Indian Journal of Chemistry Vol. 39A, November 2000, pp. I 140-1144

Synthesis and characterization of some chromium(III) complexes with N ,S, 0-donor thiohydrazones

Kamalendu Dey* & Kartick Chakraborty

Department of Chemistry, University of Kalyani, Kalyani 741235, India

Received 17 August 1999; revised 8 February 2000

The preparation and characterization of some new chromium(III) complexes synthesized by the reactions of salicylaldehyde morpholine N-thiohydrazone (H,smth) and 2-hydroxyacetophenone morpholine N-thiohydrazone (H,apmth) with different chromium(III) salts, under varied reaction conditions are reported. The isolated solid chromium(III) complexes have been characterised by elemental analyses. molar conductance, magnetic susceptibilities, molecular weights and spectroscopic (UV-Vis and IR) data. It has been observed that the ligands H,smth and H,apmth can functi on either as a monobasic tridentate or dibasic tridentate (N,S,O-donor) fashion depending on the reaction conditions.

The toxic effects of chromium are well established. Chromium compounds are carcinogens and are corrosive to human tissue; insoluble chromium compounds are retained in the lungs and are implicated in the occuJTence of lung cancer. Chromium has also been shown to cause cancer in the respiratory system and the antrum1

. The principal toxic effect of most metals, at the molecular level, is their ability to bind to peptide residues of proteins, notably to histidine and cysteine residue. Hence, complexes in which the metal is coordinated to an L-amino acid (say, L-histidine) may be better models for the therapeutic action of D­

penicillarnine and its analogues than are complexes of the free metal ion. Besides, the biological importance of chromium(III) in glucose tolerance is well established, the more active glucose tolerance factor preparations known to date all involve glutathione or its constituent amino acids2

• The N,S,O-donor ligands are involved in the above mentioned biologically important chromium(III) compounds. We, therefore, have initiated a thorough study of chromium(III) complexes involving N,S,O-donor ligands and related Iigands3

. In this paper we report the synthesis and characterization of a series of chromium(III) complexes with salicylaldehyde morpholine N­thiohydrazone (H2smth) and 2-hydroxyacetophenone morpholine N-thiohydrazone (H2apmth), both having N.S.O-donor sites.

Materials and Methods All the chemicals used were of AR grade. Solvents

were purified and dried before use. The complexes

[Cr(Urea)6]Ch.3Hz0 and K3[Cr(SCN)6]4Hz0 were prepared by following the reported methods4

• IR spectra were recorded in KBr discs, Nujol and HCB mulls using a Perkin-Elmer 1330 spectrophotometer and the electronic spectra on a Hitachi spectrophotometer model 200-20. Conductance measurements were made with a conductivity bridge of Elico Pvt. Ltd. Model CM 180. Molecular weights were determined by Rast' s method. The magnetic susceptibility measurements were made with a Gouy balance at room temperature. Micro analyses of C, H and N of the isolated complexes were carried out at RSIC, CDRI, Lucknow.

Preparation of the ligands

The ligands H2smth and H2apmth were synthesized by our previously published method5

.

Preparation of complexes [(Hsmth)(smth)Cr] (1)

To a hot solution of H2smth (1.32g, 0.005 mol) in ethanol (40 em\ a hot solution of CrCI3 . 6Hz0 (0.67g, 0.0025mol) in ethanol (25cm3

) was added followed by immediate addition of anhydrous sodium acetate (1.23g, 0.015 mol) in hot ethanol (20cm\ The resulting brown solution (pH - 5) was heated under reflux for 2h and filtered while hot. The snuff coloured solid compound thus obtained was collected by filtration, washed with water and cold ethanol and dried in vacuo, yield - 40%. NH4[Cr(smthhl (2)

DEY et al.: Cr(III) COMPLEXES WITH N,S,O-DONORS 1141

The filtrate (from the complex (1)) was concentrated and ammonium hydroxide solution added to raise the pH to - 9. This on standing in a refrigerator yielded a ligilt brown compound. It was filtered off, washed with aqueous methanol and dried in vacuo, yield - 30%.

