PtII complexes

Accepted Manuscript Photoluminescence and in vitro cytotoxicity of benzimidazole-based CuI/PtII complexes Jin’an Zhao, Dandan Zhao, Yang Zhao, Hang Shu, Jiyong Hu PII: DOI: Reference:

S0277-5387(16)30363-1 http://dx.doi.org/10.1016/j.poly.2016.08.004 POLY 12141

To appear in:

Polyhedron

Received Date: Revised Date: Accepted Date:

13 May 2016 27 July 2016 2 August 2016

Please cite this article as: J. Zhao, D. Zhao, Y. Zhao, H. Shu, J. Hu, Photoluminescence and in vitro cytotoxicity of benzimidazole-based CuI/PtII complexes, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.08.004

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Photoluminescence

and

in

cytotoxicity

vitro

of

benzimidazole-based CuI/PtII complexes Jin’an Zhaoa,∗, Dandan Zhaob, Yang Zhaob, Hang Shub, and Jiyong Hua a

College of Chemical and Material Engineering, Henan University of Urban Construction,

Pingdingshan 467036, Henan, P.R. China b

School of Chemical Engineering, Henan Vocational College of Applied Technology, Zhengzhou

450042, Henan, P.R. China

Abstract Three

novel

complexes

{Cu2(pzbmb)2(I)2}n (1), Pt(pzbmb)(Cl)2(DMSO)

(2)

and

Pt(pdbmb)(Cl)2 (3) based on two novel V-shaped flexible ligands 1-((2-pyrazinyl)-1Hbenzoimidazol-1-yl)methyl)-1H-benzotriazole benzoimidazol-1-yl)methyl)-1H-benzotriazole

(pzbmb) (pdbmb)

and have

1-((2-(pyridine-2-yl)-1Hbeen

synthesized

under

solvothermal conditions. Complex 1 possesses a 1D chain structure with short Cu···Cu distance being 3.008 Å, whereas complex 2 and 3 are mononuclear motifs. Complexes 1–3 exhibit strong phosphorescence at different temperatures in the range of 13–298 K, which is attributed to the presence of intersystem crossing from singlet to triplet caused by the heavy-atom effect. After being tested against SH-SY5Y (neuroblast tumor cell line) by standard MTT assay, complex 3 displayed promising cytotoxicity.

Keywords: V-shaped ligand; Crystal structure; Photoluminescence property; Cytotoxicity

1. Introduction The new transition metal complexes with organic and inorganic building blocks have undergone rapid development in the past two decades, because of their remarkably different physical and chemical properties [1-5]. In most cases, the key factors in constructing different

* Corresponding author. Tel. and fax: 86-375-2089090 E-mail address: [email protected] (J. A, Zhao).

1

structures and properties of coordination polymers primarily depend on the organic linkers with various configurations, which offer different charge balance requirements, skeleton structure, alternative linking, and electronic nature [6-8]. In light of recent success in constituting potentially useful coordination complexes with original structural frameworks, using benzimidazole derivatives as organic linkers for transition metal center have gained much attention due to the advantages of their coordination abilities and structural diversity, which provide an important tool in the formation of the complexes [9,10]. Also, such moieties may have valid biological activities as antitumor, anti-HIV, anti-Parkinson, and antimicrobial agents [11,12]. Moreover, owing to the presence of flexible –CH2– groups, the multidentate groups can freely twist to provide variable coordination modes so that the ligands can aggregate with transition-metal centers more flexibly.

