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Mononuclear homoleptic organotin(IV) dithiocarbamates: Syntheses, structures and antimicrobial activities
Journal of Organometallic Chemistry 853 (2017) 27e34
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Mononuclear homoleptic organotin(IV) dithiocarbamates: Syntheses, structures and antimicrobial activities Mamata Mahato a, Shayantan Mukherji b, Kristof Van Hecke c, Klaus Harms d, Abhrajyoti Ghosh b, Hari Pada Nayek a, * a
Department of Applied Chemistry, Indian Institute of Technology (Indian School of Mines), Dhanbad, 826004, Jharkhand, India Department of Biochemistry, Bose Institute, Kolkata, West Bengal, India XStruct, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, B-9000, Ghent, Belgium d €t Marburg, Hans Meer-wein Strasse, Marburg, Germany Fachbereich Chemie, Philipps Universita b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2017 Received in revised form 12 October 2017 Accepted 19 October 2017 Available online 21 October 2017
Six mononuclear organotin(IV) complexes of two dithiocarbamato ligands, [Ph3SnL1] (1), [Bu2Sn(L1)2] (2), [Ph2Sn(L1)Cl] (3), [Ph2Sn(L1)2] (4), [Ph2Sn(L2)2] (5) and [Ph3Sn(L2)] (6) where L1 ¼ thiomorpholine-4carbodithiolate and L2 ¼ 2,6-dimethylmorpholine-4-carbodithiolate have been synthesized in good yields. Both ligands and complexes 1e6 were characterized by elemental analyses, FT-IR spectroscopy, UV-visible spectroscopy and 1H, 13C{1H} 119Sn{1H} NMR spectroscopy. In addition, the solid-state structures of the complexes were established through single-crystal X-ray diffraction analyses. The Xray analyses reveal that the Sn(IV) center is five-coordinated in 1, 3 and 6. In complexes 2, 4 and 5, Sn(IV) is six-coordinated and occupies the center of a distorted octahedron. Moreover, an asymmetric coordination mode of the dithiocarbamato ligands was observed in all complexes. The optical properties and thermal stabilities of all complexes were investigated. All complexes were evaluated for their in vitro antimicrobial properties against E. coli. Complex 1 shows a maximal biological activity whereas the least activity is found for complex 6. © 2017 Elsevier B.V. All rights reserved.
Keywords: Organotin(IV) complex Dithiocarbamato ligand 119 Sn NMR Single-crystal X-ray diffraction Antimicrobial activity
1. Introduction Organotin compounds have consistently been a potential area of research because of their immense structural diversities [1]. When combined with carboxylate ligands, organotin compounds exhibit a variety of structures ranging from monomers, dimers, oligomers, polymers and even, one-, two- or three-dimensional frameworks [2,3]. However, recent research work has been slowly replacing carboxylate ligands by sulfur donor ligands because of their resemblance with sulfur-containing biomolecules such as vitamins and amino acids [4]. In this context, the synthesis of metal complexes using a dithiocarbamate anion (R2NCS 2 ) has continued to gain attention in the last decades. Dithiocarbamate anions constitute an important class of ligands and can easily be isolated as alkali metals or ammonium salts by reacting an amine with carbon disulfide (CS2) in the presence of a base [5]. Further reaction of it with metal salts results in the formation of the corresponding metal
* Corresponding author. E-mail address: [email protected] (H.P. Nayek). https://doi.org/10.1016/j.jorganchem.2017.10.027 0022-328X/© 2017 Elsevier B.V. All rights reserved.
dithiocarbamates. Dithiocarbamato ligands contain two soft sulfur atoms which can bind to the metals in a monodentate, bidentate, anisobidentate or triconnective fashion (Scheme 1) [6]. These ligands can often generate a broad variety of molecular and supramolecular structures [7]. In addition to their peculiar structural diversities, these ligands and their metal complexes have attracted attention as potential candidates for various applications in material science. For example, they are used as single-source precursors for the preparation of metal sulphides as thin films or nanoparticles [8e10]. A variety of dithiocarbamato metal complexes of transition metals and lanthanides have been prepared and used as precursors for the synthesis of metal sulphides [11e13]. These ligands also play an active role in medical science [14e16]. However, the chemistry of dithiocarbamato derivative of main group elements is less widely explored compare to transition metals or lanthanides [6]. In this context, organotin dithiocarbamates continue to be the focus of recent research works.
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Scheme 1. Coordination modes of dithiocarbamate ligands.
Analogous to carboxylate derivatives, organotin dithiocarbamates generate a variety of structures [17]. Occasionally, they form macrocycle or supramolecular structures. For example, several 22-, 23-, 26- and 27-membered macrocyclic diorganotin(IV) bisdithiocarbamates have recently been reported and few of them have been explored for their sensing abilities towards inorganic and organic anions [18,19]. Moreover, tin sulphides (SnS, SnS2 and Sn2S3) which are synthesized from organotin dithiocarbamate complexes exhibit semiconducting properties with a band gap of 0.95e2.18 eV [20]. These sulphides are used as solar energy absorber, and in holographic recording and infrared detection [21]. In addition, organotin dithiocarbamates exhibit important biological activities such as anti-fungal, anti-microbial, anti-cancer activities etc [22]. For instance, organotin complexes of morpholine dithiocarbamate showed cytotoxic activity when tested against human HeLa and K562 tumor cell lines [23]. Moreover, it was found that these organotin complexes were more active than cisplatin. The antifungal activity of several organotin(IV) dithiocarbamates against Candida albicans (ATCC 18804), Candida tropicalis (ATCC 750) and resistant Candida albicans collected from HIV-positive patients was also tested [24]. A detailed application of organotin dithiocarbamate was documented by Tiekink [25]. However, the organotin moiety, organic substituents on the ligands and coordination number of the tin center play an active role in determining their biological activities [26]. Therefore, the design and synthesis of new organotin(IV) dithiocarbamate complexes by varying the organic groups on tin or the dithiocarbamato ligands has been a challenging task. During the last few years, we have been working on organotin compounds [27,28]. We are also working with dithiocarbamato ligands to prepare complexes of transition metals and lanthanides [29]. In continuation of our work, we have now chosen two dithiocarbamato ligands, potassium thiomorpholine-4carbodithiolate (KL1) and 2,6-dimethylmorpholine-42 carbodithiolate (KL ) for the present study (Scheme 2). These ligands have been reacted with various organotin compounds to prepare six organotin(IV) dithiocarbamate complexes [Ph3SnL1] (1), [Bu2Sn(L1)2] (2), [Ph2Sn(L1)Cl] (3), [Ph2Sn(L1)2] (4), [Ph2Sn(L2)2] (5) and [Ph3Sn(L2)] (6). All ligands and complexes were characterized by multinuclear NMR spectroscopy and FT-IR spectroscopy. Moreover, the solid-state molecular structures of complexes 1e6 were determined by single-crystal X-ray diffraction analysis. The optical properties, thermal stability and antimicrobial activity of all complexes are documented.
2. Experimental 2.1. Materials and analytical techniques All reactions were executed under aerobic conditions. Starting materials were used as received from Aldrich (thiomorpholine, 2,6dimethylmorpholine and dibutyltin dichloride), Acros organics (triphenyltin chloride), Alfa aesar (diphenyltin dichloride) and Merck (carbon disulfide) without any further purification. Solvents were distilled prior to use. Carbon, hydrogen and nitrogen microanalyses were carried out on a Thermo Scientific (FLASH 2000) CHNS elemental analyzer. FT-IR spectra were recorded in the solid state (ATR mode) using a Perkin Elmer- Spectrum RX-IFTIR spectrometer in the region of 4000e400 cm1. The electronic spectra of 1e6 were recorded on a Shimadzu UV-1800 spectrometer. 1H, 13C {1H}, 119Sn{1H} NMR of the complexes in solution were recorded on an FT NMR Spectrometer, Avance II (Bruker, 400 MHz). Thermogravimetric analyses were carried out using a Perkin Elmer, Diamond TG/DTA. 2.2. Procedure for the syntheses of ligands KL1 and KL2 2.2.1. Synthesis of KL1 A solution of thiomorpholine (1.002 mL, 10 mmol) in methanol (5 mL) was cooled in an ice bath. A cold solution of potassium hydroxide (0.561 g, 10 mmol) in H2O-MeOH (10 mL, 1:1) was added to it. After stirring 15 min, an ice cold solution of carbon disulfide (0.604 mL, 10 mmol) in methanol (5 mL) was added maintaining the reaction temperature below 10 C. A solid did appear which was stirred for 2 h, filtered and washed with cold methanol followed by drying in vacuum. The ligand was air stable and soluble in methanol at room temperature (25 C). Yield (89%, 1.934 g): IR (ATR, cm1) n ¼ 1450 (C-N), 993 (C-S). 1H NMR (DMSO, 400 MHz): d ¼ 2.52 (4H, t, S-CH2), 4.59 (4H, t, N-CH2) ppm. 13C{1H} NMR (100 MHz, DMSO): d ¼ 26.5 (C-S), 51.7 (C-N), 213.8 (CS2) ppm. 2.2.2. Synthesis of KL2 Ligand KL2 was synthesized following same procedure as KL1. Here, 2,6-dimethylmorpholine (1.232 mL, 5 mmol) was used instead of thiomorpholine. Yield (86%, 1.974 g). The ligand KL2 was white in color, air stable and was soluble in methanol at room temperature (25 C). IR (ATR, cm1) n ¼ 1448 (C-N), 952 (C-S).1H NMR (400 MHz, DMSO): d ¼ 1.06e1.08 (6H, m, CH3), 2.39 (2H, m, NCH), 3.36 (2H, m, N-CH), 5.80 (2H, m, O-CH) ppm. 13C{1H} NMR (100 MHz, DMSO): 18.6 (CH3), 47.1(N-CH2), 54.6 (N-CH2), 68.7 (CO), 70.8(C-O), 213.6 (CS2) ppm. 2.3. General procedure for the syntheses of complexes 1e4
Scheme 2. Potassium salts of thiomorpholine-4-carbodithiolate (KL1) and 2,6dimethylmorpholine-4-carbodithiolate (KL2).
