Inorganica Chimica Acta 443 (2016) 141–150

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Inorganica Chimica Acta

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Addition of tetraethylthiuram disulfide to antimony(III) iodide;synthesis, characterization and biological activity

http://dx.doi.org/10.1016/j.ica.2015.12.0280020-1693/� 2016 Elsevier B.V. All rights reserved.

⇑ Corresponding authors. Tel.: +30 26510 08374; fax: +30 2651008786(S.K. Hadjikakou).

E-mail addresses: iiozturk@nku.edu.tr (I.I. Ozturk), shadjika@uoi.gr(S.K. Hadjikakou).

O.S. Urgut a, I.I. Ozturk a,⇑, C.N. Banti b, N. Kourkoumelis c, M. Manoli d, A.J. Tasiopoulos d, S.K. Hadjikakou b,⇑aDepartment of Chemistry, Namık Kemal University, 59030 Tekirdag, Turkeyb Section of Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, GreececMedical Physics Laboratory, Medical School, University of Ioannina, Ioannina 45110, GreecedDepartment of Chemistry, University of Cyprus, Nicosia, Cyprus

a r t i c l e i n f o a b s t r a c t

Article history:Received 2 November 2015Received in revised form 18 December 2015Accepted 28 December 2015Available online 4 January 2016

Keywords:Antimony(III) complexesCrystal structuresN,N-diethylcarbamodithioic acidCytotoxicityStructure Activity Relationship (SAR)

Three new antimony(III) iodide complexes with the N,N-diethylcarbamodithioic acid of formulae{[(SbI(Et2DTC)2)(I2)]n} (1), {[(Sb(Et2DTC)2)4 (SbI6) (I3)]n} (2) and {[SbI(Et2DTC)2]2} (3), (Et2DTCH: N,N-diethylcarbamodithioic acid, C5H11NS2) were synthesized from the reaction of antimony(III) iodide withtetraethylthiuram disulfide in 1:1 stoichiometry. The complexes 1–3 were characterized by meltingpoint, elemental analysis, FT-IR spectroscopy, Raman spectroscopy, 1H, 13C NMR spectroscopy andThermal Gravimetry–Differential Thermal Analysis (TG–DTA). Moreover, crystal structures of complexes1–3 were determinated with single crystal X-ray diffraction analysis. Complexes 1–3 derived from ligandreduction with concomitant degradation of the tetraethylthiuram disulfide to dithiocarbamates.Complexes 1 and 2 are polymer but complex 3 is dimmer. Complex 1 consists of two residues, [SbI(Et2DTC)2] and [I2], while 2 consists of three residues, four cationic [Sb(Et2dtc)2]+, one [SbI6]3� and one[I3]

� counter anion.Complexes 1–3 were evaluated for their in vitro cytotoxic activity against human breast adenocarci-

noma (MCF-7) and human cervix adenocarcinoma (HeLa) cells. Structure Activity Relationship (SAR)studies reveal that the high activity of the complexes is positively correlated with the low H-all atomsintermolecular contacts.

� 2016 Elsevier B.V. All rights reserved.

1. Introduction

The medicinal applications of antimony can be traced back tothe sixteenth century when it was used as an emetic drug [1].Nowadays there is an increasing interest in medicinal applicationof antimony, and significant progress has been made [2]. Atpresent, antimony complexes are clinically used for the treatmentof Leismaniasis [3]. Recently, the antitumor activity of antimonycompounds is also reported [4–6]. Antimony(III) compounds weretested, in vitro, for their inhibitory effects on the proliferation ofcancerous cell lines, with different tissues such as, leimyosarcoma(LMS), human breast adenocarcinoma (MCF-7), murine leukemia(L1210), murine mammary (FM3A), human T-lymphocyte(Molt4/C8, CEM) and human cervix (HeLa) cells. Antimony(III)

halide complexes were found to exhibit strong antiproliferativeactivity against HeLa, LMS and MCF-7 cell lines [5,7].

Thiuram disulfides are a class of organic disulfides and they arethe thiocarbamoyl esters of dialkyldithiocarbamic acids [8]. Thegeneral formula of thiuram disulfides are shown in Scheme 1.Tetraalkylthiuram disulfide compounds, known as disulfiram arebioactive materials, which possess applications as fungicides,agents of alcoholism therapy and as arrestors of human immunod-eficiency virus infections such as AIDS [8–11].

Threedifferentkindsofproductswereobtained fromthe reactionof thiuram disulfides: (a) adducts; (b) thiuram oxidation productsand (c) ligand reductionwith concomitant degradation to dithiocar-bamate and/or thiocarboxamide ligands [11]. Example of thiuramdisulfide adducts include the [Hg(Et4tds)I2] (Et4tds: Tetraethylthiu-ram disulfide) complex [12]. Besides, five membered dicationiccyclic derivatives which are neutralized by metal halides counteranions may obtained; e.g. [Et4biit-3]2+[Hg2I6]2� (Et4biit-3: 3,5-bis(N,N0diethylammonium)-1,2,4-trithiolane) [13a], [Et4biit-3]2+2[FeCl4]� and [Bu4biit-3]2+[Cu2X6]2� (Bu4biit-3: 3,5-bis(N,N0dibutylammonium)-1,2,4-trithiolane, X:Cl, Br) [13b]. In the case

C

S

SN

R1

R2 SC

S

N

R3

R4

Scheme 1. General structure of thiuram disulfides (R2NC(S)S2C(S)NR2).

