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February-13-4 p6.5
J. Indian Chem. Soc.,
Vol. 90, February 2013, pp. 1-6

Synthesis, characterization, luminescent properties and biological activity
studies of mixed ligand complexes of nickel (II) with sulphur and some
nitrogen donors

Mahesh K. Singha*, Sanjit Sutradhara, Bijaya Paula, D. Barmanb and Arijit Dasc*
aDepartment of Chemistry, Tripura University, Suryamaninagar-799 022, Tripura, IndiabDepartment of Microbiology, Agartala Govt. Medical College, Agartala-799 006, Tripura (West), IndiacDepartment of Chemistry, Govt. Degree College, Dharmanagar-799 251, Tripura (North), India E-mail : Manuscript received online 23 March 2012, revised 18 April 2012, accepted 19 April 2012 Abstract : Mixed ligand complexes of NiII ion with 1-cyano-l-carboethoxyethylene-2,2-dithiolate {CED2– =
[S2C=C(COOC2H5)(CN)]2–} and heterocyclic nitrogen bases such as pyridine (py),
D-picoline (D-pic), E-picoline (E-pic)
or J-picoline (J-pic) have been isolated and characterized by analytical data and physico-chemical techniques such as
molar conductance, magnetic susceptibility, electronic, infrared and fluorescence spectral studies. The complexes do not
decompose up to 300 ºC and are only soluble in coordinating solvents such as DMF and DMSO. The molar conductance
data of complexes in DMF solution show its non electrolytic nature. The magnetic moment values of the complexes indicate
paramagnetic character corresponding to two unpaired electrons. Distorted octahedral stereochemistry around NiII ion
in these complexes have been proposed on magnetic and electronic spectral studies. Infrared spectral studies suggest
bidentate chelating behaviour of CED2– ion and unidentate behavior of nitrogen donors in these complexes.

Fluorescence study of the complexes show the binding of ligand to metal. These complexes also show antibacterial
and antifungal activity in vitro.
Keywords : Mixed ligand complexes, nicke(II), 1,1-dithiolates, luminescent properties, antibacterial and antifungal.
ethylene-2,2-dithiolate (CED2–) shows exciting coordina- A variety of dithiolate ligands have been used to syn- tion properties by virtue of its chelating and bridging thesize transition as well as non-transition metal com- behaviour which have been found in its binary, ternary plexes to study their coordination behavior. Thus the co- and heterobimetallic complexes1,2,12–16.
ordination chemistry of metal dithiolate has been an area The literature survey reveals that there is no report on of interest for several years1,2. The interest in this area mixed ligand complexes of NiII ion involving l-cyano-l- stems from various reasons such as optical recording carboethoxyethylene-2,2-dithiolate and heterocyclic ter- materials3, radio-protective activities4, anti-tumor activ-ity3, stabilization of transition metal ions in its higher oxidation stales5,6,14–16, facile redox behavior17, stabili- In view of the above, we undertake the synthesis and zation of square planar geometry around transition metal characterization of mixed ligand complexes of NiII ion ions18,19, interesting spectral and magnetic properties4–16, with l-cyano-l-carboethoxyethylene-2,2-dithiolate electron transfer reactions and electrically conducting (CED2–) and some heterocyclic nitrogen donors such as materials7–11 along with industrial and biological appli- pyridine (py), D-picoline (D-pic), E-picoline (E-pic) or J- picoline (J-pic). The results of our investigations are re- Among 1,1-dithioligands, l-cyano-l-carboethoxy- J. Indian Chem. Soc., Vol. 90, February 2013 Experimental
All the chemicals used in this study, obtained from E.
The complexes were analyzed for nickel and sulphur Merck, were of GR grade or equivalent quality, D-, E- using standard literature procedures21. Carbon, hydro- and J-picolines were obtained from Aldrich Chemical gen and nitrogen were determined micro-analytically on Company. The complexes, Ni(D-pic)2(CED), Ni(E- CE 440 Exeter, USA.
pic)2(CED), Ni(J-pic)2(CED) and the ligand K2CED.H2O were prepared by known literature procedure14,20.
The molar conductance of the complexes in DMF so- lution were measured using Systronics direct reading con- Synthesis of Ni(D-pic)2(py)2(CED) (1) :
ductivity meter 304. Magnetic susceptibility measure- ments were made at room temperature on a Cahn-Fara- 25 cm3 of pyridine slowly with vigorous stirring which day electro balance using [CoHg(SCN)4] as calibrant.
resulted a blackish yellow solution. The solution was fil- Experimental magnetic susceptibility values have been tered and filtrate was allowed to evaporate naturally. Af- corrected for diamagnetism by the procedures given by ter one month a sticky black product was obtained which Figgis and Lewis22 and Earnshaw23. Infrared spectra were was washed with ether several times resulting a teak brown recorded in nujol (4000–200 cm–1) and in KBr pellets powder. Finally, it was suction filtered and air-dried; (4000–400 cm–1) on a Bomem DA-8 FT-IR spectropho- UV-Vis bands (nm) : 917, 816, 708, 600, 520, 465 in tometer. The electronic and fluorescence spectra of the solid state at RT; 916, 614, 580, 467 in DMF solution; complexes in the solid state were recorded on a Foster- Fluorescence emission band (nm) : 473 in solid state at Freeman Video Spectral Comparator-5000 while electronic spectra in DMF solution were recorded on Perkin-Elmer Model Lamda-25 UV-Vis spectrophotometer. Analytical 2(py)2(CED) (2) :
data together with colour, yield, magnetic moment and The complex (2) was synthesized similar to the com-
molar conductance values are presented in Table 1. Im- plex (1) with starting materials Ni(E-pic)2(CED); UV-Vis portant infrared spectral data and biological activities data
bands (nm) : 926, 815, 710, 589, 518, 465 in solid state are listed in Tables 2 and 3 respectively.
at RT; 920, 603, 539, 446 in DMF solution; Fluores-cence emission band (nm) : 474 in solid state at RT with Results and discussion
The analytical data and stoichiometries of the com- Synthesis of Ni(J-pic)2(py)2(CED) (3) :
plexes reveal the formation of mixed ligand complexes of The complex (3) was synthesized similar to the com-
the composition, NiL2(py)2(CED) [L = D-pic, E-pic or plex (1) with starting materials Ni(J-pic)
J-pic; CED2– = l-cyano-l-carboethoxyethylene-2,2- bands (nm) : 926, 870, 709, 584, 518, 465 in solid state dithiolate]. The complexes are insoluble in common or- at RT; 917, 604, 535, 476 in DMF solution; Fluores- ganic solvents but soluble in highly coordinating solvents cence emission band (nm) : 473 in solid state at RT with such as DMF and DMSO. The complexes do not decom- Table 1. Analytical data, molar conductance and magnetic moments of NiII complexes
Ni(D-pic)2(py)2(CED) (l)
Ni(E-pic)2(py)2(CED) (2)
Ni(J-pic)2(py)2(CED) (3)
Singh et al. : Synthesis, characterization, luminescent properties and biological activity studies etc. Table 2. Characteristic IR bands (cm–1) for the NiII mixed ligand complexes
vs = very strong, s = strong, m = medium, w = weak.
Table 3. Antibacterial and antifungal activity of ligand and NiII complexes
pose up to 300 ºC. The molar conductance values of the have been interpreted in the light of earlier investiga- complexes in DMF solutions indicate non-electrolytic tions1,20,26–28 on transition and non-transition metal dithiolates. The IR spectra of the mixed ligand complexes Magnetic moment and electronic spectra : display characteristic stretching frequencies associated with The magnetic moment values of complexes (1-3) lie
-CN, >C=O, >C=CS2, C–S and M–S from CED2– in the range 2.77–2.87 B.M. suggesting paramagnetism and aryl ring vibrations with metal heterocyclic nitrogen corresponding to two unpaired electrons. The solid state vibrations from py, D-pic, E-pic or J-pic.
electronic spectra show three absorption bands in the re- The Q(CN) band, appearing at 2190 cm–1 in gions 10800–12270, 14084–19305 and 21505 cm–1 assign- K2CED.H2O, is observed with positive shifts in the range able to 3A2g ƒ3T2g (F) (Q1), 3A2g ƒ3T1g (F) (Q2) and 2202–2205 cm–1 in its mixed ligand complexes suggest- 3A2g ƒ 3T1g (P) (Q3) respectively suggesting octahedral ing non-involvement of a nitrile group of the ligand in coordination around NiII in these complexes. The Q1 and bonding. The existence of Q(C–O) band in the region Q2 bands show definite splitting suggesting distortion of 1638–1640 cm–1 in these mixed ligand complexes are in octahedral stereochemistry around NiII in these complexes.
the same region as observed for K2CED.H2O suggesting The splitting of Q2 bands are observed in the regions the non-involvement of carbonyl oxygen in bonding. The 14084–14124 and 16667–19305 cm–1 in the spectra of complexes exhibit three strong to very strong bands in these complexes which may arise due to spin-orbit cou- the region 1368–1402, 1026–1027 and 918–925 cm–1 as- pling that mixes the 3T1g (F) and 1Eg states, which are signable to Q 1[Q(C=C)], Q2[Qas(=CS2)] and Q3[Qs(=CS2)] present in these mixed ligand complexes25. The electronic spectra of the complexes in DMF solution also show three 2CED.H2O at 1320, 1020 and 930 cm–1 res- pectively12,20. In some complexes Q(C=C) appear as absorption bands in the ranges 10917–10869 (Q1), 16583– splitted (doublet or triplet) indicating lowering of its sym- 18691 (Q2) and 21008–22421 cm–1 (Q3). The definite split- metry. The positive shifts in Q(C=N) and Q(C=C) bands ting of Q2 bands in three complexes suggest distortion in suggest that dinegative chelating form of ligand, 1-cy- octahedral geometry around NiII ion in these complexes.
ano-1-carboethoxyethylene-2,2-dithiolate, is dominant in IR spectra of ligand and complexes : these complexes. The occurrence of a single weak to strong The infrared spectra of the mixed ligand complexes band in the region 810–847 cm–1 for Q(C–S) in these J. Indian Chem. Soc., Vol. 90, February 2013 complexes indicates symmetrical bonding of both the sul- which are very close to emission band at 476 nm ob- phur atoms of the ligand to the metal ion26.
served for free ligand, K2CED.H2O, under similar con- The mixed ligand complexes containing heterocyclic dition. This indicates that intra ligand excitation is res- nitrogen donors show in-plane ring and out-of-plane ring ponsible for this emission of complexes. It is clear that deformation bands in the ranges 611–665 and 405–420 blue-shift of emission occurs, which is probably due to cm–1 respectively indicating coordination through nitro- the coordination of ligands, because photoluminescencebehaviour is closely associated with the local environ- gen atom as these bands have found positive shifts with respect to its corresponding bands in its free form. TheQ(C–H) (aromatic ring) arising from aromatic ligands inthese complexes is observed as weak band(s) in the re-gion 3000–3100 cm–1. The Q(C–H) (aliphatic) for com-plexes containing D-pic, E-pic, J-pic and/or CED2– isobserved as weak intensity bands in the region 2930–2980 cm–1 suggesting their presence in the mixed ligandcomplexes.
The non-ligand bands observed in the ranges 405–420 and 300–320 cm–1 in the spectrum of mixed ligand com-plexes are tentatively assigned to Q(M–N) [27] and Q(M–S)28 modes respectively.
Luminescent properties :
The complexes (1), (2) and (3) show fluorescence
emission bands at 473, 474 and 473 nm respectively in NiL2(py)2(CED); L = D-pic, E-pic or J-pic solid state at RT when they are excited at 365 nm (Fig. 2) Fig. 1. Proposed structure of the NiII complexes.
Fig. 2. Emission spectrum of the ligand and NiII complexes : (a) K2CED.H2O, (b) Ni(D-pic)2(py)2(CED), (c) Ni(E-pic)2(py)2(CED),
Singh et al. : Synthesis, characterization, luminescent properties and biological activity studies etc. Antibacterial and antifungal activity studies : 3. Chem. Abstr., 1984, 100, 115000a; 1985, 102, l95283z,
31934m; 1986, 104, l92920k, 88608d; 1987, 106, 67474h.
The synthesized complexes were screened for their 4. V. K. Mukhomorov, Radiobiology, 1986, 26, 560.
antibacterial activity in vitro against Gram-positive (B.
subtilis, S. aureus
etc.) and Gram-negative (E. coli, 5. D. Coucouvanis, F. J. Hollander and M. L. Caffery, Inorg. Chem., 1974, 96, 4682; 1974, 96, 5646; 1976, 15, 1853.
P.aerugenosa etc.) microorganism by disc diffusion 6. D. Coucouvanis, F. J. Hollander and R. Pedelly, Inorg. method and were compared with the standard drug Strep- Chem., 1974, 96, 4032; 1977, 16, 2691.
tomycin. The complexes showed better antibacterial ac- 7. H. R. Wen, C. H. Li, Y. Song, J. L. Zuo, B. Zhang and X.
tivity on the basis of their M.I.C. values than their corres- Z. You, Inorg. Chem., 2007, 46, 6837.
ponding ligand (K2CED.H2O) and standard drug one.
8. K. Kubo, A. Nakao, Y. Ishii, T. Yamamoto, M. Tamura, The synthesized complexes were also screened for their R. Kato, K. Yakushi and G. E. Matsubayashi, Inorg. Chem., antifungal activity in vitro against fungi Candida albicans 2008, 47, 5495.
by microplate method of Eloff, using broth nutrient as 9. F. Guyon, A. Hameau, A. Khatyr, M. Knorr, H. Amrouche, the medium and were compared with the standard drug D. Fortin, P. D. Harveg, C. Strohmann, A. L. Ndiaye, V.
Fluconazole. The complexes also showed better antifun- Huch, M. Veith and N. Avarvari, Inorg. Chem., 2008, 47,
gal activity on the basis of their M.I.C. values than their 10. E. Fujiwara, K. Hosoya, A. Kobayashi, H. Tanaka, corresponding ligand (K2CED.H2O) and standard drug M. Tokumoto, Y. Okano, H. Fujiwara, H. Kobayashi, Y. Fujishiro, E. Nishibori, M. Takata and M. Sakata, Inorg. Chem., 2008, 47, 863.
The distorted octahedral stereochemistry around NiII 11. N. Singh and V. K. Singh, Trans. Met. Chem., 2001, ion in these complexes have been proposed based on ana-lytical data, magnetic susceptibility and spectral studies.
12. R. C. Aggarwal and R. Mitra, Indian J. Chem., Sect. A, 1994, 33, 55.
The infrared spectral studies suggest bidentate chelating 13. N. K. Singh, P. P. Aggarwal and N. Singh, Trans. behaviour of CED2– and unidentate bonding mode of hete- Met. Chem., 1990, 15, 325; Synth. React. Inorg.
rocyclic nitrogen bases in these complexes. Theses com- Metal-Org. Chem., 1991, 21, 541.
plexes show blue-shift emission at room temperature with 14. M. K. Singh, A. Das and B. Paul, Trans. Met. Chem., respect to ligand at 365 nm excitation wavelength. These 2005, 30, 655; 2007, 32, 732.
complexes show antimicrobial activity against Gram-posi- 15. M. K. Singh, A. Das and B. Paul, J. Coord. Chem., tive (B. subtilis, S. aureus) and Gram-negative (E. coli) 2009, 62, 2745.
microorganism. These complexes also show antifungal 16. M. K. Singh, A. Das, R. Laskar and B. Paul, J. In- activity against fungi Candida albicans. The proposed dian Chem. Soc., 2008, 85, 485; 2009, 86, 143; M.
structure of the complexes is shown in Fig. 1.
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rector, State Forensic Science Laboratory, Tripura, for 19. B. G. Werden, E. Billing and H. B. Gray, Inorg. recording fluorescence and IR spectra. Help received from Chem., 1966, 5, 78.
Head of the Department of Chemistry, Banaras Hindu 20. K. A. Jensen and L. Henriksen, Acta Chem. Scand., University, Varanasi for measuring magnetic susceptibil- 1968, 22, 1107.
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