Solvent-dependentfac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part

Abstract

Tris-chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers,facial(fac) andmeridional(mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of thefac/merisomers of the triply helical FeIIcomplexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example offac/merisomerism of a labile tris(2,2′-bipyridine) FeIIcomplex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only thefacisomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.