142 O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150

of ligands degradation, the S–S bonds are cleaved resulting in theformation of dithiocarbamate and/or thiocarboxamide fragments.These fragments can then coordinate to metal ions. Examples ofligand reduction with simultaneous ligand degradation include:[Cu(Et2dtc)]4, [Cu{(i-Pr)2dtc}Br2] [14], Tl(Me2dtc)3 [15a], [Me3Sb(dtc)2] [15b], [V2(l-S2)2(Et2dtc)4] [15c], [Mo(R2dtc)4] (R: Me, Et,Ph) [15d–f], {[SbX(Me2dtc)2]n} (X: Cl, Br or I) [7], {[Bi(Et2dtc)3]2} [7].

Reactions of antimony(III) or bismuth(III) containing specieswith thiuram sulfides are characterized by the oxidizing properties

S

SN S

S

NSbI3

CH3CN

CH3OHCH2Cl2

I

SbS

S

S

SN

I I

Sb

S

S

S

S

N

N

ISbI

I I

II

4

+

(1)

(2)

Scheme 2. Reaction scheme

Table 1Chemical shifts (ppm) of the resonance signals observed in 1H and 13C NMR spectra of sta

Compounds 1H NMR chemical shifts (ppm

Et4tds 1.17–1.20, t, 6H, (CH3A of Et41.38–1.40, t, 6H, (CH3A of Et43.94–4.00, q, 8H, (ACH2A of E

1 1.23–1.27, t, 12H, (CH3A of 2)3.75–3.82, q, 8H, (ACH2A of 2

2 1.23–1.27, t, 12H, (CH3A of 2)3.75–3.82, q, 8H, (ACH2A of 2

3 1.22–1.27, t, 12H, (CH3A of 3)3.75–3.82, q, 8H, (ACH2A of 3

of the thiuram [7]. Reduction of the ligand and cleavage of the S–Sbond results in the coordination of the dithiocarbamate fragmentsinto the antimony or bismuth coordination sphere [7]. Dithiocarba-mates coordinate strongly with a variety of metal ions especiallywith antimony(III) and bismuth(III) [16,17]. Dithiocarbamates,already play an important role in medicine [18]. Metal-dithiocar-bamate complexes have been investigated for their anti-cancerpotential, most notably with platinum(IV), palladium(II), tin(IV)and gold(I/III) [18]. Diethyldithiocarbamates can inhibit tumorinduction caused by benzo[a]pyrene [18]. In recent studies, the bis-muth diethyldithiocarbamate complex Bi(Et2dtc)3 inhibits in vitroseven human cancer cell lines (A498 (renal), MCF-7 (breast),EVSA-T (breast), H226 (non-small cell lung), IGROV (ovarian),M19 MEL (melanoma), WIDR (colon)) [18].

In the progress of our studies on the design and development ofnew metallotherapeutics containing elements of the group 15[4,5,7], we have synthesized and characterized new antimony(III)iodide complexes with the ligand tetraethylthiuram disulfide(Et4tds). Reactions of tetraethylthiuram disulfide with antimony(III) iodide lead to the ligand degradation with the simultaneous

N YELLOW POWDER

recryst. Acetone

YELLOW POWDER

recryst. Acetone

I

SbS

S

S

SNN

I I I

3- -

(3)

for the synthesis of 1–3.

rting compound (Et4tds) and complexes 1–3 in DMSO-d6.

) 13C NMR chemical shifts (ppm)

tds) 11.18, (CH3A of Et4tds)tds) 13.29, (CH3A of Et4tds)t4tds) 47.25, (ACH2A of Et4tds)

51.52, (ACH2A of Et4tds)190.85, (C@S of Et4tds)

12.05, (CH3A of 1)) 48.83, (ACH2A of 1)

194.14, (C@S of 1)

12.06, (CH3A of 2)) 48.84, (ACH2A of 2)

194.11, (C@S of 2)

12.03, (CH3A of 3)) 48.79, (ACH2A of 3)

194.56, (C@S of 3)

Table 2Selected bond lengths (Å) and angles (�) for 1–3 complexes.

1 2 3a 3b

Bond length (Å)Sb1� � �I1 3.364 I1–Sb1 3.0990(18) Sb4–S2 2.528(6) I1–Sb1 3.0745(7) I1–Sb1 3.0760(3)Sb1–S2 2.4924(11) I2–Sb1 3.0773(16) Sb4–S3 2.530(6) Sb1–S1 2.6202(18) Sb1–S1 2.6216(7)Sb1–S3 2.5108(12) I3–Sb1 3.0395(16) Sb3–S5 2.525(7) Sb1–S2 2.5339(17) Sb1–S2 2.5335(7)Sb1–S4 2.6391(11) I4–I5 2.817(6) Sb3–S6 2.603(6) Sb1–S4 2.4933(19) Sb1–S4 2.4960(8)Sb1–S1 2.6663(11) I5–I6 3.016(4) Sb3–S7 2.502(6) S1–C1 1.717(6) S1–C1 1.729(2)S1–C5 1.713(4) Sb4–S1 2.669(7) Sb3–S8 2.700(6) S2–C1 1.761(7) S2–C1 1.742(3)S2–C5 1.738(4) Sb4–S4 2.662(5) S3–C6 1.724(8) S3–C6 1.697(3)S3–C6 1.742(4) S4–C6 1.739(6) S4–C6 1.743(2)S4–C6 1.720(4) I1_a� � �Sb1 3.625 I1_a� � �Sb1 3.627I2–I2_a 2.7663(4)

