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Journal of Molecular Structure 875 (2008) 478–485

Piperazine pivoted transition metal dithiocarbamates

Sadaf Khan, Shahab A.A. Nami, K.S. Siddiqi *

Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India

Received 8 January 2007; received in revised form 14 May 2007; accepted 17 May 2007Available online 26 May 2007

Abstract

A quadridentate ligand disodium bis(2,2 0-dithiopiperazinato-2,2 0-diamino diethylamine) Na2L2 and its self assembled transition metalcomplexes of the type, M2(L2)2 {M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)} have been reported. The piper-azine pivoted homodinuclear complexes have been characterized by a range of spectral, thermal, microanalytical and conductometrictechniques. On the basis of IR and 1HNMR data a symmetrical bidentate coordination of the dithiocarbamato moiety has been observedin all the cases. The TGA profile of the ligand exhibits two stage thermolytic pattern although the complexes decompose in three steps,respectively. Metal sulfide is found to be the end product. The formation of homodinuclear complexes has been ascertained on the basisof FAB mass spectral data and a probable fragmentation pattern has been proposed. On the basis of UV–visible spectroscopic resultsand room temperature magnetic moment data a tetrahedral geometry has been proposed for all the complexes except for the Ni(II) andCu(II) which are found to be square-planar.� 2007 Elsevier B.V. All rights reserved.

Keywords: Quadridentate ligand; Diethylamine; Symmetrical bonding; Dithiocarbamate

1. Introduction

The ability to control the construction of coordinationsupramolecular arrays based on covalent interactions orhydrogen bonding has been a major focus of researchefforts in recent years for the rationale design of functionalmaterials [1]. Journaux et al. [2] have recently indicatedthat the pathways used to obtain these species are based,essentially, on the following synthetic schemes: (i) the selfassembly method, (ii) the use of polynucleating ligandsand (iii) the use of complexes as ligands. However, themetal directed self-assembly of polydentate ligands pro-vides a facile route to novel supramolecular structuresbased on the metal coordinate interactions [3,4]. Throughimaginative multidentate ligand design and judiciouschoice of the metal ion, a novel range of polymetallic inor-ganic assemblies including helicates, cages, ladders, racks,grids and tubes have been constructed [5]. These frame-

0022-2860/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2007.05.020

* Corresponding author.E-mail address: khwajas_siddiqi@yahoo.co.in (K.S. Siddiqi).

works can also act as receptors to detect anions in solutions[6].

Among various sulfur containing ligands the dithiocarb-amato (dtc) moiety has proved as a useful structural motiflending itself to the metal directed assembly of a range ofstructures like nanosized resorcarene based assemblies,catenanes, cryptands, etc. [7]. The small bite angle (�2.8–2.9 A) of the dtc makes it appropriate for the stabilizationof a range of oxidation states of various metal ions [8].They are used as vulcanizers, higher pressure lubricatingagents, fungicides, pesticides antialkylating agents, antiox-idants, spin trapping agents and anti-HIV agents [9–12].Dithiocarbamates are also used as molecular precursorsfor CVD processes. Water-soluble dialkyldithiocarbamatecomplexes are known to have been tested in various medi-cal applications [13].

Piperazine is a well known building block for novelsupramolecular structures due to the presence of twoweakly held terminal amino protons [14]. Of the two read-ily interconvertible conformations of the piperazine, thechair form is thermodynamically more stable since it is17.2 kJ/mol higher than the boat form [15]. However, the

Cl

SOCl2

Cl

NHHNHNNH2

HNH2N

L1

Fig. 1. Synthesis of the ligand Na2L1.

S. Khan et al. / Journal of Molecular Structure 875 (2008) 478–485 479

boat form gives mononuclear whereas the chair form givesdinuclear complexes with no exogenous bridging for trans-N,N 0 coordination [16,17].

