Geometrically restricted intermediates in the self-assembly of an M₁₂L₂₄ cuboctahedral complex

The self-assembly of a cuboctahedral M₁₂L₂₄ complex is traced by time-dependent NMR spectroscopy and mass spectrometry. The metastable intermediate structures that exist during the self-assembly process are not a chaotic mixture of numerous species, but instead are geometrically restricted. Short-lived M₈L₁₆ (D_4d) and relatively long-lived M₉L₁₈ (D_3h) are fully characterized as major intermediates. Employing a ligand with a smaller bend angle (112°) allows these two species to be kinetically trapped and more clearly observed by NMR spectroscopy. X-ray crystallography shows that M₉L₁₈ has the framework topology predicted by geometric discussion.