To a solution of KL1 (0.1 g, 0.5 mmol) in methanol (5 mL), a solution of organotin(V) chloride in methanol (5 mL) was added. A white precipitate was immediately observed, which was stirred for 2 hrs. Thereafter it was filtered, washed with cold methanol and
M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
dried. Single crystals, suitable for X-ray diffraction analysis, were obtained by layering methanol over a solution of the resulting complex in dichloromethane, after two weeks. [Ph3SnL1] (1): Ph3SnCl (0.1927 g, 0.5 mmol) used. Yield (82%, 0.199 g), Anal. Calc. for C23H23N1S3Sn1 (528.29): C 52.29%, H 4.39%, N 2.65%. Found C 52.04%, H 4.10%, N 2.36%. IR (ATR, cm1) n ¼ 1479 (C-N), 998, 950 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 2.74 (4H, t, SCH2), 4.32 (4H, m, N-CH2), 7.38e7.43 (6H, m, Ph), 7.57e7.74 (9H, m, Ph) ppm. 13C{1H} NMR (100 MHz, DMSO): d ¼ 26.7 (C-S), 54.3 (C-N), 128.5 (Ph), 129.0 (Ph), 136.0 (Ph), 142.4 (Ph), 201.2 (CS2) ppm. 119Sn {1H} NMR (133.3 MHz, DMSO): d ¼ 195.9 ppm. [Bu2Sn(L1)2] (2): Bu2SnCl2 (0.076 g, 0.25 mmol) was used. Yield (68%, 0.185 g), Anal. Calc. for C18H34N2S6Sn1 (589.52): C 36.67%, H 5.81%, N 4.75%. Found: C 36.9%, H 5.71%, N 4.16%. IR (ATR, cm1): 1467 (C-N), 1023, 997 (C-S). 1H NMR (400.13 MHz, DMSO): d ¼ 0.88 (6H, t, CH3), 1.38 (4H, m, CH3-CH2), 1.82 (4H, m, CH3-CH2-CH2), 1.97 (4H, t, Sn-CH2), 2.73 (8H, m, S-CH2), 4.32 (8H, m, N-CH2) ppm. 13C {1H} NMR (100 MHz, DMSO): d ¼ 13.6 (CH3), 25.6 (CH3-CH2), 26.7 (CH3-CH2-CH2), 34.5 (C-Sn), 28.1(C-S), 53.6 (C-N), 203.8 (CS2) ppm. 119 Sn{1H} NMR (133.3 MHz, DMSO) d ¼ 543.7 ppm. [Ph2Sn(L1)Cl] (3): Ph2SnCl2 (0.0859 g, 0.25 mmol) was used. Yield (82%, 0.184 g), Anal. Calc. for C17H18N1S3Sn1Cl1 (486.64): C 41.95%, H 3.73%, N 2.88%. Found: C 41.80%, H 3.66%, N 2.45%. IR (ATR, cm1): 1505 (C-N), 1002, 943 (C-S). 1H NMR (400 MHz, DMSO) d ¼ 2.80 (4H, t, S-CH2), 4.21 (4H, m, N-CH2), 7.27e7.61 (4H, m, Ph), 7.85e8.09(6H, m, Ph) ppm. 13C{1H} (100 MHz, DMSO) NMR: d ¼ 26.9 (C-S), 54.7 (C-N), 128.7 (Ph), 129.9 (Ph), 134.9 (Ph), 143.8 (Ph), 193.7 (CS2) ppm. 119Sn{1H} NMR (133.3 MHz, DMSO): d ¼ 340.5 ppm. [Ph2Sn(L1)2] (4): Ph2SnCl2 (0.0859 g, 0.25 mmol) was used. Yield (74%, 0.214 g), Anal. Calc. for C22H26N2S6Sn1 (629.50): C, 41.97%; H 4.16%; N 4.45%. Found: C, 41.53%; H, 4.25%; N, 4.39%. IR (ATR, cm1) 1478(C-N), 1008, 945 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 2.79 (8H, t, S-CH2), 4.22 (8H, m, N-CH2), 7.46e7.51(4H, m, Ph), 7.82e8.05 (6H, m, Ph) ppm. 13C{1H} (100 MHz, DMSO) NMR: d ¼ 26.8 (C-S), 54.6 (C-N), 128.3 (Ph), 128.7 (Ph), 129.8 (Ph), 134.8 (Ph), 182.3 (CS2) ppm. 119Sn{1H} NMR (133.3 MHz, DMSO): d ¼ 353.4 ppm. 2.4. General procedure for the syntheses of complexes 5e6 A solution of organotin(V) chloride in methanol (5 mL) was added to a solution of KL2 (0.1 g, 0.44 mmol) in methanol (5 mL) while stirring. A heavy white precipitate was observed within 30 min. It was then stirred for 2 hrs. It was then filtered and washed with cold methanol and dried. Single crystals of 5e6 were observed after 10 days by layering methanol over a solution of the complex in dichloromethane. [Ph2Sn(L2)2] (5): Ph2SnCl2 (0.0749 g, 0.22 mmol) was used. Yield (80%, 0.227 g), Anal. Calc. for C26H34N2S4Sn1O2 (653.48): C 47.78%, H 5.24%, N 4.29%. Found: C 47.49%; H, 5.06%; N, 3.48%. IR(ATR, cm1) 1456 (C-N), 990, 955 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 1.11 (12H, s, CH3), 2.88 (4H, m, N-CH), 3.49e3.73 (4H, m, N-CH), 4.02 (2H, m, O-CHMe), 4.62 (2H, m, O-CHMe), 7.30e7.45 (6H, m, Ph), 7.68e8.00 (4H, m, Ph) ppm. 13C NMR (100 MHz, DMSO): d ¼ 17.1 (CH3), 18.2 (CH3), 56.1 (N-CH2), 62.9 (N-CH2), 65.7 (C-O), 70.6 (C-O), 128.3 (Ph), 128.6 (Ph), 133.7 (Ph), 134.4(Ph). 119Sn{1H} NMR (133.3 MHz, DMSO) d ¼ 335.4 ppm. [Ph3Sn(L2)] (6): Ph3SnCl (0.168 g, 0.44 mmol) was used. Yield (76%, 0.179 g), Anal. Calc. for C25H27N1S2Sn1O1 (540.28): C 55.57, H 5.04, N 2.59%. Found: C 55.58, H 4.91, N 1.71%. IR (ATR, cm1) 1470(C-N), 990 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 1.10 (6H, m, CH3), 2.86 (2H, m, N-CH), 3.54 (2H, m, N-CH), 4.01 (1H, m, O-CHMe), 4.11 (1H, m, O-CHMe), 7.41e7.44 (9H, m, Ph), 7.61e7.74 (6H, m, Ph) ppm. 13C{1H} (100 MHz, DMSO) NMR: d ¼ 17.2 (CH3), 18.2 (CH3),
29
56.11 (N-CH2), 56.2 (N-CH2), 65.7 (C-O), 70.6 (C-O), 128.5 (Ph), 129.1 (Ph), 136.0 (Ph), 142.4 (Ph), 200.9 (CS2) ppm. 119Sn{1H} NMR (133.3 MHz, DMSO) d ¼ 198.4 ppm. 2.5. X-ray crystallography X-ray intensity data of single crystals of 1 and 5e6 were collected on a Bruker D8 Quest diffractometer equipped with a Photon 100 CMOS area detector system, using MoKa radiation with a graphite monochromator (l ¼ 0.71073 Å) at T ¼ 100(2) K. Single crystals of 2e4 were used to collect X-ray intensity data on a Rigaku Oxford Diffraction Supernova Dual Source (Cu at zero) diffractometer equipped with an Atlas CCD detector using u scans and MoKa (l ¼ 0.71073 Å) or CuKa (l ¼ 1.5418 Å) radiation at T ¼ 100(2) K. The structures were solved by direct methods (SIR92) [30] and refined on F2 by full-matrix least-squares methods using SHELXL-2013 [31,32]. All non-hydrogen atoms were anisotropically refined. Hatoms were included in the refinement on calculated positions riding on their parent atoms. The function minimized was P [ w(Fo2- Fc2)2] (w ¼ 1/[s2 (Fo2) þ (aP)2 þ bP]), where P ¼ (Max(Fo2,0) þ 2Fc2)/3 with s2(Fo2) from counting statistics. The function R1 and wR2 were (sjjFoj - jFcjj)/sjFoj and [sw (Fo2 - Fc2)2/ s(wFo4)]1/2, respectively. Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as a supplementary publication no. CCDC 1540412e1540417. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: þ (44)1223-336-033; email: [email protected]. uk). 2.6. Antimicrobial study The antibacterial activities of both ligands and complexes 1e6 were studied against E. coli XL-1 Blue cells (Stratagene, USA) following the agar disc-diffusion method. Briefly, centrifuged pellets of overnight grown E. coli XL-1 Blue cells containing approximately 104e106 CFU/mL were spread on the surface of nutrient agar plates. Filter paper discs [6 mm diameter cut out of Whatman filter paper-42 (CAT No. 1442-125)] dipped in the test compounds at different known concentrations (2 mM, 18 mM, 40 mM, 80 mM, and 130 mM dissolved in 5% DMSO) were positioned on the media surface. Ampicillin (0.5 mg/ml, 5.0 mg/ml, and 50 mg/ml dissolved in H2O) and kanamycin (0.5 mg/ml, 5.0 mg/ml, and 50 mg/ml dissolved in H2O) were used as standards for antibacterial activity. The culture plates were incubated at 37 C in a bacteriological incubator overnight. The antibacterial activity was assessed by measuring the diameters of inhibition zones surrounding the filter paper discs following methods described earlier [33]. 5% DMSO was used as negative control. 3. Results and discussion 3.1. Synthesis Two new potassium dithiocarbamate salts [KL1] and [KL2] where L1 and L2 are thiomorpholine-4-carbodithiolate and 2,6dimethylmorpholine-4-carbodithiolate, respectively, have been prepared by reacting appropriate amines with carbon disulfide (CS2) in the presence of base. The ligands were isolated as colorless solids with yield higher than 80%. Complexes 1e6 were obtained by reacting various organotin chlorides with respective dithiocarbamato ligands (Schemes 3 and 4). The detailed synthetic procedures are illustrated in the experimental section. All six complexes were isolated as white crystalline solids. They are air stable and soluble in halogenated solvents but insoluble in
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M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
Scheme 3. Syntheses of complexes 1e4.