Bond angles (�)I1–Sb1–S1 119.52 I4–I5–I6 179.9(4) S7–Sb3–S8 68.83(19) I1–Sb1–S1 148.98(4) I1–Sb1–S1 148.94(2)I1–Sb1–S2 79.51 S1–Sb4–S4 140.1(2) S5–Sb3–S8 83.8(2) I1–Sb1–S2 79.32(4) I1–Sb1–S2 79.33(2)I1–Sb1–S3 147.63 S2–Sb4–S3 92.3(2) S5–Sb3–S6 69.7(2) I1–Sb1–S4 84.93(4) I1–Sb1–S4 84.98(2)I1–Sb1–S4 78.44 S2–Sb4–S4 84.2(2) S5–Sb3–S7 91.9(2) S1–Sb1–S2 69.76(6) S1–Sb1–S2 69.70(2)S1–Sb1–S2 69.47(3) S3–Sb4–S4 68.61(19) S6–Sb3–S7 84.3(2) S1–Sb1–S4 92.04(6) S1–Sb1–S4 92.09(2)S1–Sb1–S3 86.26(4) S1–Sb4–S2 68.2(2) I2–Sb1–I3 87.59(4) S2–Sb1–S4 89.09(6) S2–Sb1–S4 89.21(3)S1–Sb1–S4 145.09(3) S1–Sb4–S3 83.8(2) I1–Sb1–I2 91.23(5)S2–Sb1–S3 93.49(4) S6–Sb3–S8 141.6(2) I1–Sb1–I3 92.52(4)S2–Sb1–S4 86.71(4)S3–Sb1–S4 69.58(3)Sb1–S1–C5 84.23(14)

O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150 143

formation of the complexes 1–3. Complexes 1–3 have been charac-terized by a variety of analytical methods; FT-IR, FT-Raman, 1H, 13CNMR, TGA–DTA and single crystal X-ray diffraction (XRD) analysis.Compounds 1–3 were also tested for their in vitro cytotoxicityagainst MCF-7 and HeLa cell lines.

2. Results and discussion

2.1. General aspects

Antimony(III) iodide complexes 1–3 have been synthesized byreacting the tetraethylthiuram disulfide with antimony(III) iodide(SbI3) in 1:1 ligand to metal ratio, as shown by the following reac-tions (Scheme 2). Complex 1 was isolated by reacting thetetraethylthiuram disulfide with antimony(III) iodide in acetoni-trile solution and complex 2 was obtained by reacting dichloro-methane solution of tetraethylthiuram disulfide with methanolsolution of antimony(III) iodide in 1:1 ligand to metal ratio. Com-plex 3was derived through two different routes: either by reactingtetraethylthiuram disulfide with antimony(III) iodide in methanol-dichloromethane following by re-crystallization in acetone solu-tion (3a) or by using acetonitrile in the reaction media followingby re-crystallization in acetone solution (3b) (Scheme 2). The crys-tals structures obtained from the products are identical (3a and 3b)(3a: Triclinic in P�1; a = 9.1083(10), b = 10.3455(10), c = 11.1572(10) Å, a = 69.966(8), b = 74.125(9), c = 64.277(10)�; Z = 2; 3b: Tri-clinic in P�1; a = 9.1187(6), b = 10.3532(8), c = 11.1533(6) Å,a = 70.028(6), b = 74.163(5), c = 64.308(7)�; Z = 2). Crystal of com-plexes 1–3, suitable for X-ray analysis, was grown by slow evapo-ration of their solutions. During these reactions the S–S bonds arecleavaged and the dithiocarbamate fragments are coordinated tothe metal ions. The complexes 1–3 are air stable.

2.2. Vibrational spectroscopy

The IR spectra of complexes 1–3 (Figs. S1–S3) show a distinctvibration band at 1504 cm�1 (1 and 2) and 1520–1492 cm�1 (3),respectively which are attributed to the m(CN) vibrations, 984–839 cm�1 (1 and 2) and 983–837 cm�1 (3) which are assigned tothe m(CS) vibrations. The IR spectra of complexes 1–3 show two

m(CS) vibration bands and one strong m(CN) band. This is an indica-tion of the anisobidentate character of the S2CNR2 ligands [17b].The corresponding m(CN) and m(CS) vibration bands of the freeligand is found at 1496 cm�1, 967 cm�1 and 817 cm�1,respectively [7] (Fig. S4).

The Sb–S and Sb–I vibrations are Raman active. Thus, bands at193 cm�1 (1), 206 cm�1 (2) and 201 cm�1 (3) in the Raman spectraof complexes 1–3 are due to the Sb–I vibration [5d,19] (Figs. S5–S7). Bands at 377 cm�1 in 1 and 386 cm�1 in 2 and 3 areattributed to the Sb–S vibration [5a,20]. Complexes 1 and 2 showm(I–I) vibration. Thus, the vibration band at 162 cm�1 in theRaman spectrum of 1 is due to the free I2 and the correspondingone at 120 cm�1 in 2 to the I3� ion [21].

