Synthesis, characterization and crystal structure of platinum(II) complexes with thiourea derivative ligands European Journal of Chemistry 9 (4) (2018) 360-368 European Journal of Chemistry View Journal Online View Article Online Synthesis, characterization and crystal structure of platinum(II) complexes with thiourea derivative ligands Ebru Keskin 1, Ummuhan Solmaz 2, Gun Binzet 3, Ilkay Gumus 2,* and Hakan Arslan 2 1 Advanced Technology Research and Application Center, Mersin University, Mersin, TR-33343, Turkey ebruuvacin@mersin.edu.tr (E.K.) 2 Department of Chemistry, Faculty of Arts and Science, Mersin University, Mersin, TR-33343, Turkey ummuhansolmaz@mersin.edu.tr (U.S.), ilkay.gumus@mersin.edu.tr (I.G.), hakan.arslan@mersin.edu.tr (H.A.) 3 Department of Chemistry, Faculty of Education, Mersin University, Mersin, TR-33343, Turkey gunbinzet@mersin.edu.tr (G.B.) * Corresponding author at: Department of Chemistry, Faculty of Education, Mersin University, Mersin, TR-33343, Turkey. Tel: +90.324.3610001/14559 Fax: +90.324.3610047 e-mail: ilkay.gumus@mersin.edu.tr (I. Gumus). 10.5155/eurjchem.9.4.360-368.1774 Received: 16 July 2018 Received in revised form: 12 October 2018 Accepted: 15 October 2018 Published online: 31 December 2018 Printed: 31 December 2018 Thiourea derivatives [N-(di-n-propylcarbamothioyl)-4-fluorobenzamide (HL1) and N-(di-n- propylcarbamothioyl)-4-bromobenzamide (HL2)] and their platinum complexes have been successfully synthesized and structurally characterized by spectroscopic 1H NMR, 13C NMR, COSY, HMQC, and FT-IR techniques. The structure of both complexes was also confirmed by single crystal X-ray diffraction studies. The study of X-ray single crystal diffraction shows that the supramolecular aggregation of the complexes is stabilized via weak interactions as well as stacking interactions such as C-H⋅⋅⋅π and π⋅⋅⋅π. The cis-[Pt(L1-S,O)2 showed C–H⋯π and π⋯π stacking interactions, whereas only C–H⋯π stacking interaction was observed in cis-[Pt(L2-S,O)2]. In addition, the strong classical and non-classical intermolecular hydrogen bonds are not found in the prepared complexes. Therefore, it can be said that the C–H⋯π and π⋯π stacking interactions play an important role in the formation of supramolecular structures of the complexes. Thiourea Synthesis Platinum complexes Benzamide derivative Supramolecular structure Single crystal X-ray diffraction Cite this: Eur. J. Chem. 2018, 9(4), 360-368 Journal website: www.eurjchem.com 1. Introduction Thiourea containing compounds are versatile molecules which are capable of coordinating with metal ions to form stable complexes. For example N-(alkyl/aryl)-N'-acylthiourea and N-di(alkyl/aryl)-N'-acylthiourea derivatives which have oxygen, nitrogen and sulphur donor atoms, exhibit prevalent coordination modes. Organic ligands that have thiourea moiety are able to bind metal ions in several ways, like: (i) acting as monodentate ligands through sulphur atom in mononuclear complexes [1-4] (ii) binding to metal ions forming S-bridges in dinuclear complexes [4-8] or (iii) chela- ting sulphur and nitrogen atoms [4-6,8-16] Thiourea derivatives as a ligand have a large dipole moment and these ligands can also form extensive network of hydrogen bonds due to their unique structures. For example in 3-monosubstituted arylthioureas [17-19], the carbonyl group and the proton on the nitrogen attach in a strong hydrogen bond interaction which unite into a planar six-membered ring structure forming an “S” shaped conformation of the C=O and C=S groups [20,21]. Further, it can also be stated that amine- thiourea compounds might have