Scheme 4. Syntheses of complexes 5e6.
water and alcohols. Various conventional analytical techniques were utilized to characterize the ligands and complexes. Elemental analyses, FT-IR spectroscopy, UV-vis spectroscopy and 1H, 13C{1H}, 119 Sn{1H} NMR spectroscopy were employed to demonstrate the formation of ligands and complexes. Moreover, single-crystal X-ray diffraction was used to establish the solid-state structure of complexes 1e6. 3.2. FT-IR spectroscopy FT-IR spectroscopy was employed to assign different functional groups present in the ligands as well as in complexes. The FT-IR spectra of KL1 and KL2 exhibit a strong band due to the ѵ(N-CS2) stretching at 1450 and 1448 cm1, respectively (see supplementary data). A sharp band assigned to the asymmetric ѵ(C-S) stretching is observed at 995 and 952 cm1 for KL1 and KL2, respectively. The FTIR spectra of complexes 1e6 show the ѵ(N-CS2) stretch at 14561505 cm1. These values are in between reported values of ѵ(C¼N) and ѵ(C-N) stretching and even higher than ѵ(N-CS2) stretching vibration of similar ligands [34]. Thus, it confirms the existence of the partial double bond character of the N-CS2 bond in complexes 1e6 [35]. The ѵ(N-CS2) stretch is maximum (1505 cm1) for complex 3 due to the coordination of the electron withdrawing chloride ligand to Sn(IV) [36]. Generally, the ‒CS2 fragment generates a unique set of bands that provides important information regarding the coordination mode of ligands in the complexes [37]. It is well established that one ѵ(C-S) stretching band (ѵasym) is observed
when the dithiocarbamato ligand is bonded to a metal in a bidentate fashion. However, this band splits into two close bands because of asymmetry in bonding through two sulfur atoms of the ligand [38]. Two closely spaced signals are observed for complexes 1e5 in the range of 943e1023 cm1 indicating an asymmetric bidentate bonding mode of the ligands to the metal [39]. However, the IR spectrum of 6 shows only one sharp signal at 990 cm1 and thus suggests a symmetrical bidentate coordination of the ligands to tin center. 3.3. NMR spectroscopy The 1H NMR spectra of KL1 shows signals for two ‒CH2 protons at 2.53 (S‒CH2) and 4.59 (N‒CH2) ppm, respectively. The resonance of ‒CH3 in KL2 appear at 1.08 ppm. The methylene (N‒CH2) and methyne (O‒CHMe) protons display signals at 2.39e3.24 and 5.79 ppm, respectively. The 13C{1H} resonance signals for the dithiocarbamato (CS2) moiety are observed at 213.9 and 213.6 ppm for KL1 and KL2, respectively. These values are similar to previously reported data [36]. Other carbon atoms exhibit signals in the expected region. Complexes 1e6 display the expected pattern in the 1 H and 13C{1H} NMR spectra (experimental section). The 119Sn{1H} NMR chemical shift provides further structural evidence and is useful for determining the coordination environment of the metal center. Among the six complexes, complexes 1 and 6 show a chemical shift at 196.0 and 198.5 ppm and thus indicating the existence of a five-coordinated tin(IV) center in these complexes
M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
[40,41]. A119Sn{1H} chemical shift of 3 at 340.5 ppm indicates that the Sn(IV) center maintains a penta-coordinated geometry in solution. Similar values were documented for chlorodiphenyltin N,Ndiethyldithiocarbamate, [Ph2Sn(Et2dtc)Cl] and other chlorodiphenyltin(IV) dithiocarbamate complexes [40,41]. The tin center remains in a six-coordinated environment in complexes 2 and 4e5 as the 119Sn{1H} NMR values lie in the range of 335.5 to 543.8 ppm [42]. These results are in full agreement with previously reported 119Sn NMR data [23,38]. NMR spectra of both ligands and complexes 1e6 can be found in the supplementary data. 3.4. Description of the structures Single crystals of complexes 1e6 were obtained by layering methanol over a solution of the respective complexes in dichloromethane. The solid-state structures of all complexes were established by single-crystal X-ray diffraction analyses. Data collection and refinement statistics for complexes 1e6 are listed in Table 1. Crystallographic analyses revealed that all complexes contain one tin(IV) center in it. The molecular structures of 1e6 are presented in Fig. 1. One or two thiomorpholine-4-carbodithiolate (L1) ligands are present in complexes 1, 3 or 2, 4, respectively. The tin(IV) center is five-coordinated in 1 and 3. The tin(IV) center is coordinated by two sulfur atoms (S1 and S2) and three carbon atoms of three phenyl groups in 1. The Sn1‒S1 and Sn1‒S2 bond lengths are 2.9839(1) and 2.4808(4) Å, respectively, thus indicating the presence of an asymmetry in the coordination mode of L1 in 1. One Cl atom (Cl1) is bonded to tin atom (Sn1) in addition to one dithiocarbamato ligand and two phenyl groups with a Sn1‒Cl1 bond length of 2.4791(15) Å in 3 [41]. The Sn‒S bond lengths are provided in Table 2. The tin(IV) center is staying in a distorted octahedral coordination environment in 2 and 4. Four sulfur atoms of two L1 and two carbon atoms of two butyl (2) or phenyl (4) moieties are bonded to the tin atom. The asymmetric coordination mode of the ligands is observed in both complexes. Four sulfur atoms of two ligands are occupying the equatorial positions of the octahedron in complex 2. The two axial sites are engaged by two butyl moieties. In complex 4, the equatorial plane is formed by three sulfur
31
atoms (S1, S2 and S4) and one carbon atom (C27). Two axial positions are involved in bonding with one sulfur atom (S5) of L1 and one carbon (C21) of one phenyl group. Detailed Sn‒S and Sn‒C bond lengths and relevant angles are given in Table 2. There are two asymmetrically coordinating dithiocarbamato ligands (L2) bonded to tin(IV) center in 5 resulting in a distorted coordination environment around tin(IV) center. Similar to 2, four sulfur atoms of two ligands and two phenyl groups are occupying the equatorial and axial sites of the octahedron, respectively. The Sn‒Sshort and Sn‒Slong bond lengths in all complexes lie in the range of 2.4546(13)-2.5906(8) and 2.6257(9)-3.1433 Å, respectively. These values are in close agreement with reported values of similar compounds [43]. The Sn(IV) center in complex 6 is also fivecoordinated and bonded asymmetrically by two sulfur atoms (S1 and S2) of L2 and three phenyl groups. Interestingly, the longest Sn‒ S bond of 3.1433 Å was observed in 6 among all six complexes. Similar observations were previously observed for diorganotin(IV) complex of morpholine carbodithiolate ligand [44,45]. 3.5. UV-visible spectroscopy Electronic spectra of complexes 1e6 were recorded in a wavelength range of 200e800 nm at ambient temperature in dichloromethane. The spectra exhibit bands in the range of 240e270 and 280e313 nm which can be assigned to intraligand charge transfer of the C¼S chromophore and charge transfer from the ligand orbital to the vacant metal (tin) orbitals, respectively. Fig. 2 shows the absorption spectra of complexes 1e6. 3.6. Thermogravimetric analyses Thermogravimetric analysis of the complexes 1e6 were carried out in the temperature range of 200e800 C with a heating rate of 10 C under nitrogen atmosphere to check the thermal stability and/or volatility of the complexes. The TG curves (Fig. 3) of all complexes show a single-step degradation with maximum mass loss in the temperature range 210e370 C. One could observe that complexes 1 and 6 are thermally more stable among all complexes.
Table 1 Single-crystal data collection and structure refinement statistics for complexes 1e6. Complexes
1
2
3
4
5
6
Formula Formula mass T/K l/Å Crystal system Space group a/Å b/Å c/Å a/ b/ g/ V/Å3 Z Dc/g cm3 m/mm1 F(000) q Range/ Measured reflections Independent reflections Rint Parameters R1 (I > 2s(I)) wR2 (all data) Goodness-of-fit on F2 Drmax, min/e Å3
C23H23NS3Sn 528.29 100(2) 0.71073 triclinic P-1 9.1094(4) 10.9839(5) 12.3300(5) 70.388(2) 73.0950(10) 84.585(2) 1111.90(8) 2 1.578 1.440 532 7.638e27.843 18641 3868 0.0231 253 0.0161 0.0388 1.087 0.375,-0.217
C18H34N2S6Sn 589.52 100(2) 0.71073 monoclinic C 2/c 20.5322(12) 6.7386(3) 19.6858(8) 90 99.228(5) 90 2688.4(2) 4 1.456 1.424 1208 3.129e29.132 10638 1510 0.0530 123 0.0603 0.1289 1.016 0.532,-0.287
C17H18ClNS3Sn 486.64 100(2) 0.71073 orthorhombic P212121 10.2220(4) 12.3651(5) 15.5761(5) 90 90 90 1968.76(13) 4 1.642 1.749 968 3.091e28.858 12411 3765 0.0331 209 0.0351 0.0665 1.027 0.437, 0.438
C22H26N2S6Sn 629.50 100(2) 1.54184 monoclinic P21/c 9.0237(10) 22.9477(3) 12.4253(10) 90 98.5570(10) 90 2544.30(5) 4 1.643 12.697 1272 3.853e74.999 23402 5026 0.0671 280 0.0538 0.1532 0.927 4.681,-2.527
C26H34N2O2S4Sn 653.48 100(2) 0.71073 monoclinic P 21/c 9.4066(4) 20.1936(8) 16.4712(6) 90 109.942(2) 90 2941.1(2) 4 1.476 1.178 1336 2.303e25.318 48653 4491 0.0715 331 0.0377 0.0904 1.084 1.269,-0.830
C25H27N1S2Sn1O1 540.28 100(2) 0.71073 monoclinic Cc 15.9990(5) 9.8710(6) 14.9750(7) 90 91.4740(10) 90 2364.2(2) 4 1.518 1.274 1096 2.425e25.290 12423 4076 0.0271 270 0.0230 0.0539 1.047 2.076,-0.611
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M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
Fig. 1. Molecular structures of complex 1e6 in ball-and-stick representation. Hydrogen atoms are omitted for clarity.