2.3. Thermal analysis

The thermal stability of complexes 1–3 was tested by TG–DTAanalysis (under nitrogen flow). The data shows that compounds1–3 remain stable up to 175 (1), 120 (2), and 223 (3) �C(Figs. S8–S10). The thermal analysis of all complexes 1–3 showone decomposition steps (175–420 �C (1), 120–400 �C (2) and223–410 �C (3)) involves 90.1% (1), 88.9% (2) and 96.0% (3) masslosses.

2.4. NMR spectroscopy

Since biological experiments and QSAR studies require the sta-bility of the compounds in solution, NMR spectra contribute in theverification of the retention of the structure in solutions. The 1Hand 13C NMR spectra of 1–3 and the corresponding one of the freeligand Et4tds have been recorded in DMSO-d6 (Figs. S11–S18). Sig-nificant resonances are summarized in Table 1. The resonance sig-nals for the methyl protons of complexes 1–3 are at 1.23–1.27 ppm(1 and 2) and 1.22–1.27 ppm (3) which split into a triplet andmethylene protons of complexes 1–3 are at 3.75–3.82 ppm whichsplit into a quartet, while the singlet at 3.46 ppm is due to the H2Oin DMSO-d6.

The 13C NMR spectra of Et4tds ligand shows signal at190.85 ppm, due to the >C(@S) carbon. The 13C(NCS2) resonancesignals in the 13C NMR spectra of 1–3 are observed at194.14 ppm, 194.11 ppm, 194.56 ppm, respectively compare to

Fig. 1. (A) Molecular diagram together with labeling scheme of 1. (B) Intermole-cular l2-I� � �Sb and l2-I� � �I interactions leading to polymerization in complex 1.

Fig. 2. Molecular diagram together with labeling scheme of 2.

Fig. 3. (A) Molecular diagram together with labeling scheme of 3. (B) Intermole-cular l2-I� � �Sb interactions leading to polymerization in complex 3.

144 O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150

similar dithiocarbamate complexes. The methyl carbons wereobserved at 12.05 ppm (1), 12.06 ppm (2) and 12.03 ppm (3),respectively. The methylene carbons were observed at 48.83 ppm(1), 48.84 ppm (2) and 48.79 ppm (3), respectively.

2.5. Crystal and molecular structure of {[(SbI(Et2DTC)2)(I2)]n} (1), {[(Sb(Et2DTC)2)2.(SbI6)�(I3)]n} (2) and {[SbI(Et2DTC)2]2} (3)

Selected bond distances and angles of complexes 1–3 are givenin Table 2, while their molecular diagrams are shown in Figs. 1–3.In the case of the crystal and molecular structure of 2 the highvalue of R allows only its brief description.

Complex 1 is polymer with five coordinated metal centersunder distorted square pyramidal (SP) geometry. It consists oftwo neutral units, [SbI(Et2DTC)2] and [I2]. The Et2DTC ligandbridged metal ions in 1 with anisobidatate l2-bridging mode.[SbI(Et2DTC)2] units are connected to each other by one l2-S� � �Sband one l2-I� � �Sb bridging interaction (Sb� � �I1: 3.463 Å, Sb� � �S2:3.692 Å) and these two interactions in 1 leads to polymeric chainwith a pentagonal bipyramidal (PBP) geometry around antimonyions. Each polymeric chain is connected to each other by I2 mole-cule through L2SbI� � �I–I� � �ISbL2 contacts, (I2� � �I2 = 2.766 andI1� � �I2: 3.361 Å).

C

N

SS

CH2H2C

CH3

C

N

SS

CH2H2C

CH3CH3

trans cis

CH3

Scheme 3. Isomers observed in N,N-diethylcarbamodithioic acid ligand (definedbased on the CCNC torsion angles).

O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150 145

Complex 3 is dimmer and the metal center is five coordinatedwith distorted square pyramidal (SP) geometry in each monomericunit. Four sulfur atoms from dithiocarbamate ligands and oneiodide ion are bound to antimony ions forming the building blockof the dimmer. Two strong intramolecular interactions betweenl2-I and Sb atoms (Sb1� � �I1: 3.625 Å (3a), Sb1� � �I1: 3.627 Å (3b))lead to dimerism with distorted octahedral geometry around anti-mony(III) ion. There are two different N,N-diethylcarbamodithioicacid ligands in 3, one with cis and the other with trans dispositionof the methyl carbons of ligands (Scheme 3) (3a: C1–N1–C2–C3 = 101.5(8)�, C1–N1–C4–C5 = 87.9(8)�, C6–N2–C7–C8 = �85.8(8)�, C6–N2–C9–C10 = 82.3(9)�; 3b: C1–N1–C2–C3 = 101.4(3)�,C1–N1–C4–C5 = 88.6(3)�, C6–N2–C7–C8 = 83.3(4)�, C6–N2–C9–C10 = �84.8(3)�).

