**4. Instrumental methods**

*Stability and Applications of Coordination Compounds*

in oxovanadium(IV) compounds [10].

complexes high effect on anticancer activity [21].

**2. Preparation of substituted chalcone**

**3. Preparation of complexes**

*Reaction scheme for chalcones (R* 〓 *H, 4-OH, 4-NO2 and 3-chloro).*

dependent. Moreover vanadyl ion is less toxic. In last year's research has been directed towards the synthesis of efficient bioactive compounds with low toxicity, in order to achieve this goal the type and the position of substituent into ligand were varied [6]. A wide variety of oxovanaduim(IV) complexes have been prepared and characterized by various physicochemical methods. Oxovanadium(IV) complexes have a square pyramidal geometry with apical oxygen and the vanadium atom lying above the plane defined by the donor atoms of the equatorial ligands. These square pyramidal complexes generally exhibit strong tendency to remain five coordinate [7, 8]. The coordination chemistry of vanadium(V) compounds is dominated by oxo complexes, containing the VO3+ or the VO2+ moiety [9]. The absorption band due to V〓O stretching vibration of oxovanadium(IV) complexes is usually observed at a higher wavenumber compared to those of vanadate(V) complexes. However, the V〓O stretching vibration is susceptible to a number of influences including electron donation from basal plane ligand atoms, solid-state effects, and coordination of additional molecules. Therefore, there has been considerable work done to assign the V〓O stretching frequencies

An increasing research interest of vanadium in coordination chemistry is not only due to its exhibiting a range of oxidation dates from +5 to −1 but also complexities exhibited by vanadium complexes and their industrial [11, 12], biological [13, 14] and medicinal [15, 16] applications. Vanadium complexes have been reported to have interesting antibacterial activities [17–20]. It has been reported that V(IV)

The substituted chalcones prepared by stirring the equimolar concentration mixture of 2-hydroxy-4,5-dimethyl acetophenone (0.01 mol) and substituted aromatic benzaldehyde (0.01 mol) in 20 ml ethanol for 1 h in presence of 50% NaOH. The mixture stirred till completion of the reaction (progress of reaction checked by TLC). The crude mixture poured into ice water then acidified the product with 10% hydrochloric acid. The coloured compound formed was filtered, washed with water

To a hot suspension of ligand (0.02 M) in ethanol, ethanolic solution (0.01 M) of the metal salt vanadyl sulphate (VOSO4) was added drop wise with constant stirring and refluxed for 2–3 h. The resulting reaction mixture was cooled to room temperature and maintained up to pH 8.0 by adding ammonia then refluxed further for 30 min. The resultant product was filtered through Whatman filter paper no. 1 and repeatedly washed with ethanol until the washing were free from the excess of ligand. These complexes were finally dried under vacuum in desiccator over fused CaCl2.

and dried. The compounds recrystallized from absolute ethanol (**Figure 1**).

**72**

**Figure 1.**

The IR spectra of complexes were recorded on a Perkin-Elmer instrument in KBr pallets in the range of 4000–400 cm<sup>−</sup><sup>1</sup> . TGA analysis of metal complexes were carried out in nitrogen atmosphere in the range 25–900°C on Rigaku Thermo Plus-8120 TG-DTA instrument with a heating rate 10°C min<sup>−</sup><sup>1</sup> using Alumina as a standard. UV-Visible spectra were recorded using DMF as solvent on Shimadzu UV-VIS spectrophotometer in the range 250–950 nm. Electron spin resonance spectra complexes were recorded on E-112 ESR Spectrometer as '*g*' marker ( *g* = 2.00277) at room temperature. The conductance was measured in DMF solvent on Equiptronics Conductivity meter (EQ-664A).