bifunctional properties due to the intra- and inter-molecular interactions via hydrogen bonding [22-25]. The interplay of intermolecular and intramolecular hydrogen bonding has direct relevance on chemical properties of these compounds, including their use as ligand in metal complexes [26] and also their conformational properties, which have influence in the applied fields [27]. Metal complexes of these compounds have long been known not only for their wide range of biological applications but also for their role in analytical sciences [28-30], as inhibitors in the corrosion field [31] and as catalysts in chemical reactions [21,32]. Because of the significant properties that thiourea deriva- tives have, their synthesis, structure, biological activity and application to these kinds of compounds have drawn attention from the past to the present. Numbers of studies, involving structural ligand design and the synthesis of complexes for different purposes in various fields, have increased. As a part of our research, we report herein the synthesis and charac- terization of thiourea derivative ligands (N-(di-n-propyl- carbamothioyl)-4-fluorobenzamide (HL1) and N-(di-n-propyl- ABSTRACT RESEARCH ARTICLE KEYWORDS European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2018 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. http://dx.doi.org/10.5155/eurjchem.9.4.360-368.1774 http://dx.doi.org/10.5155/eurjchem.9.4.360-368.1774 https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.9.4.360-368.1774&domain=pdf&date_stamp=2018-12-31 http://www.eurjchem.com/ http://dx.doi.org/10.5155/eurjchem.9.4.360-368.1774 mailto:ebruuvacin@mersin.edu.tr mailto:ummuhansolmaz@mersin.edu.tr mailto:ilkay.gumus@mersin.edu.tr mailto:hakan.arslan@mersin.edu.tr mailto:gunbinzet@mersin.edu.tr mailto:ilkay.gumus@mersin.edu.tr http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.9.4.360-368.1774&domain=pdf&date_stamp=2018-12-31� Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 361 Scheme 1. Synthesis of thiourea ligands. carbamothioyl)-4-bromobenzamide (HL2)) and their platinum complexes (cis-[Pt(L1-S,O)2] and cis-[Pt(L2-S,O)2). Conforma- tional properties of synthesized complexes have also been investigated by intermolecular contacts obtained from X-ray single crystal diffraction study. 2. Experimental 2.1. Instrumentation Infrared measurement was recorded in the range 400- 4000 cm−1 on a Perkin Elmer Spectrum 100 series FT- IR/FIR/NIR Spectrometer Frontier, ATR Instrument. The NMR spectra were recorded in CDCl3 solvent on Bruker Avance III 400 MHz NaNoBay FT-NMR spectrophotometer using tetra- methylsilane as an internal standard. The X-ray diffraction data were recorded on a Bruker APEX-II CCD diffractometer. A suitable crystal was selected and coated with Paratone oil and mounted on a Nylon loop on a Bruker APEX-II CCD diffractometer. The crystal was kept at T = 100 K during data collection. The data were collected with MoKα (λ = 0.71073 Å) radiation at a crystal-to-detector distance of 40 mm. Using Olex2 [33], the structure was solved with the Superflip [34-36] structure solution program, using the Charge Flipping solution method and refined by full-matrix least-squares techniques on F2 using ShelXL [37] with refine- ment of F2 against all reflections. Hydrogen atoms were const- rained by difference maps and were refined isotropically, and all non-hydrogen atoms were refined anisotropically. 2.2. Reagents Potassium thiocyanate, 4-fluorobenzoyl chloride and 4- bromobenzoylchloride were purchased from Merck and used as received. All other chemicals and solvents were obtained from commercial suppliers and used without further purify- cation. 