Some oxovanadium(IV) complexes of SA/SSA and 5, 10, 15, and 20-meso-tetraphenylporphyrin (H2tpp) with unidentate and bidentate nitrogen donors have been synthesized and characterized by elemental analysis, conductivity measurements, magnetic susceptibility, UV-Vis, IR, mass spectroscopy, TGA/DTA, and 1H, 13C and 51V NMR studies to investigate the steric and electronic effects of axial ligands on the properties of porphyrins. On the basis of these studies, it has been investigated that the axial ligands bind to the sixth coordination site of the vanadium ion to form a relatively stable six-coordinate-porphyrin complex where as in the case of SA/SSA complexes the nitrogen donors bind to the equatorial position giving square pyramidal geometry. The in vitro cytotoxicity against human cancer cell lines and antimicrobial activities of the synthesized compounds have been done against various fungal and bacterial pathogens. The [VO(SA/SSA)L/L-L] complexes were found to possess higher antibacterial, antifungal activity and in vitro cytotoxicity against human cancer cell lines than VO(tpp)L complexes. 1. Introduction Macrocyclic nitrogen donor ligands [1] have received special attention because of their versatile coordination modes [2] and for their biological activities, that is, toxicity against bacterial [3] and fungal growth, anticancerous [4], and other biochemical properties [5]. Such ligands, for example, porphyrins, salicylates, and sulphosalicylates, are known to play a very important and vital role in the stability of the metal complexes with the factor of having specific cavity size, stereochemical rigidity, flexibility, and ability to coordinate with metal atom [6]. SA/SSA ligands and their complexes are widespread in nature and of considerable relevance in medicinal chemistry [7] and also in industries [8, 9] (e.g., in the preparation of heterometallic precursors to oxide materials). VO2+ complexes have extensive clinical applications. However, there have been no reports on the corresponding organo oxovanadium(IV) salicylates, sulphosalicylates and porphyrins, though these compounds are expected to be biomedically relevant [10, 11]. We report herein the synthesis of some mixed ligand complexes (containing different donor atoms) and characterisation by means of spectral and magnetic studies as well as in vitro biological assays of some of the complexes. Structural correlation of these complexes has also been made and a square pyramidal geometry around [VO(SA/SSA)L/L-L] and an octahedral geometry around [VO(tpp)L] complexes are proposed on the basis
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