SYNTHESIS AND SPECTRAL STUDIES OF Ni(II) COMPLEXES WITH 2-HEPTANONESEMICARBAZONE AND 2-HETANONETHIOSEMICABAZONEHTML Full Text
SYNTHESIS AND SPECTRAL STUDIES OF Ni(II) COMPLEXES WITH 2-HEPTANONESEMICARBAZONE AND 2-HETANONETHIOSEMICABAZONE
Pravita Kumar, Roopakumari and Sulekh Chandra*
Department of Chemistry, Zakir Husain Delhi College, JLN Marg, New Delhi-110002, India
ABSTRACT: Complexes of Nickel(II) with 2-heptanonesemicarbazone (hsc) and 2-heptanonethiosemicabazone (htc) have been synthesized and characterized by elemental analysis, molar conductance measurements, magnetic moments, mass, IR and electronic/spectral studies. Synthesized complexes were found to have a general composition of Ni(L)2X2 (where X=Cl-, 1/2SO42-, NO3-, ClO4-, NCS-, CH3COO- and L=hsc or htc). Molar conductance indicates that all the complexes are non-electrolytes in nature whereas chloro complexes are 1:1 electrolytes. Metal complexes of 2-heptanonesemicarbazone were soluble in hot ethanol, methanol, acetone and DMSO and insoluble in chloroform, benzene and water, whereas metal complexes of 2-hepatanonethiosemicarbazone were soluble in ethanol, methanol and acetone, insoluble in chloroform and benzene. On the basis of IR and electronic spectral analysis thiocyanato, sulphato, perchlorato, acetato and nitrato complexes of were found to have six-coordinate octahedral geometry whereas chloro complexes were five-coordinate and having trigonal bipyramidal geometry.
thiosemicabazones Ni(II), Heptanonesemicarbazones
INTRODUCTION: Transition metal complexes of semicarbazones and thiosemicabazones have received considerable attention because of their antibacterial, antifungal, antitumor, antiamoebic, antimalarial, antiviral, radioprotective, trypanocidal and anti-inflammatory activities1-5. Semicarbazones and thiosemicarbazones are among the most relevant nitrogen-oxygen/nitrogen-sulphur donor ligands 2, 3. Thiosemicarbazone complexes have imine group (-N=CH-), which provides the biological activity and chelating properties favoring the central metal atom 10.
Some significant bioactivities of transition metal complexes of semicarbazones (antiprotozoa, and anticonvulsant) and thiosemicarbazones (antibacterial, antifungal, antitumoral, antiviral) have been reported 3, 7. The biological activity is considered to involve three kinds of mechanisms: (a) inhibition of ribonucleoside diphosphate reductaseenzyme (essential for DNA synthesis); (b) creation of lesions in DNA strand by oxidative rupture; (c) binding to the nitrogen bases of DNA or RNA, hindering or blocking base replication 1, 9.
It has been found that certainthiosemicarbazones are specific inhibitors of ribonucleotide reductase (an important metabolic target for the development of chemotherapeutic agents against cancer) 11. Thiosemicarbazones and semicarbazones have the ability to produce some new and unique complexes with enhanced biological and analytical properties 4, 6. Metal complexes of Ni(II) are found to act as a sensor 8 in many of the diseases for which thiosemicarbazones have been shown to effective4. The present paper reported the synthesis and characterization of Ni(II) complexes with 2-heptanonesemicarbazone (hsc) and 2-heptanonethiosemicabazone (htc).
MATERIALS AND METHODS:
All chemicals used were of A. R. grade and produced from sigma Aldrich, Bangalore, India. Metal salts were purchased from E. Merck, India and were used as received.
Synthesis of Schiff’s base Ligand L1 (hsc):
Ethanolic solution of semicarbazide hydrochloride (1.11g, 0.01mol) and sodium acetate (0.82g, 0.01mol) were dissolved in 50 mL of distilled water followed by the addition of 2-heptanone (1.42mL, 0.01mol). The reaction mixture was refluxed for about an hour on a water bath. White colour precipitate was formed. The precipitate was filtered and washed with ethanol. The same was dried over P4O10. The purity of ligand was checked by TLC.
Synthesis of Schiff’s base Ligand L2 (htc):
Ethanolic solution of thiosemicarbazide (0.91g, 0.01mol) and ethanolic solution of the 2-heptanone (1.42 mL, 0.01 mol) were mixed together in equimolar ratio (1:1), 2-3 drops of glacial acetic acid was added and the contents were refluxed on a water bath for about one hour and then concentrated. On cooling the reaction mixture in an ice bath, a yellowish coloured product was separated out. The purity was checked by TLC. Table 1 is showing analytical data of the Schiff’s base Ligands (hsc&htc).
