Spectroscopic, magnetic and thermogravimetric studies of piperazine-bis-(dithiocarbamate) complexes

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Vol. 4OA, No. 4, pp. 343-346,

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Spectroscopic, magnetic and thermogravimetric studies of piperazine-bis-(dithiocarbamate) complexes ANTONIO COSTANTINO FABRETTI,FABRIZIAFORGHIERI,ALEARD~ GIUSTI, CARLO PRETI* and GIUSEPPETOSI

Istituto di Chimica Generale e Inorganica, University of Modena, 41100 Modena, Italy (Received 3 August 1983) Abstract-A new 1,4-piperazine-bis-dithiocarbamate sodium salt and its metal complexes have been prepared and characterized by elemental analyses, conductivity measurements, magnetic susceptibilities, thermal analyses (TG and DTG) and spectroscopic (i.r., electronic and EPR) techniques. The ligand is tetrasulphur coordinated to the metals in polymeric structures. The magnetic measurements are indicative of one unpaired electron in the copper(I1) complex; a p value typical of planar low-spin complexes has been obtained in the case of the cobalt(H) derivative,while a distortion from the planarity is suggested in the case of the nickel(I1) complex. Tentative structures of the complexes are proposed on the basis of the obtained results. INTRODUCTION

spectrophotometer of the Instruments Centre of Modena University as KBr discs or Nujol mulls supported between polyethylene sheets The electronic spectra were recorded with a Shimadzu MPS-SOL spectrophotometer in the solid state. X-EPR spectra have been recorded on a Varian E9 instrument at room temperature and at 143 K for powderlike undopped samples with DPPH as frequency calibrant. Magnetic susceptibilities were measured by the absolute Gouy method at room temperature and corrected by Pascal’s

Continuing our earlier work on heterocyclic containing dithiocarbamate ligands with p-and d-block metals and on the reactivity of the obtained complexes

towards bidentate nitrogen donor ligands [l-17], we report here the synthesis and characterization of piperazine-bis-(dithiocarbamate) complexes of cobalt(II), nickel(II), copper( zinc(U), cadmium(II) and mercury(I1):

constants.

The thermogravimetric analyses were performed with a Mettler TA 3000 thermal analysis system equipped with a TC 10 processor. Open AlzOJ crucibles were used; the heating rate was 10°C min- ‘. Elemental analyses. Carbon, nitrogen, hydrogen and sulphur were determined using a Carlo Erba 1106 analyser.

Pz(bis)dtcNa,. This paper extends the previously reported studies on the dithiocarbamates in which just one NC& group was present in the molecule; from a structural point of view the dithiocarbamates have been found acting always as bidentate chelating S,S’-donors, in spite of their dual nature of acting both as chelates or monodentate ligands. EXPERIMENTAL Preparation of the ligand. The ligand was prepared by treating piperazine in dry ethyl ether and isopropyl alcohol with CS2 and adding NadH under vigorous sti&iover a 5h period. Molar ratios amine: CS, :NaOH = 1: 2: 2. The crude product was recrystallized from acetone or isopropyl alcohol. S Na2.4.5Hz0 Analyses: for C 6H sN 24 (calcd.): C 19.8; N 7.7; H 4.7; S 35.3 y, (found): C 19.8; N 7.8; H 4.5; S 35.5%. Preparation of the complexes. The complexes were prepared by adding a methanolic solution of the ligand to a hydromethanolic (1:l) solution of the metal chloride (or bromide in the case of the mercury compound) in a 1: 1 ligand to metal molar ratio. The CoL.2H20 complex was prepared in HZ0 in a 1.5: 1 ligand to metal molar ratio. Physical measurements. The i.r. spectra have been recorded in the 400&50 cm-’ region with a Perkin-Elmer 180

*Author to whom all correspondence should be addressed.

RESULTSAND DISCUSSION

All the complexes studied are reported in Table 1 together with their analytical data and other physical properties. The i.r. spectra in the 4000-50 cm-’ range are summarized in Table 2, while Table 3 reports the principal features of the electronic spectra. The results of the thermogravimetric studies are presented in Table 4. The compounds are dark green or white, stable at room temperature and microcrystalline or powdery. Since they were insoluble in methanol, ethanol, nitrobenzene, nitromethane, acetone, NJ’dimethylformamide and acetonitrile, conductivity measurements could not be made. I.r. spectra

The most important i.r. peaks for the free ligand sodium salt and for the complexes are reported in Table 2. As for the vibrational mode involving the NH groups of the free amine, the i.r. spectrum of the piperazine-bis-(dithiocarbamate) sodium salt showed the absence of any NH stretching frequency; this absorption band was present at 3460 cm- ’ in the piperazine and in the piperazine dithiocarbamate sodium salt and its disappearance indicates the re343

344

ANTONIO COSTANTINO FABRETTI YI ul

Table 1. Analytical

data and some physical

Compounds

Colour

Found N

( ‘5,) C

H

S

CoL,2HZ0 NiL.O.SH*O CuL.2Hz0* ZnL,HZO CdL,H*O HgL.H20

dark green dark green dark brown white white yellow-green

8.4 9.3 8.3 8.9 7.5 6.3

21.6 23.9 21.2 22.6 19.4 16.2

3.9 2.1 3.5 2.7 2.2 2.3

38.7 42.3 38.2 40.8 35.2 28.6

*Cu 0,j: found

properties

Calculated ( I’,,,) C H N

s

i*elT B.M.

