A molybdenum mediated transformation of a carbohydrazone ligand leading to the formation of a hydrazone with an enhancement of fluorescence emission

A combined effect of acid catalysis and Mo mediated C=N bond cleavage on the Schiff base ligand N'-[(5-bromo-2-hydroxyphenyl)methylidene]-5-methyl-1H-pyrazole-3-carbohydrazide(L) which is prepared by the condensation of 5-methyl 3-pyrazole carbohydrazide with 5-bromo salicylaldehyde, leads to its transformation to the compound 2,2'-[(hydrazine-1,2-diylidenedimethylylidene]bis(4-bromophenol) (1) with the formation of a Mo(IV) complex in the reaction media. The resulting bis salicylhydrazone was characterized by UV–Vis, IR, NMR and also by X-ray crystallography. The compound 1 was found to have a more pronounced emission behavior as compared to the used ligand L. But the Mo(IV) complex which was produced in the reaction medium as a result of the oxidative cleavage of the ligand, was found to suffer fluorescence quenching with respect to the ligand.