TABLE 1: ANALYTICAL DATA OF THE SCHIFF’S BASE LIGANDS (HSC&HTC)
|Elemental analysis found /(calculated)|
|L1 = hsc (C8H17N3O)||White||85||127||56.14
|L2 =htc (C8H17N3S)||Yellow||80||77
Synthesis of Complexes:
Hot ethanolic solution of corresponding metal salts (0.05 mol) (NiCl2, NiSO4.6H2O, Ni(NO3)2, Ni(CH3COO)2, Ni(SCN)2 and Ni(ClO4)2) were mixed with hot ethanolic solution schiff’s base ligand L1& L2 (0.1mol). The mixture was refluxed for about 3 hours on a water bath. On cooling metal complexes of different colors were separated out. The obtained complexes were washed with 50% ethanol and dried.
Elemental analysis was performed on a Carlo-Erba 1106 elemental analyzer. Molar conductance was measured on the Elico (CM82T) conducting bridge. Magnetic susceptibility was measured at room temperature on a Gouy balance using CuSO4.5H2O as a calibrant. A mass spectrum was recorded on JEOL, JMS.DX-303 mass spectrometer. IR spectra were recorded on a FTIR spectrum BX-II spectrophotometer. The electronic spectra were recorded in DMSO on Shimadzu UV mini-1240 spectrophotometer.
RESULT AND DISCUSSION: Metal complexes were synthesized by reacting ligands 2-heptanonesemicarbazone (hsc) or 2-heptanonethiosemicarbazone (htc) with metal ion in 2:1 ratio in ethanolic medium. Elemental analysis of the complexes reveal that the complexes have general composition, [Ni(L)2X2] (where L=hsc or htc and X=Cl-, 1/2SO42-, NO3-, ClO4-, NCS-, CH3COO-). Chloro complexes of semicarbazone or thiosemicarbazone of heptanone are 1:1 electrolytes and may be formulated as [NiL2X]X.
The ligands behaved as bidentate and coordinate through sulphur/oxygen and nitrogen donor atoms. Table II reveals the color, composition and magnetic moment of the complexes of Ni(II) with 2–heptanonesemicarbazone or 2-heptanonethiosemicarbazone.
These complexes exhibit different stereochemistry, varying from five-coordinate square pyramidal or trigonal bipyramidal to six-coordinate octahedral. All the complexes were found to be soluble in DMSO. Magnetic moment of all complexes of present study lies in the range of 2.95-3.05 B.M., which correspond to two unpaired electrons. Metal complexes of 2-heptanonesemicarbazone were soluble in hot ethanol, methanol, acetone and DMSO and insoluble in chloroform, benzene and water, whereas metal complexes of 2-hepatanonethiosemicarbazone were soluble in ethanol, methanol and acetone, insoluble in chloroform and benzene.
TABLE 2: COLOUR, COMPOSITION AND MAGNETIC MOMENT OF THE COMPLEXES OF Ni(II) WITH 2-HEPTANONESEMICARBAZONE AND 2-HEPTANONETHIOSEMICARBAZONE
The proposed formula of ligand L1 and L2 were confirmed by electronic impact mass spectrum. The ligand L1 showed a molecular ion peak at m/z =171amu corresponding to species [C8H17N3O]+ and ligand L2 showed a molecular ion peak at m/z=187 amucorresponding to the species [C8H17N3S]+ .
IR & Electronic Spectra:
For first Ligand 2-heptanonesemicarbazone, the characteristic absorption of the carbonyl group was observed at 1900-1700 cm-1 12, 13. The amide band in semicarbazone has been observed at 1556-1588 cm-1. The band at 1650-1600 cm-1 in 2-heptanonesemicarbazone apparently has large contribution from ν(C=N) 12, 14.
In all metal-ligand complexes, coordination through ‘O’ increases double bond character of the
ν(C=N) band as compared to the ligand, which shows that 2-heptanonesemicarbazone behaves as bidentate ligand.
The second ligand, 2-heptanonethiosemicarbazone may exihibits thione-thiol tautomerism as it contains a thioamide –NH-C=S functional group. In the IR spectrum of ligand,ν(S-H) band at 2560 cm-1 is absent but ν(N-H) band at ca.3214 cm-1 is present, which indicats ligand remains as the thione-thiol tautomer in the solid state. In thiosemicarbazone the position of ν(C=N) band appeared at 1600 cm-1, which is shifted towards lower wave number in the complexes indicating coordinated via the azomethine nitrogen 12,15,16.
The spectra of [Ni(L)2(NCS)2] complexes, under the study, show three bands at 9220-10520cm-1, 13800-19230 cm-1 and 23800-29410 cm-1, (Table III) which clearly rule out tetrahedral geometry for these complexes. The thiocyanato complexes show only one thiocyanatoν(C=N) absorption at 2100 cm-1suggesting that both the NCS groups being in the same environment and coordinated through nitrogen atom17, 18.
