Tunable construction of transition metal-coordinated helicene cages

Abstract

We report a facile and tailored method to prepare globally twisted chiral molecular cages through tunable coordination of bis-bipyridine-terminated helicene ligands to a series of transition metals including Fe(II), Co(II), Ni(II) and Zn(II). This system shows an efficient remote transfer of stereogenecity from the helicene core to the bipyridine-metal coordination sites and subsequently the entire cages. While the Fe(II), Co(II) and Ni(II)-derived M2L3 (M for metal and L for ligand) cages exhibit quasi-reversible redox features, the Zn(II) analogues reveal prominent yellow circularly polarized luminescence. Interestingly, with the addition of Na2SO4, the Zn2L3 cages reassemble into sextuple-stranded Zn6L6(SO4)4 cages in which three Zn2L2 units are bound together by four sulfates and further coalesced by offset inter-ligand π-π interactions.