Table 2 Selected bond lengths (Ǻ) and bond angles ( ) for complexes 1e6. Bond/Angle
1
2
3
4
5
6
Sn1-S1 Sn1-S2 Sn1-S4 Sn1-S5 Sn1-C21 Sn1-C27 Sn1-C33 C1-S1 C1-S2 C6-S4 C6-S5 C1-N1 C6-N2 Sn1-Cl1 S1-Sn1-S2 S4-Sn1-S5
2.9839(1) 2.4804(6) e e 2.160(2) 2.131(2) 2.139(2) 1.753(2) 1.684(2) e e 1.334(3) e e 64.805(1) e
2.9213(15) 2.5433(14) e e 2.148(8) e e 1.687(5) 1.735(5) e e 1.336(6) e e 65.03(4) e
2.6350(14) 2.4789(14) e e 2.137(5) 2.136(5) e 1.715(5) 1.742(5) e e 1.314(6) e 2.4791(15) 70.27(4) e
2.6257(9) 2.5906(8) 2.5689(8) 2.6928(8) 2.167(4) 2.161(4) e 1.713(4) 1.733(4) 1.740(4) 1.708(4) 1.329(5) 1.330(5) e 68.97(3) 68.47(3)
2.9132(10) 2.5271(10) 2.9237(10) 2.5163(10) 2.137(4) 2.137(4) e 1.691(4) 1.751(4) 1.689(4) 1.752(4) 1.319(6) 1.322(6) e 65.70(3) 65.641(1)
3.1433 2.4546(13) e e 2.138(4) 2.132(5) 2.156(5) 1.683(5) 1.767(5) e e 1.320(6) e e 63.028 e
M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
33
Table 3 Zone of inhibition (mm) for complexes 1e6 against E. Coli. Complex
Zone of Inhibition (mm)
1 2 3 4 5 6 Conc (mM)
6.3 ± 0.14 6.05 ± 0.07 6.3 ± 0.14 6.25 ± 0.21 6.45 ± 0.21 6.1 ± 0.14 2
7.2 ± 0.14 6.95 ± 0.21 7.7 ± 0.28 6.95 ± 0.21 7.15 ± 0.21 7 ± 0.28 18
7.8 ± 0.14 7.5 ± 0.14 8.45 ± 0.21 8.25 ± 0.21 8.6 ± 0.28 7.8 ± 0.28 40
9.6 ± 0.14 9.55 ± 0.21 9.65 ± 0.49 9.4 ± 0.28 9.65 ± 0.21 9.05 ± 0.21 80
10.75 ± 0.21 10.4 ± 0.14 10.2 ± 0.28 10.4 ± 0.14 10.6 ± 0.14 10.1 ± 0.14 130
Table 4 Zone of inhibition (mm) for standard antibiotics ampicillin and kanamycin against E. Coli.
Fig. 2. UV-vis spectra of complexes 1e6.
Antibiotic
Zone of Inhibition (mm)
Ampicillin Kanamycin Conc (mg/ml)
9.2 ± 0.14 22.5 ± 0.28 50
7.25 ± 0.21 13.5 ± 0.14 5
6.1 ± 0.14 6.3 ± 0.28 0.5
Fig. 4. Zone of inhibition versus concentration for complexes 1e6 against E. Coli. Fig. 3. TG curve of complexes 1e6.
drugs (Ampicillin and Kanamycin) toward E. Coli XL-1 Blue cells. 3.7. Antimicrobial studies
4. Conclusions
The in vitro antibacterial activity of tin complexes (1e6) were evaluated against Escherichia coli XL-1 Blue cells by the disc diffusion method. The ligands decomposed during the experimental conditions (incubation at 37 C for 24 h) and therefore their antimicrobial activity were not explored. The stability of complexes 1e6 was checked by UV-vis spectroscopy in DMSO during 24 h. The results show that all complexes do not degrade significantly during the experimental condition (see supplementary data). All complexes showed considerable antibacterial activity (in 5% DMSO in water) at concentrations of 2 mM, 18 mM, 40 mM, 80 mM, and 130 mM dissolved in 5% DMSO. The solvent (DMSO) did not show any activity against E. coli XL-1 Blue cells in the present study. The inhibition zone of all complexes at different concentrations is summarized in Table 3. The effect of antibiotics as positive control used in the present study is summarized in Table 4. The zone of inhibition of all complexes showed an increase with increase in concentration of the corresponding complexes (Fig. 4). The zone of inhibition of all complexes with a concentration of 130 mM ranges from 10.1 ± 0.14 to 10.75 ± 0.21 mm. Thus, they exhibit nearly identical activities towards E. Coli XL-1. It is observed that all complexes are significantly less effective than clinically approved
In conclusion, potassium salts of two dithiocarbamato ligands were synthesized. These ligands were successfully employed to prepare a series of mononuclear organotin(IV) complexes (1e6). Both ligands and complexes were characterized by a number of analytical techniques. Both the solution and solid-state structure determination revealed that tin(IV) centre is five- or sixcoordinated in these complexes. A bidentate coordination mode of dithiocarbamato moiety was observed in all complexes. All complexes showed significant in vitro antimicrobial activity against E. Coli. Among them, complex 1 exhibited the highest activity and complex 6 was the least active one. Acknowledgements This work was financially supported by Science and Engineering Research Board (SERB), India (Order No. SB/EMEQ-013/2014, dated 17/06/2014). We thank SAIF, Punjab University for providing analytical facilities. KVH thanks the Hercules Foundation (project AUGE/11/029 “3D-SPACE: 3D Structural Platform Aiming for Chemical Excellence”) and the Research Foundation e Flanders (FWO) for funding.
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Appendix A. Supplementary data FT-IR spectra, NMR spectra of ligands, complexes 1-6 and UV-vis spectra of complexes 1-6 in DMSO are provided in the supplementary data. Supplementary data related to this article can be found at https://doi.org/10.1016/j.jorganchem.2017.10.027. References [1] V. Chandrasekhar, K. Gopal, P. Sasikumar, R. Thirumoorthi, Coord. Chem. Rev. 249 (2005) 1745e1765. [2] V. Chandrasekhar, S. Nagendran, V. Baskar, Coord. Chem. Rev. 235 (2002) 1e52. [3] E.R.T. Tiekink, Appl. Organometal. Chem. 5 (1991) 1e23. [4] L.A. Komarnisky, R.J. Christopherson, T.K. Basu, Nutrition 19 (2003) 54e61. [5] H.P.S. Chauhan, J. Carpenter, S. Joshi, Appl. Organometal. Chem. 28 (2014) 605e613. [6] S. Sivasekar, K. Ramalingam, C. Rizzoli, Polyhedron 85 (2015) 598e606. € pfl, M.A. Garcia-Garibay, Organ[7] A. Torres-Huerta, B. Rodríguez-Molina, H. Ho ometallics 33 (2014) 354e362. [8] N. Hollingsworth, A. Roffey, H.-U. Islam, M. Mercy, A. Roldan, W. Bras, M. Wolthers, C.R.A. Catlow, G. Sankar, G. Hogarth, N.H. de Leeuw, Chem. Mater 26 (2014) 6281e6292. [9] E.A. Lewis, P.D. McNaughter, Z. Yin, Y. Chen, J.R. Brent, S.A. Saah, J. Raftery, J.A.M. Awudza, M.A. Malik, P. O'Brien, S.J. Haigh, Chem. Mater 27 (2015) 2127e2136. [10] S. Tamilvanan, G. Gurumoorthy, S. Thirumaran, S. Ciattini, Polyhedron 121 (2017) 70e79. [11] M.D. Regulacio, N. Tomson, S.L. Stoll, Chem. Mater 17 (2005) 3114e3121. [12] T. Mirkovic, M.A. Hines, P.S. Nair, G.D. Scholes, Chem. Mater 17 (2005) 3451e3456. [13] K. Ramasamy, M.A. Malik, J. Raftery, F. Tuna, P. O'Brien, Chem. Mater 22 (2010) 4919e4930. [14] F. Sunderman, Ann. Clin. Lab. Sci. 9 (1979) 1e10. [15] D.L. Bodenner, P.C. Dedon, P.C. Keng, R.F. Borch, Cancer Res. 46 (1986) 2745e2750. [16] C. Nardon, G. Boscutti, C. Gabbiani, L. Massai, N. Pettenuzzo, A. Fassina, L. Messori, D. Fregona, Eur. J. Inorg. Chem. (2017) 1737e1744. [17] I. Rojas-Leon, J.A. Guerrero-Alvarez, J. Hernandez-Paredes, H. Hopfl, Chem. Commun. 48 (2012) 401e403. € pfl, L.G. Hern [18] A. Torres-Huerta, J. Cruz-Huerta, H. Ho andez-V azquez, nez-S ndez-Ahuactzi, J. Escalante-García, A. Jime anchez, R. Santillan, I.F. Herna
M. S anchez, Inorg. Chem. 55 (2016) 12451e12469. rquez, H. Ho € pfl, A. Torres-Huerta, J. Guerrero[19] M.G. Vasquez-Ríos, V. Reyes-Ma nchez, I.F. Hern nezAlvarez, M. Sa andez-Ahuactzi, K. Ochoa-Lara, A. Jime nchez, R. Santill Sa an, Eur. J. Inorg. Chem. (2016) 3429e3440. [20] D.J. Lewis, P. Kevin, O. Bakr, C.A. Muryn, M.A. Malik, P. O'Brien, Inorg. Chem. Front. 1 (2014) 577e598. [21] K. Ramasamy, V.L. Kuznetsov, K. Gopal, M.A. Malik, J. Raftery, P.P. Edwards, P. O'Brien, Chem. Mater 25 (2013) 266e276. [22] N. Khan, Y. Farina, L.K. Mun, N.F. Rajab, N. Awang, Polyhedron 85 (2015) 754e760. [23] M. Yousefi, M. Safari, M.B. Torbati, V.M. Kazemiha, H. Sanati, A. Amanzadeh, Appl. Organometal. Chem. 26 (2012) 438e444. s, M.P. Ferreira, [24] D.C. Menezes, F.T. Vieira, G.M. de Lima, J.L. Wardell, M.E. Corte M.A. Soares, A. Vilas Boas, Appl. Organometal. Chem. 22 (2008) 221e226. [25] E.R.T. Tiekink, Appl. Organometal. Chem. 22 (2008) 533e550. [26] S.K. Hadjikakou, N. Hadjiliadis, Coord. Chem. Rev. 253 (2009) 235e249. [27] H.P. Nayek, W. Massa, S. Dehnen, Inorg. Chem. 47 (2008) 9146e9148. [28] H.P. Nayek, G. Hilt, S. Dehnen, Eur. J. Inorg. Chem. 2009 (2009) 4205e4208. [29] M. Mahato, P.P. Jana, K. Harms, H.P. Nayek, RSC Adv. 5 (2015) 62167e62172. [30] G.M. Sheldrick, SHELXS-97, Program of Crystal Structure Solution, University € ttingen, Germany, 1997. of Go [31] G.M. Sheldrick, SHELXL-97, Program of Crystal Structure Refinement, Uni€ ttingen, Germany, 1997. versity of Go [32] G.M. Sheldrick, Acta Crystallogr. sec. A 64 (2008) 112e122. [33] N.G. Heatley, Biochem. J. 38 (1944) 61e65. [34] S. Hussain, S. Ali, S. Shahzadi, M.N. Tahir, S. Ramzan, M. Shahid, Polyhedron 119 (2016) 483e493. [35] S. Hussain, S. Ali, S. Shahzadi, S.K. Sharma, K. Qanungo, M. Altaf, H.S. Evans, Phosphorus, Sulfur, Silicon Relat. Elem. 186 (2011) 542e551. [36] S. Ali, R. Zia ur, R. Muneeb ur, I. Khan, S.N.A. Shah, R.F. Ali, A. Shah, A. Badshah, langer-Gariepy, J. Coord. Chem. 67 (2014) 3414e3430. K. Akbar, F. Be [37] F. Bonati, R. Ugo, J. Organomet. Chem. 10 (1967) 257e268. [38] I.P. Ferreira, G.M. de Lima, E.B. Paniago, W.R. Rocha, J.A. Takahashi, C.B. Pinheiro, J.D. Ardisson, Eur. J. Med. Chem. 58 (2012) 493e503. [39] N. Singh, S. Bhattacharya, J. Organomet. Chem. 700 (2012) 69e77. [40] D. Dakternieks, H. Zhu, D. Masi, C. Mealli, Inorg. Chem. 31 (1992) 3601e3606. n-Bravo, P.G.y. García, [41] J.P. Fuentes-Martínez, I. Toledo-Martínez, P. Roma pez-Cardoso, H. Morales-Rojas, Polyhedron 28 (2009) C. Godoy-Alc antar, M. Lo 3953e3966. [42] P. Kevin, D.J. Lewis, J. Raftery, M. Azad Malik, P. O'Brien, J. Cryst. Growth 415 (2015) 93e99. €hn, A. Kumar, Inorg. [43] R. Yadav, M. Trivedi, R. Chauhan, R. Prasad, G. Kociok-Ko Chim. Acta 450 (2016) 57e68. [44] V. Vrabel, E. Kello, Acta Crystallogr. sec. C 49 (1993) 873e875. [45] W. Ng Seik, in: Z. Kristallogr. New Cryst. Struct, 1997, p. 285.
