Piperazine pivoted transition metal dithiocarbamates

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Journal of Molecular Structure 875 (2008) 478–485 www.elsevier.com/locate/molstruc

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 2007 Available 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 metal complexes 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 piperazine pivoted homodinuclear complexes have been characterized by a range of spectral, thermal, microanalytical and conductometric techniques. On the basis of IR and 1HNMR data a symmetrical bidentate coordination of the dithiocarbamato moiety has been observed in 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 basis of FAB mass spectral data and a probable fragmentation pattern has been proposed. On the basis of UV–visible spectroscopic results and room temperature magnetic moment data a tetrahedral geometry has been proposed for all the complexes except for the Ni(II) and Cu(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 coordination supramolecular arrays based on covalent interactions or hydrogen bonding has been a major focus of research efforts in recent years for the rationale design of functional materials [1]. Journaux et al. [2] have recently indicated that the pathways used to obtain these species are based, essentially, on the following synthetic schemes: (i) the self assembly method, (ii) the use of polynucleating ligands and (iii) the use of complexes as ligands. However, the metal directed self-assembly of polydentate ligands provides a facile route to novel supramolecular structures based on the metal coordinate interactions [3,4]. Through imaginative multidentate ligand design and judicious choice of the metal ion, a novel range of polymetallic inorganic assemblies including helicates, cages, ladders, racks, grids and tubes have been constructed [5]. These frame-

*

Corresponding author. E-mail address: [email protected] (K.S. Siddiqi).

0022-2860/$ - see front matter  2007 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2007.05.020

works can also act as receptors to detect anions in solutions [6]. Among various sulfur containing ligands the dithiocarbamato (dtc) moiety has proved as a useful structural motif lending itself to the metal directed assembly of a range of structures like nanosized resorcarene based assemblies, catenanes, cryptands, etc. [7]. The small bite angle (2.8– ˚ ) of the dtc makes it appropriate for the stabilization 2.9 A of a range of oxidation states of various metal ions [8]. They are used as vulcanizers, higher pressure lubricating agents, fungicides, pesticides antialkylating agents, antioxidants, spin trapping agents and anti-HIV agents [9–12]. Dithiocarbamates are also used as molecular precursors for CVD processes. Water-soluble dialkyldithiocarbamate complexes are known to have been tested in various medical applications [13]. Piperazine is a well known building block for novel supramolecular structures due to the presence of two weakly held terminal amino protons [14]. Of the two readily interconvertible conformations of the piperazine, the chair form is thermodynamically more stable since it is 17.2 kJ/mol higher than the boat form [15]. However, the

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

boat form gives mononuclear whereas the chair form gives dinuclear complexes with no exogenous bridging for transN,N 0 coordination [16,17]. In continuation of our earlier work on piperazinato mono as well as bisdithiocarbamato complexes [18] we have attempted to use piperazine moiety as a structural motif rendering it to exist in its preferred chair form [19]. Recently, polypyridine dithiocarbamates and piperazine bridged homodinuclear transition metal dithiocarbamates have been reported from our laboratory [20,21]. In the present communication the piperazine moiety is exploited to form the dithiocarbamate in a way it assembles to form a barrel shaped structure (Fig. 3) unlike the linear arrays reported by Hogarth et al. [22]. Herein we report the synthesis and spectroscopic characterization of piperazine pivoted 3d-transition metal dithiocarbamates in order to study the symmetrical and unsymmetrical bonding of the dithiocarbamate and their thermal behavior supported by TGA/ DSC. The FAB-MS has been done for prototype compounds to ascertain the formation of binuclear complexes on 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) were used as received. Methanol was distilled prior to use. Elemental analyses (C, H, N and S) were carried out with a Carlo Erba EA-1108 analyzer. The metal contents were estimated by complexometric titration [23]. IR spectra (4000–400 cm1) were recorded on a RXI FT-IR spectrometer as KBr disc while the 600–200 cm1 range was scanned with CsI on a Nexus FT-IR Thermo Nicolet, (Wisconsin). The Electronic spectra were recorded on a Cintra 5GBC spectrophotometer in DMSO. The NMR spectra were recorded on a DPX-300 spectrometer in DMSO at room temperature. The conductivity measurements were carried out on a CM-82T Elico conductivity bridge in DMSO. Magnetic susceptibility measurements were done with a 155 Allied Research vibrating sample magnetometer at room temperature. TGA was performed with a Perkin– Elmer (Pyris Diamond) thermal analyzer under nitrogen atmosphere using alumina powder as reference. The weight of the sample was kept between 8 and 12 mg and the heating rate was maintained at 10 C/min. The FAB mass spectra were recorded on a JEOL SX 102/Da-6000 Mass Spectrometer/Data System using Argon/Xenon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was 10 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 dropwise added to a methanolic solution of diethylene triamine

H2N

N H

NH2

SOCl2

479

HN

N H

Cl

NH Cl

L1

Fig. 1. Synthesis of the ligand Na2L1.

