 Solution

An individual bipyramid is chiral. Matching helicities at the two iron centres give the homochiral $\Delta \Delta$ and $\Lambda \Lambda$ enantiomers, with the three spanning connections winding in opposite senses in the two structures. The idealized molecular framework has a threefold axis but no mirror plane, inversion centre or improper rotation that converts it into itself. Achiral synthesis can give a racemic mixture of these chiral cages; racemic bulk composition does not make each cage achiral. The corresponding experimentally characterized methyl-substituted Fe–Pd bipyramid contains both homochiral enantiomers in its crystal.^[ref]