Synthesis, characterisation and substitution reaction of <i>trans-</i>(diaqua) (N ,Nʹ-ethylene-<i>bis</i>-salicylamide )chromium(III) ion

Abstract

<i>Trans</i>-[Cr(Salm)(OH₂)₂]NO₃ has been synthesized and characterized by various physicochemical methods. The kinetics of substitution of [Cr(Salm)(OH₂)₂]⁺ with different nucleophiles, viz., thiocyanate (SCN^-), azide (N₃^-)' imidazole (Imz), pyridine (Py), pyridine-2-caroxylic acid (pyc-2) and pyridine-3-caroxylic acid (Pyc-3) has been studied

spectrophotometrically at 25-45°C (<i>I</i> = 0.5 mol dm^-1 (KNO₃), 4.0 ≤ <i>p</i>H ≤ 7.5). The reactions take place via outer sphere association between the Cr(III) complex and various nucleophiles followed by transformation of the outer into inner sphere complexes by slow interchange. <i>k</i>_an (25°C ,10⁴) values are 18.91 (SCN^-1), 11.50 (N3^-), 9.51 (Imz), 14.54 (Py), 17.6 (Pyc-2), and 18.76 (Pyc-3) and the corresponding Δ<i>H^# </i>(kJ/mol) values are 63.1 ± 3.2, 70.6 ± 7.2, 46.4 ± 2.4, 40.7 ± 4.8,28.3 ± 0.2 and 38.33 ± 6.5 , the Δ<i>S^# </i>(JK^-1mol^-l) values are -95.9 ± 9.5, -73 ± 2 1.5, -144 ± 3, -169 ± 16, -201 ± 0.6 and -172 ± 19. The higher value of <i>k</i>_an in comparison to <i>k</i>_exand highly negative values of activation entropy and wide variation of <i>k</i>_an by changing nu cleophiles, support <i>I</i>_a<i> </i>mechanism for the substitution reactions.