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Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Mononuclear homoleptic organotin(IV) dithiocarbamates: Syntheses, structures and antimicrobial activities Mamata Mahato a, Shayantan Mukherji b, Kristof Van Hecke c, Klaus Harms d, Abhrajyoti Ghosh b, Hari Pada Nayek a, * a
Department of Applied Chemistry, Indian Institute of Technology (Indian School of Mines), Dhanbad, 826004, Jharkhand, India Department of Biochemistry, Bose Institute, Kolkata, West Bengal, India XStruct, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, B-9000, Ghent, Belgium d €t Marburg, Hans Meer-wein Strasse, Marburg, Germany Fachbereich Chemie, Philipps Universita b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2017 Received in revised form 12 October 2017 Accepted 19 October 2017 Available online 21 October 2017
Six mononuclear organotin(IV) complexes of two dithiocarbamato ligands, [Ph3SnL1] (1), [Bu2Sn(L1)2] (2), [Ph2Sn(L1)Cl] (3), [Ph2Sn(L1)2] (4), [Ph2Sn(L2)2] (5) and [Ph3Sn(L2)] (6) where L1 ¼ thiomorpholine-4carbodithiolate and L2 ¼ 2,6-dimethylmorpholine-4-carbodithiolate have been synthesized in good yields. Both ligands and complexes 1e6 were characterized by elemental analyses, FT-IR spectroscopy, UV-visible spectroscopy and 1H, 13C{1H} 119Sn{1H} NMR spectroscopy. In addition, the solid-state structures of the complexes were established through single-crystal X-ray diffraction analyses. The Xray analyses reveal that the Sn(IV) center is five-coordinated in 1, 3 and 6. In complexes 2, 4 and 5, Sn(IV) is six-coordinated and occupies the center of a distorted octahedron. Moreover, an asymmetric coordination mode of the dithiocarbamato ligands was observed in all complexes. The optical properties and thermal stabilities of all complexes were investigated. All complexes were evaluated for their in vitro antimicrobial properties against E. coli. Complex 1 shows a maximal biological activity whereas the least activity is found for complex 6. © 2017 Elsevier B.V. All rights reserved.
Keywords: Organotin(IV) complex Dithiocarbamato ligand 119 Sn NMR Single-crystal X-ray diffraction Antimicrobial activity
1. Introduction Organotin compounds have consistently been a potential area of research because of their immense structural diversities [1]. When combined with carboxylate ligands, organotin compounds exhibit a variety of structures ranging from monomers, dimers, oligomers, polymers and even, one-, two- or three-dimensional frameworks [2,3]. However, recent research work has been slowly replacing carboxylate ligands by sulfur donor ligands because of their resemblance with sulfur-containing biomolecules such as vitamins and amino acids [4]. In this context, the synthesis of metal complexes using a dithiocarbamate anion (R2NCS 2 ) has continued to gain attention in the last decades. Dithiocarbamate anions constitute an important class of ligands and can easily be isolated as alkali metals or ammonium salts by reacting an amine with carbon disulfide (CS2) in the presence of a base [5]. Further reaction of it with metal salts results in the formation of the corresponding metal
* Corresponding author. E-mail address: [email protected] (H.P. Nayek). https://doi.org/10.1016/j.jorganchem.2017.10.027 0022-328X/© 2017 Elsevier B.V. All rights reserved.
dithiocarbamates. Dithiocarbamato ligands contain two soft sulfur atoms which can bind to the metals in a monodentate, bidentate, anisobidentate or triconnective fashion (Scheme 1) [6]. These ligands can often generate a broad variety of molecular and supramolecular structures [7]. In addition to their peculiar structural diversities, these ligands and their metal complexes have attracted attention as potential candidates for various applications in material science. For example, they are used as single-source precursors for the preparation of metal sulphides as thin films or nanoparticles [8e10]. A variety of dithiocarbamato metal complexes of transition metals and lanthanides have been prepared and used as precursors for the synthesis of metal sulphides [11e13]. These ligands also play an active role in medical science [14e16]. However, the chemistry of dithiocarbamato derivative of main group elements is less widely explored compare to transition metals or lanthanides [6]. In this context, organotin dithiocarbamates continue to be the focus of recent research works.
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M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
Scheme 1. Coordination modes of dithiocarbamate ligands.
Analogous to carboxylate derivatives, organotin dithiocarbamates generate a variety of structures [17]. Occasionally, they form macrocycle or supramolecular structures. For example, several 22-, 23-, 26- and 27-membered macrocyclic diorganotin(IV) bisdithiocarbamates have recently been reported and few of them have been explored for their sensing abilities towards inorganic and organic anions [18,19]. Moreover, tin sulphides (SnS, SnS2 and Sn2S3) which are synthesized from organotin dithiocarbamate complexes exhibit semiconducting properties with a band gap of 0.95e2.18 eV [20]. These sulphides are used as solar energy absorber, and in holographic recording and infrared detection [21]. In addition, organotin dithiocarbamates exhibit important biological activities such as anti-fungal, anti-microbial, anti-cancer activities etc [22]. For instance, organotin complexes of morpholine dithiocarbamate showed cytotoxic activity when tested against human HeLa and K562 tumor cell lines [23]. Moreover, it was found that these organotin complexes were more active than cisplatin. The antifungal activity of several organotin(IV) dithiocarbamates against Candida albicans (ATCC 18804), Candida tropicalis (ATCC 750) and resistant Candida albicans collected from HIV-positive patients was also tested [24]. A detailed application of organotin dithiocarbamate was documented by Tiekink [25]. However, the organotin moiety, organic substituents on the ligands and coordination number of the tin center play an active role in determining their biological activities [26]. Therefore, the design and synthesis of new organotin(IV) dithiocarbamate complexes by varying the organic groups on tin or the dithiocarbamato ligands has been a challenging task. During the last few years, we have been working on organotin compounds [27,28]. We are also working with dithiocarbamato ligands to prepare complexes of transition metals and lanthanides [29]. In continuation of our work, we have now chosen two dithiocarbamato ligands, potassium thiomorpholine-4carbodithiolate (KL1) and 2,6-dimethylmorpholine-42 carbodithiolate (KL ) for the present study (Scheme 2). These ligands have been reacted with various organotin compounds to prepare six organotin(IV) dithiocarbamate complexes [Ph3SnL1] (1), [Bu2Sn(L1)2] (2), [Ph2Sn(L1)Cl] (3), [Ph2Sn(L1)2] (4), [Ph2Sn(L2)2] (5) and [Ph3Sn(L2)] (6). All ligands and complexes were characterized by multinuclear NMR spectroscopy and FT-IR spectroscopy. Moreover, the solid-state molecular structures of complexes 1e6 were determined by single-crystal X-ray diffraction analysis. The optical properties, thermal stability and antimicrobial activity of all complexes are documented.
2. Experimental 2.1. Materials and analytical techniques All reactions were executed under aerobic conditions. Starting materials were used as received from Aldrich (thiomorpholine, 2,6dimethylmorpholine and dibutyltin dichloride), Acros organics (triphenyltin chloride), Alfa aesar (diphenyltin dichloride) and Merck (carbon disulfide) without any further purification. Solvents were distilled prior to use. Carbon, hydrogen and nitrogen microanalyses were carried out on a Thermo Scientific (FLASH 2000) CHNS elemental analyzer. FT-IR spectra were recorded in the solid state (ATR mode) using a Perkin Elmer- Spectrum RX-IFTIR spectrometer in the region of 4000e400 cm1. The electronic spectra of 1e6 were recorded on a Shimadzu UV-1800 spectrometer. 1H, 13C {1H}, 119Sn{1H} NMR of the complexes in solution were recorded on an FT NMR Spectrometer, Avance II (Bruker, 400 MHz). Thermogravimetric analyses were carried out using a Perkin Elmer, Diamond TG/DTA. 2.2. Procedure for the syntheses of ligands KL1 and KL2 2.2.1. Synthesis of KL1 A solution of thiomorpholine (1.002 mL, 10 mmol) in methanol (5 mL) was cooled in an ice bath. A cold solution of potassium hydroxide (0.561 g, 10 mmol) in H2O-MeOH (10 mL, 1:1) was added to it. After stirring 15 min, an ice cold solution of carbon disulfide (0.604 mL, 10 mmol) in methanol (5 mL) was added maintaining the reaction temperature below 10 C. A solid did appear which was stirred for 2 h, filtered and washed with cold methanol followed by drying in vacuum. The ligand was air stable and soluble in methanol at room temperature (25 C). Yield (89%, 1.934 g): IR (ATR, cm1) n ¼ 1450 (C-N), 993 (C-S). 1H NMR (DMSO, 400 MHz): d ¼ 2.52 (4H, t, S-CH2), 4.59 (4H, t, N-CH2) ppm. 13C{1H} NMR (100 MHz, DMSO): d ¼ 26.5 (C-S), 51.7 (C-N), 213.8 (CS2) ppm. 2.2.2. Synthesis of KL2 Ligand KL2 was synthesized following same procedure as KL1. Here, 2,6-dimethylmorpholine (1.232 mL, 5 mmol) was used instead of thiomorpholine. Yield (86%, 1.974 g). The ligand KL2 was white in color, air stable and was soluble in methanol at room temperature (25 C). IR (ATR, cm1) n ¼ 1448 (C-N), 952 (C-S).1H NMR (400 MHz, DMSO): d ¼ 1.06e1.08 (6H, m, CH3), 2.39 (2H, m, NCH), 3.36 (2H, m, N-CH), 5.80 (2H, m, O-CH) ppm. 13C{1H} NMR (100 MHz, DMSO): 18.6 (CH3), 47.1(N-CH2), 54.6 (N-CH2), 68.7 (CO), 70.8(C-O), 213.6 (CS2) ppm. 2.3. General procedure for the syntheses of complexes 1e4
Scheme 2. Potassium salts of thiomorpholine-4-carbodithiolate (KL1) and 2,6dimethylmorpholine-4-carbodithiolate (KL2).
To a solution of KL1 (0.1 g, 0.5 mmol) in methanol (5 mL), a solution of organotin(V) chloride in methanol (5 mL) was added. A white precipitate was immediately observed, which was stirred for 2 hrs. Thereafter it was filtered, washed with cold methanol and
M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
dried. Single crystals, suitable for X-ray diffraction analysis, were obtained by layering methanol over a solution of the resulting complex in dichloromethane, after two weeks. [Ph3SnL1] (1): Ph3SnCl (0.1927 g, 0.5 mmol) used. Yield (82%, 0.199 g), Anal. Calc. for C23H23N1S3Sn1 (528.29): C 52.29%, H 4.39%, N 2.65%. Found C 52.04%, H 4.10%, N 2.36%. IR (ATR, cm1) n ¼ 1479 (C-N), 998, 950 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 2.74 (4H, t, SCH2), 4.32 (4H, m, N-CH2), 7.38e7.43 (6H, m, Ph), 7.57e7.74 (9H, m, Ph) ppm. 13C{1H} NMR (100 MHz, DMSO): d ¼ 26.7 (C-S), 54.3 (C-N), 128.5 (Ph), 129.0 (Ph), 136.0 (Ph), 142.4 (Ph), 201.2 (CS2) ppm. 119Sn {1H} NMR (133.3 MHz, DMSO): d ¼ 195.9 ppm. [Bu2Sn(L1)2] (2): Bu2SnCl2 (0.076 g, 0.25 mmol) was used. Yield (68%, 0.185 g), Anal. Calc. for C18H34N2S6Sn1 (589.52): C 36.67%, H 5.81%, N 4.75%. Found: C 36.9%, H 5.71%, N 4.16%. IR (ATR, cm1): 1467 (C-N), 1023, 997 (C-S). 1H NMR (400.13 MHz, DMSO): d ¼ 0.88 (6H, t, CH3), 1.38 (4H, m, CH3-CH2), 1.82 (4H, m, CH3-CH2-CH2), 1.97 (4H, t, Sn-CH2), 2.73 (8H, m, S-CH2), 4.32 (8H, m, N-CH2) ppm. 13C {1H} NMR (100 MHz, DMSO): d ¼ 13.6 (CH3), 25.6 (CH3-CH2), 26.7 (CH3-CH2-CH2), 34.5 (C-Sn), 28.1(C-S), 53.6 (C-N), 203.8 (CS2) ppm. 119 Sn{1H} NMR (133.3 MHz, DMSO) d ¼ 543.7 ppm. [Ph2Sn(L1)Cl] (3): Ph2SnCl2 (0.0859 g, 0.25 mmol) was used. Yield (82%, 0.184 g), Anal. Calc. for C17H18N1S3Sn1Cl1 (486.64): C 41.95%, H 3.73%, N 2.88%. Found: C 41.80%, H 3.66%, N 2.45%. IR (ATR, cm1): 1505 (C-N), 1002, 943 (C-S). 1H NMR (400 MHz, DMSO) d ¼ 2.80 (4H, t, S-CH2), 4.21 (4H, m, N-CH2), 7.27e7.61 (4H, m, Ph), 7.85e8.09(6H, m, Ph) ppm. 13C{1H} (100 MHz, DMSO) NMR: d ¼ 26.9 (C-S), 54.7 (C-N), 128.7 (Ph), 129.9 (Ph), 134.9 (Ph), 143.8 (Ph), 193.7 (CS2) ppm. 119Sn{1H} NMR (133.3 MHz, DMSO): d ¼ 340.5 ppm. [Ph2Sn(L1)2] (4): Ph2SnCl2 (0.0859 g, 0.25 mmol) was used. Yield (74%, 0.214 g), Anal. Calc. for C22H26N2S6Sn1 (629.50): C, 41.97%; H 4.16%; N 4.45%. Found: C, 41.53%; H, 4.25%; N, 4.39%. IR (ATR, cm1) 1478(C-N), 1008, 945 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 2.79 (8H, t, S-CH2), 4.22 (8H, m, N-CH2), 7.46e7.51(4H, m, Ph), 7.82e8.05 (6H, m, Ph) ppm. 13C{1H} (100 MHz, DMSO) NMR: d ¼ 26.8 (C-S), 54.6 (C-N), 128.3 (Ph), 128.7 (Ph), 129.8 (Ph), 134.8 (Ph), 182.3 (CS2) ppm. 119Sn{1H} NMR (133.3 MHz, DMSO): d ¼ 353.4 ppm. 2.4. General procedure for the syntheses of complexes 5e6 A solution of organotin(V) chloride in methanol (5 mL) was added to a solution of KL2 (0.1 g, 0.44 mmol) in methanol (5 mL) while stirring. A heavy white precipitate was observed within 30 min. It was then stirred for 2 hrs. It was then filtered and washed with cold methanol and dried. Single crystals of 5e6 were observed after 10 days by layering methanol over a solution of the complex in dichloromethane. [Ph2Sn(L2)2] (5): Ph2SnCl2 (0.0749 g, 0.22 mmol) was used. Yield (80%, 0.227 g), Anal. Calc. for C26H34N2S4Sn1O2 (653.48): C 47.78%, H 5.24%, N 4.29%. Found: C 47.49%; H, 5.06%; N, 3.48%. IR(ATR, cm1) 1456 (C-N), 990, 955 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 1.11 (12H, s, CH3), 2.88 (4H, m, N-CH), 3.49e3.73 (4H, m, N-CH), 4.02 (2H, m, O-CHMe), 4.62 (2H, m, O-CHMe), 7.30e7.45 (6H, m, Ph), 7.68e8.00 (4H, m, Ph) ppm. 13C NMR (100 MHz, DMSO): d ¼ 17.1 (CH3), 18.2 (CH3), 56.1 (N-CH2), 62.9 (N-CH2), 65.7 (C-O), 70.6 (C-O), 128.3 (Ph), 128.6 (Ph), 133.7 (Ph), 134.4(Ph). 119Sn{1H} NMR (133.3 MHz, DMSO) d ¼ 335.4 ppm. [Ph3Sn(L2)] (6): Ph3SnCl (0.168 g, 0.44 mmol) was used. Yield (76%, 0.179 g), Anal. Calc. for C25H27N1S2Sn1O1 (540.28): C 55.57, H 5.04, N 2.59%. Found: C 55.58, H 4.91, N 1.71%. IR (ATR, cm1) 1470(C-N), 990 (C-S). 1H NMR (400 MHz, DMSO): d ¼ 1.10 (6H, m, CH3), 2.86 (2H, m, N-CH), 3.54 (2H, m, N-CH), 4.01 (1H, m, O-CHMe), 4.11 (1H, m, O-CHMe), 7.41e7.44 (9H, m, Ph), 7.61e7.74 (6H, m, Ph) ppm. 13C{1H} (100 MHz, DMSO) NMR: d ¼ 17.2 (CH3), 18.2 (CH3),
29
56.11 (N-CH2), 56.2 (N-CH2), 65.7 (C-O), 70.6 (C-O), 128.5 (Ph), 129.1 (Ph), 136.0 (Ph), 142.4 (Ph), 200.9 (CS2) ppm. 119Sn{1H} NMR (133.3 MHz, DMSO) d ¼ 198.4 ppm. 2.5. X-ray crystallography X-ray intensity data of single crystals of 1 and 5e6 were collected on a Bruker D8 Quest diffractometer equipped with a Photon 100 CMOS area detector system, using MoKa radiation with a graphite monochromator (l ¼ 0.71073 Å) at T ¼ 100(2) K. Single crystals of 2e4 were used to collect X-ray intensity data on a Rigaku Oxford Diffraction Supernova Dual Source (Cu at zero) diffractometer equipped with an Atlas CCD detector using u scans and MoKa (l ¼ 0.71073 Å) or CuKa (l ¼ 1.5418 Å) radiation at T ¼ 100(2) K. The structures were solved by direct methods (SIR92) [30] and refined on F2 by full-matrix least-squares methods using SHELXL-2013 [31,32]. All non-hydrogen atoms were anisotropically refined. Hatoms were included in the refinement on calculated positions riding on their parent atoms. The function minimized was P [ w(Fo2- Fc2)2] (w ¼ 1/[s2 (Fo2) þ (aP)2 þ bP]), where P ¼ (Max(Fo2,0) þ 2Fc2)/3 with s2(Fo2) from counting statistics. The function R1 and wR2 were (sjjFoj - jFcjj)/sjFoj and [sw (Fo2 - Fc2)2/ s(wFo4)]1/2, respectively. Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as a supplementary publication no. CCDC 1540412e1540417. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: þ (44)1223-336-033; email: [email protected]. uk). 2.6. Antimicrobial study The antibacterial activities of both ligands and complexes 1e6 were studied against E. coli XL-1 Blue cells (Stratagene, USA) following the agar disc-diffusion method. Briefly, centrifuged pellets of overnight grown E. coli XL-1 Blue cells containing approximately 104e106 CFU/mL were spread on the surface of nutrient agar plates. Filter paper discs [6 mm diameter cut out of Whatman filter paper-42 (CAT No. 1442-125)] dipped in the test compounds at different known concentrations (2 mM, 18 mM, 40 mM, 80 mM, and 130 mM dissolved in 5% DMSO) were positioned on the media surface. Ampicillin (0.5 mg/ml, 5.0 mg/ml, and 50 mg/ml dissolved in H2O) and kanamycin (0.5 mg/ml, 5.0 mg/ml, and 50 mg/ml dissolved in H2O) were used as standards for antibacterial activity. The culture plates were incubated at 37 C in a bacteriological incubator overnight. The antibacterial activity was assessed by measuring the diameters of inhibition zones surrounding the filter paper discs following methods described earlier [33]. 5% DMSO was used as negative control. 3. Results and discussion 3.1. Synthesis Two new potassium dithiocarbamate salts [KL1] and [KL2] where L1 and L2 are thiomorpholine-4-carbodithiolate and 2,6dimethylmorpholine-4-carbodithiolate, respectively, have been prepared by reacting appropriate amines with carbon disulfide (CS2) in the presence of base. The ligands were isolated as colorless solids with yield higher than 80%. Complexes 1e6 were obtained by reacting various organotin chlorides with respective dithiocarbamato ligands (Schemes 3 and 4). The detailed synthetic procedures are illustrated in the experimental section. All six complexes were isolated as white crystalline solids. They are air stable and soluble in halogenated solvents but insoluble in
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Scheme 3. Syntheses of complexes 1e4.
Scheme 4. Syntheses of complexes 5e6.
water and alcohols. Various conventional analytical techniques were utilized to characterize the ligands and complexes. Elemental analyses, FT-IR spectroscopy, UV-vis spectroscopy and 1H, 13C{1H}, 119 Sn{1H} NMR spectroscopy were employed to demonstrate the formation of ligands and complexes. Moreover, single-crystal X-ray diffraction was used to establish the solid-state structure of complexes 1e6. 3.2. FT-IR spectroscopy FT-IR spectroscopy was employed to assign different functional groups present in the ligands as well as in complexes. The FT-IR spectra of KL1 and KL2 exhibit a strong band due to the ѵ(N-CS2) stretching at 1450 and 1448 cm1, respectively (see supplementary data). A sharp band assigned to the asymmetric ѵ(C-S) stretching is observed at 995 and 952 cm1 for KL1 and KL2, respectively. The FTIR spectra of complexes 1e6 show the ѵ(N-CS2) stretch at 14561505 cm1. These values are in between reported values of ѵ(C¼N) and ѵ(C-N) stretching and even higher than ѵ(N-CS2) stretching vibration of similar ligands [34]. Thus, it confirms the existence of the partial double bond character of the N-CS2 bond in complexes 1e6 [35]. The ѵ(N-CS2) stretch is maximum (1505 cm1) for complex 3 due to the coordination of the electron withdrawing chloride ligand to Sn(IV) [36]. Generally, the ‒CS2 fragment generates a unique set of bands that provides important information regarding the coordination mode of ligands in the complexes [37]. It is well established that one ѵ(C-S) stretching band (ѵasym) is observed
when the dithiocarbamato ligand is bonded to a metal in a bidentate fashion. However, this band splits into two close bands because of asymmetry in bonding through two sulfur atoms of the ligand [38]. Two closely spaced signals are observed for complexes 1e5 in the range of 943e1023 cm1 indicating an asymmetric bidentate bonding mode of the ligands to the metal [39]. However, the IR spectrum of 6 shows only one sharp signal at 990 cm1 and thus suggests a symmetrical bidentate coordination of the ligands to tin center. 3.3. NMR spectroscopy The 1H NMR spectra of KL1 shows signals for two ‒CH2 protons at 2.53 (S‒CH2) and 4.59 (N‒CH2) ppm, respectively. The resonance of ‒CH3 in KL2 appear at 1.08 ppm. The methylene (N‒CH2) and methyne (O‒CHMe) protons display signals at 2.39e3.24 and 5.79 ppm, respectively. The 13C{1H} resonance signals for the dithiocarbamato (CS2) moiety are observed at 213.9 and 213.6 ppm for KL1 and KL2, respectively. These values are similar to previously reported data [36]. Other carbon atoms exhibit signals in the expected region. Complexes 1e6 display the expected pattern in the 1 H and 13C{1H} NMR spectra (experimental section). The 119Sn{1H} NMR chemical shift provides further structural evidence and is useful for determining the coordination environment of the metal center. Among the six complexes, complexes 1 and 6 show a chemical shift at 196.0 and 198.5 ppm and thus indicating the existence of a five-coordinated tin(IV) center in these complexes
M. Mahato et al. / Journal of Organometallic Chemistry 853 (2017) 27e34
[40,41]. A119Sn{1H} chemical shift of 3 at 340.5 ppm indicates that the Sn(IV) center maintains a penta-coordinated geometry in solution. Similar values were documented for chlorodiphenyltin N,Ndiethyldithiocarbamate, [Ph2Sn(Et2dtc)Cl] and other chlorodiphenyltin(IV) dithiocarbamate complexes [40,41]. The tin center remains in a six-coordinated environment in complexes 2 and 4e5 as the 119Sn{1H} NMR values lie in the range of 335.5 to 543.8 ppm [42]. These results are in full agreement with previously reported 119Sn NMR data [23,38]. NMR spectra of both ligands and complexes 1e6 can be found in the supplementary data. 3.4. Description of the structures Single crystals of complexes 1e6 were obtained by layering methanol over a solution of the respective complexes in dichloromethane. The solid-state structures of all complexes were established by single-crystal X-ray diffraction analyses. Data collection and refinement statistics for complexes 1e6 are listed in Table 1. Crystallographic analyses revealed that all complexes contain one tin(IV) center in it. The molecular structures of 1e6 are presented in Fig. 1. One or two thiomorpholine-4-carbodithiolate (L1) ligands are present in complexes 1, 3 or 2, 4, respectively. The tin(IV) center is five-coordinated in 1 and 3. The tin(IV) center is coordinated by two sulfur atoms (S1 and S2) and three carbon atoms of three phenyl groups in 1. The Sn1‒S1 and Sn1‒S2 bond lengths are 2.9839(1) and 2.4808(4) Å, respectively, thus indicating the presence of an asymmetry in the coordination mode of L1 in 1. One Cl atom (Cl1) is bonded to tin atom (Sn1) in addition to one dithiocarbamato ligand and two phenyl groups with a Sn1‒Cl1 bond length of 2.4791(15) Å in 3 [41]. The Sn‒S bond lengths are provided in Table 2. The tin(IV) center is staying in a distorted octahedral coordination environment in 2 and 4. Four sulfur atoms of two L1 and two carbon atoms of two butyl (2) or phenyl (4) moieties are bonded to the tin atom. The asymmetric coordination mode of the ligands is observed in both complexes. Four sulfur atoms of two ligands are occupying the equatorial positions of the octahedron in complex 2. The two axial sites are engaged by two butyl moieties. In complex 4, the equatorial plane is formed by three sulfur
31
atoms (S1, S2 and S4) and one carbon atom (C27). Two axial positions are involved in bonding with one sulfur atom (S5) of L1 and one carbon (C21) of one phenyl group. Detailed Sn‒S and Sn‒C bond lengths and relevant angles are given in Table 2. There are two asymmetrically coordinating dithiocarbamato ligands (L2) bonded to tin(IV) center in 5 resulting in a distorted coordination environment around tin(IV) center. Similar to 2, four sulfur atoms of two ligands and two phenyl groups are occupying the equatorial and axial sites of the octahedron, respectively. The Sn‒Sshort and Sn‒Slong bond lengths in all complexes lie in the range of 2.4546(13)-2.5906(8) and 2.6257(9)-3.1433 Å, respectively. These values are in close agreement with reported values of similar compounds [43]. The Sn(IV) center in complex 6 is also fivecoordinated and bonded asymmetrically by two sulfur atoms (S1 and S2) of L2 and three phenyl groups. Interestingly, the longest Sn‒ S bond of 3.1433 Å was observed in 6 among all six complexes. Similar observations were previously observed for diorganotin(IV) complex of morpholine carbodithiolate ligand [44,45]. 3.5. UV-visible spectroscopy Electronic spectra of complexes 1e6 were recorded in a wavelength range of 200e800 nm at ambient temperature in dichloromethane. The spectra exhibit bands in the range of 240e270 and 280e313 nm which can be assigned to intraligand charge transfer of the C¼S chromophore and charge transfer from the ligand orbital to the vacant metal (tin) orbitals, respectively. Fig. 2 shows the absorption spectra of complexes 1e6. 3.6. Thermogravimetric analyses Thermogravimetric analysis of the complexes 1e6 were carried out in the temperature range of 200e800 C with a heating rate of 10 C under nitrogen atmosphere to check the thermal stability and/or volatility of the complexes. The TG curves (Fig. 3) of all complexes show a single-step degradation with maximum mass loss in the temperature range 210e370 C. One could observe that complexes 1 and 6 are thermally more stable among all complexes.