2.3. Synthesis and characterization 2.3.1. General procedure for the synthesis of ligands (HL1,2) HL1,2 ligands were prepared according to previously published methods [38-40]. A solution of substituted benzoyl chloride (4-fluorobenzoyl chloride and 4-bromobenzoyl chloride, 5 mmol) in dry acetone (50 mL) was added dropwise to a suspension of potassium thiocyanate (5 mmol, 0.490 g) in acetone (30 mL). The reaction mixture was heated under reflux for 30 min and then cooled to room temperature. A solution of di-n-propylamine (5 mmol, 0.54 g) was added and the resulting mixture was stirred for 2 h. After that, the reaction mixture was poured into hydrochloric acid (0.1 M, 300 mL), and the solution was filtered. The solid product was washed with water and purified by recrystallization from an ethanol:dichloromethane mixture (1:1, v:v) (Scheme 1). N-(Di-n-propylcarbamothioyl)-4-fluorobenzamide (HL1): Colour: White. Yield: %70. FT-IR (ATR, ν, cm-1): 3271 (NH), 2968, 2934, 2877 (CH), 1643 (C=O), 1275 (C=S), 753 (C-F). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.42 (s, 1H, NH), 7.86 (d, 2H, Ar-H), 7.15 (d, 2H, Ar-H), 3.92 (t, 2H, N-CH2), 3.51 (t, 2H, N- CH2), 1.83 (m, 2H, -CH2-), 1.71 (m, 2H, -CH2-), 1.02 (t, 3H, CH3), 0.88 (t, 3H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 180.10 (C=S), 162.83 (C=O), 130.61 (C-Ar), 130.52 (C-Ar), 115.96 (C- Ar), 115.74 (C-Ar), 54.99 (C-N), 54.89 (C- N), 21.46 (CH2), 19.73 (CH2), 11.31 (CH3), 11.27 (CH3). N-(Di-n-propylcarbamothioyl)-4-bromobenzamide (HL2): Colour: White. Yield: %88. FT-IR (ATR, ν, cm-1): 3207 (NH), 2962, 2947, 2871 (CH), 1685 (C=O), 1261 (C=S), 750 (C-Br). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.38 (s, 1H, NH), 7.64 (d, 2H, Ar-H), 7.62 (d, 2H, Ar-H), 3.95 (s, 2H, N-CH2), 3.50 (s, 2H, N- CH2), 1.84 (m, 2H, -CH2-), 1.67 (m, 2H, -CH2-), 1.04 (s, 3H, CH3), 0.91 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 179.88 (C=S), 162.97 (C=O), 132.02 (C-Ar), 131.40 (C-Ar), 129.55 (C- Ar), 127.78 (C-Ar), 55.02 (C-N), 54.95 (C- N), 21.48 (CH2), 19.75 (CH2), 11.35 (CH3), 11.31 (CH3). 2.3.2. General procedure for the synthesis of platinum complexes A solution of HL1,2 (2.0 mmol, HL1: 0.56 g; HL2: 0.67 g) in ethanol (50 mL) at 70 ○C was added dropwise to a solution of potassium tetrachloroplatinate(II) (1.0 mmol, 0.416 g) in water (50 mL) at 70 ○C. The reaction mixture was stirred for 30 min and then cooled to room temperature. A yellow–brown precipitate formed, which was filtered off and recrystallized from ethanol:dichloromethane (2:1, v:v) (Scheme 2) [41-50]. Bis[4-Fluoro-N-(di-n-propylcarbamothioyl)benzamido-O, S] platinum(II), cis-[Pt(L1-S,O)2]: Color: Yellow. Yield: 78%. FT-IR (ATR, ν, cm−1): ν(C–H) 2962, 2927, 2868 (w), ν(C–N) 1578 (w), ν(C–O) 1487 (vs), ν(C–S) 1088 (s). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.16 (td, 4H, Ar–H), 7.01 (td, 4H, Ar–H), 3.65 (q, 4H, N– CH2), 3.58 (q, 4H, N–CH2), 1.76 (p, 4H, N–CH2-CH2), 1.63 (p, 4H,N–CH2-CH2), 0.90 (m, 12H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 167.68 (C–S), 167.40 (C–O), 133.82 (C–Ar), 133.79 (C–Ar), 131.64 (C–Ar), 131.55 (C–Ar), 115.15 (C–Ar), 114.93 (C–Ar) 54.54 (C–N), 53.75 (C–N), 21.27 (CH2), 20.53 (CH2), 11.40 (CH3). Bis[4-Bromo-N-(di-n-propylcarbamothioyl)benzamido-O, S] platinum(II), cis-[Pt(L2-S,O)2]: Color: Yellow. Yield: 72%. FT-IR (ATR, ν, cm−1): ν(C–H) 2972, 2957, 2898 (w), ν(C–N) 1565 (w), ν(C–O) 1492 (vs), ν(C–S) 1090 (s). 1H NMR (400 MHz, CDCl3, δ, ppm): 8.10 (td, 4H, Ar–H), 7.57 (td, 4H, Ar–H), 3.75 (q, 4H, N– CH2), 3.67 (q, 4H, N–CH2), 1.85 (p, 4H, N–CH2-CH2), 1.76 (p, 4H, N–CH2-CH2), 0.99 (m, 12H, CH3). 