Accordingly, two

1-((2-pyrazinyl)-1H-benzoimidazol-1-yl)methyl)-1H-benzotriazole

V-shaped flexible ligands (pzbmb)

and

1-((2-(pyridine-2-yl)-1H-benzoimidazol-1-yl)methyl)-1H-benzotriazole (pdbmb) are beneficial for construction of diverse coordination complexes. Although the V-shaped flexible ligands are ideal candidates for new architectures, the selection of the metal center is an essential part in the process of synthesizing complexes as well. Heavy-metal complexes with phosphorescent emission have provided the bright promise to exploit functional luminescent materials [13,14]. The Cu(I) complexes always exhibit fascinating luminescence characters because of the unusually large number of assignments of the emitting excited state and the challenges in identifying the nature of the emitting state [15,16]. The Pt(II) complexes have also attracted great attention in recent years because of their intriguing spectroscopic properties and potential applications in biomedical field. For example, the strong spin-orbital coupling of the Pt(II) can insure a high quantum yield of triplet emission [17,18]. Although attractive structures and applications of Cu(I) and Pt(II) complexes have been extensively reported, it is still a attractive challenge to design structural diversity and further effectively explore the correlative properties. Taking these factors into consideration, by the reactions of the multidentate ligands and CuI/PtII salts, three complexes, namely, {Cu2(pzbmb)2(I)2}n (1), Pt(pzbmb)(Cl)2(DMSO) (2) and Pt(pdbmb)(Cl)2 (3) have been assembled under solvothermal conditions. The central metal centers and different structures could have a profound influence on their photoluminescence 2

features of complexes 1–3. In addition, complex 3 depicted promisingly cytotoxic properties against neuroblast tumor cell line (SH-SY5Y).

2. Experimental Section 2.1. Materials and methods All the chemicals were reagent grade or better, used without further purification. K2PtCl4, benzimidazole and Picolinic acid were purchased from Saen Chemical Technology (Shanghai) Co., Ltd. CuI was purchased from Tianjin Institute of Chemical Reagents. The 2-(2- pyrazine)benzimidazole and 2-(2-pyridyl)-benzimidazole have been prepared as previously reported [19]. 1-((2-pyrazinyl)-1H-benzoimidazol-1-yl)methyl)-1H-benzotriazole (pzbmb) and 1-((2-(pyridine -2-yl)-1H-benzoimidazol-1-yl)methyl)-1H-benzotriazole (pdbmb) were synthesized according to the reported procedures in the literature [20]. The IR spectra were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in the region of 400–4000 cm-1. Elemental analyses (C, H and N) were performed on a Flash EA 1112 elemental analyzer. Photoluminescence measurements were carried out on Edinburgh Analytical Instruments FLS920 (Spectrofluorimeter) at 13, 77, 100, 150, 200, 250 and 298 K separately in the solid state. The excitation and emission slit widths are 0.5 nm and 1 nm, respectively. Thermogravimetric experiments were performed on a METTLER TOLEDO TGA/SDTA instrument at a heating rate of 10 °C·min–1. The absorbance for MTT assay was measured at test wavelength of 492 nm using a Tecan Infinite M1000 Promicroplate reader.

2.2. Synthesis 2.2.1 Synthesis of {Cu2(pzbmb)2(I)2}n (1) A mixture of CuI (0.0152 g, 0.08 mmol), pzbmb (0.0065 g, 0.02 mmol), acetonitrile (1 mL) and chloroform (0.5 mL) was placed in a glass reactor (10 mL), which was heated at 85 °C for 3 days and then gradually cooled to room temperature at a rate of 5 °C·h–1. Yield: 65% (based on pzbmb). Elemental analysis (%) Calcd for C18H13Cu 2I2N7: C, 30.53; H, 1.85; N, 13.84. Found: C, 30.32; H, 1.72; N, 13.90. IR (KBr/pellet, cm-1): 3081(w), 2166(w), 1590(w), 1456(m), 1447(s), 3