21.7 23.1 21.4 22.5 19.6 15.8

38.7 42.2 38.2 40.1 35.0 28.2

2.49 0.89 1.82 dia. dia. dia.

8.4 9.2 8.3 8.8 7.6 6.2

3.6 3.0 3.6 3.1 2.7 2.2

19.4. calcd. 18.9. Table 2. Most important Compounds Pz(bis)dtcNa, CoL.ZH,O NiL.O.SH,O CuL,2H,O ZnL.H20 CdL,H20 HgL,H,O

v(C 2 N)

i.r. bands

v(C L S) _____

1452~s 1470vs 1487~s 1475vs 1475m 1470m 1470s

moval of both hydrogen atoms in the bis(dithiocarbamate) under study. The i.r. spectrum of the uncomplexed ligand shows one band attributed to the prevailing contribution of the carbon-nitrogen stretching at 1452 cm- ‘, a value clearly indicative of a considerable double bond character. Ail the metal complexes reported here show bands assigned to v(C-N) in the 1487-1470cm-’ range, which lie between v(C=N) and v(C-N), in the 169&l 640 and 135&l 250 cm ’ ranges respectively. The band present in the 995-989 cm- ’ region is attributed to v(C-S) [l&13,17,18]; the presence of only one strong band in this region is diagnostic of symmetrical coordination of the dithiocarbamate moiety, whereas two closely spaced bands in the 1000 + 70 cm-’ range would be expected in the case of unsymmetrically bound dithiocarbamate group [19-221. Analysis of the position of the v(C-N) mode gives further confirmation of such behaviour; this band, in fact, undergoes blue shifts in all the complexes, while for unidentate coordination of the CS, group the frequency of the carbon-nitrogen stretching would decrease or remain unchanged at the same value as for the free dithiocarbamate sodium salt [23]. The v(C-N) in the piperazine-bis-(dithiocarbamate) complexes appear at slightly lower frequency compared to those of aliphatic dithiocarbamates. We can conclude, according to our previous studies, that in the equilibrium regarding the dithiocarbamate anion the contribution of the structure (b) is greatest

\‘(A4 -S) ~. ~~__

~~

998vs 989s 990s 995s 991s 990s 989s

355m 380m 370sh,350m 364m 369m 364m

Table 3. Electronic

spectra

(kK)

Compounds

do d bands

CoL,2H,O NiL.0.5HZ0 CuL,2Hz0

26.66. 20.00, 15.62, 8.70 24.69, 22.22, 20.00. 15.70 21.00, 14.92

complexes and lower for the heterocyclit derivatives. Perhaps owing to the rigid heterocyclic ring system, which shows less tendency to release electrons to the carbon--nitrogen bond, this bond has less double-bond character. The piperazine-bis-(dithiocarbamate) ligand acts as a quadridentate moiety coordinating through both the dithiocarbamate units. The far i.r. region (60&50 cm- ‘) is very important for the assignment of the M-S absorption bands. The bands of the ligand are unchanged in the spectra of the complexes; in addition, new bands, absent in the spectra of the starting materials, are observed in the 38G350 cm- ’ region, assignable to metalLsulphur stretching frequencies. for the dialkyl

Elrctronic

spectra

and magnetic

mrasuremenrs

The electronic spectra of the cobalt(H) complex exhibit ligand field bands characteristic for a tetracoordinate planar CoS, chromophore [ 171, confirmed by the value of its magnetic moment too. The abnormal magnetic moment of the nickel(H) derivative is very likely due to a miscoplanarity of the

C-1s\ C-J (a)

(cm-‘)

S/

&y

CH4H,yiLc,S ‘CH,-C”/

(b)

C-1 \S

(-)

Studies of piperazine-bis-(dithiocarbamate)

complexes

345

Table 4. Thermal analyses data

Observed and (calculated) weight losses (X) I step (H,O)

Compounds

22.21 (22.31) 9.20 ( 9.20) 2.91 ( 2.96) 11.45 (10.72) 5.04 ( 5.63) 4.60 ( 4.91) 3.82 ( 3.96)

III step

II step 34.70 47.34 51.73 45.05 59.32 53.19 51.87

(34.17) (47.15) (51.38) (44.42) (58.88) (52.63) (51.96)

metal with respect to the four sulphur ligand atoms. As expected, three spin-allowed d-d transitions corresponding to ‘Al, + ’ Azg + ‘B,, and -+ ‘E, are found. The orbital parameter A1 (18.5 kK), calculated [24] from the x2 - yz -+ xy in plane transition (at 15.7 kK) assuming a correction factor of 2.8 kK [25], places this ligand in the spectrochemical series of sulphur donors. The electronic spectrum of the copper(I1) derivative shows two bands at 14.9 kK and 21.0 kK which can be assigned, according to other authors[26], to the d,, -+ dlZ (vl) and dxy -+ d,,, d,, (vg) transitions respectively in a D,, point symmetry.