13C NMR (100 MHz, CDCl3, δ, ppm): 167.74 (C–S), 167.47 (C–O), 136.64 (C–Ar), 131.36 (C– Ar), 131.13 (C–Ar), 130.85 (C–Ar), 126.27 (C–Ar), 54.60 (C–N), 53.51 (C–N), 20.49 (CH2), 20.53 (CH2), 11.40 (CH3). 3. Results and discussion 3.1. NMR and FT-IR spectral analysis The synthesized compounds have been characterized by spectroscopic 1H NMR, 13C NMR, COSY, HMQC and FT-IR techniques. The NMR spectra of the ligands and their platinum complexes were recorded in CDCl3. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 362 Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 Scheme 2. Synthesis of thiourea complexes. Figure 1. COSY NMR spectrum of cis-[Pt(L1-S,O)2] complex. The NMR data of the compounds are given in the experi- mental section and are consistent with the structural results. In the 1H NMR of the ligands (HL1,2) characteristic NH proton signals were observed at δ 8.42 and 8.38 ppm, respectively, as a singlet. After the complexation, the signals that belong to NH group were not observed due to the deprotonation. The ligands have shown bidentate coordination via the sulfur and oxygen atoms to platinum metal atom. Slight diffrences were observed in the 1H NMR spectra of the complexes related to attached subtituent groups (F or Br), altering the electronic structure of the ligand. The signals for the aromatic protons were observed in the range of δ 7.15-7.86 ppm for each ligand, with small differences in their environments. After the metalation, diffrently from the free ligand, the aromatic proton resonance values shifted to downfield, between the range of δ ~7-8 ppm. The resonance values, obtained from the 1H NMR spectra of the complexes, were almost similar. The most observed distinct shift values were aliphatic protons in cis- [Pt(L2-S,O)2] comp-lexes. Compared to free ligands, the resonance values that were obtained for the aliphatic protons shifted to upfield, only the observed signals, which belong to the methyl group shifted to downfield region in cis-[Pt(L1- S,O)2] and cis-[Pt(L2-S,O)2] complexes. In 13C NMR spectrum of free ligands, thiocarbonyl (C=S) and carbonyl (C=O) carbons appeared at δ 180-162 ppm range. It has been observed from the 13C NMR spectra of the complexes, that the C–S carbon resonance values shifted to upfield while the resonance values of the C–O appeared at the downfield region for both complexes as a result of the complexation process. The two-dimensional nuclear magnetic resonance spectra is used for resolving the interactions between carbon and hydrogen atoms, or neighboring protons. These spectral analysis are based on effective magnetic fields, interactions of the nuclear spin with adjacent atoms and the number of equivalent protons. To elucidate the structures of compounds, 2D NMR experiments (HMQC and COSY) were carried out. According to the COSY spectrum of the platinum complexes, for the benzamide moiety, correlations between aromatic protons were observed at δ 8.16; 7.00 and 8.15; 6.99 ppm for cis-[Pt(L1-S,O)2] and δ 8.12;7.58 and 8.10; 7.57 ppm for cis- [Pt(L2-S,O)2] complexes, respectively. In addition, the COSY spectrum of the complexes revealed the CH2-CH2 and CH2-CH3 interactions between aliphatic neighboring protons (Figures 1 and 2). CH2-CH2 interactions were detected between the peaks, appearing as a quartet close to the electronegative N atom and as a pentet, for both complexes. Also, the correlations of CH2- CH3 protons were observed between the peaks at δ 1.65 (CH2) with 0.86 (CH3) and 1.67 (CH2) with 0.85 (CH3) ppm for cis- [Pt(L1-S,O)2] complex and between the peaks at δ 