{ ( Hsnzth) Cr(Clh(H20))] SH20 (3) This snuff coloured compound was isolated in

about 70% yield by the reaction of H2smth (0.005 mol) and CrCI3.6H20 (0.005 mol) and following a method similar to that described above.

{ (HsmthhCr(Cl) ]SH20, (4) The filtrate of the above reaction was concentrated

and cooled overnight to yield light brown compound. It was collected by filtration, washed withcold ethanol and dried in vacuo, yield 15% (approx).

{ (smth)Cr(SCN) (NH3) (H20)] 2H20, (5)

To a hot solution of H2smth (1.32g, 0.005 mol) in ethanol (50cm\ a hot ethanolic solution (50cm3

) of NH4 [Cr(NHJ)z (SCN)4] H20 (1.77g, 0.005mol) was added. The mixture was heated under reflux for 3h on water bath when a solid compound separated out. It was filtered, washed with cold ethanol and dried in vacuo, yield 50%.

NH4{(smth)2Cr]H20, (6) When a hot ethanolic solution ( - 50 cm3

) of H2smth (1.32g, 0.005 mol) was added to a hot ethanolic solution ( - 50cm3

) of NH4[Cr(NH3h (SCN)4] HzO (0.88g, 0.0025 mol), a brown solution (pH - 5) was obtained. The mixture was then heated under reflux for 3h and the brown compound precipitated during reflux was separated by filtration, washed with ethanol and dried in vacuo, yield 60%.

[ (Hsnzth) (smth)Cr] H20, (7) A hot solution of [Cr(Urea)6]CldH20 ( 1.43g,

0.0025 mol) in ethanol containing a few drops of water was added to a hot solution of H2smth ( 1.32g, 0.005 mol) in ethanol ( - 50 cm3) immediately followed by the addition of sod ium acetate (1.23g, 0.015 mol). The mixture (pH-5) was then heated under reflux on water bath for 7h and filtered while hot. The filtrate on reduction of volume and cooling yielded light brown compound. It was separated by filtration, washed with ethanol and dried in vacuo, yield 67%.

However, no pure product could be isolated in the solid state when the ~bove reaction was carried out in the molar ratio (1: 1).

NH4[(smth) Cr(SCNh (H20) ], (8) A hot ethanolic solution ( - 50 cm3

) of H2smth ( 1.32g 0.005 mol ) was added to a hot ethanolic solution of K3[Cr(SCN)6] (2.58g, 0.005 mol) and the mixture (pH- 5) was heated under reflux for about 3h and filtered while hot. The volume of the filtrate was reduced to half of its original volume and the pH of the solution was raised to about 9 by dropwise addition of 15% aqueous ammonia solution. It was then heated on water bath for further 15min to remove excess ammonia. On cooling, a brown coloured solid compound was precipitated out, which was collected by filtration, washed with cold ethanol and dried in vacuo, yield - 45%.

{(Hapmth) Cr(Clh (H20)], (9) This brown compound was prepared by the

reaction of H2apmth (0.005 mol), CrCI3.6H20 (0.005 mol) and sodium acetate (0.015 mol) following a method similar to that used for compound (1) described above, yield 50%.

{ (apmth)Cr(SCN) (NH3) (H20)] H20 (10) To a hot ethanolic solution ( - 50 cm3

) of H2apmth (0.79, 0.005 mol), a hot ethanolic solution (- 503 of N~[Cr(NH3h (SCN)4] H20 (0.88g, 0.0025 mol) was added. The reddish brown solution was heated under reflux for 5h and filtered while hot. The filtrate, on volume reduction, yielded brown compound. It was collected by filtration, washed with cold ethanol and dried in vacuo, yield - 50%.