(5 mmol, 0.56 mL) in an ice bath. The reaction mixture was stirred for 2 h, cooled to room temperature and then refluxed on a water bath for about an hour, which afforded a whitish pink precipitate under reflux. It was then cooled, filtered, washed with methanol and dried in vacuo over P2O5 (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 in the same solvent (20 mL) was added dropwise with continuous stirring and then refluxed for about 2 h. The mixture was cooled to 5 C followed by addition of carbon disulfide (2 mmol, 0.12 mL) and NaOH (2 mmol, 0.08 g) dissolved in aqueous methanol to afford a light green precipitate. The compound was filtered, washed with methanol and dried in vacuo over P2O5 (Fig. 2). [Na2L2] yield (80%); m. p. 165 C; KM = 33 X1cm2 mol1 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/cm1 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 the substitution reaction of Na2L2 (2 mmol, 0.93 g) with MCl2ÆxH2O (2 mmol) in equimolar ratios in methanol. [Mn2(L2)2] yield (62%); m. p. 208 C; KM = 27 X1 cm2 mol1 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/cm1 3447s (NAH), 1468s (C N), 1284w, 1254m (ring vib.), 992s (CAS), 378 (MnAS). [Fe2(L2)2] yield (67%); m. p. 210 C; KM = 42 X1 cm2 mol1 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/cm1 3421s (NAH), 1459s (C N), 1278w, 1244m (ring vib.), 993s (CAS), 397 (FeAS). [Co2(L2)2] yield (70%); m. p. 211 C; KM = 17 X1 cm2 mol1 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/cm1 3422s (NAH), 1465s (C N), 1275w, 1248m (ring vib.), 994s (CAS), 393 (CoAS). [Ni2(L2)2] yield (68%); m. p. 220 C; KM = 11 X1 cm2 mol1 found (calcd. for C28H54Ni2N14S8) C, 34.86(35.0),

480

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

HN

NH

N H

N L1

H2C 2 HN(CH2)4NH

2 CS2

2 NaOH

2 HCl, 2 NaCl

H2C

N CH2

H2C

CH2

H2C

N

CH2 CH2 N

C

C S Na

S

S

S Na

2

Fig. 2. Synthesis of the ligand Na2L .

H, 5.60(5.66), N, 20.24(20.41), S, 26.86(26.69), Ni, 12.45 (12.22). IR (KBr): mmax/cm1 3422s (NAH), 1478s (C N), 1274w, 1261m (ring vib.), 991s (CAS), 397 (NiAS). [Cu2(L2)2] yield (55%); m. p. 262 C; KM = 09 X1 cm2 mol1 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/cm1 3401s (NAH), 1488s (C N), 1268w, 1254m (ring vib.), 990s (CAS), 406 (CuAS). [Zn2(L2)2] yield (62%); m. p. 230 C; KM = 10 X1 cm2 mol1 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/cm1 3477s (NAH), 1473s (C N), 1280w, 1244m (ring vib.), 995s (CAS), 384 (ZnAS). [Cd2(L2)2] yield (72%); m. p. 208 C; KM = 15 X1 cm2 mol1 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/cm1 3434s (NAH), 1462s (C N), 1279w, 1260m (ring vib.), 996s (CAS), 392 (CdAS). [Hg2(L2)2] yield (70%); m. p. 218 C; KM = 22 X1 cm2 mol1 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/cm1 3400s (NAH), 1477s (C N), 1284w, 1265m (ring vib.), 997s (CAS), 414 (HgAS). 3. Results and discussion The metal dithiocarbamates, M2(L2)2 were conveniently obtained in high yield by substitution reaction of sodium salt of functionalized secondary amine or dithiocarbamate with hydrated transition metal halides in methanol (Fig. 3). 2 Na2 L2 + 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 mass spectrometry, UV–visible and IR spectroscopy were used to characterize the complexes.The amorphous complexes are soluble in DMSO and DMF only. The conductivity measurement (103 M) in DMSO indicated them to be non-electrolytes [24].