In continuation of our earlier work on piperazinatomono as well as bisdithiocarbamato complexes [18] wehave attempted to use piperazine moiety as a structuralmotif rendering it to exist in its preferred chair form [19].Recently, polypyridine dithiocarbamates and piperazinebridged homodinuclear transition metal dithiocarbamateshave been reported from our laboratory [20,21]. In thepresent communication the piperazine moiety is exploitedto form the dithiocarbamate in a way it assembles to forma barrel shaped structure (Fig. 3) unlike the linear arraysreported by Hogarth et al. [22]. Herein we report the syn-thesis and spectroscopic characterization of piperazine piv-oted 3d-transition metal dithiocarbamates in order to studythe symmetrical and unsymmetrical bonding of the dithio-carbamate and their thermal behavior supported by TGA/DSC. The FAB-MS has been done for prototype com-pounds to ascertain the formation of binuclear complexeson the basis of fragmentation pattern.

2. Experimental

Hydrated metal chlorides, sodium hydroxide (Merck),diethylene triamine, thionyl chloride, carbon disulfide (s.d. fine) and piperazine hexahydrate (Loba Chemie) wereused as received. Methanol was distilled prior to use. Ele-mental analyses (C, H, N and S) were carried out with aCarlo Erba EA-1108 analyzer. The metal contents wereestimated by complexometric titration [23]. IR spectra(4000–400 cm�1) were recorded on a RXI FT-IR spectrom-eter as KBr disc while the 600–200 cm�1 range was scannedwith CsI on a Nexus FT-IR Thermo Nicolet, (Wisconsin).The Electronic spectra were recorded on a Cintra 5GBCspectrophotometer in DMSO. The NMR spectra wererecorded on a DPX-300 spectrometer in DMSO at roomtemperature. The conductivity measurements were carriedout on a CM-82T Elico conductivity bridge in DMSO.Magnetic susceptibility measurements were done with a155 Allied Research vibrating sample magnetometer atroom temperature. TGA was performed with a Perkin–Elmer (Pyris Diamond) thermal analyzer under nitrogenatmosphere using alumina powder as reference. The weightof the sample was kept between 8 and 12 mg and the heat-ing rate was maintained at 10 �C/min. The FAB mass spec-tra were recorded on a JEOL SX 102/Da-6000 MassSpectrometer/Data System using Argon/Xenon (6 kV,10 mA) as the FAB gas. The accelerating voltage was10 kV and the spectra were recorded at room temperature.M-nitrobenzoyl alcohol (NBA) was used as the matrix.

2.1. Synthesis of 2,2 0-diamino-2,2 0-dichlorodiethylamine

(L1)

Neat thionylchloride (10 mmol, 0.73 mL) was dropwiseadded to a methanolic solution of diethylene triamine

(5 mmol, 0.56 mL) in an ice bath. The reaction mixturewas stirred for 2 h, cooled to room temperature and thenrefluxed on a water bath for about an hour, which affordeda whitish pink precipitate under reflux. It was then cooled,filtered, washed with methanol and dried in vacuo overP2O5 (Fig. 1).

2.2. Synthesis of disodium bis(2,2 0-dithiopiperazinato-2,2 0-

diaminodiethylamine) Na2L2

To a stirred methanolic solution (20 mL) of L1 (1 mmol,0.10 g), piperazine (2 mmol, 0.39 g) hexahydrate solution inthe same solvent (20 mL) was added dropwise with contin-uous stirring and then refluxed for about 2 h. The mixturewas cooled to �5 �C followed by addition of carbon disul-fide (2 mmol, 0.12 mL) and NaOH (2 mmol, 0.08 g) dis-solved in aqueous methanol to afford a light greenprecipitate. The compound was filtered, washed with meth-anol and dried in vacuo over P2O5 (Fig. 2).

[Na2L2] yield (80%); m. p. 165 �C; KM = 33 X�1cm2

mol�1 found (calcd. for C14H27N7Na2S4) C, 35.78(35.96),H, 5.59(5.82), N, 20.79(20.97), S, 27.74(26.42); IR (KBr):mmax/cm�1 3430s (NAH), 1450s (C N), 1300w, 1270m(ring vib.), 998s (CAS).