{ (Hapmthh Cr(SCN) (NHJ)] H20 , (11) The above reaction when carried out in 2: 1 molar

ratio (metal : ligand), afforded this light brown compound. The rest of the procedure were same as used f01: (10) above, yield- 50%.

Results and Discussion

The reactions of salicylaldehyde and 2-hydroxyacetophenone with morpholine N­thiohydrazide in 1: 1 molar ratio in ethanol yielded salicylaldehyde morpholine N -thiohydrazone (H2smth) and 2-hydroxyacetophenone morpholine N­thiohydrazone (H2apmth), respectively. The thioketo

1142 INDIAN J CHEM, SEC A, NOVEMBER 2000

Complexes !able 1-Characterisation data of chromium(lll) complexes

Found (Calcd) % mol wtc

c H

[(Hsmth)(smth) Cr], (1) 49.62 4.67 (Cz4H27N604SzCr) (49.74) (4.66)

NH4[Cr(smthM (2) 48.59 5.22 (Cz4H3oN704S2Cr) (48.32) (5 .03)

[(Hsmth)Cr(CIMH20)]5H20 ,(3) 29 .93 5.00 (C,zH26N30 8SCI2Cr) (29.09) (5.25)

[(Hsmth)2CrCI]5H20, (4) 40.73 5.08 (Cz4H3sN609SzCICr) (40.82) (5.38) ( [(smth)Cr(SCN)(NH3)(H20)]2H20 , (5) 35 .72 5.00 C13H22 N50 5S2Cr) (35.13) (4.95)

NH4[(smth)2Cr]H20, (6) 46.06 5.07 (Cz4H32N10sSzCr) (46.90) (5.21)

[(Hsmth)(smth)Cr]H20, (7) 48.15 4.74 (C24H29N60 5S2Cr) (48.24) (4.85) NH4[(smth)Cr(SCN)2 (H20)], (8) 36.08 4.25 (C,4H19N6SP3Cr) (35.97) (4.06) [(Hapmth)Cr(Cih(H20)], (9) 36.99 4.86 (CnH 1sN303SCizCr) (37 .28) (4.29) [(apmth)Cr(SCN) (NH3)(H20)] 38.23 5.36 H20, (10) (38.18) (5.00) (C,4H22N504S2Cr) [(Hapmthh Cr(SCN)( NH3)]H20. (11) 46.32 5.43 (C27H37N80 5S3Cr) (46.2 1) (5.27)

a) Gouy method in the solid state at room temperature b) 10·3 (M) solution in DMSO c) Rast's method.

and thiol forms of the ligands may remain in equilibrium in solution5

. Both the ligands have a proton adjacent to the thione group, which is relatively unstable in the monomeric form and tends to turn to more stable C-S bond by enolisation6

. The ligands depending on the reaction conditions, may behave as a tridentate dibasic or tridentate monobasic fashion, bonding through 0, N and S atoms with metal ion and also as bidentate monobasic fashion in some complexes bonding through 0 and N atoms having C=S group remaining free. In the complex (5), (6) and (8), the ligand H2smth behaves in a dibasic tridentate fashion. Similar mode of bonding has been observed in the complex (10) with the ligand H2apmth. Dual nature of the ligand H2smth (both as monobasic tridentate and dibasic tridentate) has been found in the complexes (1) and (7). It is interesting to note that in the complex [(Hsmthh Cr(CI)] 5H20, (4) both monobasic tridentate and monobasic bidentate

J..l ~If Ah M

N Cl M (BM) (cm2mor' (Calcd) ohm-1)

14.32 8.82 3.62 5.80 588 ( 14.50) (8.98) (579)

16.02 8.60 3.7 1 50.10 610 (16.45) (8.72) (596)

8.36 14.82 10.19 3.70 28.30 479 (8.48) (14.34) (10.50) (495)

11.71 5.22 7.04 3.69 22.55 698 (11.90) (5.03) (7.37) (705.5)

