Exploring the effect of hydroxylic and non-hydroxylic solvents on the reaction of [V IV O(β-diketonate) 2 ] with 2-aminobenzoylhydrazide in aerobic and anaerobic conditions.

Refluxing [VIV O(β-diketonate)2 ], namely [VIV O(acetylacetonate)2 ] and [VIV O(benzoylacetonate)2 ], separately with an equivalent or excess amount of 2-aminobenzoylhydrazide (ah) in laboratory grade (LG) CH3 OH in aerobic conditions afforded non-oxidovanadium(iv) and oxidovanadium(v) complexes of the type [VIV (L1 )2 ] (1), [VV O(L1 )(OCH3 )]2 (3) and [VIV (L2 )2 ] (2), and [VV O(L2 )(OCH3 )] (4), respectively. (L1 )2- and (L2 )2- represent the dianionic forms of 2-aminobenzoylhydrazone of acetylacetone (H2 L1 ) and benzoylacetone (H2 L2 ), respectively, (general abbreviation, H2 L), which was formed by the in situ condensation of ah with the respective coordinated [β-diketonate] in medium-to-good yield. The yield of different resulting products was dependent upon the ratio of ah to [VIV O(β-diketonate)2 ]. For example, the yield of 1 and 2 complexes increased significantly associated with a decrease in the amount of 3 and 4 with an increase in the molar ratio of ah. Upon replacing CH3 OH by a non-hydroxylic solvent, LG CHCl3 , the above reaction yielded only oxidovanadium(v) complexes of the type [VV O(L1 )(OH)]2 (5), [VV O(L2 )(OH)] (6) and [VO3 (L)2 ] (7, 8) whereas, upon replacing CHCl3 by another non-hydroxylic solvent, namely LG CH3 CN, only the respective [VO3 (L)2 ] (7, 8) complex was isolated in 72-78% yield. However, upon performing the above reactions in the absence of air using dry CH3 OH or dry CHCl3 , only the respective [VIV (L)2 ] complex was obtained, suggesting that aerial oxygen was the oxidising agent and the type of pentavalent product formed was dependent upon the nature of solvent used. Complexes 3 and 4 were converted, respectively, to 7 and 8 on refluxing in LG CHCl3 via the respective unstable complex 5 and 6. The DFT calculated change in internal energy (ΔE) for the reactions 2[VV O(L2 )(OCH3 )] + 2H2 O → 2[VV O(L2 )(OH)] + 2CH3 OH and 2[VV O(L2 )(OH)] → [VO3 (L2 )2 ] + H2 O was, respectively, +3.61 and -7.42 kcal mol-1 , suggesting that the [VV O(L2 )(OH)] species was unstable and readily transformed to the stable [VO3 (L2 )2 ] complex. Upon one-electron reduction at an appropriate potential, each of 7 and 8 generated mixed-valence [(L)VV O-(μ-O)-OVIV (L)]- species, which showed valence-delocalisation at room temperature and localisation at 77 K. Some of the complexes showed a wide range of toxicity in a dose-dependent manner against lung cancer cells comparable with that observed with cis-platin.