Some New Thorium ( IV ) Complexes of Azoester Ligands ( Part-II ) KISHOR ARORA

Some new complexes of thorium (IV) metal by varying anions ( viz. Cl,I,NO3 and OAc -) with azoester ligand have been synthesized. These complexes are characterized by conventional methods viz. melting point, conductance measurements as well as by spectral methods viz. IR including far IR, UV –visible spectral studies. Thermal studies viz. DTA analysis of some of the representatives have also been done and reported. Some of the representative complexes were also screened against some microbes to check their antimicrobial activities. Coordination number of the complexes on the basis of these studies were proposed to be 8,10 and 12. The tentative structures of these complexes were also reported.


INTRODUCTION
A number of complex forming compounds or ligands have been used to prepare the metal complexes of different metals including lanthanides and actinides [1][2][3][4][5] .Schiff bases are one of these important class of compounds used as ligands.
So far as the ligands are concerned, ligands which are capable of forming chelates are dominating in the area of higher polyhedra, in scope, in numbers and in kinetics as well as in thermodynamic stability.In fact more compact the ligands and the smaller the bite more effective is it in generating higher coordination structures.
The main synthetic application of azo compound decomposition is in synthesis of strained ring systems.The required azo compounds can be prepared by dipolar cycloadditions of diazocompunds and the cyclic azo-esters so formed can be photochemically or thermally decomposed to strained ring system.Such reactions have been developed for pyridazine -3, 6 -dicarboxylate esters; 1,2,4-triazines and 1,2,4,5-tetrazines etc.
Ligands used for formation of complexes are reported in figure 2 below

EXPERIMENTAL
All the chemicals used for the preparation of new compounds were obtained in the sealed containers from standard companies e.g.Emerck, Aldrich, CDH and BDH.Thorium chloride, Thorium nitrate, Thorium acetate, Thorium iodide salts were obtained from the RJ (Robbert Johson Company Ltd.) and the BDH (British Drug House), Poole, England.All the chemicals were of AR, AnalR grade.
Thorium iodide was also prepared in laboratory by the reaction of Thorium nitrate with potassium iodide.

Formation of Azo-ester Ligands and their complexes
Jolly et al [11][12] have reported synthesis of many new azo-esters and have explored their activity and reactions.The complex forming capabilities of some of the azo-esters have been explored in the present investigation with thorium and dioxouranium metal salts.
The azo-ester compounds [IUPAC Name: 2-Aceto-2-N (substituted phenyl) azoethylethanoates] were prepared by the methods reported in literature [13][14] .All the substituted azo-ester compounds obtained are deeply coloured reddish brown solids with low melting points and most of them became viscous in the hot summer season of this north central region of Madhya Pradesh where the temperature in this season reaches almost 44-45 0 C.

The new coordination compounds of
Thorium were obtained by the reaction of the azoester ligand with suitable moiety at the pH ranging from 8 to 10 at the room temperature in water medium containing small amount of alcohol/ butanol/mixture of two alchohols.
All the analysis or studies done on the newly synthesized compounds were carried out as reported earlier in related literature [6][7][8][9][10] .

RESULTS AND DISCUSSIONS
Physical Data viz.yield, color, mol.weight etc. of Azoester Ligands are reported in table 1 Mass spectral data of the ligands are also reported in the tables 2,3.The prominent peaks are listed in these tables for these compounds.Base ion peak are marked and shown in the tables itself for these compounds.Though spectra of azosters show the peaks related to fragments that may be formed after fragmentation but investigator was not able to record parent ion peak.
Despite of the semi solid physical state of the azo ester ligands during summer season the new coordination compounds obtained were all crystalline solid with generally high melting points and were packed in polythene tubes after filtration and re-crystallization.The purity of the new compounds was checked by the chromatographic methods.The new complexes prepared are listed below along with their physical data in table 4. 1.
[Bis (ethyl-α-(4-bromo phenylazo) acetoacetato) tetrakis acetato] Thorium (IV)   Fig. 1: All the complexes are insoluble in common organic solvents.They are sparingly soluble in DMF and DMSO.Conductance measurement in DMF are too low account for disassociation of these complexes in DMF at the concentration of the 10 -5 M. Hence the complexes may be regarded as non electrolytes.

IR spectral studies
IR spectral analysis of azoester ligands along with that of representative complexes are reported in the tables 5-10.The N=N stretching vibration 15 of a symmetrical trans-azo compound is forbidden in the infra red spectrum but absorbs in   the 1576 cm -1 region of the Raman spectrum.Unsymmetrical para-substituted azobenzenes in which the substituent is an electron donating group absorb near 1429 cm -1 .The bonds are weak because of the non-polar nature of the bond. Infrared (IR) spectroscopy has proved to be a tool to establish anions in the complexes.In this present report nitrate (NO 3 -); acetate (CH 3 COO - ); and halo (X= Cl -and I -) are chiefly used as counter part to metal ions in these complexes.
Lever separation rule may be applied to distinguish between monodentate or bidentate nitrato ions.Lever et.Al 18 showed that this to be true that the separation for monodentate nitrate in (u 1 -    ) is appeared to be 5 -26 cm -1 and that for bidentate nitrato group this may lies in 20-60 cm -1 .This method has been tried in present case of complexes and a separation of Ca 250 -200 cm -1 in the combination bands in the region 1550 -1290 cm -1 suggest that nitrato ion is bidentate in nature in these complexes [19][20][21] .Similar to nitrato acetate ion in the present study of complexes also appears to be bidentate ligand.In case of halo complexes (M-X) vibrations could not be assigned because they are out of the range of studied region in the present investigations.

UV-Visible spectral studies
UV-Visible spectral analysis of the representatives complexes are also done and are reported in tables 11,12 below

Magnetic Behaviour of Complexes
Complexes of Thorium (IV) metal salts are diamagnetic in nature depending upon the other ions present and the corresponding ligand field.The magnetic susceptibilities are independent of field strength and temperature.In the present studies complexes are weakly diamagnetic as observed 22- 24 as they contain no unpaired electrons.

DTA studies of the Complexes
The results of these studies done on representative complexes are reported in Table 13 -14.The observed DTA graphs clearly show the stability of complexes upto considerably higher temperature range.The Exo and Endo peaks are located in these DTA graphs and are mentioned in Tables.In all the cases oxides are formed as final product of analysis viz.stable ThO 2 and U 3 O 8 .These metal oxides are formed over a comparatively high range of temperatures.These studies confirm the high stability of these complex compounds under studies upto high temperature.In intermediate steps ligands may left the complex molecules.
Based on the studies done on newly synthesized complexes of thorium (IV) metal salts their structures were proposed along with their coordination numbers.These are given in figure 3 below.

Antimicrobial studies of Complexes
The biological activity of different representative samples were tested against different microbial species using Methods reported earlier 25- 27 on NA medium and paper disc method.Results are reported in the table 15,16 given below.After 24 hrs incubation observed the plates for zone of inhibition around the well & the results are recorded in tabulated form.None of the products showed any significant antimicrobial activity