15.68 11 .86 3.56 26.00 467 (15.76) (11.71) (444)

15.69 8.58 3.59 48 .22 578 (15 .96) (8.46) (614)

13.99 8.07 3.62 20.5 1 608 (14.07) (8.71) (597) 18.00 11 .60 3.78 46.58 488 (17.98) (1l.l3) (467) 10.92 16.42 12.02 3.72 28.00 452 (10.02) (16.94) (12.41) (419)

16.00 11 .61 3.90 25.99 482 (15.90) (11.81) (440)

15.91 7.24 3.78 26.25 695 ( 15.97) (7.41) (701)

(C=S being free) mode of linkages are found to be present. Basicity and denticity of these ligands in other complexes can also be inferred as above from the physicochemical data (see later discussion).

All the isolated complexes are stable at laboratory conditions and the analytical data support their formulations (see Table 1). All of them are soluble in coordinating solvents and some of them [e.g. (3), (4), (5), (7), (8) ] are also soluble in common organic solvents.

The molar conductance values (Table 1) of the complexes, excepting the complexes (6) and (8), in DMSO are found in the range 5.8 to 28.30 cm2

ohm- 1 mor 1 suggesting their non-electrolytic nature. 7

On the other hand, the values 50.10, 48.22 and 46.58 cm2 ohm- 1mor 1 in DMSO for the complexes (2), (6), and (8) respectively suggest the presence of 1:1 electrolyte in solution5

'7

. These values are in

DEY er al.: Cr(III) COMPLEXES WITH N,S,O-DONORS 1143

conformity with the proposed formulations, which is further supported by the molecular weights (Table 1).

The room temperature magnetic moments are slightly lower than the spin only value for a d3 ion in an octahedral field and this aspect has been discussed thoroughly elsewhere8

·9

.

The electronic absorption spectra of the isolated chromium (III) complexes in solution show three absorption bands (in ethanol and DMSO as the case may be depending on solubility limitations) in the range 18,000-20,750 cm·1 (shoulder), 21,000-23,000 cm-1(£- 3500) and 25 ,500-28,000 cm·1 (E- 5000). Some of the chelates when taken in nujol mull give almost identical spectra, specially in the range 18,000-25,000 cm·1. This suggests that the environment of chromium(III) is almost the same in the solid and as well as in solution state. The bands observed in the range 18,000-25,000 cm·1 may be considered as the split components of the 4Tzg(011 ) and 4T18 (F)(Oh) terms despite their high molar extinction coefficients. Similar high extinction coefficients were observed for band in this region in the chromium(III) complexes of N-substituted salicylaldimines 10

, N,N' -ethylenebis (salicylaldimines)9

'11 and N,N' -ethylenebis(acetyl­

acetoneiminate)11 . If these are at all d-d bands, then high molar extinction coefficients are possibly due to contributions from ligand transitions. However, according to Yamada et al. 11 the d-d bands in such complexes might appear -15,000 cm-1, which in the present case are masked by more intense bands.

The UV spectra of all the complexes exhibit an intense absorption in solution (DMSO) at - 35,000 cm·1, which may be compared with the results reported earlier for other complexes with a Cr-S bond12. This intense band is usually attributed to S ~ Cr ligand-to-metal charge transfer. The intensities of the charge transfer bands in the complexes (1) and (7) are almost twice the intensity compared to other complexes. We tentatively propose that two sulphur atoms are bonded in the complexes (1) and (7), while only one sulphur is coordinated to other complexes.

The infrared spectra of the free ligand H2smth and H2apmth do not display any vSH bands13 at 2570 cm-1, instead an intense band for vC=S located at 800 cm·1 is observed, suggesting that in the solid state both the ligands remain in thioketo form. However, in solution they may remain as an equilibrium mixture of both thioketo and thiolo tautomeric forms 14.