2.3. Synthesis of complexes M2(L2)2

The metal complexes are conveniently obtained by thesubstitution reaction of Na2L2 (2 mmol, 0.93 g) withMCl2ÆxH2O (2 mmol) in equimolar ratios in methanol.

[Mn2(L2)2] yield (62%); m. p. 208 �C; KM = 27 X�1 cm2

mol�1 found (calcd. for C28H54Mn2N14S8) C, 34.93(35.28),H, 5.53(5.71), N, 20.48(20.57), S, 27.24(26.90), Mn,11.82(11.82). IR (KBr): mmax/cm�1 3447s (NAH), 1468s(C N), 1284w, 1254m (ring vib.), 992s (CAS), 378 (MnAS).

[Fe2(L2)2] yield (67%); m. p. 210 �C; KM = 42 X�1 cm2

mol�1 found (calcd. for C28H54Fe2N14S8) C, 35.01(35.21),H, 5.57(5.70), N, 20.42(20.53), S, 27.08(26.85), Fe,11.85(11.69). IR (KBr): mmax/cm�1 3421s (NAH), 1459s(C N), 1278w, 1244m (ring vib.), 993s (CAS), 397(FeAS).

[Co2(L2)2] yield (70%); m. p. 211 �C; KM = 17 X�1 cm2

mol�1 found (calcd. for C28H54Co2N14S8) C, 34.73(34.99), H, 5.70(5.66), N, 20.13(20.40), S, 26.81(26.68),Co, 12.48(11.26). IR (KBr): mmax/cm�1 3422s (NAH),1465s (C N), 1275w, 1248m (ring vib.), 994s (CAS), 393(CoAS).

[Ni2(L2)2] yield (68%); m. p. 220 �C; KM = 11 X�1 cm2

mol�1 found (calcd. for C28H54Ni2N14S8) C, 34.86(35.0),

L1 2 HN(CH2)4NH 2 CS2 2 NaOH2 HCl 2 NaCl,

H2C

H2C

CH2

CH2

H2C

H2C

CH2

CH2

SSSS

CC

NN

NN

NHHNHN

Na Na

Fig. 2. Synthesis of the ligand Na2L2.

2 MCl2 + 2 Na2L2

HN NH

NH

N

N

C

S S S

SSSS

CC

NN

NN

HNHN

MM- 4 NaCl

CH2

CH2

H2C

H2C

CH2

CH2

H2C

H2C

NH

CH2H2C CH2 H2C

CH2CH2 H2CH2C

N

N

C

S

Fig. 3. Synthesis of the complexes M2(L2)2 where M = Mn(II), Fe(II),Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II).

480 S. Khan et al. / Journal of Molecular Structure 875 (2008) 478–485

H, 5.60(5.66), N, 20.24(20.41), S, 26.86(26.69), Ni, 12.45(12.22). IR (KBr): mmax/cm�1 3422s (NAH), 1478s(C N), 1274w, 1261m (ring vib.), 991s (CAS), 397 (NiAS).

[Cu2(L2)2] yield (55%); m. p. 262 �C; KM = 09 X�1 cm2

mol�1 found (calcd. for C28H54Cu2N14S8) C, 34.37(34.66),H, 5.62(5.61), N, 20.31(20.20), S, 26.75(26.43), Cu, 13.27(13.09). IR (KBr): mmax/cm�1 3401s (NAH), 1488s (C N),1268w, 1254m (ring vib.), 990s (CAS), 406 (CuAS).

[Zn2(L2)2] yield (62%); m. p. 230 �C; KM =10 X�1 cm2 mol�1 found (calcd. for C28H54Zn2N14S8) C,34.20(34.52), H, 5.45(5.59), N, 20.32(20.13), S, 26.40(26.33),Zn, 13.69(13.42). IR (KBr): mmax/cm�1 3477s (NAH), 1473s(C N), 1280w, 1244m (ring vib.), 995s (CAS), 384 (ZnAS).

