Molecular structures of nickel(II) monochelates of a racemic tridentate ligand and co-ligand induced structural variations

Using a racemic mixture of the tridentate ligand, (((2-pyridyl)ethylamine)methyl)phenolate ion (L−) and N3-, NCS−, (NC)2N−, OAc− as coligands, complexes having the formula [Ni(L)(N3)] (1), [Ni(L)(NCS)]2 (2), [Ni2(L)2(OAc)(N(CN)2)]n (3) were prepared and structurally characterized. In 1, Ni(II) has a square planar geometry and phenolate oxygen is involved in dipolar OPδ-⋯Nδ+ interaction with electrophilic central nitrogen atom of coordinated azide ion. Complex 2 is dimeric in nature and nickel(II) is penta-coordinated. Compounds 1 and 2 exist as centrosymmetric dimers made up of a pair of R and S enantiomers of L. In 3, an acetate and phenoxo bridged dinickel complex is present which is further linked to a zig-zag coordination polymer by the dicyanamide ion. In a given chain of 3, both L have same enantiomeric form and either RR or SS dimers are repeated along the chain. The magnetic properties are described.

Synthesis, structural characterization of complexes having the formula [Ni(L)(N3)], [Ni(L)(NCS)]2 and [Ni2(L)2(OAc)((NC)2N)]·(CH3CN)·(H2O) reveal the presence of (a) involvement of the electrophilic central nitrogen atom of coordinated azide in a OPδ-⋯Nδ+ type dipolar interaction with the phenolate oxygen (b) existence of a distorted square-pyramidal coordination geometry around Ni(II) ion and (c) a co-ligand dependent enantiomeric or conglomeric dimerization of monochelates.Figure optionsDownload as PowerPoint slide