The free ligands show bands due to vNH in the region 3,300-3,100 cm·1. But the vOH band at 3,500

cm·1 is not observed and this may be due to strong hydrogen bonding which probably shifts vOH to lower frequency. The lowering of vNH in the infrared spectra of H2smth and H2apmth respectively suggest intermolecular hydrogen bonding. As expected, the bands due to vOH/NH are shifted or disappeared in most of the complexes indicating coordination of the oxygen atom. But in some cases, the presence of H20 and NH3 molecules makes the interpretation very difficult. The C=N stretching vibration of the free ligands occur15, at - 1620-1615 cm·1 but on complexation this band, in almost all the complexes, is shifted towards the lower frequency region suggesting that the ligands are coordinated to the metal via azomethine nitrogen atom16. The lowering of C=N stretching mode may tentatively be attributed to lowering of the C=N bond order as a result of M-N bond formation 17 as evident from the appearance of new M-N bands in the far infrared region. The free ligands possess potential thioamide groups and thereby display characteristic thioamide I to IV bands in the region 1530-800 cm·1. The thioamide bands of the free ligands are located at 1540-1530,1485-1470, 1315-1300 and 800 cm-1

and these are affected appreciably in the metal complexes 18'19

. The thioamide band IV, mainly due to vC=S is either disappeared or shifted to lower frequency region in most of the metal complexes indicating the coordination of sulphur to the metal ion20

·21 , which gets further support by the appearance

of new M-S bands in far infrared region . The bands at 1210-1200 (vCO), 1250-1240 (vCN), 1105 and 920-895 cm·1 (out of plane and inplane deformation) of the morpholine ring moiety are not affected appreciably in the metal complexes, indicating that morpholine ring oxygen and nitrogen are not involved in coordination22

.

It is evident that in the complexes (3) and (9) the thioamide band IV (vC=S) is shifted to lower frequency region by 20-10 cm-1 and the vOH band disappears , suggesting the coordination of the ligands through thioketo sulphur and phenolic oxygen via deprotonation. The vC=N stretching mode is also lowered by 15-10 cm·1. Thus, in these complexes, the ligands function as monobasic tridentate O,N,S-donor ligand. On the other hand, in complexes (5),(6),(8) and (10), both the phenolic OH and thioamide band IV disappear and instead, a new band due to vC-S

760-750 cm- 1 is observed suggesting the coordination of metal ion through thiol sulphur and phenolic oxygen via deprotonation . Moreover, the

1144 INDIAN J CHEM, SEC A, NOVEMBER 2000

vC=N stretching mode is also lowered by 15-10 cm- 1

in these complexes. This is further substantiated by the appearance of strong to medium band diagonistic of azine chromophore(>C=N-N=C</3 - 1605-1600 em-'. Thus,in these complexes, the ligands function as dibasic tridentate fashion bonding through O,N and S atoms. However, in the complexes (5),(8) and (9), the presence of water molecule makes the interpretation very difficult. In the complex (11), the ligand functions as monobasic bidentate way bonding through nitrogen and phenolic oxygen as evident from the disappearance of vOH band and vC=S band is unaffect~d.

The coordination of NH3 in the complexes (5), (10) and (11) is indicated by the appearance of bands at 3300-3100, 1590, 1280 and 850 em-' assignable to vNH3, OctNHJ, o,NH3 and p,NH3 respectivel/4

'25

. The complexes (3)-(11) under discussion show broad medium bands in the region 3550-3300 em-' which are assignable to OH stretching vibrations due to the presence of water molecule. Nevertheless, additional bands - 950-940 em-' are observed in the complexes (3),(5),(8) (9) and (10) due to wagging modes of water24

. Besides, drastic conditions required to dehydrate these complexes also favour a structure containing coordinated water molecule.

The presence of ammonium ion in the complexes (2), (6) and (8) is inferred from the infrared bands in the region 3040 and 1400 cm-1 (refs 24,26). In the complexes (6) and (8), however, due to the presence of water molecule and thioamide chromophore (in all the complexes), the interpretation of the bands appearing in the region is very difficult.