1376(m), 1294(m), 1200(w), 1159(s), 1104(s), 932(w), 747(s), 632(w). 2.2.2 Synthesis of Pt(pzbmb)(Cl)2(DMSO) (2) A mixture of K2PtCl4 (0.0083 g, 0.02 mmol), pzbmb (0.0065 g, 0.02 mmol), acetonitrile (1 mL), DMSO (1 mL) and water (0.5 mL) was placed in a glass reactor (10 mL), which was heated at 85 °C for 2 days and then gradually cooled to room temperature at a rate of 5 °C·h–1. Yield: 65% (based on pzbmb). Elemental analysis (%) Calcd for C20H19PtCl2N7OS: C, 35.77; H, 2.85; N, 14.60. Found: C, 35.58; H, 2.96; N, 14.45. IR (KBr/pellet, cm-1): 3096(w), 2167(w), 1672(w), 1519(m), 1452(s), 1332(w), 1283(m), 1206(s), 1134(w), 1043(s), 946(m), 745(s), 657(m). 2.2.3 Synthesis of Pt(pdbmb)(Cl)2 (3) Complex 3 was prepared by a similar procedure as described for 1, with the exception that pdbmb (0.0065 g, 0.02 mmol) was used instead of pzbmb (0.0065 g, 0.02 mmol). Yield: 70% (based on pdbmb). Elemental analysis (%) Calcd for C19H14Cl2N6Pt: C, 38.53; H, 2.38; N, 14.19. Found: C, 38.60; H, 2.51; N, 14.03. IR (KBr/pellet, cm-1): 3073(w), 2164(w), 1611(w), 1480(s), 1453(s), 1350(m), 1288(m), 1161(w), 1137(s), 974(m), 779(s), 679(m). 2.3 X-ray crystallography Crystals suitable for X-ray diffraction were mounted on a glass fiber. The data for 1 and 2 were collected on a SuperNova diffractometer with graphite monochromated Cu-Ka radiation (λ = 1.54184 Å) at 290.80(10) K for 1 and at 293(2) K for 2, whereas the structure of complex 3 was obtained on a SuperNova with graphite monochromated Mo-Ka radiation (λ = 0.71073 Å) at 160(10) K. The structures were solved by direct methods and expanded with Fourier techniques. The calculations of complexes 1–3 were conducted with the OLEX2 and the SHELXL-97 crystallographic programs [21-24]. All the non-hydrogen atoms were refined with anisotropic thermal parameters. The final cycle of full-matrix least-squares refinement was based on observed reflections and variable parameters. Crystal data containing space group, lattice parameters and other relevant information for the title complex is summarized in Table 1. Relevant bond lengths and bond angles are displayed in Table 2. 2.4 Cell culture SH-SY5Y cells were routinely maintained in the logarithmic phase at 37 °C in a highly 4

humidified atmosphere of 95% air with 5% carbon dioxide, using the DMEM medium supplemented with 10% (v/v) heat inactive fetal bovine serum (FBS). 2.5 In vitro cytotoxicity assay Complex 3 was dissolved in DMSO (cell culture reagent) just before the experiment, and a counted amount of complexes solution was added to the growth medium containing cells with a final solvent concentration of 5 ‰, which turns out to have no discernible effect on cell killing. The growth inhibitory effect of the tittle complexes on human tumor cell lines was evaluated by means of MTT (MTT = 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, in which MTT is transformed by living cells to produce a DMSO soluble product (formazan) that can be detected through colorimetric analysis. Briefly, cells were seeded in 96-well microplates in growth medium (100 µL), and then incubated at 37 °C in a highly humidified atmosphere with 5% CO2. Amount of cells are generally 5×103 cells/well. The medium was eliminated and replaced with a fresh one (200 µL) containing the complex at five different concentrations (ranging from 10 µM to 50 µM) after 24 h. Three test timescales (24 h, 48 h, 72 h) were established for each treatment. After this time, 20 µL of MTT solution (5 mg/mL) were added to each well and further incubated for 4 h at 37 °C. Then the medium with MTT were discarded and 150 µL of DMSO was added to each well to dissolve the formazan crystals at room temperature. The absorbance was measured at test wavelength of 492 nm using a microplate reader. The % cell inhibition was determined as follow: % cell inhibition = (1-Abstreated cells/Abscontrol

cells)

× 100%. Results of complex 3 were expressed as IC50 values,

which were determined by plotting the percentage viability versus concentration on a logarithmic graph and reading off the control. Each experiment was independently repeated three times, and the final IC50 values were calculated by the average of triplicate experimental results.