1.77 (CH2) with 0.97 (CH3) and 1.83 (CH2) with 0.99 (CH3) ppm for cis- [Pt(L2-S,O)2] complex (Figures 1 and 2). The HMQC shows the interactions between the protons and their attached heteronuclei through the heteronuclear coupling. In the HMQC spectrum of the complexes, it is evident that the peaks which were observed in the 13C NMR spectra (δ 167.68 (C–S) and 167.40 (C–O) ppm for cis-[Pt(L1-S,O)2], 167.74 (C–S) and 167.47(C–O) ppm for cis-[Pt(L2-S,O)2]) did not appear because of being non-protonated carbons. The aromatic and aliphatic carbons that have coupled with protons appeared to be compatible with the peaks in the HMQC spectra. Besides, the interactions between carbon and proton atoms, which have attached to electronegative N atom, were detected at δ 3.60 with 54.01 and 3.65 with 53.73 ppm for cis-[Pt(L1-S,O)2] complex and δ 3.71 with 54.54 ppm, for cis-[Pt(L2-S,O)2]) complex, respectively (Figures 3 and 4) [51,52]. The infrared spectra of ligands with their metal complexes have been studied in order to characterize their structures and to confirm the presence of characteristic groups. The IR spectra of free ligands and metal chelates were carried out in the 4000-400 cm–1 range. In the IR spectrum of the ligands the vibration band was observed nearly at ~3200 cm−1 assigned to ν(NH) stretching vibration. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 363 Figure 2. COSY NMR spectrum of cis-[Pt(L2-S,O)2] complex. Figure 3. HMQC NMR spectrum of cis-[Pt(L1-S,O)2] complex. Figure 4. HMQC NMR spectrum of cis-[Pt(L2-S,O)2] complex. This band disappears upon metal complex formation. The vibration band observed at 1643 and 1685 cm−1 are assigned to carbonyl ν(C=O) for HL1 and HL2, respectively. The vibration bands for HL1 and HL2 ligands, which belong to ν(C=S) group, appeared at 1275 and 1261 cm−1, respectively. After the complexation, carbonyl ν(C=O) and thiocarbonyl ν(C=S) vibration bands shifted to lower values as a result of the coordination via sulfur and oxygen atoms to platinum ions [53-55]. 3.2. Crystal structure analysis The molecular structure of the obtained complexes was determined with single crystal X-ray diffraction. Block shaped yellow coloured crystal of the complexes was obtained by slow evaporation of their ethanol:dichloromethane solution (2:1, v:v). The complexes cis-[Pt(L1-S,O)2] and cis-[Pt(L1-S,O)2] crystallized in orthorombic space group Fdd2 and triclinic space group P1, respectively. The crystal and structure refine- ment data are given in Table 1. The asymmetric unit of the cis- [Pt(L1-S,O)2] consists of half unique molecules, while four crystallographically independent molecules are observed in the cis-[Pt(L1-S,O)2] (Figures 5 and 6). Calculating the root mean square deviations between the X-ray geometries of the four independent molecules of the cis- [Pt(L2-S,O)2] we can see that all molecules are slightly differ (propyl regions) from the equilibrium geometry (RMSD(A-C) = 0.692 Å with inversion, RMSD(A-C) = 0.992 Å without inversion, RMSD(A-B) = 1.113 Å with inversion, RMSD(A-B) = 0.716 Å without inversion, RMSD(A-D) = 0.084 Å with inversion, RMSD(A- D) = 1.299 Å without inversion). 