HN

N H

NH N

N H2C

CH2

H2C

CH2

H2C

CH2

H2C

CH2

N

N C

C S 2 MCl2

+ 2 Na2L

2

- 4 NaCl

S

S

S

S

M S

S M

C

S C

N

N

H2C

CH2

H2C

CH2

H2C

CH2

H2C

CH2

N HN

N H N

NH

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).

3.1. IR spectra The chair and boat conformation of piperazine can be distinguished by IR spectroscopy. The chair form has been confirmed on the basis of skeletal vibration modes of both the ligand and complexes [25]. For dithiocarbamato systems the (CAS) stretching frequency in the region 1000 ± 70 cm1 is quite diagnostic for distinguishing the symmetrical dithiocarbamates from unsymmetrical ones. A single sharp band in the above region implies a symmetrical bidentate coordination while the splitting of this band into a doublet may be attributed to the monodentate unsymmetrical nature of the dithiocarbamato group [26]. The structure of the dithiocarbamato complexes can be represented by the following formalism.

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

S R2N

C

S

S C

M S

R2N

NR 2

S

C

M S

S

481

C

NR 2

S

(I)

(II) S

S R2N

C

M S

C

NR2

S (III)

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 cm1 is indicative of a symmetrical coordination of the dithiocarbamato moiety [27]. The thioureide band m(C N) was observed around 1450 cm1 in the free ligand and was found to be shifted around 1488–1450 cm1 range, in the complexes. This band is intermediate between (CAN) single bond and (C@N) double bond implying the metal coordination due to the delocalization of electrons resulting in a partial double bond character. Moreover it was also observed that the m(C N) in our case occurs at lower wavenumber than in the corresponding diethyl and dimethyl analogues [28]. This behavior may be ascribed to the rigid heterocyclic ring system of piperazine molecule, which has a low tendency to release electrons to the carbon–nitrogen bond thereby decreasing its double bond character. Some medium to weak intensity bands are observed in the far IR region [29]. Since the increase in CAN bond increases the MAS bond strength, a relative trend is observed in the m(MAS) for the metal complexes. There are two factors which effect the MAS peak position occurring in the far-IR region: (i) the nature of the metal ion and (ii) the substituents attached with the nitrogen [30]. However, we have observed medium to weak intensity bands in the region (378– 414 cm1), which is assigned to MAS stretching frequencies [31]. An increase in m(MAS) is observed on moving from Zn(II) to Hg(II) however, no such behavior is observed along the period (Mn(II) to Cu(II)).

3.2. Electronic spectra and magnetic moments The electronic spectral data along with room temperature magnetic moment is presented in Table 1. The absorption spectra of the complexes in DMSO have similar pattern in 220–390 nm region and exhibit two strong bands, possibly due to intraligand and charge transfer transitions [32]. It is not easy to differentiate between ligand field and charge transfer bands due to dp–pp mixing. The exact interpretation of the spectra of tetrahedral complexes is therefore, difficult. The Mn2(L2)2 exhibits spin-forbidden bands unlike its octahedral complexes which show both spin forbidden and parity forbidden transitions. Due to the presence of five unpaired electrons 6A1 was found to be the ground state term. Two strong broad bands were observed at 20640 and 22430 cm1 corresponding to 4T1(G) ‹ 6A1 and 4A1(G) ‹ 6A1 transitions, respectively. The magnetic moment (5.77 BM) is in proximity with the calculated spin-only value of 5.9 BM indicative of a high-spin tetrahedral arrangement around the Mn(II) ion [33]. The Fe(II) complex, Fe2(L2)2 shows one spin allowed d–d band (23, 529 cm1) corresponding to 5E ‹ 5T2 transition. The magnetic moment for such complexes (5.0– 5.5 BM) corresponds to four unpaired electrons and we have obtained a value of 5.32 BM, which is consistent with a high spin tetrahedral nature of Fe(II) ion [34]. The electronic spectrum of Co2(L2)2 displays two strong d–d bands at 11,380 and 17,460 cm1 corresponding to 4 T1(F) ‹ 4A2(F) and 4T1(P) ‹ 4A2(F) transitions, respec-

Table 1 Magnetic susceptibility, electronic spectra and ligand field parameters of the complexes Complex 2

Mn2(L )2 Fe2(L2)2 2

Co2(L )2 Ni2(L2)2 Cu2(L2)2

Magnetic moment (BM) 5.77 5.32 4.52 Diamagnetic 2.13

Electronic bands (cm1)