Two stronger antimony–sulfur bonds, with shorter antimony–sulfur lengths (Sb1–S2 = 2.4924(11) Å and Sb1–S3 = 2.5108(12) Å(1), Sb1–S2 = 2.5339(17) Å and Sb1–S4 = 2.4933(19) Å (3a), Sb1–S2 = 2.5335(7) Å and Sb1–S4 = 2.4960(8) Å (3b)) and two weakerbond with longer antimony–sulfur distances (Sb1–S1 = 2.6663(11) Å and Sb1–S4 = 2.6391(11) Å (1), Sb1–S1 = 2.6202(18) Å andSb1–S3 = 2.889 Å (3a), Sb1–S1 = 2.6216(7) Å and Sb1–S3 = 2.891 Å(3b)) are formed. The equatorial angles in 1, 3a and 3b are:I1–Sb1–S1 = 119.52�, I1–Sb1–S4 = 78.44�, S1–Sb1–S3 = 86.26(4)�,S3–Sb1–S4 = 69.58(3)� (1), I1–Sb1–S3 = 125.11�, I1–Sb1–S2 = 79.32(4)�, S1–Sb1–S3 = 80.70�, S1–Sb1–S2 = 69.76(6)� (3a),

Table 3IC50 values for cell viability found for complexes 1–3 and other complexes Sb(III) against

Complexes Volume (A3)

{[(SbI(Et2DTC)2)(I2)]n} (1), 552.3{[(Sb(Et2DTC)2)4 (SbI6) (I3)]n} (2) 1229.2{[SbI(Et2DTC)2]2} (3) 431.7{[SbI(Me2DTC)2]n} (4) 338.78{[(Me2DTC)2Sb(l2-I)Sb(Me2DTC)2]+�I3�} (5) 795.43{[SbBr(Me2DTC)2]n} (6) 330.08{[SbCl(Me2DTC)2]n} (7) 330.6{[SbCl(Me2DTC)2]n}(8) 331.19{[SbI3(HDTOA)1.5]�C6H6}n (9) 1327.48{[SbBr3(HDTOA)1.5]}n (10) 1376.07{[SbCl3(HDTOA)1.5]}n (11) 1375.44{[(SbI2(l2-I)(Hthcl)2)2]} (12) 1044.64{[(SbBr2(l2-Br)(Hthcl)2)2]} (13) 974.73{[SbCl2(l2-Cl)(Hthcl)2]n} (14) 498.77{[SbBr2(DETU)2]+Br�}n (15) 493.92{[mer-SbCl3(DIPTU)3][fac-SbCl3(DIPTU)3] C6H6} (16) 458.93Cisplatin

Me2DTCH = dimethyldithiocarbamate; HDTOA = N,N-dicyclohexyldithiooxamide; Hthclpropyl-2-thiourea

* This work.a The close contacts (%) of all elements inside the area with the outer hydrogen atom

I1–Sb1–S3 = 125.16�, I1–Sb1–S2 = 79.33(2)�, S1–Sb1–S3 = 80.65�,S1–Sb1–S2 = 69.70(2)� (3b), while the corresponding basal Saxial–Sb–Xbasal (X: S or I) angles lie between: S1–Sb1–S2 = 69.47(3)� toS2–Sb1–S3 = 93.49(4)� (1), S3–Sb1–S4 = 66.32� to S1–Sb1–S4 = 92.04(6)� (3a) and between S3–Sb1–S4 = 66.09� to S1–Sb1–S4 = 92.09(2)� (3b) indicating high deviation from their idealgeometry. This deviations from the 90� of the ideal SP geometryare due to the repulsions between the free electrons pair locatedon the Sb and those of the covalent Sb–X bonds (X: S or I) in accor-dance to the Valance Shell Electron Pair Repulsion (VSEPR) theory.

The structure of complex 2 consist of three residues, four catio-nic [Sb(Et2dtc)2]+, one [SbI6]3� and one [I3]� counter anions, shownin Fig. 2. Six iodide ions form a anionic [SbI6]3� counter ion withoctahedral (Oh) geometry around antimony ion, Sb–I bond dis-tance varied between 3.040–3.099 Å. The basal angles are almost90� (Table 2) confirming the octahedral arrangement. The counterion, [I3]� is linear with two asymmetric I–I bond lengths of I3�

(I4–I5 = 2.817(6) Å and I5–I6 = 3.016(4) Å). The coordinationgeometry of the antimony atom can be described as a pseudotrig-onal bipyramid with a stereochemically active lone pair in equato-rial position in [Sb(Et2dtc)2]+ cations. The axial (S1–Sb4–S4 andS6–Sb3–S8) and equatorial (S2–Sb4–S3 and S5–Sb3–S7) anglesare reduced to 140.1(2)–141.6(2)� and 92.3(2)–91.9(2)� withrespect to the values of 180� and 120� found for an ideal trigonalbipyramid. The intramolecular Sb� � �I interaction between the [Sb(Et2dtc)2]+ cation with [SbI6]3� counter anion ion isSb3� � �I1 = 3.392 Å, while the intramolecular Sb� � �I interactionbetween the I3� counter anion and the [Sb(Et2dtc)2]+ isSb4� � �I6 = 3.440 Å. Four antimony–sulfur bonds, with short anti-mony–sulfur bond lengths (Sb3–S5 = 2.525(7) Å, Sb3–S7 = 2.502(6) Å, Sb4–S2 = 2.528(6) Å and Sb4–S3 = 2.530(6) Å) and fourweaker bond with longer antimony–sulfur distances (Sb3–S6 =2.603(6) Å, Sb3–S8 = 2.700(6) Å, Sb4–S1 = 2.669(7) Å and Sb4–S4 =2.662(5) Å) are formed.

