Versatile Host for Metallo Anions and Cations

The crystal structures of two metallo oxides, perrhenate and
dichromate, are reported with a diprotonated tetraamido/diamino-based macrocycle, L, in which the floppy ligand assumes a folded
conformation. When the four amides are deprotonated, this same
ligand binds transition-metal ions in its tetraanionic form, H-4L.
For the divalent metal ions Cu2+ and Ni2+, H-4L again folds and
dinuclear complexes are formed. With trivalent metal ions Co3+
and Fe3+, the ligand wraps about the metal ions, resulting in
mononuclear complexes.