19.73 21.74 12.16 11.82 8.21 44.89

(19.36) (21.10) (12.22) (10.04) ( 8.97) (44.09)

IV step

13.80 (14.33)

evaporation of the metal takes place, while in the latter case CuS, is formed which undergoes then conversion to cue. Acknowledgments-We thank G. Pistoni for elemental analyses and the Instruments Centre of Modena University for recording the i.r. spectra.

REFERENCES [l]

EPR

spectra

No hyperfine

profile can be seen in the EPR spectrum of the powder copper complex. However, the go value (2.049) is in accord to the gvalues found for other CUS, chromophores [ 171.

Thermogravimetric

studies

The thermal analyses were performed both on the free ligand and on the complexes and the Table 4 shows the relative observed and calculated weight losses. The ligand sodium salt, after losing its 4.5 moles of crystallization water between 35 and 15O”C, leaves in the range 15&375”C a polysulphide of the Na#,., type, which then undergoes oxidation to Na2S04 and Na,O. For the complexes, the data up to 900°C suggest a multistep decomposition. With the exception of the copper and mercury derivatives, all the other complexes, after the loss of the crystallization water in the 35-175°C range, show a second step leading to polysulphides (NiS2,5, Co!&, ZnS,.,, CdSI.S) in the region up to 500°C. The second step (lOG35o”C) for the copper deriva-

G. MARCOTRIGIANO,G. C. PELLACANIand C. PRETI, J. inorg. nucl. Chem. 36, 3709 (1974). [2] G. MARCOTRIGIANO,G. C PELLACANI, C. PRETI and G. Tosr, Bull. Chem. Sot. Japan. 48, 1018 (1975). [3] C. PRETI and G. Tosr, J. inorg. nucl. Chem. 38, 1746 (1976). [4] C. PRETI, G. TOSI and P. ZANNINI, J. inorg. nucl. Chem. 41. 485 (1979). [S] C..PRET;, G. TOSI and P. ZANNINI, J. molec. Struct. 65, 283 (1980). [6] C. PRETI, G. TOSI and P. ZANNINI, Z. anorg. al/g. Chem. 469, 234 (1980). [7] C. PRETI and G. TOSI, Z. anorg. allg. Chem. 419, 185 (1976). [8] C. PRETI and G. TOSI, Z. anorg. al/g. Chem. 418, 188 (1975). [9] C. PRETI,G. TOSI and P. ZANNINI, J. molec. Struct. 53, 35 (1979). Cl01A. GIUSTI, C. PRETI,G. TOSI and P. ZANNINI, J. molec. Struct. 98, 239 (1983). Pll A. C. FABRETTI, M. FERRARI, G. C. FRANCHINI, A. GIUSTI, C. PRETIand G. To%, Transition Met. Chem. 8, 8 (1983). [121F. FORGHIERI,G. GRAZIOSI, C. PRETI and G. TOSI, Transition Met. Chem., in press. Cl31 C. PRETI, G. TOSI, and P. ZANNINI, Transition Met. Chem. 4, 360 (1979). Cl41 A. BENEDETTI,C. PRETIand G. TOSI, J. molec. Strut., 98, 115 (1983). Cl51 C. FURLANI, G. POLZONE~I, C. PRETI and G. Tow, Inorg. Chim. Ada, 73, 105 (1983). Cl61 C. FURLANI, G. POLZONETTI,C. PRETI and G. TOSI, Gazz. chim. ital., in press.

while for

Cl71 A. C. FABRETTI,F. FORGHIERI,A. GIUSTI, C. PRETIand G. TOSI, lnorg. Chim. Acta, in press.

the mercury compound the “intact” ligand moiety is lost in the 17&296”C range. The third step leaves a MO residue for all the complexes with the exception of the mercury and copper derivatives. In the former case a complete

iY81 M. HONDA, M. KOMURA, Y. KAWASAKI,T. TANAKA~~~ R. OKAWARA, J. inorg. nuci. Chem. 30, 2221 (1968). [I91 G. H. MANOUSSAKIS, C. A. TSIPIS and C. C. HADJIKOSTAS,Can. J. Chem. 53, 1530 (1975). c201 F. BONATI and R. UGO, J. Organomet. Chem. 10, 257 (1967).

tive leaves as a residue H&-N-C

S*(A) 40:4-B

/‘\Cu, ,s,

346 [21] [22] [23]

ANTONIO COSTANTINO FABRETTI et al.

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