[Cd2(L2)2] yield (72%); m. p. 208 �C; KM = 15 X�1 cm2

mol�1 found (calcd. for C28H54Cd2N14S8) C, 31.30(31.48),H, 4.89(5.10), N, 18.25(18.36), S, 24.28(24.01), Cd,21.47(21.04). IR (KBr): mmax/cm�1 3434s (NAH), 1462s(C N), 1279w, 1260m (ring vib.), 996s (CAS), 392(CdAS).

[Hg2(L2)2] yield (70%); m. p. 218 �C; KM =22 X�1 cm2 mol�1 found (calcd. for C28H54Hg2N14S8) C,27.05(27.02), H, 4.21(4.37), N, 15.62(15.76), S,20.67(20.61), Hg, 11.82(11.82). IR (KBr): mmax/cm�1 3400s(NAH), 1477s (C N), 1284w, 1265m (ring vib.), 997s(CAS), 414 (HgAS).

3. Results and discussion

The metal dithiocarbamates, M2(L2)2 were convenientlyobtained in high yield by substitution reaction of sodiumsalt of functionalized secondary amine or dithiocarbamatewith hydrated transition metal halides in methanol (Fig. 3).

2 Na2L2 + 2 MCl2 ! M2(L2)2 + 4NaCl

where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II),Cd(II) and Hg(II).

Elemental analysis, TGA/DSC, 1HNMR, FAB massspectrometry, UV–visible and IR spectroscopy were usedto characterize the complexes.The amorphous complexesare soluble in DMSO and DMF only. The conductivitymeasurement (10�3 M) in DMSO indicated them to benon-electrolytes [24].

3.1. IR spectra

The chair and boat conformation of piperazine can bedistinguished by IR spectroscopy. The chair form has beenconfirmed on the basis of skeletal vibration modes of boththe ligand and complexes [25].

For dithiocarbamato systems the (CAS) stretching fre-quency in the region 1000 ± 70 cm�1 is quite diagnosticfor distinguishing the symmetrical dithiocarbamates fromunsymmetrical ones. A single sharp band in the aboveregion implies a symmetrical bidentate coordination whilethe splitting of this band into a doublet may be attributedto the monodentate unsymmetrical nature of the dithio-carbamato group [26]. The structure of the dithiocarbama-to complexes can be represented by the followingformalism.

R2N C

S

S

S

S

CR2N

S

CR2N

S

C

M

S

S

C M

M

S

S

C

S

S

R2N

NR22RN

(I) (II)

(III)

S. Khan et al. / Journal of Molecular Structure 875 (2008) 478–485 481

where M is the divalent metal ion.In the complexes reported under this study the

appearance of a single sharp m(C@S) band at 1000 cm�1

is indicative of a symmetrical coordination of the dithio-carbamato moiety [27]. The thioureide band m(C N) wasobserved around 1450 cm�1 in the free ligand and wasfound to be shifted around 1488–1450 cm�1 range, in thecomplexes. This band is intermediate between (CAN)single bond and (C@N) double bond implying the metalcoordination due to the delocalization of electrons result-ing in a partial double bond character. Moreover it wasalso observed that the m(C N) in our case occurs at lowerwavenumber than in the corresponding diethyl anddimethyl analogues [28]. This behavior may be ascribedto the rigid heterocyclic ring system of piperazine molecule,which has a low tendency to release electrons to thecarbon–nitrogen bond thereby decreasing its double bondcharacter.

Some medium to weak intensity bands are observed in thefar IR region [29]. Since the increase in CAN bond increasesthe MAS bond strength, a relative trend is observed in them(MAS) for the metal complexes. There are two factorswhich effect the MAS peak position occurring in the far-IRregion: (i) the nature of the metal ion and (ii) the substituentsattached with the nitrogen [30]. However, we have observedmedium to weak intensity bands in the region (378–414 cm�1), which is assigned to MAS stretching frequencies[31]. An increase in m(MAS) is observed on moving fromZn(II) to Hg(II) however, no such behavior is observed alongthe period (Mn(II) to Cu(II)).

