Complexes of general formulation [Cr(Schiff-base)(H2O)2]X, where Schiff-base=1, 2-bis(salicylideneamino)ethane (salen), 1, 3-bis(salicylideneamino) propane (salprn) and 1, 4-bis(salicylideneamino)butane (salbuen) and X=ClO4 or Cl have been prepared and characterised. Single-crystal structure of the complexrans[Cr(salprn)(H2O)2]Cl has been resolved. Evidence for less distorted coordination geometry around chromium in the salprn analogue as compared to that intrans-[Cr(salen)(H2O)2]+ has been presented. The kinetics of the aqua ligand substitution in the complexes Cr(Schiff-base)(H2O)2+ by thiocyanate have been investigated under pseudo-first order conditions with [NCS−]≫[Cr(III)],T=10–50°C, [H+]=10−8−10−1 M,I=1.0M (LiClO4). An attempt has been made to discuss the anomalous lability oftrans-[Cr(salen)(H2O)2]+ reported earlier in comparison to the reactivities of salprn and salbuen analogues. Bimolecular rate constants for the aqua ligand substitution by NCS− in [Cr(Schiff-base)(H2O)2]+ at 25°C vary by more than two orders of magnitude depending on the nature of the Schiff-base ligand. The reactivity order is discussed in terms of the possible steric strain imposed by the equatorially coordinated quadridentate ligand.
Volume 134, 2022
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