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 364 Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 Table 1. Crystal data and details of the structure refinement for complexes. Compound cis-[Pt(L1-S,O)2] cis-[Pt(L2-S,O)2] Empirical formula C28H36F2N4O2PtS2 C28H36Br2N4O2PtS2 Formula weight 757.82 879.64 Temperature (K) 298 99.99 Crystal system Orthorhombic Triclinic Space group Fdd2 P1 a, (Å) 26.819(9) 15.7174(6) b, (Å) 12.131(5) 17.5696(6) c, (Å) 18.880(6) 25.3974(9) α, (ᵒ) 90 80.253(2) β, (ᵒ) 90 85.604(2) γ, (ᵒ) 90 63.8880(10) Volume (Å3) 6142(4) 6206.7(4) Z 8 8 ρcalc (g/cm3) 1.639 1.883 μ (mm-1) 4.748 12.990 F(000) 3008.0 3424.0 Crystal size (mm3) 0.21 × 0.21 × 0.12 0.18 × 0.17 × 0.12 Radiation MoKα (λ = 0.71073) CuKα (λ = 1.54178) 2Θ range for data collection (°) 6.058 to 53.434 5.666 to 146.486 Index ranges -33 ≤ h ≤ 33, -15 ≤ k ≤ 15, -23 ≤ l ≤ 23 -19 ≤ h ≤ 19, -20 ≤ k ≤ 21, -31 ≤ l ≤ 31 Reflections collected 45369 257871 Independent reflections 3256 [Rint = 0.0754, Rsigma = 0.0368] 24579 [Rint = 0.0527, Rsigma = 0.0235] Data/restraints/parameters 3256/1/179 24579/0/1421 Goodness-of-fit on F2 1.075 1.052 Final R indexes [I≥2σ (I)] R1 = 0.0267, wR2 = 0.0476 R1 = 0.0322, wR2 = 0.0743 Final R indexes [all data] R1 = 0.0425, wR2 = 0.0516 R1 = 0.0483, wR2 = 0.0818 Largest diff. peak/hole (e.Å-3) 0.97/-0.92 1.56/-2.36 (a) (b) Figure 5. (a) The asymmetric unit of the cis-[Pt(L1-S,O)2] and (b) molecular structure of cis-[Pt(L1-S,O)2]. Figure 7a shows the overlay diagram of four independent molecules in cis-[Pt(L2-S,O)2]. The overlay diagram illustrates that the conformation of the molecule A is more similar to the molecule D, while the conformation of the molecule B is more similar to the molecule C. The packing diagram of cis-[Pt(L2- S,O)2] is shown in Figures 7b. In the crystal packing of cis- [Pt(L2-S,O)2], molecules A, B, C and D are represented in green, red, pink and blue, respectively, forming an inverted head-to- tail arrangement without any significant hydrogen bond interactions. In both complexes, the reactions between ligands and Pt(II) produces metal-complexes with the expected ligand- metal ratio of 2:1 in a square-planar geometry. The chelating two benzamide ligands are coordinated with Pt ion in a monoanionic bidentate mode, forming two six membered chelate rings (Pt-SCNCO). The six membered rings are formed via oxygen and sulphur atoms, and dihedral angles between these rings in the cis-[Pt(L1-S,O)2] and cis-[Pt(L2-S,O)2] are 6.89 and 20.37°, respectively. The bond angles around the platinum ion are S1–Pt1–O1 = 94.99(17)° for cis-[Pt(L2-S,O)2] and S1–Pt1–O1 = 94.91(9) and S2–Pt1–O2 = 93.89(10)° for cis-[Pt(L2-S,O)2] (Table 3). The platinum center, surrounded by oxygen and sulphur atoms in complexes, is caused by a slightly distorted square planar geo- metry as shown in Figure 3. The bite angles of the complexes deviate slightly from the ideal angle (90°). The value of the smallest and largest bite angles are 93.89(10) and 94.99(17)°, respectively. The sum of the equatorial angles S1-Pt1-O1, S2- Pt1-O2, S1-Pt1-S2 and O1-Pt1-O2 are 360.01° and equal to the ideal value of 360.00°, which is consistent with square planar geometry. Other values of bond angles are given in Table 3. In the both complexes, the C(O) and C(S) bond lenghts are 1.292(9) and 1.721(8) Å for cis-[Pt(L1-S,O)2] and 1.277(5) and 1.736(4) Å for cis-[Pt(L2-S,O)2], which are slightly longer than the corresponding distance found in similar free ligands [47]. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 365 (a) (b) Figure 6. (a) The asymmetric unit of the cis-[Pt(L2-S,O)2], (b) molecular structure of molecule A in cis-[Pt(L2-S,O)2]. Table 2. Selected bond lengths of the complexes. Atom Atom Length (Å) cis-[Pt(L1-S,O)2] Pt(1) S(1) i 2.238(3) Pt(1) S(1) 2.238(3) Pt(1) O(1) 2.002(7) Pt(1) O(1) i 2.002(7) S(1) C(1) 1.721(8) F(1) C(6) 1.360(11) O(1) C(2) 1.292(9) N(1) C(1) 1.342(10) N(1) C(2) 1.307(9) N(2) C(1) 1.338(9) N(2) C(9) 1.470(10) cis-[Pt(L2-S,O)2] Pt(1) S(1) 2.2344(12) Pt(1) S(2) 2.2355(10) Pt(1) O(2) 2.021(3) Pt(1) O(1) 2.013(3) N(1) C(1) 