3. Results and discussion 3.1 IR spectra When compared with the free ligands, the slightly red shift of emission bands results from the change of electron richness caused by the participation of metal center. The peaks ranging from 5

3100–3030 cm–1 may be assigned to the C–H stretching vibrational modes of benzene moieties. The peaks in the 1680–1640 cm–1 range may be attributed to the C=C stretching vibrational bands of aromatic ring. The bands near 1456, 1452 and 1453 cm–1 are typical for ν(C=N) of the imidazole ring. 3.2 Crystal structure of {Cu2(pzbmb)2(I)2}n (1) Single crystal X-ray crystallographic analysis reveals complex 1 features a 1D chain structure. The asymmetric unit of 1 consists of two Cu(I) centers, two pzbmb and two I–. As shown in Fig. 1, the structure contains two kinds of Cu(I) centers with different coordination environments. Cu1 displays a distorted tetrahedral geometry (CuN2I2), ligated by two nitrogen atoms (N1 and N3) from two pzbmb and two iodine atoms (I1 and I2a). Cu2 center lies in a distorted tetrahedral geometry formed by three iodine atoms (I1, I1a and I2a) and one nitrogen atom (N7) from pzbmb. Both Cu–N and Cu–I lengths are in the normal range for other Cu(I) complexes [25]. There are two different I– ions in the asymmetric unit. I1 links three Cu centers (I1–Cu1, I2–Cu2, and I1–Cu2a) with the µ 3-coordinating mode, while I2 links two Cu centers (I2–Cu1 and I2–Cu2) with the µ 2-coordinating mode. With this connectivity, the molecule forms a chain (Fig. S1). The distances between diagonal copper atoms (Cu1–Cu2 and Cu2–Cu2a) are 3.037(2) and 3.008(3) Å, respectively, which are little longer to sum of the van de walls radii of two Cu(I) atoms (2.80 Å), indicating the weak interactions between them [26]. Complex Cu[C9H7O4]2 has been reported and the copper cation is octahedrally coordinated with five oxygen atoms of the aspirinate ligands and one adjacent Cu with shorter Cu···Cu contact distances than those of {Cu2(pzbmb)2(I)2}n (1) [27]. In contrast, the differences of coordination modes and the conformations of the ligands play important roles in determining Cu···Cu distances. The construction of luminescent copper(I) iodine complexes attracts much attention due to their rich structural and photophysical properties. For example, in the mononuclear Cu(I) complex, Cu is coordinated by three ligands solely via their phosphorus atom and an iodide ligand yielding a neutral tetrahedral L3CuI-type complex [28]. In iodine-bridged dinuclear complexes [Cu(µ-I)dppb]2, two Cu(I) centers are bridged by two iodine ligands to form a dinuclear structure with a four-membered Cu 2I2 ring [29]. In [Cu 2I2L2]·THF·CH3CN is a dimeric species, in which the Cu(I) center shows a distorted tetrahedral coordination geometry by two bridging 6

iodide atoms and two chelating N atoms from the pyridine arms of one L [30]. In (2,2'-bipy)Cu 3I3, the type of Cu coordinated with the 2,2'-bipy molecule shares corners via µ 3-I to form an extended 1-D zigzag chain [31]. Moreover, the centroid-to-centroid separations are 3.729(5) Å for the triazole ring and triazole ring with the corresponding dihedral angle of 0º. Furthermore, there is one C–H···π force between the C9 and the centroid of triazole ring with the separation of 3.709(13) Å. Complex 1 is further expanded into a 3D supra-molecular framework (Fig. 2). Consequently, the presence of the π···π interactions may play an important role in the target structure formation. 3.3 Crystal structure of Pt(pzbmb)(Cl)2(DMSO) (2) Complex 2 with a mononuclear motif crystallizes in the monoclinic system, space group P2 1/n. The asymmetric unit of 2 consists of one Pt(II) center, one pzbmb, one DMSO molecule and two Cl–. As shown in Fig. 3, Pt1 center lies in a square planar with slight distortions defined by two nitrogen atoms (N1, N3) from a pzbmb and two terminal coordination chlorine atoms (Cl1, Cl2). Both the Pt–N and Pt–Cl distances are in the normal range in other Pt(II) complexes [32]. Notably, the DMSO molecules reside in the interlayer void spaces and hydrogen bonds are formed among pzbmb ligands and the Cl– ions, as well as with the DMSO molecules [C1–H1···Cl1, 3.184(6) Å; C12–H12A···O1, 3.103(7) Å; C2–H2···N7, 3.355(8) Å; C15–H15···O1, 3.331(7) Å]. Also, there exists C–H···π interaction between methyl and the benzene ring [C19–H19A···centroid 3.691(9) Å]. Through hydrogen bonds and π···π interactions, complex 2 is further extended into 3D supra-molecular network (Fig. 4). 3.4 Crystal structure of Pt(pdbmb)(Cl)2 (3) Single crystal X-ray crystallographic analysis reveals complex 3 comprises two crystallographically mononuclear motifs. As shown in Fig. 5, there are two crystallographic independent Pt(II) centers and both of them are four-coordinated with a distorted square planar (PtN2Cl2) provided by two N atoms from a pdbmb and two chlorine atoms. Both Pt–N and Pt–Cl distances are comparable to those reported in other Pt(II) complexes [32]. There is a C–H···π interaction between methyne and the benzene ring [C32–H32A···centroid 3.635(12) Å]. Notably, hydrogen bonds are formed between the pdbmb ligands [C1–H1···Cl2, 7

3.124(10) Å; C20–H20···Cl3, 3.176(12) Å; C23–H23···N11, 3.309(14) Å]. Thus, the C–H···π interactions and the hydrogen bonds play significant roles in constructing and stabilizing the 3D supra-molecule structure (Fig. S2). 3.5 Luminescence properties The photoluminescence properties and corresponding lifetimes of complexes 1–3 (Figs. 6–8) from room temperature to 13 K were investigated in the solid state. Upon the excitation wavelength of 377 nm, the pzbmb consists of two types of photoluminescence emission bands at each certain temperature (Fig. S3). For pdbmb excited at 285 nm, only singlet state emissions with λmax=384 nm at 10–298 K are observed (Fig. S4). Complex 1 displays fluorescence emission band at 378 nm (λex = 340 nm) with lifetimes in nanosecond range and show phosphorescence emission band at 644 nm (λex = 340 nm) with lifetimes in microsecond range. Complex 2 and 3 show unobvious fluorescence emission band and display strong phosphorescence emission band at 640 nm (λex = 369 nm), 645 nm (λex = 340 nm) with lifetimes in microsecond range, respectively. In contrast to 1, the strong phosphorescence behaviors for 2 and 3 suggest that the Pt(II) center may lead to enhancement of intersystem crossing efficiency and larger spin-orbin constant to improve the chances of producing triplet emission, which reduces the fluorescence emission [32]. The fluorescence lifetimes for pzbmb, pdbmb and 1–3 at room temperature, yield τ = 0.80 ± 0.0088, 1.55 ± 0.0066, 0.068 ± 0.0023, 144.36 ± 43.19, 211.40 ± 44.66 ns, respectively. The phosphorescence lifetimes for solid 1–3 at 298 K, 250 K, 200 K, 150 K, 100 K, 77 K and 13K, yield τ = 1.24 ± 0.14, 2.27 ± 0.12, 2.51 ± 0.099, 5.18 ± 0.12, 6.97 ± 0.12, 9.14 ± 0.49, and 9.48 ± 0.13 ms for 1; τ = 0.31 ± 0.026, 0.36 ± 0.031, 0.65 ± 0.022, 0.74 ± 0.024, 0.91 ± 0.021, 1.24 ± 0.0021, and 5.88 ± 0.36 ms for 2; τ = 0.23 ± 0.022, 0.35 ± 0.020, 0.50 ± 0.026, 0.89 ± 0.021, 1.21 ± 0.020, 1.28 ± 0.022, and 5.74 ± 0.094 ms for 3, respectively. At cryogenic temperatures, phosphorescence intensity and long lifetime are enhanced remarkablely, which may be rationalized as a result of the inhibition of the nonradiative decay of the emitting triplet-excited state with decreasing temperature [33]. The emission discrepancy of the three complexes is probably due to the differences of metal centers and their coordination environments, which have close relationship to the photoluminescence behavior. CuI/PtII center, as a heavy atom, can effectively enhance the rate of 8