Log e (l mol1 cm1)

Possible assignments

10 Dq (cm1)

B (cm1)

b

22,430 20,640

3.2 2.7

4

20,075

944

0.75

23,529

4.1

5

–

–

–

17,460 11,380

3.0 2.1

4

–

–

–

23,696 15,503

3.2 2.8

1

15,560

1613

0.64

18,529 14,814

1.8 1.2

2

–

–

–

6

A1(G) ‹ A1 T1(G) ‹ 6A1

4

E ‹ 5T2 4

T1(P) ‹ A2(F) T1(F) ‹ 4A2(F)

4

B1g ‹ 1A1g A2g ‹ 1A1g

1

A1g ‹ 2B1g Eg ‹ 2B1g

2

482

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

plexes, which has four NiAS bonds in approximately square-planar fashion [38]. Since the electronic spectrum (Table 1) of the Ni2(L2)2 is identical to that of square planar tetraazamacrocyclic nickel(II) complexes, it is inferred that they have similar ligand field strength [39]. On the basis of electronic spectrum and magnetic properties, a square-planar geometry has, therefore been proposed for the Ni2(L2)2 complex. The electronic spectrum of Cu2(L2)2 exhibits two well defined d–d absorption bands at 18,529 and 14,814 cm1 assigned to 2A1g ‹ 2B1g and 2Eg ‹ 2B1g transitions,

tively, which are characteristic of a tetrahedral Co(II) ion [35]. Since the position of the latter band is shifted to higher wave numbers it may be attributed to the existence of strong field ligand in the present case [36]. The observed magnetic moment (4.52 BM) is close to that found for tetrahedral [CoCl4]2, also supports a tetrahedral geometry for the Co2+ ion in the present case [37]. Square-planar complexes of the d8 configuration are spin-paired type. For Ni2(L2)2 however, only two bands were observed in the visible region (Table 1). A similar behavior has also been reported for dithiooxamide com-

Table 2 Thermal degradation of ligand and its complexes Complex First decomposition stage

Second decomposition stage

Third decomposition stage

Residue

Fragments Temperature Mass loss data, Fragments Temperatue Mass loss data, Fragments Temperature Mass loss data, – range (C) found (calcd.) (%) range (C) found (calcd.) (%) range (C) found (calcd.) (%) Na2L2 Mn2(L2)2 Fe2(L2)2 Co2(L2)2 Ni2(L2)2 Cu2(L2)2 Zn2(L2)2 Cd2(L2)2 Hg2(L2)2

C10H16N4S4 C4S6 -do-do-do-do-do-do-do-

165–255 172–288 -do-do-do-do-do-do-do-

HN

68.31 24.86 24.96 24.20 24.33 19.87 23.90 21.46 18.94

(68.48) (25.18) (25.13) (24.73) (24.98) (20.84) (24.64) (22.47) (19.28)

C4H11N3 C16H32N8 -do-do-do-do-do-do-do-

NH

N H

N

HN

N CH2

H2C

CH2

H2C

CH2

H2C

CH2

CS2

N

H2C

CH2

H2C

CH2

N

SNa

S

N H2C

CH2

H2C

CH2

H2C

CH2

N

N

C S Na

S

C 413 (44)

N H2C

HN

NH

N H

H2C

CH2

N

H2C

CH2

H2C

H2C

CH2

H2C

N Na

2 (CH2)2NCS2Na 259 (63)

NH

N H

N

N CH2

S

S Na

467 (n.o.)

HN

NH

N H

CH2

C S Na

2 CSS 76 (100)

Scheme 1. Fragmentation pattern of the ligand, Na2L2.

– 2 2 2 2 2 2 2 2

(21.22) (21.18) (20.84) (21.05) (20.84) (20.76) (18.94) (16.25)

H2C

N

C

– 21.17 20.86 20.23 20.91 19.65 20.55 18.17 15.99

N CH2

391 (28)

– 440–700 -do-do-do-do-do-do-do-

HN

H2C

S

– C8H22N6 -do-do-do-do-do-do-do-

NH

N H

CH2

N Na S Na

(21.63) (35.29) (35.23) (34.67) (35.02) (34.67) (34.54) (31.49) (27.03)

H2C

C S

20.44 34.20 35.15 34.44 34.64 33.20 33.23 31.20 26.99

N

H2C

N

260–400 295–430 -do-do-do-do-do-do-do-

CH2 CH2 N Na

MnS FeS CoS NiS CuS ZnS CdS HgS

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

3.3. 1H NMR

respectively. However, a slight change in the position of the above bands may be ascribed to the perturbation energies arising from the inductive and delocalization effects of the substituents on the S2CN moiety. Magnetic moment (2.13 BM) is consistent with a square-planar configuration. These results are similar to that obtained by Escobal et al. in for square-planar acetylacetanato Cu(II) complexes [40].

H N

H2 C

H2 C

C H2

C H2

H2 C

H2 C

N

N

The NMR spectrum of, Na2L2 in CDCl3 displays a singlet at 2.30 ppm due to eight protons of four CH2 groups of the diethylenetriamine moiety [41]. On comparing the spectrum of free diethylenetriamine and Na2L2 it was found that the imine protons were resonating at 5.82 ppm while the amino protons were shifted downfield [42]. The H2 C

H2 C

S

C H2

C H2

S

H2 C

H2 C

C H2

C H2

S

S Co

C

C

S

H N

N

N

HN

NH N H

S

N

N C H2

C H2

H2 C

H N

Co

C S

N

N

C

Co

C

C H2

H2 C

S

H2 C

N

H N

N C H2

S

C28H54N14

N H

N

S

S N

C H2

C S

961 (23)

H2 C

C H2

NH

NH S

S Co

HC

NH2

C

S

H2 C

H2 C

C H2

C H2

H2 C

H2 C

C H2

C H2

N

S

N H

N

879 (72)

C6H9N2S4M

H N

H2 C

H2 C

C H2

C H2

S

S

N

N

C

Co

C S

N

S

H N

N

NH

NH 583 (64)

H 2N

NH2

H2 C

H2 C

C H2

C H2

HN

S

S N

Co

C

C

S

483

S

381 (81)

H2 C

H2 C

C H2

C H2

N

NH

C10H18N4 MS4 187 (84) Scheme 2. Fragmentation pattern of the complex Co2(L2)2.

2 CoS4 374 (100)

484

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

downfield shift (6.24 ppm) in the amino protons may be attributed to the attachment of piperazinium moiety [43]. The absence of NAH proton at ca 2.15 ppm value in the ligand and its complexes confirm the double deprotonation of piperazine moiety. The methylene protons of piperazine appear at 2.64 ppm in case of ligand while they negligibly move to 2.66–2.69 ppm in the complexes indicating that they are not affected by complexation [44]. 3.4. TGA/DSC The thermochemistry of metal dithiocarbamates has been thoroughly reviewed [45]. The mass loss data and temperature range of various fragments are presented in Table 2. The comparison of the TGA and DSC plots implies that the ligand and its complexes are stable upto 165 C since there were no peak or humps observed in the DSC plots. Since there occurs no thermal change below this temperature it confirms the absence of water or solvent molecule. Also it suggests that the complex restructuring does not occur prior to the decomposition of the complex [46]. The TGA profile of the ligand consists of two discrete steps while the complexes exhibit a three stage pyrolytic pattern. The ligand shows first cleavage between from 165 to 255 C corresponding to the degradation of the CSS group and piperazinium moiety [47]. The second decomposition runs through 260–400 C resulting in the elimination of remaining part of the organic moiety, (20.44%). The thermogram of the complexes does not show any change until 172 C. The first degradation stage stretches from 172 to 288 C corroborating the pyrolysis of C4S6 moiety while the second stage corresponds to the degradation of four piperazinium entities. The third stage results in the expulsion of the remaining organic moiety leaving behind metal sulfide as the end product [48]. Comparison of the TGA and DSC curves leads to the conclusion that the plots contain very complicated thermal effects. In the case of ligand the first endothermic curve is small and sharp whereas a broad exothermic hump centered at 540 C is obtained in the case of complexes. The broad and continuous humps imply slow decomposition leading to volatilization upon heating. 3.5. Mass spectrometry The FAB mass spectral data and fragmentation pattern of the ligand and its complexes are given under Schemes 1 and 2. The mass spectrum of disodium bis(2,2 0 -dithiopiperazinato-2,2 0 -diaminodiethylamine), did not show the molecular ion peak. However, the base peak is observed at m/z (76) due to [M391] fragment. The other fragments at m/z 413(44), 391(28) and 259(63) are observed for [M54], [M76] and [M208] fragment, respectively. In the case of Co2(L2)2 the molecular ion peak is observed at m/z 961(23) while the other peaks are observed at m/z 879(72), 583(64), 381(81) and 374(84) corresponding to [M82], [M378], [M580] and [M587], respectively