1.322(6) N(1) C(8) 1.345(6) C(1C) C(2C) 1.488(6) N(2) C(12) 1.476(6) N(2) C(9) 1.472(5) N(2) C(1) 1.338(9) N(2) C(9) 1.470(10) i 1/2-x, 1/2-y, +z. This indicates the existence of an electron delocalization over the six-member chelate ring due to the coordination of the oxygen and sulfur atoms with the platinum ion. All other bond lengths are within normal ranges (Table 2). The planar configuration of cis-[Pt(L1-S,O)2] molecule is stabilized by intramolecular C-H⋅⋅⋅O, C-H⋅⋅⋅S and C-H⋅⋅⋅N hydrogen bonds(C-H⋅⋅⋅O 2.41 Å and ∠ 101°, C-H⋅⋅⋅S 2.45 Å and ∠ 112°, and C-H⋅⋅⋅N 2.42 Å and ∠ 100°). All the four independent molecules form similar intramolecular C-H⋅⋅⋅O, C- H⋅⋅⋅S and C-H⋅⋅⋅N hydrogen bonds that stabilize the structure of complexes. In the both complexes, there are no strong classical and non-classical intermolecular hydrogen bonds to be found. Overall, our data suggest that the supramolecular aggregation of the complexes is stabilized by weak interactions as well as stacking interactions such as C-H⋅⋅⋅π and π⋅⋅⋅π. The crystal packing of cis-[Pt(L1-S,O)2] is stabilized by C-H⋅⋅⋅π and π⋅⋅⋅π staking cooperative interactions, and van der Waals forces. In the cis-[Pt(L1-S,O)2], the two strongest C-H⋅⋅⋅π interactions occur between dipropylamine hydrogen atoms and platinum chelate rings (C9-H9A⋅⋅⋅π 2.76 Å with symmetry code 3/4-x, 1/4+y, -1/4+z and C9-H9B⋅⋅⋅π with symmetry code 1/4+x, 3/4-y, -1/4+z), as seen in Figure 8. The C–H··· π angles, 137° for both interactions, are still below the optimal value (180°) for the strongest CH···π interaction, which may be due to the steric constraints in the molecules [56]. Table 3. Selected bond angles of the complexes. Atom Atom Atom Angle (°) cis-[Pt(L1-S,O)2] S(1) i Pt(1) S(1) 87.42(15) O(1) Pt(1) S(1)i 175.9(2) O(1) Pt(1) S(1) 94.99(17) O(1) i Pt(1) S(1) 175.9(2) O(1) i Pt(1) S(1) i 94.98(17) O(1) Pt(1) O(1) i 82.8(4) C(1) S(1) Pt(1) 108.1(3) C(2) O(1) Pt(1) 128.6(6) C(2) N(1) C(1) 128.5(7) C(1) N(2) C(9) 124.0(6) C(1) N(2) C(12) 119.9(6) cis-[Pt(L2-S,O)2] S(1) Pt(1) S(2) 88.48(4) O(2) Pt(1) S(1) 176.61(8) O(2) Pt(1) S(2) 94.91(9) O(1) Pt(1) S(1) 93.92(10) O(1) Pt(1) S(2) 176.74(11) C(26) N(4) C(23) 116.6(3) C(22) N(4) C(23) 122.7(4) C(22) N(4) C(26) 120.7(4) C(15) N(3) C(22) 127.6(4) O(1) C(1) N(1) 131.1(4) O(1) C(1) C(2) 112.9(4) i 1/2-x, 1/2-y, +z. The crystal packing is also supported by π⋅⋅⋅π staking interactions. In the crystal packing of cis-[Pt(L1-S,O)2], Cg1, Cg2 and Cg3 are centroids of the Pt(1)-S(1)-C(1)-N(1)-C(2)-O(1) chelate ring, Pt(1)-S(1)a-C(1)a-N(1)a-C(2)a-O(1) a chelate ring and C3-C8 ring, respectively. Cg1 exhibits a series stacking interactions with Cg3 of the adjacent molecule with a centroid- to-centroid distance of 3.902(5) Å (Cg(1)⋅⋅⋅Cg(3) 3.901(5) Å with symmetry code: 3/4-x, 1/4+y, -1/4+z; Cg(1)⋅⋅⋅ Cg(3) 3.902(5) Å with symmetry code: -1/4+x, 1/4-y, -1/4+z; 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 366 Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 (a) (b) Figure 7. (a) Overlay diagrams of the cis-[Pt(L2-S,O)2], (b) packing diagram of the cis-[Pt(L2-S,O)2] coloured by symmetry equivalence (Green molecule A, red molecule B, pink molecule C and blue molecule D). Figure 8. Supramolecular structure in cis-[Pt(L1-S,O)2] generated via C-H⋯π stacking interactions. Figure 9. Supramolecular structure in cis-[Pt(L1-S,O)2] generated via π⋯π stacking interactions. Cg(3)⋅⋅⋅Cg(1) 3.902(5) Å with symmetry code: 3/4-x, -1/4+y, 1/4+z and Cg(3)⋅⋅⋅Cg(1) 3.902(5) Å with symmetry code: 1/4+x, 1/4-y, 1/4+z) (Figure 9). These two important stacking interactions in the cis-[Pt(L1-S,O)2] contribute to the