intersystem crossing, which reduces the fluorescence emission and enhances the rate of triplet excited state formation, and spin-orbit coupling effects [34]. In conjunction with the large Stokes shift from the excitation maximum to the low energy emission maximum of 1–3, the ns and ms range transitions are fluorescence and phosphorescence features, respectively, which are consistent with the low-energy emissions being typical of emission origins for triplets [32]. Additionally, the emission bands of 1 and pzbmb are similar in corresponding energy and band shape, and therefore the emissions of 1 is tentatively assigned to metal-perturbed intraligand transitions [35]. Square planar Pt(II) complexes reduces the D2d distortion that may lead to radiationless decay process, which increases the emission of these complexes[36,37]. In addition, their photophysical properties can be adopted by varied conformations and coordination modes of the ligands to meet the requirements for diverse applications. The property of the lowest excited state of the complexes can be adjusted among the ligand-to-ligand charge transfer (LLCT) state, intraligand charge transfer (ILCT) state, intraligand (IL) π, π* state and metal-to-ligand charge transfer (MLCT) state, which is up to the characteristic of the ligand [38,39]. Based on the photophysical characteristics of 2 and 3, the new emission peak could be assigned to the MLCT state as observed in [[Pt(Cl-4-terpy)Cl]Cl (Cl-4-terpy = 4-Chloro-2,2',6',2''-terpyridine) and [Pt(Nttpy)Cl] (4'-(p-nicotinamide-N-methylphenyl)-2,2',6',2''-terpyridine) systems [40,41]. 3.6 Cytotoxicity results Complex 3 was assessed with the standard MTT assays using for its cytotoxic property against SH-SY5Y (neuroblastoma tumor cell line) at different times. Complex 3 was dissolved in 5‰ DMSO and a blank sample with the same volume of DMSO was provided as a control at the same time. To deeply understand the cytotoxic property, IC50 values of ligand pdbmb and cisplatin were also investigated under the same experimental condition. IC50 values, which can be seen in Fig. 9, were calculated from the dose–survival curves obtained after 24 h, 48 h and 72 h drug treatment by MTT assay. The concentrations of the complex 3 ranged from 10 µM to 50 µM, and the cytotoxicity of the complex was found to be concentration-dependent, which is to say that the average cell viability ratio decreased with increasing concentrations of the tested compound. Complex 3 exhibited 9

clearly reduced cell viability in a dose-dependent manner showing a cytotoxicity always higher than that exerted by cisplatin (with IC50 values being 40.24, 38.09, and 30.36 µM for 24 h, 48 h, 72 h, respectively), which suggested that the cytotoxic effects of complex 3 against SH-SY5Y are sort of time-dependent, but not obviously. In general, IC50 values against SH-SY5Y cells demonstrated by complex 3 are much lower than those of pdbmb, which could possibly be attributed to the synergic effect of combination. In parallel with these findings, complex 3 depicted promisingly cytotoxic properties against SH-SY5Y cells. 3.7 Thermal analyses To estimate the stability of the coordination architectures, thermogravimetric analyses (TGA) were carried out (Fig. S5). The three complexes are air-stable and can retain their crystalline integrity at ambient temperature. The TGA curve shows that complex 1 is stable up to 265 °C and then the coordination framework begins to collapse. For complex 2, the weight loss takes place between 89 °C and 200 °C, and the total weight loss in this temperature range is 10.3%, which is attributed to the uncoordinated DMSO molecule (calcd 11.6%). Further heating indicates decomposition of the coordination framework. No obvious weight loss is observed for complex 3 until the decomposition of the framework occurs at 304 °C.