Table 1Magnetic susceptibility, electronic spectra and ligand field parameters of the c

Complex Magnetic moment (BM) Electronic bands (cm�1) Log e (l

Mn2(L2)2 5.77 22,430 3.220,640 2.7

Fe2(L2)2 5.32 23,529 4.1

Co2(L2)2 4.52 17,460 3.011,380 2.1

Ni2(L2)2 Diamagnetic 23,696 3.215,503 2.8

Cu2(L2)2 2.13 18,529 1.814,814 1.2

3.2. Electronic spectra and magnetic moments

The electronic spectral data along with room tempera-ture magnetic moment is presented in Table 1. The absorp-tion spectra of the complexes in DMSO have similarpattern in 220–390 nm region and exhibit two strongbands, possibly due to intraligand and charge transfer tran-sitions [32]. It is not easy to differentiate between ligandfield and charge transfer bands due to dp–pp mixing. Theexact interpretation of the spectra of tetrahedral complexesis therefore, difficult.

The Mn2(L2)2 exhibits spin-forbidden bands unlike itsoctahedral complexes which show both spin forbiddenand parity forbidden transitions. Due to the presence offive unpaired electrons 6A1 was found to be the groundstate term. Two strong broad bands were observed at20640 and 22430 cm�1 corresponding to 4T1(G) ‹ 6A1

and 4A1(G) ‹ 6A1 transitions, respectively. The magneticmoment (5.77 BM) is in proximity with the calculatedspin-only value of 5.9 BM indicative of a high-spin tetrahe-dral arrangement around the Mn(II) ion [33].

The Fe(II) complex, Fe2(L2)2 shows one spin allowedd–d band (23,529 cm�1) corresponding to 5E ‹ 5T2 transi-tion. The magnetic moment for such complexes (5.0–5.5 BM) corresponds to four unpaired electrons and wehave obtained a value of 5.32 BM, which is consistent witha high spin tetrahedral nature of Fe(II) ion [34].

The electronic spectrum of Co2(L2)2 displays two strongd–d bands at 11,380 and 17,460 cm�1 corresponding to4T1(F) ‹ 4A2(F) and 4T1(P) ‹ 4A2(F) transitions, respec-

omplexes

mol�1 cm1) Possible assignments 10 Dq (cm�1) B (cm�1) b4A1(G) ‹ 6A1 20,075 944 0.754T1(G) ‹ 6A1

5E ‹ 5T2 – – –

4T1(P) ‹ 4A2(F) – – –4T1(F) ‹ 4A2(F)

1B1g ‹ 1A1g 15,560 1613 0.641A2g ‹ 1A1g

2A1g ‹ 2B1g – – –2Eg ‹ 2B1g

482 S. Khan et al. / Journal of Molecular Structure 875 (2008) 478–485

tively, which are characteristic of a tetrahedral Co(II) ion[35]. Since the position of the latter band is shifted to higherwave numbers it may be attributed to the existence ofstrong field ligand in the present case [36]. The observedmagnetic moment (4.52 BM) is close to that found for tet-rahedral [CoCl4]2�, also supports a tetrahedral geometryfor the Co2+ ion in the present case [37].

Square-planar complexes of the d8 configuration arespin-paired type. For Ni2(L2)2 however, only two bandswere observed in the visible region (Table 1). A similarbehavior has also been reported for dithiooxamide com-

Table 2Thermal degradation of ligand and its complexes

Complex First decomposition stage Second decomposition

Fragments Temperaturerange (�C)

Mass loss data,found (calcd.) (%)

Fragments Temperaturange (�C)

Na2L2 C10H16N4S4 165–255 68.31 (68.48) C4H11N3 260–400Mn2(L2)2 C4S6 172–288 24.86 (25.18) C16H32N8 295–430Fe2(L2)2 -do- -do- 24.96 (25.13) -do- -do-Co2(L2)2 -do- -do- 24.20 (24.73) -do- -do-Ni2(L2)2 -do- -do- 24.33 (24.98) -do- -do-Cu2(L2)2 -do- -do- 19.87 (20.84) -do- -do-Zn2(L2)2 -do- -do- 23.90 (24.64) -do- -do-Cd2(L2)2 -do- -do- 21.46 (22.47) -do- -do-Hg2(L2)2 -do- -do- 18.94 (19.28) -do- -do-

2 (CH2)2NCS2Na

HN NH

N N

CH2H2CCH2H2C

HN

Na

S

HN NH

N N

H2C CH2CH2 H2C

CH2H2CCH2H2C

Na

C

S

N N

HN

CS2

HN

N

H2C CH2

CH2H2C

Na

C

SS

N

HN

467 (391 (28)

259 (63)

Scheme 1. Fragmentation pat

plexes, which has four NiAS bonds in approximatelysquare-planar fashion [38]. Since the electronic spectrum(Table 1) of the Ni2(L2)2 is identical to that of squareplanar tetraazamacrocyclic nickel(II) complexes, it isinferred that they have similar ligand field strength[39]. On the basis of electronic spectrum and magneticproperties, a square-planar geometry has, therefore beenproposed for the Ni2(L2)2 complex.

The electronic spectrum of Cu2(L2)2 exhibits two welldefined d–d absorption bands at 18,529 and 14,814 cm�1

assigned to 2A1g ‹ 2B1g and 2Eg ‹ 2B1g transitions,

stage Third decomposition stage Residue

e Mass loss data,found (calcd.) (%)

Fragments Temperaturerange (�C)

Mass loss data,found (calcd.) (%)

–

20.44 (21.63) – – – –34.20 (35.29) C8H22N6 440–700 21.17 (21.22) 2 MnS35.15 (35.23) -do- -do- 20.86 (21.18) 2 FeS34.44 (34.67) -do- -do- 20.23 (20.84) 2 CoS34.64 (35.02) -do- -do- 20.91 (21.05) 2 NiS33.20 (34.67) -do- -do- 19.65 (20.84) 2 CuS33.23 (34.54) -do- -do- 20.55 (20.76) 2 ZnS31.20 (31.49) -do- -do- 18.17 (18.94) 2 CdS26.99 (27.03) -do- -do- 15.99 (16.25) 2 HgS

Na Na

2 CSS

NH

NN

H2C CH2 H2C CH2

H2CCH2 CH2H2C

NN

NHHN

NH

N

SC

N

S S

C

Na

H2C CH2 H2C CH2

H2CCH2 CH2H2C

NN

NHHN

SNa

NH

N

CH2H2C

CH2H2C

Na

C

SS

N

n.o.) 413 (44)

76 (100)

tern of the ligand, Na2L2.

S. Khan et al. / Journal of Molecular Structure 875 (2008) 478–485 483

respectively. However, a slight change in the position ofthe above bands may be ascribed to the perturbationenergies arising from the inductive and delocalizationeffects of the substituents on the S2CN moiety. Magneticmoment (2.13 BM) is consistent with a square-planarconfiguration. These results are similar to that obtainedby Escobal et al. in for square-planar acetylacetanatoCu(II) complexes [40].

CS

S

S

SC

NCS

S

S

SCN

H2

H2

C

C

H2

C

H2C

N

N

HN

HN

NH

NCH2

CH2

C

C

H2

H2

N

Co

Co

961 (23)

NH

NH

NH2

NCH2

CH2

C

C

H2

H2

N CS

S

S

SC

CS

S

S

SCH

CS

S

S

SCN

H2

H2

C

C

H2

C

H2C

N

NH2

HN

NH

C6H9N2S4M

879 (72)

583 (64)

Co

Co

Co

NCH2

CH2

C

C

H2

H2

N CS

SCo

S

SCH

MS4

C10H18N4

381 (81)

187 (84)

Scheme 2. Fragmentation patte

3.3. 1H NMR

The NMR spectrum of, Na2L2 in CDCl3 displays a sin-glet at 2.30 ppm due to eight protons of four CH2 groupsof the diethylenetriamine moiety [41]. On comparing thespectrum of free diethylenetriamine and Na2L2 it wasfound that the imine protons were resonating at 5.82 ppmwhile the amino protons were shifted downfield [42]. The

NH

NH

N

H2

H2

C

C

H2

C

H2C

CH2

CH2

C

C

H2

N

CoS42C28H54N14

H2

HN

374 (100)

N N

H2

H2

C

C

H2

C

H2C

CH2

CH2

C

C

H2

H2

NN

HN

HN

NH

NH

NH

NH

N N

H2

H2

C

C

H2

C

H2C

2

CH2

CH2

C

C

H2

H2

NN H

rn of the complex Co2(L2)2.

484 S. Khan et al. / Journal of Molecular Structure 875 (2008) 478–485

downfield shift (6.24 ppm) in the amino protons may beattributed to the attachment of piperazinium moiety [43].

The absence of NAH proton at ca 2.15 ppm value in theligand and its complexes confirm the double deprotonationof piperazine moiety. The methylene protons of piperazineappear at 2.64 ppm in case of ligand while they negligiblymove to 2.66–2.69 ppm in the complexes indicating thatthey are not affected by complexation [44].

3.4. TGA/DSC

The thermochemistry of metal dithiocarbamates hasbeen thoroughly reviewed [45]. The mass loss data and tem-perature range of various fragments are presented in Table2. The comparison of the TGA and DSC plots implies thatthe ligand and its complexes are stable upto 165 �C sincethere were no peak or humps observed in the DSC plots.Since there occurs no thermal change below this tempera-ture it confirms the absence of water or solvent molecule.Also it suggests that the complex restructuring does notoccur prior to the decomposition of the complex [46].The TGA profile of the ligand consists of two discrete stepswhile the complexes exhibit a three stage pyrolytic pattern.The ligand shows first cleavage between from 165 to 255 �Ccorresponding to the degradation of the CSS group andpiperazinium moiety [47]. The second decomposition runsthrough 260–400 �C resulting in the elimination of remain-ing part of the organic moiety, (20.44%). The thermogramof the complexes does not show any change until 172 �C.The first degradation stage stretches from 172 to 288 �Ccorroborating the pyrolysis of C4S6 moiety while the sec-ond stage corresponds to the degradation of four piperaz-inium entities. The third stage results in the expulsion ofthe remaining organic moiety leaving behind metal sulfideas the end product [48].

Comparison of the TGA and DSC curves leads to theconclusion that the plots contain very complicated thermaleffects. In the case of ligand the first endothermic curve issmall and sharp whereas a broad exothermic hump cen-tered at 540 �C is obtained in the case of complexes. Thebroad and continuous humps imply slow decompositionleading to volatilization upon heating.

3.5. Mass spectrometry

The FAB mass spectral data and fragmentation patternof the ligand and its complexes are given under Schemes 1and 2. The mass spectrum of disodium bis(2,2 0-dithiopipe-razinato-2,2 0-diaminodiethylamine), did not show themolecular ion peak. However, the base peak is observedat m/z (76) due to [M�391] fragment. The other fragmentsat m/z 413(44), 391(28) and 259(63) are observed for[M�54], [M�76] and [M�208] fragment, respectively. Inthe case of Co2(L2)2 the molecular ion peak is observedat m/z 961(23) while the other peaks are observed at m/z879(72), 583(64), 381(81) and 374(84) corresponding to[M�82], [M�378], [M�580] and [M�587], respectively

(Scheme 2). Unlike the ligand the base peak in the caseof Co2(L2)2 is observed at m/z 374 corresponding to[2CoS4] fragment [49].

4. Conclusion

The present paper describes the synthesis of tailoredhomodinuclear transition metal complexes. Although noneof the complexes have been obtained in the crystallineform, the experimental results suggest that dithiocarbama-to ligand coordinates in a bidentate fashion leading to aclosed ring system. The stoichiometry of the ligand:metalwas confirmed from their mass spectral data while theTGA explains a greater stability of the metal complexes.

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