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Halide Ion Mediated Aldehyde-Amine Condensation Leading to Schiff-base and Cyclized Non-Schiff-base Ligand Complexes of CdII: A Combined Experimental and Theoretical Investigation
Published in Wiley
Volume: 1
Issue: 15
Pages: 4539 - 4549

The reactions of pyridine-2-carbaldehyde with aminoalcohols N-(2-hydroxyethyl)ethylenediamine and 2-(3-amino- propylamino)ethanol in presence of CdIIX2 (X=Cl, Br, I) have been investigated. Structure analyses reveal that four com- plexes, namely [Cd2(L1 )2(Br)4] (2), [Cd(L1 )(I)2](3), [Cd(L1 )(Br)2] (5) and [Cd(L2 )(I)2] (6) are formed with the expected Schiff-base li- gands (E)-2-(2-(pyridin-2-ylmethyleneamino)ethylamino)ethanol (L1 ) and (E)-2-(3-(pyridin-2-ylmethyleneamino)propylamino)e- thanol (L2 ). Interestingly, when X=Cl two dinuclear complexes of general formula [Cd2(L1C/L2C)2(Cl)4] (complex 1 and 4, re- spectively) have been structurally characterized, where the li- gands are no longer Schiff-bases but contain an imidazolidine/ hexahydro-pyrimidine cyclic part instead [L1C = 2-(2-Pyridin-2-yl-imidazolidin-1-yl)-ethanol and L2C = 2-(2-Pyridin-2-yl-tetrahy- dro-pyrimidin-1-yl)-ethanol]. In order to understand whether the solid state structure is retained in solution various NMR analysis like 1 H, 13CNMR and DEPT-135 have been performed. When X=I, the equilibrium is shifted towards the formation of the Schiff-base ligands, thus complexes 3 and 6 are obtained as sole products. However, with X=Br or Cl, a mixture of products is present, comprising complexes containing both Schiff-bases as well as cyclized ligands. DFT calculations have been per- formed to rationalize the influence of the halide ligands on the reactivity of the Schiff-base and the formation of the cyclized ligand.

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Open AccessYes