Exchanging water for acetonitrile turns the crystals of Co-MAHF-9 A8Q-hydrated from light pink to deep purple, signifying conversion to another unique site with tetrahedral-like geometry. The crystals maintain their shape even once the acetonitrile has evaporated. SC-XRD analysis shows a framework with two types of tetrahedral Co(II) centers with a 2His-2Glu environment (Co-MAHF-9 A8Q- dehydrated) (Figure ). The sites differ mainly by the presence of secondary sphere H-bonding with Gln8. There is also a switch from Nε to Nδ on His7 during the dehydration, implying transient dissociation of His ligands during the process. The switch from tetragonal to tetrahedral causes further helix shifts, creating two new pore shapes.