Electronic Spectra of these complexes are also characteristic of pseudo octahedral Ni(II), with ν1 at 3A2g(F)→3T2g(F), ν2 at 3A2g(F) →3T1g(F) and ν3 at 3A2g(F)→3T1g(P), laying at 9793-l0400 cm-1, 17968 —19050 cm-1 and 25700-26315 cm-1 respectively, the ν2/ν1 and ν3/ν1 ratio in these complexes is 1.945-1.727 and 2.471-2.687, well within the characteristic range19 (1.5-2.9) for octahedral nickel(II).
The electronic spectra of [Ni(hsc)2X2] (X-sulphate, perchlorate, acetate) complexes display absorption bands at 9220-9880 cm-1(ν1), 15873-19230cm-1(ν2) and 25641-29410 cm-1(ν3), which may arise from both six-coordinate and five-coordinate complexes of nickel(II) and ν2/ν1 ratio is found in the range of 1.682-1.946, which suggests octahedral geometry for the complexes. The sulphatocomplexes show IR S-O stretching frequencies at 1270, 1153, 1097 and 977 cm-1, suggesting that the ligand behaves asbidentate chelating agent coordinating through azomethine nitrogen and thiolate sulphur 20, 21.
The perchloratocomplexes show absorption bands at 1150 cm-1(ν1), 1020 cm-1(ν2) and 970 cm-1(ν4) cm-1suggesting unidentatebehavior of perchlorato group.The acetato complex under study shows infrared carboxyl stretching frequencies at 1585 cm-1for ν(C=O)and 1370cm-1 forν(C-O). The 210cm-1difference between ν(C=O) and ν(C-O) suggests a unidentate 22 behaviour of both the acetato groups in this complex.
IR spectra of nitrato complexes show bands corresponding to both coordinated and uncoordinated nitrato 23. The coordinated nitrato show infrared bands at 1505-1490 cm-1(ν1), 1325-1275 cm-1 (ν5), 1045-1020 cm-1 (ν2), and 808-803 cm-1 (ν6). The complexes under the study show infrared bands at 1510-1468 cm-1(ν1) 1383 cm-1 (ν3), 1230-1300 cm-1 (ν5), 1040 cm-1 (ν2) and 870 cm-1 (ν6). The separation of >200 cm-1 between ν1 and ν5 indicates the bidentate behaviour of nitrato group 23. The broad absorption band at 1383 cm-1is assigned toν3 of uncoordinated nitrate 23. [Ni(htc)2X2] (X-sulphate, acetate, perchlorate) complexes display absorption bands at 9500- l0520cm-1 (ν1), 15873-19050 cm-1 (ν2), and 23800-26310 cm-1 (ν3) (Table III), these spectra are identical to 2-heptanone, which suggest octahedral geometry 23 for these complexes.
Chloro complexes of semicarbazones and thiosemicabazones of heptanoneare 1:1 electrolytes and may be formulated as [NiL2X]X, these complexes show electronic spectral bands at 10280-10400 cm-1 (ν1) , 17625-18150 cm-1 (ν2) and 24400-26315 cm-1 (ν3), which may be assigned to 1E’(F)→3E”(F), 3E’→3E”(P) and 3E’→3A’2(P) transitions respectively (Table III). 3E’→3A”1, 2A”2 transition may be mixed with 3E’→3A’2(P) transition 24. Thus, five coordinate trigonal bipyramidal geometry may be suggested for these complexes.
TABLE 3: ELECTRONIC SPECTRAL BANDS (cm-1)Ni(II) COMPLEXES OF 2-HEPANONESEMICARBAZONE AND 2- HEPTANONETHOSEMICARBAZONES
Ligand Field Parameters:
Various field parameters are calculated25 for the complexes and listed in Table-IV. The nephelauxetic parameter ß = B (complex)/B (free ion), where B free ion for Nickel(II) is 1041 cm-1. The value of ß lies in the range 0.84-0.99. These values indicate the appreciable covalent character of metal ligands sigma bond.
TABLE 4: LIGAND FIELD PARAMETERS OF Ni(II) COMPLEXES OF 2-HEPTANONESEMICARBAZONE AND 2-HEPTANONETHIOSEMICARBAZONES
CONCLUSION: The Ni(II) complexes of 2- heptanonethiosemicarbazone and 2-heptanonesemicarbazone have been synthesized and studied. The sulphato, perchlorato, acetato, nitrato and thiocyanato complexes of Ni(II) were found to have six-coordinate octahedral geometry, while chloro complexes are assigned to have five-coordinate trigonal bipyramidal geometery.
ACKNOWLEDGEMENT: Authors are thankful to UGC, New Delhi and University of Delhi, Delhi for IR.
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Pravita Kumar, Roopakumari and Sulekh Chandra*
Department of Chemistry, Zakir Husain Delhi College, JLN Marg, New Delhi-110002, India.
15 September, 2014
14 November, 2014
27 January, 2015
01 May, 2015