Double-Stranded Monohelical Complexes from an Unsymmetrical Chiral Schiff-Base Ligand

A new Schiff-base ligand is prepared by a two-step reaction of 3-formylsalicylic acid and (1R, 2R)-diaminocyclohexane
in alcoholic solvents. The 1:1 condensation product exists as a zwitterion in the solid state and forms pleated
hydrogen-bonded sheets. Metalation of the ligand with divalent iron, nickel, cobalt, and zinc resulted in the formation
of double-stranded monohelices with exclusively M-helicity. Each complex has two tridentate ligands, with the
carboxylic acid groups remaining uncoordinated. In the crystal lattice, these complexes form extended M-helical
strands through intermolecular hydrogen bonding interactions. Metalation of the ligand with copper salts resulted
in a distinctly different type of complex, in which the ligand has transformed into a symmetric tetradentate salen
ligand with uncoordinated carboxylic acid groups.