Table 1 Single-crystal data collection and structure refinement statistics for complexes 1e6. Complexes
1
2
3
4
5
6
Formula Formula mass T/K l/Å Crystal system Space group a/Å b/Å c/Å a/ b/ g/ V/Å3 Z Dc/g cm3 m/mm1 F(000) q Range/ Measured reflections Independent reflections Rint Parameters R1 (I > 2s(I)) wR2 (all data) Goodness-of-fit on F2 Drmax, min/e Å3
C23H23NS3Sn 528.29 100(2) 0.71073 triclinic P-1 9.1094(4) 10.9839(5) 12.3300(5) 70.388(2) 73.0950(10) 84.585(2) 1111.90(8) 2 1.578 1.440 532 7.638e27.843 18641 3868 0.0231 253 0.0161 0.0388 1.087 0.375,-0.217
C18H34N2S6Sn 589.52 100(2) 0.71073 monoclinic C 2/c 20.5322(12) 6.7386(3) 19.6858(8) 90 99.228(5) 90 2688.4(2) 4 1.456 1.424 1208 3.129e29.132 10638 1510 0.0530 123 0.0603 0.1289 1.016 0.532,-0.287
C17H18ClNS3Sn 486.64 100(2) 0.71073 orthorhombic P212121 10.2220(4) 12.3651(5) 15.5761(5) 90 90 90 1968.76(13) 4 1.642 1.749 968 3.091e28.858 12411 3765 0.0331 209 0.0351 0.0665 1.027 0.437, 0.438
C22H26N2S6Sn 629.50 100(2) 1.54184 monoclinic P21/c 9.0237(10) 22.9477(3) 12.4253(10) 90 98.5570(10) 90 2544.30(5) 4 1.643 12.697 1272 3.853e74.999 23402 5026 0.0671 280 0.0538 0.1532 0.927 4.681,-2.527
C26H34N2O2S4Sn 653.48 100(2) 0.71073 monoclinic P 21/c 9.4066(4) 20.1936(8) 16.4712(6) 90 109.942(2) 90 2941.1(2) 4 1.476 1.178 1336 2.303e25.318 48653 4491 0.0715 331 0.0377 0.0904 1.084 1.269,-0.830
C25H27N1S2Sn1O1 540.28 100(2) 0.71073 monoclinic Cc 15.9990(5) 9.8710(6) 14.9750(7) 90 91.4740(10) 90 2364.2(2) 4 1.518 1.274 1096 2.425e25.290 12423 4076 0.0271 270 0.0230 0.0539 1.047 2.076,-0.611
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Fig. 1. Molecular structures of complex 1e6 in ball-and-stick representation. Hydrogen atoms are omitted for clarity.
Table 2 Selected bond lengths (Ǻ) and bond angles ( ) for complexes 1e6. Bond/Angle
1
2
3
4
5
6
Sn1-S1 Sn1-S2 Sn1-S4 Sn1-S5 Sn1-C21 Sn1-C27 Sn1-C33 C1-S1 C1-S2 C6-S4 C6-S5 C1-N1 C6-N2 Sn1-Cl1 S1-Sn1-S2 S4-Sn1-S5
2.9839(1) 2.4804(6) e e 2.160(2) 2.131(2) 2.139(2) 1.753(2) 1.684(2) e e 1.334(3) e e 64.805(1) e
2.9213(15) 2.5433(14) e e 2.148(8) e e 1.687(5) 1.735(5) e e 1.336(6) e e 65.03(4) e
2.6350(14) 2.4789(14) e e 2.137(5) 2.136(5) e 1.715(5) 1.742(5) e e 1.314(6) e 2.4791(15) 70.27(4) e
2.6257(9) 2.5906(8) 2.5689(8) 2.6928(8) 2.167(4) 2.161(4) e 1.713(4) 1.733(4) 1.740(4) 1.708(4) 1.329(5) 1.330(5) e 68.97(3) 68.47(3)
2.9132(10) 2.5271(10) 2.9237(10) 2.5163(10) 2.137(4) 2.137(4) e 1.691(4) 1.751(4) 1.689(4) 1.752(4) 1.319(6) 1.322(6) e 65.70(3) 65.641(1)
3.1433 2.4546(13) e e 2.138(4) 2.132(5) 2.156(5) 1.683(5) 1.767(5) e e 1.320(6) e e 63.028 e
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Table 3 Zone of inhibition (mm) for complexes 1e6 against E. Coli. Complex
Zone of Inhibition (mm)
1 2 3 4 5 6 Conc (mM)
6.3 ± 0.14 6.05 ± 0.07 6.3 ± 0.14 6.25 ± 0.21 6.45 ± 0.21 6.1 ± 0.14 2
7.2 ± 0.14 6.95 ± 0.21 7.7 ± 0.28 6.95 ± 0.21 7.15 ± 0.21 7 ± 0.28 18
7.8 ± 0.14 7.5 ± 0.14 8.45 ± 0.21 8.25 ± 0.21 8.6 ± 0.28 7.8 ± 0.28 40
9.6 ± 0.14 9.55 ± 0.21 9.65 ± 0.49 9.4 ± 0.28 9.65 ± 0.21 9.05 ± 0.21 80
10.75 ± 0.21 10.4 ± 0.14 10.2 ± 0.28 10.4 ± 0.14 10.6 ± 0.14 10.1 ± 0.14 130
Table 4 Zone of inhibition (mm) for standard antibiotics ampicillin and kanamycin against E. Coli.
Fig. 2. UV-vis spectra of complexes 1e6.
Antibiotic
Zone of Inhibition (mm)
Ampicillin Kanamycin Conc (mg/ml)
9.2 ± 0.14 22.5 ± 0.28 50
7.25 ± 0.21 13.5 ± 0.14 5
6.1 ± 0.14 6.3 ± 0.28 0.5
Fig. 4. Zone of inhibition versus concentration for complexes 1e6 against E. Coli. Fig. 3. TG curve of complexes 1e6.
drugs (Ampicillin and Kanamycin) toward E. Coli XL-1 Blue cells. 3.7. Antimicrobial studies
4. Conclusions
The in vitro antibacterial activity of tin complexes (1e6) were evaluated against Escherichia coli XL-1 Blue cells by the disc diffusion method. The ligands decomposed during the experimental conditions (incubation at 37 C for 24 h) and therefore their antimicrobial activity were not explored. The stability of complexes 1e6 was checked by UV-vis spectroscopy in DMSO during 24 h. The results show that all complexes do not degrade significantly during the experimental condition (see supplementary data). All complexes showed considerable antibacterial activity (in 5% DMSO in water) at concentrations of 2 mM, 18 mM, 40 mM, 80 mM, and 130 mM dissolved in 5% DMSO. The solvent (DMSO) did not show any activity against E. coli XL-1 Blue cells in the present study. The inhibition zone of all complexes at different concentrations is summarized in Table 3. The effect of antibiotics as positive control used in the present study is summarized in Table 4. The zone of inhibition of all complexes showed an increase with increase in concentration of the corresponding complexes (Fig. 4). The zone of inhibition of all complexes with a concentration of 130 mM ranges from 10.1 ± 0.14 to 10.75 ± 0.21 mm. Thus, they exhibit nearly identical activities towards E. Coli XL-1. It is observed that all complexes are significantly less effective than clinically approved
In conclusion, potassium salts of two dithiocarbamato ligands were synthesized. These ligands were successfully employed to prepare a series of mononuclear organotin(IV) complexes (1e6). Both ligands and complexes were characterized by a number of analytical techniques. Both the solution and solid-state structure determination revealed that tin(IV) centre is five- or sixcoordinated in these complexes. A bidentate coordination mode of dithiocarbamato moiety was observed in all complexes. All complexes showed significant in vitro antimicrobial activity against E. Coli. Among them, complex 1 exhibited the highest activity and complex 6 was the least active one. Acknowledgements This work was financially supported by Science and Engineering Research Board (SERB), India (Order No. SB/EMEQ-013/2014, dated 17/06/2014). We thank SAIF, Punjab University for providing analytical facilities. KVH thanks the Hercules Foundation (project AUGE/11/029 “3D-SPACE: 3D Structural Platform Aiming for Chemical Excellence”) and the Research Foundation e Flanders (FWO) for funding.
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