Synthesis, Characterisation and Electrochemical Studies Of Transition Metal Complexes with Bis-(Macro-Cyclic) Ligands

Introduction

The vast family of macrocyclic ligands and their complexes has now been established as an   integral part of coordination chemistry. The preference for macrocylic ligand over unidentate and bidentate ligands has arisen from being close to the biological system (1-3),the greater stability and    inertness of their complexes (4,5) and often the    extreme physical properties in their complexes due to strong ligand field.

Keeping these facts in view,new bis (macrocylic)ligands having unique and unusual      features has been prespared, characterised and its transition metal complexes have been prepared.

Experimental

All the chemicals and reagents used were of A.R.grade or equivalent purity. The ligand and its complexes were subjected to elemental  analyses for C,H & N at CDRI, Lucknow, M.P.,molar conductance and gravimetric estimation of the matals were carried out in the college lab. Magnetic susceptibility was determined by Gouy’s balance using CuSO4. 5H2O as calibrant. Electronic spectra of the complexes were recorded by Beckmann-Du spectrometer.  IR specta were recorded in KBr phase at CDRI, Lucknow.

Preparation of Ligand and Metal Complexes.

Ethylene diamine and cyanoetheno were treated by reflux to N,N,N’,N’-tetrak(2-cyanoethyl)-1,2-diaminoethane, which on suceesseve treatment with diborane and HCl gave N,N,N, N’tetrakis(3-aminopropyl)-1,2-diamino ethane. This on treatment with thiodiglycolic acid, CH3COONa and the respective metal salt gave the desired complexes. The chemical reactions involved may be represented as

Results and Discussion

The colours of the complexes were noted and are given in the table. The solubility of the     complexes was checked in various solvents. The melting points of the ligand and the corresponding metal complexes were determined by open capillary method and are uncorrected (Table-1). The measurment of molar conductance at 10-3 M         dilution and 25oC    suggested 1:4 electrolytic nature for all the synthesised complexes.

The magnetic susceptibility was determined at room temperature by Gouy’s method. The value of      magnetic moment  values of the complexes are given in table-1. The values suggested expected   paramagnetic nature for the synthesised complexes.

The IR spectra of the ligand and its  metal complexes were compared in order to find out the possible coordination sites. The comparison revealed that the ligand has coordinated through sulphur atoms and azomethine nitrogen atoms. The IR peaks of the ligand due to these groups show downward shifts of about 10-15cm-1 and 20-25cm-1 in the IR spectra of the complexes. The IR spectra respectively of the complexes show bands in the 1597-1621cm-1 region attributed to C=N(6). The bands due to coordinated C-S groups appeared in the   region of 1060cm-1(7). Together with these results, the most important feature is that the spectra of bis(macrocylic)complexes have no bands assignable to carbonyl group stretching modes. A band in the 1172-1182 is assigned to C-N vibration in all complexes(8). The absorption bands in the 2800-2850cm-1 and 1445-1455cm-1 region correspond to (C-H) and (C-H) respectively. The O-H bands appeared in the region of 3280-90 cm-1 and remained unaffected in the complexes,excluding the possibility of coordination of these groups with the metal.

The non ligand bands in the far IR region of the complexes at 445-466cm-1 and 360-365cm-1 may be assigned to (M-N) and (M-S) vibrations respectively(9). This further supported the coordination sites mentioned above .

The electronic spectrum of the copper(II) complex shows broad band at 17000 cm-1 with a shoulder at 14100cm-1, which may be assigned to 2B1g2Eg and 2B1g2A1g transitions respectively in square planar configuration (10). The electronic spectrum of Ni(II)complex shows two absorption bands at 15385 and 25975cm-1 assignable to 3A2g3T1g(f) and 3A2g3T1g(p) transitions (II). The electronic spectrum of cobalt(II)complex also shows two bands at 14080 and 17090cm-1. These bands may be assigned to 1A1g1B1g and charge transfer transitions respectively(12). These are characteristic of square planar geometry(12).The electronic spectrum of Mn(II)complex shows absoption bands at 14950, 24690,31950cm-1 assignable to 6A1g4T1g(G), 6A1g4A1g and 6A1g 6A1g(G) charge transfer  respectively(13) The magnetic    moments of Cu(II)complex is 1.79B.M. that of Co(II)complex is 3.29B.M.  Ni(II) & Zn(II)complexes are diamagnetic indicating square planar geometry for these complexes(12). The magnetic moments of Mn(II)complex is 5.98 corresponding to the presence of five unpaired electrons and characteristic of octahedral geometry.

Conclusion

From above discussion square planar geometry has been proposed for Cu(II),Zn(II), Co(II) and Ni(II) complexes and  octahedral geometry for Mn(II)complex. The ligand and complexes show antifungal activity and the antifungal activity of the ligand increased on complexation.      

Fungicidal  Activity

The ligand and its corresponding metal     complex were screened for furgicidal activity by mycelial dry weight method (MDW) against Asper gillus niger in glueose nitrate media (GN). The ligand showed toxicity in inhibition,which has increased in the complexes. The order of inhibition is ligand <Zn<Cu <Ni <Co<Mn.

Table – Fungicidal Activity

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