymer containing zigzag polynuclear [Ba(CO2)2(H2O)]n chain with Ba…Ba distance of 0.435 2 nm; (c) inter-chain C(sp2)—H…N (C9…N1 0.3714 nm) and face-to-face π…π interactions (Cg1…Cg2 0.374 74 nm, Cg1: N1-C7-C8-C11-C10-C9, Cg2: N2-C4-C3-C2-C6-C5) between adjacent aromatic rings; (d) 3D supramolecular aggregate

    Symmetry codes: #1:-x+1, y, -z+1/2; #2: x, -y+1, z-1/2; #3: -x+1, -y+1, -z+1, #4: -x+1, -y+1, -z

    下载: 全尺寸图片 幻灯片

    Figure 3  Crystal structure of complex 3: (a) coordination modes and C(sp2)—H…O hydrogen bonds of crystallographic independent Zn1 and Zn2 centers and two tpc- (N1, N4) ligands; (b) 1D Zn-organic coordination polymeric chain; (c) supramolecular double-chain unit from 1D chains by interchain C—H…O H-bonds and face-to-face π…π contacts (Cg1…Cg2, Cg1: N4-C25-C24-C23-C22-C21, Cg2: N5-C20-C19-C18-C26-C27) and its simplified motif

    Symmetry codes: #1: x, y, z-1, #2: x, y, z+1

    下载: 全尺寸图片 幻灯片

    Figure 4  (a) Coordination modes of Pb(Ⅱ) center and Htpc ligand in 4; (b) Double aggregate [Pb(Htpc)(NO3)2]2 of 4 formed by O—H…O H-bonds and π…π contacts (Cg1…Cg2, Cg1: N1-C12-C13-C14-C15-C16, Cg2: N2-C5-C6-C2-C3-C4) (Symmetry code: #1: -x+1, -y+1, -z+1); (c) 1D supramolecular chain of 4 from the double aggregate by face-to-face π…π contacts; (d) Coordination modes of Rh(Ⅲ) center and Htpc ligand in 5; (e) 1D supramolecular chain of 5 from the monomer [Rh(Htpc)Cl3] by π…π contacts (Cg1…Cg2 and Cg1…Cg3, Cg1: N1-C5-C6-C2-C3-C4, Cg2: N2-C7-C8-C11-C9-C10, Cg3: N3-C12-C13-C14-C15-C16)

    下载: 全尺寸图片 幻灯片

    Figure 5  Solid-state luminescence emission spectra of complexes 2-5 and the free ligand Htpc at room temperature

    Inset: the images of crystals 2-5 radiated at 365 nm ultraviolet light

    下载: 全尺寸图片 幻灯片

    Table 1.  Crystallographic data and structure refinement summary for complexes 1-5

    Parameter 1 2 3 4 5
    Formula C34H32N6O14Cr2 C32H24N6O6Ba C32H20N8O10Zn2 C16H13N5O10Pb C17H15Cl3N3O4Rh
    Formula weight 852.65 725.91 807.30 642.50 534.58
    Crystal size / mm 0.25×0.21×0.18 0.21×0.20×0.20 0.21×0.21×0.20 0.25×0.22×0.20 0.30×0.25×0.19
    Crystal system Triclinic Monoclinic Triclinic Triclinic Monoclinic
    Space group P1 C2/c P1 P1 P21/c
    a / nm 0.815 8(5) 2.033 22(10) 0.731 63(6) 0.891 6(3) 1.142 2(5)
    b / nm 1.013 3(5) 1.746 43(9) 1.354 38(11) 1.024 4(4) 1.037 0(4)
    c / nm 1.115 6(5) 0.835 32(4) 1.627 54(12) 1.276 7(5) 1.706 6(8)
    α/(°) 87.338(19) 103.111 2(14) 83.917(2) 71.798(9) 97.603(13)
    β/(°) 78.236(18) 86.203(2) 85.843(13)
    γ/(°) 72.241(15) 74.925(3) 72.719(12)
    V / nm3 0.859 6(8) 2.888 8(2) 1.547 2(2) 1.057 4(7) 2.003 5(15)
    Z 1 4 2 2 4
    Dc / (g·cm-3) 1.647 1.669 1.733 2.018 1.772
    F(000) 438 1 448 816 612 1 064
    μ / mm-1 0.715 1.433 1.626 8.042 1.281
    Total reflection, unique 18 895, 3 022 24 211, 2 526 56 516, 5 430 36 904, 3 718 37 283, 3 509
    Rint 0.090 0 0.023 8 0.030 7 0.041 7 0.103 1
    GOF 1.039 1.139 1.032 1.059 1.083
    R1, wR2* 0.040 5, 0.095 0 0.017 3, 0.046 0 0.037 7, 0.097 1 0.018 3, 0.047 2 0.064 4, 0.181 0
    *R1=∑||Fo|-|Fc||/∑|Fo|, wR2={∑[w(Fo2-Fc2)2]/∑[w(Fo2)]2}1/2.
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  • 发布日期:  2023-05-10
  • 收稿日期:  2022-10-13
  • 修回日期:  2023-01-19
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