Selective complexation of 3d metal(ii) ions with multidentate and chiral isomers derived from condensation of 2-pyridinecarboxaldehyde with triethylenetetramine

Abstract

Condensation of 2-pyridinecarboxaldehyde with a stoichiometric amount of triethylenetetramine in isopropyl alcohol yields a mixture of at least two products, a Schiff dibase L¹ and a cyclization product with two imidazolidine rings L², and possibly a Schiff monobase with one imidazolidine ring L³. The 3d metal(II) salts, Mn(SCN)₂, MnCl₂, CuBr₂, MnI₂ and ZnBr₂, react selectively with L¹ or L² in this mixture solution to produce Mn(L²)(NCS)₂1, Mn(L²)Cl₂2, [Cu(L²)Br]Br·H₂O 3, [Mn(L¹)]I₂4, and [Zn(L¹)][ZnBr₄] 5, respectively. The presence of the two imidazolidine rings in the coordinated ligand L² of 1–3 generates two chiral carbon centers. The Mn(II) ion coordinates stereo-selectively to the [R,R] or [S,S] form of the L² in hexa-coordinate Mn(II) compounds 1 and 2, whereas the Cu(II) ion coordinates with the meso [R,S] form of L² in 3.