The Sb–S bond distances varied from 2.492 to 2.891 Å in com-plexes 1–3 and they are in agreement with those found previouslyfor similar complexes [5,7]. The Sb–I bond distances varied from3.040 to 3.364 Å in complexes 1–3, [5d,5g]. These distances areshorter than the sum of antimony and sulfur or iodide van derWaals radii (Sb–S = 4.0–4.47 Å, Sb–I = 4.3–4.63 Å) [22]. The I–Ibond distances lie between 2.766 and 3.016 Å in complexes 1–2

HeLa (cervix), MCF-7 (breast).

Contactsa(%) IC50 (lM) Refs.

HeLa MCF-7

70.3 0.07 ± 0.007 0.04 ± 0.002 *

68.1 0.75 ± 0.04 0.5 ± 0.04 *

74.4 1.8 ± 0.2 0.05 ± 0.005 *

66.1 0.037 ± 0.001 0.047 ± 0.003 [5k]61.2 0.023 ± 0.001 0.019 ± 0.002 [5k]66.7 0.046 ± 0.004 0.09 ± 0.003 [5k]65.2 0.46 ± 0.07 0.02 ± 0.003 [7]66.5 0.51 ± 0.10 0.024 ± 0.004 [7]78.2 11.82 ± 1.10 18.42 ± 1.41 [5i]79 8.49 ± 0.65 21.64 ± 1.89 [5i]78.6 – 12.4 ± 1.56 [5h]74.8 – 0.76 ± 0.16 [5g]76.6 – 1.44 ± 0.36 [5g]70.1 – 12.23 ± 2.27 [5g]78.8 12.4 ± 2.1 17.6 ± 1.7 [5j]84 7.7 ± 1.3 13.2 ± 1.2 [5j]

10 6.8 [5k]

= 1-azacycloheptane-2-thione; DETU = N,N0-diethylthiourea and DIPTU = 1,3-diiso-

s.

Fig. 4. The Hirshfeld surface volume of the complexes 1–3 (A) and the close contacts of all elements inside the area with the outer hydrogen atoms (B). Points on the plot withno contribution on the surface are left uncolored, and points with a contribution to the surface are coloured blue for a small contribution through green to red for points withthe greatest contribution. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

146 O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150

and they are in agreement with those values previously found foriodide complexes [21].

The C–S bonds varied between 1.637 and 1.818 Å in complexes1–3; this distance is in the range of the free tetraethylthiuramdisulfide (1.643 Å). The C–S single bonds in free ligand are1.820–1.825 Å for tetraethylthiuram disulfide [23].

2.6. Biological studies

The most prevalent cancer in the world among women today isthe breast cancer while uterine cancer is the second one [5k]. TheMCF-7 cells have been used as a model for human breast cancer,while HeLa cells are common cervical cancer model [5k]. The

50

55

60

65

70

75

80

85

90

4 4.5 5 5.5 6 6.5 7 7.5 8p(IC50)

Con

tact

s (%

)

16

1015

9 3

2 87

1

6 4

5

(A)

50

55

60

65

70

75

80

85

90

4 4.5 5 5.5 6 6.5 7 7.5 8p(IC50)

Con

tact

s (%

)

16

14

10

9

15 1113 12

26

3

1

475

8

(B)

Fig. 5. (A) p(IC50) (�log(IC50)) of the complexes against HeLa cells vs. the close contacts (%) of all elements inside the area with the outer hydrogen atoms(y = �5.9867x + 108.5, R2 = 0.76). (B) p(IC50) of the complexes against MCF-7 cells vs. the close contacts (%) of all elements inside the area with the outer hydrogen atoms(y = �4.3057x + 99.141, R2 = 0.68).

O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150 147

complexes 1–3 were evaluated for their cytotoxic activity againstadenocarcinoma cancerous cells lines: MCF-7 (breast) and HeLa,(cervix) with sulforhodamine B (SRB) assay for a period of 48 h(Table 3).

The IC50 values of the complexes lie to 0.07–1.8 lM in the caseof HeLa cells, while increased sensitivity is observed against MCF-7cells, where the IC50 values lie between 0.04 and 0.5 lM. The com-plexes are more active than cisplatin up to 143 times against ofHeLa and 97 times against MCF-7 cells.

Comparison between antimony tri-halide complexes ofdiethyldithiocarbamate, dimethyldithiocarbamate, N,N-dicyclo-hexyldithiooxamide, 1-azacycloheptane-2-thione N,N0-diethylth-iourea or 1,3-diisopropyl-2-thiourea (Table 3) shows that thecomplexes of dimethyldithiocarbamate are significantly moreactive against cancerous cell lines than others. This confirms ourprevious findings about the influence of the ligand type on thebioactivity of the metal complexes [4,5,7].

2.7. Hirshfeld surface analysis

The Hirshfeld surface is defined as the volume of space wherethe molecule electron density exceeds that from all neighbouringmolecules [5k]. Hirshfeld surfaces also provide a three-dimensional (3D) picture of the close contacts in a crystalstructure and these contacts can be summarized in a 2D

fingerprint plot [5k]. The 2D fingerprint plot is formed by thecombination of the distances from the Hirshfeld surface to thenearest nucleus inside the surface (di) and outside the surface(de) [5k]. When dnorm is mapped, close intermolecular distancesare characterized by two identically colored regions, red (i.e.distances shorter than sum of van der Waals radii) through whiteto blue (i.e. distances longer than sum of van der Waals radii) [5k].

