A photometric method for the determination of molybdenum with thiocarbohydrazide derivatives and evaluation of stepwise metal-ligand stability constants

Abstract

Molybdenum(VI) reacts with di-methylethylketone-thiocarbohydrazone (3,9-dimethylundeca-3,8-diene-'4,5,7 ,8-tetraza-6-thione) anddi-acetone-thiocarbohydrazone(2,8-dimethylnona-2, 7-diene-3,4,6, 7-tetraza-5-thione) to form reddish brown complexes in ethanol-water medium in the <i>p</i>H ranges 0.5-1.8 and 1.2-2.8, respectively. Both the complexes show absorption maximum at 380 nm. The molar absorptivity and Beer's law range are 6.66 x 10<sup >3 </sup>dm<sup >3</sup>-mo<sup >-1</sup>cm<sup >-1</sup>, 1-15 ppm and 8.48 x 10<sup >3</sup> dm<sup >3</sup>-mol<sup >-1 </sup>cm<sup >-1</sup>, 0.5-14 ppm, respectively. The composition of the complexes (1:2, M:L) determined by Job's and mole-ratio methods has been verified on the basis of the values of <img src='http://www.niscair.res.in/jinfo/nbar1.gif' border=0>. The stepwise stability constants of the complexes have been determined. Estimation of Mo(VI) in steel and the effects of foreign ions on its determination have been described. The relative standard deviations are ± 0.18 and ± 0.15%, respectively.