The infrared spectra of (5), (8), (10) and (11) show bands at - 2060 (s) and 760 cm-1(m) due to C=N and C S h. "b . . I 24 n Th - stretc mg VI ratiOns respective y ·- . e bonding thiocyanato group with chromium (III) ion occurs through nitrogen as evident from the band due to C-S stretching appearing at 750 em-'. Based on the data available in literature, it may be concluded that thiocyanato group coordinates through nitrogen for first row transition metal and through sulphur for second row transition metals.

Acknowledgement One of us (KC) is thankful to the University of

Kalyani for providing a senior research fellowship. KD is grateful to CSIR, New Delhi, for financial grant. We are also thankful to RSIC,CDRI, Lucknow for some analytical data.

References

Meester P de & Hodgson D J, J chem Soc Daltons Trans, (1976) 618 and references cited therein .

2 Abdullah M, Barrett J & Brien P.O., J clum Soc Dalton Trans, ( 1985) 2085 and references cited therein.

3 Dey K, Bhowmick R, Nag S K, Chakraborty K & Biswas S, J Indian chem Soc, 76 ( 1999) 427.

4 Brauer G, Handbook of preparative inorganic chemistry Vol 2, edited by G Brauer (Academic Press, New York), 1965, 1359, 1274.

5 Dey K & Bandyopadhyay D, Indian J Chem, 3IA.(I992) 34.

6 Mayer R, Organosulphur chemistry, edited by M J Jansen (lnterscience, New York) 1967,2 19.

7 Geary W J, Coord chem Rev, 7 (1971) 113.

8 Coggon P, Me Phil A T, Mabbs F E, Richards A & Thornley A S, J chem SocA , ( 1970) 3296.

9 Figgis B N & Lewis J, Modem coordination chemistry, edited by J Lewis & H G Wilkins (lnterscience, New York), 1960,400.

10 O'Connor M S & West B 0 , Aust J Chem, 21 (1968) 369.

II Yamada S & Yamanouchi S K, Bull chem Soc Japan , 45 (1972) 2140.

12 Weschler J C J & DeutschE, lnorg Chem, 12 (1973) 2682.

13 Colthup N B, Daly L H & Wiberly S E, Introduction to infrared and Raman spectroscopy (Academic Press, New York) 1964, 305.

14 AliMA &Tarafder M T H, J inorg llllcl Chem, 39 (1977) 1785.

15 Kolinski R A & Korybut-Daszkiecoicz B, lnorg chim Acta, 14 (1975) 237.

16 McGlynn S P & Smith J K, J molec Spectrosc, 6 ( 1961) 164.

17 Baby Kutty P V, Prabhakaran C P, Anantaraman R & Nair C G R, J inorg nucl Chem, 36 ( 1974) 3685.

18 Rao C N R, Venkataraghavan R & Kasturi T R, Can J Chem, 82 ( 1964) 36.

19 Laksmi (Miss), Singh B & Agarwala U, /norg Chem, 7 (1968) 2341.

20 Geetharani K & Satyanarayan N, Aust J Chem, 30 (1977) 1617.

21 Singh B & Srivastava U, Synth react inorg met-org Chem , 18 (1988) 515.

22 Chandrasekhar T C & Krishnan V, J inorg 1111cl Chem, 43 (1981) 3287.

23 Biradar N S & Kulkarni V H, J inorg nucl Chem, 33 ( 1971) 2451 .

24 Nakamoto K, Infrared spectra of inorganic and coordination compounds (John Wiley, New York) 1963.

25 Care E, Critim A, Diaz A & Panticalli G, J chem Soc Dalton Trans, (1972) 527.

26 Gosavi R K & Rao C N R, J inorg nucl Chem, 29 (1967) 1937.

27 Lewis J, Nyholm R S & Smith P W, J chem Soc, ( 1961) 4590.