Fig. 4 shows the dnorm surfaces of the complexes 1–3 (A). Thenature of the intermolecular interactions was clarified by the 2Dfingerprint plot (B) [5k]. The close contacts of all elements insidethe area with the outer hydrogen atoms were calculated for thecomplexes 1–3 are: 70.3% (1), 68.1% (2) and 74.4% (3)respectively. Fig. 5 compares the p(IC50) = �log(IC50) of thecomplexes against HeLa cells and MCF-7 cells (Table 3) versusthe calculated close contacts values. The high activity of thecomplexes (low IC50 value) is positively correlated with the lowH-all atoms intermolecular contacts. Thus, complexes with lowerH-all atoms inter-molecular interactions exhibit higher activityagainst both cancerous cells lines (HeLa and MCF-7).

3. Conclusions

Three new antimony(III) iodide complexes of formulae {[(SbI(Et2DTC)2)(I2)]n} (1), {[(Sb(Et2DTC)2)2.(SbI6).(I3)]n} (2) and {[SbI(Et2DTC)2]2} (3) were synthesized. Reaction of tetraethylthiuram

148 O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150

disulfide with antimony(III) iodide (SbI3) lead to ligand reductionwith concomitant degradation to N,N-diethylcarbamodithioic acidligand. Antimony iodide complexes exhibit significant higher activ-ity against cancer cells tested than the corresponding bromide orchloride ones (Table 3). Moreover, complexes of alkyldithiocarba-mates (1–8) show higher activity than those of other ligands used(Table 3), indicating that the ligand type affects the bioactivity ofthe metal complexes [4,5,7]. Finally, the H-all atoms intermolecu-lar contacts are positively correlated with the activity of thecomplexes.

4. Experimental

4.1. Materials and instruments

All solvents used were of reagent grade; antimony(III) iodide(Aldrich) and tetraethylthiuram disulfide (Aldrich) were used withno other purification prior to use. Elemental analyses for C, H, N,and S were carried out with a Carlo Erba EA MODEL 1108 elemen-tal analyzer. Melting points were measured in open tubes with aSTUART SMP10 scientific apparatus and are uncorrected. FT-IRspectra were recorded in the 4000–400 cm�1 region with BrukerOptics, Vertex 70 FT-IR spectrometer using ATR techniques. MicroRaman spectra (64 scans) were recorded at room temperatureusing a low-power (�30 mW) green (514.5) mm laser on aRenishaw In Via spectrometer set at 2.0 resolution. 1H and 13CNMR spectra were recorded with a Bruker 300 MHz Avance Ultra-shield spectrometer in DMSO-d6 with chemical shifts given in ppmreferenced to internal TMS (H). Thermal Gravimetry–DifferentialThermal Analysis (TG–DTA) of complexes were carried out on aSeiko SII TG/DTA 7200 apparatus under N2 flow (50 cm3 min�1)with a heating rate of 10 �C min�1.

4.2. Synthesis and crystallization of {[(SbI(Et2DTC)2)(I2)]n} (1), {[(Sb(Et2DTC)2)2�(SbI6)�(I3)]} (2) and {[(SbI(Et2DTC)2)]2} (3)

A dichloromethane (10 cm3) solution of 0.5 mmol tetraethylth-iuram disulfide (0.148 g) was added to a methanol (10 cm3) solu-tion of antimony(III) iodide (0.5 mmol, 0.251 g). The solution wasstirred under reflux for 1 h and the resulting clear solution wasthen filtered off. The solution was concentrated to dryness at roomtemperature to give red crystals (1) and a yellow powder. Theyellow powder formed was collected and dried in vacuo. Recrystal-lization of this powder with acetone (20 cm3) yield yellow crystalsof complex 3a.

Table 4Crystallographic data for antimony iodide complexes 1–3.

1 2

Empirical formula [(SbI(C5H11NS2)2)(I2)] {[(Sb(C5H11NSCrystal system Orthorhombic MonoclinicSpace Group Pbcn C2/ca (Å) 21.8678(7) 19.1419(7)b (Å) 9.9373(3) 20.3964(7)c (Å) 18.8017(6) 22.0936(10)a (�) 90 90b (�) 90 101.974(4)c (�) 90 90V (Å3) 4085.7(2) 8438.2(6)Z 4 4T (K) 100(2) 293(2)qcalcd (g/cm3) 2.185 2.512l (mm�1) 4.8 48.1Total unique data, Rint 11830, 3595, 0.040 15003, 7522, 0Observed data [I > 2.0 r(I)] 3163 6354R, wR, S 0.0267, 0.0603, 0.99 0.1625, 0.4195

A solution of antimony(III) iodide (0.5 mmol, 0.251 g) in ace-tonitrile (10 cm3) was added to a solution of tetraethylthiuramdisulfide (0.5 mmol, 0.148 g). This solution was stirred for 2 hunder reflux and then filtered off. The resulting clear solutionwas concentrated to dryness at room temperature to give red crys-tals (2) and a yellow powder. The yellow powder was collected anddried in vacuo. Recrystallization of this powder with acetone(20 cm3) yield yellow crystals of complex 3b.