4. Conclusions Three new luminescent coordination complexes have been successfully constructed by the self-assembly of V-shaped flexible ligands and CuI/PtII ions under solvothermal conditions. The strong phosphorescence behaviors of 1–3 suggest that Cu I/PtII can effectively enhance the rate of intersystem crossing and may be good candidates for potential luminescence materials. Besides, the in vitro cytotoxicity studies of the complex 3 on human neuroblastoma cell (SH-SY5Y) were evaluated by MTT assay and the result indicated it has promisingly cytotoxic property. The interaction between complex and DNA, the effect of complex on the cell cycle and the pharmacokinetics of complex will be the future work in our research.

5. Appendix A. Supplementary data 10

Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center, CCDC reference numbers 1404094-1404096. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.htm (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033). The additional figures can be obtained from the web free of charge.

Acknowledgements We gratefully acknowledge the financial support by the National Natural Science Foundation of China (No. 21371046) and the He’nan key science and technology research (No. 132102310121), the training and funding Program for young key teacher of Henan University of Urban Construction, the funding program for young key teacher of He’nan colleges and universities (No. 2013GGJS-175).

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Figures

Fig. 1 Coordination environments of Cu(I) atoms in 1 (all the hydrogen atoms are omitted for clarity).

Fig. 2 View of the 3D crystal packing of the structure of 1 (all hydrogen atoms have been omitted for clarity).

Fig. 3 The coordination environment of Pt(II) center for 2 (all the hydrogen atoms are omitted for clarity).

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Fig. 4 The 3D supramolecular structure of 2 stabilized by hydrogen bonds and π···π interactions (all hydrogen atoms are omitted for clarity).

Fig. 5 Molecular structure of 3 with hydrogen atoms omitted for clarity.

Fig. 6 The photoluminescence emission spectra of 1 (λex = 340 nm) at 298K and low temperatures.

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Fig. 7 The photoluminescence emission spectra of 2 (λex = 369 nm) at 298K and low temperatures.

Fig. 8 The photoluminescence emission spectra of 3 (λex = 340 nm) at 298K and low temperatures.

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Fig. 9 The IC50 values of complex 3 against SH-SY5Y.

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Table 1 Crystal data and structure refinements for complexes 1–3 Complex

1

2

3

Empirical formula

C18H13Cu2I2N7

C20H19Cl2N7OPtS

C19H14Cl2N6Pt

Formula weight

708.23

671.47

592.35

Temperature (K)

290.80(10)

293(2)

160(10)

Wavelength (Å)

1.54184

1.54184

0.71073

Crystal system

monoclinic

monoclinic

monoclinic

Space group

C2/c

P21/n

P21/c

a

15.8262(6)

17.33853(19)

14.0813(3)

b

13.1421(4)

7.12476(7)

10.86175(19)

c

20.2522(7)

18.08217(18)

24.4419(5)

α

90.00

90.00

90.00

β

104.859(4)

99.6276(10)

103.434(2)

γ

90.00

90.00

90.00

Volume (Å3), Z

4071.4(3), 8

2202.28(4), 4

3636.05(13), 8

F (000)