(Scheme 2). Unlike the ligand the base peak in the case of Co2(L2)2 is observed at m/z 374 corresponding to [2CoS4] fragment [49]. 4. Conclusion The present paper describes the synthesis of tailored homodinuclear transition metal complexes. Although none of the complexes have been obtained in the crystalline form, the experimental results suggest that dithiocarbamato ligand coordinates in a bidentate fashion leading to a closed ring system. The stoichiometry of the ligand:metal was confirmed from their mass spectral data while the TGA explains a greater stability of the metal complexes. References [1] J.M. Lehn (Ed.), Supramolecular Chemistry, Concepts and Perspectives, VCH, Weinheim, 1995. [2] A. Aukaulooa, X. Ottnwaelder, R. Ruiz, Y. Journaux, Y. Pei, E. Riviere, M.C. Munoz, Eur. J. Inorg. Chem. (2000) 951. [3] M.A. Withersby, A.J. Blake, N.R. Chapness, P. Hubberstey, W.S.B. Li, M. Schroder, Angew. Chem. Int. Ed. Eng. 36 (1997) 2327; D. Whang, J. Heo, C.A. Kim, K. Kim, Chem. Commun. (1997) 2361. [4] P.J. Stang, S.R. Seidel, Acc. Chem. Res. 35 (2002) 972. [5] F.M. Tabellion, S.R. Seidel, A.M. Aril, P.J. Stang, Angew. Chem. Int. Ed. 40 (2001) 1529; J. Rojo, F.J. Romero-Salguero, J.M. Lehn, G. Baum, D. Fenske, Eur. J. Inorg. Chem. (1999) 1421; E. Breuning, U. Zeiner, J.M. Lehn, E. Wegelius, K. Rissanen, Eur. J. Inorg. Chem. (2001) 1515. [6] M. Aoyagi, K. Biradha, M. Fujita, J. Am. Chem. Soc. 121 (1999) 7457. [7] M.D. Pratt, P.D. Beer, Tetrahedron 60 (2004) 11227; O.D. Fox, M.G.B. Drew, P.D. Beer, Angew. Chem. Int. Ed. Eng. 39 (2000) 136; M.E. Padilla-Tosta, O.D. Fox, M.G.B. Drew, P.D. Beer, Angew. Chem. Int. Ed. Eng. 40 (2001) 4235; P.D. Beer, N.G. Berry, A.R. Cowley, E.J. Hayes, E.C. Oates, W.W.H. Wong, Chem. Commun. (2003) 2408. [8] G. Hogarth, Prog. Inorg. Chem. 53 (2005) 71. [9] G.D. Thorn, R.A. Ludwig, The Dithiocarbamates and Related Compounds, Elsevier, New York, 1962. [10] T. Nagano, Chem. Rev. 102 (2002) 1235. [11] L. Monser, N. Adhoum, Sep. Purif. Technol. 26 (2002) 137; E.D. Caldas, J. Trbssou, P.E. Boon, Food and Chem. Toxicol. 44 (2006) 1562. [12] C.A. Mandon, C. Diaz-Latoud, A.-P. Arrito, L.J. Blum, J. Biotech. 124 (2006) 392; M. Hosni, N. Meskini, A.-F. Prigent, G. Anker, C. Joulian, R.E. Habib, M. Lagarde, Biochem. Pharmacol. 43 (1992) 1319. [13] J. Xie, T. Funakoshi, H. Shimada, S. Kojima, Res. Commun. Mol. Pathol. Pharmacol. 86 (1994) 245. [14] J. Ratilainen, K. Airola, R. Frohlich, M. Nieger, K. Rissanen, Polyhedron 18 (1999) 2265. [15] H.M. Niemyer, J. Mol. Struct. 57 (1979) 241. [16] Z. Smekal, Z. Travnycek, J. Mrozimski, J. Marek, Inorg. Chem. Commun. 6 (2003) 1395. [17] M. Bera, J. Ribas, W.T. Wong, D. Ray, Inorg. Chem. Commun. 7 (2004) 1242. [18] K.S. Siddiqi, F.R. Zaidi, S.A.A. Zaidi, Synth. React. Inorg. Met. Org. Chem. 10 (1980) 569. [19] K. Rissanen, J. Huuskonen, A. Koskinen, J. Chem. Soc. Chem. Commun. (1993) 771.

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