stability of its three dimensional supramolecular structure. The supramolecular structure of cis-[Pt(L2-S,O)2] is governed by the formation of a series C-H∙∙∙π stacking interactions, which contribute to the stability of the complex, namely the asymmetric unit of cis-[Pt(L2-S,O)2]. The four independent molecules in the asymmetric unit of cis-[Pt(L2- S,O)2] are kept together via C-H∙∙∙π stacking interactions. These interactions occur between the hydrogen atoms of dipropyl moiety and the platinum chelate rings (Figure 10). In the crystal lattice, molecules of cis-[Pt(L2-S,O)2] are again held together by strong C-H···π stacking interactions. However, these interactions occur between the hydrogen atoms of dipropyl moiety and the hydrogen atoms, which are different from the others (C11-H11B⋅⋅⋅π 2.92 Å, ∠156° with symmetry code: x, y, z; C11C-H11E⋅⋅⋅π 2.89 Å, ∠156° with symmetry code: x, 1+y, z; C11A-H11H⋅⋅⋅π 2.92 Å, ∠164° with symmetry code: x, -1+y, z; C11B-H11K⋅⋅⋅π 2.95 Å, ∠162° with symmetry code: x, y, z). 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 Keskin et al. / European Journal of Chemistry 9 (4) (2018) 360-368 367 (a) (b) Figure 10. (a) C-H⋯π stacking interactions in asymmetric unit of cis-[Pt(L2-S,O)2], (b) strong C-H⋯π stacking interactions in crystal lattice of cis-[Pt(L2-S,O)2]. The C–H···π lengths in the crystal lattice are about 2.90 Å, and are very close the optimal values (from 2.8 to 3.2 Å) for the strongest CH···π interactions [57-59]. 4. Conclusion Two platinum(II) compounds, having the general formula, cis-[Pt(L1,2-S,O)2] with ligands N-(di-n-propylcarbamothioyl)- 4-fluoro benzamide and N-(di-n-propylcarbamothioyl)-4- bromo benzamide, have been prepared and characterized, where two monobasic O,S donor ligands coordinate to platinum in a cis-O2S2 conformation. The obtained complexes cis-[Pt(L1-S,O)2] and cis-[Pt(L2-S,O)2] crystallized in an orthorombic space group Fdd2 with half molecules per unit cell and in a triclinic space group P1 with four molecules per unit cell, respectively. The supramolecular structure of studied compounds were further examined by non-covalent interact- tion studies. The results of non-covalent interaction studies revealed that both complexes lack strong hydrogen bonds between classical and non-classical molecules. However, the supramolecular aggregation of the complexes is stabilized by van der Waals forces as well as stacking interactions such as C- H⋅⋅⋅π and π⋅⋅⋅π. Acknowledgements This work was supported by the Mersin University Research Fund [Project No: 2016-AP4-1426]. This academic work was also linguistically supported by the Mersin Technology Transfer Office Writing Center of Mersin University. Supporting information CCDC-1882277 and 1882278 contain the supplementary crystallographic data for compounds cis-[Pt(L1-S,O)2] and cis- [Pt(L2-S,O)2], respectively. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by e- mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033. Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. 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This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.360-368.1774 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Instrumentation 2.2. Reagents 2.3. Synthesis and characterization 2.3.1. General procedure for the synthesis of ligands (HL1,2) 2.3.2. General procedure for the synthesis of platinum complexes 3. Results and discussion 3.1. NMR and FT-IR spectral analysis 3.2. Crystal structure analysis 4. Conclusion Acknowledgements Supporting information Disclosure statement Funding ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: