Synthetic and Structural Studies of Some Bivalent Transition Metal Complexes with Oxygen and Nitrogen Containing Schiff Base

INTRODUCTION

Complexes of semicarbazone ligands exhibit remarkable attention, primarily due to bioinorganic relevance. Semicarbazone complexes exhibit wide medicinal applications such as antimalarial, antiviral, antibacterial, and   antitumor^1-10. In order to consider above features of semicarbazone Schiff bases ligands and its complexes and in continuation of our recent works^11-15 in this field., we herein reported synthesis and characterization of Cu(II), Co(II) and Ni(II) complexes with Schiff base, 3-amino 2- ethyl quniazoline 4(3H) semicarbazone.

EXPERIMENTAL

Analytical and physical data of the ligand and its metal complexes are given in Table-1. The ligand is soluble in common organic solvents, but the complexes are found to be soluble in DMF and DMSO. The molar conductance value in DMF (Table-1) adequately support the 1:2 electrolytic metal of the metal complexes. All the chemicals  used were of analytical grade. Metal contents were determined using standard procedures. IR Spectra of the ligand and complexes were recorded on Perkin Elmer model 577 spectrophotometer using KBr disc. Electronic spectra were recorded on Cary-2390 spectrophotometer using DMF as a solvent. Molar conductivity of the complexes were measured by using Systronic conductivity meter. Model 303 in DMF. Magnetic susceptibility was carried out by Gouy method using Hg[Co(NCS)₄]

Synthesis of the ligand, AEQS

A hot ethanolic solution of semicarbazide hydrochloride (0.02mol) and an ethanolic solution(20ml) of 3-amino 2-ethyl quinazoline-4(3H) one (0.02mol) were mixed slowly with constant stirring. This mixture was reflused for 4h. On cooling, a colourless compound was precipitated out. It was filtered, washed with cold ethanol and dried in oven m.p. 160+1⁰ C, yield 65%.

Preparation of the complexes

The complexes of Co(II), Ni(II) and Cu(II) have been synthesized by reacting ethanolic solution of the ligand (0.02mol) with respective metal halide (0.01mol). The reaction mixture was refluxed for 4–5 h. On cooling, a coloured compound was precipitated out in each case. The compound was filtered, washed with ethanol and dried in oven. Yield-65-70%.

RESULTS AND DISCUSSION

The important infrared frequencies of the ligand and its complexes along with their tentative assignments are given in Table-2. The IR spectra of the ligand exhibit strong and broad band at 3300 cm^-1 assigned¹⁷ n_N–H vibrations. In the spectra of the complexes this band suffered downward shift proposing coordination through N-atom of Primary amino group. A medium intensity band at 1580   cm^-1 in the ligand due to n_C=N of azomethine¹⁸ is shifted to lower frequencies at 1555 cm^-1 upon complexation because of coordination of azomethine nitrogen with metal ions. The enxt IR spectra of the ligand exhibit strong and broad band at 1700 cm^-1 assigned¹⁹ to n_C=O. In the spectra of the complexes this band suffered downward shift clearly indicating coordination through carbohyl oxygen of semicrabazone. The linkage with N atom primary amino group as well as azomethine N and carbohyl/ oxygen is further supported by two far IR spectral bands present at 535-505 cm^-1 and 425-395 cm^-1 assigned²⁰ to n_M–O and n_M–N respectively.

 

Table-1:    Analytical, colour, mol. wt., magnetic susceptibility values, conductivity measurement and decomposition temperature of ligand AEQS and its metal complexes Click here to View table

Table – 2:  Important IR spectral bands (cm-1) of ligand AEQS and its complexes   Click here to View table

Fig.1  [M(AEQS)2] X2M = Co(II) and Ni(II); X = Cl–,  Br– and I– ; M = Cu(II); X = Cl– and  Br–  R = Ethyl Click here to View table

 

Molar Conductivity

The observed molar conductance of complexes of Co(II), Cu(II) and Ni(II) were taken 10^-3 DMF solution are in the range 146.3-167.8 ohm^-1 cm² mol^-1. The molar conductance values are consistent with the electrolytic²¹ in nature of 1:2 type.

Electronic spectra and magnetic susceptibility of the complexes

The Co(II) complexes exhibits three spectral bands in the regions 10700-11300cm^-1 19330-19500 cm^-1 and 23100-23300 cm^-1 assigned to ⁴T­_2g(F) ¬ ⁴T_1g(F) and ⁴A­_2g(F) ¬ ⁴T_1g(F)  and  ⁴T_1g(P) ¬ ⁴T_1g(F) transitions respectively.  The above mentioned spectral bands proposes octahedral²² geometry for Co(II) complexes. The octahedral geometry for Co(II) complexes is further supported^23,24 by m_eff value in the range 4.89-5.13 B.M. The Ni(II) complexes exhibits three absorption bands in the regions, 9700-10200 cm^-1, 16100-16400cm^-1 and 24300-24700cm^-1 assigned to ³T­_2g(F) ¬ ³A_2g(F),  ³T­_1g(F) ¬ ³A_2g(F)  and   ³T_1g(P) ¬ ³T_2g(P) transitions respectively. The above mentioned spectral bands of Ni(II) complexes proposes octahedral²² geometry. The octahedral geometry of Ni(II) complexes is also supported^23,24 by m_eff value in the range 3.11-3.17 BM. The Cu(II) complexes display two ligands field bands in the regions, 12700-13100 cm^-1 and 18200-18430cm^-1 assigned ²T­_2g(F) ¬ ²E_g and charge transferband respectively, which proposes octahedral²² geometry for cu(II) complexes. The magnetic susceptibility^23,24 value of Cu(II) complex lies in the range 1.87-1.91 B.M.

Conclusion

The present studies show that the ligand AEQS behaves as neutral tridentate chelating ligand and coordination proposes through amine nitrogen, imine nitrogen and Carbonyl oxygen atom of semicarbozone moiety. Thus on the basis of above mentioned studies it is proposed that the complexes of Co(II) and Ni(II) have octahedral geometry where as distorted octahedral geometry is recorded for Cu(II) complexes [Fig-1].

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