1: Red crystals, yield: 35%, melting point: 132–136 �C, Elemen-tal Anal. Calc. for C10H20I3N2S4Sb: C, 15.03; H, 2.52; N, 3.51; S,16.05. Found: C, 15.10; H, 2.49; N, 3.56; S, 16.11. IR (cm�1):2982w, 2970w, 2928w, 2358w, 2341w, 1504s, 1433s, 1377w,1356m, 1330w, 1271s, 1198m, 1146m, 1072m, 984m, 906m,839m, 779m, 683w, 669w, 601w, 561w, 500w, 457w.

2: Red crystals, yield: 30%, melting point: 126–129 �C, Elemen-tal Anal. Calc. for C20H40I9N4S8Sb3: C, 11.44; H, 1.92; N, 2.67; S,12.21. Found: C, 11.52; H, 1.85; N, 2.63; S, 12.34. IR (cm�1):2982w, 2970w, 2928w, 1504s, 1433m, 1375w, 1352m, 1269s,1198m, 1146m, 1072m, 984m, 904m, 839m, 772m, 738w, 704w,561m, 500w, 424w.

3: Yellow crystals, yield: 50% (Method A) and 56% (method B),melting point: 155–158 �C, Elemental Anal. Calc. for C10H20IN2S4Sb:C, 22.03; H, 3.70; N, 5.14; S, 23.53. Found: C, 22.09; H, 3.65; N,5.03; S, 23.68. IR (cm�1): 2983w, 2971w, 2929w, 2867w, 1520s,1492s, 1436s, 1373m, 1351s, 1278s, 1200m, 1142m, 1076m,983m, 906m, 842m, 782m, 772w, 602w, 558m, 501w, 468w, 444w.

4.3. X-ray structure determination

Intensity data for the crystals of 1–3 were collected on anOxford Diffraction CCD instrument, using graphite monochro-mated Mo radiation (k = 0.71073 Å). Cell parameters were deter-mined by least-squares refinement of the diffraction data from25 reflections [24]. All data were corrected for Lorentz-polarizationeffects and absorption [24,25]. The structures were solved withdirect methods with SHELXS97 [26] and refined by full-matrixleast-squares procedures on F2 with SHELXL97 [27]. All non-hydro-gen atoms were refined anisotropically, hydrogen atoms werelocated at calculated positions and refined via the ‘‘riding model”with isotropic thermal parameters fixed at 1.2 (1.3 for CH3 groups)times the Ueq value of the appropriate carrier atom. Significantcrystal data of 1 and 3b are given in Table 4. The high R value inthe refinement of the crystal structure of 2 prevents its thoroughanalysis. Since the structure of 3 has been solved twice (3a and3b) only the structure of the best refinement is deposited to CCDC.

3a 3b

2)2)4 (SbI6) (I3)]n} {[SbI(C5H11NS2)2]2} {[SbI(C5H11NS2)2]2}Triclinic TriclinicP�1 P�19.1083(10) 9.1188(6)10.3455(10) 10.3533(8)11.1572(10) 11.1534(6)69.966(8) 70.027(6)74.125(9) 74.163(5)64.277(10) 64.308(7)880.11(17) 882.06(12)2 2100(2) 100(2)2.057 2.0533.8 3.8

.073 5189, 3100, 0.041 5829, 3967, 0.0192844 3744

, 1.76 0.0404, 0.1547, 1.19 0.0231, 0.0582, 1.05

O.S. Urgut et al. / Inorganica Chimica Acta 443 (2016) 141–150 149

The cif files of both structures 2 and 3a are available on requestform the Authors (AJT and SKH).

4.4. Biological tests

Cell viability was determined as previously described [5k].Biological experiments were carried in dimethyl sulfoxide inDulbecco’s Modified Eagle’s Medium solutions (DMEM)DMSO/DMEM (0.0002–0.3% v/v) for the complexes 1–3. Stock solutionsof the complexes 1–3, (0.01 M) in DMSO were freshly preparedand diluted in with cell culture medium to the desiredconcentration. The low concentration of the complexes used forthe cells screening tests allows the formation of clear solution.MCF-7 and HeLa cells were seeded onto 96-well plates at adensity of 6 � 103 and 4 � 103 cells per well, respectively, andincubated for 24 h before the experiment. Results are expressedin terms of IC50 values, which is the concentration of drugrequired to inhibit cell growth by 50% compared to control, afterof 48 h incubation of the complexes towards cell lines.

4.5. Hirshfeld surface analysis

The volumes of Hirshfeld surface were calculated with Crys-talExplorer (Version 3.1) [28].

Acknowledgements

This research was carried out in partial fulfillment of therequirements for the Master thesis of O.S.U., under the supervisionof I.I.O., at the Namik Kemal University. I.I.O. and O.S.U. acknowl-edge the financial support from Namik Kemal University ScientificResearch Project (Project No. NKUBAP.00.10.YL.12.03). C.N.B. and S.K.H. would like to thank the Unit of bioactivity testing of xenobi-otics, the University of Ioannina, for providing access to the facili-ties. C.N.B. and S.K.H. acknowledge the National ScholarshipsFoundation of Greece (IKY) for the post doctoral research fellow-ship of excellence programm IKY-Siemens.

Appendix A. Supplementary material

CCDC 1434672 and 1434673 contains the supplementary crys-tallographic data for complexes 1 and 3b. These data can beobtained free of charge from The Cambridge Crystallographic DataCentre via www.ccdc.cam.ac.uk/data_request/cif. Supplementarydata associated with this article can be found, in the online version,at http://dx.doi.org/10.1016/j.ica.2015.12.028.

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