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

2406-2411Trans-[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 = 0.5 mol dm-1 (KNO3), 4.0 ≤ pH ≤ 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. kan (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 ΔH# (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 ΔS# (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 kan in comparison to kex and highly negative values of activation entropy and wide variation of kan by changing nu cleophiles, support Ia mechanism for the substitution reactions