2672.0

1296.0

2256.0

θ range for data collection (°) Goodness-of-fit F2

4.435 to 76.922

3.269 to 73.455

2.975 to 30.755

1.049

1.019

0.0336, 0.0819

0.0551, 0.1328

Final R1a, wR2b

on 1.013 0.0601, 0.1425

a

R1 = [|F0|-|Fc|]/|F0|. bwR2 = [w(F02-Fc2)2]/[w(F02 )2]1/2. w = 1/[σ2(Fo)2+ 0.0297 P2+27.5680P ], where P = ( F2o+ 2 F2c)/3

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Table 2 Selected bond lengths and angles for complexes 1–3 Complex 1

1#Cu(2)-N(7) 2#Cu(1)-N(1) Cu(2)-I(2) Cu(1)-I(2) 2#N(1)-Cu(1)-I(2) 2#N(1)-Cu(1)-I(1)#3 I(2)-Cu(2)-I(1)#3 N(3)-Cu(1)-N(1)#2 Complex 2 Pt(1)-Cl(1) Pt(1)-N(3) Cl(2)-Pt(1)-Cl(1) N(1)-Pt(1)-Cl(2) N(3)-Pt(1)-Cl(2) Complex 3 Pt(1)-Cl(1) Pt(1)-N(2) Pt(2)-Cl(4) Pt(2)-N(7) Cl(2)-Pt(1)-Cl(1) N(1)-Pt(1)-Cl(2) N(2)-Pt(1)-Cl(2) Cl(3)-Pt(2)-Cl(4) N(27)-Pt(12)-N(8)

2.070(7) 2.089(7) 2.6575(17) 2.6153(15) 103.7(2) 101.0(2) 108.55(5) 110.2(3)

Cu(2)-I(2) 3#Cu(1)-I(1) Cu(1)-N(3) Cu(2)-I(1) N(3)-Cu(1)-I(2) N(3)-Cu(1)-I(1)#3 4#N(7)-Cu(2)-I(2) 4#N(7)-Cu(2)-I(1)#3

2.6575(17) 2.7408(15) 2.030(8) 2.6993(17) 120.5(2) 110.9(2) 111.3(2) 108.3(2)

2.2962(12) 2.005(4) 88.25(5) 176.48(13) 98.21(13)

Pt(1)-Cl(2) Pt(1)-N(1) N(3)-Pt(1)-Cl(1) N(1)-Pt(1)-N(3) N(1)-Pt(1)-Cl(1)

2.3086(14) 2.009(5) 173.53(13) 79.48(18) 94.06(13)

2.252(2) 2.023(7) 2.288(3) 1.980(7) 88.76(8) 94.0(2) 174.0(2) 89.71(10) 81.0(3)

Pt(1)-Cl(2) Pt(1)-N(1) Pt(2)-Cl(3) Pt(2)-N(8) N(2)-Pt(1)-Cl(1) N(1)-Pt(1)-Cl(1) N(1)-Pt(1)-N(2) N(7)-Pt(2)-Cl(4) N(8)-Pt(2)-Cl(3)

2.313(2) 1.975(7) 2.272(3) 2.001(8) 97.2(2) 177.1(2) 80.1(3) 96.2(2) 93.1(2)

Symmetry transformations used to generate equivalent atoms: #1 -1/2+X, -1/2+Y, +Z; #2 -X, 1-Y, 1-Z; #3 1/2-X, 3/2-Y, 1-Z; #4 1/2+X, 1/2+Y, +Z for 1.

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Graphical abstract: Synopsis

Photoluminescence and in vitro cytotoxicity of benzimidazole-based CuI/PtII complexes Jin’an Zhaoa,∗∗, Dandan Zhaob, Yang Zhao b, Hang Shub, and Jiyong Hua The reactions of CuI/PtII metal centers and V-shaped flexible ligands bring about complexes 1–3 with different motifs. Complexes 1–3 exhibit strong phosphorescence and complex 3 has promisingly cytotoxicity.

Graphical abstract: picture

* Corresponding author. Tel. and fax: 86-375-2089090 E-mail address: [email protected] (J. A, Zhao).

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