Synthesis , Analytical and Spectral Studies of Novel Schiff Base Complexes of Th ( IV ) and UO 2 ( VI ) Along with their X-Ray Diffraction Data and Toxic Effects

Schiff base was obtained using furfuraldehyde and 2-amino pyridine to prepare new complexes of thorium(IV) and dioxouranium(VI) metals by various anions. The synthesized ligands and complexes were analytically studied through spectral data, elemental analysis and conductance measurements along with x-ray diffraction pattern. The complexes showed various coordination number and their toxic effects to bacterial and fungal genus was studied by two different methods of measurement.


Introduction
Thorium(IV) and dioxouranium(VI) metal ions have atomic radii 1.17Å and 1.90 Å respectively and have high positive charge, so that these metals can easily achieve high coordination number 1 .
According to the definition of Pearson 2 these metals are hard acids and possess vacant inner d-orbitals, hence can expand their co-valency with increase in their coordination number.Their enormous complex forming tendency is attributed to the vacant inner 5f sub shell which can expand greatly to accommodate a number of ligands.The greater spatial extension of 5f orbitals of actinides along with the fact that these orbitals are diffused at the periphery of atom make them suitable to form number of complexes because in such situation the orbitals are disturbed by ligands 3 .Coordination number greater than four can be achieved by them through donations of electrons from ligands into the d-orbitals of these metal atoms.The hybridization may be predicted by assuming the contribution of atomic orbitals towards the combination of hybridization orbitals.In this present work the Schiff base was derived from furfuraldehyde and 2-amino pyridine to obtain 2N-(Furfuralidiene)amino pyridine {2-FAPy}.

Experimental
All the chemicals used were of AR grade and were used without further purification.Elemental analysis was carried on Elemental Vario EL III Carlo Erba 1108 CDRI Lucknow.Conductivity measurements for the complexes have been carried out on Elico 01/01 cell type conductivity bridge.Molecular weights were determined in freezing PhNO 2 using Beckmann Thermometer method cryoscopically in the laboratory.IR spectra were taken through Schimadzu 8201 PC (4000-400 cm -1 ).Mass spectra were obtained through JEOL SX-102 (FAB) PMR spectra of selected samples were recorded on τ scale through Bruker Avance IT 400 NMR spectrometer.Electronic spectral studies were done through Perkin Elmer Lambda 15 x-ray diffraction studies were conducted through powder pattern method at wavelength λ 1.54 A 0 .Biocidal studies of representative complexes were conducted on fungal and bacterial species by paper disc method on PDA medium in our laboratory in DMF solvent.

Preparation of complexes
Th 4+ and UO 2 2+ complexes of Schiff base 2-FAPy were prepared by refluxing the nitrate, iodide, isothiocynate, perchlorate salts of Th 4+ and UO 2 2+ in proper M:L ratio using ethanol solvent.Uranyl acetate was also complexed with 2-FAPy in proper M:L ratio.The complexes were left in petri dish to obtain crystalline product and were recrystallised with solvent and washed with solvent and ether.

Synthesis of ligand
Solution of furfuraldehyde (1 mmole) in approx.30 mL ethanol was mixed with solution of 2amino pyridine (1 mmole) in approx.30mL ethanol.The resultant solution was refluxed in RB flask fitted with water condenser for six hours.On cooling Schiff base crystallized out which was filtered and re-crystallized with proper solvent.The structure of ligand is given in Figure 1.

Results and Discussion
The analytical data for the ligand metal complexes are listed in Table 1.It is observed that most of the complexes are non-hygroscopic and anhydrous as is evident from molecular weight and percentage of H values; which are nearly same for theoretical and experimentally calculated data.It is evident from the results that ratio of molecular weights for ThX 4 .2L(X= NO 3 -), ThX 4 .4L(X=NCS -), for observed and calculated approaches unity (0.98); suggestive of the fact that no change corresponding to ionization occurs in solution for these complexes.This fact is found valid for UO 2 X 2 .2L(X= NO 3 -, NCS -, CH 3 COO -) also 4 .
For ThI 4 .4L,this ratio is approximately one-third ie., 0.53; 0.36 for UO 2 (ClO 4 ) 2 4L and approximately one -fifth for Th(ClO 4 ) 4. 6L.This is suggestive of the fact that anions of the complexes are ionisable, primary valencies of complex and that they ionize furnishing more than one ion in solution 5,6 .

Mass spectral studies
Mass spectra of Schiff base was recorded.For 2-FAPy the parent ion peak is obtained at 173 m/z (M+1) peak.Base peak at 154 m/z is formed from parent ion through loss of H 3 O + .Other significant peaks are recorded at 136 and 289 m/z values.

IR spectral studies
IR spectra of Schiff base were recoded.For 2-FAPy the prominent peak at 1603 cm -1 shows variation in its complexes.This peak is of aromatic aldehydic system involved in azomethine linkage.When the IR spectra of ligands are compared with those of complexes then shift in the azomethine (-C=N-) peaks are observed through which the metal atom is believed to be bonded thus the azomethine bond is considered to be a part of coordination 7,8 .The important peaks of Th(IV) and UO 2 2+ (VI) are listed in Tables 2 & 3.

PMR spectral studies
In the PMR spectra of 2-FAPy and its iodide complex with dioxouranium(VI) the furan protons imparted their characteristic peaks between 7.38 ppm values 9 on δ scale.Interaction of αα' and ββ' as well as αβ protons of the heterocycle produced peak between 7.3 to 7.8 ppm values on δ scale.The azomethine proton also produce its significant peak in the same scale proton of the pyridine ring produces multiplet in 4.9-5.7 cps range because of α-β interactions .Significant peaks of iodide complexes are in form of multiplet in the range 7.69-7.83and a pentet in 6.72-6.75ppm range.

X ray diffraction studies
In this present investigation two representatives samples were chosen for x-ray diffraction studies through powder method viz [Th(2-FAPy) 2 (NO 3 ) 4 ], [Th(2-FAPy) 4 I 2 ] (Figure 2 & 3).The analysis was based on Bragg's equation and a, b, c; angles and constants hkl along with inter planar distance 'd' were obtained 10-14.The results were analyzed to obtain crystal system along with other parameters.The results are tabulated in Tables 4 & 5. [Th(2-FAPy) 2 (NO 3 ) 4 ] belongs to orthorhombic system with a = 15.393{8}Ao , b = 76.94{4}Ao , c = 7.479{9}A o (Table 4).[Th(2-FAPy) 4 I 2 ], belongs to orthorhombic system with a = 16.757{2}Ao , b = 9.937{3}A o , c = 4.068{2} A o (Table 5).] for toxic effects study.Thorium perchlorate complex of this ligand was found to be least effective for E.coli and uranium perchlorate was found to be most effective for bacterial toxicity.It was interesting to note that moderate concentration of complex of uranium salt is found to be maximum toxic for bacterial growth.For Aspergillus species maximum concentration of thorium and dioxouranium complexes is 60%; it was found to be most potent fungal inhibitor.The uranyl complexes showed maximum toxicity as the development of fungal colony was farthest from this complex sample disc.The significant results are shown in Table 6.
Cause of toxicity might be accumulation of heavy metals in microbes affecting its mobility and confirming its toxicity in further exposure of intracellular metal binding site and increasing passive.Intracellular accumulation of these heavy metals occur through ion pump and ion channel etc. Permeability of cell membrane to toxic metals can result accumulations [15][16][17][18][19] .

Table 1 .
Analytical results of 2-FAPy and its complexes.

Table 6 .
Colony diameter/ radial distance of colony around sample disc (cm).