Synthesis,characterisation and substitution reaction of trans-(diaqua) (N,N'-ethylene-bis-salicylamide)chromium(III) ion

摘要

Trans-[Cr(Salm)(OH_2)_2]NO_3 has been synthesized and characterized by various physicochemical methods.The kinetics of substitution of [Cr(Salm)(OH_2)_2]~+ with different nucleophiles,viz.,thiocyanate (SCN~-),azide (N_3~-),imidazole (Imz),pyridine (Py),pyridine-2-caroxylic acid (pyc-2) and pyridine-3-caroxylic acid (Pyc-3) has been studied spectrophotometrically at 25-45 deg C (I = 0.5 mol dm~)-3) (KNO_3),4.0 < =pH <= 7.5).The reactions take place via outersphere association between the Cr(III) complex and various nucleophiles followed by transformation of the outer into inner sphere complexes by slow interchange.k_(an) (25 deg C,10~4) values are 18.91 (SCN~-),11.50 (N_3~-),9.51 (Imz),14.54 (Py),17.6 (Pyc-2),and 18.76 (Pyc-3) and the corresponding DELTA H~# (kJ/mol) values arc 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 DELTA AS~# (JK~(-1) mol~(-1)) values are-95.9 +- 9.5,-73 +-21.5,-144 +-3,-169 +- 16,-201 +- 0.6 and -172 +- 19.The higher value of k_(an) in comparison to k_(ex) and highly negative values of activation entropy and wide variation of k_(an) by changing nucleophiles,support I_a mechanism for the substitution reactions.